Semiconductor apparatus having a column region with differing impurity concentrations

1. A semiconductor apparatus comprising:

a gate electrode;

a gate insulating layer;

a drift region of the first conductivity type formed over a semiconductor substrate of the first conductivity type;

a base region of a second conductivity type formed over the drift region;

a source region of the first conductivity type formed on the base region; and

a column shaped region formed in the drift region under the base region in a depth direction, the column region having at least one portion that has at least twice an impurity concentration of an average impurity concentration of the column region, an entirety of an uppermost surface of said column region directly contacting said base region.

2. The semiconductor apparatus according to claim 1 , wherein the gate electrode extends from the base region to the drift region, the gate electrode is formed in a trench formed in the drift region.

3. The semiconductor apparatus according to claim 2 , wherein the at least one portion having the higher impurity concentration is deeper than a bottom of the trench.

4. The semiconductor apparatus according to claim 1 , wherein the at least one portion having the higher impurity concentration includes a bottom of the column region.

5. The semiconductor apparatus according to claim 1 , further comprising:

a trench formed in the base regions; and

wherein the trench is filled with an electrically conductive material, and the column shaped region is formed below the trench.

6. The semiconductor apparatus according to claim 1 , wherein the column shaped region is substantially annular in horizontal cross-section.

7. The semiconductor apparatus according to claim 1 , wherein the column shaped region is substantially elliptical in horizontal cross-section.