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

Surface-wave plasma (SWP) in SiH 4 highly diluted with H 2 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 (SiO 2 ) caused by many hydrogen radicals in high-density plasma. By replacing the quartz window with an alumina (Al 2 O 3 ) window, oxygen impurity level is markedly reduced, along with the increase in the grain size of films.