Role of etch pattern fidelity in the printing of optical proximity corrected photomasks

Abstract

Optical proximity effect correction has been proven to improve critical dimension control, increase overlay margins, and, when used with phase-shifting masks and/or modified illumination and mask-plane nonprinting assist features, also extend resolution and increase depth of focus of current generation lithographic exposure technology. While the potential enhancements afforded by such schemes are enticing, their successful implementation is imposing demands on mask fabrication, inspection, and repair which surpass the state of the art in industry today. This article focuses on the influence of the mask pattern fidelity on the ensuing wafer lithographic performance. Both wet and dry etch techniques were applied to an ensemble of proximity-corrected test patterns using standard binary chrome-on-glass test masks. The chrome was wet etched with polybutene sulfone as the masking resist using an optimized zero-bias process. For comparison, the same test structures delineated with a silicon containing resist were also reactive ion etched with Cl2/O2/N2 chemistry, developed to retain submicron pattern fidelity, and anisotropic absorber wall profile. Comparative wet and dry-etched mask and resulting wafer metrology results are presented for 5× i-line and 4× deep ultraviolet exposures.