The effects of process conditions on the residual stress and composition of electroless nickel films for MEMS

摘要

Properties of six-micron-thick films of electroless nickel grown on evaporated Ni seed layers were measured as a function of bath conditions. The bath variables were temperature, pH, and hypophosphorous acid concentration. Residual mechanical stress at room temperature was measured by a bulge test method. Growth rate was determined by profilometry, crystalline composition by XRD, and phosphorus content by EDS. Stress was sensitive to all bath variables, and the range encountered was - 4 MPa to 250 MPa. Phosphorus content correlated strongly with pH and nickel crystallinity as reported elsewhere, and a possible mechanism for its effect on stress is discussed. The properties of some of the films make them promising candidates for structural applications in microelectromechanical devices.