Dr. Julian Held

University of Minnesota, USA
Julian obtained his PhD in Physics from the Ruhr University Bochum, Germany in 2021. There, he worked in the group of Achim von Keudell, focusing on plasma diagnostics of magnetron sputtering discharges. In particular, he has worked extensively on spokes, a wave phenomenon encountered in magnetron sputtering plasmas, as well as ion transport and ionization. Following a year of post-doc in Bochum, he is now working in the group of Uwe Kortshagen at the University of Minnesota in the United States, where he investigates the plasma synthesis of nanoparticles, as well as plasma processing for environmental applications.

Talk title: Ionization of sputtered material in high power impulse magnetron sputtering plasmas

Julian Held^1,2,, Volker Schulz-von der Gathen² and Achim von Keudell²¹Department of Mechanical Engineering, University of Minnesota, USA
²Experimental Physics II, Ruhr University Bochum, Germany

The high degree of ionization among sputtered species is the reason for the favorable properties - like improved adhesion and increased hardness - that are often observed in films deposited using high power impulse magnetron sputtering (HiPIMS). However, where this ionization occurs within the discharge is not really understood. In this contribution, the ionization of sputtered species in HiPIMS of titanium, chromium, and aluminum targets is analyzed using Abel-inverted spectroscopic imaging. From the spatial emission of neutrals, it is deduced that most of the sputtered titanium particles become ionized within 0.5 mm distance from the target, whereas sputtered aluminum or chromium can travel much further through the discharge before ionization occurs. Probe measurements reveal the reason for this difference to be the unusually high electron temperature of around 4.5 eV for titanium compared to 2.6 eV and 1.5 eV for aluminum and chromium as the target material, respectively. This difference between the three discharges can be traced back to be mostly caused by the sputter yield. Thus, we propose that ionization in discharges with low-yield materials should generally be expected to occur closer to the target surface, leading the ions to be affected more strongly by the electric field across the magnetic trap region, resulting in a more severe deposition rate loss compared to high-yield materials.

This work was supported by the DFG as part of the SFB TR-87.