Semiconductor device and method of manufacturing the same

A method of manufacturing a semiconductor device, comprising:

• forming, on a substrate, an insulator that includes a first portion including a first material;
• oxidizing the insulator to form a second portion including a second material different from the first material, on an upper face of the first portion in the insulator;
• forming at least one concave portion in the insulator after forming the second portion, and dividing the insulator into a plurality of insulators;
• and
• oxidizing the plurality of insulators to form a third portion including the second material on a side face of the first portion in one of the plurality of insulators.

A method of manufacturing a semiconductor device, comprising:

• alternately forming a plurality of first films and a plurality of second films on a substrate;
• forming a trench in the first and the second films;
• forming, in the trench, an insulator that includes a first portion including a first material and first and second charge trapping layers sandwiching the insulator;
• oxidizing the insulator to form a second portion including a second material different from the first material, on an upper face of the first portion in the insulator;
• forming at least one concave portion in the insulator after forming the second portion, and dividing the insulator into a plurality of insulators;
• oxidizing the plurality of insulators to form a third portion including the second material on a side face of the first portion of one of the plurality of insulators;
• and
• forming at least one semiconductor layer in the concave portion after the third portion is formed.