Method of forming a bottle-shaped trench in a semiconductor substrate

1. A method of forming a bottle-shaped trench in a semiconductor substrate, suitable for formation of the capacitor of DRAM, comprising the steps of:

(a) forming a hard mask having an opening on the semiconductor substrate;

(b) etching the semiconductor substrate through the opening of the hard mask to create a trench, wherein the trench has a top portion and a bottom portion;

(c) forming an nitride film on the surfaces of the trench and the hard mask;

(d) filling a shield material in the bottom portion of the trench;

(e) removing a part of the nitride film to leave the nitride film protected by the shield material and expose the surface of the semiconductor substrate at the top portion of the trench;

(f) removing the shield material to expose the nitride film formed on the bottom portion of the trench;

(g) forming a oxide film on the top portion of the trench;

(h) removing the nitride film to expose the surface of the semiconductor substrate at the bottom portion of the trench;

(i) forming a rugged polysilicon layer on the exposed surface of the semiconductor substrate at the bottom portion of the trench;

(j) etching the rugged polysilicon layer and the semiconductor substrate through the bottom portion of the trench by a diluted ammonia solution as the etchant to form a bottle-shaped trench having a rugged surface; and

(k) removing the oxide film.

2. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 1 , wherein the semiconductor substrate is silicon substrate.

3. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 1 , wherein the hard mask comprises a pad oxide formed on the semiconductor substrate and a pad nitride formed on the pad oxide.

4. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 1 , wherein step (b) is performed by anisotropic reactive ion etching (RIE).

5. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 1 , wherein the nitride film is silicon nitride formed by chemical vapor deposition using a silicon-containing gas and a nitrogen-containing gas as the reactive gas.

6. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 5 , wherein the silicon-containing gas is silane, dichlorosilane, or trichlorosilane, the nitrogen-containing gas is ammonia or nitrogen gas.

7. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 1 , wherein step (d) further comprises the steps of:

coating a photoresist material into the trench; and

partially removing the photoresist material formed at the top portion of the trench to leave the photoresist material formed at the bottom portion of the trench to serve as the shield material.

8. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 1 , wherein step (e) is performed by a phosphoric acid solution.

9. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 2 , wherein the oxide film is silicon oxide formed by reaction of the semiconductor substrate in a high temperature ambient containing oxygen and/or water.

10. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 1 , wherein the diluted ammonia solution has a mix ratio of 1:5˜1:50 diluted by water.

11. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 1 , wherein the rugged polysilicon layer is deposited by chemical vapor deposition using silane as the reactive gas.

12. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 11 , wherein the rugged polysilicon layer is deposited at a temperature of about 565° C. to 585° C.

13. A method of forming a bottle-shaped trench in a semiconductor substrate, suitable for formation of the capacitor of DRAM, comprising the steps of:

selectively etching the semiconductor substrate to form a trench, wherein the trench has a top portion and a bottom portion;

forming a oxide film on the top portion of the trench;

forming a rugged polysilicon layer on the bottom portion and the top portion of the trench;

etching the rugged polysilicon layer and the semiconductor substrate through the bottom portion of the trench by diluted ammonia solution as the etchant to form a bottle-shaped trench; and

removing the oxide film.

14. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 13 , wherein the semiconductor substrate is silicon substrate.

15. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 14 , wherein formation of the oxide film further comprises the steps of:

forming a nitride film on the bottom portion of the trench and exposing the surface of the semiconductor substrate at the top portion of the trench; and

forming an oxide film on the surface of semiconductor substrate at the top portion of the trench.

16. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 13 , wherein the diluted ammonia solution has a mix ratio of 1:5˜1:50 diluted by water.

17. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 13 , wherein the rugged polysilicon layer is deposited by chemical vapor deposition using silane as the reactive gas.

18. The method of forming a bottle-shaped trench in a semiconductor substrate as claimed in claim 17 , wherein the rugged polysilicon layer is deposited at a temperature of about 565° C. to 585° C.