| 1. |
- Brenning, Nils, et al.
(författare)
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HiPIMS optimization by using mixed high-power and low-power pulsing
- 2021
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Ingår i: Plasma sources science & technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 30:1
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Tidskriftsartikel (refereegranskat)abstract
- The possibility to optimize a high-power impulse magnetron sputtering (HiPIMS) discharge through mixing two different power levels in the pulse pattern is investigated. Standard HiPIMS pulses are used to create the ions of the film-forming material. After each HiPIMS pulse an off-time follows, during which no voltage (or, optionally, a reversed voltage) is applied, letting the remaining ions in the magnetic trap escape towards the substrate. After these off-times, a long second pulse with lower amplitude, in the dc magnetron sputtering range, is applied. During this pulse, which is continued up to the following HiPIMS pulse, mainly neutrals of the film-forming material are produced. This pulse pattern makes it possible to achieve separate optimization of the ion production, and of the neutral atom production, that constitute the film-forming flux to the substrate. The optimization process is thereby separated into two sub-problems. The first sub-problem concerns minimizing the energy cost for ion production, and the second sub-problem deals with how to best split a given allowed discharge power between ion production and neutral production. The optimum power split is decided by the lowest ionized flux fraction that gives the desired film properties for a specific application. For the first sub-problem we describe a method where optimization is achieved by the selection of five process parameters: the HiPIMS pulse amplitude, the HiPIMS pulse length, the off-time, the working gas pressure, and the magnetic field strength. For the second sub-problem, the splitting of power between ion and neutral production, optimization is achieved by the selection of the values of two remaining process parameters, the HiPIMS pulse repetition frequency and the discharge voltage of the low-power pulse.
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| 2. |
- Rudolph, Martin, et al.
(författare)
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On how to measure the probabilities of target atom ionization and target ion back-attraction in high-power impulse magnetron sputtering
- 2021
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 129:3
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Tidskriftsartikel (refereegranskat)abstract
- High-power impulse magnetron sputtering (HiPIMS) is an ionized physical vapor deposition technique that provides a high flux of ionized target species for thin film growth. Optimization of HiPIMS processes is, however, often difficult, since the influence of external process parameters, such as working gas pressure, magnetic field strength, and pulse configuration, on the deposition process characteristics is not well understood. The reason is that these external parameters are only indirectly connected to the two key flux parameters, the deposition rate and ionized flux fraction, via two internal discharge parameters: the target atom ionization probability alpha (t) and the target ion back-attraction probability beta (t). Until now, it has been difficult to assess alpha (t) and beta (t) without resorting to computational modeling, which has hampered knowledge-based optimization. Here, we present a simple method to deduce alpha (t) and beta (t) based on measured deposition rates of neutrals and ions. The core of the method is a refined analytical model, which is described in detail. This approach is furthermore validated by independent calculations of alpha (t) and beta (t) using the considerably more complex ionization region model, which is a plasma-chemical global discharge model.
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| 3. |
- Rudolph, Martin, et al.
(författare)
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On the electron energy distribution function in the high power impulse magnetron sputtering discharge
- 2021
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Ingår i: Plasma sources science & technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 30:4
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Tidskriftsartikel (refereegranskat)abstract
- We apply the ionization region model (IRM) and the Orsay Boltzmann equation for electrons coupled with ionization and excited states kinetics (OBELIX) model to study the electron kinetics of a high power impulse magnetron sputtering (HiPIMS) discharge. In the IRM the bulk (cold) electrons are assumed to exhibit a Maxwellian energy distribution and the secondary (hot) electrons, emitted from the target surface upon ion bombardment, are treated as a high energy tail, while in the OBELIX the electron energy distribution is calculated self-consistently using an isotropic Boltzmann equation. The two models are merged in the sense that the output from the IRM is used as an input for OBELIX. The temporal evolutions of the particle densities are found to agree very well between the two models. Furthermore, a very good agreement is demonstrated between the bi-Maxwellian electron energy distribution assumed by the IRM and the electron energy distribution calculated by the OBELIX model. It can therefore be concluded that assuming a bi-Maxwellian electron energy distribution, constituting a cold bulk electron group and a hot secondary electron group, is a good approximation for modeling the HiPIMS discharge.
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