Conjunction of ellipsometry and IBA:Ellipsometry provides information on the sample structure complementary to that obtained from ion beam analysis (IBA). Information on film thicknesses, on dielectric functions (or refractive index and extinction coefficient), as well as on structural properties like density, roughness, texture and crystallographic orientation (anisotropy) is obtained. This information is necessary for unambiguous IBA-data analysis and the information on the composition provided by IBA is needed for optical data analysis.
The major advantages of ellipsometry are:
- absolutely non-destructive
- capable of mono-layer sensitivity
- can be applied in almost every environment (vacuum, gases, liquids)
- typical time-resolution in the range of ms up to seconds (ms possible)
Basics:Ellipsometry is an optical technique that measures the change in polarization state of a light beam after it has interacted with a sample. Two parameters, related to the change in polarization, are measured at a given wavelength l and angle of incidence (F). They are expressed as a complex number, r, or as an amplitude and a phase: r(l,F) = tan Y * exp (i D). The phase parameter D has no counterpart in reflectivity and transmission measurements and is largely responsible for the extraordinary, monolayer sensitivity of ellipsometry.
One main advantage of ellipsometry compared to reflectometry is that, no absolute intensities have to be measured but only intensity ratios. Thus, the intensity of the source, the sensitivity of the detector, or absorption by windows or other components do not influence the data, resulting in significantly smaller absolute errors of ellipsometric data compared to reflectivity data.
Like all optical techniques for thin film analysis, the evaluation of ellipsometric data requires optical multi-layer model calculations in combination with regression algorithms to determine the model parameters that provide the best fit of calculated to measured data. It has to be verified, that the model is physically meaningful and that it is the only model that provides a good fit of calculated to measured data. All additional information on the sample structure like that from IBA is helpful in finding the appropriate model.
- Variable Angle of Incidence Spectroscopic Ellipsometer (VASE), l=250-1700 nm,
- Spectroscopic in-situ ellipsometer (M-44), J.A.Woollam Co. Inc.
- single wavelength (HeNe) in-situ ellipsometer, self-made
with AutoRetarder option, J.A.Woollam Co. Inc.
44 wavelengths, l=340-630 nm
Topics of the current research:
- boron nitride thin films
- in-situ analysis of growth
- ex-situ analysis of anisotropy
- in-situ plasma process diagnostic
- plasma etching I (depth profiling in conjunction with in situ ERD)
- plasma etching II (Si, SiO2, Si3N4)
- damage and phase formation in 6H-SiC
- He bubbles in Si