Distribution of flat-band voltages in laterally nonuniform MIS capacitors and application to a test for nonuniformities

Interface states and lateral nonuniformities produce very similar abnormalities in theC-Vcurves of MIS capacitors. The effect of a laterally nonuniform distribution of fixed charge in the insulator can be characterized by a flat-band-voltage distribution function. Here we present a simple, approximate method for determining this distribution from the quasi-static and high-frequencyC-Vcurves of the capacitor, and we apply the result to a test for distinguishing between interface states and laterally nonuniform fixed charge. The test is based on a principle that is implicit in the results of an analysis previously published by Brews and Lopez; namely, that interface states and lateral nonuniformities cannot produce identical distortions in both the quasi-static and high-frequencyC-Vcurves. The presence of either lateral nonuniformities or interface states can be tested by assuming allC-Vdistortion to be due to the other cause. TheC-Vcurves are regenerated under this assumption, and discrepancies between the measured and regenerated curves indicate the presence of the effect assumed not to be present.