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SEMI S18-1102 © SEMI 2002 10 13.2.4 A cylinder should be secured to t he structure (directly or indirectly) with at least two no n- combustible securing devices p ositioned to prev ent cylinders fro m falling sideways as…
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NOTE 23: Leak testing alone (as in SEMI F1 purity testing)
will not detect potential increased-pressure failures.
12.2 Pressurization Testing
12.2.1 Pressurization testing should be performed to
determine the integrity of the assembled piping.
12.2.2 Pressurization testing should be performed at
150% of the pressure to which the piping section can
be exposed if a single component fails.
NOTE 24: There may be pressure requirements to higher
levels under some regulations.
12.2.3 Procedure Seal the test target with the test
gas and pressurize to the test pressure. Maintain the
test condition for 24 hours. Read the pressure gauge
and confirm that the pressure deviation (with
temperature correction) is within the error of the gauge.
12.3 Leak Testing
12.3.1 Use one of the following two methods:
NOTE 25: Leak testing should be performed with a gas such
as Helium or Helium/balance Nitrogen.
12.3.2 Inboard Leak Testing
12.3.2.1 Generate a vacuum within the test section with
a leak check system. Expose the exterior of the piping,
its joints and fittings to a tracer gas source. While
exposing the exterior of the piping to the tracer gas
watch the leak detection system for detection of the
tracer gas.
12.3.2.2 Detection of any tracer gas indicates a leak.
12.3.3 Outboard Leak Testing
12.3.3.1 Pressurize the test section with the test gas to
150% of the pressure expected during normal operation
at room temperature. Use a leak detection system to
search the exterior of the piping for presence of the
tracer gas.
NOTE 26: Authorities Having Jurisdiction (AHJs) may
require higher pressures.
12.3.4 Corrective Actions — If any pressure or tracer
gas gauge change is detected, repair the leak and retest.
12.4 Exhaust Piping
NOTE 27: Pressurized exhaust piping does not include
facility exhaust ducts.
12.4.1 Pressurized Exhaust Pipe Leak Testing
Exhaust and treatment system piping should be pressure
tested to 100% of what could be the expected pressure
within the piping during a catastrophic reaction within
the piping. The expected pressure is determined by
evaluation of the foreseen operating pressure and
exhaust piping contents.
13 Storage
13.1 General Considerations
13.1.1 Storage area construction materials should be
non-combustible and compatible with the hazards
presented by the silane family gases present.
NOTE 28: For certain gases, it may be necessary to consider
multiple hazards, such as in the case of dichlorosilane, which
is both pyrophoric and corrosive.
13.1.2 Silane family gases should be separated from
other gases per SEMI S4.
13.1.3 The recommended storage temperature is less
than 40°C.
13.1.4 A water deluge or sprinkler system should be
installed over storage area for silane family gases to
cool the gas containers during a fire event and reduce
the effect of impingement of flame from one container
on another.
EXCEPTION: Cylinders of volume of 1 liter or less may be
exempt from this criterion.
NOTE 29: 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.
13.1.4.1 Access to a source of fire protection water
should be provided.
13.2 Cylinder Storage
13.2.1 Cylinders of silane family gases in storage
should maintain cylinder valve plug securely tightened
and cylinder valve protective cap in-place.
13.2.2 Cylinders should be stored in an area adequately
designed to protect the building from reasonably
foreseeable incidents in the cylinder storage area.
13.2.2.1 Cylinders not located in bunkers should be
provided with a security open chain-link fence. The
cylinders should be separated from adjacent structures
and the fence by a minimum distance of 2.7m (9ft) as
shown in Figure 2. [NFPA 318]
13.2.2.2 If cylinders which contain silane family gases
are stored in a structure independent from occupied
building, mechanical or natural ventilation at a
minimum of
0.005 meter/second (about 1cfm/square
foot) should be provided for the structure in which the
cylinders are stored.
NOTE 30: Refer to standards such as NFPA 318 or High
Pressure Gas Safety Law for more details.
13.2.3 The construction or location of the cylinder
storage should not inhibit safe cylinder transfer.
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13.2.4 A cylinder should be secured to the structure
(directly or indirectly) with at least two non-
combustible securing devices positioned to prevent
cylinders from falling sideways as might be
experienced when only a single device is installed.
NOTE 31: Jurisdictions may impose additional requirements.
14 Supply Systems
14.1 Bulk Silane — Bulk silane supply systems should
incorporate the following features:
14.1.1 Location and Construction
14.1.1.1 The container and its peripherals should be
constructed outside of buildings with set back from
buildings and property lines as required by NFPA 318
or regulation. An example of the recommended layout
is shown in Figure 1.
NOTE 32: There may be some jurisdictions that require more
separation than NFPA 318.
NOTE 33: Additional protective barriers may be required to
shield nearby structures or activities from potential flying
objects.
14.1.1.2 A full risk assessment should be performed to
determine if there are other risks with the location such
as vehicular traffic and sabotage.
14.1.1.3 The storage configuration should be of open
construction and have natural ventilation that does not
allow for pocketing of silane that could result in
explosion, unless regulations require enclosures.
14.1.1.4 Bulk silane systems should be separated from
each other and from the regulator station by 2-hour-
rated firewalls.
14.1.2 Access control should be installed to protect
from unnecessary approach of persons.
14.1.2.1 The storage area should have at least two
exits.
14.1.2.2 Workers from the gas supplier and trained site
personnel should be the only persons authorized to
work in a bulk silane gas area.
14.1.3 Controls and Safeguards
14.1.3.1 The arrangement of piping, valving, controls,
and valve manifold boxes as recommended for
liquefied silane Gas Bulk system should be considered.
14.1.4 Flow Components
14.1.4.1 The Flow Limiting Device [e.g., restricted
flow orifice (RFO)] size used in bulk systems should be
as small as possible to meet combined process needs.
NOTE 34: Combined process needs include the influences of
the length of the delivery line.
14.1.4.2 A Flow Limiting Device should be placed in
the outlet valve of the delivery manifold from the tube
trailer.
14.2 Liquefied Silane Family Gas Bulk Systems
14.2.1 Liquefied silane family gas bulk systems should
be equipped with the following controls and safeguards:
a) Excess flow protection,
b) Secondary containment for spills,
c) A manual shutdown valve at both the point of
supply and the point of use and dispensing,
d) Overpressure monitors with pressure relief
and automatic gas shut off, and
e) A system to prevent overfilling for automated
delivery systems.
14.2.2 If heating mechanisms for liquefied gas
containers are required, over-temperature interlocks
should be provided. Indirect heating is recommended.
14.3 Gas Cylinder (Rack) Systems
14.3.1 Open dispensing racks for silane should not be
located in rooms inside the building.
14.3.2 Exterior dispensing areas should be separated
from structures in accordance with Figure 2. The
dispensing area should be open on at least three sides
with cylinders secured to steel frames. Where a canopy
is provided, the height should be a minimum of 3.7 m
(12 ft). [NFPA318].
14.3.3 The construction or location of the on-line
cylinder system should not inhibit safe cylinder
transfer.
NOTE 35: Jurisdictions may impose additional requirements.
14.3.4 A system of controls regarding how many and
which cylinders are on-line should be implemented.
This includes how many cylinders can be connected in
any given bundle as well as the size and capacity of
cylinders.
14.3.5 Cylinders should be equipped with normally
closed automatic pneumatic shutoff valves and
restricted flow orifices.
NOTE 36: The industry has moved almost exclusively to this
condition.
NOTE 37: For cylinder pack systems, a gas detection system
may be required by some jurisdictions. The detection should
close all cylinders ESOVs upon activation.
NOTE 38: An example of the recommended arrangement in a
cylinder gas supply system is shown in Related Information 3.
14.3.6 If multiple cylinders are used, in parallel, for
continuous supply during a cylinder replacement, an
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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.