Chemically selective formation of Si–O–Al on SiGe(110) and (001) for ALD nucleation using H2O2(g)

Abstract

Passivation and functionalization via atomic hydrogen, hydrogen peroxide (H2O2(g)), and trimethylaluminum (TMA) on clean silicon–germanium (Si0.5Ge0.5(110) and Si0.47Ge0.53(001)) surfaces were studied and compared at the atomic level using ultra-high vacuum (UHV) scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and X-ray photoelectron spectroscopy (XPS) to understand the topological, electronic, and chemical structures of the surfaces. STM and XPS indicate that a sputter-cleaned SiGe(110) surface is terminated with adatoms, while a SiGe(001) surface is terminated with germanium dimers. STS demonstrates that the Fermi level on a clean SiGe(110) surface is pinned near mid-gap due to surface dangling bonds, while the Fermi level on a clean SiGe(001) surface is consistent with unpinning. A saturation dose of H2O2(g) at 25°C chemisorbs to SiGe surfaces, leaving the Fermi level at the surface consistent with unpinning, and the surface is functionalized mainly with Si–OH, Ge–OH, and Si–O–Ge bonds on both SiGe(110) and (001). After a subsequent TMA dose at 25°C, XPS and STM verify that a thermally stable and well-ordered monolayer of Al2O3 is formed on SiGe(110) and (001) surfaces, resulting in the formation of Al–O–Si bonds. The H2O2(g) functionalization provides three times more oxygen sites on the surface and three times as great a TMA nucleation density than does H2O(g) at both 25°C and 120°C. STS demonstrates that H2O2(g)- and TMA-dosed SiGe surfaces show a Fermi level consistent with unpinning and a local density of states (DOS) without any states between the conduction and valence band edge, indicating an ideal template for further atomic layer deposition (ALD) nucleation of high-k materials on SiGe(110) and (001) surfaces.