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SEMI F13-1101 © SEMI 199 3, 2001 3 differ ent mixture r atios o f the sa me pro cess ga s class. A check valve should be in stalled in each line connecting the purg e gas to the process panel equ ip ment. 6.3.2 Process G…
SEMI F13-1101 © SEMI 1993, 2001 2
5 Terminology
5.1 automatic shut-off (ASO) — A remotely actuated
valve, preferably the cylinder valve, but possibly a
valve located close to the cylinder valve, which can
isolate the product as close to the cylinder valve as
possible. It may also be a device which attaches to the
cylinder valve stem or handle to close the valve.
5.2 compressed gas association (CGA) —
Organization that sets standards for the handling and
safe use of gases. Used in this document to refer to the
cylinder valve outlet connection for each product as
designated by the CGA.
5.3 cylinder — A pressure vessel designed for
pressures higher than 276 kPa (40 pounds per square
inch absolute) and having a circular cross section. It
does not include a portable tank, multi-unit tank car
tank, cargo tank, or tank car. It also refers to non-DOT
low pressure containers used for liquid product having
low vapor pressure.
5.4 gas source control equipment (GSCE) — Refers to
the equipment assembly beginning at the product exit
from the cylinder valve to the beginning of the
distribution piping leading to the point of use (POU).
These assemblies are usually mounted on panels and
are sometimes referred to as process panel systems.
5.5 hazardous production material (HPM) — A solid,
liquid, or gas that has a degree-of-hazard rating in
health, flammability, or reactivity of Class 3 or 4 as
ranked by NFPA 704 and which is used directly in
research, laboratory, or production processes which
have, as their end product, materials which are not
hazardous.
5.6 high pressure isolation (HPI) valve — A shut-off
valve located on the high-pressure side of a gas piping
system that, when closed, isolates the purged volume
from the pressure regulator and other downstream
components.
5.7 low pressure isolation (LPI) valve — A shut-off
valve located on the low-pressure side of a gas system
that, when closed, isolates the purged volume from the
distribution piping and all other downstream
components.
5.8 point of use (POU) — Refers to the manufacturing
tool which uses the product. Point of use is
distinguished from the GSCE by having its own design
criteria, separate function, and physical separation from
the GSCE.
5.9 product — Refers to the gas phase in the cylinder.
6 Configuration
6.1 Manual/Auto Operation
6.1.1 Manual equipment without automation is
adequate if it includes an ASO plus excess flow device.
(Where required, per UFC articles 51 and 80.)
Automated purging is generally more efficient than
manual purging and is, therefore, recommended. The
ASO function is achieved if the ASO valve
automatically defaults to a closed position via a
pneumatically actuated valve, or separate actuator that
will close a manual cylinder valve. Either method
should be fail-safe (default to a closed position on loss
of power and/or pneumatics). This could also be
initiated by any number of abnormal circumstances.
6.1.2 Fully Automatic — This is a broad category of
designs using any number of transducers, remotely
operated valves, and logic to accomplish safeguarding,
monitoring, and automatic purging. Extension of this
approach to central data collection, analysis, and
reporting via computers and special programs offers the
capability of further reducing hazards and enhancing
safety.
6.2 Cylinder Connections
6.2.1 Compressed gas cylinders are connected to the
panel equipment using the connection on the outlet of
the cylinder valve. The appropriate regulatory agency
has designated one or more connections for each
product gas.
6.2.2 Other containers for liquid or low vapor pressure
materials may require the connection of two fittings.
One of these is used to admit gas, which either
pressurizes the product, allowing liquid withdrawal, or
absorbs the product, allowing withdrawal of a gas-
phase mixture of the product and the gas. The other
fitting is used for withdrawal. The types and labeling of
the connections vary among suppliers.
6.2.3 High Pressure Pigtail — A semi-flexible
assembly of piping, subjected to cylinder pressure,
which is used to connect the cylinder to the rigidly
mounted components on the panel. The intent of this
flexible assembly is to accommodate the location of the
cylinder outlet.
6.2.4 No Pigtail — An alternate acceptable method
allows cylinders to be elevated or lowered to match the
fixed height of the connection point on fixed panel
equipment.
6.3 Cross Contamination
6.3.1 Purge Gas Cylinder Contamination by Process
Gas — Purge gas is supplied from cylinders, with each
purge gas cylinder limited to a single process gas panel
or several panels using the same process gas class or
SEMI F13-1101 © SEMI 1993, 20013
different mixture ratios of the same process gas class. A
check valve should be installed in each line connecting
the purge gas to the process panel equipment.
6.3.2 Process Gas Cylinder Contamination by Purge
Gas — The purpose of purging is to remove air or
residual process gas from the panel equipment (or part
of it) back to the internal cavity of the closed cylinder
valve.
WARNING: Check valves are not acceptable in this
part of the process gas system because purging would
be defeated. Cross contamination can only be prevented
by safeguards which assure complete cylinder valve
closure and process gas venting, before purging begins.
6.4 Materials — All materials furnished should be
manufactured to nationally recognized standards.
Metals used for the wetted surfaces should be type 3l6L
stainless steel, or other materials that provide equal or
improved compatibility with the gas in service.
Nonmetallic seals that are used in valve or regulator
seats must also be compatible with the product in
service.
6.5 Joints — All welded joints should be butt welded
(no socket welds) and should comply with SEMI F3.
Connection fittings should be face seal type.
6.6 Particle Control — Particle contamination is
controlled through the proper selection of components
and system hardware, good design practices, clean
fabrication methods, and proper operation of the
system.
6.7 Internal Volume — The internal cavities should be
configured for minimum surface area and internal
volume to enhance purging. Dead end legs should be
eliminated or kept to a minimum volume and length.
6.8 Maintainability — Planned maintenance or forced
repair is facilitated or inhibited by specific design
concepts and features. From a safety point of view, it is
mandatory to be able to purge the entire GSCE (all
cavities) and to have a downstream shutoff (low
pressure isolation valve) and disconnect fitting.
7 Performance Recommendations
7.1 Functional Recommendations
7.1.1 The ASO should be designed to close based on
an alarm or fail signal from an auxiliary component. It
should be designed to fail closed and should have a
working pressure at least 1.1 times the product cylinder
pressure. If a pressure sensor is located between the
ASO and the cylinder valve, as depicted in Figure 1, it
should also have a working pressure at least 1.1 times
the product cylinder pressure.
7.1.2 Pressure Reduction — Gases are most
commonly required at POU at less than 100 psig.
Cylinder pressure is reduced to the lower pressure by a
gas pressure regulator, when necessary.
CONNECTION
Figure 1
Typical Gas Source Control System
SEMI F13-1101 © SEMI 1993, 2001 4
7.1.3 Excess Pressure Control — Provisions should be
made to protect the distribution piping and process
equipment from excessive pressure. This protection
may include a pressure transducer, pressure switch, or
indicating transmitter connected to close the ASO, a
relief valve piped into the exhaust, or a redundant
pressure regulator with primary regulator failure
indication.
7.1.4 Cylinder Contents — The product remaining in
the cylinder is determined by gas pressure measured by
either a pressure transducer or gauge, or in the case of
material in liquid/vapor phase, by the cylinder weight
measured by a scale.
7.1.5 Delivery Pressure — The pressure delivered by
the regulator is displayed by a pressure indicator. This
can be either a gauge or transducer readout.
7.1.6 Filters — Particles from ambient sources,
entering with the product or generated by the system
elements, can be captured by including one or more
filters at a variety of locations within the system. This
practice tends to protect the components and the
process.
7.1.7 Purge Gas Connection — A purge gas
connection is provided via a branched connection to
admit clean, dry, inert purge gas through an on-off
valve. This is commonly located between the cylinder
connection and high pressure isolation valve in the
panel system. Gas purging is used for installation of a
new system, before disconnecting a spent cylinder, after
connecting a fresh cylinder, and for removal of
equipment for maintenance purposes.
7.1.8 Vent Outlets — The normal purpose of the vent
valves is to discharge process gas, air, and purge gas in
conjunction with purging operations. Under special
circumstances, they are used to reduce pressure in the
equipment and/or transfer product. One or more vents
may be used at various locations, and downstream
venting may be either atmospheric pressure or vacuum
from a venturi or pump. Vacuum venting is strongly
recommended.
7.1.9 High Pressure Indication — A pressure indicator
in common with the high pressure line connected to the
cylinder valve is required to indicate the presence of
residual process gas, or an open or leaking cylinder or
panel valve. It also shows application of adequate purge
gas pressure, and, in cases where vacuum-assisted
purging is employed, an indication of the vacuum level
should be included.
7.1.10 Cylinder Connection Makeup — After a fresh
cylinder has been connected, the integrity of the
cylinder valve connection can be tested with the use of
the pressure indicator mentioned in Section 7.1.9.
7.2 Failure Modes — Any one of a number of
conditions will require emergency action. Some are
more serious than others. In some cases, the
consequence is shutdown of the panel equipment and
venting to a properly controlled discharge system.
These failures should be addressed in the hardware and
operational design phase of the system.
7.2.1 Excessive Delivery Pressure — Due to
equipment malfunction or operator error.
7.2.2 Leaking fitting or component malfunction may
require gas detection monitor.
7.2.3 Excess Flow — This can be the result of operator
error or catastrophic conditions, such as a sheared
delivery line.
7.2.4 Cabinet exhaust failure.
7.2.5 Mechanical failure of panel equipment parts or
downstream equipment.
7.2.6 Destruction to plant through fire, explosion,
earthquake, crash, etc.
7.2.7 Inadvertent mishandling of distribution
equipment.
7.2.8 Process tool problems.
7.2.9 Control system failure.
7.2.10 System Abuse/Misuse — Source gas quality may
affect service life and operability of the system. Poor
gas product quality may cause a reduction in
performance of the system that can lead to premature
hardware component failures.
8 Acceptance Test
8.1 All gas source control equipment should undergo
an acceptance test, agreed to and understood by the
customer and supplier, before it is delivered. This test
should ensure that all control and operational functions
perform as required by the customer’s and/or supplier’s
specifications.
9 Qualification Test
9.1 GSCE should be qualified at its installed location
with an inert gas prior to installing the process gas
cylinder. This test should include the operation of all
control and hardware functions, interface with the
process tool and all interconnected safety devices,
systems, and alarms. This should also include a system
wide leak test of all possible leak points, such as fittings
and welds.