Surface Smoothing of Electroless Pure Nickel Films Using Hydrazine as a Reducing Agent

This investigation of hydrazine usage as a reducing agent for surface smoothing of electroless pure nickel films suggests that hydrazine oxidation generates inert nitrogen gas and reducing hydrogen species simultaneously. From a basic bath containing 0.40 M hydrazine, a pure, black nickel film was obtained at a 2.88 μm/h deposition rate, but the film exhibited needle-like crystalline morphology. Electrochemical measurements revealed the oxidation current density of hydrazine as markedly higher than that of either hypophosphite or dimethylamine borane（DMAB）. Thermal desorption spectroscopy （TDS） revealed that the nickel film obtained from the basic bath contained little hydrogen and that nitrogen species were simultaneously adsorbed onto the surface. Even when the hydrazine concentration was reduced to 0.04 M, no marked decrease in the deposition rate was observed. A smooth, light-gray crystalline film was obtained. Investigation into aeration and agitation effects on the deposition rate revealed that nitrogen bubbling had no noticeable effect, that air bubbling suppressed deposition, and that agitation enhanced it considerably. Addition of Te （IV） compounds enabled excellent coverage and selective deposition, even in thin films. Successful formation of smooth pure nickel films has greatly enhanced the applicability of electroless nickel plating.