Remote plasma chemical vapour deposition of silicon films at low temperature with H2 and He plasma gases

Abstract

Silicon films were deposited at low temperature by remote plasma-enhanced chemical vapour deposition with H2 and He plasma gases. The effects of H2 and He plasma gases and plasma power on the film growth kinetics were studied. The composition, microstructure and optical properties of the deposited Si films were characterized by x-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, ultraviolet-visible spectroscopy, Raman spectroscopy, x-ray diffraction, transmission electron microscopy and atomic force microscopy. It was found that He plasma is effective in increasing the deposition rate and reducing the hydrogen content in the film. H2 plasma supplies excess atomic hydrogen which helps the formation of crystalline Si. The Si films deposited in H2 plasma are polycrystalline with very small needle-like grains, which are perpendicular to the substrate and distributed uniformly in the thickness of the film. The structure of the Si films deposited in He plasma is amorphous. The crystallization mechanisms are discussed in terms of gas phase species and film surface reaction. It is believed that atomic hydrogen plays an important role in crystalline Si deposition. A linear relationship was found between the hydrogen concentration and optical band gap.