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Fabrication of aluminum nitride and alumina composite film by d.c. plasma processes under different conditions

Composite films of aluminum nitride and alumina were fabricated on 6061 aluminum alloys in a d.c. plasma chamber. Samples were treated by three main processes. They were (1) Ar plasma etching, (2) NH{sub 3}/Ar plasma with low pressure and low current density, and (3) NH{sub 3} plasma with high pressure and high current density. The oxygen-free Al surface was obtained after 10 min. 2.8 keV Ar{sup +} sputtering in an ultra-high vacuum analysis chamber after the sample was treated by processes 1 and 2. Composite films of aluminum nitride and alumina were obtained on samples treated by processes 1, 2, and 3. The surface compositions and bonding environments of the composite films were characterized by Auger electron spectroscopy and x-ray photoelectron spectroscopy. The thicknesses of the films were estimated by argon sputtering in the ultra-high vacuum chamber. The surface morphologies of samples after fabrication processes in d.c. plasma were investigated by scanning electron microscopy. Al with the composite films exhibits six times high hardness than that of untreated Al. A possible formation mechanism of the composite film is proposed.