Comparison of the structural and optic al properties of amorphous silicon thin films prepared by direct current, bipolar pulse, and high-power impulse magnetron sputtering methods

Abstract

This paper presents a comparative study of amorphous silicon (a-Si) thin films deposited by three different techniques: direct current magnetron sputtering (DCMS), bipolar pulse magnetron sputtering (bipolar pulse MS) and high-power impulse magnetron sputtering (HiPIMS). The structurafl properties of the a-Si films with a thickness of ∼112 nm were characterized by X-ray reflectivity and Raman spectroscopy. The surface morphology, optical and mechanical properties of a-Si films with a thickness of ∼400 nm were investigated using a field emission secondary electron microscope, an atomic force microscope, spectroscopic ellipsometry and nanoindentation. It was found that for the same time-averaged discharge power, the deposition rate of the HiPIMS method was lower compared to DCMS and bipolar pulse MS. The a-Si film prepared by HiPIMS method had the lowest root mean square roughness of 0.65 nm and the highest density of 2.21 g/cm3. These results are consistent with the highest refractive index (400–700 nm) of 3.66 and a hardness of 9.09±0.19 GPa in the film, indicating that the HiPIMS method produces denser films than the DCMS and bipolar pulse MS methods. The amorphous silicon thin films fabricated by HiPIMS have the potential to improve the structural and mechanical properties for high performance thin film semiconductor applications.