Contrast mechanisms in electron beam images of interface structures

Abstract

A technique for imaging internal structures in MIS devices has been developed. The device is scanned by an electron beam in a scanning electron microscope and the induced current is used to modulate a CRT display. Direct−current bias on the sample and incident beam energy determine which structure (metal−insulator interface, semiconductor−insulator interface, or insulator bulk) is observed. Secondary electron images, C−V measurements, and bias temperature stress data are used to facilitate image interpretation. A variety of structures have been observed at both interfaces on MOS capacitors with lateral resolution on the order of 1000 Å. Experimental results support a model with field variations across the oxide film providing the dominant contribution to image contrast.