Phase formation due to high dose aluminum implantation into silicon carbide

High doses of 350 keV aluminum (Al) ions were implanted into hexagonal silicon carbide (6H-SiC) single crystals at 500 degrees C. Phase formation was studied by transmission electron microscopy, secondary-ion mass spectrometry, and Auger electron spectrometry. A critical Al concentration of about 10 at. % was found below which the 6H-SiC structure remains stable. The Al atoms occupy preferentially silicon (Si) sites in the SiC lattice. The replaced Si atoms seem to be mobile under the implantation conditions and diffuse out. At higher Al concentrations the SiC matrix is decomposed and precipitates of Si and aluminum carbide (Al4C3) are formed. The Al4C3 precipitates have a perfect epitaxial orientation to the SiC matrix. The phase transformation is accompanied by atomic redistribution and strong volume swelling. The resulting changes in the atomic depth profiles can be accounted for by a simple chemical reaction model. (C) 2000 American Institute of Physics. [S0021-8979(00)09001-0].