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SEMI E12-0303 © SEMI 1986, 2003 1 SEMI E12-0303 STANDARD FOR STANDARD PRESSU RE, TEMPERATURE, DENSITY, AND FLOW UNITS USED IN MASS FL OW METERS AND MASS FLOW CONTROLLERS This standard was technically approved b y the Glo…

SEMI E10-0304

R1-7 Intended Process-Flow and Multi-Path

Cluster-Tool Metrics

R1-7.1 Once the IPF and multi-path cluster tool state

histories have been prepared, evaluation of metrics may

be performed in a similar manner to that used for

evaluating non-cluster or single-path cluster tools or

modules. The metrics are defined below with sample

calculations based on Example 3 from Section R1-6.

NOTE 13: The multi-path cluster tool metrics presented here

reflect the reliability of the multi-path cluster tool against total

failure rather than partial failure. It is recognized that these

metrics proposed here will reflect more favorably on systems

with higher levels of redundancy at each process step. The

cost or “trade-off” of this redundancy may be evaluated using

other metrics from SEMI E10, SEMI E79, SEMI E35, or from

non-standard evaluations. It also is recognized that these

metrics will not reflect the partial loss of throughput for an

IPF that is “up,” but some of its alternative modules are

“down.” Once again the analyst is encouraged to consult other

metrics from SEMI E10, SEMI E79, or from non-standard

evaluations.

R1-7.2 Multi-Path Cluster Tool Reliability

R1-7.2.1 Multi-Path Cluster Tool Mean Productive

Time Between Failure (MTBF

p-CT

) — mean productive

time between failure where productive time occurs

when at least one module is in the productive state, and

a failure occurs when there are no available IPFs

through the multi-path cluster tool due to module-level

unscheduled downtime.

p-CT

5 hours

umber of Multi–Path Cluster Tool Failures

ulti

–

Path Cluster Tool Productive Time

5 hours

1 failure

R1-7.2.2 Multi-Path Cluster Tool Failure Time

(MFT

) — mean time when there are no available IPFs

through the multi-path cluster tool due to module-level

unscheduled downtime.

2 hours

umber of Multi–Path Cluster Tool Failures

ulti

–

Path Cluster Tool Unscheduled Downtime

2 hours

1 failure

NOTE 14: Since multi-path cluster tool productive time and

multi-path cluster tool unscheduled downtime are mutually

exclusive; they may be compatible with approaches based on

renewal cycle models. Other renewal cycle results (e.g., the

limiting probability of finding the cluster-tool productive or

failed when approaching it at random) similarly may apply, as

determined by the analyst.

R1-7.3 Multi-Path Cluster Tool Availability

R1-7.3.1 Multi-Path Cluster Tool Aggregate IPF

Uptime (Uptime

CT-IPF

) — availability of the multi-path

cluster tool as a function of module

“up/downtime/unscheduled downtime” states and is

evaluated as the aggregate uptimes of all IPFs.

43.3%

10 + 10 + 10

3 + 5 + 5

100

all IPFs

IPF Uptime

Uptime

CT-IPF

≈

all IPFs

IPF Operations Time

100

NOTE 15: For reference, the value of the aggregate

availability efficiency metric from SEMI E79 for the same

example is 20/30 or 66.7%. This difference clearly

demonstrates that depending on which combination of

modules is “down,” the effect on the multi-path cluster tool’s

availability may be substantially different than the aggregate

module availability.

NOTICE: SEMI makes no warranties or

representations as to the suitability of the standards set

forth herein for any particular application. The

determination of the suitability of the standard is solely

the responsibility of the user. Users are cautioned to

refer to manufacturer’s instructions, product labels,

product data sheets, and other relevant literature

respecting any materials mentioned herein. These

standards are subject to change without notice.

The user’s attention is called to the possibility that

compliance with this standard may require use of

copyrighted material or of an invention covered by

patent rights. By publication of this standard, SEMI

takes no position respecting the validity of any patent

rights or copyrights asserted in connection with any

item mentioned in this standard. Users of this standard

are expressly advised that determination of any such

patent rights or copyrights, and the risk of infringement

of such rights, are entirely their own responsibility.

International), 3081 Zanker Road, San Jose, CA 95134. Reproduction o

the contents in whole or in part is forbidden without express written

consent of SEMI.

SEMI E12-0303 © SEMI 1986, 2003 1

SEMI E12-0303

STANDARD FOR STANDARD PRESSURE, TEMPERATURE, DENSITY,

AND FLOW UNITS USED IN MASS FLOW METERS AND MASS FLOW

CONTROLLERS

This standard was technically approved by the Global Gases Committee and is the direct responsibility of the

North American Gases Committee. Current edition approved by the North American Regional Standards

Committee on October 25, 2002. Initially available at www.semi.org December 2002; to be published March

2003. Originally published in 1986, previously published in 1996.

1 Purpose

1.1 In the past, confusion has existed in the values of

standard temperature and standard pressure when gas

flow is expressed in “standard” volumetric units. To

eliminate this confusion, the Mass Flow Controllers

Committee has established this standard.

2 Scope

2.1 This standard provides a common basis for

communication between manufacturers and users.

NOTICE: This standard does not purport to address

safety issues, if any, associated with its use. It is the

responsibility of the users of this standard to establish

appropriate safety and health practices and determine

the applicability of regulatory or other limitations prior

to use.

3 Referenced Standard

3.1 ASTM Standard

E 380-89a — Standard Practice for Use of the

International System of Units (the Modernized Metric

System)

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

4 Terminology

None.

5 Standard Temperature

5.1 Standard temperature is defined as 273.15 K

(0.0° C).

1 American Society for Testing and Materials, 100 Barr Harbor

Drive, West Conshohocken, Pennsylvania 19428-2959, USA.

Telephone: 610.832.9585, Fax: 610.832.9555 Website:

www.astm.org

6 Standard Pressure

6.1 Standard pressure is defined as 101,325 pascals (1

atm, 760 Torr).

7 Standard Density

7.1 The standard density is defined as Mw/22,413.6

grams per standard cubic centimeter (g/scc), where Mw

is the molecular weight of the gas in grams per mole

(g/mol), and 22,413.6 is the standard molar volume in

cubic centimeters (scc/mol) (i.e., the volume of one

mole of a perfect gas at standard temperature and

standard pressure).

8 Standard Flow Rate

8.1 Standard flow rate is the volumetric flow rate of the

gas at the standard density defined in Section 7.1.

9 Units

9.1 Units for standard flow rate may be expressed as

standard cubic centimeters per minute (sccm), standard

liters per minute (slm), standard cubic decimeters per

minute (scdm), or as standard cubic meters per minute

(scmm).

1 sccm = 1 × 10

-3

* slm

= 1 × 10

-3

* scdm

= 1 × 10

-6

* scmm

NOTE 1: Units in this document have been editorially

changed to sccm, slm, scdm, and scmm in line with

international standards which require all units to be expressed

in SI terms. While neither “minute” nor “liter” is a primary SI

unit, each is acceptable under the system, and eliminating the

use of these units in this standard would seriously diminish its

acceptability.

10 Background

10.1 In the absence of this specification, there has been

confusion in the definition of standard conditions.

“Standard” temperature in particular has been variously

defined as 59° F, 68° F, 70° F, 20° C, 22° C, etc. to reflect

“normal” test conditions. The scientific community has

generally accepted 0° C, as has the semiconductor

industry, in its definition of sccm. Standard pressure has

almost universally been accepted as one atmosphere,

except for rounding errors in different units.

10.2 Further confusion has existed in the definition of

standard density when extended to vapors. For perfect

gases (most light gases are nearly perfect), the standard

density can be defined as the density of the gas at

standard temperature and pressure. Since one gram

mole of a perfect gas occupies 22,414 cubic centimeters

at standard pressure and standard temperature, it

follows that a flow rate of 22,414 sccm of any perfect

gas is one mole per minute.

10.3 By defining standard density as in Section 7.1, the

correlation between sccm and moles/minute is retained,

even for vapors. If standard density were defined as the

actual density of the vapor at standard temperature and

pressure, then the correlation with moles per minute

would differ by the vapor' s compressibility factor (Z).

This is not an acceptable alternative because the

compressibility of many vapors is not accurately

known, and, in fact, does not exist for those materials

that are liquid at standard temperature and pressure.

11 Implications for Calibration

11.1 Since the standard flow units are defined at a

standard density, they represent units of mass flow

rather than volumetric flow.

11.2 Gravimetric calibration readings in grams per

minute (g/min) can be converted to standard cubic

centimeters per minute (sccm) by dividing by the

standard density (g/scc) as defined in Section 7.1.

11.3 Rate-of-rise (ROR) data will generally have

negligible compressibility error when operated over a

low absolute pressure range. If compressibility errors

are significant, they will cause the rate of pressure rise

to be reduced and become pressure-dependent as the

pressure increases. In this case, the pressure range must

be reduced, or correction made, for compressibility.

11.4 Volumetric flow data must be corrected from

actual density of the real gas at the test conditions to the

standard density. The actual density can be

approximated for near-perfect gases by ratios of

absolute pressure and temperature to the standard

density. For vapors, the actual density at the test

conditions must be known from other data.