Sol-gel fabrication of high-quality photomask substrates

Abstract

Synthetic silica photomask substrates are currently manufactured by cutting from glass boules, which are prepared using a flame hydrolysis process. An alternative technique based on sol-gel processing demonstrates several potential advantages in fabricating high-quality substrates. This new approach allows near net shape fabrication of synthetic silica photomask substrates, eliminating the need for cutting and grinding. The complex relationship between glass properties and process parameters in the formulation, drying, and sintering steps has been determined, and a repeatable process has been established. The resulting substrates meet all SEMI specifications for ultra-low thermal expansion (ULTE) photomasks for 248-nm lithography. The technology may also be extended to 193-nm and 157-nm photomask substrates. This sol-gel-based process may represent a unique and cost-effective alternative for manufacturing photomask substrates for deep UV lithography.