"Full-Field Exposure Control Implications of the Mask Error Function"
SPIE Microlithography 2006 conference
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FullField implications of MEF_ML 6155-12.pdf
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Process Setup, Feature Profile Control and OPC Qualification
using the Local Mask Error Function!
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Is MEEF constant across an exposure field?
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Have you ever considered how the local MEEF varies for each individual site or OPC feature?
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What exposure conditions minimize the process impact of local MEEF sensitivity?
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What are the exact pattern sensitivities of each feature as process conditions and the exposure environment changes?
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Do you know the relative response of one feature type to another not only at the IsoFocal Dose as also as the exposure conditions vary?
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Consider using MEEF calculation as an evaluation tool for OPC manufactured reticles.
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Discover the behavior of local MEEF near the IsoFocal bias for each site and it's resulting influence on the feature uniformity budget.
Abstract
This report considers a detailed method of rapid and accurate experimental calculation of the Mask Error Enhancement Function (MEF or MEEF) using localized CD variation across the exposure field. MEEF is defined as the non-constant bias of wafer-image replication to small changes in the reticle image. The extraction method of the MEEF response of a reticle to it’s process environment is shown to contain a method of measuring the robustness of the OPC design structures on the reticle and their ability to compensate wafer-image replication across the scope of production-process perturbations.
This study demonstrates that a MEEF response can be characterized by a regressive comparison of reticle and wafer image sizes for any reticle OPC structure. Expanding the analysis to a focus-dose matrix that approximates normal production variations allows the MEEF response sensitivities to be deconvolved into their component contributions to critical feature variation across the wafer. IntraField dependencies such as sensitivity to the direction of the scan, and thus reticle-stage drive loading are investigated and their contributions are presented at the end of the report. Process induced perturbations such as focus and dose can also change the MEEF and their response is characterized and shown to be a significant contributing factor.
An algorithm is then used to extract the full-wafer systematic sensitivity of MEEF to slowly changing perturbations such as film thickness changes in the Anti-Reflective Coating (ARC) and Photoresist thickness. Correlation of the MEEF response to film thickness is discussed and shown to be significant for some films.
A budget summary of the systematic perturbation inherent in these MEEF factors is compared against the needs of sub-90 nm nodes with considerations toward the necessity of process-specific OPC design for critical layers.
TEA Systems
TEA Systems offers products to model films, photomasks, wafers, feature profiles, process and lens data for characterization and setup of semiconductor design, simulators, tools and the process.
TEA Systems, a privately held corporation since 1988, specializes in advanced, intelligent modeling of the semiconductor process and toolset. Products from TEA allow the user to decouple process, tool and random perturbations for enhanced process setup & control.
TEA Systems products include:
Weir PSFM: Full-wafer/field/scan analysis tool for FOCUS derived from proprietary defocus sensitive features.
Weir PW: Reticle/Full-wafer/field/scan analysis for any metrology with advanced process window capabilities for both wafer and photomask control.
LithoWorks PEB: A tool to link and correlate profile, film and critical element control to thermal reactions such as PEB and ChillPlate
Weir DMA: Macro Automation interface for Weir PSFM and Weir PW for external program calling, automated data gathering or one-button analysis of commonly used sequences. Includes data trending and web interface.
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