Device isolation with improved thermal conductivity

1. A method of making a semiconductor structure, comprising:

forming a shallow trench isolation (STI) structure in a substrate;

forming a barrier layer on and contacting the STI structure and the substrate, wherein the barrier layer is composed of nitride or oxynitride;

forming an insulator layer on and contacting the barrier layer;

forming a trench through the STI structure and into the substrate;

forming a liner comprising an electrical insulator material on sidewalls and a bottom of the of the trench;

forming a core comprising a high thermal conductivity material in the trench and on the liner, wherein the liner is between the core and the substrate across the bottom of the trench; and

forming a cap in the trench and on the core,

wherein the forming the trench comprises forming the trench adjacent to a heterojunction bipolar transistor (HBT) comprising a collector, a base formed over the collector, and an emitter formed over the base; and

an uppermost surface of the core is above an interface region between the collector and the base.

2. The method of claim 1 , further comprising recessing the core to form a second trench.

3. The method of claim 2 , wherein the forming the cap comprises depositing a cap material in the second trench, and the liner contacts the insulator layer.

4. The method of claim 1 , wherein the forming a trench comprises:

forming the trench with a first etch through the insulator layer, the barrier layer, and the STI structure using a photoresist as a mask;

stripping the photoresist after the first etch; and

after the stripping, extending the trench into the substrate with a second etch using the insulator layer as a mask.

5. The method of claim 1 , further comprising forming a contact through the cap and contacting the core.

6. The method of claim 5 , further comprising forming a wire contacting the contact and providing a heat transfer path away from the core through the contact and the wire.

7. The method of claim 5 , wherein the high thermal conductivity material comprises a phase change material.

8. The method of claim 5 , further comprising forming electrical contacts to the collector, the base, and the emitter in an insulator layer over the HBT, wherein the contact and the electrical contacts are formed in a same process.

9. A semiconductor structure, comprising:

a transistor structure;

a plurality of shallow trench isolation structures adjacent to the transistor structure on multiple sides of the transistor structure; and

a plurality of trench isolation structures formed through the plurality of shallow trench isolation structures,

wherein each one of the plurality of trench isolation structures comprises:

a trench formed through an insulator layer, one of the plurality of shallow trench isolation structures, and into a substrate;

a liner comprising an insulator material on sidewalls of the trench; and

a core comprising a high thermal conductivity material on the liner;

the transistor structure comprises a heterojunction bipolar transistor (HBT) comprising a collector, a base, and an emitter; and

an uppermost surface of the core is above an interface region between the collector and the base.

10. The structure of claim 9 , further comprising a cap in the trench over the core, wherein the cap, the insulator layer, and the liner comprise the insulator material.

11. The structure of claim 9 , wherein the insulator layer covers and contacts the transistor structure and the plurality of shallow trench isolation structures, the insulator layer contacts the liner, and the liner covers the sidewalls and an entire bottom surface of the trench.

12. A method of forming a semiconductor structure, comprising:

forming a transistor structure;

forming a plurality of shallow trench isolation structures adjacent to the transistor structure on multiple sides of the transistor structure; and

forming a plurality of trench isolation structures formed through the plurality of shallow trench isolation structures,

wherein each one of the plurality of trench isolation structures comprises:

a trench formed through an insulator layer, one of the plurality of shallow trench isolation structures, and into a substrate;

a liner comprising an insulator material on sidewalls of the trench; and

a core comprising a high thermal conductivity material on the liner;

the transistor structure comprises a heterojunction bipolar transistor (HBT) comprising a collector, a base, and an emitter; and

an uppermost surface of the core is above an interface region between the collector and the base.

13. The method of claim 12 , further comprising forming a cap in the trench over the core, wherein the cap, the insulator layer, and the liner comprise the insulator material.

14. The method of claim 12 , wherein the insulator layer covers and contacts the transistor structure and the plurality of shallow trench isolation structures, the insulator layer contacts the liner, and the liner covers the sidewalls and an entire bottom surface of the trench.