In situ AFM study of the effect of additives on the morphology of electrodeposlted copper

The effect of thiourea and polyethylene glycol (PEG) on the early stages of the electrodeposition of copper on a polycrystalline gold substrate in acidic CuSO₄ was examined by in situ atomic force microscopy (AFM). Addition of 1 ppm thiourea resulted in much smaller more nodular features. Feature size decreased as the thiourea concentration was increased. At any given concentration of thiourea, the RMS roughness initially increased as the film thickness increased but eventually reached a saturated value. Copper electrodeposited in the presence of 300 ppm PEG showed much smaller feature sizes than in the absence of additives but not as small as those obtained in the presence of 20 ppm thiourea. The lateral size of surface features was also estimated. After 800 s of deposition at -100 mV (Cu/Cu²⁺), lateral feature sizes were 730 nm, 460 nm and 280 nm in the case of no additives, 300 ppm PEG and 20 ppm thiourea respectively. copyright The Electrochemical Society.