PECVD氮化硅薄膜的沉积和退火特性

利用等离子增强化学气相沉积(PECVD)方法沉积了氮化硅薄膜,反应气体为氨气和硅烷.这些薄膜在不同条件(温度、时间和气氛)下进行了炉温或快速退火.对太阳电池而言,氮化硅薄膜不仅是有效的减反射层而且也有表面钝化和体钝化作用.利用椭圆偏振光谱、反射谱、红外吸收谱和准稳态光电导(QSSPC)分析了氮化硅薄膜的特性.实验发现随着退火温度的增加,氮化硅薄膜的厚度下降而折射率增加,可以归因于在退火过程中,薄膜愈加致密.红外吸收谱的研究发现,氮化硅中氢的含量在退火过程中有明显的下降,而QSSPC测量的样品寿命有同样的变化.这些结果显示氮化硅的钝化作用与其中的氢含量有关.

Characterization of As-deposited and Annealing SiN Films Deposited by Plasma Enhanced Chemical Vapour Deposition

Silicon nitride (SiN) thin films were deposited by PECVD (Plasma Enhanced Chemical Vapour Deposition) of silane (SiH4) and ammonia (NH3) reactants. Subsequently they were annealed in a furnace or rapid thermal processing (RTP) on different conditions (temperature, time and ambient). SiN thin films are used not only as very efficient antireflection coating but also as surface and bulk passivation on silicon solar cells. The characterization of SiN thin films was studied by spectral ellipsometry, reflection spectra, infrared absorption spectroscopy (IR) and quasi-steady state photoconductance (QSSPC) measurements. It was found by means of spectral ellipsometry that the thickness of SiN films decreased and the refractive index increased as the annealing temperature increased, which were most likely due to the more and more compact structure of SiN films. The reflection index was also investigated. There was significant hydrogen incorporation as well as the characteristic Si-N bands in the IR spectra. The hydrogen content in SiN thin films can be determined followed by integration of Si-H and N-H absorption bands. The effective minority carrier lifetimes of the samples were measured by QSSPC. The efficiency of SiN passivation was related with hydrogen content.