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SEMI S18-1102 © SEMI 2002 12 14.4.2.1.1 The design of automatic-seque nce contro l systems for cylinder cabinets should incorporate the following features: a) Fault-tolerant design, b) The ability to perfor m a leak chec…
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automated switching system should be employed for
the system.
14.3.7 Flow Limiting Devices should be only as large
as necessary to meet process flow requirements.
NOTE 39: UFC 80-1 requires maximum 0.010-inch orifice
for cylinders in silane service.
14.3.8 Cylinder Systems Using Gas Cabinets
14.3.8.1 Exhaust Requirements
14.3.8.1.1 A forced exhaust system should be provided
for cabinets. Air flow should be directed across
potential leak points to prevent pocketing.
NOTE 40: Recommendations for cabinet exhaust are
provided in RI-2.
14.3.8.1.1.1 The forced exhaust system for silane
family gas should have capability of treating worst case
leak. The treatment may be accomplished by either an
abatement system or dilution of silane family gas to
below 25% of the lower flammable limit.
14.3.8.1.1.1.1 A worst case leak is typically a full-flow
release rate from the largest cylinder installed through
the Flow Limiting Device at full cylinder pressure.
14.3.8.1.2 The exhaust system should be provided with
automatic emergency source of backup power.
NOTE 41: Jurisdictional requirements may define backup
power.
NOTE 42: Many jurisdictions require sensors, detectors, and
lighting fixtures all to be of electrical construction meeting
hazardous location requirements (e.g., not less than NEC
Class 1 Div. 2.) in rooms classified as flammable rooms.
NOTE 43: In some jurisdictions, the exhaust and abatement
system may not be required to operate continuously, provided
when a leak is detected, the forced exhaust and abatement
system be activated to abate the leak.
14.3.8.2 Mechanical ventilation should be provided for
the gas cabinet to keep inner pressure of the cabinet
negative to atmosphere. The effectiveness of the
ventilation should be monitored.
14.3.8.3 Vent lines of the high pressure side of the
regulator of silane family gas cylinders should be
routed to an abatement system when applicable to meet
jurisdictional requirements. The system should have the
capability to abate the largest possible flow through the
cylinder flow restrictor.
14.3.8.4 Excess flow switches should be provided
upstream of the regulator, either in conjunction with
high pressure process valves or on the pigtail
immediately downstream of the cylinder valve. This is
to limit the maximum flow of gas to the regulator.
14.3.9 Special Cylinder Issues
14.3.9.1 Cylinder Change Procedures
14.3.9.1.1 A well defined method of leak checking
should be performed after a new cylinder is installed
and prior to final pigtail purging to insure cylinder
connection leak-tight integrity.
14.3.9.1.2 Appropriate personal protective equipment
(PPE) should be worn during cylinder handling and
changing.
14.3.9.1.3 Before opening the cabinet door to replace a
cylinder, a visual inspection for silicon dioxide (SiO
2
)
powder should be performed. If SiO
2
is present, it is
evidence of a leak in the system, and the door should
not be opened until the gas supply is shut off and, if
possible, purged remotely. Adequate precautions should
be taken as trapped pockets of silane may ignite.
14.3.9.2 Cylinder should be transported with the
cylinder valve plug securely tightened and the cylinder
valve protective cap in-place.
14.3.9.3 Cylinder replacement should be performed by
two persons. Each should have received appropriate
training to perform their tasks safely.
14.3.9.4 Cylinders should be transported on
appropriate carriages with adequate means for fixing
the cylinder to the carriage.
14.4 Changing Sources
14.4.1 To prevent air from entering a silane family gas
system during container change, a constant purge of the
connection should be operating during the entire time
the supply is not connected.
14.4.1.1 To prevent accidental intake of air into the
source container, the source container pressure should
be maintained above atmospheric pressure and replaced
by new one before the pressure drops to atmospheric
pressure.
14.4.1.2 At a certain minimum pressure, a warning
should be provided to an attended location and the gas
shut down.
14.4.2 Auto-sequence Controllers Auto-sequence
controllers are recommended whenever possible to
reduce the potential for human error in supply change-
out.
14.4.2.1 When an auto sequence controller is used, the
leak test after replacement of the cylinder should be
designed to monitor the pressures continuously within
the purging supply system. Interrupted monitoring may
not capture a pressure change that indicates ineffective
purging.
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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.