Analysis on steady plasma process of high-rate microcrystalline silicon by optical emission spectroscopy

Abstract

The ratio of I(Hα*)/I(SiH*), obtained from the real time optical emission spectroscopy (OES) measurement in the high-rate microcrystalline silicon deposition process, as a function of time is used to analyze the cause of increasing crystallinity along the growth direction. Hydrogen dilution gradient method which means silane concentration gradient and hydrogen flow gradient method is adopted to improve vertical structure uniformity of the material. High-quality microcrystalline material around 53%-62% of Xc can be prepared through silane concentration gradient compared with 55%-75% of Xc prepared in the traditional method. In the silane depleted cases, by increasing the hydrogen flow the longitudinal uniformity of the material can be effectively improved. The vertical crystallinity around 53%-60% can be obtained. This is mainly due to the increase of the hydrogen flow that makes the collision probability increased, as a result, electron temperature of plasma reduced. Thus, the decomposition of hydrogen decreases and the reaction of hydrogen annihilation is suppressed. At the same time, the influence of back diffusion of SiH4 is suppressed. The gradually increasing trend of the ratio of I(Hα*)/I(SiH*) is controlled during the deposition of microcrystalline silicon film.