高速微晶硅薄膜沉积过程中的等离子体稳态研究

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

通过光发射光谱监测高速沉积微晶硅薄膜过程中I(Hα+)/I(SiH+)随沉积时间的变化趋势,分析高速率微晶硅薄膜纵向晶化率逐渐增大的原因.通过氢稀释梯度法,即硅烷浓度梯度和氢气流量梯度法来改善材料的纵向均匀性.结果表明:硅烷浓度梯度法获得的材料晶化率从沉积300s时的53%增加到沉积600s时的62%,相比于传统方式下纵向晶化率从55%到75%的变化有了明显的改善.在硅烷耗尽的情况下,增加氢气流量一方面增加了气体总流量,使得电子碰撞概率增加,电子温度降低,从而降低氢气的分解,抑制SiHx基团的放氢反应,同时背扩散现象也得到了一定的缓解,使得I(Hα+)/I(SiH+)在沉积过程中逐渐增加的趋势有所抑制,所制备的材料的纵向晶化率在240s后维持在53%—60%范围内,同样改善了薄膜的纵向结构.

The ratio of I（Ha）H（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（H＊a）/I（SiH＊） is controlled during the deposition of microcrystalline silicon film.