Isolation structure for semiconductor device including double diffusion isolation region forming pn junction with neighboring wells and isolation region beneath

Abstract

In a semiconductor device of the present invention, an N type epitaxial layer is formed on a P type single crystal silicon substrate. The substrate and the epitaxial layer are partitioned into a plurality of element formation regions by isolation regions. Each of the isolation regions is formed of a P type buried diffusion layer and a P type diffusion layer coupled thereto. The P type buried diffusion layer is joined to N type buried diffusion layers on both sides thereof to form PN junction regions. On the other hand, the P type diffusion layer is joined to N type diffusion layers on both sides thereof to form PN junction regions. This structure suppresses extension of widthwise diffusion of the P type buried diffusion layer and the P type diffusion layer, thus making it possible to reduce the device size.