Semiconductor device and method for manufacturing the same

1. A semiconductor device comprising:

a semiconductor substrate having a main surface and an isolation trench formed in the main surface;

a source region of a first conductivity type arranged in the main surface of the semiconductor substrate;

a drain region of the first conductivity type arranged in the main surface so as to sandwich the isolation trench between the drain region and the source region;

a drift region of the first conductivity type located below the isolation trench and connected to the drain region; an isolation insulation film filling the isolation trench and having a recessed portion in a top surface;

a gate electrode facing the main surface sandwiched between the source region and the drift region while being insulated from the main surface sandwiched between the source region and the drift region, and filling the recessed portion; and

a first impurity region of a second conductivity type having a portion located below the drift region and directly below the recessed portion, wherein the first impurity region is vertically aligned with a vertical side surface of the recessed portion and located only directly below the recessed portion.

2. The semiconductor device according to claim 1 , wherein

a length of the isolation trench in a direction from the source region toward the drain region is denoted as Ld, and

the first impurity region is located within a dimensional range of one third of the length Ld from an end of the isolation trench on a source region side.

3. The semiconductor device according to claim 1 , wherein

an end of the first impurity region on a drain region side is located closer to the source region than a position distanced from the recessed portion toward the drain region side by a dimension in a depth direction from a bottom portion of the recessed portion to a bottom portion of the isolation trench.

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

a first well region of the second conductivity type located below the drift region; and

a second well region of the second conductivity type located in the main surface between the source region and the drift region, wherein

the first well region has an impurity concentration lower than that of the second well region.

5. The semiconductor device according to claim 1 , further comprising

a second impurity region of the first conductivity type located inside the drift region and directly below the recessed portion.

6. The semiconductor device according to claim 5 , wherein

the second impurity region has a concentration peak lower than that of the first impurity region.

7. The semiconductor device according to claim 5 , wherein

an end of the second impurity region on the drain region side is located closer to the source region than a position distanced from the recessed portion toward the drain region side by a dimension in a depth direction from a bottom portion of the recessed portion to a bottom portion of the isolation trench.

8. The semiconductor device according to claim 5 , wherein

the recessed portion has a plurality of concave portions, and

the second impurity region has a plurality of second region portions located in regions directly below the plurality of concave portions, respectively.

9. The semiconductor device according to claim 1 , wherein

the recessed portion has a plurality of concave portions, and

the first impurity region has a plurality of first region portions located in regions directly below the plurality of concave portions, respectively.

10. The semiconductor device according to claim 9 , wherein

a width of each of the plurality of concave portions is greater than a distance between adjacent concave portions of the plurality of concave portions.