Electroless deposition of CoNi alloy thin films on a Si substrate was investigated by varying different processing parameters. The quality of the film was strongly influenced by the concentration of the electrolyte and the presence of NH4F. A quality adhesive CoNi thin film was formed when the concentration of NiSO4 center dot 6H(2)O exceeded 0.03 M, and this is attributed to self-activation at higher Ni ion concentrations. The presence of NH4F in the electrolyte influenced the crystallinity of the film and the deposition rate. The dominant growth mechanism was demonstrated by OCP (open-circuit potential). The concentration of NH4F affected the composition of CoNi thin films, exerting a complexing effect of ammonium ions in the bath containing more than 0.5 M NH4F. The deposition rate of the film increased with increased NH4F concentration. Hydrazine, used as a reducing agent, did not affect the composition of the CoNi thin film, but the deposition rate increased with an increase of hydrazine. The microstructure and crystalline phase of CoNi thin films deposited by electroless deposition were characterized by a X-ray diffraction (XRD) technique and X-ray photoelectron spectroscopy (XPS). A detailed study of the effects of other processing parameters such as metal ion concentrations, the presence of NH4F, and the amount of hydrazine was also carried out. (C) 2012 Elsevier Ltd. All rights reserved.