Novel Resin-Based Ultrapurification System for ... - ACS Publications

They also underline the importance of point-of-use recycling and reprocessing of the waste IPA in the semiconductor industry. Yeo et al. have examined...
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Ind. Eng. Chem. Res. 1996, 35, 3149-3154

3149

Novel Resin-Based Ultrapurification System for Reprocessing IPA in the Semiconductor Industry Partha V. Buragohain, William N. Gill, and Steven M. Cramer* Department of Chemical Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180-3590

There is an urgent need for the development of energy-efficient recycling and ultrapurification processes for 2-propanol solvent wastes generated from the semiconductor industry. In this paper, experimental results are presented that set the stage for the development of efficient resin-based closed-loop recycling systems for 2-propanol drying applications in the semiconductor industry. The process employs ion exchange resins to reduce cations and anions to low and sub-part-per-billion levels. Batch adsorption experiments were carried out in 2-propanol to determine the adsorption isotherms of various ions on commercially available ion exchange resins. The results indicate that ion exchange resins indeed have both high affinity and capacity for ions in the relatively nonpolar 2-propanol solvent. Under dynamic flow conditions, columns of appropriate column diameter and length packed with the resins were indeed capable of reducing ionic impurities to low parts-per-billion levels. In fact, long-term experiments indicate that these systems can generate ultrapure 2-propanol from relatively large volumes of solvent waste. In addition to the ionic impurities, it is necessary to remove water and organic contaminants from the solvent. Columns packed with activated carbon and molecular sieves were shown to be efficacious in removing organic and water impurities, respectively, from 2-propanol to low levels required for semiconductor applications. Introduction The solvent 2-propanol (IPA) is widely employed during the manufacture of semiconductor wafers for removal of water from the surface of the wafer after cleaning operations. Liebetreu and Rynders (1994) described the wafer drying process with IPA and its advantages over the conventional dryers. They also underline the importance of point-of-use recycling and reprocessing of the waste IPA in the semiconductor industry. Yeo et al. have examined the effects of metallic contaminants in IPA on high-temperature minority carrier lifetime (MCLT). They have reported that metal ions (e.g., vanadium) even at sub-parts-perbillion concentrations can be detrimental to the minority carrier lifetime. Clearly, it is very important to develop closed-loop recycling systems that can purify IPA down to low or sub-parts-per-billion levels for use in the semiconductor industry. Ion exchange is a well-established process for aqueous-based systems (Helffreich, 1962; Wankat, 1990). Many studies have been reported on the ability of different ion exchange resins for metal ion adsorption from water. King et al. (1978) have studied the separation of metal ions using an aromatic o-hydroxy oxime chelating ion exchange. These systems were able to selectively adsorb copper(II), molybdenum(VI), and zinc and nickel(II) under appropriate mobile phase conditions. Nair et al. (1993) have reported the separation of alkali and alkaline earth cations on polybutadienemaleic acid-coated ion exchangers with mineral acid eluents. Schmidt et al. (1980) examined the separation of metal ions on ion exchange resins with EDTA functional groups and found that these stationary phase materials were able to adsorb some transition metal ions with very high affinity. The behavior of ion exchange resins in solvents such as ethanol, benzene, acetone, glycerol, acetic acid, and * Phone: (518) 276-6198. Fax: (518)-276-4030. E-mail: [email protected].

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petroleum ether was examined by Bodamer et al. (1953). In that early work, the authors examined the ion exchange capacity and the swelling characteristics of the resins in these solvents using batch experiments. While the ion exchange process was shown to occur in nonaqueous media, the rates of ion exchange were generally slower than in aqueous media. Buechelle et al. (1982) have examined the effect of an organic mobile phase modifier (methanol) on the ion chromatographic determination of monovalent ions. In this work, various concentrations of methanol were added to the mobile phase, and its effects on the selectivity and retention times were measured. The results indicated that an increase in the methanol concentration produced a concomitant increase in the selectivities for various cations. Kawazy (1977) compared the efficiency of various cation exchange resins for the separation of metal ions using aqueous acetone-HCl solutions. In that work, macroporous and microporous cation exchange resins were examined for their efficiency for removing cationic impurities from aqueous acetoneHCl solutions. Detailed studies were carried out on the distribution coefficient as a function of the acetone content. Multistep gradient separations were carried out (by changes in the acetone and/or HCl content) and were successful in separating many cations in a single separation experiment. An IPA reprocessor based on distillation has previously been developed (SDC Isopure 300 distillation reprocessor, Stainless Design Corporation, Saugerties, NY). However, energy costs, system economics, and safety concerns make this approach impractical. In this paper, the utility of ion exchange is examined for removing ionic impurities in IPA. Batch adsorption and column studies are carried out. In addition, column experiments are carried out with activated carbon and molecular sieves to examine the utility of these operations for removing organic and water impurities, respectively, from IPA to low levels required for semiconductor applications. The work presented here sets the stage for the development of efficient resin-based closed© 1996 American Chemical Society

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loop recycling systems for 2-propanol drying applications in the semiconductor industry. Experimental Section Materials. Spectrophotometric grade 2-propanol, various salts (sodium chloride, potassium chloride, lithium chloride, nickel sulfate), and EDTA were obtained from Aldrich Chemicals (Milwaukee, WI). Sodium hydroxide pellets and concentrated sulfuric acid were obtained from Fisher Scientific (Springfield, NJ). The DI water used in the experiments was obtained from Nanopure water system of Barnstead/Thermolyne (Dubuque, IA). The molecular sieves type 3A were obtained from UOP (Des Plains, IL). The synthetic activated carbon, Ambersorb, was donated by Rohm and Haas Company. The ion exchange resins employed in this study were Amberlite IR 120+ (cation exchange) and Amberlite IRA 402 (anion exchange) donated by Rohm and Haas Company, Dowex M31 (cation exchange) donated by Dow Chemical Company, and Ionac CFP 110-H(SG) (cation exchange) and Ionac A 641-OH(SG) (anion exchange) donated by Sybron Chemicals. Analytical scale column (0.46 × 10 cm empty column) was obtained from Upchurch Scientific (Oak Harbor, WA), preparative column (2.54 × 10cm) was obtained from Bodman (Aston, PA), and the longer preparative columns (2.54 × 25.4, 38.1, 50.8 cm) were obtained from Stainless Design Corporation (Saugerties, NY). For ion chromatographic analysis, Waters IC Pak cation M/D and anion HC columns (Water Chromatography, Milford, MA) were used for the chromatographic analysis of the ions. Apparatus and Equipment. For ion chromatographic analysis, a Waters 431 conductivity detector was used for ion detection, a Waters 745B data module was used for data collection, and a Pharmacia LKB 2248 HPLC pump was used for pumping the eluent. For preparative scale experiments, Waters Delta Prep 300 pump was employed. Teflon bottles precleaned by ChemTrace (Hayward, CA) were used for sample collection. For moisture analysis, a Karl Fisher titration apparatus (Mitsubishi) was employed. For high precision metal ion and organic analyses, samples were sent out to ChemTrace (Hayward, CA). Analyses carried out included inductively coupled plasma with mass spectrometer detector (ICP-MS) and graphite furnace atomic adsorption spectroscopy (GFAAS) for ions and GC/MS analysis for organics. Procedure. Ion Chromatographic Analysis. The ion chromatographic analysis was performed using Waters IC Pak columns. For cation analysis, IC Pak cation M/D column was used for the separation of the ions with an eluent that consisted of 3 mM nitric acid and 0.1 mM EDTA. The samples were injected with a 60-µL loop, and the eluent volumetric flow was 1.0 mL/min. The detection was performed using a Waters 431 conductivity detector, and the data (chromatogram) were obtained using a Waters 745B integrator. For anion analysis, IC Pak anion HC was used with an eluent containing lithium borate, gluconate, acetonitrile, and 1-butanol. The samples were injected with a 100-µL loop, and the eluent volumetric flow was 2.0 mL/min. The detector and the data collection device were same as for cation analysis. Batch Experiments. Pretreatment. Prior to the batch experiments, pretreatment of the resins was carried out. Cation and anion exchange resins were first regenerated with 5% sulfuric acid and 5% NaOH, respectively. They

were then washed with DI water until neutral pH was achieved and conditioned with spectrophotometric grade IPA. (Note: all conditioning experiments were carried out in the batch mode.) The resins were then dried in an oven at 120 °C for 24 h. Adsorption Experiments. The following protocol was carried out for each batch adsorption experiments: 0.25 g of dry and pretreated resins was placed in polypropylene test tubes containing 2.0 mL of pure 2-propanol. Various volumes of 100 000 ppm stock ion solutions were added to the test tubes containing the resins. The mixture in all the test tubes were allowed to incubate for 48 h to attain equilibrium. The supernatant was then analyzed by ion chromatographic analysis, and a mass balance was carried out to determine the stationary phase compositions. A separate batch experiment was performed for each data point in the adsorption isotherms. Column Experiments. Pretreatment. Prior to column experiments, pretreatment of the resins was carried out in-situ in the packed columns. The cation and anion exchange resins were regenerated with 18-20 column volumes of 5% H2SO4 and 5% NaOH aqueous solutions, respectively. The resins were then washed with 1820 column volumes of DI water at a flow rate of 10 mL/ min to remove the acid and the alkali from cation exchange and anion exchange column, respectively. Finally, the resins are conditioned by passing 10-15 column volumes of spectrophotometric grade 2-propanol. Column Experiments. Column experiments were carried out on several cation and anion exchange resins packed in analytical, preparative (2.54 cm × 10 cm) and long preparative (2.54 cm × 25.4 cm) columns. Single and Multicomponent Column Experiments. Single component column experiments with the cation exchange resins were carried out with feed solutions containing 25-50 ppm of Na+ ions in IPA. Experiments were carried out by constant infusion of the feed solution into various columns at various flow rates. Fractions of the column effluents were periodically taken and subjected to chromatographic and/or more rigorous analysis. Similar experiments were carried out with a long preparative column packed with the Ionac A641OH(SG) anion exchange resin using feed solutions containing 20-40 ppm of chloride, sulfate, and nitrate ions in IPA. Long-Term Experiments. A long-term column experiment was carried out using a single component feed of 30 ppm of Na+ in IPA. In order to avoid the use of a large volume of IPA, the experiment was performed in a semibatch mode by reusing purified IPA from the column outlet after adding appropriate amounts of Na+ to assure a constant inlet concentration. A cation exchange column (2.54 × 25.4 cm) was employed at a flow rate of 10 mL/min. A total of 35 L of IPA was processed in the column. Effluent fractions were collected and subjected to analysis by ion chromatography, ICP/MS, and GFAAS. Organic Adsorption by Activated Carbon. A column experiment was carried out using a 2.54 cm × 38.1 cm stainless steel column packed with Ambersorb. The column was first conditioned in-situ by sequential perfusion with 15 column volumes of 5% sulfuric acid, 10 column volumes of DI water, and 10 columns of IPA. A feed solution containing 5 ppm of N-methylpyrilidone (NMP) was pumped into the conditioned column at 10 mL/min. Samples of the column effluent were collected in Teflon bottles and sent out for GC/MS analysis.

Ind. Eng. Chem. Res., Vol. 35, No. 9, 1996 3151

Figure 1. Adsorption isotherm of Na+ ions on (a) Ionac CFP 110 and (b) Amberlite IR 120+. Data obtained from batch adsorption experiments at carried out at 25 °C.

Molecular Sieve Adsorption of Water from 2-Propanol. Column experiments were carried out using a stainless steel column (10.16 cm × 76.2 cm) packed with the molecular sieves. The column was first regenerated by blowing hot nitrogen gas at a flow rate of 25.5 m3/h for 45 min. The dynamic adsorption capacity of the resins for water were then evaluated by pumping IPA containing 5% water through the column at 75 mL/min. Samples of the column effluent were collected and evaluated for water content using a Karl Fisher titration apparatus. Results and Discussions Batch adsorption experiments were carried out to determine the inherent affinity of these resins for various ions in IPA. The adsorption isotherms of Na+ ions on Ionac CFP 110 and Amberlite IR 120+ in IPA are shown in Figure 1. As seen in the figure, the adsorption isotherms were square shaped, indicating that the resins have extremely high affinity for this cation in IPA. Thus, even in this relatively nonpolar environment, the resins exhibited high affinity for the cations. Furthermore, the binding capacity of these cation exchange resins in IPA was quite high, approximately 90 mg of Na+ ions/g of dry resin for relatively low fluid phase concentrations of the Na+ ion. These batch results are important in that they indicate that these cation exchange resins have sufficient inherent affinity and capacity to reduce cations in IPA to parts-per-billion levels at a low level of the mobile phase concentrations. Initial column studies were carried out with analytical scale columns (0.46 × 10 cm). These results indicated that improper packing of these relatively large resin beads (0.4-1.2 mm diameter) in these small diameter columns resulted in channeling and premature leakage of Na+ ion on the order of 200-300 ppb. (Note: although this concentration was significantly lower than the inlet concentration of 25 ppm, it was unacceptable for semiconductor applications.)

Figure 2. Effect of flow rate on the leakage of Na+ ions. Column: 2.54 × 10 cm preparative column. Flow rates: 2.0, 5.0, 7.5, and 10.0 ml/min. Spiked IPA concentration: 25-50 ppm. Experiments were carried out at 25 °C.

The effect of volumetric flow rate was examined in a series of experiments using a larger diameter column (2.54 cm × 10 cm). The results of this study are presented in Figure 2. As seen in the figure, flow rate had a dramatic effect on the degree of ion leakage. After an initial stabilization period, the effluent composition stabilized at different levels for the various flow rates. The compositions ranged from 100 ppb at 10 mL/min down to 20 ppb at 2 mL/min. In fact, it is important to note that the chromatographic ion analysis was limited to 20 ppb due to background interference. Thus, the results at 2 mL/min could well be improved over 20 ppb. These results indicated that residence time of the ions in the column played an important role in the leakage level. In order to increase the residence time in these systems, a longer column was employed. Frontal chromatographic experiments were carried out at 10 mL/ min using high concentrations of Na+ and/or K+ feed in IPA with a 2.54 × 25.4 cm column. These experiments were carried out with columns packed with Amberlite IR 120+, Ionac CFP 110, and Dowex M31. Fractions of the column effluent were collected and sent out for rigorous metal ion analysis. As seen in Table 1, in all cases, the columns were able to reduce the cation concentration to low and sub-parts-per-billion levels. A similar set of experiments was carried out with anion exchange systems. Ion chromatographic analysis of the column effluent from columns packed with anion exchange resins showed that inlet concentrations of 2030 ppm of chlorides, sulfates, and nitrates were all reduced to lower than 0.1 ppm (detection limit of the assay). In order to examine the long-term behavior of these systems, the 25.4 cm long Ionac CFP 110 column was perfused with 35 L of 45 ppm Na+ in IPA. A detailed analysis of the composition of both the inlet and column effluent (after 35 L was perfused) is presented in Table 2. As seen in the table, the column was indeed able to reduce the concentrations of all 34 ions analyzed by ICP/ MS and GFAAS to low and sub-parts-per-billion levels.

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NMP

Internal Standard

a

Internal Standard

b

Figure 3. GC-MS scan of (a) inlet solution containing 5 ppm of NMP in IPA and (b) sample taken from column effluent after nine column volumes.

Ind. Eng. Chem. Res., Vol. 35, No. 9, 1996 3153 Table 1. Leakage Values of Different Resins (Packed in 1 in. × 10 in. Stainless Steel Column) Obtained by Flow Experimentsa resin name

Na+ (ppb) (inlet IPA)

K+ (ppb) (inlet IPA)

Na+(ppb) (postcolumn)

K+ (ppb) (postcolumn)

Amberlite IR 120+ Ionac CFP 110 Dowex M 31

32 000 42 200 69 500

15 000 18 100 25 500

0.91 0.83 1.7

0.60 0.80 1.8

a

IPA was spiked with Na+ and K+ ions. The analysis was performed by ICP/MS.

Table 2. Analysis of Postcolumn IPA (by ICP/MS) Obtained from Long-Run Experiment

element

detection limit (ppb)

spiked IPA front (precolumn concn (ppb)

Ionac CFP 110 IPA (postcolumn) concn (ppb)

aluminum antimony arsenic barium beryllium bismuth boron cadmium calcium chromium cobalt copper gallium germanium gold iron lead lithium magnesium manganese molybdenum nickel niobium potassium silver sodium strontium tantalum thallium tin titanium vanadium zinc zirconium

0.05 0.05 0.10 0.01 0.05 0.05 0.05 0.01 0.10 0.05 0.01 0.05 0.01 0.05 0.10 0.10 0.05 0.05 0.10 0.05 0.05 0.05 0.05 0.10 0.05 0.10 0.01 0.01 0.01 0.05 0.05 0.01 0.01 0.01

0.27 < 0.05 < 0.10 0.015 < 0.05 < 0.05 < 0.1 < 0.01 14.0 < 0.05 < 0.01 1.70 < 0.01 < 0.05 < 0.10 0.49 < 0.05 < 0.05 1.5 0.053 0.095 0.24 < 0.05 26.0 < 0.05 44916.0 0.32 < 0.01 < 0.01 < 0.05 0.08 < 0.01 0.52 < 0.01

< 0.05 < 0.05 < 0.10 < 0.01 < 0.05 < 0.05 < 0.1 < 0.01 0.48 < 0.05 < 0.01 1.0 < 0.01 < 0.05 < 0.10 0.36 < 0.05 0.053 < 0.10 < 0.05 0.11 < 0.05 < 0.05 1.0 < 0.05 1.50 < 0.01 < 0.01 < 0.01 < 0.05 < 0.05 0.34 0.093 < 0.01

In addition, analysis of the column effluents by GC/MS indicated that no organic leaching was observed in any of these experiments. Experiments were also carried out to examine the utility of the synthetic activated carbon, Ambersorb, for the removal of n-methyl-2-pyrrolidone (NMP), a common organic contaminant, from IPA. Samples of the column effluent were collected and evaluated by GC/ MS. An internal standard of 10 ppm, 2,6,10,14-tetramethylenepentadecane (TMPD), was employed in these analyses. Figure 3a presents the GC/MS scan of the inlet solution containing 5 ppm of NMP in IPA. Peaks corresponding to both NMP and the internal standard TMPD are clearly seen in the figure. Figure 3b shows the GC/MS scan of a sample taken from the column effluent after nine column volumes have passed through the column. As seen in the figure, the NMP in this sample is below the detection limits of 0.5 ppm. These results indicate that organic contaminants such as NMP can be readily removed using packed columns of activated carbon. Furthermore, analysis of the column effluent indicated that the carbon bed did not release any detectable amounts of ions during this experiment. IPA coming out of vapor phase dryers employed in the semiconductor industry typically have water con-

Figure 4. Water breakthrough curve on column packed with molecular sieve type 3A. Column: 4 in. × 30 in. stainless steel column (with approximately 3965-g molecular sieves). Flow rate of wet IPA (5.08% water): 75 mL/min.

tents of approximately 5% (w/w). In order to recirculate the IPA solvent back to the dryers, it is necessary to reduce the water content to 0.01% (w/w). A 4 in. × 30 in. column packed with molecular sieve (type 3A) was evaluated for water removal from IPA. IPA containing 5% (w/w) water was pumped into the column at 75 mL/ min. Samples of the column effluent were collected and evaluated for water content using a Karl Fisher titration apparatus. Figure 4 shows the column effluent profile. As seen in the figure, the molecular sieve column was readily able to remove the water content to 0.0075% (w/w). In fact, the dynamic capacity of the column (based on a breakthrough concentration of 0.015% (w/w)) was approximately 10% water by weight (i.e., 10 g of water/100 g of molecular sieve). Conclusions Commercially available ion exchange resins have been shown to have high affinity and capacity for ions present in IPA and can thus be readily employed for removal of these ionic impurities to low and sub-parts-per-billion levels. Under column operation, the high dynamic capacity of these resins enables the processing of large volumes of IPA waste without resin regeneration. Since these systems must reduce ionic impurities down to extremely low levels, care must be taken with respect to column, tubing, and collection vessels that come in contact with the IPA stream. Electropolished stainless steel 316 L or inert materials such as Teflon are recommended. Since commercial resins may leach out organics during the initial contact with IPA, it is essential to pretreat the resins with an appropriate protocol (as described above). In addition to the ionic impurities, it is necessary to remove water and organic contaminants from the solvent. Columns packed with activated carbon and molecular sieves were shown to be efficacious in removing organic and water impurities, respectively, from 2-propanol to low levels required for semiconductor applications. The work presented here sets the stage for the development of efficient resin-

3154 Ind. Eng. Chem. Res., Vol. 35, No. 9, 1996

based closed-loop recycling systems for 2-propanol drying applications in the semiconductor industry. Such a reprocessing system is anticipated to consist of cation and anion exchange beds, molecular sieve beds, activated carbon beds for removal of organics and organometallics, and various filters for eliminating particulates (>0.02 µm). Critical issues in this system will be the design of the various columns as well as the optimum configuration of the complete reprocessing system. In addition, it is anticipated that this system will be fully automated and will apply state-of-the-art microprocessor-based controls. Acknowledgment The authors of this paper gratefully acknowledge New York State Energy Research and Development Authority (NYSERDA) for supporting this research. The authors also acknowledge the help and support provided by Kevin Golden and Tom Isaacs of Stainless Design Corporation (SDC), Saugerties, NY. Literature Cited Bodamer, G. W.; Kunin, R. Behavior of Ion Exchange Resins in Solvents Other than Water. Ind. Eng. Chem. 1953, 45, 2577. Buechelle, R. C.; Reuter, D. J. Effect of methanol in the mobile phase on the ion chromatographic determination of some monovalent ions. J. Chromatogr. 1982, 240, 502. Helfferich, F. Ion Exchange; McGraw-Hill: New York, 1962; Chapter 5. IUPAC Commission on Electroanalytical Chemistry. Analytical Chemistry Division U.K. Recommended methods for the purification of solvents and tests for impurities: 1-propanol, 2-propanol. Pure Appl. Chem. 1986, 58 (10), 1411. Kagiyama, Y.; Doi, K.; Nonaka, T.; Ishiyama, Y.; Komatsubara, S. Purification and recovery of organic solvents after washing of semiconductor substrates. U.S. Patent 4,788,043, 1986.

Kawazy, K.; Comparison of efficiency of cation-exchange resins in the chromatographic separation of metal ions with aqueous acetone-hydrochloric acid solution. J. Chromatogr. 1977, 137, 381. King, J. N.; Fritz, J. S. Separation of metal ions using an aromatic o-hydroxy oxime resin. J. Chromatogr. 1978, 153, 507. Kiser, D. L. Removal of water from aqueous alcohol mixtures. U.S. Patent 4,696,720, 1987. Liebetreu, G.; Rynders, S. Chemical reprocessing and treatment: Here and Now; Wafer drying with reprocessed isopropyl alcohol. Solid State Technol. 1994, 37, 53. Marton-Schmidt, E.; Inczedy, J.; Laki, Z.; Szabadka, O. Separation of metal ions on ion-exchange resins with ethylenediamine functional groups. J. Chromatogr. 1980, 201, 73. Sergeev, G. M.; Lukuttsov, A. A.; Maiorova, T. F. Spectrophotometric determination and study of sorption by ion exchangers of small quantities of chloride ion and iron(III) in alcohol media. Izv. Vyssh. Uchebn. Zaved., Khim. Khim. Tekhnol. 1991, 34 (5), 45. Sokolova, L. P.; Skornyakov, V. V.; Kargman, V. B.; Saldad, K. M. Selective separation of components [Copper, Nickel, Zinc, Chromium(VI)] in the process of ion exchange purification of waste waters. J. Chromatogr. 1986, 364, 135. Wankat, P. C. Rate-Controlled Separations; Elsevier Science: London, 1990; Chapter 9. Yeo, S. K.; Sivaramasubramaniam, R.; Chang, R.; Wang, F. C. Impact of metallic contaminants in IPA on high temperature MCLT. Conference Proceedings of Semiconductor Pure Water and Chemicals Conference, San Francisco, CA, February 2223, 1995; Balazc Analytical Laboratory: Santa Clara, CA, 1995.

Received for review January 16, 1996 Revised manuscript received April 25, 1996 Accepted April 27, 1996X IE960017J

X Abstract published in Advance ACS Abstracts, August 15, 1996.