Sciences et Techniques Industrielles de la Lumière STIL - Le Mercure Batiment C - 80, rue Charles Duchesne - 13851 Aix en Provence Cedex 3 - France Téléphone

Sciences et TechniquesIndustrielles de la Lumière

STIL - Le Mercure Batiment C - 80, rue Charles Duchesne - 13851 Aix en Provence Cedex 3 - FranceTéléphone : 33 (0)4.42.39.45.85 - Télécopie : 33 (0)4.42.24.38.05

STIL - Email : [email protected]

QUASI CONFOCAL EXTENDED FIELD SURFACE SENSING

Joseph COHEN-SABBAN, Pierre-Jean CREPIN, Jérôme GAILLARD-GROLEAS

STIL SA

Optical Metrology for the Semicon, Optical and Data Storage Industries

SPIE’s 46th Annual Meeting - San Diego, CA 2-3 August, 2001



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CONFOCAL IMAGING

The « SINGLE POINT » viewing system

Confocal imaging consists in :

1) Imaging a point source S into a sharply focused point S’

2) Reversely, imaging this sharply focused point S’ onto a tiny spatial filter S’’

Such an optical setup is absolutely blind for all the space except for the sharply focused point S’.

S

S’

S’’

L

point source

spatial filter

- Email : [email protected]





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defocused specular object defocused backscattering object

The Property of « Optical Sectioning »

L

S

A’S’’

A

L

S

B’S’’

B

sharp focusposition S’

CONFOCAL IMAGING






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« Z-axis » FIELD EXTENSION IN CONFOCAL IMAGING

The field extension can be obtained by stretching the chromatic aberration of the focusing lens L.

The new optical system is then the assembling of an infinity of purely confocal systems, one for each wavelength.

Such a compound system is absolutely blind for all the space except for the sharply focused color coded segment [S’(S’(n]

Continuum of monochromaticimages S’ (i)

PolychromaticPoint Source

Spatial filter

L

S

S’’

1

n

i

The SINGLE LINE viewing system






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EXTENDED FIELD CONFOCAL IMAGING

The property of PERFECT FOCUS




The SINGLE LINE viewing system presents the unique property of « PERFECT FOCUS » over all the chromatic EXTENDED FIELD since at any given point of the axial field of view there is only one wavelength perfectly focused on the object, all the other wavelengths being absolutely inactive.

L

Extended field



STIL - Email : [email protected]

EXTENDED FIELD CONFOCAL SCANNING OPTICAL MICROSCOPY

AVOIDS THE Z-AXIS STEPPING PROCESS USED TO GENERATECONFOCAL SLICES THAT ARE COLLECTED TO CREATE

A PERFECTLY FOCUSED IMAGE



EF - CSOM

AVOIDS THE TIME CONSUMING COMPUTER RECONSTRUCTION OF THE OBJECT IMAGE

CAN PROVIDE HIGHLY ACCURATE3D SURFACE METROLOGY

WHEN AN ADEQUATE SPECTRAL DECODING IS IMPLEMENTED



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3D SURFACE METROLOGY (1)




3D SURFACE METROLOGY CAN BE ACHIEVED WHEN SUCCESSIVELY PERFORMINGTHE FOLLOWING STEPS.

SPACE CODING

By stretching the axial chromatic aberration of the illuminating beam

SPACE DECODING

By analysing the spectral content of the backscattered / backreflected beam



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The confocal spatial filter limits the wavelengths bandwidth to a narrow band centered on the wavelength i coming in perfect focus onto the object surface.




Continuum ofmonochromaticimages S’ (i)

PolychromaticPoint Source

Spatial Filter

monochromatic image

Object Surface

Spectrometer

S’’(i)

S’

L

1

n

I

I

i

S

The spectral decoding is performed by the spectrometer (position of the return quasi monochromatic beam on the CCD linear array).



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I

i

The system is volontarily renderedQuasi-Confocal by enlarging the Point Source and the Spatial Filter pinholes.

Consequently, the filtered bandwidth is enlarged in order to enable a highly resolved post processing and to get 30000 resolved points along the color coded segment [S’(1), S’(n)].



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CHR 150 BLOCK DIAGRAM



Fiberoptic linkOptical pen

Polychromaticlight source Spectrometer

Digital Signal Processing

Analogic and digitaloutputs

OPTOELECTRONIC CABINET

Fiberoptic coupler

n




STILOptical Metrology for the Semicon, Optical and Data Storage Industries




CHR 150 OPTICAL PENS

Depth of field 20 µm 80 µm 300 µm 350 µm 3 mm 6 mm 10 mm

Working distance 0,6 mm 2,1 mm 4,5 mm 12 mm 38 mm 53 mm 65 mm

Z axis resolution 1 nm 3 nm 10 nm 10 nm 100 nm 200 nm 300 nm

Accuracy 10 nm 30 nm 0,1 µm 0,1 µm 1 µm 2 µm 1 µm

Spot diameter 1 µm 2 µm 4 µm 1,5 µm*

10 µm 40 µm 50 µm

Lateral resolution 0,5 µm 1 µm 2 µm 0,75µm

5 µm 20 µm 25 µm

Numerical aperture 0,69 0,57 0,5 0,5 0,26 0,26 0,17

Max angular slope(+/-)**

44° 35° 30° 30° 15° 15° 10°

* With an optical fiber of 10 microns core diameter** On specular surfaces. For scattering surfaces the maximum angular slope can reach 80 degrees



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CHR 150 SIGNAL OUTPUTS (1)




MEASURING MODE :

* Single Surface mode :

- Intensity, Height : Both data are acquired simultaneously

* Double Surface mode :

- Intensity and height of the first surface- Intensity and height of the second surface- Thickness : calculated in real time

acquired simultaneously



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CHR 150 SIGNAL OUTPUTS (2)




Analog Signals :

- 2 configurable outputs 0 - 10 V

Digital Signals:

- RS 232 serial link at 115200 bauds. - Birectionnal link used to :

. transmit the measuring data to a PC . configure and drive the sensor from a PC

Synchronization input and output :

- 5V TTL signals.






CHR 150 Optical Sensor

Optoelectronic Cabinet

Optical pens



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Diamond machined Diffractive Germanium lens

CHR 150 Optical Sensor 80 µm depth of field optical pen

3D surface mappingHeight measurement

Photorealistic renderingIntensity measurement





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Diamond machined Diffractive Germanium lens


3D surface mapping - Height measurement

Profile extracted along the black line





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Holographic Transmission diffraction grating (ZnSe)








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Groove top of a Holographic Transmission diffraction grating (ZnSe)


Roughness component filteredwith a 0.04 mm cut-off

Waviness component filteredwith a 0.04 mm cut-off



Groove top area





CCD matrix area


3D surface metrologyof a CCD matrix area

Surface wavinessof the same CCD matrix area





CCD matrix area


3D surface metrologyof a CCD matrix area

Surface wavinessof the same CCD matrix area



STILSciences et Techniques

Industrielles de la Lumière

STIL

CHR 150 Optical Sensor80 µm depth of field optical pen



Photogravure processed in LIGA technology





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Optical Waveguide








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Ball Grid Array (BGA)





Profile extracted along the white line

Zoom on one bumps line



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Field Emission Display flat screen










Micro Opto Electro Mechanical System (MOEMS)









Microlens array

3D surface mapping - Height measurement





Molded microlens



Photographic representation





Scratch on a Germanium lens



Extracted profile n°1 Extracted profile n°2

Extracted profile n°3

3

1

2



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Gold deposition on Alumina substrate









Laser marking on a component packaging



Profile extracted from the black line





Paper






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Microwave Generator






Alumina

Gold



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Roughness of S1

Roughness of S2

Thickness mapping : e = e ( x , y )




THICKNESS MAPPING

DUAL SURFACE ROUGHNESS MAPPING

Advantages

* single side information pick-up* purely optical measurement* very fast* very accurate

Dedicated software

Polychromatic point source

White light

Spectrometer

S1

S2



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Advantages

* thickness measurement mode* single side information pick-up* purely optical measurement* very fast* very accurate


Dedicated software

White light

Spectrometer

Object surface : S2Thickness mappinge = e ( x , y )

S2 = S ( x , y )

Reference Surface : S1


ABSOLUTE 3D SURFACE MAPPING





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OPTICS MANUFACTURING QUALITY CONTROL

Advantages

* no need to reverse the lens* purely optical measurement* very fast* very accurate

Single Shot, FRONT and BACK SURFACES PICK-UP

Dedicated software


White light

Spectrometer

Radiuses : R1 R2

Tilt, Centeringdiameter Central thickness

R1

R2diameter






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Advantages

* purely optical measurement* no moving parts* very fast* very accurate

z2 (2) - z1 (1) = R

Spherical objectRadius R

Spectrometer


White light

C




SINGLE SHOT SPHEROMETRY






CONCLUSION

Implementation of controlled axial chromatic aberration to

CONFOCAL SCANNING OPTICAL MICROSCOPY

opens new ways to the application fields of :

The proposed optical setup is capable of giving both information simultaneously.

* Perfect Focus Free Shape Surface Microscopy

* Free Shape 3D Surface Metrology

Documents

Sciences et Techniques Industrielles de la Lumière STIL - Le Mercure Batiment C - 80, rue Charles Duchesne - 13851 Aix en Provence Cedex 3 - France Téléphone