Noninvasive scanned probe potentiometry for integrated circuit diagnostics

This paper describes a simple noncontact scanned probe microscope for the static potential measurement of operating integrated circuits. The instrument extracts the local potential on the integrated circuit by nulling the electrostatic force between a small cantilever probe and the circuit test point. The force is detected by monitoring the mechanical deflection of the probe with an optical fiber interferometer. The constructed instrument has demonstrated a millivolt accuracy with a spatial resolution of less than 3 μm. Measurements can be made directly in air on circuits both with and without a top insulating passivation layer. The nulling technique allows absolute potential measurements to be performed without complex calibration requirements