Low temperature (<=550 degrees C) fabrication of CMOS TFT's on rapid-thermal CVD polycrystalline silicon-germanium films

Abstract

N-channel and p-channel metal-oxide-semiconductor (MOS) thin-film transistors (TFT's) have been fabricated on rapid thermal chemical vapor deposition (RTCVD) polycrystalline silicon-germanium (poly-Si0.88Ge0.12) films by a low temperature (less than or equal to 550 degrees C) process. These devices employ in-situ n(+) doped poly-Si0.65Ge0.35 films as gate electrodes to reduce the process time and temperature, dual-offset spacers to reduce the electric field in the drain junction region, and silicon capping layers to protect the poly-Si1-xGex films against oxygen. The I-d-V-g characteristics in n-channel TFT's, as well as in p-channel TFT's, exhibit good behavior after remote-PECVD hydrogenation. Further improvements on electrical properties in n-channel TFT's are limited by trap-inducing Ge behaviors in poly-Si1-xGex films.