HiPIMS

HiPIMS is a variation of more conventional magnetron sputtering. In sputtering a negative potential on a target surface accelerates ions in a plasma towards the surface. The momentum transfer of this impinging flux results in the release of material from the target surface through a cascade collision process in the target. In a magnetron system, the use of a cusp magnetic field over the target surface locally traps the discharge electrons confining the plasma at the target surface. The result is a substantial increase in the plasma density allowing larger currents to be drawn from the plasma at lower pressures. This allows films of higher quality to be fabricated by increasing the average energy reaching the substrate since the lower operating pressures used increase the mean free path between collisional events.

A limitation of magnetron sputtering is the thermal load on the target material since most of the energy input in a sputtering process is converted to heat. By pulsing the magnetron, very high instantaneous currents and powers can be achieved while maintaining a reduced thermal load on the target. Power densities can reach levels of 2,800 W/cm2 compared to 4 W/cm2 for conventional magnetron systems. There are a number of advantages to HiPIMS deposition unrelated to the thermal benefits for the target. For example, the high peak power produces energetic deposition ions with energies in the range of 50 eV to 100 eV. Because of this, very dense coatings are produced that do not have the porosity and columnar features often found in coatings deposited using conventional sputtering techniques, where the add-atom energy is only about 2 eV to 10 eV. The high energy ions essentially compact the coating as it grows. HIPIMS allows dense coatings with excellent properties to be produced at lower substrate temperatures, because additional thermal energy from the substrate is not needed to form tight crystal structure. In addition, the energetic ions tend to produce coatings with better adhesion properties, because they have sufficient energy to slightly implant into the substrate surface, producing a tenacious bond. Because of the compaction effect of the ions, HIPIMS coatings also tend to be under compressive stress. The compressive film stress level is controllable by setting the peak power density, since the ion energy scales with peak power. HIPIMS is also capable of higher deposition rates than conventional sputtering approaches since the power can be increased without detrimental target temperatures being reached.

As can be noted from the above HiPIMS is an energetic deposition processes. The deposition flux is largely ionized increasing its reactivity in the gas phase and the deposited energy at the substrate. The background gas also becomes ionized through collisional and charge exchange coupling. For reactive processes, such as oxide deposition from a metal target, the result is an ionized metal and reactive gas flux. This leads to increased reactivity at the film surface and higher quality films.