Optical characterization

The optical reflectivity of a laser beam is measured continuously during the film deposition in order to determine the deposition rate and the optical constants n and k at one wavelength. The analysis of the data is performed using the reflectivity formula of a single layer on the substrate for the numerical fitting [15]. The experimental set up involves an incident laser beam at 532 nm and the detection of the reflected intensity with a synchronous modulator [16].

Spectroscopic ellipsometry is a non-destructive optical measurement of the polarization change occurring when the incident light interacts with layers. The two ellipsometric functions A and ‘Fare measured at each wavelength across the spectral range of interest of the reflected light. The optical constants n and k and the thicknesses of any individual thin films inside a multilayer coating are determined from a model-based regression limited to the experimental available data. For this reason, ellipsometry is performed at different angle of incidence. The films on silicon substrates with its native oxide are subjected to ellipsometry measurements, performed by ellipsometer (SENTECH SE 850) in the range of 300 — 850 nm with variable angle of incidence ranging between 40° and 70° by steps of 10°.

The total hemispherical reflectivity at 7° angle of incidence and transmission at 0° angle of incidence measurements in the UV, VIS and NIR are performed on a Varian Cary 5 spectrophotometer.

Silicon wafers have been used as a substrate for in-situ real-time laser reflectometry and ex-situ ellipsometrywhile glass substrates have been used forex-situ spectrophotometry.

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