A study on H 2 plasma treatment effect on a-IGZO thin film transistor
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Hyungtak Seoa) Department of Materials Science & Engineering, Ajou University, Woncheon-Dong, Yeongtong-Gu, Suwon 443-739, Korea
Hyeongtag Jeonb) Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Korea (Received 4 January 2012; accepted 1 June 2012)
We report the effect of H2 plasma treatment on amorphous indium–gallium–zinc–oxide (a-IGZO) thin-film transistor (TFT). 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 brings device stability by affecting oxygen vacancy and trap content in channel bulk and channel/dielectric interface.
I. INTRODUCTION
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2012.199
process compared to conventional silicon-based TFT.1,2 To improve the performance of practical a-IGZO applications, most of the studies focused on adjusting process variables such as gas partial pressure, chemical components of a-IGZO, contact resistance, and different plasma treatments. Some research group introduced the effect of hydrogen on the properties of oxide semiconductor.3,4 Additionally, Tsao et al.5 found that the hydrogen-induced passivation of interface trap states between a-IGZO and dielectric layer caused an improvement in subthreshold swing (SS). Even though there are many advantages, it is important to control the hydrogen dose because device stability is sensitive to the amount of hydrogen after plasma treatment. Also, it is important to analyze the role of hydrogen in a-IGZO film. Therefore, through this study, we show the change in characteristics of TFT, the role of hydrogen in a-IGZO, and the change of oxygen vacancy and trap charge density with the amount of hydrogen dose. We fabricated a-IGZO TFTs with different hydrogen plasma treatment time. Al2O3 passivation layer was deposited to protect the TFT from the ambient atmosphere. Temperature instability test was carried out to examine the electrical property change, and x-ray photoelectron spectroscopy (XPS)/ secondary ion mass spectroscopy (SIMS) was used to analyze the chemical changes. Based on the Arrhenius equation, the activation energy for devices was calculated, which would account for the change of the oxygen vacancy and trap charge density.
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Ó Materials Research Society 2012
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