Treatment of Cu-CMP Waste Streams Containing Copper(II) using Polyethyleneimine (PEI)

The semiconductor industry has been growing at a fast pace in the last several decades and this growth is expected to continue in the future. One process that is repeated several times in a microchip fabrication is the Chemical Mechanical Planarization (CMP). CMP is a critical process that must be employed after the metal deposition step to eliminate any topography over which the next layer must be processed. Today, copper interconnect is widely used. In addition to possess a high resistance to electro migration effects and low electrical resistivity, copper techniques require fewer (approximately 25%) processing steps. CMP and post-CMP cleaning processes are projected to account for 50 percent of the water consumed by fabrication's ultra pure water. While there are a variety of treatment schemes currently available for the removal of heavy metals from CMP wastewater streams, many introduce additional chemicals to the process, have large space requirement, or are not effective. Polyethyleneimine (PEI) is well known to use in the ion metal affinity chromatography (IMAC) due to the great metal ion binding abilities. While work has been conducted on the use of PEI on membrane filtration for binding metals from industrial wastewaters, the experiments performed in this research are novel with respect to the waste (Cu CMP) treated as well as the method of packed bed column treatment. This research focused primarily on the study of an alternative technique to remove both metal ions and metal-chelated complexes from Cu CMP wastewater streams. Not only copper, wastewater often contains chelating agents, surfactant, organic compounds, and inhibitors. Thus, most of the time copper ions form complexes with chelating agents, which made typical ion exchange resins ineffective. The work, then, explored the effect of components typically found in Cu CMP waste streams on the binding of copper ions to PEI. The competitive binding of copper between PEI and other complexing agents were also investigated. A secondary focus of this study was to fully develop and characterize the column performance and behavior. This includes the understanding of the chemistry of CMP waste characterization. This treatment technique using a PEI packed bed column showed great copper binding capacity. The column is capable of removing Cu CMP waste streams, which contain both copper ions and copper complexes, due to the unique ability of PEI that can play both cation and anion exchanger roles. This waste treatment technique is feasible for the semiconductor industry as large volumes of copper contaminated solutions from actual waste can be concentrated twelve-fold for metal recovery using hydrochloric acid. The adsorbent can be regenerated more than hundred of times with changing in the performance and the reproducibility