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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

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spectroscopic ellipsometry

Spectroscopic Ellipsometry

University of Texas at El Paso

Lynn Santiago

Dr. Elizabeth Gardner

Chem 5369

ellipsometry an essential tool for characterizing nanomaterials
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

Introduction

How it works

Setup

Light Source

Components and Functions

Equation

Advantages

Single Wavelength Ellipsometry

Setup

Components and Functions

Advantages/Disadvantages

Imaging Ellipsometry

Setup

Components and Functions

Advantages/Disadvantages

Outline
introduction to spectroscopic ellipsometry
Introduction to Spectroscopic Ellipsometry
  • It is used for a variety of measurements:
    • Thickness of films.
    • Optical properties.
    • Modeling of surface roughness.
  • Ellipsometry is:
    • well known
    • non-destructive
    • precise
    • accurate
    • analytical technique
using ellipsometry to characterize nano electronic based materials
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.
    • 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
How does ellipsometry work?
  • 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

5. Detector

Linearly Polarized Light

1. Light Source

4. Analyzer

2. Linear Polarizer

3. Compensator

Sample

Elliptically Polarized Light

Spectroscopic Ellipsometry Setup
light source
Light Source
  • The light source consists of wavelengths in the following regions
    • Ultraviolet
      • 185nm – 260nm
    • Visible
      • 0.4nm – 0.7nm
    • Infrared
      • 0.7nm – 1.1μm

http://www.flame-detection.net/flame_detector/flame_detection_school/flame_spectrum.htm

swe components and functions
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

  • Depending on orientation, it transforms the ellipse of polarization
    • 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
Calculating Change in Polarization
  • This is the equation used to calculate the change in polarization.

Ρ=Rp/Rs=tan(Ψ)eiΔ

    • 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 r p and r s components

rp

rs

What are Rp and Rs components?

Rp = |rp|2

Rs = |rs|2

se advantages
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
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
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

5. Detector

Linearly Polarized Light

1. Light Source

4. Analyzer

2. Linear Polarizer

3. Compensator

Sample

Elliptically Polarized Light

Single Wavelength Ellipsometry Setup
swe light source
Light Source – This is a laser with a specific wavelength

Commonly a HeNe laser with the wavelength of 632.8 nm

SWE Light Source

This is not from an ellipsometer but shows what a HeNe laser looks like.

http://www.technology.niagarac.on.ca/courses/phtn1333/

pros and cons of swe
Pros and Cons of SWE
  • Advantages:
    • Laser can focus on a specific spot
    • Lasers have a higher power than broad band light sources
  • Disadvantage:
    • Experimental output is restricted to one set of Ψ and Δ values per measurement
taking it a step further
Taking it a Step Further

Now there exists the technology to use ellipsometry and view a sample while it is being analyzed.

imaging ellipsometry
Imaging Ellipsometry
  • Combines SWE with Microscopy
  • High Lateral Resolution
    • Possible to see tiny samples
  • High contrast imaging capabilities to detect various properties of samples
    • surface defects
    • Inhomogenities
  • Provides spatial resolution for a variety of areas
    • 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

Imaging Ellipsometry Setup

Two New

Components

imaging components and functions
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
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
Acknowledgements
  • David Echevarría – Torres
  • Dr. Elizabeth Gardner
references
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/Ellipsometry_principle__150dpi_s.pdf
  • http://www.wikipedia.org