| 摘要 |
PURPOSE:To suppress a rise in a substrate potential directly under a gate insulating film and to prevent source/drain/breakdown, by providing a diffusion layer for substrate contact use which is formed to be disposed adjacent to a source diffusion layer and extended to a region directly under the gate insulating film. CONSTITUTION:An N channel field effect transistor is composed of a P type silicon substrate 1, a thick film field insulating film 2, a gate insulating film 5, a gate electrode 6, and the like. n<+> layers serving as source diffusion layers 3a, 3b and respective P<+> layers serving as diffusion layers for substrate contact use 7a, 7b, 7c are formed to be extended to a region directly under the gate insulating film 5 and disposed adjacent to each other by ion implantation in which the gate electrode 6 is used as a mask. When the P<+> diffusion layers for fixture of a substrate potential are thus extended to a position in contact with the gate part, an effective resistance PSUB of the substrate is much decreased to almost zero and hence a breakdown voltage VB can be much increased.
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