Effect of Deposition Temperature and Source Gas Chemistry in PE-CVD SiO2 Passivation on InGaZnO TFTs

Bottom-gate InGaZnOx thin-film transistor (IGZO TFT) with plasma-enhanced chemical vapor deposited (PE-CVD) SiO2 passivation layer were fabricated and their characteristics were analyzed. Two different gas chemistries, SiH4/N2O/N2 and TEOS/02 were explored for the deposition of SiO2 with varying the deposition temperature from 180 to 380°C. Passivation ability of TEOS/O2 based SiO2 is slightly better than that of SiH4/N2O/N2 based SiO2 one when the films were deposited at 180°C, despite an almost identical electrical properties. However, the significant differences were observed when the deposition temperature increased to 300°C or higher. Although the TFTs with the SiO2 passivation deposited using TEOS/02 gas chemistry maintained TFT characteristics, the TFTs with the passivation layer deposited by SiH4/N2O/N2 gas chemistry exhibit conductive behavior.