In ellipsometry, the polarization change of a reflected light beam on a substrate is analyzed to determine the dielectric properties of thin films or their layer thickness. Once the thin films have been sufficiently precise defined, further conclusions can be drawn from the dielectric properties of the material regarding composition, crystal structure, anisotropy, conductivity, doping or roughness.
For the analysis, the incident light is initially polarized linearly and directed onto the substrate. Polarization is usually adjusted at an angle of 45° to the plane of incidence, so that the electromagnetic field of the incident beam can be divided equally into a parallel and a vertical component. The behaviour of these components in the reflection on a thin film or layer system can be described by the Fresnel formulas.
An analyzer detects the amplitude ratio and phase shift of the vertical and parallel components in the reflected beam. In addition to these measured values, a model system is also required which is created from the known parameters, e. g. layer thicknesses of the thin film or the layer system. The analysis software now adapts the parameters still unknown from the model in Fresnel's formulas until the experimental data are reproduced with the smallest possible error.
Woollam M2000
The M2000 is a spectroscopic ellipsometer that offers a wide spectral range and enables very fast measurements. With 470 wavelengths, the M2000 covers a wavelength range of 245 nm - 1000 nm. The near infrared upgrade installed in 2015 extends the measuring range with an additional 190 wavelengths from 1005 nm to 1690 nm. The angle of incidence can be traversed fully automatically from 45° - 90°. A measurement typically takes only a few seconds per angle of incidence. The modular design also enables operation directly on coating systems for in-situ growth control.
