We investigated the optimum growth condition and initial growth process of AIN on 6H-SiC(0 0 0 1) substrates prepared by H-2 etching in the plasma-assisted molecular beam epitaxy (MBE). In X-ray rocking curve measurements, a small full-width at half-maximum of about 50 arcsec was obtained for a 150 nm thick AIN layer. The AIN layers have contained a lot of pits over a grown surface. Pit densities were markedly decreased by reducing the amount of residual impurities (O, OH and H2O) in an MBE chamber. A very low pit density of 10(4)-10(5) cm(-2) was realized. (C) 2004 Elsevier B.V. All rights reserved.