Laser modulation mapping on an unmodified laser scanning microscope

Laser modulation mapping is a non-invasive technique to make visible those transistors inside an IC that carry a given signal. The ability to map out those locations where a signal is present, and those where it is absent (for example, because of a defect) has clear applications to in-circuit fault localisation. Recent publications have demonstrated modulation mapping on infrared laser scanning microscopes (LSM), but have without exception made use of non-standard, high performance lasers and detectors. In this paper we show how to achieve modulation mapping on a standard LSM. We discuss in particular the practical aspects of obtaining modulation mapping signals, explain some artefacts and important experimental procedures, before illustrating its practical application.