IGBT and method of manufacturing the same

1. A method of manufacturing an IGBT, comprising:

forming an n-type emitter region in a range to be exposed to an upper face of a semiconductor substrate, the emitter region having a depth;

forming a p-type top body region below the depth of the emitter region by implanting p-type impurities into the upper face of the semiconductor substrate such that the p-type impurities stop within the depth of the emitter region, and diffusing the implanted p-type impurities, the top body region having a depth;

forming an n-type floating region below the depth of the top body region by implanting n-type impurities into the upper face of the semiconductor substrate such that the n-type impurities stop within the depth of the emitter region, and diffusing the implanted n-type impurities, the floating region having a depth;

forming a trench in the upper face of the semiconductor substrate, and forming a gate insulating film that covers an inner face of the trench, and a gate electrode that is arranged in the trench; and

forming a p-type bottom body region below the depth of the floating region by implanting p-type impurities into the upper face of the semiconductor substrate such that the p-type impurities stop at a depth below the floating region, after forming the trench, the gate insulating film, and the gate electrode, wherein

in the forming of the trench, the trench is arranged so that, after the respective formings are carried out, the trench penetrates the emitter region, the top body region, the floating region, and the bottom body region, and when a distribution of a concentration of p-type impurities in the top body region and the floating region, which are located below the emitter region, is viewed along a thickness direction of the semiconductor substrate, the concentration of the p-type impurities decreases as a downward distance increases from an upper end of the top body region that is located below the emitter region, and reaches a local minimum value at a predetermined depth in the floating region.

2. The manufacturing method according to claim 1 , wherein

the forming of the top body region and the forming of the floating region are carried out prior to of forming of the trench, the gate insulating film, and the gate electrode.

3. The manufacturing method according to claim 1 , wherein

the p-type impurities are implanted into the semiconductor substrate with an upper face of the gate electrode present below the upper face of the semiconductor substrate, in the forming of the bottom body region.

4. A method of manufacturing an IGBT, comprising:

causing an epitaxial layer of an n-type semiconductor to grow on an upper face of a base substrate;

forming an n-type emitter region in a range to be exposed to an upper face of the epitaxial layer;

forming a p-type top body region below a depth of the emitter region by implanting p-type impurities into the upper face of the epitaxial layer such that the p-type impurities stop within the depth of the emitter region, and diffusing the implanted p-type impurities;

forming a trench in the upper face of the epitaxial layer, and forming a gate insulating film that covers an inner face of the trench, and a gate electrode that is arranged in the trench; and

forming a p-type bottom body region in the base substrate by implanting p-type impurities into the upper face of the epitaxial layer such that the p-type impurities stop in the base substrate, after forming the trench, the gate insulating film, and the gate electrode, wherein

the n-type epitaxial layer remains between the top body region and the bottom body region to constitute a floating region, and the trench is arranged to penetrate the emitter region, the top body region, the floating region, and the bottom body region, after the causing and the respective formings are carried out, and when a distribution of a concentration of p-type impurities in the top body region and the floating region, which are located below the emitter region, is viewed along a thickness direction of the semiconductor substrate, the concentration of the p-type impurities decreases as a downward distance increases from an upper end of the top body region that is located below the emitter region, and reaches a local minimum value at a predetermined depth in the floating region.

5. The manufacturing method according to claim 4 , wherein

the forming of the top body region is carried out prior to the forming of the trench, the gate insulating film, and the gate electrode.

6. The manufacturing method according to claim 4 , wherein

the p-type impurities are implanted into a semiconductor substrate with an upper face of the gate electrode present below an upper face of the semiconductor substrate, in the forming of the bottom body region.