Semiconductor device including normally-off type junction transistor and method of manufacturing the same

1. A semiconductor device comprising:

(a) a semiconductor substrate of a first conductive type to be a drain layer;

(b) an epitaxial layer of a first conductive type formed on the semiconductor substrate;

(c) a plurality of trenches each formed so as to reach an inside of the epitaxial layer from a surface of the epitaxial layer;

(d) a source layer of a first conductive type formed on a surface region of the epitaxial layer interposed between trenches adjacent to each other;

(e) a gate layer of a second conductive type formed in the epitaxial layer so as to contact with side walls and a bottom portion of each of the plurality of trenches;

(f) a channel-formed region of a first conductive type formed in the epitaxial layer between portions of the gate layer adjacent to each other;

(g) a drain electrode formed on a rear surface of the semiconductor substrate;

(h) a source electrode formed so as to connect to the source layer; and

(i) a gate electrode formed so as to connect to the gate layer, wherein

in a horizontal direction, an impurity concentration of a first conductive type impurity doped in a junction region forming a p-n junction with the gate layer in the channel-formed region formed between the portions of the gate layer adjacent to each other is higher than an impurity concentration of a first conductive type impurity doped in a center region in the channel-formed region.

2. The semiconductor device according to claim 1 , wherein

a peak of the impurity concentration of the junction region forming the p-n junction with the gate layer in the channel-formed region is twice or more and five times or less as high as that of the epitaxial layer.

3. The semiconductor device according to claim 2 , wherein

the impurity concentration of the epitaxial layer is lower than that of the semiconductor substrate.

4. The semiconductor device according to claim 1 , wherein

a substrate material of the semiconductor substrate is silicon carbide.

5. The semiconductor device according to claim 4 , wherein

the first conductive type is an n type, and the second conductive type is a p type.

6. The semiconductor device according to claim 5 , wherein

impurities doped in the gate layer are aluminum or boron, and

impurities doped in the channel-formed region are nitrogen or phosphorus.

7. The semiconductor device according to claim 1 , wherein

a substrate material of the semiconductor substrate is gallium nitride.

8. A semiconductor device comprising:

(a) a semiconductor substrate of a first conductive type to be a drain layer;

(b) an epitaxial layer of a first conductive type formed on the semiconductor substrate;

(c) a plurality of trenches each formed so as to reach an inside of the epitaxial layer from a surface of the epitaxial layer;

(d) a source layer of a first conductive type formed on a surface region of the epitaxial layer interposed between trenches adjacent to each other;

(e) a gate layer of a second conductive type formed in the epitaxial layer so as to contact with a bottom portion of each of the plurality of trenches;

(f) a channel-formed region of a first conductive type formed in the epitaxial layer between portions of the gate layer adjacent to each other;

(g) a drain electrode formed on a rear surface of the semiconductor substrate;

(h) a source electrode formed so as to connect to the source layer; and

(i) a gate electrode formed so as to connect to the gate layer, wherein

in a horizontal direction, an impurity concentration of a first conductive type impurity doped in a junction region forming a p-n junction with the gate layer in the channel-formed region formed between the portions of the gate layer adjacent to each other is higher than an impurity concentration of a first conductive type impurity doped in a center region in the channel-formed region.

9. The semiconductor device according to claim 8 , wherein

a peak of the impurity concentration of the junction region forming the p-n junction with the gate layer in the channel-formed region is twice or more and five times or less as high as that of the epitaxial layer.

10. A semiconductor device comprising:

(a) a semiconductor substrate of a first conductive type to be a drain layer;

(b) an epitaxial layer of a first conductive type formed on the semiconductor substrate;

(c) a source layer of a first conductive type formed so as to dispose portions of the source layer apart from each other at a constant distance on a surface region of the epitaxial layer;

(d) a gate layer of a second conductive type formed in the epitaxial layer between portions of the source layer adjacent to each other, the gate layer being deeper than the source layer;

(e) a channel-formed region of a first conductive type formed in the epitaxial layer between portions of the gate layer adjacent to each other;

(f) a drain electrode formed on a rear surface of the semiconductor substrate;

(g) a source electrode formed so as to connect to the source layer; and

(h) a gate electrode formed so as to connect to the gate layer, wherein

in a horizontal direction, an impurity concentration of a first conductive type impurity doped in a junction region forming a p-n junction with the gate layer in the channel-formed region formed between the portions of the gate layer adjacent to each other is higher than an impurity concentration of a first conductive type impurity doped in a center region in the channel-formed region.

11. The semiconductor device according to claim 10 , wherein

a peak of the impurity concentration of the junction region forming the p-n junction with the gate layer in the channel-formed region is twice or more and five times or less as high as that of the epitaxial layer.