Paper EM-MoA9
Passivation, Functionalization, and Atomic Layer Deposition Nucleation of SiGe(100) via H₂O and H₂O₂

Monday, October 28, 2013, 4:40 pm, Room 101 B

Silicon-germanium is a promising candidate for potential channel or contact materials due to its higher hole and electron mobility. To minimize the oxide-semiconductor interfacial defect density, a chemical and electronic passivation layer must be formed before the oxide layer is deposited. In this study, a monolayer of H₂O or H₂O₂ chemisorbates is shown to activate Trimethylaluminum (TMA) chemisorption due to the Si/Ge-OH bonds catalyzing the formation of an ultrathin passivation layer which can serve as an ideal ALD nucleation template on SiGe. However, since H₂O chemisorption results in equal density of Si/Ge-H and Si/Ge-OH sites on the SiGe(100), H₂O can only provide a maximum of 0.5 monolayer of Si/Ge–OH sites, limiting the TMA nucleation density. By using H₂O₂ dosing, the density of Ge–OH sites can be doubled thereby increasing the potential TMA nucleation density. This study compares the passivation of the SiGe(100) surface via H₂O and H₂O₂, for the application of nucleating ALD growth on the surface, using scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and x-ray photoelectron spectroscopy (XPS).

Using a differentially pumped dosing system, a clean SiGe(100) sample was dosed at room temperature with a saturation dose of either H₂O or H₂O₂. STM and XPS measurements indicate that H₂O₂ dosing leaves the SiGe(100) surface, which is mostly Ge atoms due to surface segregation, terminated with an ordered monolayer Ge-OH sites. A very small density of unreacted atoms are left unpassivated on the surface and have half filled dangling bond states causing a large local amount of conduction band edge states in the bandgap. STS measurements of the Ge-OH sites show the conduction band edge dangling bond states are eliminated due to the passivating Ge–OH bonds, but the Fermi level is pinned near the valence band edge due to the large surface dipole . When the surface is annealed to 310°C, XPS measurements indicate that the –OH species on the surface break bonds with the Ge atom and bond instead to the Si atoms, raising Si atoms towards the surface. XPS also verifies that no oxygen leaves the surface due the 310°C anneal. Instead, the oxygen remains on the surface in the form on Si-OH or SiO_x species. It is hypothesized that a lower temperature anneal would prevent SiO_x species from forming, leaving a surface which is only terminated by Si-OH bonds which would serve as an ideal template for ALD nucleation of TMA for Al₂O₃ growth. STS measurements show that TMA nucleation on the H₂O₂ functionalized SiGe(100) surface unpins the Fermi level and has a wide bandgap with no band edge states demonstrating very good interface quality.