The Effect of Doping Conditions on Amorphous IGZO Electrical Conductivity
Authors: Choi Seung jun , Choi SeYong , Moon Seung Jae , Bae Byung Seong 
Published: December 2024

In recent years, there has been a noticeable increase in interest in thin-film transistors (TFTs) employing oxide semiconductors in the display industry. Among various oxide semiconductors, amorphous indium gallium zinc oxide (a-IGZO) has emerged as a particularly promising material and being used for the backplane of the OLED (organic light emitting diode) TV. It offers several advantages over conventional materials such as amorphous silicon (a-Si) and organic semiconductors, including higher electron mobility, lower leakage current, and wide area process applicability.

For the top-gate self-aligned structure offers distinct advantages over the bottom-gate structure, reducing parasitic capacitance between source/drain and gate electrodes. For low contact resistance between the source/drain electrodes and a-IGZO, the doping process on the IGZO layer is necessary to enhance conductivity at the source and drain region. Various doping techniques are employed for a-IGZO, including ultraviolet (UV) irradiation [1], ion implantation, and plasma treatment [2]. Ion implantation is a widely used method in semiconductor manufacturing, where ions are injected into the semiconductor using high-energy ion beams. UV irradiation, on the other hand, utilizes ultraviolet light to shift the Fermi level below the conduction band, thereby making the semiconductor conductive. Plasma doping, the focus of this study, typically involves using equipment such as PECVD (Plasma Enhanced Chemical Vapor Deposition) or RIE (Reactive Ion Etching) to dope a-IGZO within a low-pressure chamber using plasma generated. Reactive gases are introduced, and plasma ions with high energy disrupt the metal-oxygen bonds within a-IGZO, enhancing conductivity and reducing sheet resistance.

In this study, plasma doping was employed and the changes in sheet resistance was investigated under different plasma conditions, particularly focusing on various reaction gases. Doping experiments were conducted for various gases, while the effects of plasma treatment were evaluated through the sheet resistance measurements and comprehensive composition analysis. The results of this study provide insights into the relationship between plasma doping through controlled reaction gases and changes in sheet resistance in a-IGZO.

Our experimental results reveal that plasma treatment leads to a decrease in the electrical conductivity of the IGZO layer. Moreover, we explore how varying plasma treatment time and power levels influence this conductivity reduction. Furthermore, we examine the effect of post-annealing on the electrical conductivity of plasma treated IGZO layers. Our findings demonstrate that post-annealing conditions play a crucial role in determining the final electrical conductivity of IGZO layers after plasma treatment.

[1] H. Seo, et al. "Permanent optical doping of amorphous metal oxide semiconductors by deep ultraviolet irradiation at room temperature," Appl. Phys. Lett.
96, 222101 (2010).

[2] W. -S. Liu, C. -H. Hsu, Y. Jiang, Y. -C. Lai, and H. _C. Kuo, “Improving device characteristics of dual-gate IGZO thin-film transistors with Ar-O2 mixed plasma treatment and rapid thermal annealing,” Membranes 12, 49 (2022).