Target poisoning during CrN deposition by mixed high power impulse magnetron sputtering and unbalanced magnetron sputtering technique

Target poisoning phenomenon in reactive sputtering is well-known and has been studied in depth over the years. There is a clear agreement that this effect has a strong link on the quality, composition, properties and pronouncedly on the deposition rate of PVD coatings. With the introduction of IPVD techniques such as the relatively novel High Power Impulse Magnetron Sputtering (HIPIMS), which have highly ionized plasmas of the depositing species (metal and gas ions), target poisoning phenomenon is highly contested and thus has been left wide open for discussion. Particularly there have been contradicting reports on the presence of prominent hysteresis curves for reactive sputtering by HIPIMS. More work is needed to understand it which in turn will enable reader to simplify the coating deposition utilizing HIPIMS. This work focuses on the study of Chromium (Cr) targets when operated reactively in argon + nitrogen atmosphere and in different ionizing conditions, namely (a) pure HIPIMS (b) HIPIMS combined with UBM (Unbalanced Magnetron Sputtering) and (c) pure UBM. Nitrogen flow rate was varied (5 sccm to 300 sccm) whereas the average power on target was maintained around 8kW. Target resistance vs N2 flow rate curves for these conditions have been plotted in order to analyze the poisoning effect. When only one UBM target was operating target poisoning effect was prominent between the flow rates of 80 and 170 sccm. However it appeared reduced and in nearly same flow rate ranges (90 and 186 sccm) when only one HIPIMS target was operating. When 4 UBM targets were operated, target poisoning effect was evident however expectedly moved to higher flow rates (175 sccm and above) whereas appeared diminished when 2 UBM and 2 HIPIMS were running simultaneously. Further, to analyze the effect of actual target conditions (poisoning) on deposition rate and on the properties of the films deposited, commercially widely used Chromium nitride (CrN) coatings were deposited in mixed HIPIMS and UBM plasma and at 5 different flow rates of nitrogen. Detail characterization results of these coatings have been presented in the paper which will assist the reader in deposition parameter selection. Keywords : HIPIMS, UBM, CrN, Nitrogen flow rate, target poisoning, PVD coatings