Distinction between interfacial layer effect and trap passivation effect of N2 plasma treatment on LTPS-TFTs

•N2 plasma surface treatment on LTPS-TFTs with HfO2 gate oxide is demonstrated.•Interfacial layer growth effect and trap passivation effect are observed.•The individual impacts of these two effects are investigated.•Interfacial layer growth and trap passivation are the same important.

In this paper, N2 plasma surface treatment on high performance low-temperature poly-Si thin-film transistors (LTPS-TFTs) with HfO2 gate dielectric is demonstrated. A significant performance improvement by N2 plasma surface treatment is observed, including the threshold voltage VTH reduction ∼ −0.94 V, subthreshold swing S.S. improvement from 0.227 V/dec. to 0.188 V/dec., field effect mobility μFE enhancement ∼ +61% and driving current Idrv enhancement ∼ +95%. The individual impacts of interfacial layer growth effect and trap passivation effect of poly-Si channel film are investigated by the plasma induced interfacial layer (PIL) removal process. The results show that the PIL growth effect has more contribution to the improvement of VTH reduction and Idrv enhancement than the trap passivation effect of poly-Si channel film. Consequently, the interfacial layer engineering would be very important for the development of high performance LTPS-TFTs.