Silicon-germanium polycrystalline films for TFT applications

The formation of polycrystalline-Si/sub 1-x/Ge/sub x/ thin films on oxide-coated Si substrates is discussed. Two modes of deposition, thermal growth and plasma-enhanced deposition, were studied using PE-VLPCVD (Plasma-Enhanced Very-Low-Pressure CVD) at /spl les/600/spl deg/C. In both cases, growth rates and grain sizes increase with Ge content, and the polyerystalline-to-amorphous transition temperature is lower for Si/sub1-x/Ge/sub x/ than Si. Compared to thermal growth, plasma-enhanced deposition promotes higher growth rates and improved structural properties such as smoother surface morphology, more columnar [220] oriented grain texture, and direct deposition onto oxide. Post-deposition techniques were explored to enlarge the decreased grain sizes associated with plasma deposition of poly-Si/sub 1-x/Ge/sub x/ compared to thermal growth, without sacrificing other improved properties. Compared to plasma-deposited poly-Si/sub 1-x/Ge/sub x/films, plasma deposition of amorphous-Si/sub1-x/Ge/sub x/ followed by a crystallization anneal at 600/spl deg/C results in films with an even smoother surface and grain sizes enhanced by an order of magnitude. The largest grain sizes, /spl tilde/1.3/spl mu/m, were achieved in poly Si/sub 1-x/Ge/sub x/ films formed by Si+ ion implantation for amorphization with a subsequent recrystallization anneal.