Controlling preferential growth of chromium – Nitrogen R-HiPIMS and R-DCMS films by substrate magnetic biasing

Abstract

The effect of magnetic biasing on the structure of Cr-N coatings deposited on silicon substrates by reactive magnetron sputtering has been investigated. The magnetic biasing setup consisted of a permanent magnet placed close to the substrate holder to modify the plasma species dynamics and deposition flux. Three magnetic field configurations for reactive direct current magnetron sputtering (R-DCMS) and reactive High Power Impulse Magnetron Sputtering (R-HiPIMS) were compared. Deposition parameters such as deposition time, gun power, substrate distance, temperature, gas pressure, and gas composition were constant through the six R-DCMS/HiPIMS-magnetic-field combinations. Processes were monitored through optical emission spectroscopy (OES) and closely compared to the voltage and current curves at the target/substrate. An excitation mechanism was proposed accounting for the enhanced ionization detected by OES and the implications in the film’s growth. The films’ stoichiometry, structure, thickness, morphology, and crystal texture were characterized and associated with the process parameters. The R-DCMS processes led to Cr-N solid solution films, while the enhanced reactivity of R-HiPIMS plasma species increased the N content and formed CrN. Overall, the R-DCMS deposited samples were thicker than the R-HiPIMS deposited samples, but the different magnetic field biasing setups allowed for specific control of films’ thickness, texture, and microstructure.