High-Quality Gate-Oxide Films for Low-Temperature Fabricated Poly-Si TFTs

ABSTRACTHigh-quality gate-oxide films for poly-Si TFTs (Thin Film Transistors) are successfully produced by oxygen-argon sputter deposition at a low temperature (200°C). Silicon-oxide films that are sputter-deposited in an oxygen-argon mixture has higher resistivity and breakdown field than films that are sputterdeposited only in argon and thermal oxides grown on poly-Si. Moreover, TFT field-effect mobilities are considerably improved by mixing oxygen into the sputtering gas, resulting in 350 cm2 /V.sec. Subthreshold slope and threshold voltage are also reduced to 5.5 V and 0.8 V/decade. A temperature-dependence measurement of the drain current shows that these improvements in TFT characteristics result from a lowering of the barrier height at the poly-Si grain boundaries, indicating a reduction in the trap density at these boundaries. Results confirm the usefulness of gate-oxide films that are sputter-deposited in an oxygen-argon mixture, for lowtemperature fabricated poly-Si TFTs.