A heterojunction bipolar transistor (HBT) structure comprising:
- a semiconductor workpiece;
- an inter-device isolation structure that includes a first layer of silicon dioxide formed on the semiconductor workpiece, a first layer of silicon nitride formed on the first layer of silicon dioxide, a second layer of silicon dioxide formed on the first layer of silicon nitride, and a second layer of silicon nitride formed on the second layer of silicon dioxide;
- trench formed in the inter-device isolation structure, the trench including a deep trench region that extends from an upper surface of the second layer of silicon nitride to a lower surface of the first layer of silicon dioxide such that an upper surface area of the semiconductor workpiece forms the bottom of the deep trench region, the trench further including a shallow trench region adjacent to the deep trench region and that extends from the upper surface of the second layer of silicon nitride to a lower surface of the second layer of silicon dioxide such that an upper surface area of the first layer of silicon nitride forms the bottom of the shallow trench region;
- a first region of epitaxial silicon formed in the deep trench region to extend from the bottom of the deep trench region to the upper surface of the first layer of silicon nitride;
- a second region of epitaxial silicon formed in the deep trench region on an upper surface of the first region of epitaxial silicon, the second region of epitaxial silicon comprising the collector of the HBT structure;
- a first region of polysilicon formed on the bottom of shallow trench region;
- a third layer of silicon dioxide formed on the upper surface of the second layer of silicon nitride, the upper surface of the second region of epitaxial silicon and the upper surface of the first region of polysilicon, the third layer of silicon dioxide having an opening formed therethrough to expose an upper surface area of the second region of epitaxial silicon;
- a Si—Ge region formed on the third layer of silicon dioxide to extend over the second layer of silicon nitride and to extend into the opening formed through the third layer of silicon dioxide to be in electrical contact with the exposed upper surface area of the second region of epitaxial silicon, the Si—Ge region comprising the base of the HBT structure;
- a fourth layer of silicon dioxide formed on the upper surface of the Si—Ge region and having a first opening formed therethrough to expose a first upper surface area of the Si—Ge region;
- and
- a second region of polysilicon formed to extend into the opening formed in the fourth layer of silicon dioxide to be in electrical contact with the exposed upper surface area of the Si—Ge region, the second region of polysilicon comprising the emitter of the HBT structure.