New silica glass for 157-nm lithography

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Abstract
Projection photolithography at 157 nm is now under research as a possible extension of current 248 nm and planned 193 nm technologies. Although the conventional silica glass used for 248 nm and 193 nm lithography cannot be applied for 157 nm lithography because of its low transmittance, we have already developed the modified fused silica glass 'AQF' for 157 nm lithography. In this paper, we report on the fabrication of 'AQF' 6 inch photomask substrate. 157 nm transmission and its uniformity is better than 75 plus or minus 3%, and flatness is less than 0.5 micrometer. Defects over 0.4 micrometer in size are free. The physical and mechanical properties are also shown to be similar with our conventional silica glass 'AQ.'

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