A STUDY ON H2 PLASMA TREATMENT EFFECT ON a-IGZO THIN FILM TRANSISTOR

Abstract

In recent years, a new class of high-performance thin-film transistors (TFTs) has emerged comprising amorphous oxide channel materials composed of heavy-metal cations (HMCs) with (n - 1)d10ns0 (n ≥ 4, where ‘n’ refers to the row of the periodic table) electronic configuration. This thesis is devoted to the characterization of TFTs employing amorphous oxide channel: indium zinc gallium oxide (IGZO). There are substantial interests in the use of transparent oxide semiconductor as an active layer of thin film transistor. Among these semiconductor materials, amorphous Indium-Gallium-Zinc-Oxide (IGZO) has been emerged as a promising solution for high performance backplane and investigated its realistic possibility. In spite of their many merits, the electrical reliability of oxide semiconductor based TFT devices remains a very important and critical issue. Most studies on improving stability focus on adjusting process variables such as gas partial pressure, chemical components of a-IGZO, and different plasma treatments. Among them, plasma treatment can be a good method due to simple process and reliable effect. In this study, the effect of H2 plasma treatment on amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) thin film transistor (TFT) is reported. The changes in electrical characteristics and stability of the a-IGZO TFT treated by H2 plasma were evaluated under thermal stress. Each device exhibited a change in the subthreshold swing, turn on voltage shift, and hysteresis depending on the amount of hydrogen atom. It was found that there occurred a decrease of oxygen deficiency and an increase of hydrogen content in channel layer and channel/dielectric interface with increasing treatment time. The proper hydrogen dose well-passivated the oxygen vacancies, however, more hydrogen dose acted as excessive donors. The change of oxygen vacancy and total trap charge were explained by the activation energy from Arrhenius plot. Through this study, we found that the optimized H2 plasma treatment, bring device stability by affecting oxygen vacancy and trap content in channel bulk and channel/dielectric interface.