Growth of Bn Thin Films by Pulsed Laser Deposition
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GROWTH OF BN THIN FILMS BY PULSED LASER DEPOSITION J. A. KNAPP Sandia National Laboratories, Div. 1111, P.O. Box 5800, Albuquerque, NM 87185 ABSTRACT A new UHV system for pulsed laser deposition of materials is described, together with results from preliminary experiments for depositions of BN on Si. The system is designed to allow for in-situ diagnostics of the ablation plasma, as well as UHV preparation and characterization of clean sample substrates. The room temperature depositions of BN result in amorphous, B-rich films, whose particle content is a strong function of laser wavelength.
INTRODUCTION Pulsed laser deposition (PLD) is a simple, relatively new technique for fabricating thin films.[1] PLD is particularly interesting for potential application to high-temperature materials such as ceramics or high-To superconductors, where it is already finding wide application. Another interesting area is the deposition of cubic-BN films (cBN), which if successful would have wide application similar to diamond thin films, such as hard coatings and wide bandgap semiconductors, as well as important use with tool steels. Films of BN have been deposited using PLD in the past[2,3], and more recently Doll, et al.[4-6] have reported using PLD to form epitaxial thin films of cBN on Si(100). However, reproducing this result with consistent, thick films of epitaxial cBN has proven difficult.[7] In the experiments reported here, cBN is not expected or seen, because the substrate is at room temperature. Instead, particle density and B/N stochiometry were examined as a function of ablating wavelength. The system described here has been developed to provide capabilities for in-situ characterization of the laser ablation process and to allow preparation of clean, wellcharacterized surfaces as substrates. An overview of the all-metal, UHV chamber is in Fig. 1, with the main features shown, some of which are not yet operational. The sample, at the center of this top view, is mounted on a manipulator with two orthogonal rotation axes and XYZ motion. Z travel of 6" is sufficient to raise the sample out of the way for plume diagnostics and to lower it 4" below the deposition for transfer with a loadlock arrangement. An ohmic heater allows sample temperatures up to 1000 OC. Up to 6 targets can be mounted on the target wheel, which is moved under computer control to select targets (allowing convenient growth of multilayers) and to raster the targets during deposition, to prevent cratering. The system has been designed to include a shutter wheel between the targets and the substrate, synchronized with the laser in order to pass the plume while blocking slower moving particles. A number of additional ports, not shown in the figure, point at either the target or substrate positions. In these are mounted an ion sputter gun for sample preparation, a pulsed gas doser for providing a background gas in synchronization with the laser, and a camera for monitoring the plume. Planned additions include a pulsed ion gun for modifying the deposition pro
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