Modeling of high power impulse magnetron sputtering (HiPIMS) discharges with graphite target

High ionization fraction of carbon is essential when depositing tetrahedral amorphous carbon (ta-C) or diamond like carbon (DLC) thin films as energetic ion bombardment promotes the formation of films with high sp³ content. The deposition of DLC films by high power impulse magnetron sputtering (HiPIMS) has been explored extensively, but the ionization fraction of the carbon appears to be low. Here, the ionization region model (IRM) [1] is applied to model a HiPIMS discharge in argon with a graphite target. The discharge develops into working gas recycling, 90 % of the discharge current at the cathode target surface composed of Ar⁺ ions, while the contribution of the C⁺ ions is below 5 %, even for peak current densities as high as 3 A/cm² [2]. This is due to a combination of four mechanisms: a high ionization energy, a small ionization cross section, a short residence time of sputtered carbon in the ionization region, and a high ion back-attraction probability. This insight suggests promising handles for fine-tuning of the process. We explore how the addition of neon to the working gas influences the operating parameters.