인듐-갈륨-아연 산화막 박막 트랜지스터 특성에 미치는 열처리 분위기 효과에 대한 연구

Abstract

There are substantial interests in the use of transparent oxide semiconductor as an active layer of thin film transistor. Among these semiconductors materials, amorphous Indium-Gallium-Zinc-Oxide (IGZO) has been emerged as a promising solution for high performance backplane and investigated its realistic possibility. Especially, in the research for improvement in the IGZO-TFTs performance, the contact resistance between the IGZO channel and the source/drain (S/D) is an important issue. Most studies on reducing this contact resistance focused on process variables such as the S/D electrode materials, channel length, gate to S/D overlap, and plasma treatment. Among these processes, the post annealing process has been widely used due to simple process and low cost. However, the post annealing process can not only reduce the contact resistance but also induce the change in chemical composition of the IGZO film and interface properties between IGZO and gate dielectric. Therefore, it was required to get the effect of the post annealing process on the entire device performance and each part such as contact resistance between active layer and electrode, IGZO bulk characteristics, and interface between active layer and dielectric. In this study, we fabricated the metal-semiconductor-metal (MSM) structures and IGZO-TFTs annealed 250℃ for 1 hour in various gases ambient such as air, O2, N2, and vacuum. As a result, the contact resistance between the IGZO film and metal electrode were improved by annealing process. It was observed that the chemical characteristics of IGZO film was dependent with the post anneal process by using X-ray Photoelectron Spectroscopy (XPS). Impact of interface between active layer and dielectric was obtained from the capacitance hysteresis. The device properties were also related to the post annealing process in various ambient. TFTs annealed in O2 and air exhibited high performance such as a saturation mobility (>7cm2/Vs), subthreshold swing (<0.33V/decade), threshold voltage (<5V) and Ion/off (>107) compared to TFTs annealed in vacuum, N2, and N2-H2 (5%). Consequently, by verifying the annealing effect of each section in IGZO TFT, we found the post annealing process was critical to control device performance.