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SEMI E12-0303 © SEMI 1986, 2003 2 generally accepted 0° C, as has the semiconductor industry, i n its defi nition of sc cm. Standard pressure has almost univers ally been accepted as one atmosphere, except for rounding e…

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

SEMI E12-0303 © SEMI 1986, 2003 2

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.

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 E15-0698

(Reapproved 0703)

SPECIFICATION FOR TOOL LOAD PORT

This standard was technically reapproved by the Global Physical Insterfaces & Carriers Committee and is the

direct responsibility of the North American Physical Interfaces & Carriers Committee. Current edition

approved by the North American Regional Standards Committee on March 12, 2003. Initially available at

www.semi.org May 2003; to be published July 2003. Originally published in 1990; previously published

March 2003.

This specification was editorially modified in November 2004 to correct an editorial error. Changes were

made to Table 1.

1 Purpose

1.1 This standard is intended to unify the interface

between process/inspection tools and automated wafer

carrier transport systems while maintaining

compatibility with human transport.

2 Scope

2.1 This specification deals with the mechanical

interface (load port) for wafer carrier transfer between

wafer carrier material transport systems, including

humans, and wafer fabrication/inspection equipment

(tools). The concept defines the placement and

orientation of a wafer carrier on a tool to allow

reasonable interfacing with mechanized material

movement systems without compromising human

access to perform the material exchange function.

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 Impact

3.1 Compliance with this specification requires the

placement of load ports on tools to specific heights,

orientations, and load depths. Restrictions are also

placed on clearances to obstructions which may be

adjacent to such ports.

4 Referenced Standards

4.1 SEMI Standards

SEMI E1 — Specification for 3 inch, 100 mm, 125

mm, and 150 mm Plastic and Metal Wafer Carriers

SEMI E19 — Standard Mechanical Interface (SMIF)

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

5 Terminology

5.1 Definitions

5.1.1 box — A protective portable carrier for a cassette

and/or substrate(s).

5.1.2 cassette — An open structure that holds one or

more substrates.

5.1.3 cassette centroid — A datum representing the

theoretical center of a stack of wafers in a cassette

formed by the pocket centerline and the “center” pocket

as defined by the location associated with dividing

dimension B3 by two (see SEMI E1, Figure 1).

5.1.4 cassette envelope — A rectangular volume with

vertical sides which completely contains a cassette,

even if the cassette is tilted (see Figure 1).

5.1.5 enclosed load port — A load port with overhead

clearance obstructed by the tool.

5.1.6 global orientation — The general orientation of a

wafer carrier in a tool; may be vertical or horizontal.

5.1.7 load depth — The horizontal distance from the

load face plane to cassette centroid or carrier centroid

(see Figures 2 and 3 (D)).

5.1.8 load face plane — The furthest physical vertical

boundary plane from cassette centroid or carrier

centroid on the side (or sides) of the tool where loading

of the tool is intended (see Figures 2 and 3).

5.1.9

load height — The distance from the bottom of

the cassette or carrier to the floor at the load face plane

(see Figure 3 (H)).

5.1.10 load port — The interface location on a tool

where wafer carriers are delivered. It is possible that

wafers are not removed from, or inserted into, the

carrier at this location.

5.1.11 open load port — A load port with overhead

clearance unobstructed by the tool.

5.1.12 pod — A box having a Standard Mechanical

Interface (SMIF) per SEMI E19.