Effect of voltage pulse characteristics on high-power impulse magnetron sputtering of copper

Abstract

We present a model analysis of high-power impulse magnetron sputtering of copper. A non-stationary two-zone model is used to calculate the deposition rate and the ionized fraction of sputtered copper atoms in the flux onto the substrate for various pulse lengths (20–400 µs), pulse shapes (a fixed target voltage of 900 V and stepwise ascending (800–1000 V) or descending (1000–800 V) target voltages), repetition frequencies (100–2000 Hz) and magnetic field strengths in front of the target (350–450 G) at an argon pressure of 1 Pa. We show that sufficiently long pulses (at least 100 µs), which allow for the build-up of a high-density plasma in front of the target (diameter of 50 mm), are necessary to achieve high target power densities in a pulse and, consequently, high degrees of ionization of the sputtered atoms. However, the high degree of ionization of the sputtered copper atoms leads necessarily to lower deposition rates when compared with dc magnetron sputtering at the same target power density. This is mainly due to the return of ionized sputtered atoms onto the target. The model results show that the average target power density in a pulse is, in addition to the target voltage, a fundamental quantity which determines the average ionized fraction of sputtered atoms in the flux onto the substrate and the deposition rate per average target power density in a period applied to the discharge. Such model calculations can be beneficial for determining the optimum working conditions for specific deposition applications.