|About this Abstract
||2010 Electronic Materials Conference
||TMS 2010 Electronic Materials Conference
||T4, Morphological Development of Homoepitaxial AlN Thin Films Grown by MOCVD
||Anthony Rice, Ramon Collazo, Seiji Mita, James Tweedie, Jinqiao Xie, Rafael Dalmau, Zlatko Sitar
|On-Site Speaker (Planned)
AlN thin films were grown on single crystalline (0001)-oriented, Al-polar AlN substrates by metalorganic chemical vapor deposition (MOCVD) to determine the effects of deposition parameters on the thin film microstructure. AlN deposition was conducted at 1100–1250°C under 20 Torr total pressure in H<sub>2</sub> diluent. Trimethylaluminum and ammonia were used as precursors with V/III ratios of 250-500. Triple axis high-resolution x-ray diffraction measurements of the (0002) Bragg peaks of AlN thin films indicated that the films were epitaxial and strain-free. Atomic force microscopy characterization suggests step-flow growth with bi-layer terrace widths of 40 nm and 130 nm for AlN films deposited at 1100°C and 1250°C, respectively. Periodic crystalline faceting was observed with alternating high symmetry (0001) facets and high Miller index facets. The periodic spacing of such facet arrays varied from 80 nm to 450 nm for substrates miscut relative to (0001) by 13° and less than 1°, respectively. Hexagonal pits of up to 800 nm width and 400 nm depth were observed in AlN homoepitaxial thin films deposited at 1100°C. Such pits exhibited an inverted hexagonal pyramid morphology with sidewalls inclined ~45° relative to the surface normal for films deposited on (0001)-oriented substrates. For substrates miscut 13° from (0001), the inclination of pit sidewalls perpendicular to the miscut direction became ~30° or ~60° relative to the surface normal. The average dimension of such pits was found to increase with epitaxial film thickness for AlN deposited at 1100°C: the average pit widths were 400 nm, 600 nm, and 800 nm for film thicknesses of 1 μm, 2 μm, and 3 μm, respectively. No pitting was observed in homoepitaxial AlN thin films deposited at 1250°C. However, pit formation was also observed for multi-layer AlN thin films that consisted of an AlN layer deposited at 1250°C and a subsequent AlN layer deposited at 1100°C. The pit dimensions observed in such multi-layer AlN thin films were found to depend only on the thickness of the layer deposited at 1100°C and were similar to pit dimensions in single-layer AlN thin films of equal thickness deposited at 1100°C. These results are consistent with observations of V-shaped defects in other III-nitride materials in which treading dislocations possessing an edge component intersecting the crystal surface may yield hexagonal pitting. Increasing the radius of curvature of bi-layer terraces by increasing the deposition temperature was found to inhibit the formation of such pits, as predicted by capillary equilibrium theory, but does not prevent the later formation of pits during subsequent deposition at lower temperatures.