The new silica glass for 157 nm lithography

Projection photolithography at 157 nm is now under research as a possible extension of current 248 nm and planned 193 nm technologies. However, the conventional silica glass used for 248 nm and 193 nm lithography cannot be applied for 157 nm lithography because of its low transmittance. In order to develop the modified silica glass for 157 nm lithography, the transmittance in the vacuum-UV region and the optical properties induced by vacuum-UV irradiation were investigated. The OH group and the ODC(I) in the silica glass markedly affect the initial transmittance at 157 nm and the former also affects the resistance to vacuum-UV irradiation. The hydrogen bonded OH group was observed after vacuum-W irradiation. From these results, the new silica glass "AQF" for 157 nm lithography has been successfully developed with a high internal transmittance (more than 80 % per cm) at 157 nm and a excellent resistance to F-2 laser.