Influence of Deposition Temperature and Source Gas in PE-CVD for SiO 2 Passivation on Performance and Reliability of In–Ga–Zn–O Thin-Film Transistors

In this paper, we investigated the influence of both source gas and deposition temperature in plasma-enhanced chemical vapor deposition (PE-CVD) for a SiO 2 passivation layer on the electrical properties and reliability of a bottom-gate In–Ga–Zn–O thin-film transistor (IGZO TFT). Two gas chemistries consisting of SiH 4 –N 2 O–N 2 and tetraethoxysilane (TEOS)–O 2 were utilized as the source gases for the PE-CVD SiO 2 deposition, and the deposition temperature ( ${T}_{D}$ ) was adjusted from 180 °C to 380 °C. The TFT properties were basically identical for both gas chemistries at ${T}_{D}$ of 180 °C. When ${T}_{D}$ increased to 300 °C or higher, the TFTs with the SiO 2 passivation deposited by SiH 4 –N 2 O–N 2 gas chemistry (SiH 4 -SiO 2 ) drastically changed from the transistor to the conductor. In contrast, the TFT with TEOS-SiO 2 passivation maintained its TFT characteristics even at ${T}_{D}$ of 380 °C, despite the degradation of subthreshold characteristics and a negative shift of turn-on voltage were observed due to an electron injection barrier lowering as ${T}_{D}$ increased to 310 °C or higher. We also revealed that a stacked SiO 2 passivation that is deposited at a different ${T}_{D}$ is an effective technique to improve the performance and reliability of the IGZO TFT.