Spectroscopic ellipsometry study

Increasing applications of thin polymer layers on solid substrates are of high technological importance. Spectroscopic ellipsometry study has appropriate characterization methods which are necessary for the design and analysis of devices made using such materials. In general, ellipsometry is the method of choice for the correct determination of optical constants; it provides polarization degree and phase as well as the amplitude information of the optical response.

These quantities may be derived within one experiment and thereby optical simulations and quantitative interpretation are improved for many applications. For many polymers, no characteristic absorption bands are observed in the visual spectral range. Therefore, extension of the spectral range to the IR and ultraviolet (UV) regions is desirable because characteristic vibrational or electronic absorptions are available within these ranges. However, it must be considered that many polymers might be degraded by intense UV irradiation. Visual ellipsometry is a standard method for determination of the optical constants, roughness and film thickness.  Bare polymer surfaces, single polymer spectral range has become established over recent years because of the large amount of valuable information that can be derived from the analysis of characteristic vibrational bands. As with visual ellipsometry, optical constants and structural properties of thin films and layered systems can reliably be derived using IR ellipsometric measurements by strict correlation with optical theory. The extensive analytical potential of IR ellipsometry is based on:

• Contactless and non-invasive measurement,
• Monolayer sensitivity,
• Identification of chemical bonds of the film and interface by characteristic vibrational absorption bands,
• Optical modeling with respect to molecular orientations, composition, miscibility, inter-diffusion and interactions at interfaces

Thus, the combined application of IR and visual ellipsometry are powerful tool for quantitative analysis of thin isotropic and anisotropic polymer layers. The determined optical constants of the single materials are important quantities for the quantitative interpretation of optical spectra and can, moreover, be used as input for interpretation of spectra of thin films.