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SEMI F49-0200 © SEMI 2000 6 7.6.3 C o mpu ter design tools sh ould b e used to model the electrical distribution sy stem in order to calculate anticipated voltage sa gs for utility or site originated faults. If limitatio…

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SEMI F49-0200 © SEMI 20005
7.4 Support and Facilities Infrastructure Equipment
Performance
7.4.1 The effects that support equipment and facilities
infrastructure equipment have on process equipment
should be considered.
7.4.2 Process and support equipment typically contain
flow, temperature, or pressure sensors. If facility
infrastructure equipment malfunctions due to a voltage
sag event, the diminished flow of a required fluid or gas
will cause the support or process equipment to alarm,
malfunction, or stop.
7.4.3 A typical interconnection of facility
infrastructure equipment with process and support
equipment is illustrated in Figure 2. The various
support and facilities infrastructure systems that can
have an indirect effect on process equipment
performance when subjected to voltage sag events are
listed below:
• Process cooling water,
• Scrubbed exhaust,
• Volatile organic compound (VOC) exhaust,
• Gas cabinets and gas monitoring system
controllers,
• Compressed dry air,
• Process vacuum,
• Automated wafer transport systems,
• Computer integrated manufacturing (CIM)
systems,
• Gas leak detection systems,
• Exhaust abatement systems, and
• Bulk chemical delivery system.
7.4.4 Since the supplied utility power quality effects
all the equipment within the factory, performance
requirements for support equipment and facilities
infrastructure equipment should be specified using the
same standards used for processing equipment.
Applying the same voltage sag susceptibility
specifications for semiconductor processing equipment
(see industry specification for semiconductor
processing equipment voltage sag immunity) to the
support equipment and the facilities infrastructure
equipment has the following benefits: (See Related
Documents section.)
a) Use of the same specification for all
equipment allows for consistency when
monitoring and conditioning for the effects of
voltage sag events.
b) The same performance verification test
methods as those used for processing
equipment can be applied to the support
equipment and facilities infrastructure
equipment.
7.4.5 Where it is inefficient to have support and/or
facilities infrastructure equipment supplied to meet the
same specifications as process equipment, the facility
electrical distribution system may be required to
compensate for any specification gap.
7.5 Monitoring Strategies
7.5.1 Use power disturbance monitors and/or digital
fault recorders to monitor voltage to detect compliance
(see IEEE 1159). Monitor current to identify
disturbance sources and assist in solutions.
7.5.2 Locate continuous monitoring at the electrical
utility service, all major facility electrical distribution
centers, and all critical equipment electrical points of
connection. Perform periodic monitoring for at least
one location of each equipment type in order to
characterize the electrical environment under normal
conditions (i.e., to create a baseline). Additional
monitoring should be performed when experiencing
unexplained operational problems. A comparison of
baseline data to monitored data for equipment
experiencing problems is recommended for evaluating
the power supplied to the equipment.
7.5.3 Provide time synchronization for multiple
monitors to allow for the correlation of a single voltage
sag event between all monitors.
7.5.4 In order to understand the impact, correlate
monitored voltage sag events with known wafer
processing effects within the process equipment.
7.6 Measuring and Modeling Strategies
7.6.1 A single voltage sag event originating outside
the factory will vary in magnitude and duration when
measured at differing locations throughout the facility.
This is largely due to differing lengths and type of
distribution conductors feeding equipment located
throughout the facility. In addition, the electrical
interactions of the reactive and non-linear elements of
equipment effect the voltage sag measurements.
7.6.2 Voltage sag events that originate within the
facility electrical distribution system will vary in
magnitude and duration when measured at differing
locations throughout the facility. These voltage sag
events are usually a result of a current flow increase and
the associated voltage drop across the conductors
between the source and load. The location along the
current flow path greatly effects the voltage sag
measured.
SEMI F49-0200 © SEMI 2000 6
7.6.3 Computer design tools should be used to model
the electrical distribution system in order to calculate
anticipated voltage sags for utility or site originated
faults. If limitations exist such that voltage sag
monitors are not located at every piece of equipment,
then event measurements can be adjusted from
modeling information to determine voltage sag values
at other locations.
7.6.4 As a means for measuring effectiveness in a
business environment, it would be useful to statistically
model the effect of voltage sag events on the
manufacturing processes. The variations mentioned in
Section 7.3.2, above, preclude a deterministic approach
to how well a wafer fabrication process will perform for
a given voltage sag event. A statistical correlation
model would aid in estimating the correlation between
voltage sags and manufacturing cost, and can be used to
validate the effectiveness of power enhancement and
conditioning programs.
7.6.5 Example of Voltage Sag Event Modeling
7.6.5.1 A voltage sag event originating on the
electrical utility system often exhibits different
characteristics when measured at different locations on
facility electrical distribution systems. The variance in
voltage sag characteristics can create different effects
on similar equipment. Variances can usually be
explained by examining 1) the characteristics of voltage
sag at the utility interfaces, 2) the type and connection
configuration of voltage transformations, and 3) the
voltage levels and corresponding phase relationships at
the terminals of infrastructure, support, and process
equipment within the facility.
7.6.5.2 The types of faults that can occur on a utility
system are:
• Line to line to line,
• Line to line to line to ground,
• Line to line,
• Line to line to ground, and
• Line to ground.
7.6.5.3 The utility network can be modeled to predict
the voltage sag characteristics due to various types of
faults at the electrical interfaces between a
semiconductor manufacturing facility and utility. The
most common utility system fault type is a single line to
ground fault. An example of the translation of a
voltage sag resulting from a line to ground voltage sag
event is provided in the following sections.
7.6.5.4 Typical voltage transformations from the
utility interface to utilization voltage levels are
illustrated in Figure 3. Under normal conditions, the
three phase voltages are all approximately equal and
displaced 120º from each other. During a voltage sag
event due to an unbalanced fault, this relationship
changes. Delta-wye transformers between the origin of
the fault and the equipment being studied will further
affect the phase and magnitude relationships. The
degree to which voltage phase shift and magnitude
changes occur at each transformation throughout the
facility distribution system should be considered when
examining impacts on individual equipment.
Transmission System
Medium Voltage Distribution System
138kV (L-L Nominal)
φ
C
φ
B
φ
A
Substation Transformer
First Step-down Transformer
Second Step-down Transformer
Low Voltage Distribution System
F
A
C
I
L
I
T
Y
U
T
I
L
I
T
Y
12.47 kV (L-L Nominal) 7.2 kV (L-N Nominal)
480 or 208 volt (L-L) 277 or 120 volt (L-N)
208 volt (L-L) 120 volt (L-N)
Figure 3
Typical Semiconductor Factory Voltage
Transformations
7.6.5.5 Figure 4 illustrates the variations in magnitude
of a voltage sag event within a facility during a single
line to ground fault on a utility transmission line. This
example illustrates a worst case situation, where a
single-phase fault occurs at a substation transformer
primary-side terminal. (See Related Documents
section.)
7.6.5.6 Many devices in process, support, and facilities
infrastructure equipment are not connected to all three
phases. Because the voltage sag response of these
devices may dictate the sag response for the entire
equipment assembly, understanding device connection
configuration and sag response characteristics is of
critical importance. Sag depth and duration, the point
on the wave at which the sag begins, and the
corresponding phase relationships are all known to be
SEMI F49-0200 © SEMI 20007
factors in determining the sag response of many
common devices.
138kV (L-L Nominal)
φ
C
φ
B
φ
A
Substation Transformer
First Step-down Transformer
Second Step-down Transformer
12.47 kV (L-L Nominal) 7.2 kV (L-N Nominal)
480 or 208 volt (L-L) 277 or 120 volt (L-N)
208 volt (L-L) 120 volt (L-N)
Sag Voltage
(% of Normal)
V
AB
58%
V
BC
100%
V
CA
58%
Sag Voltage
(% of Normal)
V
AB
88%
V
BC
88%
V
CA
33%
Sag Voltage
(% of Normal)
V
AN
58%
V
BN
100%
V
CN
58%
Sag Voltage
(% of Normal)
V
AB
58%
V
BC
100%
V
CA
58%
Sag Voltage
(% of Normal)
V
AB
88%
V
BC
88%
V
CA
33%
Sag Voltage
(% of Normal)
V
AN
88%
V
BN
88%
V
CN
33%
Sag Voltage
(% of Normal)
V
AN
58%
V
BN
100%
V
CN
58%
φ
Α
L-G Fault
F
A
C
I
L
I
T
Y
U
T
I
L
I
T
Y
Figure 4
Example of Voltage Sag Levels during a Single Line
to Ground Fault
7.6.5.7 Figure 4 illustrates the importance of phase
relationships in the sag response of a 120-volt control
circuit emergency off (EMO) relay which is connected
to phase A (or phase B) in a 208-volt facility
distribution system derived with only one low voltage
transformation. In this example the voltage sags to only
88% of nominal on these phases, but drops to 33% of
nominal on phase C. The industry specification for
semiconductor processing equipment voltage sag
immunity does not specify that equipment ride-through
a sag to 33% of nominal voltage.
7.6.5.8 If two low voltage transformations were used
to derive the 208-volt facility system (see Figure 4),
phase B voltage would be unaffected during the utility
voltage sag, but phases A and C would sag to 58% of
nominal. Industry standards typically require
equipment to ride-through a sag of this depth.
However, a tolerance designed into the facility system
may be necessary to provide adequate system
protection.
7.7 Power Enhancing and Conditioning Strategies
7.7.1 While it is desirable to reduce and eliminate
battery storage devices provided by equipment
suppliers with individual pieces of process equipment,
battery storage devices may be appropriate as a
centralized or distributed part of a facilities distribution
system (when evaluated in a systems approach to power
enhancement and conditioning).
7.7.2 Facility power systems enhancements should be
examined on a case-by-case approach to determine the
appropriate measure of power conditioning to be
applied. In general, the following types of equipment
are frequently used to mitigate the effects of utility
voltage sag events in semiconductor factories.
• Constant voltage transformers (typically applied on
control systems)
• Diesel engine based uninterruptible power supplies
(UPS)
• Magnetic synthesizers
• Motor-generators
• Rotary UPS
• Static UPS
• Static transfer switches with alternate power
systems
7.7.3 Other power enhancement techniques and
equipment available for use in facilities electrical
distribution systems include but are not limited to the
following:
• Capacitors for voltage regulation,
• Filters for power conditioning,
• High resistance grounding,
• Isolation of electrical circuit from other loads,
• Power line conditioners,
• Primary and secondary selective rather than radial
distribution systems,
• Super-conducting magnetic energy storage
systems,
• Transformer load tap changers, and
• Voltage regulators.
7.7.4 Power enhancement and conditioning equipment
can be applied at selected equipment components,
selected distribution circuits, or selected distribution
buses. For power conditioning equipment application
guidelines see IEEE 1100 and 1346.