Low GWP Alternatives to P

P

Heat Transfer Fluids Heat Transfer Fluids 

As a Means to Decrease Facility Greenhouse Gas EmissioWilliam Liaw Technical Service Supervisor Weli Lin T h ec nical Service Speciali st

Phillip TumaAdvanced Application Development Specialist 3M Electronic Markets Materials Division 
1. Background
 

	 Semiconductor manufacturing processes such as etch, plasm

deposition (PECVD), ion implant and test use heat transfer liqcomponent temperatures. 

	 The liquid is most often pumped from the sub fab by a chiller t

process tool 

	 The liquid must be dielectric to The liquid must be dielectric to	 Process Tool Process Tool 

maintain electrical isolation or to prevent damage to electronics should the liquid leak
 

Fab Sub Fab Sub Fab 

T

	 Two 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 

Fluorinated liquids like Perfluorocarbon (PFC) or Perfluoropolyethe
1. Background
 

 PFC and PFPE liquids are growing in popularity for the

 Chemically inert and non-flammable  High dielectric strength and electrical resistivity do not cha

maintenance
 

 Evaporate cleanly and are practically non-toxic.  Can span a temperature range of -115°C to over 200°C
 
2. Semiconductor Industry’s PFC Gas Emis

Reduction Efforts 

	 Pledged to reduce GASEOUS emissions of CF4, C2F6, 

and SFgenerated by plasma wafer etch and PECVD 

6 generated by plasma wafer etch and PECVD 

processes 

 1996 Memorandum of Understanding (MOU) between Se

Association (SIA) and US EPA. Renewed 2001, 2004, 

	 In 1999 the World Semiconductor Council (WSC) establish

semiconductor industry goal to reduce normalized emissio

	 Emissions are quantified via WSC Tier 2 methods 	 Reduction strategies include: process optimization; abatem

programs; and the adoption of alternative plasma chemist
A l SIA PFC P E i i (B ) 2004 

2. Semiconductor Industry’s PFC Gas EmisReduction Efforts Reduction Efforts  Emission reduction efforts have been successful 

Annual SIA PFC 

Partner 

Emissions (Beau). 2004 em

25% from 1999 despite 55% increase in wafer deman
3. PFC/PFPE Liquid Environmental Impa

	 PFC and PFPE Liquids have high Global Warming Pot

gases 

 PFC/PFPE GWP is about 9,000 to 12,000  1 Liter = 1.7kg = 17 Metric Tons CO2 Equivalent (MTCE) 

	 Semiconductor tools lose fluid 

 Leak Sources: Spills evaporation from reservoir diffusion 

Leak Sources: Spills, evaporation from reservoir, diffusion 

 Tools average about 2 liter per month ≈ 400 MTCE/yr  Fluid is very rarely captured and incinerated. It evaporates.  Average high volume fab consumes/emits about 1900 liter/yr ≈ 

 It is estimated that a fab It is estimated that a fab s ’PFC/PFPE liquid emissions can 

PFC/PFPE liquid emissions can 

PFC emissions... 
3. PFC/PFPE Liquid Environmental Impa

If PFC/PFPE liquid emissions are included, emission rmay not be met. 
t t t t 

4. PFC/PFPE Alternatives
 	 The best strategy for reducing PFC/PFPE liquid emiss

with commercially-available low-GWP alternatives: 

 Hydrofluoropolyethers (HFPEs)
 

 Have GWPs about 48% those of PFC/PFPE liquids
 

 Not a significant reduction vs. PFC/PFPE
 

 Segregated hydrofluoroethers (HFEs) 

 Term “Segregated” refers to the chemical structure. Fluorinate

segregated from hydrogenated portion, RH, by an ether oxyge

Example C7F15OC2H5 

	 Have GWPs from 1% to 4% those of PFC/PFPE liquids  Have alread y been wid ely ad opted i A dnutomati T cest Equi 

pme

some Etch tools
 
4. PFC/PFPE Alternatives
 
4. PFC/PFPE Alternatives
 
4. PFC/PFPE Alternatives
 

 Practical Considerations 

 Segregated HFE liquids are often but not always “drop-in” 

liquids 

	 Segregated HFE Electrical Properties
 

 Lower electrical resistivity than PFC/PFPE liquids
  Higher electrical resistivity than the best attainable DI water
  Usually adequate Usually adequate 
 

	 Material Compatibility 

 Like PFC/PFPE liquids, segregated HFE liquids are compatible  Segg re ated HFE liquids are not comp atible with some elastom

 Because they are hydrogenated, HFE liquids are better so Many hydrocarbon elastomers contain hydrocarbon oils  Must use elastomers approved for use with HFE liquids 

	 Thermal Stability 

 Experience indicates that segregated HFE liquids may not be s
4. PFC/PFPE Alternatives 

	 New liquid chemistry is needed for applications above 

	 New liquids are being developed by 3M 

 Boiling points 150-250°C  Thermal stabilities comparable to PFCs  GWPs<150 
Conclusions 

	 A fab’s PFC heat transfer liquid emissions are a signific

its total PFC emissions. 

	 Use of commercially available Segregated HFE liquids 

emissions attributable to PFC liquids by 96% to over 9

	 Segregated HFE heat transfer liquids possess a balance o

well suited for semiconductor heat transfer applications well suited for semiconductor heat transfer applications.
 

 They are not always drop-in replacements
  Their thermal stability limits their use to sub-150°C applica

	 Alternative liquid chemistries are being developed for a

like high temperature heat transfer and vapor phase so
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References 	 L. Beu “Reduction of PFC Emissions: 2005 State of the Technology Re

Manufacturing Initiative (ISMI) Technology Transfer # 05104693A Manufacturing Initiative (ISMI), Technology Transfer # 05104693A -ENG 

ENG

	 C. Shepherd Burton, USES AND AIR EMISSIONS OF LIQUID PFC HE

ELECTRONICS SECTOR, EPA Document # EPA-430-R-06-901. 

	 P. Tuma and L. Tousignant, “Reducing Emissions of PFC Heat Transfer 

West 2001 Technical Symposium, San Francisco, Ca. 

	 IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contri

Fourth Assessment Report of the Intergovernmental Panel on Climate CManning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eCambridge, United Kingdom and New York, NY, USA, 996 pp, 2007.