Semiconductor device and method for manufacturing semiconductor device

A storage device, comprising:

• a semiconductor layer;
• a plurality memory cells on the semiconductor layer in a first region;
• and
• a peripheral circuit formed on the semiconductor layer in a second region that is adjacent to the first region in a first direction, wherein
• the peripheral circuit includes a transistor comprising:
• a well region at a surface of the semiconductor layer;
• a gate insulating film on a surface of the well region;
• a gate electrode on the gate insulating film;
• an insulator layer on the surface of the well region and a side surface of the gate electrode, the insulator layer surrounding the gate electrode, and
• an element isolation embedded in the semiconductor layer and surrounding the well region, the element isolation having:
• a first portion recessed to a level lower than the surface of the well region, and
• a second portion between the well region and the first region and including a protrusion protruding above the level of the first portion.

A method of manufacturing a semiconductor device, the method comprising:

• forming an insulating film on an upper surface of diffusion region that is in a semiconductor layer;
• forming a semiconductor film on the insulating film;
• forming an element isolation extending through the semiconductor film and insulating film into the semiconductor layer, the element isolation surrounding the diffusion region;
• forming a recess in an upper surface of the element isolation by removing a part of the element isolation;
• forming a conductive film on the semiconductor film and the recessed upper surface of the element isolation;
• forming a gate electrode by removing portions of the insulating film, the semiconductor film, and the conductive film;
• and
• forming an insulator layer on the upper surface of the diffusion region to surround the gate electrode, wherein
• in forming the gate electrode, a first region of the element isolation is recessed to be lower than the upper surface of the diffusion region and a second region of the element isolation includes a protruding portion that protrudes to a level higher than the upper surface of the diffusion region, the second region being between the first region and the diffusion region.