Single-photon optical-beam-induced current microscopy of semiconductor devices with enhanced contrast

Abstract

We analyze images taken from optical-beam-induced current (OBIC) microscopy by single-photon absorption of semiconductor devices. Focusing laser light at specific regions of an integrated circuit (IC), where traces of semiconductors absorb photons, results in the generation of excess electron-hole pairs and thereby producing current. Single-photon OBIC images suffer from low-contrast because of its inability to discriminate absorption of the excitation light in the out-of-focus planes. On the other hand, the confocal microscope yields high contrast images but with the resulting reflection image, it is unable to distinguish metal traces from semiconductors. By combining the images from reflection confocal and OBIC, topographical traces of semiconductors as well as conductors in an IC can be clearly defined. The internal circuitry of an Erasable Programmable Read Only Memory (EPROM) was viewed using a laser-scanning microscope with confocal and OBIC mode and image with enhanced metal traces are differentiated from images with enhanced semiconductor traces.