Fabrication of integrated circuit structures for bipolar transistors

1. A method of forming an integrated circuit (IC) structure, the method comprising:

providing a substrate including: a first semiconductor region, a second semiconductor region, and a trench isolation (TI) laterally between the first and second semiconductor regions;

forming an epitaxial layer on at least the first semiconductor region of the substrate by forming a precursor base material above the second semiconductor region of the substrate and a first semiconductor base material positioned above the first semiconductor region of the substrate;

forming an insulator region on at least the first semiconductor base material, the trench isolation (TI), and the second semiconductor region;

forming a first opening in the insulator region over the second semiconductor region to expose the precursor base material; and

growing a second semiconductor base material on the precursor base material in the first opening, wherein a height of the second semiconductor base material above the substrate is greater than a height of the first semiconductor base material above the substrate.

2. The method of claim 1 , wherein forming the insulator region includes:

forming a first portion of the insulator region on the TI and the second semiconductor region, before forming the epitaxial layer; and

forming a second portion of the insulator region on the first semiconductor region, after forming the epitaxial layer.

3. The method of claim 1 , further comprising:

removing a portion of the insulator region between the first and second semiconductor base materials to expose the TI; and

forming a semiconductor material on the TI of the substrate to yield an extrinsic base material.

4. The method of claim 1 , further comprising:

forming an additional insulator over the first and second semiconductor base materials;

forming a second opening in the additional insulator to expose the first semiconductor base material;

forming a third opening in the additional insulator to expose the second semiconductor base material; and

forming a first emitter on the first semiconductor base material and a second emitter on the second semiconductor base material, wherein the first semiconductor region defines a collector of a first bipolar transistor, and wherein the second semiconductor region defines a collector of a second bipolar transistor.

5. The method of claim 1 , wherein the first and second semiconductor base materials each include silicon germanium.

6. A method of forming an integrated circuit (IC) structure, the method comprising:

providing a substrate including: a first semiconductor region, a second semiconductor region, and a trench isolation (TI) laterally between the first and second semiconductor regions;

forming a seed layer on the TI of the substrate, leaving the first and second semiconductor regions exposed;

forming an epitaxial layer on the first and second semiconductor regions of the substrate, and on the seed layer, wherein the epitaxial layer includes: a first semiconductor base material positioned above the first semiconductor region of the substrate, a precursor base positioned above the second semiconductor region of the substrate, and an extrinsic base material positioned above the seed layer;

forming an insulator on the first semiconductor base material, the precursor base, and the extrinsic base material;

forming an opening within the insulator to expose the precursor base; and

growing a semiconductor material on the precursor base to yield a second semiconductor base material, wherein a height of the second semiconductor base material above the substrate is greater than a height of the first semiconductor base material above the substrate.

7. The method of claim 6 , wherein the precursor base and the second semiconductor base material each include silicon germanium.

8. The method of claim 6 , further comprising:

removing a portion of the insulator to expose the first semiconductor base material; and

forming a first emitter on the first semiconductor base material and a second emitter on the second semiconductor base material, wherein the first semiconductor region defines a collector of a first bipolar transistor, and wherein the second semiconductor region defines a collector of a second bipolar transistor.

9. The method of claim 8 , wherein the first bipolar transistor comprises a low-noise amplifier (LNA) transistor, and the second bipolar transistor comprises a power amplifier (PA) transistor, the PA amplifier transistor having a lower base-emitter capacitance and a higher base resistance than the LNA amplifier transistor.

10. The method of claim 8 , wherein forming the first emitter on the first semiconductor base material and the second emitter on the second semiconductor base material includes:

forming an insulator stack on an upper surface of the first semiconductor base material, the second semiconductor base material, and the extrinsic base material;

forming a first emitter opening within the insulator stack above the first semiconductor base material, and a second emitter opening within the insulator stack above the second semiconductor base material; and

filling the first and second emitter openings with a semiconductor material.

11. The method of claim 8 , wherein a remaining portion of the extrinsic base material positioned between the first bipolar transistor and the second bipolar transistor defines an extrinsic base region of one of the first bipolar transistor or the second bipolar transistor.

12. The method of claim 6 , wherein forming the opening within the insulator includes etching the insulator and a portion of the precursor base before epitaxially growing the second semiconductor base material on the precursor base.

13. A method of forming an integrated circuit (IC) structure, the method comprising:

providing a substrate including: a first semiconductor region, a second semiconductor region, and a trench isolation (TI) laterally between the first and second semiconductor regions;

forming a first mask on the TI and the second semiconductor region of the substrate, leaving the first semiconductor region exposed;

forming a first semiconductor base material on the first semiconductor region of the substrate;

forming a sacrificial insulator on the first semiconductor base material;

after forming the sacrificial insulator, removing a portion of the first mask to expose the second semiconductor region of the substrate;

forming a second semiconductor base material on the second semiconductor region of the substrate, wherein a height of the second semiconductor base material above the substrate is greater than a height of the first semiconductor base material above the substrate; and

removing the sacrificial insulator after forming the second semiconductor base material.

14. The method of claim 13 , further comprising:

removing a portion of the first mask between the first and second semiconductor base materials to expose the TI; and

forming a semiconductor material on the TI of the substrate to yield an extrinsic base material.

15. The method of claim 13 , further comprising forming a first emitter on the first semiconductor base material and a second emitter on the second semiconductor base material, wherein the first semiconductor region defines a collector of a first bipolar transistor, and wherein the second semiconductor region defines a collector of a second bipolar transistor.

16. The method of claim 15 , wherein the first bipolar transistor comprises a low-noise amplifier (LNA) transistor, and the second bipolar transistor comprises a power amplifier (PA) transistor, the PA amplifier transistor having a lower base-emitter capacitance and higher base resistance than the LNA amplifier transistor.