DEPOSITION AND PROPERTIES OF LOW-PRESSURE CHEMICAL-VAPOR-DEPOSITED POLYCRYSTALLINE SILICON-GERMANIUM FILMS

The deposition of undoped polycrystalline silicon-germanium (poly-Si1-xGex) alloy films onto SiO2 by the pyrolysis of SiH4 and GeH4 in a low-pressure chemical vapor deposition system is described. The deposited films are compatible with standard wet-cleaning baths, and their formation and patterning are very controllable processes; therefore, their application should not introduce significant process complexity into silicon-based technologies. Depending upon their Ge content, Si1-xGex films can be deposited in polycrystalline form at temperatures as low as approximately 400-degrees-C, because the transition temperature between polycrystalline and amorphous film deposition decreases with increasing Ge content. Poly-Si1-xGex grains are columnar in structure and have a relatively low density of microtwins, and their average size is larger than that of grains in poly-Si films deposited at the same temperature. These properties of Si1-xGex make it a promising material for thin film transistor applications in three-dimensionally integrated circuits and large-area electronics technologies, which have limited thermal process budget requirements.