Sputtering of Al-Cr and Al-Ti composite targets in pure Ar and in reactive Ar-N 2 plasmas

Abstract

Al-Cr-(N) and Al-Ti-(N) coatings were deposited on glass slides by reactive magnetron sputtering of composite concentric Al-Cr or Al-Ti targets in different Ar-N 2 gaseous mixtures (N 2 mass flow <2 sccm). When sputtering occurs in pure argon, the chromium or titanium content increases with the insert diameter of chromium or titanium. For a given insert diameter, the introduction of nitrogen into the reactor yields changes in the Ti/Al or Cr/Al content ratio in the coatings. Both plasma diagnostics, performed by optical emission spectroscopy, and computer simulation allow description of the mechanisms of matter transfer. The composition changes observed can clearly be attributed to a combined effect of differential nitriding of the target with respect to its current density distribution and to the nitride-to-metal sputtering yield ratios involved. However, preferential nitriding of the outer zones of the targets was also observed when the crown was aluminium (with titanium insert) or titanium (with aluminium insert). This behaviour can be related to the sputtering wind (wind effect), which has also been simulated by considering a sinusoidal attenuation of the impinging flux of reactive species from the external zone to the centre of the target.