Electronic Structure of Adsorbed Trimethylaluminum on Clean Si(100) Surfaces
- PDF / 418,248 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 43 Downloads / 204 Views
ELECTRONIC STRUCTURE OF ADSORBED TRIMETHYLALUMINUM ON CLEAN Si(100) SURFACES
T. Motooka, P. Fons, and J.E. Greene Department of Materials Science, University of Illinois, Urbana, IL 61801
ABSTRACT The electronic structure of dimerized trimethylaluminum (TMA), AI 2(CH 3 )6. adsorbed on Si(100) surfaces has been investigated using molecular orbital (MO) calculations based on a cluster description of TMA/Si(100). The calculated results suggest that the interactions between TMA and the Si(100) surface are described by overlap of the TMA electron-deficient bond and Si surface dangling-bond orbitals. The electron-deficient bond orbital is the highest occupied MO of TMA and acts as an electron acceptor for charge transfer from a surface Si atom to TMA consistent with observed core-level and valence photoelectron spectra.
INTRODUCTION Trimethylaluminum (TMA) is an organometallic molecule used as source material for metal and compound film growth by chemical vapor deposition. There has recently been a growing interest in UV-laser stimulated chemical reactions in surface-adsorbed TMA layers for direct writing of Al metallization on integrated circuits.[1,2] We have previously reported on the analysis of TMA adsorption on clean Si(100) using X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS).[3] The valence electron spectra from condensed thick (=10nm) TMA layers contained three peaks whose positions were in good agreement with the calculated molecular orbital (MO) energies of the isolated dimerized TMA, A12 (CH3 )6 molecule.[4] Core level spectra for C is, Al 2p, and Si 2p from single TMA layers adsorbed on Si(100) were acquired in both surface-normal and grazing directions and the Al 2p (Si 2p) peak from the interface region was found to shift toward lower (higher) binding-energies.[3] Based on these core level shifts, a structure model for TMA/Si(100) was proposed in which the dimerized TMA molecule adsorbs on Si(100) with its Al-Al axis perpendicular to the Si surface. In this paper, we have investigated the electronic structure of dimerized TMA adsorbed on Si(100) using MO calculations based on a cluster description of the structure model for TMA/Si(100) described above. An essential feature in the adsorbed-TMA/Si interaction has been found to be the overlap between the Si surface dangling-bond and the electron-deficient bond orbitals in Al2 (CH3 )6 resulting in charge transfer from the Si surface atom to the TMA molecule.
Mat. Res. Soc. Symp. Proc. Vol. 131. '1989 Materials Research Society
346
EXPERIMENTAL RESULTS
UPS: hz/=40.8eV
a
TMA Condensed Layer The experiments were carried out Y %a -. in an ultra-high vacuum (< 10-1° Torr) j-_./_..• system and the experimental details have been described previously.[3] UPS and •-.,. / XPS spectra were taken using a He resoTMA/Si(lO0) nance lamp and Mg Kc X-ray source, respectively. The substrates used in the experiments were optically flat 7-13 K2cm p-type Si(100) wafers and the sur•..'"• Clean faces were cleaned by in-situ sputter etching with 5keV Ne+ ion
Data Loading...
