High-performance thin-film transistors in large grain size polysilicon deposited by thermal decomposition of disilane

The characteristics of polycrystalline silicon thin-film transistors (TFTs), fabricated on films deposited in an LPCVD system using disilane, were investigated as a function of grain size. The grain size and its statistical distribution were correlated with processing conditions; optimum conditions to maximize grain size for device applications were determined. The dependence of the ON current and the OFF (leakage) current of polysilicon TFTs, as well as of their statistical distributions, on the grain size, the gate dielectric processing temperature, the channel length, and the device structure are reported and discussed. Larger grain size polycrystalline silicon films were found to yield devices with higher mobilities and lower leakage currents. TFTs, fabricated in polysilicon films with average grain sizes of 1.8 μm with thermally grown silicon dioxide as gate dielectric, had ON/OFF current ratio well above 10⁸, average effective mobility value of 170 cm²/V.s and subthreshold slope of 0.3 V/dec