Material sensitive scanning probe microscopy of subsurface semiconductor nanostructuresvia beam exit Ar ion polishing

Abstract

Whereas scanning probe microscopy (SPM) is highly appreciated for its nanometre scaleresolution and sensitivity to surface properties, it generally cannot image solid statenanostructures under the immediate sample surface. Existing methods of cross-sectioning(focused ion beam milling and mechanical and Ar ion polishing) are either prohibitivelyslow or cannot provide a required surface quality. In this paper we present a novel methodof Ar ion beam cross-section polishing via a beam exiting the sample. In this approach, asample is tilted at a small angle with respect to the polishing beam that enters fromunderneath the surface of interest and exits at a glancing angle. This creates analmost perfect nanometre scale flat cross-section with close to open angle prismaticshape of the polished and pristine sample surfaces ideal for SPM imaging. Usingthe new method and material sensitive ultrasonic force microscopy we mappedthe internal structure of an InSb/InAs quantum dot superlattice of 18 nm layerperiodicity with the depth resolution of the order of 5 nm. We also report using thismethod to reveal details of interfaces in VLSI (very large scale of integration) lowk dielectric interconnects, as well as discussing the performance of the new approach for SPMas well as for scanning electron microscopy studies of nanostructured materials and devices.