Applications of Photoacoustic Microscopy in Dynamic Analyses of Integrated Circuits

Abstract

Recently, photoacoustic (PA) and thermal wave techniques have been applied successfully to study the semiconductor materials and devices, especially applied to study the surface and subsurface features of integrated circuits (IC)¹, as well as the PN jiunctions in which the interface of the PN junction is parallel to the surface^2,3,4. However, in most previous researches, the IC devices are imaged by the PA microscopy in static state (not in operation), in which some structures having similar properties cannot be distinguished apparently. In this work, we present mainly the PA images of IC devices in dynamic state (in operation), and find out that, as pointed out by Lu et al.2, PA images of IC devices obtained in dynamic state reflect the electronic structures and logical principles more effectively than those in static state. Besides, a one-dimensional model is proposed to study the effect of the external electric field on the PA signal in the lateral PN junction area, in which the interface of the PN junction is perpendicular to the surface. In theory, the heat absorption and/or heat release of the PN junction are the important factors to affect acoustic wave through thermoelastic coupling. Therefore, the external electric field enhances the influence of the electric properties on the PA signal of the devices. Thus the dynamic PA images (i.e., the PA images of the devices obtained in the operational condition) can show some electric components, which cannot be displayed by the static PA imaging, where the devices are in static condition. The theoretical analysis can properly be used to explain the experimental results.