Hydrogen Impacts of PEALD InGaZnO TFTs Using SiOx Gate Insulators Deposited by PECVD and PEALD

Abstract

Amorphous indium gallium zinc oxide (IGZO) deposited by plasma-enhanced atomic layer deposition (PEALD) thin-film transistors (TFTs) was fabricated using SiO2 gate insulators synthesized via plasma-enhanced chemical vapor deposition (PECVD, device A) or PEALD (device B). The electrical performance of B devices was higher than that of device A. The mobilities of A and B devices were 19.39 and 21.11 cm2/Vs, and the subthreshold slopes were 0.25 and 0.22 V /decade, respectively. In addition, the device reliability of A devices shows an abnormal threshold voltage ( ${V}_{\text {th}}$ ) shift of –1.25 V under positive bias temperature stress (PBTS), caused by hydrogen diffusion from the gate insulator to the channel region near the source/drain electrode. However, B devices had a normal ${V}_{\text {th}}$ shift of +2.87 V. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FT-IR) results showed that PECVD SiO2 has a large amount of hydrogen bonding, such as Si-OH, compared to PEALD SiO2. Rutherford backscattering spectroscopy (RBS) and elastic recoil detection (ERD) measurement results confirmed that the hydrogen content of PECVD SiO2 was 2.24%, whereas that of PEALD SiO2 was lower at 1.45%.