Investigation on the initial growth of nanocrystalline silicon prepared from hydrogen-diluted SiCl4 at low temperatures

Abstract

Ultrathin nanocrystalline silicon films have been fabricated by plasma enhanced chemical vapour deposition from hydrogen-diluted SiCl4 at a low temperature of 250 °C. The Raman spectra measurements and high resolution transmission electron microscopy observations reveal that nanocrystalline silicon can be directly grown on an insulator glass substrate at the initial growth of the deposition process. The crystallinity and the grain size increase with the increase in the deposition period. Furthermore, the crystalline fraction as well as the grain size also increase with the decrease in the hydrogen dilution ratio. The I–V characteristic curves measured by a tuned Langmuir probe in the SiCl4/H2 plasma region at a substrate temperature of 100 °C show that silicon films with higher conductivity were deposited on the probe surface in the deposition process. This behaviour is completely different from that observed in the SiH4/H2 system. It is considered that the formation of nanometre size grains occurs in the gas phase reaction process at the initial stage of film growth, while the growth of grains is mainly governed by the surface reaction process where chlorine and hydrogen play an important role. The direct growth of nanocrystalline Si on the insulator surface at low temperatures using SiCl4/H2 opens up the possibility of directly fabricating nc-Si/SiO2 or nc-Si/a-SiNx systems at low temperatures.