Effects of Flow Rate Variation on SiCl_n (n<3) Densities in SiCl₄ Plasmas

Radicals produced by the plasma enhanced chemistry vapour deposition technique in SiCl₄ plasma are identified by mass spectrometry using our newly proposed straight-line fit method. Since flow rate is one of the most important parameters in depositing thin films, we present the effects of SiCl₄ flow rate variation on SiCl_n (n<3) densities. The experimental results demonstrate that Si and SiCl_n (n=1,2) densities decrease with increasing SiCl₄ flow rate. After reaching the minimum values at a flow rate of 17 and 13sccm, respectively, Si and SiCl_n (n=1,2) densities slightly increase with further increase of flow rate to 20.5sccm. These results could be interpreted to which the depletion fraction of SiCl₄ decreases and the residence time of SiCl₄ molecule becomes shorter, with the increasing SiCl₄ flow rate. In order to obtain high-quality poly-Si films with high growth rate, it is better to use smaller flow rate of SiCl₄ source gas for depositing films.