Sputtering Power on the Microstructure and Properties of MgF₂ Thin Films Prepared with Magnetron Sputtering

To reduce the F deficiency defect in MgF 2 thin films deposited with magnetron sputtering, SF 6 was added to the working gas Ar 2 as the reactive gas, and MgF 2 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 MgF 2 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 MgF 2 film improved first, then decreased, and finally changed into amorphous state. Profile of particles composing MgF 2 film became clearer at first, and finally became blurred. Refractive index of MgF 2 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 MgF 2 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%.