| 摘要 |
A modification of the self-aligned double poly fabrication process for bipolar transistors employs a thin sacrificial dielectric film to protect the wafer surface during the etching of an emitter opening through an overlying polysilicon contact layer. The sacrificial layer, which is preferably silicon dioxide for a silicon wafer, is thick enough to serve as an etch stop but thin enough to permit dopant from the polysilicon contact to be driven-in through the film to form an extrinsic base region. The dielectric film is left in place under the base contact polysilicon, but removed from the emitter area. It is preferably about 10-20 Angstroms thick when implemented as a silicon dioxide film. With this material system, the extrinsic base drive-in is preferably performed either by a rapid isothermal anneal at about 1,000 DEG C. for about 30-40 seconds, or in a furnace at about 975 DEG C. for about 10 minutes.
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