Insulating trench forming method

1. A method of manufacturing an insulating trench, the method comprising:

forming a trench having trench walls in a surface of a substrate;

covering the trench walls with an insulating material;

filling the trench with doped polysilicon; and

forming a silicon oxide plug over the polysilicon, an upper surface of the silicon oxide plug located above the surface of the substrate and a lower surface of the silicon oxide plug being substantially at or below the surface of the substrate; and

forming an insulator layer on the surface of the substrate and the upper surface of the silicon oxide plug.

2. The method of claim 1 , wherein the lower surface of the silicon oxide plug is below the surface of the substrate.

3. The method of claim 1 , wherein forming the silicon oxide plug comprises:

selectively etching the polysilicon; and

performing a thermal oxidation to form said oxide plug.

4. The method of claim 1 , wherein forming the silicon oxide plug comprises:

selectively etching the polysilicon;

depositing silicon oxide over the polysilicon; and

planarizing the silicon oxide.

5. The method of claim 1 , further comprising:

forming, on the surface of the substrate, a first masking structure having a layer of a selectively etchable first material, the first material being silicon nitride.

6. The method of claim 1 , wherein the trench is a first trench, and after forming the silicon oxide plug, the method further comprising

forming a second trench in the surface of the substrate, the second trench having a smaller depth than the first trench;

depositing a second insulating material to fill said second trench; and

planarizing exposed surface to a same level of said oxide plug.

7. The method of claim 6 , wherein said second insulating material is silicon oxide.

8. The method of claim 1 , further comprising:

depositing, on the insulator layer, at least one layer of a conductive gate stack; and

masking and etching the at least one layer of the conductive gate stack to form a gate.

9. The method of claim 1 , wherein the covering of the trench walls with the insulating material includes forming a thermal silicon oxide layer, a silicon oxide layer, and a silicon nitride layer.

10. The method of claim 1 , wherein the filling of the trench includes depositing a doped polysilicon layer in the trench and over the surface of the substrate.

11. The method of claim 10 , wherein the depositing of the doped polysilicon layer is followed by planarizing the doped polysilicon layer.

12. An insulating structure formed in a semiconductor substrate, the insulating structure comprising:

a trench having trench walls formed in a first surface of the substrate;

an insulating material covering the trench walls;

doped polysilicon in the trench; and

a silicon oxide plug formed over the polysilicon, an upper surface of the silicon oxide plug located above the first surface of the substrate, and a lower surface of the silicon oxide plug being below the first surface of the substrate and in the trench.

13. The insulating structure of claim 12 , wherein the lower surface of the silicon oxide plug is below the surface of the substrate.

14. The insulating structure of claim 12 , wherein the trench has a depth in the substrate that is greater than 2 μm.

15. The insulating structure of claim 12 , wherein the insulating material covering the trench walls includes a plurality of insulating materials.

16. The insulating structure of claim 15 , wherein the plurality of insulating materials includes a thermal silicon oxide layer, a silicon oxide layer, and a silicon nitride layer.

17. A semiconductor structure comprising:

a semiconductor substrate having a surface;

a plurality of trenches having sidewalls formed in the substrate at the first surface, the plurality of trenches being spaced apart from each other;

a first layer of insulating material conforming to the sidewalls of a first trench of the plurality of trenches;

doped polysilicon in the first trench over at least a portion of the first layer of insulating material;

a silicon oxide plug formed over the polysilicon in the first trench, an upper surface of the silicon oxide plug located above the substrate and a lower surface of the silicon oxide plug being below the first surface of the substrate;

a second layer of insulating material formed over the silicon oxide plug and

a conductive gate located between two adjacent trenches.

18. The semiconductor structure of claim 17 , wherein the lower surface of the silicon oxide plug is below the surface of the substrate.

19. The semiconductor structure of claim 17 , wherein the at least one insulating materials includes a plurality of insulting materials including a thermal silicon oxide layer, a silicon oxide layer, and a silicon nitride layer.

20. The semiconductor structure of claim 17 , further comprising insulating material filling a second trench of the plurality of trenches, the first trench having a first depth, the second trench having a second depth that is smaller than the first depth.

21. A method of manufacturing an insulating trench, the method comprising:

forming a trench having trench walls in a surface of a substrate;

covering the trench walls with an insulating material;

filling the trench with doped polysilicon;

forming a silicon oxide plug over the polysilicon, a first surface of the silicon oxide plug located above the surface of the substrate and a second surface of the silicon oxide plug being substantially at or below the surface of the substrate, the forming of the silicon oxide plug including:

performing a thermal oxidation to form said oxide plug; or

depositing silicon oxide over the polysilicon and planarizing the silicon oxide.

22. The method of claim 21 , further comprising:

forming a masking layer on the surface of the substrate; and

removing the masking layer subsequent to the forming of the silicon oxide plug.

23. A method of manufacturing an insulating trench, the method comprising:

forming, on a surface of the substrate, a masking structure having a layer of a selectively etchable first material, the first material being silicon nitride;

forming a trench having trench walls in the first masking structure and the substrate;

covering the trench walls with an insulating material;

filling the trench with doped polysilicon; and

forming a silicon oxide plug over the polysilicon, a first surface of the silicon oxide plug located above the surface of the substrate and a second surface of the silicon oxide plug being substantially at or below the surface of the substrate.

24. The method of claim 23 , further comprising removing the masking structure.

25. A method of manufacturing an insulating trench, the method comprising:

forming a first trench having trench walls in a surface of a substrate;

covering the trench walls with a first insulating material;

filling the trench with doped polysilicon; and

forming a silicon oxide plug over the polysilicon, an upper surface of the silicon oxide plug located above the surface of the substrate and a lower surface of the silicon oxide plug being substantially at or below the surface of the substrate;

forming a second trench in the surface of the substrate, the second trench having a smaller depth than the first trench;

depositing a second insulating material to fill the second trench; and

planarizing the second insulating material to have an upper surface that is coplanar with the upper surface of the silicon oxide plug.

26. The method of claim 25 , further comprising forming an insulating layer on the upper surface of the silicon oxide plug.