ELSEVIER Physica B 225 (1996) 225-229 Electronic structure of Cu3Si L. Magaud *, S. Guillet, T. Lopez-Rios Laboratoire d'Etudes des PropriOtOs Electroniques des Solides, Centre National de la Recherche Scientifique, associO g~ l'universitO Joseph Fourier, B.P. 166, 38042 Grenoble COdex 9, France Received 6 July 1995; revised 23 February 1996 Abstract The electronic structure of Cu3Si is calculated with a self-consistent scalar relativistic linear muffin tin orbitals code in the atomic sphere approximation. The results are compared to UPS and differential reflectivity measurements on the reacted Cu-Si interface layer where Cu3Si formation is generally admitted. Both theoretical and experimental results show a shift of the d band towards lower energies with respect to pure Cu. The disappearance of a sharp absorption edge at 2.1 eV in differential reflectivity is related to the broadening of the Cud band due to Si p--Cu d hybridization as shown by the calculation. 1. Introduction In the last few years, the possible use of Cu as an interconnecting material in integrated circuits stimu- lated new studies of Cu-Si interaction. Many exper- iments were devoted to the study of Si-Cu interface formation in ultrahigh vacuum by Cu deposition on Si surfaces [1--6]. It was shown that, at room tempera- ture (RT), Cu and Si intermix in an interfacial region several nanometer wide, the actual depth depending on the experimental conditions (evaporation rate, im- purities at the surface etc.) [7]. Auger spectroscopy shows a splitting of the Si LVV Auger peak in this re- gion which clearly indicates that Auger electrons come from Si atoms located in a metallic environment. UV photoemission, XPS and electron microscopy corrob- orate this observation. It is then generally admitted that at RT the deposition of Cu on Si leads to the formation of a metal-rich silicide whose composition is close to Cu3Si [8], which is also known to have very interesting catalytic properties for silicon oxida- * Corresponding author. tion at RT [9]. To our knowledge, up to now, there are no data available on the electronic structure of this compound. In the following, we present calculations of the elec- tronic properties (total energy and densities of states) ofCu3 Si. These calculations are performed with a self- consistent scalar relativistic linear muffin tin orbitals (LMTO) method. We also present photoemission and optical absorption of small Cu deposits on Si(100) 2 x 1 surfaces maintained at RT and we analyze these results in view of our LMTO calculations. 2. Calculation details 2.1. Cu3Si crystal structure The crystallography of Cu3Si compounds is rather complicated. At RT, Cu3Si crystallizes in the so- called r/n phase. This structure, determined from X-ray diffraction by Solberg [8], is a two-dimensional long-period supperlattice with stacking faults and vacancies and, therefore, it is difficult to treat with 0921-4526/96/$15.00 (~) 1996 Elsevier Science B.V. All rights reserved