Optimum physical-chemical pre-treatment of copper damascene wastewater

Chemical and mechanical polishing (CMP) of copper damascene circuits will typically produce copper levels in excess of regulatory limits in wastewater with a unique process chemistry, including high solids. Physical-chemical methods were investigated to determine the optimum treatment depending upon pre-treatment and/or water reuse requirements. Jar test studies revealed that an alum dose of 150-200 mg/L together with anionic polymer aid provided a good removal of turbidity. If the treatment objective is simply solids and copper reduction for discharge to a sewer system, then solids removal can combined with precipitation of copper hydroxide for relatively inexpensive pre-treatment. The presence of peroxide from the process solution, however, may make it difficult to achieve copper values below 5 mg/L, depending on the associated process conditions. If the objective is to remove solids and recover copper, which may also allow recovery of water for reuse, then solids removal by alum and polymer can be followed by ion exchange by a strong acid cation resin. As with precipitation, however, effective copper removal by ion exchange requires pre-treatment of peroxide by chemical reduction. The exchange of dissolved aluminum also reduces the capacity of the resin for copper.