Ellipsometry thin films

In the case of Langmuir monolayers, film thickness and index of refraction have not been given much attention. While several groups have measured A versus a, [143-145], calculations by Knoll and co-workers [146] call into question the ability of ellipsometry to unambiguously determine thickness and refractive index of a Langmuir monolayer. A small error in the chosen index of refraction produces a large error in thickness. A new microscopic imaging technique described in section IV-3E uses ellipsometric contrast but does not require absolute determination of thickness and refractive index. Ellipsometry is routinely used to successfully characterize thin films on solid supports as described in Sections X-7, XI-2, and XV-7. 

D. D. Eley, ed., Adhesion, The Clarendon Press, Oxford, 1961. E. Passaglia, R. R. Stromberg, and J. Kruger, eds., Ellipsometry in the Measurement of Surfaces and Thin Films, National Bureau of Standards Miscellaneous Publication 256, Washington, DC, 1964. 

Ellipsometry measurements can provide infomiation about the thickness, microroughness and dielectric ftinction of thin films. It can also provide infomiation on the depth profile of multilayer stmctiires non-destmctively, including the thickness, the composition and the degree of crystallinity of each layer [39]. The measurement of the various components of a complex multilayered film is illustrated m figure Bl.26.17 [40]. 

Ellipsometry can be sensitive to layers of matter only one atom thick. For example, oxidation of freshly cleaved single-crystal graphite can be monitored from the first monolayer and up. The best thicknesses for the ellipsometric study of thin films are between about 1 nm and 1000 nm. Although the spectra become complicated, films thicker than even 1 pm can be studied. Flat planar materials are optimum, but surface and interfacial roughness can be quantitatively determined if the roughness scale is smaller than about 100 nm. Thus ellipsometry is ideal for the investigation of interfacial surfaces in optical coatings and semiconductor struc-... 

RAIRS spectra contain absorption band structures related to electronic transitions and vibrations of the bulk, the surface, or adsorbed molecules. In reflectance spectroscopy the ahsorhance is usually determined hy calculating -log(Rs/Ro), where Rs represents the reflectance from the adsorhate-covered substrate and Rq is the reflectance from the bare substrate. For thin films with strong dipole oscillators, the Berre-man effect, which can lead to an additional feature in the reflectance spectrum, must also be considered (Sect. 4.9 Ellipsometry). The frequencies, intensities, full widths at half maximum, and band line-shapes in the absorption spectrum yield information about adsorption states, chemical environment, ordering effects, and vibrational coupling. 

Ellipsometry in the vacuum UV (< 190 nm) enables the analysis of materials for the next generation lithography (photoresist, AR coatings) at the latest exposure wavelengths (157 nm and 193 nm). The short wavelengths increase the sensitivity of ellipsometric measurements of ultra thin films (<10 nm). New prospects are expected for the analysis of thin metallic and dielectric layers. 

Infrared ellipsometry is typically performed in the mid-infrared range of 400 to 5000 cm , but also in the near- and far-infrared. The resonances of molecular vibrations or phonons in the solid state generate typical features in the tanT and A spectra in the form of relative minima or maxima and dispersion-like structures. For the isotropic bulk calculation of optical constants - refractive index n and extinction coefficient k - is straightforward. For all other applications (thin films and anisotropic materials) iteration procedures are used. In ellipsometry only angles are measured. The results are also absolute values, obtained without the use of a standard. 

Infrared (IR) spectroscopy and elUpsometry are used to measure the thickness of thin films with angstrom resolution. Ellipsometry has proven to be very useful in studies of dy-... 

The excitation of an SEW using a single prism is seen as a dip in the reflectivity from the prism base (see Fig. 8) when the angle of incidence satisfies Eq. (8). The location in angle of the minimum in reflectivity, the depth of the minimum and its width are very sensitive to the presence of an overlayer on the metal substrate. Pockrand, et al.— have pointed out that this technique is considerably more sensitive than ellipsometry for measuring the optical properties of thin films. They also discuss the problems due to the fact that the dye films are really anistropic. 

H. Roseler Infrared Spectroscopic Ellipsometry (Akademie Verlag, Berlin, 1990) O.S. Heavens Optical Properties of Thin Films (Butterworths Scientific Publications, London, 1955) S. Adachi Optical Properties of Crystalline and Amorphous Semiconductors (Kluwer, Boston, 1999)... 

Ellipsometry is the study of the change of polarization of a light wave impinging on a solid surface and partially reflected from it, which is modified by the wavefunction of the substrate or of the molecules adsorbed on it (Fig. 11.36) (see Section 2.15 for the mathematics). It is a nondestructive method to study the optical properties of thin films and is sensitive to even just a monolayer of inorganic, organic, or biochemical adsorbates on a flat surface. 

Spectroscopic ellipsometry repeats all measurements at several source wavelengths, and a Cauchy77 fit to the data will yield values for n, k, and t for a thin film. For crystals, the dielectric tensor can also be obtained. 

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