Factors Affecting the Growth Rate of Plasma Anodized Al₂O₃

This paper discusses the affects of anodization parameters on the growth rate of plasma anodized Al2O3. Variations in growth rate were inferred by observing the variations in the anodic current decay while anodizing at a constant bias potential. The following effects have been observed: (a) Sputtered cathode oxide was found to contribute significantly to the total film thickness unless adequate shielding was employed, (b) Heating the substrate from 30°C to 100°C caused the current to decay tenfold faster, (c) A maximum growth rate (quickest current decay) was observed at an O2 pressure of approx. 50m Torr. Probe measurements taken at the location of the sample showed a maximum electron density at this pressure. The maximum electron density and quickest decay rate shifted to higher pressures (approx. 100m Torr) as the discharge current was increased, (d) The presence of small amounts of water vapor in the discharge slightly increased the anodic current decay rate. © 1971, by The Electrochemical Society, Inc. All rights reserved.