Target ion and neutral spread in high power impulse magnetron sputtering

The ionization region model (IRM) is applied to explore working gas rarefaction in high power impulse magnetron sputtering discharges operated with graphite, aluminum, copper, titanium, zirconium, and tungsten targets. For all cases the working gas rarefaction is found to be significant, the degree of working gas rarefaction reaches values of up to 83 %. The various contributions to working gas rarefaction, including electron impact ionization, kick-out by the sputtered species or hot argon atoms, and diffusion, are evaluated and compared for the different target materials, and over a range of discharge current densities. The relative importance of the various processes varies between different target materials. In the case of a graphite target with argon as the working gas at 1 Pa, electron impact ionization (by both primary and secondary electrons) is the dominating contributor to working gas rarefaction, with over 90 % contribution, while the contribution of sputter wind kick-out is small < 10 %. In the case of copper and tungsten targets, the kick-out dominates, with up to ∼60 % contribution at 1 Pa. For metallic targets the kick-out is mainly due to metal atoms sputtered from the target, while for the graphite target the small kick-out contribution is mainly due to kick-out by hot argon atoms and to a smaller extent by carbon atoms. The main factors determining the relative contribution of the kick-out by the sputtered species to working gas rarefaction appear to be the sputter yield and the working gas pressure.

Section: Overviewmentioning

confidence: 99%

Section: Titanium Targetmentioning

confidence: 99%

On working gas rarefaction in high power impulse magnetron sputtering

Barynova,

Rudolph,

Suresh Babu

et al. 2024

“…The magnet configurations explored here were the same as in the experimental work of Hajihoseini et al [44], where the ionized flux fraction and deposition rate was reported for the various magnet configurations, while keeping the average power constant, by either maintaining fixed discharge voltage or fixed peak discharge current. The discharges explored by Hajihoseini et al have been studied extensively, including exploring the influence of magnetic field on the discharge current, the electron density and the ionization probability [35], to determine the transport parameters of the neutrals and ions of the sputtered species [59], as well as demonstrate how to minimize variations of the flux parameters, the deposition rate and the ionized flux fraction, as the target erodes [45]. The size of the IR is an input parameter when modeling the HiPIMS discharge, using models such as the IR model [26,27].…”

Section: Ir Modelsmentioning

confidence: 99%

Influence of the magnetic field on the extension of the ionization region in high power impulse magnetron sputtering discharges

Antunes

Rudolph

Kapran

et al. 2023

Self Cite

The high power impulse magnetron sputtering (HiPIMS) discharge brings about increased ionizationof the sputtered atoms due to an increased electron density and efficient electron energizationduring the active period of the pulse. The ionization is effective mainly within the electron trappingzone, an ionization region (IR), defined by the magnet configuration. Here, the average extensionand the volume of the IR are determined based on measuring the optical emission from an excitedlevel of the argon working gas atoms. For particular HiPIMS conditions, argon species ionizationand excitation processes are assumed to be proportional. Hence, the light emission from certainexcited atoms is assumed to reflect the IR extension. The light emission was recorded above a 100mm diameter titanium target through a 763 nm bandpass filter using a gated camera. The recordedimages directly indicate the effect of the magnet configuration on the average IR size. It is observedthat the shape of the IR matches the shape of the magnetic field lines rather well. The IR is foundto expand from 10 and 17 mm from the target surface when the parallel magnetic field strength 11mm above the racetrack is lowered from 24 to 12 mT at a constant peak discharge current.

“…The two most important parameters are the target atom ionisation probability α t , which describes the likelihood of a sputtered atom being ionised, and the target ion back-attraction probability β t , which is the likelihood that an ionised target ion cannot escape the cathode potential fall and is accelerated back to the target. Since the spatial distribution of ions and neutrals is generally not the same, an additional parameter ξ tn, HiPIMS /ξ ti, HiPIMS , the ratio of the neutral and ion transport parameters [57], is needed to describe the ionised flux fraction [56]…”

Section: Data Availability Statementmentioning

confidence: 99%

Insights into the copper HiPIMS discharge: deposition rate and ionised flux fraction

Fischer,

Renner,

Gudmundsson

et al. 2023

Self Cite

The influence of pulse length, working gas pressure, and peak discharge current density on the deposition rate and ionised flux fraction in high power impulse magnetron sputtering discharges of copper is investigated experimentally using a charge-selective (electrically biasable) magnetically shielded quartz crystal microbalance (or ionmeter). The large explored parameter space covers both common process conditions and extreme cases. The measured ionised flux fraction for copper is found to be in the range from ≈10% to 80%, and to increase with increasing peak discharge current density up to a maximum at ≈ 1.25 A cm − 2 , before abruptly falling off at even higher current density values. Low working gas pressure is shown to be beneficial in terms of both ionised flux fraction and deposition rate fraction. For example, decreasing the working gas pressure from 1.0 Pa to 0.5 Pa leads on average to an increase of the ionised flux fraction by ≈ 14 percentage points (pp) and of the deposition rate fraction by ≈ 4 pp taking into account all the investigated pulse lengths.