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SEMI F5-1101 © SEMI 1990 , 2001 17 remains. Potassium hydroxide (KOH) or (sodium hydrox ide (NaOH) solu tions have to be increased to approxim ately 5% to ensure dissolu t ion of silicat es. Chemical dos ing adds anot he…
SEMI F5-1101 © SEMI 1990, 2001 16
APPENDIX 2
POU ABATEMENT TECHNOLOGY TYPES
NOTE: The material in this appendix is an official part of SEMI F5 and was approved by full letter ballot
procedures on August 27, 2001.
A2-1 POU Abatement Technology Types:
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
A2-2 Wet Scrubbing Systems
A2-2.1 Water Scrubber
A2-2.1.1 Principle of Operation — Exhaust gas is
passed through an enclosed space into which water is
sprayed. The desired result is that gases will dissolve in
or react with the water. A large contact area between
gas and water is required to maximize the dissolution or
reaction. Numerous designs exist to achieve this. The
“packed-bed” scrubber is filled with open structure
objects (e.g., hollow balls) that are fully wetted by the
water spray. The gas passes over this large wet surface
area. If the water spray is in the opposite direction to
the gas path the design is “counter current”; if in the
same direction, it is “co-current”; and if at 90° it is
“cross flow”. Other designs to maximize gas/water
contact use meshes, atomized sprays, or multi chamber
systems that reverse the gas direction several times.
A2-2.1.2 Capacity — Total gas flow is determined by
the size of the unit.
A2-2.1.3 Efficiency — Efficiency is determined by the
solubility of the gas in water and retention time in the
unit as well as the given mass transfer from gas to
liquid phase. Acid gases are best removed; many other
process gases may not be removed. If gas does dissolve
in water then effectiveness of unit will be determined
by design input gas flow and inlet compound
concentrations.
A2-2.1.4 Limitations — Water scrubbers are only
suitable for water-soluble gases. Many process gases
(e.g., silicon compounds) will produce insoluble solids
(silica) on contact with water resulting in solids forming
that may block the water sprays, scrubber packing or
gas inlet port.
NOTE 1: Compatibility of scrubber drains with the
compounds being entrained in the liquid effluent should be
considered.
A2-2.2 Water Scrubber with Energy Input (e.g.,
Venturi)
A2-1.2.1 Principle of Operation — Same as water
scrubber but gas and water are forced to mix by the
input of energy. Most commonly this is done by a
venturi through which the gas and water pass. Other
designs have used rapidly rotating blades in the
enclosed scrubbing space. The “active” scrubbing area
is often combined with a passive spray chamber or
packed bed.
A2-2.2.2 Capacity — Energy enhanced water
scrubbers have the same capacity as water scrubbers.
A2-2.2.3 Efficiency — Added energy improves
efficiency over water scrubbers due to forced mixing,
which improves efficiency of particulate removal.
A2-2.2.4 Limitations — The limitations are the same
as for water scrubbers.
A2-2.3 Chemical Dosed Scrubber
A2-2.3.1 Principle of Operation — Chemical Dosed
Scrubbers operate the same as a water scrubber but a
chemical solution is added to the water. This increases
the range of gases that can be removed, from those that
dissolve in water to those that will react with the chosen
chemical solution. The chemical medium is selected to
react with the known input gases producing water-
soluble salts. The two reaction systems most
commonly employed are acid/base and
reduction/oxidation (redox). Addition of solutions of
sodium hydroxide (NaOH), potassium hydroxide
(KOH) or sulfuric acid are frequently used to enhance
effectiveness, and where chemical oxidation is needed
hypochlorites, periodates, or peroxides are introduced.
A2-2.3.2 Capacity — Same as water scrubber.
A2-2.3.3 Efficiency — Same as water scrubber but
increased efficiency by using chemical dosing. The
number of gases, which can be removed, will also
increase.
A2-2.3.4
Limitations — Even though a wider range of
gases can be removed with this chemical dosing, it is
applicable only to those emissions that can be water
scrubbed. The potential for fouling by silica solids
SEMI F5-1101 © SEMI 1990, 200117
remains. Potassium hydroxide (KOH) or (sodium
hydroxide (NaOH) solutions have to be increased to
approximately 5% to ensure dissolution of silicates.
Chemical dosing adds another hazardous material and
may result in liquid wastes that require treatment.
A2-2.4 Chemical Dosed Scrubber with Energy Input
(e.g., Venturi)
A2-2.4.1 Principle of Operation — Same as Water
Scrubber with Energy Input (e.g., Venturi) above, with
the benefits of Chemical Dosed Scrubber.
A2-3 Oxidation Systems
A2-3.1 Burn Systems
A2-3.1.1 Principle of Operation — Burn systems are
designed for silane abatement by utilizing the
pyrophoric properties of this gas. The process gas
containing silane is injected into a steel container
through which a stream of air is passing. The silane
auto-ignites and oxidizes to form silica powder, which
deposits in the system or is carried into the exhaust
duct.
A2-3.1.2 Capacity — Governed by the build up of
powders, small units may need cleaning out every few
months, larger units will provide a year’s capacity.
A2-3.1.3 Efficiency — When burn systems are correctly
set up, nearly complete oxidation will occur, providing
that the input silane concentration is greater than 1.5%.
A2-3.1.4 Limitations — Burn systems are suited only
to silane (or other pyrophoric effluent) abatement. Not
appropriate for mixed gas process. If silane is diluted
to less than 1.5% in nitrogen before input no
measurable oxidation will occur and the silane will pass
directly to the exhaust.
A2-3.2 Flame Oxidation
A2-3.2.1 Principle of Operation — Oxidation of
hydride gases by combustion. These systems use a
chamber containing a fuel gas flame through which the
process gas is passed. The resulting oxides from
combustion pass into the exhaust and may be abated
downstream.
A2-3.2.2 Flow Capacity — To calculate flow capacity,
combine the total discharge flows that constitute input
to the abatement device. Include pump dilution and
purge quantities. .
A2-3.2.3 Efficiency — For simple burner designs,
efficiency can vary widely as gas flow changes; specific
units have been designed to ensure good mixing of
fuel/air and gas; these can deliver efficiencies greater
than 99.9%.
A2-3.2.4 Limitations — Suited only to processes where
the input gases can be safely combusted. Design must
ensure by-products are minimized (e.g., chlorinated
compounds like phosgene/dioxins and oxides of
nitrogen). Produces combustion byproducts of process
gases, therefore, is often combined with a wet scrubber
to remove by-products or other water-soluble gases.
A2-3.3 Hot Chamber Oxidation
A2-3.3.1 Principle of Operation — Exhaust gas is
passed into an electrically heated chamber (typically
800° C) where it is mixed with air. The heated mixture
oxidizes, more quickly than in a simple burn system,
but without a flame from fuel oxidation to assist.
A2-3.3.2 Flow Capacity — To calculate flow capacity,
combine the total discharge flows that constitute input
to the abatement device. Include pump dilution and
purge quantities.
A2-3.3.3 Efficiency — Hydride gases will be oxidized
and removed to below the OEL.
A2-3.3.4 Limitations — On its own, hot chamber
oxidation technology is suited only to hydrides or other
gases that will readily oxidize at the temperature of the
hot chamber. This method is often combined with a
wet scrubber to remove oxidized by-products or other
water-soluble gases.
A2-3.4 Non-Flame Oxidation
A2-3.4.1 Principle of Operation — Non-flame systems
use an incandescent porous wall for combustion
without a flame. Fuel and air are mixed and passed
through the matrix of the porous wall, which operates at
around 900° C. When process exhaust gases are passed
into this zone, they are oxidized.
A2-3.4.2 Flow Capacity — To calculate flow capacity,
combine the total discharge flows that constitute input
to the abatement device. Include pump dilution and
purge quantities.
A2-3.4.3 Efficiency — Hydride gases can be oxidized
by a method similar to other combustion techniques.
High efficiency oxidation is needed to oxidize more
stable fluorinated compounds.
A2-3.4.4 Limitations — Non-flame oxidation produces
oxidation by-products, and therefore must often be
combined with a wet scrubber to remove particulate
matter or water-soluble gases.
A2-4 Cold Bed Systems (Adsorbers/
Chemisorbers)
A2-4.1 Adsorption
A2-4.1.1 Principle of Operation — Exhaust gas is
passed through a container (cylinder, canister, or drum)
SEMI F5-1101 © SEMI 1990, 2001 18
filled with adsorbent granules. These are commonly
based on activated charcoal. Some gases are
physically adsorbed into the granules while the non-
adsorbed gases pass through into the facility exhaust.
A2-4.1.2 Flow Capacity and Removal Capacity —
Both capacities of these systems are a function of the
container size (mass of granules) and surface area.
A2-4.1.3 Efficiency — For a single gas, efficiency can
approach 100% until the bed capacity is reached.
However, since the gas is only held physically it can be
displaced by another compound, causing the efficiency
to drop significantly.
A2-4.1.4 Limitations — Adsorption traps hazardous
compounds and does not destroy them. Gases are
adsorbed at different rates and the capacity of the bed
for different gases will also vary. A more strongly
adsorbed gas entering the bed after a less strongly
adsorbed compound can displace the first gas re-
releasing the first gas to the exhaust. The waste material
must be kept sealed in the container and evaluated for
hazards. Exposure to air, water, or heat can cause gases
adsorbed in the material to be released.
A2-4.2 Chemisorption
A2-4.2.1 Principle of Operation — Exhaust gas is
passed through a container of granules that consist of
either:
• adsorbent granule coated with some reactive
chemical;
• reactive porous medium e.g., soda lime; or
• a resin matrix coated with some reactive chemical.
A2-4.2.1.1 Gases are adsorbed into the porous matrix
and then chemically react either with the granules
themselves or with the coating. These reactions are
designed to convert the gas into a solid material
(typically a salt) that remains attached to the granules.
A2-4.2.1.2 Reactive chemicals are typically either
bases (metal hydroxides) or oxidizers (e.g.,
permanganates, or metal oxides).
A2-4.2.2 Flow Capacity and Removal Capacity —
Both capacities of these systems are a function of the
container size (mass of granules) and surface area.
A2-4.2.3 Efficiency — Acid/Base and Redox reactions
are most readily accomplished. Therefore, with acidic
gases and hydride gases, efficiency can be high; with
removal below OEL. With other gases, e.g., PFCs and
halogenated carbon compounds, efficiency is often
minimal or none.
A2-4.2.4 Limitations — There may be adsorption as
well as chemisorption, so the spent material must be
evaluated for hazards, since gases can desorb from it.
This is especially true for chlorine (Cl
2
) when the bed
uses hydroxides. These will form OCl compounds that
on exposure to air or moisture will regenerate chlorine.
A2-4.2.4.1 Materials used for chemisorption can
themselves be hazardous (e.g., heavy metals or caustic
(KOH/NaOH)) therefore, unused canisters may be
classified as hazardous items.
A2-4.3 Adsorption with Subsequent Air Oxidation
A2-4.3.1 Principle of Operation — These systems are
designed and offered mainly for high flows of arsine
(AsH
3
) and phosphine (PH
3
), used in the deposition of
III-V materials (such as gallium arsenide (GaAs),
indium phosphide (InP)). These gases are adsorbed
into a carbon bed, into which air is subsequently fed at
a controlled rate to oxidize the adsorbed hydride into
oxides that will remain in the granules.
A2-4.3.2 Flow Capacity and Removal Capacity—
Both capacities of these systems are a function of the
container (drum) size (mass of granules) and surface
area.
A2-4.3.3 Efficiency — Capable of removing hydrides
to below OEL.
A2-4.3.4 Limitations — Hydride is adsorbed into the
carbon bed, the oxidation of this is exothermic. When
air is fed in to oxidize the hydride, it is possible to start
combustion of the carbon bed, unless the flow rate is
well controlled.
A2-5 Hot Chemical Bed Systems
A2-5.1 Hot Bed Reactors
A2-5.1.1 Principle of Operation — Exhaust gases are
passed through a steel container (cartridge/drum) that is
filled with reactive material. The material is
maintained at an elevated temperature, typically 250 to
550 degrees C. The gases chemically react with the fill
material and are converted into inorganic salts that
remain fused into the matrix of the fill material. There
are versions with a single fill material that are specific
to abatement of one gas, and versions with two or more
zones of fill material that can abate a wide range of gas
compounds.
A2-5.1.2 Flow Capacity and Removal Capacity —
Both capacities of hot bed systems are a function of the
cartridge size (mass of granules) and surface area.
A2-5.1.3 Efficiency — Efficiency of these systems is
generally high, with gases removed to below OELs.
Stable PFC gases are not removed by all systems.