Nonvolatile semiconductor storage device and method of manufacturing the same

1. A nonvolatile semiconductor storage device comprising:

a semiconductor substrate;

a first insulating film disposed above the semiconductor substrate;

a first electrode film disposed above the first insulating film;

a second insulating film disposed above the first electrode film;

a second electrode film disposed above the second insulating film;

a third electrode film filling a first trench and overlying the second electrode film, and the first trench having a first width and a first depth and extending through the second electrode film and the second insulating film and into the first electrode film; and

a first barrier metal film and a first metal film formed in the listed sequence above the third electrode film;

wherein the third electrode film above the second electrode film has a first thickness equal to or less than ½ of the first width of the first trench.

2. The device according to claim 1 , wherein a surface of the third electrode film located above the first trench has a step.

3. The device according to claim 1 , wherein a surface of the third electrode film located above the first trench is planar.

4. The device according to claim 1 , further comprising:

a third insulating film disposed above the semiconductor substrate;

a fourth electrode film disposed above the third insulating film;

a fourth insulating film disposed above the fourth electrode film;

a fifth electrode film disposed above the fourth insulating film;

a sixth electrode film extending along a second trench so as to partially fill the second trench and overlying the fifth electrode film and, the second trench having a second depth and a second width greater than the first width and extending through the fifth electrode film and the fourth insulating film and into the fourth electrode film; and

a second barrier metal film and a second metal film formed in the listed sequence above the sixth electrode film;

wherein the sixth electrode film has the first thickness above the fifth electrode film and above a bottom surface of the second trench, and

wherein a thickness of the sixth electrode film along a sidewall of the fifth electrode film becomes thicker from an upper side to a lower side.

5. The device according to claim 4 , further comprising an interlayer insulating film covering an upper surface of the second metal film and a contact disposed above the second trench and extending through the interlayer insulating film and into the second metal film.

6. The device according to claim 5 , wherein a central surface of the sixth electrode film located in the second trench is planar.

7. A nonvolatile semiconductor storage device comprising:

a semiconductor substrate;

a first insulating film disposed above the semiconductor substrate;

a first electrode film disposed above the first insulating film;

a second insulating film disposed above the first electrode film;

a second electrode film disposed above the second insulating film;

a third electrode film filling a first trench and, the first trench having a first width and a first depth and extending through the second electrode film and the second insulating film and into the first electrode film; and

a first barrier metal film formed above the second and the third electrode film, and

a first metal film formed above the first barrier metal film.

8. The device according to claim 7 , wherein an upper surface of the third electrode film located in an upper portion of the first trench has a step.

9. The device according to claim 7 , further comprising an interlayer insulating film covering an upper surface of the first metal film, and a contact extending through the interlayer insulating film and into the first metal film.

10. The device according to claim 7 , further comprising:

a third insulating film disposed above the semiconductor substrate;

a fourth electrode film disposed above the third insulating film;

a fourth insulating film disposed above the fourth electrode film;

a fifth electrode film disposed above the fourth insulating film;

a sixth electrode film extending along sidewalls of fifth electrode film and the fourth insulating film in a second trench, a thickness of the sixth electrode film becoming thicker from an upper side to a lower side, and the second trench having the first depth and a second width greater than the first width and extending through the fifth electrode film and the fourth insulating film and into the fourth electrode film; and

a second barrier metal film and a second metal film formed in the listed sequence above the sixth electrode film.

11. The device according to claim 10 , wherein the second barrier metal film directly contacts the fourth electrode film.

12. The device according to claim 10 , wherein an inclination of the upper surface of the sixth electrode film located in the second trench is more gradual than an inclination of the fifth electrode film and the fourth insulating film exposed by the second trench.

13. A method of forming a nonvolatile semiconductor device, comprising:

forming a first insulating film and a first electrode film in the listed sequence above an upper surface of a semiconductor substrate;

forming a second insulating film above the first electrode film;

forming a second electrode film above the second insulating film;

forming a first trench having a first width and a first depth extending through the second electrode film and the second insulating film and into the first electrode film;

forming a third electrode film filling the first trench and overlying the second electrode film, wherein the third electrode film overlying the second electrode film has a first thickness greater than ½ of the first width of the first trench;

thinning the third electrode film overlying the second electrode film to a second thickness equal to or less than ½ of the first width of the first trench; and

forming a barrier metal film and a metal film in the listed sequence above the thinned third electrode film.

14. The method according to claim 13 , wherein thinning the third electrode film comprises an anisotropic etch back.

15. The method according to claim 13 , wherein thinning the third electrode film comprises a chemical mechanical polishing.

16. The method according to claim 13 , further comprising forming a third insulating film, a fourth electrode film, a fourth insulating film, and a fifth electrode film in the listed sequence, and

wherein forming the first trench includes forming a second trench extending through the fifth electrode film and the fourth insulating film and into the fourth electrode film and having the first depth and a second width greater than the first width, and

wherein forming the third electrode film includes forming a sixth electrode film filling the second trench and overlying the fifth electrode film, wherein the sixth electrode film overlying the fifth electrode film, and the sixth electrode film have the first thickness, and

wherein thinning the third electrode film includes thinning the sixth electrode film overlying the fifth electrode film and located in a central portion of the second trench while leaving the sixth electrode film in the second trench and

wherein forming a barrier metal film and a metal film includes simultaneously forming the barrier film and the metal film above the fifth electrode film and into the second trench.

17. The method according to claim 16 , wherein thinning the sixth electrode film comprises an anisotropic etch back.