Trench-gate MOS transistor composed of multiple conductors

1. A semiconductor device, comprising:

a first semiconductor layer of a first conduction type;

a second semiconductor layer of the first conduction type formed on a surface of said first semiconductor layer;

a semiconductor base layer of a second conduction type formed on said second semiconductor layer;

a semiconductor diffusion layer of the first conduction type formed on a surface of said semiconductor base layer;

a trench formed from a surface of said semiconductor diffusion layer to a depth reaching said second semiconductor layer;

a gate electrode formed of a conductor film buried in said trench with a gate insulator interposed therebetween;

a first main electrode brought into contact with said semiconductor diffusion layer and said semiconductor base layer; and

a second main electrode formed on a rear surface of said first semiconductor layer,

wherein said conductor film includes a first conductor film formed along an inner wall of said trench covering the trench at its bottom and side to have a recess inside said trench, the recess formed to reach the second semiconductor layer, and a second conductor film formed to fill said recess,

said first and second conductor films being composed of the same material but being different in crystal grain.

2. The semiconductor device according to claim 1 , wherein one of said first conductor film and said second conductor film is formed of a silicon-based conductor film.

3. The semiconductor device according to claim 1 , wherein one of said first conductor film and said second conductor film is formed of polysilicon.

4. The semiconductor device according to claim 1 , wherein one of said first conductor film and said second conductor film is formed of a metal silicide.

5. The semiconductor device according to claim 1 , wherein said second conductor film contains a void therein.

6. A semiconductor device comprising:

a first semiconductor layer of a first conduction type;

a second semiconductor layer of the first conduction type formed on a surface of said first semiconductor layer;

a semiconductor base layer of a second conduction type formed on said second semiconductor layer;

a semiconductor diffusion layer of the first conduction type formed on a surface of said semiconductor base layer;

a trench formed from a surface of said semiconductor diffusion layer to a depth reaching said second semiconductor layer;

a gate electrode formed of a conductor film buried in said trench with a gate insulator interposed therebetween;

a first main electrode brought into contact with said semiconductor diffusion layer and said semiconductor base layer; and

a second main electrode formed on a rear surface of said first semiconductor layer,

wherein said conductor film includes a first conductor film formed along an inner wall of said trench covering its bottom and side to have a recess inside said trench, the recess formed to reach the second semiconductor layer, and a second conductor film formed to fill said recess, with an interlayer film formed between said first conductor film and said second conductor film and along the surface of said recess in said first conductor film,

wherein the first and second semiconductor films are electrically connected to each other.

7. The semiconductor device according to claim 6 , wherein said interlayer film is a silicon oxide film.

8. The semiconductor device according to claim 6 , wherein said first conductor film is a silicon-based conductor film, wherein said interlayer film is a silicon oxide film formed through natural oxidation of said first conductor film.

9. A semiconductor device comprising:

a first semiconductor layer of a first conduction type;

a second semiconductor layer of the first conduction type formed on a surface of said first semiconductor layer;

a semiconductor base layer of a second conduction type formed on said second semiconductor layer;

a semiconductor diffusion layer of the first conduction type formed on a surface of said semiconductor base layer;

a trench formed from a surface of said semiconductor diffusion layer to a depth reaching said second semiconductor layer;

a gate electrode formed of a conductor film buried in said trench with a gate insulator interposed therebetween;

a first main electrode brought into contact with said semiconductor diffusion layer and said semiconductor base layer; and

a second main electrode formed on a rear surface of said first semiconductor layer,

wherein said conductor film includes a first conductor film formed along an inner wall of said trench covering the trench and its bottom and side to have a recess inside said trench, the recess formed to reach the second semiconductor layer, and a second conductor film formed to fill said recess,

wherein the first and second conductor films are electrically connected to one another, and

wherein one of said first conductor film and said second conductor film is a silicon-based conductor film, and the other one of said first conductor film and said second conductor film is a metal film.

10. The semiconductor device according to claim 9 , further comprising an interlayer film formed between said first conductor film and said second conductor film and along the surface of said recess in said first conductor film.

11. The semiconductor device according to claim 6 , wherein said second conductor film contains a void therein.

12. The semiconductor device according to claim 9 , wherein said second conductor film contains a void therein.