Metal Migration into Polysilicon Emitter After Very High Current Stress

TEM analyses show metal migration into the polysilicon emitter of a bipolar transistor after high current stress. At the edges of the polysilicon emitter where the current density was expected to be the highest, a metal filament was seen penetrating into the edge of the polysilicon emitter after stressing at a current density of 16.3 mA/ μm2 for 1.68 x 105 s at 90°C. The metal penetration into polysilicon offers a possible cause for the previous electrical measurement [1], in which a slight lowering of the emitter contact resistance occurs after the same stress. © 1992 IEEE