Study Of High Quality Polycrystalline Si、SiGe Fabricated By Aluminum Induced Crystallization

Polycrystalline silicon(Poly-Si) thin film is considered as one of photovoltaic materials with highly efficience and low energy consuming since it has a relatively high photosensitivity and low cost. There are many approaches to fabricate poly-Si films, among which metal induced crystallization is a relatively advisable method. There are many advantages for it, such as lower the processing temperature and producing high quality poly-Si films with large grains. So it has attracted much attention, especially AIC since Al is shallow impurity for Si. In this thesis, we made the poly-Si and poly-SiGe material using AIC method, and the influence of factors in the process of AIC on the polycrystalline thin film structure and properties have been investigated through a series of characterization analyse methods. The main works are summarized as follows:(1) Al/Al2O3/a-Si structure was prepared on quartz. The effect of the thickness of Al layer on the AIC result was investigated. Three samples were designed and the thickness of Al layer was100nm、300nm and440nm, respectively. The thickness of Al layer and that of a-Si layer were almost same. When the thickness was increase, the size of poly-Si grain was increased and the quality of poly-Si induced by AIC became better. For the thick Al layer (440nm) sample, crystallization quality was pretty well(Raman peak519.03cm-1, FWHM5.92cm-1).(2) AIC process of thick Al layer (440nm) sample was investigated. Under the experimental conditions of this thesis, layers exchange of the Al layer and the Si layer did not happen completely. Polysilicon particles with quality close to single crystal silicon appeared in the original Al layer. The particle size was about8-20μm and more residual aluminum between the particles. Further to annealing, the particles did not become larger obviously, while the crystallization rate of the upper a-Si layer has been increased continually. It is suggested that amorphous silicon layer was almost no diffusion of silicon atoms but directly crystallizing so polycrystalline silicon in the Al layer had no significant increase of the particle size after a predetermined time annealing. We discussed the AIC mechanism which showed the growth of the layer thickness, annealing temperature and oxide thickness had an important impact on the results of AIC.(3) The effects of the a-Si layer and the Al layer thickness ratio on AIC formation was investigated. Under the same annealing condition, larger the a-Si layer and the Al layer thickness ratio was, more the continuity of the polysilicon film was formed. Silicon atoms diffused into the Al layer and formed polysilicon grains, then aluminum atoms were swapped out. The aluminum atoms swapped into the amorphous silicon layer induced crystallization of amorphous silicon near them, which resulted small crystal silicon particles, so it was difficult to diffuse into the original Al layer for these stabilized silicon atoms. Finally, if the thickness ratio of a-Si layer and the Al layer was small, the small crystallization ratio was formed. When the ratio of the Si-Al thickness increased, there was an adequate supply of silicon atoms, which could obtain a greater proportion of the final polysilicon.(4) When inserting12nm Ge layer among Al layer and a-Si layer and annealing at450℃or500℃, crystallization process was much faster than that of samples without Ge layer. It was due to the annealing temperature was higher than the eutectic temperature of Al-Ge and growth mode changed. The grown film was filled with large grains which were found to be SiGe alloy grains. When inserting a2nm Ge thin film and annealing at500℃for0.5h, the process of Al induced crystallization of a-Si was done. XRD analysis confirm that highly (111) oriented poly-Si was formed.(5) When Ge layer was at the same thickness12nm and Al layer was50nm, the larger thickness of the a-Si layer was, the more uniform composition of polycrystalline SiGe alloys were. Temperature is an important factor of the composition of polycrystalline SiGe after annealing. The process proceeded faster and the silicon composition of SiGe alloy formed by AIC became higher when the annealing temperature rose.