Comparison of N-2 and NH3 plasma passivation effects on polycrystalline silicon thin-film transistors

Abstract

The passivation effects of pure N-2 plasma on polycrystalline silicon (poly-Si) thin-film transistors (TFTs) have been studied and compared with those of NH3 plasma. We found that, similar to the recently-proposed NH3 plasma passivation, N-2 plasma passivation can also effectively improve device parameters such as field effect mobility, threshold voltage subthreshold swing, off current, and on/off current ratio. While the improvement of NH3-passivated devices can be attributed to both hydrogen and nitrogen passivation effects, nitrogen passivation alone is mainly responsible for the improvement of N-2-passivated devices. Zn addition, we round that N-2-passivated devices exhibit much better hot-carrier reliability than NH3-passivated devices. The better hot-carrier reliability of N-2-passivated devices can be explained by the formation of strong Si-N bonds which are difficult to break, while effectively eliminating the weaker N-H bonds, which are inevitable in NH3-passivated devices. The results of a Fourier. transform infrared (FTIR) spectrum analysis performed in this study are consistent with this proposition.