Process optimization of e-beam lithography with high-accelerated voltage

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Along with the rapid generation change of lithography and widened application of OPC, the process for High Accelerated Voltage E-Beam reticle is changing from Wet Etching to Dry Etching. Establishment and optimization of Dry Etching process becomes urgent need for mask manufacturers. However, the current resist commonly used for Dry Etching has a problem, which is resist film thickness loss on high pattern density area. Unless we can solve this problem, we can not say the Dry Etching process is suitable for next generation lithography. We selected and evaluated Chemically Amplified (CA) Resist to improve Dry Etching process of high-accelerated E-Beam. At first, as a reference of present quality, we evaluated both Dry Etching and Wet Etching process with a non-CA resist, which is commonly used. As a result advantages of Dry Etching over Wet Etching are confirmed in Linearity, pattern profile and resolution. But the problem of Dry Etching, which is pattern dependent CD variation caused by the uneven loss of resist thickness was also materialized. It is also confirmed that the amount of resist thickness loss is strongly related to pattern density. Then we did basic evaluation about several CA resists. As a result, it was confirmed that CA resist had advantages over non-CA resist on almost all aspects such as Contrast, film thickness loss and cross-sectional profile. And CA resist also solved the problem of resist thickness loss related to pattern density, which we observed when we used non-CA resist. Among several candidates, we selected one CA resist which has high contrast, vertical cross sectional profile, and enough remaining film thickness. We decided that the resist is suitable for Dry Etching optimization, then we did patterning evaluation using this resist. As a result the reticle quality was satisfactory. We could confirm big improvement on both pattern dependent CD variation and pattern profile compared to Dry Etching process using non-CA resist.