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Light interactions with periodic nanoline arrays for nanoelectronic applications

Boek - Dissertatie

Periodic nanolines arrays are ubiquitous in modern nanoelectronics, covering both the front- and back-end-of-line in the form of, respectively, semiconductor-based fin field-effect transistors (FinFETs) and metallization made of copper, tungsten, or, in the future, the platinum-group metals. Due to their non-contact nature, optical techniques are a promising candidate for the metrology and manufacturing of such devices. However, the introduction of optical tools in a routine in-line integration scheme of nanoline-based devices is still very challenging, as they rely on the efficiency of the light coupling and absorption inside 3D nanoscale arrays, which both are strongly geometry-dependent. In this thesis, we develop the fundamental understanding of the light interactions with periodic nanoline arrays.In order to build the sought understanding, we first derive a simple semi-analytical model capable of quantifying the light interactions, e.g. reflectance, with periodic nanoline arrays. The model replaces a nanoline array with an effective homogeneous uniaxial medium (i.e. a crystal whose refractive index along one axis differs from this along two other axes) optically characterized by the complex effective refractive indices of the dominant waveguide modes excitable within the array.Subsequently, we use the model to qualitatively explain how geometry impacts the optical responses, e.g. reflectance or transmittance, of various periodic nanoline arrays, calculated using numerical simulations. As we demonstrate, the light interactions with the structures of industry-relevant dimensions are governed by the excitation and thin-film interference of the fundamental waveguide mode, i.e. the lowest order mode supported by such arrays. Therefore, the optical properties of such volumes can be associated with the complex effective refractive index of the fundamental mode.Next, we use the complex effective refractive index of the fundamental mode to investigate the size- and direction-dependent optical properties of the Si nanoline arrays with the industry-relevant dimensions. Among others, we show that the optical properties of such arrays can be tailored to values larger or smaller than these of the materials constituting the array. For example, specific dimensions allow to slow down the light, resulting in an enhanced absorption of Si nanolines as compared to bulk Si, when using a wavelength from the vicinity of the resonance in the refractive index of Si. Moreover, we prove that such geometries can indeed be optically treated as effective homogeneous uniaxial media, when the incidence from air is considered.Finally, we use the model to quantitatively explain Raman scattering and reflectance spectra measured experimentally on periodic arrays of semiconducting and metallic nanolines. This allows us to verify the correctness of the developed model as well as extend the applicability of Raman spectroscopy towards the metrology of nanolines.The fundamental physical understanding developed in this thesis serves as an enabler for laser-based metrology and fabrication of 3D nanoscale devices for nanoelectronics and nanophotonics.
Jaar van publicatie:2021
Toegankelijkheid:Open