Evaluating and treating CMP wastewater

With the transition to copper interconnect material comes concern over the toxicity and necessary treatment of copper in CMP wastewater. Examination of copper chemistry in wastewater reveals mostly insoluble copper oxides and hydroxides, except at pH<7 where cupric ion (Cu²⁺) occurs in solution. A simple mass balance on a CMP polisher revealed a copper concentration in the fab's final effluent of approx. 0.5 ppm. We review methods for treating and removing copper from wastewater, including coagulation and flocculation as well as different methods of filtration. Microfiltration results compare favorably with more mature processes, while offering higher throughput (5000 gal/min of effluent) in a smaller footprint.