Microcrystalline silicon by plasma enhanced chemical vapor deposition from silicon tetrafluoride

Abstract

The amorphous and microcrystalline silicon growth from SiF4–H2–He plasmas has been studied by exploring various parameters, such as He addition, rf power, H2 dilution, and frequency. The dilution of SiF4–H2 plasmas with He gas has been found to promote the crystalline phase and entirely microcrystalline silicon films have been obtained at low temperature (120 °C) under optimized experimental conditions. All the obtained results are discussed on the basis of etching/growth competition mechanism, in which the etching process by F atoms is selective for the amorphous phase. As such, all the experimental conditions enhancing the etching channel let the microcrystalline growth prevail. The net deposition rate, monitored by the laser reflectance interferometry, results from the difference between growth rate, rG, and etching rate, rE. Optical emission spectroscopy is a powerful in situ diagnostic tool to monitor the crystallinity degree in the material, since the [F*]⋅[He*]/[SiF2*]⋅[Hα] ratio, obtained from the peak intensities and called the Γ ratio, has been found to be proportional to the rE/rG ratio.