Electrodeposition of nanometer-thick epitaxial films of silver onto single-crystal silicon wafers

Abstract

Silver films were deposited epitaxially for the first time onto low-index, single-crystal silicon wafers through an electrochemical method in an aqueous silver acetate bath. A negative potential of −2.34 V vs. Hg/Hg₂SO₄ was used for both pre-polarization and during the deposition to avoid Si oxidation. The epitaxy of Ag films on Si(111), (110) and (100) was characterized by X-ray diffraction symmetric scans and pole figures. The Ag films showed [111], [110] and [100] out-of-plane orientations, respectively, with in-plane order determined by the Si substrates. Interface models consistent with the observed orientations invoke coincident site lattices (CSLs), in which four unit meshes of Ag coincide with three unit meshes of Si. These CSLs reduce the lattice mismatch from −24.9% to +0.13%. A thickness of about 10 nm was obtained for Ag deposited for ten minutes. A comparison of silver acetate electrolyte and cyanide electrolyte was also performed, showing advantages of the acetate bath over the cyanide bath for growth of epitaxial films of Ag on Si surfaces.