Defect reactivation and structural relaxation in deposited amorphous SiO2

Si dangling-bond defects present in films of amorphous SiO2 deposited by plasma-enhanced chemical vapor deposition and induced by exposure to ultraviolet radiation present in low-pressure Kr, Kr/20%F, and O2 plasmas have been studied. It is demonstrated that defects are created and self-annealing occurs during the deposition process. It is argued that low deposition rates should result in the least defective films. Exposure to ≊300-nm wavelength radiation reveals defects whereas ≤260-nm radiation bleaches them. The process of excitation-bleaching can be cycled without apparent loss in total defect density. Studies of defect revelation as a function of substrate temperature during exposure down to 80 K indicate that the process is more efficient at high temperature than at low. Thermal annealing and reactivation measurements show that irreversible annealing begins for temperatures ≳400 °C and after 800 °C no measurable densities of defects can be reactivated. This regime is demonstrated to correspond with a change in the microscopic structure of the deposited films.