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SEMI S18-1102 © SEMI 2002 13 monitored and should alarm at a constan tly attended location when a change occurs. 15.2.2.3.1 The alarm should also shut off the si lane family gas at the nearest up-s tream valve. 15.2.2.4 …

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14.4.2.1.1 The design of automatic-sequence control
systems for cylinder cabinets should incorporate the
following features:
a) Fault-tolerant design,
b) The ability to perform a leak check of the
container by measuring pressure rise in the
system, with the container valve closed, under
the condition that the container has been
connected and the purge gas eliminated,
c) Continuous pressure monitoring of the system
during all purges and operating conditions, and
d) Written procedures for safe source container
replacement including verification
requirements for the leak testing and
verification of the sensing system function.
NOTE 44: All tasks assessed as high risk (from the risk
assessment) should minimize human interaction as much as
possible.
15 Distribution Systems for Gas Supply
15.1 General Considerations
15.1.1 To enable purging without venting into unsafe
locations, a purge port should be installed at locations
where sealed systems require purging. Purge ports
should have a stop valve, if not connected to the purge
gas, should be sealed with a cap or plug.
15.1.2 Dead leg sections (internal piping which can
trap silane family gases) should be minimized to the
smallest volume possible.
15.1.3 An excess flow control valve should be installed
on every silane family gas piping system as close as
practical to the source. The excess flow control valve
should be sized to deliver only as much gas as
necessary to the process requirements.
NOTE 45: See Related Information 3 for an example.
15.1.3.1 Silane family gas delivery systems should be
equipped with the following controls and safeguards:
a) Excess flow protection,
b) A manual shutdown valve at both the point of
dispensing and in the distribution line near or
in the equipment gas box, and
c) Over-pressure monitors with pressure relief
and automatic gas shutoff when pressure is
detected above the designed limit.
15.2 Location and Construction
15.2.1 Piping General
15.2.1.1 Piping should be welded throughout or
contained within an exhausted enclosure.
EXCEPTION: Non-welded piping, outdoors, may not require
an enclosure.
15.2.1.2 Piping should be labeled with the gas name
and flow direction.
15.2.1.3 If the piping diverges into two or more lines,
each line should be provided with a shut off valve.
NOTE 46: Some jurisdictions require both manual and
automatic shut off valves.
15.2.1.3.1 These valves should enable cycle purging of
each line.
15.2.1.3.2 These valves should be provided with an
exhausted enclosure.
15.2.1.3.3 The enclosure should be monitored with
detectors for the silane family gases present.
15.2.1.4 The ventilated enclosures should have exhaust
monitoring per SEMI S2.
15.2.1.5 The piping of oxidizer gases should be
isolated from the piping of silane family gases. The
isolation should also be applied to silane family gas
purge lines.
15.2.2 Coaxial Piping
NOTE 47: Some jurisdictions require building-runs of silane
family gas piping to be of secondarily contained (coaxial)
construction. Some believe there is little evidence that
coaxial piping for these gases is appropriate, as long as non-
welded fittings are within secondary enclosures. Coaxial
piping may add substantial costs and other hazards which
should then be addressed. However, pressurized, monitored,
and interlocked coax lines provide a local warning to persons
who accidentally damage the jacket. The sound of the
escaping inert gas used to pressurize the jacket alerts the
worker. The interlock alerts the facility of the breach, and
reduces the total amount of process gas lost if the inner line is
damaged.
15.2.2.1 When coaxial piping is installed, the annular
space should be pressurized with helium or other inert
gas, purged, or maintained at a vacuum.
15.2.2.2 If a purge method is used, the purge gases
from the coaxial piping should be monitored with
detectors for the specific silane family gas.
15.2.2.2.1 This detector should shut down the source
when a leak is detected.
15.2.2.3 If a pressure or vacuum method is used, the
pressure or vacuum in this annular space should be
SEMI S18-1102 © SEMI 2002
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monitored and should alarm at a constantly attended
location when a change occurs.
15.2.2.3.1 The alarm should also shut off the silane
family gas at the nearest up-stream valve.
15.2.2.4 A procedure for responding to an annular
space alarm, and determining the nature of the hazard
condition, should be created.
15.3 Flow Components
15.3.1 The state of a valve (open or closed) should be
indicated through display or on the valve itself. The
supplier should provide the user with reliability data for
repeated operations, and the user should replace the
valve within its expected lifetime.
15.4 Heaters and Heat Insulation Materials —
External heating of piping and regulators may be
required in outside locations or long distance lines to
prevent re-liquification. In such cases, the following
should be considered:
15.4.1 If electrical resistance heating is used with
insulation, the insulation should be visually inspected
periodically for degradation or exposed wiring to avoid
electrical arcing and damage to the piping.
15.4.1.1 Electrical resistance piping heating systems
should not be placed in wet areas because of the
increased possibility of damage from corrosion.
15.4.2 Electrical resistance piping heating systems
should be monitored. Monitors should alarm in the
event of over temperature, an open circuit or a short
circuit and should shut off the power supply and gas
supply.
15.4.2.1 Gas supply shutdown may be required by
some jurisdictions.
NOTE 48: Heaters must conform to jurisdictional
requirements for the device type.
16 Equipment Using Silane Family Gases
16.1 Design
16.1.1 Coaxial piping within process equipment is not
usually practical, but piping between equipment gas
box and process chambers should be coaxial piping if
the piping is both pressurized and outside of exhausted
and leak-monitored enclosures.
16.1.2 Safe State Equipment should be designed so
that detection of a silane release immediately sends the
equipment into a safe state. Safe shutdown of the
equipment itself or silane family gas sources may be
appropriate.
16.1.2.1 Any silane process vacuum pump, when used,
should be maintained and monitored for its ability to
safely remove potentially hazardous silane family gases
from equipment for maintenance and repair.
NOTE 49: For fire detection, suppression, and alarm criteria
see Section 9.
16.1.3 Fire detection system activation should shut off
flammable and pyrophoric gases supplying the
equipment being monitored, as this is the only safe
method of extinguishing gas fires.
16.1.4 Equipment using silane family gases should be
capable of performing a purge/vacuum sequence to
purge the silane family gas to prevent chemical reaction
damage before service or maintenance.
16.1.4.1 The minimum number of purge/vacuum
cycles should be decided according to the results of
tests that evaluate the sequence effectiveness.
16.1.4.2 The equipment supplier should provide the
minimum safe number of cycles to the user based upon
the baseline process.
16.1.4.3 If adjustable, this minimum number of cycles
should be controlled in such a way that the user is
aware of the consequences of changing the cycle count,
and access to the means of changing the cycle count is
limited to maintenance or service personnel, but not
operators.
16.1.5 When the appropriate number of purge cycles
for the user’s own process are determined by the user,
the number should not be less than the minimum
number of cycles recommended by the equipment
supplier.
16.1.5.1 If unusual circumstances appear to reduce the
number of cycles needed, the supplier should be
consulted for a recommendation specific to the
circumstances.
16.1.6 If a system is designed to supply a silane family
gas and a gas with which the silane family gas can
react, to a chamber simultaneously, the flows should be
controlled to avoid concentrations and pressures of
those gases that would pose unacceptable risks.
16.1.6.1 The equipment should be designed so that it
will not initiate the next process step if a gas mixture
condition that would pose unacceptable risks exists.
16.1.6.2 The equipment should not allow additional
gas to flow until any unsafe gas condition alarm has
been manually reset.
16.1.6.3 Silane family gases and incompatible gases
should have separate piping up to the point where a
system EMO or a safe-state function can shut them off.
SEMI S18-1102 © SEMI 2002
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16.1.6.4 A hazard analysis of the system, beyond the
safe-state shut off, should be used to determine
adequate protection.
16.1.6.5 No single component failure should allow for
incompatible gases to mix, in manifolds or other areas,
in pressures and concentrations that would pose
unacceptable risks.
16.2 Construction
16.2.1 Equipment interface points for the gas supply
piping should be designed with seismic bracing as
needed to achieve the seismic protection detailed in
SEMI S2.
16.2.1.1 The external force on the bending point should
be minimized by use of reverse bending or other
methods.
16.2.1.2 The tensile strength of joints should be
compliant with the appropriate piping standard for the
jurisdiction (such as ASTM/ANSI, ISO, or JIS).
16.2.2 Dead leg sections (internal piping which can
trap silane family gases) should be minimized to the
smallest volume possible.
16.2.3 Chambers intended for silane family gas
processes should be evaluated for their ability to
withstand reasonably foreseeable events related to the
silane family gases such as fire or explosion that arise
from single point failures.
16.2.3.1 If viewing ports are used they should be
designed to the same capability as the chamber, or be
provided with safety devices to capture any potential
flying debris before it affects personnel or other
equipment.
16.2.3.1.1 If viewing ports are intended to be user
replaceable, the user documentation should specify the
part and the change procedure and warn the user of the
possible consequences of using an alternate part.
16.2.3.2 If an enclosure is required to contain chamber
rupture, such an enclosure should be ventilated and
evaluated per SEMI S2 and SEMI S6.
16.2.3.2.1 If the chamber rupture protection is an
enclosure, the enclosure panels should be interlocked to
prevent process initiation or continuance if the
enclosure is open.
16.2.4 Flame sensors or leak detectors should be
installed in all areas that may accumulate silane family
gases from a leak.
16.2.5 The results of the tracer gas tests specified in
SEMI S2 and SEMI F15, should indicate that ambient
concentration of silane family gases will be less than
the level specified in SEMI S2 during maintenance
activities or delivery system failure.
16.3 Vacuum Pump Systems
16.3.1 Materials of construction for vacuum pumps
that are exposed to the gas stream should be compatible
with the gas stream.
16.3.2 Vacuum pumps that are exposed to the gas
stream should be dry type or use inert (non-
hydrocarbon) oil.
16.3.3 Purge gases for vacuum pumps should be
nitrogen (N
2
) or other inert gas. The flow rate of the
purge gas should be sufficient to dilute the silane family
gas to below the lower explosive limit until the gas has
safely passed into the burn box or abatement system. If
a combined pump/abatement system is used, this
criterion is not applicable.
16.3.3.1 The flow rate of purge gas flow should be
interlocked to shut off the silane family gases if the
purge gas flow drops below the amount needed to
insure adequate dilution.
16.4 Protection
16.4.1 Fire Detection and Suppression
16.4.1.1 Use the results of the risk assessment
described in SEMI S14 to determine the need for fire
detection and suppression.
16.4.1.2 Fire detection and suppression system(s)
should be operational at all times, including when
equipment or facilities are shut down or in maintenance
mode.
EXCEPTION: Maintenance of the fire detection system.
16.4.2 As for any other safety design consideration
aspect of process equipment, SEMI S2 provides criteria
for assessing and managing safety risks.
16.5 Information on Exhaust
16.5.1 The equipment supplier should provide exhaust
information to the user. The information should be
based on the baseline process including:
• the chemicals and their composition,
• compatibility requirements and type of connection
expected at outlet of the vacuum pump,
• the potential hazards expected if duct is open to air
during the maintenance,
• recommended maintenance procedures when the
equipment is connected to a point-of-use gas
treatment system,