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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. “[The ellipsometry] methods are the workhorse analyses

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Spectroscopic Ellipsometry

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  1. Spectroscopic Ellipsometry University of Texas at El Paso Lynn Santiago Dr. Elizabeth Gardner Chem 5369

  2. 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

  3. 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

  4. 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

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. 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

  10. 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

  11. rp rs What are Rp and Rs components? Rp = |rp|2 Rs = |rs|2

  12. 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

  13. 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.

  14. 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

  15. 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

  16. 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/

  17. 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

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

  19. 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

  20. 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

  21. 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

  22. 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

  23. Acknowledgements • David Echevarría – Torres • Dr. Elizabeth Gardner

  24. 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

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