Electrocoagulation as a viable technique to treat (Cu-)CMP wastes

CMP has become a major process technology. As a result, high volumetric CMP waste streams containing suspended slurry particles and residues, polished from the wafer surface, are generated. This imposes severe demands on the treatment of these effluent streams, since the presence of the high TSS-content and metals like Cu and W is considered as environmental hazardous. In the present study it is demonstrated that the simple technique of electrocoagulation (EC) is a viable alternative to treat (Cu-)CMP wastes. A wide range of silica and alumina-based slurries (and mixtures thereof) have been tested in a lab-scale setup. Electrocoagulation has been found to destabilize in a relatively short time these suspensions. As a result, a transparent supernatant is formed, besides a compact, low volume sludge residual, which can be readily removed by simple, classical filtration. Moreover, the Cu and W present in the waste are removed from the liquid phase with efficiencies >99%, resulting in final metal concentrations below 100 ppb, thus well below water discharge limits. Experiments were done with both simulated and real wastes, which exhibited basically the same behavior