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.

12/12/2013 Page 2

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.

Page 13

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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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12/12/2013

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.

Page 15

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

12/12/2013 Page 18

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.

12/12/2013 Page 31

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?