Composition Control of R.F.-Sputtered Ni₂MnGa Thin Films Using Optical Emission Spectroscopy

Abstract

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 nm, 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 Ar 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.