Organo-germanium adsorption on a silicon surface by excimer-light irradiation

Abstract

This is the first demonstration of photo-chemical adsorption of organo-germanium on a hydrogen terminated atomically flat silicon (111) surface using xenon (Xe) excimer light ( λ = 172 nm). The gas source of organo-germanium was either tetra-ethyl-germanium (TEGe) or tri-methyl-germanium-chloride (TMGC). The substrate was exposed to the gas and the light simultaneously at room temperature. In the case of TEGe exposure, germanium (Ge) adsorption occurred independently of the excimer light irradiation. From the results of angle-resolved X-ray photoelectron spectroscopy (XPS), the adsorbed layers contained Ge, carbon (C) and oxygen (O). The peak positions of these elements were independent of the detection angle. There were no significant differences between the XPS spectra of samples with adsorbed TEGe with or without excimer light irradiation. On the other hand, in the case of TMGC exposure, Ge adsorbed only when the substrate was directly irradiated with excimer light. The adsorbed layers contained Ge, C, O and Cl. The peak position of C, O and Cl were also independent of the detection angle. However, the peak position of Ge shifted to high binding energy side with decreasing detection angle. This result indicates that the chemical state of Ge changed from metallic near the interface to covalent near the surface. The metallic and covalent Ge were assigned to Ge bonded to the substrate and physically adsorbed TMGC, respectively. Comparing these results, it is revealed that the photo-selective adsorption of TMGC is caused by the formation of GeSi bonds with Xe excimer light irradiation.