EUV Lithography has become the leading and perhaps only, candidate for extension of semiconductor lithography into the sub-50nm realm. This paper reviews the requirements for high volume, semiconductor lithography and examines the capability of EUVL to meet those challenges. The current state of EUVL technology is reviewed and the remaining challenges for insertion of EUVL into manufacturing are discussed.

The Engineering Test Stand (ETS) is a developmental lithography tool designed to demonstrate full-field EUV imaging and provide data for commercial-tool development. In the first phase of integration, currently in progress, the ETS is configured using a developmental projection system, while fabrication of an improved projection system proceeds in parallel. The optics in the second projection system have been fabricated to tighter specifications for improved resolution and reduced flare. The projection system is a 4-mirror, 4x-reduction, ring-field design having a numeral aperture of 0.1, which supports 70 nm resolution at a k₁ of 0.52. The illuminator produces 13.4 nm radiation from a laser-produced plasma, directs the radiation onto an arc-shaped field of view, and provides an effective fill factor at the pupil plane of 0.7. The ETS is designed for full-field images in step-and-scan mode using vacuum-compatible, magnetically levitated, scanning stages. This paper describes system performance observed during the first phase of integration, including static resist images of 100 nm isolated and dense features.

After the successful completion of the European program EUCLIDES in which core competence for Extreme UltraViolet Lithography (EUVL) technology was generated, ASML (system integration), Carl Zeiss (optics), and their partners have entered the next phase of the program: design and realization of an exposure tool called the alpha tool ((alpha) -tool). This tool should be completed in 2003, and will demonstrate 50-nm-node compliant imaging using full- field all-reflective four-times reducing optics, as well as high performance vacuum scanning wafer- and reticle stages. IN this paper we present the status of the project, as well as highlight the progress in the optics development and optics contamination mitigation efforts.

One of the most critical tasks in the development of extreme ultraviolet lithography (EUVL) is the accurate deposition of reflective multilayer coatings for the mirrors comprising the EUVL tool. The second set (Set 2) of four imaging optics for an alpha-class EUVL system has been coated successfully. All four mirrors (M1, M2, M3, M4) were Mo/Si- coated during a single-deposition run with a production- scale DC-magnetron sputtering system. Ideally, the multilayer coatings should not degrade the residual wavefront error of the imaging system design. For the present EUVL camera, this requirement is equivalent to depositing multilayer coatings that would add a figure error of less than 0.11 nm rms. In addition, all mirrors should be matched in centroid wavelength, in order to insure maximum throughput of the EUVL tool. In order to meet these constraints, the multilayer deposition process needs to be controlled to atomic precision. EUV measurements of the coated mirrors determined that the added figure errors due to the multilayer coatings are 0.032 nm rms (M1), 0.037 nm rms (M2), 0.040 nm rms (M3) and 0.015 nm rms (M4), well within the aforementioned requirement of 0.11 nm rms. The average wavelength among the four projection mirrors is 13.352 nm, with an optic-to-optic matching of 1(sigma) =0.010 nm. This outstanding level of wavelength matching produces 99.3% of the throughput of an ideally matched four-mirror system. Peak reflectances are 63.8% (M1), 65.2% (M2), 63.8% (M3) and 66.7% (M4). The variation in reflectance values between the four optics is consistent with their high frequency substrate roughness. It is predicted that the multilayer coatings will not introduce any aberrations in the lithographic system performance, for both static and scanned images of 70 nm - dense features.

EUV lithography is a successor to DUV/VUV lithography, and is the final photon base lithography technology. The concept of EUV scanners for 50nm node and below is considered by clarifying the similarities and differences between EUV scanners and DUV scanners. Illumination optics, projection optics, wafer alignment sensors and wafer focus sensors are examined. And the throughput model, overlay budget and focus budget are introduced. The concrete design of illumination optics and the requirements for sources are described. Numerical aperture, magnification and field size are discussed. EUV scanners for 50nm node and below are realized.

The IBM/Nikon alliance is continuing pursuit of an EPL stepper alpha tool based on the PREVAIL technology. This paper provides a status report of the alliance activity with particular focus on the Electron Optical Subsystem developed at IBM. We have previously reported on design features of the PREVAIL alpha system. The new state-of-the-art e-beam lithography concepts have since been reduced to practice and turned into functional building blocks of a production level lithography tool. The electron optical alpha tool subsystem has been designed, build, assembled and tested at IBM's Semiconductor Research and Development Center (SRDC) in East Fishkill, New York. After demonstrating subsystem functionality, the electron optical column and all associated control electronics hardware and software have been shipped during January 2001 to Nikon's facility in Kumagaya, Japan, for integration into the Nikon commercial e-beam stepper alpha tool. Early pre-shipment results obtained with this electron optical subsystem are presented.

The latest development status of EB Stepper is reported. The experimental data include the latest resist image data exposed by 100keV electron beam, mask error factors and dosage margins at several backscattered electron levels, transmission data of continuous membrane reticles, and recommended structures for alignment marks, etc. The basic studies related to system design are also explained, those are the strategy for the management of reticle deformation and the stitching accuracy in overlaid layers, etc. Through these data, the resolution capability down to 50nm technology node is clearly shown and alignment/stitching capability is also described. The requirement to a continuous membrane reticle is indicated from experimental data.

In electron beam projection lithography (EPL), one of the most crucial tasks is to develop a data post-processing system, namely, a specific tool to expose a faithful pattern for every subfield on the wafer based on the pattern layout data. This system includes two basic flows. The 1st flow is common for reticle fabrication, and the 2nd flow is unique for EPL. During the 2nd flow, based on the LSI pattern data, electron optics space-charge effect correction will be automatically and rapidly executed and output to the EPL system in order to adjust parameters such as focus, magnification, rotation and astigmatism. In addition, this system should perform such tasks as segmentations of subfields (including complementary division), arrangement of stripes and reticlets, and alignment mark insertion. For proximity effect correction, we will first use a pattern shape modulation first. Shape modification at stitching boundaries is also investigated. In summary, to achieve conformable EPL delivery to customers, a new data post- processing system is developed in collaboration with some suppliers.

Electron projection lithography (EPL) uses 100keV electrons to minimize the effects of beam blur, minimize forward scattering, and expose high aspect ratio resist patterns. When these electrons undergo collisions in the substrate, they decelerate and emit Bremsstrahlung photons. The Bremsstrahlung photons have a continuum spectrum with high energy, and absorption of these photons might damage device layers already present during the electron lithography step. A simulator that uses a Monte Carlo approach to track electron trajectories in this substrate calculates the Bremsstrahlung spectrum and its spatial distribution. The Bremsstrahlung temporal spectrum and spatial distribution was calculated with a model selected after reviewing various approaches described in the literature. The density of the Bremsstrahlung photons absorbed by the film stack of device layers is then calculated. Bremsstrahlung absorption by thin oxide layers on silicon is small compared to the SiO₂ bond density. For gate dielectrics containing high atomic number metals such as HfO₂, the absorbed flux of photons generated by the electron exposure is about one order of magnitude larger than for SiO₂ gate dielectrics. Because the gate dielectric for future CMOS devices is only a few nanometers in thickness and the pixel exposure time is only a fraction of a millisecond, few of the photons generated by electron exposure are absorbed in the gate dielectric. The effects of absorption in other layers is negligible. The calculated number of charges in the gate dielectric that result from photon absorption is not large enough to shift the flat band voltage by more than ~1 mV. For the cases simulated with this model, electron projection lithography is not expected to cause significant effects on CMOS gate dielectric properties, even for metal oxide dielectrics.

The Berkeley Electron Beam Simulator (BEBS) has been used with positive particles and induced lens aberrations to diagnose and partially compensate beam blur at high current. Simulation shows up to a 24% spot size reduction at 30(mu) A beam current with positive ions introduced in the beam column. Results also show that a proper amount of lens aberration can partially cancel the aberration induced by the global space charge effect. Over a 30% beam blur reduction has been achieved at 30(mu) A beam current. A 30(mu) A simulation requires roughly one hour with ten 500MHz processors. Results are also reported for using BEBS with both positrons and electrons as a stochastic effect simulator. This enables the isolation of the stochastic coulomb interactions from the space charge effect in any beam configuration and the direct measurement of the stochastic beam blur. Our simulation shows that the stochastic blur scales proportionally to I^0.62, in comparison with Jansen's prediction of I^0.67, where I is the beam current.

With the production of the first High-Throughput Alpha Tools, Electron Beam Projection Lithography (EPL) is entering the commercialization phase. Here, we report on the realization of the electron column modules for the SCALPEL HT/Alpha EPL systems, designed to demonstrate high wafer throughput at resolutions at and below 100 nm. We describe our highly modular setup of each electron optical component targeted at maximum flexibility and enabling a fast and smooth evolution towards higher throughput and resolution. By applying strict design and process rules we were able to set-up the complete production flow from the design, construction and manufacturing of the components of the ferrite/dielectric deflector based projection optics up to established qualification schemes within less than one year. A crucial point for the overall tool performance is the timely availability of system alignment and metrology strategies. Here we adapt state-of-the-art techniques from light optical lens manufacturing to a maximum amount. We discuss our metrology and alignment approach based on aerial image analysis combined with extensive electron optical imaging simulations and present first theoretical and experimental sub-100 nm results.

SCALPEL Differs from optical lithography in its use of high- energy electron imaging, electron-scattering contrast, a segmented mask, and a sub-field stitching architecture. Imaging performance of a high-throughput SCALPEL tool is primarily determined by geometric and space-charge aberrations, which both have unique dependencies on key optics parameters. A complete understanding of the imaging point-spread function (PSF) is vital to the optimization of a high throughput SCALPEL optical subsystem and the optimum use of mask pattern data bias for proximity effect correction (PEC). Previous image modeling with an assumed Gaussian PSF model was updated to use the PSF result of Monte-Carlo analysis of electron landing distributions. We find substantially different behaviors as a result of this more rigorous analysis. A proper evaluation of the true nature of the SCALPEL electron optics PSF and its dependencies in a scanning exposure mode allows for meaningful optimization and performance prediction in the area of critical dimension (CD) control.

The high-energy (100KeV) electron imaging process used by SCALPEL causes a dynamic heat load and wafer expansion response. Despite good thermal contact between the wafer and chuck, the dynamic distortion on a die length scale is too large to allow in the overlay error budget, and is fundamentally difficult to prevent or dissipate. However, the sub-field scanning strategy of SCALPEL allows us to implement a dynamic distortion-correction algorithm, by making a real-time position adjustment of the imaging sub-field. Analytical tools developed for understanding these phenomena could be applied in a purely predictive correction algorithm, in principle. However, these predictions are limited by the variability of chuck thermal contact, as well as by difficulty in handling the frictional chuck-attachment boundary condition. Hence, a means of improving upon a basic prediction is necessary to support a robust correction strategy. In this paper, I will explore the practical real-time implementation of a correction algorithm based on Adaptive Kalman Filter techniques, using dynamic alignment updates. Simulations demonstrate the feasibility of this approach to make a very close estimate of the ideal correction.

We developed highly precise x-ray masks and used them to fabricate 100-nm-rule gate and contact-hole (C/H) level masks for 4-Gb DRAM test processes. The masks consisted of 350-nm-thick TaBN absorbers, 3-micrometers -thick SiC membranes, 1- mm-thick Si substrates and 6.63-mm-thick Pyrex glass frames. The membranes and absorbers were deposited in facilities at Hoya Corporation. The frames were bonded to the Si substrates using anodic bonding resulting in a convex surface. An EB-X3 high-precision 100-kV electron-beam writer was used to delineate the patterns. The image placement (IP) accuracy was within +/- 15 nm in both the gate- and C/H-level masks. The critical dimension (CD) variations for 100 nm features measured in a 24 mm square chip area were within +/- 6 nm in the best case. The x-ray masks were used for overlay and CD control evaluating of he XRA mass production x-ray stepper developed by Canon, Inc. The overlay evaluation was done using a double exposure method. The C/H layer was exposed aligning to the gate marks by using the advanced dual grating lens (ADGL) method in global-alignment mode. The total overlay accuracy between the gate and C/H levels was better than +/- 30 nm, including the intra-chip IP errors caused by mask distortion. The overall CD variation for the resist patterns was within +/- 13.1 nm in the gate level and +/- 8.2 nm in the C/H level.

We have developed a new production of x-ray stepper for 100- nm device fabrication and beyond. In this paper, at first we introduced two techniques that are installed into our new stepper. The second, we reported a series of exposure results using the new stepper. First technique is a new method for gap setting, which we call direct gap setting (DGS) system. The DGS system is composed of a capacitive sensor and a reflective displacement laser sensor. Since this approach does not require any preexisting mark on the substrate, three channels of the DGS system automatically complete the gap setting with an accuracy of 1.5 micrometers in a measurement range of 10-50micrometers . Second technique is a scattered light alignment system (SLA), which is a video- based optical sensor. The digital signal processing of the SLA system calculates the relative displacement between mask mark and wafer mark. The stepper is installed in our Tanashi works for x-ray exposure test. In double exposure test using one x-ray mask, the stepper achieved an overlay accuracy (mean +/- 3(sigma) ) of -1 +/- 15nm for x-axis and 4 +/- 11nm for y-axis. The result demonstrates that PXL is a strong candidate for manufacturing as we approach 100-nm scale device replication and sub-100nm region.

Although the process of deep x-ray lithography with PMMA achieves good resolution, it requires significant exposure times because of the low sensitivity of PMMA to x-rays. Therefore resist materials, which can achieve high resolution, but which are inherently more sensitive than PMMA, are desirable. Here it is shown, that x-ray exposures of the SU-8 resist can achieve high resolution with substantially reduced exposure times. Irradiation at the synchrotron source of DCI at Lure (Paris) and MAXLAB (Lund, Sweden) demonstrated a reduced exposure time for a 600 micrometers thick SU-8 relative to PMMA. The does needed to obtain standing structures was 30 J/Cm³ for DCI and 52 J/CM³ for MAXLAB. A 600 micrometers thick PMMA resist requires a typical bottom does of 4 kJ/cm³, so Su-8 is considerably more sensitive to x-rays than PMMA. Preliminary critical dimension measurements (CD) of the 600 micrometers SU-8 resist structures have been obtained for the entire height of the structure, which was exposed at DCI. The CD measurements were made in a Scanning Electron Microscope (SEM) using 10 micrometers wide structures, which have a 20micrometers pitch, this being used to calibrate the measurements. These measurements show that the gain in the critical dimension per structure edge is dependent on the bottom dose. Doses of 30 J/cm³ achieved a CD gain per edge of +0.5 micrometers , while doses of 40 J/cm³ Yielded a CD gain per edge of 0.9 micrometers . However, the gain in the CD per edge is critically dependent on the solvent content in the resist. Doses of 40 J/cm³ into a resist with a 2% residual solvent content yielded CD gains per edge of 0.3micrometers . In addition, the dose profile in the resist does not change the CD values significantly. It has been shown that the resolution of the x-ray exposed SU-8 structures compare quite favorable with PMMA, but the exposure time for SU-8 is approximately 100 times less than that for PMMA. This significantly improves throughput for deep x-ray lithography processes.

The Vacuum Spark X-ray Source (VSX) embodies a miniature, high-repetition rate discharge emitting radiation in a broad spectrum optimized to emit soft X-rays with about 10 + wavelength. We have obtained over 100 (mu) J of energy per pulse in a narrow bandwidth centered around 7 Angstroms and pulse width less than 30 ns. The system operates with an ALFT proprietary pulser that yields a power output of 1 to 10 Watts of X-rays. A proprietary nested cone collimator is used to optimize the collection of the solid angle and direct parallel radiation towards the wafer. We predict this design will yield a throughput of 5 to 20 WLPH on 200 mm wafers. Presently, we are validating results obtained in the 1 - 5 WLPH range. ALFT's goal is to create an X-ray Point Source suitable for Next Generation Lithography. To date, two prototypes have been created to validate our theories and guide future development. The latest prototype has been designed to accept modifications to allow us to meet our 2001 performance goals. This year we achieved two major breakthroughs. We created a unique regenerating anode design that will enable thermal and debris management at the desired output levels, and we designed a trigger that ensures reliable discharge at repetition rates above 5 kHz. Following our previous SPIE Conference reports (SPIE Volume 3676-1, P. 410), the progress on the VSX Source is described here. Moreover, our technical roadmap is presented and the anode and trigger designs are disclosed.

There are some candidates discussed as potential high power EUV sources for EUV lithography. Laser produced and discharge produced plasmas are most promising. In principle, the most efficient steady state plasma can be well defined with respect to plasma temperature and density. However, the conversion efficiency of a practical EUV source is mainly determined by the efficiency of plasma generation and heating and by the dynamics during the emitting phase. The different approaches to achieve the most efficient EUV source imply different heating mechanisms, different plasma geometries, different plasma densities and different time scales. Moreover, each approach has individual technical aspects that influence the efficiency and the technical chances of realization. A general approach for comparing different EUV source concepts is presented based on a discussion of fundamental aspects of the plasma generation and based on technical issues.

The source is a critical factor for the success of Extreme Ultraviolet Lithography (EUVL). This paper presents an update of the EUV source requirements. A comparison of the currently measured source performance with the specification is presented. For the source choice, it is also essential to understand the limits of the source and the way the source or the total source/lithography system could be improved to meet the lithography tool requirements in time. Although none of the currently known plans is compliant with requirements for an EUVL production tool, significant further improvement of their performance in the future seems feasible. Detailed analysis of the source requirements and the way to meet production tool specification, including increase in repetition rate for all the sources, are presented. Increase in energy per pulse, determined by dose reproducibility limit, for some of the sources is also discussed. Additional attention is paid to optimization of the tool wavelength and heat load within the source chamber and of the optical components due to of-band source radiation.

Progress continues on the development of the EUV Electric Capillary Discharge Source. Over the past year we have studied the high average power operational characteristics, used interferometry to measure the in-capillary electron density, and further reduced the debris deposition rate on plasma facing optics. A pulser capable of driving the source at up to 1 kHz was acquired and preliminary testing is in progress. EUV flux and spectral emission measurements were made for pure xenon and xenon-helium mixtures using a new electrode designed to prevent debris from depositing on multilayer optics. Finally, through improvements in capillary and electrode design and material properties coupled with the assistance of mitigation approaches, we have been able to significantly reduce the amount of debris generated by the source thereby increasing the reflectance lifetime of plasma-facing optics.

Recent advances in the Dense Plasma Focus (DPR) under investigation by Cymer as an EUV light source have increased both the total energy storage capacity and the peak drive current. Previous generation DPF tools built by Cymer produced no measurable EUV radiation while employing Xenon as a source gas, but instead employed Lithium vapor due to its higher emission efficiency at low plasma temperatures. With Xenon as a source gas, this generation DPF exhibits efficiency similar to other sources employing direct electrical drive of the Xenon plasma. An emission efficiency of greater than 0.20% has been measured into 2(pi) str and 2% bandwidth centered at 13.5 nm. Other characteristics of this DPF have been measured such as energy stability, spectrum, source size, position stability, and operation at high repetition rates. In addition, the out-of-band radiation in the UV/Vis region (130nm-1300nm) has been measured and found to be only 0.38% of all radiation emitted by this source. Such low out-of-band radiation opens up the possibility of eliminating the Spectral Purity Filter and the problems associated with its use. This source concept does not use a multi-layer dielectric mirror as the first collector, but instead employs a grazing incidence collector that is more tolerant to debris. Progress has been made in the fabrication quality of this optic. Recent measurements of prototypes show that this optic will not degrade the source brightness. Also, a more efficient design has been created that consist of two shells coated with Ruthenium. This design collects and re-images 18.6% of the EUV radiation emitted into 2(pi) str.

An EUV light source, created when a high-average power (750 W) Nd:YAG laser forms a plasma in a xenon liquid-spray jet, has been characterized. This source has shown improved conversion from laser to EUV, and a more uniform angular distribution, as the laser pulse energy and average power are increased. System performance has been analyzed and compared with the requirements for future EUV microlithography tools for semiconductor manufacturing. EUV power scaling requirements and factors influencing Cost-of-Ownership are discussed.

New acetal or ketal blocking reagents were investigated for use in e-beam lithography and compared with the performance of ethyl vinyl either (EVE). Three blocking groups, (alpha) -Angelicalactone (AL), 6-methylene-5,6-benzo-1,4- dioxane (MBD), and MANA50 (an undisclosed blocking group used to show the potential of this chemistry) were reacted with poly(p-hydroxystyrene) (PHS) under acid catalyzed conditions to form AL-PHS, MBD-PHS, MANA50-PHS. The performance objectives pursued in the design of these new materials was to use acetal (ketal) chemistry to deliver wide process latitudes (e.g. good PED performance and minimal PEB sensitivity), use high molecular weight blocking groups to eliminate outgassing, and use the novel concept of multiple anions to deliver lithographic performance. These new materials are called Multiple Anion Nonvolatile Acetal (MANA) resists. Resists films were exposed with 50kV electrons, post exposure baked (PEB), and developed with 0.26 N TMAH. Resists prepared with the third blocking group, MANA50, gave contrast and imaging performance independent of PEB humidity and were relatively insensitive to PEB temperature and post exposure delay (PED). These resists gave the best resolution (90 nm) and profiles of all the materials tested, as well as showing no outgassing (as measured by film thickness loss).

Recently, there is significant interest in using CA resists for electron beam (E-Beam) applications including mask making, direct write, and projection printing. CA resists provide superior lithographic performance in comparison to traditional non CA E-beam resists in particular high contrast, resolution, and sensitivity. However, most current CA resists exhibit very large sensitivity to PAB and/or PEB temperatures resulting in significant impact on CD control. In addition, image collapse issues associated with high aspect ratio patterning as well as electron scattering effects in low KeV tools necessitate thinner resists. Therefore, there is a need to have a high etch resistant resist system that can withstand the demanding chrome etch process. Previously, we reported on the KRS-XE resist which exhibits dry etch resistance surpassing the industry standard, novolak, in the chrome etch process. This new resist also exhibits excellent lithographic performance - 75 nm lines/space and 55nm/110 space/lines delineated and requires no PEB. This paper will highlight the lithographic and etch performance of this new resist.

A theoretical comparison between the linear absorption coefficients at EUV wavelengths of 13 nm and 11 nm for more than 140 polymers revealed that the absorbance of organic polymers at 11 nm is ~30% lower than that at 13 nm. IN addition, the effects of oxygen content and density on the absorbance at 13 nm was theoretically investigated for organic polymers containing oxygen atoms. This investigation showed that, for organic polymers with about half the oxygen content of Novolak, the transmittance is 50% at a thickness of 200 nm and 60% at 140 nm. This further means that at 11 nm, the transmittance of the polymers should be 60% at 200 nm and 70% at 140 nm. These results suggest that a single-layer resist (SLR) process may very well be suitable for EUV resist processes. Further theoretical studies on silicon-containing polymers showed that, for a thickness of 200 nm and a wavelength of 13 nm, the transmittance would be in the range of 40-45% for silsequioxane polymers with some organic hydrocarbon parts, and in the range of 45-50% for siloxane polymers with some organic hydrocarbon parts.

Delay effects were evaluated for various chemically amplified resist (CAR) types in view of exposure conditions, vacuum and atmosphere. Since the mask is exposed in the vacuum chamber for a long period of time, unexpected phenomenon has been emerging in CAR such as pattern degradation, line width variation owing to vacuum delay effect (VDE). In the acetal resist based on ethyl vinyl ether (EVE), the VDE emerges as space CD decrease, while post exposure delay (PED) in an optical process shows space CD increase. Acrylate resist and modified acetal resist are superior in VDE as well as PED to EVE resist. VDE seems to be caused by out-gassing. It can be overcome by choosing out-gassing free chemistry such as acrylate and modified acetal. An over-coating method was evaluated to prevent any volatile materials in CAR from being evaporated in the vacuum, but it is disclosed ineffective to VDE. CAR linearity reaches to 0.2micrometers , and its resist and Cr pattern as well as OPC was equivalent to current e-beam resist, ZEP7000. Finally, we can have achieve 8.3nm CD non- uniformity in 3(sigma) in 135*135 mm² area that allows beyond 0.13micrometers device mask application.

A critical requirement for using thin polymer films in many microelectronics applications is the ability to selectively immobilize materials on patterned polymer templates. Selective surface functionalization using covalent solution- phase chemistries is the most direct approach, but suffers several drawbacks, including reduced reaction rates or yields on a surface compared to solution environments; surface template distortion due to reagent/polymer incompatibilities; and concerns arising from the use of hazardous or expensive materials. We describe here an alternative noncovalent patterning approach based on selective trapping of ligands in solvent-imprinted nanocavities on aromatic polymer film surfaces. Noncovalent binding is based upon exclusion of a ligand from aqueous solution into hydrophobic cavities within the polymer film. Spatial control of the binding is accomplished either by: increasing local hydrophilicity sufficiently to suppress ligand binding (masked DUV, STM, proximity x-ray), selective placement of the ligand on the film (microcontact printing) or selective removal of pre-loaded ligand from the film (25 kV or 50 kV e-beam). Retained reactivity of the adsorbed ligands is illustrated by fabrication of metal or fluorescent patterns on treated polymer surfaces. The fabrication of features in metal films with resolutions to ~40 nm is demonstrated.

New microlithography patterning technologies must be developed in order to meet the demands of advanced semiconductor manufacturing. This paper describes the development of a new top surface imaging technique that is designed to circumvent the difficulties associated with developing next generation single layer resists. Graft polymerization lithography is an extension of top surface imaging in which exposure creates an acidic surface that activates monomer deposition on top of the base layer. Silicon-containing monomers were synthesized in order to meet the graft polymerization process requirements. A QCM-monitored deposition system was developed to study the fundamental behavior of the deposition process as a function of temperature, pressure, and photoacid generator (PAG) loading. Volumetric, bulk polymer sorption measurements were used to provide insight into the critical sorption behavior that drives the deposition process. These fundamental studies led to a proposed process mechanism that explains the experimentally observed behavior. Finally, proof of concept imaging experiments were conducted that demonstrate the graft polymerization process through all lithographic steps.

In order to examine the suitability of nanoimprinting for wafer scale pattern definition, a commercially available hot embossing system, the EV520HE of EVGroup, Austria, has been used to imprint 4 inch substrates. The EV520HE is based on a production-proven wafer bonding system which guarantees compatibility with semiconductor fabrication conditions. A 4 inch silicon wafer fully patterned with structures from 400 nm to 100 micrometers size was used as a stamp. The patterns, having a nominal height of 260 nm were defined in poly-Si over SiO₂ by reactive ion etching. Different anti- sticking layers were applied to the stamps by monolayer self-assembling, among them (1,1,2,2 H perfluoroctyl)- trichlorosilane. Two different polymers, polymethylmethacrylate (PMMA) and a commercially available nanoimprint resist were used to spin-coat the substrates. Imprints were performed with temperatures of up to 225 degree(s)C, forces between 10 bar and 55 bar and holding times of 5 and 15 minutes. After separation of stamp and sample the imprints were characterized by a surface profiler and inspected by an optical microscope as well as a scanning electron microscope. Different qualities of pattern transfer according to the used process parameters were achieved, but patterning of the whole sample surface was always observed. In contrast to radiation-based lithography, the difficulties are based in imprinting of larger features whereas structures of 400 nm size were reproduced with high quality. Therefore the largest patterns of the stamp, 100 micrometers square bond pads, were used for imprint quality assessment, judged by the degree of stamp cavity filling around the pads. High quality was achieved by embossing at 225 degree(s)C with a hold time of 5 minutes at a pressure of 55 bar. For full wafer imprint only a small degradation of imprint quality from the center towards the periphery was observed. Further optimization of the process is required to minimize residual layer thickness for the hot embossing lithography step, taking into account the visco-elastic properties of the polymer material.

The Step and Flash Imprint Lithography (SFIL) process is a low-cost, high-throughput patterning technique with a sub- 100 nm resolution capability. Investigation by this group and others indicates that the resolution of replication by imprint lithography is limited only by the size of the structures that can be created on the template. It has also been demonstrated that the SFIL process is capable of eliminating contaminants from the template (master) during a step and repeat imprinting process. The low pressure, room temperature nature of SFIL and the transparent imprint templates make it particularly attractive for high- resolution layer-to-layer alignment. Another aspect of SFIL that assists in the layer to layer alignment is the presence of a thin layer of low viscosity liquid between the template and wafer prior to UV curing. The liquid maintains a small gap (~0.2 micrometers ) and acts as lubrication and damping agents, which allows for accurate in situ error measurement and compensation. In this paper, we present results from overlay alignment experiments using the SFIL process. A Canon mask aligner was modified to implement a layer-to-layer alignment scheme for SFIL. The objective of this research was to achieve alignment accuracy of about 0.5 micrometers , which is the practical limit of the X-Y stage in the mask aligner. The overlay alignment error measurements and the corresponding corrections in X,Y and Theta were performed using the modified mask aligner. In its current state, the alignment resolution appears to be limited by the resolution of the mask aligner stage. It is expected that other high resolution alignment techniques have been developed for optical projection lithography and X-ray lithography processes can be adapted to the SFIL process to significantly improve the alignment resolution.

Proximity printing is a high throughput and cost effective lithographic technique for production of e.g. large area flat panel displays. The resolution of this technique, however, is limited due to diffraction effects that occur at mask pattern edges. We can improve the resolution drastically by replacing the conventional photomask with a mask which compensates these diffraction effects. The resulting mask modulates phase and amplitude of the exposure beam in such a way that the required image is formed at a predetermined distance behind the mask. In this work we describe the basic principles behind the resolution enhancement technique and explain the mathematical model to design this new type of proximity mask. The feasibility of th method is demonstrated by theoretical calculations as well as by practical experiments. The diffractive structures that have been examined are designed to form an image at a distance of 50 micron behind the mask. The mask contains 2 amplitude and 4 phase levels and the pixel size is 1 micron. Under these conditions a 3-micron line/space pattern is clearly resolved, whereas under conventional conditions the image is completely distorted.

Masks for electron projection lithography require the use of thin membrane structures due tot he short scattering range of electrons in solid materials. The two leading mask formats for electron projection lithography are the continuous membrane scatterer mask and the stencil mask. The reduced mechanical stability of the membranes used for electron projection masks relative to conventional optical masks leads to increased levels of process induced image placement distortions. This paper evaluates the image placement distortions due to the pattern transfer processes on the continuous membrane mask format. Image placement was measured from both a cross-mask and intramembrane perspective to evaluate the effects of different patterns, pattern densities and density gradients on the observed image placement and the experimental results obtained were then compared to those predicted by finite element modeling.

EUV masks generally mandate rigorous scattering models as the thickness to wavelength ratio is typically on the order of 30:1. In addition, boundary conditions at the absorber/air interface lead to non-zero electric fields even in the absorber region while the phase itself generally experiences a complex cross mask behavior that is pattern type as well as size dependent. Using two different types of rigorous simulators that are based on the differential method (LithoLand) and the time-domain finite-element method (EMFLEX) we explore and quantify the subtleties associated with the EUV mask when compared to a thin mask obeying the Kirchoff approximation. Both rigorous simulators predict that 30 nm isolated pattern, especially for NA >0.20 experience a focus shift of about 50 nm relative to best focus for the thin mask case. This effect occurs even when the illumination is normally incident to the mask. Furthermore, the Bossung curve for isolated patterns show an asymmetry through focus that is absent for the thin mask case and is sensitive to the partial coherence condition of the illuminator. Nested features seem to be far more immune to this unexpected anomaly. The origin of the predicated focus shift and asymmetry is explained through the complex phase behavior for the EUV mask which is fundamentally different from the thin mask case.

The three-layer absorber stack for EUVL reticles currently consists of an absorber, repair buffer and etch stop layers. The repair buffer should exhibit high etch selectivity during the absorber etch processes (i.e. pattern transfer and focused ion beam (FIB) repair), be thermally and electrically conductive, optimally thin and have high etch selectivity to the silicon-capping layer over the Mo/Si multi-layer mirror. The absorber materials that have been studied in the past are TaSiN and Cr with SiON as the repair buffer on top of a Cr etch stop layer. The SiON repair buffer is insulating, exhibiting low thermal and electrical conductivity. Also, the required thickness for FIB repair is greater than 750 Angstroms using a standard 30-keV Ga⁺ FIB tool, while the etch selectivity to the silicon capping layer during pattern transfer is less than five to one necessitating a Cr etch stop. A sputtered carbon repair buffer exhibiting the required qualities has been studied. The carbon film is thermally and electrically conductive and exhibits extremely high reactive ion etch selectivity to the silicon-capping layer. Carbon also has the lowest sputter yield out of all the elements opening a larger FIB repair process window without using gas-assisted etching. A conductive repair buffer also prevents the possibility of static charge buildup on the mask that could damage patterns during an electrostatic discharge.

The EUV mask patterning process development depends on the choice of EUV mask absorber material, which has direct impact on the mask quality or performance such as CD control, defect control, and registration. In the past, several EUV mask absorber material candidates that include Al-Cu, Ti, TiN, Ta, TaN, and Cr have been evaluated. Our research indicated that TaN and Cr are the better candidates among the others evaluated. Cr absorber has been used for many optical lithography generations. Further extending Cr mask absorber to EUV lithography presents minimum impact to the currently mask technology infrastructure. TaN is a new film that has not been used in the currently mask technology. However, Ta based metal compound has been studied previously in x-ray mask technology. Its performance in EUV mask fabrication and printing was found compatible and comparable in many process steps and performance aspects to that of Cr absorber. In this paper, we will present our research and development work on TaN absorber EUV mask fabrication and characterization. The studies include material deposition study, etch development, cleaning compatibility evaluation, and mask printing test. The TaN absorber etch was able to achieve good etch profile and high etch selectivity to the buffer oxide layer. The cleaning benchmarking results showed that TaN absorber is compatible to the currently acid based Cr cleaning procedures and solution. No material damage or loss was found in the case of extreme harsh cleaning conditions used. The TaN thin absorber mask was successfully fabricated and printed in 10x microstepper at Sandia National Lab. Minimum feature of 70nm L/S were obtained.

Electron-beam lithography is the technique of choice to generate in a flexible and accurate way structures and components in the micrometer region and below. Due to its particular exposure strategy, i.e. matching equidistant subfields to a complete pattern, electron-beam systems show typical displacement effects known as stitching errors. These errors can be of dramatic disturbance if they occur in high resolution patterns. This paper presents an exposure scheme which essentially reduces stitching errors by using a multiple exposure technique. The influence of this technique on the value of stitching errors and its interference with the process window as well as total processing time is reported.

Most important issues in a precise X-ray mask fabrication are the mask materials and EB writing to achieve good accuracy in critical dimension (CD) control and image placement (IP). However, 1-to-1 X-ray mask is required severe accuracy in comparison with photo reticles. The following discussions focus on how to realize the precise IP accuracy. We installed and evaluated 100-kV electron-beam (EB) mask writer (EB-X3), and developed the writing process on a thin membrane. Key factors in accurate EB mask writing include not only EB positioning accuracy but also mask distortions caused by mask holding and the temperature change of the mask and a mask holder. This paper presents mask distortion characteristics due to the holding, temperature change, and then, good results of mask accuracy of 4-Gb dynamic random access memory (DRAM) test patterns (gate and contact layers) and 90 nm SRAM test patterns. In addition, we employed the advanced PAT method with 4-multi-pass writing that adequately compensates the process-induced mask distortion and the beam drift. These improvements resulted in IP accuracy of better than 10 nm (3(sigma) ), 100 nm CD uniformity within 8 nm (mean shift +/- 3(sigma) ) and the overlay accuracy within 10 nm for 4-Gb gate and contact layers with a 24 mm x 24 mm area on the X-ray membrane mask. These results demonstrate that we can actually fabricate precise X-ray membrane masks that meet our final target of IP accuracy corresponding to the 100 nm technology node.

We have developed a new registration technique for low energy electron beam lithography. A notable feature of this technique is the use of voltage contrast images caused by charging at the resist surface. Using the electron beam of incident energy range of 1keV to 4.5keV, we detected the mark buried by thick insulator films; even if direct access tot he marks by the primary beam is prevented, the mark detection is possible. The detection time is a few milliseconds, and it is sufficiently fast. We confirmed that this technique is available for various layers of DRAM. Also the possible mechanism that may explain the voltage contrast image caused by negative charging is discussed.

Ion Projection Lithography (IPL) uses electrostatic ion- optics for reduction printing of stencil mask patterns to wafer substrates. Key advantages of the technology are the high, non diffraction limited resolution, the great depth of focus associated with the very low numerical aperture, the stabilization of the image with pattern lock techniques and the fine tuning of the ion-optical system with multipole electrodes which allows for comparatively high mechanical tolerances of the tool. O demonstrate, that IPL will be able to met the requirements for industrial production a Process Development Tool has been designed, integrated and put into operation. Currently the adjustable ion optics is being optimized for full resolution and current. A waferstage designed for later integration into the PDT has been successfully tested at ambient air in a separate test bench system. A resist process and the stencil masks necessary for the ion optical experiments are available: Several chemically amplified resists have been tested under ion exposure and showed good sensitivity, contrast and dose latitude. Masks designed for resolution and overlay experiments have been manufactured.

Stencil masks, based on 150mm Si-wafers, with large diameter membrane fields have been fabricated for use in an ion projection lithography (IPL) tool. With a current membrane diameter of 126mm, the control of pattern placement is one of the major challenges. As the masks are produced by a wafer flow process, pattern distortions after membrane etch, caused by stiffness changes, have to be controlled. Additionally, stress inhomogenity resulting from SOI wafer blank fabrication, boron implantation and other process steps has to be addressed. These parameters will be discussed on a global and local scale. Results by both, experiments and FE modeling simulations are presented.

The production of high aspect ratio microstructures requires a lithographic technique capable of producing microstructures with vertical sidewalls. There are few techniques (eg proton beam micromachining, LIGA and Stereolithoghaphy) capable of producing high aspect ratio microstructures at sub-micron dimensions. In Proton Beam Micromachining (PBM), a high energy (eg 2 MeV) proton beam is focused to a sub-micron spot size and scanned over a resist material (eg SU-8 and PMMA). When a proton beam interacts with matter it follows an almost straight path, the depth of which is dependent on the proton beam energy. These features enable the production of multilevel microstructures with vertical sidewalls of high orthogonality. Proton beam micromachining is a fast direct write lithographic technique; in a few seconds a complicated pattern in an area of 400 x 400 micrometers ² can be exposed down to a depth of 150 micrometers . These features make proton beam micromachining a technique of high potential for the production of high-aspect-ratio-structures at a much lower total cost than the LIGA process, which requires a synchrotron radiation source and precision masks. Research is currently under way to improve the process that employs the SU-8 negative photo-resist as a mold to electroplate Ni. Experiments have shown that post-bake and curing steps are not required in this SU-8 process, reducing the effects of cracking and internal stress in the resist. Plated Ni structures can be easily produced which are high quality negative copies of the SU-8 produced microstructures.

The first environmental data from the Engineering Test Stand (ETS) has been collected. Excellent control of high-mass hydrocarbons has been observed. This control is a result of extensive outgas testing of components and materials, vacuum compatible design of the ETS, careful cleaning of parts and pre-baking of cables and sub assemblies where possible, and clean assembly procedures. As a result of the hydrocarbon control, the residual ETS vacuum environment is rich in water vapor. Analysis of witness plate data indicates that the ETS environment does not pose a contamination risk to the optics in the absence of EUV irradiation. However, with EUV exposure, the water rich environment can lead to EUV- induced water oxidation of the Si-terminated Mo/Si optics. Added ethanol can prevent optic oxidation, allowing carbon growth via EUV cracking of low-level residual hydrocarbons to occur. The EUV environmental issues are understood, mitigation approaches have been validated, and EUV optic contamination appears to be manageable.

Carbon deposition and removal experiments on Mo/Si multilayer mirror (MLM) samples were performed using extreme ultraviolet (EUV) light on Beamline 12.0.1.2 of the Advanced Light Source, Lawrence Berkeley National Laboratory (LBNL). Carbon (C) was deposited onto Mo/Si multilayer mirror (MLM) samples when hydrocarbon vapors where intentionally introduced into the MLM test chamber in the presence of EUV at 13.44 nm (92.3eV). The carbon deposits so formed were removed by molecular oxygen + EUV. The MLM reflectivities and photoemission were measured in-situ during these carbon deposition and cleaning procedures. Auger Electron Spectroscopy (AES) sputter-through profiling of the samples was performed after experimental runs to help determine C layer thickness and the near-surface compositional-depth profiles of all samples studied. EUV powers were varied from ~0.2mW/mm² to 3mW/mm²(at 13.44 nm) during both deposition and cleaning experiments and the oxygen pressure ranged from ~5x10^-5 to 5x10^-4 Torr during the cleaning experiments. C deposition rates as high as ~8nm/hr were observed, while cleaning rates as high as ~5nm/hr could be achieved when the highest oxygen pressure were used. A limited set of experiments involving intentional oxygen-only exposure of the MLM samples showed that slow oxidation of the MLM surface could occur.

Electron beam (EB) lithography has often been used for fabricating advanced ULSIs. Recently, to increase the writing throughput, electron beam projection lithography (EBPL) technology has been proposed (100kV acceleration voltage and 20-30(mu) A total currents). When we introduce the EBPL to practical use, it is important to develop a projection mask and a mask data conversion system, because there are many differences between the EBPL mask data and the conventional EB data. In EBPL mask conversion system, it is necessary to divide a full chip data into several 1mm X 1mm (250micrometers X 250micrometers on the wafer) sub-fields, which size is as same as one EBPL shot with format conversion. In this paper, we show the data conversion system that converts pattern data (GDS+U) to EBPL mask data. This system can maintain the hierarchy data structure in the dividing process. The patterns that located on the boundary between neighboring fields were treated as belonging in either field for preventing critical division. As a result, a data conversion system for EBPL mask, that can divide the device data with high speed and high quality, was successfully obtained.

A direct means of measuring an image blur of electron beam projection lithography (EPL) tools is described. An aerial image sensor used for the image blur measurement was fabricated and evaluated. The signal to noise ratio (SNR) was very high and the signal contrast was 97%. The measured image blur, defined as the distance between 12% and 88% of the beam edge profile, under the optimum condition was 13 nm and the measurement repeatability was 3 nm (e sigma). The measurement error due to the sensor was extremely small, and a quantitative measurement of the image blur can be realized using this technique. The application of this technique to a system calibration is demonstrated. Focus and astigmatism were measured and the optimum settings of focus coils and stigmators were determined with an excellent repeatability. The potential for this technique to provide an automated self-calibration system on the EPL tools is clearly shown.

Generation of x-ray and extreme ultraviolet (EUV) radiation from laser-produced source with a new double-stream gas puff target has been investigated. The target was formed by pulsed injection of heavy gas (argon, or xenon) into a hollow gas stream from helium by using a double-nozzle setup. This new approach allows to form a high-density gaseous target at a relatively large distance from the nozzle output. X-ray emission was produced by irradiation of the argon/helium target with pulses of 1 ns time duration with energy up to 20 J from a Nd:glass laser. Strong x-ray emission at the wavelength near 0.4 nm from the argon target, similar to the emission from the solid sulphur target irradiated in the same conditions, have been observed. These new results may be useful to develop a laser-produced radiation source for x-ray lithography. To generate EUV radiation the xenon/helium target was irradiated using a Nd:YAG laser producing pulses of 10 ns and 0.7 J or energy. Efficient production near 11 nm from the xenon target exceeding emissions from solid targets was observed that should be useful for EUV lithography.

Home made masks having thick (35-50 micrometers ) silicon membranes as blanks were used in deep X-ray lithography of SU8 - a negative tone photoresist. X-ray masks were fabricated by the following sequence of steps: (a) vacuum deposition of Ti and Au thin layers on a 220 micrometers thick (100) silicon wafer, (b) optical lithography of two different patterns in both negative (SU-8) or positive (AZ4620) photoresist (c) gold electroforming and (d) silicon substrate thinning with KOH etch to form the membrane. X-ray exposures was performed in the X-ray beam line of the LNLS synchrotron light source. The samples consisted of 125 micrometers thick layers of SU-8 supported on silicon and assorted substrates. The optimum dose for silicon substrates have been used in the remaining substrates, namely, metallic thin films (Cr, Cu, Au, Pt), printed circuit board (PCB), quartz, alumina ceramic and glass. The influence of mask defects, substrate type and X-ray dose values on the lithography of SU-8 is discussed. Criteria for defining upper and lower dose values for SU-8 X-ray deep lithography was proposed on the basis of characteristic defects. Advantages in using SU-8 rather than PMMA in the LIGA technology are commented.

Laser produced plasmas (LPP) provide a stable source of EUV making them well suited for use in next-generation lithography tools. The plasma is generated by directing a laser at a target composed of a partially condensed gas after it undergoes a supersonic expansion through a nozzle and enters a vacuum chamber. The expansion process results in very cold temperatures such that the gas partially condenses forming a mixture of gas and small clusters. The clusters absorb the laser energy leading to the formation of the plasma, but the excess gas absorbs some of the emitted EUV reducing the net output of the LPP. Calculations were carried out to determine the amount of EUV absorbed by the gaseous xenon that surrounds the plasma. The Navier-Stokes equations were solved to obtain the gas density field. Observations from experiments were used for the shape of the plasma, which showed it to be approximately that of a prolate spheroid. The relative EUV signal strength was obtained as a function of the direction angle by calculating the absorption of EUV in the gas surrounding the plasma and integrating over the plasma surface. Calculated results for the normalized EUV energy distribution compare well with measurements of the EUV angular distribution obtained in experiments.

Thermal deformations of lithographic reticles during the exposure process may become an important consideration for all candidate Next-Generation Lithography technologies as these reticles are subject to stringent image placement and flatness requirements. The reflective reticles used for extreme ultraviolet lithography (EUVL) absorb energy during exposure producing temperature gradients and thermomechanical distortions that result in pattern placement errors. As throughput requirements of EUVL are increased, the necessary illumination power levels rise producing higher reticle temperatures. The use of a low-thermal-expansion substrate material reduces, but does not eliminate, reticle distortions, and the thermal and structural boundary conditions greatly influence the thermomechanical response. These factors make the accurate predictions of the reticle thermal and structural response essential to the design of EUVL systems. Previously published analyses focused on relatively low throughputs, 10 wafers-per-hour (wph), and 200-mm diameter wafer substrates. Proposed production systems have throughputs of 80 wph and use 6-in. square substrates. Finite element models of current format EUV reticles have been developed to simulate the reticle's thermomechanical response to high-throughput exposure heating and assess the resulting image placement errors. The results of thermal and structural analyses for a variety of EUVL load and boundary conditions are presented.

According to the International Technology Roadmap (ITRS) EUV exposure tools are expected to support both logic and memory manufacturing for the 70 nm node and beyond. In order to meet the CD control and overlay requirements at the expected tolerance levels for high volume manufacturing, tool performance from ideal need to be assessed and quantified, the impact of lens aberrations and flare to the aerial image at the system level were studied for three different technology nodes of interest: 70, 50, and 35 nm. This was done by computing the electric field at the mask level by making use of a rigorous mask simulator based on the differential method. The subsequent aerial image was then computed by suing a standard scalar imaging model. The effects on critical dimensions (CDs) through focus as well as overlay were investigated in order to arrive at a tolerance level for lens aberration and flare contribution at the system level. It is shown that isolated line CD control requirements set an upper limit on the overall imaging performance while for overlay both feature types seem to play a similar role that defines the tolerance limit. Mandating a 10% CD control range leads to a 30 milli Wave (RMS) aberration requirement. This conclusion was reached by analyzing the response of each of 37 Zernike coefficients separately for both isolated and nested lines. Employing two separate sets of KrF PMI data that were scaled to a range of RMS values seemed to further reinforce the previous aberration tolerancing conclusion. A separate but similar flare analysis indicates that cross field flare variations need o be controlled to within 2% to meet CD control requirements that are consistent with ITRS roadmap.

In this article we describe a laser plasma source for Extreme Ultraviolet Lithography (EUVL) based on a liquid water jet target. Although jet targets are known for some time now, no attempts have been made to prove the functionality of the target under conditions similar to an EUVL production-line facility, that means illumination with high average power laser systems (in the multi-kW regime) at repetition rates in the kHz region. Such systems are currently under development. We used the MBI-burst laser to simulate these extreme illumination conditions. We examined the hydrodynamic stability of the target as a function of the laser repetition rate at different average laser powers (0.6kW and 5kW per burst). Additionally, the dependence of the conversion efficiency on pulse duration in the range from 30ps to 3ns was investigated. From our results one can conclude parameters for future design of driver lasers for EUVL systems.

An advanced point diffraction interferometer for measuring EUV aspherical mirrors with high accuracy has been developed. It is designed for measuring various EUV mirrors with high accuracy and high precision. It can measure the surface figure of all mirrors that will be used in high numerical aperture systems. Using this interferometer, 0.1nm rms precision and 0.2nm rms accuracy are expected.

Models for the printability of buried 3D EUV defect are analyzed and extended using rigorous electromagnetic simulation by TEMEPST. Parallel simulation on a network of workstation was used to examine the classical assumptions of coherent illumination, uniformly filling the entrance pupil and vertical propagation in the theoretical model of Gullikson for Gaussian defects. Results show that the limitation of the model is the lack of uniformity of filling the pupil for defects with diameter (2*sigma) larger than 0.20 (lambda) /NA at the wafer plane. Beyond this diameter the dip in the clear field intensity no longer follows the quadratic decrease with size and height of the model. Rather the dip quickly goes through its worst-case minimum intensity near 70 nm and then rises as the size further lowers the local surface slope. The worst-case image decrease from the clear field value for any sized Gaussian defect is roughly 18% per nm of height. Thus isolated Gaussian defects with height less than 2 nm will never reduce the field intensity to less than 60% of the clear field value.

A laser-based EUV plasma source for diagnostics purposes was developed, which is going to be utilized primarily for characterization of EUV optical components and sensoric devices. The emission characteristics of the generated 13nm radiation is monitored by the help of different diagnostic tools, including a pinhole camera, an EUV spectrometer and various EUV photodiodes. Moreover, first wavefront measurements of EUV radiation were performed with the help of a specially designed wavefront analyzer based on the Hartmann-Shack principle, which was sensibilized for 13nm radiation.

In this work, ablative and gas capillary discharges have been investigated as potential sources for the EUV lithography technology. Carbon and lithium ablative discharge spectroscopy and EUV energy measurements have been performed. Gas (O₂, Ne, Ar, Kr and Xe) capillary discharge were powered by fast, nanosecond, high voltage Blumlein-like pulser. Detailed investigation of capillary length and diameter, gas pressure, capacitance and inductance of the electrical driver are documented. The energy density, expressed in J cm^-3, appears as a monitoring factor for an efficient production of 13.5 nm radiation band. The measurement and the evaluation of measurement uncertainties lead to the conclusion that the in band, 13.5 nm +/- 0.9 nm, energy radiated by the Xe lamp developed in this work ranges from 0.5 mJ/sr/shot to 20 mJ/sr/shot for a 7 J energy input. Repetition rate investigation of the first prototype have shown operation at 50 Hz in continuous mode and up to 350 Hz in burst mode.

We demonstrate the use of a 13.4-nm wavelength, 10x-demagnification Schwarzschild optical system to expose high-resolution test patterns, extending well beyond the conventional resolution limit to dense feature sizes of 50 nm and below. We have successfully used a spatial frequency doubling technique to print equal line and space patterns with line widths as small as 30 nm. Simulations show that by using the fully extended numerical aperture, the system may achieve line widths as small as 12 nm. This configuration shows great potential for use in evaluating the ultimate performance and extendibility of resist materials for EUV lithography.

We proposed a new adjustment method for the beam-intensity distribution. On the 2nd shaping aperture plate, a small aperture is positioned sufficiently apart from the aperture for variable shaping. The center of the 1st shaping aperture image is moved to the small aperture by adjusting an alignment coil. The beam current, which passes through the small aperture, is measured by the Faraday cup on the target while the 1st shaping aperture image is scanned over the small aperture by operating the shaping deflector. Using this method the beam-intensity distribution of the 1st shaping aperture image on the 2nd shaping aperture plane is obtained. The beam-intensity distribution obtained is ideally a series of concentric circles and the maximum value is reached at the center circle. The center is shifted when the alignment of the limit aperture at the illumination or at the 1st shaping aperture is incorrect. The position of the maximum in the beam intensity is adjusted to the center of the 1st shaping aperture image. At the beam-current-density of 20 A/cm², the slope of the distribution is usually under 1 percent. To evaluate the adjustment accuracy, resist profile of drawn pattern is measured by AFM. The resist profiles in a beam shot coincide well with the beam intensity distribution.

A stable high-resolution electromagnetic deflection control circuit for an electron-beam lithography (EBL) system has been developed. This deflection control circuit has enabled an EBL system to deal with a wide deflection area of 2.5-mm square having fine address units for a pattern placement of 1.25 nm. The deflection-control circuit consists of a new digital to analog converter (DAC) circuit, whose resolution is 21 bits, and a low-drift current-amplifier circuit. To achieve such high-stability and high-resolution, we had to develop a low noise-current cell structure for the new DAC circuit, because the output-signal noise of the DAC circuit is a major source of interference at the desired resolution. A local temperature control technique has been incorporated into the circuit to reduce fluctuations of the deflection control signal caused by ambient thermal variations. The low noise-current cell structure, which consists of multiple current buffers and low-pass filters, is placed between a constant current source circuit and a differential-switch circuit for each bit of the DAC circuit. The simulation results of the DAC circuit showed that the output-signal noise of the DAC circuit could be reduced to less than 0.4 nm rms, which is small enough to achieve the desired resolution. As the results of the experimentally evaluation of the deflection control circuit show, the total noise of the deflection-control signal obtained was less than 0.6 nm rms and the signal stability obtained was better than 0.3 nm rms. An evaluation of the performance of the new EBL system to which the new deflection control circuit was applied, showed that the critical-dimension accuracy obtained was better than 5 nm (3sigma) and the positioning accuracy obtained was better than 10 nm (3sigma) for the area controlled by electromagnetic deflector.

We have developed a stitching accuracy measurement system for electron beam (EB) direct writing and electron beam projection lithography (EPL). This system calculates the amount of a stitching error between two EB shots from SEM images. It extracts a representative edge line of each pattern from the graphical format files (BMP, JPEG etc.) of SEM images and calculates a distance between each edge line as a stitching error. For obtaining a higher stitching accuracy of EB direct writing or EPL machines, it can analyze the relation of amounts and direction of a stitching error with a field size or a field position of these machines. We could successfully measure about 2.0 nm as a stitching error value in 0.1 micrometers L/S resist patterns on a bare-Si substrate and obtain 1.2 nm (3(sigma) ) as the measurement repeatability. It took 2.5 sec. for this system to measure one stitching region.

A reduction efficiency of shot numbers in character projection (CP) electron-beam (EB) lithography with memory device application depends on a design rule (cell size) and a pattern complexity within a memory cell. Many researchers reported that it was approximately 1/10 to 1/100 compared with conventional variable-shaped beam (VSB) method. The reduction of shot numbers in memory devices mainly comes from allowance to place multiple cells in one CP-cell area and simplicity of the cell's placement (regular pitch with adjacent allocation). On the other hand, there are few reports concerning reduction efficiency of shot numbers with logic specific application in CP EB lithography due to the complexity of logic cell's allocation to CP-cell area. To analyze this, logic device layout data in 70nm node was prepared by shringking actual functional device data of 350 nm node in the ratio of 1/5 and extracting random logic region. The size of this region was 1,094 x 283 micrometers . The height of logic cell was 2.64micrometers and it was smaller than typical one CP-cell size in second aperture (5 x 5micrometers ). The pattern data in GDS-II stream format was converted into EB exposure data: divided figures (rectangles). By this procedure, numbers of figures and cells were obtained. The total number of referred logic cell was 26,812. Among 26,812 cells, only 111 common (unique) logic cells were used for the logic region. The sum of figures in gate layer was 412,251 and this value was assumed to be equal to a total number of shots in conventional VSB method. Among the 111 common cells, only 6 cells in the gate layer showed width more than 5micrometers (maximum CP-cell size). Most frequently referred cell was an inverter and the number of reference was 5,395. The referred frequency of each cell exponentially decreased when the cells were arranged in descending order of reference. Among the total figures, top cell showed 66,120 accumulated number of figures (referred number=2,204, figures in cell=30). The cumulative number of total shots also exponentially decreased when cells were arranged in descending order of total shots. So it is necessary to decide the appropriate maximum number of CP- cell for futur CP EB exposure systems considering the reductoin efficiency of the shot numbers. For the current CP EB exposure tool of Hitachi (HL system), allowed number of CP-cell is 21 which means only 5 different (frequently referred) logic cells can be allocated in CP aperture with typical placement in 4 orientations. But even in this case, total required shot numbers of this logic region for EB Exposure can be reduced to approximately ½. For the ADVANEST CP EB system (allowed number of CP-cell = 100), reduction ratio of shot numbers is 1/4. For the pseudo CP EB system with 500 CP-cells in second aperture, reduction ratio of shot numbers would be 1/15. So, CP EB lithography is one of the promising candidates for small or medium volume production technology especially memory with logic device application after 70 nm node if the maximum number of CP-cell is appropriately increased.

For electron beam projection lithography system, it is one of the most important issues to stitch desired patterns accurately. We have found a way to stitch the patterns with high accurate critical dimension by a pattern edge deformation that moderates a stitching error by as much as 2.5 times compared with no-deformed edge.

An electron beam mask writing system JBX-9000MV for 150- 190nm technical node masks was improved to cope with the production of masks for 130nm technology node. Some of the new technologies developed for the improvement and their results are reported in this paper.

The vibratory response of Electron-beam Projection Lithography (EPL) masks has been characterized for two applications: to support the processes for mask cleaning (e.g., PLASMAX) and to preclude resonance conditions during metrology and inspection. The analysis of a 200-mm SCALPEL mask has been completed using experimental and numerical procedures to determine the dynamic response; the procedures characterized transverse vibrations by identifying the natural frequencies with their respective mode shapes. For mask cleaning applications, dominant modes were superimposed to form a more uniform acceleration field within the grillage area for effective removal of contaminants. In order to assess potential resonance issues, a finite element model was used to simulate the four-pad support, which is currently proposed for the EPL mask standard chuck. The fundamental frequency of the mask in the four-pad support was over 300Hz.

The characteristics of Ru film were examined to determine its suitability as a buffer layer for EUV mask patterning. When etched in an O₂/Cl₂ gas mixture with a high Cl₂ content at a low total gas flow rate, Ru exhibited a high etching selectivity with respect to a-Si, the otp layer of a Mo/Si multilayer mirror. This could enable use of a simpler mask patterning process without any damage to the multilayer. The patterning of a mask with a TaN absorber layer and a Ru buffer layer was demonstrated. Etching the TaN with an Ar/Cl₂ gas mixture yielded a high etching selectivity with respect to Ru of over 30:1. In addition, the use of Ru rather than SiO₂ for the buffer layer improved the DUV inspection contrast of TaN mask patterns before and after buffer layer etching. Finally, Ru is etched more slowly than SiO₂ by a focused ion beam, which makes it more suitable as a sacrificial layer during repair.

We proposed and discussed several fabrication processes for an arc-shaped and a rectangular fly-eye mirror, used in an EUVL illumination system proposed by Komatsuda. In particular, in the present study, we focused on one process in which all elements are fabricated individually and then arranged side-by-side to from the mirror. Thus, as the first step in this process, we fabricated arc-shaped and rectangular elements; the former and the latter were made of invar and fused silica, respectively. The slope accuracies of the surfaces for the arc-shaped and the rectangular mirror elements were +/- 15 and +/- 22 seconds, respectively. These values indicate that the mirror elements were fabricated with sufficient accuracy to satisfy the fly-eye mirror specifications. Moreover, both mirrors had the midfrequency roughness of about 0.25 nm RMS which satisfies the desired specifications. However, the high- frequency roughnesses of the former and the latter were 1.08 nm RMS and 0.59 nm RMS respectively, which must be improved.

Substrate or phase defects on EUVL masks are considered non- repairable because they lie underneath or are imbedded in the multi-layer mirror. One defect specification requires that no more than three defects greater than 80nm can be present on a starting substrate. Finding and removing these small defects before multi-layer deposition can be very difficult tasks. It has been shown that very small defects can have an influence on the patterned absorber stack and the printed image from an EUVL system. Substrate defect mitigation using TaSiN smoothing layers has been investigated. Programmed Cr defects were formed using standard semiconductor processing techniques and subsequently buried by the defect mitigating film. Experimental results are presented showing that a sputtering process can be used to deposit very smooth and thick TaSiN films (i.e. less than 0.2-nm RMS surface roughness and greater than 1.5-microns thick) as a substrate defect mitigation layer.

Tantalum nitride (Ta_xN) films were evaluated for use as the absorber material of masks for extreme ultraviolet lithography (EUVL). Ta_xN films deposited by DC sputtering using an Ar+N₂ gas mixture had a low stress of less than 300 MPa, an amorphous-like structure, and a low deep ultraviolet (DUV) reflectivity. This film provides a DUV contrast of 30% with respect to the Mo/Si multilayer whose top is on Si layer. A Ta_xN film deposited using a Xe+N₂ gas mixture was found to be better in the following ways: the stress was below 100 MPa, the change in stress was below 30 MPa, and the density was more than 1 g/cm³ higher. Furthermore, treating the surface of Ta_xN film with O₂ plasma or sputtering a Ta_xO film on it using an Ar+O₂ gas mixture improved the DUV contrast because the resulting surface has a lower DUV reflectivity than Ta_xN film. These results indicate that Ta_xN film is one of the most suitable materials for the absorber of EUVL masks.

The Semiconductor Industry Association (SIA) has placed stringent requirements on Next Generation Lithography mask critical dimension (CD) control. A new chemically amplified (CA) positive resist, Shipley XP2040D was evaluated for mask making application. This resist exhibited an extraordinary post exposure bake (PEB) sensitivity, less than 0.6 nm/ degree(s)C, along with a sub-50 nm resolution. The PEB stability in ambient was larger than 4.5 hours and the line-edge-roughness (LER) was less than 2.9 nm.

Chemically amplified resists have been widely used in deep UV optical lithography. In this paper, we characterized positive deep UV resists for high-resolution electron beam lithography applications. Results indicate this deep UV resist is very high sensitive and suitable for high throughput e-beam lithography applications. In general, deep UV resists are not suitable for sub-100 nm resolution lithography, except for strictly process control. After a simple thermal flow procedure, the trench-width can be easily down to 70 nm. It is also convenient to get a sub-70 nm contact hole pattern by utilizing commercial deep UV resists with this strategy. Many factors influence performance or resists such as soft bake, post exposure bake, exposure dose, and thermal flow, which are discussed and optimized. Suitable dry etching properties of deep UV resists are also characterized for pattern transfer.

Lithium containing droplet and cluster targets irradiated by laser pulses are proposed as prospective source of for soft x-ray lithography. Analytical model and simulations show that laser with repetition rate of several MHz with energy of several mJ and pulse duration 10 ps is required.

There is a window of opportunity for optical lithography between wavelengths of 100 nm and 157 nm that warrants exploration as a next generation technology. We will present activities underway to explore the feasibility of VUV optical lithography in this region with respect to source, optical design, materials, processes, masks, resolution enhancement, and compatibility with existing technologies. We have constructed a small field prototype lithography system using the second continuum 126nm emission wavelength of the Argon excimer. This has been accomplished using a small dielectric barrier discharge lamp with output on the order of 10mW/cm² and small field catoptric imaging systems based on a modified Cassegrain system. Capacitance focus gauge and piezo electric stage has been installed for fine focusing. In order to achieve sub-half wavelength resolution that would be required to compete with 157nm lithography and others, we have started exploring the feasibility of using liquefied noble gas immersion fluids to increase effective value of lens numerical aperture by factors approaching 1.4x. Conventional silylation process works well with 126nm with high sensitivity. Chemically amplified DUV negative resist looks very good material for 126 nm. Initial contact printing image shows good selectivity and process control. An effort is also underway to explore the use of inorganic resist materials, as silver halide material for instance, to replace the conventional polymeric imaging systems that are currently employed at longer wavelengths, but may be problematic at these VUV wavelengths. Early accomplishments are encouraging. Prototype optical research tools can be used to reveal issues involved with 126nm lithography and solve initial problems. Though many challenges do exist at this short wavelength, it is quite feasible that lithography at this wavelength could meet the part of the needs of future device generations.

Extensive work has been done in recent years to establish nanoimprint lithography (NIL) as a low-cost technology for nanometer-scaled resist pattern definition. Investigations have revealed that creating of small and periodic nanometer-scaled patterns adjacent to larger patterns is difficult due to the flow behavior of the resist material. In this paper mix and match of NIL and UV lithography is proposed to solve this problem and moreover to attain profiled structures within one coating. A chemically amplified broadband negative tone photoresist based on SU-8 is used to realize this idea.

Extreme-ultraviolet (EUV) lithography based on reflective optics is expected to require at least one filter window to 1) reduce out-of-band radiation in the ultraviolet, visible and infrared, 2) partially protect the optics from debris from the radiation source and any outgassing from the resist on the wafer, and 3) perhaps to serve as a barrier for EUV absorbing gasses. To maximize wafer throughput, the filter window or windows will need to provide the highest possible transmittance at 13.4 nm. EUV filters must operate in a harsh vacuum environment. They will be irradiated with high energy EUV light and will absorb out-of-band radiation that will cause temperature increases of greater than 100 degree(s)C. Outgassing from the filters must be minimal, and they must survive handling as well as pressure differentials during pump-down operation, and return-to-atmospheric pressure. Prototype filters were fabricated for Sandia's Engineering Test Stand (ETS) and are being utilized in on-going EUV lithography demonstrations. Their in and out-of-band transmittance has been measured and found to meet Sandia's performance specifications, and they have been exposed to various environments with good results.

Patterning sub-150 nm features in dielectric stacks using single layer resist processes in conjunction with organic anti-reflective coatings (ARCs) is becoming very difficult. Typical organic ARC-open etch processes suffer from poor ARC-to-resist selectivities (~0.7), and are accompanied by critical dimension (CD) losses. The resist remaining is often not sufficient to prevent artifacts such as substrate microrevicing during subsequent etches. PECVD-Deposited titanium nitride and silicon oxynitride films have been investigated as ARC layers but their basic nature has caused residue formation at the resist/ARC interface. We have developed a PECVD-deposited material, TERA (Tunable Etch-Resistant ARC) that acts as an ARC at 248 nm and 193 nm wavelengths and provides excellent etch selectivity to resist surpassing those attained with organic ARCs. In addition, this material demonstrates excellent hard mask properties for subsequent dielectric etch steps. The optical properties of these films can be easily tuned to minimize substrate reflectance at either imaging wavelength by controlling the precursor composition and deposition conditions. The films are compatible with 248 nm and 193 nm resists - no footing, undercut or residue is observed during patterning. The films can be etched selectively to resist (selectivity ~2.5) that translates to less resist consumption during th ARC-open etch. Compared to resists, TERA demonstrates better etch resistance while patterning dielectric stacks - the silicon oxide-to-TERA Selectivity exceeds 8. In this paper, the excellent optical tunability and substrate reflectivity control achieved with TERA are discussed. Clean lithography using 248 nm, 193 nm and e- beam resists is shown. The etch characteristics of TERA in fluorocarbon and halogen-based plasma chemistries are discussed. Finally, the formation of 135 nm and 120 nm deep trench patterns in thick dielectric stacks using TERA in conjunction with commercial 248 nm and 193 nm resists, respectively is demonstrated. The extendability of this approach to pattern silicon without roughening or microrevicing using sub-200 nm thick resists is motivated.

In order to satisfy the metrology requirements of multilayer coatings for EUVL optics and masks, improvements have been made to the reflectometry beamline at the Advanced Light Source. The precision in determining multilayer peak reflectance and wavelength has been improved by reducing the measurement noise. The peak reflectance of a typical Mo/Si multilayer can now be measured with a precision of 0.08% rms (relative) and the centroid wavelength with a precision of 0.007% rms. It has now been possible to determine the contribution of scattered light to the spectral purity. Under the typical measurement conditions the scattered light accounts for about 1.3% of the incident beam. With an appropriate slit it is possible to reduce the scattered light to 0.25%. By correcting for the remaining scattered light, it is estimated that a reflectance accuracy of 0.1% (absolute) is obtained for a typical Mo/Si multilayer.

We developed an in-situ stress monitoring system using variable electrostatic capacitance with a Si wafer cantilever as the moveable electrode of a parallel capacitor. The stress behaviors during the deposition of thick molybdenum (Mo) single layers, conventional molybdenum/silicon (Mo/Si) multilayers and low-stress multilayers (Mo/Si multilayers modified using sub-multilayering and ion beam polishing (IBP)) were observed. In the case of a Mo single layer, at an early stage of deposition to about 40 Angstroms thickness the partial stress was tensile, and after that the partial stress became compressive. In the case of conventional Mo/Si multilayers, a modulation of stress was observed. After Mo-layer deposition the partial stress became tensile, whereas after Si-layer deposition it became compressive, leading to a compressive total stress. In the case of the low-stress multilayers that we developed, we observed the suppression of compressive stress changes of the Si-layer after the IBP of the Mo surface. The control of the partial stress changes of each layer will make it possible to control the total stress of multilayers.

We have successfully developed a simple, laboratory-sized EUV reflectometer EUMOR (extreme Ultraviolet Monochromatic Reflectometer). A CO₂ gas-jet-target laser-plasma source was employed as the EUV source for EUMOR. EUMOR uses a single line emission at the wavelength of 12.98 nm from a CO₂ gas-jet-target laser-plasma source without a grating, therefore it can achieve simultaneous high spectral resolution and high throughput. The intensity of EUV emission from the CO_{2 gas-jet target laser-plasma was quantitatively evaluated, and the EUV flux that irradiated the surface of a sample was estimated to be 5x10(superscript 5} photons/shot. Four Mo/Si multilayer mirrors which were deposited under the same conditions with different layer periods were measured by EUMOR. The parameters of these multilayer mirrors, which were obtained by parameter fitting to the measured angular distribution of the reflectivity, showed good agreement with each other, demonstrating the reliability of EUMOR data.

Applications of multilayer mirrors for extreme ultraviolet lithography (EUVL) require not only a high normal incidence reflectivity but also a long lifetime and a minimum residual stress. We focused our interests on a comparative study of two perspective Si-based multilayer systems: Mo/Si and Mo₂C/Si. The mirrors were designed for normal incidence reflection at about 13 nm wavelength. The multilayer mirrors were deposited by dc magnetron sputtering. X-ray scattering, transmission electron microscopy, atomic force microscopy and mechanical stress measurements were used for the characterization of the multilayer structures. Maximum normal incidence reflectivities of 67.5% 13 nm for Mo/Si multilayer mirrors and 66.3% 12.8 nm for Mo₂C/Si have been achieved. Investigating the thermal stability of the multilayers in the temperature range from 200 degree(s)C to 600 degree(s)C it was shown that the reflectivity of Mo/Si mirrors is drastically decreasing after annealing above 300 degree(s)C, whereas the Mo₂C/Si multilayers show a superior thermal stability up to 600 degree(s)C. It was found that as-deposited Mo/Si and Mo_{2/C/Si multilayer mirrors have a similar level of compressive stress of -520+/- 20 MPa. The reduction of residual stress in Mo/Si and Mo(subscript 2}C/Si multilayer systems with post-deposition thermal treatment has been investigated. Using a slow thermal annealing (2 degree(s)C/min), it is possible to reduce the stress form -520 MPa to nearly zero by heating the Mo/Si specimen up to ~310 degree(s)C. However, it results in a reflectivity drop of ~3% (absolute) at the wavelength of 13 nm. For the Mo₂C/Si system, a stress reduction from -520 MPa to nearly zero is possible by a post annealing at ~290 degree(s)C without a considerable drop in the reflective properties.

According to Sematech International's analysis extreme ultraviolet (EUV) photolithography is one of the most promising approaches for next generation lithography (NGL). The insertion point of NGL is likely at the 50 nm node. To establish EUV lithography all basic technologies have to be developed t material suppliers, source suppliers, coating manufacturers, optics, lens and tool manufacturers, mask houses, pellicle manufacturers and resist suppliers over the next years. To achieve the required throughput in production various concepts of EUV sources are currently under investigation. Here we discuss new results of design studies on gas discharge Z-pinch sources. Form the EUV source 1 W output power at 100 Hz repetition rate could be obtained in continuous operation. Pulse energy stability is 4% (sigma). In burst operation repetition rate of up to 400 Hz is possible with the current design.

Sometimes, glass mirrors are cut to final shape after they are polished. The cuts may relieve residual stresses in the glass, thereby leading to distortion of the carefully polished reflecting surfaces. To aid in selecting a glass blank for making a mirror, it would be useful if we could predict the amount of post-polish distortion that a specific choice of blank would lead to. In this note, I describe how to make such predictions, using an example. Cases considered so far indicate that Corning Ultra Low Expansion glass (ULE) blanks, if properly chosen, lead to post-polish distortion that is low enough to be acceptable for extreme ultraviolet lithography applications.

As a participant of the French Extreme UltraViolet (EUV) program PREUVE, our laboratory has been involved for one year in the development of Mo/Si blanks free of defects using an Ion Beam Sputtering deposition technique (IBS). Among the different tasks to end at an EUV stepper, the achievement of the blank and its characterization in terms of defect counting is probably one of the most challenging. This is the reason why a characterization tool based on the well known scattering method is under progress in our laboratory. In addition to defect counting, the possibility of cleaning a sample (substrate, blanks,.) with a powerful laser source is allowed on the same facility. This set up is fully computerized. Its first performances are illustrated with several examples on our blanks and silicon substrates. Our system is designed to optimize the laser cleaning parameters (wavelength, incidence, polarization,.) and to decrease the detection limit size. Today, our facility currently enables the detection of the defect as small as 200 nm in size. Our strategy is to reach the defect size as low as possible and at least until 50 nm, which is the size of interest for the EUV lithography. The major developments under consideration in order to lessen the detection limit size are described in details in this paper. Moreover, the roughness of the EUV blanks may be evaluated with our device. This surface parameter has to be optimized, at least for two reasons : to reduce the optical losses and to decrease the number of defects. The mean to quench the roughness signal in order to detect the smallest defect size and the possibility to evaluate the component roughness are combined on the same facility. The major trumps of our experiment are the visualization of the defects in live, the measurement of the defect sizes and the quick evaluation of the laser cleaning efficiency versus various experimental conditions. The cleaning part of the set up is built up to use various powerful laser sources and to shoot, with the laser, only the locations where the defects remain. Finally, this facility allows to evaluate and to optimize our defect free blank process.

While interferometry is routinely used for the characterization and alignment of lithographic optics, the ultimate performance metric for these optics is printing in photoresist. Direct comparison of imaging and wavefront performance is also useful for verifying and improving the predictive power of wavefront metrology under actual printing conditions. To address these issues, static, small-field printing capabilities are being added to the extreme ultraviolet (EUV) phase-shifting point diffraction interferometer (PS/PDI) implemented at the Advanced Light Source at Lawrence Berkeley National Laboratory. This Sub- field Exposure Station (SES) will enable the earliest possible imaging characterization of the upcoming Engineering Test Stand (ETS) Set-2 projection optics. Relevant printing studies with the ETS projection optics require illumination partial coherence with (sigma) of approximately 0.7. This (sigma) value is very different from the coherent illumination requirements of the EUV PS/PDI and the coherence properties naturally provided by synchrotron undulator beamline illumination. Adding printing capabilities to the PS/PDI experimental system thus necessitates the development of an alternative illumination system capable of destroying the inherent coherence of the beamline. The SES is being implemented with two independent illuminators: the first is based on a novel EUV diffuser currently under development and the second is based on a scanning mirror design. Here we describe the design and implementation of the new SES, including a discussion of the illuminators and the fabrication of the EUV diffuser.

For EUV lithography mask blank substrates of the 6025 type will be made from Near Zero Thermal Expansion (NZTE) materials. The low thermal expansion of EUV substrates shall provide for the required better thermal stability during mask-writing and lithography exposure. The manufacturing of such NZTE mask blank substrates requires modified finishing processes in comparison to standard mask blanks. Super polishing takes place to provide high spatial frequency roughness of less than 2 Angstroms RMS. To improve the flatness and the roughness at the mid spatial frequencies another correction step is required. Such step can be Ion Beam Figuring for example. We evaluate the results for the different spatial frequencies by interferometry and atomic force microscopy. We have a closer look how the additional finishing steps improve the flatness and mid spatial frequency roughness. The impact of these newly introduced finishing steps for the high spatial frequency roughness is studied. We examine the processes for two different substrate materials with near zero thermal expansion (ZERODUR and ULE).

Spectroscopic ellipsometry has long been recognized as the technique of choice to characterize thin films and multilayers. In 1983, SOPRA has developed the first commercial spectroscopic ellipsometers for research and development. Since this date, the wavelength range has been extended from visible to near infrared (2micrometers ) and far infrared up to 18micrometers . For 193nm micro-lithography, deep UV option down to 190nm has also been developed and delivered more recently. Instrumentation for the next generation of VUV lithography at 157nm requires special optical setup since O₂ and H₂O are extremely absorbing below 190nm. A new system has been developed which works into a purged glove box to reduce the oxygen and water contamination in the part per million range. The optical setup includes a premonochromator in the polarizer arm to avoid photobleaching. The wavelength range of the instrument is 140-700nm. The system works in rotating analyzer configuration to minimize the parasitic residual polarization. Ellipsometric and photometric measurements versus wavelength and angle of incidence can be performed. Scatterometric measurements can also be made. In this wavelength range, the samples are extremely sensitive to any surface contamination and surface roughness. It is why a grazing x-ray option has been added on the same instrument to provide a better picture of the analyzed samples. This paper presents in details the new system with its two measurement methods, and including experimental results on resist, antireflective coatings and gate dielectrics for use in the field of micro-lithography.

In this paper we present the results of an elaborate study to investigate the properties of luminescent materials for EUV detection in EUV lithographic tools. The study presented here involves both bulk single crystalline samples and thin film samples. Bulk single crystalline samples with polished surfaces are industrially available, while thin film samples were home-made by performing physical vapor deposition of several luminescent materials on polished quartz substrates. Careful pre-selection of these phosphors was based on multiple strong criteria. The measured results presented here include time-resolved luminescence decay, luminescence spectra and luminescence linearity measurements under deep-UV (248 nm) and extreme-UV (13.5 nm) excitation. Our results indicate the possible use of two luminescent materials, being YAG:Ce (bulk) and CaS:Ce (thin film), for EUV detection in extreme-UV lithographic tools. Practical use of these luminescent materials, however, will require high extreme-UV powers in order to obtain a sufficient signal to noise ratio.

In the calculation of wafer throughput for EUV production tools, the multilayer mirrors are often approximated as a pass-band with a flat response equal to the highest reflectivity of the mirrors and a bandwidth equal to the FWHM of the reflectivity curve. However, the actual reflectivity response of the mirrors is an extended curve which peaks at wavelengths typically between 11-15 nm. With a broadband source, photons with wavelength outside the FWHM of the mirror are also reflected, contributing to the throughput of the multimirror optical system. We present calculations to compare this simple model with the actual reflectivity curve for Mo/Si mirrors, The result shows that the model is a good approximation for throughput calculations. In this paper, the optimal parameter values and center wavelengths for maximum throughput were also calculated for Mo/Si mirrors at different incidence angles and (sigma) values. The simulation results confirm that for near-normal incidence, the optimal center wavelength for maximum integrated reflectivity is around 14.4 nm, in agreement with the previous work by R. Stuik et. al. As the off-normal incidence angle ((phi) ) increases, the integrated reflectivity is reduced faster at longer wavelengths. The maximum integrated reflectivity centered at 13.4 nm is closer to that at the optimal center wavelengths for larger value of (phi) . The effect is more distinct for smaller (sigma) . For (phi) equal to 15 degree(s) (NA ~ 0.25) and peak reflectivity of 70%, the maximum integrated reflectivity of a 9-mirror optical system at 13.4 nm is only 2% less than that at 14.4 nm. If a 2-nm thick SiO₂ capping layer with roughness of 0.2 nm is included in the simulation, the optimal wavelength is unaffected and only the integrated reflectivity is reduced.

We report some new results in the use of high energy radiation in proximity x-ray lithography for the 50 nm node. The higher energy of the incoming radiation, 2.6-2.7 KeV, has two primary benefits: (1) it reduces the diffraction and allows printing of higher resolution features, and (2) it increases the effective depth of exposure allowing larger gap setting; however, the absorption of these photons creates hot electrons, which redistributes the energy in the resist, thus creating a uniform blur that limits the resolution by reducing contrast. The impact of the energy redistribution needs to be investigated when increasing the energy of the radiation, and in considering the materials used in both the optics and the mask and resist combination.

In the PC Era, Microcomputer ((mu) C) and memory were the components that drove growth of the PC industry. In the Internet Era, Digital Signal Processor (DSP) and Analog will be the components that drive growth in Internet Products. Over the next 10 years, technology will continue to follow Moore's Law of scaling, and in addition, System-on-a-Chip (SOC) integration will drive technology. Of the many challenges to continued scaling, lithography will continue to rank near the top throughout most of this decade. However, toward the end of the decade, other limitations will retard scaling. Continued system cost reduction will result from expanded SOC integration, consistent with the needs of the Internet.