Characterization of arc discharge plasmas in the combined steered arc/unbalanced magnetron deposition process

Cathodic arc discharges have been used successfully as sources of highly ionized flux of particles in substrate etching and implantation providing an improved adhesion of PVD coatings deposited by the combined steered arc/unbalanced magnetron method. Substrates biased at -1,200 V in arc plasmas are subjected to ion bombardment which cleans the surface and creates implantation defects thus modifying the interface with subsequently sputter deposited coatings. The etching rate depends on the magnitude of the ion flux while the implantation profiles are dominated by the energy of the bombarding species. In the present work, diagnostic studies of Cr cathodic arc discharges with a current of 100 A show a strong dependence of ion fluxes on the pressure and type of residual gas. The increase of the Ar gas pressure increases the ion saturation current density measured by Langmuir probes. Optical emission spectroscopy measurements of the emission from different charge states of Cr ions revealed an increased fraction of neutral metal atoms after a critical pressure of 10-2 Pa. These results indicate that at higher pressures a significant fraction of the ion flux is comprised of Ar+ and that the mean charge state decreases. The etching rate of substrates biased at -1,200 V in the Cr arc plasma increases from 4 nm.min-1 to 8 nm.min -1. The obtained results suggest a two-stage etching procedure starting with arc operation at high Ar pressure (PAr = 0.09 Pa) to achieve faster metal removal by Ar and Cr ion bombardment. In the second stage pure Cr ion bombardment at residual gas pressure (PAr &le 6 10-4 Pa) allowed an enhanced ion implantation up to 20 nm and Cr accumulation of approximately 37 at % at the interface substrate/coating. TixAl(1-x)N films deposited after the two stage etching method have lower stress gradients at the interface and improved critical load values up to 85 5 N.