Method for manufacturing semiconductor device

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

• forming a first ion implantation expendable film on a first conductive type semiconductor substrate;
• forming a film for an etching mask on said first ion implantation expendable film;
• patterning said film for the etching mask into a shape of an active region and of a field region;
• forming a first mask pattern by a photolithography method in accordance with said film for the etching mask which has been patterned;
• introducing first or second conductive type dopant into said first conductive type semiconductor substrate;
• forming a trench groove on said first conductive type semiconductor substrate, after removing said mask pattern, by an etching method using said film for the etching mask as a mask;
• forming an insulation film in said trench groove;
• forming a first well by carrying out an annealing thermal treatment;
• flattening said insultation film after forming said trench groove;
• selectively removing said film for the etching mask;
• removing the whole of said first ion implantation expendable film;
• forming a second ion implantation expendable film on said first conductive type semiconductor substrate;
• forming a second mask pattern shape by a photolithography method in accordance with said trench groove;
• and
• forming a second well by introducing another first or second conductive type dopant into said first conductive type semiconductor substrate.