Accelerator Aging Effects During Copper Electrodeposition

Slow sweep rate voltammetric analysis of the Cu/Cu(II) deposition reaction is shown to be an effective tool for examining aging effects associated with thiol and disulfide additives that are widely employed as brighteners. Sulfonate-terminated short chain thiols are spontaneously oxidized by Cu(II) to form disulfide molecules with the conversion being complete within a few hours of electrolyte preparation. An additional aging effect occurs during electrolysis in conventional unseparated electrochemical cells. At the anode, the disulfide is reduced by Cu(I) forming thiolate complexes which subsequently affect the copper deposition reaction occurring at the cathode. The latter effect may be avoided by using a cation selective membrane to isolate the anode compartment.