Pulse plating of copper onto a rotating disk electrode with and without additives

Pulse plating of copper onto a rotating disk electrode in a sulfate plating bath with and without additives has been studied. Unlike most previous studies which have been limited to a range of low pulse frequencies, this research has been concerned with pulse plating over a wide range of pulse frequencies (50 Hz to 50 kHz), partially to move thoroughly investigate the effect of the electrical double layer. It has included the development of a mode for pulse plating of copper in the absence of additives and an experimental study of the effect of DC and pulse plating on the morphology of copper deposits in the presence of the additives chloride, thiourea (TU), benzotriazole (BTA) and polyethylene glycol (PEG).;A model for galvanostatic pulse plating via pulse current (PC) and pulse reverse (PR) modes has been developed and compared with experimentally obtained electrode responses during copper deposition. In addition to all forms of mass transport, electrode kinetics and homogeneous reactions, the model incorporates capacitance effects due to double layer charging and adsorption of an intermediate. A fully transient model in which the adsorption pseudocapacitance and faradaic reaction occur in series provides excellent quantitative agreement with the experimental results for both PR and PC plating over the entire range of conditions studied. This behaviours explains why the observed electrode responses do not totally become DC-like at frequencies as high as 50 kHz. In order to successfully fit the model to the experimental model, the double layer capacity cannot remain constant over the range of conditions studied and, in fact, varies inversely with the square root of the pulse frequency for pulses of 500 Hz or more.;Pulse plating in solutions containing no additive has been shown to produce finer-grained, more compact, smooth and more reflective deposits than DC plating. PC plating at 500 Hz and 20% duty cycle has been found to produce the highest quality deposits in the absence of additives. When thiourea or BTA is added to the plating solution, no substantial difference between the deposits obtained by DC and PC plating are observed except PC plating at 50 Hz and 20% duty cycle where duller surfaces are obtained. PR plating has been found to produce poor deposits whenever the dissolution of copper occurs during the reverse-time, regardless of bath compositions used. However, during PR plating at high frequencies (≥5 kHz) when copper dissolution does not appear to take place, deposits similar to those obtained by PC or DC plating are obtained. The interactions of chloride with thiourea and BTA during copper deposition are evidently different since the combination of chloride and thiourea is found to improve deposit morphology microscopically but produce a macroscopically rough surface, whereas the combination of chloride and BTA is found to worsen deposit morphology in all respects. However, through the use of suitable pulse parameters, DC plating in the presence of thiourea and chloride has been found to produce the highest quality deposits of this study, comparable to the polished undeposited copper substrate.