complete target surface can occur before it is sputter-cleaned again, leading to arc events.) A setting of 10 rpm is sufficient for most reactive processes.
Finally, rotating cylindrical magnetrons have also proven to be useful for applications that require AC sputtering from two targets. The AC switching technology was introduced to circumvent the problems caused by arc discharges (by periodically discharging the cathode) and the disappearing anode problem (by sputter cleaning the target, which becomes an anode in the next cycle). However, on planar magnetrons, the magnetic field above the target surface that is used to enhance the plasma density impedes the flow of electrons to the target, resulting in a limited anode functionally. In rotating cylindrical magnetrons, the magnetic field-free area and the total effective surface are much larger, resulting in enhanced anode functionality.
Bottom Line BenefitsFor planar magnetrons, the presence of a racetrack groove limits target consumption, thereby increasing the cost of operating the technology. Although a stationary plasma track is also present during sputter deposition with a rotating cylindrical target, no racetrack groove corresponding to the magnet configuration is formed in the rotating target. As a result, very high target material utilization can be achieved.
Although the target utilization of cylindrical magnetrons is several times higher than a planar magnetron, up to 40% of that utilization can be gained or lost by the target and magnet setup at the end of the target tube. Using a dog bone-shaped target rather than a straight target can help increase target consumption (see Figure 4). Additionally, by strategically placing additional magnets on the target tube to provide a “double racetrack,” in which the turns are slightly shifted, virtually complete target consumption (up to 90%) can be achieved (see Figure 5).
In addition to providing increased target consumption efficiency, rotating cylindrical magnetrons also enhance the production process in several other ways. In some coating applications, higher deposition rates are preferred. This requires both a higher machine throughput (achieved through higher power levels) and an increased coating capacity. For planar targets, the use of higher power levels is not always possible because the target material can melt or crack under the thermal load. In rotating cylindrical targets, the thermal load is uniformly distributed over the complete circumference of the target, resulting in much more efficient cooling of the target tube and the ability to use higher power densities.
Rotating cylindrical targets also offer a higher coating capacity compared to a similar standard planar target. This is due to the higher target utilization of the rotating cylindrical target, as well as the larger amount of available target material. (In some cases, the available target material is up to three times larger because of the circumferential design.) As a result, the life of the cylindrical target is often five to 10 times higher than with a planar magnetron.
Optimized SputteringThe rotating cylindrical magnetron provides a valuable alternative to planar magnetrons. Because the target tube rotates over a stationary closed-loop racetrack, the system overcomes most of the shortcomings associated with the typical erosion groove formation in planar magnetrons. Almost complete target consumption can be achieved by optimizing the magnet bar configuration. The system offers a reduced arc rate and better anode functionality in an AC switching mode, and it can also generate higher power densities and sputter yields because the heat load is uniformly spread over the complete target tube surface. Finally, since a tubular target contains about three times more material than a planar target for the same width, the target lifetime or coating volume can be five to 10 times higher compared to planar magnetrons.
With the rotating cylindrical magnetron, high-quality coatings can be applied easily and cost-effectively even in large-area and high-volu