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SEMI E77-1104 © SEMI 1998, 2004 2 5.2.8 nameplate ga s — the gas intended to be controlled by the MFC in operat ion. 5.2.9 range — the algebraic difference between the maximum and minimum values. 5.2.10 setpoint — the in…

SEMI E77-1104 © SEMI 1998, 2004 1

SEMI E77-1104

TEST METHOD FOR CALCULATION OF CONVERSION FACTORS FOR

A MASS FLOW CONTROLLER USING SURROGATE GASES

This test method 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 July 11, 2004. Initially available at www.semi.org September 2004; to be published

November 2004. Originally published September 1998.

1 Purpose

1.1 The purpose of this test method is to quantify a

nominal average conversion factor from one gas to

another for an MFC and to quantify the conversion

factor as function of flow for an MFC.

2 Scope

2.1 This procedure describes a method to determine the

MFC conversion factor and function between two

gases.

2.2 This document provides a common basis for

communication between manufacturers and users.

2.3 The intent of this document is not to suggest any

specific testing program, but to specify the test method

to be used when testing for parameters covered by this

method. Reference operating conditions represent the

environmental conditions where the “best” performance

can be expected.

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 Limitations

3.1 It is not practical to evaluate performance under all

possible combinations of operating conditions. This

test procedure should be applied under laboratory

(reference) conditions; its intent is to collect sufficient

data to form a judgment of the field performance of the

MFC being tested.

3.1.1 The results from this test represent the

performance of the specific device tested (i.e., make,

model, full scale flow and operating conditions). The

results may not apply to devices of different

manufacture, model, full scale flow or under different

operating conditions.

3.2 This procedure does not apply to pressure based

MFC.

4 Referenced Standard

4.1 None.

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

5 Terminology

5.1 Abbreviations & Acronyms

5.1.1 CF (gasA/gasB) — conversion factor from Gas A

to Gas B.

5.1.2 D.U.T.— device under test

5.1.3 kPa — kiloPascal

5.1.4 MFC — mass flow controller

5.1.5 psia — pounds per square inch absolute

5.1.6 sccm — standard cubic centimeters per minute

5.1.7 slm — standard liters per minute

5.1.8 %F.S. — percent full scale

5.2 Definitions

5.2.1

actual flow — the flow rate as determined by the

flow standard used in the test procedure.

5.2.2 conversion factor — the ratio of the mass flow-

rate of Gas A flowing through an MFC for a given

setpoint to the mass flow rate of Gas B flowing through

the same MFC and setpoint.

5.2.3 conversion function — a relationship that

describes the flow dependency of the conversion factor.

The conversion function is graphically determined.

5.2.4 indicated flow — the flow rate as determined by

the output of the D.U.T.

5.2.5 mean — the sum of a group of measurements

divided by the number of measurements; average.

5.2.6 measured value — the actual flow through a

D.U.T., expressed in sccm or slm.

5.2.7 measured value, average — the sum of all

readings (both upscale and downscale) for all cycles, at

a single setpoint, divided by the number of these

readings.

SEMI E77-1104 © SEMI 1998, 2004 2

5.2.8 nameplate gas — the gas intended to be

controlled by the MFC in operation.

5.2.9 range — the algebraic difference between the

maximum and minimum values.

5.2.10 setpoint — the input signal provided to achieve

a desired flow, reported as sccm, slm, or percent full

scale.

5.2.11 span — the full scale range of the D.U.T.

5.2.12 surrogate gas — the gas substituted for the

nameplate gas during the calibration process.

5.2.13 zero drift — the undesired change in electrical

output (i.e., indicated flow), at a no-flow condition,

over a specified time period, reported in sccm or slm.

5.2.14 zero offset — the deviation from zero at a “no-

flow” condition reported in sccm, slm, or mV.

6 Summary of Test Method

6.1 Gas flow and setpoint data are collected for two

gases. This data is reduced to quantify the relationship

between the flow measurement by the MFC on one gas

to another gas.

6.2 This method allows the user to determine the

conversion factor between two gases for the MFC and

to determine the onset of errors in the MFC calibration

due to the conversion factor/function effects.

7 Interferences

7.1 The accuracy rating of the measuring equipment

shall be superior to that of the D.U.T. Preferably the

measuring equipment will have an accuracy that is four

times better than the D.U.T. Calibration equipment

must have a valid calibration certificate.

7.2 Take care when using test instruments with a

specified accuracy expressed in percent of full scale.

7.3 Installation effects on the flow should be

minimized. Monitor pressure upstream of the D.U.T.

to ensure that flow variations due to pressure are

minimized.

7.4 Verify electrical signals directly at the D.U.T.

connector to ensure that the signals at the D.U.T. and

standard agree with the signals at the data recording

equipment.

7.5 Certain gases will contaminate the D.U.T. This

test should be considered a destructive test in such

cases.

7.6 All electrical measurements should be read on

devices with at least 4.5 digits of resolution. These

devices must have valid calibration certifications.

7.7 The device mounting position must be in

accordance with the manufacturer’s specifications.

8 Apparatus (See Figure 1.)

8.1 Flow Standard — A device or system that

accurately measures the flow and reports the actual

flow.

8.2 Data Acquisition System — The system that

measures the electrical signals from the device under

test. The data acquisition system may also read the

signals from the flow standard, record test data and

control the test sequence.

8.3 Temperature Probe — A device to measure the

temperature of the flowing gas.

8.4 Three-Way Valve — A special valve to switch the

system from one gas source to another.

8.5 Manual Isolation Valves — Valves that will

positively shut off the gas line.

8.6 Pressure Regulator — A device that regulates gas

pressure to a set value.

8.7 Pressure Transducer — An instrument to measure

the gas pressure and report it as an electrical signal.

9 Materials

9.1 Clean, Dry N

— With 99.999% minimum purity,

to be used for purging.

9.2 Test Gas “A”

9.3 Test Gas “B”

10 Safety Precautions

10.1 This test method may involve hazardous

materials, operations, and equipment. This test method

does not purport to address the safety considerations

associated with its use. It is the responsibility of the

user to establish appropriate safety and health practices

and to determine the applicability of regulatory

limitations before using this method.

10.2 Follow the manufacturer’s specifications and

instructions for installation and operation whenever

possible. Note any exceptions in the test report.

11 Test Specimen

11.1 Allow all components in the test apparatus to

warm up following the manufacturer’s specification.

11.2 Take necessary steps when switching gases to

ensure that only the desired gas is in the D.U.T. and

flow standard at the time the test is performed.

12 Preparation of Apparatus

12.1 Locate the D.U.T. in the test environment to

stabilize temperature for 24 hours prior to warm up.

12.2 The reference operating conditions shall be as

follows:

12.2.1 Ambient Temperature — 23 ± 2°C

12.2.2 Gas Temperature — Same as ambient. In the

case of a condensible gas, the gas temperature should

be maintained as a gradient, with highest temperature at

the outlet end of the test set up, and slightly reduced

temperatures back to the source. This will ensure that

condensing vapors do not accumulate in the test set up.

Gradient should simulate actual process parameters

where the MFC will be installed.

12.2.3 Ambient Pressure — 101.3 kPa (+ 4.7 or – 15.3

kPa)

12.2.4 Gas Pressure, Inlet — 172 ± 34 kPa unless the

gas is not capable of delivering this pressure, then

normal fab operating conditions should be observed.

12.2.5 Gas Pressure, Outlet — < 80 kPa

12.2.6 Relative Humidity — 40% ± 5%, non-

condensing (suggestion: record if outside this range)

12.2.7 Magnetic Field —  50 µT

12.2.8 Electromagnetic Field —  100 µV/m

12.2.9 Vibration —  0.5 m/s at 50 to 200 Hz

12.3 Following the conditioning period (See Section

12.1), warm up the device according to manufacturer’s

specifications.

12.4 Perform an adequate nitrogen purge to ensure all

previous gases and moisture have been removed from

the system. Prior to corrosive gas testing, a cyclic

pump and purge operation is recommended, alternately

backfilling with nitrogen, and evacuating the test

manifold.

12.5 Leak check the manifold, using available

methodologies to verify the test system leak integrity.

Introduce the test gas at a sufficient rate and time to

ensure the test apparatus is completely filled with the

test gas and only the test gas.

12.6 Record the zero offset with line pressure inside

the MFC to best simulate normal operating conditions.

Line pressure during testing is to be 170.30 kPa (24.7

psia) unless safety practices for the gas under test

dictate that a lower line pressure be used.

NOTE 1: In addition, if this test is performed on hazardous

gases, bleeding off gas pressure to obtain atmospheric

pressure inside the MFC may not be easy to do.

12.7 Command 100%, and establish flow, then close

the downstream isolation valve; then close the upstream

isolation valve (see Figure 1).

12.8 With both isolation valves closed, and a 100%

setpoint wait until the pressure drop across the MFC is

dissipated, ensuring a “no flow” condition through the

MFC. Dissipation of the pressure across the MFC is

indicated when the indicated flow drops to a steady

state value near zero.

12.9 After the electrical output signal has stabilized for

at least three minutes, record the MFC zero offset in

Table 1.

Figure 1

Mass Flow Controller Test Fixture