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SEMI F5-1101 © SEMI 1990 , 2001 9 8.9.3 T hese gases may be pr ohibited, in so me jur isdict ions, fr om b eing d ischar ged wit h no othe r treatment than dilution. 8.9.4 H ighl y toxic ga ses have al so b een known to …
SEMI F5-1101 © SEMI 1990, 2001 8
8.4.3 Emission Sources and Chemicals Emitted
8.4.3.1 VOCs usually have high vapor pressures and
can be hazardous, flammable, or may tend to form
photochemical smog. Processes using them (such as
solvent cleaning, photoresist application, vapor
degreasing and photoresist stripping) are carried out
under local exhaust hoods or in exhausted enclosures.
8.4.3.2 Chemicals emitted may include: acetone, ethyl
benzene, ethyl lactate, hexamethyldisilazane (HMDS),
isopropyl alcohol, methanol, methyl ethyl ketone
(MEK), n-butyl acetate, n-methyl-2-pyrrolidone
(NMP), petroleum distillates (VM&P naphtha),
propylene glycol monomethyl ether acetate (PGMEA)
and xylenes.
8.4.3.3 The chemical species emitted are typically
vapors of the specific VOCs being used. These vapors
are entrained in large volume air streams and are thus
diluted to low levels.
8.4.4 Current Practices
8.4.4.1 New regulations and proposed legislation,
being implemented worldwide, require significant
reductions in total VOC emissions (often measured in
terms of mass discharged).
8.4.4.2 Removal of VOCs from exhaust streams can be
accomplished by adsorption, (e.g., fluidized bed and
concentrator systems), oxidation, or a combination of
adsorption and oxidation systems. Adsorption
technologies, with subsequent desorption and
condensation, can be used to recover VOCs as a liquid.
8.4.4.3 End-of-pipe abatement is most commonly used
for VOCs. Point-of-use systems, using the same
technologies as end-of-pipe, are employed where
exhaust facilities preclude use of an end-of-pipe unit, or
as additional abatement to meet regulatory
requirements.
NOTE 6: See Appendix 1 for VOC abatement design and
selection criteria.
8.5 Group 5 — Pyrophoric Gases
8.5.1 Where separate exhausts for pyrophoric gases
have been installed, it has been practice to fit a large air
dilution chamber at the end of pipe. The reasoning has
been that this will ensure safety by dilution and result in
oxidation of any residual pyrophoric gases. However,
oxidation may not occur since research has shown that
silane, once diluted to <1.5 % in nitrogen, does not
undergo appreciable oxidation when subsequently
mixed with air.
8.5.2 Due to the risks associated with ducting
pyrophoric gases through a facility, it is strongly
recommended that these gases be abated at point-of-
use. This avoids the need for a separate pyrophoric gas
exhaust. If POU abatement is provided, the discharge
from the POU abatement system can be directed to the
acid or general exhaust system.
NOTE 7: See Appendix 2 for POU abatement of pyrophoric
gases.
8.6 Group 6 — See section 10 for Emergency Release
Discharge Exhaust provisions.
8.7 Group-7 — Special/Direct
8.7.1 Recovery of specific gases such as hydrogen (H
2
)
may be necessary to reduce the massive risk of duct fire
when large quantities of flammable gases are
discharged.
8.7.2 PFC reclamation maybe required by
environmental permits in some jurisdictions.
8.7.3 Abatement of Oxides of Nitrogen (NO
x
) may be
necessary to meet environmental regulations in some
jurisdictions.
8.8 Group 8 — General Exhaust
8.8.1 This exhaust group is used to handle exhaust
emissions that include heat and excessive nitrogen flow.
8.8.2 Heat exhaust is used to reduce the heat load on
the balance of the building.
8.8.3 Exhaust of large volumes of nitrogen or other
asphyxiant gas is used to keep potential asphyxiation
hazards away from people.
8.8.4 Discharge from general exhaust should be to a
location where the heat or reduced oxygen will not be a
hazard to personnel.
8.8.5 General exhaust can sometimes be used for
discharge of post-treatment emissions from POU
abatement systems.
8.8.5.1 In such a case, the discharge permit for the
POU abatement system should be consulted for proper
management.
8.9 Group 9 — Highly Toxic Gases
8.9.1 Gases such as arsine, phosphine, diborane,
germane, etc., can be treated in a variety of ways,
depending upon their concentration and their
byproducts (e.g., gas reactor columns, adsorption
systems).
8.9.2 These gases would not likely be allowed in a
burn system (even though many of them might be
pyrophoric) because they could release hydrides from
the air intake.
SEMI F5-1101 © SEMI 1990, 20019
8.9.3 These gases may be prohibited, in some
jurisdictions, from being discharged with no other
treatment than dilution.
8.9.4 Highly toxic gases have also been known to
create problems in a thermal oxidation system, because
of the residue they leave behind and the periodic need
for personnel to clean oxidation systems.
8.9.5 Selectors of systems for discharge of highly toxic
gases should be careful to meet all regulatory
requirements and should be conscious of the discharge
location for the emission residue.
9 Point-of-Use (POU) Abatement Technologies
9.1 The selection of a suitable POU abatement device
is dependent on the process exhaust gases to be abated.
9.2 To determine a valid abatement method, identify
the exhaust composition from the process as well as the
input process gases in order to select a suitable
abatement technology.
9.3 The choice may also depend on other factors (e.g.,
whether removal of PFC gases is required or not).
9.4 The location of a POU abatement system in the
process exhaust train must be reviewed for pressure
drop, condensation, particles, moisture backstreaming,
etc.
9.5 Many types of POU abatement devices are
available and they can broadly be divided into six types
of technologies listed below.
1. Wet scrubbing systems,
2. Oxidation systems,
3. Cold bed systems (adsorbers/ chemisorbers),
4. Hot chemical bed systems,
5. Reactor systems (e.g., plasma, microwave),
6. Traps/filters/cyclones/precipitators,
NOTE 8: See Appendix 2 for explanations of each technology
type.
9.6 Units may employ one or more of these
technologies, depending on the application.
9.7 Where a technology using an exhaustible
cartridge/canister is employed, consideration must be
given to adequate means of detecting bed exhaustion
and to proper disposal techniques.
10 Provisions For Emergency Release
10.1 Routine releases, from hazardous gas cylinders
and sources are usually minimal (e.g., from gas line
purges).
10.2 Emergency or accidental releases, from gas
cylinders in use, may be controlled through mechanical
systems that lower the frequency, time and rate of
releases.
10.3 Enclosing gas cylinders and non-welded
mechanical fittings in exhausted gas cabinets that
protect the systems from damage can minimize the
frequency of accidental releases.
10.3.1 Proper design and installation of gas delivery
and purge systems can reduce the likelihood of severe
leaks.
10.4 The duration of accidental releases can be
lessened by activation of fail-closed valves or gas
cylinder closure devices activated by monitoring and/or
alarm systems.
10.5 Equipping gas cylinders with restrictive flow
orifices can lower the rate of accidental release. SEMI
S5 - Safety Guideline for Flow Limiting Devices
provides guidance on the use of restrictive flow
devices.
10.6 Exhaust of the gas cabinets should be designed to
contain sudden unanticipated releases of gas from
cylinders and piping.
10.6.1 These exhausts are typically used to manage gas
cabinets and other very high volume exhaust flow
systems that will only occasionally have emissions
present.
10.6.2 Some jurisdictions do not allow for discharge
without treatment of emergency release discharges.
10.7 Each system selector should research their own
regulations before determining the proper route and
method for discharging and treating emergency
releases.
10.8 Accidental releases from gas cylinders in use may
be controlled through mechanical systems that lower
the concentration exhausted into the environment. In
some jurisdictions there are requirements (e.g.,
Uniform Fire Code, Article 80) to lower the
concentration of accidental release, in exhaust to the
environment, below a threshold (such as one-half (1/2)
of Immediately Dangerous to Life and Health (IDLH)
levels).
10.8.1 Dilution air, in excess of otherwise required gas
cabinet exhaust, can be used to reduce the concentration
of gas accidentally released into the exhaust, except
where a jurisdiction specifically prohibits this practice.
10.8.2 As another method to reduce the concentration
of gas in the atmospheric discharge during accidental
releases, abatement devices serving the gas cabinet
SEMI F5-1101 © SEMI 1990, 2001 10
exhaust can be used instead of, or in addition to,
dilution air.
10.8.2.1 Accidental release abatement devices may be
any of the types described in this guide.
10.8.2.2 In some applications, gas cabinet exhaust is
diverted to an abatement device only upon detection of
an accidental release.
10.8.2.3 When designing diversion systems, the ability
of the abatement device to operate after extended
periods of disuse must be considered.
11 Summary Table
11.1 See Table 1 for suggestions about using POU and
end-of-pipe abatement systems for different types of
processes, materials, and exhaust systems.
12 Alternative Approaches
12.1 This guide is primarily concerned with handling
gas effluents that arise from semiconductor processing.
Capture and abatement is not the only approach to
avoid release of hazardous materials. If possible, use of
the hazardous materials should be avoided. In theory
the following approach should be used:
12.1.1 Replace the hazardous material with one that is
non-hazardous or less hazardous.
12.1.2 If replacement is not possible, use less of the
material.
12.1.3 If possible, totally enclose the system so all
material is recovered and reused.
12.1.4 If none of the above can be achieved, fit
effective abatement devices.
13 Related Documents
NOTE 9: Unless otherwise indicated, all documents cited
shall be the latest published versions.
13.1 SEMATECH Documents
3
TT97093364A-XFR — Point-of-Use (POU) Control
Systems for Semiconductor Process Emissions
(ESHC003), October 30, 1997, J. Michael Sherer, P.E.,
Motorola (available online from
www.sematech.org\ public\ docubase\ summary\ 3364AX
FR.htm)
13.2 FM Global Documents
4
3 SEMATECH/International SEMATECH, 2706 Montopolis Drive,
Austin, Texas 78741-6499
4 FM Global Corporation, 1151 Boston-Providence Turnpike,
Norwood, MA 02062 or the FM Global Web Site at:
www.fnglobal.com
Property Loss Prevention Sheet 7-78 — Industrial
Exhaust Systems
13.3 Other Documents
Design and Selection of Spray/Mist Elimination
Equipment
5
Toxicological Investigation in the Semiconductor
Industry
6
Reactions of Exhaust Deposits from Silicon Deposition
Tools
7
Treatment of Organochlorines from Plasma Etch
Processing
8
Toxicological Hazards of Plasma Etch Waste Products
9
Packed Column Internals
10
13.4 I300I/International Sematech
11
Emissions Characterization 2.4b — www.I300I.org,
Zero Impact Process Team.
5 Chemical Engineering Volume 91, No. 21, 82–89 (October 15,
1984), Holmes, T. L.; and Chen, G. K.
6 Toxicology & Industrial Health 8 (141) 1992 by Bauer; et. al.
7 Semiconductor Safety Association Conference, Orlando, April
1997 by Creighton S.; Plaster, M.; and Nicholson, T.
8 Semiconductor Safety Technology, March 1995 by Baker, D.;
Smith, J.; and Mawle, P.
9 Semiconductor Safety Technology, July 1996 by Bauer. F; Wolff,
I.; and Schmidt, R.
10 Chemical Engineering, Volume 91, No. 5, pp 40–51 March 5,
1984 by Chen, G. K.
11 I300I/International Sematech, 2706 Montopolis Drive, Austin,
Texas 78741-6499