Titanium Atom and Ion Number Density Evolution in Reactive HiPIMS with Oxygen‚ Nitrogen and Acetylene Gas
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| Year of publication | 2019 |
| Type | Conference abstract |
| MU Faculty or unit | |
| Citation | |
| Description | Reactive high power impulse magnetron sputtering (R-HiPIMS) offers a great opportunity for high quality coating production thus understanding the processes accompanying deposition is of great importance. The hysteresis curve in R-HiPIMS generally exhibits a narrower shape compared to dcMS‚ or it can even be entirely suppressed‚ which is beneficial for high-rate deposition of stoichiometric compound films. The main reason of the hysteresis suppression is not yet completely understood. A recently developed effective branching fraction method is utilized to determine absolute ground state number densities of sputtered titanium species from the optical-emission signal. We report on evolutions of titanium atom and ion ground state densities in R-HiPIMS discharges in oxygen‚ nitrogen and acetylene gases for constant mean power and pulse duration‚ when varying the repetition frequency. A fast feedback system is employed to allow working in the transition region of the hysteresis curve in a well-controlled manner. The ionization fraction of sputtered species increases with the partial pressure of the reactive gas. The increased ionization of titanium is attributed to the combination of the following effects: a longer residual time of sputtered species in the target vicinity; a higher maximal discharge current attained at the end of the pulse; lower amount of sputtered species due to the target poisoning which may positively affect electron distribution function. It is furthermore found that the hysteresis curve shape changes when varying the repetition frequency at the same mean power. The difference is more pronounced for R-HiPIMS with higher sputtered species ionization fraction. The experimental results are compared to the results obtained by a reactive ionization region model (R-IRM). The absolute ground state number densities of Ti atoms and Ti ions measured at the target vicinity are also substituted into the Berg model modified to include ion back attraction‚ and a rather good match between the measurements and simulation results for different experimental conditions is found. |
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