Poly-SiGe TFTs fabricated by low temperature chemical vapor deposition at 450°C

Low temperature growth of poly-SiGe has been investigated by reactive thermal chemical vapor deposition technique, which is a newly developed technique for preparing polycrystalline materials with using redox reactions in a set of source materials, Si2H6 and GeF4. In order to prepare high uniformity and reproducibility of Si-rich poly-SiGe, total pressure, gas flow ratio, and residence time are optimized at 450degreesC of substrate temperature. Through optimizing the conditions, poly-Si1-xGex (x < 0.04) films have been prepared in the reproducibility more than 90% and uniformity more than 88%. Bottom gate type of n-channel thin film transistors has been fabricated in various grain size of poly-Si1-xGex on SiO2 (100nm)/Si substrates. 5-36 cm(2)/Vs of field effect mobility of thin film transistors (L/W = 50mum/50mum) have been achieved after hydrogenation, whose threshold voltage is around 2 +/- 0.5V, and on/off ratio is more than 10(4).