From Color to Chemometrics
Strategies to determine coating thickness and quality
Preliminary Version
AIMCAL Web Coating & Handling Conference 2016
02.06.2016
Chris Hellwig
Agenda
1
About us
2
Process and Quality Control
3
Color as Quality Criterion
4
Color as Thickness Indicator
5
Chemometrie as Thickness Indicator
6
Conclusion
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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ZEISS Business Groups
Industrial Metrology
Microscopy
Medical Technology
4.51
Billion EUR Revenue
369
Million EUR (EBIT)
~25,000
Employees (worldwide)
Semiconductor
Manufacturing Technology
Vision Care
Financial Highlights of the ZEISS Group
Consumer Optics
Carl Zeiss Jena GmbH
Carl Zeiss Spectroscopy GmbH
Subsidiary of Carl Zeiss Jena GmbH
Update 30 September 2015
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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Agenda
1
About us
2
Process and Quality Control
3
Color as Quality Criterion
4
Color as Thickness Indicator
5
Chemometrie as Thickness Indicator
6
Conclusion
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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Quality and process control
Measured value
- Full transmission spectra
- Full reflectance spectra
Calculated / derived values
- Color metrics (e.g. L*,a*, b*)
- Spectral results (e.g. min/max)
- Layer thickness
- Chemometrics (Layer content
analyses, derived layer thickness)
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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Review: AIMCAL 2014
Not precise and not accurate
Accurate, but not precise
Precise, but not accurate
Precise and accurate

Process control capable
Quality control capable
Tolerances influenced by:
- Measurement System
- Reference Method
- Calibration Standards
- Process Conditions
Source: wikipedia.org
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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Use Cases of a Process / Quality Control System
3 scenarios when using a process
control software: Commisioning,
product developement and
improvement
Where do we generally need
precision, where accuracy?
precision
accuracy
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
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Absolute Measurements
Traditional way to calibrate spectral measurements
• Use of certified calibration standard
(mirror, white standard)
Absolute Measurements
• No need of certified standards
• Internal calibration by switching between
calibration and measurement
(enables absolute measurements even with the
sample in measurement position)
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
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•
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Peak method:
The layer thickness is derived from the
maxima and minima of the interference
spectrum
White light interference
The layer thickness is calculated from
the periodicity of the interference
spectrum
Color as a thickness indicator
Color changes with the layer thickness
Model based approaches
A layer stack is described by formulas
(the model), the result is compared with
measurement results, parameters of the
model like thickness are varied as long
as they fit the measurement results
Chemometric models
Chemometric prediction models provide
thickness informrmation
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
complexity
Methods to evaluate Coating Thickness
Interference spectrum
Poly-crystalline silicon layers on silicon oxide
W.Theiss Hard- and Software
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Agenda
1
About us
2
Process and Quality Control
3
Color as Quality Criterion
4
Color as Thickness Indicator
5
Chemometrie as Thickness Indicator
6
Conclusion
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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Color as Quality Criterion: Basics
If color appearance itself is a quality
criterion it can be measured directly:
-
-
ISO / CIE standardized setup for
accurate measurements (comparable
with standards, inter-instrument
agreement)
full spectrum sensor requested by ISO /
CIE organization to overcome
metamerism issues
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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Agenda
1
About us
2
Process and Quality Control
3
Color as Quality Criterion
4
Color as Thickness Indicator
5
Chemometrie as Thickness Indicator
6
Conclusion
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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Color as Thickness Indicator: Preparation
For simple layer designs a correlation of the
thickness and a color value may exist and this
correlation needs to be found. This theoretical
calculation can be performed prior to any real
measurement (using modelling software)
The data show a good correlation between
thickness and the b* value for this specific layer.
For process control a 3rd order polynomial based
on the data was used to calculate the coating
thicknesses from the measured b* values.
On six ZnO coated glass panes (S1 – S6) the b*
values were measured and the predicted
thickness results are shown
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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Color as Thickness Indicator: Result
The example shown demonstrates the
tuning of the coating process to bring the
layer to specified thickness.
x
Cross section plots of coating thickness
variation
x
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
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Agenda
1
About us
2
Process and Quality Control
3
Color as Quality Criterion
4
Color as Thickness Indicator
5
Chemometrie as Thickness Indicator
6
Conclusion
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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Determination of Grammage on Paper:
Preparation
The paper samples were measured on a 45°:0°
diffuse reflectance probe connected to an NIR
spectrometer with a spectral range of 1340 –
2000 nm.
The setup was calibrated with a diffuse reference
material. The paper samples’ grammage values
ranged from 0.19 to 4.14 g/m².
Each of the 13 samples was measured at three
spots. The spectra of the samples with a
grammage of 0.19, 1.80, and 4.14 g/m² were
used to develop a calibration function
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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Agenda
1
About us
2
Process and Quality Control
3
Color as Quality Criterion
4
Color as Thickness Indicator
5
Chemometrie as Thickness Indicator
6
Conclusion
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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The Importance of Accuracy
•
•
Color as thickness indicator: Photometric accuracy is important for this method
Chemometric prediction: Will work with non-accurate (but precise) systems as well:
BUT: The developed methods will only work on the system they are developed with
• No scaling possible
• In case an instrument or parts of the system needs to be changed, the method needs
to be adopted
•
Peak method: Only wavelength accuracy needed
•
White light interference: Only wavelength pitch accuracy needed
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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The Freedom of Choice
Different methods of thickness evaluation
Choose the simplest possible method to obtain thickness information
(peak method,, color, model based, chomometrics)
Example: Silicone on paper and PET substrates
< 100 nm
150 nm - 600 nm
0.5 µm - 3 µm
Paper
Method
Result
Instrument
on request (but
'questionable')
Chemometric
Thickness
NIR 2.2 µm
Chemometric
Thickness
NIR 2.2 µm
PET
Method
Result
Instrument
spectra eval
on request (but
YES vs NO
'questionable')
VIS / Trans
Modell based
Thickness
VIS / T or R
FFT
Thickness
VIS (NIR) / T or R
Substrate
Silicone Thickness
20 nm
Chemometric: We need a bunch of samples, thickness evaluation for set of test samples with comparision method; additional (embedded) software necessary
Modell based: We need optical parameters of substrate and material(s) and some samples with known properties for check; additional (embedded) software necessary
FFT: Wee need optical parameters of coating material, only 1 sample to check performance
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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Complete Quality and Process Control
The final product quality is defined as a combination of many features like color
appearance or coating thickness.
Since inline spectrometers measure the full spectrum these quality-related parameters
can be evaluated in one single step.
Broadband inline spectrometer systems allow chemometric prediction in the NIR range as
well as color evaluation, even within a single measurement system.
+
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
= Result
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General Conclusion
It is shown that inline spectrometers and combined analysis of the results are versatile
and stable process-capable measurement systems to
• commission new production lines
• develop new coating products
• keep a production line stable
• ensure the final product quality
The data provided by such instruments can be used
• for direct monitoring of the production process.
• as an input for automated control loops
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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Contact
http://www.zeiss.com/spectroscopy/en_de/industries/glass-solar-.html
Chris Hellwig
Product Manager ThinFilm
Phone: +49 3641 64 3788
E-Mail: [email protected]
Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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Carl Zeiss Spectroscopy GmbH, Chris Hellwig, SPC-P
Preliminary Version 2016-04-01
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