A new type of oscillation emerging during copper immersion plating on silicon in solutions containing HF was observed. It is the spontaneous oscillation of open-circuit potential rather than the oscillations which have been observed on silicon under high polarization. The oscillation appears at less-noble potential and in a limited HF concentration range, and the amplitude is small. The behavior is affected by the type of dopant and dopant concentration and by the surface condition. The phenomenon is likely to be explained based on reactions occurring during immersion plating in the presence of fluoride ions: the oxide formation-breakdown-repair model. However, some results cannot be simply explained by the model. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.1946369] All rights reserved.