One of the more recent entries in the field of Physical Vapor Deposition (PVD), and more specifically to Magnetron Sputtering, is being referred to as High Power Impulse Magnetron Sputtering (HiPIMS) discharge. This has evolved from an academic research tool to an extremely useful technology for industrial applications. HiPIMS is a plasma-based process, like conventional magnetically enhanced sputtering technology, yet applies a different method of operation.
The material that is being sputtered is highly ionized during the coating process. Utilizing conventional magnetron sputtering cathode assemblies, HiPIMS incorporates power supplies that are specially designed and developed pulsed power signals at very high peak power densities.
In HiPIMS, a high peak voltage and high power density is applied directly to the surface of the sputtering target in unipolar pulses at relatively short pulse lengths (the length of time that the signal is in the “on” state) with equally low frequencies (length of time to complete a cycle) and long periods of time between cycles (“off” state). Pulse durations can vary in the range of 50 to 200 microseconds (µs) with frequencies in the range of 500 cycles per second (Hz) while the time between cycles can be as little as several hundredths of a second with a duty cycle of <10%.
What all this provides is a high ionization potential (plasma density) to the sputtered species. This is a significant advantage over conventional DC magnetron sputtering where the plasma species consist mainly of neutral particles. As a result, this minimizes the heat generated at the target surface. For poorly conductive or ceramic (metal oxide or metal nitride) compositional target materials that are typically bonded to water cooled backing plates with low melting temperature solders, this provides a tremendous advantage for many industrial applications where high deposition rates for maximum product throughput are desirable.
Additionally, HiPIMS discharge provides for much better control of the nucleation and growth associated with the formation of the resultant films. The lack of radiant heat emanating from the target surface allows for a much shorter substrate-to-source distance.
To operate a conventional magnetically enhanced cathode assembly in an HiPIMS mode the pulse technique requires a specially designed power supply that generates unipolar pulses. The HiPIMS power supply operates at the same average power levels as comparable DC or MF power supplies, but the
discharge is pulsed with a low duty cycle resulting in peak power in the megawatt range and current in the kiloampere range.
One of the main advantages to using the HiPIMS technology is to provide greater control of the deposition parameters that determine the morphology and structure of the resultant films. The ionized target material in the plasma results in significant modification and improvements to the properties of the films being produced on the substrate surfaces. Such properties as film density, hardness, surface topography, refractive index, adhesion, etc. etc. etc. can all be modified and enhanced based on the selection and control of the applied deposition parameters. HiPIMS discharge results in a high-density plasma and a high ionization fraction of the sputtered vapor which enables better control of film growth by controlling the energy and direction of the deposition species.
