| 摘要 |
PROBLEM TO BE SOLVED: To prevent the deterioration of the breakdown strength of the drain diffusion layer of a high-breakdown-strength MOS transistor by having the third diffusion layer of the same conductivity type as the semiconductor substrate existing apart from the first and second diffusion layers and higher in impurity concentration than the semiconductor substrate, under these first and second diffusion layers. SOLUTION: B<+> is implanted by 4.0E12 as p-type impurities with energy of 100keV by ion implantation method, as it stands as a resist pattern. Or, B<+> is implanted by 1.5E12 with energy of 50keV as p-type impurities by ion implantation method. Then, the impurities to control the Vth of a MOS transistor are implanted to oxidate the surface of a substrate and form a gate oxide film 1307 by 10nm. By the heat treatment for twenty minutes at 900 deg.C at oxidation, the impurities implanted before diffuse thermally, thus a heavily doped p-type diffusion region 1308, a p-type channel stop region 1309, and a p-type diffusion region 1310 are made. A p-type well is made of these p-type diffusion regions. Hereby, the deterioration of the breakdown strength is prevented. |
