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Aluminum Migration on the Die Surfaces of a Power Transistor in High-Intensity Electric Fields
Keywords: power electronics, metal migration, breakdown
This paper presents the results of an investigation on a phenomenon of aluminum migration across a 50 micron insulation gap on the die surface of a power silicon transistor under a high-intensity electric field. The transistor is manufactured using an ordinary planar process with aluminum as the metallization material. The electric field is induced by a reverse bias of over 500V across the 50 micron insulation gap between the collector and the base, and therefore, the intensity of the electric field is estimated to be at the magnitude of 105V/cm. A preliminary energy dispersive x-ray (EDX) analysis has verified the migration material of aluminum. Obviously, this migration described above is not so-called electromigration, a process that takes place under the condition of high-density current when significant momentum transfer occurs from moving charge carriers to crystal lattice. The results of a preliminary study also indicate that this migration is dissimilar to electrochemical migration, because no evidence has so far been found that moisture and the existence of electrolyte is a noticeable condition for the occurrence of the migration. The migration being discussed here also shows a lower threshold voltage, which is generally not a necessary condition for electrochemical migration either. The study presented in this paper is to verify the chemical elements and substances involved in the migration process, and to identify the environmental conditions on temperature and relative humidity, and the electric field and reverse bias conditions necessary to initiate the migration process. The migration process will also be characterized under different conditions in this study to provide information for reliability modeling and failure prediction in follow-up studies.
Jingsong Xie,
Beihang University
HaiDian, Beijing 100083,
China


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