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 form ation 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 bet ween polycrystalline and amorphous film deposition decreases with incr easing 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 tem perature. These properties of Si1-xGex make it a promising material fo r thin film transistor applications in three-dimensionally integrated circuits and large-area electronics technologies, which have limited t hermal process budget requirements.