Visualization of interior structures with nanoscale resolution using ultrasonic-atomic force microscopy

Ultrasonic-Atomic Force Microscopy (U-AFM) was applied to determine the feasibility of visualizing interior features in an ultra-thin film system. As the amplitude and phase of the cantilever resonance frequency changes with local contact stiffness, U-AFM can obtain both surface and subsurface topographic and elastic images. Specimens with nanostructured silicon dioxide (SiO₂) patterns deposited on silicon (111) surfaces were fabricated and covered with polymethyl methacrylate (PMMA) films with thicknesses of 800 nm and 1400 nm, respectively. While subsurface features were barely distinguishable beneath the 1400 nm film, 100 nm SiO₂ features were clearly visualized for PMMA film thicknesses below and up to 800 nm. This research demonstrates the potential of U-AFM as a powerful technique for visualizing nanoscale subsurface features in microelectronic devices.