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Développement de systèmes de contrôle in situ des propriétés optiques de filtres interférentiels

Abstract : The FRESNEL Institute’s Research Team on Optical Thin Films (RCMO) owns a set of vacuum deposition machines using technologies based on physical vapor deposition (PVD). The realization of complex filtering functions requires a perfect mastering of the deposition process as well as accurate real-time monitoring of the optical thickness of the deposited layers. There are different monitoring techniques based on physical or optical methods, the principle consisting in the latter case to follow the evolution of the spectral performance of the stack during its formation. As an example, we can cite the monitoring methods called Monochromatic or Broadband. During my Ph.D. thesis, devoted to the development of new methods of in situ optical monitoring, I was particularly interested in two different subjects, namely : - On the one hand, the determination of the spectral dependence of optical constants (refractive index and extinction coefficient) of dielectric materials. Indeed, the knowledge of these constants is a key issue for the manufacturing of high-performance optical filters and a possible way to achieve this determination consists of using a broadband optical monitoring system in order to record the transmission spectra, in real-time, of the stack during its formation. Indeed, the temporal evolution, at each wavelength, of these transmission spectra provide quantitative information related to the optical constants that we wish to determine. I therefore theoretically established the mathematical nature of this relation, and applied this method to determine the optical constants of tantala (Ta2O5) and silica (SiO2) layers deposited through a Dual Ion Beam Sputtering (DIBS), and this without the use of index dispersion models. - On the other hand, the real-time measurement of the reflection coefficient (r) of a stack, in amplitude and phase, during its deposition. Indeed, the optical monitoring methods based on intensity properties present some limitations that the knowledge of phase information should overcome. This measurement is performed by low coherence digital holographic interferometry on a substrate illuminated by its rear face and whose front face is equipped with an annular mask. This gives access to desired phase and amplitude information while avoiding the parasitic influence of the substrate motions induced by the vibrations of the deposition machine, and the rotation of the substrate holder at 120 rounds per minute. This method allows us to perform a phase mapping of the central zone of the substrate during the deposition runs of high and low index materials. Obviously, this method can be extended to the monitoring of more complex stacks.
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Séverin Landry Nadji. Développement de systèmes de contrôle in situ des propriétés optiques de filtres interférentiels. Optique / photonique. Aix Marseille Université, 2018. Français. ⟨tel-02794833⟩

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