The influence of ion induced damage on lateral charge collection and IBIC image contrast

Abstract

High resolution, calibrated ion beam induced charge (IBIC) measurements from integrated circuit test structures have demonstrated that the measured charge collection in a device can exhibit significant change after only a few hundred ions/μm 2 exposure, which may easily be exceeded in the initial targeting of a structure. For the purposes of determining a circuit's upset immunity or undamaged charge collection characteristics, such behaviour must be accounted for in evaluating IBIC measurements. This paper examines the influence of low level, ion induced damage on the magnitude of the measured lateral charge collection and also its resulting impact on IBIC image contrast. The lateral charge collection process is first characterised by calculating the amount of charge which diffuses to a collecting junction as a function of carrier diffusion length and the distance between the ion strike and junction edge. The effect of accumulated ion induced damage on lateral charge collection is then incorporated as a decrease in the resultant diffusion length. Calibrated IBIC measurements from the drain of a test FET structure are then explained using this predicted behaviour.