Atomic imaging and modeling of H2O2(g) surface passivation, functionalization, and atomic layer deposition nucleation on the Ge(100) surface

Abstract

Passivation, functionalization, and atomic layer deposition nucleation via H2O2(g) and trimethylaluminum (TMA) dosing was studied on the clean Ge(100) surface at the atomic level using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Chemical analysis of the surface was performed using x-ray photoelectron spectroscopy, while the bonding of the precursors to the substrate was modeled with density functional theory (DFT). At room temperature, a saturation dose of H2O2(g) produces a monolayer of a mixture of -OH or -O species bonded to the surface. STS confirms that H2O2(g) dosing eliminates half-filled dangling bonds on the clean Ge(100) surface. Saturation of the H2O2(g) dosed Ge(100) surface with TMA followed by a 200 °C anneal produces an ordered monolayer of thermally stable Ge-O-Al bonds. DFT models and STM simulations provide a consistent model of the bonding configuration of the H2O2(g) and TMA dosed surfaces. STS verifies the TMA/H2O2/Ge surface has an unpinned Fermi level with no states in the bandgap demonstrating the ability of a Ge-O-Al monolayer to serve as an ideal template for further high-k deposition.

Atomic imaging and modeling of passivation, functionalization, and atomic layer deposition nucleation of the SiGe(001) surface via H2O2(g) and trimethylaluminum dosing

“…The OH\Ge\O\Ge\OH site appearing darker in filled state imaging than the OH\Ge\Ge\OH site is consistent with the bridging O atoms causing the valence electrons to be more tightly bound. This difference in STM imaging is consistent with STM simulations previously shown on the H 2 O 2 (g) dosed Ge(100) surface [45]. The red box highlights the small portion of the surface that remains unreacted leaving undercoordinated surface atoms with dangling bonds which have a high tunneling current and image as very bright spots.…”

“…The proposed models were developed using bond enthalpy calculations and are confirmed below using DFT calculations. As previously shown on the pure Ge(001) surface, the bonding configuration shown in the green box occurs when H 2 O 2 (g) dissociates on a Ge dimer terminating each Ge atom with an \OH species [45]. The blue box shows the bonding configuration where an \O atom has inserted into the Ge dimer bond which is already terminated by two \OH species.…”

“…3(A) only shows a bulk-like component, H 2 O 2 (g) dosing at room temperature (RT) generated a higher binding energy peak which is assigned as GeO x H y . As previously shown, dosing H 2 O 2 (g) onto a Ge surface results in a variety of bonding configurations involving a complete \OH and \O termination [45]. Therefore, the resulting bonding configurations on the surface have been collectively assigned as a single broad GeO x H y peak centered at 1.5 eV higher than the bulk Ge feature.…”

“…Fig. 2 (001) surface which also image as dark sites [45]. Models of the \OH or \O species are shown in Fig.…”

Combined wet and dry cleaning of SiGe(001)

“…Pinning of Si 0.6 Ge 0.4 (001) results in a Fermi level near the valence band similar to Ge(001) so STS of n-type is sufficient to determine the unpinning of the surface. 45 STS measures the local density of states (LDOS) by lock-in measurement of the AC signal from AC modulation of the sample bias during an I-V (current-voltage) sweep of the DC sample bias to obtain (dI/dV)/(I/V), which is considered to be proportional to the LDOS. 46,47 STS curves in Fig.…”