Method for manufacturing semiconductor device having element isolation portions

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

• forming an opening in an insulating layer, which is formed on a semiconductor substrate, using a photoresist pattern formed on the insulating layer as a mask;
• forming a first element isolation portion in the semiconductor substrate by implanting an ion into the semiconductor substrate using the photoresist pattern as a mask;
• removing the photoresist pattern after the forming the first element isolation portion;
• forming a second element isolation portion, in the semiconductor substrate, whose outer edge is outside an outer edge of the opening, by implanting an ion into the semiconductor substrate through the opening at an implantation intensity lower than an implantation intensity in the forming the first element isolation portion, after the removing the photoresist pattern;
• and
• forming a third element isolation portion, providing electrical insulation, which is inside the outer edge of the second element isolation portion, by embedding an insulating member in the opening and removing the insulating layer.