This PDF file contains the front matter associated with SPIE Proceedings Volume 7636, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Multilayer defects embedded in EUV mask blanks are of primary concern in making usable mask because the multilayer defects as small as 1.5 nm in height cause phase shifts and are most likely to be printable on wafers. To detect such phase defects, we have developed an actinic (at wavelength) full-field EUV mask blank inspection tool equipped with dark-field imaging optics. Inspection performance was demonstrated by a full-field mask blank inspection of a test mask blank to detect its programmed phase defects and native phase defects. A potential of detecting phase defects among the absorber patterns was also explored by inspecting masks with dot bump defects sitting among the absorber lines and line bump defects perpendicular to the absorber lines. For the phase defect printability study, the test mask was exposed using an EUV exposure tool (EUV1) at Selete. Simulation of projected image was also conducted using FDTD method. Multilayer defect printability for varying location of the multilayer phase defects relative to the absorber line patterns were evaluated

In 2005, Carl Zeiss SMT AG has shipped two sets of Optics for ASML's Alpha Demo Tools. This was the starting point for the introduction of full field EUV systems. Meanwhile imaging down to 25 nm was demonstrated with the ADT tools. Based on the learning from these tools ASML has built the NXE platform - a multi-generation EUV production platform. Shipping in 2010, the NXE:3100 will be the first generation of the EUV exposure platform. We review the current status of EUV optics production for the NXE:3100 tools. Four optical systems of the 3100 series have been shipped so far. These sets of optics are characterized by significantly lower flare and wave-front levels compared to the ADT. In addition a new illumination system with higher partial coherence has been developed. In this paper we focus on mirror fabrication and at wavelength qualification results of the optical systems produced so far. We also will give an outline of the next generation, a 0.32NA exposure tool including EUVL off-axis illumination for resolutions down to 16nm. We take the expected imaging requirements as a starting point and compare it with the current status of our technology development. A brief overview for further tool extensions by higher NA will be given as well.

Extreme ultraviolet lithography (EUVL) is the most effective way to print sub-30 nm features. We characterized EUVL readiness of the three major resist platforms for sub-30 nm half-pitch (HP) manufacturability using a full-field ASML alpha demo tool (ADT) scanner and studied the extendibility of EUV chemically amplified resist (CAR). Based on an "M-factor" analysis, which shows the maturity of EUV resist for 28 nm HP manufacturability, a polymer-bound photoacid generator (PAG) resist was 78% ready, a PHS hybrid resist was 81%, and a molecular glass EUV resist was 58%. The polymer-bound resist showed good resolution for 25 nm HP using the ASML ADT. It also demonstrated fair linewidth roughness (LWR) and a good lithographic process margin of 18% exposure latitude (EL) and 160 nm depth of field (DOF) for 28 nm HP patterning compared with the other resist platforms, but its resist collapse and etch resistance need to be improved for manufacturability. PHS hybrid resist showed a fair etch resistance and resist collapse performance compared to the other resist platforms, but LWR needs to be improved. The molecular resist needs to mature further, especially in resist collapse and iso-dense (ID) bias. When considering its many strong points and control of lower acid diffusion, the polymer-bound PAG resist appears to be the most suitable platform for manufacturability and EUV CAR extension. We therefore would like to encourage the development of next generation polymer-bound PAG resist with a higher etch resistance. A process window of 80 nm DOF was demonstrated for 26 nm HP patterning and a measurable DOF for 25 nm HP was achieved with the polymer-bound PAG resist. Resist collapse and LWR are major issues for 22 nm HP patterning in manufacturing. LWR improvements were achieved with various techniques, and resist collapse was greatly improved with a novel approach that uses a residual resist layer. 16 nm HP line/space (L/S) image modulation and 18 nm HP resolution were demonstrated with an EUV CAR, indicating that EUV CAR could be extended to sub-20 nm HP patterning.

Line edge roughness evolutions in EUV resist patterns are investigated. Three dimensional scanning electron microscopy images show the pattern sidewall roughness to be highly anisotropic and the roughness to be propagating from the resistsubstrate interface up the resist pattern sidewall. In ultrathin resist films, (film thickness ca. 100 nm and below) roughness is found to be fully correlated from the resist-substrate interface to the resist-air interface. This behavior is seen regardless of the resist platforms being used. Underlayer stack roughness contributions to the pattern sidewall roughness leading to resist LER were examined and no correlations between the two were found. At the same time, the chemical properties of the underlayer stacks are shown to have strong influences on the resist roughness and process performance. Exact mechanisms behind this are not clearly understood at present.

The 1st generation Laser-Produced Plasma source system "ETS" device for EUV lithography is under development. We report latest status of the device which consists of the original concepts (1) CO₂ laser driven Sn plasma, (2) Hybrid CO₂ laser system that is combination of high speed (>100kHz) short pulse oscillator and industrial cw-CO₂, (3) Magnetic mitigation, and (4) Double pulse EUV plasma creation. Maximum burst on time power is 69W (100kHz, 0.7 mJ EUV power @ intermediate focus), laser-EUV conversion efficiency is 2.3%, duty cycle is 20% at maximum. Continuous operation time is so far up to 3 hours. Debris is efficiently suppressed by pre-pulse plasma formation and magnetic field mitigation system. Long-term performance is now under investigation. Also future plan is updated.

With EUV Lithography readying for production, the need for commercially available actinic mask inspection tools is critical. A key to developing a successful tool is a reliable high brightness EUV light source. The Energetiq EQ-10 is a commercially available EUV light source, with demonstrated reliability of over 15 sources in the field. It is being used today for laboratory based actinic mask blank inspection at Selete⁴. Results will be presented from a program to optimize the EQ-10 for higher brightness. The platform used for this work is a new version of the EQ-10. The redesigned source demonstrates increased EUV power and brightness compared to the standard EQ-10. The program aims to optimize source operating conditions and pinch geometries of the new source to maximize brightness.

Efficient laser systems are essential for the realization of high volume manufacturing in extreme ultraviolet lithography (EUVL). Solid-state Nd:YAG lasers usually have lower efficiency and source suppliers are alternatively investigating the use of high power CO₂ laser systems. However, CO₂ laser-produced plasmas (LPP) have specific characteristics and features that should be taken into account when considering them as the light source for EUVL. The analysis of recent experimental and theoretical work showed significant differences in the properties of plasma plumes produced by CO₂ and the Nd:YAG lasers including EUV radiation emission, source formation, debris generation, and conversion efficiency. The much higher reflectivity of CO₂ laser from liquid, vapor, and plasma of a tin target results in the production of optically thinner plumes with higher velocity and in a better formation of plasma properties (temperature and density values) towards more efficient EUV source. However, the spikes in the temporal profiles of current CO₂ laser will additionally affect the properties of the produced plasma. We have developed unique combination of state-of-the-art experimental facilities (CMUXE Laboratory) and advanced computer simulation (HEIGHTS) package for studying and optimizing various lasers, discharge produced plasmas (DPP), and target parameters as well as the optical collection system regarding EUV lithography. In this work, detailed characteristics of plasmas produced by CO₂ and Nd:YAG lasers were analyzed and compared both experimentally and theoretically for optimizing EUV from LPP sources. The details of lower overheating of plasma produced by CO₂ laser are given with time and explain how to utilize the high reflectivity of such lasers in plasmas produced in different target geometries to significantly enhance the conversion efficiency of EUV radiation.

The tin (Sn) debris contamination is one of the technical challenges for the development of high power EUV light source with Sn fuel with a long lifetime of EUV collectors. The debris mitigation techniques (DMTs) can considerably minimize the Sn debris coming out of the source thereby reducing the need or effort for cleaning. However, for HVM, which requires higher EUV power output than today, it is questionable if the DMTs alone will completely eliminate the Sn contamination. Besides, at abnormal instances, we also need to clean thick Sn debris from the mirror surface. For this purpose, the Center for Plasma-Material Interactions (CPMI) at University of Illinois at Urbana-Champaign has developed a plasma-based Sn cleaning method using chlorine plasma with densities and temperature around ~9×10⁹/cm³ and ~ 4 eV respectively. From the previous studies at CPMI, it was shown that chlorine plasma etching can remove Sn debris from Ru mirror surface in a fast (> 400 nm/min) and in situ manner. In this study, we applied the same method to clean Sn contamination on the mock-up collector in our XTS13-35 DPP EUV source system. The mock-up is made of two shells with different gap widths (4 cm, 7.5 cm and 10 cm) in similar size with the actual collector optic. The cleaning rate at different locations on the mockup was experimentally investigated, and it was found that the cleaning rates vary largely with the distance from the chlorine plasma in the range of 20 - 100 nm/min. In addition, a simple analytical model to predict the cleaning rate was developed based on the plasma-surface reactions and the plasma transport. The model describes how plasma transport, chlorine radical distribution and pumping flow affect the Sn cleaning rate with chlorine plasma. Finally, the model is then compared to the experimental results and validated. Based on the knowledge of chlorine plasma and Sn interactions obtained in this study, a remote plasma cleaning technique was also investigated and the results obtained therein are presented. The experimental results along with the model predictions will help design an integrated cleaning system for collector optic in the high power EUV source system for HVM.

Media Lario Technologies (MLT), leveraging off its unique in-field collector experience, has designed the Grazing Incidence Collector (GIC) for the Sn-fueled Discharge Produced Plasma (DPP) source developed by Philips Extreme UV (PEUV) and XTREME technologies (XT) for High Volume Manufacturing (HVM) deployment. The performance of the HVM GIC described in this work shows a point-source collection efficiency of 24%, and is enabled by an integrated thermal control system designed to ensure optical stability for an absorbed thermal load of 6 kW. The GIC reflective layer has been custom tailored to match the debris mitigation strategy developed and characterized by PEUV and XT, supporting at least a 1-year lifetime proposition of the source-collector module. Leveraging off the experience gained in GIC, MLT is developing the processes to manufacture the Normal Incidence Collector (NIC) for Laser Produced Plasma (LPP) sources. Using its proprietary disruptive replication technology by electroforming, MLT is developing thermal management designs for NIC enabling stable operation at room temperature. This work reports on the performance of (symbol) 150 mm thermally managed NIC demonstrators. The mirror substrates have been integrated with new proprietary thermal management designs that are well suited to the electroformed mirrors. We also report on the reflectivity of the Mo/Si multilayer coated mirror, achieving maximum reflectivity values of 62% and a center wavelength (FWHM) of 13.52 nm, which demonstrates acceptable performance in an LPP NIC application.

Experimentally observed density profile of CO₂ laser-produced Sn plasma was compared with that predicted by one dimensional hydrodynamic radiation numerical code. Experimental data showed a much smaller corona and a much shorter shift distance of the critical density from the initial target surface as compared with those predicted by an isothermal model and the numerical simulation. The possible reason may come from thin localized laser deposition region, less energy transport into the corona and into the dense region beyond the critical density. This research suggests that more efforts to understand the fundamental dominating the interaction of CO₂ laser with high Z plasma are necessary to form a more solid foundation for the application of numerical method to the development of the EUVL source.

The goal of our ongoing optics-contamination program is to estimate the magnitude and scaling laws of the contamination rates of optics exposed to extreme-ultraviolet (EUV) radiation in the presence of various contaminant species expected in the EUV-lithography-tool environment by exposing samples to in-band 13.5 nm light from our synchrotron in the presence of fixed partial pressures of admitted gases. We report contamination rate measurements on TiO₂-capped samples for species observed in separate resist-outgassing measurements (benzene, isobutene, toluene and tert-butylbenzene) in the pressure range (10^-8 to 10^-5) Pa. We use two spatially-resolved surface probe techniques, spectroscopic ellipsometry and X-ray photoelectron spectroscopy, to determine the thickness of deposited carbon. The correlation and sensitivities of these techniques are discussed. The high sensitivity of ellipsometry shows that contamination rates for some species have a pronounced non-linear intensity dependence and can be strongly influenced by admixtures of water vapor, while the rates for other species are linear over the same intensity range and are less affected by ambient water. Understanding scaling laws is critical when estimating optic lifetimes or cleaning cycles by extrapolating over the 3-to-6 orders of magnitude between accelerated-testing and tool-environment partial pressures.

The aim of this work is to explore the thermal and non-thermal interaction of toluene, benzene and isobutene vapor with a crystalline Ru(10-10) surface, a model surface for Ru capping layers used in EUV lithography. Our main objective is to provide insights into the basic processes that affect the reflectivity of Ru-coated Mo/Si multilayer mirrors that are exposed to EUV radiation. A low energy electron beam is employed to mimic excitations initiated by EUV radiation. Temperature programmed desorption (TPD), x-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS), and electron-stimulated desorption (ESD) are used to analyze the surface reactions. Pyrolysis of a chemisorbed hydrocarbon layer on the Ru surface leads to the dehydrogenation and buildup a self-limited carbon monolayer. Carbon film growth on the Ru(10-10) crystalline surface under 100 eV electron bombardment in hydrocarbon vapor is measured over a range of pressures and temperatures near 300 K. The carbon growth rate is ~10 times higher in the presence of toluene vapor than in the presence of benzene or isobutene vapor. The estimations of the adsorption energy, the steadystate coverage of the molecules on the surface and the cross-sections for electron-stimulated dissociation are presented. A graphene-like carbon layer is probed as possible way to reduce the surface contamination rate.

The impact of carbon contamination on extreme ultraviolet (EUV) masks is significant due to throughput loss and potential effects on imaging performance. Current carbon contamination research primarily focuses on the lifetime of the multilayer surfaces, determined by reflectivity loss and reduced throughput in EUV exposure tools. However, contamination on patterned EUV masks can cause additional effects on absorbing features and the printed images, as well as impacting the efficiency of cleaning process. In this work, several different techniques were used to determine possible contamination topography. Lithographic simulations were also performed and the results compared with the experimental data.

Molecular contamination risk to an EUV reticle exposed to up to 1600J/cm² of 13.5 nm EUV radiation in ASML Alpha Demo Tool (ADT) is negligible. Carbon film (< 0.5 nm) deposition and oxidation (surface oxides ~1 nm) are the two main molecular contaminants observed on this EUV reticle. These results run counter to recent empirical results obtained from EUV micro-exposure tools (MET) which suggest that molecular contamination of EUV reticles, even at the very low partial pressures expected in the exposure chamber of EUV exposure tools, poses challenges in the implementation of EUV lithography in large-scale volume manufacturing of devices. To assess the molecular contamination risk to the use and lifetime of a given EUV reticle, we monitored the contamination buildup on a specially designed reticle during one year as it was exposed on ASML ADT located in Albany, New York. The reticle was analyzed with a suite of complementary surface analytical technique (such as Auger Electron Spectroscopy, AES) and chemical analytical techniques (such as Grazing Incidence Reflection Fourier Transform Infra-red Spectroscopy, GIR-FTIR), as well as imaging technique (such as Scanning Electron Microscopy). The influence of molecular contamination on the reflectivity of this reticle was measured at the Lawrence Berkeley Advanced Light Source EUV reflectometry. The differences in the contamination outcome of EUV reticles exposed in ASML ADT and MET may be related to the implementation of active contamination mitigation schemes in ADT and the lack of similar schemes in METs.

This paper assesses the readiness of EUV masks for pilot line production. The printability of well characterized reticle defects, with particular emphasis on those reticle defects that cause electrical errors on wafer test chips, is investigated. The reticles are equipped with test marks that are inspected in a die-to-die mode (using DUV inspection tool) and reviewed (using a SEM tool), and which also comprise electrically testable patterns. The reticles have three modules comprising features with 32 nm ground rules in 104 nm pitch, 22 nm ground rules with 80 nm pitch, and 16 nm ground rules with 56 nm pitch (on the wafer scale). In order to determine whether specific defects originate from the substrate, the multilayer film, the absorber stack, or from the patterning process, the reticles were inspected after each fabrication step. Following fabrication, the reticles were used to print wafers on a 0.25 NA full-field ASML EUV exposure tool. The printed wafers were inspected with state of the art bright-field and Deep UV inspection tools. It is observed that the printability of EUV mask defects down to a pitch of 56 nm shows a trend of increased printability as the pitch of the printed pattern gets smaller - a well established trend at larger pitches of 80 nm and 104 nm, respectively. The sensitivity of state-of-the-art reticle inspection tools is greatly improved over that of the previous generation of tools. There appears to be no apparent decline in the sensitivity of these state-of-the-art reticle inspection tools for higher density (smaller) patterns on the mask, even down to 56nm pitch (1x). Preliminary results indicate that a blank defect density of the order of 0.25 defects/cm² can support very early learning on EUV pilot line production at the 16nm node.

The availability of defect-free masks remains one of the key challenges for inserting extreme ultraviolet lithography (EUVL) into high volume manufacturing, yet little data is available for understanding native defects on real masks. In this paper, a full-field EUV mask is fabricated to investigate the printability of various defects on the mask. The printability of defects and identification of their source from mask fabrication to handling were studied using wafer inspection. The printable blank defect density excluding particles and patterns is 0.63/cm². Mask inspection is shown to have better sensitivity than wafer inspection. The sensitivity of wafer inspection must be improved using through-focus analysis and a different wafer stack.

Impact of EUV mask absorber defect with pattern-roughness on lithographic images was studied. In order to reduce systematic line width roughness (LWR) of wafer printed pattern, mask making process was improved; and in order to reduce random LWR, low line edge roughness (LER) resist material and a CD averaging method of multiple exposure shots were introduced. Then by using a Small Field Exposure Tool (SFET), mask induced systematic printed LWR was quantified and estimated at 32nm HP and 28nm HP. The measurement results of the critical mask absorber defect size were compared with simulation; and the results are then discussed.

Assessing the printability of EUV (extreme ultraviolet) lithography mask pattern defects is critical for determining EUV mask patterning, defect metrology, and repair technology requirements. Printability of mask defects at the wafer level depends on defect size, defect shape, defect location, and the line width and pitch of the structure being printed. Earlier reports showed the relationship between the defect size on the mask and the printed critical dimension for 40-70 nm dense lines. Improvements in the EUVL process now enable assessment of mask pattern defect printability for 22-40 nm half-pitch features. We report here the smallest mask pattern defects that printed at different locations in 22-40 nm structures using the Intel Micro-Exposure Tool (MET). Various types of defects such as indentations or protrusions were purposely incorporated into features on an EUV mask. The sizes of the patterned defects on the mask were drawn between 10-250 nm (= 2-50 nm on the wafer). The minimum printable defect size varied by over 100 nm, depending on the defect shape and location.

The particle removal efficiency (PRE) of cleaning processes diminishes whenever the minimum defect size for a specific technology node becomes smaller. For the sub-22 nm half-pitch (HP) node, it was demonstrated that exposure to high power megasonic up to 200 W/cm² did not damage 60 nm wide TaBN absorber lines corresponding to the 16 nm HP node on wafer. An ammonium hydroxide mixture and megasonics removes ≥50 nm SiO₂ particles with a very high PRE. A sulfuric acid hydrogen peroxide mixture (SPM) in addition to ammonium hydroxide mixture (APM) and megasonic is required to remove ≥28 nm SiO₂ particles with a high PRE. Time-of-flight secondary ion mass spectroscopy (TOFSIMS) studies show that the presence of O₂ during a vacuum ultraviolet (VUV) (λ=172 nm) surface conditioning step will result in both surface oxidation and Ru removal, which drastically reduce extreme ultraviolet (EUV) mask life time under multiple cleanings. New EUV mask cleaning processes show negligible or no EUV reflectivity loss and no increase in surface roughness after up to 15 cleaning cycles. Reviewing of defect with a high current density scanning electron microscope (SEM) drastically reduces PRE and deforms SiO₂ particles. 28 nm SiO₂ particles on EUV masks age very fast and will deform over time. Care must be taken when reviewing EUV mask defects by SEM. Potentially new particles should be identified to calibrate short wavelength inspection tools. Based on actinic image review, 50 nm SiO₂ particles on top of the EUV mask will be printed on the wafer.

System cleanliness is a major issue facing the lithographic community as the prospects of integrating EUV lithography into integrated circuit manufacturing progress. Mask cleanliness, especially of particles in the sub-micron range, remains an issue for the implementation of EUV lithography since traditional mask cleaning processes are limited in their ability to remove nanometer scale contaminants. The result is lower wafer throughput due to errors in pattern transfer to the wafer from the particulate defects on the mask. Additionally, carbon contamination and growth on the collector optics due to energetic photon interactions degrade the mirror and shortens its functional life. Plasma cleaning of surfaces has been used for a variety of applications in the past, and now is being extended to cleaning surfaces for EUV, specifically the mask and collector optics, through a process developed in the Center for Plasma-Material Interactions (CPMI) called Plasma Assisted Cleaning by Metastable Atom Neutralization (PACMAN). This process uses energetic neutral atoms (metastables) in addition to a high-density plasma (Te ≈ 3 eV and ne ≈ 10¹⁷ m^-3) to remove particles. The PACMAN process is a completely dry process and is carried out in a vacuum which makes it compatible with other EUV related processing steps. Experiments carried out on cleaning polystyrene latex (PSL) nanoparticles (30 nm to 500 nm) on silicon wafers, chrome coated mask blanks, and EUV mask blanks result in 100 % particle removal with a helium plasma and helium metastables. Removal rates greater than 20 nm/min have been achieved for PSL material. Similar removal rates have been achieved for the PACMAN cleaning of carbon from silicon wafers (simulating collector optic material) with 100% removal with helium plasma and helium metastables. The PACMAN cleaning technique has not caused any damage to the substrate type being cleaned either through roughening or surface sputtering. Current results of cleaning various particle types from surfaces through the PACMAN process are presented.

The International Technology Roadmap for Semiconductors (ITRS) denotes Extreme Ultraviolet (EUV) lithography as a leading technology option for realizing the 22nm half pitch node and beyond. Readiness of EUV materials is currently one high risk area according to recent assessments made at the 2009 EUVL Symposium. The main development issue regarding EUV resist has been how to simultaneously achieve high sensitivity, high resolution, and low line width roughness (LWR). This paper describes the strategy and current status of EUV resist development at Intel Corporation. Data collected utilizing Intel's Micro-Exposure Tool (MET) is presented in order to examine the feasibility of establishing a resist process that simultaneously exhibits ≤22nm half-pitch (HP) L/S resolution at ≤ 12.5mJ/cm² with ≤ 4nm LWR.

EUV resists have been developed to be able to print sub-30nm L/S features with EUV ADT having 0.25NA. However, a lithographic performance especially line width roughness (LWR) of EUV resist is not comparable to that of DUV resist. Shot noise effect has been regarded as a main reason for this poor performance of EUV resist [1-2]. Polymer bound PAG with sensitizer is considered as one of solutions to overcome this problem. The champion resist based on polymer bound PAG shows good performance at 30nm L/S and 27nm L/S patterns, although LWR is still worse than target. Additional processes such as smoothing process, chemical treatment process and surfactant rinse process are evaluated. Surfactant rinse process which can improve LWR and pattern collapse simultaneously is regarded as a best solution. A new resist which can overcome out-of band radiation problem is required for EUV lithography. A resist which is totally transparent at DUV or a resist which is very opaque at DUV wavelength is expected to be a solution for OOB problem of EUV lithography.

Accurate and flexible simulation methods may be used to further a researcher's understanding of how complex resist effects influence the patterning of critical structures. In this work, we attempt to gain insight into the behavior of a state-of-the-art EUV resist through the use of stochastic resist simulation. The statistics of photon and molecule counting are discussed. A discrete, probabilistic ionization and electron scattering simulator for acid generation at EUV is discussed. At EUV, acid generators are hypothesized to be activated by secondary electrons yielded by ionization of the resist upon absorption of photons. Model fit to experimental data of mean CD and LWR for a state-of-the-art EUV resist is shown.

Extreme ultraviolet (EUV) lithography is the leading candidate for the manufacture of semiconductor devices at the hp- 22-nm technology node and beyond. The Selete program covers the evaluation of manufacturability for the EUV lithography process. So, we have begun a yield analysis of hp-2x-nm test chips using the EUV1 full-field exposure tool. However, the resist performance does not yet meet the stringent requirements for resolution limit, sensitivity, and line edge roughness. We reported on Selete standard resist 4 (SSR4) at the EUVL Symposium in 2009. Although it has better lithographic performance than SSR3 does, pattern collapse limits the resolution to hp 28 nm. To improve the resolution, we need to optimize the process so as to prevent pattern collapse. An evaluation of SSR4 for the hp-2x-nm generation revealed that a thinner resist and the use of a TBAH solution for the developer were effective in mitigating this problem. Furthermore, the use of an underlayer and an alternative rinse solution increased the exposure latitude by preventing pattern collapse when the resist is overexposed. These optimizations improved the resolution limit to hp 22 nm.

In order to achieve targeted resist performance for EUV in practical applications, we have developed new materials such as molecular glass (MG), PAG, and acid amplifiers (AA). Protected NORIA, a molecular glass, was examined for extending resolution limits. The resist with protected NORIA showed 22 nm hp resolutions under EUV exposure. PAG acid diffusion effect on LWR was also investigated. It was found that acid diffusion control was one of the most important factors for LWR improvement. To improve sensitivity, application of AA (acid amplifier) was investigated. The resist with AA gained 25% sensitivity improvement over the original formulation. Elemental technologies for major progress of EUV resist were made.

Total quality on EUV mask blanks have to be improved toward future volume production. In this paper, progress in EUV blank development and improvement in flatness, bow and ML blank defects as critical issues on EUV blanks were reported. Steadily progress in flatness improvement was made in the past five years by improving polishing processes. A LTE substrate with a high flatness of 78 nm PV in 142 mm square area was achieved in average. Annealing process was developed to make small bow of less than 600 nm after ML coating. It was confirmed that annealed ML blank has stable performance in bow and centroid wavelength values through mask making process. Small bow of less than 300 nm was successfully demonstrated using annealing process and a CrN back side film with high compressive stress. Low defects of 0.05 defects/cm² at 70 nm SiO₂ sensitivity inspected by a Lasertec M1350 was demonstrated on a multilayer (ML) blank with a LTE substrate as best. Small defects over 50 nm in a M7360 were effectively reduced by improvement of polishing process consisting of local polish, touch polish and cleaning.

Reticle quality and the capability to qualify a reticle are key issues for EUV Lithography. We expect current and planned optical inspection systems will provide inspection capability adequate for development and production of 2X HP masks. We illustrate inspection technology extendibility through simulation of 193nm-based inspection of advanced EUV patterned masks. The influence of EUV absorber design for 193nm optical contrast and defect sensitivity will be identified for absorber designs of current interest.

Image placement (IP) and overlay error specifications are serious concerns for lithography at each successive technology node. Some of the primary contributors to image placement error (IPE) in EUV lithography are reticle and chuck surface non-flatness and chucking flatness non- uniformity. Flatness compensation has been proposed as a method to relax flatness specification for EUV substrates. However, in order for flatness compensation to work effectively, the various components of IPE i.e., reticle flattening and as-chucked z-height variation needs to be estimated accurately. Flatness compensation models assume a completely flat, rigid chuck and conformal clamping of the reticle backside. In this paper we will describe experiments designed to verify the different assumptions that the flatness compensation models are based on. The experiments involve printing wafers using a set of reticles of different flatness specifications on the ASML EUV Alpha Demo Tool (ADT) in Albany, NY. We will discuss results from these experiments and use Finite Element Modeling to simulate reticle chucking to correlate these results to physical properties electrostatic chuck on the ADT.

Thinner absorber structure in EUVL mask is supposed to be applied in 2x HP node since it shows several advantages including H-V bias reduction. Here, lithographic performances of EUVL masks as a function of absorber stack height are investigated using ADT exposure experiments. Wafer SEM images show that minimum resolution is almost identical at ~27.5 nm with absorber thickness ranging from 45 to 70 nm. Simulations also exhibit that NILS and contrast become maximized and saturated in those ranges. However, thinner absorber structure using 50-nm-thick absorber shows much lower H-V bias than conventional structure using 70-nm-thick absorber. MEEF, EL, DOF, and LWR are also slightly improved with thinner absorber. One of the noticeable issues in thin absorber is low OD which results in pattern damages and CD reduction at shot edges due to light leakage from the neighboring exposures. To overcome these issues, appropriate light shielding process during mask fabrication as well as minimizing OoB radiation in EUVL scanner are required. Another item to prepare for 2x HP node is to increase defect detection sensitivity with 19x nm inspection tools. Thus, absorber stacks with new ARC layer optimized for 19x nm inspection should be developed and applied in EUVL mask blanks.

Mask defectivity is an acknowledged road block for the introduction of EUV lithography (EUVL) for manufacturing. There are significant challenges to extend the conventional methods of cleaning developed for standard 193nm optical photomask to meet the specific requirements for EUV mask structure and materials. In this work, the use of UV activated media for EUV mask surface cleaning is evaluated and the effects on Ru capping layer integrity are compared against conventional cleaning methods. Ru layer surface is analyzed using roughness measurements (AFM) and reflectivity changes (EUV-R and optical).

Data and simulation results characterizing the capability of a DUV system to inspect EUV mask blanks and substrates are reported. Phase defects and particles on multilayer (ML) surfaces, ARC-coated absorber, and substrate material are considered. In addition to the previously reported results of inspecting phase defects on multilayer surfaces, phase defects on a quartz substrate surface are shown. The principle of phase detection is described. Simulations show that the 22-nm node requirement for phase defect detection should be met, assuming a reduction in the multilayer roughness. Initial inspections of deposited SiO₂ spheres show sensitivities of at least 40 nm on ML and quartz; however, the availability of calibrated spheres of smaller diameters has limited testing below this value. Simulation results show relative sensitivities for detecting SiO₂ spheres of different diameters on various EUV materials.

For industrial EUV (extreme ultra-violet) lithography applications high power EUV light sources are needed at a central wavelength of 13.5 nm. Philips Extreme UV GmbH, EUVA and XTREME technologies GmbH have jointly developed tin DPP (Discharge Produced Plasma) source systems. This paper focuses in the first part on the results achieved from the Alpha EUV sources in the field. After integration of power upgrades in the past, now the focus is on reliability and uptime of the systems. The second part of this paper deals with the Beta SoCoMo that can be used in the first pre-production scanner tools of the lithography equipment makers. The performance will be shown in terms of power at Intermediate Focus, dose stability and product reliability but also its reachable collector lifetime, the dominant factor for Cost of Operation. In the third part of the paper the developments for the high volume manufacturing (HVM) phase are described. The basic engineering challenges in thermal scaling of the source and in debris mitigation can be proven to be solvable in practice based on the Beta implementation and related modeling calibrated with these designs. Further efficiency improvements required for the HVM phase will also be shown based on experiments. The further HVM roadmap can thus be realized as evolutionary steps from the Beta products.

For extreme ultraviolet light lithography to be a viable process for the future development of computer chips, it is necessary that clean photons are produced at the intermediate focus (IF). To measure the flux at the IF, the Center for Plasma-Material Interactiosn (CPMI) at the University of Illinois at Urbana-Champaign has developed a Sn IF flux emission detector (SNIFFED) apparatus that is capable of measuring charged and neutral particle flux at the IF. Results will be presented that diagnose debris produced at the IF, as well as methods by which this debris can be mitigated. Advanced Materials Research Center, AMRC, International SEMATECH Manufacturing Initiative, and ISMI are servicemarks of SEMATECH, Inc. SEMATECH, and the SEMATECH logo are registered servicemarks of SEMATECH, Inc. All other servicemarks and trademarks are the property of their respective owners.

We investigated the angular dependence of atomic and ionic debris from CO₂ and YAG laser-produced tin plasmas. Several diagnostic techniques were employed for this study including a Faraday cup, witness plates and subsequent x-ray photoelectron spectroscopic analysis, optical emission spectroscopy etc. It was found that the debris emission from the Nd:YAG laser-produced plasmas fell sharply from the target normal. In contrast, the debris emission from the CO₂ laser-produced plasmas was almost constant at short angles from the target normal. Our results also indicated that the plasma produced by the CO₂ laser emitted less atomic and ionic debris compared to a plasma produced by Nd:YAG laser.

The leading candidate for the manufacture of next generation semi-conductor devices is extreme ultraviolet lithography, with laser-produced plasmas as a candidate 13.5nm light source. A primary challenge for continuous operation is elimination of the debris load on the collector, without compromising the radiation intensity at the intermediate focus. A novel combination of thermal management and debris mitigation is developed in order to reduce the deformation and degradation of collector optics. This patent-pending novel debris mitigation technique enables the continuous operation of the source. The paper shows atomic force microscope measurements of the collector surface deposition. The debris mitigation system run at 50% design operating condition gives 90% debris mitigation effectiveness. The average temperature of the cooled collector is 36.5°C at the design point, with a peak-to-peak difference of 0.8°C. The collector geometry, after being adapted to compensate the thermal deformation, yields a spot size of 30μm at IF. Computational simulations, using ETH's multi-scale computational tools, complement the presented experimental results.

Conventional EVUL mask has 80nm absorber height which brings considerable shadowing effect. H-V CD bias of 40nm line and space by shadowing effect is more than 4nm, and that is expected to increase much more for narrower patterns by simulation. However various reports have been presented on mask shadowing bias correction, experimental results are not reliable to derive required mask bias correctly. Even more difficulty will arise when complex 2D structures are taken into account. Therefore minimization of shadowing effect by reducing absorber thickness is desirable. To transfer EUV lithography from experimental stage to HVM era, we need to find optimum absorber height of EUVL mask which allows us less shadowing effect with minimum loss of process window. In this paper, we present optimal absorber height of EUV mask which has been found in terms of shadowing effect and process window by simulation and exposure. To find minimized absorber height experimentally, we will compare the printing result of conventional and thin mask stack using simple 1:1 line and space and island patterns. Simulated H-V CD bias and process window will be presented.

Extreme Ultraviolet Lithography (EUVL) is currently the most promising technology for advanced manufacturing nodes: it recently demonstrated the feasibility of 32nm and 22nm node devices, and pre-production tools are expected to be delivered by 2010. Generally speaking, EUVL is less in need of Optical Proximity Correction (OPC) as compared to 193nm lithography, and the device feasibility studies were indeed carried out with limited or no correction. However, a rigorous optical correction strategy and an appropriate Electronic Design Automation (EDA) infrastructure is critical to face the challenges of the 22nm node and beyond, and EUV-specific effects such as flare and shadowing have to be fully integrated in the correction flow and properly tested. This study aims to assess in detail the quality of a full chip optical correction for a EUV design, as well to discuss the available approaches to compensate for EUV-specific effects. Extensive data sets have been collected on the ASML EUV Alpha-Demo Tool (ADT) using the latest IMEC baseline resist Shin-Etsu SEVR59. In total about 1300 CD measurements at wafer level and 700 at mask level were used as input for model calibration and validation. The smallest feature size in the data set was 32nm. Both one-dimensional and two-dimensional structures through CD and pitch were measured. The mask used in this calibration exercise allowed the authors to modulate flare by varying tiling densities within the range expected in the final design. The OPC model was fitted and validated against the CD data collected on the EUV ADT. The shadowing effect was modeled by means of a single bias correction throughout the design. Horizontal and vertical features of different type through pitch and CD were used to calibrate the shadowing correction, and the extent of the validity of the single bias approach is discussed. In addition, the quality of the generated full-chip flare maps has been tested against experimental results, and the model has been validated in the full flare range available within the mask. The model calibration yielded an RMS of about 1nm, and a EUV mask fully corrected for OPC, flare and shadowing was finally fabricated and qualified.

We introduce techniques of flare compensation for Extreme Ultraviolet Lithography that can reduce the calculation time of a flare map and flare correction. In the first approach, the range of a flare point spread function is divided into several regions and the size of meshes for the flare map in each region is selected. In the second approach, the size of the mask pattern is controlled by referring to the flare map in the mask-making process. In the third approach, dosage of each point in a mask corresponding to the flare map is modulated when transferring the mask pattern onto the resist. Use of these approaches in the proper combination is effective for TAT reduction and accuracy of the flare compensation.

In this paper, the corner rounding bias of a commercially available extreme ultraviolet photoresist is monitored as molecular weight, photoacid generator (PAG) size, and development time are varied. These experiments show that PAG size influences corner biasing while molecular weight and development time do not. Large PAGs are shown to exhibit less corner biasing, and in some cases, lower corner rounding, than small PAGs. In addition, heavier resist polymers are shown to exhibit less corner rounding than lighter ones.

Extreme ultraviolet lithography (EUVL) is one of the most promising candidates for the next-generation lithography. For the adoption of EUVL, however, there are some technological issues to be solved. One of the critical issues is flare which is an undesirable scattered light that reduces the aerial image contrast leading to a reduction in the process window such as exposure latitude. Therefore, new methods to compensate for the anticipated flare effect have to be devised. At Selete, flare correction based on a flare point-spread function (PSF) is investigated. We succeeded in achieving a CD control of within a few nm over various pattern densities for the half-pitch (HP) 32-nm node. However, our estimation shows that the previous flare correction scheme could not meet the accuracy criteria of flare computation for HP 22-nm node. Therefore, we have modified the flare correction flow to implement a variable gridding for pattern-density calculation. The variable gridding based on the shape of a PSF enables highly accurate flare calculation within a reasonable runtime. Furthermore, we will use model-based OPC for HP 22-nm node, whereas we normally use rule-based OPC for HP 32- nm node. This is because the lithography process is reaching the low k1 regime. In this work, we investigate the feasibility of model-based OPC incorporating flare correction.

In this paper, we discuss the performance of EUV resist models in terms of predictive accuracy, and we assess the readiness of the corresponding model calibration methodology. The study is done on an extensive OPC data set collected at IMEC for the ShinEtsu resist SEVR-59 on the ASML EUV Alpha Demo Tool (ADT), with the data set including more than thousand CD values. We address practical aspects such as the speed of calibration and selection of calibration patterns. The model is calibrated on 12 process window data series varying in pattern width (32, 36, 40 nm), orientation (H, V) and pitch (dense, isolated). The minimum measured feature size at nominal process condition is a 32 nm CD at a dense pitch of 64 nm. Mask metrology is applied to verify and eventually correct nominal width of the drawn CD. Cross-sectional SEM information is included in the calibration to tune the simulated resist loss and sidewall angle. The achieved calibration RMS is ~ 1.0 nm. We show what elements are important to obtain a well calibrated model. We discuss the impact of 3D mask effects on the Bossung tilt. We demonstrate that a correct representation of the flare level during the calibration is important to achieve a high predictability at various flare conditions. Although the model calibration is performed on a limited subset of the measurement data (one dimensional structures only), its accuracy is validated based on a large number of OPC patterns (at nominal dose and focus conditions) not included in the calibration; validation RMS results as small as 1 nm can be reached. Furthermore, we study the model's extendibility to two-dimensional end of line (EOL) structures. Finally, we correlate the experimentally observed fingerprint of the CD uniformity to a model, where EUV tool specific signatures are taken into account.

We describe the imaging and characterization of native defects on a full field extreme ultraviolet (EUV) mask, using several reticle and wafer inspection modes. Mask defect images recorded with the SEMATECH Berkeley Actinic Inspection Tool (AIT), an EUV-wavelength (13.4 nm) actinic microscope, are compared with mask and printed-wafer images collected with scanning electron microscopy (SEM) and deep ultraviolet (DUV) inspection tools. We observed that defects that appear to be opaque in the SEM can be highly transparent to EUV light, and inversely, defects that are mostly transparent to the SEM can be highly opaque to EUV. The nature and composition of these defects, whether they appear on the top surface, within the multilayer coating, or on the substrate as buried bumps or pits, influences both their significance when printed, and their detectability with the available techniques. Actinic inspection quantitatively predicts the characteristics of printed defect images in ways that may not be possible with non-EUV techniques.

Printability and inspectability of phase defects in EUVL mask originated from substrate pit were investigated. For this purpose, PDMs with programmed pits on substrate were fabricated using different ML sources from several suppliers. Simulations with 32-nm HP L/S show that substrate pits with below ~20 nm in depth would not be printed on the wafer if they could be smoothed by ML process down to ~1 nm in depth on ML surface. Through the investigation of inspectability for programmed pits, minimum pit sizes detected by KLA6xx, AIT, and M7360 depend on ML smoothing performance. Furthermore, printability results for pit defects also correlate with smoothed pit sizes. AIT results for patterned mask with 32-nm HP L/S represents that minimum printable size of pits could be ~28.3 nm of SEVD. In addition, printability of pits became more printable as defocus moves to (-) directions. Consequently, printability of phase defects strongly depends on their locations with respect to those of absorber patterns. This indicates that defect compensation by pattern shift could be a key technique to realize zero printable phase defects in EUVL masks.

Management of mask defects is a major challenge for the introduction of EUV for HVM production. Once a defect has been detected, its printing impact needs to be predicted. Potentially the defect requires some repair, the success of which needs to be proven. This defect review has to be done with an actinic inspection system that matches the imaging conditions of an EUV scanner. During recent years, several concepts for such an aerial image metrology system (AIMS™) have been proposed. However, until now no commercial solution exists for EUV. Today, advances in EUV optics technology allow envisioning a solution that has been discarded before as unrealistic. We present this concept and its technical cornerstones.While the power requirement for the EUV source is less demanding than for HVM lithography tools, radiance, floor space, and stability are the main criteria for source selection. The requirement to emulate several generations of EUV scanners demands a large flexibility for the ilumination and imaging systems. New critical specifications to the EUV mirrors in the projection microscope can be satisfied using our expertise from lithographic mirrors. In summary, an EUV AIMS™ meeting production requirements seems to be feasible.

Reducing mask blank and patterned mask defects is the number one challenge for extreme ultraviolet lithography. If the industry succeeds in reducing mask blank defects at the required rate of 10X every year for the next 2-3 years to meet high volume manufacturing defect requirements, new inspection and review tool capabilities will soon be needed to support this goal. This paper outlines the defect inspection and review tool technical requirements and suggests development plans to achieve pilot line readiness in 2011/12 and high volume manufacturing readiness in 2013. The technical specifications, tooling scenarios, and development plans were produced by a SEMATECH-led technical working group with broad industry participation from material suppliers, tool suppliers, mask houses, integrated device manufacturers, and consortia. The paper summarizes this technical working group's assessment of existing blank and mask inspection/review infrastructure capabilities to support pilot line introduction and outlines infrastructure development requirements and tooling strategies to support high volume manufacturing.

EUVL is the strongest candidate for a sub-20nm lithography solution after immersion double-patterning. There are still critical challenges for EUVL to address to become a mature technology like today's litho workhorse, ArF immersion. Source power and stability, resist resolution and LWR (Line Width Roughness), mask defect control and infrastructure are listed as top issues. Source power has shown reasonably good progress during the last two years. Resist resolution was proven to resolve 32nm HP (Half Pitch) lines and spaces with good process windows even though there are still concerns with LWR. However, the defectivity level of blank masks is still three orders of magnitude higher than the requirement as of today. In this paper, mask defect control using wafer inspection is studied as an alternative solution to mask inspection for detection of phase defects on the mask. A previous study suggested that EUVL requires better defect inspection sensitivity than optical lithography because EUVL will print smaller defects. Improving the defect detection capability involves not only inspection system but also wafer preparation. A few parameters on the wafer, including LWR and wafer stack material and thickness are investigated, with a goal of enhancing the defect capture rate for after development inspection (ADI) and after cleaning inspection (ACI). In addition to defect sensitivity an overall defect control methodology will be suggested, involving mask, mask inspection, wafer print and wafer inspection.

To protect the reticle during shipping, storage and tool handling, various reticle pod concepts have been proposed and evaluated in the last 10 years. MIRAI-Selete has been developing EUV reticle handling technology and evaluating EUV reticle pods designed using "Dual Pod Concept" for four years. The concept was jointly proposed by Canon and Nikon at the EUV mask technology and standards workshop at Miyazaki in November 2004; a mask is doubly protected by an inner pod and an outer pod and the mask is carried into an exposure tool with the inner pod. Canon, Nikon and Entegris have started collaboration in 2005 and developed three types of EUV pod prototypes, alpha, beta and gamma. The gamma pods were evaluated by MIRAI-Selete and the superiority of the dual pod concept has been verified with many experimental data on shipping, storage and tool handling. The dual pod concept was standardized as SEMI E152-0709 "Mechanical Specification of EUV Pods for 150mm EUVL Reticles" in 2009. Canon, Nikon and Entegris have developed a new pod design compatible with SEMI E152; it has a Type A inner baseplate for uses with EUV exposure tools. The baseplate has two alignment windows, a window for a data matrix symbol and five pockets as the front edge grip exclusion volumes. In addition to the new features, there are some differences between the new SEMI compliant pod design and the former design "CNE-gamma", e.g. the material of the inner cover was changed to metal to reduce outgassing rate and the gap between the reticle and the side supports were widened to satisfy a requirement of the standard. MIRAI-Selete has evaluated the particle protective capability of the new SEMI compliant pods "cnPod" during shipping, storage and tool handling in vacuum and found the "cnPod" has the excellent particle protective capability and the dual pod concept can be used not only for EUVL pilot line but also for EUVL high volume manufacturing.

Nikon has been developing the full field exposure tool called EUV1 for process development of 32nm hp node and beyond. The unique feature of EUV1 is the capability of variable illumination coherence and off-axis illumination. EUV1 was installed in Selete and used for EUV lithography process development. Nikon also has conducted continuous collaborative works with customers using EUV1. Since the last SPIE Symposium in 2009, many exposure results with EUV1 tools were obtained. They showed excellent resolution capability beyond 24nm L/S with off-axis illumination and stable overlay capability of 10nm (Mean + 3 sigma). Process development exposures of test chip patterns are ongoing. With regard to HVM tool development, imaging capability with high NA projection optics and throughput capability are reviewed.

The NXE platform is a multi-generation EUV production platform that builds the technology, design and experience of both TWINSCAN™ and the two 0.25NA EUV tools (Alpha Demo Tools or ADT's) in use at two research centers for EUV process development. This paper reviews the EUV Industry status, presents recent imaging and device work carried out on the two 0.25NA ADT EUV tools and the status of the 1st production tool. Shipping in 2010, the NXE:3100 will be the 1st generation of the EUV exposure platform. With an NA of 0.25 and a productivity of 60wph this tool is targeted for EUV process implementation and early volume production at the 27nm node. We will highlight the key features of the NXE:3100. On our way towards shipment we describe the manufacturing status and performance data of optics, source and stages. The 0.32NA 2nd generation tool is designed as a lithography solution for high volume manufacturing with EUV at the 22nm node and below. With a productivity >125wph the NXE:3300 will be a cost effective solution for Lithography at the 22nm node and below. A 3rd generation with off-axis illumination at full transmission ensures extendibility of the NXE:3300 for resolutions down to 16nm.

Laser produced plasma (LPP) systems have been developed as a viable approach for the EUV scanner light source to support optical imaging of circuit features at sub-22nm and beyond nodes on the ITRS roadmap. This paper provides a review of development progress and productization status for LPP extreme-ultra-violet (EUV) sources with performance goals targeted to meet specific requirements from leading scanner manufacturers. The status of first generation High Volume Manufacturing (HVM) sources in production and of prototype source operation at a leading scanner manufacturer is discussed. The EUV power at intermediate focus is discussed and the lastest data is presented. An electricity consumption model is described, and our current product roadmap is shown.

Microfield exposure tools (METs) play a crucial role in the development of extreme ultraviolet (EUV) resists and masks. One of these tools is the SEMATECH Berkeley 0.3 numerical aperture (NA) MET. Using conventional illumination this tool is limited to approximately 22-nm half pitch resolution. However, resolution enhancement techniques have been used to push the patterning capabilities of this tool to half pitches of 18 nm and below. This resolution was achieved in a new imageable hardmask which also supports contact printing down to 22 nm with conventional illumination. Along with resolution, line-edge roughness is another crucial hurdle facing EUV resists. Much of the resist LER, however, can be attributed to the mask. We have shown that intenssionally aggressive mask cleaning on an older generation mask causes correlated LER in photoresist to increase from 3.4 nm to 4.0 nm. We have also shown that new generation EUV masks (100 pm of substrate roughness) can achieve correlated LER values of 1.1 nm, a 3× improvement over the correlated LER of older generation EUV masks (230 pm of substrate roughness). Finally, a 0.5-NA MET has been proposed that will address the needs of EUV development at the 16-nm node and beyond. The tool will support an ultimate resolution of 8 nm half-pitch and generalized printing using conventional illumination down to 12 nm half pitch.

Interferometry, the long-standing method for optical characterization, is difficult to perform at EUV wavelengths due to the lack of high power coherent EUV sources and difficult experimental setup. These problems are exacerbated by systematic errors from geometrical effects as EUV tools move to higher numerical apertures (NA) which require stricter tolerances for the optical elements involved in interferometry. In this paper we propose an iterative, image-based, in-situ method for optical characterization that is independent of the operating wavelength of light, illumination coherence, and NA of the system. In this method, a known pattern is imaged through focus, and matched to an experimental model with a trial set of pupil aberrations. The aberrations are then changed iteratively until the modeled images match the ones from the experiment. The Reduced Optical Coherent Sum (ROCS) decomposition for partially coherent aerial image calculation greatly reduces the computation time of each iteration which makes this method more computationally tractable.

The 22nm technology node is the target for insertion of Extreme Ultra-Violet (EUV) lithography into pre-production. To prepare this insertion, the issues that arise with the use of an EUV lithographic scanner in a pre-production environment need to be addressed. To gain better understanding of the issues that come with an EUV lithographic scanner, the Alpha Demo Tool (ADT) from ASML was installed at IMEC and is now in use since mid of 2008. In July 2009, the source was upgraded to a 170W/2π source to allow for higher uptime and wafer output by means of the semi-automatic tin refill. Also a new advanced resist, the SEVR-59 resist was introduced after the installation of the 170W/2π source to allow printing of 32nm Lines-Spaces (LS). After these changes, the ADT has been monitored closely with respect to the imaging performance. In this paper, we report on both the CD fingerprint analysis and the exposure tool stability. For 32nm dense LS, the ADT shows a wafer CD Uniformity (CDU) of 2.5nm 3σ, without any corrections for process or reticle. As for 40nm LS, the wafer CDU is correlated to different factors that are known to influence the CD fingerprint from traditional lithography: reticle CD error, slit intensity uniformity, focal plane deviation but also EUV specific reticle shadowing. The ADT shows excellent wafer-to-wafer stability (<0.5nm CD range in a 5-wafer lot) and the average CD as a function of exposure sequence is stable (<0.5nm 3σ in a 5-wafer lot). The ADT shows good CD stability over 5 months of operation with the 170W/2π source, both intrafield and across wafer. There is a 5nm difference in overlay performance (measured or after corrections) between the ADT and the XT:1900Gi production tool (using the same etched silicon wafers as a reference). Below 32nm, the ADT shows good wafer CDU for 30nm dense LS (60nm pitch). First 27nm dense line CDU data are achieved (54nm pitch). The results indicate that the ADT can be used effectively for EUV process development before installation of the pre-production tool, the ASML NXE:3100 at IMEC.

We are evaluating the readiness of extreme ultraviolet (EUV) lithography for insertion into production at the 15 nm technology node by integrating it into standard semiconductor process flows because we believe that device integration exercises provide the truest test of technology readiness and, at the same time, highlight the remaining critical issues. In this paper, we describe the use of EUV lithography with the 0.25 NA Alpha Demo Tool (ADT) to pattern the contact and first interconnect levels of a large (~24 mm x 32 mm) 22 nm node test chip using EUV masks with state-of-the-art defectivity (~0.3 defects/cm²). We have found that: 1) the quality of EUVL printing at the 22 nm node is considerably higher than the printing produced with 193 nm immersion lithography; 2) printing at the 22 nm node with EUV lithography results in higher yield than double exposure double-etch 193i lithography; and 3) EUV lithography with the 0.25 NA ADT is capable of supporting some early device development work at the 15 nm technology node.

Extreme ultraviolet lithography (EUVL) is moving into the phase of the evaluation of integration for device fabrication. This paper describes its applicability to the fabrication of back-end-of-line (BEOL) test chips with a feature size of hp 35 nm, which corresponds to the 19-nm logic node. The chips were used to evaluate two-level dual damascene interconnects made with low-k film and Cu. The key factors needed for successful fabrication are a durable multi-stack resist process, accurate critical dimension (CD) control, and usable overlay accuracy for the lithography process. A multi-stack resist process employing 70-nm-thick resist and 25-nm-thick SOG was used on the Metal-1 (M1) and Metal- 2 (M2) layers. The resist thickness for the Via-1 (V1) layer was 80 nm. To obtain an accurate CD, we employed rulebased corrections involving mask CD bias to compensate for flare variation, mask shadowing effects, and optical proximity effects. With these corrections, the CD variation for various 35-nm trench and via patterns was about ± 1 nm. The total overlay accuracy (|mean| ± 3σ) for V1 to M1 and M2 to V1 was below 12 nm. Electrical tests indicate that the uses of Ru barrier metal and scalable porous silica are keys to obtaining operational devices. The evaluation of a BEOL test chip revealed that EUVL is applicable to the fabrication of hp-35-nm interconnects and that device development can be accelerated.

Extreme ultraviolet lithography (EUVL) is the most promising candidate for the manufacture of devices with a half pitch of 32 nm and beyond. We are now evaluating the process liability of EUVL in view of the current status of lithography technology development. In a previous study, we demonstrated the feasibility of manufacturing 32-nm-node devices by means of a wafer process that employed the EUV1, a full-field step-and-scan exposure tool. To evaluate yield, a test pattern was drawn on a multilayer resist and exposed. After development, the pattern was replicated in SiO2 film by etching, and metal wires were formed by a damascene process. Resolution enhancement is needed to advance to the 22- nm node and beyond, and a practical solution is off-axis illumination (OAI). This paper presents the results of a study on yield improvement that used a 32-nm-node test chip, and also clarifies a critical issue in the use of EUVL in a wafer process for device manufacture at the 22-nm node and beyond.

Comparative lifetime studies of Mo/Si multilayer mirrors have been conducted at the Exposure Test Stand (ETS) using a pulsed Xe-discharge EUV source at XTREME Technologies GmbH (Göttingen, Germany). Due to the large, homogeneous exposed sample area a multi-technique study of EUV induced carbon contamination and cleaning can be conducted using standard surface science techniques. EUV-reflectometry, X-ray photoelectron spectroscopy (XPS), small-angle X-ray reflectometry (SAXR), and Out-of-band (OOB) reflectometry (200 - 1000 nm) were applied to investigate exposed samples and study EUV-induced changes of the surface composition. With this approach the influence of EUV-dose, cleaning-gas pressure and composition, and capping-layer material of the Mo/Si multilayer samples on the degradation and cleaning mechanism can be studied.

The problem of carbon contamination on extreme ultraviolet (EUV) optics, causing unacceptably low reflectivity in mirrors, must be solved before industry will adopt the technology on a production scale. Breaking vacuum, removing and then cleaning mirrors is a time-consuming and expensive method for dealing with the problem. A safe yet effective in situ method for cleaning EUV optics and maintaining vacuum chamber cleanliness is important for progress in EUV lithography. Carbon contamination has also been a problem for the scanning electron microscopes (SEMs) leading to reduced image quality. The use of low power downstream plasma cleaner has been shown to be effective in removing carbon contamination from SEMs. The plasma dissociates oxygen molecules into neutral oxygen radicals. These radicals flow throughout the SEM vacuum chamber and chemically remove the carbon contamination. Since the process works by chemical etch and not by sputter etch, the capping layer on EUV mirrors will not be damaged by the cleaning process. The production of chemically etching oxygen radicals by plasma cleaning was measured using a quartz crystal microbalance. The effectiveness of the downstream plasma cleaning process was also tested on EUV mirrors.

Dedicate beam line for R&D on contamination of EUV exposure tools (BL18) was constructed at Saga Light Source (SAGA-LS) and its operation has been started. BL18 has an advantage of long time exposure, which gives accurate data compared with high-EUV-intensity and short-time experiments using an undulator beam line at New SUBARU synchrotron facility. Carbon contamination growth under low irradiance EUV radiation with fluorocarbon gas injection was examined using Mo/Si multilayer mirror samples. In the EUV intensity region from 11 W/cm² to 0.01 W/cm², degradation rate of reflectivity did not depend on the EUV intensity. The degradation rate was proportional to the EUV intensity in the range of less than 0.01 W/cm². Carbon contamination due to resist outgas during EUV exposure was also investigated.

Outgassing of photoresist material and the related risk for optics contamination in extreme ultraviolet (EUV) exposure tools are concerns in the development of EUV lithography, especially towards the high volume manufacturing tools. The characterization however of which resist species are important for the contamination, and their quantification, is still very challenging. Currently various techniques are explored worldwide, but there is still no full consensus on which technique is most adequate. On one hand, investigation is done by measuring only the resist outgassing by residual gas analysis (RGA), pressure rise or other related analysis techniques. Another investigation approach is focusing on the measurement of EUV optics contamination by analyzing the contamination generated on a witness sample which is exposed in the vicinity of resist outgassing. In this paper, we have focused mainly on the witness sample approach as a possible candidate for photoresist qualification. Contamination results obtained at ASML's and imec's test equipment are compared, which enables better understanding of the parameters that can affect the resist related contamination growth. Moreover, the contamination generated on the witness samples is characterized in detail towards thickness as well as composition, by using various material analysis techniques. Finally the contamination behavior is compared to the RGA resist outgassing information for better understanding of the over-all issue. These findings form a solid basis to quantify the risks involved of using specific photoresist materials in high volume manufacturing exposure tools with a simple but adequate test method, applied to qualify resists.

Optics contamination remains one of the challenges in extreme ultraviolet (EUV) lithography. In addition to the desired wavelength near 13.5 nm (EUV), plasma sources used in EUV exposure tools emit a wide range of out-of-band (OOB) wavelengths extending as far as the visible region. We present experimental results of contamination rates of EUV and OOB light using a Xe plasma source and filters. Employing heated carbon tape as a source of hydrocarbons, we have measured the wavelength dependence of carbon contamination on a Ru-capped mirror. These results are compared to contamination rates on TiO₂ and ZrO₂ capping layers.

A host of complementary imaging techniques (Scanning Electron Microscopy), surface analytical technique (Auger Electron Spectroscopy, AES), chemical analytical and speciation techniques (Grazing Incidence Reflectance Fourier-Transform Infrared Spectroscopy, GIR-FTIR; and Raman spectroscopy) have been assessed for their sensitivity and effectiveness in analyzing contamination on three EUV reticles that were contaminated to varying degrees. The first reticle was contaminated as a result of its exposure experience on the SEMATECH EUV Micro Exposure Tool (MET) at Lawrence Berkeley National Laboratories, where it was exposed to up to 80 hours of EUV radiation. The second reticle was a full-field reticle, specifically designed to monitor molecular contamination, and exposed to greater than 1600J/cm² of EUV radiation on the ASML Alpha Demo Tool (ADT) in Albany Nanotech in New York. The third reticle was intentionally contaminated with hydrocarbons in the Microscope for Mask Imaging and Contamination Studies (MIMICS) tool at the College of Nanoscale Sciences of State University of New York at Albany. The EUV reflectivities of some of these reticles were measured on the Advanced Light Source EUV Reflectomer at Lawrence Berkeley National Laboratories and PTB Bessy in Berlin, respectively. Analysis and characterization of thin film contaminants on the two EUV reticles exposed to varying degrees of EUV radiation in both MET and ADT confirm that the two most common contamination types are carbonization and surface oxidation, mostly on the exposed areas of the reticle, and with the MET being significantly more susceptible to carbon contamination than the ADT. While AES in both surface scanning and sputter mode is sensitive and efficient in analyzing thin contaminant films (of a few nanometers), GIRFTIR is sensitive to thick films (of order of a 100 nm or more on non-infra-red reflecting substrates), Raman spectroscopy is not compatible with analyzing such contaminants because of laser-induced evaporation of the contaminant film. SEM and EUV reflectometry are effective in quantifying the impact of contamination on imaging performance and reflectivity, respectively.

We describe a null-field ellipsometric imaging system (NEIS) that provides for the real-time imaging of carbon deposition profiles on extreme-ultraviolet (EUV) optics in a vacuum system. NEIS has been demonstrated at NIST on a small chamber that is used for EUV optics lifetime testing. The system provides images of carbon deposition spots with sub-nanometer resolution thickness measurements that maintain good agreement with those from ex-situ spectral ellipsometry (SE) and x-ray photoelectron spectroscopy (XPS). The system will be implemented on several synchrotron beamlines for real-time monitoring of carbon film growth on optics during EUV irradiation.

As regard to EUV-Mask natural defect printability evaluation, several methods have been employed in the past. However, because of their inherent difficulties those methods have not been able to provide precise answers. In this paper, we used two improved methods for the evaluation of EUV-Mask natural defect printability capable of providing precise answers. One improvement involves marking of the defect locations which makes it easier to find the wafer printed defects; the other method involves CD-averaging of multiple exposure shots that results in more quantifiable answers.

A method for actinic inspection of EUV mask blanks is described, in which EUV photoresist is applied to the blank, flood exposed with EUV, and developed. The effect of both phase and reflectivity defects on the reticle is described in terms of a variation in intensity and phase of the standing wave in the resist. Thin film simulations are performed to evaluate the contrast generating mechanism for various blank defects. The method was introduced earlier by others 3 and was shown in experiments to transfer reflectivity defects on the reticle to the developed resist. We propose to reevaluate the technique with current state-of-the-industry capabilities of resist processing, contamination control and inspection. Various possible development directions are described.

Two methods will be presented to compensate for buried defects in patterned extreme ultraviolet (EUV) masks. The goal of the methods in this work is to prescribe modifications to the absorber pattern on an EUV mask with a buried defect so that the final image printed on the wafer matches the intended pattern through focus. The first method uses pre-calculated design curves to determine the required absorber modification for a given defect. This method is able to compensate for a defect in focus, but not through focus. A second method is presented, covering the defect with absorber, which reduces the effect of the defect through focus. Both of these methods work for pit and bump defects.

When EUV light is used to inspect mask defects, the reflective photons reveal information for both the mask structure and the mask defects. The number of reflective photons has to be enough for generating sufficient detector signals. A modeling technique based on Feynman path integral is utilized to calculate the number of reflective extreme-ultraviolet (EUV) photons scattered from photomask surfaces. For a 2D semicircular silicon defect, the capability of predicting the moving direction for each reemitting photon and the intensity of photons in different direction has been demonstrated.

With the projected rollout of pre-production extreme ultraviolet lithography (EUVL) scanners in 2010, EUVL pilot line production will become a reality in wafer fabrication companies. Among EUVL infrastructure items that must be ready, EUV mask carriers remain critical. To keep non-pellicle EUV masks free from particle contamination, an EUV pod concept has been extensively studied. Early prototypes demonstrated nearly particle-free results at a 53 nm PSL equivalent inspection sensitivity during EUVL mask robotic handling, shipment, vacuum pump-purge, and storage. After the passage of SEMI E152, which specifies the EUV pod mechanical interfaces, standards-compliant EUV pod prototypes, including a production version inner pod and prototype outer pod, were built and tested. Their particle protection capability results are reported in this paper. A state-of-the-art blank defect inspection tool was used to quantify their defect protection capability during mask robotic handling, shipment, and storage tests. To ensure the availability of an EUV pod for 2010 pilot production, the progress and preliminary test results of pre-production EUV outer pods are reported as well.

To accurately estimate the flare contribution from the out-of-band (OOB), the integration of a DUV source into the SEMATECH Berkeley 0.3-NA Micro-field Exposure tool is proposed, enabling precisely controlled exposures along with the EUV patterning of resists in vacuum. First measurements evaluating the impact of bandwidth selected exposures with a table-top set-up and subsequent EUV patterning show significant impact on line-edge roughness and process performance. We outline a simulation-based method for computing the effective flare from resist sensitive wavelengths as a function of mask pattern types and sizes. This simulation method is benchmarked against measured OOB flare measurements and the results obtained are in agreement.

EUV lithography is widely viewed as a main contending technology for 16nm node device patterning. However, EUV has several complex patterning issues which will need accurate compensation in mask synthesis development and production steps. The main issues are: high flare levels from optical element roughness, long range flare scattering distances, large mask topography, non-centered illumination axis leading to shadowing effects, new resist chemistries to model very accurately, and the need for full reticle optical proximity correction (OPC). Compensation strategies for these effects must integrate together to create final user flows which are easy to build and deploy with reasonable time and cost. Therefore, accuracy, usability, speed and cost are important with methods that have considerably more complexity than current optical lithography mask synthesis flows. In this paper we analyze the state of the art in accurate prediction and compensation of several of these complex EUV patterning issues, and compare that to 16nm node expected production needs. Next we provide a description of integration issues and solutions which are being implemented for 16nm EUV process development. This includes descriptions of OPC model calibration with flare, shadowing, and topography effects. We also propose a realistic (in terms of accuracy and mask area) flare parameter calibration flow to improve short and longer range flare correction accuracy above what can be achieved with only a measured EUV flare PSF.

The challenge of the Integrated Circuit size reducing leads to the development of new processes for future years. In the lithography domain, since several years, the EUV Lithography appears as a possible technique to reach the ITRS roadmap requirements. The EUV interferometry Lithography is still nowadays an efficient way to study and improve the EUV resist behaviors. Although the interferometer principle seems to be obvious, the optimization of its use is only reached regarding some huge constraints. In this work accurate numerical models and experimental studies have been developped. It shows that some undesirable effects can reduce the interference region and disturb the contrast of the resist printed lines. The EUV light is identified as the first issue. The beam divergence of EUV light affects the contrast quality of the fringes. The photometry computation, taking into account the optimum angular source light width is then detailed. The second cause is the Fresnel diffraction of light due to boundaries of the grating windows. Its superimposition with diffraction orders induces a damage of local printed interferences. This phenomenon leads to an edge disturbance of the interference fringes. The third cause addressed is the decrease of the interference area by the position of the wafer out of the focal distance. Possible shadowing effects are also shown.

Flare is a critical impact on extreme ultraviolet (EUV) lithography. Flare can be calculated by integrating flare point spread function (PSF) within the bright field. Flare PSF is defined as (1-TIS)δ(r)+PSF^SC(r); where TIS, total integrated scatter, is traditonally defined as integration of PSFSC to infinity, and r is distance on wafer. PSF^SC is traditionally derived from power spectral density (PSD) of surface roughness of mirrors of optics. However, the amount of scatter light depends on mirror PSDs, while a portion of scatter light having a larger scatter angle cannot reach wafer; this means there is energy loss in optics. Hence TIS should be defined as total amount of as-scattered light, while PSF^SC should be defined as amount of light reaching wafer for use to calculate image intensity. We then introduced two PSFs: PSF^SC and PSF^SC0. PSF^SC0 is directly derived from mirror PSDs and used to calculate TIS. PSF^SC is derived based on amount of light reaching wafer taking obscuration inside optics into account. We also applied other considerations: release of approximation in domain conversion from PSD to PSF, and scatter extinct effect by multilayer. Using these considerations we can calculate flare behaviors which agree well with experiments.

Flare is hard to control only by hardware-wise means in EUV lithography. Therefore flare compensation through layout correction is necessary. PSF is measured along various slit positions by using clearing resist pad with various sizes in EUV Alpha Demo Tool (ADT) in IMEC. The measured PSF is compared to that derived from mathematically calculated PSD modeling from surface roughness of the projection optics by suppliers. Degree of variation in flare level of real device is measured experimentally with real device layout with clearing pads in it. Flare is calculated as convolution of PSF (Point Spread Function) and pattern density. This requires astronomical amount of computational time, because PSF in EUV has a very long tail that could even reach around several tens of thousands micron range. Therefore we investigated the pattern density of real devices with increasing radius of annulus. If the pattern densities in each annulus are saturated in some level, convolution integral with shorter range is sufficient and longer tail part of PSF can be approximated with fixed DC flare level dependent on saturated pattern density. Finally we discuss about the pending issues regarding flare correction for real devices application of EUV lithography.

In the fabrication of interconnect test chips with a half pitch of 35 nm, we used an EUV full-field scanner (EUV1) for three critical layers: Metal 1, Via 1 and Metal 2. In this study, we focused on the Via-1 layer and investigated the printing characteristics of 35-nm via-hole patterns. There are three types of major via-hole patterns; aligned, staggered, and isolated. Simple optical proximity effect correction (OPC) and shadowing effect correction (SEC) were applied to the mask patterns to reduce the iso-dense bias and anisotropy of hole shapes. Mask critical-dimension (CD) correction enabled the fabrication of all three types of patterns with almost the same CD. A simulation analysis revealed the mask error enhancement factor (MEEF) to be about 2.5, the exposure latitude to be about 18%, and the depth of focus (DOF) to be about 100 nm for 35-nm via holes when the resist CD was 35 nm. The experimental results agree fairly well with the simulation results. The intra-field CD uniformity of 35-nm via holes is 3.3 nm (3σ). The intra-field overlay accuracy (Mean+3σ) between the Via-1 and Metal-2 layers is better than 15 nm. We used a multi-stacked resist to fabricate 35-nm via holes in a low-k dielectric layer. Moreover, we fabricated interconnect test chips and measured their electrical properties. The resistance of 32-nm vias is 12.4Ω, which meets the target of International Technology Roadmap for Semiconductors (ITRS). The yield of 40k dense via chains was over 70%. The results demonstrate that EUV lithography is useful for the fabrication of ULSI devices with a half pitch of 35 nm and beyond.

Berliner Glas KGaA is specialized on the manufacturing of high performance wafer and reticle chucks. Electrostatic chucks (ESC) are especially used in vacuum environments e.g. during lithographic processing, coating and etching. The main task of the chuck is to provide a well defined positioning and thermal stabilization of the wafer or reticle. Typical wafer materials are semiconductors like silicon and in some special cases dielectrics like magnesia, alumina or glass. For a functional characterization of the ESC clamps Berliner Glas has developed a measurement method to determine the clamp pressure with a Fizeau interferometer. The setup utilizes the local bending of clamped wafers to determine the effective clamp pressure. The clamp pressure is measured in the range of 20...500 mbar. This new method allows for a lateral resolution of the clamp pressure measurement. It can be calibrated by various methods. Direct computation of the clamp pressure based on the bending height or comparative measurements with vacuum chucking by the same chuck gives evidence for the quantitative results. Transient clamp pressure variation can be measured with a resolution of 2 mbar. The results can be used to qualify and optimize ESC´s and even for a local correction of the clamp force.

Much work has already been done on how both the resist and line-edge roughness (LER) on the mask affect the final printed LER. What is poorly understood, however, is the extent to which system-level effects such as mask surface roughness, illumination conditions, and defocus couple to speckle at the image plane, and currently factor into LER limits. Here, we propose a "rule-of-thumb" simplified solution that provides a fast and powerful method to obtain mask roughness induced LER. We present modeling data on an older generation mask with a roughness of 230 pm as well as the ultimate target roughness of 50 pm. Moreover, we consider feature sizes of 50 nm and 22 nm, and show that as a function of correlation length, the LER peaks at the condition that the correlation length is approximately equal to the resolution of the imaging optic.

Line-edge roughness (LER) remains the most significant challenge facing the development of extreme ultraviolet (EUV) resist. The mask, however, has been found to be a significant contributor to image-plane LER. This has long been expected based on modeling and has more recently been demonstrated experimentally. Problems arise from both maskabsorber LER as well as mask multilayer roughness leading to random phase variations in the reflected beam and consequently speckle. Understanding the implications this has on mask requirements for the 22-nm half pitch node and below is crucial. Modeling results indicate a replicated surface roughness (RSR) specification of 50 pm and a ruthenium capping layer roughness specification of 440 pm. Moreover, modeling indicates that it is crucial to achieve the current ITRS specifications for mask absorber LER which is significantly smaller than current capabilities.

The development of EUV lithography is critically based on the availability of suitable metrology equipment. The Physikalisch-Technische Bundesanstalt (PTB) operates an EUV reflectometry facility at the electron storage ring BESSY II, particularly to support the development of Extreme Ultraviolet Lithography. It has been shown that EUV scatterometry is a versatile metrology for characterizing periodic structures regarding critical dimension (CD) and other profile properties. The short wavelength of EUV is particularly advantageous, since it increases the sensitivity to structure roughness. On the other hand, structure roughness also modifies the diffraction intensities used for structure reconstruction based on rigorous calculations of EUV diffraction. We present here first investigations of the influence of roughness-induced modifications of diffraction intensities on the subsequent reconstruction of line profiles. A method is developed to numerically estimate changes in measured diffraction intensities induced by line edge and line width roughness. Finally, the reconstructed profiles for undisturbed and disturbed diffraction intensities are compared. For absorber lines of trapezoidal cross section, the height and mean CD at 50% height appear to be rather insensitive even for unrealistically large roughness amplitudes of up to 14 nm 1σ. The sidewall angle, however, decreases significantly with increasing roughness, with a particular sensitivity to line edge roughness as compared to line width roughness.

In extreme ultraviolet lithography (EUVL), the mask hangs on an electrostatic chuck and is moved laterally during exposition. For proper control of the chucked mask under corresponding inertial forces, static friction of the mask on the chuck is critical and an important input parameter for reliable theoretical modelling. To determine static and dynamic friction values, measurements were performed in vacuum on a mask blank with a test chuck, smaller than a real EUVL mask chuck, but otherwise nearly identical in its characteristics. Experimental results were obtained at various voltages for a materials combination of Low Thermal Expansion Glass (LTEM) for the pin chuck surface and a mask blank with a chromium metal backside metallisation, respectively. Dynamic friction was found to be only marginally smaller than static friction and values in the range from 0.27 to 0.33 were determined for the static friction coefficient under vacuum conditions.

Extreme Ultraviolet Lithography (EUVL) is one of the patterning technologies for the 22 nm node and below. Generally, EUVL used a reflectivity type mask consist of absorber layer on a mask blank substrate coated with Mo/Si multilayer. Especially, reflectivity from EUV mask multilayer could be one of the important factors to make EUV process to be ready for 22 nm node. In spite of the developed technologies, the reported experimental reflectivity (60-66 %) is much less than the theoretical reflectivity (73 %) from the perfect EUV mask multilayer because of the Mo/Si rough boundaries and multilayer top surface roughness. The surface roughness that occurs in deposition of multilayer makes the reflectivity loss. It seems that it might be difficult to reach the ideal reflectivity and 22 nm node process has to live up with the imperfect reflectivity. In this study, we focused on the influence of the surface roughness on the Mo/Si multilayer for 22 nm node. First we studied the reflectivity loss for the multilayer surface roughness. The magnitudes of short, medium, and long range roughness are compared in terms of the amplitude and phase non-uniformity because even 1 nm roughness can make huge difference in EUV. The aerial image and process latitude with surface roughness are studied and the possibility of 22 nm node patterning with surface roughness will be reported.

EUV-wavelength actinic microscopy yields detailed information about EUV mask patterns, architectures, defects, and the performance of defect repair strategies, without the complications of photoresist imaging. The measured aerial image intensity profiles provide valuable feedback to improve mask and lithography system modeling methods. In order to understand the photon-flux-dependent pattern measurement limits of EUV mask-imaging microscopy, we have investigated the effects of shot noise on aerial image linewidth measurements for lines in the 22 and 16-nm generations. Using a simple model of image formation near the resolution limit, we probe the influence of photon shot noise on the measured, apparent line roughness. With this methodology, we arrive at general flux density requirements independent of the specific EUV microscope configurations. Analytical and statistical analysis of aerial image simulations in the 22 and 16-nm generations reveal the trade-offs between photon energy density (controllable with exposure time), effective pixel dimension on the CCD (controlled by the microscope's magnification ratio), and image log slope (ILS). We find that shot-noise-induced linewidth roughness (LWR) varies inversely with the square root of the photon energy density, and is proportional to the imaging magnification ratio. While high magnification is necessary for adequate spatial resolution, for a given flux density, higher magnification ratios have diminishing benefits. With practical imaging parameters, we find that in order to achieve an LWR (3σ) value of 5% of linewidth for dense, 88-nm mask features with 80% aerial image contrast and 13.5-nm effective pixel width (1000× magnification ratio), a peak photon flux of approximately 1400 photons per pixel per exposure is required.

This paper presents the development of a practical system for super-precise evaluation of zero-CTE temperatures T(zero- CTE) of TiO₂-SiO₂ glasses for extreme ultraviolet lithography (EUVL) by measuring leaky surface-acoustic-wave (LSAW) velocity VLSAW with a line-focus-beam ultrasonic material characterization (LFB-UMC) system. This new system can evaluate T(zero-CTE) from 20 to 150°C on the surfaces of glass substrates for photomasks and optical mirrors located at different positions in EUVL systems. This system operates in a stabilized temperature measurement environment (e.g., 23.00°C). It was demonstrated at 225 MHz for homogenized TiO₂-SiO₂ glass specimens with different annealing temperatures and realized an extremely homogeneous glass ingot with a ΔT(zero-CTE) of 1.6°C around 23.2°C. This ultrasonic system enables both glass manufacturers and users to speedily inspect all glass substrates with reliable data of T(zero-CTE).

We present first damage threshold investigations on EUV mirrors and substrate materials using a table-top laser produced plasma source. A Schwarzschild objective with Mo/Si multilayer coatings for the wavelength of 13.5 nm was adapted to the source, generating an EUV spot of 5 μm diameter with a maximum energy density of ~6.6 J/cm². Singlepulse damage tests were performed on grazing incidence gold mirrors, Mo/Si multilayer mirrors and mirror substrates, respectively. For gold mirrors, a film thickness dependent damage threshold is observed, which can be partially explained by a thermal interaction process. For Mo/Si multilayer mirrors two damage regimes (spot-like, crater) were identified. Fused silica exhibits very smooth ablation craters, indicating a direct photon-induced bond breaking process. Silicon shows the highest damage threshold of all investigated substrate and coating materials. The damage experiments on substrates (fused silica, silicon, CaF₂) were compared to excimer laser ablation studies at 157 nm.

The development of EUV lithography is critically based on the availability of suitable metrology equipment. To meet the industry's requirements, the Physikalisch-Technische Bundesanstalt (PTB) operates an EUV reflectometry facility at the electron storage ring BESSY II. It is designed for at-wavelength metrology of full-sized EUVL optics. A total uncertainty of 0.10% for peak reflectance is achieved with a reproducibility of 0.05% and a reproducibility of 1 pm for the centre wavelength. Measurements at PTB use almost linearly polarized radiation, whereas EUV lithography machines are operated with unpolarized sources and the status of polarization changes throughout the optical system. Therefore, to transfer these high-accuracy measurements to the EUV optical components under working conditions, it is essential to study the polarization dependence. We present a detailed characterization of the state of polarization for our EUV reflectometry system. We will discuss the uncertainties of PTB's reflectometry for large oblique angles with respect to the influence of polarization. An example of such measurements is the characterization of large 5 sr collector mirrors for LPP EUV sources, the largest EUV optical components presently available.

In this study, multilayer morphology near the key anomalies in grating-like structures, namely sharp step-edges and steep walls, are examined. Different deposition schemes are employed. Based on cross section TEM analysis an explanatory model describing the morphology of the successive layers is developed. A further insight into the periodicity and the general performance of the multilayer is obtained by EUV microscopy. The main distortions in multilayer structure and hence EUV performance are found to be restricted to a region within a few hundred nanometers from the anomalies, which is very small compared to the proposed grating period (50-100 μm). These multilayer coated blazed gratings can thus be considered a viable option for spectral purity enhancement of EUV light sources.

Reported is a summary of multilayer deposition results by FOM on three elements of the projection optics of the ASML Extreme UV Lithography HVM tools. The coating process used is e-beam evaporation in combination with low-energy ion-beam smoothening. The reflectance of the coatings, which are covered with a special protective capping layer, is typically around 68%, with a maximum value of 69.6% and a non-correctable figure error added by the full multilayer stack of better than 35 picometer. The results are compared to the earlier coatings of the EUVL Process Development Tool.

Optical properties, including refractive index, photoabsorption coefficient, and film thickness, were derived with a specular extreme ultraviolet reflectivity (SEUVR) method at 13.5 nm using a newly built ultrahigh-vacuum reflectometer. Light at 13.5 nm was delivered from the 08A1BM-LSGM beamline at the National Synchrotron Radiation Research Center in Taiwan. Samples of thin-film polymethylmethacrylate (PMMA), round-robin resist (RRR), and underlayer materials were investigated. We observed an evolution in the reflectivity curve of most samples, which was ascribed mainly to a loss of thickness in the film caused by photoabsorption followed by an ablation effect. The thickness-loss rates of PMMA and RRR were (0.32±0.15) and (0.12±0.02) nm mJ^-1 cm², respectively, whereas the outgassing rate of RRR, scaled to a 0.4 W cm^-2 power density, was estimated as 1.3×10¹⁵ molecules cm^-2 s^-1. The loss of thickness was further proven by examining the thickness profile of overexposed samples with a profilometer. From these results, we have established a satisfactory correlation between the thin-film thickness losses with a structural metric, [σ_abs/doublebond equivalent per carbon atom]. The reflectivity curve stopped changing when the sample was overexposed. EUV photochemical reaction mechanisms were proposed, including outgassing by first-order exposure kinetics from the surface, which corresponded approximately to the linear ablation rate, and a slower diffusion process for outgassing from underneath the surface, which was observed for the overexposed sample as the stop of changes in the thickness.

This paper reports the extracted risk issues on practical EUV resist processes and discusses verifications of them. The risk issues were extracted with emphasis on critical dimension, defectivity and productivity for mass production EUV resist processes. The authors verified these risk factors by utilizing available empirical knowledge. The authors found that the micro loading effect of by-product in the resist development process was a key factor for CD uniformity. Also discovered, was that high surface energy differences on the patterned wafers were a key factor for defectivity. As a result, application of scan-dynamic development and dynamic scan rinse to EUV processes on a mass production level will contribute greatly to CD and defect control as well as productivity.

This paper summarizes the investigation of the evaluation methods of EUV resist outgassing based on pressure-rise, gas chromatography mass spectrometry (GC-MS) and quadrupole mass spectrometry (QMS). We discuss the merit and demerit about these three methods and propose an optimal employment of each evaluation method. In addition, detail results of resist outgassing evaluated from GC-MS were reported.

In this paper the contrast behavior of photoresists upon EUV exposure is addressed. During a lithographic exposure, the intended shape undergoes contrast loss which can be divided into two portions. One part is assigned to exposure tool induced contrast loss (e.g. aberrations of the exposure optics, mechanical stability of the system), while the other part is due to chemical processes in the resist during exposure and development. Both contributors have to be decoupled from each other in order to solely analyze the resist contrast loss. The method presented here is based on an experimental evaluation of dense line/space patterns obtained from EUV exposures. For decoupling of the resist induced contrast loss from the exposure tool contrast, the aerial image has to be determined. As an alternative EUV exposure tool the EUV interference lithography (EUV-IL) beamline at Paul Scherrer Institute is applied for resist qualification. The theoretical description of the sinusoidal aerial image of the EUV-IL tool is presented as well as the experimental method applied to analyze resist patterns in terms of resist contrast. Finally, the results are compared with data obtained from ASML's ADT EUV scanner.

Recently published experimental results indicate that current resists seem to be very hard to meet the International Roadmap for Semiconductors (ITRS) goals for Resolution, Line Width Roughness (LWR) and Sensitivity (RLS) simultaneously. This RLS trade-off has also been demonstrated through modeling work. RLS goals may not be possible for lithographers to achieve all three simultaneously by applying current standard chemically amplified resists and processes. In this paper, we have synthesized the various PAG(photo-acid generator) bound polymers for different anion size and other molecular weight (Mw). In order to reach the EUV resist targets, we investigate the effect of diffusion length on energy latitude(EL), resolution and LWR under DUV light and EUV exposure. We will also use DUV light to explore the impact of DUV contrast on the RLS relationships in EUV performances. We have measured Eth and LWR in DUV patterning process and correlated them with those obtained in EUV process. By using DUV light source we have setup EUV resist pre-screening and improving method.

This is the study report about post-develop defect on EUV resist. The resolution, sensitivity, LWR, etc. of EUV resist have been currently studied in the development phase. We have acknowledged that resist generates a lot of defects in its transition from i-line, KrF, ArF and immersion-ArF. However, those were just a couple of defect types in the transition, and they were eliminated through resist improvement. In this study, we confirmed EUV defect type using EUV exposure tool. We also evaluate defect generation using tetrabutyl- ammonium-hydroxide (TBAH) developer. We finally discuss on the difference of defect between using KrF and EUV exposure tool, furthermore difference of defect between using TMAH and TBAH developer.

As Extreme ultraviolet (EUV) lithography technology shows promising results below 40nm feature sizes, TOKYO ELECTRON LTD.(TEL) is committed to understanding the fundamentals needed to improve our technology, thereby enabling customers to meet roadmap expectations. TEL continues collaboration with imec for evaluation of Coater/Developer processing sensitivities using the ASML Alpha Demo Tool for EUV exposures. The results from the collaboration help develop the necessary hardware for EUV Coater/Developer processing. In previous work, processing sensitivities of the resist materials were investigated to determine the impact on critical dimension (CD) uniformity and defectivity. In this work, new promising resist materials have been studied and more information pertaining to EUV exposures was obtained. Specifically, post exposure bake (PEB) impact to CD is studied in addition to dissolution characteristics and resist material hydrophobicity. Additionally, initial results show the current status of CDU and defectivity with the ADT/CLEAN TRACK ACT^TM 12 lithocluster. Analysis of a five wafer batch of CDU wafers shows within wafer and wafer to wafer contribution from track processing. A pareto of a patterned wafer defectivity test gives initial insight into the process defects with the current processing conditions. From analysis of these data, it's shown that while improvements in processing are certainly possible, the initial results indicate a manufacturable process for EUV.

This paper communicates the use of cobalt-containing polymers in extreme ultra-violet lithography (EUVL). The polymers were synthesized in a two-step process through the complexation of dicobalt octacarbonyl, Co2(CO)8 to a mainchain alkyne-functional polyester obtained by polycondensation protocol. As indicated by thermal analysis, the cobaltcontaining polymers are characterized by a thermal transition around 110 °C assigned to a crosslinking process, a key factor in considering these materials as candidates for patterning assist layers (PAL) in EUVL. Positive and negative impacts of the metal component introduced through PAL upon the resolution, line-width roughness (LWR), and sensitivity (RLS) of the resist were investigated. The potential utility of these materials as wet developable PAL is also described.

For improving resist performance, we have developed new Low-Molecular resists for which the substituted position and number of protecting group have no dispersion for controlling the chemical properties, such as solubility rate to alkaline developer. And we evaluated their Electron beam (EB) and Extreme Ultraviolet (EUV) patterning performance. The EUV lithographic evaluation of these resists was carried out at SFET (small field exposure tool) in Semiconductor Leading Edge Technologies Inc. (Selete). Newly synthesized resists have shown high performance of sensitivity and resolution under EB or EUV exposures. In this paper, we outline the design of new low molecular weight resists. The material properties, EUV outgassing analysis and the patterning capability of these newly synthesized low molecular weight resists are reported.

The main development issue for EUV resists is how to concurrently achieve high sensitivity, resolution below 22-nm half-pitch (hp), and low line width roughness (LWR) in the required fine patterns. Sensitivity and resolution continue to be improved through advances in EUV resist material research. However, through the material-approach, LWR remains a difficult issue. Thus, LWR-reduction from the point of view of alternative resist processes was investigated. As a result, LWR improvement was obtained utilizing alternative developer and rinse solutions. However, a difference in the LWR-reduction effect of these processes depending on the type of resist material used was observed.

A new type of scissionable polymer based on main-chain acid-labile acetal linkages is reported as a photoresist for e-beam and EUV lithography. Four kinds of copolymers were synthesized via ring-opening metathesis polymerization (ROMP) using various ratios of acetal and norbornene-derivative monomers. Differential scanning calorimetry (DSC) analysis demonstrated that incorporation of bulky structure, i.e., norbornene-derivatives, provided copolymers with high T_g. According to thermogravimetric analysis (TGA), these copolymers had slight weight loss in the temperature range from 100 to 250°C. This weight loss is tentatively assigned to a cleavage process due to the presence of the acetal units. Both GPC and NMR analyses revealed that the main-chain of these copolymers was steadily chopped at scission moieties of acetal units by strong acids in solution, and was also chopped by photo-generated acid from PAG in thin-film. A steric barrier to the scissionable moiety is considered to hinder acidolysis, leading to improvement of main-chain stability. These copolymers were confirmed to make fine patterns by e-beam exposure, demonstrating them to be promising materials as photoresists for EUV lithography. Significant improvements are needed to meet the required resolution and photospeed performance for incorporation into viable EUV resists.

Some initial EUVL patterning results for polycarbonate based non-chemically amplified resists are presented. Without full optimization the developer a resolution of 60 nm line spaces could be obtained. With slight overexposure (1.4 × E₀) 43.5 nm lines at a half pitch of 50 nm could be printed. At 2x E₀ a 28.6 nm lines at a half pitch of 50 nm could be obtained with a LER that was just above expected for mask roughness. Upon being irradiated with EUV photons, these polymers undergo chain scission with the loss of carbon dioxide and carbon monoxide. The remaining photoproducts appear to be non-volatile under standard EUV irradiation conditions, but do exhibit increased solubility in developer compared to the unirradiated polymer. The sensitivity of the polymers to EUV light is related to their oxygen content and ways to increase the sensitivity of the polymers to 10 mJ cm^-2 is discussed.

Planar slabs of pure Sn and Li were irradiated with 1064 nm, 9 ns Nd:YAG laser pulses. The resulting plasmas were evaluated with an absolutely calibrated extreme ultraviolet (EUV) power tool, a transmission grating spectrograph, a pinhole camera, and a Faraday cup. These diagnostic tools have allowed us to determine EUV conversion efficiency (CE), EUV spectral emission features, EUV-emitting plasma size, and the kinetic energies and fluxes of ions at various laser intensities for both Sn and Li plasmas. The maximum estimated CE values for Li and Sn plasmas are 1 ± 0.1 % and 2 ± 0.2 %, respectively. The Li²⁺ Lyman-α line and Sn^8-13+ lines generate the in-band emissions of Li and Sn. The intensity of Li²⁺ lines was found to increase with laser intensity. However, the Sn unresolved transmission array (UTA) showed remarkable changes with at higher laser intensities, including the appearance of a spectral dip. EUV plasma images showed that Sn plasmas take on a conical shape, as opposed to the hemispherical shape of Li plasmas. Ion debris analysis showed the kinetic energies for Li ions are less than that of Sn ions under similar conditions. Moreover, the kinetic spread of Li ions has been found to be narrower compared to the kinetic energy distribution of the Sn ions. We also compared the ion flux emitted by Sn and Li plasmas.

Laser produced plasmas (LPP) of tin offer a promising source of EUV radiation for next generation lithography. By optimizing the laser power density the emission from the unresolved transition array (UTA) in tin can be centered around 13.5 nm thus providing a compact source of EUV light required by the semiconductor industry. However, there remains much to be discovered about the fundamental details of the plasma itself and the conditions for optimizing conversion efficiencies (CE). In the present work we have developed a system to investigate EUV emission from the Sn UTA in the temporal domain. Results are reported for 5, 10 and 50 ns gate widths with 5 ns resolution. The development and collapse of the UTA are shown to closely match the behavior of laser pulse over time.

This paper describes the development of laser-produced-plasma (LPP) extreme-ultraviolet (EUV) source architecture for advanced lithography applications in high volume manufacturing. EUV lithography is expected to succeed 193nm immersion technology for sub-22nm critical layer patterning. In this paper we discuss the most recent results from high EUV power testing and debris mitigation testing on witness samples and normal incidence collectors. Subsystem performance will be shown including the CO2 drive laser, debris mitigation, normal incidence collector and coatings, droplet generation, laser-to-droplet targeting control, intermediate-focus (IF) metrology and system use and experience. In addition, a number of smaller lab-scale experimental systems have also been constructed and tested. This presentation reviews the experimental results obtained on systems with a focus on the topics most critical for an HVM source.

EUV source for actinic mask metrology, particularly for defect inspection, requires extremely high brightness. The selfabsorption of radiation limits the in-band EUV radiance of the source plasma and the etendue constraint limits the usable power of a conventional single unit EUV source. Theoretical study and numerical modelling has been carried out to address fundamental issues in tin and xenon plasmas and to optimize the performance of EUV sources. The highly ionized xenon plasma in the presence of fast electrons demonstrates the enhanced radiance. Theoretical models and robust modelling tools are being further developed under an international collaboration project FIRE in the frame of the EU FP7 IAPP program. NANO-UV is delivering a new generation of EUV light source with an intrinsic photon collector. Extensive numerical modelling has provided basic numbers to select the optimal regimes for tin and xenon based source operation. From these designs, a family of specially configured multiplexed source structures is being introduced to address the mask metrology needs.

EUV sources for actinic mask metrology, particularly for defect inspection, require extremely high brightness. The selfabsorption of radiation limits the in-band EUV radiance of the source plasma and makes it difficult to attain the necessary brightness and power from a conventional single unit EUV source. One possible solution is through multiplexing of multiple low etendue sources. NANO-UV is delivering a new generation of EUV light source with an intrinsic photon collector, the i-SoCoMo™ concept, where a micro plasma pulsed discharge source is integrated to a photon collector based on an in situ active plasma structure. The source is characterized by high brightness, low etendue and very high irradiance, at moderate output power, without the use of external physical optics. Such a source could form the basic building block, through multiplexing of several units, to satisfy the very high brightness and moderate power requirement of the EUV sources required for actinic mask metrology. Based upon this multiplexing concept, a family of specially configured multiplexed source structures, the HYDRA™ design, is being introduced to address the mask metrology needs.

The development status of key technologies for a HVM laser-produced plasma EUV light source is presented. This includes the high-power RF-excited CO₂ laser, the Sn droplet target and the collector mirror lifetime enhancement technology. In this paper, we mainly discuss countermeasures for Sn ions and neutrals which cause mirror reflectivity degradation. The effectiveness of ion mitigation by a strong magnetic field was measured. We also observed that Sn neutrals were removed by etching gases and that the etching process did not degrade the effectiveness of the ion mitigation by the magnetic field. A part of this work was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan.

We show an atomic model of Sn for the EUV sources. We show an improvement of the model in terms of the selection of energy levels and correction of the wavelength of the emission lines including resonance and satellite lines of combined 4d-4f and 4p-4d transition arrays. Calculated spectrum agrees well with experiments, showing that the present model is useful both for theoretical investigation of the optimum conditions the EUV sources, and for the analysis of experimental spectrum. A modeling method to estimate the initial spatial profile of the discharge path for the analysis of laser-assisted discharge pumped plasma sources is also proposed.

The life-time of normal incidence collectors used in LPP EUV sources has been computationally investigated. A two-dimensional/ axisymmetric hydrodynamic-particle code is used to model the plasma expansion from the laser-droplet interaction up to the collector optic. The plasma is formed from the interaction of a Nd:YAG laser, operating at the fundamental frequency, with 50μm tin droplets. The simulation results show non-uniform mass-density distributions at the end of the laser pulse. As the expansion continues up to the collector, the non-uniformities continue to develop. Sn⁵⁺ is the most energetic ion impinging on the collector, with kinetic energies up to 7keV. The sputtering yields for Sn ions onto Mo and Si show a strong dependence on both the ion energy and their impact angle. The deposition of neutral tin atoms on the collector has also been assessed with a large scale hydrodynamic simulation. These results are used to investigate the build-up of tin vapor at the irradiation site.

Since its installment in 2004, Intel's extreme ultraviolet (EUV) micro-exposure tool (MET) has demonstrated significant improvements in ultimate resolution capability. Initially capable of printing 45nm half-pitch (HP) lines with a 160nm depth of focus (DOF), it is now capable of printing 22nm HP lines with up to a 275nm DOF and demonstrating modulation down to 18nm HP. Initial improvements in resolution have been chiefly attributable to the maturation of EUV masks and photoresists. Recent improvements that have enabled the 22nm HP imaging with a sizeable process window are largely due to new illumination options that have become available as a result of recent tool upgrades. In particular, the installation of a new nested Wolter collector with an additional outer shell that extended the maximum partial coherence (σ) from 0.55 to 0.68, in conjunction with an updated pupil wheel and apertures, has enabled new rotated quadrapole and on-axis dipole illumination settings with 0.36 inner σ and 0.68 outer σ. Here we present simulated contrast curves alongside the experimental imaging results for the Intel MET using the newly available quadrapole and on-axis dipole illumination settings and discuss our future plans for continued improvements to the Intel MET aerial image.