As semiconductor device fabrication moves towards 2 nm technology nodes with EUV lithography, new EUV absorber materials will be needed to replace the current Ta-based EUV photomasks. The industry is looking for new absorber materials with a low refractive index (n) and a high extinction coefficient (k), to produce an attenuated phase-shift EUV photomask capable of minimizing 3D effects. The challenge is that these new materials are often difficult to etch. To identify the etching pathway for new EUV material candidates, this paper proposes the approach of thermodynamic characterization for various chemistries as etching byproducts. The Gibbs free energy of formation for these compounds can be collected at standard state conditions, so the potential for such chemical reactions can be evaluated. Meanwhile, the volatility of these reaction products can be estimated by the respective boiling points, which can be calculated from respective heats of vaporization at reduced pressures typically found in a plasma etch chamber. Collectively, this information can help to screen for new low-n / high-k absorber materials, to focus the selection only to candidates with potential etching feasibilities.
While the industry is making progress to offer EUV lithography schemes to attain ultimate critical dimensions down to 20 nm half pitch, an interim optical lithography solution to address an immediate need for resolution is offered by various integration schemes using advanced PSM (Phase Shift Mask) materials including thin e-beam resist and hard mask. Using the 193nm wavelength to produce 10nm or 7nm patterns requires a range of optimization techniques, including immersion and multiple patterning, which place a heavy demand on photomask technologies. Mask schemes with hard mask certainly help attain better selectivity and hence better resolution but pose integration challenges and defectivity issues. This paper presents a new photomask etch solution for attenuated phase shift masks that offers high selectivity (Cr:Resist > 1.5:1), tighter control on the CD uniformity with a 3sigma value approaching 1 nm and controllable CD bias (5-20 nm) with excellent CD linearity performance (<5 nm) down to the finer resolution. The new system has successfully demonstrated capability to meet the 10 nm node photomask CD requirements without the use of more complicated hard mask phase shift blanks. Significant improvement in post wet clean recovery performance was demonstrated by the use of advanced chamber materials. Examples of CD uniformity, linearity, and minimum feature size, and etch bias performance on 10 nm test site and production mask designs will be shown.
For advanced binary and PSM mask etch, final profile control is critically important for achieving desired mask
specifications. As an aid to attain profile control, an etch profile simulation method has been developed. The method
starts with an initial photoresist profile and incorporates etch rate and directionality information to predict the final etch
profile. In this paper, simulated results are compared to measured etch profiles for PSM substrates. The results highlight
the importance and implications of incoming resist profile and etch selectivity on final profile.
As lithography requirements mandate ever-thinner resist thickness, the need for in-situ monitoring has become more
urgent. In this paper we present an in-situ optical methodology-based system to determine residual photoresist thickness
during advanced photomask etch with < 1000 Å photoresist. Several types of phase-shift masks and photoresists were
examined. A series of masks were etched to demonstrate the performance of the system. Results show an average
accuracy of better than 2%, with a maximum absolute range of all tests within 8%.
Mask defectivity is often highlighted as one of the barriers to a manufacturable EUV solution. As EUV lithography
matures, other components of mask making also emerge as key focus areas in the industry: critical dimension (CD)
control, film variability, selectivity, and profile tolerance. Mask materials and specifications continue to evolve to meet
the unique challenges of EUV lithography, creating the need for etch capabilities that can keep pace with the latest
developments. In this study, the performance of a new EUV mask etch system will be evaluated using a variety of mask
blanks to determine the relative performance of each blank type. Etch contributions to mean to target (MTT), CDU,
linearity, selectivity, capping layer uniformity, line edge roughness (LER), and profile quality will be characterized to
determine tool performance. The new system will also be used to demonstrate multilayer etching capabilities, important
for opaque frame and alternating phase shift applications. A comprehensive summary of the etch performance of various
EUV films and the readiness for manufacturing applications will be provided.
Both Langmuir probe and spatial optical emission spectroscopy (OES) measurements have
been used to characterize the TetraTM chrome etch chamber. Langmuir data was measured over a
range of process pressures between 1.5mT and 10mT and source powers between 150W and 500W.
At 350W, the data show electron and ion densities near 1 x 109 cm-3 for Ar and for Cl2/O2 etch
plasmas. Ion density trends with pressure were observed to be opposite for the two plasmas.
The effect of the third electrode designed in the chamber was demonstrated to reduce ion
density by more than an order of magnitude for Ar plasma and still lower for Cl2/O2 plasma.
Electron temperature and plasma potential are also reduced.
Radial OES measurements are reported with a new apparatus that yields direct spatial
emission data. Spatial scans of infrared emission from atomic Cl were measured under a range of
several chamber conditions already measured with the Langmuir probe. The scans showed that the
emission uniformity above the mask can be adjusted to a flat profile by selection of the process
condition.
A method is described to monitor etch selectivity real time in Applied Materials' advanced TetraTM mask etcher module.
With the built-in Transmission Endpoint (TEP) capability, the transmission information for a wide range of spectra is
collected. As resist thickness continues to be reduced during photomask etching process, interference fringes can be
observed at selected wavelengths on the TEP spectrum. Based on known value from n & k simulation, the peak/valley
positions of interference fringes can be defined. With the help from an algorithm developed to determine the
corresponding time for each peak/valley position, the average resist etch rate can be obtained. In addition, the starting
and ending resist thickness on the plate being etched can be calculated, so the incoming resist quality can be verified and
being monitored. Combined with Cr etch rate derived from the endpoint time with plasma emission spectra, the Cr to
photoresist etch selectivity can be monitored for each production plate automatically.
Optical emission represents the bulk property of plasma, which in turn can be correlated to the
chamber surface condition and can be exploited for monitoring and characterizing chamber
condition. This presentation demonstrates the approach of utilizing plasma optical emission spectra
(OES) for the application on Applied Materials' TetraTM etcher chamber condition monitor. Time-resolved
plasma optical emission spectra are collected with a spectrometry unit built in to the
TetraTM photomask etch module. Studies on OES analysis show that information related to chamber
surface condition can be correlated to the changes in emission spectrum of plasma. The effectiveness
of this methodology can be verified by Cr etch rates. Results can lead to procedure development for
chamber monitoring, chamber recovery and chamber seasoning applications.
As technology advances with feature size shrinking for the
state-of-the-art integrated circuit (IC) fabrication, the degree
of reduction in critical dimension (CD) features on a photomask shrinks at a faster pace, thanks to the ever aggressive
optical proximity correction (OPC) design. In addition to stringent CD requirement, defect control has also become one
of the most difficult challenges for advanced photomask manufacturing as a result of reduction in printable defect size.
Therefore, keeping a photomask etching chamber at an optimal condition becomes very critical for controlling in both
defectivity and CD fidelity.
In the present study, analyses on optical emission spectrum (OES) collected in an Applied Materials' TetraTM chrome
etch module have been performed to understand (1) the impact of Cr etching on the chamber condition, and (2) the
effectiveness of in-situ chamber dry clean for chamber condition control and potential particle reduction. Results showed
that, with the right selection of chamber materials (to be compatible with process chemistry and etching condition), the
main impact of Cr etching on chamber condition and particle performance is from resist etch-by-products. Various
plasma dry clean chemistries have been explored to address the effectiveness for the removal of such etch-by-products.
As a result, an in-situ chamber clean (ICC) procedure is developed and has been validated to be production-worthy for
desired particle control and chamber stability control.
Increasingly complex RET techniques need to be used in the sub wavelength regime
which will drive up the mask costs, as well as the design costs. Some of the RET
techniques used involves the use of OPC, PSM and hard mask. In order to reduce the
costs it is desirable to have uniform performance on shuttle masks, which can help to
reduce manufacturing costs. The micro loading and macro loading are of concern to mask
makers because of the varying loads being etched within the mask. It is critical to have a
mask etcher that provides excellent CD uniformity, CD bias, CD linearity and etch profile
in order to have image fidelity of the OPC structures as well as sustainable yields. This
paper discusses micro and macro loading challenges on BIM and APSM masks and the
advantages of using the Applied Materials' next generation mask etcher.
Increasingly complex RET techniques need to be used in the sub wavelength regime
which will drive up the mask costs, as well as the design costs. Some of the RET
techniques used involves the use of OPC, PSM and hard mask. In order to reduce the
costs it is desirable to have uniform performance on shuttle masks, which can help to
reduce manufacturing costs. The micro loading and macro loading are of concern to mask
makers because of the varying loads being etched within the mask. It is critical to have a
mask etcher that provides excellent CD uniformity, CD bias, CD linearity and etch profile
in order to have image fidelity of the OPC structures as well as sustainable yields. This
paper discusses micro and macro loading challenges on BIM and APSM masks and the
advantages of using the Applied Materials' next generation mask etcher.
Requirements to meet the 45nm technology node place significant challenges on Mask makers.
Resolution Enhancement Techniques (RET) employed to extend optical lithography in order to
resolve sub-resolution features, have burdened mask processes margins. Also, Yield compromises
loom with every nanometer of error incurred on the Mask and the Device platforms. RET techniques,
such as Optical Proximity Correction (OPC), require the Mask Etcher to achieve exceptionally tight
control of Critical Dimensions (CD). This ensures OPC feature integrity on the mask and resultant
image fidelity of OPC structures, as well as, subsequently high and sustainable yields.
This paper talks about 45 nm Chrome etch challenges and how Applied Materials next generation
mask etcher provides solutions to these challenges.
One means of extending the limits and lifetime of current lithography platforms for 45nm and
beyond is the development of resolution enhancement techniques (RET) in the form of optical
phase-shifting masks (PSM). By employing optical interference from 180° shifted lithography
emission, PSM masks are able to enhance feature resolution at the wafer. This is particularly
important for sub-wavelength features (i.e., features with critical dimensions less than the
lithography wavelength) where line resolution can be severely degraded without such techniques.
For these PSMs, the challenge is to provide highly uniform quartz etch performance across the entire
active area of the mask for various feature sizes and local loads. Micro-loading (a.k.a. RIE lag or
reactive ion etch lag) and phase angle range are key performance parameters to control. As the
demands for these parameters tighten and mask costs rise, strict performance control is required for
all PSM mask varieties utilized in the mask shop.
In this paper we will discuss process results using Applied Materials next generation mask etch
system in the area of APSM etch application. In particular, the discussion will focus on recent
process results in phase uniformity and RIE lag for Quartz etch process. Feature profiles are also
discussed with examples showing near vertical sidewalls and no micro-trenching.
Requirements to meet the 45nm technology node place significant challenges on Mask makers. Resolution Enhancement Techniques (RET) employed to extend optical lithography in order to resolve sub-resolution features, have burdened mask processes margins. Also, Yield compromises loom with every nanometer of error incurred on the Mask and the Device platforms. RET techniques, such as Optical Proximity Correction (OPC), require the Mask Etcher to achieve exceptionally tight control of Critical Dimensions (CD). This ensures OPC feature integrity on the mask and resultant image fidelity of OPC structures, as well as, subsequently high and sustainable yields.
This paper talks about 45 nm Chrome etch challenges and how Applied Materials Tetra IITM etcher provides solutions to these challenges.
One means of extending the limits and lifetime of current lithography platforms for 45nm and beyond is the development of resolution enhancement techniques (RET) in the form of optical phase-shifting masks (PSM). By employing optical interference from 180° shifted lithography emission, PSM masks are able to enhance feature resolution at the wafer. This is particularly important for sub-wavelength features (i.e., features with critical dimensions less than the lithography wavelength) where line resolution can be severely degraded without such techniques. For these PSMs, the challenge is to provide highly uniform quartz etch performance across the entire active area of the mask for various feature sizes and local loads. Micro-loading (a.k.a. RIE lag or reactive ion etch lag) and phase angle range are key performance parameters to control. As the demands for these parameters tighten and mask costs rise, strict performance control is required for all PSM mask varieties utilized in the mask shop. In this paper we will discuss process improvements for the Applied Materials Tetra IITM chromeless phase lithography (CPL) etch application. In particular, the discussion will focus on recent process improvements in phase uniformity and RIE lag for our chrome hard mask CPL etch process. Results from modifications to the etch process are presented. Feature profiles are also discussed with examples showing near vertical sidewalls and no micro-trenching.
Requirements to meet the 45nm technology node place many challenges on photomask makers. Resolution Enhancement Techniques (RET), employed to extend optical lithography in order to resolve sub-resolution features have burdened mask processes margins. Also, yield compromises rise with every nanometer of error incurred on the photomask (and device) platforms.
As photomask costs rise, strict performance control is required for all photomask varieties utilized in the mask shop. Mask etching for future technology nodes, requires a system-level data and diagnostics strategy. This necessity stems from the need to control the performance of the mask etcher at increasingly stringent and diverse requirements of the photomask production environment.
From etch applications perspective, alternating phase-shift masks (APSMs) and OPC masks pose key challenges. Specifically, the etcher needs to provide highly uniform CD performance across the entire active area of the photomask - for various feature sizes and load distributions, with no degradation to profiles. It is challenging to strike this balance, yet maintain adequate process window. Future etch systems require sensitive controls and knobs to provide this high precision and repeatable performance. Additionally, incoming variation in plate characteristics and quality necessitate tuning knobs capable of targeting the optimum performance across a diversity of applications.
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