Low-temperature Growth And Its Characteristic Research Of Poly-silicon Thin Films Deposited By ECR-PECVD

As an important electronic material in energy-information industry, Poly-Silicon thinfilms are widely used in large scale integration (LSI) and semiconductor discrete devicesbecause of its excellent photoelectric characteristics and low-cost of preparation. In order toreduce its cost, more and more researchers have devoted to the research of the method toprepare the Poly-Si film at low temperature using cheap glass as substrate. Plasma enhancedchemical vapor deposition (PECVD) is one of the main technique among the thin filmdeposition methods. It can be used to deposit large area high-uniformity film at lowtemperature.Poly-crystalline silicon thin films are deposited on silicon and glass substrates byelectron cyclotron resonance-PECVD (ECR-PECVD) at low temperature using SiH₄ and H₂plasma as hytrogen and Si sources, respectively. Compared with the conventional PECVD,the ECR semiconductor processing device (ESPD) has the following characteristics: (1) Thenon-equilibrium plasma induced by microwave source at low pressure is helpful for thedecomposition of SiH₄, thus greatly reducing the deposition temperature. (2) The precursor isSiH₄ (95% of the doped Ar gas) with higher vapor pressure, which results in the silicon atomsto separate out and deposit thin films composed of pure silicon without impurities such as Cl,F. (3) The Adding of Ar is beneficial for discharge, so the rate of dissociation of SiH₄ can beraised.On the substrate of Si, thin film of high quality is prepared by changing the parameterssuch as the deposition temperature, the ratio of H₂ and SiH₄. The film crystal structure andsurface morphology are observed by transmission electron microscopy (TEM) and atomicforce microscopy (AFM), respectively. The growth parameters are optimized and the idealgrowth conditions have been obtained by comparing the results of reflect high electrondiffraction (RHEED). The results indicate that: at the temperature of 350～500℃, the higherthe temperature is, the better crystalline quality of Poly-Si is; when the flow rate of SiH₄ isfixed, increasing the ratio of H₂ is favorable for the formation of Poly-Si film.Using glass as substrate, in spite of increasing the ratio of H₂ and the substratetemperature, the Poly-Si thin film of high quality can't be prepared directly. The main reasonis that the silicon is homogenous substrate while the glass is not, which has great influence onthe deposition of the Poly-Si thin film. In order to resolve this problem, we have introduced the buffer layer. The effects of buffer layer are investigated by means of RHEED, X-raydiffraction (XRD) and Raman spectrum. By analyzing the images of Poly-Si thin film, thebest deposition conditions are obtained at low temperature.