Preparation of highly oriented polycrystalline AlN thin films deposited on glass at oblique-angle incidence
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Preparation of highly oriented polycrystalline AlN thin films deposited on glass at oblique-angle incidence A. Rodr´ıguez-Navarro Instituto Andaluz de Ciencias de la Tierra-CSIC, Campus de Fuentenueva, 18002 Granada, Spain
W. Ota˜no-Rivera Materials Research Lab., The Pennsylvania State University, University Park, Pennsylvania 16802
J. M. Garc´ıa-Ruiz Instituto Andaluz de Ciencias de la Tierra-CSIC, Campus de Fuentenueva, 18002 Granada, Spain
R. Messier and L. J. Pilione Materials Research Lab., The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 8 August 1996; accepted 23 December 1996)
A new method to prepare polycrystalline AlN thin films biaxially oriented on amorphous substrates has been demonstrated. The films were deposited at different angles of incidence with a rf sputtering system. Population-1 crystallites, oriented with their c-axis pointing toward the incoming flux with random orientation in aximuthal directions, predominate at low angle of incidence (near normal). Population-2 crystallites result from non-normal incidence and have their c-axis tilted away from the incoming flux and predominate at high, near glancing, angle of incidence. The alignment of crystallites (population-2) increases with angle of incidence. Crystallites align along the [11*0] channeling direction, characterized by a low sputtering yield, while misoriented crystal grains suffer a higher resputtering and their growth is inhibited. For films deposited at 75±, the FWHM of an x-ray f scan profile is 25±, indicating a high in-plane alignment.
Aluminum nitride (AlN), which crystallizes with a hexagonal close-packed (wurtzite-type) structure (Fig. 1) is an interesting material for optoelectronic applications such as uv photonic detectors1 and surface acoustic wave sensors and filters.2 Many devices require single crystal films for optimum properties, but the limited availability of lattice-matched substrates is a restrictive factor in the fabrication of such films. For instance, biaxial inplane alignment greatly improves the performance of high temperature superconductor films with respect to random in-plane oriented films because of the reduction in high angle grain boundaries.3–5 Recently, Nd and yttria-stabilized zirconia films with different degrees of in-plane alignment deposited on amorphous substrates have been reported.6,7 These films were deposited by ion beam assisted deposition (IBAD) to induce an alignment along a crystallographic direction. In this communication, it is shown that a nearly complete orientation in three dimensions of the AlN films, grown on silica glass substrates, can be achieved by rf sputter deposition using a combination of collimators and substrates oriented at oblique angles. AlN thin films were deposited on silica glass substrates using a rf-diode sputtering system at low substrate temperature (,150 ±C) and 15 mTorr total AryN2 pressure.8 A specially designed collimator was used to J. Mater. Res., Vol. 12, No. 7, Jul 1997
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