In this study, Al thin films deposited on silicon wafers by direct current rnagnetron sputtering were oxidized under radio frequency 13.56 MHz O-2 plasma at temperatures up to 550 degrees C. During oxidation, plasma powers as well as oxidation temperature and time were varied to investigate the oxidation behavior of the Al films. X-ray photoelectron spectroscopy and Auger electron spectroscopy results show that the apparent alumina could be observed after O-2 plasma treatment with powers above 200 W as well as at temperatures above 250 degrees C. However, no alumina increment could be discerned after individual either heat treatment at 550 degrees C or plasma treatment at room temperature. The thickness of alumina layers increased remarkably with plasma power and could reach about 60 mm when undergone 400 W 0, plasma treatment at 550 degrees C for 2 h. Moreover, the thickness of alumina increased parabolically with time during plasma oxidation aided by thermal treatment. The deduced activation energy of such plasma oxidation was 19.1 +/- 0.5 W/mol. (C) 2007 Elsevier B.V. All rights reserved.