Modelling of plasma-target interaction during reactive magnetron sputtering of TiN

The nitrogen incorporation at the target during reactive magnetron sputtering of TiN is described by a simple stationary global model of the magnetron plasma, in combination with an analytical two-layer stationary surface model or dynamic collisional computer simulation (TRIDYN) of the surface processes. Results are shown for different nitrogen gas additions in Ar/N2 and Xe/N2 gas mixtures at a total pressure of 0.3 Pa and a magnetron current of 0.3 A. The nitrogen incorporation predicted by the analytical model significantly less than obtained from computer simulation. The computer simulation yields nitrogen depth profiles which extend to about 2.5 nm, exhibiting a quasi-rectangular shape in case of stoichiometric saturation with an integrated nitrogen areal density of ~1.25•1016 N/cm2. The stationary-state nitrogen incorporation results from the balance of surface adsorption in connection with recoil implantation, direct ion implantation, and re-sputtering. The most relevant species are nitrogen gas molecules for adsorption, molecular nitrogen ions for implantation, and inert gas ions for recoil implantation and sputtering. The model results are in good agreement with experiment provided that unity sticking of nitrogen gas molecules is assumed on the unsaturated surface. The analytical surface model is preferable, which favours the picture of a continuous transition to bulk and surface saturation rather than discrete local saturation which is inherent in TRIDYN. Also the relative nitrogen incorporation for Xe/N2 versus Ar/N2 gas mixtures is well described.