Continuous operation cathodic vacuum arcs (DC-CVA) are widely employed in PVD coating industries. In general, pulsed cathodic vacuum arcs (pulsed-CVA) have a greater current and plasma density as well as a more stable and repeatable plasma density than their DC counterparts.
If a high repetition rate can be achieved, the deposition rate of pulsed-CVAs is comparable to or higher than that of conventional DC-CVAs, but the macroparticle production rate decreases.
The pulsed arc system is required for fabricating ultrathin films and multilayers with carefully regulated thickness.
DC-CVAs generate many macroparticles, however the density of filtered DC-CVAs varies on a millisecond timeline due to unstable arc spots and on a few-second timescale due to variations in the plasma coupling to the magnetic macroparticle filter. In these circumstances, it is very difficult to produce ultrathin, repeatable films, and there is a great deal of colour instability for decorative coatings. First, it impedes production by establishing greater cathode-to-target distances and, clearly, by producing varied thicknesses and hues on 3-D surface components.
Pulsed plasma sources are also constructed such that plating-free implantation may be accomplished. Most of the ions in the plasma sheath will be implanted at the bias voltage if a DC bias is applied to a substrate in pulsed arc plasma. If the plasma is totally ionized, as is the case with a continuous or filtered cathodic vacuum arc, there is no deposition of neutral metal atoms during the pulse, which results in pure metal ion implantation and, as a result, the loss of wider colour variations in the decorative coatings.
Instead, a pulsed vacuum arc (pulsed-CVA) may produce plasma with a steady density during each pulse. This facilitates the regulation of the sheath's dynamics and the uniform density of the plasma. Pulsed-CVA technique may be utilized to deposit films with predetermined thicknesses. This is accomplished by calculating the amount of material deposited each pulse and the number of pulses required to obtain the desired thickness.
Pulsed-CVA studies imply that as long as the arc pulse is brief, the plasma density is not too low, and that the sheath will not grow to the chamber walls during the pulse if the plasma drift speed is kept high.
For economically viable thin film deposition, a pulsed arc must have a comparable deposition rate to other sources. There are two straightforward approaches to raise the deposition rate: increasing the pulse frequency or the arc current. These two measurements are constrained by power supply electronics.
The figure below shows SEM images of different TiAlN compositions as a function of increasing the duty cycle, a consequence of increasing the frequency.
Given that the erosion rate is proportional to the arc current, this current profile results in an extremely high erosion rate towards the center of the cathode, where the arc spots are triggered, and a very low erosion rate around the cathode's perimeter. To balance out the erosion profile over the cathode surface, a power source with a current profile that continuously rose throughout the pulse is required.
The current manipulation must be regulated to match the velocity of the cathode spots to obtain maximum cathode surface coverage and prevent the spots from exceeding the cathode surface's edge. The circuit breaker is necessary to redirect the current away from the plasma while maintaining the circuit's remaining energy.
The deposition rate of a pulsed arc may be increased in two ways: by increasing the current or the frequency. It is always recommended by electrical engineering experts to raising the current while modifying the frequency to establish a compromise between frequency and current.
The arc current should be maintained at a level sufficient to sustain the benefits of the retrograde repulsion caused by many arc spots, notably the reduction in macroparticle emission and the improvement in erosion profile management.