The effects of nitrogen additives on the plasma hydrogenation of polycrystalline silicon thin film transistors (poly-Si TFTs) have been investigated with various radio-frequency (RF) power densities, substrate heating temperature, gas flow rates, as well as chamber pressures. The nitrogen-containing hydrogen ( H 2 N 2 ) plasma treatments show better passivation effects on the electrical characteristics of the poly-Si TFTs than the pure H 2 hydrogenation. It is attributed to the passivation effect of the nitrogen radicals themselves and the promotion of the hydrogen plasma generation due to the radical collision. The passivation effects have been enhanced by properly chosen RF power density, gas flow rate and chamber pressure. Furthermore, the H 2 N 2 plasma were also utilized to passivate the poly-Si TFTs with different grain structures.