Ellipsometry of individual layers

The ellipsometric data consist of the / and A spectra in the range 300 to 850 nm for different incident angles between 40° and 70°. Consequently, we have made a systematic study of the optical properties of individual dielectric layer for Ti02, Si02 and Al203. The model consists of a single uniform film on silicon substrate. These data were fitted with a widely used Cauchy dispersion formula for Ti02, Si02 and Al203i where the refractive index n and extinction coefficients kare given by:

n(A)= n0 + + C^

(1)

k(A) = k0 + + C1k4.

(2)

Пі, ki, Ci are constants and я is the wavelength in nm. We take C0 =102 and C1 =107, which are mostly used, to avoid large values of ni, ki, n2 and k2.

The films were modeled as homogeneous dielectric layers on a semi-infinite silicon substrate. A native silicon dioxide interlayer was included in the model. Surface roughness was neglected.

The experimental / and A for deposited Ti02, Si02 and Al203 on silicon substrate combined with the best theoretical fits using the Cauchy dispersion model, permits to determine the optical properties of individual films. A good agreement between the fit and the experimental data is observed between 250 and 850 nm for Si02 and Al203, and above 350 nm in the case of Ti02 thin film, which confirms our results previously obtained for the same deposition conditions [11].

Figure 1 shows the refractive index n as a function of the wavelength in the UV-Vis for Ti02, Si02 and Al203 on silicon substrate. The results of the fit parameters confirm that no absorption occurs in the films. It should be noted here that the thicknesses of dielectric layers are in a good agreement and are within 5% of the determined one by the laser reflectometry.

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