UV-Vis-IR Ellipsometry ELL

Ellipsometry is a method of measuring the film thickness, refractive index, and extinction coefficient of single films, layer stacks, and substrate materials with very high sensitivity. Rough surfaces, interfaces, material gradients and mixtures of different materials can be analyzed. 

Film thicknesses between 0.1 nm and 100 pm can be measured, depending on the spectral range used for the analysis and the homogeneity of the thicker films. Thicknesses 1 pm can be determined with a sensitivity better than 0.01 nm. Thicknesses in the micron-range can be analyzed with sensitivity typically better than 1 nm. 

The refractive index of a film or a substrate material can be measured with a sensitivity better than 5 x 10, the best available for non-invasive optical measurement methods, especially for thin films. The extinction coefficient can be measured with almost the same sensitivity, which corresponds to a lower limit of 10-100 cm for the absorption coefficient of the material. 

The number of measurable layers of a stack is limited only by the optical contrast between the different layers. In practice stacks of ten layers and more can be analyzed by ellipsometry. Further advantages of ellipsometry compared with other metrological methods are the non-invasive and non-destructive character of the optical method, the low energy entry into the sample, the direct measurement of the dielectric function of materials, and the possibility of making the measurement in any kind of optical transparent environment. 

The principal of measurement is shown schematically in Fig. 4.61. Linear polarized light is reflected from a sample surface which must be flat and sufficiently reflecting. The state of polarization of the incident light is changed, by reflection, into ellipti- 

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