Method of forming a deep trench isolation structure for isolation of high-voltage devices

1. A method comprising:

forming a shallow trench isolation (STI) structure that extends into a substrate;

forming a masking layer over the substrate, wherein the masking layer comprises an opening that directly overlies the STI structure;

performing a first removal process to remove portions of the STI structure that directly underlie the opening of the masking layer;

performing a second removal process to laterally remove portions of the substrate arranged below the STI structure;

performing a third removal process to further remove portions of the substrate that directly underlie the opening of the masking layer;

forming an insulator liner layer within inner surfaces of the substrate as defined by the first, second, and third removal processes;

performing a fourth removal process to remove portions of the insulator liner layer covering a lower surface of the substrate defined by the third removal process; and

forming a semiconductor material over the SOI substrate and contacting the insulator liner layer.

2. The method of claim 1 , further comprising:

performing a planarization process to remove portions of the semiconductor material arranged above a topmost surface of the substrate.

3. The method of claim 1 , further comprising:

forming a semiconductor device arranged on and/or within a topmost surface of the substrate, wherein the insulator liner layer and the semiconductor material continuously surround the semiconductor device.

4. The method of claim 1 , wherein the insulator liner layer has a maximum width measured between outer sidewalls defined by the second removal process.

5. The method of claim 1 , wherein the substrate is a silicon on insulator (SOI) substrate comprising an insulator layer between an active layer and a base layer, and wherein the third removal process removes portions of the insulator layer and the base layer arranged below the opening of the masking layer, and wherein after the third removal process, the SOI substrate comprises a trench that extends through the STI structure, the active layer, the base layer, and the insulator layer, and wherein the trench directly underlies the opening of the masking layer.

6. The method of claim 1 , wherein the opening of the masking layer is narrower than the STI structure.

7. A method comprising:

forming a shallow trench isolation (STI) structure that extends into a substrate;

forming a masking layer over the substrate, wherein the masking layer comprises an opening that directly overlies the STI structure;

performing a removal process to remove portions of the STI structure and the substrate according to the opening of the masking layer, wherein after the removal process, the substrate comprises a trench defined by inner sidewalls of the STI structure and the substrate as well as a lower surface of the substrate, wherein the trench has a first width along a bottom of the STI structure, which is a maximum width of the trench and is greater than a second width of the trench at a bottom of the trench;

forming an insulator liner structure on inner sidewalls of the substrate to partially fill the trench; and

forming a semiconductor core structure to fill remaining portions of the trench.

8. The method of claim 7 , further comprising:

grounding the semiconductor core structure.

9. The method of claim 7 , wherein the semiconductor core structure has a width that varies as the width of the semiconductor core structure is measured at different heights above a bottommost surface of the substrate, and wherein the width of the semiconductor core structure decreases, increases, and then decreases when measured at various heights in a direction from a topmost surface of the substrate to the bottommost surface of the substrate.

10. The method of claim 7 , wherein the opening of the masking layer is less than the maximum width of the trench.

11. The method of claim 7 , wherein the removal process comprises:

using a first etchant to remove portions of the STI structure arranged under the opening of the masking layer in a vertical direction;

using a second etchant to remove portions of the substrate arranged under the STI structure in a horizontal direction; and

using a third etchant to remove portions of the substrate arranged under the opening of the masking layer in the vertical direction.

12. The method of claim 11 , wherein the maximum width of the trench is defined by the second etchant.

13. The method of claim 11 , wherein the second etchant exposes a bottommost surface of the STI structure.

14. A method of forming a deep trench isolation structure in a substrate, the method comprising:

forming a shallow trench isolation (STI) structure that extends into an active layer of a silicon-on-insulator (SOI) substrate;

forming a masking layer over the active layer of the SOI substrate, wherein the masking layer comprises an opening that directly overlies the STI structure;

performing a first removal process to remove portions of the STI structure that directly underlie the opening of the masking layer, thereby exposing the active layer of the SOI substrate;

performing a second removal process to laterally remove portions of the active layer below the STI structure;

performing a third removal process to remove remaining portions of the active layer of the SOI substrate and an insulator layer of the SOI substrate that directly underlie the opening of the masking layer, thereby exposing a base layer of the SOI substrate;

forming an insulator liner layer within inner surfaces of the active layer, the insulator layer, and the base layer of the SOI substrate as defined by the first, second, and third removal processes;

performing a fourth removal process to remove portions of the insulator liner layer covering the base layer of the SOI substrate; and

forming a semiconductor material over the SOI substrate and contacting the insulator liner layer.

15. The method of claim 14 , wherein portions of the insulator liner layer directly underlie the STI structure.

16. The method of claim 14 , wherein the semiconductor material is polysilicon.

17. The method of claim 14 , wherein the first, second, third, and fourth removal processes each comprises dry etchants.

18. The method of claim 14 , wherein the first, third, and fourth removal processes are vertical etching processes.

19. The method of claim 14 , wherein the second removal process is an isotropic etching process and comprises a dry etchant.

20. The method of claim 19 , wherein the dry etchant in the second removal process comprises xenon and fluoride.