Semiconductor device with a first parallel pn structure in the active region and a second parallel pn structure in the termination region wherein the depth of the second parallel structure becomes stepwise shallower towards the periphery

A superjunction semiconductor device having an active region and a termination structure portion disposed on an outer side of the active region so as to surround a periphery of the active region in a plan view of the superjunction semiconductor device, the superjunction semiconductor device comprising:

• a semiconductor substrate of a first conductivity type;
• a buffer layer of the first conductivity type, provided on a surface of the semiconductor substrate and having an impurity concentration that is lower than an impurity concentration of the semiconductor substrate;
• a drift layer of the first conductivity type, provided on an upper surface of the buffer layer and having an impurity concentration that is lower than the impurity concentration of the buffer layer;
• a plurality of first column regions of the first conductivity type and a plurality of second column regions of a second conductivity type, repeatedly alternating one another in a first direction parallel to the surface of the semiconductor substrate, to thereby form a first parallel pn structure in the active region, and form a second parallel pn structure in the termination structure portion;
• a plurality of base regions of the second conductivity type, provided in the first parallel pn structure at a surface thereof;
• a plurality of source regions of the first conductivity type, selectively provided in the base regions at surfaces thereof;
• and
• a plurality of gate electrodes, each provided, via a gate electrode film, on a portion of the surface of one of the base regions, between one of the plurality of source regions and one of the plurality of first column regions, wherein
• the plurality of first column regions and the plurality of second column regions of the first parallel pn structure are provided in the drift layer and reaching the buffer layer,
• the plurality of first column regions and the plurality of second column regions of the second parallel pn structure have depths that become shallower stepwise in said first direction parallel to the surface of the semiconductor substrate toward an end portion of the semiconductor substrate,
• bottoms of the plurality of second column regions of the second parallel pn structure are in the drift layer, and
• at least one of the plurality of second column regions of the second parallel pn structure protrudes, in a second direction towards, and perpendicular to, the upper surface of the buffer layer, beyond two of the plurality of first column regions of the second parallel pn structure that are immediately adjacent to, and in the first direction sandwich, said at least one of the plurality of second column regions, said at least one of the plurality of second column regions having a bulged end.