Semiconductor device and method for manufacturing the same

A method for manufacturing a semiconductor device, the semiconductor device including:

• a drift layer of a first conductivity type;
• a base layer of a second conductivity type disposed on a surface layer portion of the drift layer;
• an impurity region of the first conductivity type disposed on a surface layer portion of the base layer, the impurity region having an impurity concentration higher than that of the drift layer;
• a trench gate structure including a gate insulating film disposed on a wall surface of a trench that penetrates the base layer and the impurity region and reaches the drift layer, and a gate electrode disposed on the gate insulating film;
• a first deep layer of the second conductivity type disposed below the trench in the drift layer, and separated from the trench;
• a second deep layer of the second conductivity type connecting the base layer and the first deep layer;
• a high-concentration layer of the first conductivity type or the second conductivity type disposed opposite to the base layer with respect to the drift layer, the high-concentration layer having an impurity concentration higher than that of the drift layer;
• a first electrode electrically connected to the base layer and the impurity region;
• and
• a second electrode electrically connected to the high-concentration layer, wherein
• the semiconductor device is configured to be an on state so that a current occurs between the first electrode and the second electrode when the gate electrode is applied with a gate voltage being equal to or higher than a predetermined voltage, and to be an off state when the gate electrode is applied with a gate voltage being lower than the predetermined voltage,
• the first deep layer has a high-concentration region and a low-concentration region in a concentration profile of an impurity concentration along a depth direction that corresponding to a stacking direction of the drift layer and the base layer,
• the high-concentration region has a high concentration peak at which the impurity concentration is maximum, and includes a region that is not depleted in the off state,
• the low-concentration region is disposed adjacent to the high-concentration layer than the high-concentration region, has a region in which a gradient of change in the impurity concentration is smaller than a predetermined value, and is depleted in the off state,
• a position closest to the base layer in the first deep layer is referred to as a first position, a position of the high concentration peak is referred to as a second position, a position closest to the base layer in the low-concentration region is referred to as a third position, the high-concentration region is disposed between the first position and the third position, and
• a first length between the first position and the second position is shorter than a second length between the second position and the third position,
• the method for manufacturing the semiconductor device, comprising:
• preparing a constituent substrate including a part of the drift layer adjacent to the high-concentration layer;
• forming the first deep layer by performing ion-implantation to the constituent substrate;
• and
• forming the drift layer having the first deep layer therein by epitaxially growing a constituent layer on the first deep layer.