Epitaxial Growth of Ni on Si by Ion Beam Assisted Deposition
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EPITAXIAL GROWTH OF Ni ON Si BY ION BEAM ASSISTED DEPOSITION K.S. GRABOWSKI, R.A. KANT and S.B. QADRI* Naval Research Laboratory, Code 4670, Washington, DC *Sachs/Freeman Associates, Inc., Landover, MD 20785
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ABSTRACT Epitaxial Ni films were grown on Si(lll) substrates to a thickness of The about 500 nm by ion beam assisted deposition at room temperature. films were grown using 25-keV-Ni ions and electron-beam evaporation of Ni The at a relative arrival ratio of one ion for every 100 Ni vapor atoms. ion beam and evaporant flux were both incident at 450 to the sample surface. Standard 0-20 X-ray diffraction scans revealed the extent of measurements crystallographic texture, while Ni (2201 pole figure Films identified the azimuthal orientation of Ni in the plane of the film. grown without the ion beam consisted of nearly randomly oriented fine grains of Ni whereas with bombardment the Ni (111) plane was found parallel to the Si (111) plane. In all the epitaxial cases the Ni [110] direction was perpendicular to the axis of the ion beam, suggesting that the azimuthal orientation of the film was determined by channeling of the ion Additional experiments beam down 1110) planar channels in the Ni film. with different ions, energies, and substrates revealed their influence on the degree of epitaxy obtained.
INTRODUCTION It has been shown that Ni can be grown epitaxially on a number of substrates at temperatures near 200°C; for example on ZnSe [1], diamond [2], sapphire [3], NaCl [4], and a variety of other substrates tabulated in Unfortunately, Ni has been shown to react with a Si substrate at [5]. these temperatures to form silicides [6,7]. An alternative approach would be to reduce the temperature required for epitaxy by simultaneously bombarding the surface with sub-keV energy ions during Ni deposition. This approach has succeeded for a number of other systems as has been reviewed by Greene [8] and Smidt [9], and since it has been shown to work for Cu on Si [10], may be expected to work for Ni on Si. While that approach may yet be shown to work, this work describes the rather remarkable formation of epitaxial or perhaps pseudo-epitaxial Ni films on Si at room temperature by using 25-keV-Ni ion bombardment during Ni deposition. Considering the relatively high energy utilized where substantial radiation damage would be expected, such good epitaxy was not anticipated. This result may be related to the observation that grains in as-deposited thin films can reorient under keV-ion bombardment to encourage channeling of the incident ion beam. Such observations have been reviewed by Smidt [9] and Dobrev [11], and shown specifically for Ni films by Wang et al. [12].
EXPERIMENTAL PROCEDURE Electron beam evaporation was used to deposit 500-nm-thick Ni films on room temperature substrates lxO.5 cm in size. During growth, the films were typically bombarded with 25-keV Ni+ ions supplied by an ion implanter. Selected samples were bombarded instead with Ar+ ions either from an ion The implanter at 25 keV, or from a Kaufman ion
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