Role of Seed Crystal Layer in Two-Step-Growth Procedure for Low Temperature Growth of Polycrystalline Silicon Thin Film from SiF4 by a Remote-Type Microwave Plasma Enhanced Chemical Vapor Deposition

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Abstract
Role of seed crystal layer which played in low temperature growth of polycrystalline silicon (poly-Si) thin films was investigated by two-step-growth (TSG) process. The TSG involves two different deposition processes, which are called as `seed process' and `growth process'. In order to satisfy the conflicting demands such as low temperature, high rate and high quality crystal growth, the deposition conditions in the seed and growth processes were examined. As a result, it is confirmed that the seeding of high quality crystal layer is effective to improve crystallinity of growing poly-Si film, especially for the case grown at lower temperature than 300°C. In order to fully promote crystallinity, some thick and high crystallinity seed layer is needed. In addition, epitaxial-like growth on the seed layers can be realized by optimizing deposition conditions both during the seed and growth processes. When H2/SiF4 flow ratios larger than those used during the seed process were used during the growth process, lower growth temperatures were possible with maintaining a smooth interface between the seed and the grown poly-Si layers. In essence, the hydrogen mixing ratio and deposition temperature are complementary parameters, thus it was possible to reduce deposition temperatures with maintaining large crystal fraction and oriented structure, if the hydrogen mixing ratio was increased to an appropriate amount. Furthermore, in situ ellipsometry analysis indicated that, under optimal conditions, the interface between the seed and the growing film can indeed be smooth and epitaxial-like. TSG is a promising technique by which to fabricate high quality poly-Si thin films on glass substrates at low temperatures.