Effect of Crystal Orientation of InGaAs on the Surface Reactions in Acidic Solutions

Abstract

Indium gallium arsenide (InGaAs) is one of the candidate materials to replace silicon as a channel of NMOS for its excellent electrical properties [1, 2]. In particular, because InGaAs has a high electron mobility as high as 11000 cm2/V·s, it is suitable as a channel material for high-speed devices [3]. However, InGaAs is easily oxidized in aqueous solution and its oxides can also be dissolved in H2O. In addition, since the InGaAs surface has a ternary crystal structure, the reactivity of each crystal plane may be different. Therefore, in order to introduce InGaAs into the channel material of the future transistor, it is necessary to understand the effect of the various crystal orientations of the InGaAs surface and their constituent elements on the InGaAs surface reactions. In order to investigate the effect of crystal orientation on the surface reaction of InGaAs, InGaAs (100) surface patterned with square shapes. InGaAs samples were dipped in the solutions of HCl/H2O2, H3PO4/H2O2 and HNO3/H2O2 mixtures. The etched amount and etching profile of InGaAs were measured by scanning electron microscope (SEM). The top etching profiles of InGaAs structure after treatments in HCl/H2O2, H3PO4/H2O2 and HNO3/H2O2 mixtures were shown in Fig. 1. It was first found that the etched amounts of the InGaAs structure were the largest after the treatment of HNO3/H2O2 mixture and the smallest after the treatment of HCl/H2O2 mixture. It is considered that the overall etching rate of InGaAs is increased because the surface oxidation reaction of InGaAs is accelerated by HNO3 having strong oxidizing power. On the other hand, the etched amounts of InGaAs along the [100], [010], and [110] directions were similar each other, but that along the [-110] direction was relatively small. In addition, it was observed that the slope of inclined plane formed after the InGaAs surface etching along the [-110] direction was more gentle than that of the other crystal directions. It is believed that the InGaAs surface is etched in the [-110] direction, revealing the {-1-12}A or {-111}A surface with low surface reactivity [4, 5]. In order to better understand the effect of the various crystal orientations of the InGaAs surface, the cross-sectional etching profiles of photoresist-masked InGaAs after treatment of HCl/H2O2, H3PO4/H2O2 and HNO3/H2O2 mixtures were observed as shown in Fig. 2. It was observed that {-1-12} plane was formed after treatment of HCl/H2O2 mixture and {-111} plane was formed after treatment of H3PO4/H2O2 or HNO3/H2O2 mixture. The results show that the surface reaction of InGaAs is strongly influenced by crystal orientation.