Stoichiometry and impurities in sputtered alumina films on copper

Abstract

Alumina films were prepared on copper substrates using different sputtering techniques (r.f., d.c., diode, magnetron, reactive) and process parameters. Stoichiometry and impurities were analysed by Rutherford backscattering spectrometry and nuclear resonance broadening. The alumina films were found to be oxygen deficient, stoichiometric or oxygen rich depending on the method and sputtering parameters used. R.f. magnetron sputtered films were oxygen deficient if they were sputtered from an alumina target in pure argon. An addition of oxygen resulted in coatings with correct stoichiometry and a low argon content. Also, nitrogen could be used to compensate the sub-stoichiometry of r.f. magnetron sputtered alumina films. Reactive magnetron sputtering in d.c. or r.f. discharges with an aluminium target resulted in alumina films with an excess of oxygen. R.f. diode sputtered alumina films were found to be relatively close to correct stoichiometry when they were sputtered from an alumina target in pure argon. However, the argon content was found to be high, of the order of several atomic per cent. The use of oxygen resulted in films with an excess of oxygen and a lower argon concentration. Reactively r.f. diode sputtered films with oxide-like properties were found to be oxygen rich.