Structure and physical properties of nickel films deposited by microwave plasma-assisted cathodic sputtering

Nanocrystalline nickel films have been deposited by microwave plasma-assisted sputtering from pure argon discharges on steel and (100)-oriented single crystal silicon wafers mounted on a water-cooled substrate holder biased to various direct current voltages ranging from 0 to -120 V. The crystallographic structure and surface morphology of films were determined by x-ray diffraction techniques and atomic force microscopy, respectively. The magnitude of compressive residual stresses (intrinsic stress) calculated from the radius of curvature of Si substrates reached a maximum value of -250 MPa in films deposited on grounded substrates and decreased with increasing negative substrate bias voltage. The hardness of films was determined by nanoindentation as a function of the substrate bias voltage. Alumina ball-on-disk tribological tests of films deposited on steel substrates were conducted in room air at 20 deg C under a load of 1 N with a sliding speed of 50 mm s-1. The value of the stabilized friction coefficient was in the range 0.35-0.45 for 5000 cycles. Beyond 5000 cycles, the films were worn and the friction coefficient increased rapidly. The electrical resistivity of films deduced from the thickness and sheet resistance of films determined by four point probe measurements was approximately equal to 13 muOmega cm.