Fluorinated Gate Oxide Films Utilized in Polysilicon Thin Film Transistors

Abstract

ABSTRACTSilicon dioxide films have been grown on polysilicon films at low temperatures in dry ambients by utilizing NF3 - enhanced oxidation, which affords markedly enhanced oxidation kinetics. This facilitates thin film transistor applications, for which low thermal budget processing is essential. The grown oxide films are thicker than corresponding oxides grown on (100) single crystal silicon. Thin film transistors having a polysilicon self-aligned gate structure were fabricated on polycrystalline silicon. The gate oxide films were thermally grown by NF3 -enhanced oxidation at 650°C or 800°C. Electrical characterization of the TFTs having 800°C gate oxides showed on/off current ratios up to 5×107, effective electron mobilities (μneff) of 26 to 38 cm2/Vsec, threshold voltage (VT) values of 0±0.7 V and subthreshold swing (S) values as low as 0.3 V/dec. The devices were stable under dc electrical stressing at a field of 3 MV/cm. Further, the source to drain current activation energy was determined as a function of the gate voltage. The 650°C gate oxide TFTs exhibited on/off current ratio of 105, VT of 3.5 V, Uneffof10 cm2/V.sec and S of 0.7 V/dec.