Enhanced birefingence of MgF₂ thin film at 193 nm by serial bideposition

Abstract

Magnesium fluoride films were coated by serial bideposition with a varying number of sub-deposited layers. The deposition angle 70° remained constant throughout the process by a single electron-beam source. One, 4, 20, and 100 sub-deposition layers were prepared. The microstructure, residual stress, absorption of water, and linear birefringence of serial bideposition of anisotropic thin film at 193 nm were investigated and discussed. Microstructures of the films were observed by scanning electron microscopy. The residual stress was measured by phase-shifting interferometer. The water absorption bands of the thin films were measured by Fourier transform infrared (FTIR) spectroscopy, and refractive indices in two different directions (S- and P-polarized) were determined from a spectrometer equipped with a polarizer. The linear birefringence would increase and the stress would decrease when the sub-deposited layers were increased. When the number of layers was 100, the difference between the refractive indices for two different polarizations was able to reach 0.082.