Time dependence of internal stress and optical characteristics of SiO_2 optical thin film

摘要

Recently, optical thin films have been increasingly needed in optical components. SiO_2 is most frequently used as a low-refractive-index material of optical thin films. The stress of the film is an important parameter that relates to the adhesion of the film. However, the long-term time dependence of the stress has not been thoroughly discussed for SiO_2 optical thin films. In this report, the time dependence of the stress of SiO_2 optical thin film is discussed in terms of optical characteristics in the infrared region. The optical properties and the structure of SiO_2 optical thin films deposited by vacuum deposition (using an EB) and ion-assisted deposition (IAD) were observed by FT-IR, XRD and SEM. The stress of SiO_2 optical thin films was measured using an interferometer to determine the change in the substrate shape. The SiO_2 thin films prepared by both vacuum deposition and IAD exhibited compression stress. Decreases in the stress of the films deposited by vacuum deposition were observed to continue for more than 1000 hours. This result is different from that of the conventional stress model in which the stress changes stop after about one week. The stresses of the films prepared by IAD were observed to change little. Optical absorption by Si-O bonds was observed at 1100cm~(-1). The change in bonds from Si-O to Si-OH was observed in the film deposited by vacuum deposition. It is thought that this result of the change in bonds was related to the decrease in the stress of the films.