Physical Measurement Laboratory Semiconductor and Dimensional Metrology Division

1

Physical Measurement Laboratory

Semiconductor and Dimensional Metrology Division

Nanoscale Metrology Group

MEMS Measurement Science and Standards Project

MEMS 5-in-1 RM Slide Set #2

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

– Preliminary 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 thePreliminary DetailsTopic Contents

Preparation, storage & handling

1a Processing RM 8096 and 8097

1b Post processing RM 8096

1c Packaging

1d Storage and handling

Instruments & check standards

2a Instruments used

2b Interferometer

2c Vibrometer

2d Check standards / Traceability

Uncertainties, limits, and length of certification

3a Expanded uncertainties and limits

3b Length of certification

MEMS Calculator

4a MEMS Calculator

4b Correction terms and specific standard deviations

Contents

5a Contents of each measurement slide set

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1a. Processing RM 8096 and 8097

• RM 8096– Fabricated in a multi-user 1.5 µm CMOS process– Followed by a bulk-micromachining etch at NIST

• STEP 1: CF4+O2 etch• STEP 2: XeF2 etch

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

micromachining MEMS process with a backside etch

– No additional processing is needed.

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• STEP 1: Remove the nitride cap (CF4+O2 for ~4 min.) since Young’s modulus standard applies to one layer

• Removal of nitride cap verified with stylus step height measurements (before + after the etch)

after CF4+O2

etch

Approx. same thickness for

oxide over m2 and nitride

cap.

Nitride cap removed if

~0.5 m stylus measurement.

1b. Post-Processing RM 8096(CF4+O2 Etch)

~2.7 µm SiO2

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• STEP 2: Release the beams (i.e., to etch the exposed Si around and beneath the designed beams)

Isotropic XeF2 etch (using ~25 cycles) 1 cycle: Start with pressure at 1.0 Torr

XeF2 released until 3.0 Torr Wait 10 seconds then suck out the XeF2

• Release verified with microscope or interferometer

• Biggest issue: debris in attachment corners of beams

after XeF2 etch

unreleased after etch

released after etch

1b. Post-Processing RM 8096 (XeF2 Etch)

~2.7 µm SiO2

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1c. Packaging the RMslid

non-conductive epoxy

chipPZT Contents:

•RM unit• RM chip atop PZT• Within hybrid package• Lid secured with plastic

clip

•Sits atop a piece of cleanroom paper•Sealed within a ULO bag with argon gas•Placed within a foam padded wooden box •With a memory stick of pertinent files

• Read Me First• ROI• SP260-177• Data sheets

•Shrink wrapped

NIST RM 8096

Cus

tom

er

sto

rage

:.. …

……

…

To

rem

ove

pla

stic

c

lip:…

…..

NIS

Tmemory

stick

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1d. Storage and Handling• Upon receipt of the RM:

– Remove the package assembly from the wooden box– Remove the plastic clip– Store in a dust-free inert atmosphere (such as, in N2 or

Ar gas) or under an oil-free vacuum at a temperature of 20.5 C ± 1.1 C for optimal parametric stability.

• Handling:– Handle using the metal package, without contacting the test chip– The lid should be carefully placed atop the package when the RM

is not in use.– Avoid exposing the RM to large temperature variations,

temperature cycling, large humidity variations, or mechanical shock.

– Particulate contamination may be removed with a low velocity dry N2 flow. Too high or turbulent flow can break the cantilevers so only remove it if it is near the test structure being measured.

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Topic ContentsPreparation, storage & handling



1c Packaging



2a Instruments used

2b Interferometer

2c Vibrometer





MEMS Calculator

4a MEMS Calculator


Contents


Outline for thePreliminary Details

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2a. Instruments Used

1. Optical interferometric microscope (or comparable instrument)

– In-plane length– Residual strain– Strain gradient– Step height – Thickness

• RM 8096: When applicable platforms are reflective

• RM 8097: For measurement of B and/or C (and perhaps A)

2. Optical vibrometer (or comparable instrument)

– Young’s modulus

3. Stylus profilometer (or comparable instrument)

– Thickness • RM 8096: When applicable platforms are not reflective

• RM 8097: For measurement of A (for a lower uncertainty value), if used

C

11(For in-plane length, residual strain, strain gradient, and step height measurements)

2b. A Typical Interferometer (Operated in Static Mode)

Obtains sample height data at each pixel location within the field of view.

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2b. Static Interferometric Data

20 m deflection at 220 m along a 400 m long CMOS cantilever

(at 25x)

Note that there are some data dropouts as you get farther along the cantilever

13Plot height vs. frequency to obtain resonance frequency.

2b. A Typical Interferometer (Operated in Dynamic Mode)

Obtains successive 3D images as the sample cycles through its range of motion.

For L =300 m, R02- R01 vs. Frequency

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8

9

10

11

12

13

26.0 26.5 27.0 27.5 28.0Frequency (kHz)

R02

-R01

( m

)

For L =300 m, R02- R01 vs. Phase(choose phase = 255 degrees)

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8

9

10

11

12

13

0 50 100 150 200 250 300 350Phase (degrees)

R0

2-R

01

(

m)

z

For L =300 m, Phase = 250 degreesR02- R01 vs. Frequency

(f resapp = 26.820 kHz)

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9

10

11

12

13

26.0 26.5 27.0 27.5 28.0Frequency (kHz)

R0

2-R

01

(

m)

(For Young’s modulus measurements)

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2c. A Typical Vibrometer

Obtains voltage proportional to instantaneous velocity.

(For Young’s modulus measurements)

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2c. Dual Beam Laser Doppler Vibrometer Data

Lcan=100 m, fres=168 kHzLcan=400 m, fres=14.3 kHz

Note 1: This vibrometer “flattens” the z-data and then the oscillation is exaggerated such that it looks like it is oscillating both above and below the xy-plane of the test chip, when in fact it is oscillating entirely above this plane.

Note 2: The use of a reference beam gives a wonderfully stable support!

Plot magnitude vs. frequency to determine resonance frequency.

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2d. Check Standards / Traceability• Step height standards

– To calibrate the interferometer and stylus profilometer (or comparable instruments) in the z-direction

• Every data session

– Calibrated at NIST (therefore, NIST traceable measurements)• Recalibrate at NIST once every 3 years

• Stage micrometer– To calibrate the interferometer (or comparable instrument) in the x- and

y-directions• On a yearly basis• Or, after the instrument has been serviced

– Has a calibration certificate traceable to NIST measurements• Recalibrate at NIST once every 5 years • Or, purchase a new one

• Frequency counter– To calibrate the frequency of the vibrometer (or comparable instrument)

• Every data session

– Calibrated by the vendor to provide NIST-traceable measurements• Have vendor recalibrate it (with NIST-traceable measurements) once every 5 years

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1c Packaging



2a Instruments used

2b Interferometer

2c Vibrometer





MEMS Calculator

4a MEMS Calculator


Contents



18

3a. Expanded Uncertainties and Limits

• Stability expanded uncertainty, Ustability

• Expanded uncertainty for the ROI, UROI

• Homogeneity expanded uncertainty, Uhomog

• Heterogeneity limits, Ulimit

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3a. Stability Expanded Uncertainty, Ustability

UR=exp. unc.reference value

UM=exp. unc. of newmeasured value

UD=exp. unc. of difference where D=|M-R|

•From SP 260-177 [Eq. (30)]:•If assume UM=UR=Uave, then•For a uniform distribution,

•Stability expanded uncertainty• (multiply by two, since the initial value is considered the “lowest” value and not the midpoint)

•Use for material parameters (YM, RS, SG, RStress, and StressG)•For dimensional parameters (SH, IPL, and T), assume Ustability = 0.0 µm•Can assume that Ustability.For.P1=Ustability.For.P2

3

22 avestability

UU

aveD UU 2

22RMD UUU

3

2

3aveD

stability

UUU

3232

|)()(|

32

||Dcclowhigh

stability

Uuparamuparamparamparamu

--

-

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3a. Expanded Uncertainty for the ROI, UROI

•The data sheet expanded uncertainty, UDS, and the stability expanded uncertainty, Ustability, are added in quadrature:

22stabilityDSROI UUU

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3a. Homogeneity Expanded Uncertainty, Uhomog

• Uhomog = 2 * stdev(of at least 6 parametric measurements)• Include in ROI for information purposes only

• Since each RM was individually measured at NIST• Since adding this component would make the uncertainty

unnecessarily high• Can assume that Uhomog.For.P1=Uhomog.For.P2

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3a. Heterogeneity Limits

Parameter x for 8096 x for 8097 (Lot 95 and Lot 98)

1. YM 2 2

2. RS 3 5

3. SG 5 3

4. SH 1.5 1.3

5. IPL 1.3 1.3

6. RStress 2 2.5

7. StressG 3 2.5

8. T 2.5 1.2

• Used to accept or reject RM units received from fabricator• Suggested Ulimit = xUave

• Where x is given in the table below• Include in ROI for information purposes only• Can assume that Uave.For.P1=Uave.For.P2

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• Connect 2nd and 4th points• Assume 3rd point an estimate for max separation• D=|C-M| • UD=SQRT(UC

2+UM2)

• Plot C+UD and find intersection• Recommended length of certification is 2 years (to ensure D < UD)

3b. Length of CertificationResidual Strain Data Taken at the Same Laboratory

on the Same Test Chip over a Period of Time (L =650 m, 0 degree orientation)

30

35

40

45

50

55

Jan-02 Jul-02 Jan-03 Jul-03 Jan-04 Jul-04 Jan-05 Jul-05

Month

-er

(x10

- 6)

May-02> 2 years

Aug-05M U M

C U C

C+U D

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3b. Length of Certification (for Material Parameters)

ParameterLength of

Certification Reason for Expiration

1. residual strain 2 years See last slide (variation with time)

2. residual stress 2 years residual strain is used to calculate residual stress

3. Young’s modulus

2 years Young’s modulus is used to calculate residual stress(even though this parameter is not expected to vary as a function

of time, its value may be questioned if the chip experienced unexpected environmental variations)

4. stress gradient 2 years Young’s modulus is used to calculate stress gradient

5. strain gradient 2 years strain gradient is used to calculate stress gradient(even though this parameter is not expected to vary as a function

of time, since the value of the other material parameters may be in question, this one may be as well if the chip experienced unexpected environmental variations)

• Domino effect with material parameters– For stability tests, monitor the residual strain

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3b. Length of Certification (for Dimensional Parameters)

ParameterLength of

Certification Reason for Expiration

6. step height 2 years to allow for improvements in equipment and procedures

7. thickness 2 years to allow for improvements in equipment and procedures

8. in-plane length 2 years to allow for improvements in equipment and procedures

• Dimensional parameters not expected to change with time

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1c Packaging



2a Instruments used

2b Interferometer

2c Vibrometer





MEMS Calculator

4a MEMS Calculator


Contents



27

4a. MEMS Calculator Websiteaccessible via http://srdata.nist.gov/gateway/ with the keyword

“MEMS Calculator”

Includes:1) Symbol (to help navigate the website)2) User’s Guide (for downloading)3) Data Sheets (for calculations/verification)

a) Sample data traces (analyzed)4) The MEMS 5-in-1 RMs (contact information for ordering)5) Design and tiff files (for downloading)6) SEMI standards (and links for ordering)7) ASTM standards (and links for ordering)8) MEMS terminology standards (and links for ordering)9) Other references (for downloading)

next slide

http://srdata.nist.gov/gateway/

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4a. Data Sheets(for calculations and verification)

• Young’s modulus– Data Sheet YM.3

• Residual strain– Data Sheet RS.3

• Strain gradient– Data Sheet SG.3

• Step height– Data Sheet SH.1.a

• Thickness– Data Sheet T.1 (for RM 8096)– Data Sheet T.3.a (for RM 8097)

• In-plane length– Data Sheet L.0

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4a. Data Sheets(for calculations and data verification)

• Each data sheets includes:– Identifying information– Input boxes to fill in– Estimates (if needed)– Sample data– Calculate and verify button– Outputs– How to report the results– Data verification

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4b. Correction Terms and Specific Standard Deviations

• The correction terms and specific standard deviations used at NIST in the data sheets can be found in the SP 260-177 – In Table 3 on p. 26 (for RM 8096) – In Table 4 on p. 27-28 (for RM 8097)

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1c Packaging



2a Instruments used

2b Interferometer

2c Vibrometer





MEMS Calculator

4a MEMS Calculator


Contents



32

5a. Each Measurement Slide SetIncludes (if applicable):

1 References to consult

2 Parametric description a. Overview b. Equation used c. Data sheet uncertainty equation d. ROI uncertainty equation

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

4 Test structure description 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

Documents

Physical Measurement Laboratory Semiconductor and Dimensional Metrology Division