Atmospheric-pressure Plasma Chemical Vapor Deposition For Polycrystalline Silicon Preparation From SiCl₄ And OES Diagnosis

Recently,as the crisis of conventional energy sources,the renewable solar energy is developing rapidly.The strong growth of the solar cell industry has led to a major shortage of its starting material,polycrystalline silicon feedstock.A serious environmental problem caused by silicon tetrachloride,the by-product from the manufacture of polycrystalline silicon, needs to be solved.In this paper,the one-step fabrication of polycrystalline silicon using SiCl₄ as Si precursor was explored.This approach can make good use of the by-product of polycryatalline silicon industry.In order to avoid the use of expensive vacuum equipment and complicated discharge system,atmospheric-pressure plasma chemical vapor deposition (AP-PCVD),which attracted much attention recently,was employed.1) In this paper,the effect of plasma source was firstly investigated on the preparation of polycrystalline silicon by AP-PCVD,using the single power sources of positive pulse,8 kHz AC,100 kHz AC,and dual power sources(positive pulse and 100 kHz AC).The results of XRD and Raman characterizations indicated that the samples fabricated by positive pulse and 8 kHz AC power sources were amorphous,while the samples were highly crystallized produced by 100 kHz AC and dual power sources.It can be seen from the SEM images that the samples fabricated by dual power sources had a big grain size.The EDX measurement reveals silicon is the main element with trace amount of residue chlorine.The influence factors,which are discharge power and partial pressures of He diluent gas,H₂ and SiCl₄ on fabrication of polycrystalline silicon using 100 kHz AC and dual power sources were also investigated.2) The PCVD process for preparing polycrystalline silicon using SiCl₄ was diagnosed by Optical Emission Spectrometry(OES).In the SiCl₄/H₂ discharge system,the emission spectra at different frequency,discharge power and partial pressures of He diluent gas,H₂ and SiCl₄ were examined.The H atom excitation temperature was achieved from the two spectral lines of H_α(656.6 nm) and H_β(486.1 nm).Actinometric optical emission spectroscopy(AOES) was employed to study quantitatively the atomic hydrogen density and the dissociation fraction of H₂.In the process of plasma chemical vapor deposition,a strong emission spetrum at 288.2 nm derived from excited Si^*[3s²3p²(¹D)-3s²3p4s(¹p^o)]was detected.Thereby,it can be inferred that the excited Si^*,generated from SiCl₄ dissociation in plasma,is an important active species for the formation of polycrystalline silicon.