Date of Award
Doctor of Engineering Science in Electrical Engineering
Raj Pratap Misra
This research was directed towards the occurrence and im-portance of surface leakage in reverse biased semiconductor diodes and the relation of this leakage to the reliability of a device under use conditions. As a result of this study, it is possible to predict one important leakage mechanism after such back-biased diode units have been subjected to long periods of temperature and humidity. This theory is consistent with tests of commercially available units, some of which have very slight surface leakage and others very large surface leakage.
Further, the usefulness of various possible passivating coatings is critically analyzed on the basis of comparative physical constants and film formation techniques. The process of comparison of physical constants has led to further concepts that can result in fabrication techniques with an end product semiconductor with superior reliability characteristics.
A table of physical properties of Si, SiO, SiO2, Si3N4 and A12O3, more extensive than is available in a single published source, is contained in this dissertation.
In epoxy molded SCR's, used as diodes, the predominant leakage mode involves leakage along the oxide surface, and this mode of leakage does not occur until the epoxy resin has become saturated with moisture. Silicon nitride, glass molded diodes have not exhibited this mode of leakage in tests exceeding 5000 hours.
Coatings of SiO2 on silicon have been made by evaporation of silicon dioxide utilizing a CO2 Laser in a vacuum chamber. High purity films can be deposited by this technique, both because of the rate of deposition and the lack of internal heaters or other complications.
These insulating layers, namely SiO, SiO2, Si3N4 and A12O3, can be removed by intense radiation of a wavelength of 10.5 microns. The use of this technique may eliminate chemical etch-operations, with the inherent possibility of surface retention of ions.
McMillan, Robert Edward, "Reliability aspects of semiconductor surface protective coatings" (1970). Dissertations. 1343.