A Preliminary Study on Electrochemical Treatment of Oxide-CMP Wastewater Using Self-Prepared Carbon/Al2O3 Tubular Inorganic Composite Membranes

*Gordon C. C. Yang
Institute of Environmental Engineering, National Sun Yat-Sen University, Taiwan

Chi-Ming Tsai
Institute of Environmental Engineering, National Sun Yat-Sen University, Taiwan

*Cyuan-Jia Li
Institute of Environmental Engineering, National Sun Yat-Sen University, Taiwan

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     Last modified: May 12, 2006

Abstract
Chemical mechanical polishing/planarization (CMP) has been widely adopted in the semiconductor manufacturing. With the abrasive slurry used in the CMP process, a large amount of ultrapure water should be used to wash out the abrasives adhered to the surface of wafers. Generally, the same quantity of wastewater would be generated. The resulting wastewater stream needs proper treatment to comply with local discharge regulations for suspended solids (in the range of nanometers to micrometers) and possibly other contaminants. Previous studies have demonstrated the superiority of electrocoagulation/electrofiltration using polymeric membranes in treating CMP wastewater and obtaining permeate of good quality. Therefore, the objective of this work was to investigate the feasibility of treating CMP wastewater by self-prepared carbon/Al2O3 tubular inorganic composite membranes (TICMs). The substrates of TICMs with a nominal pore size of 0.97 mm, derived from alumina powder, were prepared using the extrusion method. On the tops of substrates thin layers of carbon were coated by the chemical vapor deposition (CVD) method resulting in a pore size distribution of 2 to 10 nm. The finished TICMs were further characterized by scanning electron microscopy and permporometry. These TICMs were incorporated into a novel treatment module capable of simultaneously enacting crossflow electrocoagulation and electrofiltration (EC/EF). Then an investigation for the effects of various operating parameters on oxide-CMP wastewater treatment was followed. The experimental factors studied include the electric field strength, crossflow velocity, and transmembrane pressure. The preliminary experimental results have demonstrated that the self-prepared carbon/Al2O3 TICMs incorporated into the self-designed EC/EF treatment module used in this study is capable of treating oxide-CMP wastewater in a proper manner. Permeate thus obtained had a turbidity of below 0.5 NTU and the removal efficiency of TS (total solids) and Si were 80% and 93 %, respectively.