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SEMI S15-0200 © SEMI 2000 4 6.31 Repeatability — W hat is the ab i li t y of the gas detection syste m to produce the same detectio n results within a certain percentage, when repeatedly exposed to the same gas conce ntr…

SEMI S15-0200 © SEMI 20003

6.13 Environmental Conditions — What are the

temperature and relative humidity specifications for the

gas detection system for normal operation as well as for

storage of consumable parts? Could environmental

changes such as quick humidity transients or

temperature changes cause the gas detection system to

spike or drift into an alarm condition?

6.14 Equipment Failure — Is the gas detection system

capable of reporting all single point failures that disable

detection? What failure mode disables both detection

of gas and reporting failure?

6.15 Expansion Flexibility — Is the gas detection

system capable of expansion to accommodate

additional detection points? How easy is it to integrate

into the user’s system (hardware, installation,

programming, etc.)?

6.16 Extraction Detection Systems

6.16.1 Sampling Distance — What is the maximum

sampling distance for the gas detection system? Will

all the gas entering the sample line at the point of

detection reach the central monitor? What is the

sample loss due to the challenge gas absorbing onto the

sample tubing walls?

6.16.2 Sample Cycle Time — How frequently, if

multiple points are sampled, is the same detection point

surveyed by the extraction detection system, at the

desired alarm level?

6.16.3 Sample Contamination — What, if any, is the

potential for contamination of the sample line tubing

and manifolding equipment when multiple gases are

monitored within the same extraction system? What

combination of gases should be avoided due to

chemical interaction on wetted materials?

6.17 Filter Lag — Does the gas detection system use

any mechanical, chemical or electronic filters (for cross

sensitivity, particles, etc.) which could slow the

sampling response? If so, what lag time is expected for

each gas type?

6.18 Installation - Wiring Configuration — How many

wires are required per detection point? Can the system

be wired in a highway configuration (bus, ring, star,

etc.)? Are special barriers or grounds required to

ensure no earth loop faults exist?

6.19 Isolation — Does the gas detection system

require any special electrical isolation or grounding?

6.20 Limits of Detection

6.20.1 Lowest Alarm Level — What is the lowest

alarm level setting for the gas detection system which

will not activate due to sensor drift or insufficient signal

to noise ratio?

6.20.2 Limit of Detection — What is the absolute

lowest value that a sensor can detect, for each gas?

6.20.3 Upper Limit of Detection — What is the

highest level of gas that can be quantified reliably by

the gas detection system?

6.21 Linearity — What is the linearity over the full

measuring range of the gas detection system output?

6.22 Maintenance Interval — What is the

manufacturer’s recommended maintenance frequency?

What is involved to perform this maintenance? What

items potentially require maintenance or periodic

replacement (pumps, sensors, tapes, etc.)?

6.23 Other Utilities — In addition to electrical power,

what other utilities are required to operate the system

(e.g., compressed air, hydrogen, oxygen, etc.)?

6.24 Outputs — Does the gas detection system have

analog, digital, and relay outputs? How many are

available per system?

6.25 Physical Size — What is the physical size of the

gas detection system for both the detection head (or

sampling point) and the control systems or central

monitor, including the required floor space?

6.26 Poisoning — Is the gas detection system

susceptible to gases or vapors which would reduce the

performance (ability to detect gas) of the system or

render it contaminated and inoperative?

6.27 Position Effect (Attitude Sensitivity) — Is there a

specific orientation of the sensor, detector, or sampling

point required for the gas detection system to function

optimally?

6.28 Power Outage — When system power is lost,

what happens to the gas detection system? Once power

is restored, what is the time lag before the system is

fully functional?

6.29 Power Requirements — What are the power

requirements (i.e., AC, DC, voltage, and amperage) of

the system? What is the power draw of the total gas

detection system?

6.30 Recovery Time — What is the amount of time it

takes the gas detection system, once exposed to

challenge gas, to recover to 10% of the original target

gas concentration value?

SEMI S15-0200 © SEMI 2000 4

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).

SEMI S15-0200 © SEMI 20005

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

particles which are created by the

burning of certain gases such as silane, TEOS and

TEOA. SiO

“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

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)

— Threshold Limit Values for

Chemical Substances in the Work Environment

8.3 Uniform Fire Code

UFC Article 51 — Semiconductor Fabrication Facilities

UFC Article 80 — Hazardous Materials

8.4 National Fire Protection Association

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

8.6 Santa Clara, California Uniform Fire Code,

Amendments 1998 Edition

8.7 Southern Building Code Congress International

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