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Spectroscopic
Ellipsometry
University of Texas at El Paso
Lynn Santiago
Dr. Elizabeth Gardner
Chem 5369
Ellipsometry – An Essential Tool for
Characterizing Nanomaterials
“[The ellipsometry] methods are
the workhorse analyses
of a laboratory, as they are used on
almost every project involving
surface chemistry, whether it be a
silicon surface or a metal surface.”
James, D.K., Tour, J.M.. Analytica Chimica Acta 568 (2006) 2-19
Outline
 Spectroscopic
Ellipsometry
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Introduction
How it works
Setup
Light Source
Components and Functions
Equation
Advantages
 Single Wavelength
Ellipsometry
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Setup
Components and Functions
Advantages/Disadvantages
 Imaging Ellipsometry
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Setup
Components and Functions
Advantages/Disadvantages
Introduction to Spectroscopic Ellipsometry
 It is used for a variety of measurements:
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Thickness of films.
Optical properties.
Modeling of surface roughness.
 Ellipsometry is:
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well known
non-destructive
precise
accurate
analytical technique
Using Ellipsometry to Characterize
Nano-electronic-based Materials
 The technique is used for the determination of physical
properties of organic molecular electronic-based
devices.
 It is commonly used for the characterization of self-
assembled monolayers (SAMS), substrates, polymers
and thin layers.
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It can probe molecular assemblies such as SAMS.
Doesn’t change their physical characteristics.
Determines whether you have single or multiple layers
assembled on a surface.
How does ellipsometry work?
1.
2.
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4.
5.
6.
7.
Light is shined from a light source.
The light is polarized by passing through a linear polarizer.
The light is then elliptically polarized by passing through a
compensator.
The light hits the sample, is reflected and is linearly
polarized.
The analyzer detects the change of polarization.
The detector catches the light and send it to the computer
to process the data.
The measured data combined with computerized optical
modeling gives information of the film thickness and
refractive index values of a sample.
Spectroscopic Ellipsometry Setup
Multiple Wavelengths
Unpolarized Light
Linearly Polarized Light
1. Light Source
4. Analyzer
2. Linear Polarizer
3. Compensator
Sample
Elliptically Polarized Light
5. Detector
Light Source
1. The light source consists of wavelengths in the
following regions
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Ultraviolet
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Visible
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185nm – 260nm
0.4nm – 0.7nm
Infrared
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0.7nm – 1.1μm
http://www.flame-detection.net/flame_detector/flame_detection_school/flame_spectrum.htm
SWE Components and Functions
2. Polarizer - produces light in a special state of
polarization at the output
3. Compensator - used to shift the phase of one
component of the incident light
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Depending on orientation, it transforms the ellipse
of polarization
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Linearly polarized light into elliptically polarized light
when set to 45° in respect to the linear polarization
axis.
4. Analyzer – second polarizer that detects the
linearly polarized light reflected off the sample
5. Detector
http://www.nanofilm.de/fileadmin/cnt_pdf/technology/Ellipsometry_principle__150dpi_s.pdf
Calculating Change in Polarization
 This is the equation used to calculate the change
in polarization.
Ρ = Rp/Rs = tan(Ψ)eiΔ
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Ρ = change in polarization
Rp = component oscillating in the plane of incidence
Rs = component is oscillating perpendicular to the plane
of incidence
Tan Ψ = amplitude ratio of reflection
Δ = phase shift
What are Rp and Rs
components?
rp
Rp =
2
|rp|
Rs = |rs|2
rs
SE Advantages
 No contact with the films is required for the
analysis of films
 Technique does not require a reference or
standards
 It provides both the phase and amplitude ratio of
a sample
 Analysis is less sensitive to the fluctuations of
light intensity
Concentrating the Light Source
We have seen that spectroscopic ellipsometry
uses a range of wavelengths to analyze a sample.
Now we will see an instrument that uses the
same concept but uses one particular
wavelength of light to analyze a sample.
Single Wavelength Ellipsometry
 Also known as Laser Ellipsometry
 Used in Imaging Ellipsometry
 Uses a light source with a specific wavelength
http://www.eas.asu.edu/nanofab/capabilities/metrology.html
Single Wavelength Ellipsometry
Setup
One Wavelength
Unpolarized Light
Linearly Polarized Light
1. Light Source
4. Analyzer
2. Linear Polarizer
3. Compensator
Sample
Elliptically Polarized Light
5. Detector
SWE Light Source
This is not from an
ellipsometer but shows what
a HeNe laser looks like.
 Light Source – This is a laser with a specific
wavelength
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Commonly a HeNe laser with the wavelength of
632.8 nm
http://www.technology.niagarac.on.ca/courses/phtn1333/
Pros and Cons of SWE
 Advantages:
Laser can focus on a specific spot
 Lasers have a higher power than broad
band light sources
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 Disadvantage:
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Experimental output is restricted to one
set of Ψ and Δ values per measurement
Taking it a Step Further
Now there exists the technology to use
ellipsometry and view a sample while it is
being analyzed.
Imaging Ellipsometry
 Combines SWE with
Microscopy
 High Lateral Resolution
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Possible to see tiny samples
 High contrast imaging
capabilities to detect various
properties of samples
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surface defects
Inhomogenities
 Provides spatial resolution
for a variety of areas
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Microanalysis
Microelectronics
Bio-analysis
http://www.soem.ecu.edu.au/physics/physics_facilities.htm
Imaging Ellipsometry Setup
Unpolarized Light
CCD Camera
Linearly Polarized Light
Laser Light Source
Analyzer
Linear Polarizer
Compensator
Objective
Sample
Elliptically Polarized Light
Two New
Components
Imaging Components and
Functions
 Objective – images the illuminated
area of the sample onto the camera
 CCD Camera - a camera with an
image sensor that is an integrated
circuit made with light sensitive
capacitors
http://www.nanofilm.de/fileadmin/cnt_pdf/technology/Ellipsometry_principle__150dpi_s.pdf
Pros and Cons of Imaging Ellipsometry
 Advantages:
 Provides film thickness and refractive index
 Provides a real time contrast image of the sample
 Ability to restrict ellipsometric analysis to a
particular region of interest within the field-of-view
 The signal provided is spatially resolved to show
the details of the sample
 Disadvantages:
 The inclined observation angle
 Only a limited area of the image appears to be
well-focused when using conventional optics
Acknowledgements
 David Echevarría – Torres
 Dr. Elizabeth Gardner
References
 James, D.K., Tour, J.M.. Analytica Chimica Acta 568 (2006) 2-19.
 Goncalves, D., Irene, E.A.. Quim. Nova, Vol. 25, No. 5, 794-800.
 Nanofilm Surface Analysis
http://www.nanofilm.de/fileadmin/cnt_pdf/technology/Ellipsom
etry_principle__150dpi_s.pdf
 http://www.wikipedia.org
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