Stress and microstructure in electrodeposited copper nanofilms and the effect of chloride and polyethylene glycol (PEG)

Both atomic force microscopy (AFM) imaging and stress measurements were carried out in situ during potentiostatic electrodeposition of copper on gold in 0.05 mol dm^-3 CuSO₄ in 0.1 mol dm^-3 H ₂SO₄ with and without chloride ion (Cl^-) and polyethylene glycol (PEG) additives. Our in-situ stress measurement technique allowed us to develop an accurate and reliable method of determining local stress in newly deposited copper films. Stress increases in the tensile direction with thickness and eventually reaches a plateau value. We attribute the initial increase in tension to the coalescence of previously isolated islands and the associated formation of grain boundaries. Stress was observed to be higher at higher overpotentials. The addition of 3 ppm Cl^- reduced stress significantly but had very little effect on deposition rate. The addition of 5 ppm PEG with the Cl^- enhanced stress reduction.