Semiconductor device including a field effect transistor

1. A semiconductor device including a transistor formed on a semiconductor substrate, comprising:

a gate insulating film formed on the semiconductor substrate;

a first conductive film being a metal film, a metal nitride film, a metal silicide film or a metal carbide film, and formed on and in contact with the gate insulating film;

a middle layer formed on an upper surface of the first conductive film and in contact with the first conductive film and containing a silicon material, the middle layer being separated from the gate insulating film by the first conductive film;

a second conductive film, comprising of different aterial from the middle layer, formed on an upper surface of the first conductive film and in contact with the first conductive film and in contact with a sidewall of the middle layer, and

the first conductive film has a different chemical composition from the second conductive film.

2. The semiconductor device of claim 1 , further comprising:

a third conductive film formed on and in contact with the middle layer,

wherein the second conductive film is also formed in contact with a sidewall of the third conductive film.

3. The semiconductor device of claim 2 , wherein the third conductive film is comprised of a silicide material or a metal material.

4. The semiconductor device of claim 3 , wherein when the third conductive film is comprised of the silicide material, the third conductive film contains at least one selected from the group consisting of Ni, Co, Ti, W, Pt, and Mo.

5. The semiconductor device of claim 1 , wherein the middle layer is comprised of a material containing silicon as a major component, the material being polysilicon, amorphous silicon, or porous silicon.

6. The semiconductor device of claim 5 , wherein

the material containing silicon as a major component is an undoped silicon film or a silicon film doped with an atom other than silicon, and

the doped silicon film is a film comprised of a material doped with at least one selected from phosphorus (P), arsenic (As), boron (B), indium (In), carbon (C), fluorine (F), nitrogen (N), oxygen (O), germanium (Ge), platinum (Pt), nickel (Ni), cobalt (Co), titanium (Ti), iron (Fe), tungsten (W), and molybdenum (Mo).

7. The semiconductor device of claim 5 , wherein the middle layer contains a P-type carrier and an N-type carrier in the material containing silicon as a major component so that the middle layer has a PN junction in a plane perpendicular to a main surface of the semiconductor substrate.

8. The semiconductor device of claim 5 , wherein the middle layer contains a P-type carrier and an N-type carrier in the material containing silicon as a major component so that the middle layer has a PN junction in a plane parallel to a main surface of the semiconductor substrate.

9. The semiconductor device of claim I wherein the middle layer is comprised of an insulating film material which is silicon oxide, silicon nitride, or silicon oxynitride.

10. The semiconductor device of claim 1 , wherein

the middle layer is formed of a multilayer film including a material containing silicon as a major component and an insulating film material,

the material containing silicon as a major component is polysilicon, amorphous silicon, or porous silicon, and

the insulating film material includes silicon oxide, silicon nitride, silicon oxynitride, yttrium oxide, aluminum oxide, and aluminum nitride.

11. The semiconductor device of claim 1 , wherein the middle layer is a film configured to apply or release stress to a channel surface of a gate electrode included in the transistor, and is formed of a film of silicon nitride, porous silicon, silicide, SiGe, or SiC.

12. The semiconductor device of claim 1 , wherein the middle layer is a film configured to transmit light, and is formed of a film of silicon oxide, silicon nitride, or silicon oxynitride.

13. The semiconductor device of claim 1 , wherein the first conductive film is a film configured to set a threshold of a gate electrode included in the transistor, the film being a metal film comprised of at least one metal selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, or a film comprised of a nitride, silicide, or carbide of at least one metal selected from the metal group, where the nitride of Ti, Ta, Zr, Hf, or Nb does not have a stoichiometric composition and contains a smaller amount of N.

14. The semiconductor device of claim 1 , wherein the first conductive film is a film configured to set a threshold of a gate electrode included in the transistor, the film being a metal film comprised of at least one metal selected from the group consisting of Ni, Pd, Pt, Co, Rh, Ru. Cu, Ag, and Au, a film comprised of a nitride, silicide, carbide, or oxide of at least one metal selected from the metal group, a film comprised of a nitride of Ti, Ta, Zr, Hf, or Nb having a stoichiometric composition of TiN, TaN, ZrN, HfN, or NbN, a film comprised of Ru oxide, or a film comprised of Ir oxide.

15. The semiconductor device of claim 1 , wherein the first conductive film has a disconnection in a gate electrode included in the transistor in a plane perpendicular to a main surface of the semiconductor substrate.

16. The semiconductor device of claim 1 , wherein the second conductive film is formed of a metal film.

17. The semiconductor device of claim 16 , wherein the second conductive film is a metal film comprised of at least one metal selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, or a film comprised of a nitride, silicide, or carbide of at least one metal selected from the metal group, where the nitride of Ti, Ta, Zr, Hf, or Nb does not have a stoichiometric composition and contains a smaller amount of N.

18. The semiconductor device of claim 16 , wherein the second conductive film is a film configured to set a threshold of a gate electrode included in the transistor, the film being a metal film comprised of at least one metal selected from the group consisting of Ni, Pd, Pt, Co, Rh, Ru, Cu, Ag, and Au, a film comprised of a nitride, silicide, carbide, or oxide of at least one metal selected from the metal group, a film comprised of a nitride of Ti, Ta, Zr, Hf, or Nb having a stoichiometric composition of TiN, TaN, ZrN, HfN, or NbN, a film comprised of Ru oxide, or a film comprised of Ir oxide.

19. The semiconductor device of claim 16 , wherein the second conductive film is comprised of the same material for the first conductive film.

20. The semiconductor device of claim 16 , wherein

the second conductive film is formed of a multilayer film including an inner conductive film and an outer conductive film,

the inner conductive film is a film comprised of Ti, Zr, Hf, V. Nb, Ta, Cr, Mo, W, Ni, Pd, Pt, Co, Rh. Ru, Cu, Ag, or Au, and

the outer conductive film is an oxidation resistant film comprised of TiN, TaN, Ir oxide, Ru oxide, Pt, or Au.

21. The semiconductor device of claim 1 , wherein the second conductive film is formed of a silicide film.

22. The semiconductor device of claim 21 , wherein the second conductive film contains at least one selected from the group consisting of Ni, Co, Ti, W, Pt, and Mo.

23. The semiconductor device of claim 21 , wherein

the second conductive film is formed of a multilayer film including an inner conductive film and an outer conductive film,

the inner conductive film is a film containing at least one selected from the group consisting of Ni, Co, Ti, W, Pt, and Mo, and

the outer conductive film is an oxidation resistant film comprised of TiN, TaN, Ir oxide, Ru oxide, Pt, or Au.

24. The semiconductor device of claim 3 , wherein when the second conductive film is formed of a silicide film and the third conductive film is formed of the silicide material, the second conductive film is comprised of the same material for the third conductive film.