Effect of pulse frequency on the morphology and nanoindentation property of electroplated nickel films

This paper reports the effect of pulse current with different frequencies on the morphology and mechanical properties of nickel (Ni) films deposited by electroplating. The pulse frequency varies from 0 (DC) to 500 Hz while the duty cycle (T-on/T-off) is 1 during electroplating. The average roughness and deposition rate of Ni films decrease with the increasing frequency. The smoothest Ni surface with average roughness of 16.5 nm is achieved at the frequency of 500 Hz while the deposition rate reaches a nearly stable rate of 0.04 mu m/min. The surface concentration of ions does not vary with time at a sufficiently high frequency with a long off time for ion to diffuse onto the surface. It will result in much more nuclei formed on the surface of cathode at a limited growth rate to get small grains for smooth morphology. The nanohardness of Ni film initially decreases rapidly from 3.9 to 1.18 GPa at 0 to 10 Hz, respectively, then increases to about 4.87 GPa in the range of 100-200 Hz, and decreases slowly to 4.0 GPa at 500 Hz. The stiffness of Ni films electroplated by pulse current at 100-200 Hz is higher than that by dc electroplating. The compromised Ni film with smooth morphology, good hardness and proper deposition rate is obtained at frequency of 100-200 Hz under the current density of 3 Adm(-2).