Nanocrystalline silicon thin films prepared by radiofrequency magnetron sputtering

Abstract

The effects of the hydrogen dilution and pressure on the structural and electrical properties of hydrogenated nanocrystalline silicon (nc-Si:H) films deposited at 250°C by radiofrequency (RF) magnetron sputtering method have been studied in a large range of total pressure (1–15 Pa) and H 2 dilution percentage (30–100%) in the gas phase mixture (Ar+ x% H 2). A combination of Raman spectroscopy, infrared (IR) absorption, X-ray diffraction, DC electrical conductivity and intrinsic stress measurements has been used to characterize the films. Only SiH 2 and (SiH 2) n bonds essentially in grain boundaries, corresponding to well-defined doublets in the bending (844–877 cm −1) and the stretching (2083–2100 cm −1) vibrational modes regions, have been detected. The best properties in terms of structure (crystalline volume fraction) and electrical conductivity of the nc-Si films are obtained for H 2 percentage of 70%, where the crystalline volume fraction f c is approximately 80% for 5 Pa and increases up to 92% with increasing pressure up to 15 Pa. An increase of approximately three orders of magnitude in the room temperature DC electrical conductivity is also obtained for these deposition conditions. The intrinsic stress is very low and not significantly affected by the changes in the crystalline volume fraction.