Semiconductor device having element isolation region
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. A semiconductor device comprising:
a substrate of a first conductivity type;
an epitaxial layer of a second conductivity type formed on said substrate;
a buried diffusion layer of the second conductivity type formed in an upper surface layer of a prescribed area of said substrate and formed in an under surface of said epitaxial layer on the prescribed area of the substrate;
a high-concentration diffusion layer of the first conductivity type formed directly on said, buried diffusion layer of the second conductivity type;
a first high-concentration isolation diffusion layer of the first conductivity type formed in the upper surface layer of an area of said substrate and formed in the under surface of said epitaxial layer on the area of said substrate so as to surround said buried diffusion layer, and said first high-concentration isolation diffusion layer is in both the epitaxial layer and the substrate;
a second high-concentration isolation diffusion layer of the first conductivity type formed in said epitaxial layer on said first high-concentration isolation diffusion layer;
a p-type well region formed on said high-concentration diffusion layer;
an n-type well region formed on said buried diffusion layer adjacent said p-type well region; and
a low-concentration isolation diffusion layer of the first conductivity type formed on said second high-concentration isolation diffusion layer, for isolating said epitaxial layer into a plurality of island regions, wherein
one each of immediately adjacent said first high-concentration isolation diffusion layer, second high-concentration isolation diffusion layer, and low-concentration isolation diffusion layer form a first isolation diffusion region,
another one each of immediately adjacent said first high-concentration isolation diffusion layer, second high-concentration isolation diffusion layer, and low-concentration isolation diffusion layer form a second isolation diffusion region,
one of said plurality of island regions is located between said p-type well region and said first isolation diffusion region,
another one of said plurality of island regions is located between said n-type well region and said second isolation diffusion region, and
as seen in a cross-sectional view only said one of said plurality of island regions is between said p-type well region and said first isolation diffusion region along a straight line extending from said p-type well region to said first isolation diffusion region, and only said another one of said plurality of island regions is between said n-type well region and said second isolation diffusion region along a straight line extending from said n-type well region to said second isolation diffusion region.
2. The semiconductor device according to claim 1 , further comprising:
a first circuit element formed in a first island region of said epitaxial layer, said first circuit element having a diffusion region of the first conductivity type; and
a second circuit element formed in a second island region of said epitaxial layer, said second circuit element having a diffusion region of the second conductivity type.
3. The semiconductor device according to claim 2 , wherein said first circuit element is a diffused resistor element of the first conductivity type, and said second circuit element is a bipolar transistor.
4. The semiconductor device according to claim 3 , further comprising:
a first diffusion layer of the first conductivity type formed in a third island region of said epitaxial layer on said high-concentration diffusion layer; and
a second diffusion layer of the second conductivity type formed in said third island region adjacent to said first diffusion layer.
5. The semiconductor device according to claim 2 , further comprising:
a first diffusion layer of the first conductivity type formed in a third island region of said epitaxial layer on said high-concentration diffusion layer; and
a second diffusion layer of the second conductivity type formed in said third island region adjacent to said first diffusion layer.
6. The semiconductor device according to claim 1 , further comprising:
a first diffusion layer of the first conductivity type formed in a third island region of said epitaxial layer on said high-concentration diffusion layer; and
a second diffusion layer of the second conductivity type formed in said third island region adjacent to said first diffusion layer.
7. The semiconductor device according to claim 6 , further comprising:
a third circuit element formed in said first diffusion layer, said third circuit element having a diffusion region of the second conductivity type; and
a fourth circuit element formed in said second diffusion layer, said fourth circuit element having a diffusion region of the first conductivity type.
8. The semiconductor device according to claim 7 ,
wherein said third circuit element is an insulated gate field effect transistor of the second conductivity type, and
said fourth circuit element is an insulated gate field effect transistor of the first conductivity type.