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

Abstract

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 physical vapor deposition coatings. With the introduction of ionized physical vapor deposition 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, (1) pure HIPIMS, (2) HIPIMS combined with unbalanced magnetron sputtering (UBM), and (3) pure UBM. Nitrogen flow rate was varied (5–300 sccm) whereas the average power on target was maintained around 8 kW. Target resistance versus 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 four UBM targets were operated, target poisoning effect was evident, however, expectedly moved to higher flow rates (175 sccm and above) whereas appeared diminished when two UBM and two 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 five 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.