| 摘要 |
In one disclosed embodiment, a silicon-germanium base is formed, which includes an extrinsic base region, a link base region, and an intrinsic base region. An etch stop layer, which can be silicon oxide, is deposited over the silicon-germanium base. A polycrystalline silicon layer is then formed on the etch stop layer above the silicon-germanium base. The polycrystalline silicon layer is patterned to form a temporary emitter. The link base regions can be implant doped after fabricating the temporary emitter, for example, to reduce the resistance of the link base regions. Link spacers are then fabricated on the sides of the temporary emitter. The link spacers can be formed by depositing a conformal layer of silicon oxide over the temporary emitter and then etching back the conformal layer. The length of the link base regions, which are below the spacers, can be determined by the deposition thickness of the conformal layer. The extrinsic base regions are implant doped after fabricating the link spacers. A protective layer of silicon oxide can be deposited over the extrinsic base regions, link spacers and temporary emitter prior to patterning the temporary emitter and link spacers by opening a photoresist mask. The temporary emitter is then etched away and the etch stop layer is removed, forming a cavity between the link spacers. A final emitter is then formed in the cavity. For example, the final emitter can be formed by depositing polycrystalline silicon in the cavity and forming a base-emitter junction within the intrinsic base region.
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