Reactive direct current magnetron sputtering of aluminum oxide coatings

Aluminum oxide coatings were reactively direct current magnetron sputtered using an arc suppression unit to stop arcing on the cathode. The process was very controllable when the arc suppression unit was used, and it did not produce any debilitating arcing as is commonly found with conventional reactive direct current magnetron sputtering. Arc suppression is a major advancement in reactive dc magnetron sputtering technology. With the automatic feedback partial pressure control of the reactive gas, all compositions of AlOx, where 0≤x≤1.5, are possible. There are no forbidden compositions as there are with flow control of the reactive gas. All coatings were deposited with a floating substrate bias, and the color of the AlOx films ranged from metallic when there was no or a small partial pressure of oxygen during deposition to a very clear film when the oxygen partial pressure was 0.08 mTorr. The clear film was amorphous, and its average index of refraction, n, was 1.6. The Vickers hardness of the clear film was only 830 kgf mm−2 due to its amorphous structure, and the scratch test critical load for a 1.9 μm thick film on an M2 steel substrate, was only 0.4 kgf. It is believed that substrate bias will improve the mechanical and optical properties of the films.