In the past, we have discussed numerous forms of Physical Vapor Deposition (PVD) technologies including Sputtering (r.f. and DC), Resistance Evaporation, Electron Beam Evaporation, and Pulsed Sputter Deposition. In this article I would like to review Cathodic Arc Deposition. This is a form of Physical Vapor or Arc – PVD whereby an electric arc is directed toward a target material and vaporizes the cathodic target in a vacuum. When properly configured in a vacuum deposition system, this vapor can be condensed onto a substrate forming a thin film. Originally developed in the Soviet Union during the cold war, Arc-PVD has become a widely used technology in both Research & Development applications as well as a broad range of production applications including hard coatings and decorative coatings.
The basic process utilizes a DC Power Supply to apply an electric arc of low voltage high current which is directed toward a cathodic target of the desired composition to be deposited. The arc forms a highly focused stream of electrical energy forming a small spot size area on the target surface, heating it to above the melting point. This “Cathodic Spot” generates a great deal of heat over a small area, usually in the neighborhood of 1500°C or so, vaporizing the target material on a localized level, creating a bore or crater in its wake. The arc is self extinguishing, and then reignited in an area of close proximity to the previous location on the target surface. This charge – recharge (ignite – reignite) process of arc formation is continuous, forming a series of spot formations, or arcs, across the target surface. Like the stream of electrons formed in an Electron Beam Source, this localized arc has a high power density with an associated high ionization potential. This allows for the introduction of a magnetic field to be applied to the arc which, in turn, can direct the current around the profile of the target surface. This electromagnetic field can be programmed to provide a uniform deposition across the entire cathodic target surface. Again, this magnetic flux is similar to that of an Electron Beam source design. The magnetic fields must be controlled systematically, usually through a numerically controlled system or computer, in such a way as to not allow the cathode spot to stay in any one area too long, forming droplets of liquid evaporant which can cause pinholes or other detrimental flaws when condensed onto the substrate as resultant films.
Over the last 30 – 50 years or so, the basic Russian design has been altered and improved over time but the original concept, mainly developed by L.P. Sablev, et al., consisting of a short cylindrical target of conductive material with a top face exposed for deposition. Like the dark space shield used in the design of a sputtering cathode assembly, the Sablev cathode design uses an electrically floating ring assembly just outside the parameter of the target source as an arc confinement ring. In practice a simple remote ground potential, or igniter, is applied to temporarily short circuit the system to initiate the arc. The arc is then sustained and directed via. the electromagnetic field to provide a uniform homogeneous resultant film. A reactive gas can be introduced in the chamber during the evaporation processing to provide for disassociation, ionization and excitation during with the ion flux to provide composite resultant films.
As previously stated, the electric arc striking the target surface generates a great deal of heat, although localized. However, over time, as the arc location is directed through the use of a computer program, the entire target heats up. This heat must be dissipated through the water cooling channels associated with the cathode design. For highly conductive metallic targets this can easily be facilitated through a cooling channel in the cathode assembly which surrounds the electromagnets at the bottom of the target. For ceramic materials, with lower thermal conductivities, this can be a problem. Since the geometry of the cylindrical targets are usually quite “thick” or “long”, to provide for greater target utilization, the heat that is generated at the target surface has to be dissipated through the thickness of the target through to the water cooling channel within the cathode design – at the bottom of the target cylinder. In addition, many designs utilize some form of “quick disconnect” to allow for the rapid change of the targets after they are fully eroded. This design may include a simple threaded rod or cavity located on the bottom of the target or it may incorporate a “Bayonet” design with flutes built into the sidewalls of the target. For ceramic targets these designs offer a challenge in the manufacturing process as they may require diamond grinding of surfaces or the bonding of conductive backing plates, adding to cost of the assembly.
The same principles can be employed for rectangular cathode assemblies for use in systems requiring a linear deposition process. Although less popular, there are many cathodic arc designs used for decorative and hard coating applications where a broader coating area is required. Large cathodic arc systems are often used in industrial and decorative coating applications where substrates are rotated around a series of linear cathodic arc sources, usually vertically, in a batch process to produce a variety of thin film species.
There is a broad range of applications for Cathodic Arc Deposition. It is possible to synthesize extremely hard coatings (TiN, CrN, TiAlN, AlCrTiN, TiAlSiN, etc.) for wear resistance on tooling surfaces such as cutting tools, dies and machinery parts. Additionally, it is possible to process carbon ion deposition to produce diamond like coatings with improved wear resistance. Industries served include aerospace, marine, automotive, pumps, hydraulics, pneumatics, defense, medical, machinery, tool & die, etc.
Plasmaterials, Inc. provides Cathodic Arc Sources for almost all commercial systems as well as those independently developed. Please contact your Plasmaterials, Inc. Sales Engineer for a price and delivery quotation for your production as well as developmental material requirements.