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Sol-gel fabrication of high-quality photomask substrates

Synthetic silica photomask substrates are currently manufactured by cutting, grinding, and polishing glass boules prepared using a flame hydrolysis process. YTC America is developing an alternative technique, based on sol-gel processing, to fabricate high quality substrates. This new technology allows near net shape fabrication of synthetic silica monoliths, thus 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. These substrates meet all SEMI specifications for ULTE hard surface photomask substrates 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.