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For many years, laser patter generation has been printing on i-line resists. As features sizes continue to shrink, laser pattern generation is moving to DUV laser wavelengths, and a production worthy resist process is needed. Characteristics such as standing waves, resist foot and CD drift during and after the exposure have previously challenged efforts to migrate to 248nm stepper chemically amplified resists (CARs) to mask making applications. In this study the performance of a commercially available 248nm laser/e-beam resist solution is examined on the Sigma7000 series laser patter generators.To achieve virtually no resists foot as well as tight CD control, the optimum process conditions for optical laser applications were sought. Cross-sectional and top-down scanning electron microscopy was performed to evaluate the resist and dry etch processes. A comparison is made with the resist DX1100P, used in initial stages for DUV laser pattern generators development. The new resist also benefit from being well established in mask making with e-beam mask writers.

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A continuing improvement in resist process is a necessity for high-end photomask fabrication. In advanced chemically amplified resist systems the lithographic performance is strongly influenced by diffusion of acid and acid quencher (i.e. bases). Beside the resist properties, e.g. size and volatility of the photoacid, the process conditions play important roles for the diffusion control. Understanding and managing these properties influences lithographic characteristics on the photomask such as CD uniformity, CD and pitch linearity, resolution, substrate contamination, clear-dark bias and iso-dense bias. In this paper we have investigated effects on the lithographic characteristics with respect to post exposure bake conditions, when using the chemically amplified resist FEP-171. We used commercially available mask blanks from the Hoya Mask Blank Division with NTAR7 chrome and an optimized resist thickness for the 248 nm laser tool at 3200Å. The photomasks were exposed on the optical DUV (248nm) Sigma7300 pattern generator.Additionally, we investigated the image stability between exposure and post exposure bake. Unlike in wafer fabrication, photomask writing requires several hours, making the resist susceptible to image blur and acid latent image degradation.

Managing the total CD error in advanced mask manufacturing requires that error contributions from writing, process and metrology are minimized. This paper describes how both the writing and process contributions have been addressed in the Sigma7500 DUV laser pattern generator, which prints masks by imaging a programmable spatial light modulator (SLM). System enhancements have reduced the writing contribution to global CD uniformity to 5 nm (3s). Processrelated CD error sources, such as the signatures from mask developing and etching can be significant contributors to the total CD error in mask manufacturing. These errors are classified as being either pattern-independent or patterndependent, and the effects of both can be reduced using the ProcessEqualizer feature of the Sigma7500. This software tool performs CD sizing during writing based on pattern density maps derived during mask data preparation, along with tunable parameters that are determined experimentally. The CD sizing function has no effect on system throughput and does not require flattening and re-fracturing of the pattern data.