Electric Force Microscope, Capacitive Coupling, and Scanning Magnetoresistive Probe

Abstract

Electric force microscope (EFM) testing is based on Coulombic force interactions between an EFM probe and a test point. An electric signal on an interconnected line creates an electric force between the tip and the device under test which causes a detectable bending of the cantilever. This bending amount is optically detected and electrically analyzed by a lock-in amplifier. In capacitive coupling method, an electrode is placed in close proximity to a pad on the wafer. The voltage transients on the pad induce weak displacement currents on the electrode. This effect can be used to detect electrical pulses propagating through an IC. For current measurements, scanning magnetoresistive probe has also been suggested to detect currents in a contactless manner.