Semiconductor device and method for manufacturing the same

1. A semiconductor device comprising:

a substrate;

a semiconductor layer disposed on a main surface of the substrate; and

a first main electrode and a second main electrode, which are disposed on the substrate separately from each other with the semiconductor layer sandwiched therebetween and are individually end portions of a current path of a main current flowing in an on-state,

wherein the semiconductor layer includes:

a first conductivity-type drift region through which the main current flows;

a second conductivity-type column region that is disposed inside the drift region and extends in parallel to the current path; and

an electric field relaxation region that is disposed in at least a part between the drift region and the column region and is either a low-concentration region in which an impurity concentration is lower than in a same conductivity-type adjacent region or a non-doped region, the electric field relaxation region being at least disposed on a side surface of the column region facing the second main electrode via the drift region, and

wherein the respective regions of the semiconductor layer are formed of a same material.

2. The semiconductor device according to claim 1 ,

wherein the electric field relaxation region is disposed on a side surface of the column region, the side surface facing the drift region in parallel to the current path.

3. The semiconductor device according to claim 1 ,

wherein impurity concentrations of the drift region and the column region are set so that the drift region and the column region are depleted by a depletion layer generated between the drift region and the column region in an off-state in which the main current is cut off.

4. The semiconductor device according to claim 1 ,

wherein the electric field relaxation region reaches the substrate.

5. The semiconductor device according to claim 1 ,

wherein the semiconductor layer includes a second conductivity-type well region disposed between the drift region and the first main electrode and between the column region and the first main electrode.

6. The semiconductor device according to claim 5 ,

wherein the semiconductor layer includes a first conductivity-type source region disposed between the well region and the first main electrode and electrically connected to the first main electrode,

wherein the semiconductor device further includes a control electrode embedded in the semiconductor layer while facing the drift region, the well region and the source region with an insulating film interposed therebetween, and

wherein the semiconductor device operates as a transistor that controls the main current by the control electrode.

7. The semiconductor device according to claim 1 , further comprising an electric field relaxation electrode disposed so as to cover at least a part of a region where the drift region and the column region face each other and electrically connected to the first main electrode or the second main electrode.

8. The semiconductor device according to claim 1 ,

wherein, on a side surface of a groove formed in the substrate, the drift region and the column region are arranged alternately with each other along a surface normal direction of the side surface of the groove.

9. The semiconductor device according to claim 1 ,

wherein the drift region and the column region are arranged alternately with each other along a thickness direction of the substrate.

10. The semiconductor device according to claim 1 ,

wherein the semiconductor layer is formed of a wide band gap semiconductor.

11. The semiconductor device according to claim 1 ,

wherein the substrate is a semi-insulating substrate or an insulating substrate.

12. The semiconductor device according to claim 1 ,

wherein the substrate is a silicon carbide substrate.

13. A method for manufacturing a semiconductor device, the method comprising:

forming a semiconductor layer comprising:

a first conductivity-type drift region on a main surface of a substrate;

a second conductivity-type column region inside the drift region, the column region extending in parallel to the drift region, and

an electric field relaxation region in at least a part between the column region and the drift region, the electric field relaxation region being either a lower-concentration region in which an impurity concentration is lower than in a same conductivity-type adjacent region or a non-doped region; and

forming a first main electrode and a second main electrode separately from each other on the substrate along a direction where the drift region extends, the first main electrode and the second main electrode facing each other with the drift region and the column region interposed therebetween,

wherein the drift region and the column region are formed by ion-implanting impurities into the substrate, the electric field relaxation region being at least disposed on a side surface of the column region facing the second main electrode via the drift region, and

wherein the respective regions of the semiconductor layer are formed of a same material.

14. The semiconductor device of claim 6 , wherein the control electrode comprises silicon carbide, SiGe or Al.