10 things you should know about high power impulse magnetron sputtering (HiPIMS)

1. In HiPIMS the power is applied in pulses of low duty cycle leading to high peak power during the pulse on time while cooling the target during the pulse off time avoiding thereby target overheating.

2. The peak power density is the range of few kW.cm-2 compared to few W.cm-2 in conventional magnetron sputtering (dcMS).

3. As a result, the plasma density is 3 orders of magnitude higher than that in dcMS which significantly increases the ionization probability by electron impact allowing the ionization of the sputtered species.

4. The ionization fraction of the sputtered species is a function of the target material and the peak power at the target. The ionization fraction is low for elements with low electron impact ionization cross-section (σi) and high ionization potential (IP) such as carbon (4.5%), but high for element with high (σi) and low (IP) such as titanium (90%).

5. It is possible to increase the ionization fraction for materials such as carbon by increasing the pulse length which is especially desirable for DLC coating deposition to increase the content of sp3 bonding.

6. The high ionization degree leads to high ion flux towards the growing film which enhances the coating properties while avoiding argon atoms sub plantation resulting from flux made of argon ions accompanied by high bias voltage.

CrN coatings deposited by DCMS vs HiPIMS PVD

CrN coatings deposited by DC magnetron sputtering using a conventional magnetron setup (A), and optimized setup with regard to balance and strength configurations (E), and by HiPIMS using three pulse configurations with increasing peak current densities from (B) to (D) and using the configurationin (C) for the optimized magnetron setup.

Reference: J.Alami et al. / Surface & Coatings Technology 255 (2014) 43-51

7. The deposition rate in HiPIMS is lower as compared to conventional sputtering especially in the case of metal deposition because of self-sputtering that translates the fact that metal ions are back attracted by the negatively bias voltage.

8. The deposition of compound materials with reactive HiPIMS can result in high deposition rate as the hysteresis effect is reduced.

9. Optimizing the magnetic field strength and unbalancing degree of the magnetron’s magnet can lead to high deposition rate through a significant reduction of the back attraction probability and increase of ionization probability near the substrate.

10. Some relevant parameters to consider in the optimization of pulsing configuration are the gas rarefaction, the degree of ionization of the sputtered metal species, and the reduction of deposition rate due to self-sputtering.