Superposition of HiPIMS with RF on a single magnetron: Generation of high ion energies

The superposition of HiPIMS (high power impulse magnetron sputtering) and RF (radio-frequency, 13.56 MHz) on a single magnetron equipped with a copper target in argon atmosphere was investigated, using a multi-diagnostics approach including energy-selective mass spectrometry, optical emission spectroscopy and calorimetric probe measurements. The addition of RF to the HiPIMS plasma results in an increased RF plasma potential by approximately 50 V, depending on the RF power. This elevated potential accelerates ions in the sheath towards the grounded substrate, generating high ion energies and increased energy flux. Plasma potentials were estimated from the ion energy distributions and floating potential measurements. The high-energetic metal ions arrive in the off-time of the HiPIMS pulse on the substrate, as the RF sheath is recovering after the HiPIMS pulse and the dense HiPIMS plasma is diffusing away from the target. Optical emission spectroscopy provided insight into plasma composition dynamics, revealing a transition from a copper-dominated plasma during the HiPIMS pulse to an argon RF plasma during the off-time. The potential of this process is demonstrated by the deposition of copper thin films, showing significant influence of the deposition mode for their properties. • HiPIMS and RF operated in continuous superposition on a single copper target. • RF plasma provides pre-ionization to HiPIMS pulses. • Transition from copper plasma (during HiPIMS pulse) to argon plasma (HiPIMS off-time). • Superposition of RF increases the plasma potential, resulting in higher ion energies. • Differences in thin film structure depending on the deposition mode.