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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
X
Y
Z
White light source
CCD Camera
Cylindrical
lenses
Y
Z
X
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0.7000
0.8000
0.9000
1.0000
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.
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0.7000
0.8000
0.9000
1.0000
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 = 0.5127 waves, Fringes/Wave = 1.0000.Surface: ImageExit Pupil Diameter: 6.7863E+000 MillimetersXtilt = 0.00, Ytilt = 0.00.
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0.7000
0.8000
0.9000
1.0000
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 = 2.5638 waves, Fringes/Wave = 1.0000.Surface: ImageExit Pupil Diameter: 6.7867E+000 MillimetersXtilt = 0.00, Ytilt = 0.00.
X Tilt: 0.005° X Tilt: 0.001° X Tilt: 0.05°
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0.7000
0.8000
0.9000
1.0000
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 = 1.1305 waves, Fringes/Wave = 1.0000.Surface: ImageExit Pupil Diameter: 6.7863E+000 MillimetersXtilt = 0.00, Ytilt = 0.00.
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0.7000
0.8000
0.9000
1.0000
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 = 0.5652 waves, Fringes/Wave = 1.0000.Surface: ImageExit Pupil Diameter: 6.7863E+000 MillimetersXtilt = 0.00, Ytilt = 0.00.
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0.7000
0.8000
0.9000
1.0000
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 = 0.2261 waves, Fringes/Wave = 1.0000.Surface: ImageExit Pupil Diameter: 6.7863E+000 MillimetersXtilt = 0.00, Ytilt = 0.00.
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
Z
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
0.6563
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
10000.00
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
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 : 2614.66 2616.96 2626.02GEO radius : 4856.06 4854.59 4850.17Scale bar : 1e+004 Reference : Chief Ray
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
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 : 2860.34 2907.06 2819.04GEO radius : 4850.37 4877.73 4901.96Scale bar : 1e+004 Reference : Chief Ray
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.
0 50 100 150 20010
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Pixel number
He
igh
t (µ
m)
0 50 100 150 2006
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He
igh
t (µ
m)
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
(a)
(b)
(c)
Average Height: 29.893 µm
(a)
(b)
(c)
Measurement results
Length of profile
up to 10mm
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