| AVS 58th Annual International Symposium and Exhibition | |
| Electronic Materials and Processing Division | Tuesday Sessions |
| Session EM-TuA |
| Session: | High-k Dielectrics for MOSFETs Part 2 |
| Presenter: | Tobin Kaufman-Osborn, University of California San Diego |
| Authors: | T. Kaufman-Osborn, University of California San Diego J.S. Lee, University of California San Diego K. Kiantaj, University of California San Diego W. Melitz, University of California San Diego A.C. Kummel, University of California San Diego A. Delabie, IMEC, Belgium S. Sioncke, IMEC, Belgium M. Caymax, IMEC, Belgium G. Pourtois, IMEC, Belgium |
| Correspondent: | Click to Email |
Germanium is a promising channel material for next generation MOSFET. The best method to passivate Ge(100) is to form a layer of GeO2, free of Ge suboxides, using high pressure O2 or O3. However, there are three challenges: (1) it is difficult to keep a stoichiometric GeO2 monolayer (ML) at elevated temperatures, (2) the thermal oxidation process creates a rough interface degrading mobility at high field, and (3) scaling the passivation layer to only 1 ML is a challenge. This study presents a process to form a ½ ML of Ge-H and ½ ML of Ge-OH bonds without disrupting the Ge(100) surface. In-situ scanning tunneling microscopy (STM), in-situ scanning tunneling spectroscopy (STS), and in-situ X-ray photoelectron spectroscopy (XPS) were employed to determine the atomic and electronic structure of the passivation monolayer.
Using a differentially-pumped H2O dosing system, an ordered, flat monolayer of H2O chemisorption sites on Ge(100) was formed with a low density of unreacted dangling bonds at 300K. STS data showed that the Ge-H and Ge-OH sites removed the bandgap states from the Ge(100) dangling bonds. Annealing the surface between 20°C and 250°C gradually decreased the coverage of H2O sites. However, even at 300K, the H2O surface is highly reactive to trimethyl aluminum (TMA) since it contains a half monolayer of Ge–OH which catalyzes the breaking of Al-CH3 bonds thereby inducing the formation of Al-O bonds, and the Ge-H sites block ALD ligand chemisorptions. STM experiments showed that the H2O chemisorbed Ge surface provides a half monolayer of nucleation centers with approximately 0.5 nm spacing for TMA dissociative chemisorption at 300K. High resolution XPS experiments indicated that thermally unstable Ge-OH bonds were converted to thermally stable Al-O bonds. Furthermore, passivating the surface with H2O prior to TMA dosing doubles the aluminum coverage compared to the TMA only dosed Ge(100) surface. The higher nucleation density from the two step functionalization process, TMA + H2O, should be favorable for pinhole reduction. DFT calculations are consistent with the data showing TMA reaction with either –Ge-H and –Ge-OH is exothermic, but the reaction of TMA on the –Ge-OH site has both a low activation barrier and higher exothermicity (-41.4 kcal/mol) compared to TMA reaction on the –Ge-H site (-10.8 kcal/mol). The calculation is consistent with the key to full monolayer nucleation, the formation of a full monolayer of Ge-OH chemisorption sites, which is being studied with HOOH dosing.