Insulated gate power semiconductor device and method for manufacturing such a device

A method for manufacturing an insulated gate power semiconductor device comprising a substrate of a first conductivity type having a first side and second side opposite to the first side, such part of substrate having unamended doping concentration in the finalized device forming a drift layer, wherein the first side forms the emitter side and the second side forms the collector side in the finalized device the method comprises the following steps

• (a) on the first side forming a recess in the substrate up to a first depth, which recess has lateral sides and a first bottom, which is at least half of a trench depth,
• (b) applying a dopant of the first conductivity type at the first bottom,
• (c) performing a heating step so that the dopant of the first conductivity type diffuses into the substrate, such that a first conductivity doping concentration decreases towards the first side from a maximum doping concentration to a value of not more than half the maximum doping concentration,
• (d) removing material from the substrate in the recess such that the depth of the recess is increased up to the trench depth, wherein the recess has a second bottom, wherein the lateral sides of the recess form the trench lateral sides and the second bottom forms a trench bottom, wherein the remaining region, into which the dopant of the first conductivity type has been diffused in step (c), forms a second protection pillow,
• (e) applying a dopant of the second conductivity type, which is different from the first conductivity type, at the second bottom after step (d),
• (f) forming a first protection pillow by diffusing the dopant of the second conductivity type such that the first protection pillow covers the second bottom (85),
• (g) forming a base layer of the second conductivity type and a source layer of the first conductivity type on the first side,
• (h) forming a first electrically insulating gate layer in the recess after step f and filling the recess with electrically conductive material thereby forming the gate layer, wherein a trench gate electrode comprises the gate layer and the first insulating layer,
• (i) forming an emitter electrode on the first side, which contacts the base layer and the source layer, and a collector electrode on the second side, and
• (j) forming an enhancement layer of the first conductivity type, which separates the base layer from the drift layer in the finalized device, in or before step (h), wherein the enhancement layer has a maximum doping concentration in a second depth, which is lower than the first depth and wherein the doping concentration has a local doping concentration minimum between the second depth and the first depth.