The Condition of Optimum Coagulation for Recycling Water from CMP Slurry

Water usage in the semiconductor industries is dramatically increased by not only using bigger wafer from 8 inches to 12 inches but also by adapting new process such as Chemical Mechanical Planarization (CMP) process invented by IBM in late '80. However, The document published by International Semiconductor Association suggests the decreasing ultra pure water (UPW) use from 22 gallon/in$^2$in 1997 to 5 gallon/in$^2$ in 2012. The criteria will possibly used as exporting obstacle in the future. Generally, Solid content of CMP slurry is about 15wt%. The slurry is diluted with UPW before fed to a CMP process. When the slurry is discharged from the process as waste, it contains 0.1~0.6wt% of solid content and 9~10 at pH. The CMP waste slurry is discharged to stream with minimum treatment. In this study, to find optimum condition of coagulation for water recovery from the waste CMP slurry various condition of coagulation were examined. After coagulation far 0.1 wt% solid content of waste CMP slurry, the sludge volume was 10~15% after 30 min of sedimentation time. For the 0.5 wt%, sludge volume was 50~55% after one hour of sedimentation time. For more than 80% of water recycling, the solid content should be in the range of 0.1 to 0.2wr%. Based on the result of the turbidity removal, the Zeta Potential and the analysis of heavy metals, the optimum condition for 0.1 wr% of waste CMP slurry was with 20 mg/L of PACI at 4 to 5 of pH. The result showed that the optimum conditions fer the 0.1 wt% waste CMP slurry were 100mg/L of Alum at 4~5 of pH, 100 mg/L of MgCI$_2$at pH 10 to 11 and 100 mg/L of Ca(OH)$_2$at pH 9 to 11, respectively.