Two-dimensional simulations of multi-hollow VHF SiH4/H2 plasma

Li-Wen Su,Yoshinobu Kawai,Weiting Chen,Kiichiro Uchino

doi:10.1063/1.5003911

Abstract

A triode multi-hollow VHF SiH4/H2 plasma (60 MHz) was examined at a pressure of 20 Pa by two-dimensional simulations using the fluid model. In this study, we considered the effect of the rate constant of reaction, SiH3 + SiH3→SiH2 + SiH4, on the plasma characteristics. A typical VHF plasma of a high-electron density with a low-electron temperature was obtained between two discharge electrodes. Spatial profiles of SiH3+, SiH2+, SiH3- and SiH3 densities were similar to that of the electron density while the electron temperature had a maximum value near the two discharge electrodes. It was found that the SiH3 radical density did not decrease rapidly near the substrate and the electron temperature was lower than 1 eV, suggesting that the triode multi-hollow plasma source can provide high quality amorphous silicon with a high deposition rate.

Highlights

Very high frequency (VHF) capacitively coupled plasma sources are widely used for fabrication of thin-film silicon solar cells[1,2,3,4,5,6,7,8] because of high electron density and low electron temperature, leading to high-rate depositions of silicon films
It is interesting from the point of view of plasma physics that low electron temperatures is required for reducing the higher order silanes contributions to the film growth
To the best of our knowledge, there is no report of the simulation of VHF SiH4 plasmas using the rate constant of NIST-PML for the reaction (1)

Summary

INTRODUCTION

Very high frequency (VHF) capacitively coupled plasma sources are widely used for fabrication of thin-film silicon solar cells[1,2,3,4,5,6,7,8] because of high electron density and low electron temperature, leading to high-rate depositions of silicon films. There have been many reports on simulations of SiH4 plasmas relating to fabrication of amorphous silicon.[16,19,20,21,22] As is well known, the main deposition precursor in SiH4 plasmas is SiH3 and the contribution of SiH2 is much smaller than that of SiH3, and SiH2 affects the quality of deposited films, that is, SiH2 is considered to be precursors to form higher-order silanes. To the best of our knowledge, there is no report of the simulation of VHF SiH4 plasmas using the rate constant of NIST-PML for the reaction (1). Comparison with the results for Perrin et al’s rate constant was tried

MODELLING

RESULTS AND DISCUSSION

SUMMARY AND CONCLUSIONS