Patent ID: 8552492

Claim:
A semiconductor device comprising: a substrate; a source region and a drain region, both of which are of a first conductivity and arranged in the substrate; a channel region of a second conductivity arranged, in the substrate, in a first direction between the source region and the drain region; a first low-concentration region of the first conductivity formed in the substrate between the source region and the channel region and having a first conductivity dopant concentration lower than the first conductivity dopant concentration of the source region; a second low-concentration region of the first conductivity formed in the substrate between the drain region and the channel region and having a first conductivity dopant concentration lower than the first conductivity dopant concentration of the drain region; a trench formed in the substrate between the first low-concentration region and the second low-concentration region and having a side surface extending in the first direction between the first low-concentration region and the second low-concentration region, underlying a portion of a bottom of the trench including a lower corner portion thereof, the first and second low concentration regions both being in contact the bottom and sides of the trench; a gate insulating film formed in the bottom and the side surface of the trench; and a gate electrode formed in the trench through the gate insulating film such that the first direction of the gate electrode serves as a gate length direction, wherein a depth direction, in the substrate, of the gate electrode serves as a gate width direction such that a portion of the channel region sideward, in a second direction crossing the first direction in a plane view of the substrate, from the side surface of the trench is arranged between the first low-concentration region and the second low-concentration region, wherein a portion of the second low-concentration region extends under the bottom of the trench and extends beyond a width of the gate insulation film formed in the side surface of the trench so as to cover the lower corner portion such that a sum of length measurements of the underlying portion of the second low-concentration region measured from the lower corner portion of the trench in the first direction parallel to the substrate and in a depth direction perpendicular to the substrate is 0.1 μm or greater.