Field effect transistor

A field effect transistor comprising:

• a semiconductor substrate having a plurality of trenches provided from an upper surface of the semiconductor substrate;
• a gate insulating film covering an inner surface of each of the plurality of trenches;
• a gate electrode disposed inside each of the plurality of trenches and being insulated from the semiconductor substrate by the gate insulating film;
• and
• a source electrode being in contact with the upper surface of the semiconductor substrate, wherein
• the semiconductor substrate includes:
• a source layer of n-type being in contact with the source electrode and in contact with the gate insulating film on a side surface of each of the plurality of trenches;
• a body layer of p-type being in contact with the gate insulating film at a position below the source layer;
• a plurality of trench lower layers of p-type;
• a plurality of deep layers of p-type;
• and
• a drain-side layer of n-type,
• each of the plurality of trench lower layers is disposed directly below a corresponding one of the plurality of trenches, extends along a longitudinal direction of the plurality of trenches when the semiconductor substrate is viewed from above, and is electrically connected to the source electrode,
• each of the plurality of deep layers is disposed directly below the body layer, extends to a position below a lower end of each of the plurality of trench lower layers, extends along a first direction intersecting the plurality of trenches when the semiconductor substrate is viewed from above, and is electrically connected to the source electrode,
• respective deep layers in the plurality of deep layers are arranged at intervals along a second direction orthogonal to the first direction when the semiconductor substrate is viewed from above,
• the drain-side layer is distributed from a position in contact with a lower surface of the body layer to a position below a lower end of each of the plurality of deep layers through each of the intervals between the deep layers, and is in contact with the gate insulating film at a position below the body layer,
• the drain-side layer includes:
• a high concentration layer of n-type;
• an intermediate concentration layer of n-type disposed directly below the high concentration layer and having an n-type impurity concentration lower than an n-type impurity concentration of the high concentration layer;
• and
• a drift layer of n-type disposed directly below the intermediate concentration layer and having an n-type impurity concentration lower than the n-type impurity concentration of the intermediate concentration layer,
• and
• the intermediate concentration layer is in contact with a side surface of each of the plurality of deep layers.