Semiconductor device having semiconductor regions with an impurity concentration distribution which decreases from a respective peak toward different semiconductor layers

A semiconductor device, comprising:

• a first semiconductor layer of a first conductivity type and having a first main surface and a second main surface;
• a second semiconductor layer of a second conductivity type provided on the first main surface of the first semiconductor layer;
• a third semiconductor layer provided on the second main surface of the first semiconductor layer;
• a plurality of first semiconductor regions of the first conductivity type and provided at differing depths in the first semiconductor layer, the plurality of first semiconductor regions having an impurity concentration higher than that of the first semiconductor layer;
• a second semiconductor region of the first conductivity type, constituting a part of the third semiconductor layer in contact with a first semiconductor region that of the plurality of first semiconductor regions is nearest the third semiconductor layer, the second semiconductor region having an impurity concentration that is higher than that of the plurality of first semiconductor regions;
• a third semiconductor region of the second conductivity type and constituting a part of the third semiconductor layer in contact with the first semiconductor region, the third semiconductor region being in contact with the second semiconductor region along a direction parallel to the second main surface;
• a first electrode in contact with the second semiconductor layer;
• and
• a second electrode in contact with the second semiconductor region and the third semiconductor region,
• wherein
• a first maximum value of the impurity concentration of the plurality of first semiconductor regions is lower than a second maximum value of the impurity concentration of the second semiconductor region and a third maximum value of an impurity concentration of the third semiconductor region, the first maximum value being a peak, the plurality of first semiconductor regions having an impurity concentration distribution that decreases from the peak toward the second semiconductor layer and toward the third semiconductor layer,
• the impurity concentration of the third semiconductor region at an interface with the first semiconductor region is lower than the impurity concentration of the second semiconductor region at an interface with the first semiconductor region,
• a part among parts of the first semiconductor region closer toward the third semiconductor layer than is the peak has an impurity concentration that is 0.5 times the first maximum value or less reaches a predetermined depth from an interface of the third semiconductor region and the first semiconductor region, and
• a distance from the predetermined depth to the interface of the third semiconductor region and the first semiconductor region is longer than a thickness of the third semiconductor region.