Study on SiO2 thin film modified by post hot isostatic pressing

Abstract

SiO2 thin film is one of the important low refractive index films commonly used in the field of optical thin films. In this paper, the Hot Isostatic Pressing (HIP) technique is applied to the post-treatment of SiO2 thin film materials for the first time. The thin film samples were prepared by ion beam sputtering deposition technique. The samples were heated at 300 °C for 50 MPa under vacuum argon atmosphere for 24 h. The samples were analyzed by the spectra in the visible and infrared bands and surface deformation. The effects of HIP treatment on the refractive index, physical thickness, stress, Si-O-Si bond angle and relative density of films were obtained. The results show that the refractive index decreases from 1.4685 to 1.4591, the physical thickness increases 0.6%, the stress changes from −493 MPa to −226 MPa, and the Si-O-Si bond angle increases from 129.85° to 131.32°. The fundamental physical mechanism of the change for all the characteristics is the film stress. The release of film stress leads to the decrease of the density of the film, and the variation of the thin film density is proved by the change of asymmetric stretching vibration frequency of SiO2 thin film. In addition, the HIP treatment can reduce the OH-group chemical defects in the SiO2 thin film.