Accumulation and Decay of Mobile Surface Charges on Insulating Layers and Relationship to Reliability of Silicon Devices

Reverse biased diodes of various geometrical dimensions, oxide preparation techniques and breakdown voltages were used to measure surface contact potential differences and surface ion distributions in various ambients. The experimental data of ion accumulation were compared to complementary error function solutions expected for a distributed capacitance and sheet resistance. After bias removal the accumulated positive and negative charges were allowed to decay. Significant differences of decay times could be observed determined by the sign of the charge and the chemical preparation of the sample. The influence of mobile surface charges on device characteristics, particularly on the diode breakdown voltage, is described. The relationship between the surface breakdown voltage and the external bias applied to a metal strip located geometrically above the p-n junction is established. Finally, it is shown that a "freezing" of the surface charges can change and stabilize the diode V-I characteristics considerably.