AVS 64th International Symposium & Exhibition
    Plasma Science and Technology Division Thursday Sessions
       Session PS-ThM

Paper PS-ThM4
On Electron Heating in Magnetron Sputtering Discharges

Thursday, November 2, 2017, 9:00 am, Room 22

Session: Plasma Sources
Presenter: Jon Tomas Gudmundsson, University of Iceland
Authors: J.T. Gudmundsson, University of Iceland
D. Lundin, Université Paris-Sud, France
M.A. Raadu, KTH-Royal Institute of Technology, Sweden
T.M. Minea, Université Paris-Sud, France
N. Brenning, KTH-Royal Institute of Technology, Sweden
Correspondent: Click to Email
The magnetron sputtering discharge has been applied successfully in various industrial functions for over four decades. Sustaining a plasma in a magnetron sputtering discharge requires energy transfer to the plasma electrons. In the past, the magnetron sputtering discharge has been assumed to be maintained by cathode sheath acceleration of secondary electrons emitted from the target, upon ion impact. These highly energetic electrons then either ionize the atoms of the working gas directly or transfer energy to the local lower energy electron population that subsequently ionizes the working gas atoms. This is the essence of the well-known Thornton equation, which in its original form [1] is formulated to give the minimum required voltage to sustain the discharge. However, recently we have demonstrated that Ohmic heating of electrons outside the cathode sheath is typically of the same order as heating due to acceleration across the sheath in dc magnetron sputtering (dcMS) discharges [2]. The secondary electron emission yield γsee is identified as the key parameter determining the relative importance of the two processes. In the case of dcMS Ohmic heating is found to be more important than sheath acceleration for secondary electron emission yields below around 0.1. For the high power impulse magnetron sputtering (HiPIMS) discharge we find that direct Ohmic heating of the plasma electrons is found to dominate over sheath acceleration by typically an order of magnitude, or in the range of 87 – 99 % of the total electron heating. A potential drop of roughly 80 - 150 V, or 15 - 25% of the discharge voltage, always falls across the plasma outside the cathode sheath [3]. We also discuss the influence of the magnetic field strength on the discharge properties.

[1] J A Thornton, J. Vac. Sci. Technol. 15 (1978) 171

[2] N. Brenning et al., Plasma Sources Sci. Technol. 25 (2016) 065024

[3] C Huo et al., Plasma Sources Sci. Technol. 22 (2013) 045005