QC-i can be mass-produced due to substantially reduced production costs, which makes it the world's first substrate for ArF immersion photolithography(3) to be mass-produced. This development is expected to dramatically advance the ultra-fine processing technology that is indispensable for semiconductor fabrication.
As more advanced, sophisticated integration and ultra-fine techniques for devices mounted on LSI chips are required for semiconductor manufacturers, they seek shorter wavelength light sources for the photolithography process by which semiconductor patterns are formed. These manufacturers recently have begun to use 248 nanometer(4) KrF (krypton fluoride) lasers and 193nm ArF lasers, as light sources.
Meanwhile, the semiconductor device manufacturers(5), aiming to further advance ultra-fine processing technologies, are developing photolithography processes using much shorter wavelength lasers such as the 157nm-F2 (fluoride dimmer) and 13nm-EUV (extreme ultraviolet) lasers. Asahi Glass in 1999 developed photomask substrate and pellicle materials for F2 lasers, and is currently developing photomask materials for EUV lasers jointly with International Sematech of the U.S. (Headquarters: Austin, Texas). Through these efforts, Asahi Glass has strived to shorten the wavelength of light sources. Although development of materials for an F2-laser photolithography process has progressed much, manufacturing costs, including equipments, are still a major barrier to commercialization. It is expected to take from four to six more years before mass-production of an EUV photolithography process is realized, considering the progress of development of peripheral materials. Therefore, the most pressing task for the industry is to develop a photolithography process that can be commercialized at an earlier date and requires less investment.
Facing such circumstances, semiconductor device manufacturers began using conventional ArF laser steppers to develop a liquid-immersion photolithography process that can improve the accuracy of ultra-fine processing, and they are nearing commercialization. In the liquid immersion photolithography process, pure water is put between the stepper lens and silicon wafer to significantly refract the light passed through the lens, so that ultra-fine processing on the wafer is made possible. Synthetic quartz photomask substrates for liquid immersion photolithography require the "glow birefringence(6)" property that minimizes irregularities in light polarization(7).
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Asahi Glass Succeeds in Development and Mass-Production of Synthetic Quartz Photomask Substrate (QC-i) for ArF Liquid Immersion Lithography
Asahi Glass Co., Ltd. has succeeded in the development of "QC-i" a synthetic quartz photomask(1) substrate, which complies with the liquid immersion technology used in ArF (argon fluoride) laser steppers(2) that use ArF lasers as a light source for photolithography in semiconductor production.