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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 #10

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

– Thickness Measurements (for RM 8097)

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 Thickness Measurements

(for RM 8097)1 References to consult

2 Thickness for RM 8097 a. Overview b. Equation used c. Data sheet uncertainty equations d. ROI uncertainty equation

3 Location of test structure on RM chip

4 Test structure description

5 Calibration procedure

6 Measurement procedure

7 Using the data sheet

8 Using the MEMS 5-in-1 to verify measurements

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• Overview1. J. Cassard, J. Geist, and J. Kramar, “Reference Materials 8096 and 8097 – The

Microelectromechanical Systems 5-in-1 Reference Materials: Homogeneous and Stable,” More-Than-Moore Issue of ECS Transactions, Vol. 61, May 2014.

2. J. Cassard, J. Geist, C. McGray, R. A. Allen, M. Afridi, B. Nablo, M. Gaitan, and D. G. Seiler, “The MEMS 5-in-1 Test Chips (Reference Materials 8096 and 8097),” Frontiers of Characterization and Metrology for Nanoelectronics: 2013, NIST, Gaithersburg, MD, March 25-28, 2013, pp. 179-182.

3. J. Cassard, J. Geist, M. Gaitan, and D. G. Seiler, “The MEMS 5-in-1 Reference Materials (RM 8096 and 8097),” Proceedings of the 2012 International Conference on Microelectronic Test Structures, ICMTS 2012, San Diego, CA, pp. 211-216, March 21, 2012.

• User’s guide (Section 8, pp. 137-156)4. J.M. Cassard, J. Geist, T.V. Vorburger, D.T. Read, M. Gaitan, and D.G. Seiler, “Standard

Reference Materials: User’s Guide for RM 8096 and 8097: The MEMS 5-in-1, 2013 Edition,” NIST SP 260-177, February 2013 (http://dx.doi.org/10.6028/NIST.SP.260-177).

• Standard5. SEMI MS2-1113, “Test Method for Step Height Measurements of Thin Films,” November 2013.

(Visit http://www.semi.org for ordering information.)

• Thickness article6. J.C. Marshall, “New Optomechanical Technique for Measuring Layer Thickness in MEMS

Processes,” J. of Microelectromechanical Systems, Vol. 10, No. 1, pp. 153-157, March 2001.

• Fabrication7. The RM 8097 chips were fabricated at MEMSCAP using MUMPs-Plus! (PolyMUMPs with a

backside etch). The URL for the MEMSCAP website is http://www.memscap.com.

1. References to Consult

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2a. Thickness (for RM 8097) Overview

• Description: The height of one or more thin-film layers• Purpose: Used in the determination of thin film material

parameters, such as Young’s modulus• Test structure: Cantilever exhibiting stiction• Instrument: Interferometric microscope, stylus profilometer, or

comparable instrument(s)• Method: Calculated from step height measurements of:

a) the height of the anchor to the underlying layer (A),b) the height of the stuck portion of the cantilever to the anchor (B), and/orc) the height of the stuck portion of the cantilever to the

underlying layer (C)

C

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whereA height from the underlying layer to the anchor B height from the anchor to the top of the stuck portion of the

cantileverCcalc calculated height from the underlying layer to the top of the

stuck portion of the cantileverH anchor etch depthJ height from the top of the underlying layer to the bottom of the

stuck portion of the cantilever that takes into consideration theroughness of the surfaces, any residue present between the layers and a tilting component

2b-2c. P1 or P2 Thickness Equationsand Data Sheet Uncertainty Equations

(for RM 8097)

BACcalc

HBJ

22cSHBcSHAcCcalc uuu

22cHcSHBcJ uuu

6/HucH

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• Determine the thickness, α, three different ways:

• Choose the value for α (i.e., αi, αii, or αiii) that has the smallest uncertainty unless the value for α has been preselected

• The data sheet (DS) expanded uncertainty equation is

where k=2 is used to approximate a 95 % level of confidence

HAi 22cHcSHAic uuu

estiii JC 22cJestcSHCiiic uuu

2b-2c. P1 or P2 Thickness Equations and Data Sheet Uncertainty Equations

(for RM 8097)

cDS uUU 2

estcalcii JC 22cJestcCcalciic uuu

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UROI expanded uncertainty recorded on the Report of Investigation (ROI)

UDS expanded uncertainty as obtained from the data sheet (DS)

Ustability stability expanded uncertainty

2d. ROI Uncertainty Equation

22stabilityDSROI UUU

0stabilityU

DSROI UU

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• RM 8097– Fabricated using a polysilicon multi-user surface-micromachining

MEMS process with a backside etch– Material properties of the first or second polysilicon layer are reported– Chip dimensions:

1 cm x 1 cm

Lot 95 Lot 98

3. Location of Cantilever on RM 8097(The RM 8097 Chips)

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3. Location of Cantilever on RM 8097For RM 8097

Layer poly1 or poly2

W (µm) 20

L (µm) Thickness cantilevers:600 (poly1 only), 650, 700, 750, and 800In-plane length cantilevers:24, 80, 200, 500, and 1000

Orientation Thickness: 0ºIn-plane length: 0º (poly1 only) and 90º

Quantity of cantilevers

3 of each length for each orientation Thickness: 15 poly1 and 12 poly2In-plane length: 30 poly1 and 15 poly2

10Locate the cantilever in one of these groups given the information on the NIST-supplied data sheet

Top view of thickness test structure

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4. Test Structure Description (For RM 8097)

Top view of thickness test structure

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4. Test Structure DescriptionFor RM 8097

p2

Top view of cantilevers in in-

plane length group

p1

Unconventional anchor design

Same anchor design as in thickness test structures

Top view of thickness test structures

p1

p2

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• Calibrate instrument in the z-direction– As specified for step height calibrations

5. Calibration Procedure

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• Measure A (using a stylus profilometer) – optional– Obtain 3 data traces– Level the data with respect to the poly0 layer– From platX

• Obtain platXa1, platXb1, and platXc1• Obtain splatXa1, splatXb1, and splatXc1

– From platY• Obtain platYa1, platYb1, and platYc1• Obtain splatYa1, splatYb1, and splatYc1

• Measure C (using an optical interferometer)– Use a high magnification objective– Obtain 3 data traces (typically perpendicular to the beam and

crossing the pegged portion of the beam)– Level the data with respect to the poly0 layer– From platZ

• Obtain platZa2, platZb2, and platZc2• Obtain splatZa2, splatZb2, and splatZc2

– From platX• Obtain platXa2, platXb2, and platXc2• Obtain splatXa2, splatXb2, and splatXc2

6. Measurement Procedure

C

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• Obtain– From the NIST-supplied data sheet:

repeat(samp)N relative step height repeatability standard deviation• H anchor etch depth H range of the anchor etch depth• Jest estimated value for the dimension J• ucJest estimate for the combined standard

uncertainty of Jest

– sroughX smallest of all the values obtained for splatXt1 and splatXt2

– sroughY = sroughZ smallest of all the values obtained for splatYt1 and splatZt2

• Typically, choose – Fate of A = 1 to disregard i as a possible thickness– Fate of B = 1 to disregard ii as a possible thickness– Fate of C > 0 if > 0, to force the selection of iii (calculated using C and Jest)

as the thicknessif = 0, to let the software determine the thickness by

the smallest uncertainty value

6. Measurement Procedure (continued)

C

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• Find Data Sheet T.3.a– On the MEMS Calculator website (Standard Reference Database 166)

accessible via the NIST Data Gateway (http://srdata.nist.gov/gateway/) with the keyword “MEMS Calculator”

– Note the symbol next to this data sheet. This symbol denotes items used with the MEMS 5-in-1 RMs.

• Using Data Sheet T.3.a– Click “Reset this form”– Supply INPUTS to Tables 1 through 4– Click “Calculate and Verify”– At the bottom of the data sheet, make sure all the pertinent boxes say

“ok.” If a pertinent box says “wait,” address the issue and “recalculate.”

– Compare both the inputs and outputs with the NIST-supplied values

7. Using the Data Sheet

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• If your criterion for acceptance is:

whereDα positive difference between the thickness value

of the customer, α(customer), and that appearing on theROI, α

Uα(customer) thickness expanded uncertainty of the customerUα thickness expanded uncertainty on the ROI, UROI

8. Using the MEMS 5-in-1To Verify RM 8097 Thickness Measurements

22)()( UUD customercustomer

• Then can assume measuring the poly1 (or poly2) thickness according to SEMI MS2 according to your criterion for acceptance if:– Criteria above satisfied and– No pertinent “wait” statements at the bottom of your Data Sheet T.3.a