Reactive sputtering for coatings has been widely used in many industrial applications. The target poisoning issue is important for reactive sputtering when a compound thin film is deposited at the sputtering target surface causing a decreased deposition rate. High power impulse magnetron sputtering (HiPIMS), which has been under development for more than 20 years, has opened a new era in surface engineering and functionalization of coatings for many applications. In terms of process control, reactive HiPIMS has greater challenges than its non-reactive counterpart, as such, proper working conditions must be chosen including: the duty cycle, frequency, reactive gas ratio, etc. Consequently, plasma monitoring and diagnostic techniques for understanding the plasma status and target poisoning ratio become very useful during the reactive HiPIMS. The latter include, plasma sampling mass spectrometry (PSM), optical emission spectroscopy (OES) and plasma emission monitoring (PEM) techniques. The time-averaged ion energy distribution function (IEDF) provided by a PSM plasma ion analyzer can give information on ions arriving at the substrate during deposition. Meanwhile, the OES signal supplies information on the level of target poisoning and/or the partial pressure of the reactive gas in the chamber. Through a rapid feedback control of piezoelectric valves by the PEM system, the partial pressure, the inlet reactive gas rate into the sputtering system and the stoichiometry of a thin film can be well controlled.
In this work, PSM, OES and PEM techniques were used to study the fabrication of TiN, ZrN, TiCrSiN, TiCrBN and CrxCy hard coatings by reactive HiPIMS and reactive superimposed HiPIMS-MF systems. The PSM technique was employed to diagnose the influence of the radio frequency target power on the plasma status during the deposition of TiCrSiN hard coatings by a reactive hybrid HiPIMS-RF system. The PEM technique was adopted for growing TiN, ZrN, TiCrSiN, TiCrBN and CrxCy hard coatings at different target poisoning ratios by a reactive superimposed HiPIMS-MF technique. Effects of different PEM controlled target poisoning ratios on the microstructure, chemical composition and mechanical properties of such hard coatings are discussed. The important key factors of plasma monitoring and diagnostic techniques for the deposition of hard coatings by reactive HiPIMS are highlighted in this work.
Figure 1: Hardness and elastic modulus of TiCrBN coatings grown under different target poisoning ratios.
 A. Anders., “Tutorial: Reactive high power impulse magnetron sputtering (R-HiPIMS),” J. Appl. Phys. 121 (2017) 171101-34.
Keywords: Reactive high power impulse magnetron sputtering (HiPIMS), Plasma sampling mass spectrometry (PSM), Optical emission spectroscopy (OES), Plasma emission monitoring (PEM), TiN, ZrN, TiCrSiN, TiCrBN, CrxCy