Electron power absorption in magnetron sputtering discharges

We demonstrate a self-consistent and complete description of electron power absorption in magnetron sputtering discharges. The electron energization in radio frequency magnetron sputtering (RFMS), direct current magnetron sputtering (DCMS), and high power impulse magnetron sputtering (HiPIMS) discharges is studied via fully kinetic 1d3v/2d3v particle-in-cell/Monte Carlo collision (PIC/MCC) simulations. Some primary electron energization mechanisms are identified in these discharges, and their transition modes are observed. In RFMS discharges, the electron power absorption can be primarily decoupled into the positive Ohmic power absorption in the bulk plasma region and the negative pressure-induced power absorption near the target surface. Ohmic power absorption is the dominant electron power absorption mechanism, mostly contributed by the azimuthal electron current. The contribution of secondary electrons is negligible under typical RFMS discharge conditions. In DCMS discharges, however, secondary electrons are necessary to maintain the discharge. Scale-invariant breathing oscillations are observed in similar DC magnetron discharges and microdischarges. With the onset and development of breathing oscillations, the electron energization mechanism shifts from sheath energization to Ohmic heating in the ionization region. During the discharge runaway phase in HiPIMS discharges, i.e., the transition from the low-current DCMS regime to the high-current HiPIMS regime, metal ions gradually replace gas ions as the dominant, the sheath width decreases drastically with the increase in plasma density, and the electron energization transforms from sheath energization to Ohmic heating. These results are beneficial for the design, optimization, and scaling of magnetron sputtering discharges under various power sources in practical applications.