Early Stage in Polycrystalline Growth of Si by Fluoro-Oxidation of Silane
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EARLY STAGE IN POLYCRYSTALLINE FLUORO-OXIDATION OF SILANE
GROWTH OF Si BY
KENJI ENDO, MASAHIRO BUNYO, ISAMU SHIMIZU' AND JUN-ICHI HANNA Tokyo Institute of Technology, Imaging Science and Engineering Laboratory "Interdisciplinary Graduate School of Science and Engineering Nagatsuta, Midori-ku, Yokohama 227, JAPAN ABSTRACT We have studied the polycrystalline growth of Si prepared by a reactive gas flow of SiH 4 and F2 . In a very early stage of the film growth on the amorphous substrates, a thin layer of the amorphous phase was deposited even in the favorable condition for the crystal growth, whose thickness was determined by the growth condition and reached to 2003O0nm in a certain condition. The crystalline phase consisted of closely packed small grains perpendicular to the substrate, 200-500nm in diameter, each of which displayed a tooth-like shape with fine structures, indicating a formation of the crystal nuclei in the amorphous phase and their growth to the grains. The generation probability of the nuclei was not uniform in the amorphous phase, high at the region far from the substrate, and very sensitive to the growth temperature, judging from cross sectional TEM micrographs of the films. These suggest that the network propagation of Si in which fluorine, participates the chemical process in the vicinity of the growing surface enhances a formation of the long range ordering in the network, resulting in the generation of the crystal nuclei. INTRODUCTION Polycrystalline Si is the most promising material for a TFT array fabricated with the driver circuit, which is expected for the high quality and high performance LCD devices in the next generation. The key technology is a low cost production of the material and the major effort has been made on the laser annealing of the amorphous film which is one of the methods to realize the low temperature process for the crystallization. On the other hand, the low temperature CVD for ploy-Si is a counterpart for the practical application in terms of the overall throughput and has attracted a considerable attention. The low temperature growth of crystalline Si from silane has been reported at limited growth conditions in the plasma and photo-CVDs.')- 4 ) In some of the CVD processes in which the fluorinated raw materials such as SiF 4 and SiH 2F2 are used, however, several groups have reported that the low temperature crystal growth takes place very easily and does not degrade at the hiNher deposition rate.5 )- And we have reported recently that at the low temperature of 370 C poly-Si was deposited on the glass substrates and the high quality epitaxy on the Si (100) substrate at a high deposition rate of 12A/sec by a new type of the CVD termed "Spontaneous Chemical Deposition", in which a reactive gas flow t for the film growth was generated by mixing silane with fluorine at the reduced pressure. )9) In spite of these outstanding features of the crystal growth in the fluorine-related CVD process, the mechanism of the crystal growth has remained to be understood and investi
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