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- Minea, T. M., et al.
(författare)
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Kinetics of plasma species and their ionization in short-HiPIMS by particle modeling
- 2014
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 255, s. 52-61
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Tidskriftsartikel (refereegranskat)abstract
- The ionization efficiency of High Power Impulse Magnetron Sputtering (HiPIMS) discharges is the key parameter leading to (i) gas ion production and consequently controlling the sputtering effectiveness and (ii) sputtered vapor ionization, self-consistently linked to self-sputtering and thin film properties. To study the HiPIMS discharge time dependent two dimensional Particle in Cell (2D PIC) modelling coupled with Monte Carlo treatment of the plasma kinetics is discussed in terms of numerical scheme and stability criteria. The first microscopic results are presented for very short pulses (similar to 5 mu s) using superimposed DC pre-ionization. During this modeled HiPIMS short-pulse the plasma density increases at least two orders of magnitude driven by the pulse voltage, which also continues for a short time in the afterglow. During the pulse voltage plateau, the plasma potential shows a linear dependency going away from the target with two slopes over two space regions. First region is very narrow (<0.5 mm), corresponding to the cathode sheath in front of the race-track, while the second region, much larger, corresponds to the pre-sheath or Ionization Region (IR). Modeling results show an increasing electric field in the sheath with the voltage rise of the pulse, while it stays almost constant in the IR, corresponding to about 150 Vcm(-1), in agreement with reported probe measurements. The local electron energy distribution functions in the IR and further out in the Diffusion Region (DR) are very different. IR electrons are much more energetic compared to the ones found in the DR, which have an important low energy population as a result of the ionization processes. The transport of sputtered metal vapor from the target is simulated by 3D Monte Carlo (MC) modeling, in the intermediary pressure range - between ballistic and diffusive. Using the self-consistent output of plasma density maps from PLC with MC transport of sputtered vapor including their possible ionization when they cross the HiPIMS dense plasma, it is possible to estimate the metal ionization fraction, found here slightly lower than in previous reported works.
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