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ICSG: Integrated Circuit Safety Group January 2000 Page 1 of 29





The information and recommendations contained in this publication were compiled from
sources believed to be reliable. However the authors make no guarantees as to the
sufficiency or accuracy of the information.

This guideline is intended to show what one company has done to address the issue of wet
bench safety. As such it may not include information which is important for a particular
user. The primary reference sources used for the guidelines are listed in sections 5 and 6.
The reader should consult these sources, other references applicable to their operations,
and the appropriate individuals in their organization in order to obtain a more complete
understanding of the subject.

Note: This document contains intranet links to internal Hewlett Packard / Agilent
Technologies documents that will not be accessible to people outside the company.

This document contains links to International Sematech documents that are

available only to Sematech member companies.

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ICSG: Integrated Circuit Safety Group January 2000 Page 2 of 29
1.0 Overview
2.0 Applicability
3.0 Definitions
4.0 Design Criteria
4.1 General
4.2 Ventilation
4.3 Electrical
4.4 Materials of Construction
4.5 Fire Prevention and Protection
4.6 Heating Devices
4.7 Ergonomic Design
4.8 Layout Considerations
4.9 Environmental Considerations
4.10 Chemical Use
4.11 Other Issues
4.11.1 Decontamination and decommissioning
4.11.2 Ozone usage
4.11.3 New equipment purchase
4.11.4 Installation procedures
4.11.5 Seismic Requirements
5.0 References
6.0 Guidance Documents
6.1 Wet Bench diagram and terms
6.2 Fire Suppression Systems
6.3 Acceptable Heating Sources
6.4 Capital Equipment Purchase Process
6.5 Installation and Start-up Permit
6.6 Equipment Decontamination/Decommissioning Procedures
6.7 Wet Bench Code Reference Table
6.8 Recommendations for existing wet benches
6.9 Visual Exhaust Check Procedures

Though this is a guideline, there are some statements that state “shall” or “must”. Those
terms are used when there is an enforceable code or standard that states specific
requirements. These are referenced in section 6.7.
Exceptions to these guidelines may be considered only after review by the EHS and
Facilities departments. Any exception should be documented with assumptions about
operating and administrative controls.

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1.0 OVERVIEW
The purpose of this guideline is to establish minimum design and performance
criteria for wet benches used in semiconductor manufacturing and R&D operations
in order to assure that:
1) Employees are not exposed to unsafe levels of airborne contaminants.
2) Employee exposure to ergonomic risk factors is controlled (See H&S Manual –
Ergonomic Process Standard 535.033).
3) Environmental impacts associated with wet bench use are minimized.
4) Through proper design and construction of wet benches, fire and electrical
hazards are reduced and/or eliminated.
2.0 APPLICABILITY
This document contains the minimum guidelines for new wet benches used in
semiconductor manufacturing. Paragraph 6.8 also recommends the minimum safety
requirements for existing wet benches. Each site should establish a time-table for
bringing existing wet benches up to the criteria specified in Paragraph 6.8.

3.0 DEFINITIONS
3.1 Capture Velocity: The air velocity at any point in front of the hood opening
necessary to overcome opposing air currents and to capture the contaminated
air at that point by causing it to flow into the hood usually measured in feet
per minute (fpm) or linear feet per minute lfm.
3.2 Chemical bath: Recessed cavity extending from the deck down into the
plenum.
3.3 Combustible Liquid: A liquid having a flash point at or above 100 degrees
Fahrenheit (37.8* C).and less than 200 degrees Fahrenheit (93.3 C)
3.4 Combustible Material: A material that will ignite and act as fuel in a
self-sustaining reaction. Polypropylene is an example of a combustible
material.
3.5 Ergonomic design: Designed to meet SEMI S8-95A (Safety Guidelines for
Ergonomics/Human Factors Engineering of Semiconductor Manufacturing
Equipment) and H&S Manual, Ergonomics Process Standard).
3.6 Exhausted Vertical Laminar Flow Hood: The combination of a vertical
laminar flow hood and a wet bench; it is used when both hazard control and
particle control are required.
3.7 Explosion-proof: Electrical devices meeting National Electric Code
requirements for use in potentially hazardous environments (Class I,
Division 1).
3.8 Face: The cross sectional area through which air flow enters.
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3.9 Face Velocity: The average exhaust flow velocity at the face of an exhaust
hood or enclosure; measured in linear feet per minute (lfm).
3.10 Fire-safe material: A material that meets FM4910 protocol. (See FM4910
definition.)
3.11 Fire Suppression System: A system designed to automatically discharge
fire suppression agent upon the detection of low levels of heat, smoke or
flame.
3.12 Flammable Liquid: A liquid having a flash point less than 100 degrees
Fahrenheit (37.8o C).
3.13 Flash Point: The minimum temperature at which a liquid gives off vapor in
sufficient concentration to form an ignitable mixture with air.
3.14 FM 4910 Protocol: Abbreviation for the specification test standard titled,
Factory Mutual Research Corporation (FMRC), Clean Room Materials
Flammability Test Protocol (Class 4910). This specification test standard
establishes testing procedures and maximum levels for Fire Propagation,
Smoke and Corrosive products of combustion. A “fire-safe” material meets
the following criteria
3.14.1 Fire propagation Index <6.0
3.14.2 Smoke Damage Index <0.4
3.14.3 Corrosion Damage Index <2.0
NOTE: Email from Factory Mutual in May 1999 indicated the
Corrosion Index might be dropped because it was not
reproducible.
3.15 Freeboard: The distance from the top of the sink down to the liquid’s
surface.
3.16 Freeboard Height: The distance from the top of the solvent or solvent drain
to the top of the sink (Bay Area Air Quality Management District
Regulation 8, Rule 30) .
3.17 Freeboard Ratio: The freeboard height divided by the smaller of the length
or width of the sink or reservoir.
3.18 Hazardous Production Material (HPM): Any gas, liquid, or solid with a
degree of hazard rating in health, flammability, or reactivity of Class 3 or 4
as ranked by UFC Standard 79-3 and NFPA Standard 704-M.
3.19 Heated Bath: A heated bath is a bath containing liquids above room
temperature. This is achieved by a device used to heat liquids by transferring
heat from heating elements to the liquid.
3.20 Hot Plate: An electrical heating device that operates by conducting heat

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through the wall of a container and into the liquid.
3.21 Immersion Heater: A device used to heat liquids by immersing an
electrically heated element directly into the liquid to be heated.
3.22 In-line IR Heater: A system to heat liquids. Very useful with large baths of
chemicals. The chemical in the bath is circulated and passes through
"tubing" that is surrounded by heat-lamp like devices.
3.23 Laboratory Fume Hood: A device enclosed on five sides except for the
exhaust face which is designed to draw air inward by means of mechanical
ventilation, operated with insertion of only the hands and arms of the user,
and in which hazardous substances are used. This Wet Bench Guideline
does not apply to laboratory fume hoods.
3.24 Laminar Flow Bench: An enclosure designed to draw, filter (through a
HEPA filter), and provide clean air to a work surface. In a vertical laminar
flow unit, the air is drawn and filtered through the top of the unit to provide
a down-flow of clean air to the work surface. With a horizontal laminar
flow unit, the air is drawn and filtered through the rear of the unit across the
work surface towards the operator. These units ARE NOT designed for
handling or storage of hazardous materials, but rather, for particle control.
3.25 LFPM: Linear Feet Per minute. Also abbreviated lfm.
3.26 LEL: "Lower explosive limit" is the minimum volume percent of a
substance in air that can be ignited. This is synonymous with the Lower
Flammable Limit (LFL).
3.27 LFM: See LFPM.
3.28 Lip Exhaust: Exhaust slots at the top edge of workstation deck.
3.29 Make-up Air: Air supplied to a building or a space to replace air that is
exhausted.
3.30 Modify vs Move: To modify a workstation means that some essential
element of the plenum or process operation has been changed, e.g. change
chemistry, add heat sources. Moving a workstation without changes to the
physical configuration of the bench or its process flow is not considered a
modification, e.g. the same bench is used for the same purpose but in a
different location.
3.31 OS&Y Valves: "Outside screw and yoke" valve-used for isolating a section
of an automatic sprinkler system.
3.32 PEL: Permissible exposure limit as defined by OSHA.
3.33 Plenum Exhaust: Exhaust provided for a workstation cavity.
3.34 Safe Level: (referring to airborne contaminant concentrations) ½ of the
Occupational Exposure Level (such as TLV, PEL). The reference in SEMI
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S2 to <1% of TLV, PEL is for ventilation design.
3.35 Significant Modification: Change of a wet bench that increases the health,
environmental or safety hazards. A change in plumbing system, a change in
the heating systems or change in sink size is typically a significant
modification. Moving a wet bench to a different location is not considered a
significant modification.
3.36 Slot Exhaust: Slots located above the source, designed to draw
contaminants away from the operator.
3.37 Splash Shield: Device used to alter the direction of air flow; secondary
benefit from the use of a splash shield is that it provides limited protection
for the operator against splashes.
3.38 TLV: Threshold Limit Value as defined by the American Conference of
Governmental Industrial Hygienists (ACGIH)
3.39 UEL: "Upper explosive limit" is the maximum volume percent of a
substance in air that can be ignited. This is synonymous with the Upper
Flammable Limit (UFL).
3.40 Wet Bench: A workstation that may be free-standing or enclosed on as
many as three sides and is used for chemical processes. The configuration of
these units usually includes sink or wells locally exhausted (through the
plenum below the deck). In a free-standing unit, the work surface may be
partially or completely perforated for exhaust, as well as for drainage of
liquids. An enclosed unit will most likely have adjustable slots in the back
wall and may also have front lip exhaust.
3.41 Wipe Sample Results: The method used to determine if surface
contamination is acceptable is taken from the Industrial Hygiene manual.
The criteria is: “A wipe standard does not exist, however, one simple
generic approach that is often used follows the steps below:
3.41.1 take the airborne standard (e.g., 10 µg/m3 for arsenic, 50 µg/m3 for
lead...);
3.41.2 use the average amount of air inhaled during an 8-hr shift, 10 m3;
3.41.3 assuming total retention of the inhaled material during the shift,
calculate an effective dose (e.g., 100 µg for arsenic, 500 µg for
lead...);
3.41.4 apply it to the typical surface area that is wiped to obtain the
sample, 100 cm2, to obtain the "standard" for the material (e.g., 100
µg/100 cm2 for arsenic, 500 µg/100 cm2 for lead.).
3.42 Work Station: A space or independent principal piece of equipment using
hazardous production materials where a specific function, laboratory
procedure, or research activity occurs. Approved cabinets shall serve the
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work station whenever flammable liquids are used. The station may contain
ventilation equipment, fire protection devices, hazardous materials sensors,
electrical devices, and other processing and scientific equipment.
4.0 DESIGN CRITERIA
4.1 General
New wet benches should be evaluated against the SEMI S2 and SEMI S8
guidelines. Any discrepancies noted during these evaluations should be addressed
by the local EHS department. Existing wet benches should be evaluated against the
minimal acceptable guidelines listed in paragraph 6.8.
4.1.1 Sinks containing chemicals should be located in the back row of the
deck. (Rinse stations are typically in front.)

4.2 Ventilation
The term “adequate ventilation” needs to consider several factors. These include
health hazards, fire hazards and quality of workplace issues. In general, ventilation
should maintain airborne concentrations in the employees’ breathing zone to below
½ of occupational exposure limit. (Typically the OSHA –PEL; ACGIH-TLV or
other country’s recognized airborne exposure limit.) (Be sure to include
maintenance operations also.) Adequate ventilation also should assure
concentrations below 10% of the LEL outside of the ventilation exhaust system.
This is a “shall” requirement per UFC 5101 unless equipment within 5 feet of the
wet bench is constructed to meet Class1 Division 2 electrical requirements.
Adequate ventilation can also be defined as the absence of odors if odors are
adversely affecting employees and/or adversely affecting production. The absence
of chemical odors in the workplace should be a goal. SEMI S2 guidelines
recommend controlling exposures to <1% of PEL, TLV in their design criteria.
Adequate exhaust may be achieved through exhaust slots around sinks, lateral
exhaust slots in the rear of the bench, plenum exhaust, lip exhaust or any
combination.
Laminar flow in a cleanroom environment often means typical ventilation control
methods need to be modified to assure adequate exhaust is achieved. Paragraph 6.9
gives some alternative evaluation methods.

4.2.1 To help provide adequate capture velocity, wet benches should have
the following design criteria:
4.2.1.1 A splash shield that:
4.2.1.1.1 Hangs down from the vertical laminar flow unit or
extends outward from the wet bench control head
case toward the front of the wet bench.
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4.2.1.1.2 Is hinged, flexible, removable or slides to allow
access to the bench
4.2.1.2 Side baffles that extend along side of the deck
4.2.2 Sinks containing chemical baths should have slot/lip exhaust designed
with sufficient velocities to capture and control any airborne
contaminants. (See ACGIH Industrial Ventilation Design Criteria –
Reference in 23rd edition Page 3-10 Figure 3.9 titled “Flow
capture/velocity”)
4.2.3 The face of the wet bench where ventilation face velocities are
measured is defined as the plane between the splash shield, the front
edge of the sinks containing the chemicals and the side baffles. The
average face velocity of the plane should be at least 100 fpm with no
point less than 80 fpm and no point should be greater than 120 fpm.
Higher flow rates have been shown to cause eddy currents that can
actually increase emissions into the employee working area. Higher
flow rates also do not support our company’s energy conservation
principles. See the H&S Manual, Section 535.082 for evaluation
methods. Heated chemicals, carcinogens or compounds with high
vapor pressures may need alternative capture methods. Contact your
EHS department for determining specific needs for these situations.
4.2.4 A means to determine adequate ventilation should be in place on all
wet benches.
4.2.4.1 The preferred device is one that provides a continuous reading.
These devices include (but are not limited to):
4.2.4.1.1 Magnehelics,
4.2.4.1.2 Photohelics
4.2.4.1.3 Incline manometers
4.2.4.1.4 Sail switches
Readings must be recorded and documented at least monthly, and
records must be maintained for 5 years per corporate Hewlett-
Packard/Agilent Technologies H&S manual requirements. If using
these methods, an annual check, compared to a primary standard,
needs to be completed. Also, these devices must be maintained per
manufacturer recommendations.
4.2.4.2 Other methods that meet corporate requirements include
quarterly evaluations with velocity measuring devices. (See
Hewlett-Packard/Agilent Technologies H&S Manual Section
535.082 for minimum requirements.)
4.2.5 Ventilation performance must be recorded and maintained for 5 years
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(Hewlett-Packard/Agilent Technologies H&S Manual -- Process
Ventilation 535.082). It is also recommended that the minimum
specification and performance to that specification be posted on the
wet bench. Parameters may include static pressure measurements,
total pressure measurements, actual CFM and actual fpm.
4.2.6 Methods for Evaluating Ventilation Systems
4.2.6.1 Laminar flow requirements in a clean room often complicates
exhaust ventilation measurements. Other test methods may be
beneficial in evaluating the adequacy of wet bench ventilation.
Paragraph 6.9 describes the various systems. Some alternative
methods are:
4.2.6.1.1 Dry ice visual observations
4.2.6.1.2 Water mist visual evaluation
4.2.6.1.3 Tracer gas analysis per SEMI F15
4.2.6.1.4 Smoke tubes measurements may also be useful in
areas where particulate generation is not a concern.
4.3 Electrical
Electrical installations must conform to the applicable standards (National
Electric Code and/or OSHA NRTL Certifications 29CFR1910.303 and .399)
Some jurisdictions require a third party electrical certification in addition to
the equipment meeting SEMI S2. In Europe, the equipment must meet CE
electrical requirements -- EN60204-1 (TEC204-1).

4.3.1 Electrical equipment and devices within five feet of a wet bench in
which flammable liquids are used shall comply with the requirements
of the NEC for Class I Division 2 hazardous locations. (UFC 5101)
(EXCEPTION):If adequate air removal within the wet bench can
provide a non-flammable atmosphere, (less that 10% LEL measured
outside of the wet bench) on a continuous basis, the requirement for
Class I, Division 2 locations does not apply.
4.3.2 An emergency off device [EMO (emergency machine off) or EPO
(emergency power off)] should be installed to interrupt all power to the
wet bench in the case of an emergency. This device should be placed
in accordance with the recommendations of SEMI S8.
4.3.3 All electric heaters should have ground fault protection (SEMI S3)
4.3.4 Controls should be located away from the wet surfaces and their
placement should not require the operator to reach over any hazardous
process. Controls should be located in the head case or in front of the
wet bench and should meet SEMI S8 guidelines.
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4.3.5 Electrical equipment within the head case of the wet bench does not
need to meet Class 1 Division 2 requirements if the head case is
purged with an inert gas on a continuous basis. {NEC 501-8(a)(3)}
4.3.6 Electric junction boxes, wires and connections should be mounted in a
non-combustible surface.
4.3.7 A means of lock-out/tag out should be readily accessible.

4.4 Materials of Construction

4.4.1 Materials used in the construction of wet benches should be
compatible with the chemicals and processes for which the wet bench
is used.
4.4.2 Materials used in construction should meet FM 4910 protocol. (See
definitions) SEMATECH has tested several materials that meet the
FM4910 criteria and has determined the materials will not adversely
affect production. (SEMATECH TECH TRANSFER DOC
#98123623A-ENG)
http://www.sematech.org/public/docubase/abstract/3623aeng.htm
4.5 Fire Prevention and Protection
4.5.1 Prevention is the first defense to eliminate fire hazards in wet benches,
Protection is the second choice. There are two fire hazards that need to
be addressed: 1) The hazard posed by the use of combustible materials
in the construction of the bench and 2) The hazard posed by the use of
combustible or flammable liquids in an otherwise noncombustible
bench. No bench should include both combustible construction and
the use of flammable or combustible liquids.
4.5.1.1 New wet benches should be made of fire safe materials –
meeting FM4910 protocol.
4.5.1.2 New connections of exhaust ducts and drain lines should be
made of fire safe materials.
4.5.1.3 Whenever possible, process liquid heating should be done
using heat transfer systems using hot water or other
noncombustible heat transfer media.
4.5.2 Fire Protection must be considered when a fire hazard can not be
prevented through design.
4.5.2.1 Wet benches with combustible/flammable liquids must have
fire protection. Fire suppression systems must be of adequate
design. Some examples include fine mist water spray, FM200
and high pressure CO2.

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4.5.2.2 Detection of fire should be accomplished using an UV/IR
sensor. When the sensor is activated, the fire extinguisher
agent should automatically discharge. In addition, a means to
manually activate the fire suppression system should be
provided. Discharge of the fire suppression system must
activate an audible and visual alarm and disable all electrical
inputs to the bench. (UFC97 8003.1.11) However, the exhaust
ventilation for the bench should remain functional. (FM7-7
2.5.1,3 fire protection for wet benches and other process tools)
In addition to electrical sources, bulk chemical delivery
systems and other possible conditions that increase the risk of
fire propagation should also be shut down.
4.5.2.3 Wet bench manufacturers and FM should be consulted to
properly design a fire suppression system, especially the
placement of fire suppression discharge heads.
4.5.2.4 Sprinkler coverage of the horizontal work surface of the wet
bench shall not be obstructed. If coverage is blocked (e.g., by
vertical laminar flow hoods, sashes, splash shields, etc.),
additional sprinkler heads should be installed. In lieu of
additional fire sprinklers, a fire suppression system could be
installed.
4.5.2.5 Exhaust Ducts
4.5.2.5.1 Exhaust ducts greater than 10” in diameter and made
with non-fire safe materials must have sprinkler heads
or other approved fire suppression system. The first
head shall be placed between the wet bench and the
duct damper. It must also be within two feet
downstream of the wet bench connection. (UFC
Article 5101.11)
4.5.2.5.2 A sprinkler head shall be required if the duct is
greater than 10” in diameter and carries flammable
gases or vapors. (97UFC5101.11) The ICSG
recommends this if >10% LEL concentrations are
routinely anticipated.
4.5.2.5.3 Wet benches made of fire safe materials and that do
not contain combustible solvents are the only tools
exempt from duct fire protection.
4.5.2.5.4 The sprinkler head, and its connecting piping within
the duct should be coated with a corrosion inhibitor
(such as bee's wax), if necessary, to prevent corrosion.
The head should be accessible through an access port
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for periodic visual inspections. Sprinkler heads shall
be inspected for corrosion on an annual basis.
4.5.3 For fire prevention and protection of existing wet benches, see 6.6.2.
4.5.4 Maintenance of fire suppression systems.
4.5.4.1 Proper maintenance is important to assure a system will
function when needed. Be sure to follow manufacturer’s
recommendations regarding routine maintenance.
4.6 Heating Devices
4.6.1 Whenever possible, process liquid heating should be done using heat
transfer systems using hot water or other noncombustible heat transfer
media. Another option would be to remotely heat the chemicals
themselves in a properly designed heat exchanger that is external to the
tool.
4.6.2 The heating of any flammable/combustible liquid shall only be done in
a noncombustible (metal) bench or tool.
4.6.3 Preventive maintenance and testing of all safety interlock systems
should be conducted as follows:
4.6.3.1 At least monthly, low liquid level and high temperature
interlocks should be tested to assure proper operation.
4.6.3.2 All electrical connections to heating systems and their controls
should be visually inspected at least semiannually. (FM also
recommends an IR scan of all electrical components annually)
4.6.4 Heating sources for wet benches should incorporate the following
4.6.4.1 A non-combustible outer jacket/enclosure
4.6.4.2 A liquid temperature control (e.g., thermocouple controller
feedback)
4.6.4.3 A heater over-temperature interlock
4.6.4.4 A liquid level interlock
4.6.4.5 A ground fault protection
4.6.4.6 A manual reset
4.6.5 The interlocks listed above should interrupt power to the heating
elements and activate an alarm if the set points are reached. Activated
interlocks must be manually reset prior to allowing resumed operation
of the bath. Float-type liquid level sensors shall not be used for
corrosive applications. Optical or capacitance sensors are
recommended. All safety devices must be successfully tested prior to
the initial use. All safety devices should be placed on a regular
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preventative maintenance schedule to be tested at least annually or as
recommended by manufacturer or per local requirements. FM
recommends monthly checks of interlocks, 7-7 2.4.2, 6a
4.6.6 SEMI S3 and NFPA 318 Paragraph 8-4 should be reviewed for
guidelines in the design of heated chemical sinks.
4.7 Ergonomic Considerations
4.7.1 SEMI S8 criteria should be used in the design of wet benches.
4.7.2 If manual filling of sinks is required, systems should be added to the
wet bench to eliminate the ergonomic and safety hazards associated
with this task.
4.7.2.1 Maximum reach distance to the point of pour - 325 mm (13")
(measured from the front edge of the module to the point where
the chemical flow from the bottle enters the module)
4.7.2.2 Pour height - minimum 900 mm (35") - maximum 1025 mm
(40") (vertical distance from standing surface to average hand
position during pour)
4.7.2.3 Hand and arm clearances when pouring - minimum width 550
mm (22"), minimum height - bottle height plus 130mm (5").
4.7.2.4 Visual clearance - If pouring directly into a bath where visual
access into the bath is required, the module should be designed
such that all operators can view the bath without obstructions
and without bending or twisting.
4.7.2.5 If pouring into a module where the level of the chemical is not
readily seen or requires non-neutral postures to view, an
indicator light or other mechanism for visually alerting the
operator that the module is full should be present.
4.7.2.6 Whenever possible, a funnel or other mechanism should be
provided to reduce the precision associated with the pouring
task.
4.7.2.7 Whenever possible, a funnel or other mechanism should be
provided upon which the operator may rest the weight of the
bottle during the pour.
4.7.2.8 If a sash is required on a wet bench for proper ventilation
design, the minimum opening required is 400 mm (15”). (This
may need to be adjusted depending on the height of the work
surface and the anthropometric measurements of the operator.)

4.8 Layout Considerations

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4.8.1 Wet benches should be designed so that the deck surface is at a
comfortable height for the expected operator(s). This should be within
a range of 850 to 925 mm (34”-36”). Additionally, the depth of the
work surface should range from 450 to 550 mm (18-22”). Depths
greater than 550 mm (22”) should include robotics or other reach
enhancement designs.
4.8.2 The deck surface of a wet bench should be longitudinally divided into
a front (safe) zone, and a rear (hazardous) zone. All chemical
processes should occur in the hazardous zone, so operators need never
reach over chemical baths. Placement of hazardous processes in the
rear of the work station also improves contaminant capture by the local
exhaust ventilation.
4.8.3 Aspirators, chemical drains, air or nitrogen guns should be positioned
so operators are not required to reach over hazardous processes.
Aspirators should only reach the compatible classes for which they
were intended. The recommended location would be at the sides of the
deck.
4.9 Environmental Considerations
4.9.1 Solvent baths should (This is a requirement in areas that fall under the
Bay Area Air Quality Management District) be designed with
sufficient freeboard to minimize solvent vapor emissions; this
freeboard shall be maintained as long as solvent is kept in the bath.
The freeboard height shall be at least 75 percent of the smaller surface
of the two dimensions, length or width. [Note: The Bay Area Air
Quality Management District requirements state, “All unheated solvent
sinks containing VOC with a vapor pressure higher than 30 mm Hg at
20 degrees C AND all heated solvent sinks shall have a freeboard ratio
greater than or equal to 0.75, unless one of the following requirements
is satisfied. All sinks which are subject to a freeboard ratio requirement
shall be clearly marked to indicate the liquid level corresponding to the
minimum allowed freeboard ratio and this level shall not be exceeded.]
4.9.2 All chemical baths should have a lid in place whenever the bath is not
in use; this is to prevent evaporation of the chemicals. This lid should
be affixed to the wet bench, but should not block or hinder airflow
when opened (e.g., a retractable cover). If possible, it is desirable for
the lids to be self-closing / normally closed, particularly when solvents
are used. . [Note: The Bay Area Air Quality Management District
requirements state: BAAQMD Regs: 304.1 All solvent sinks
containing VOC shall be provided with a cover unless the sink is
abated by an approved emission control device as described in
subsection 304.5. These covers must remain closed unless production,
sampling, maintenance, loading or unloading procedures require
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operator access.]
4.9.3 Wet benches should be designed with means of preventing chemical
spills. This may include lips or sills, or diversion to secondary
containment or a drainage system.
4.9.4 Consider various exhaust abatement systems when installing a wet
bench. Point of use systems may have the highest destruction
efficiency and lowest cost. Also, separation of exhaust streams is
warranted, i.e. solvent versus corrosive. Separation of acidic and
alkaline exhaust also is warranted if your site has opacity issues. This
typically is caused by ammonia and chloride combining in the exhaust
stream.
4.10 Chemical Use
4.10.1 Quantities in a wet bench (workstation) shall not exceed:
4.10.1.1 * 15 gallons of flammable, combustible, or poisonous
liquids.
4.10.1.2 * 25 gallons of corrosive liquids.
4.10.1.3 * 12 gallons of oxidizing liquids.
4.10.1.4 * 20 pounds of corrosive or oxidizing solids.
* UFC Article 51 allows a doubling of these quantities if a filtering
system (re-circulation system) is connected to the wet bench.
4.10.2 Baths of incompatible chemicals should not be contained within the
same wet bench. If there is a need to have baths of incompatible
chemicals within the same wet bench, then a physical separation
between incompatible chemicals shall be provided to prevent contact
in the event of leakage or breakage occur. Any exceptions shall be
reviewed and approved by the local EHS department.
4.10.3 Canisters used to dispense chemicals should be constructed with a
material compatible with the chemical(s) being used or stored.
4.10.4 Pressurized containers of hazardous production materials shall meet
the following criteria:
4.10.4.1 Be placed in a fully ventilated enclosure.
4.10.4.2 The canister shall be constructed of at least 18 gauge
(1.2mm;0.0478”) steel for flammable and combustible
chemicals.
4.10.4.3 Piping between the canister and the wet bench must be
secondarily contained. (i.e. a spill tray – coax piping not
required.)

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4.10.4.4 If the chemical is flammable, the additional criteria
must be added to the design. (UFC 7903.1.3.5)
4.10.4.4.1 Tubing must be metal braid/Teflon, flexible
steel, or welded metal tubing. If chemical
compatibility issues need the tubing to be of
combustible materials, the outer piping needs to
be of fire safe material.
4.10.4.4.2 Pressurized containers of Class 1 and Class 2
flammables are allowed in containers of less
than 20 liters (5.3 gallons).
4.10.4.4.3 If dispensed using pressure, the gas must be inert.
4.10.4.4.4 The canister must have a pressure relief device.
4.10.4.4.5 Bonding and grounding procedures must be in place
4.10.5 All chemical containers shall be marked with approved hazard
communication labels. Approved labels include chemical identity and
hazard warning appropriate to that chemical.
4.11 Other Issues
4.11.1 Decommissioning and decontamination of wet benches should be
completed before they are removed or shipped. (For a recommended
procedure see paragraph 6.6)
4.11.2 If ozone is used in the wet bench, the ICSG Semiconductor HPM Gas
Safety Standard should be reviewed regarding delivery and monitoring
recommendations.
4.11.3 A New Equipment Purchase process (Hewlett-Packard/Agilent
Technologies H&S Manual Section 535.100) shall be followed with
each purchase requisition for a wet bench. A form addressing this
process must be reviewed and approved by EHS, or their designated
representative, before a purchase order is issued. It is strongly
recommended that arrangement be made with equipment suppliers to
review internal requirements prior to the construction of the tool. See
paragraph 6.4 for an example of the new equipment purchase process.
4.11.4 Prior to equipment being released to engineering and production, an
EHS review and check sheet should be completed. See paragraph 6.5
as an example.
4.11.5 Seismic Considerations -- Wet bench construction must be designed to
withstand general seismic activity expected in the local seismic rating
zone. In seismic zones, wet benches must be seismically braced
against movement that would damage chemical lines, drain lines, and
exhaust connections. For additional seismic considerations, see SEMI
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S2, section 17 Earthquake protection and FM 7-7, 2.7
5.0 REFERENCES AND TECHNICAL GUIDANCE
5.1 See Code Reference Table (paragraph 6.7) for specific code references
5.2 Semiconductor Exhaust Ventilation Guidebook, First Edition, D. Jeff
Burton, 1995
5.3 Water Mist Generator Procedure
http://sjntweb1.sj.hp.com/icsg/water-mister.pdf
6.0 Guidance Documents
6.1 Wet Bench diagram and terms

Magnehelic

Headcase

Wet Bench Robot Arm Open Front with hinged

lateral exhaust For Wafer shields and plexi-glass sides
slots

Wet bench diagram and terms

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Face plane of wet Front Bath/

Rear Bath
bench – for face Water
Process Chemical
velocity measurements

Wet bench diagram and terms

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6.2 Fire Suppression Systems

6.2.1 Refer to the FM 7-7 17-12 Semiconductor Fabrication Facilities
Loss Prevention Data Sheets. Section 2.5 of the May, 99 version
discusses Fire Protection for Wet Benches and specifically the
requirements for fine mist water spray, CO2 and FM200.
6.3 Acceptable Heating Sources
6.3.1 Refer to the FM 7-7 17-12 Semiconductor Fabrication Facilities
Loss Prevention Data Sheets. Section 2..4.2 Process Liquid
Heating Equipment of the May, 99 version for FM’s
recommendations.
6.4 Capital Equipment Purchase Process
6.4.1 The Hewlett-Packard/Agilent Technologies H&S manual forms
can be found in section 5 of the following New Equipment
Purchase document.
http://hpehs.corp.hp.com/health_safety/ref/hs_man/535-100.htm
6.5 Installation and Start-up Permit
6.5.1 The following SEMATECH Document can be used as a guideline.
http://mirror.sematech.org/public/docubase/abstract/3579axfr.htm
6.6 Equipment Decontamination / Decommissioning procedures
6.6.1 See the Wet Bench Removal Procedures flowchart.

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Wet Bench Removal Procedures

(Before Disconnecting Drain lines or Exhaust Ducts)
Responsibi

Designate process personnel to clean sink.

Clean inside horizontal and vertical surfaces thoroughly

to remove any chemical residues. Wipe air plenum
surfaces. Flush sink plenum. Flush Drain (1)

Were Test surfaces with pH paper

Yes
Corrosives in use? and a few drop of clean
water. Yes
No
No

Request EHS to Yes No

take wipe samples Metals or metal salts Is pH >9 or <5

maint .
In use
No

Process Area Supervisor and/or line/equip

Results Yes
Close exhaust damper and tape off exhaust from inside of the hood
Below criteria(2)

Remove air velocity tags carefully and send to health and

safety Dept. Send original to HVAC

Remove and dispose of chemical labels, sink number and

process notes etc from sink

Place a “Safety Shutdown Tag” on equipment

Environmental attaches decontamination tag

Facilities to dispose
of sink as a Non Submit WO to facilities for physical removal of sink from area
Hazardous waste
Facilities to disconnect drain services and cut exhaust
connection
Facilities

Facilities to evaluate
for possible exhaust Facilities to cap all disconnected services
re-balancing
(1) For benches containing corrosives, rinse with water. For benches containing organic solvents,
rinse with appropriate solvent
(2) See Definition “Wipe Sample Results”

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6.7 Wet Bench Code Reference Table

Wet Bench Code Reference Table

Required CA Code Guidelines
Company ICSG
Reference H&S Recommended
# Criteria Specification UBC/UFC OSHA Manual EPA BAAQMD SEMI NFPA 318 FM practice

General Chemicals in back Row X

4.2 Ventilation <50% OEL X

<1% TLV X
<10% LEL X
Face Velocity >100lfm X X
Flow indicators X X

Class 1 Div 2 within 5

feet of wet station (See
4.3 Electrical exception) X
Electric heaters need
GFCI X X
Class 1 Div 2
requirements X

Materials of
4.4 Construction Meets FM4910 protocol X

Fire Prevention Non-combustible heat

4.5 and Protection transfer mechanisms X
Fire protection for
flammable liquids X X
UV/IR Fire Detector X X
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Wet Bench Code Reference Table
Required CA Code Guidelines
Company ICSG
Reference H&S Recommended
# Criteria Specification UBC/UFC OSHA Manual EPA BAAQMD SEMI NFPA 318 FM practice
Unobstructed sprinkler
coverage X X
Sprinkler for exhaust
ducts >10" X X X
Corrosion inhibitor
coated sprinkler head in
exhaust duct X X
Shut down of power
sources upon fire
suppression discharge X
Local Alarm for Fire
suppression systems X X
Process liquid heating
Heating using noncombustible
4.6 Devices heat transfer media X

The heating of any

flammable/combustible
liquid shall only be done
in a noncombustible
(metal) bench or tool X X
Preventive
maintenance and
interlock check X X
Float-type liquid level
sensors shall not be
used for corrosive
applications X

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Wet Bench Code Reference Table
Required CA Code Guidelines
Company ICSG
Reference H&S Recommended
# Criteria Specification UBC/UFC OSHA Manual EPA BAAQMD SEMI NFPA 318 FM practice
Interlocks should
interrupt power to the
heating element X
Ergonomic ergonomic guidelines
4.7 Considerations specified in 4.6.2 X
Front safe zone and
rear hazardous zone X
Position of aspirators,
chemical drains,
air/nitrogen guns X
Manual filling of sinks X
Environmental
4.8 Considerations Freeboard ratios X
Lid on chemical baths X X
Design fo preventing
chemical spills X X
Exhaust abatement and
separation X X
4.9 Chemical Use Quantities X
Incompatible Chemical
not allowed in the same
bench X
Canister's construction
material must be
compatible with
chemical X X
Requirements for
pressurized containers X

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Wet Bench Code Reference Table
Required CA Code Guidelines
Company ICSG
Reference H&S Recommended
# Criteria Specification UBC/UFC OSHA Manual EPA BAAQMD SEMI NFPA 318 FM practice
Tubing requirements X
Labeling of containers X X
Other Decommissioning
4.10. considerations procedures X
New Equipment
purchase process
requirements X
EHS review prior
release of equipment X

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6.8 Recommendations for existing Wet Benches

6.8.1 The following table gives the ICSG’s recommendations for
existing wet benches.

Recommendations for Existing Wet Benches

Chemical Usage Flammable or combustible Non-flammable or non-combustible
Material of non - fire safe non - fire safe
Construction fire safe material material fire safe material material
Heating Source Y N Y N Y N Y N

Automatic Shut R R _____ R _____

Down Device (1)
Manual Shut R R R R R R
Down Device (2)
Wet bench fire
R-3a R-3a
Prohibited R - 3b R - 3b R-3a R-3a
suppression
system (3)
Exhaust duct fire
suppression R R _____ _____ R R
system (4)

(1) Automatically shuts down power (I.e. electrical, pneumatic, chemical dispense) within the wet
bench upon detection of flame or over-temperature condition.
(2)
Shuts down power (I.e. electrical, pneumatic, chemical dispense) within the wet bench upon
activation of manual button.
(3a) Fire suppression system covers deck, plenum and headcase (if not under inert purge) (This is in
addition to house sprinkler system)
(3b) Unobstructed sprinkler protection required
(4) When required, duct material must be of fire safe material and must have sprinkler system in
exhaust ducts of >10" diameter within 2 feet downstream of the wet bench/exhaust duct
connection.

6.9 Visual Exhaust Check Procedures

6.9.1 Specific guidance for the construction and use of water mist
generators can be found in the document titles “Water Mist
Generator – Construction & Use.” See the following for
additional information. http://sjntweb1.sj.hp.com/icsg/water-
mister.pdf
6.9.1.1 Guidance on the professional methods for visual
checks of exhaust ventilation systems can be found
in D.J. Burton’s “Semiconductor Exhaust
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Ventilation Guidebook” (ISBN 1-883992-08-7), in
the chapter titled, “System testing and Monitoring.”
The System Testing & Monitoring section of the
guidebook contains a paragraph on qualitative tests,
including: smoke, water mist, dry ice, etc. This
guidebook is designed to be used in conjuction with
the ACGIH “Industrial Ventilation Manual.” See
attached images.)
6.9.1.2 SEMATECH conducted a study regarding exhaust
optimization of wet benches. That information can
be found at the following web site.
http://sjntweb1.sj.hp.com/icsg/exhaust.pdf

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