Kinetics of residual stress evolution in evaporated silicon dioxide films exposed to room air

Abstract

Deposition of silicon dioxide thin films on silicon, germanium, and glass substrates has been accomplished by electron gun evaporation under various experimental conditions. The level of compressive residual stresses in evaporated SiO2 films determined just after deposition of films on Si or Ge substrates and the mass density of silica were found to be dependent on the substrate temperature and oxygen partial pressure in the evaporation chamber. Moreover, the intensity of compressive residual stresses decreased linearly as the logarithm of the exposure time of films to room air (aging time) was increased. After a compressive–tensile stress transition observed at a given aging time for films with relatively low densities, the intensity of tensile stresses continued to increase progressively with increasing aging time. The relative variation of residual stresses in SiO2 films was dependent on the mass density of the deposited material. Since the intensity of the absorption band of Si–OH radicals in the infrared spectra of SiO2 films exposed to room air increased with increasing aging time, the evolution of residual stresses was attributed to the effect of the hydration of silica by water vapor contained in room air. A reaction mechanism involving the physical adsorption of water vapor molecules on the SiO2 surface and reaction between adspecies and Si–O–Si species is proposed and discussed to interpret the logarithmic kinetics of residual stress evolution in evaporated SiO2 films exposed to room air.