Aluminum migration on the die surfaces of a power transistor in high-intensity electric fields

This paper presents the results of an investigation on a phenomenon of aluminum migration across a 50 micron semi-insulation gap on the die surface of a power silicon transistor under a high-intensity electric field. The transistor is manufactured using a typical planar process with aluminum as the metallization material. The electric field is induced by a reverse bias of over 500V across the 50 micron semi-insulation gap between the collector and the base. A preliminary energy dispersive x-ray (EDX) analysis has verified the migration material of aluminum. It is clear that this migration described above is not the 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 investigation results obtained in this preliminary study also indicate that this migration is different from the electrochemical migration, because no evidence has so far been found that moisture and the existence of electrolyte is noticeably a necessary condition for the occurrence of the migration. In addition, the existence of a lower threshold voltage observed in the study for this migration phenomenon is not considered a necessary condition for electrochemical migration either. This paper presents a preliminary study to verify the chemical composition of the substances involved in the migration process, and to identify the environmental conditions of temperature and relative humidity, as well as 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.