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SEMI S15-0200 © SEMI 2000 5 7.4 Electrochemical — Electroche m i ca l gas s ensors measure tox ic gases and contain compon e nts (electrodes and electroly te) designed to react when exposed to a specif ic toxic gas or a …

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6.31 Repeatability — What is the ability of the gas
detection system to produce the same detection results
within a certain percentage, when repeatedly exposed to
the same gas concentration?
6.32 Reliability — What is the expected life of the
various portions of the gas detection system (including
the main unit, detection sensors, and consumables)?
6.33 Replacement/Replenishment — Does the system
contain consumable items? How frequently must they
be replaced? Can they be replaced by the user or is a
factory person required for servicing?
6.34 Resolution — What is the level of resolution for
changes in gas concentration? That is, to what extent
can the gas detection system detect a changing
challenge gas concentration? Is this user selectable?
6.35 Response Time — From the point of release of
the challenge gas, how long does it take the gas
detection system to reach 90% of the challenge gas
concentration?
6.36 RFI/EMI Susceptibility — Does the gas detection
system meet the requirements for CE Marking for
RFI/EMI immunity and per SEMI E33?
6.37 Self-Test — Does the gas detection system have
an automatic or user initiated self-test routine? How is
it accomplished? What is the interval for the self-test?
Can the operator override the self-test? Is the self-test
just an electrical check or is gas actually generated? Is
the generated gas the target gas?
6.38 Sensor Exchange — Do sensors require on-site
calibration only or can they be factory calibrated? Are
additional adjustments or programming operations
required when replacing a sensor? Is there a warm-up
period for the sensors before they are functional (for
calibration purposes)? If so, how long?
6.39 Sensor Specificity — Are gas specific sensors
available for every gas that must be monitored? What
are the known interferences to the gas detection system
that could cause a false alarm or mask a real alarm?
6.40 Service & Support — What is the manufacturer’s
capabilities to service and support their equipment once
it is has been installed? Does the manufacturer have a
24 hour/7 day service support program in place?
6.41 Spare Parts Availability — What is the
availability of spare parts from the manufacturer? Are
emergency spare parts always available?
6.42 Special Handling Considerations — Are there
items that require special handling, storage, or disposal?
If so, what are the considerations?
6.43 Storage and Shelf-Life Requirements — What are
the storage (environmental) requirements for the
consumable items (e.g., electrochemical sensors and
paper tapes)? Do these items have a shelf-life and if so
how long?
6.44 System Check — Does the gas detection system
have a system check facility? If so, is this done on a
continuous or interval basis? What is the interval?
6.45 System Expandability & Flexibility — Is the gas
detection system universal, in the sense that the user
can change from one gas sensor to another by only
exchanging the sensing elements? How much
modification is required? Can this be done in the field
by the user or must the detection system be returned to
the manufacturer for service?
6.46 Wake Up Requirement — Does the gas monitor’s
sensor require periodic doses of challenge gas or
electrical charges to ensure the sensor will continually
operate? If so, what is the interval required for each gas
type or electrical challenge?
6.47 Warm Up Period — Upon installation or sensor
replacement, how long does it take for the gas detection
system’s sensor to stabilize after power is applied?
6.48 Warranty — What is the warranty period of the
gas detection system?
7 Gas Detection Technologies Available
7.1 Several gas detection technologies are described in
the following paragraphs. As additional technologies
become available, they should be considered, using the
performance characteristics described above.
7.2 Acoustic (Hydrogen Gas Measurement Only) —
Piezoelectric crystals send and receive pulsed
ultrasound. These sound waves travel through two
tubes of air, one tube filled with sample air, the other
with reference air. The returned pulses are counted,
normalized for temperature, and compared. Through
mathematical calculations the result represents the
concentration of hydrogen gas present in percent by
volume or percent LEL.
7.3 Catalytic — Catalytic gas sensors measure
flammable gases by comparison of the change in
resistance across a Wheatstone bridge. The sensor
contains two resistive elements (beads), one active
which increases its resistance when exposed to gas, and
the other which maintains a constant resistance. The
sensor output is then conditioned by the gas detection
system and generates a current output proportional to
the gas concentration in percent of lower explosive
limit (LEL).
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7.4 Electrochemical — Electrochemical gas sensors
measure toxic gases and contain components
(electrodes and electrolyte) designed to react when
exposed to a specific toxic gas or a family of gases; the
reaction generates a current which is measured and
conditioned by the gas detection system and represents
an output which is proportional to the concentration of
gas, measured in parts per million (ppm) or parts per
billion (ppb).
7.5 FTIR — Fourier-transform infrared (FTIR) gas
detection systems use spectrophotometric techniques to
detect and measure gas. Infrared light is passed through
a gas sample, and the resulting absorbency spectrum is
analyzed to determine its constituents. A current output
is generated which is proportional to the concentration
of gas present.
7.6 Infrared — Monochromatic infrared gas detection
systems measure the absorption of radiation (light) by a
gas sample. The absorption is translated into a current
output which is proportional to concentration. Each gas
has a unique absorption wavelength which the system
must be tuned to make an accurate measurement.
7.7 Ion Detection — Ion detection is useful for
detecting SiO
2
particles which are created by the
burning of certain gases such as silane, TEOS and
TEOA. SiO
2
“smoke” is created when these gases are
burned, and this can be detected with an ionization
detector chamber, which operates similarly to a smoke
detector. SiO
2
particles entering the chamber create a
signal that is calibrated to represent the presence of a
known concentration of the target gas. A gas detection
system using this method is typically used in a sample
draw system and can be used either by itself or in
conjunction with a pyrolyzer to condition (burn) the gas
entering the detection head.
7.8 Molecular Emission Spectrom eter — Sample air is
injected into a reaction chamber. In the reaction
chamber, a flame, fed by hydrogen and sample air, is
the activating reaction. When a sample gas enters the
flame, reactions of the target gas result in additional
light emissions. The resulting light passes through two
optical filters and is converted to electronic signals in a
dual photomultiplier tube. The signals are combined to
produce a linear, quantitative output.
7.9 Paper Tape — Paper tape systems use the color
change of a chemically impregnated tape to detect toxic
gases. The tape changes color when exposed to a
challenge gas; the color change is then detected by a
photocell, analyzed, and converted into a concentration
value (ppm or ppb).
7.10 Solid State — One type of solid state sensor is
made of a metal oxide (typically tin-oxide) material that
changes resistance in response to the presence of a toxic
gas; the gas detection system measures this resistance
change and converts it into a concentration value. Thin
film semiconductor sensors absorb the target gas onto
the semiconductor, resulting in a transfer of electrons
which causes a measured change in the resistance of the
semiconductor and reported as a ppm or ppb
concentration.
8 Related Documents
8.1 SEMI Documents
SEMI S2 — Environmental, Health, and Safety
Guideline for Semiconductor Manufacturing Equipment
8.2 American Conference of Governmental Industrial
Hygienists (ACGIH)
1
— Threshold Limit Values for
Chemical Substances in the Work Environment
8.3 Uniform Fire Code
2
UFC Article 51 — Semiconductor Fabrication Facilities
UFC Article 80 — Hazardous Materials
8.4 National Fire Protection Association
3
NFPA 49 — Hazardous Chemical Data
NFPA 70 — National Electric Code
NFPA 72 — National Fire Alarm Code
NFPA 318 — Protection of Cleanrooms
8.5 International Fire Code
4
8.6 Santa Clara, California Uniform Fire Code,
5
Amendments 1998 Edition
8.7 Southern Building Code Congress International
6
Standard Building Code — Chapter 22: Hazardous
Materials, 1994 Edition
1 American Conference of Governmental Industrial Hygienists
(ACGIH), 1330 Kemper Meadows Drive, Cincinnati, OH 45240-
1634
2 Published by International Conference of Building Officials and
Western Fire Chiefs Association, 5360 South Workman Mill Road,
Whitter, CA 90601
3 National Fire Protection Association, 1 Batterymarch Park, Quincy,
MA 02269
4 International Fire Code Institute, 9300 Jollyville Road, Suite 105,
Austin, TX 78759
5 Santa Clara Fire Department, 777 Benton Street, Santa Clara, CA
95050
6 Southern Building Code Congress International (SBCCI), 900
Montclair Road, Birmingham, AL 35213
SEMI S15-0200 © SEMI 2000 6
8.8 US Government
Occupational Safety and Health Organization (OSHA)
7
29 CFR - Sections 1910.119 and 1910.1000
US Environmental Protection Agency (EPA)
8
40 CFR
68.13, Subpart C
7 US Government Printing Office, Washington, D.C. 20402
8 Superintendent of Documents, US Government Printing Office,
Washington, D.C. 20402