High Resolution Microsphere-Assisted Interference Microscopy for 3D Characterization of Nanomaterials

Nanoscale materials are nowadays widely used in many different modern technologies. Special attention is thus required for their characterization in order to optimize fabrication processes. However, current characterization systems which can achieve nanometric resolution over a large area and in three dimensions are few. Classical optical microscopy presents a resolving power limited by diffraction, making impossible the visualization of elements with a size under half the wavelength. Recently, several methods have thus been developed to overcome this limitation, among them microsphere-assisted microscopy. Indeed, using a transparent microsphere, a full-field image of the sample can be retrieved with a higher resolution than the diffraction-limit. In this paper, this new imaging technique is combined with phase-shifting interferometry in order to reconstruct the 3D surface of nanostructures. An enhancement of a factor of 4.0 in the lateral resolution is demonstrated while combining this with the nanometric axial sensitivity of interferometry. Results are shown of the topography of reference gratings as well as periodic Ag nano-dots on silicon and laser induced ripples in steel, spaced by a few hundred nanometres. A comparison of these results is made with those from SEM and atomic force microscopy.