HIGH-SPEED SELF-ALIGNED POLYSILICON EMITTER/BASE BIPOLAR DEVICES USING BORON AND ARSENIC DIFFUSION THROUGH POLYSILICON.

In order to enhance the performance of silicon bipolar devices, it is important not only to minimize the emitter, base, and collector areas but also to make shallow emitter and base layers. The self-aligned polysilicon emitter/base structure using deep-trench isolation greatly contributed to minimize the emitter, base, and collector capacitances as well as to reduce the extrinsic base resistance. The shallow emitter can be formed by diffusing arsenic impurities from the arsenic-doped emitter-polysilicon. However, as far as the base layer is formed by direct implantation of boron ions, it is rather difficult to obtain a base width less than 1000 Angstrom because of the projected range of boron ions and the tailing effect in boron impurity profile. Although BF//2 implantation is an alternative approach for obtaining a narrow base width, the defects created by BF//2 implantation are a concern. The authors demonstrate the technique to form a shallow emitter junction less than 500 Angstrom and a narrow base width less than 1000 Angstrom.