Accurate 3D reconstruction of silicon micro/nanostructures, based on high resolution FIB-SEM tomography: Application to Black Silicon

We present an accurate 3D reconstruction method for silicon micro/nanostructures with high aspect ratio, that was developed and implemented using a dual beam (Focused ion beam and scanning electron microscopy (FIB-SEM)) tomography. Black Silicon (BSi) samples were processed by alternating steps of FIB etching and SEM imaging, that allow obtaining sequential cross section images of the sample, including micro/nano-scale details. After performing a series of image data processing steps, 3D models of BSi surfaces are obtained. Comparison with SEM micrographs recorded prior to the etching yields striking resemblance, down to the nanometer-scale details of the structure. This method allows accurate determination of the topography even for very high aspect ratio structures, where competing non-destructive 3D reconstruction techniques based on SEM pixel intensity are limited by the SEM dynamical range. The resulting 3D models allow us to perform accurate simulations of black silicon's optical properties, and calculate topographic parameters, such as height distribution, average ratio and obtain exact figures for the total surface area enhancement. The imaging techniques we have developed allow us to confirm that our BSi samples consist of a bottom-up auto generated pattern and not the result of micro-masking.