Research Of Poly-Si Films Deposited By ECR-PECVD At Low-temperature

For its high property of light sensation, high light absorption in long-wavelength region, poly-Si thin film has became the most important material for Solar cells. Compare to a-Si thin film, poly-Si has higher transformation rate and carrier mobility rate, and no S-W effect; compare to single crystal Si film, poly-Si thin film can be deposit with large scale on cheaper substrate at very low temperature, and it has been recognized as ideal photovoltaic materials for its highly efficient and low cost. In addition, Poly-Si is substitute new semiconductor material for sensing device and Poly-Si thin film transistors.Today various methods were used to deposit poly-Si such as CVD, PECVD (Plasma Enhence Chemical Vaper Deposition) , HWCVD (Hot Wire CVD), LIC(Laser-Induced-Crystallization), MILC(Metal-Induced-Lateral-Crystallization) et al. Among those technique, the PECVD technique can decrease the temperature of deposition, and the parameters can be control easily, so it can improve the quality of the thin films. This methods are suitable for large-scale production, more and more people become interested in PECVD.Poly-Si thin films are deposited on Si and glass substrates by electron cyclotron resonance-PECVD (ECR-PECVD) at low temperature using SiH₄ and H₂ as gas sources. The non-equilibrium plasma induced by microwave source at low pressure is helpful for the decomposition of SiH₄, thus greatly reducing the deposition temperature. Useing SiH₄ and H₂ as reactant can pure silicon film reduce the content of halide. The Adding of Ar is beneficial for discharge and helpful to etch the weak Si-Si bond, accelerate the deposition rate of poly-Si films.It is difficulty to deposit poly-Si thin film on glass substrate directly, because glass is heterogeneity amorphous substrates for poly-Si thin film. The substrate structure has very importante impact on the poly-Si thin film. We use seed layer to solve this problem. The poly-Si thin film structure was studied by the in-situ Reflection High Energy Electron Diffraction (RHEED) method, the X-ray diffraction (XRD) method, Raman Spectroscopy (Raman) and the Transmission Electronic Microscope (TEM). Through the result of the test, the influence of the seed layer was studied, and we optimized the experiment parameters, got the best results.