Oxide Removal and Selective Etching of In from InSb(100) with TiCl4

Abstract

The reaction of TiCl4 with a native oxide-covered InSb(100) film grown epitaxially on GaAs(100) was investigated using X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. At room temperature and low pressure (∼3 × 10–7 Torr), TiCl4 reacted with In and Sb oxides, producing a stable indium chloride overlayer and removing a small amount of Sb, likely as SbCl3, after a subsequent vacuum annealing step at 500 K. About 25% of the O was removed, likely as TiOCl2, and a submonolayer of TiO2 was deposited, which competed with oxide etching. When TiCl4 was dosed with the substrate temperature maintained at 470–560 K, the etching reaction prevailed, resulting in complete removal of the native oxide without depositing TiO2. Heating alone could not account for the results because the oxide desorption onset was 550 K and some oxide was present even after annealing in vacuum to 650 K. TiCl4 exposure at elevated temperatures not only removed the native oxide but also preferentially etched substrate In atoms by forming volatile indium chlorides. Residual indium chlorides remained on the surface in the 470–530 K range but were completely removed at 500–560 K. The depletion of In from the surface promoted the out-diffusion of In from the substrate, allowing bulk etching and accumulation of at least a 72 Å thick Sb layer. Accumulation of Sb on the surface is consistent with a higher kinetic barrier for chlorination of Sb compared to In. The atomic ratio of Ti to Sb in elemental states was 0.43–0.46, suggesting TiSb2 alloy formation. Surface height modulations on the order of 100 nm and the presence of pits and grain boundaries were observed.