Preparation of wide optical spectrum and high antireflection MgF2 thin film with SF6 as reactive gas

Abstract

Abstract In order to suppress F-deficiency, SF6 was added into the working gas Ar2 as the reaction gas to deposit MgF2 thin film on quartz glass substrate with radio frequency (RF) magnetron sputtering, and the effects of working pressure on the chemical compositions, microstructure and property of MgF2 thin film were investigated. The results show that with the working pressure increase from 1.0 to 2.5 Pa, the atomic ratio of F: Mg decreased continuously, and reached 2.02 at 2.0 Pa, very close to the ideal stoichiometric ratio of 2:1; the crystallinity of MgF2 film improved first then decreased, and finally changed into amorphous state; the particles’ profile of MgF2 film became clearer and their size increased significantly at first, but finally their profile became blurred. The refractive index of MgF2 film decreased first and then increased, and got the lowest value at 2.0 Pa, 1.384, almost equal to that of MgF2 bulk crystal. The transmittance of the coated glass within 300–1100 nm (hereinafter referred to as the transmittance of the thin film) increased first and then decreased. The transmittance of all films was higher than that of the bare glass substrate (93.2%), that is to say, all films had antireflection effect. The film transmittance reached 94.99% at 2.0 Pa, higher than that of the bare glass substrate by 1.79%, and higher than the simulated value calculated with G-Solver software by about 0.5%.