Characterization of metal films on corundum substrates

Abstract

Gold layers on corundum, α-Al₂O₃, substrates, with intermediate sputtered copper and chromium layers, are used for microwave integrated circuit applications. The existance of “islands” of monocrystalline Au and Cu in otherwise polycrystalline material has been verified using X-ray and electron diffraction techniques. In these monocrystalline regions, a discrete Cr layer, under the Au and Cu layers, is no longer present. Investigations on specially prepared samples established the monocrystalline Cu to be a twinned epitaxic layer with (111)Cu//(0001)α-Al₂O₃; [¯1¯12] Cu//[2¯1¯10]α-Al₂O₃. In a sample consisting of a single Cr layer on α-Al₂O₃, the Cr was found to be epitaxic with (110) Cr//(0001)α-Al₂O₃. Epitaxic “islands” are detrimental to device performance, and their formation has been suppressed by reducing the sputtering power density.