dawei tang , centre for precision technologies, university of...

White Light Channeled Spectrum Interferometry

for the On-line Surface Inspection Dawei Tang , Centre for Precision Technologies, University of Huddersfield

Conclusion The performance of the proposed WLCSI was evaluated by measuring two step samples. Both 2D profile results and 3D surface maps closely align with the calibrated specifications given by the manufacturers, which verifies our setup is effective for applications like the R2R surface inspection, where only defects on the film surface are concerned in terms of the quality control.

Optical simulation The WLCSI was modeled using Zemax software to get better understand the influence from the alignment errors.

Tilts of cylindrical lens (CY) only lead to the deformation of the line focusing beam on the tested surface.

Tilts of the beamsplitter (BS) will lead to a tilt of the optical axis and thus the light beam will no longer travel on the same path, which in this case straight fringes with equal interval are generated on the image plane.

BS is much more sensitive to the tilt than CY.

The authors gratefully acknowledge the UK’s Engineering and Physical Sciences Research Council (EPSRC) funding of the First Grant (Grant Ref: EP/K007068/1), the funding of EPSRC Centre for Innovative Manufacturing in Advanced Metrology (Grant Ref: EP/I033424/1) and the funding with Grant Ref: EP/K018345/1. Feng Gao gratefully acknowledge the EPSRC High Value Manufacturing Catapult Felloships.

Introduction The rapidly developing industries such as MEMS, micro fluidics, photovoltaic thin film, Si wafers and hard disks critically rely on micro/nano scale and ultra-precision structured surfaces.

The proposed WLCSI in this research project is effective for applications in on-line surface inspection because it can obtain a surface profile in a single shot. It has an advantage over existing spectral interferometry techniques by using cylindrical lenses as the objective lens in a Michelson interferometric configuration to enable the measurement of long profiles.

Experimental setup

Fig. 3. Designed prototype of WLCSI

CCD

Iris diaphragm

Collimator 2

Compressor objective

Reference mirror

Cylindrical lens

Measured surface

Diffraction grating

Imaging lens

White light source

Pin hole

Collimator 1

Fibre coupler lens

Optical fibre path cable

PC PC

Fig. 1. Schematic diagram of WLCSI

Fig. 2. Experimental optical setup

Fig. 4. Simulation results: (a) 3D layout, (b) misalignment—tilt, (c) spot diagram and interferograms resulting from alignment error

(a) (b) (c)

2014 SRWLI configuration 1_one BS_microscope.zmxConfigurations 1,2

3D Layout

SD-LCI system 26/02/2014

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White light source

CCD Camera

Cylindrical

lenses

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2014 alignment error Michelson Interferometer configuration 1_one BS_microscope.zmx

Interferogram between Configurations 1 and 2

SD-LCI system27/02/20140.5876 µm at 0.0000, 0.0000 mm.Peak to Valley = 0.2564 waves, Fringes/Wave = 1.0000.Surface: ImageExit Pupil Diameter: 6.7863E+000 MillimetersXtilt = 0.00, Ytilt = 0.00.

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X Tilt: 0.005° X Tilt: 0.001° X Tilt: 0.05°

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Y Tilt: 0.0002° Y Tilt: 0.0005° Y Tilt: 0.001°

2014 alignment error Michelson Interferometer configuration 1_one BS_microscope.zmxConfigurations 1,2

3D Layout

SD-LCI system27/02/2014

X

Y

Z

2014 alignment error Michelson Interferometer configuration 1_one BS_microscope.zmxConfigurations 1,2

3D Layout

SD-LCI system27/02/2014

X

Y

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Tilt of the cylindrical lens

Tilt of the beamsplitter

X Tilt:20° Y Tilt:10° Z Tilt:10°

Surface: 21

10000.00

OBJ: 0.0000, 0.0000 mm

IMA: 0.000, 0.123 mm

OBJ: 0.0000, 0.1250 mm

IMA: 0.000, -0.152 mm

OBJ: 0.0000, 0.2500 mm

IMA: 0.000, -0.428 mm

0.4861

0.5876

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2014 alignment error Michelson Interferometer configuration 1_one BS_microscope.ZMXConfiguration 2 of 2

Spot Diagram

SD-LCI system23/03/2014 Units are µm.Field : 1 2 3RMS radius : 2712.20 2699.10 2681.88GEO radius : 4748.89 4727.60 4703.43Scale bar : 1e+004 Reference : Chief Ray

Surface: 21

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OBJ: 0.0000, 0.0000 mm

IMA: 0.691, 0.000 mm

OBJ: 0.0000, 0.1250 mm

IMA: 0.691, -0.295 mm

OBJ: 0.0000, 0.2500 mm

IMA: 0.691, -0.590 mm

0.4861

0.5876

0.6563


Spot Diagram


Surface: 21

10000.00

OBJ: 0.0000, 0.0000 mm

IMA: 0.000, 0.000 mm

OBJ: 0.0000, 0.1250 mm

IMA: -0.028, -0.302 mm

OBJ: 0.0000, 0.2500 mm

IMA: -0.055, -0.603 mm

0.4861

0.5876

0.6563


Spot Diagram


Supervisor: X. Jiang & Feng Gao

Aim This research project aims to explore an environmentally robust surface measurement system for on-line surface inspection by using cylindrical lenses based White Light Channeled Spectrum Interferometry (WLCSI) , and to realize large dynamic measurement ratio with a high signal-to-noise ratio.

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Fig. 5. Measurement results of 9.759 µm and 30 µm step heights :(a) captured interferogram, (b) 2D profile result, (c) 3D surface map

Average Height: 9.741 µm

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(b)

(c)

Average Height: 29.893 µm

(a)

(b)

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Measurement results

Length of profile

up to 10mm

dawei tang , centre for precision technologies, university of...

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