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SEMI E124-1103 © SEMI 2003 5 av ailability ef f i ci ency fi n i s h e d units out av er age cycle t i me good unit equiv alents out (12) WI P capac i ty the or etic al pr oduc ti on time per unit total time scra p p ed …
SEMI E124-1103 © SEMI 2003 4
theoretical unit throughput is equal to the reciprocal of
theoretical production time per unit (SEMI E79).
5.1.33 throughput rate — the number of units of
production that pass through a process per period of
time.
5.1.34 throughput-rate and cycle-time efficiency — the
best-case cycle time divided by the average cycle time
(shows the relative performance of the factory with
respect to throughput rate and cycle time). See
Equation 13. See Section R1-1.6 in Related
Information 1 for a discussion of this metric.
5.1.35 total time — all time (at the rate of 24 hours per
day, seven days per week) during the period being
measured. In order to have a valid representation of
total time, all six basic equipment states must be
accounted for and tracked accurately (SEMI E10).
NOTE 8: For factory-level productivity metrics, total time
should be larger than the average cycle time (and is
recommended to be twice as large as the average cycle time
and larger than the cycle time of any individual unit in
finished units out).
5.1.36 unit (of production) — the basic entity in the
factory (such as a wafer in a fab, a glass pane in a flat
panel factory, or a die in a post-wafer back-end chip
production facility) which acts as a product substrate
(and moves through the factory with no assembly or
disassembly processes). Only product units are
included (as opposed to test wafers or other non-
product devices).
NOTE 9: This definition is more restrictive than that given in
SEMI E10 in order to be sufficiently specific.
NOTE 10: Production lot sizes can (and typically do) include
multiple units of production, and units can (and typically do)
contain multiple product devices (usually of the same type but
possibly of different types). The user may chose to have the
production lot be the unit of production, but that is not
recommended because:
• the choice of lot size (and its inherent waiting time while
its individual units are serially processed) would no
longer be a relevant factor in evaluating how well the
factory is running,
• lots can vary in size (even in the same factory),
• the meaning of unit would be inconsitent with other
SEMI standards, and
• scrapped units out would not be properly accounted for.
5.1.37 uptime (equipment uptime) — the hours when
the equipment is in a condition to perform its intended
function. It includes productive, standby, and
engineering time, and does not include any portion of
non-scheduled time (SEMI E10).
5.1.38 volume efficiency — the normalized production
efficiency times the balance efficiency (measures the
total efficiency of the process with respect to factory
dynamics). See Equation 2.
5.1.39 WIP capacity (W
max
) — the maximum number
of units of production the factory can contain (including
on shelves, in stockers, on material handling transport
vehicles, on equipment load ports, in internal carrier
buffers, and in process chambers, but not including
space required for non-product units such as test
wafers, dummy wafers, and monitor wafers).
NOTE 11: This is not a practical WIP level, because it
represents total gridlock of the factory.
5.1.40 WIP efficiency — the quotient of the smaller of
the critical WIP and the average WIP divided by the
larger of the two (measures the efficiency of WIP levels
with respect to factory dynamics). See Equation 14.
5.1.41 WIP turnover — the finished units out divided
by the average WIP (shows how often the inventory of
work in process was replaced during the period being
measured). See Equation 22.
5.1.42 work in process (WIP) — the number of units of
production that have been released into the factory but
have not yet been scrapped, sent out for external
rework, or finished processing through all of their
production steps.
5.1.43 yield efficiency — the line yield times the test
yield (shows overall material efficiency). See Equation
3.
NOTE 12: This metric is similar to (but not the same as) the
quality efficiency metric (see Section 5.1.21) from SEMI E79.
6 Calculated Metrics
6.1 Figure 1 shows how the terms defined in Section 5
feed into each other. Arrows go from subordinate terms
to the term in which they are cited as a part of the
primary definition. Shown in the top row (in red
rounded rectangles) are the basic building-block metrics
for which no equations are needed in this guide; the
remaining metrics have their equation numbers given.
At the very bottom is the overall factory efficiency
metric into which almost everything feeds, although
many of its subordinate terms are useful in their own
right (if data availability or reliability is a problem).
Along the left side (in green rounded rectangles) are the
quality metrics that show the efficiency of the process
with respect to use of materials. The remainder of the
metrics (in blue rectangles) are production metrics that
show the efficiency of the process with respect to
factory dynamics (without the effects of yield and scrap
losses). Related Information 1 gives an exposition of
the underlying science behind these production metrics.
SEMI E124-1103 © SEMI 2003 5
availability
efficiency
finished
units out
average
cycle time
good unit
equivalents out
(12)
WIP
capacity
theoretical production
time per unit
total
time
scrapped
units out
overall factory
efficiency
(1)
yield
efficiency
(3)
line
yield
(6)
test
yield
(7)
volume
efficiency
(2)
normalizing
exponent
(9)
critical
WIP
(10)
best-case
cycle time
(18)
best-case
throughput rate
(20)
average
WIP
(15)
theoretical
throughput rate
(21)
WIP
turnover
(22)
actual
throughput rate
(19)
theoretical
cycle time
(16)
bottleneck
throughput rate
(17)
throughput-rate and
cycle-time efficiency
(13)
operational
efficiency
WIP
efficiency
(14)
production
efficiency
(8)
normalized
production efficiency
(4)
balance
efficiency
(5)
process
capacity
(11)
Figure 2
Definition Tree for Factory-Level Productivity Metrics
SEMI E124-1103 © SEMI 2003 6
6.2 Unlike OEE, OFE and its factors are not
dimensioned in time divided by time, because not all
equipment in the factories is present or operating for the
same amount of time. Similar to OEE, this metric:
• is dependent on product mix, process flow,
operations, and time period, so be aware of this
when comparing different factories or even
comparing different time periods in the same
factory when the product mix or process has
changed (although such comparisons are still valid)
especially when the factory variability is due to
external factors (such as demand or excess capacity
in non-bottleneck equipment).
• does not comprehend down-stream demand or the
varying importance of different products (which
might be addressed by a separate metric).
• varies between zero (total chaos or gridlock) and
one (unobtainable perfection).
• is a product of dimensionless efficiencies.
(
)
(
)
(
)
overall factory volume yield
efficiency efficiency efficiency
=× (1)
() ()
normalized
volume balance
production
efficiency efficiency
efficiency
=×
(2)
(
)
(
)
(
)
()( )
yield line test
efficiency yield yield
equivalent good units out
finished scrapped
units out units out
=×
=
+
(3)
()()
()
normalizing
exponent
normalized production
production efficiency efficiency
=
(4)
(
)
critical WIP
balance
efficiency
process capacity
=
(5)
()
()( )
finished units out
line
yield
finished scrapped
units out units out
=
+
(6)
(
)
g
ood unit equivalents out
test
yield
finished units out
=
(7)
() ()
-
-
throughput rate
production WIP
and cycle time
efficiency efficiency
efficiency
=×
(8)
(
)
()()
()()
{}
2
1
1
log
min ,
normalizing
exponent
average critical
WIP WIP
average critical
WIP WIP
=
+−
(9)
NOTE 13: For x>0, log
2
(x) = log
10
(x)/log
10
(2) = ln(x)/ln(2).
(
)
(
)
(
)
critical theoretical bottleneck
WIP cycle time throughput rate
=×
(10)
()
maximum
average
number of
number
units processed
of tools
simultaneously
in
on a tool of
equipment
equipment
type
type
process
capacity
eE
e
e
=×
∈
∑
(11)
NOTE 14: The symbol e, e*, E, f, F, p, P, s, and S are defined
in Sections 5.1.23 through 5.1.27.
total number
of good
p
roduct devices
of type in
number of product
devices on each
unit of type
p
good unit
finished units out
equivalents
out
pP
p
=
∈
∑
(12)
(
)
-
-
-
best case cycle time
throughput rate and
cycle time efficiency
average cycle time
=
(13)
()
(
)
(
)
{
}
()( )
{}
min ,
max ,
critical average
WIP WIP
WIP
efficiency
critical average
WIP WIP
= (14)
(
)
(
)
(
)
average average actual
WIP cycle time throughput rate
=×
(15)
(
)
theoretical
cycle time
minimum
number
cycle
of units
time of
of
a single
product
unit of
type
product
in
type in
step on
equipment
type
pe
p
eEsS
p
finished
s
units
out
e
×
∈∈
=
∑∑
pP
finished units out
∈
∑
(16)