氢稀释对多晶硅薄膜结构特性和光学特性的影响

Effect of hydrogen dilution on structure and optical properties of polycrystalline silicon films

以SiCl4和H2为气源,用等离子体增强化学气相沉积技术,在250℃的低温下,研究氢稀释度对多晶硅薄膜结构特性的影响.实验结果表明,对于以SiCl4和H2组成的反应源气体,氢对薄膜生长特性的影响有异于SiH4/H2,在一定功率下,薄膜的晶化率随氢稀释度的减小而增加,在一定的氢稀释度下薄膜晶化度达到最大值85%;随着氢稀释度的继续减小,薄膜晶化度迅速下降,并逐渐向非晶态结构转变.随氢稀释度的减小,薄膜的光学带隙由1·5eV减小至约1·2eV,而后增大至1·8eV.沉积速率则随氢稀释度的减小先增加后减小,在无氢条件下,无薄膜形成.在最佳氢稀释度条件下,Cl基是促进晶化度提高,晶粒长大的一个主要因素.

Polycrystalline silicon films were prepared from SICl4 diluted with hydrogen by plasma-enhanced chemical vapor deposition at a low temperature of 250℃. The effect of hydrogen dilution on their structure and optical properties were investigated. It was found that the effect of hydrogen on the growth behavior of the films deposited using SICl4 ＋ Hz are completely different from that of using SiH4/Hz. The crystalline fraction increases with decreasing the hydrogen dilution ratio R and reaches a maximum value of 85% at a low hydrogen dilution. However, further decreasing hydrogen dilution ratio leads the crystallinity to deteriorate and a phase transition between microcrystalline silicon and amorphous silicon is observed. The optical band gap gradually decreases from - 1 .SeV to - 1.2eV and then increases up to 1.8eV with the decrease of the hydrogen dilution ratio. The deposition rate initially increases and then decreases with decreasing hydrogen dilution ratio, and no film is formed by using pure SiCl4. According to these results, we conclude that under the eondition of optimum hydrogen dilution ratio, the enhanced crystalline fraction and the increase in grain size are attributed to the Cl radicals which play important roles in the low-temperature growth of crystalline silicon films.