Effect of ion irradiation during deposition on the structure of alumina thin films grown by plasma assisted chemical vapour deposition

Alumina thin films were deposited on hot work tool steel AISI H11 at a growth temperature of 500 to 600 degrees C by plasma assisted chemical vapour deposition and were studied with respect to the structure and composition by X-ray diffraction and electron-probe microanalysis, respectively. The electrical power density at the cathode was varied from 2.7 to 6.6 W/cm(2). Within the investigated process window the following characteristic phases could be identified: gamma-alumina and alpha-alumina as well as mixtures thereof. The alumina phase formation was found to be strongly influenced by deposition temperature and electrical power density at the substrate. It is shown that constitution changes due to a reduction in substrate temperature can be avoided by increasing the electrical power density at the cathode, which leads to an increase in both ion flux and ion energy at the substrate surface.