Plasma passivation effects on polycrystalline silicon thin-film transistors utilizing nitrous oxide plasma

A novel defect passivation process in polycrystalline silicon (poly-Si) thin-film transistors (TFTs) utilizing nitrous oxide (N₂O) plasma has been performed to significantly improve the electrical characteristics of poly-Si TFTs. For example, the on/off current ratio increased to 6.58 × 10⁶; the threshold voltage decreased to 0.55 V, and the field effect mobility increased to 48.2 cm²/Vs. The distribution of N incorporated in this oxide and these poly-Si films was examined by means of secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES). It is believed that the nitrogen radicals which dissociated from the N₂O gas as well as the hydrogen radicals which dissociated from the residual H₂O can both diffuse into the active poly-Si layer to passivate the grain-boundary defect states and accumulate at the gate SiO₂/poly-Si interface to reduce the interface state density. Thus, the hot-carrier reliability of TFTs was also enhanced after the N₂O plasma treatments.