Transcript korea3 - University of Arizona

PFC Reduction Technologies:
Destruction
Recovery
Optimization
Phyllis Pei, Walter Worth
Sematech
Semicon/Korea 1997
 1999 Arizona Board of Regents for The University of Arizona
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
Pei, et al.
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Outline
• General Comments on PFC Abatement
• PFC Destruction:
– Combustion
– Chemical/Thermal
– Plasma
• Recovery/Recycle
• Optimization
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SEMATECH GLOBAL WARMING
PROGRAM OBJECTIVE
Decrease the use and reduce the emissions of potential global
warming semiconductor processing materials; specifically the
perfluorocompounds (PFCs), such as CF4, C2F6, NF3, SF6 and
substituted PFCs such as CHF3
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Typical FAB
Atmosphere
PFC’s
CF4
C2F6
NF3
SF6
Etch or
CVD Tool
Vacuum
System
Fab
Scrubber
(water)
N2 Purge
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Project Strategy
Alternative *
Chemicals
Global
Warming
Gas
Reduction
Destruction/ *
Decomposition
Combustion *
Process *
Optimization
Recovery *
& Recycle
Plasma *
Thermal/
Chemical
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Typical Etch and CVD Systems
Atmosphere
N2
Scrubber
L/min
PFC
cc/min
Chamber
Pre-Pump
Treatment
Optimization
Recovery/Recycle
Alternatives
Plasma Destruction
Pump
Abatement
Combustion
Chem/Thermal
Absorption
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Example Conversions in
Chamber Clean Applications *
PFC
CF4
C2F6
C3F8
NF3
CHF3
SF6
*
% Consumed
in Tool
5
30
60
60
40
20
% Emitted
95
70
40
40
60
80
Actual values may vary significantly based on process, tool, recipe, etc.
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Technology Options
Process Optimization
Recovery/Recycle
Greener,
Preferred
Technology
Alternative Chemicals
Commercial
Availability
Plasma Destruction
Thermal/Chemical Reaction
Combustion
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PFC Abatement Options / Devices
Combustion
Centrotherm Flawamat
DAS Escape
Delatech CDO*
EcoSys Guardian
EcoSys Phoenix*
Edwards TPU*
Chemical/Thermal
Destruction
CS Systems
Edwards GRC
Kanto Denka
Plasma
Destruction
MIT Microwave*
ETC DryScrub*
Texas A&M rf surface
wave *
Los Alamos Pulsed
Corona *
PRC *
* Evaluation supported by SEMATECH
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Typical Etch and CVD Systems
Atmosphere
N2
Scrubber
L/min
PFC
cc/min
Chamber
Pre-Pump
Treatment
Optimization
Recovery/Recycle
Alternatives
Plasma Destruction
Pump
Abatement
Combustion
Chem/Thermal
Absorption
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Main Features of a Combustion Device
a. A combustion chamber followed by water scrubber in POU
cabinet
b. Handles up to four tool chambers (200 lpm), each with
separate inlet to avoid mixing reactive materials such as silane
and NF3
c. Uses either methane (CH4) or hydrogen (H2) as fuel
d. Operates in 850-1000 ºC range for CF4 destruction, the most
difficult to combust
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Main Features of a Combustion Device
(Cont’d)
e. The best can achieve > 95% destruction for all PFCs
f. Combustion by-products include: COF2, HF, NOX, CO, CO2
g. Integral scrubber uses 6-8 gpm of water to remove HF, COF2
and heat of combustion
h. Foot print approx. 24” x 36” x (60” high)
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Concerns with PFC Abatement
a. Difficult for PFCs, especially CF4, due to stability
b.
Often creates other environmental problems: NOx and HAPs
c. Generally expensive
d. Potential safety concerns: combustion, fuel gas, high
temperatures and toxic byproducts
e. May impact process tool uptime
f. Fab floor space limitations
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Combustion Technology
•
Strengths
– Industry is familiar with
combustion
– Industry is currently using
“burn boxes” to treat
pyrophorics
– One device may be able to
abate pyrophorics and
PFCs
– Most devices have an
integral scrubber to remove
HF
– Technology is closest to
being production-worthy
•
Issues
– Need open flame and high
temperatures (> 850 ºC) to
break down PFCs
– Produces HF, CO2 (more GW
gas) & NOx (in some cases)
– Costs for fuel and water (for
scrubber) are significant
– Fab may not be piped for fuel
– Uses valuable fab floor space
– Cost of ownership is high
($50-$100K)/year
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Typical Etch and CVD Systems
Atmosphere
N2
Scrubber
L/min
PFC
cc/min
Chamber
Pre-Pump
Treatment
Optimization
Recovery/Recycle
Alternatives
Plasma Destruction
Pump
Abatement
Combustion
Chem/Thermal
Absorption
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Main Features of Chemical/Thermal
Device
a. Gases are chemisorbed on reactive granular solids
b. Chemistry is generally trade secret
c. Solids are held in disposable or reusable stainless steel
cartridge
d. Solids are electrically heated to 300-500 °C
e. PFCs are converted to stable, non-hazardous salts
f. Solids are replaced when the bed is exhausted
g. Footprint of dual cartridge cabinet is 30” x 57” (72” high)
h. Limited ability to destroy CF4 in some cases
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Example: CS System
a.
b.
c.
d.
e.
f.
g.
A packed-bed reactor filled with iron-based granules
Irreversible chemisorption on catalytically active absorbents
Laboratory tests show it can treat all PFCs (99% DRE)
Conversion of PFCs to stable, non-hazardous salts
Capacity for CF4 and C2F6 not yet known
Operating temperatures are 300 - 450 °C
Foot print for dual bed cabinet: 57” x 30” x 71” (H)
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Chemical/Thermal Destruction Technologies
•
Strengths
– Reaction product is a nonhazardous solid that can be
landfilled
– Industry is familiar with
concept (technology is used
in fabs today to treat toxic
hydrides)
– Low energy cost
– It is a passive system; no
moving parts
– Scalable, and can
accommodate intermittent
operations
•
Issues
– Cartridge has limited
capacity, may only be
suitable for etch tools (low
PFC flow rates)
– Packed bed reactor issues
(e.g., plugging, breakthrough, pressure drop)
– Disposal of solids is a
concern (e.g., long term
liability of landfilled waste)
– Cost of ownership is high
– Uses valuable fab floor space
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Typical Etch and CVD Systems
Atmosphere
N2
Scrubber
L/min
PFC
cc/min
Chamber
Pre-Pump
Treatment
Optimization
Recovery/Recycle
Alternatives
Plasma Destruction
Pump
Abatement
Combustion
Chem/Thermal
Absorption
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Example: ETC DryScrub
a. RF plasma device normally installed downstream of the tool
and ahead of the vacuum pump
b. Electrode consists of multi-turn, high-conductance spirals that
form the path for the gas flow (45 sq. ft. of surface area)
c. The residual process gases leaving the tool are reacted to
depletion as they pass through device
d. The electrode is both the reaction and collection chamber for
the solid products formed from the reaction
e. The solids-laden electrode is replaced and discarded
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Plasma Destruction Technology
•
Strengths
– Industry is familiar with
plasma technology
– Treats tool exhaust upstream
of pump (no N2 dilution
form vacuum pump)
– Promises to have low cost of
ownership
– Products of destruction may
all be water-scrubbed
•
Issues
– Commercially available RF
plasma devices have shown
limited effectiveness for PFCs
– May require microwave plasma
based on successful laboratory
tests
– Technology still in experimental
phase
– May not be transparent to
process tool
– May require additional water
scrubber
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Status of PFC Abatement Technology
a. Suppliers are working feverishly to develop new devices and
improve existing ones.
b. Chip manufacturers have committed significant resources to
evaluate the systems under development.
c. Progress is slow, but significant progress has already been
made and further advances are on the horizon.
d. Combustion technology is the most advanced and has the most
players.
e. Packed bed, thermal/chemical destruction is becoming viable.
f. Plasma decomposition is still in the experimental phase.
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Typical Etch and CVD Systems
Atmosphere
N2
Scrubber
L/min
PFC
cc/min
Chamber
Pre-Pump
Treatment
Optimization
Recovery/Recycle
Alternatives
Plasma Destruction
Pump
Abatement
Combustion
Chem/Thermal
Absorption
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PFC Recovery Technologies
• Membrane Separation (Air Liquide)
• Pressure Swing Absorption (Air Products/Radian, BOC)
• Cryogenic Extraction (Praxair/Ecosys)
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Example: MEGASORBTM Approach
a. Process developed by Air Products & Dow Environmental
(now Radian International LLC)
b. Uses SORBATHENETM resins proven for VOCs
c. Captures all PFCs for central abatement, recovery and/or
purification
d. Flexible for varying recipes, fab sizes, purity levels, flow rates
e. Synergistic with MEGASYSTM onsite services and analytical
expertise
f. Demonstrated recovery >99% possible
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MEGASORB ™ Process Flow Scheme
Process Chamber
Pretreatment
Packaging
Wet Scrubber
Cryo Distillation
Dryer
Sorbathene PSA
Condenser
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Recycling/Recovery Technology
•
•
Strengths
– Closed loop system with no
PFC emissions
– Recovers costly PFC gases
– High recovery using
currently available
technologies
– Purification uses proven
cryogenic techniques
Issues
– Requires pre-treatment of
gases prior to recovery
– Repurifying PFCs to “like
new” may not be cost effective
– Need to replumb PFC exhaust
to a common manifold
– NF3 and CF4 have almost
identical boiling points separation may be difficult
– Low concentration of
recovered PFC using pressure
swing absorption
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Typical Etch and CVD Systems
Atmosphere
N2
Scrubber
L/min
PFC
cc/min
Pre-Pump
Treatment
Chamber
Optimization
Alternatives
Recovery/Recycle
Pump
Abatement
Combustion
Chem/Thermal
Absorption
Plasma Destruction
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Process Optimization Example
•
•
•
IBM Burlington optimized the TEOS & PSG CVD processes
– Used endpoint detection (Fourth State RF metrology) to optimize twostep clean; PFC reduction was not the major objective
Achieved the following :
– 50% reduction in C2F6 usage
– 100% reduction in NF3 usage
– 25% reduction in chamber consumable parts
– increased throughput
Implementation in one fab produced annual savings of:
– $1.2 M in added throughput
– $300 K in chemicals
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Validation of C3F8
as Drop-in Replacement for C2F6
•
Project Tasks:
– Perform Design of Experiments (DOE) to compare C3F8 vs
C2F6
– Marathon wafer run to monitor TEOS film properties
(particle count, stress, thickness uniformity)
– Compare PFC emission and etch gas utilization
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C3F8 Tests at AMD
•C3F8 DOE optimization conditions:
–1000 sccm C3F8, 1400 sccm O2 and 3.6 torr
•With C3F8:
–C3F8 flow is 60% less (45% fewer pounds)
–O2 flow is 30% less
–etch gas utilization = 60-70% (vs 30-40% for C2F6)
–net greenhouse gas reduction = 70%
•No TEOS film or chamber hardware degradation
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Optimization
•
Strengths
– Most desirable, chemical
and cost saving option
– Good for CVD chamber
clean applications
– Equipment suppliers are
active in this area
•
Issues
– Requires experimentation on
process, which may be too
costly, risky, and time
consuming
– Needs beta test demonstration
to transfer technology
– May require equipment retrofit
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Status of Technology
•
Alternative Chemistries
–
–
–
–
–
•
Most desirable, but probably most difficult
A long-term solution
Most likely flourine-based, less stable and more hazardous
MIT study underway to find suitable replacements
Schumacher, 3M, DuPont also doing R&D
Process Optimization
– Very desirable
– Reduces chemical cost & emissions, may increase throughput and
prolong life of reactor internals
– End-point detection and reactor modifications
– Progress already made, room for more (reductions of 50% have been
demonstrated on some processes)
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Status of Technology (cont’d)
•
Recovery/ Recycle of Unused PFCs
–
–
–
–
•
Preferred over abatement
“Greener” technology with potential pay-back
Significant appeal for larger fabs
Five gas companies are developing systems currently
Combustion
–
–
–
–
–
Abatment option closest to commercialization
Need flame and high temperatures to break down PFCs
Produces HF, NOx , COF2 and CO2 (more GW gas)
Fuel and water (for scrubber) costs are significant
Cost of Ownership ranges from $47 - $106K/year for device handling
four chambers
– Opportunities for suppliers to optimize
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Technology Status (cont’d)
•
Chemical/Thermal Destruction
–
–
–
–
•
Involves reacting the PFCs with granular solids
Technology is well developed for hydrides, but treating PFCs requires new
chemistries and elevated temperatures
Cartridge has limited capacity, may only be suitable for etch tools
Disposal of spent solids a concern
Plasma Destruction
–
–
–
–
Advantage: treats tool exhaust upstream of pump (no N2 purge dilution)
MIT study showed excellent abatement of CF4, C2F6 & SF6 in a microwave
plasma reactor
Commercially available RF plasma devices such as DryScrub and PRC are
not effective
Requires water scrubber
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