The cathode spot of a vacuum arc generates a spray of liquid droplets directed almost parallel to the cathode surface as well as a highly ionized plasma jet directed normal to the cathode surface. Theories include droplet ejection by the reaction force of back-streaming ions on the underlying microscopic liquid pool and formation from explosive debris. The droplets have an exponentially decreasing size distribution and velocities ranging from 10 to 800 m s-1. During their motion in the arc, the macroparticles can be further accelerated and deflected, obtain a negative charge, be heated to temperatures of around 2000 °C and evaporate. The macroparticle mass emission rate from the cathode increases with increasing arc current and average cathode surface temperature and decreases with increasing cathode material melting temperature. Cathodes with gaseous surface layers have less macroparticle erosion than clean cathodes. Droplet production can be reduced by maintaining as low a temperature as possible on the cathode surface near the cathode spots by providing effective cooling, by operating at low cathode current densities, by using magnetic fields to provide for directed rapid cathode spot movement and, in reactive deposition, by operating a poisoned cathode. Macroparticle inclusions can be reduced by substrate biasing and by concentrating the plasma flow with magnetic fields and can be eliminated completely by using a curved magnetic plasma duct.

Macroparticle contamination in cathodic arc coatings: generation, transport and control☆

An apparatus for the application of coatings in a vacuum comprising a plasma duct surrounded by a magnetic deflecting system communicating with a first plasma source and a coating chamber in which a substrate holder is arranged off of an optical axis of the plasma source, has at least one deflecting electrode mounted on one or more walls of the plasma duct. In one embodiment an isolated repelling or repelling electrode is positioned in the plasma duct downstream of the deflecting electrode where the tangential component of a deflecting magnetic field is strongest, connected to the positive pole of a current source which allows the isolated electrode current to be varied independently and increased above the level of the anode current. The deflecting electrode may serve as a getter pump to improve pumping efficiency and divert metal ions from the plasma flow. In a further embodiment a second arc source is activated to coat the substrates while a first arc source is activated, and the magnetic deflecting system for the first arc source is deactivated to confine plasma to the cathode chamber but permit electrons to flow into the coating chamber for plasma immersed treatment of the substrates. A load lock shutter may be provided between the plasma duct and the coating chamber further confine the plasma from the first arc source.

Filtered cathodic arc deposition method and apparatus

Vacuum arc plasma deposition combined with magnetic filtering of the plasma to remove macroparticles is a promising technique for the production of metallic, compound and hard amorphous carbon thin films. High efficiency of the magnetic filter is a crucial parameter for the application of this technique. We report investigations of the influence of different filter designs, magnetic field configurations and electric potentials on the filter efficiency. We analyse the transport mechanisms on which the flow of plasma through the filter is based, and describe and discuss the occurrence of instabilities in magnetic filters. With an optimum filter arrangement we were able to obtain a filter output of 25% of the total number of ions produced by the vacuum arc discharge.

http://iopscience.iop.org/article/10.1088/0963-0252/4/1/001/pdf

Transport of vacuum arc plasmas through magnetic macroparticle filters

The investigation concerned the corrosion behaviour of macroparticle and growth defects in PVD CrN/NbN superlattice coatings formed by are bond-sputtering (ABS) process on a mild steel BS6323. The electrochemical behaviour of the coatings was firstly studied by potentiodynamic polarising in de-aerated 0.5 M (Na2CO3-NaHCO3) buffer and 5% NaCl solutions, respectively. The coating and defects were then examined in planar view and cross-section by scanning electron microscopic analyses and the results were compared with those prior to the electrochemical measurement. It is found that the overall coating/substrate corrosion process is closely related to the deleterious effect of the macroparticles and growth defects in the PVD coatings. It is further demonstrated that for through thickness macroparticle inclusions, corrosion initiates by galvanic or crevice corrosion between the defect and the coating matrix, subsequently permitting solution access to those defects with eventual substrate pitting and corrosion at the coating/substrate interface. On the basis of the experimental findings and the macroparticle formation theory, the mechanisms of the growth defect-related coating/substrate corrosion are finally proposed. (C) 2000 Published by Elsevier Science S.A. All rights reserved.

The corrosion behaviour of macroparticle defects in arc bond-sputtered CrN/NbN superlattice coatings

The macroparticle contamination of vacuum-arc-deposited thin films generated by a plasma source with an optional axial magnetic field is studied. Emphasis is placed on the macroparticle flux near the discharge axis. The arc current, metal species, deposition system geometry and axial magnetic field strength are varied. Distribution functions for macroparticles of Pb, Ag, Cu, Pt, W, and Ni are determined, normalized to the film thickness deposited or the charge transferred. The application of the axial magnetic field leads to a considerable reduction of the normalized macroparticle flux since the plasma is effectively focused by the field, whereas the macroparticle production is not influenced. The macroparticle content normalized to the deposited film thickness is reduced to about 20-35% of that without an additional magnetic field. >

On the macroparticle flux from vacuum arc cathode spots

In this study, thin films of titanium nitride were prepared by the arc ion plating process and deposited onto polished WC-Co substrates to investigate macroparticles (MPs), morphology and surface roughness. The deposition variables explored were arc current, deposition time, substrate distance, nitrogen pressure, substrate bias, target thickness and electromagnetic coil current of the target. The results show that the number of MPs and their area ration vary directly with arc current, deposition time and target thickness, inversely with substrate distance, substrate bias and nitrogen pressure. Positive relationships exist between the deposition rate and the number of MPs, and between the deposition rate and the surface roughness.

Macroparticles on TiN films prepared by the arc ion plating process

Preparation of films using the arc ion plating (AIP) process encounters a significant problem in that macroparticles are produced. To overcome this problem, the effect of a modified AIP source, characterized by the presence of a magnetic field on the plasma stream, has been investigated. The surface properties of TiN films were examined by varying the magnetic field strength and the pressure of nitrogen; quantitative measurements were made using an image analyser. It was found that the number of macroparticles could be reduced to 10% of that of the conventional process and that a high deposition rate, similar to that of the conventional process, could be achieved.

K. Akari

Papers

Macroparticles on TiN films prepared by the arc ion plating process

Reduction in macroparticles during the deposition of TiN films prepared by arc ion plating