Suppression of Oxygen Impurity Incorporation into Silicon Films Prepared from Surface-Wave Excited H₂/SiH₄Plasma

Abstract

Surface-wave plasma (SWP) in SiH4 highly diluted with H2 at 2.45 GHz and 2 kW is applied to the deposition of polycrystalline silicon thin films. When a quartz window is used as a microwave injection for discharge, an oxygen impurity level of up to ∼1.5% is observed in the deposited films. Mass spectrometry reveals that the origin of oxygen is water, i.e., the chemical erosion product of the quartz window (SiO2) caused by many hydrogen radicals in high-density plasma. By replacing the quartz window with an alumina (Al2O3) window, oxygen impurity level is markedly reduced, along with the increase in the grain size of films.