Coherence Scanning Mircroscope

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SureshK.RamasamyPhDMarch 2013

COHERENCESCANNINGINTERFEROMETRY

Part1.Basics,CalibrationandAdjustment

SKRCSI1ASMETUTORIALS2013

Noncontact areal surface measurement systems Coherence scanning interferometer Standards ISO, ASME Part standards Vibration test Calibration, adjustment procedures Objective focus optimization

Email id: [email protected]

OUTLINE

Sciencestartswheremeasurementstarts D.I.Mendeleev

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QUESTIONS?


Potential3DMeasurementInstruments

Contacting StylusChromatic Length Aberration Confocal MicroscopySEM StereoscopyScanning Tunneling MicroscopyAtomic Force MicroscopyOptical Difference Profiling Angle Resolved SEM

Areal TopographySenses Z(X,Y) or

Z(X) as a function of Y

TriangulationFastMoirInterferometerConfocalMicroscopePhaseShiftingInterferometerVerticalScanning(WhiteLight)Interferometer

Promise Speed & accuracy Laboratory

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Triangulation

1 . F a n g J u n g S h i o u , M i n X i n L i u , D e v e l o pm e n t o f a n o v e l s c a t t e r e dt r i a n g u l a t i o n l a s e r p r o b e w i t h s i x l i n e a r c h a r g e c o u p l e d d e v i c e s ,O p t i c s a n d L a s e r s i n E n g i n e e r i n g , 4 7 ( 2 0 0 9 ) 7 1 8

2 . S t a g e o n e : L i g h t R e f l e c t i o n Mo d e l s f r om we b s i t eh t t p : / /www . g r a p h i c s . c o r n e l l . e d u / r e s e a r c h / g l o b i l l um / r e f l mo d e l . h tm l ,a s o f 0 5 / 0 5 / 2 0 1 0

Working principle of a triangulation probe based on Scheimpflugs principle

Bi-directional reflectance distribution model


MoirInterferometer

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ChromaticLengthAberration


Top

Bottom

ConfocalMicroscopy

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-20 -10 0 10 20z axis (micrometers)

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Focu

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Fig 3b20X

Gradient

LED Light source480 nm

PBS Microdisplay

CCD

Objective

ConfocalMicroscopy


Waves of Light

Wavelength

Light is comprised of wavelengths of energy

The length determines the color of l ight

White l ight (a combination of different wavelengths) provides a larger measurement range.

TheoryofLight

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Interference is the phenomenon caused by superposition of two electromagnetic waves

When these two waves are in phase then the result is a bright band and if they are out of phase the result would be a dark band

Mathematical Representation :

is the interference term.

(2 1) is the phase difference between two waves.

Constructive Interference

Destructive Interference

TheoryofInterference


TheoryofInterference

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SampleSurfacesandtheirpatterns


WLI.Underthehood

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Differentwaystofindthepeak


InterferenceFringes

Fromfringesto3Dsurfacemap

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CoherenceScanningInterferometera

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a Light source (halogen / LED)b Dichoric mirrorc Laser source (optional)d Opticse Aperture stopf Field stopg 45 Mirrorh Beam splitteri Interferometric objectivej Reference mirrork Measured surfacel Scanner (PZT / Stepper motor)m Zoom / magnification tube setupn Beam splittero Polarizer (Optional)p Detector 2 (Optional)q Polarizerr Detector 1 (CCD / CMOS)



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NT8000 (Veeco) CCI (Taylor Hobson) NV6300 (Zygo)

ExamplesofCSIsystems


Configurations

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ISOStandards ISO / TC 213 / WG16 25178

NominalCharacteristics 602 Confocalchromaticprobe 603 Phaseshifting interferometric microscopy 604 Coherencescanning interferometric microscopy 605 Pointautofocusprobe 606 Focusvariation 607 ImagingconfocalmicroscopyCalibration 702 Confocalchromaticprobe 703 Interferometric microscopy


NPLGPGs Good Practice Guide No. 108: Guide to the Measurement of

Smooth Surface Topography using Coherence Scanning Interferometry

Good Practice Guide No. 116: Guide to the Measurement of Rough Surface Topography using Coherence Scanning Interferometry

Giusca CL, Leach RK, Calibration of the metrological characteristics of areal surface topography measuring instruments, Proceedings of the 2nd International Conference on Surface Metrology 2010, WPI, USA pp. 145153.

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ReferenceFlatStandard Silicon Carbide Surface SubAngstrom level flatness Used to establish bestcase measurement capability


StepHeightStandard Chromium coated on etched Quartz surface NIST Traceable Calibration and adjustment of Z axis measurements

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LateralCalibrationStandard Platinum coating on etched Silicon dioxide surface NIST Traceable Setting magnification and TRC


OpticalDimensionalStandard Chrome on glass photomask NPL Traceable

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SurfaceRoughnessSpecimens ISO 5436 1:2000

TypeC(Spacingmeasurementstandards) TypeD(Roughnessmeasurementstandards)

NIST Traceable ITF and Algorithm depenedencies

a

b

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Cross sectional profiles of (a) random surface (b) sinusoidal surface and (c) square wave surface.


Siemens Star

Weckenmannetal,Practiceorientedevaluationoflateralresolutionformicro andnanometermeasurementtechniques,MeasurementScienceandTechnology,20(2009)065103(8pp)

ITF and Algorithm dependencies

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Vibrations

(a) Measurements taken under ideal environment (b) under high vibration levels, seen as ripples of missing data.

a b


Vibrations

y = 0.6255x + 2.3434R2 = 0.9951

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Peak to peak noise level (nm)

Mea

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(1 S

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Calibration

Z axis Systemswithreferencesignal Systemswithoutreferencesignal

Stepheightartifactbasedusercalibration XY axis

Presetmagnification Usertunablemagnification

Lateralcalibrationstandardbasedusercalibration Specificforeachobjectiveandzoomtubesetting Linear doesntincludewarpingerrors


ZaxisCalibration

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LateralCalibration


LateralCalibration steps

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TRCSetup

Image of one corner of Lateral calibration standard used for finding offset between different magnifications


ReferenceMirrorFlatnessError

Reference mirror surface error map for a chosen magnification (objective and zoom tube combination)

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ObjectiveFocusOptimization

Effect of focus on roughness for selected samples with varying roughness values

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Part 1 Part 2 Part 3 Part 4 Part 5 Part 6

Low (< 40 nm) Medium (41 - 80 nm) High (81 - 120 nm)

Pa (n

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After 50x Focus Pa (nm) After Defocus Pa (nm) After Refocus Pa (nm)

Coherence Scanning Mircroscope

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