Effects of vacuum rapid thermal annealing on the electrical characteristics of amorphous indium gallium zinc oxide thin films

Hyun-Woo Lee,Won-Ju Cho

doi:10.1063/1.5009895

Abstract

We investigated the effects of vacuum rapid thermal annealing (RTA) on the electrical characteristics of amorphous indium gallium zinc oxide (a-IGZO) thin films. The a-IGZO films deposited by radiofrequency sputtering were subjected to vacuum annealing under various temperature and pressure conditions with the RTA system. The carrier concentration was evaluated by Hall measurement; the electron concentration of the a-IGZO film increased and the resistivity decreased as the RTA temperature increased under vacuum conditions. In a-IGZO thin-film transistors (TFTs) with a bottom-gate top-contact structure, the threshold voltage decreased and the leakage current increased as the vacuum RTA temperature increased. As the annealing pressure decreased, the threshold voltage decreased, and the leakage current increased. X-ray photoelectron spectroscopy indicated changes in the lattice oxygen and oxygen vacancies of the a-IGZO films after vacuum RTA. At higher annealing temperatures, the lattice oxygen decreased and oxygen vacancies increased, which suggests that oxygen was diffused out in a reduced pressure atmosphere. The formation of oxygen vacancies increased the electron concentration, which consequently increased the conductivity of the a-IGZO films and reduced the threshold voltage of the TFTs. The results showed that the oxygen vacancies and electron concentrations of the a-IGZO thin films changed with the vacuum RTA conditions and that high-temperature RTA treatment at low pressure converted the IGZO thin film to a conductor.

Highlights

Amorphous oxide semiconductors (AOSs) have recently been intensively studied in various fields owing to their many advantages, such as a high transmittance, low cost, and large-area fabrication at low temperature
Because Amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs) have higher mobility than conventional hydrogenated amorphous silicon (a-Si:H) TFTs or organic TFTs and are advantageous for large-area processing at low temperatures (
In order for a-IGZO TFTs to be used as driving elements of a flat-panel display, defects in the a-IGZO channel layer or at the interface of the channel layer/gate insulator need to be removed through a post-deposition annealing (PDA) process.[7]

Summary

Introduction

Amorphous oxide semiconductors (AOSs) have recently been intensively studied in various fields owing to their many advantages, such as a high transmittance, low cost, and large-area fabrication at low temperature. Hyun-Woo Lee and Won-Ju Choa Department of Electronic Materials Engineering, Kwangwoon University, 447-1, Wolgye-dong, Nowon-gu, Seoul 139-701, Korea (Received 20 October 2017; accepted 29 December 2017; published online 9 January 2018)

Results

Conclusion