In situ determination of sputtered Ni–Cu film composition from emission intensities

In situ elemental analysis of films comprising multielements deposited by sputtering is necessary to improve the reliability of the films because small changes in the film composition affect the properties of the films. Recently, we developed a method to determine the composition of Cu–Zn films by measuring the intensities of emission lines of Cu and Zn during sputter deposition. However, this method was only applicable to a constant chamber pressure, and only a narrow composition range (65.9–80.6 at. % of Cu in the target) was investigated. In this study, the applicability of this method was investigated for a wide range of film compositions, and the combination of emission lines that can be used to determine the film composition regardless of the chamber pressure was determined. This was achieved using Ni–Cu alloy targets, whose Cu composition ranged from 29.4 to 85.3 at. %, by evaluating the linearity (R2 value) between the emission intensity ratio of Ni/Cu lines and the atomic ratio of Ni/Cu in the films. An R2 value of 0.9870 was obtained for the combination of Ni 338.1 nm and Cu I 296.1 nm lines at chamber pressures from 1 to 5 Pa. This result indicates that the composition of Ni–Cu films can be determined from the intensities of the emission lines of Ni and Cu during sputter deposition regardless of the chamber pressure.