Low-temperature Deposition Of Poly-silicon Thin Films By ECR-PECVD And Its Characteristic Analysis

By its outstanding photoelectricity performance and the low cost of manufacture, the polycrystalline silicon(poly-Si) thin film becomes one kind of extremely important electronic material in the energy and information industries, and applied widely in the large scale integrated circuit and the semiconductor separation component. Recently, in order to reduce the manufacturing cost of the poly-Si thin film, many kinds of low temperature deposition technology have been developed. But each one has it's adverse factor in commercial process. For the high technical maturity and the high deposition quality, traditional plasma enhanced chemical vapour deposition (PECVD) technology was wide applied in the large-scale industrial production. Based on this technic, we improved the deposition system, use the electron cyclotron resonance (ECR) microwave plasma enhanced chemical vapour deposition (ECR-PECVD) to deposition poly-Si films directly on the glass substrate and silicon wafer at low temperature. ECR is a particularly good means of depositing thin films at low temperatures because ion energy is very low and eletron energy is high, and it has the advantage of high plasma density and activity.Although SiH₄ is more expensive than other silicon halide, but it avoid introduing more other impurities in the deposited films. We use hydrogen as the plasma source gas, it was introduced directly to the quartz windows, and the silane (diluted by Ar, SiH₄:Ar=1:19) was introduced downstream in the plasma.Research result showed that, when substrate temperature is 500℃, we can deposit the high qualit of polycrystalline silicon thin films. Through compares with other response gas, we prepare polycrystalline silicon thin film of pure silicon elemental composition. And for the glass substrate, we found that the grain size of the poly-si films is increased with the increases of the thickness of the films. It means that, if the thin film is thicker, then the crystal grain can be bigger. For the silicon wafer substrate, the completely crystallized poly-si can be obtained at low microwave power. Further study showed that the cleaning time and the hydrogen flow during hydrogen plasma cleaning before deposition can affect the quality of the poly-si films. We analysised the microstructure of the films by TEM, XRD, AFM and SEM, and we obtained the optimum parameters for depositing poly-si at low temperature.