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SEMI S2-0703a E © SEMI 1991, 2004 35 Hood Type Recommended Test Methods Typical Design and Test Exhaust Parameters (See NOTE 1.) References Parts-Cleaning Hoods Primary: face velocit y , vapor visualization Supplemental:…

SEMI S2-0703a

APPENDIX 2

DESIGN PRINCIPLES AND TEST METHODS FOR EVALUATING

EQUIPMENT EXHAUST VENTILATION — Design and Test Method

Supplement Intended for Internal and Third Party Evaluation Use

NOTICE: The material in this appendix is an official part of SEMI S2 and was approved by full letter ballot

procedures on December 15, 1999 by the North American Regional Standards Committee.

A2-1 Introduction

A2-1.1 This appendix provides specific technical

information relating to Section 22. In general, it

provides guidelines for:

 ventilation design for semiconductor manufac-

turing equipment, and

 test validation criteria.

A2-1.2 This appendix is intended to be used as a

starting point for reference during equipment design.

A2-1.3 This appendix is not intended to limit hazard or

test evaluation methods or control strategies (e.g.

design principles) employed by manufacturers or users.

Many different methods may be employed if they

provide a sufficient level of protection.

A2-1.4 This appendix is not intended to provide

exhaustive methods for determining final ventilation

specifications. Other methods may be used where they

provide at least equivalent sensitivity and accuracy.

A2-1.5 The exhaust velocities, volume flow rates and

pressures listed are derived from a mixture of

successful empirical testing and regulatory

requirements.

A2-1.6 Test validation criteria are generally referenced

from the applicable internationally recognized standard.

It is the user’s responsibility to ensure that the most

current revision of the standard is used.

Table A2-1 Ventilation

Hood Type Recommended Test Methods Typical Design and Test Exhaust

Parameters (See NOTE 1.)

References

Wet Station Primary: vapor visualization, air

sampling

Supplemental: Capture velocity, slot

velocity, tracer gas, air sampling

0.28–0.50 m/s (55–100 fpm) capture

velocity for non-heated

0.36–0.76 m/s (70–150 fpm) capture

velocity for heated

110–125% of the laminar flow

volume flow rate across the top of

the deck

ACGIH Industrial

Ventilation Manual

SEMI F15

Gas Cylinder

Cabinets

Primary: face velocity, tracer gas

Supplemental: vapor visualization

1.0–1.3 m/s (200–250 fpm) face

velocity

ACGIH Industrial

Ventilation Manual

SEMI F15

Equipment Gas

Panel Enclosure

Primary: tracer gas, static pressure

Supplemental: vapor visualization

4–5 air changes per minute

–1.3 to –2.5 mm (–0.05 to –0.1 in.)

O static pressure

ACGIH Industrial

Ventilation Manual

SEMI F15

Diffusion

Furnace

Scavenger

Primary: face velocity, vapor

visualization

Supplemental: tracer gas, air sampling

0.50–0.76 m/s (100–150) fpm face

velocity

NOTE: Do not use hot wire

anemometer.

ACGIH Industrial

Ventilation Manual

SEMI F15

Chemical

Dispensing

Cabinets

Primary: static pressure

Supplemental: vapor visualization, air

sampling where safe, tracer gas where

emission rates can be accurately

calculated

–1.3 to –2.5 mm (–0.05 to –0.1 in.)

O static pressure

2–3 air changes per minute

ACGIH Industrial

Ventilation Manual

SEMI F15

SEMI S2-0703a

Hood Type Recommended Test Methods Typical Design and Test Exhaust

Parameters (See NOTE 1.)

References

Parts-Cleaning

Hoods

Primary: face velocity, vapor

visualization

Supplemental: tracer gas, air sampling

0.40–0.64 m/s (80–125 fpm) face

velocity

ASHRAE Standard 110

SEMI F15

ACGIH Industrial

Ventilation Manual

Pump and

Equipment

Exhaust Lines

Primary: static pressure

Supplemental: tracer gas

–6 to –25 mm (–0.25 to –1.0 in.)

O static pressure

125% maximum volume flow rate

from pump

ACGIH Industrial

Ventilation Manual

SEMI F15

Glove Boxes Primary: static pressure, tracer gas

Supplemental: vapor visualization, air

monitoring

No consensus for a reference at the

time of publication of this guideline.

ACGIH Industrial

Ventilation Manual

SEMI F15

Drying/ Bake/

Test Chamber

Ovens

Primary: static pressure, tracer gas

Supplemental: vapor visualization, air

monitoring

–1.3 to –2.5 mm (–0.05 to –0.1 in.)

O static pressure

SEMI F15

ACGIH Industrial

Ventilation Manual

Spin-Coater

(cup only)

Primary: vapor visualization,

velometry

Supplemental: air sampling

(see SEMI S2 Sections 23.5.1–3) ACGIH Industrial

Ventilation Manual

Supplemental

Exhaust

Primary: capture velocity, vapor

visualization, air sampling

0.50–0.76 m/s (100–150 fpm)

capture velocity

ACGIH Industrial

Ventilation Manual

NOTE 1: All measurements should be within ± 20% of average for face velocity, ± 10% of average along the length of each slot for slot velocity,

and ± 10% of average between slots for slot velocity.

A2-2 Exhaust Optimization

A2-2.1 Exhaust optimization is the use of good

ventilation design to create efficient equipment exhaust.

The design and measurement methods discussed below

confirm that equipment exhaust is acting as the

manufacturer intended. This information is not meant to

prohibit alternate methods of achieving or verifying

good ventilation design. References for ventilation

design are included at the end of this Appendix.

A2-2.2 Design Recommendations

A2-2.2.1 Equipment exhaust design can attempt to

reduce inefficient static pressure losses caused by:

friction losses from materials; openings, and duct

geometries (elbows, duct expansions or contractions);

turbulent air flow; fans; internal fittings such as blast

gates and dampers; directional changes in airflow.

A2-2.2.2 Other good design principles can include

minimizing distance between the source and hood, and

reducing enclosure volumes.

A2-2.2.3 For non-chemical issues such as heat from

electrical equipment, heat recapture rather than exhaust

may be appropriate.

A2-2.2.4 The possible impact of highly directional

laminar airflow found in most fabs should be

considered when designing equipment exhaust.

A2-2.3 Recommended Equipment Controls — The

location of internal blast gates or dampers inside

equipment, and their appropriate settings, should be

clearly identified. The number of equipment dampers

and blast gates should be minimized. Gates/dampers

should be lockable or otherwise securable. Static

pressure or flow sensors installed on equipment by the

manufacturer should have sufficient sensitivity and

accuracy to measure exhaust flowrate fluctuations that

place the equipment out of prescribed ranges.

A2-2.4 Recommended Measurement/Validation

Method — Measurements should be made to identify

optimal exhaust levels and confirm that safety and

process requirements are being addressed. The

manufacturer should be able to identify any critical

equipment locations for chemical capture, and quantify

appropriate exhaust values. Multiple validation/

measurement methods may be needed.

A2-2.4.1 Measurements should be done after

equipment components are assembled.

A2-2.4.2 Computer modeling can be done to predict

exhaust flow and hazardous material transport in

equipment by solving fluid mechanics conservation of

energy and mass equations. Modeling can be used in

the equipment design stage or to improve existing

equipment. Computer models should be verified

experimentally, using one or more of the methods

discussed below.

A2-2.4.3 Tracer gas testing provides a method to test

the integrity of hoods by simulating gas emission and

measuring the effectiveness of controls. Testing until

SEMI S2-0703a

there is a failure, and then slightly increasing the flow

rate until the test is successful, can be used to help

minimize air flow specifications.

A2-2.4.4 Chemical air or wipe monitoring can be used

to confirm that chemical transport is not occurring into

unintended areas of the equipment.

A2-2.4.5 Velocity profiling will confirm expected

airflows, the direction of flow, and the effect of

distance.

A2-2.4.6 Vapor visualization will confirm expected

airflows, the direction of flow, and the effect of

distance. Vapor visualization is the observation of

aerosols (e.g., aerosols generated by using water, liquid

nitrogen, or dry ice) so that exhaust flow patterns can

be observed. Smoke tubes or aerosols may also be used,

however they can produce contamination.

A2-3 Chemical Laboratory Fume Hoods, Parts

Cleaning Hoods

Lab fume hoods and part cleaning hoods are designed

to control emission by enclosing a process on five sides

and containing the emission within the hood.

A2-3.1 Design Recommendations

A2-3.1.1 Fully enclosed on five sides, open on one side

for employee access and process/parts placement and

removals.

A2-3.1.2 Front (employee access side) should be

provided with sliding door and/or sash.

A2-3.1.3 Minimize size of the hood based on process

size.

A2-3.1.4 Minimize front opening size based on size of

process and employee access needs.

A2-3.1.5 Ensure hood construction materials are

compatible with chemicals used.

A2-3.2 Control Specifications — Face velocity is the

specification generally used with hoods open on only

one side.

A2-3.2.1 Generally acceptable laboratory fume hood

face velocities range from 0.40 to 0.60 m/s (80–120

fpm) with no single measurement  20 % of average.

0.64 to 0.76 m/s (125–150 fpm) is recommended for

hoods in which carcinogens or reproductive toxicants

may be used.

A2-3.2.2 Velocities as low as 0.30 to 0.40 m/s (60–80

fpm) can be effective but require no cross drafts or

competing air movement in the work area.

A2-3.2.3 An average face velocity of 0.50 m/s (100

fpm) is generally found to be acceptable in most

applications.

A2-3.2.4 Face velocities of 0.64 to 0.76 m/s (125 to

150 fpm) may be required when a lab hood is installed

in an area with laminar air flow.

A2-3.2.5 Face velocity above 0.76 m/s (150 fpm)

should be avoided to prevent eddying caused by a lower

pressure area in front of an employee standing at the

hood.

A2-3.3 Recommended Measurement/Validation

Method

A2-3.3.1 The preferred method is measurement of

average face velocity and hood static pressure.

Measurements are taken with a velometer or

anemometer. Multiple measurements are taken in a

grid, at least 10 to 40 per square meter (1–4 per square

foot) of open area, in the plane opening of the hood.

This allows representative, evenly spaced

measurements to be taken (see also open-surface tanks).

A2-3.3.2 Additional confirmation by visualization

check of containment using smoke or vapor testing.

A2-3.3.3 ASHRAE Method 110, or equivalent (use

appropriate sections), for tracer gas testing of lab hoods

may be used as a supplemental verification provided

that an accurate emission rate can be defined.

(ASHRAE 110 lists 3 tests: “as manufactured,” “as

used,” and “as installed.” The “as manufactured” test is

the test that is used most frequently.)

A2-4 Wet Stations

Wet stations are slotted hoods designed to capture

laminar air flow while also capturing wet process

emissions from the work area. Wet stations can be open

on the front, top and both sides (it is usually preferable

to enclose as much as possible).

A2-4.1

Design Recommendations

A2-4.1.1 Slots should be provided uniformly along the

length of the hood for even distribution of airflow.

A2-4.1.2 Additional lip exhaust slots should be

provided around tanks or sinks to control emissions.

A2-4.1.3 The plenum behind the slots should be sized

to ensure even distribution of static pressure. These

slots should be designed to ensure adequate airflow is

provided by the side slots, and to minimize turbulence

that could reduce exhaust performance.

A2-4.1.4 Velocity along length of slot should not vary

by more than 10% of the average slot velocity.

A2-4.1.5 Additional use of end or side panels/baffles

can reduce negative impact of side drafts.