IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Wednesday Sessions
       Session SS+SC-WeM

Paper SS+SC-WeM2
Scanning Tunneling Microscope Investigation of Adsorption of Titanium Atoms on Si(111)-7x7 Surface

Wednesday, October 31, 2001, 8:40 am, Room 122

Session: Adsorption on Semiconductor and Metal Oxide Surfaces
Presenter: H.F. Hsu, National Tsing Hua University, Taiwan, R.O.C.
Authors: H.F. Hsu, National Tsing Hua University, Taiwan, R.O.C.
M.C. Lu, National Tsing Hua University, Taiwan, R.O.C.
H.-L. Hsiao, Tunghai University, Taiwan, R.O.C.
L.J. Chen, National Tsing Hua University, Taiwan, R.O.C.
Correspondent: Click to Email
C54-TiSi@sub 2@ has been the primary silicide for contact application in ULSI devices. The initial stages of interfacial reactions of Ti thin films on silicon are of both scientific and the technological interests. The strong reactivity of Ti with Si was manifested by the interatomic mixing at room temperature. The atomic scale studies of initial Ti-Si reactions at very low coverage have been scarce. In particular, it is not clear whether Ti atoms react with the Si substrate from the very beginning of deposition or the formation of a silicide-like compound starts at some critical coverage. In the present study, an atomic-scale characterization of room temperature titanium adsorption on the Si(111)-7x7 surface has been investigated. Preferential adsorption of Ti atoms on the Si center adatom sites at very low coverage was found. At higher coverage, a peculiar contrast feature is observed. The observed feature is attributed to the charge redistribution caused by the adsorption of more than one Ti atoms on this subunit cell. At very low Ti coverage (~0.007 ML), some of the Si adatom sites appear to be brighter in both filled-state and empty-state STM images. The contract behavior is likely to be due to the adsorption of Ti atoms on the Si adatom sites. It was found that Ti atoms adsorb preferentially on top of the Si center adatoms and, to a less extent, on top of the Si corner adatoms. Upon further deposition of Ti, two center adatoms and corresponding corner adatom become darker and the center of these three adatoms become brighter. The observed change in the apparent height is caused by the redistribution of charge near the Si adatom sites. The result indicates that more than one Ti atoms were adsorbed on a triangular subunit cell.