Modeling High Power Impulse Magnetron Sputtering Discharges

Abstract: HiPIMS, high power impulse magnetron sputtering, is a promising technology that has attracted a lot of attention ever since its appearance. A time-dependent plasma discharge model has been developed for the ionization region in HiPIMS discharges. As a flexible modeling tool, it can be used to explore the temporal variations of the ionized fractions of the working gas and the sputtered vapor, the electron density and temperature, and the gas rarefaction and refill processes. The model development has proceeded in steps. A basic version IRM I is fitted to the experimental data from a HiPIMS discharge with 100 μs long pulses and an aluminum target. A close fit to the experimental current waveform, and values of density, temperature, gas rarefaction, as well as the degree of ionization shows the validity of the model. Then an improved version is first used for an investigation of reasons for deposition rate loss, and then fitted for another HiPIMS discharge with 400 μs long pulses and an aluminum target to investigate gas rarefaction, degree of ionization, degree of self sputtering, and the loss in deposition rate, respectively. Through these results from the model, we could analyse further the potential distribution and its evolution as well as the possibility of a high deposition rate window to optimize the HiPIMS discharge. Besides this modeling, measurements of HiPIMS discharges with 100 μs long pulses and a copper target are made and analyzed. A description, based on three different types of current systems during the ignition, transition and steady phase, is used to describe the evolution of the current density distribution in the pulsed plasma. The internal current density ratio is a key transport parameter. It is reported how it varies with space and time, governing the cross-B resistivity and the energy of the charged particles. From the current ratio the electron cross-B transport can be obtained and used as essential input when modeling the axial electric field, governing the back-attraction of ions.