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Properties of 6-μm-thick films of electroless, phosphorus-containing nickel grown on evaporated Ni seed layers were measured as a function of bath conditions. The bath variables were temperature, pH, and hypophosphorus acid concentration. Residual mechanical stress at room temperature was measured by a bulge test method, as was elastic modulus. Growth rate, crystallinity, and phosphorus content were also measured. Stress was sensitive to all bath variables, and the range encountered was 4 MPa compressive to 255 MPa tensile. A proper set of nickel growth conditions combined with the use of a stiction-inhibiting parylene-D film led to the successful fabrication of a self-supported roof structure forming a large-area, sealable cavity.