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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 #6

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

– Step Height Measurements

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 forStep Height Measurements

1 References to consult

2 Step height a. Overview b. Equation used c. Data sheet uncertainty equations d. ROI uncertainty equation

3 Location of test structure on RM chip a. For RM 8096 b. For RM 8097

4 Step height test structure a. For RM 8096 b. For RM 8097

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 5, pp. 96-113)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.)

• Fabrication6. 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.

7. 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. Step Height Overview

• Definition: The distance in the z-direction between an initial, flat surface and a final, flat surface

• Purpose: To determine the thin film thickness values, which can be used in the determination of thin film material parameters, such as Young’s modulus

• Test structure: Step height test structure• Instrument: Interferometric microscope or comparable instrument• Method: Obtained from multiple measurements taken along the

width of a step height test structure

x

z

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wherestepNXYtstep height measurement from trace “t”stepNXY average of the step height measurementsplatNYt height measurement of platform “Y” from trace “t”platNXt height measurement of platform “X” from trace “t”calz z-calibration factor

2b. Step Height Equation

zXYt calplatNXtplatNYtstepN (for one trace)

3/XYcXYbXYaXY stepNstepNstepNstepN

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• Step height combined standard uncertainty, ucSH, equation

where

uLstep due to measurement uncertainty across length of stepuWstep due to measurement uncertainty across width of stepucert due to the uncertainty of the value of the step height

standard used for calibrationucal due to the uncertainty of the measurements taken

across the step height standardurepeat(shs) due to repeatability of measurements taken on step

height standardudrift due to the amount of drift during the data sessionulinear due to the deviation from linearity of the data scanurepeat(samp) due to the repeatability of similar step height

measurements

2c. Data Sheet Uncertainty Equations

2)(

222)(

2222samprepeatlineardriftshsrepeatcalcertWstepLstepcSH uuuuuuuuu

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• 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

cSHSHDS uUU 2

Effective value reported?(RM 8096)

Effective value reported?(RM 8097)

Step Height No No

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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

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3. Location of Structure on RM Chip (The 2 Types of Chips)

• 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

• 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

Lot 95 Lot 98

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3a. 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)

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3b. Location of Structure on RM 8097

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 8097

Step from poly1 to poly2 (or vice versa)

Reference platform layer

poly0

Orientation 0º, 90º, 180º, and 270º

Quantity 3 small quads and 2 large quads, where each quad has 4 step height test structures each with a different orientation

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4a. Step Height Test Structure (For RM 8096)

Top view of a step height test structure

Cross section along Trace a, b, or c

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4b. Step Height Test Structure (For RM 8097)

Top view of a step height test structure

Cross section along Trace a, b, or c

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5. Calibration Procedure

• Calibrate instrument in the z-direction• Before the data session

• Record height of step height standard at 6 locations = mean value of the 6 measurementsbefore = standard deviation of the 6 measurements

• Record height of step height standard at same location for 6 measurements

= mean value of the 6 measurementssame1 = standard deviation of the 6 measurements

• After the data session• Record height of step height standard at 6 locations

= mean value of the 6 measurementsafter = standard deviation of the 6 measurements

• Record height of step height standard at same location for 6 measurements

= mean value of the 6 measurementssame2 = standard deviation of the 6 measurements

beforez

1samez

afterz

2samez

• Determine the following:

1.

2.

3.

4.

5.

6.

7.

if , then and

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5. Calibration Procedure (continued)

cert = certified uncertainty of the step height standard zlin = maximum relative deviation from linearity over the total scan range of the instrument

2afterbefore

ave

zzz

avez z

certcal cert = certified value of the step height standard

2same1samedrift zzz

afterbefore beforeave6 beforeave6 zz

if , then andafterbefore afterave6 afterave6 zz

if , then and2same1same 1samesame6 1samesame6 zz

if , then and2same1same 2samesame6 2samesame6 zz

• Supply the following inputs to the data sheet:• cert, cert

• 6ave, • 6same, • zdrift, calz, and zlin

ave6z

same6z

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• Obtain 3 2D data traces

• Obtain the platform heights (and standard deviations) from each 2D data trace

6. Measurement Procedure

zABt calplatNAtplatNBtstepN (for one trace)

3/ABcABbABaAB stepNstepNstepNstepN

All measurements are with respect to the height of the reference platform (used to level and zero the data)

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• Find Data Sheet SH.1.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 SH.1.a– Click “Reset this form”– Supply INPUTS to Tables 1 and 2– 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:

whereDSH positive difference between the step height value

of the customer, step1AB(customer), and that appearing onthe ROI, step1AB

USH(customer) step height expanded uncertainty of the customerUSH step height expanded uncertainty on the ROI, UROI

8. Using the MEMS 5-in-1To Verify Step Height Measurements

22)()( SHcustomerSHABcustomerABSH UU1step1stepD

• Then can assume measuring step height 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 SH.1.a