PURPOSE: To simplify processes, by forming silicate glass including low concentration impurities, performing heat treatment with said glass as diffusion source, diffusing the impurities into source and drain regions, forming an N layer, and performing high-concentration ion implantation with the N layer as a mask.
CONSTITUTION: On a P-type silicon substrate 101, an oxide film 102 and polysilicon 103 are formed. With resist 204 as a mask, a gate electrode is formed. PSG (phosphorus silicate glass) 109 is grown by a chemical vapor deposition method. After anisotropic etching, heat treatment is performed in an oxygen atmosphere, and a thin oxide film 107 is grown. By utilizing the heat treatment at this time, phosphorus is diffused in the silicon substrate 101 with the phosphorus in the PSG 109 as a diffusing source. Thus an N layer 110 is formed. In order to form an N + layer 108 for a source and a drain in the next process, As ions are implanted, and heat treatment is performed in nitrogen atmosphere. Thus the N + layer is formed.