Electrochemical treatment of simulated copper CMP wastewater using boron doped diamond thin film electrodes-a feasibility study

The overall goal of this research was to develop a single treatment process that will economically treat wastewater generated during chemical-mechanical planarization (CMP) processing of integrated circuits. Present treatment technologies require multiple steps, are expensive, and generate secondary waste streams requiring further treatment or disposal. This research investigated the feasibility of electrochemical treatment of CMP wastewater using boron doped diamond (BDD) film electrodes. BDD electrodes were selected for their absence of catalytic activity for water electrolysis and their high stability under anodic polarization. Cyclic voltammetry and constant potential batch deposition experiments were performed to study removal of Cu²⁺ ions at BDD cathodes. Galvanostatic oxidation experiments were performed to study removal of citrate and benzotriazole from aqueous solutions. For all conditions tested, Cu²⁺ removal was mass transfer limited. Average Faradaic current efficiencies for removing Cu²⁺ from solutions with initial concentrations between 15 and 50 mg/L ranged from 43% to 87%. The oxidation experiments showed that citrate could be completely oxidized to CO₂ and that its rate of oxidation was independent of the current density under the conditions tested. In contrast, rates of benzotriazole oxidation were proportional to the current density. Based on the results, a novel, flow-through electrochemical reactor capable of simultaneously removing metal ions and organic additives in a single pass has been proposed.