Removal of nanoparticles from copper chemical mechanical planarization wastes via novel separation methods

Chemical mechanical planarization (CMP) wastewater emanating from semiconductor processing contains many compounds including copper (II) ions and alumina and/or silica particles abrasives with an average size of 100 nm. Recycle of CMP wastes requires treatment to remove copper, while disposal of treated wastewater requires that all potential pollutants including copper be removed. Coagulation and filtration were studied in order to identify the most viable and optimal way to employ coagulants using common methodologies for wastewater treatment to primarily remove nanoparticles. It is difficult to separate nanoparticles from CMP wastewater through settling and conventional filtration. Chemical aggregation of nanoparticles was found to enhance the settling and filtration characteristics. The efficiency of four coagulant reagents was evaluated, and reagents were based on aluminum and iron salts, natural coagulant and polyelectrolytes with different electrical charge. Optimal operating conditions such as coagulant dosage, pH, type of coagulant, and sedimentation time were established. The parametric studies demonstrated the viability of coagulants to reduce the amount of particles in wastes. Over 95% turbidity reduction was achieved and less than 5 NTU (the recommended value for good quality water) was realized. Filtration characteristics of aggregated particles were also established.