AVS 61st International Symposium & Exhibition
    Thin Film Monday Sessions
       Session TF+PS+SE-MoM

Paper TF+PS+SE-MoM9
Growth and Phase Stability of Zirconium Diboride Thin Films

Monday, November 10, 2014, 11:00 am, Room 305

Session: Advanced PVD Methods 
Presenter: David Stewart, University of Maine
Authors: D.M. Stewart, University of Maine
D.J. Frankel, University of Maine
R.J. Lad, University of Maine
Correspondent: Click to Email
Zirconium diboride (ZrB2) has metallic-like electrical and thermal conductivities up to its melting point of 3246°C and is also thermal shock resistant, making it an excellent material for use in harsh, high temperature environments. Presently, much of the literature on boride materials concerns bulk, sintered materials, and less is known about ZrB2 thin films. Here we demonstrate the growth of ZrB2 thin films by e-beam co-evaporation of elemental Zr and B sources on sapphire, silicon, and silica substrates. Films were deposited over a range of Zr:B compositions and were characterized before and after annealing up to 1000°C in air or under vacuum (10-8 Torr). Scanning electron microscopy and X-ray photoelectron spectroscopy (XPS) indicated that as-deposited films are homogeneous, with a smooth morphology and covalent bonding character. X-ray diffraction (XRD) revealed that films deposited at temperatures from ambient to 600°C are typically amorphous, and annealing in vacuum up to 1000°C can cause the formation of a ZrB2 crystalline phase that coexists with an amorphous matrix, depending on the Zr:B ratio. Films annealed in air as low as 800°C become heavily oxidized and boron-depleted, leaving behind a monoclinic ZrO2 polycrystalline film. XPS depth profiles suggest the formation of a boron oxide phase in air that evaporates from the surface at high temperatures, consistent with surface oxidation behavior reported for bulk ZrB2 materials. Electrical conductivities of as-deposited films, measured with a 4-point probe, range from 0.3 – 8.3 x 106 S/m depending on the Zr:B ratio, and the films retain their conductive nature after vacuum annealing. The ZrB2 crystalline phases exhibit a preferred (100) crystallographic texture, and valence band XPS measurements confirm the existence of hybridized B2p-Zr4d bonding states. Understanding the high temperature stability of ZrB2 films is important for developing it as a potentially stable conducting film for electronic device applications in harsh environments.