1. |
- Gudmundsson, Jon Tomas, 1965-, et al.
(författare)
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Are the argon metastables important in high power impulse magnetron sputtering discharges?
- 2015
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 22:11
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Tidskriftsartikel (refereegranskat)abstract
- We use an ionization region model to explore the ionization processes in the high power impulse magnetron sputtering (HiPIMS) discharge in argon with a titanium target. In conventional dc magnetron sputtering (dcMS), stepwise ionization can be an important route for ionization of the argon gas. However, in the HiPIMS discharge stepwise ionization is found to be negligible during the breakdown phase of the HiPIMS pulse and becomes significant (but never dominating) only later in the pulse. For the sputtered species, Penning ionization can be a significant ionization mechanism in the dcMS discharges, while in the HiPIMS discharge Penning ionization is always negligible as compared to electron impact ionization. The main reasons for these differences are a higher plasma density in the HiPIMS discharge, and a higher electron temperature. Furthermore, we explore the ionization fraction and the ionized flux fraction of the sputtered vapor and compare with recent experimental work.
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2. |
- Stancu, G. D., et al.
(författare)
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Argon metastables in HiPIMS : Validation of the ionization region model by direct comparison to time resolved tunable diode-laser diagnostics
- 2015
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Ingår i: Plasma sources science & technology. - : Institute of Physics Publishing (IOPP). - 0963-0252 .- 1361-6595. ; 24:4
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Tidskriftsartikel (refereegranskat)abstract
- The volume plasma interactions of high power impulse magnetron sputtering (HiPIMS) discharges operated with a Ti target is analyzed in detail by combining time-resolved diagnostics with modeling of plasma kinetics. The model employed is the ionization region model (IRM) with an improved and detailed treatment of the kinetics of the argon metastable (Arm) state, called m-IRM. The diagnostics used is tunable diode-laser absorption spectroscopy (TD-LAS) of the Arm state, which gives the line-of-sight density integrated along the laser path parallel to the target surface. The TD-LAS recordings exhibit quite complex temporal evolutions Arm(t), with distinct features that are shown to reflect the time evolution of the plasma (the electron density and temperature), and of the argon gas (gas rarefaction and refill). The Arm(t) function is thus a tracer for the most important aspects of internal discharge physics, and therefore suitable for model testing and validation. The IRM model is constructed to be locked to obey specific experimental macroscopic discharge parameters, specifically the discharge current ID(t) and the voltage UD(t). It has to this purpose been run with the appropriate process gas pressures (from 0.67 to 2.67 Pa), with the experimentally applied voltage pulse profiles UD(t), and with the resulting current pulse profiles ID(t) (with maxima from 0.5 to 70 A). It is shown that the model reproduces the features in the TD-LAS measurements: both the Arm(t) evolution in single pulses, and how the pulse shapes change with gas pressure and with pulse amplitude. The good agreement between the measurements and model output is in this work taken to validate the basic assumptions of the m-IRM. In addition, the m-IRM results have been used to unravel the connections between volume plasma kinetics and various features recorded in the TD-LAS measurement, and to generalize the foremost characteristics of the studied discharges.
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3. |
- Vitelaru, C., et al.
(författare)
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Argon metastables in HiPIMS : time-resolved tunable diode-laser diagnostics
- 2012
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Ingår i: Plasma sources science & technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 21:2, s. 025010-
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved tunable diode-laser absorption spectroscopy measurements were performed on the argon metastable (Ar-m) level 3s(2)3p(5)(P-2(3/2)degrees)4s excited at 801.478 nm, in the dense plasma region in front of the magnetron target in a high power impulse magnetron sputtering (HiPIMS) discharge. From the Doppler profile the evolution of the temperature and density was derived during the pulse as well as during the plasma decay, i.e. in the afterglow. It is shown that the Ar-m density sharply increases at the beginning of the discharge pulse, followed by a severe Ar-m depletion along with increasing gas temperature around the peak of the HiPIMS discharge current. The strong dynamics of these parameters involve many elementary processes such as electron-impact excitation, electron-impact de-excitation and ionization of Ar-m, gas rarefaction, electron temperature increase at the end of the pulse and gas diffusion. These phenomena are discussed with respect to several parameters: distance from the target, peak discharge current during the pulse, pulse length, and gas pressure.
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