| 1. |
- Eliasson, H., et al.
(författare)
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Modeling of high power impulse magnetron sputtering discharges with graphite target
- 2021
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Ingår i: Plasma sources science & technology. - : IOP Publishing Ltd. - 0963-0252 .- 1361-6595. ; 30:11
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Tidskriftsartikel (refereegranskat)abstract
- The ionization region model (IRM) is applied to model a high power impulse magnetron sputtering discharge in argon with a graphite target. Using the IRM, the temporal variation of the various species and the average electron energy, as well as internal parameters such as the ionization probability, back-attraction probability, and the ionized flux fraction of the sputtered species, is determined. It is found that thedischarge develops into working gas recycling and most of the discharge current at the cathode target surface is composed of Ar+ ions, which constitute over 90% of the discharge current, while the contribution of the C+ ions is always small (<5%), even for peak current densities close to 3 A cm(-2). For the target species, the time-averaged ionization probability is low, or 13-27%, the ion back-attraction probability during the pulse is high (>92%), and the ionized flux fraction is about 2%. It is concluded that in the operation range studied here it is a challenge to ionize carbon atoms, that are sputtered off of a graphite target in a magnetron sputtering discharge, when depositing amorphous carbon films.
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| 2. |
- Hajihoseini, H., et al.
(författare)
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Target ion and neutral spread in high power impulse magnetron sputtering
- 2023
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 41:1
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Tidskriftsartikel (refereegranskat)abstract
- In magnetron sputtering, only a fraction of the sputtered target material leaving the ionization region is directed toward the substrate. This fraction may be different for ions and neutrals of the target material as the neutrals and ions can exhibit a different spread as they travel from the target surface toward the substrate. This difference can be significant in high power impulse magnetron sputtering (HiPIMS) where a substantial fraction of the sputtered material is known to be ionized. Geometrical factors or transport parameters that account for the loss of produced film-forming species to the chamber walls are needed for experimental characterization and modeling of the magnetron sputtering discharge. Here, we experimentally determine transport parameters for ions and neutral atoms in a HiPIMS discharge with a titanium target for various magnet configurations. Transport parameters are determined to a typical substrate, with the same diameter (100 mm) as the cathode target, and located at a distance 70 mm from the target surface. As the magnet configuration and/or the discharge current are changed, the transport parameter for neutral atoms xi(tn) remains roughly the same, while transport parameters for ions xi(ti) vary greatly. Furthermore, the relative ion-to-neutral transport factors, xi(ti)/xi(tn), that describe the relative deposited fractions of target material ions and neutrals onto the substrate, are determined to be in the range from 0.4 to 1.1.
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| 3. |
- Rudolph, M., et al.
(författare)
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Influence of the magnetic field on the discharge physics of a high power impulse magnetron sputtering discharge
- 2022
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 55:1
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic field is a key feature that distinguishes magnetron sputtering from simple diode sputtering. It effectively increases the residence time of electrons close to the cathode surface and by that increases the energy efficiency of the discharge. This becomes apparent in high power impulse magnetron sputtering (HiPIMS) discharges, as small changes in the magnetic field can result in large variations in the discharge characteristics, notably the peak discharge current and/or the discharge voltage during a pulse. Here, we analyze the influence of the magnetic field on the electron density and temperature, how the discharge voltage is split between the cathode sheath and the ionization region, and the electron heating mechanism in a HiPIMS discharge. We relate the results to the energy efficiency of the discharge and discuss them in terms of the probability of target species ionization. The energy efficiency of the discharge is related to the fraction of pulse power absorbed by the electrons. Ohmic heating of electrons in the ionization region leads to higher energy efficiency than electron energization in the sheath. We find that the electron density and ionization probability of the sputtered species depend largely on the discharge current. The results suggest ways to adjust electron density and electron temperature using the discharge current and the magnetic field, respectively, and how they influence the ionization probability.
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| 4. |
- Rudolph, M., et al.
(författare)
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On the population density of the argon excited levels in a high power impulse magnetron sputtering discharge
- 2022
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 29:2, s. 023506-
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Tidskriftsartikel (refereegranskat)abstract
- Population densities of excited states of argon atoms in a high power impulse magnetron sputtering (HiPIMS) discharge are examined using a global discharge model and a collisional-radiative model. Here, the ionization region model (IRM) and the Orsay Boltzmann equation for electrons coupled with ionization and excited states kinetics (OBELIX) model are combined to obtain the population densities of the excited levels of the argon atom in a HiPIMS discharge. The IRM is a global plasma chemistry model based on particle and energy conservation of HiPIMS discharges. OBELIX is a collisional-radiative model where the electron energy distribution is calculated self-consistently from an isotropic Boltzmann equation. The collisional model constitutes 65 individual and effective excited levels of the argon atom. We demonstrate that the reduced population density of high-lying excited argon states scales with (p*)(-6), where p * is the effective quantum number, indicating the presence of a multistep ladder-like excitation scheme, also called an excitation saturation. The reason for this is the dominance of electron impact processes in the population and de-population of high-lying argon states in combination with a negligible electron-ion recombination.
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| 5. |
- Antunes, V. G., et al.
(författare)
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Influence of the magnetic field on the extension of the ionization region in high power impulse magnetron sputtering discharges
- 2023
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Ingår i: Plasma sources science & technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 32:7
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Gudmundsson, Jon Tomas, 1965-, et al.
(författare)
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An ionization region model of the reactive Ar/O-2 high power impulse magnetron sputtering discharge
- 2016
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Ingår i: Plasma sources science & technology. - : Institute of Physics (IOP). - 0963-0252 .- 1361-6595. ; 25:6
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Tidskriftsartikel (refereegranskat)abstract
- A new reactive ionization region model (R-IRM) is developed to describe the reactive Ar/O-2 high power impulse magnetron sputtering (HiPIMS) discharge with a titanium target. It is then applied to study the temporal behavior of the discharge plasma parameters such as electron density, the neutral and ion composition, the ionization fraction of the sputtered vapor, the oxygen dissociation fraction, and the composition of the discharge current. We study and compare the discharge properties when the discharge is operated in the two well established operating modes, the metal mode and the poisoned mode. Experimentally, it is found that in the metal mode the discharge current waveform displays a typical non-reactive evolution, while in the poisoned mode the discharge current waveform becomes distinctly triangular and the current increases significantly. Using the R-IRM we explore the current increase and find that when the discharge is operated in the metal mode Ar+ and Ti+ -ions contribute most significantly (roughly equal amounts) to the discharge current while in the poisoned mode the Ar+ -ions contribute most significantly to the discharge current and the contribution of O+ -ions, Ti+ -ions, and secondary electron emission is much smaller. Furthermore, we find that recycling of atoms coming from the target, that are subsequently ionized, is required for the current generation in both modes of operation. From the R-IRM results it is found that in the metal mode self-sputter recycling dominates and in the poisoned mode working gas recycling dominates. We also show that working gas recycling can lead to very high discharge currents but never to a runaway. It is concluded that the dominating type of recycling determines the discharge current waveform.
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| 7. |
- 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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| 8. |
- Gudmundsson, Jon Tomas, 1965-, et al.
(författare)
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ON ELECTRON HEATING IN MAGNETRON SPUTTERING DISCHARGES
- 2017
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Ingår i: 2017 IEEE International Conference on Plasma Science (ICOPS). - : IEEE.
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Summary form only given. The magnetron sputtering discharge is a highly successful tool for deposition of thin films and coatings. It has been applied for various industrial applications for over four decades. Sustaining a plasma in a magnetron sputtering discharge requires energy transfer to the plasma electrons. In the past, the magnetron sputtering discharge has been assumed to be maintained by cathode sheath acceleration of secondary electrons emitted from the target, upon ion impact. These highly energetic electrons then either ionize the atoms of the working gas directly or transfer energy to the local lower energy electron population that subsequently ionizes the working gas atoms. This leads to the well-known Thornton equation, which in its original form is formulated to give the minimum required voltage to sustain the discharge. However, recently we have demonstrated that Ohmic heating of electrons outside the cathode sheath is typically of the same order as heating due to acceleration across the sheath in dc magnetron sputtering (dcMS) discharges. The secondary electron emission yield γsee is identified as the key parameter determining the relative importance of the two processes. In the case of dcMS Ohmic heating is found to be more important than sheath acceleration for secondary electron emission yields below around 0.1. For the high power impulse magnetron sputtering (HiPIMS) discharge we find that direct Ohmic heating of the plasma electrons is found to dominate over sheath acceleration by typically an order of magnitude, or in the range of 87 - 99 % of the total electron heating. A potential drop of roughly 100 - 150 V, or 15 - 25% of the discharge voltage, always falls across the plasma outside the cathode sheath.
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| 9. |
- 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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