semi合集-English.pdf - 第1353页

SEMI E30-1103 © SEMI 1992, 2003 27 reaches the UPPERDB and tr ansitions into the upper zone, it will no t return to the lower zone u ntil it falls back to the LOWERDB. The difference between UPPERDB and LOWERDB should al…

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SEMI E30-1103 © SEMI 1992, 2003
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Thus, UPPERDB and LOWERDB as a pair define a
limit.
LOWERDB — A variable limit attribute that defines the
lower boundary of the deadband of a limit.
18
The value
applies to a single limit (LIMITID) for a specified VID.
Thus, UPPERDB and LOWERDB as a pair define a
limit.
UPPER ZONE — The range of values lying above a
limit.
LOWERZONE — The range of values lying below a
limit.
LIMITMAX — The maximum value for any limits of a
specific equipment variable. This value is set by the
equipment manufacturer and typically coincides with
the maximum value allowed for the monitored variable.
LIMITMIN — The minimum value for any limits of a
specific equipment variable.
19
This value is set by the
equipment manufacturer and typically coincides with
the minimum value allowed for the monitored variable.
Undefined — When used in reference to variable limits,
it indicates that monitoring/reporting of zone transitions
involving that particular limit are disabled.
4.2.4.3 Description — The limits monitoring capability
provides the host with a minimum of seven
configurable limits or barriers that may be applied to
selected equipment status variables (SV’s) of the types
floating point, integer, and boolean. When one of these
barriers is crossed, a collection event is generated to
alert the host to a change in monitoring zone or state of
the monitored variable. These seven limits may be
combined in a variety of ways to match the needs of the
host system.
19
An illustration of a combination of five
of the limits to provide one type of variable monitoring
is shown in Figure 4.2.1.
20
This section describes the
key aspects of limits monitoring. Detailed
implementation examples of limits monitoring are
provided as Application Note A.7.
NOTE 6: While the SEMI E5 standard allows SV’s to be lists,
such variable lists are not allowed under this capability.
4.2.4.3.1 Monitoring Limit Characteristics — A limit
is defined by a set of attributes that include the variable
(VID) to which the limit corresponds, the units of that
variable, the maximum and minimum possible values of
19 Note that while at least seven limits per variable are available from
the equipment, the host need not use all seven.
20 This illustration shows the reading which might be available to the
equipment, not the limit excursions reported to the host. Reporting is
covered later in the section.
the limit (LIMITMAX and LIMITMIN) and the
specific borders of the limit (UPPERDB and
LOWERDB). See Figure 4.2.2. There is a limitation to
the values of UPPERDB and LOWERDB which may
be stated as:
LIMITMAX≥UPPERDB≥LOWERDB≥LIMITMIN
A limit divides the possible range of variable values
into two parts, the upper zone and the lower zone. At
any time, the monitored variable is considered to be in
one and only one of these zones. However, as Figure
4.2.2 shows, these two zones have an area of overlap.
This is called the deadband.
Figure 4.2.1
Limit Combination Illustration: Control
Application
Figure 4.2.2
Elements of One Limit
The deadband is a key concept of limits monitoring,
especially for floating point variables. Its purpose is to
prevent a phenomenon known as chattering — the
repeated changing of zones due to small, rapid
fluctuations in variable value while near the zone
boundary. In practice, the value of a variable must
reach the opposite boundary of the deadband before a
zone transition can occur. Thus, if a variable’s value
SEMI E30-1103 © SEMI 1992, 2003
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reaches the UPPERDB and transitions into the upper
zone, it will not return to the lower zone until it falls
back to the LOWERDB. The difference between
UPPERDB and LOWERDB should always be greater
than the typical amplitude of those fluctuations deemed
to be insignificant. In some cases, the width of the
deadband may set to zero (i.e., UPPERDB =
LOWERDB). At first glance, this would seem to make
indeterminate the current zone when an integer value
sits on the limit. This is not the case, however, when
movement of the value is considered. To illustrate, an
example is given, assuming that UPPERDB =
LOWERDB = 100. The list shows consecutive readings
of the variable and the resultant zone:
99 Lower Zone (Initial Reading)
101 Upper Zone (Zone Transition)
100 Lower Zone (Zone Transition)
100 Lower Zone
99 Lower Zone
100 Upper Zone (Zone Transition)
Transition from one zone into another generates a
collection event, as might be reported via S6,F11. The
host has the option of receiving notification by enabling
event reporting for the event. For each variable that has
monitoring capability, one CEID is reserved to indicate
zone transitions for that variable. To aid in the
determination of the nature of a transition event, three
DVVAL’s have been defined:
LimitVariable — The VID of the monitored variable to
which the collection event refers.
EventLimit — Contains the LIMITID of the limit
reached or crossed by LimitVariable.
TransitionType — Defines the direction of the zone
transition which has occurred: 0 = transition from lower
to upper zone, 1 = transition from upper to lower zone.
Sampling frequency is an important element of limits
monitoring and should be considered during equipment
specification. If changes in variable value are relatively
fast compared to sampling frequency, it is possible for
some zone transitions to be missed or for multiple zone
transitions to occur between readings. Since it is
possible for zone transitions to occur “simultaneously”
or for limits to be identically defined, the DVVAL
EventLimit has been defined to allow for a list of
multiple zone transitions of a variable to be reported
with a single collection event.
It also should be emphasized that a single CEID is used
to report transitions in both directions across a limit.
Thus, reporting for one direction but not the other
cannot be configured.
The functionality of each limit for each variable can be
described with the state model shown in Figure 4.2.3.
Below, the three states are described more fully,
followed by a table defining the transitions.
Figure 4.2.3
Limit State Model
ABOVE LIMIT
A variable is considered to be above a limit when its
value increases to equal or exceed the upper boundary
of the deadband, UPPERDB. The significance attached
to this state is a function of the host’s usage.
BELOW LIMIT
A variable is considered to be below a limit when its
value decreases to equal or fall below the lower
boundary of the deadband, LOWERDB. The
significance attached to this state is a function of the
host’s usage.
NO ZONE
In some circumstances it is possible for the variable
value to be in neither the upper zone nor the lower
zone. This may occur upon definition of a new limit or
upon equipment startup when the value of the variable
lies in the deadband. In this case, the active state of the
limit is considered to be NO ZONE. The limit shall
remain in this state until the variable value reaches
either boundary of the deadband.
SEMI E30-1103 © SEMI 1992, 2003
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4.2.4.3.2 Modification of Limit Values — Values for
the monitoring limits on any monitored variable may be
modified by the host using the message transaction
S2,F45/F46 (Define Variable Limit Attributes). The
equipment must reject any S2,F45 message which
contains limit information which conflicts with the
following rules:
— LIMITMAX≥UPPERDB≥LOWERDB≥LIMIT-
MIN;
— If either UPPERDB or LOWERDB is defined,
both must be defined; if either UPPERDB or
LOWERDB is undefined, both must be undefined.
The first rule is defined and graphically depicted in
Figure 4.2.2. The second rule refers to the host’s ability
to turn any limit “on” or “off”. While a minimum of
seven limits must be available for each monitored
variable, it will be common for the host application to
require less than seven or even none of the limits be
used. The limits not needed can be disabled by leaving
the values for UPPERDB and LOWERDB
“undefined”. Limits may be disabled for a VID or for
all monitored VIDs by using zero length lists in the
S2,F45 message.
All monitored variables must be one of three types:
integer, floating point, or Boolean. This may be
accomplished by using the following formats: 11, 20,
3(), 4(), 5().
NOTE 7: The binary format is not allowed. If the ASCII
format is used, the equipment shall perform a conversion into
one of the numeric types before performing any value
comparisons, both for limit validations and zone transitions.
4.2.4.3.3 Limit Values Request — The host may
request the current limit values for a specified VID
using the message transaction S2,F47/F48 (Variable
Limit Attribute Request).
4.2.4.4 Requirements
— A minimum of seven limits per monitored variable
must be available.
— One CEID per monitored variable must be supplied
for zone transition reporting.
— All limit definitions must be kept in non-volatile
storage.
— The equipment must enforce the limit validation
rules defined above.
— The specification and documentation of which
variables may be monitored with this capability is
the responsibility of the equipment manufacturer
based on the specific instance of equipment. This
subject also may be addressed by equipment models
of classes of semiconductor equipment.
Table 4.2 Limit State Transition Table
# Current State Trigger New State Action Comment
1 DISABLED Limit attributed defined w/
S2,F45.
ENABLED None The substate of ENABLED is
determined by the current value of
the monitored variable.
2 ENABLED Limit attributes set to
undefined w/ S2,F45.
DISABLED None None
3 BELOW LIMIT Variable Increased to be
≥UPPERDB
ABOVE LIMIT None Zone Transition.
4 ABOVE LIMIT Variable decreases to be
≤LOWERDB
BELOW LIMIT None Zone Transition.
5 NO ZONE Variable decreases to be
≤LOWERDB
BELOW LIMIT None Zone Transition.
6 NO ZONE Variable increases to be
≥UPPERDB
ABOVE LIMIT None Zone Transition.