Time-Resolved Ion and Electron Energy Distributions in a HiPIMS Discharge with Cathode Voltage Reversal

When the voltage on a magnetron cathode is reversed at the end of the pulse in high-power impulse magnetron sputtering (HiPIMS), plasma is ejected toward the substrate. The electron energy distribution at the substrate was measured with a Langmuir probe by setting the probe to a given voltage and collecting the current at all times. The voltage is then incremented, and complete current-voltage plots are reconstructed for every time. Results show that in the first micro-second after reversal, fast electrons diffuse to the substrate, commuting the plasma potential such that the entire sheath voltage appears at the substrate. Ion energy distributions were measured with a gridded energy analyzer as a function of time and corroborate those findings. The ion energy equals the positive voltage applied to the substrate. This ability to tailor the exact value of both the target and gas ions leads to superior film density, control of stress, and allows the magnetron system to be used as a sputter-etch device immediately before deposition. Several examples will be shown related to sustainable development in the energy and semiconductor processing fields. In addition it is shown that the after the plasma potential rises to the voltage of the cathode, the electron energy distribution becomes Druyvesteyn. This is also simulated in a Boltzmann solver which can match both the high-energy Maxwellian at the very start of the positive kick pulse, and predict the Druyvesteyn distribution parameters.