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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 #9

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

– Thickness Measurements (for RM 8096)

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 8096)1 References to consult

2 Thickness for RM 8096 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 and P.T. Vernier, “Electro-physical technique for post-fabrication measurements

of CMOS process layer thicknesses,” NIST J. Res., Vol. 112, No. 5, pp. 223-256, 2007.

• Fabrication7. The RM 8096 chips were fabricated through MOSIS on the 1.5 µm On Semiconductor (formerly

AMIS) CMOS process. The URL for the MOSIS website is http://www.mosis.com. The bulk-micromachining was performed at NIST.

1. References to Consult

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2a. Thickness (for RM 8096) Overview

• Definition: 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: Step height test structures• Instruments: Interferometric microscope and stylus profilometer or

comparable instruments• Method: Calculated using the results of six step height

measurements taken from four different step height test structures

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wheret4 glass thicknesst3 deposited oxide after the m1 deposition [between the pmd

(poly-to-metal dielectric) layer and the glass layer]t2 deposited oxide before the m1 deposition [between the field

oxide and the imd (inter-metal dielectric) layer]t1 field oxide thickness (between the substrate and the pmd layer)toxide composite oxide thickness

2b. Thickness Equations (for RM 8096)

4321oxide ttttt

t1 = tfox(pmd/sub)

t4 = t(gl)

t2 = tpmd(imd/fox)

t3 = timd(gl/pmd)toxide = t1+ t2+ t3+ t4

7• Consult the thickness article reference for the nomenclature

2b. Thickness Equations (for RM 8096)

ZYXttttt 4321oxide

EDCBtttX elec1m2mimd43 )/(

and where Y=Y1, Y2, Y3, or Y4

MtttY elec1m2mimd21d1 )/(

LKAtttY elec1m2mimd21c2 )/(

OJAtttY elec1m2mimd21b3 )/(

OFAtttY elec1m2mimd21a4 )/(

where

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• Composite oxide thickness combined standard uncertainty, ucoxide, equation

• The data sheet (DS) expanded uncertainty equation is

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

2c. Data Sheet Uncertainty Equations

),,,(MIN 4z3z2z1zncoxide uuuuuu

noxide Zt

coxideoxideDS uUU 2

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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

DSROI UU

0stabilityU

• RM 8096– Fabricated on a multi-user 1.5 µm CMOS process followed by a bulk-

micromachining etch– Material properties of the composite oxide layer are reported– Chip dimensions:

4600 µm x 4700 µm

3. Location of Structure on RM 8096(The RM 8096 Chip)

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3. Location of Structure on RM 8096

Locate the step height test structure in this group given the information on the NIST-supplied data sheet

Top view of a step height test structure

For RM 8096

Step For the first structure: a m2 over poly1 step from active area to field oxide

Reference platform layer

m2 atop active area

Orientation 0º

Quantity 4 distinct step height test structures (with 3 occurrences of each structure) to obtain 6 step height measurements for a composite oxide thickness calculation

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4. Test Structure Description (For RM 8096)

z

x

z

x

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

5. Calibration Procedure

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• Obtain a step height measurement (according to SEMI MS2 and using Data Sheet SH.1.a) for the 6 steps pointed to in the figure below.

– Step 1 [i.e., step1AB]

– Step 2 [i.e., step2rA]

– Step 3 [i.e., step1EF]

– Step 4 [i.e., step1GH]

– Step 5 [i.e., step3AB(n)] – use a stylus profilometer (or comparable instrument) due to the top layer being non-reflective

– Step 6 [i.e., step3BC(0)] – use the NIST-supplied value since this is a measurement taken before the post-processing.

• Record the step heights and uncertainties in Data Sheet T.1

6. Measurement Procedure

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• Find Data Sheet T.1– 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.1– Click “Reset this form”– Supply INPUTS to Tables 1 through 3

• Using Data Sheet SH.1.a results for Table 1 inputs– 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:

whereDoxide positive difference between the thickness value of

the customer, toxide(customer), and that appearing onthe ROI, toxide

Uoxide(customer) thickness expanded uncertainty of the customerUoxide thickness expanded uncertainty on the ROI, UROI

8. Using the MEMS 5-in-1To Verify RM 8096 Thickness Measurements

22)()( oxidecustomeroxideoxidecustomeroxideoxide UUttD

• Then can assume measuring the composite oxide beam 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.1