Semiconductor device having element isolation region

Abstract

An n-type buried diffusion layer is formed on the surface layer of the prescribed area of a p-type silicon substrate, and a p-type first high-concentration isolation diffusion layer is formed in the silicon substrate so as to surround the buried diffusion layer. An n-type epitaxial layer is formed on the silicon substrate, the buried diffusion layer, and the first high-concentration isolation diffusion layer. A p-type second high-concentration isolation diffusion layer is formed in the epitaxial layer on the first high-concentration isolation diffusion layer. A p-type low-concentration isolation diffusion layer for isolating the epitaxial layer into a plurality of island regions is formed in the epitaxial layer on the second high-concentration isolation diffusion layer.

1 - 20 . (canceled) 
     
     
         21 . A method for manufacturing a semiconductor device, comprising the steps of:
 forming a buried diffusion layer of a second conductivity type in the surface layer of a prescribed area of a substrate of a first conductivity type;   forming a first high-concentration isolation diffusion layer of the first conductivity type in the substrate so as to surround the buried diffusion layer;   forming an epitaxial layer of the second conductivity type on the substrate, the buried diffusion layer, and the first high-concentration isolation diffusion layer;   forming a low-concentration isolation diffusion layer of the first conductivity type in the epitaxial layer on the first high-concentration isolation diffusion layer, the low-concentration isolation diffusion layer isolating the epitaxial layer into a plurality of island regions;   forming a second high-concentration isolation diffusion layer of the first conductivity type in the junction area between the first high-concentration isolation diffusion layer and the low-concentration isolation diffusion layer; and   forming a high-concentration diffusion layer of the first conductivity type in direct physical contact with an upper layer of said buried diffusion layer.   
     
     
         22 . The method for manufacturing a semiconductor device according to  claim 21 , further comprising the steps of:
 forming, after formation of the second high-concentration isolation diffusion layer, a first circuit element having a diffusion region of the first conductivity type in a first island region of the epitaxial layer; and   forming a second circuit element having a diffusion region of the second conductivity type in a second island region of the epitaxial layer.   
     
     
         23 . The method for manufacturing a semiconductor device according to  claim 21 , further comprising the steps of:
 forming, after formation of the epitaxial layer, a first diffusion layer of the first conductivity type in a third island region of the epitaxial layer on the buried diffusion layer;   forming a second diffusion layer of the second conductivity type in the third island region adjacent to the first diffusion layer; and   forming a high-concentration diffusion layer of the first conductivity type in the junction area between the buried diffusion layer and the first diffusion layer.   
     
     
         24 . The method for manufacturing a semiconductor device according to  claim 23 , further comprising the steps of:
 forming, after formation of the high-concentration diffusion layer, a third circuit element having a diffusion region of the second conductivity type in the first diffusion layer; and   forming a fourth circuit element having a diffusion region of the first conductivity type in the second diffusion layer.