Interfacial photovoltage microscopy : a new diagnostic for silicon-on-insulator materials

The interface between silicon and various dielectric materials is of great technological importance for the operation of solid-state devices. The sign and magnitude of trapped charge at these interfaces is of particular importance, since it is often a controlling factor in device performance. Interfacial photovoltage microscopy is a technique for measuring the electric fields at such interfaces that is nondestructive, process compatible, and relatively fast. The microscope applies an intense flux of photons to generate an electron-hole plasma in the silicon. The plasma polarizes in response to the electric field generated by interfacial charge and the polarization can be sensed outside the wafer by a capacitive sensor. We infer interfacial charge as a function of position by scanning the photon beam across the sample and measuring the resulting polarization. Micrographs generated from these measurements show the sign, magnitude, and uniformity of the charge at the interface. The system has been tested by intentionally modifying the charge density at the interface using x rays. A description of the instrument, the results of experiments, and a comparison of the results with simple physical models are presented.