Semiconductor device with multi-layer gate electrode
The semiconductor device of the present invention includes a semiconductor region made of a material to which conductive impurities are added, an insulating film formed on a surface of the semiconductor region, and an electroconductive gate electrode formed on the insulating film. The gate electrode is made of a material whose Fermi level is closer to a Fermi level of the semiconductor region than a Fermi level of Si in at least a portion contiguous to the insulating film.
1. A semiconductor device comprising:
a semiconductor region made of a material to which conductive impurities are added;
an insulating film formed on a surface of the semiconductor region; and
an electroconductive gate electrode formed on the insulating film, the gate electrode being made of a material whose Fermi level is closer to a Fermi level of the semiconductor region than a Fermi level of Si in at least a portion contiguous to the insulating film;
wherein the gate electrode comprises an electroconductive first layer that is contiguous to the insulating film and that is made of a material whose Fermi level is closer to a Fermi level of the semiconductor region than a Fermi level of Si, and an electroconductive second layer that is stacked on the electroconductive first layer and that is made of a material different from the material of the electroconductive first layer.
2. The semiconductor device according to claim 1 , wherein the semiconductor region has a wider band gap than a band gap of Si.
3. The semiconductor device according to claim 2 , wherein the gate electrode has a wider band gap than the band gap of Si.
4. The semiconductor device according to claim 1 , wherein the electroconductive first layer is P-type Poly-SiC, and the electroconductive second layer is P-type Poly-Si containing a P-type impurity.
5. The semiconductor device according to claim 4 , wherein the P-type impurity is B (boron).
6. The semiconductor device according to claim 1 , wherein the semiconductor region and the gate electrode are the same in material as each other.
7. The semiconductor device according to claim 6 , wherein the material of the semiconductor region is P-type SiC, and the material of the gate electrode is P-type Poly-SiC.
8. The semiconductor device according to claim 1 , wherein the semiconductor region has an impurity concentration of 1×10 18 cm −3 or less in a portion whose depth from the insulating film is 1000 Å or less.
9. The semiconductor device according to claim 1 , wherein
the semiconductor region is formed on a semiconductor substrate, and
an off-angle of the semiconductor substrate is less than 4° exceeding 0°.
10. A semiconductor device comprising:
a SiC substrate;
an epitaxial layer formed on a side of one surface of the SiC substrate;
a gate trench dug downwardly from a principal plane of the epitaxial layer, wherein
an off-angle of the SiC substrate is less than 4° exceeding 0;
a gate electrode;
a gate insulating film; and
a body region;
wherein the gate electrode comprises an electroconductive first layer that is contiguous to the gate insulating film and that is made of a material whose Fermi level is closer to a Fermi level of the body region than a Fermi level of Si, and an electroconductive second layer that is stacked on the electroconductive first layer and that is made of a material different from the material of the electroconductive first layer.
11. The semiconductor device according to claim 10 , wherein one surface of the SiC substrate is a C plane.
12. The semiconductor device according to claim 10 , wherein a bottom surface of the gate trench is a surface inclined by the off-angle in a direction of a [11-20] axis with respect to a just (000-1) plane.
13. The semiconductor device according to claim 10 , wherein an off-angle of the SiC substrate is 0.3° or more and less than 4°.
14. The semiconductor device according to claim 10 , wherein an off-angle of the SiC substrate is 1°.
15. The semiconductor device according to claim 10 , wherein the gate insulating film is formed on a bottom surface and side surfaces of the gate trench, wherein
a thickness of a portion on the bottom surface in the gate insulating film is greater than a thickness of a portion on the side surface in the gate insulating film.
16. The semiconductor device according to claim 10 , wherein the gate trench is formed in a tapered manner.
17. The semiconductor device according to claim 10 , wherein
the epitaxial layer contains the body region, the body region being formed beside the gate trench,
the gate electrode faces the body region via the gate insulating film, the gate insulation film being formed on a side surface of the gate trench, and
the gate electrode is formed by use of a same material as the body region.
18. The semiconductor device according to claim 17 , wherein
a material of the body region is P-type SiC, and
a material of the gate electrode is P-type Poly-SiC.
19. The semiconductor device according to claim 17 , wherein
a material of the body region is P-type SiC, and
the electroconductive first layer of the gate electrode is made of P-type Poly-SiC and the electroconductive second layer of the gate electrode is made of P-type Poly-Si.
20. The semiconductor device according to claim 17 , wherein the body region has an impurity concentration of 1×10 18 cm −3 or less in a portion whose depth from the gate insulating film is 1000 Å or less.
21. A semiconductor device comprising:
a first conductivity type SiC substrate;
a first conductivity type epitaxial layer formed on a side of one surface of the SiC substrate;
a second conductivity type body region formed at a surface portion of the epitaxial layer;
a gate trench formed in the epitaxial layer so as to penetrate the body region from a surface of the epitaxial layer;
a gate insulating film formed on an inner surface of the gate trench; and
a gate electrode formed on the gate insulating film, wherein an off-angle of the SiC substrate is less than 4° exceeding 0°, and the gate electrode is made of a same material as the body region, and
the gate electrode comprises an electroconductive first layer that is contiguous to the gate insulating film and that is made of a material whose Fermi level is closer to a Fermi level of the body region than a Fermi level of Si, and an electroconductive second layer that is stacked on the electroconductive first layer and that is made of a material different from the material of the electroconductive first layer.
22. The semiconductor device according to claim 21 , wherein
a material of the body region is P-type SiC, and
a material of the gate electrode is P-type Poly-SiC.
23. The semiconductor device according to claim 21 , wherein the body region has an impurity concentration of 1×10 18 cm −3 or less in a portion whose depth from the gate insulating film is 1000 Å or less.
24. The semiconductor device according to claim 21 , wherein
the gate insulating film includes a first portion on the bottom surface of the gate trench and a second portion on the side surface of the gate trench, and
the first portion is thicker than the second portion.