Preferentially Oriented Cubic Boron Nitride Films Grown on Si (001) Substrates By ION Assisted Pulsed Laser Deposition
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PREFERENTIALLY ORIENTED CUBIC BORON NITRIDE FILMS GROWN ON Si (001) SUBSTRATES BY ION ASSISTED PULSED LASER DEPOSITION A. K. BALLAL, L. SALAMANCA-RIBA, G. L. DOLLt, C. A. TAYLOR IIt AND R. CLARKEI Materials and Nuclear Engineering Department, University of Maryland, College Park, MD 20742-2115; t Physics Department, General Motors Research Laboratories, Warren, MI 48090-9055; $ Physics Department, University of Michigan, Ann Arbor, MI 48109-1120. ABSTRACT Preferentially oriented and extremely adherent cubic boron nitride films have been obtained using ion-assisted pulsed laser deposition on (001) Si substrates. The films were - 1800A thick, optically transparent and formed an antireflective coating on the Si substrate. Infrared transmittance spectra showed a strong absorption peak at 1080 cm- 1 , indicating sp 3 bonded film. Cross-sectional and plan-view transmission electron microscopy indicate that the cubic boron nitride films are polycrystalline having cubic zinc-blende crystal structure and a lattice constant of 3.62 A. A preferred texture is observed with the [110] axis of cubic boron nitride parallel to [001] axis of silicon. INTRODUCTION The growth and characterization of cubic boron nitride (c-BN) films have recently received considerable attention. C-BN is of interest since it has high potential for use as a high temperature, radiation resistant semiconductor. The physical properties of c-13N are very similar to those of diamond. However, c-BN enjoys an advantage over diamond in that c-BN can be doped both n- and p- type whereas diamond cannot. Several deposition techniques have been used to grow c-BN films, but the one gaining popularity is pulsed laser deposition (PLD). An excellent review on the topic of PLD has been provided by Cheung and Sankur[1]. Previously, we have reported the crystallinity, composition, morphology, and chemical bonding of BN films (total thickness 1000 - 2000 ;wn by PLD using transmission electron microscopy (TEM) [2], X-ray diffraction
3,4jX-ray Photoelectron spectroscopy (XPS) [5], and Rutherford back scattering spec-
troscopy (RBS) [2]. A complete review of the results is discussed by Doll et. al. ý6].
In brief, the results from these investigations showed that a thin (< 200A), nitrogen deficient, epitaxial c-BN layer was present at the interface with the substrate with the remainder of the film being incoherent sp 2 bonded BN. To circumvent the problem of nitrogen deficiency of the BN films and to improve adhesion of the film to the substrate, ion-assisted PLD was undertaken [7, 9]. This paper discusses the structural characterization of BN films grown on (001) Si substrates by ion-assisted pulsed laser deposition using infrared spectroscopy, plan-view and crosssectional TEM. EXPERIMENTAL DETAILS Cubic boron nitride films were grown on (001) Si substrates using ion-assisted pulsed laser deposition. The details on the growth conditions have been discussed earlier7. In brief, a KrF excimer laser was used, which had a wavelength of 248 nm. The pulse energies used were 300 mJ
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