Effects of fluorine dimer excimer laser radiation on the optical transmission and defect formation of various types of synthetic SiO2 glasses

Abstract

Changes in the optical absorption and the formation of point defects in three types of synthetic SiO2 glasses, wet (OH content; 120 ppm), dry (OH content <1 ppm), and fluorine (F)-doped (∼1 mol %) SiO2 glasses, by irradiation with fluorine dimer (F2) excimer laser light pulses (∼8 mJ/cm2/pulse×3.6×105 pulses) were examined by various spectroscopic methods. Intense optical absorptions were induced in the wet and dry silicas in the range of 4–8 eV, whereas the intensity of absorptions induced in the F-doped silica was smaller by an order of magnitude than that in the F-free glasses. The optical transmission at the wavelength of 157 nm after the irradiation was F-doped silica≫wet silica>dry silica. The dominant electron spin resonance-active defect in the irradiated specimens was the nonbridging oxygen-hole center (NBOHC) for the wet silica, or the E′ center in the dry silica. The concentration of NBOHCs or E′ centers in the F-doped silica was lower by an order of magnitude than that in the wet or dry silica. The present results suggest the possibility of using F-doped silica glasses as photomask materials for F2 laser lithography.