Microwave Plasma Assisted VHF-PECVD of Micro-Crystalline Silicon

Abstract

AbstractGrowth of intrinsic micro-crystalline silicon layers by means of VHF-PECVD, assisted by remote microwave (MW) plasma has been investigated. The aim of the MW plasma is to enhance the deposition rate by introducing excited hydrogen and Ar atoms from the MW plasma in the VHF deposition zone. For this purpose a remote microwave plasma source was constructed in which a H2/Ar plasma is generated in a 20 mm diameter quartz tube. A gasshower has been constructed for homogeneous distribution of the flow of excited gas species from the microwave source into the deposition zone of the VHF-PECVD reactor where the dissociation of silane takes place. In a first series of experiments we applied high microwave power (< 500 W) and pure hydrogen in the MW source. This resulted in a larger deposition rate, but all layers – even grown at low silane concentrations – were amorphous and had a high oxygen content. The oxygen contamination was partly due to reduction of the quartz tube by the hydrogen plasma. In a second series of experiments Ar dilution and reduced MW power were used to eliminate the effect of etching of the tube by the microwave hydrogen plasma. In this series of experiments an increase of the growth rate of micro-crystalline silicon by about 15 % due to assistance of the microwave plasma was found. Optical emission spectroscopy indicates that – in these experiments – the main mechanism for the increased dissociation of silane is through molecular quenching reaction of Ar* metastables.