Sol-gel fabrication of high-quality photomask substrates for 157-nm lithography

Abstract

Modified fused silica is a strong candidate material for photomask substrates in 157-nm lithography. Such a material must possess improved transmission and birefringence characteristics compared to conventional photomask substrates. Although there has been some success in producing modified silica using chemical vapor deposition, substantial improvements in quality and cost are desirable. A novel sol-gel based technique to inexpensively produce high quality 157-nm photomask substrates is being developed to address these issues. The complex relationships between glass properties and glass forming parameters were determined. Methods to improve the ultraviolet transmission at 157-nm were established, and modified silica without striae or optical defects were developed. Glasses produced using the sol-gel process displayed low birefringence and good homogeneity. With further improvement in transmission at 157 nm this glass may demonstrate technical and cost superiority to commercially available 157-nm photomask substrates.