The origin of Bohm diffusion, investigated by a comparison of different modelling methods

Bultinck, Evi; Mahieu, Stijn; Depla, Diederik; Bogaerts, Annemie

doi:10.1088/0022-3727/43/29/292001

Cited by 27 publications

(18 citation statements)

References 17 publications

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“…266 Measurements of oscillating electric fields in the megahertz range in this and other devices 262,267 are also consistent with the MTSI as discussed earlier. Lundin et al 262 demonstrated that the frequency dependence on the ion mass and the magnetic field strength corresponds to lower hybrid oscillations when the fraction of the ions of the sputtered vapor is roughly 80% of the total ion density.…”

Section: Arsupporting

confidence: 81%

High power impulse magnetron sputtering discharge

Guðmundsson¹,

Brenning²,

Lundin³

et al. 2012

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

603

437

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The high power impulse magnetron sputtering (HiPIMS) discharge is a recent addition to plasma based sputtering technology. In HiPIMS, high power is applied to the magnetron target in unipolar pulses at low duty cycle and low repetition frequency while keeping the average power about 2 orders of magnitude lower than the peak power. This results in a high plasma density, and high ionization fraction of the sputtered vapor, which allows better control of the film growth by controlling the energy and direction of the deposition species. This is a significant advantage over conventional dc magnetron sputtering where the sputtered vapor consists mainly of neutral species. The HiPIMS discharge is now an established ionized physical vapor deposition technique, which is easily scalable and has been successfully introduced into various industrial applications. The authors give an overview of the development of the HiPIMS discharge, and the underlying mechanisms that dictate the discharge properties. First, an introduction to the magnetron sputtering discharge and its various configurations and modifications is given. Then the development and properties of the high power pulsed power supply are discussed, followed by an overview of the measured plasma parameters in the HiPIMS discharge, the electron energy and density, the ion energy, ion flux and plasma composition, and a discussion on the deposition rate. Finally, some of the models that have been developed to gain understanding of the discharge processes are reviewed, including the phenomenological material pathway model, and the ionization region model.

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Section: Arsupporting

confidence: 81%

High power impulse magnetron sputtering discharge

Guðmundsson¹,

Brenning²,

Lundin³

et al. 2012

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

603

437

View full text Add to dashboard Cite

show abstract

“…ge EFF   , a result also reported from recent particle in cell Monte Carlo simulations [22]. In pulsed DCMS and…”

Section: Transport Driven Electric Fields E Ztranssupporting

confidence: 74%

Understanding deposition rate loss in high power impulse magnetron sputtering: I. Ionization-driven electric fields

Brenning¹,

Huo²,

Lundin³

et al. 2012

Plasma Sources Sci. Technol.

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The lower deposition rate for high power impulse magnetron sputtering (HiPIMS) compared to direct current magnetron sputtering for the same average power is often reported as a drawback. The often invoked reason is back-attraction of ionized sputtered material to the target, due to a substantial negative potential profile from the location of ionization towards the cathode. Emitting and swept Langmuir probes have yielded space-and time resolved electric potential profiles and electron energy distributions, Rogowski coils have been used to obtain current density distributions. Also, space-and time resolved, and fast imaging techniques show how the time evolution of the discharge structure varies with gas pressure and species. This combined data set is here used to benchmark two different types of plasma models for different regions of the HiPIMS discharges, with special focus on the problem of electric fields z E in the high density plasma region and their effect on the transport of ionized sputtered material. We propose two different mechanisms to be dominating in different regions: "ionization driven" , z ioniz E in a rather stable ionization region extending a few cm from the target, and "transport driven" , z trans E in the highly dynamic surrounding bulk plasma.2

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“…The simulation study based on the high frequency electric field instabilities showed matched Bohm diffusion parameter of 0.05 [6] albeit the key parameter in this paper is the ratio of electron gyro-frequency to the electron collisional frequency, which is different from the discussions in this paper since here the key parameter is the ratio of ion gyrofrequency to the ion-neutral collision frequency. In this paper, an alternative explanation for the cases of large amount of cross-field diffusion is introduced, which is based on the gyro-center shift current.…”

Section: Introductioncontrasting

confidence: 63%

Analysis of Bohm Diffusions Based on the Ion-Neutral Collisions

Lee

2015

IEEE Trans. Plasma Sci.

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Three experimental cases of cross-field diffusions in the magnetized plasmas reported to be related with Bohm diffusion are investigated based on the ion current induced by the ion-neutral collisions. High diffusion coefficient for the original Bohm/Simon experiments and the recent experiments of strongly pulsed plasmas can be explained by the gyro-center shift current combined with the short circuit effect, which is different from the turbulence-induced transport of nuclear fusion devices. It can be deduced that Bohm's interpretation of diffusion with 1/B dependence came from the fact that the short circuit effect of his experiment was limited by the parallel ion velocity. The ratio of azimuthal current density to the discharge current density measured in the pulsed magnetron experiments is analyzed to be constant and independent from the magnitude of magnetic field due to the maximum condition for the Pedersen conductivity.Index Terms-Bohm diffusion, ion-neutral collision, plasma confinement, short circuit effect.

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The origin of Bohm diffusion, investigated by a comparison of different modelling methods

Cited by 27 publications

References 17 publications

High power impulse magnetron sputtering discharge

High power impulse magnetron sputtering discharge

Understanding deposition rate loss in high power impulse magnetron sputtering: I. Ionization-driven electric fields

Analysis of Bohm Diffusions Based on the Ion-Neutral Collisions

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