Air Filtration Technology and Future Developments for AMC ... Muller_Purafil_Air... · Air...
Transcript of Air Filtration Technology and Future Developments for AMC ... Muller_Purafil_Air... · Air...
Air Filtration Technology and Future
Developments for AMC Control
Chris MullerASHRAE Distinguished Lecturer
Member 2013 ITRS Yield Enhancement & Wafer Environment
Contamination Control Technical Working Groups
Technical Director
Purafil, Inc.
2654 Weaver Way
Doraville, GA USA
Introduction
• Contamination control in the microelectronics industry still has a
primary focus on the removal of airborne particulate matter.
• However, all leading-edge manufacturers have incorporated preventive
airborne molecular contamination (AMC) measures into their operational,
facilities, and contamination control activities.
• As wafer size approach 450 mm and device geometries drop below 20 nm,
the effects of AMC become magnified.
• Manufacturers have fully recognized the fact that sensitive electronic and
electrical equipment and components will be damaged if they are exposed
to AMC.
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The ITRS and AMC
• The development of the ITRS AMC control guidelines has come through
the Yield Enhancement (YE) Technical Working Group (TWG) and more
specifically, with the Wafer Environment Contamination Control (WECC)
sub-TWG.
• The WECC provides guidance on the types and
levels of AMC found in and around manufacturing
facilities, recommended control levels for AMC,
as well as options for effective assessment,
control and monitoring.
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Wafer Environment Contamination Control
• Wafer environment control includes the ambient space
around the wafer at all times, whether the wafers are open
to the cleanroom air or stored in PODs/FOUPs.
• AMC needs to be controlled in the front-end and back-end
of line operations in semiconductor fabs.
• This control may be achieved fab-wide or at
certain critical processes, potentially also at
different levels for different processes.
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WECC – Recent Activities
• Introduction of two new tables in the latest ITRS roadmap
version:
• “AMC monitoring methods”
• “Supporting table for on-line methods”
• Chapter review and text update for the WECC section and AMC
information.
• Clarification on refractory limits and footnote explanations have been
introduced.
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WECC – Ongoing & Planned Activities
• Introduction of “AMC Definition” as a new table.
• Review requirements for 450 mm manufacturing.• Update of “Potential Solutions” for 450 mm process.
• Investigation of EUV related contamination.
• Introduction of moisture as new chemical contaminant for
critical processes and reticle environment.
• Investigate HNOx impact on different process steps and
clarification of analytical procedures.
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AMC Control Drivers for 300 mm
• Definition of Airborne Molecular Contamination (AMC).
• Ultra-clean manufacturing.
• Unintended contamination of layers.
• Dimensional, structural and compositional information.
• Depth resolved quantification.
• Non-volatile organic surface contamination.
• Current AMC levels for 300 mm wafers / 45nm devices.
Correlation of contamination level to yield !!!
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Work Plan for 450 mm Wafer Readiness
• Critical Contamination on fab level down to the wafer level.
• Particle Contamination, Airborne Molecular Contamination.
• Contamination at the Fab interface (POE) on a wider scope (particles/AMC).
• Contamination of FOUPs & Pods, new FOUP
materials.
• Which effects can be expected solely
from wafer size?
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Work Plan for 450 mm Wafer Readiness (2)
• Challenges
• Litho zone AMC cleanliness has to be improved for service situations on
exposure tools.
• Metrology has to be described and adapted to minienvironment definitions
of metrology tools.
• Potential Solutions
• New definition of lithography / metrology lithography zone cleanliness,
application of AMC control measures in lithography zones including
operational measures.
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Requirements for AMC Control
• Although previous versions of the Roadmap treated the entire
fab as the wafer environment, increasingly automated wafer
handling and processing meant that the wafer is now only
rarely, if ever, exposed to the ambient cleanroom environment.
• The wafer environment has shrunk to minienvironments, process tools,
SMIF pods, and FOUPs.
• Understanding this and to reduce operation costs for the same
level of AMC control, WECC was divided into process areas
and requirements were categorized by manufacturing materials
or environment.
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Yield Enhancement WECC AMC interfaces by process areas – Summary
Airborne Molecular Contaminants in Gas Phase Short-term (long-
term) Limits in pptM
Lithography (cleanroom ambient)
Total inorganic acids (as SO4) 22,,550000
Total organic acids (as SO4) TTBBDD
Total bases (as NH3) 5500,,000000 Total condensable organics (w/ GCMS retention times ≥benzene, calibrated to hexadecane) 2266,,000000
Refractory compounds (organics containing sulfur, phosphorus, silicon, calibrated to hexadecane) 110000
Total surface molecular refractory condensable (SMRC) organics, 22 nngg//ccmm22//ddaayy
Gate/Furnace area wafer environment cleanroom/POD/FOUP ambient)
Total metals (as copper) 11 ((00..55))
Dopants (as elements B, P, As, etc.) 1100
Total surface molecular condensable (SMC) organics on wafers, 22 ((00..55)) nngg//ccmm22//ddaayy
Salicidation Wafer Environment cleanroom/POD/FOUP ambient)
Total inorganic acids (as SO4) 110000 ((1100))
Total organic acids (as SO4) TTBBDD
Exposed Copper Wafer Environment (cleanroom/POD/FOUP ambient
Total inorganic acids (as SO4) 550000
Total organic acids (as SO4) TTBBDD
Total other corrosive (oxidizing) species (as Cl2) 11,,000000
Exposed Aluminum Wafer Environment (cleanroom/POD/FOUP ambient)
Total inorganic acids (as SO4) 550000
Total organic acids (as SO4) TTBBDD
Total other corrosive (oxidizing) species (as Cl2) 11,,000000
Reticle Exposure (Cleanroom/POD/Box ambient)
Total inorganic acids (as SO4) 550000 ((TTBBDD))
Total organic acids (as SO4) TTBBDD
Total bases (as NH3) 22,,550000 ((TTBBDD))
Total surface molecular condensable (SMC) organics on wafers, 00..2299 nngg//ccmm22//ddaayy
Requirements for AMC Control (2)
• One of the major challenges identified for future editions is that
of “AMC integration” with other working groups: especially
Factory Integration (FI) and Lithography (Litho).
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The Total AMC Concept
• One focus area requiring innovative solutions for Factory Integration (FI)
is the prevention and control of AMC.
• Increased importance of AMC requires revisiting contamination control procedures with
new methods and materials, which could also affect facility components used during
construction.
• Facility operations will also require coordination with production equipment vendors to
ensure proper AMC control.
• FI needs to specify general cleanroom conditions with respect to
environmental AMC limits.
• Although FOUPs and pods have help to shrink the exposed wafer environment significantly,
they are now considered to be concentrators (multipliers) and distributors for contaminants.
• Discussions between FI and YE are ongoing to determine whose responsibility this will be.
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The Total AMC Concept (2)
• AMC control guidelines for Lithography are based in large part on inputs
from the photolithography tool suppliers.
• Control of AMC is critical to maximizing yield by minimizing local
poisoning of the photoresist and mitigating the formation of progressive
defects on masks during exposure.
• All photolithography tools should have chemical filters on the makeup air
to the internals of the tools.
• These filters have a finite lifetime, which is dependent on the contaminant load.
• Providing a chemically cleaner cleanroom ambient environment will extend the life of these
filters.
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The Total AMC Concept (3)
• The use of inert environments to transport and store wafers is expected to
increase with process sensitivities.
• Pre-gate and pre-contact clean and salicidation are processes that
currently require this capability.
• Other potential solutions for WECC relative to AMC include:
• On-line monitoring for AMC contaminants,
• Reduced cost of ownership for AMC control,
• Development of emergency response procedures and measures for fugitive emissions,
• Verification for AMC limits relative to metal corrosion.
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The Total AMC Concept (4)
• Discussions of an “AMC integrated option” between the WECC sub-TWG
and the FI and Litho working groups have identified that:
• FOUP characterization and monitoring is becoming more important due to the introduction
of new construction materials, e.g., flame retardants and the potential for cross
contamination.
• AMC is becoming much more of a concern in reticle handling.
• SEMI (Semiconductor Equipment and Materials International) Standards are not optimized
and because of this no testing has or is being done, due in large part to the high costs for
non-standardized tests. SEMI is interested in updating these standards but it will take time.
• The Total AMC Concept illustrates the responsibility interface between
YE, FI, and Litho.
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AMC-Related Aspects & Interfaces to FI
FOUP FOUPFOUP
AMC
FilterTools / ME
NV
Stocker/Purgable LP
Data collection +
integration
AMC Integrated Option
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The ITRS Today
• Previous editions of the ITRS took advantage of experts from around the
world to help identify the technical challenges related to AMC and
establish AMC control strategies and guidelines for advanced
semiconductor device manufacturing.
• Requirements have been added for the control of total acids in addition to total bases in the
cleanroom ambient for lithography.
• In the 2014 update (and beyond), YE will put in requirements addressing
specific acids – not just total.
• Additional changes for AMC control proposed include total acids being reduced to < 20
ppbv (5 ppbv long-term), total condensable organics being reduced to < 100 ppbv, and
dopants being reduced to < 10 pptv.
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WECC Near-term Challenges
• Process stability vs. absolute contamination level• Methods and data are needed for correlating defects caused by wafer environment and
handling.
• Requires determination of control limits for gases, chemicals, air, precursors, ultrapure
water and substrate surface cleanliness.
• Challenges exist for accurate measurement of AMC• In low-volume compartments (Pods, carriers).
• Quickly under highly dynamic conditions.
• Precisely standardized from surface depositions.
• Detection of non-volatile organic contamination on surfaces.• The detection and speciation of nonvolatile organics on surfaces is currently not possible in
the fab.
• There is no laboratory scale instrumentation available.
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AMC Control Technology
• As the semiconductor industry has progressed, so, too, has
AMC control technology. This progress comes in the form of:
• AMC filters that can address essentially any AMC issue.
• Filtration systems that can be integrated into existing air handling
equipment (MAU, RAU, FFU, tools).
• Monitoring instrumentation and devices that can provide real-time, accurate
environmental assessments.
• The technical competence to work with manufacturers to provide effective
and economical solutions to AMC-related problems.
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AMC Filter Application Matrix
Application
Areas:Outside Air Recirculation Air
Filter Fan Units (FFU),
Minienvironments,
Point-of-Use Filters
Exhaust Air,
Emergency Gas Scrubbers
Target
Contaminants:
SOX, NOX, O3,Cl2, NH3, VOCs
NH3, NMP, amines, acids, alcohols, VOCs, AsH3, BF3
NH3, NMP, amines,Cl2, HCl, HF, VOCs
AsH3, PH3, BF3, Cl2,HCl, HF, ClF3, VOCs
Media:
GAC, impregnated carbons/alumina, extruded carbon
composites (ECC)
GAC, impregnated carbon/alumina, ECC,
adsorbent-loaded
nonwovens
Adsorbent-loaded nonwovens, ion exchange
Specially impregnated carbon/alumina
Filters:
Thick/thin bed trays/modules, flat
panel filters
Thin bed trays/ modules, pleated media filters, flat
panel filters
Pleated media filters, flat panel trays, flat panel
filtersBulk media
Equipment:Front/rear access
frames, 2-3 passesFront/rear access frames,
1-2 passes
Top/side access systems, integrated recirculation air filters, OEM filter housings
Deep-bed scrubbers, emergency gas scrubbers
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AMC SourcesAMC Class Contaminants Sources Effects
Molecular
Acids
Fluoride, chloride, bromide,
sulfates, phosphates,
nitrogen/oxygen compounds
Etch chambers, diffusion furnaces, CVD processes, wet
benches using HCl, HF, BOE
Hazing of reticles / wafers, optics of
exposure & metrology tools, corrosion of
Al & Cu metal lines, inhibits CAR
Molecular
Bases
Ammonia, amines, amides,
trimethylamine, triethylamine,
cyclohexylamine, dimethylamine,
methylamine, ethanolamine,
morpholine
Ammonia sources: CVD, HMDS, CMP, slurries, wafer
cleaning processes, TiN / Si3N4 films deposition. Amine
sources: photoresist strippers, polymers, epoxies, TMAH
decomposition. Amide sources: solvents such as NMP,
dimthyl acetamide, polyimides
Neutralizes photoacids in resists,
reactions with acids can cause hazing,
particle formation, nitrides on wafer
surface
Molecular
Condensables
Dibutyl phthalate,
organophosphates, siloxanes,
HMDS, PGMEA
Outside air, process chemicals, outgassing from filters,
sealants, walls, adhesives, floors, wafer shippers, FOUPS,
pods, gaskets, sealing tape, bagging materials, flame
retardants
Hazing of exposure tool optics and masks
from HMDS byproducts, delamination of
PR and ARCs, unwanted n-doping of
wafer, interference with thin film
metrology
Molecular
Dopants
Boron, phosphorus,
organophosphorus, arsenic,
antinomy
Outside air, degradation of HEPA/ULPA filters, exhaust
from RIE, EPI, CVD processes, flame retardantsUnwanted n- and p-doping of wafers
Molecular
MetalsOrganometallic compounds
Cross-contamination of wafers, plastic additives containing
organo-tin/bismuth compounds, corroded ductworkParticulates in air & on wafers
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AMC Monitoring
• There remains a need for real-time monitoring instrumentation in the
cleanroom to measure AMC at the part per trillion (PPT) levels.
• Low cost, routine monitoring will be required as devices approach molecular dimensions.
• Semi-quantitative monitoring in being used with increasing frequency
• Not all process steps are impacted by AMC, however, the potential for
AMC to impact new processes is considered in all integration studies.
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Fab Contamination Control
• Optimum control of airborne contamination is by application of both
particulate and AMC filters.
• Particulate control requires as many as five stages of filters including HEPA/ULPA filters.
• Many facilities provide only a single stage of AMC filters to treat outdoor
air and a single stage of AMC filters for recirculation air and in FFUs.
• Lack of space in the air handling systems
• Cost of the chemical filters
• Increased energy costs
• There is a general lack of understanding of AMC control technology and
the requirements for its proper control.
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• New chemical filter technology has been developed that applies
granular adsorbent and chemisorbent media to a bi-component
non-woven fiber matrix.
• Activated carbon, engineered carbons, permanganate-impregnated
alumina, ion exchange (resins, fibers).
• Available as combination chemical + particulate filters.
• Particulate filter rating of MERV 8 (G4/F5, 25-30% dust spot) up to MERV
15, (F9, >95% dust spot).
• AMC filter performance of 90-95% removal efficiency for many contaminant
types (e.g., acids, bases, condensables, dopants, refractory compounds).
Combination Filters for AMC Control
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Adsorbent-Loaded Nonwoven Fiber Filters
• These combination filters are being used for contamination
control in makeup air handlers, recirculating air systems, fan
filter units (FFUs), wafer and reticle stocker cabinets,
minienvironments, and process tools.
ALNF filters installed on top of FFUs for
control of acid gases and VOCs. ALNF filters installed on top of FFUs. One for
control of acid gases and other for ammonia.
ALNF filters installed on top of process
tool for control of acid gases and VOCs
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• The newest chemical filter to gain acceptance for AMC control
consists of a one-piece integral monolithic structure consisting
of an extruded carbon composite (ECC) structure.
• The most effective is composed of essentially 100% adsorbent materials
that allow the entire structure to function as a chemical filter.
• Activated carbon, engineered carbons.
• In development – impregnated activated
alumina composite.
• Filter has been certified to meet
ISO Class 4 for particle emissions.
Extruded Carbon Composites
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Extruded Carbon Composites (2)
Left: Air diffuser, ECC filter, and HEPA filter.
Right: ECC filter assembly installed in filter housing for acid gas control.
Example of ECC filter applied to
clean process air going to a tool.
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Summary – ITRS & AMC
• Since the 2005 ITRS, WECC includes the ambient space around
the wafer at all times, whether the wafers are open to the
ambient cleanroom air or stored in PODs/FOUPs.
• As the list of chemical contaminants to be controlled broadens
one important WECC challenge is the accurate modeling of
cleanrooms for AMC sources and distribution.
• The reduced air volumes in many cleanroom designs cannot dilute AMC as
well as before – whether it comes from sources outside or inside the fab.
• Current and future AMC control technologies
• Requires preventive defect and contamination control.
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Summary – ITRS & AMC (2)
• The ITRS takes advantage of expertise from around the world
to help identify the technical challenges related to AMC control.• Offers recommendations that can be used in establishing AMC control
strategies and guidelines for advanced semiconductor device
manufacturing.
• Requirements have been added for the control of total acids in addition to
total bases in lithography applications.
• Subsequently, the YE TWG has put in requirements addressing specific
acids – not just total acids.
• Additional changes for AMC control that have been proposed include total
acids, total condensable organics, and dopants being reduced from current
levels.
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Summary – AMC Control
• Given the proper considerations for the specification of an
AMC control program, one can be successful in applying an
effective and economical solution for most applications.
• This has become easier with new chemical filter products that
have been developed for AMC control.
• Ion exchange filters for the control of (primarily) bases and acids.
• PIA-Na media for enhanced control of acid gases.
• Combination particulate +chemical filters employing adsorbent-loaded
nonwoven fibers.
• Extruded carbon composite filters.
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• A properly designed, installed and maintained AMC control system can
easily achieve the removal efficiencies required for specific target
contaminants.
• How long a system will meet specific performance criteria depends on the
average and peak values of ALL contaminants present, which must be
considered in the final design of the AMC control system.
• Cost effective integration of AMC controls into factory design and
operation should incorporate a variety of measures all the way from
detection of AMC sources through control methods up to the active
protection of the wafer environment.
Summary – AMC Control (2)
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Thank you for
your attention!
Any Questions?