Abstract
The study was devoted to optical characterization of non-stoichiometric silicon nitride films prepared by reactive magnetron sputtering in argon-nitrogen atmosphere onto cold (unheated) substrates. It was found that these films exhibit the combination of three defects: optical inhomogeneity (refractive index profile across the films), uniaxial anisotropy with the optical axis perpendicular to the boundaries and random roughness of the upper boundaries. The influence of the uniaxial anisotropy was included into the corresponding formulae of the optical quantities using the matrix formalism and the approximation of the inhomogeneous layer by a multilayer system consisting of large number thin homogeneous layers. The random roughness was described using the scalar diffraction theory. The processing of the experimental data was performed using the multi-sample modification of the least-squares method, in which experimental data of several samples differing in thickness were processed simultaneously. The dielectric response of the silicon nitride films was modeled using the modification of the universal dispersion model, which takes into account absorption processes corresponding to valence-to-conduction band electron transitions, excitonic effects and Urbach tail. The spectroscopic reflectometric and ellipsometric measurements were supplemented by measuring the uniformity of the samples using imaging spectroscopic reflectometry.
Highlights
Silicon nitride thin films are intensively utilized in practice
They are employed as antireflection coatings in silicon solar cells because of their suitable optical properties owing to the silicon optical properties
The optical characterization of the samples of the amorphous SiNx films prepared by reactive magnetron sputtering onto silicon single substrates was performed. These films exhibit three defects, i.e., inhomogeneity represented by profiles of the optical constants across the films, artificial optical anisotropy in the optical constants corresponding to uniaxial anisotropy with the optical axis perpendicular to the boundaries and random roughness of the upper boundaries
Summary
Silicon nitride thin films are intensively utilized in practice. They are employed as antireflection coatings in silicon solar cells because of their suitable optical properties owing to the silicon optical properties (see, e.g., [1,2,3,4]). In [11], spectroscopic ellipsometry was employed for the optical characterization of the SiNx films deposited onto silicon single substrates in spectral range 1.5–4.0 eV. The optical characterization of the samples of the amorphous SiNx films prepared by reactive magnetron sputtering onto silicon single substrates was performed. These films exhibit three defects, i.e., inhomogeneity represented by profiles of the optical constants across the films, artificial optical anisotropy in the optical constants corresponding to uniaxial anisotropy with the optical axis perpendicular to the boundaries and random roughness of the upper boundaries. On the basis of the results achieved for these samples, the practical usefulness of the method is presented
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