Publication details

The single-shot spatial-resolved OES of the spoke in non-reactive HiPIMS

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Year of publication 2021
Type Conference abstract
MU Faculty or unit

Faculty of Science

Description The rotating plasma patterns, also known as ionisation zones or spokes, firstly observed in non-reactive high power impulse magnetron sputtering discharges (HiPIMS) are at certain conditions present in direct current magnetron sputtering (dcMS) and radio frequency magnetron sputtering discharges (rfMS) as well. The spokes are investigated due to their high impact on the deposition process and sputtered species' transport. To better understand the spoke phenomena, it is necessary to acquire comprehensive data of the plasma parameters inside the spoke; however, in HiPIMS, preferably by non-invasive diagnostics. This contribution presents the non-invasive spatial-resolved optical emission spectroscopy (OES) of the plasma inside the spoke conducted in non-reactive HiPIMS discharge. The pulses have a duration of 100 µs with a repetition rate of 5 Hz. The 3-inch titanium target was utilised. The experiment was run at argon pressures of 0.4 Pa, 1.0 Pa, and 1.6 Pa to investigate both triangular and round spokes. The fast photodiode and the cylindrical probe were used to capture and determine the passing spoke position. The photodiode's signal and the probe signal were synchronised with the optical emission spectrum acquisition by the intensified charge-coupled device (ICCD) detector with a gate time of 100 ns. By processing these three signals and creating the normalised time scale for each spoke, the unified spoke (UNI-spoke) has been created. Consequently, the evolutions of the selected emission lines can be shown within the UNI-spoke. The spatially resolved emissions of Ar atom and ions and Ti atoms and ions spectral lines were investigated within the UNI-spoke. The spatial resolved OES measurements have shown that the Ar and Ti atoms and ions spectral lines have the characteristic evolution of a specific species' intensity and is the same for all observed spectral lines of this species within the spoke independently of applied pressure. The Boltzmann plot method was utilised to determine the excitation temperatures within the UNI-spoke. The excitation temperatures obtained using the Ar ions and Ti atoms and ions are 13000 K, 8000 K, and 19000 K. The ionisation fraction has been calculated from the selected spectral lines of titanium atom and ion. The ionisation fraction reaches approximately 40%, and its evolution and excitation temperature evolutions remain constant in the margin of standard error within the UNI-spoke for all investigated working pressures.
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