Stress and Thermal-Expansion Coefficient of Chemical-Vapor-Deposited Glass Films

Abstract

The stress in thin films of chemical-vapor-deposited (CVD) glass on Si substrates was measured by the Newton-ring method. The CVD films studied were Silane-oxidized SiO2, phosphosilicate glass and borosilicate glass deposited at 400°–450°C. Stress reduction due to moisture absorption was observed in the CVD films, but it was not observed in the sputtered SiO2 and the thermally grown SiO2 films. The initial tensile stress in the CVD films changed into compressive stress after heat treatments at 600°–900°C. By measuring the stress at elevated temperatures, the intrinsic stress was reduced from the total stress. From the thermal stress measurement, the thermal-expansion coefficient and the elastic constant of the CVD glass films were estimated.