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|Equipment||Woollam M-2000 Ellipsometer|
Ellipsometry uses elliptically polarized light reflected off of the measurement sample to allow for extraction of both thickness and optical constants (n,k or e1,e2) for transparent and semi-transparent thin films.
Woollam M-2000 Ellipsometer
Main article: Woollam M-2000 Ellipsometer
Spectroscopic ellipsometer with 190-1700nm wavelength range.
Method of operation
- Elliptically polarized light is reflected from the measurement sample and is analyzed in p- and s- vector components.
- p- polarized light is in the plane of incidence
- s- polarized light is perpendicular to that plane.
- Reflected p- and s- light will have different amplitude and phase shifts which depend on optical properties of the substrate and thin film and the film thickness. This causes polarization of the light to change.
- The change in polarization is measured as Delta (∆) and Psi (Ψ).
- Delta is the phase shift between the two vector components of the elliptically polarized light.
- Tan(Psi) is the amplitude attenuation ratio of the two components.
- A model is fit to this data to extract thin film thickness and optical parameters.
- Spectroscopic ellipsometry measures delta and psi vs. wavelength of light reflected off of the sample. Our Woollam M-2000 Ellipsometer is a spectroscopic tool. Ellipsometry measurement at only a single wavelength has shortcomings of a non-unique thickness solution (a thickness repetition cycle) and poor accuracy within a repeating cycle of certain film thickness ranges.
- Since ellipsometry measures both intensity and phase information, thickness and optical constants can be extracted. Spectroscopic reflectometry only measures reflected intensity vs. wavelength and is only capable of extracting film thickness by using a fixed set of optical constants for the thin film material in a material file stored on the tool.
Ellipsometry is most often used for the characterization of thin film thickness and material optical constants.