Composition control of RF-sputtered Ni2MnGa thin films using optical emission spectroscopy

Optical emission spectroscopy can be used to monitor the composition of Ni2MnGa thin films during sputtering. By choosing peaks of Ni:341.5 nm, Mn:403.1 nm and Ga:417.2 run, the Ar pressure is found to affect the spectrum intensities of Ni, Mn and Ga atoms, as well as the intensity ratios of I-Mn/I-Ni and I-Ga/I-Ni. However, the r.f. power has no obvious effect on them. This may be due to the ferromagnetic characteristic of Ni, or that different metals have different energy distributions of sputtered atoms, or that they need various p (.) d values to be thermalized. Here, p is the At pressure and d is the target and substrate distance. The intensity ratios of these peaks are found to be proportional to the composition ratios (mol ratio) of thin films with the relations: C-Mn/C-Ni = 0.0151(I-Mn/I-Ni) + 0.392 and C-Ga/C-Ni = 0.0720(I-Ga/I-Ni) + 0.273. Hence, the composition of sputtered thin films can be predicted by monitoring the intensity of light emission from the sputtering plasma.