semaspec provisional test method for verification … provisional test method for verification of...

SEMATECHTechnology Transfer 92071225B-STD

SEMASPEC Provisional Test Methodfor Verification of CalibrationAccuracy and Calculation of

Conversion Factors for a Mass FlowController Using Surrogate Gases

© 1996 SEMATECH, Inc.

SEMATECH and the SEMATECH logo are registered service marks of SEMATECH, Inc.

SEMASPEC Provisional Test Method for Verification of CalibrationAccuracy and Calculation of Conversion Factors for a Mass Flow

Controller Using Surrogate GasesTechnology Transfer # 92071225B-STD

SEMATECHFebruary 5, 1993

Abstract: This test method provides a procedure for characterizing mass flow controllers (MFCs) beingconsidered for installation into high-purity gas distribution systems. The method quantifies theaccuracy and linearity of an MFC when mapping an MFC’s calibration from one specific gas toanother. It also quantifies the flow dependence of an MFC’s conversion factor. This revision of thedocument incorporates changes made as a result of industry review and from corrections madeduring working session four of the MFC Test Method’s Development Task Force. This documentis in development as an industry standard by Semiconductor Equipment and Materials International(SEMI). When available, adherence to the SEMI standard is recommended.

Keywords: Testing, Mass Flow Controllers, Gas Distribution Systems

Authors: Ven Garke

Approvals: Jeff Riddle, Project LeaderVenu Menon, Program ManagerJackie Marsh, Director of Standards ProgramGene Feit, Director, Contamination Free ManufacturingJohn Pankratz, Director, Technology TransferJeanne Cranford, Technical Information Transfer Team Leader

This document is in development as an industry standard by Semiconductor Equipment and Materials International(SEMI). When available, adherence to the SEMI standard is recommended.

Technology Transfer #92071225B-STD SEMATECH

11

SEMASPEC #92071225B-STD

SEMASPEC Provisional Test Method for Verification of Calibration Accuracy andCalculation of Conversion Factors for a Mass Flow Controller Using SurrogateGases

1 Introduction

During the mass flow controller (MFC) calibration process, MFC manufacturerstypically use safer and more common gases as surrogates for the actual or nameplate gasthat the MFC is intended to control in a process tool. Conversion factors used to predictthe mass flow of the actual gas at a given setpoint from the mass flow of the surrogategas are potentially dependent on the transport properties of the gases and the design ofthe MFC. Conversion factors may or may not be independent of gas flow. If an MFC’sconversion factor is constant, linear, and independent of flow, calibration with one gascan accurately be used for numerous other gases. If the conversion factor is flow-dependent, then the MFC must be calibrated to a specific gas.

1.1 Purpose—The purpose of this test method is to quantify the accuracy and linearity of an MFCwhen mapping an MFC’s calibration from one specific gas to another and to quantify the flow-dependence of an MFC’s conversion factor.

1.2 Scope

1.2.1 This procedure describes a method to determine the MFC conversion factor between two gasesand to estimate the onset of gas dependent nonlinearities that will cause conversion factors to begas- and flow-dependent.

1.2.2 This document uses the method described in SEMASPEC #92071221B-STD to test theaccuracy, repeatability, linearity, hysteresis, and deadband of a thermal MFC on its nameplategas.

1.2.3 This document provides a common basis for communication between manufacturers and users.

1.2.4 The intent of this document is not to suggest any specific testing program, but to specify the testmethod to be used when testing for parameters covered by this method. Ultimately, thisdocument might be used to check significant performance characteristics such as accuracy,repeatability, linearity, hysteresis, and deadband under a set of reference operating conditions.Reference operating conditions represent the "best" performance that can be expected.


SEMATECH Technology Transfer #92071225B-STD

22

1.3 Limitations

1.3.1 It is not practical to evaluate performance under all possible combinations of operatingconditions. This test procedure should be applied under laboratory conditions; its intent is tocollect sufficient data to form a judgement of the field performance of the MFC being tested.

1.3.2 Molecular weight of the gas being controlled by the MFC has been used as a general indicator ofwhen the onset of nonlinearities in the MFC will occur. However, it is not the only factor, andspecific gases may display nonlinearities earlier than expected by their molecular weight. Acomparison of MFC linearity on the family of common calibration gases called out in thisspecification will, however, give information on the relative linearity of the MFCs being tested.This information may be used to estimate the molecular weight of a gas above which an MFCconversion factor gas relative to a perfect gas will change with the flow-rate of gas through theMFC.

2 Referenced Documents

2.1 ANSI1

ANSI C39.5 Safety Requirements for Electrical and Electronic Measuring andControlling Instrumentation

ANSI C42.100 Dictionary of Electrical and Electronics Terms

ANSI MC4.1 Dynamic Response Testing of Process Control Instrumentation

2.2 IEC2

IEC 160 Standard Atmospheric Conditions for Test Purposes

IEC 546 Methods of Evaluating the Performance of Controllers withAnalogue Signals for Use in Industrial Process Control

2.3 ISA3

ISA S7.3 Quality Standards for Instrument Air

ISA S51.1 Process Instrumentation Terminology

2.4 MIL–STD 4

MIL-STD 45662 Calibration Systems Requirements

1 American National Standards Institute, Inc. 1430 Broadway. New York, NY 10018.

2 International Electrochemical Commission. 3, rue de Varembe. CH-1211 Geneva 20, Switzerland.

3 Instrument Society of America. 67 Alexander Dr. Research Triangle Park, NC 27709.

4 Naval Publications. 5801 Tabor Avenue. Philadelphia, PA 19120.



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2.5 SEMATECH5

SEMASPEC SEMATECH Provisional Test Method for Determining#92071221B-STD Accuracy, Linearity, Repeatability, Short Term

Reproducibility, Hysteresis, and Deadband of Thermal MassFlow Controllers

3 Terminology

3.1 Acronyms and Abbreviations

3.1.1 CF (gasA/gasB)—conversion factor from gas A to gas B

3.1.2 DUT—device under test

3.1.3 kPa—kiloPascal

3.1.4 MFC—mass flow controller

3.1.5 NC—normally closed

3.1.6 NO—normally open

3.1.7 sccm—standard cubic centimeters per minute

3.1.8 slm—standard liters per minute

3.1.9 %FS—percent full scale

3.1.10 psi—pounds per square inch

3.2 Description of Terms

3.2.1 accuracy—the closeness of agreement between an observed value and the true value; the totaluncertainty of an observed value, including both precision and bias.

3.2.2 accuracy, device—the total uncertainty over a specified range of the device. Device accuracyover a range is stated as the worst case accuracy taken over all tested setpoints in this range.

3.2.3 actual flow—the flow rate as determined by the flow standard used in the test procedure.

3.2.4 indicated flow—the flow rate as determined by the output of the DUT.

3.2.5 conversion factor—the ratio of the mass flow-rate of gas A flowing through an MFC for a givensetpoint to the mass-flow-rate of gas B flowing through the same MFC and setpoint.

3.2.6 conversion function—a relationship that describes the flow dependency of the conversionfactor. The conversion function is graphically determined.

5SEMATECH. 2706 Montopolis Dr. Austin, TX 78741.



44

3.2.7 corrected flow standard reading—a value calculated as described in Section 13.1.1. Thecalculation takes into account the effect of the MFC having a zero offset when it is given a flowcommand and predicts the resulting flow reading of the flow standard in series with the MFC ifno zero offset were present in the MFC when the flow command was given.

3.2.8 deadband—the range through which a setpoint may be varied, upon reversal of direction,without initiating an observable change in output signal.

3.2.9 linearity—the closeness to which three or more measurements approximates a straight line overa specified range. It is usually measured as a nonlinearity and expressed as linearity.

3.2.10 linearity, terminal-based—the maximum absolute value of the deviation of the accuracy curve(average of upscale and downscale values) from a straight line through the upper and lowersetpoint limits of the accuracy curve.

3.2.11 lower setpoint limit—the minimum manufacturer specified setpoint for the MFC to operate.

3.2.12 mean—the sum of a group of measurements divided by the number of measurements; average.

3.2.13 measured value—the actual flow through a DUT, expressed in sccm or slm, as measured by astandard (preferably primary).

3.2.14 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.

3.2.15 nameplate gas—the gas intended to be controlled by the MFC in the process tool.

3.2.16 precision—the closeness of agreement among the measured values at a setpoint. It is oftenexpressed as a standard deviation.

3.2.17 range—the algebraic difference between the maximum and minimum values.

3.2.18 repeatability—the closeness of agreement among a number of measured values at a setpointunder the same operating conditions (same operator, same apparatus, same laboratory, and shortintervals of time). It is usually measured as a nonrepeatability and expressed as repeatability inpercent of reading.

3.2.19 setpoint—the input voltage provided to achieve a desired flow, reported as sccm, slm, or percentfull scale.

3.2.20 setpoint limit, lower—the lowest setpoint at which the instrument is specified to operate.

3.2.21 setpoint limit, upper—the highest setpoint at which the instrument is specified to operate,usually full scale.

3.2.22 span—the full scale range of the DUT.

3.2.23 surrogate gas—the gas substituted for the nameplate gas during the calibration process.

3.2.24 zero offset—the deviation from zero at a "no-flow" condition reported in sccm, slm, or mV.

3.2.25 zero drift—the undesired change in electrical output, at a no-flow condition, over a specifiedtime period, reported in sccm or slm.



55

4 Summary Of Test Method

4.1 SEMASPEC #92071221B-STD is performed to quantify the MFC accuracy when operating onits nameplate gas.

4.2 Gas flow and setpoint data are collected for a series of gases commonly used for surrogatecalibrations and for other gases selected to exhibit the onset of nonlinearities in the MFC atdiffering flows. Other gases of interest may be added to the test.

5 Significance And Use

5.1 The significance of accuracy calculations is to allow an MFC user to transfer a process from oneprocess tool to another and to exchange MFCs within a single process tool while maintainingprocess control. This ability directly affects the yield of a process.

5.2 This method allows the user to document the accuracy of an MFC using its nameplate gas asreceived from a manufacturer, to determine the conversion factor between two gases for theMFC, to allow the MFC to be accurately used for gases other than its nameplate gas, and todetermine the onset of nonlinearities in the MFC. The onset of nonlinearities is roughlyindicated by the molecular weight of a gas. Below the molecular weight at which this onsetoccurs, the single fixed conversion factor is not flow-dependent and may be accurately used topredict the flow of the MFC for gases other than the nameplate gas.

6 Apparatus

6.1 Heat Exchanger.

6.2 Flow Standard.

6.3 Data Acquisition System.

6.4 Temperature Probe.

6.5 Back Pressure Regulator.

6.6 Pressure Transducer.



66

7 Materials

7.1 Helium.

7.2 Nitrous Oxide.

7.3 Freon 116.

7.4 Freon 12.

7.5 Freon 112.

7.6 Clean, Dry N2, 99.999%, to be used for purging.

7.7 Air-Operated Three-Way Valves.

7.8 Filters.

7.9 Manual Isolation Valves.

8 Precautions

8.1 Safety Precautions

8.1.1 This test method may involve hazardous materials, operations, and equipment. This test methoddoes not purport to address the safety considerations associated with its use. It is theresponsibility of the user to establish appropriate safety and health practices and to determine theapplicability of regulatory limitations before using this method.

8.1.2 When hazardous and toxic gases are used, take proper precautions to ensure safe systemoperation. All environmentally hazardous gases and freons (including R12 and R112) called outin this test method must be recovered, incinerated until harmless, or appropriately scrubbed.

8.2 Technical Precautions

8.2.1 The manufacturer’s specifications and instructions for installation and operation must be appliedduring all testing.

8.2.2 Certain gases will contaminate the DUT. This test should be considered a destructive test insuch cases. Care should be taken to avoid using an MFC on incompatible gases.

8.2.3 All electrical measurements should be read on devices with at least 4.5 digits of resolution.These devices must have valid calibration certifications.

8.2.4 The device mounting position must be in accordance with the manufacturer’s specifications. Noexternal mechanical constraints beyond the manufacturer’s specifications are permitted.

8.3 Interferences

8.3.1 The accuracy rating of the measuring equipment shall be superior to that of the DUT.Measuring equipment will have an accuracy of 4× better than the DUT.

8.3.1.1 Take care when using test instruments with a specified accuracy expressed in percent of fullscale. For example, if an instrument with a specified accuracy of ± 0.1% of full scale is used tomeasure the output of the device under test, but this output signal falls only within the lower



77

third of the scale of the instrument, the effective accuracy over the range of the instrument beingused may be ± 0.3%. This is unsuitable for many applications.

8.3.2 Use special precautions to ensure that minimum effects result from pneumatic noise in flowlines. Monitor pressure both upstream and downstream of the MFC to ensure that pneumaticnoise is minimized. In addition, place more than 16 cm of straight 1/4-in. tubing (or more than32 cm of 3/8-in. tubing for flows greater than 10 slm) upstream and downstream of the MFC toensure laminar flow to and from the device.

8.3.3 Verify electrical signals directly at the MFC connector to ensure that there are no line losses inthe cables.

9 Preparation Of Apparatus

9.1 Allow the test apparatus to warm up for a period exceeding the manufacturer's specification.

9.2 Perform a purge of the DUT between subsequent tests.

9.3 Evacuate upstream plumbing prior to connection of subsequent gases when hazardous gases arebeing used.

10 Calibration And Reference Standards

10.1 Electrical measurement devices must have valid calibration certificates.

10.2 The reference standard and display electronics shall have a total uncertainty not to exceed 25%of the DUT's uncertainty, per MIL–STD 45662A.

11 Conditioning

11.1 Place the DUT in the testing environment. Apply power to the MFC for the 24 hours prior toinitiating warm-up. The valve should be in its "off" position, that is, closed for a NC valve, openfor a NO valve.

11.2 Following the conditioning period, warm up the device according to manufacturer'sspecifications.

11.3 Flush the MFC with clean, dry nitrogen or argon following the warm-up period. Allow the testgas to flow through the device under test for 10 minutes at 100% of full flow.

11.4 Record the zero offset with line pressure inside the MFC to best simulate actual factoryconditions. Line pressure during testing is to be 70 kPa (10 psi) ± 7 kPa unless safety practicesfor the gas under test dictate that a lower line pressure be used.

[Note: In addition, if this test is performed on hazardous gases, bleeding off gas pressureto obtain atmospheric pressure inside the MFC may not be easy to do.]



88

11.5 Maintain line pressure while first closing the downstream isolation valve; then close theupstream isolation valve (see Figure 1).

11.5.1 With both isolation valves closed, command a 100% setpoint to purge the MFC until thepressure 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 from100% to a steady state value near zero.

[Note: Digital MFCs may use digital-to-analog converters, which are not capable ofreading or displaying negative values. For a digital MFC, perform an auto zero at thistime to check for an unobserved zero offset on the MFC.]

11.5.2 After the electrical output signal has stabilized for at least three minutes, record the MFC zerooffset.

11.6 Open both the upstream and downstream isolation valves. Apply a 100% setpoint to the DUTand wait for the flow to stabilize for 10 seconds. Apply the lower setpoint limit to the DUT andwait for the flow to stabilize for 10 seconds. Repeat Section 11.5 a total of three times. Thisprocess exercises the device before initiating the accuracy test.

11.7 Reference Operating Conditions

11.7.1 The reference operating conditions shall be as follows:

Ambient temperature 23 ± 2 °C

Gas temperature Same as ambient

Ambient pressure 101.3 kPa. (+ 4.7 or –15.3 kPa)

Gas pressure, Inlet 172 ± 34 kPa

Gas pressure, Outlet < 80 kPa

Relative humidity 40% ± 5%, noncondensing (suggestion: record ifoutside this range)

Magnetic field ≤ 50 µT

Electromagnetic field ≤ 100 µV/m

Vibration ≤ 0.5 m/s at 50 to 200 Hz

Shock ≤ 3 g



99

11.8 Power Supply Conditions

11.8.1 The reference supply conditions used shall be the reference values specified by themanufacturer. For those instances when a range of values is specified rather than a referencevalue, the midpoint of the range shall be taken to be the reference value.

11.8.2 The power supply must be sufficiently rated for the device under test. In addition, the followingsupply conditions and tolerances shall apply:

Reference voltage

AC supply: ± 1%

DC supply: ± 0.1%

Reference frequency ± 0.1 Hz

Harmonic distortion of AC supply ≤ 1%

Ripple of DC supply ≤ 0.1% rms

12 Procedure

Refer to flow chart in Figure 2.

12.1 SEMASPEC #92071225B-STD yields information in two general areas. These areas are:

1. Information concerning how accurately the MFC manufacturer was able tocalibrate the MFC on its nameplate gas using his surrogate gas method.

2. Information concerning the range of gases (molecular weight basis) forwhich the MFC can be used and still remain linear (i.e., the gas conversionfactor remains independent of flow through the MFC).

Information from area 1 allows a user to evaluate how effective the MFC manufacturer'ssurrogate gas calibration methods are for that specific name plate gas. Area 2 yieldsinformation on the inherent linearity of the MFC, which can be used to determine whichgases can be controlled by the MFC without its gas conversion factor becoming afunction of the flow rate through the MFC (i.e., if the MFC can be used as a genericMFC for multiple gases).



1010

Should time and budget considerations prevent the user from performing #92071225B-STD as intended, an abbreviated test may be performed which only gathers informationconcerning calibration accuracy on the nameplate gas, area 1 above. This can be doneby modifying 92071225B-STD as noted below:

Delete Sections 12.4, 12.6, 12.7, 12.8, 12.9, 12.11, 13.2.4, 14.2.2, and 14.3.2.

Deleting these sections limits the test to only the nameplate gas and N2.

12.2 For the gas of interest, collect flow data for five cycles at setpoints 100%, 90%, 80%, 70%,60%, 50%, 40%, 30%, 20%, 10%, and 0% of full scale. Begin collecting data at the 50% level.

12.3 When a zero setpoint is given, perform the procedure described in Section 11.5 to ensure a "no-flow" condition through the MFC and record the zero offset indicated by the MFC’s output. (Ifusing a digital MFC, perform an auto zero before recording the zero offset.)

[Caution: If the data points show a trend in one direction, either up or down, takeadditional points until the trend reverses direction. If the trend does not reverse beforereaching the maximum number of data points, the DUT is not stable enough for the testto proceed.]

12.4 At each setpoint under test, maintain the input signal until the output of the DUT becomesstabilized at its apparent final value. Record the output values for each input value.

12.4.1 Use Table 1 to record the following:

Column A—DUT setpoint (% FS)

Column B—DUT flow indication (% FS)

Column C—Raw flow standard reading (sccm)

Column D—Corrected flow standard reading (sccm)

See Section 13.1.1.



Column B—Mean of corrected flow standard readings for data taken at equal setpoints (sccm)

Column C—Standard deviation of corrected flow standard readings for data taken atequal set points (sccm)

Column D—Normalized flow data (% max value)

Column E—Normalized standard deviation (% max value)

Column F—Nonlinearity of flow data (% max value)

See Sections 13.1.4 through 13.1.6.



1111


Column A—Test gas

Column B—MFC gain on test gas (sccm per 1% setpoint) slope of line fitted throughsetpoint and mean flow data

Column C—Nonlinearity of MFC on test gas

See Section 13.1.3 and 13.1.5.



Column B—Conversion factor from nitrogen to the nameplate gas, CF (NG/N2)

Column C—CF (He/N2)

Column D—CF (N2)

Column E—CF (SF6)

See Section 13.1.6.



Column B—CF (R12/N2)

Column C—CF (R112/N2)

Column D—CF (Gas X/N2)

Column E—CF (Gas Y/N2)



1212

12.5 Helium Data

12.5.1 With helium as the test gas, record the zero offset using the procedure described in 11.5 and 12.2through 12.4.5.

12.5.2 Using Table 1, begin collecting data at the midpoint of the span (50% setpoint) and step up thesetpoint in 10% increments until a 100% setpoint is reached.

12.5.3 Decrease the setpoint from 100% in 10% increments until a 0% setpoint is reached.

12.5.4 Continue incrementing the setpoint until Table 1 is complete. Five increasing and fivedecreasing sets of data are recorded.

12.6 Nitrogen Data—Repeat with nitrogen as the test gas instead of helium.

12.7 Nitrous Oxide Data—Repeat with nitrous oxide as the test gas instead of nitrogen.

12.8 Freon 116 Data—Repeat with SF6 as the test gas instead of nitrous oxide.

12.9 Freon 12 Data—Repeat with R12 as the test gas instead of SF6.

12.10 Freon 112 Data—Repeat with R112 as the test gas instead of R12.

12.11 Nameplate Gas Data

12.11.1 Repeat with the nameplate gas instead of R112.

12.11.2 Perform SEMASPEC #92071221B-STD using the nameplate gas as the test gas. (SEMASPEC#92071221B-STD will be used to evaluate the accuracy of the MFC's calibration as receivedfrom the manufacturer.)

12.12 Additional Gases (Gas X . . . Gas Y)—Repeat with additional test gases as desired.

13 Data Analysis

13.1 Calculations

13.1.1 Correct the raw flow data (Column C, Table 1) for zero offsets and drift that may have beenpresent during data collection as follows:

corrected flow standard reading = raw flow standard reading x {setpoint/[setpoint - (0.5x (zero offset prior to data point + zero offset after data point))]}

Record the corrected flow standard reading in Column D of Table 1.

13.1.2 For each test gas, calculate the mean and standard deviation of the corrected flow readings, forcommon setpoints on the same gas. For example, calculate the mean and standard deviation forall the 0% readings for a given gas, then repeat the calculations for the 10% readings, etc.Record the results on Table 2 in Columns B and C.

13.1.3 For each test gas, fit a straight line through the means of the corrected flow readings andsetpoints from Table 2. Use the Least Squares Method, as found in Annex A2, to determine theequation of a straight line through the data. Record the slope of the straight line (sccm per %setpoint) in Table 3 as the gain of the MFC on the test gas. See below.



1313

where

XI = DUT setpoint

YI = corrected flow

B = MFC gain

B = X Y

XI I

I2

∑∑



1414

13.1.4 Normalize the corrected flow data. To do this, divide the corrected flow at a setpoint by thecorrected flow average at the 100% setpoint:

where

X = setpoint value

13.1.5 Record the normalized flow data in column D of Table 2. Subtract the setpoint from thenormalized corrected flow and record the difference in Column F of Table 2.

13.1.5.1 The maximum absolute value obtained in 13.1.5 is the stated terminal-based nonlinearity of theMFC for this gas. Refer to column C of Table 3.

13.1.6 Conversion Factors—The conversion factor between any Gas A and any Gas B at each setpointis calculated as follows:

conversion factor GasA Gas B X setpoaverage corrected flow X setpo on G

average corrected flow X setpo on G( / ) @ % int

@ % int

@ % int=

where

X = setpoint value

13.1.6.1 Calculate the conversion factors between He and N2, between SF6 and N2, between R12 and N2,between R112 and N2, and between all additional test gases and N2. Record in Tables 4 and 5.

normalized flow = 100%xaverage corrected flow @ X% set point

average corrected flow @ 100% set point



1515

13.2 Interpretation

13.2.1 Refer to SEMASPEC #92071221B-STD for an analysis of the MFC’s accuracy on the nameplategas.

13.2.2 Figure 3 illustrates the gain and nonlinearity of the MFC on a specific gas. A comparison of thenonlinear characteristic of the MFC on one gas with its nonlinearity on another gas willdetermine if its conversion factor is dependent on flow. If the MFC has the same normalizedflow versus setpoint curve on two different gases, then the conversion factor between those twogases is independent of flow, and calibrations can be linearly mapped from one gas to the other.If the curves are not identical, the conversion factor is dependent on flow, and calibrations mustbe mapped nonlinearly from one gas to the other. In such cases, fixed conversion factors willnot be accurate over the MFC’s flow-range.

13.2.3 Figure 4 illustrates the conversion factor between two specific gases as a function of setpoint. Itmay be used to accurately map from one gas to the other and may predict the flow error that willresult if the average conversion factor is used.

13.2.4 Figure 5 illustrates the maximum nonlinearity of an MFC for different gases ordered by theirmolecular weight. The measuring section of an MFC typically exhibits little or no nonlinearitieson light gases and begins to progressively exhibit more nonlinearities as heavier gases are used.The location of the onset of nonlinearities is dependent on gas properties and on the design andsetup of the MFC. See Annex A1 for more information on nonlinearity corrections.

[Note: Mass flow controllers are often manufactured using a base design, with the setupof the components varied to achieve the level of linearity required for the nameplate gas.An MFC of the same model number may demonstrate different linearities for differentnameplate gases.]



1616

14 Data Presentation

14.1 Record the accuracy rating of the measuring equipment. Follow the data presentation fromSEMASPEC #92071221B-STD for the nameplate gas data.

14.2 MFC Gain And Linearity

14.2.1 Plot the corrected mean flow vs. DUT setpoint for the nameplate gas. See Figure 3.

14.2.1.1 Present the maximum nonlinearity recorded and note the MFC gain.

14.2.1.2 Present data points showing a 3.0 standard deviation range about the mean.

14.2.1.3 Note the following data for the MFC:

Nameplate Gas and Range

Test Gas Used

Inlet Gas Pressure

Model And Serial Number

Temperature And Barometric Pressure

Date

14.2.2 Repeat 14.2.1 for He, N2, SF6, R12, R112, and any additional test gases.

14.3 MFC Conversion Factors

14.3.1 Plot the conversion factor from nitrogen to the nameplate gas against the DUT setpoint. Notethe mean value and range of values (see Figure 4).

14.3.1.1 Note the following data for the MFC:

Nameplate Gas and Range

Test Gas Used

Inlet Gas Pressure

Model And Serial Number

Temperature And Barometric Pressure

Date

14.3.2 Repeat Section 14.3.1 for CF (He/N2), CF (N2), CF (SF6/N2), CF (R12/N2), CF (R112/N2), andthe conversion factors between any additional gases tested and nitrogen.

[Note: You may choose to present data for only one surrogate gas for a nameplate gas.]



1717

14.4 MFC Nonlinearity vs. Gas Type

14.4.1 Plot the maximum nonlinearity for each gas tested from Table 3 vs. the molecular weight of thetest gas (see Figure 5).

15 Precision And Bias

Precision and bias in this test method are a function of the uncertainty of themeasurement equipment used. The tester or end user is responsible for determining theprecision and bias of a particular setup and test.



1818

16 Illustrations

Table 1 Indicated Flow versus Actual Flow

MFC Mfg/Model/Serial # _____________________________

Name Plate Gas/Range _____________________________

Test Gas _____________________________

Temp ___________ Bar ____________ Date ___________

Factory Calibration Gas _____________________________

ColumnA

DUTSetpoint

(%)

ColumnB

DUT FlowIndication

(%)

ColumnC

Raw Data

ColumnD

Corrected

0%* _____________ 0 0

50

60

70

80

90

100

90

80

70

60

50

40

30

10

0%* _____________ 0 0

10

20

30

--Flow Standard Reading--



1919

Table 1 (continued) Indicated Flow versus Actual Flow

ColumnA

DUTSetpoint

(%)

ColumnB

DUT FlowIndication

(%)

ColumnC

Raw Data

ColumnD

Corrected

40

50

60

70

80

90

100

90

80

70

60

50

40

30

20

10

0%* _____________ 0 0

10

20

30

40

50

60

70

80




2020


ColumnA

DUTSetpoint

(%)

ColumnB

DUT FlowIndication

(%)

ColumnC

Raw Data

ColumnD

Corrected

90

100

90

80

70

60

50

40

30

20

10

0%* _____________ 0 0

10

20

30

40

50

60

70

80

90

100

90

80

70




2121


ColumnA

DUTSetpoint

(%)

ColumnB

DUT FlowIndication

(%)

ColumnC

Raw Data

ColumnD

Corrected

60

50

40

30

20

10

0%* _____________ 0 0

10

20

30

40

50

60

70

80

90

100

90

80

70

60

50

40

30

20




2222


ColumnA

DUTSetpoint

(%)

ColumnB

DUT FlowIndication

(%)

ColumnC

Raw Data

ColumnD

Corrected

10

0%* _____________ 0 0

10

20

30

40

0%* _____________ 0 0

Repeat the above for:

• N2

• He

• R12

• R112

• RSF6

• Nameplate Gas

• Additional Gases

[Note: 0%*; the MFC is not controlling gas flow in this state but rather is in a no-flow condition during which MFCzero offset is to be recorded.]




2323

Table 2 Statistical Performance

MFC Mfg/Model/Serial # _______________________________

Name Plate Gas/Range _______________________________

Test Gas _______________________________

Temp ____________ Bar _____________ Date ____________

Factory Calibration Gas _______________________________

Column

A

D.U.T.

Setpoint

(%FS)

Column

B

Mean CorrectedStandard Flow

Reading

(SCCM)

Column

C

Std. Dev. Flow

(SCCM)

Column

D

NormalizedFlow (%FS)

Column

E

Normalize

Std. Dev.

(%FS)

Column

F

Non-Linearity

(%FS)

10 __

20

30

40

50

60

70

80

90

100

Least Squares Line Fit:

Y = bX b = ____________sccm/% = MFC Gain

MFC Gain

X = Column A

Y = Column B

Maximum Nonlinearity = _____________% @ ____________%

(From Column F) Nonlinearity Setpoint

Refer to Annex A2 for additional details

Repeat the above for He, R12, Nameplate Gas and Additional Gases



2424

Table 3 Gain and Nonlinearity: Summary of All Gases Tested

MFC Mfg/Model/Serial # ___________________________________

Name Plate Gas/Range ___________________________________

Test Gas ___________________________________

Temp ____________ Bar ____________ Date ____________

Factory Calibration Gas _______________

Column

A

Gas

Column

B

Sensor Gain

(SCCM/%setpoint)

Column

C

NonLinearity

%FS

N2

He

R12

R112

SF6

Name Plate Gas

Gas X

Gas Y

From Least Squares Line Fit (see Annex A2).

Y = bX where Y = Column B Table 2

X = Column A Table 2

b = MFC Gain



2525

Table 4 MFC Conversion Factors Relative to N2

MFC Mfg/Model/Serial # _______________

Name Plate Gas/Range _______________

Test Gas _______________

Temp _______ Bar _______ Date _______


Column

A

DUT

Setpoint

(%FS)

Column

B

CF (NG/N2)

Column

C

CF (He/N2)

Column

D

CF (N2)

Column

E

CF (SF6)

100%

90

80

70

60

50

40

30

20

10



2626

Table 5 MFC Conversion Factors Relative to N2

MFC Mfg/Model/Serial # _______________

Name Plate Gas/Range _______________

Test Gas _______________

Temp _______ Bar _______ Date _______


Column

A

DUT

Setpoint

(%FS)

Column

B

CF (R12/N2)

Column

C

CF (R112/N2)

Column

D

CF (Gas X/N2)

Column

E

CF (Gas Y/N2)

100%

90

80

70

60

50

40

30

20

10



2727

Figure 1 Mass Flow Controller Test Fixture



2828

Figure 2 Test Flowchart



2929

Figure 3 DUT Setpoint versus Gas Flow



3030

Figure 4 Conversion Factors versus DUT Setpoint



3131

Figure 5 MFC Nonlinearity as a Function of Molecular Weight



3333

ANNEXES

(Mandatory Information)

A1. Correcting for Nonlinearities

A1.1 If an MFC is operating in a region after the onset of nonlinearities in its measuring section, afixed nonlinear correction may be added to the MFC to offset the nonlinearity of the measuringsection. Since this correction is fixed, but the measuring section’s nonlinearity is a function ofgas and flow rate, an MFC that uses a fixed correction may only be used for the specific gas andflow for which the offset was matched. Flows of other gases will display an error that is afunction of the difference in linearity in the MFC’s measuring section.

A1.2 If an MFC is operating in a region prior to the onset of nonlinearities, no correction is involved,and the MFC may be used for other gases prior to the onset of nonlinearities by applying a singlefixed conversion factor.

A1.3 The conversion factor between two gases is independent of the MFC setpoint only if the MFC islinear on both gases. This implies that the MFC is operating at flows prior to the onset ofnonlinearities in its measuring section for both Gas A and Gas B. Although not the onlydetermining factor, the molecular weight of the gas being controlled is a major influence on theonset of nonlinearities in the MFC’s measuring section. Identifying this molecular weight allowsthe user to estimate whether the conversion factor between two gases will be independent of thesetpoint.

A1.4 Typically, the maximum nonlinearity of an MFC on light gases will be equal in magnitude. Achange in the magnitude of the maximum nonlinearity from the value of the maximumnonlinearity exhibited by the MFC on light gases indicates the onset of nonlinearities in theMFC’s measuring section. The nonlinearity exhibited on light gases is indicative of a fixednonlinear correction that has been added by electronic or other means. See Section A1.1. Thenonlinearity exhibited on light gases would be near zero if no fixed corrections were involved.



3434

A2. Least Squares Method

NOTICE: SEMATECH DISCLAIMS ALL WARRANTIES, EXPRESSED OR IMPLIED,INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FORA PARTICULAR PURPOSE. SEMATECH MAKES NO WARRANTIES AS TO THESUITABILITY OF THE METHOD FOR ANY PARTICULAR APPLICATION. THEDETERMINATION OF THE SUITABILITY OF THIS METHOD IS SOLELY THERESPONSIBILITY OF THE USER.

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