REMOVAL OF DISSOLVED COPPER FROM SEMICONDUCTOR INDUSTRY WASTE STREAMS.
Graduate Student: Ran Ding		  
    The semiconductor industry is rapidly moving from aluminum to copper as the interconnect metal of choice. New fabrication technologies like copper electroplating, electroless plating and CMP are involved. But environmentally unfriendly wastes are generated through these processes. Advanced solutions for the waste treatment challenges presented are demanded. A basic design using ion exchange, and electrowinning may be technically viable to achieve environmental compliance and to achieve water recycling. This method also significantly reduces hazardous metal containing wastes over conventional waste treatment technology.

    We are working on this joint project funded by the STAR program of US EPA with Prof. Doyle’s group. For our part, the rotating disk electrode (RDE) is used to investigate the electrochemical kinetics of copper deposition from the simulated concentrated waste stream. A three-electrode cell is used in this research. One electrode is the rotating disc cathode onto which copper is deposited under controlled hydrodynamic conditions. The other two electrodes are a platinum anode and a reference electrode. Several organic compounds, typically encountered in semiconductor processing, are added into the concentrated cupric sulfate solution to see how they affect the kinetics of copper deposition. The figure below is a representative result. It shows the current (essentially the copper deposition rate) when the potential of the cathode is lowered. The current increases as the potential is swept (scanned) by a potentiostat from 0.05V to –0.45V. The blue curve is for an aqueous solution containing copper sulfate and sulfuric acid. The remaining curves are for solutions also containing glycine, an organic additive. The deposition is seen to be greatly hindered by the presence of glycine but this effect diminishes if the scan is repeated with the same solution. It is not restored by adding a fresh amount of glycine.

    In the next step, we are planning to use several specially designed cells to do copper electrowinning from concentrated waste solution. The copper concentration will be significantly lowered after electrowinning, then ion exchange will process the dilute waste solution, and then all the remnant solution will go into the electrowinning cell waiting for the next cycle. In this way, copper is recovered from the waste streams and the copper deposit and reclaimed water can be recycled.