Method of forming a silicon dioxide layer

1. A method of forming a silicon dioxide layer, comprising:

providing a semiconductor substrate, the semiconductor substrate including at least one silicon surface region with a curved surface;

roughening the surface of the at least one silicon surface region to produce a layer of porous silicon, wherein roughening the surface of the at least one silicon surface region includes forming pores, the pores each having a width of less than 20 nm and a pore depth of less than 20 nm;

thermally oxidizing the at least one roughened curved silicon surface region; and

oxidizing the at least one silicon surface region to produce an oxidized portion within the semiconductor substrate which ends at a depth, the depth being greater than the pore depth of the pores;

wherein the surface regions which are not to be oxidized are covered with a masking layer before roughening the surface of the at least one silicon surface region.

2. The method of claim 1 , wherein roughening the surface of the at least one silicon surface region includes producing pores, the pores each having a size of less than 10 nm.

3. The method of claim 2 , wherein roughening the surface of the at least one silicon surface region includes producing pores, the pores each having a size of less than 5 nm.

4. The method of claim 1 , wherein roughening the surface of the at least one silicon surface region includes etching the surface region.

5. The method of claim 4 , wherein etching the surface region includes etching in a solution containing phosphoric acid.

6. The method of claim 4 , wherein etching the surface region includes etching in a solution including H 2 SO 4 , HF and HNO 3 .

7. The method of claim 6 , wherein etching the surface region includes etching in a solution having a composition of H 2 SO 4 :HF:HNO 3 =7:1:0.01.

8. The method of claim 4 , wherein roughening the surface of the at least one silicon surface region includes electrochemically etching the surface region.

9. The method of claim 8 , wherein roughening the surface of the at least one silicon surface region includes etching the surface region with a mixture of hydrofluoric acid and ethyl alcohol.

10. The method of claim 9 , wherein roughening the surface of the at least one silicon surface region includes etching the surface region with a mixture of 49% aqueous hydrofluoric acid and pure ethyl alcohol at a ratio of 0.75:0.25.

11. The method of claim 8 , wherein roughening the surface of the at least one silicon surface region includes etching the surface region with a 6% aqueous solution of hydrofluoric acid.

12. The method of claim 1 , wherein the masking layer includes silicon nitride.

13. The method of claim 1 , wherein thermally oxidizing the at least one roughened silicon surface forms a silicon dioxide layer having a thickness larger than the pore depth of the pores.

14. The method of claim 1 , wherein the silicon surface region includes monocrystalline silicon.

15. A method of producing a storage trench capacitor for a memory cell including an isolation collar, comprising:

providing a semiconductor substrate, the semiconductor substrate including a main surface;

providing a trench in the semiconductor substrate, the trench extending from the main surface into the semiconductor substrate, the trench including an upper and a lower portion, the trench including a curved inner surface of silicon;

masking the silicon surface region of the upper portion of the trench which is not to be oxidized with a masking layer;

exposing the silicon surface region of the lower portion of the trench on which a silicon dioxide layer is to be formed;

roughening the exposed silicon surface region in the lower portion of the trench to produce a layer of porous silicon, the masking layer having a material which prevents roughening of an underlying material during roughening of the exposed silicon surface region;

thermally oxidizing the roughened silicon surface region;

extending the trench into the semiconductor substrate to form a bottom portion of the trench beneath the lower portion of the trench;

forming a first electrode of the capacitor in the semiconductor substrate adjacent to the bottom portion of the trench;

forming a dielectric layer of the capacitor in the bottom portion of the trench; and

forming a second electrode of the capacitor in the bottom portion of the trench.

16. The method of claim 15 , wherein the masking layer includes silicon nitride.

17. The method of claim 15 , wherein roughening the exposed silicon surface region includes etching the exposed silicon surface region.

18. The method of claim 15 , wherein roughening the exposed silicon surface region includes producing pores in the exposed silicon surface region, the pores having a diameter of less than 20 nm.

19. The method of claim 15 , wherein thermally oxidizing the roughened silicon surface region forms a silicon dioxide layer having a thickness larger than the depth of the pores.

20. A method of producing a storage trench capacitor for a memory cell including an isolation collar, comprising:

providing a semiconductor substrate, the semiconductor substrate including a main surface;

providing a trench in the semiconductor substrate, the trench extending from the main surface, the trench including an upper portion, a lower portion, and a bottom portion, the upper portion being disposed above the lower portion which is disposed above the bottom portion, and wherein the trench includes a curved inner surface of silicon;

forming a first electrode of the capacitor in the semiconductor substrate adjacent to the bottom portion of the trench, forming a dielectric layer in the bottom portion of the trench and forming a second electrode of the capacitor in the bottom portion of the trench;

masking the silicon surface region of the upper portion of the trench which is not to be oxidized with a masking layer;

exposing the silicon surface portion in the lower portion of the trench on which a silicon dioxide layer is to be formed;

roughening the exposed silicon surface region in the lower portion of the trench to produce a layer of porous silicon, the masking layer including a material which prevents roughening of an underlying material during roughening of the exposed silicon surface region; and

thermally oxidizing the roughened silicon surface region.

21. The method of claim 20 , wherein the masking layer includes silicon nitride.

22. The method of claim 20 , wherein roughening the surface of the exposed silicon surface region includes etching the exposed silicon surface region.

23. The method of claim 20 , wherein roughening the surface of the exposed silicon surface region includes producing pores in the exposed silicon surface region, the pores having a diameter of less than 20 nm.

24. The method of claim 20 , wherein thermally oxidizing the roughened silicon surface region forms a silicon dioxide layer having a thickness larger than the depth of the pores.

25. The method of claim 1 , wherein the silicon surface region includes polycrystalline silicon.

26. A method of forming a silicon dioxide layer, comprising:

providing a semiconductor substrate, the semiconductor substrate including at least one silicon surface region with a curved surface;

roughening the surface of the at least one silicon surface region to produce a layer of porous silicon, wherein roughening the surface of the at least one silicon surface region includes etching the surface region in a solution including H 2 SO 4 , HF and HNO 3 to form pores, the pores each having a width of less than 20 nm and a pore depth of less than 20 nm;

thermally oxidizing the at least one roughened curved silicon surface region; and

oxidizing the at least one silicon surface region to produce an oxidized portion within the semiconductor substrate which ends at a depth, the depth being greater than the pore depth of the pores.

27. A method of forming a silicon dioxide layer, comprising:

providing a semiconductor substrate, the semiconductor substrate including at least one silicon surface region with a curved surface;

roughening the surface of the at least one silicon surface region to produce a layer of porous silicon, wherein roughening the surface of the at least one silicon surface region includes etching the surface region with a mixture of 49% aqueous hydrofluoric acid and pure ethyl alcohol at a ratio of 0.75:0.25 to form pores, the pores each having a width of less than 20 nm and a pore depth of less than 20 nm;

thermally oxidizing the at least one roughened curved silicon surface region; and

oxidizing the at least one silicon surface region to produce an oxidized portion within the semiconductor substrate which ends at a depth, the depth being greater than the pore depth of the pores.

28. A method of forming a silicon dioxide layer, comprising:

providing a semiconductor substrate, the semiconductor substrate including at least one silicon surface region with a curved surface, wherein the at least one silicon surface region includes monocrystalline silicon;

roughening the surface of the at least one silicon surface region to produce a layer of porous silicon, wherein roughening the surface of the at least one silicon surface region includes forming pores, the pores each having a width of less than 20 nm and a pore depth of less than 20 nm;

thermally oxidizing the at least one roughened curved silicon surface region; and

oxidizing the at least one silicon surface region to produce an oxidized portion within the semiconductor substrate which ends at a depth, the depth being greater than the pore depth of the pores.