Ellipsometry is an optical technique commonly used for thin-film and surface property analysis by the reflection or transmission of polarized light. The change in polarization state is measured and correlated with material properties. Infinita Lab, USA, offers this test effectively and accurately.
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Ellipsometry is an optical measurement technique that is based upon the fact that linearly polarized light, incident at an oblique angle to a surface, becomes elliptically polarized when it is reflected, transmitted, or scattered. Ellipsometry measures the change in amplitude and the phase difference and relates it to material and surface properties using theoretical models. The ellipsometry arrangement will comprise a light source, polarization generator, test sample, polarization detector, analyzer and data processing system. There are three different types of ellipsometry, namely reflection, transmission and scattering ellipsometry. The determination of a wide range of material and surface properties such as refractive index, film thickness, film uniformity, surface roughness and surface oxides can be done by Ellipsometry.
Ellipsometry is often used to measure the thickness of thin films on top of a substrate, from sub-nanometer to a few micron thicknesses. The wavelength of the incident light needs to be adjusted appropriately to minimize light absorption by the material. Some organic films may strongly absorb light at UV and IR wavelengths but not at mid-visible wavelengths. However, in metals, all wavelengths are absorbed, so the maximum layer for film thickness by Ellipsometry is typically about 100 nm. Mie-Scattering Ellipsometry is used on particles whose size are larger than incident wavelength, to measure size and refractive index of particles using ellipsometric parameters of elastically scattered light. In the semiconductor industry, the thickness of a thin layer of SiO2 on a silicon wafer can be measured at the accuracy of angstrom units using Ellipsometry.
Common Uses of Ellipsometry
Determination of Thickness and refractive index of thin films
Calculation of pseudo-dielectric function of a substrate
Determination of surface roughness or uniformity
Study of solid-liquid or liquid-liquid interfaces
Advantages of Ellipsometry
Extremely sensitive to very thin films
Non-invasive, non-destructive, non-contact
Determines several film properties simultaneously
Rapid and reliable
Measured parameters are independent of beam intensity.
Simple and versatile, and can be performed in a wide range of experimental environments
Limitations of Ellipsometry
If the surface is too rough, it scatters the probe beam away from the detector, which prevents spectroscopic ellipsometry measurements.
Films thicker than several tens of microns experience interference oscillations