Investigation on AlN epitaxial growth and related etching phenomenon at high temperature using high temperature chemical vapor deposition process.
Résumé
Thick MN layers were grown by high temperature chemical vapor deposition (HTCVD) on 8 degrees off-axis (0 0 0 1) 4H-SiC, on-axis (0 0 0 1) 6H-SiC and on-axis (0 0 0 1) AlN templates between 900 degrees C and 1600 degrees C. The experimental set-up consists of a vertical cold-wall reactor working at low pressure in which the reactions take place on a graphite susceptor heated by induction. The reactants used are ammonia (NH(3)) and aluminum chlorides (AlCl(x)) species in situ formed via Cl(2) reaction with high purity aluminum wire. As-grown AlN layers have been characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Optical Profilometry, Atomic Force Microscopy (AFM) and Raman spectroscopy. In this study, the influence of the deposition temperature and the N/Al ratio in the gas phase is studied in order to stabilize epitaxial growth. The epitaxy on AlN template is favored using a low N/Al ratio in the gas phase and a high temperature above 1400 degrees C. The crystalline quality of epitaxial AlN layers is found to increase with increasing deposition temperature from 1400 to 1500 degrees C. Growth rates up to 14 mu m h(-1) have been reached for epitaxial AlN layers. An important etching phenomenon is also observed at high temperature: apparition of pin holes certainly around threading dislocations at 1400-1500 degrees C and substrate etching at 1600 degrees C. (C) 2011 Elsevier B.V. All rights reserved.