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Physical Measurement Laboratory

Semiconductor and Dimensional Metrology Division

Nanoscale Metrology Group

MEMS Measurement Science and Standards Project

MEMS 5-in-1 RM Slide Set #11

Reference Materials 8096 and 8097The MEMS 5-in-1 Test Chips

– Remaining Details

Photo taken by Curt Suplee, NIST

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List of MEMS 5-in-1 RM Slide SetsSlide Set # Title of Slide Set

1 OVERVIEW OF THE MEMS 5-IN-1 RMs

2 PRELIMINARY DETAILS

THE MEASUREMENTS:

3 Young’s modulus measurements

4 Residual strain measurements

5 Strain gradient measurements

6 Step height measurements

7 In-plane length measurements

8 Residual stress and stress gradient calculations

9 Thickness measurements (for RM 8096)

10 Thickness measurements (for RM 8097)

11 REMAINING DETAILS

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Outline for theRemaining Details1 Validation procedures

a. For height measurements b. For frequency measurements c. For length measurements

2 Stability test results a. For RM 8096 b. For RM 8097 Lot 95 c. For RM 8097 Lot 98

3 Homogeneity plots a. For RM 8096 b. For RM 8097

4 What’s next?

5 Summary

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• Validation procedures are used to accept an instrument back into service– For height measurements– For frequency measurements– For length measurements

1. Validation Procedures

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1a. Validation Procedure for Height Measurements

• To accept instrument back into service:• Use two step height standards (SHS)

• For example, a 1.0 µm and a 4.5 µm SHS• Calibrate the instrument using the 4.5 µm SHS

• Careful – use only the certified region along both the length and width• Obtain cal4.5

• Six measurements are taken (3 along each side of the SHS) before the session (mean = )

• Six measurements are taken after the session (mean = )

•

•

• Obtain step height measurements on the 1.0 µm SHS• Obtain platNXa, platNXb, platNXc, platNYa, platNYb, platNYc and splatNXa, splatNXb, splatNXc, splatNYa, splatNYb, splatNYc • Calculate the calibrated step height measurement, M1.0, where M1.0 = m1.0 cal4.5

2/afterbeforeave zzz

avezcertcal /5.45.4

afterzbeforez

• Calculate uM1.0

uM1.0=SQRT(uLstep1.0

2+uWstep1.02+ucert1.0

2+ucal1.02+urepeat(shs)1.0

2+udrift1.02+ulinear1.0

2+urepeat(samp)1.02)

where uLstep1.0=SQRT{[((splatNXa+splatNXb+splatNXc)/3)calz4.5]2(sroughNXcalz4.5)2

+[((splatNYa+splatNYb+splatNYc)/3)calz4.5]2(sroughNYcalz4.5)2}

uWstep1.0=STDEV(M1.0a, M1.0b, M1.0c )

ucert1.0=(cert4.5/cert4.5)|M1.0|

ucal1.0=(6ave4.5 / )|M1.0|

urepeat(shs)1.0=(6same4.5 / )|M1.0|

udrift1.0=[zdrift4.5calz4.5/(2*SQRT(3)cert4.5)]|M1.0|

ulinear1.0=[zlin4.5/SQRT(3)]|M1.0|

urepeat(samp)1.0=(repeat(samp)1.0)|M1.0|

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1a. Validation Procedure for Height Measurements

(continued)

4.5ave6z

4.5same6z

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– Determine D1.0 and uD1.0

D1.0=|M1.0cert1.0| uD1.0=SQRT(uM1.0

2+cert1.02)

– Repeat the above by switching the standards– Instrument accepted back into service if:

• D1.0 < 2uD1.0

• D4.5 < 2uD4.5

– If above satisfied, can use either SHS, preferably the one closest in size to the step to be measured.

– If above not satisfied, consider increasing zlin until the equations are in agreement.

1a. Validation Procedure for Height Measurements

(continued)

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• To accept instrument back into service:1. Use the round robin (RR) chip that was used for repeatability measurements (for C and M)

• Obtain the certified value, C, and the expanded uncertainty, UC– C = the average YM value for the RR repeatability measurements

• Obtain the measured value, M, and the expanded uncertainty, UM– M = the YM value using new measured frequencies and same inputs

to Data Sheet YM.3 as for the RR • Obtain the difference, D, and the expanded uncertainty, UD

– D = |C M|– UD = SQRT[UC

2 + UM2]

• Ensure that D < UD

2. Or, compare the YM value obtained from 2 different instruments• Obtain the certified value, C, and the expanded uncertainty, UC

1. C = the YM value found from instrument #1

1. Obtain the measured value, M, and the expanded uncertainty, UM– M = the YM value found from instrument #2

• Obtain the difference, D, and the expanded uncertainty, UD– D=|CM|– UD= SQRT[UC

2 + UM2]

• Ensure that D < UD

1b. Validation Procedure for Frequency Measurements

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1c. Validation Procedure for Length Measurements

• Accept instrument back into service:• As specified for in-plane length calibrations

• To compare measurements taken with 2 micrometers:• Compare measurements in the x- and y-directions for each

combination of lenses• For micrometer #1, obtain R = rulerx and estimate R = xcal

• Where rulerx is the maximum FOV in x-direction for the given combination of lenses

• And xcal is the estimated standard deviation of this measurement• For micrometer #2, obtain M = rulerx and estimate M = xcal

• Determine D D = |M R|• Calculate uD

uD = SQRT(uM2+uR

2) where uM=M and uR=R

• The measurements are in agreement if, for each combination of lenses used for RM measurements in both the x- and y-directions,

D < 2uD

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2. Stability Test Results

• Stability tests are used to monitor drifts in parametric values over time.

• Measurements of residual strain taken quarterly for 2 years on RM monitors with different storage conditions.– N2-filled dry box

– wooden box– clean plastic storage

• For the stability plots that follow, The parametric values are plotted with the

UROI uncertainty bars.

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2a. Stability Test Results(for RM 8096)

Dirty plastic storage can introduce plasticizers •Plasticizers have the effect of increasing residual strain. •That RM moved to clean plastic storage. •Time “zeroed” when moved.

Storage for RM Monitors•N2-filled dry box•Clean plastic storage•Wooden box

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2b. Stability Test Results(for RM 8097 Lot 95, P2)

Storage for RM Monitors•N2-filled dry box•Clean plastic storage•Wooden box

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2c. Stability Test Results(for RM 8097 Lot 98, P2)

Storage for RM Monitors•N2-filled dry box•Clean plastic storage•Wooden box

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Summary of Stability Test Results

RM 8096 (for composite oxide)•For inert atmosphere

• Residual strain appears constant over time

•For plastic storage and wooden box• Residual strain increases over time

RM 8097 Lots 95 and 98 (for P2)•For different storage conditions

• Residual strain appears constant over time

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3. Homogeneity Plots

• Homogeneity plots are used to determine whether or not the chips are acceptable candidates for use as RMs– Is the fabrication process sufficiently

homogeneous?

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3. Homogeneity PlotsInclude Expanded Uncertainties and Limits

Parametric value, Pave

Data sheet uncertainty, UDS

NOTE: The 4 quantities above are specified on the Report of Investigation.

For the homogeneity plots that follow:– The parametric values are plotted with the UROI uncertainty bars.– The average value is plotted on the right with the heterogeneity limits

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3a. Homogeneity Plots for 8096

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3a. Homogeneity Plots for 8096 (continued)

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3b. Homogeneity Plots for 8097

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3b. Homogeneity Plots for 8097 (continued)

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3b. Homogeneity Plots for 8097 (continued2)

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3b. Homogeneity Plots for 8097 (continued3)

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4. What’s Next?(Decade to Decade)

1990-1999: Decade of Innovation and Patents:Establishing credibility in MEMS research community via:a)Innovative fabrication methods and devices and b)Transferring MEMS fabrication technology and measurement methods to the MEMS community

2000-2009: Decade of Standards:Leading the development of documentary standards for MEMS measurement methods (in ASTM and SEMI)

2010-2019: Decade of Standard Reference Databases, Reference Materials, and Standard Reference Materials

Supporting the documentary standards

Decade of RoadmappingRoadmapping the future of MEMS and planning our role in that future

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4. What’s Next?

Research & Development CMOS compatible MEMSTest structure and measurement method R & DScientific publications

Documentary StandardsASTM E 2244-11e1: In-plane length E 2245-11e1: Residual strain E 2246-11e1: Strain gradientSEMI MS2–1113: Step height MS4–1113: Young’s modulus

Standard Reference Database (SRD 166)MEMS Calculator Web Pages validate industry measurements (http://srdata.nist.gov/gateway/)

with the keyword “MEMS Calculator”

Reference Materials (RMs)CMOS MEMS 5-in-1 RM 8096

MEMS 5-in-1 RM 8097

Standard Reference Material (SRM)?

Does industry want this?

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4. What’s Next?(What Would NIST Do?)

• If there is a high demand for the RMs:• Consider making more• Pass off to an interested company for them to make more?

• Develop a plan as to how to do this fairly (if more than 1 company)• Chip design – on-line• Materials used – provide them with the eDocs (which are public documents)

which includes the list of vendors, etc.?• Calibration/measurement/analysis – in standards supplemented by the SP260• DataSheets – on line for use• DataSheets (htm files) and figures – request from NIST (free of charge) or

make available for download (also available with the purchase of an RM)

• Draft DataSheets (htm files) with read and write capabilities for text files and figures – request from NIST (free of charge) or make downloadable

• Miscellaneous (e.g., handling/storage/assembly of material/shipment/etc.) – in eDocs and SP260

• How would they report their values (like on ROIs)? Is an ROI associated exclusively with NIST?

• How would their customers believe their values? Would they need to be accredited somehow?

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4. What’s Next?(What Would NIST Do? - continued)

• If there is a high demand for the RMs (continued):

• Consider turning the RMs into SRMs• Via designing using SOI

• Oxide and silicon layers may each be 70 nm

• Can put next to linewidth structures

• Can achieve a tighter control on the thickness measurements

• Cantilevers/beams may require holes in them

• Will the cantilevers and fixed-fixed beams bend enough?

• Can reasonable images be obtained with the interferometer and vibrometer?

• Look into this…..

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5. Summary

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5. Summary(Uses of the MEMS 5-in-1)

• To validate use of the documentary standards (so companies can compare their

in-house measurements taken on

the RM with NIST measurements)

• To characterize or validate a process• To take local measurements • To compare measurements meaningfully

(e.g., between suppliers and customers)

• To trouble-shoot a process (to improve yield and track failure sources

to speed development)

• To calibrate an instrument

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Photo taken by Curt Suplee, NIST

Intended for•MEMS designers•Test equipment manufacturers

– Who may want to buy in bulk to sell with their instruments

•IC and MEMS foundries and services