Effect of additives on Cu electrodeposits: electrochemical study coupled with EQCM measurements

Abstract

The effect of polyethylene glycol (PEG) and chloride ions on Cu electrodeposition mechanism is investigated. Using blank electrolyte, electrochemical measurements show that PEG adsorbs more or less on the electrode surface depending on the nature of this surface (copper, gold). Alternative current techniques and electrochemical quartz crystal microbalance (EQCM) experiments are performed at open circuit and under polarisation. They show that the PEG adsorption on the Cu electrode is weak at open circuit, but increases under polarisation. In complementary EQCM tests made on Au and on electrodeposited Cu, we conclude that the H2 gas production reduces the apparent mass of the gold surface. In contrary on Cu, H2 entrapped in the Cu deposit increases the mass. In all cases, there is an important mass hysteresis. Whatever the substrate, the addition of PEG + Cl− to solution has a beneficial effect by reducing this hysteresis due to the H2 production. For Cu electrolytes, the PEG addition to solution has little effect, while the simultaneous PEG + Cl− addition inhibits both the Cu2+ reduction current and the mass increase. Atomic force microscopy (AFM) images made on the deposits confirm the beneficial effect of the two additives in solution.