Change in UV Transmittance in Silica Photomask Glass under KrF Excimer Laser Irradiation

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Abstract
Change in optical transmittance of silica photomask glass, synthesized by flame hydrolysis of SiCl4, was measured in situ under KrF exima laser irradiation. Photoabsorbance at 215 nm has a peak at 2-3×103 pulse irradiation. The transmittance after cessation of the irradiation recovers having two relaxation times of approximately 10 and 100 s. The maximum absorbance decreases with increasing OH content in the glass. The 0.4th power dependence of the absorbance on the laser power density ( frequency×intensity) is explained by assuming that the saturated absorbance is proportional to the degree of the E ′ center formation reaction, and is reciprocal to that of the OHC related 1.9 eV photoemission reaction.