| AVS 63rd International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS+AS+EM-WeA |
| Session: | Semiconductor Surfaces and Interfaces |
| Presenter: | SangWook Park, University of California, San Diego |
| Authors: | S.W. Park, University of California, San Diego J.Y. Choi, University of California, San Diego E. Chagarov, Univeristy of California, San Diego B. Sahu, GLOBALFOUNDRIES S. Siddiqui, GLOBALFOUNDRIES N. Yoshida, Applied Materials J. Kachian, Applied Materials A.C. Kummel, University of California, San Diego |
| Correspondent: | Click to Email |
To overcome challenges when scaling down silicon-based complementary metal-oxide semiconductor (CMOS) devices, SiGe has received much attention due to its high carrier mobility and applications in strain engineering. Extremely thin oxides with appropriate band offsets can be utilized to form unpinned contacts on SiGe for a metal-insulator-semiconductor (MIS) structure. The TiO2 interfacial layer on Ge is known to form a MIS structure which reduces the tunneling resistance due to the nearly zero conduction band offset (CBO) between TiO2 and Ge. In this study, formation of TiOx monolayer on SiGe(110) via H2O2(g) functionalization was investigated using in-situ scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and x-ray photoelectron spectroscopy (XPS). H2O2(g) was employed instead of the conventional H2O(g) oxidant since H2O2(g) can form a uniform monolayer of –OH ligands on the surface without subsurface oxidation which should be ideal for forming the most stable possible interface which is a layer of Si-O-Ti bonds. STM verified that clean Si0.5Ge0.5(110) surfaces were terminated with both Si and Ge adatoms. STS measurements indicated that the Fermi level of clean Si0.5Ge0.5(110) surfaces was pinned near midgap between the valence and conduction band edges due to the half-filled dangling bonds of the adatoms. In order to passivate the dangling bonds, atomic H was dosed onto clean Si0.5Ge0.5(110) at 300°C which unpinned the Fermi level as demonstrated by STS. XPS analysis showed a saturation dose of H2O2(g) at 25°C left the Si0.5Ge0.5(110) surfaces terminated with a monolayer of both Ge-OH and Si-OH sites. STS indicated that the Fermi level on H2O2(g) dosed Si0.5Ge0.5(110) was shifted to near the valence band edge due to the formation of surface dipoles induced by hydroxyl bonds. Tetrakis(dimethylamido)titanium (TDMAT) or titanium tetrachloride (TiCl4) was subsequently dosed onto hydroxyl-terminated Si0.5Ge0.5(110) at 25°C forming Ti bonds on surface. Both TDMAT and TiCl4 dosed Si0.5Ge0.5(110) surfaces were annealed at 300°C and XPS verified that the Ti-O bonds were totally transferred from Ge atoms to Si atoms forming exclusively Ti-O-Si bonds on Si0.5Ge0.5(110) surfaces consistent with the strong bonding between Si and oxygen pulling Si atoms toward the surface to bond with oxygen while pushing Ge atoms into the subsurface during the annealing. STM demonstrated an ordered TiOx monolayer was formed with a row spacing which doubles the spacing of adatoms on clean Si0.5Ge0.5(110). In addition, STS indicated a TiOx monolayer on SiGe(110) was unpinned and therefore can serve as an ultra-thin insulating layer for a MIS structure.