semi合集-English.pdf - 第3764页

SEMI F5-1101 © SEMI 1990 , 2001 8 8.4.3 Emission Sources and Chemicals Emitted 8.4.3.1 V OCs usua lly have high va por pr essures a nd can be hazardou s, flammable, or may tend to form photoch emical sm o g. Proces ses u…

100%1 / 7923
SEMI F5-1101 © SEMI 1990, 20017
reduce the size of the scrubber, usually at the cost of
increased energy consumption).
NOTE 5: See Appendix 1 for absorber design criteria.
8.2 Group 2 — Acid Aerosols
8.2.1 Part of acid emissions may be in the form of
mists (fine droplets or aerosols) rather than gases.
These may be composed of relatively non-volatile acids
such as phosphoric and sulfuric acids.
8.2.1.1 The mechanisms of removal of particulate
matter (including liquid aerosols) from gas streams are
entirely different from those involved in the absorption
of gases (See Sections 13.1 through 13.3).
8.2.1.2 The critical factor in the collection process is
the particle size of the mist. If the mist is relatively
coarse, as apparently is the case in most instances, the
same types of scrubbers that are used for gas absorption
should collect the mists with adequate efficiency.
8.2.1.3 If a mist having a particle size in the
micrometer or sub-micrometer range is encountered, it
will be necessary to use a high-energy scrubber or a
scrubber with a high-pressure-drop, sub-micron filter to
obtain adequate collection efficiency.
8.2.1.4 Whenever such a fine mist or other aerosol is
encountered, the gas stream from the source should be
abated at point-of-use or separately from the other
exhaust gas streams in the plant so as to minimize
energy costs.
8.2.1.5 Abatement systems utilizing a scrubber with a
high-pressure-drop, sub-micron filter are being used in
the semiconductor industry to reduce emissions from
aqua-regia processes, hot nitric baths and spray etchers
using nitric acid (entrained in exhaust).
8.2.2 It has been determined experimentally that the
collection efficiency of a scrubber on a given mist or
dust is a function of the energy consumed in the
exposure of the particle to the liquid in the scrubbing
process.
8.2.2.1 The relationship between energy consumption
and efficiency is little affected by the geometry or size
of the scrubber or by the method by which the energy is
applied to making contact between the gas and the
liquid (See Sections 13.1 through 13.3).
8.2.2.2 The energy consumption required to attain a
given efficiency increases with a decrease in the size of
the aerosol (e.g., mist or dust). In most of the scrubbers
used in the semiconductor industry, the energy
consumed is drawn from the gas stream in the form of
pressure drop.
8.2.3 The energy/efficiency relationship provides a
convenient and practical method for particle and
aerosol scrubber design. It is essentially independent of
the size of the scrubber, at least down to a very small
size (perhaps 150 to 300 L/min (5–10 ft
3
/min) capacity,
and possibly even smaller). Hence, a small pilot unit
can be used to determine performance on an actual
plant exhaust stream.
8.2.3.1 Tests can also be made under laboratory
conditions, using synthetic aerosols generated for the
purpose.
8.2.3.2 The major problem in using synthetic aerosols
is in replicating the aerosols actually encountered in
practice.
8.2.3.3 The pilot plant scrubber should be tested over a
range of pressure drops to give a well-defined pressure
drop/efficiency correlation.
8.3 Group 3 — Ammonia
8.3.1 Ammonia gas (NH
3
) can be either a process gas
or evolved from ammonium hydroxide used in wet
chemical cleaning of wafers. As previously discussed,
ammonia (NH
3
) exhausted through the acid system will
react with the acids present producing an ammonium
salt aerosol that is not easily abated.
8.3.1.1 Packed-bed scrubbers are not very efficient at
removing sub-micron ammonium halide aerosols, even
though they are water-soluble.
8.3.2 Wet scrubber technologies, as listed above, are
suitable for removal of ammonia provided they are
operated and maintained at low pH (e.g., 3–5).
8.3.2.1 This is normally achieved by the use of sulfuric
acid dosing.
8.3.3 Processes that emit both ammonia and acid gases
(such as nitride deposition) should be fitted with a
point-of-use ammonia scrubber, prior to being
exhausted to the acid exhaust.
8.4 Group 4 — Volatile Organic Compounds (VOCs)
8.4.1 VOCs can represent a large proportion of
exhausted air streams within typical semiconductor
operations. The pollutants are produced from processes
such as solvent cleaning, and photoresist application
and stripping. Such processes typically contribute
flammable, hazardous, and/or environmentally harmful
compounds (e.g., VOCs, which participate in ozone
formation in the atmosphere) to the exhausted air
stream.
8.4.2 There are three primary abatement technologies
used at end of pipe for this category: adsorption,
recovery and oxidation. Adsorption generally uses
hydrophobic zeolite or activated carbon. The oxidation
process usually is thermal or may be catalytic.
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