Precision of Silicon Oxynitride Refractive-Index Profile Retrieval Using Optical Characterization

Abstract

Layers with gradient refractive-index profile are an attractive alternative to conventional homogeneous stack coatings. However, the optical characterization and monitoring of the graded refractive-index profile is a complex issue, which has been typically solved by using a simplified model of mixed materials. Although this approach provides a solution to the problem, the precision, which can be expected from optical characterization of the refractive index gradient, remains unclear. In this work, we study optical characterization of SiO x N y layers deposited via reactive dual ion beam sputtering. To characterize the deposited layers, we use several methods including reflectance, and transmittance spectra at a broad range of incident angles, together with spectral ellipsometry. All the data were simultaneously fitted with a general profile of refractive index. The expected profile used in our fit was based on characterization of SiO x N y layers with a varying stoichiometry. By altering of the profile, we discussed sensitivity of such alternation on fit quality and we studied ambiguity of merit-function minimization. We demonstrate that while the scanning of particular parameters of the profile can be seemingly very precise, we obtain a very good agreement between the experimental data and model for a broad range of gradient shapes, where the refractive-index value on major part of the profile can differ as much as 0.02 from the mean value.

Optically modified second harmonic generation in silicon oxynitride thin films via local layer heating

“…1 C. We denote silicon oxynitride layers by the flow of oxygen used during the layer deposition. While ϕ(O 2 ) = 0 sccm corresponds to the pure Si 3 N 4 , the flow of ϕ(O 2 ) = 3 sccm leads to the formation of nearly SiO 2 layers 23 . The estimate of stoichiometric factors for each sample is provided in Supplementary information, Sect.…”

“…We carried out a detailed study of the linear optical properties of the layers in Ref. 23 . The thickness of the layers varied between 300 and 3500 nm.…”

Probing buried interfaces in SiOxNy thin films via ultrafast acoustics: The role transducing layer thickness

“…The samples were prepared by using dual ion-beam sputtering (DIBS), as it is described in detail elsewhere. [2] We deposited a set of homogeneous layers of silicon oxynitride SiOxNy with distinct stoichiometry varying from Si3N4 up to SiO2 by introducing a different flow of oxygen. A Ti layer (2 ns and 10 nm) was deposited on the top of the layer.…”

“…We present a thorough study of silicon oxynitride thin films with a controlled stoichiometry of samples covering the entire range from Si3N4 up to SiO2. [2] We used ultrafast acoustics to study the properties of layers and their interface with the Si substrate. The optoacoustic response was attained by using a thin Ti layer on the top of the layer as an optoelectronic transducer.…”