Semiconductor device and method for manufacturing the same

A semiconductor device comprising:

• a semiconductor substrate including a first main surface and a second main surface opposite to the first main surface;
• a drift layer of a first conductivity type provided between the first main surface and the second main surface of the semiconductor substrate;
• a buffer layer of the first conductivity type provided on a second main surface side with respect to the drift layer and having a larger number of atoms of impurities per unit volume than the drift layer;
• and
• a first semiconductor layer and a second semiconductor layer, provided on the second main surface side with respect to the buffer layer and arranged in this order in a direction from the second main surface toward the first main surface,
• wherein the first semiconductor layer and the second semiconductor layer have conductivity types identical to each other,
• the second semiconductor layer has a larger number of atoms of impurities per unit volume than the first semiconductor layer,
• the first semiconductor layer has a peak for the number of atoms of impurities per unit volume in the direction from the second main surface toward the first main surface,
• the second semiconductor layer has a peak for the number of atoms of impurities per unit volume in the direction from the second main surface toward the first main surface, and
• a depth from the second main surface at which the peak of the number of atoms per unit volume in the first semiconductor layer is positioned and a depth from the second main surface at which the peak of the number of atoms per unit volume in the second semiconductor layer is positioned satisfy a relation of:
• R2/R1=5.0.

A semiconductor device comprising:

• a semiconductor substrate including a first main surface and a second main surface opposite to the first main surface;
• a drift layer of a first conductivity type provided between the first main surface and the second main surface of the semiconductor substrate;
• a buffer layer of the first conductivity type provided on a second main surface side with respect to the drift layer and having a larger number of atoms of impurities per unit volume than the drift layer;
• and
• a first semiconductor layer and a second semiconductor layer, provided on the second main surface side with respect to the buffer layer and arranged in this order in a direction from the second main surface toward the first main surface,
• wherein the first semiconductor layer and the second semiconductor layer have conductivity types identical to each other,
• the second semiconductor layer has a larger number of atoms of impurities per unit volume than the first semiconductor layer,
• the buffer layer has a plurality of peaks for the number of atoms of impurities per unit volume in the direction from the second main surface toward the first main surface, and
• the plurality of peaks are heightened as nearing toward the second main surface.