Interaction of F2 excimer laser with SiO2 glasses:: Towards the third generation of synthetic SiO2 glasses

Changes in optical absorption spectra and defect formation of different types of synthetic SiO2 glasses were examined by irradiation with F-2 excimer laser pulses (157 nm). Fluorine-doped, OH-free SiO2 glasses exhibit high optical transmittance (similar to 80%) at 157 nm in an as-delivered state and the intensity of Fz-laser-induced absorption is much less than that ill wet or dry F-free samples. The effect of F-doping on the blue shift of the absorption edge and suppression of color center formation was conspicuous up to 1 mol% but was slight upon further doping. It is suggested that elimination of strained Si-O-Si bonds upon F-doping is the primary reason of the improvement of resistance of SiO2 glasses to F-2-laser light. Novel optical phenomena by F-2-laser irradiation, bleaching of the vaccum UV (VUV) absorption edge and changes in the SiOH infrared absorption, were found in H-2-impregnated, or wet SiO2 glasses. These results lead to the conclusion that F-doping to 1 mol% is an effective and practical method to obtain synthetic SiO2 glasses for F-2 excirner laser optics as a photomask in optical lithography. (C) 2000 Elsevier Science B.V. All rights reserved.