VHF等离子体光发射谱(OES)的在线监测

采用光发射谱(OES)测量技术，对不同制备条件下的甚高频(VHF)等离子体辉光进行了在线监 测.实验表明，VHF等离子体中特征发光峰(Si，SiH,H_α,H^*_β 等)的强度较常规的射 频(RF)等离子体明显增强，并且在制备μc-Si：H的工艺条件下(H稀释度R(H₂/S iH₄)=23 )，随激发频率的增加而增大，这些发光峰的变化趋势与材料沉积速率的变化规律较相似.Si H峰等的强度随气压的变化则因硅烷H稀释度及功率的不同而异：高H稀释(R=23)时，SiH峰强 度在低辉光功率下随反应气压的增大单调下降，在高辉光功率下随气压的变化呈现类高斯规 律；低H稀释(R=5．7)时， SiH峰随气压的变化基本上是单调下降的，下降速率也与功率有 关，这些结果表明，VHF-PECVD制备μc-Si：H和a-Si：H的反应动力学过程存在较大差异.此 外，随着激发功率的增大，Si，SiH峰都先迅速增大然后趋于饱和，并且随着H稀释率的增大 ，将更快呈现饱和现象.通过对OES结果的分析与讨论可知，VHF-PECVD技术沉积硅基薄膜可 以有效提高沉积速率，而且，硅基薄膜的沉积速率的进一步提高需要综合考虑H稀释度、气 压和功率等的匹配与优化.关键词：甚高频等离子体化学气相沉积氢化硅薄膜光发射谱

Diagnosis of VHF plasmas with optical emission spectroscopy

Very high frequency (VHF) Plasma and its glow discharge mechanism during the deposition of μc-Si:H film have been studied by means of optical emission spectroscopy (OES) technique in this paper.From the measured OES spectra,where the valuable information on the Si,SiH,H and H₂ intensities were provided,the influence of deposition conditions on the VHF plasma has been investigated.The intensitie s of SiH,H₂ and H of VHF-gas deposition(GD) to deposit μc-Si:H were much high er than those of RF-GD to deposit a-Si:H.Under the experiment condition to depos it μc-Si:H,Si,SiH,the H and H₂ intensities increased obviously with the excit ation frequency,and the variation of the deposition rate with the excitation fre quency was similar to that of SiH.The SiH intensity of VHF-GD became higher than its Si intensity as the hydrogen dilution ratio decreased.The influences of the hydrogen dilution ratio on the plasma optical emission spectra also depended on the reaction pressure,the excitation power as well as the excitation frequency. In the case of the hydrogen ratio (R=H₂/SiH₄)R=23,the SiH intensity decrease d monotonously against the excitation pressure at a low excitation power (e.g.5W ).But the SiH intensity increased at first, then decreased with the increase of the pressure at the high excitation power (e.g.11-55W).In the case of the hydrog en ratio R=5.7,the SiH intensity decreased monotonously against the excitation p ressure for all the excitation power.The Si,SiH,H and H₂ intensities also incr eased with the excitation power and then trended to be saturated,and they are ea sier to saturate with the increase of the hydrogen dilution ratio.All the experi mental results demonstrated that the influences of the excitation frequency,the excitation power,the reaction pressure and the hydrogen dilution ratio were correlative,none of the deposition conditions is the critical factor to improve the deposition rate.