Acree Technologies Inc.

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HiPIMS- High Impulse Power Magnetron Sputtering

HiPIMS (High Power Impulse Magnetron Sputtering) is a specialized thin film deposition technique based on ionized physical vapor deposition. HiPIMS is an energetic process, and is a complex variation of more conventional magnetron sputtering. HiPIMS processes result in improved quality of the film/substrate interface, denser coatings and allow deposition on complex geometries. Another key aspect of HiPIMS is the fact that it is industrially and commercially viable. Thus HiPIMS is an important development for the thin-film coating industry.

The major difference between HiPIMS and conventional techniques such as direct-current magnetron sputtering is that HiPIMS creates substantial ionization of the flux (sputtered material). 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.

Magnetron systems use a cusp magnetic field over the target surface to locally trap the discharged electrons, which confines the plasma at the target surface. This results in a substantial increase in the plasma density, allowing larger currents to be drawn from the plasma at lower pressures.  Since the lower operating pressures increase the mean free path between collisional events, the average energy reaching the substrate increases. This creates higher quality films. However, magnetron sputtering suffers from a significant limitation- thermal load on the target material. Most of the energy in the sputtering process is converted to heat, which can degrade the properties of the target material.

In a HiPIMS process, the magnetron is pulsed, which allows very high instantaneous currents and powers to be used. Power densities can reach levels of 2,800 W/cm2 (compared to 4 W/cm2 for conventional magnetron systems), which produces energetic deposition ions with energies in the range of 50 eV to 100 eV (compared to only about 2 eV to 10 eV in conventional sputtering). These high energy ions essentially compact the coating as it grows, creating very dense coatings. Coatings deposited using HiPIMS  do not have the porosity and columnar features typically found in coatings deposited using conventional sputtering techniques.

In HiPIMS, the deposition flux is largely ionized, increasing both 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. Also, the ions, unlike neutrals, can be accelerated to desired energies and guided in any direction.

HIPIMS allows coatings to be deposited at lower substrate temperatures, because additional thermal energy from the substrate is not needed to form a 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.



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