X-ray photoelectron spectroscopy analysis of the effect of photoresist passivation on InGaZnO thin-film transistors

Abstract

Bottom-gate InGaZnO (IGZO) thin-film transistors (TFTs) with EOC photoresist (PR) passivation were fabricated. Compared to the unpassivated IGZO TFT with a mobility of 6.71 cm2 V−1 s−1, a hysteresis of 2.42 V and a poor bias stress stability, the PR-passivated IGZO TFT showed good electrical characteristics with a higher mobility of 8.85 cm2 V−1 s−1, a lower hysteresis of 0.06 V and a more reliable stability (△Vth = 0.36 V) under positive gate bias stress (PBS). The effect of PR passivation on the performance of IGZO-TFT was investigated by x-ray photoelectron spectroscopy (XPS), systemically. The result of XPS spectra of the O 1s core levels indicate that PR passivation effectively suppressed the adsorption/desorption effect on IGZO surface, resulting in fewer unstable states and higher electrical stability. Furthermore, XPS depth profile experiments show that the proportion of elements on the film surface changed and the IGZO surface was In-rich after PR passivation, enhancing the mobility. The PR passivation with low temperature (100 °C) process exhibited good dielectric quality and excellent barrier ability against water and oxygen molecules. Therefore, it may be a good candidate for high-mobility and high-stability flexible TFTs in future.