Abstract:

To reduce the F deficiency defect in MgF₂ thin films deposited with magnetron sputtering, SF₆ was added to the working gas Ar₂ as the reactive gas, and MgF₂ thin films were prepared on quartz glass substrates with radio frequency (RF) magnetron sputtering. The effects of sputtering power on the chemical compositions, microstructure and optical properties of MgF₂ thin film were investigated. The results show that with sputtering power increase from 115 to 220 W, the atomic ratio of F to Mg increased continuously, and reached 2.02 at 185 W, close to ideal stoichiometric ratio of 2: 1. The crystallinity of MgF₂ film improved first, then decreased, and finally changed into amorphous state. Profile of particles composing MgF₂ film became clearer at first, and finally became blurred. Refractive index of MgF₂ film decreased firstly and then increased, and got the lowest value at 185 W, 1.384 at 550 nm wavelength which is very close to that of MgF₂ bulk crystal. The integral transmittance of the coated glass within 300-1100 nm (hereinafter referred to as the transmittance of the thin film) increased first and then decreased, and reached 94.99% at 185 W, higher than that of the bare glass substrate by 1.79%.

Key words: MgF₂ thin film, F deficiency, transmittance, antireflection, sputtering power, magnetron sputtering