Invasive and non-invasive diagnostics of High Power Impulse Magnetron Sputtering (HiPIMS) discharges

Liebig, Bernd Invasive and non-invasive diagnostics of High Power Impulse Magnetron Sputtering (HiPIMS) discharges. Doctor of Philosophy thesis, University of Liverpool.

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Abstract

HiPIMS discharges operated with a titanium and an aluminium-doped zinc target sputtered with the working gas argon were investigated by means of optical 2d-imaging in combination with Abel-inversion. By using optical bandpass filters, the spatial and temporal evolution of the plasma-induced emission of argon atoms and ions and metal atoms and ions were studied. The discharge ignition was found to be accompanied by an intensity maximum observed remote from the target, followed by an asymmetric intensity profile. During the stage of high discharge current, the intensity distribution indicates strong rarefaction of the working gas, efficient ionisation of the sputtered particles above the target and a wider sputter distribution. The off-time is characterised by an initial drop of the intensity by 4 - 6 orders of magnitude and a transition from electron-impact excitation to excitation by electron-electron-ion recombination. Decay constants in the order of 1 ms and the spatial distribution of the emission suggest the loss of electrons and ions due to ambipolar diffusion across the magnetic field. Plasma potential measurements by means of emissive probe revealed strongly negative space potentials of up to -300 V and electric fields in the order of 10000 V/m during discharge ignition, caused by strong charge separation due to the extended sheath. The plasma potential increases to a stable level of more than -25 V during the second half of the discharge pulse, while the electric field is largely reduced to maximal 1500 V/m. It was found that the space potential is consistently 5 V lower when the substrate is kept floating compared to a grounded substrate, which can be explained by the reduced electron loss rate to the substrate due to the potential barrier. This is confirmed by spatially resolved Langmuir probe measurements, showing a density maximum of 1019 m-3 in the confined plasma zone, and an increased density in the vicinity of the floating substrate of 1.3 × �1018 m-3 compared to 0.8 × �1018 m-3 for a grounded substrate. The electron temperature was found to be spatially uniform ranging from 1 eV to 3 eV. A quasi-continuous transport model for sputtered particles confirmed the high degree of ionisation of the sputtered particles of about 90 % and revealed a return probability for titanium ions to the target of 80 % for Ti+ and 96 % for Ti2+. Varying the force caused by a modified two-stream instability [1], showed an increasing sideway defletion of ions also increasing the kinetic energy observed for these particles. The spatial distribution of the relative density confirmed efficient ionisation of sputtered particles in the dense plasma zone adjacent to the target. Average azimuthal velocities of the drifting ion fluid of 3�000 m/s for Ti+ and 7�000 m/s for Ti2+ were obtained.

Item Type:	Thesis (Doctor of Philosophy)
Additional Information:	Date: 2013-03 (completed)
Uncontrolled Keywords:	High Power Impulse Magnetron Sputtering, HiPIMS, Magnetron Sputtering, Langmuir probe, emissive probe, optical emission spectroscopy, plasma diagnostic
Subjects:	?? TK ??
Divisions:	Faculty of Science and Engineering > School of Electrical Engineering, Electronics and Computer Science
Depositing User:	Symplectic Admin
Date Deposited:	27 Aug 2013 14:56
Last Modified:	16 Dec 2022 04:38
DOI:	10.17638/00010053
Supervisors:	Bradley, James
URI:	https://livrepository.liverpool.ac.uk/id/eprint/10053