Standing waves in dc and pulsed dc magnetron sputtering

In industrial magnetron sputtering setups, recently a homogeneity issue is observed which is related to periodic discharge patterns and standing waves, respectively. This phenomenon occurs in both, dc and pulsed dc operation mode. It appears at certain process conditions – generally at higher power density – on planar and rotatable magnetron sputtering targets.

With a simulation software based on the Particle-in-Cell Monte Carlo method, we tested different hypotheses on the origin of this effect. We currently assume that periodic discharge patterns evolve from drifting ionization zones, a.k.a. spokes or plasma waves. These plasma waves – an inherent feature of all magnetron discharges – could induce plasma impedance oscillations and corresponding target voltage oscillations.

Accordant target voltage oscillations are bound to the plasma waves’ propagation velocity. Hence, a stroboscope effect could take place and the plasma waves are lightened and darkened at fixed positions on the target, making them noticeable for human eyes. This stroboscope-thesis is encouraged by modeling results as well as by Fourier analysis of corresponding voltage signals.

On the background of this hypothesis we present experimental findings and qualitatively corresponding simulation results.