Comparison of N 2 and NH 3 Plasma Passivation Effects on Polycrystalline Silicon Thin-Film Transistors

• Published in: Japanese Journal of Applied Physics 1998-07, Vol.37 (7R), p.3900
• Main Authors: Lee, Yeong-Shyang, Lin, Hsiao-Yi, Lei, Tan-Fu, Huang, Tiao-Yuan, Chang, T.-C., Chang, Chun-Yen
• Format: Article
• Language: English
• ISSN: 0021-4922; 1347-4065
• DOI: 10.1143/JJAP.37.3900

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 NH 3 plasma. We found that, similar to the recently-proposed NH 3 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 NH 3 -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. In addition, we found that N 2 -passivated devices exhibit much better hot-carrier reliability than NH 3 -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 NH 3 -passivated devices. The results of a Fourier transform infrared (FTIR) spectrum analysis performed in this study are consistent with this proposition.