A study of electrical damage to a-Si:H thin film transistor during plasma ashing by a pin-to-plate type atmospheric pressure plasma

In this study, the effect of the plasma ashing of the photoresist on a-Si:H thin film transistor (TFT) devices carried out using an atmospheric pressure plasma on the electrical damage to the TFT devices was investigated. By exposing the TFT devices to the plasma with a photoresist ashing rate of about 860 nm/min for up to 120s, their electrical characteristics were significantly degraded, possibly due to charge trapping in the SiN_x of the passivation layer and gate insulator and to bond breaking in a-Si:H. The degradation of the field effect mobility, I_off, and I _on/I_off ratio of the devices is believed to be mostly related to the bond breaking in the a-Si:H and charge trapping caused by the UV radiation, while the change in the threshold voltage appears to be mostly related to the surface charging caused by the charged species in the plasma. The damaged TFT devices, however, could be fully repaired by conventional annealing in a furnace at 290°C in N₂ for 60min.