Ellipsometry
Ellipsometry is an optical technique used to measure and characterize the physical and optical properties of surfaces. By analyzing how the polarization of light changes upon interacting with the sample, ellipsometry helps establish a multitude of information about the properties of materials including thin films, semiconductors, polymers, and coatings.
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What is ellipsometry used for?
Ellipsometry provides insight into the optical properties, such as dielectric function and refractive index, of various materials. Ellipsometry can be used to determine the thickness of thin films down to atomic levels, making the technique particularly useful in the production of semiconductors, polymers, and coatings. Its non-destructive nature makes ellipsometry an ideal technique for analyzing delicate films, including those fabricated using the ALD and MLD techniques.
How does ellipsometry work?
Ellipsometry measures the changes in the way that light is polarized after interacting with a thin film sample. To begin, light is passed through a polarizer, which restricts the orientation of the beam coming out on the other side. The beam then interacts with the sample and either reflects or transmits through it. The reflected/transmitted light is picked up by a detector that measures the changes in the polarization of the light. These changes are then compared to a model of the sample to infer information about its properties.
Single-wavelength vs. spectroscopic ellipsometry
Single-wavelength ellipsometry uses a single-wavelength laser for analysis. This allows the system to probe a very small area of the sample with a powerful light source, providing very specific data on that location. This makes single-wavelength ellipsometry ideal for in-depth analysis on a small scale. However, the drawback is that it can only record one data set per measurement.
Spectroscopic ellipsometry, on the other hand, uses a broadband light source that produces a full spectrum of wavelengths from ultraviolet to infrared. This light cannot be focused in the same way as a single wavelength source, but it can record multiple data points at once, making spectroscopic ellipsometry better suited for the overall analysis of complex structures.
Suitable samples and sample preparation
Typically, ellipsometry samples are in the form of thin films with a thickness between 1 nm and 1,000 nm. The films should be transparent or semitransparent to allow for light to be passed through. In addition, the roughness should not be too high, as this may scatter the light away from the detector.
Advantages and limitations of ellipsometry
Ellipsometry is a non-invasive, non-destructive technique that does not damage the film it is analyzing, which is essential when testing sensitive samples. It can be used on a range of sample types, and delivers consistently accurate results with high sensitivity, even to nanoscopic levels.
A significant disadvantage of ellipsometry is that the film must be as flat and free of contaminants as possible. This means that producing a suitable substrate will be challenging for some materials. Furthermore, testing transparent films set on top of a substrate can introduce interference from the substrate, which will need to be accounted for when interpreting the results.
Suitable sample matrices
- Transparent and translucent films
- Semiconductors
- Polymers
- Metal layers
- Organic and biological coatings
- ALD and MLD deposited films
Ideal uses of ellipsometry
- Measuring the thickness of single and multi-layered thing films
- Determining the optical properties of thin films
- Analyzing crystal structures and compositions
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Frequently asked questions
Ellipsometry is used to characterize the properties, such as thickness and refractive index, of thin film and bulk materials.
The measured film should be optically flat meaning that it reflects light from the surface. Too rough surfaces scatter a beam away from the detector which prevents the ellipsometric measurement. The film must also be transparent or semitransparent so that light can pass through.
The preferred thickness of the sample is between 1 nm and 1000 nm.
Ellipsometry can be used for a wide variety of thin films including semiconductors, polymers, dielectrics, and even metal layers.
Measurlabs offers a variety of laboratory analyses for product developers and quality managers. We perform some of the analyses in our own lab, but mostly we outsource them to carefully selected partner laboratories. This way we can send each sample to the lab that is best suited for the purpose, and offer high-quality analyses with more than a thousand different methods to our clients.
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