LGAlPFC/PFPEowWPiternatves toPFC/PFPEHeat Transfer FluidsHeat Transfer FluidsAs a Means to Decrease Facility Greenhouse Gas EmissionsWilliam LiawTechnical Service SupervisorWeli LinT hecnicalerviceSpecialistSPhillip TumaAdvanced Application Development Specialist3M Electronic Markets Materials Division1.BackgroundSemiconductor manufacturing processes suchas etch, plasma enhanced chemical vapordeposition (PECVD), ion implant and test use heattransfer liquids to maintain process orcomponent temperatures.The liquid is most often pumped from the sub fab by a chiller that communicates with theprocess toolThe liquid must be dielectric tooolTheliquidmustbedielectrictoProcess ToolProcessTCommunicationmaintain electrical isolation orto prevent damage toelectronics should the liquidleakFabSub FabSubFabChillerHeatTransferLiquidTwo primary types of liquids are used:Deionized water or water/Ethylene Glycol (EG)Fl i t d li id lik P fl b (PFC) P fl l th (PFPE)FluorinatedliquidslikePerfluorocarbon(PFC)orPerfluoropolyether(PFPE)21.BackgroundPFC and PFPE liquids are growing in popularity for their unique attributesChemically inert and non-flammableHigh dielectric strength and electrical resistivity do not change and require nomaintenanceEvaporate cleanly and are practically non-toxic.Can span a temperature range of -115°C to over 200°COften fluorinated liquidslike PFCs and PFPEs arethe only ones that canspan the temperaturerange of the applicationrangeoftheapplication32.Semiconductor Industry’s PFC Gas EmissionReduction EffortsPledged to reduceGASEOUSemissions of CF4, C2F6, CHF3, C3F8, c-C4F8, NF3and SFgenerated by plasma wafer etch and PECVD chamber cleaning6generatedbyplasmawaferetchandPECVDchambercleaningprocesses1996 Memorandum of Understanding (MOU) between Semiconductor IndustryAssociation (SIA) and US EPA. Renewed 2001, 2004,In 1999 the World Semiconductor Council (WSC) established an internationalsemiconductor industry goal to reduce normalized emissions of PFC gasesEmissions are quantified via WSC Tier 2 methodsReduction strategies include: process optimization; abatement, capture and recycleprograms; and the adoption of alternative plasma chemistries like NF3.4A l SIA PFC P E i i (B ) 2004 i i d2.Semiconductor Industry’s PFC Gas EmissionReduction EffortsReductionEffortsEmission reduction efforts have been successfulAnnualSIAPFCPartnerEmissions(Beau).2004emissions weredown25% from 1999 despite 55% increase in wafer demand.53.PFC/PFPE Liquid Environmental ImpactPFC and PFPE Liquids have high Global Warming Potentials (GWPs) like PFCgasesPFC/PFPE GWP is about 9,000 to 12,0001 Liter = 1.7kg = 17 Metric Tons CO2Equivalent (MTCE)Semiconductor tools lose fluidLeak Sources: Spills evaporation from reservoir diffusion through hoses leaksLeakSources:Spills,evaporationfromreservoir,diffusionthroughhoses,leaksTools average about 2 liter per month≈400 MTCE/yrFluid is very rarely captured and incinerated. It evaporates.Average high volume fab consumes/emits about 1900 liter/yr≈32,000 MTCE/yrIt is estimated that a fab’PFC/PFPE liquid emissions can be 1550% of its gaseousItisestimatedthatafab sPFC/PFPEliquidemissionscanbe15-50%ofitsgaseousPFC emissions...63.PFC/PFPE Liquid Environmental ImpactIf PFC/PFPE liquid emissions are included, emission reduction targetsmay not be met.7t t t t t4.PFC/PFPE AlternativesThe best strategy for reducing PFC/PFPE liquid emissions is to replace the fluidswith commercially-available low-GWP alternatives:Hydrofluoropolyethers (HFPEs)Have GWPs about 48% those of PFC/PFPE liquidsNot a significant reduction vs. PFC/PFPESegregated hydrofluoroethers (HFEs)Term “Segregated” refers to the chemical structure. Fluorinated portion of the molecule, RF, issegregated from hydrogenated portion, RH, by an ether oxygen atomExampleC7F15OC2H5Have GWPs from 1% to 4% those of PFC/PFPE liquidsHave alreaybeen widely aopted i AdnutomatiTcestEqupment(ATE),Handlers,Probers andddi TE)some Etch tools8Horizon (ITH).4.PFC/PFPE AlternativesGWPs of Segregated HFEsand HFPEs compared toandHFPEscomparedtoPFC/PFPE liquids usingstandard IPPC Methods and100 Year Integration TimeNovecTM is a registered trademark of 3M CompanyH-GaldenTM is a registered trademark of Ausimont94.PFC/PFPE AlternativesUse of Segregated HFEsleads to a 96-99% reductionleadstoa9699%reductionin liquid MTCE emissionsand may enable a facility tomeet their emissionreduction goals.104.PFC/PFPE AlternativesPractical ConsiderationsSegregated HFE liquids are often but not always “drop-in” replacements for PFC/PFPEliquidsSegregated HFE Electrical PropertiesLower electrical resistivity than PFC/PFPE liquidsHigher electrical resistivity than the best attainable DI waterUsually adequateUsuallyadequateMaterial CompatibilityLike PFC/PFPE liquids, segregated HFE liquids are compatible with metals and hard polymersSegreated HFE liquids are not comatible with some elastomersgpBecause they are hydrogenated, HFE liquids are better solvents for hydrocarbonsMany hydrocarbon elastomers contain hydrocarbon oilsMust use elastomers approved for use with HFE liquidsThermal StabilityExperience indicates that segregated HFE liquids may not be suitable at temperatures above 150°C.114.PFC/PFPE AlternativesNew liquid chemistry is needed for applications above 150°CNew liquids are being developed by 3MBoiling points 150-250°CThermal stabilities comparable to PFCsGWPs<150PFC/PFPE liquids are usedC but segregatedabove250CbutsegregatedHFEs are limited to about 150 

# °Cby stability considerations.above 250 

# °12ConclusionsA fab’s PFC heat transfer liquid emissionsare a significant and growing portion ofits total PFC emissions.Use of commercially available Segregated HFE liquids can reduce global warmingemissions attributable to PFC liquids by 96% to over 99%.Segregated HFE heat transfer liquids possess abalance of properties that makes themwell suited for semiconductor heat transfer applicationswellsuitedforsemiconductorheattransferapplications.They are not always drop-in replacementsTheir thermal stability limits their use to sub-150°C applicationsAlternative liquid chemistries are being developed for applications above 150°Clike high temperature heat transfer and vapor phase soldering13-ReferencesL. Beu “Reduction of PFC Emissions: 2005 State ofthe Technology Report”, International SematechManufacturing Initiative (ISMI) Technology Transfer # 05104693A-ENG December 2 2005ManufacturingInitiative(ISMI),TechnologyTransfer#05104693AENG,December2,2005.C. Shepherd Burton, USES AND AIR EMISSIONS OF LIQUID PFC HEAT TRANSFER FLUIDS FROM THEELECTRONICS SECTOR, EPA Document # EPA-430-R-06-901.P. Tuma and L. Tousignant, “Reducing Emissions of PFC Heat Transfer Fluids,”Presented at the SemiconWest 2001 Technical Symposium, San Francisco, Ca.IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to theFourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M.Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignorand H.L. Miller (eds.)]. Cambridge University Press,Cambridge, United Kingdom and New York, NY, USA, 996 pp, 2007.14