ICMCTF2004 Session B10: Surface Processing and Modeling

The Ion-induced Secondary Electron Emission (ISEE) coefficient depends strongly on the target surface condition and therefore we can retrieve from the target voltage behaviour information about the processes occurring at the target during DC reactive magnetron sputtering. Using this simply technique, the target voltage behaviour for the reactive sputtering system Si/N₂/Ar was studied in detail. The target voltage behaviour must be attributed to the presence of non-reacted nitrogen atoms implanted in the target during the reactive sputtering process. A similar effect was notice during DC magnetron sputtering of a silver target in an argon/nitrogen mixture. Also, non-reacted nitrogen atoms were detected in the target surface with in situ XPS during reactive glow discharge sputtering of copper. These experiments gave clear evidence for the important role of reactive ion implantation in the poisoning mechanism during DC magnetron sputtering.

To explain the noticed target voltage behaviour, an analytical model is proposed based on the shallow implantation of reactive gas ions in the target. The chemical reaction between the implanted atoms results in a decrease of the target surface recession speed, and consequently the surface concentration of the implanted species increases, further reducing the recession speed of the target surface, resulting in an avalanche situation when the reactive gas mole fraction in the plasma exceeds a critical value. Besides their reaction with the target atoms, the high concentration of these implanted atoms enhances also the formation of reactive molecules by reaction between two implanted atoms formed by the decomposition of the molecular ions. This second reaction can explain several features of the measured target voltage behaviour. In the case of Al/O₂/Ar, a good agreement was found between the results of the above described analytical model and those achieved by TRIDYN simulations.

Plasma electrolytic oxidation of Al alloys enables to produce hard and wear resistant ceramic layers of up to 150 micron thick with excellent adhesion to the substrate. Being a bath process it can treat parts of practically any shape and of a size upto few meters square provided appropriate source of electrical energy is developed. Industrial application of the process required creating of a Process Unit with control over four plasma electrolysis parameters to achieve a high deposition rate in the range of 3-10 microns per minute in combination with moderate specific energy consumption. The Unit applied specially modulated bipolar electrical pulses of kHz frequency range to the electrolytic bath which was supplied with aero-hydro dynamic agitation system.

The oxide ceramic layers were characterized by means of optical microscopy, SEM, EDX, XRD and surface profilometry. Microhardness, scratch and ball-on-disk tests were performed to evaluate mechanical performances. The effects of positive and negative current pulses duration and energy onto the kinetics of the layer growth, structural, morphological and mechanical characteristics are investigated.