A preliminary study on electrically enhanced crossflow microfiltration of CMP (chemical-mechanical polishing) wastewater

Abstract

Chemical-mechanical polishing (CMP) is currently one of the main technologies used by wafer plants in the semiconductor industry. Normally, a large amount of de-ionized water should be used to wash out the abrasives adhered to the surface of wafers during the grinding process. Therefore, CMP wastewater not only has a great quantity but also contains very small size of suspended solids. Generally, these suspended solids would not settle. This phenomenon results in a low visibility of CMP wastewater. To solve this problem, a study on electrically enhanced crossflow microfiltration of CMP wastewater was conducted. Normally, the membrane of traditional dead-end filtration is easily blocked by the filter cake resulting in a small flux of filtrate. Therefore, the form of crossflow filtration (CFF) is used to reduce the blocking of the membrane. Furthermore, if CFF is accompanied by an external electric field, the negatively charged suspended solids in wastewater would move toward the positive electrode. Meanwhile, the flux of filtrate would increase. In this investigation, CMP wastewater was obtained from a wafer plant and characterized by various standard methods. Before testing, the CMP wastewater was pre-filtered using a 1.2 microm pore size filter. Then it was operated by a crossflow microfiltration (0.1 microm pore size) system under an appropriate crossflow velocity, filtration pressure, and electric potential. The filtrate was also characterized by various standard methods. Experimental results show that the filtrate has a turbidity of zero value. Thus, the filtrate could be reused for other purposes. However, the suspended solids of the CMP wastewater would be concentrated by this method. Therefore, the recovery of the suspended solids would be worth considering.

Performance evaluation of a simultaneous electrocoagulation and electrofiltration module for the treatment of Cu-CMP and oxide-CMP wastewaters

“…According to Table 2, the suspended solids in both raw CMP wastewaters were associated with high negative zeta potential (i.e., −39.52 mV and −49.44 mV, respectively) and low isoelectric points (below pH 2) resulting in their good stability in the solution. CMP wastewaters of this nature can be treated effectively by electrofiltration for their suspended solids having a high negative zeta potential [18,19]. By the same token, both CMP wastewaters studied in this work should be effectively treated by the EC/EF treatment process employed.…”

“…In the literature CMP wastewaters (mainly oxide-CMP wastewater) has been treated in different manners: (1) to dilute with other process water in the fab [1], (2) to treat by chemical coagulation and precipitation [14], (3) to treat by membrane filtration [2], (4) to treat by electrocoagulation [15], (5) to treat by crossflow electrocoagulation/electrodecantation [16], (6) to treat by dissolved air flotation [17], (7) to treat by crossflow electromembrane filtration [18][19][20], (8) to treat by electrocoagulation/electroflotation [21], and (9) to treat by crossflow electrofiltration/electrodialysis process [22]. Recently, the treatment of CMP wastewater became much critical since the Cu-CMP process has moved into production of wafer.…”

“…Among various technologies mentioned above, electrocoagulation was found to be effective in removing the suspended solids and copper from Cu-CMP wastewater. Previous studies [18,19] have demonstrated that crossflow electrofiltration could reduce the formation of filter cake and increase the flux of filtrate. Therefore, a treatment method and module capable of simultaneously enacting electrocoagulation and electrofiltration were developed by the principal investigator of the present study [25].…”

CMP wastewater management using the concepts of design for environment

“…It has to be balanced against other design considerations. The following are some of the common DfE practices adopted by industry today: (1) material substitution, (2) waste Source reduction, (3) substance use reduction, (4) energy use reduction, ( 5 ) life extension, (6) design for separability and disassembly, (7) design for recyclability, (8) design for disposability, (9) design for reusability, (10) design for manufacture, and (11) design for energy recovery [131.…”

“…To eliminate or reduce the amount of "sludge" and simultaneously obtain good quality of treated water, an electrically enhanced crossflow microfiltration (EECM) technique has been used for treatment of CMP process effluent by the author's research group [9,10,261. Table 1 shows the water quality of oxide-CMP wastewater before and after treatment by this self-designed EECM system.…”