Magnetron Assisted PECVD Process for Deposition of Amorphous and Microcrystalline Hydrogen Containing Silicon Layers from a Silane-Hydrogen-Argon Gas Mixture

摘要

Amorphous and microcrystalline hydrogen doped silicon layers are used for several applications. Here a magnetron assisted PECVD process (magPECVD) using a magnetron sputter source for plasma excitation with a medium frequency (50 kHz) pulse power supply in a silane-hydrogen-argon atmosphere was investigated with emphasis on amorphous layers. The influence of different process parameters like silane-hydrogen-ratio and substrate temperature on dark and photoconductivity, microstructure parameter (ratio between different hydrogen bonds) and microcrystalline fraction was investigated. The process pressure ranges from 0.5 to 5 Pa. Therefore magPECVD is well suited for in-line processing together with magnetron sputter processes in one process chamber. The achieved deposition rate for amorphous silicon is about 5 times higher than in established processes. The measured layer properties of amorphous layers show a very good ratio of photo and dark conductivity of 2.5×10~6. This ratio has a maximum at approximately 225°C. The achieved values for photo conductivity of around 10~(-6)(Ω cm)~(-1) were still one order of magnitude lower than required. A high microstructure parameter of about 0.6 indicates that hydrogen is mainly bonded in Si-H_2 and Si-H_3 state instead of Si-H. The initial experiments for depositing microcrystalline silicon were successful and a deposition rate of more than 1 nm/s was obtained. The estimated Raman crystallinity was around 70%. Resultantly the magnetron PECVD process shows potential for the deposition of amorphous (a-Si: H) and microcrystalline (μc-Si: H) layers with high deposition rate but further investigations are necessary.