Some short notes that I have made few years back from various sources about cleanrooms overview & design in general. Just to share and hope it helps in general. Do drop me a note if things were wrong or misleading. Thanks in advances!
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Cleanrooms Overview Definition: IES RP-CC-012 FED STD 209E ISO/ TC 209 (A room in which the concentration of the airborne particles is controlled and which contains one or more clean zones) Users: Microelectronics Pharmaceutical Defense/ Aerospace Research laboratories Food Processing Medical Skis, Paints, Glass, Automotive Concerns: Pharmaceutical > sterility Bio-tech > worker and public safety Microelectronic > static control Semiconductors > practical control Cost: A CL 1 – CL 1000 ($200 to $600 per sq.ft) of clean room only A CL 1 – CL 100 ($2400 to $4800 per sq.ft) of process cleanroom Controlled environment: Particles Humidity Acoustics Temperatures Pressure Vibration Viables Etc Typical Specifications Particles: <1 particle/ cu ft 0.10or larger Temperature: 68F 0.1F Humidity: 40% RH 1.0% Pressure: Zone P = 0.05’ W.G. Acoustics: NC55 Vibration: 125inches/ sec
(A room in which the concentration of the airborne particles is controlled and which contains one or more clean zones)
Users: Microelectronics Pharmaceutical Defense/ Aerospace Research laboratories Food Processing Medical Skis, Paints, Glass, Automotive Concerns: Pharmaceutical > sterility Bio-tech > worker and public safety Microelectronic > static control Semiconductors > practical control Cost: A CL 1 – CL 1000 ($200 to $600 per sq.ft) of clean room only
A CL 1 – CL 100 ($2400 to $4800 per sq.ft) of process cleanroom
Controlled environment: Particles Humidity Acoustics Temperatures Pressure Vibration Viables Etc Typical Specifications Particles: <1 particle/ cu ft 0.10 or larger Temperature: 68F 0.1F Humidity: 40% RH 1.0% Pressure: Zone P = 0.05’ W.G. Acoustics: NC55 Vibration: 125 inches/ sec
Cleanroom Airflows Airflow patterns:
Unidirectional airflow (aka “Laminar) Used in class M3.5 (100) or cleaner 1) Horizontal airflow (older design): one wall contains filters
– air crosses room to returns on opposite wall – clean opreations next to filter wall
2) Vertical airflow: most applications today use vertical flow – air returns through floor or low sidewall
How they work? Unidirectional flow moves particles in direction of airflow > minimize turbulence and airflow interruptions
Non-unidirectional airflow (aka “Turbulent”) Used in class M4.5 (1000) and less cleaner Filters placed in various locations – returns in floor, wall
or ceiling Filters may be evenly spaced or grouped Not locate returns directly opposite supply Airflow may be unidirectional near filter and non-
unidirectional further from filter How they work? Non-unidirectional flow rooms maintain
cleanliness by dilution – area isolated from air path develop higher concentrations of particles > maintain turbulence/ mixing
Note: dilution works by continuously diluting particle laden air with particle free air & requires good mixing of air (i.e. turbulence or non-unidirectional flow) Mixed airflow Combines both unidirectional and non-unidirectional
airflow in same room Clean island configuration can be unidirectional or mixed
airflow depending on locations of returns
Airflow Measurement Airflow direction measured using IES RP-006 Section 6.5.2 (airflow parallelism test) 1. Divide the room into grid 2. Place smoke generator in approximate center of each sect. 3. Use plumb bob to measure deviation from vertical Typical spec: < 14o of vertical (deviation of 1 in 10 => 14o = 0.1) Note: “smoke” may consist of
TiO2 particle (Draeger “Smoke Sticks”) LN2 induced condensation DI water vapor condensation CO2 foggers Neutral buoyancy He bubbles
Other methods: black silk thread, “flow-vis”
Air Velocity Cleanliness class level not directly related to specific air velocity – operating protocol, flow direction and filter quality affect cleanliness Air velocity specified by average air velocity or “number of air changes per hour” Velocity just one factor in achieving uniform unidirectional airlfow – velocity uniformity varies due to may factors:
Filter media Distance from filter face Obstructions Distance from returns
Airflow Velocity in Cleanrooms Class Airflow Avg Vel (m/sec) Air Chgs/ Hr M7 / M6.5 (CL100,000) N/M .005-.04 6-48 M6/ M5.5 (CL10,000) N/M .05-.08 60-90 M5/M4.5 (CL1,000) N/M .13-.20 150-240 M4/ M3.5 (CL100) U/N/M .20-.41 240-480 M3/M2.5 (CL10) U .25-.46 300-540 M2/M1.5 (CL1) U .30-.46 360-540 M1 or cleaner U .30-.51 360-600 Air change per hour = Average airflow velocity X room area X 60min/hr (Assumed 3m ceiling) Room volume
Measurement of Air Velocity Airflow velocity measured with averaging pilot tube or thermal anemometer – results reported in units per second or per minute RP-006 6.12 test conducted at plane 0.3m (12”) from supply source – may result in uneven readings for system with low pressure drop filters – RP 006 6.12C lists equivalent airflow volume test that may be used Economics of Velocity Equipment and operating costs affected by velocity – high velocities require more recirculated air and larger (or more) equipment required Flow Area X Vel. = vol. recirculated air/ time Fan HP = CFM X Static pressure X 0.25
1000 (in inches w.g) cleanroom reciculation fans run 24 hours/ day, 365 days/ year – fan heat increases cooling heats
Airflow Supply
Plenum (Open plenum & modular plenum) Ducted
Airflow Source
Vertical fan tower Plug fans FFUs
Utility Matrix Collection/ Analysis of facts & design starting point Define processes in as much detail as possible Identify all requirements for chemicals, gases and liquids Identify size, power, temperature control, humidity, exhaust, drains,
vacuum, vibration, EMI, RFI, shielding, waste removal requirement, etc Provide both peak demand and normal usage requirement for each service
within matrix Not apply diversity factors in initial stages Diversity factors applied later through joint discussions of design
professional and process user Create matrix of detailed requirements for each piece of equipment and
for each process in the cleanroom
Identification of: Critical equipment Critical processes Critical support requirements
Contamination Control Guidelines Categorize process by type of contaminant that affect it
Old classification scheme Ionic: Process affected by electrical characteristic (on atomic
level of contaminant, ex: sodium in semiconductors) Optical: Process affected by size of contaminant: Classified as
aerosol factors (Fed Std 209) or surface factors (MIL-STD-1246, ex: “dust on optics)
Chemical: Process affected by chemical properties, ex: O2 or H2O molecules trapped inside hermetically sealed devices)
Biological: Process affected by biological properties’ ex: bacterial, viral or fungal contamination drug lots)
New classification scheme Particle:
Size range: 10-3 m to 10+3 m Prevention: mechanical filtration Effects: Chemical: reactions of (charged) ionic species
Mechanical: shear, friction effects (micro machining) & optical effects Biological: bacterial, viral or fungal contamination & related to biochemical reactions
Molecular Size range: <10-3 m Prevention: physical/ chemical adsorption Effects: Chemical: reactions of (charged) ionic species
Mechanical: film deposition caused by adsorbed molecules (often hydrocarbon)
Biological: no – known biological species > 10-3 m
Energy Size range: not applicable Prevention: depends/ miscellaneous Effects: depends/ miscellaneous Examples: EMC (EMI, RFI, ESD, etc), temperature and
vibration
Life safety Overrides all other considerations Cleanroom may (will) be required to operate with processes which affect safety Consider:
Controlled purge of segregated air circulation zones Control dispersion of hazardous gasses by zone separation Strong toxic/ flammable materials outside process floor Distribution of chemicals from outside process floor under
controlled conditions in double contained delivery system Minimize exit distance to fire protected area as required by code Maximum contiguous floor area limited by codes Isolate hazardous materials from personal Code requirements drive design Review utility matrix for identification of hazardous materials
(HPMs) Note:
Owner’s insurance company and safety group must evaluate specific safety issues
Life safety must be coordinated with cleanroom operation requirements
Any automatic shutdown of air handling systems may (will) destroy integrity of cleanroom
Environmental issues Identify internal environment required for each process
Biological Chemical emc (electromagnetic compatibility); esd (electrostatic discharge) temperature humidity vibration etc Q: 1) Critical values for criteria for each? 2) Are critical required or have they been arbitrary established? 3) Impact on external environment?
Often cleanroom protects process while creating environmental contaminants Identify environment contaminants and classify as gases, liquid, or solid wastes Evaluate types and quantities for regulatory compliance Develop secondary containment strategy to prevent ground water contamination, ex: chemically resistant coatings for exposed floors
Supply Air Quantity Calculations In more general terms,
Qsa = Ai X Vi
Qsa = Total Quantity of Supply Air Ai = Area of the ith Filter Vi = Velocity through the ith Filter
Specifically,
Qsa = Nf X Am X Vm
Nf = Total numbers of ceiling filter Am = Mean area of ceiling filter Vm = Mean velocity through ceiling filter
May perform this calculation for:
Each individual room Each individual area within each room Fed by one fan or AHU Area served by each individual fan or recirc AHU Area served by all fans or recirc AHUs in one area Computer spreadsheets help
Cleanroom air cannot be 100% recirculated due to process exhaust & room leakage
MU required to keep the room from going negative Sources of MU air
Outside air Away from exhaust stacks
Indoor building air External to cleanroom Should be made up to prevent building from going negative
Exhaust effects on HVAC configurations Many processes require extensive exhaust
Semiconductor fabs exhaust acid and solvent fumes and waste gases
Biopharm facilities use biohazard hoods or fume exhaust hoods to protect people from process
Some biopharm rooms employ “once through air” system with no recirc
Exhausted air replaced by make-up that is conditioned to required temperature and humidity, used once and then exhausted
Capital and operating costs associated with conditioning large amounts of this air are significant
Cooling determined HVAC configurations Some HVAC configurations determined primary by cooling/ heating
requirements In most applications, driving factor is cooling, not heating load Make-up air required by exhaust and room pressurization – often not
sufficient to cool room System provides for recirculation of portion of room air and introduction
of make-up
General Exhaust Systems Remove fumes, “contaminated” air, heat from people or process “Contaminated” may include
Heat Moisture Dust (fan)
Codes specify minimum exhaust for cleanrooms using Hazardous Production Materials (HPMs)
Pharmaceutical cGMPs establish exhaust requirements for validations Exhaust System Few mechanical systems affect capital and operating costs as significantly
as exhaust Exhaust determines quantity of make-up that must be provided Every m3 of exhaust must be replaced by expansive make-up If possible operations which require heat exhaust should be placed
outside cleanroom General Exhaust Design Quantities: Use matrix whenever possible Otherwise: Use rough estimates
Galvanized duct (typ.) SS (may be req. in HPM storage area)
Velocities: 6.1m/s – 7.6m/s (typical) (1200 – 1500 fpm) Note: high velocities may cause vibration
General exhaust (utility requirements) Power Emergency power
Smoke exhaust HPM exhaust
Corrosive Exhaust System Removes, treats and discharges (to atmosphere) fumes generated by
manufacturing process Collection ductwork discharges exhaust into fume scrubbers which
remove acid/ caustic fumes from airstream Fumes “scrubbed” by passing through bed of “wetted” packing material Packing material provides large surface area for gas/ liquid contact
reaction
Packing is “wetted” by spraying neutralizing water solution over bed Specified by removal efficiency (Typ.) 95% to 98% Typical chemicals removed: HF, HCl, H2SO4, NH4F, NaOH, (NH4)SO4,
NH4OH Corrosive Scrubber Usually located adjacent to cleanroom Keep away from outside air intakes Airflow modeling done to verify path of exhaust system Life safety requires N+1 redundancy Secondary containment of sump strongly recommended Fans on variable frequency drives (VFDs) Pumps and Fans on emergency power Isolation dampers between ducts and scrubbers Corrosive Exhaust Use caution if mixing various exhaust types in same exhaust system Use caution with NH3 exhaust (plume) FRP duct may require sprinklers if >25cm dia.
Facilities related issues: Corrosive of heads Maintenance of wax or poly bag Flooded duct – drain system – acid waste
Qty: Process determined (use matrix) 32 cm/h/h per 1m2 of “Fab” (5cfm per 1ft2 of Mfg. Clean Space)
Pressure: -622pa (-2.5in.) at tool Velocity: 6m/s – 10m/s (1200 – 2000fpm) Scrubber Basic Design Flow rate Composition Temperature Influent concentration Effluent concentration Design: -2.5kPa (-10 in.) to +1.0kPa (4in.) Packing: 12:1 column to Packing diameter
Larger packing => Lower >P Less scrubbing efficiency Cost vs. scrubbing efficiency
Column: low pressure drop (622Pa [2.5 in.] through packing) Velocity: 1.5m/s – 2.5m/s (300 – 500 fpm) Recirculation rates: 11 l/s/m2 (5gpm/ft2) note: area of column. Corrosive Exhaust Materials Scrubbers
– very expensive; highest quality – May be good for tool hookup
Pumps: Stainless steel FRP
Packings: 2.5cm – 9cm Polypro tetrahedrons or spheres Corrosive Exhaust Utility Requirements Power Emergency Power Industrial Water Supply (Makeup) Industrial Water Drain Instrument Air Chemical Feeds (NaOH, HCl, Biocide) Corrosive Exhaust Start-up Issues Balancing Systems at startup difficult Systems designed for full build out Systems conditions change as each tool added System balancing dampers and VFDs on scrubbers is essential
Solvent Exhaust Systems Collect, treat and release solvent fumes before release to atmosphere Typical (Organic) chemicals removed:
Regenerate with hot air/ stream Multiple units => higher capital costs Low efficiencies/ adsorbs water Rotary wheel concentration Hydrophobic Zeolite Concentrates and collects Solvent may be recovered Low concentrations/ high volumes Often followed by RTO Wheel turns 1 –6 RPH Desorbed using hot air Concentrated stream sent to:
Oxidizer for incineration Condenser/ separator for collection
Direct incineration (thermal oxidation) Direct flame 649 oC – 1093 oC
Used for mixed components High fuel consumption in low concentration exhaust streams Low thermal recovery (50%) High removal efficiency (95+%)
Regenerative thermal oxidation Direct incineration Combustion heats catalytic bed and sustains combustion (816 oC) High thermal efficiency (95%) High destruction efficiency (98.5%) Solvent exhaust design Usually located adjacent to wafer fab Keep away from outside air intakes Airflow modeling done to verify path of exhaust stream Life safety requires N+1 redundancy Fans on variable frequency drives Fans on emergency power Isolation dampers between duct and fans Emergency bypass fan Startup air/ cooling air fan Quality Process determined –use matrix System design Duct velocity 6.1m/s (1200 fpm) – 7.6m/s Ductwork pressure –870 pa (-3.5in) Fire sprinklers required if vapour conc. > 10% LFL Pressure at tool = -620pa (-2.5in) RTO –6.2kPa (-25in) Solvent exhaust specifications Fans: Type A non-sparking Non-ferrous Impeller Electric: NEMA 4 (Rated for outdoor use) Duct: Galvanised sheet metal-welded Stainless steel-welded Fuel: Natural gas with fuel oil backup Solvent exhaust utility requirements Power Emergency power Natural gas and fuel oil Instrument air Solvent waste drain Fire protection
Temperature and humidity control Cleanroom temperature specified by desired value and tolerance
Example: 22 (3) oC 75 (5) oF
Temperature fluctuation over time should be specified Example: 0.1 oC over 20 minutes
0.2 oF over one hour Design parameters Design consideration affecting specification of temperature
Personnel consideration Control temp so as to maintain environment where people can
efficiently function Smocks/ light activity:
70 oF – 76 oF (21 oC –24 oC) Full cleanroom garments
64 oF – 70 oF (18 oC –21 oC) Strenuous activities: lower temps Range usually 1.4 oC – 2.1 oC (2 o F– 3 o F)
Process-related considerations Precise dimensional stability Chemical/ physical processes Process equipment
Identify process temperature considerations early in programming
Heat-generating equipment causes localised fluctuations in temperature – very difficult to remedy if equipment runs intermittently
Economics of temperature Cleanrooms require cooling year round due to heat of mechanical
equipment, lighting, process equipment, and personnel Cooling load increases as cleanliness class improves due to larger/
more equipment Avoid placing process equipment that generates large amounts of
heat in temperature control areas Excessively stringent ranges are costly, difficult to achieve and
maintain Low cost: 1 oC => standard controls Mod cost: .5 oC => DDC controls and reheat High cost: < .5 oC => high qual. Industrial electronic controls
Temperature variations can reduced by using smaller zones – but this requires additional instrumentation
Exhaust considerations in temp. specs Increased exhaust => increase in conditioned make-up air Amount of conditioning that make-up requires depends on T
between outside air and targeted indoor temp Minimise total exhaust and T (subject to safety requirements)
Airflow pattern in temp. specs Mixing conditioned supply air and recirculated RA required for
maximum efficiency Mixing airflow room or rooms with improperly spaced inlets and
outlets – cause stagnant pockets and temperature gradients – results in high particle concentration and inefficiency in operation of a/c systems
Construction materials and temp specs Standard construction materials perform well in range of 60 oF –
80 oF (15.6 oC – 26.7 oC ) For very low and high temp – select materials that withstand
temperature cycling Monitoring and control of temperature (for temporal and spatial
uniformity) Monitor temperature on continuing basis and observe trends –
use chart recorders or data acquisition systems
Humidity and dewpoint Cleanroom humidity specified by desired value of % r.h. and tolerance
Example: 45 (5) % r.h Alternative to specifying r.h. is dew point temperature
Example: 10 (1.4) oC [50 (2) oF] Process related considerations r.h. control often required due to process corrosion occurs faster in high humidity organisms may proliferate in high humidity below 25% r.h. static electricity problems humidity requirements must be identified early to permit design and
budget response Economics of humidity specifications humidity control is energy intensive dehumidify down to 40 (+) % r.h with standard chilled water and direct
expansion refrigerant systems – dehumidification below this requires special equipment – expensive
equipment such as open baths and moisture – segregate from zones which serve humidity sensitive processes
excessively stringent ranges are costly, difficult to achieve and maintain low cost: (5) % r.h => standard controls mod cost: (2) % r.h => DDC controls, humidifier, trim coils high cost: <(2) % r.h => high qual. Industrial controls
Exhaust considerations in humidity specs more exhaust => more conditioned make-up air required humidity conditioning of make-up depends on difference in humidity of
the outside air and desired indoor humidity minimise exhaust air (subject to safety requirements) and humidity Absolute humidity, NOT r.h. Construction materials and humidity Standard construction materials do well in range of 30% - 70% r.h. – if
very low or high humidity required, select materials that withstand dry/ wet conditions
Monitoring and control of humidity (for temporal and spatial uniformity) Monitor humidity on continuing basis to observe trends – use chart
recorders or data acquisition systems Makeup air unit Preheat coil prevents coil freeze in colder climates To reach desired humidity level humidification coil lowers temperature
below desired room temperature Reheat coil raises air temperature to desired discharge temperature
If outside air is dry, the moisture is added by the humidifier Dehumification Moisture removed from air by contact with cooling coil surface operating
below the desired dewpoint: 5.6 oC (42 oF) chilled water coil capable of dehumidfying to 40% RH 0 oC (32 oF) ethylene glycol coil is used for dehumidfying to 30%RH Below 30% RH desiccant Humidification usually used
Humidification Moisture added to air by:
Direct injection of water (usually not efficient for larger systems) Evaporative Atomizing humidfiers Compressed air atomizes water into mist which evaporates
quickly Steam injection
Direct injection: used where steam is building heating medium (or otherwise available) Air quality affected by boiler water chemical additives
Electric humidifier: Electric resistance heating elements produce steam Used where steam and natural gas are not available Expensive to operate Air quality depends on quality of water being boiled
Heat exchanger humidifiers: Commonly used for microelectronics facilities Low pressure steam or water at 116 oC (240 oF) suppliers heat
to a stainless steel evaporating chamber producing “clean” steam
Frequently RO or DI is used for makeup water Advantages:
Maybe used without steam boilers Low operating cost “Clean steam”
DI water corrosive – acts as a “weak” acid “Clean steam” produced from DI water is very
aggressive Stainless steel materials downstream of humidifier Frequently RO water is used – “Clean” but not as
aggressive
Gas Distribution Systems Gas systems:
Categories: Inert Flammable Toxic Corrosive
Concerns Particle levels Purity levels Materials of construction
Typical leak rates System fabricated with “clean build” techniques Fabrication methods prevent contamination at every step during
construction Use portable cleanrooms for clean materials storage and prefabrication Use uhp argon for welding purging Extended purge intervals to displace atmospheric contaminants
Personnel protocols involving use of cleanroom gloves and other garments
Process gas design concerns UHP gas systems designed to minimize contaminants added to gas stream Contaminants added take form of either solids or gases
Solids typically submicron in size Gas phase contaminants typically in high ppt to low range
Solid vs gas phase removal mechanisms Although particles present in large numbers in atmosphere, easy to
remove from process gas stream Mechanical filtration (interception, impaction, diffusion) highly
efficient Membrane vs. fiber filters POU (or use point) gas filter near absolute in particle capture
ability Efficiencies of 10+ nines at mpps (approx. 0.05 m at rated flows)
If combine good design, clean materials and “clean build” fabrication techniques results in gas systems that are essentially particle free (better than class 1)
Design rules for UHP gas system Non-outgassing, clean, smooth, inert materials (typically EP 316L SS) Minimize plastics in the system Butt welded if possible – avoid threaded joints, sockets welds and flanges For small joints that will be broken and remade, use face seal fittings Use automatic orbital arc welder Use valves with low leak rates – both across seat and inboard/ outboard Components manufactured from bar stock or forges – avoid castings Minimize moving parts in gas stream – avoid rubbing parts in gas stream Maintenance free as possible – minimize need to open system to
atmosphere Components with minimum internal dead zones General sizing rule for gas systems Minimize turbulence – keep velocities low as feasible (typically 1.2 m/s,
20-40 fpm) Goals: system should be as close as possible to being: “particle free”,
Concerns: Particle levels Purity levels Materials of construction
Plastics for corrosive PVC, CPVC Polypropylene PVDF, PFA
Metal for flammables Stainless steel, aluminium(?)
Polyvinyls PVC (Polyvinyl chloride)
Good tensile strength Good chemical resistance Not appropriate over 60 oC (140 oF) Poor combustion characteristics
CPVC (Chlorinated polyvinyl chloride) Good for temperature up to 210 oF Self extinguishing
Polyolefins Polypropylene
Very good strength Excellent chemical resistance Good for temperatures up to 82 oC (180 oF) Excellent for industrial waste
Polyethylene Poor mechanical strength Good chemical resistance below 49 oC (120 oF) Used frequently in tanks and liners
Fluoropolymers PVDF (Polyvinylidene Fluoride)
Considerable strength Excellent chemical resistance Good for temp. to 138 oC (280 oF) Excellent for high purity systems
Fluoropolymers (Teflons) PTFE: excellent chem./ temp. properties; cannot be molded or extruded FEP: extended temp. range -54 - 204 oC (-65 - 400 oF); often used for
coatings PFA: better temperature range -54 - 260 oC (-65 - 500 oF); good molding/
machining properties
Other concerns Surface smoothness Surface area Joining techniques Valves
Ball Diaphragm
Leak rates Expansion loops for hot distribution system Heaters for hot DIW Particles in process liquids UHP liquid systems minimize contribution of particulate (and other)
contaminants to liquid stream But pumps, valves and regulators all capable of adding particles
Typically submicron in size With effort, can be removed from process liquid streams Mechanical filtration relatively efficient in removing particles Use point filter efficiencies 75 – 95+% for particles approx. 0.2m at
rated flows With multiple filtration (series or cyclical), particle levels generally
driven to acceptable levels Maintaining purity level requires good systems design, proper material
selection & “Clean build” fabrication techniques Also demands proper systems operation and maintenance techniques Design rules for UHP liquid systems Clean, smooth, inert materials (typically PFA, PVDF, or polypropylene) Butt welds preferred over socket welds – avoid threaded joints & flanges For small joints that will be broken and remade, union replace flanges
For tubing, prefer flared fittings over grooved fittings To weld, used industrial grade welding machines – minimize “hand
welds” Valves must stand up to extended service in corrosive environments
Diaphragm valves preferred over ball valves Ball valve preferred over butterfly or gate valves
Components extruded or injection molded – minimize coated components Minimize moving/ rubbing parts in liquid stream Components maintenance free as possible Minimize need to open system Components with minimum internal dead zones General sizing rule for process liquid system Minimize turbulence – keep velocities low as feasible (typically 1.2 – 2.4
m/s, 240-480 fpm)
Process Cooling Water (PCW) (AKA process chilled water) PCW is a loop system Delivered chilled water to and return CHW from process tools that
generate high heat such as: Implanters CVDs Dry etchers
Water usually circulated at 10 oC – 21 oC Water cooled by heat exchanger that is fed from 5.6 oC chilled water
system Open loop system may be used to reduce back pressure on process tools In this configuration the return tank is vented to the atmosphere Resistivity of water can be adjusted by: Draining portion of the system water Substituting DI water PCW design Redundant components common Control valve used in return loop to maintain low back pressure Control valves often used at supply and return to tools to balance flow System sizing: (use matrix…or) 2 l/s per 100m2 of clean mfg. Space (30gpm per 1000ft2 of Fab) PCW specification Heat exchanger
316L SS plate and frame EPDM gaskets
Recirculation pumps 316L SS for wetted parts variable speed drive (VFD) controlled
Storage tank FRP
Biocide metering 316L SS for wetted parts
Filters 316L SS construction 3.0 m rated
pipe/ valves: PVC CPVC Copper 304 SS
PCW utility requirement Power Emergency power
5.6 oC chilled water DI water for makeup Nitrogen for surge tank Industrial waste for tank overflow and drain
Clean dry air (CDA) Distributed through cleanroom at 760 kPa (110psig) Air is produced in a rotary screw “oil-free”, water cooled compressor at
860kPa (125psig) Air is cooled and stored in receiver tank Coalescing filter and desiccant dryers remove moisture from air Additional filters remove oil droplets and particles from the air CDA design Usually designed as low to medium purity system Located in the central plant to minimize vibration Often used for instrument and utility air (separated distribution systems) Quantity: (use matrix if possible)
12 l/s per 100m2 of clean mfg space (30cfm per 1000ft2 of Fab) Increase size minimum 10% to handle dryer regeneration Chilled water used for aftercoolers and compressor intercoolers Emergency power to cooling water and compressor Redundant unit common CDA specifications Compressors
Two stage Rotary screw Water cooled Sound attenuated cabinet (noise 75dba 1m from carbinet)
Coalescing filter 0.3 m rated
Desiccant dryers Dry air to dewpoint of –40 oC to -73 oC Tower type, blower purge Regenerative activated alumina desiccant
Final filter 0.2 m rated 316L Stainless steel housing
Distribution piping Copper 304 SS 316L SS
CDA utility requirements Power Emergency power 5.6 oC chilled water Industrial waste for condensate drain
Used for vacuum wands, load locks Produced by liquid ring pumps Redundant components common Process vacuum design Usually located in central plant (away from Fab) to minimize vibration “Quantity” (equiv. Air pumping rate)
7.6 l/s per 100m2 of Fab (15cfm per 1000ft2 of Fab) Process vacuum specifications Vacuum pumps
Process vacuum (Utility requirements) Power 5.6 oC chilled water Industrial water supply Industrial waste for separator drain Separator vent to acid exhaust Process vacuum (system sizing) Strictly process dependent
Housekeeping vacuum Used for general housekeeping Produced by vacuum blowers Not intended for wet or hazardous materials Usually located adjacent to or under Fab to minimize run lengths Process vacuum design Redundant blower common Produced at –33.8 kPa (-10” Hg) Distributed at –20 kPa to –27 kPa (-6”Hg to –8”Hg) Quantity:
0.032 outlets per 1 m2 of water Fab Design for 10 active outlets @64 cm/h per outlet (depending on…)
Housekeeping vacuum specifications Vacuum blowers
Direct drive Multi-stage centrifugal
Bag separator Motor operated shaker
Distribution piping Zinc-plated carbon steel Heat-shrink fittings 5 cm (2”) O.D. drops
* Depends on specific test Sodium <10ppt Calcium <20ppt Magnesium <20ppt Fluoride <100ppt Chloride <20ppt Potassium <20ppt Bromide <20ppt Dissolved oxygen <1ppb DI water technologies Filtration
Multimedia Cartridge/ submicron Ultrafiltration
Reverse osmosis Single pass Two pass
Deionization Ion exchange resins Electrodialysis
RO pre-treatment Multi-media filter
Layers of increasingly fine and more Dense filter media remove undissolved particles larger than 10 m May include carbon filters
RO heat exchanger Water temperature raised to 26 oC (77 oF) for maximum membrane Efficiency prior to entering RO system
Chemical pretreatment Anti-scalant chemicals added sulfuric acid injected to lower pH prior
to RO Sodium Bisulfite added to remove chlorine prior to RO system
Primary prefilters 1.0 m filters remove suspended particles and provide final mixing of
pretreatment chemicals Reverse osmosis process First stage reverse osmosis
Used to remove solutes from water Pretreated water forced through semi-permeable membrane at
pressure of 2100 – 2400 kPa (300 – 350psi) Water passes through membrane while ionic material remains behind Osmosis
Concentrated salt solution may be “purified” into a “dilute” solution using semi-permeable membrane – dilute water passes through membrane into concentrated solution causing its level to rise
Height differential between the two columns represents the osmotic pressure
Flow will continue until pressure exerted by height of the concentrated solution equals the osmotic pressure
Reverse osmosis Process can be reversed by applying pressure to concentrated
solution causing water to flow from concentrated solution to dilute solution
Second stage reverse osmosis Second RO process used to further remove solute from water Takes place at 1750 – 1850 kPa (255 – 270psi) Membrane used has different properties than first stage membrane
Vacuum degasification Removes dissolved CO2 and O2 CO2 created when acid added during pretreatment
Ozone and UV treatment Trace amount (~ 10ppb) of ozone (O3) introduced to kill and oxidize
bacteria Water passed through ultraviolet UV “sterilier” to destroy ozone and
help oxide bacterial fragments (“Pyrogens’)
Ion exchange Ions in solution absorbed onto polymer resin and replaced by ions
with same charge Anions (Na+, Mg+, Ca++) replaced with H+ ions Cations (Cl-, SO4
-) replaced with OH- ions H+ + OH- H2O
Deionized water system RO water storage
High-purity RO water stored in FRP storage tank protected from atmosphere by blanket of “high purity” N2
Ultraviolet Oxidizer Water drawn from tank passes through 185 Nm UV sterilizer which
destroys residual ozone and oxidizes bacterial fragments Primary mixed beds
Water flows through primary mixed beds and resistivity raised to ~18 meg-ohm-cm
Mixed beds contain synthetic resins which remove ionic contaminants through process of ion exchange
Cartridge filters Water passes through series of 0.5 M filters which filter out particles
and “Errant” resin passing through ion exchange process UPW storage
Ultra-pure water is stored in PVDF lined FRP tanks under high-purity nitrogen blanket
Ultraviolet sterilizer UPW drawn from tanks passes through 185 Nm ultraviolet Oxidizer
– process destroys “any” bacteria that may have “formed” in storage tank
Loop cooler/ heat exchanger Water brought to 23oC by heating or cooling – temperature critical to
performance of polishing beds Ion exchange polishing beds
Water flows through polishing beds where resistivity is raised to above 18 meg-ohm-cm
Beds maybe mixed resin beds (containing both anion and cation resins) or there maybe separate beds for each resin
Ultraviolet sterilizer/ oxidizer Water again passes through 185 Nm UV sterilizer/ oxidizer to destroy
bacteria released by resin beds Polishing loop cartridge filters
Water flows through series of 0.1 M filters and series of 0.02 M filters
Qualitative analysis On-line instrumentation continually monitors DI water quality
UPW design Makeup flow – process determined
Use matrix if possible, otherwise: 0.4 l/s per 100 m2 of cleanroom mfg space (6GPM per 1000 ft2 of
Fab) Recirculating flow (2 – 2.5 X makeup)
0.8 – 1.0 l/s per 100 m2 of cleanroom mfg space (12 – 15GPM per 1000 ft2 of Fab)
UPW utility requirements Power Emergency power City water (3 X makeup) Sanitary Sewer (3 X makeup) Industrial waste (1.5 X makeup) Instrument air Nitrogen NaOH – regenerate mixed beds HCl - regenerate mixed beds Sodium Bisulfite Biocide UPW distribution Reverse return configuration commonly used to maintain velocities and
balance system Second return leg is configured into system Water passes by and through tool and returns via reverse return leg Primary return maintains circulation for overall system Design velocities
Supply mains/ laterals: 1.1 – 1.8 m/s (3.5 – 6 fps) Return mains: 0.6 m/s (2.5fps) Control velocities because too slow bacteria will grow and too fast
erosion DI water space requirements Usually located 1) in central plant (or separate facility) and 2) “near”
clean room 17.0m2 per 100 m2 of cleanroom mfg space (170 ft2 per 1000 ft2 of
Fab)
Bulk gas distribution systems Utility gases for production process Used in most process steps Used in relatively large quantities Supplied from cryogenic tanks “Utility” grades & HP grades used Typically “non-toxic”
First law of industrial toxicology: “The dose makes the poison”
Sources of N2, Ar, O2 & H2 :cryogenic cooling & physical separation of constituent atmospheric gases
Helium (He) Sources of He: “mining”
Bulk gas systems Gas delivered in liquid form (typ.) Stored in cryogenic tanks Converted to gaseous form in vaporizer Filtered and purified extensively Distributed in EP 316L SS For very large bulk systems:
One site air separation units (ASUs) Cryogenically cool & physical separate constituent atmospheric gases
can produce N2, Ar, O2 & H2 He derived from “mining” operations Regulated, purified and filtered Piped to cleanroom(s)
Contaminants of interest: Moisture *** Oxygen Hydrocarbons Particles Purity levels Purity levels expressed in volumetric concentration of total contaminants:
PPM n/106 (parts per million) PPB n/109 (parts per billion) PPT n/1012 (parts per trillion) PPQ n/1015 (parts per quadrillion)
Current typical purity requirements:
Low PPB or high PPT ranges Typical concerns Gas particle levels Gas purity levels Materials of construction System surface smoothness System surface area More concerns Surface passivation (reduction of free ion) Virtual leaks Joining techniques
“Clean build” techniques Fabrication methods prevent contamination at every step during
construction Use portable cleanrooms for clean materials storage and prefabrication Use uhp argon for weld purging Extended purge intervals to displace atmospheric contaminants Personnel protocols involving use of cleanroom gloves and other
garments Maintaining purge at all time Bulk gas design concerns UHP gas system designed to minimize contaminants added to gas stream Contaminants take form of either aerosols or gases
Solids typically submicron in size Gas phase contaminants typically in low ppb to high ppt range
Solid vs gas phase removal mechanisms Although particles present in large numbers in atmosphere, easy to
remove from bulk gases Mechanical filtration (interception, impaction, diffusion) high
efficient Membrane vs fiber filters POU (or use point) gas filters near absolute in particle capture ability Efficiencies of 10+ nines at mpps (approx. 0.05 m at rated flows)
Design rules for bulk gas system Non-outgassing, clean, smooth, inert materials (typically EP 316L SS) Minimize plastic in the system Butt weld – avoid threaded joints, socket welds and flanges For small joints that will be broken and remade, use face seal fittings
(VCR, VCO) Use automatic orbital arc welder Use valves with low leak rates – both across seat and inboard/ outboard Components manufactured from bar store or forgings – avoid castings Minimize moving parts in gas stream – avoid rubbing parts in gas stream maintenance free as possible – minimize need to open system to
atmosphere Components with minimum internal dead zones General sizing rule for bulk gas system Minimize turbulence
Keep velocities low as feasible (typically 0.1 - 0.2 m/s, 20-40 fpm) Keep gas moving (don’t let it become “stagnant”)
System goal System should be as close as possible to being
(Not recommended for UHP applications) Joining techniques Welding
Automated orbital arc welds HP Ar internal purge Separate HP Ar external purge
Face seal fittings VCR, VCO, Vacu-seal,….
System testing Leak testing
Static pressure decay Outboard Helium leak test Inboard Helium leak test
Moisture test Purity assays (?)
Spec gas distribution Specialty gases for production process Each gas used in few process steps Used in trace to small quantities Supplied from cylinders UHP grades used Spec gases Categories include:
Inert Toxic Corrosive Flammable Pyrophoric
Spec gases may be more than one category Examples include:
Spec gas systems Gas delivered in cylinders Stored in bunkers or special gas rooms Distributed in EP316L SS tube
May be single or double contained May be distributed through VMBs Filtered, purified (?), regulated Function/ importance of purge panels VMBs (valve manifold boxes) If using one cylinder per tool:
Use gas cabinet & purge panel If using one cylinder for >1 tools (requires tees and valves)
Use gas cabinet, purge panel & VMB VMB => exhausted cabinet to provide containment of tees and
valves Spec gas system Contaminants of interest:
Moisture ** Particles
Purity levels determined by: Input gas purity System performance measures
Cylinder purging protocol Cylinder change out procedures Tool operations and performance
Typical concerns Gas particle levels Materials of construction System leak rates System surface smoothness System surface area More concerns Material selection Joining techniques
Orbital butt welds Mechanical fittings
Longitudinal compression (VCR, VCO) (“face seal fitting”) Distance from gas cylinder to tool Pressure and volume flow control Cylinder change out and purging
“Clean build techniques” Fabrication methods prevent contamination at every step during
construction Use portable cleanrooms for clean materials storage and prefabrication Use uhp argon for weld purging Extended purge intervals to displace atmospheric contaminants Personnel protocols involving use of cleanroom gloves and other
garments Maintaining purge at all times System testing Leak testing
Static pressure decay Outboard Helium leak test (?) Inboard Helium leak test
Moisture test Purity assays (?) Spec gas design concerns UHP gas system designed to minimize contaminants added to gas stream Contaminants take form of either aerosols or gases
Solids typically submicron in size Gas phase contaminants typically in low ppb to high ppt range
Solid vs gas phase removal mechanisms Although particles present in large numbers in atmosphere, easy to
remove from bulk gases
Mechanical filtration (interception, impaction, diffusion) high efficient
Membrane vs fiber filters POU (or use point) gas filters near absolute in particle capture ability Efficiencies of 10+ nines at mpps (approx. 0.05 m at rated flows)
Design rules for spec gas system Non-outgassing, clean, smooth, inert materials (typically EP 316L SS) Minimize plastic in the system Butt weld – avoid threaded joints, socket welds and flanges For small joints that will be broken and remade, use face seal fittings
(VCR, VCO) Use automatic orbital arc welder Use valves with low leak rates – both across seat and inboard/ outboard Use high quality automated purge panels maintenance free as possible – minimize need to open system to
atmosphere Components with minimum internal dead zones System goal System should be as close as possible to being
Waste collection Gravity feed (preferred) or pumped Each sep. waste stream => separate tank Common or separate backup tanks required Tanks sized for transport => ~20000L (~5000gal) Tanks sized for weekly operations Containment
Concrete structures typically Capacity = 110% X largest tank Covered Epoxy coated 6mm HDPE membrane Leak detection
Waste collection design Quantity varies with process Used matrix if possible, otherwise:
Double-contain acid piping when: Overhead Personnel exposure Exposed to elements
Waste collection utility requirements Power + emergency power Acid exhaust (collection truck vacuum) Solvent exhaust (collection truck vacuum) Utility (compressed) air Industrial waste drain Industrial city water “Acid waste” neutralization Treat corrosive (acid or base) solutions used in or generated by
May be performed off site “Other” DIW related wastes (NaOH, HCl,….)
Acid waste neutralization design Quantity: extremely process dependent Use matrix if possible – otherwise
Roughly sized to: DIW makeup quantity + safety factor (~20%)
Acid waste neutralization 1st stage reaction tank
Waste acid from holding tank continuously pumped into first stage reaction tank
When level setpoint reached and pH < 5.5 caustic pumped in When pH = 5.5 acid waste pumped to second stage reaction tank
2nd stage reaction tank When level reaches set point caustic pumped in to bring solution to
desired discharge pH (typically 6.0 – 8.0) If pH becomes < 5.5, solution is pumped back to first stage reaction Solution at target pH pumped to brine tank
Brine tank PH measured – if at target discharge level solution pumped to city
water Many municipalities require constant measurement and recording of
effluent conditions If pH varies from target solution pumped back to second stage
reaction tank for treatment AWN specifications Pumps
Air double diaphragm PVDF wetted parts PTFE body Polypro body for HF Viton, PFA or Neoprene Diaphragm
Piping PFA CPVC for HF
Tanks PVDF-lined FRP Halar-lined FRP
Pump diaphragm selection Acid Neoprene Viton
Sulfuric SD Yes Nitric SD Yes
HF SD Yes Acetic No SD
Phosphoric No Yes SD => marginally OK but Some Degradation expected AWN Utility requirements Electrical Acid exhaust Instrument/ utility air Industrial waste drain Industrial city water
Special waste treatment Some manufacturing operations produce wastes that contain slurries or
heavy metals Operations
Backgrind CMP Plating
Heavy metals Cyanide compounds Gallium Arsenide Copper Chromium
Contaminants first separated from waste water by: Settling Precipitation Flocculation
Waste sludge sent to filter press where water is forced out leaving solid sludge cake behind
Sludge cake placed in barrels for removal to approval waste dumps Decanted water from process neutralized and sent to AWN system
Greenfield site selection criteria General criteria Mechanical criteria General criteria (Factors affecting siting decisions) Vibration sources
Establish ambient vibration levels to determine site suitability Determine proximity to source of vibration Determine proximity to source of air pollutants
Soil conditions Availability of labor/ skills, water, electricity power Space availability – present and future External environmental requirements
Often cleanroom protests process must be creating environmental contaminants These environmental contaminants must be identified, treated,
controlled, removed, disposed of, reported…. Identify environmental contaminants and classify as gaseous, liquid,
or solid wastes Utilities matrix
Evaluate types and quantities of production materials for regulatory compliance
Develop secondary containment strategy to prevent ground water contamination Ex. chemically resistant coatings for exposed floors.
Other regulatory requirements Codes governing construction and operation may be adopted,
interpreted and amended by local agencies All codes must be clearly identified Local agencies may regulate what activities can occur in specific
planning/ zoning area Existing soil and water toxicity levels Tax considerations
Evaluate tax laws and government regulations for possible tax incentives or benefits
Neighbors Evaluate for zoning and compatibility with neighboring properties
Others Personnel & public relations Evaluate internal aesthetics and ergonomics Personnel flow into increasing levels of cleanliness Consider gowning, rest rooms, eating areas and access to cleanroom areas Consider actual and perceived effects on non-cleanroom personnel and
neighbors
Site selection issues Baseline site information
Demographic studies Existing ground water and soil toxicity baselines Existing air quality, water supply, and noise levels Water availability, source and quality Reporting requirements must be addressed early Regulations vary from country to country and within each country Intent of US regulations recommended as a minimum or local
equivalent Security and access control Evaluate site appropriateness for:
Security measures to protect against access by unauthorized personnel Security of proprietary information Access control layered in similar hierarchy as cleanliness protocol –
provides security and limits numbers of people in cleanroom Vibration Cleanrooms often contain equipment and processes that are sensitive to
vibration Electron/ optical microbalances/ scopes and photolithography equipment
very sensitive Few manufacturers of equipment publish specifications regarding
required vibration criteria Owners/ designers often rely on generic criteria This criteria has profound effect on cost and flexibility of facility Site selection Ambient vibration must be measured and be below criteria by
comfortable margin – evaluate both steady state and transient sources Soil conditions significantly affect site vibration – geotechnical and soils
reports essential Facility concept & layout Concept and layout are critical in determining vibration characteristic Criteria easier to achieve if cleanroom on slab on grade structure and
located “far” from major sources of vibration such as central utilities building (CUB)
Foundation and structure Stiffness and rigidity of floor often most significant factor in determining
vibration Slab on grade floors >20-30 cm (8 – 12 inches) thick – placed on stiff,
well compacted soil Supported slabs configured as deep members – rigidity increased with
shear walls working with columns and floor
Floor isolated from structure by isolated breaks Foundations; spread footings, mats, cast-in-situ or drive plus, or caissons Mechanical equipment and systems Mechanical systems are significant source of vibration Select equipment with manageable vibration characteristics and configure
systems to minimize vibration transmitted Screw or centrifugal compressors preferable to reciprocating type Use direct drive fans instead of belt-driven Specifications should include strict dynamic balance standard Piping and ductwork designed for velocities and configurations that
minimize turbulence and shock Pipes and ducts supported by vibration isolation hangers Equipment supported on engineered system that damped vibration
