An overview of the current state of vacuum-arc-based coating technology is presented, with particular emphasis on defining those areas where further investigation would reap the greatest benefits. Particular attention is given to the 'continuous' cathodic arc, which is currently the best understood approach and which has been most successfully adapted for large-scale commercial coating in the United States. It is noted that the greatest promise of ion-based coating technology based on the vacuum arc is the potential for increased control over the coating process. Unlike the case for neutral coating atoms, the presence of a charge on coating ions gives a 'handle' to exert forces on them using electrostatic fields. One can in theory control the trajectory of these ions between the coating source and part to be coated. One can also control the energy with which they impact the substrate. It may even be possible to control the extent of their reactivity. >

Coating technology based on the vacuum arc-a review

"The Foundations of Vacuum Coating Technology" is a concise review of the developments that have led to the wide variety of applications of this technology. This book is a must have for materials scientists and engineers working with vacuum coating in the invention of new technologies or applications in all industries. With over 370 references, this is an excellent starting point for those who don't want to reinvent the wheel. In particular, the book is a valuable reference for those interested in researching proposed or existing patents. This unique book provides a starting point for more in-depth surveys of past and recent work in all aspects of vacuum coating.The author uses his extensive knowledge of the subject to draw comparisons and place the information into the proper context. This is particularly important for the patent literature where the terminology does not always match industry jargon. A section of acronyms for vacuum coating and glossary of terms at the end of the book are critical additions to the information every reader needs.

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The Foundations of Vacuum Coating Technology

In this paper the ionization and energy characteristics of the particle flux impinging TiN films during arc vapor ion deposition are described. Langmuir probe measurements of voltage and current were made using a planar shielded substrate as the probe. Plasma species were observed using emission spectrometry. Substrate mass gain was measured as a function of voltage and nitrogen pressure. Ion current to the substrate was eliminated by applying a negative voltage to a fine wire screen located in front of the substrate and, at the same time, applying a positive voltage to the substrate. The ionized fraction of the titanium vapor at the substrate was determined by comparing the deposition rate obtained while excluding ions with the deposition rate obtained under normal conditions when ions were part of the depositing flux. The Langmuir probe measurements were used to estimate the plasma parameters and the average ion energy at the substrate. The results are as follows: (1) in the absence of a nitrogen gas discharge, the density of nitrogen ions is small; (2) most of the titanium vapor is ionized; (3) the average charge carried by titanium ions to the substrate during TiN deposition is (1.6 ± 0.3)e; (4) the average energy of titanium ions at the substrate is approximately 1.6e(10 + |Vs|) eV, where Vs is the negative substrate bias.

Ion flux characteristics in arc vapor deposition of TiN

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

A combined d.c.-pulse bias voltage was used in combination with a cathodic arc evaporation process for the deposition of TiN on planar plates and drilling tools at substrate temperatures T between 330 and 500 °C. This new pulse technique appeared to be a powerful tool to achieve independent control of the substrate temperature, coating adhesion and uniformity of deposition. As a result, high coating adhesion can be obtained at low substrate temperatures. The adhesion uniformity across large-area samples is considerably improved. Unpolished rough substrate parts can be coated without cauliflower-like growth defects. Because of intensive ion bombardment in the pulse period, smoother TiN coatings with a reduced droplet size were obtained.

Improved control of TiN coating properties using cathodic arc evaporation with a pulsed bias

Cathodic arc deposition is a unique technology. An arc spot on a cathode generates a plasma consisting of cathode material with a high degree of ionization. The high concentration of ions allows control of film morphology, high adhesion, efficient reactive deposition of compounds and uniform deposition over a variety of shapes. The composition of the alloys is generally retained from source to substrate. Deposition rates cover a wide range from nanometers per minute to tens of micrometers per minute. Many aspects of the technology warrant further study and its applications are only just beginning.

Gottfried K. Wehner

Papers

Cathodic arc deposition technology