Characterization of AlF3 thin films in the ultraviolet by magnetron sputtering of aluminum target

Aluminum fluoride thin films have been deposited by magnetron sputtering of aluminum target with CF4, or CF4 mixed 5% O-2 as working gas. To obtain low optical loss and high packing density, the films were investigated under different sputtering power and substrate temperatures. Their optical properties (including the transmittance, refractive index, and extinction coefficient) in the UV range and microstructure (including the cross section morphology, surface roughness, and crystallization) have been studied. AlF3 thin films deposited at low temperature and low sputtering power have better optical quality. The extinction coefficient of AlF3 thin films coated by 25W with CF4 mixed 5% O-2 as working gas is smaller than 6.5 X 10(-4) in the wavelength range of 190nm to 300nm.