The influence of residual gas on boron carbide thin films prepared by magnetron sputtering

• Several B4C single layers and W/B4C multilayers were deposited in 3 different base vacuums and 2 improved technologies. • Better base pressure leads to lower oxygen impurity. • Impurities do not change the B/C ratios in the films and include 2% Ar and less than 1% Ni. • According to the overlapping binding energy curves, the oxygen atoms are mainly in the form of boron oxides. • Ti sputtering improves the film purity and the optical performance. Boron carbide (B4C) thin films were prepared by magnetron sputtering and residual gas impurities in the films were analyzed by X-ray photoelectron spectroscopy. The impurities, mainly oxygen, decrease with improving vacuum. By using argon ion beam etching of the films, the atomic concentration was measured as a function of etching depth. The binding energy spectra were analyzed using wavelet transform and curve fitting, showing that most of the oxygen impurity is in the form of boron oxides, and that the impurities are physically trapped among columnar structures in the film. In order to improve the base vacuum before coating the film, a range of methods were used, including argon gas filling on the target surface and titanium pre-sputtering. The experimental results show that the latter is an efficient and feasible method. Based on the titanium pre-sputtering technology, the optical performance of W/B4C multilayer was improved so much.