INTERFACE EPITAXY AND SELF-EPITAXY OF METALS NEAR ROOM TEMPERATURES

The recently developed technique of metal-metal epitaxy on silicon (MMES) allows a number of metals to be epitaxially grown without an intentional heating of the substrates. Using (100) Cu epitaxially grown on (100) Si as the seed, or other metals on Cu as the seed, growth of (100)-oriented films has been obtained for fourteen metals, at a thickness of 1000 angstrom, including both face-centered cubic (fcc) and body-center cubic (bcc) metals. Two determining factors involving in such a growth are discussed: an interface heteroepitaxy, followed by a self-epitaxy of the metals. The role of lattice match in the interface epitaxy is illustrated by the growth of (100)-W and (100)-Nb films, both bcc metals, on the differently matched metal seed layers. A rotation of 45-degrees between the (100)-bcc metal grown and the (100)-fcc seed layer is suggested and confirmed. The epitaxial growth of these metals further allows a comparison of the substrate temperature used with the melting temperatures of the metals. The ratio of the substrate temperature to the melting temperature of the metals grown by the MMES technique ranges from 0.24 for Ag to 0.08 for W, using 300 K for the substrate. It is suggested that the technique be used to determine consistently the minimal substrate temperatures needed for the epitaxy of these metals, allowing a fundamental understanding of the epitaxial growth of metal films.