Growth responses of ultrathin CN_x overcoats to process parameters

Ultrathin CN_x overcoats were grown using pulsed dc magnetron sputtering. Substrates were mounted on a holder that allowed 45° tilt angle and rotation. Effects of process parameters on film growth were reviewed. AFM scans over large sampling areas show that thin CN_x films obtained at - 100 V substrate bias with 45° substrate tilt and 20-25 rpm rotation have r.m.s. roughness about 0.2-0.3 nm when sampled over 20 × 20 μm ² areas, increasing to ∼ 0.45 nm when sampled over ∼ 0.05 × 3 cm² using X-ray reflectivity measurements. These 1-2 nm thick ultrasmooth coatings reduced corrosion damage compared with coatings of the same thickness grown without substrate tilt and rotation. This improved performance is likely a result of more efficient and uniform momentum transfer parallel to the surface during deposition in this configuration. In addition, detailed X-ray reflectivity measurements showed that the mass density of these CN_x films is ∼ 2.0 g/cm³, independent of film thickness from ∼ 1 to 10 nm, consistent with ion beam analysis.