Research On Polycrystalline Silicon Thin Films By Aluminum-induced Crystallization

Polycrystalline silicon(p-Si) thin film, which holds high photosensitivity, absorbability to visible light and illumination stability that is the same as crystalline silicon(c-Si), is considered as a highly efficient and low depleted photovoltaic material on cheap substrate. Polycrystalline silicon thin film is applied widely in the field of solar cells, sensors, liquid crystal display(LCD), thin film transistor(TFT) and large-scale integrate circuits.There are many ways to fabricate polycrystalline silicon thin film. Metal induced crystallization(MIC) have the advantages of low temperature crystallization , short crystalline time and large-grained silicon, so it interests many people. Aluminum induced crystallization(AIC) method in MIC is mostly used at present.The a-Si:H films with a stack of glass/a-Si:H/Al were crystallized by aluminum-induce. It were analyzed by Raman spectrum, X-ray diffraction, and Scanning Probe Microscopy. It has been studied that factors affect on the structures and properties of polycrystalline silicon in the process of aluminum induced crystallization.The study results were obtained as fellow:1. The higher substrate temperature and evaporation velocity is, the bigger silicon grains are in the same conditions during the process of thermal evaporation of Aluminum.2. High substrate temperature is useful to increase the growth, uniformity and crystallized volume fraction of thin films during the PECVD process. The silicane concentration and the power of radio frequency have an optimal value respectively in the reaction period.3. The crystalline volume fraction and grain size increases with increasing annealing time in the process of annealing. The higher annealing temperature is, the bigger silicon grains and optical absorption coefficient are.The silicon grains that are got by annealing in H2 ambient are bigger than that in N₂ ambient.4. Aluminum film became oxidized into alumina(Al₂O₃) by air prior to hydrogenated amorphous silicon(a-Si:H) deposition. If the thicker alumina film, the harder diffusion of Al and Si atoms, the smaller concentration of Al in a-Si:H film and of Si in aluminum film, so makes nucleation density of Si smaller, that leads to the large-grained silicon growth. Otherwise, the thinner alumina is, the higher nucleation density of Si is, which results in the small-grained silicon.5. The 1:1 layer ratio of aluminum and amorphous silicon film is optimal in the process of aluminum induced crystallization.6. Si film is easily crystallined on c-Si substrate in preference to glass substrate.