Characteristics of Ag thin films sputter deposited using Ar or Kr gas under different pressure

Abstract

Recently, we found that Ag thin films with low electrical resistivity could be produced by DC sputtering using Kr gas, whose atomic mass is closer to that of Ag than Ar gas is. In contrast, sputtering using Ar caused trapping of Ar atoms in the film, leading to higher resistivity. In addition, the films sputtered using Kr gas had a much larger crystallite size than those sputtered using Ar gas. In the present study, we clarified the relation between the resistivity and crystallite size by data fitting using an equation proposed in the literature. Ag thin films with a thickness of 150 nm were deposited on glass substrates via DC magnetron sputtering in Ar or Kr gas at a pressure of 2 mTorr. The sputtering voltage was varied from 300 to 1000 V. By fitting the experimental data, we found that the model curves reproduced the experimental results for films sputtered in either Ar or Kr gas, and the electron reflection coefficient at the grain boundaries was the same for both types of film. Thus, the resistivity depends on the crystallite size, and the electron scattering behavior is basically the same for both films. Therefore, it is considered that the main reason for the lower resistivity of the film produced by sputtering in Kr is enhanced grain growth due to suppression of energetic neutral Kr bombardment of the film surface. Although it is known that the Ar gas pressure affects the characteristics of thin films, the effects of pressure have not been well investigated for Kr gas. In the present study, we examined the effect of the Kr gas pressure on the resistivity and crystallite size for sputtered Ag films. The results indicated that there was no significant effect.