Deposition of high crystallinity poly-Si films on glass substrate and fabrication of high mobility bottom-gate TFT

High crystallinity polycrystalline silicon (poly-Si) thin films have been fabricated directly on a glass substrate at 450 °C by reactive thermal chemical vapor deposition (RTCVD) with Si2H6 and F2. The film crystallinity was improved by setting either the residence time shorter or a gas flow ratio of F2/Si2H6 around 1/15–1/20, where the gas phase reaction was suppressed and the contribution of F2 to the surface reaction was enhanced. For fabricating high mobility bottom-gate TFTs (thin film transistors), the effect of thermal annealing on the TFT characteristics was investigated. With a poly-Si film with a high crystalline volume fraction over 90%, the n-channel bottom-gate TFT was fabricated on the thermally oxidized Si wafer. The thermally annealed TFTs in hydrogen ambient at 400 °C for 150 min exhibited a high field effect mobility of 54.5 cm2/Vs and a high on/off current ratio of 105.