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US 6,960,242B2 56 Wafer is cleaned up to 100 times. The Wafers are treated With supercritical ?uids to clean, strip solvents or photo-resist resins, dehydrate or otherwise treat the Wafers or structures on the Wafers. The semiconductor Wafer to be processed, or cleaned, is contacted With supercritical CO2 (SCCO2) directly in a processingchamber,suchthatthetargetresiduedissolvesin the SCCO2 or in the SCCO2 and a co-solvent. BetWeen about2% toabout50% byWeightoforganicco-solvents, suchasethanol,methanol,areoftendissolvedintheSCCO2 10 to increase the solubility of the residue in SCCO2. This dissolution may be carried out atpressures over 100 bar and temperatures betWeen approximately 40° C. and 200° C. The dissolved mixture is transferred to another vessel Wherethepressureandtemperaturearereduced,causingthe 15 residue material and co-solvent to condense out as a Waste stream. Co-solvent material can be recovered using standard distillation methods. The CO2-soluble co-solvent mixture is exhausted as a vent stream. WithreferencetoFIG.1,acarbondioxiderecoveryand 20 supply apparatus is shoWn generally at 1. From a bulk supply of liquid carbon dioxide 10, a feed stream 11 com prisingcarbondioxidevaporisdistilledina?rstpuri?cation stage, and is introduced into a purifying ?lter 13 and a particle?lter14WhichcanbeanyofanumberofknoWn, 25 commercially available ?lters, for a second stage puri?ca tion. The ?rst ?lter 13 may be a coalescing ?lter to remove condensablehydrocarbons.Asingleadsorberbed,including activatedcarbon,alumina,andcarbonmolecularsievemate rial may remove additional amounts of hydrocarbon impu rities. Valve 12 isprovided to isolate the bulk CO2 supply 10. The bulk supply 10 may be a tank of liquid CO2 maintained at about 300 psig (2.1 MPa) and about 0° F. (—18° C.). As carbon dioxide vapor is draWn out of the bulk supply tank, aportionoftheliquidcarbondioxideinthebulktankis35 draWn through conduit 16 and introduced to a pressure build device 17 such as an electric or steam vaporiZer or the like, to maintain the pressure relatively constant Within the bulk supply tank even though carbon dioxide vapor is being removed.ThevaporiZertakesliquidCO2fromthesupply40 tank and uses heat to change the CO2 from the liquid phase to the gas phase. The resulting CO2 gas is introduced back into the headspace of the supply tank. The feed stream 11 after having been puri?ed in the second stage is introduced into a condenser 18 that is 45 provided With a heat exchanger 21 to condense the carbon dioxide vapor into a liquid 19. Such condensation is effected by an external refrigeration unit 22 that circulates a refrig eration stream through the heat exchanger, preferably of shell and tube design. Isolation valves 28 and 29 can be provided to isolate refrigeration unit 22 and its refrigerant feed line 26 and return line 27. The liquid carbon dioxide is temporarily stored in a receiver vessel 30, that is, a loW pressure accumulation vessel. The level of liquid in the loW pressure accumulation receiver vessel 30 is controlled by a level sensor 53 (such as a level differential pressure transducer) Which monitors the level of liquid carbon dioxide and a pressure sensor 54 (such as a pressure transducer) Which monitors the pressure Within the receiver vessel 30, via a controller (not shoWn, such as a programmable logic computer). An intermediate liquid stream comprising high purity CO2 liquid19isintroducedfromthereceivervessel30into a high-pressure accumulation vessel 50 after further puri? cation and pressuriZation. The intermediate liquid carbon dioxidefromthereceivervessel30travelsthroughoutlet65 conduit 32 and is again puri?ed in a further puri?cation stage by one of tWo particle ?lters 41 and 42. The particle ?lters 41 and 42 can be isolated by valves 35,36 and 37,38 respectively, so that one ?lter can be operational While the other ?lter is isolated from the conduit by closure of its respective valves, for cleaning or replacement. The loW pressure,puri?edintermediateliquidcarbondioxidestream 39 emerges from the ?nal ?ltration stage for pressuriZation, such as by a compressor 45, and storage in the high pressure accumulation vessel 50 prior to use in the desired process as described above. Avalve netWorkcontrolstheHow Withintheapparatus.In thisregard,?llcontrolvalve25controlstheHowofthe intermediate liquid stream from the condenser 18 to the receiver vessel 30. Control of the How of the loW pressure intermediate liquid carbon dioxide stream through outlet conduit 32 is effected by product control valve 34. Drain valve33alsoisconnectedtooutletconduit32forsampling or venting, as needed. The venting of the loW-pressure accumulation receiver vessel 30 via vent line (conduit) 31 to the condenser 18 is controlled by vent control valve 24. An insulationjacket20,suchasoneformedofpolyure thaneortheequivalent,canbedisposedaboutthecondenser 18,theconduitforcarryingtheliquidCO2 19,thereceiver vessel 30, and the outlet conduit 32 and associated valves to maintain the desired temperature of the liquid CO2. The liquid CO2 in the high pressure accumulation vessel 50maybestoredontheorderof300bar(30MPa)pressure and 80° C., that is, above the critical pressure (7.38 MPa) andcriticaltemperature(31.1°C.)forcarbondioxide.Upon demand, the high purity supercritical carbon dioxide 51 is dispensed into a cleaning chamber 60 for the industrial part, such as semiconductor Wafers, together With at least one co-solvent for the residue to be removed from the Wafers. After the high purity supercritical CO2 stream has gone throughtheWaferproductionorcleaningprocess,thesuper critical Waste stream 61 is depressuriZed and passed through redundant valves 62, 63 to form a CO2/co-solvent stream 65 ontheorderofabout25bar(2.5MPa)pressureand50°C. LoW pressure CO2 vapor 66 can be sent to a scrubber via valve 64. The CO2/co-solvent stream 65 passes through valve 68 to be cooled using mechanical or cryogenic refrig erants in a condenser 70 to form a tWo-phase mixture, With themajorityofimpuritiesbeingintheprimarilyco-solvent liquid phase 71 that is collected in receiver 75. Conventional coolers, condensers and phase separators may be used for the vapor cooling and phase separation. After the phase separation, the vapor phase stream 72 (noWontheorderofabout25bar(2.5MPa)pressureand5° C.) containing primarily CO2 With trace amounts of impurities, passes through valves 73,74 to a ?lter 80 using a temperature controlled, packed column operating at a temperature close to the saturation temperature for CO2 at the given pressure. Residual co-solvent (such as ethanol, etc.) and solid Waste material cleaned off of the industrial part, such as target semiconductor Wafer (i.e. photomask, etching chemicals, etc. used in the manufacture of semicon ductor Wafers) is removed from the carbon dioxide vapor phase stream. The ?ltered vapor phase 81 is passed through an adsorp tion bed system 85 such that trace impurities are removed. The adsorption beds may contain activated carbon, alumina, or carbon molecular sieve material. For the separation of trace impurities, a 2-bed adsorption system 85 operated in a cyclicmannercanbeused.Eachadsorptionbed82,83can have a plurality of layers of adsorbents to ensure that all traceimpuritiesaresubstantiallyremoved.Thepuri?edCO2 stream 90 is recovered, to be converted to a high-pressure product.When oneadsorptionbed82issaturatedWithtrace impurities,theCO2streamissWitchedbyclosingvalves86 and 87 to the clean adsorption bed 83 by opening valves 88 and 89. In one embodiment, a portion of the vaporiZed 30 55 60PDF Image | CO2 RECOVERY PROCESS FOR SUPERCRITICAL EXTRACTION
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