(100) and (111) Ni films epitaxially grown on Cu by the metal-metal epitaxy on silicon technique near room temperatures

Abstract

A growth technique is described which uses the Cu films epitaxially grown on Si as seed layers for the further epitaxial growth of other metals. The technique, metal-metal epitaxy on silicon (MMES), is illustrated with the growth of both (100) and (111) Ni films. Ni, being a face-centered cubic (fcc) metal, tends to grow in the (111) orientation on various substrates, including (100) Si. The (100) Cu/Si structure, however, allows the growth of Ni in the (100) orientation near room temperatures using electron-beam evaporation in a vacuum of low 10-7Torr. A minimal thickness of the Cu seed layer needed for the growth of (100) Ni is found to be between 20 and 50 A. Using the (111) Cu/Si substrates, (111) Ni is observed. Both the single layer, Ni/Cu/Si, and the double layer, Cu/Ni/Cu/Si structures have been grown with controlled orientations. The latter allows the growth of periodic Cu-Ni structures with ultrathin layer thicknesses. The periodic structures of a Cu(50 Å)-Ni(25 Å) superlattice is well resolved for the films deposited on (100) and (111) Cu/Si, and on Cu/glass. The last structure shows both the (100) and (111) diffraction patterns of the superlattice, with well resolved satellite peaks. Heating the Cu-Ni structures shows an interesting orientation dependence for the interactions, with a higher outdiffusion rate of Cu through Ni for the (111) orientation than the (100) one. This is opposite of that observed for either the outdiffusion of Si through Au using single crystal Si substrates, or the reaction rate of Cu-Si for the Cu films epitaxially grown on Si. An interface model is used to explain the results observed. Possible applications of the epitaxial Ni films thus grown are suggested. © 1990, American Vacuum Society. All rights reserved.