Chemical Mechanical Polishing Wastewater Research Articles

Study of COD and turbidity removal from real oxide-CMP wastewater by iron electrocoagulation and the evaluation of specific energy consumption

This study explores the feasibility of reducing COD and turbidity from real oxide chemical mechanical polishing (oxide-CMP) wastewater. Based on the dynamic characteristics of batch electrocoagulation, three operating stages (lag, reactive, and stabilizing) are proposed to identify the relationships among the zeta potential of the silica particles, solution turbidity, and the corresponding mean particle size. Experiment results show that the silica particles were destabilized and settled at the critical electrolysis time, which was estimated to be about 12 min under an applied voltage of 20 V and a supporting electrolyte of 200 mg/L. The corresponding turbidity removal occurred mostly during the reactive stage. The process variables, including applied voltage and electrolyte concentration, were investigated in terms of COD removal efficiency and turbidity removal. In addition, the effects of applied voltage and supporting electrolyte on COD removal efficiency and specific energy consumption were evaluated. Under the optimum balance, satisfactory removal efficiency and relatively low energy consumption were obtained. The optimum electrolyte concentration and applied voltage were found to be 200 mg/L NaCl and 20 V, respectively. Under the optimum conditions, COD and turbidity decreased by more than 90% and 98% in real oxide-CMP wastewater, respectively.

Combined treatment of polishing wastewater and fluoride-containing wastewater from a semiconductor manufacturer

Collection and treatment of chemical mechanical polishing (CMP) wastewater and fluoride-containing wastewater in semiconductor manufacturing are conventionally separated. The combined treatment of these two streams of wastewater was studied. Polishing wastewater containing silica was mixed at different ratio with synthetic fluoride-containing (640 mg/L) wastewater. Calcium chloride (CaCl 2) was then added at neutral pH to induce calcium fluoride (CaF 2) precipitates. Fluoride removal efficiency increased when the mixing ratio (v/v) of CMP wastewater to fluoride-containing wastewater increased from 1:9 to 2:3 at molar ratio, ([Ca]:[F]), of 0.75 at neutral pH. Size of CaF 2 precipitates increased when at higher mixing ratio as well. The subsequent solid–liquid separation was very effective by the use of anionic flocculant, polyacrylic acid (PAA) of lower molecular weight (90,000 and 450,000) at dosage of 10 mg/L and at pH 7. Lower residual turbidity was obtained for mixed wastewater when flocculated by PAA. Results indicated that the combined treatment both polishing and fluoride-containing wastewater is beneficial. It is proposed that silica in CMP wastewater become adsorbed on the surface of positively charged CaF 2 particles, and enhances flocculation since repulsive force of CaF 2 particles is decreased. In addition, silica may act as nuclei for precipitation of CaF 2 as well and facilitate agglomeration. Potential advantages include lower chemical dosage, better control, and smaller footprint.

Treatment of Chemical Mechanical Polishing Wastewater for Water Reuse by Ultrafiltration and Reverse Osmosis Separation

This paper describes the treatment of chemical mechanical polishing (CMP) wastewater from a semiconductor plant through membrane-based ultrafiltration (UF) and reverse osmosis (RO) processes to improve the removal efficiency under different water recovery and to determine the possible mechanisms of membrane blocking and rejection. UF pretreatment led to 42.1–46.9% conductivity, 98.1–99.4% turbidity, and 4.5–24.5% total organic carbon (TOC) removal. These contaminants were almost completely rejected after performing subsequent RO processing: the values of the conductivity, turbidity, and TOC were reduced to 6 μS/cm, 0.01 NTU, and 1.6 mg/L, respectively. The water quality of the permeates after UF or RO membrane filtration could meet the water reuse standards for tap water, cooling water, boiler water, and the feed for a water purification machine. The variation with time of the permeate flux for the UF process was fitted to the Hermia model to examine the possible blocking mechanisms during the filtration ...

WITHDRAWN: Chemical coagulation/floculation treatment of chemical mechanical polishing (CMP) wastewater from photovoltaic industry

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Effect of mixing on spontaneous struvite precipitation from semiconductor wastewater

The objective of this study was to investigate on the effect of mixing intensity ( G) and mixing duration ( t d) on struvite precipitation in the chemical mechanical polishing (CMP) wastewater generated from the semiconductor manufacturing process. Batch-scale experiments revealed that struvite crystallization was affected by both G and t d. The mixing effect was to enhance the mass transfer of solute to the crystals in the process, resulting in the improvement of struvite crystallization and growth. By forming struvite, removal efficiencies of N and P increased logarithmic with the multiple values of G and t d, i.e., Gt d. Insufficient mixing energy with the Gt d value less than 10 5 caused an increase in the formation potential of unexpected precipitate unlike to pure struvite, causing a decrease in removal efficiencies of N and P in the process. At the Gt d value over 10 6, struvite precipitation was not restricted by fluoride, of which high level inherently contained in the CMP wastewater. The study results can be taken into consideration in the design and operation of the struvite precipitation process for both nutrient (N and P) removal and recovery.

Silica particles settling characteristics and removal performances of oxide chemical mechanical polishing wastewater treated by electrocoagulation technology

The purpose of this study was to explore the feasibility of removing silica particles and reducing turbidity from oxide chemical mechanical polishing (oxide-CMP) wastewater. Based on the dynamic characteristics of batch electrocoagulation, three operating stages (lag, reactive, and stabilizing) are proposed to identify the relationships among the zeta potential of the silica particles, solution turbidity, and the corresponding mean particle size of the silica. Experimental results show that the silica particles were destabilized and settled at the critical mean particle size, which was estimated to be above 520 nm after 10 min, and the corresponding turbidity removal mostly occurred during the reactive stage. Furthermore, the corresponding mean particle size varied from 520 to 1900 nm as the treatment time progressed from 10 to 20 min, which also occurred during the reactive stage. Several parameters, including different electrode pairs, electrolyte concentration, applied voltage, and the optimum condition of power input were investigated. Experimental results indicate that a Fe/Al electrode pair is the most efficient choice of the four electrode pair combinations in terms of energy consumption. The optimum electrolyte concentration and applied voltage were found to be 200 ppm NaCl and 30 V, respectively.

Electrochemical treatment of chemical mechanical polishing wastewater: removal of fluoride — sludge characteristics — operating cost

The aim of this paper is to propose an efficient and low-cost treatment of chemical mechanical polishing wastewater process based on electrocoagulation with iron bipolar electrodes. The performance of a pilot scale electrochemical reactor equipped with iron bipolar electrodes and an anode active area surface of about 170 cm 2 was studied. In addition, sludge settling after electrocoagulation were characterized. The pilot study yield promising results, suggesting that further in-depth development study is worth to be considered in a future work.

Electrocoagulation of chemical mechanical polishing wastewater

Treatment of chemical mechanical polishing (CMP) wastewater was investigated. The CMP wastewater, as obtained from surface treatment of photovoltaic wafers, was characterized by high suspended solids, high nephelometric turbidity unit (NTU), chemical oxygen demand (COD) and green color. This study determines the feasibility of CMP wastewater treatment by the electrocoagulation process. The COD concentration of the CMP wastewater was found in the range of 700 mg/l which is below the discharge standards. The analysis of the wastewater before and after electrocoagulation shows that the electrochemical process was a total barrier for the metal species, color and a significant reduction in the concentration of the fluoride and sulfate ions.

Nano-bubble flotation technology with coagulation process for the cost-effective treatment of chemical mechanical polishing wastewater

The feasibility of nano-bubble flotation technology (NBFT) with coagulation/flocculation process for the enhanced treatment of chemical mechanical polishing (CMP) wastewater was investigated through laboratory and pilot-scale experiments. As a precursor, the effective combination of activator/collector was identified using a laboratory-scale flotation reactor. The results showed that polyaluminum chloride (PAC)/sodium oleate (NaOl) was the best combination of activator/collector, respectively and its application in the NBFT with coagulation process increased the wastewater clarification efficiency by 40% as compared with traditional coagulation/flocculation process. More than 95% turbidity, total solids and total silica removal efficiencies were observed in the pilot-scale flotation experiments. From the results, it was found that NBFT with coagulation process could be performed effectively at an optimum PAC concentration of 50–60 mg/L (as Al), NaOl concentration of 5–10 mg/L with a recycle ratio of 10–20% and 1 h hydraulic retention time HRT. The cost and performance assessment reflected that CMP wastewater could be treated efficiently at a minimum cost using the present approach.

Dissolved air flotation of polishing wastewater from semiconductor manufacturer

The feasibility of the dissolved air flotation (DAF) process in treating chemical mechanical polishing (CMP) wastewater was evaluated in this study. Wastewater from a local semiconductor manufacturer was sampled and characterised. Nano-sized silica (77.6 nm) with turbidity of 130 +/- 3 NTU was found in the slightly alkaline wastewater with traces of other pollutants. Experimental results indicated removal efficiency of particles, measured as suspended particle or turbidity, increased with increasing concentration of cationic collector cetyltrimethyl ammonium bromide (CTAB). When CTAB concentration was 30 mg/L, pH of 6.5 +/- 0.1 and recycle ratio of 30%, very effective removal of particles (> 98%) was observed in saturation pressure range of 4 to 6 kg/cm2, and the reaction proceeded faster under higher pressure. Similarly, the reaction was faster under the higher recycle ratio, while final removal efficiency improved slightly as the recycle ratio increased from 20 to 40%. An insignificant effect of pH on treatment efficiency was found as pH varied from 4.5 to 8.5. The presence of activator, Al3+ and Fe3+, enhanced the system performance. It is proposed that CTAB adsorbs on silica particles in polishing wastewater through electrostatic interaction and makes particles more hydrophobic. The increase in hydrophobicity results in more effective bubble-particle collisions. In addition, flocculation of silica particles through bridging effect of collector was found; it is believed that flocculation of particles also contributed to flotation. Better attachment between gas bubble and solid, higher buoyancy and higher air to solid ratio all lead to effective flotation.

Treatment of Polishing Wastewater from Semiconductor Manufacturer by Dispersed Air Flotation

Treatment of chemical mechanical polishing wastewater containing nanosized silica from semiconductor industry by dispersed air flotation was investigated. Very effective removal of particles from wastewater was found when cationic surfactant, cetyltrimethyl ammonium bromide (CTAB), was used as a collector. The flotation efficiency decreased slightly under a pH of 4.5. The zeta potential increased with a increasing concentration of CTAB, and flocculation of particles by CTAB was found. It is proposed that both the change of interface properties and the aggregation of particles contributed to flotation removal of particles. Longer reaction time and higher dosage were needed when n-dodecyl amine chloride (DAC) was used as a collector, owing to its relatively weak adsorption. The flotation efficiency increased with increasing DAC concentration. The improved flotation efficiency at pH of 10.0 was probably due to the formation of DAC precipitate.

Treatment of wastewater containing nano-scale silica particles by dead-end microfiltration: evaluation of pretreatment methods

Chemical mechanical polishing (CMP) is the process to planarize wafer in the IC manufacturing. In the process, a large amount of ultra pure water is used to clean the surface of the wafer, which generates large quantity of wastewater containing high concentration of nano-scale silica particles. The wastewater is generally treated with the traditional coagulation/sedimentation process, producing large quantity of sludge. In this study, a microfiltration (MF) process coupled with chemical pretreatment was investigated to separate the nano-scale particles from the CMP wastewater to reclaim the water. Wastewater was filtered through a polytetrafluoroethylene membrane of pore size 0.5 μm at a low vacuum pressure (0.65 kg/cm 2). The permeate flux was monitored and the degree of irreversible fouling of the membrane was estimated. The SEM images of the fouled membrane and the cake layer were used to diagnose the mechanism of membrane fouling. Several coagulants and flocculants were tested for their potential use prior to microfiltration. Polyaluminum chloride (PACl) plus cationic polyacrylamide (PAA) were selected for pretreatment, and their effects on permeate flux and fouling of the membrane were examined. The results indicated that PACl improved silica removal substantially. The addition of trace amount of PAA effectively increased the size of the flocs, and subsequently enhanced the permeate flux. The performance of the dead-end MF operation depended strongly on the turbidity of the influent. The addition of oxidant, i.e. Chlorine, after the flocculation reduced the irreversible fouling and promoted flux recovery of the membrane.

Treating chemical mechanical polishing (CMP) wastewater by electro-coagulation-flotation process with surfactant

The effect of surfactants on the treatment of chemical mechanical polishing (CMP) wastewater by electro-coagulation-flotation (ECF) process was studied. Two surfactants, cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) were employed in this study to compare the effect of cationic (CTAB) and anodic (SDS) surfactants on ECF. The cationic surfactant can enhance the removal of the turbidity, but anodic surfactant cannot. It can be explained by the hetero-coagulation theory. Moreover, the addition of CTAB in CMP wastewater can reduce the sludge volume and the flotation/sedimentation time in ECF process. The residual turbidity and dissolved silicon dropped with the increase of charge loading. No CTAB pollution problem exists after the ECF process.

Nano silica removal from IC wastewater by pre-coagulation and microfiltration

Microfiltration (MF) coupled with pretreatment by coagulation was adopted in the treatment of chemical mechanical polishing (CMP) wastewater from IC manufacturing plants, containing high concentrations of silica. Poly-aluminium chloride (PACl) was the coagulant, while the cationic polyacrylamide (PAA) was the flocculant aid. Preliminary tests were performed with the raw CMP wastewater in order to determine the optimal coagulation condition for subsequent microfiltration. Analysis of the particle size distribution shows that nearly all silica particles were enlarged from nano scale to at least 4 microm in diameter after the pre-treatment. The pre-treated wastewater was then filtered through a polytetrafluoroethylene (PTFE) membrane with a pore size 0.5 microm at a constant vacuum pressure. Trace amounts of PAA in addition to the PACl coagulation can effectively increases the permeate flux.

Chemical and physical treatments of chemical mechanical polishing wastewater from semiconductor fabrication

Wastewater from chemical mechanical polishing (CMP) process of semiconductor fabrication was treated by physical methods. The CMP wastewater, as obtained from a large semiconductor manufacturer, was characterized by a high oxide particle content, high turbidity (NTU), and a chemical oxygen demand (COD) concentration up to 500 mg/l. Due to these characteristics, treatment of the CMP wastewater by either filtration or by traditional activated sludge method was inadequate. In the present work, physical methods consisting of chemical coagulation and reverse osmosis were employed to tackle the turbidity and COD problems. Experimental tests were conducted to assess the effectiveness of the treatment and to identify the optimum operating conditions. Test results clearly demonstrated the complementary advantages of the two methods. The treatment was capable of realizing over 99% oxide particle removal and lowering the wastewater COD to below 100 mg/l. The overall water quality of the final effluent was excellent and can be considered for reuse. Preliminary treatment of the RO retentate by ozonation was also attempted. The COD removal achieved in the ozonation was over 80% in an hour, rendering the treated RO retentate suitable for direct discharge.

Reclamation of high quality water from treating CMP wastewater by a novel crossflow electrofiltration/electrodialysis process

Generation of electrolytic ionized water (EIW) from chemical mechanical polishing (CMP) wastewater using a simultaneous crossflow electrofiltration/electrodialysis process was studied in this work. In the semiconductor industry, presently, CMP has become the key technique to provide global planarization on interlevel dielectrics and metal layers of wafers. In general, post-CMP cleaning requires a huge volume of ultrapure water (UPW) to remove foreign materials from the wafer surfaces. An almost the same amount of CMP wastewater thus would be generated. Therefore, treatment and reclamation of CMP wastewater is significant and important. In this study, a multi-membrane set has been incorporated into a crossflow electrofiltration/electrodialysis treatment module for treating a mixed CMP wastewater and simultaneously generating two streams of electrolytic ionized water, which has several extraordinary characteristics. Experiments were carried out based on the 2 4−1 fractional factorial design using four experimental factors to investigate their effects on the permeate qualities. After treatment, each stream of permeate has a turbidity of below 1 NTU, total organic carbon of below 3 mg/l, and total dissolved solids of below 50 mg/l. Besides, permeate has a much smaller size of water molecule cluster than that of tap water according to the 17 O NMR (nuclear magnetic resonance) relaxation measurements. Thus, EIW obtained in this study is suitable for high-level recycling.

A pilot plant study using ceramic membrane microfiltration, carbon adsorption and reverse osmosis to treat CMP (chemical mechanical polishing) wastewater

Currently, most semi-conductor plants adopt the conventional chemical coagulation and sedimentation process to treat chemical mechanical polishing (CMP) wastewater. This treatment process consumes a large quantity of coagulants, and its optimum pH operation range is rather narrow. This treatment process produces huge amounts of sludge and is hard to operate due to the unstable characteristics of the abrasive slurry of CMP wastewater. The purpose of this research is to establish a pilot plant which consists of chemical pretreatment, ceramic membrane microfiltration, carbon filtration and reverse osmosis system, which will allow the reclamation of the CMP wastewater. Actual CMP wastewater was sampled and treated in the pilot plant. The results of the pilot tests demonstrated the viability of the treatment scheme and provided data for scale-up calculations. Cost per ton of CMP wastewater reclaimed was calculated using the operating data established, and compared with the conventional chemical coagulation and sedimentation process.

Treatment of chemical mechanical polishing wastewater by electrocoagulation: system performances and sludge settling characteristics

Treatment of copper chemical mechanical polishing (CMP) wastewater from a semiconductor plant by electrocoagulation is investigated. The CMP wastewater was characterized by high suspended solids (SS) content, high turbidity (NTU), chemical oxygen demand (COD) concentration up to 500 mg l −1 and copper concentration up to 100 mg l −1. In the present study, electrocoagulation was employed to treat the CMP wastewater with an attempt to simultaneously lower its turbidity, copper and COD concentrations. The test results indicated that electrocoagulation with Al/Fe electrode pair was very efficient and able to achieve 99% copper ion and 96.5% turbidity removal in less than 30 min. The COD removal obtained in the treatment was better than 85%, with an effluent COD below 100 mg l −1. The effluent wastewater was very clear and its quality exceeded the direct discharge standard. In addition, sludge settling velocities after electrocoagulation were measured and the data were employed to verify the empirical sludge settling velocity models. Finally, the sludge settling characteristic data were also utilized to establish the relation between the solids flux ( G) and the initial solids concentration.

Electrocoagulation of chemical mechanical polishing (CMP) wastewater from semiconductor fabrication

Treatment of chemical mechanical polishing (CMP) wastewater is investigated. The CMP wastewater, as obtained from a large semiconductor manufacturer, was characterized by high suspended solids (SS) content, high Nephelometric turbidity unit (NTU), chemical oxygen demand (COD) concentration up to 500 mg/l, copper concentration over 100 mg/l and a milky color. This study was to explore the feasibility of treating the CMP wastewater by electrocoagulation with an aim of simultaneously lowering the wastewater turbidity, and copper and COD concentrations. Experiments were conducted to analyze the characteristics of the CMP wastewater and to evaluate the effects of electrocoagulation time, type of electrode pair and electrolyte dosage on the system performances. The fine suspended oxide particles were found to have an average size of 100 nm with narrow particle size distribution between 68 and 120 nm. The test results revealed that Al/Fe (anode/cathode) was a good electrode pair in terms of overall performances. Electrocoagulation with Al/Fe electrode pair was able to achieve 99% copper removal and 96.5% turbidity reduction in less than 100 min. The COD removal obtained in the treatment was better than 75%, with an effluent COD below 100 mg/l. The wastewater quality exceeded the direct discharge standard and the effluent can be considered for reuse.

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

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.