BAHIRDAR UNIVERSTY COLLEGE OF SCIENCE DEPARTMENT :MATERIAL SCIENCE AND ENGINNERING PRESENTETON ON: ELLIPSOMETRY INSTRUMENT PREPEARED BY :ZELALEM GETU AMSALE GETNET CHALE GETNET JAN 13\2017

OUTLINE Introduction Theory Working principle of Ellipsometry Type of Ellipsometry Application area Reference

Introduction Ellipsometry is an optical technique for investigating the dielectric properties (complex refractive index or dielectric function) of thin films. It enables to measure the refractive index and the thickness of semi-transparent thin films. It can be used to characterize composition, roughness, thickness (depth), crystalline nature, doping concentration, electrical conductivity and other material properties.

Cont……. An ellipsometer can be used to measure layers as thin as 1 nm up to layers which are several microns thick Applications include ; The accurate thickness measurement of thin films The identification of materials and Thin layers and the characterization of surfaces.

Cont……. Ellipsometry measures the change of polarization upon reflection or transmission and compares it to a model. In the visible, NIR, and UV, this technique is particularly well suited to semiconductors and semiconductor based structures

Theory The technique of ellipsometry was invented by Paul Drude in 1887 who used it to determine the dielectric function of various metals and dielectrics. It has since become one of the most important and powerful tools for the characterization of optical properties, in particular, of thin-film- and multi-layered materials.. Ellipsometers are widely applied in industry for characterization and on-line quality control

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Few key people in ellipsometry area Malus in 1808 : discovery of the polarization of light by reflection. Fresnel in 1823 : Wave theory of the light. Maxwell in 1873 : development of the Electromagnetic field theory. Drude in 1888 : Use of the extreme sensitivity of the ellipsometry to detect

Working principle of ellipsometry  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.

Cont……….  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

Image of Ellipsometry

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Types of Ellipsometry  Spectroscopic Ellipsometry  Single Wavelength Ellipsometry  Imaging Ellipsometry

Spectroscopic Ellipsometry spectroscopic ellipsometry measures change in polarization R p = |r p | 2 R s = |r s | 2. rprp rsrs

Cont…… This is the equation used to calculate the change in polarization. Ρ = R p /R s = tan(Ψ)e iΔ Ρ = change in polarization R p = component oscillating in the plane of incidence R s = component is oscillating perpendicular to the plane of incidence Tan Ψ = amplitude ratio of reflection Δ = phase shift

Cont……… It used for a variety of measurements: Thickness of films. Optical properties. Modeling of surface roughness

Spectroscopic Ellipsometry Setup

Spectroscopy Ellipsometry Advantages 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

Single-wavelength ellipsometry Single-wavelength ellipsometry employs monochromatic light source. This is usually a laser in the visible spectral region, for instance, a HeNe laser with a wavelength of nm. Therefore, single-wavelength ellipsometry is also called laser ellipsometry.

Single Wavelength Ellipsometry Setup

Cont……… 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

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 In homogeneities

Cont……….. Provides spatial resolution for a variety of areas Microanalysis Microelectronics Bio-analysis

Imaging Ellipsometry Setup

Cont…….. 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

Cont…….. 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

Cont…… Disadvantages: The inclined observation angle Only a limited area of the image appears to be well- focused when using conventional optics

Application area Biological material Nanoscale Industry

Reference N. W. Ashcroft and N. D. Mermin, Solid State Physics, Brooks/Cole, H. G. Tompkins and E. A. Irene, Handbook of Ellipsometry, William Andrew Publishing, 2005 J. A. Woolum Co. [ try_principle__150dpi_s.pdf

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