Wet Chemical Etching of Zn-containing oxides and HfO2 for the fabrication of Transparent TFTs
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Wet Chemical Etching of Zn-containing oxides and HfO2 for the fabrication of Transparent TFTs Jae-Kwan Kim, Jun Young Kim, Seung-Cheol Han, Joon Seop Kwak, and Ji-Myon Lee* Department of Materials Science and Metallurgical Engineering, Sunchon National University, 315 Maegok, Sunchon, Chonnam 540-742, Korea ABSTRACT The etch rate and surface morphology of Zn-containing oxide and HfO2 films after wet chemical etching were investigated. ZnO could be easily etched using each acid tested in this study, specifically sulfuric, formic, oxalic, and HF acids. The etch rate of IGZO was strongly dependent on the etchant used, and the highest measured etch rate (500 nm/min) was achieved using buffered oxide etchant at room temperature. The etch rate of IGZO was drastically increased when sulfuric acid at concentration greater than 1.5 molar was used. Furthermore, etching of HfO2 films by BF acid proceeded through lateral widening and merging of the initial irregular pits. INTRODUCTION Oxide-based thin film transistors attract much attention due to their advantageous properties such as high mobility, high electrical conductivity, and high visible transmittance [1]. Zn-containing oxide thin film transistors (TFTs) are a promising large-area backplane electronic device for flat panel displays such as liquid crystal displays and organic light-emitting displays [2,3]. Zn-containing oxide and hafnium oxide (HfOx) have been investigated for use in the fabrication of transparent thin film transistors (TTFTs). A number of studies have investigated Zn-containing oxide TFTs that used ZnO [4], In-Zn-O (IZO) [5], or In-Ga-Zn-O (IGZO) [6] as the active channel material. In addition, considerable effort has been made to reduce power consumption, such that flexible and mobile applications of oxide-based TFTs with a high-k gate dielectric can be realized. High-dielectric-constant (high-k) materials have received significant attention as gate dielectrics because they enable greater physical gate oxide thicknesses (EOT) that are equivalent to those of the conventional gate dielectrics SiO2 and SiOxNy, which results in significant reductions in gate leakage [7]. Among the potential candidates to replace SiO2 and SiOxNy as gate dielectrics, hafnium oxide is one of the most promising materials. Hafnium oxide has a high dielectric permittivity with low leakage current due to a reasonably high barrier height [8]. Etching is key step. It is very important to develop well-defined etching processes for various transparent oxides that are used in such devices [1], because the thickness of the channel layer is less than a few tens of nanometers. Moreover, because Zn-containing oxides and HfO2 might be used as the channel and gate dielectric material, respectively, it is very important to develop well-defined wet-etching processes for various transparent oxides [9] that result in low etch damage and reliable pattern transfer. In the present study, various acidic solutions were used to investigate the etch-rate and etched surface morphology of b
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