Role of SiOxNy surface passivation layer on stability improvement and kink effect reduction of ELA poly silicon thin film transistors

Abstract

The role of SiOxNy thin layer growth on excimer laser annealed (ELA) polysilicon, by N2O plasma treatment, on the stability improvement under prolonged operation and bias stress of TFT was investigated. After NH3 plasma treatment, field effect mobility in p-channel TFT devices increased from 50 to 76cm2V−1s−1, ON/OFF current ratio improved to 4.6×107, threshold voltage shrank from −9.8V to −7.7V and kink effect in the ID-VD characteristics was diminished. Using NH3 plasma treatment combined with SiOxNy layer indicated a lesser effectiveness in decreasing interface states, but better in reducing of the influence of mobile charges on TFT performance, than the previous approaches. An improvement in field effect mobility of 60.5cm2V−1s−1, excellent stability under bias stress of ±1MV·cm−1 for 2h with ΔVth~0.1V were achieved. We found that under NH3 plasma treatment combined with SiNxOy thin layer; the effect of hot carrier injection were reduced significantly due to creating the SiN, and SiO bonding at the interface of gate insulator and active layer. This result indicated that thin film transistor using NH3 plasma treatment with SiOxNy passivated layer promises to improve TFT performances with high field effect mobility, high ON/OFF current ratio, low leakage current and excellent stability.