Fundamental study of the size-dependent optical properties of periodic arrays of nanoscale semiconducting fin structures

Understanding the interaction of light with semiconducting nanostructures is of increasing importance for nanoelectronic, photonic and photovoltaic applications. However, the physical mechanisms responsible for the... [ view full abstract ]

Understanding the interaction of light with semiconducting nanostructures is of increasing importance for nanoelectronic, photonic and photovoltaic applications. However, the physical mechanisms responsible for the size-dependent optical properties of such structures are not fully understood, as typically studied with purely numerical tools. In this work, we develop an analytical model for the size-dependent optical properties, such as reflectance, of periodic arrays of nm-scale semiconducting fins. Using a mode matching technique, we show that size-dependent optical properties of such structures are due to coupling between diffraction modes existing outside the arrays and waveguide modes inside the arrays. The model is validated with scatterometry spectra collected on Si fin arrays of varying geometry (Fig.1), as well as finite-element simulations. A good agreement for sub-400 nm part of the spectra is achieved, while a red-shift of the supra-400 nm part w.r.t. the model is attributed to the tilt of the fin sidewalls. We prove that the tilt is not impacting the near-UV spectra due to high absorption and low refractive index of Si in this range. Finally, we show that for sub-40 nm fins only 2 waveguide modes are sufficient to explain the complex spectra. The generated insight is crucial for the understanding of optical properties of nm-scale structures and will mitigate manufacturing, metrology and design of nanoelectronic, photonic and photovoltaic devices.