Failure Analysis of Surface Inversion

This paper is intended to give some guidance for a workshop session on surface inversion. It first highlights the key causes of surface inversion, such as electronic and ionic charges, surface and bulk contamination, and leakage mechanisms. Second, the paper describes a number of widely used failure analysis techniques which permit the study of surface inversion and accumulation in MOS and bipolar devices and circuits. These techniques include the evaluation of test structure data, as gained by capacitor and field plate arrangements at variable temperatures, and the analysis of actual circuits using the scanning electron microscope, the photoresponse scanner, the microprobe, and electrical characterization. As examples for surface inversion, temperature-voltage inversion, surface and bulk generated currents, and lateral charge spreading are described. Some final comments lead to the more encompassing subject of device parameter stability improvement by process control.