Semiconductor device with a reduced mask count buried layer
View Patent ↗An N type buried layer is formed, in one embodiment, by a non selective implant on the surface of a wafer and later diffusion. Subsequently, the wafer is masked and a selective P type buried layer is formed by implant and diffusion. The coefficient of diffusion of the P type buried layer dopant is greater than the N type buried layer dopant so that connections can be made to the P type buried layer by P wells which have a lower dopant concentration than the N buried layer.
1. A semiconductor device comprising:
a) an oxide layer;
b) a non selective N type buried layer of an N type dopant with a first coefficient of diffusion covering the oxide layer;
c) a selective P type buried layer of a P type dopant with a coefficient of diffusion greater than said first coefficient of diffusion located over selective regions of the oxide layer; and
d) an N type layer extending over said non selective N type buried layer and said selective P type buried layer, the N type layer having a doping concentration less than the doping concentration of the non selective N type buried layer.
2. The semiconductor device set forth in claim 1 wherein said P type buried layer over compensates completely through said N type buried layer in places where said P type buried layer is formed.
3. The semiconductor device set forth in claim 1 wherein said P type buried layer does not over compensate completely through the thickness of said N type buried layer.
4. The semiconductor device set forth in claim 1 wherein a majority dopant in said N type buried layer is one of arsenic or antimony and a majority dopant in said P type buried layer is boron.
5. The semiconductor device set forth in claim 1 wherein a maximum concentration of an N type majority dopant of said N type buried layer is less than a maximum concentration of a P type majority dopant of said P type buried layer.
6. The semiconductor device set forth in claim 1 further including:
a P well extending from said P type buried layer through said N type layer.
7. The semiconductor device set forth in claim 6 wherein an N type majority dopant in said N type buried layer has a maximum concentration greater than the maximum concentration of a P type majority dopant in said P well.
8. A semiconductor device comprising:
a) an oxide layer;
b) an N type buried layer located over the oxide layer;
c) a P type buried layer;
d) wherein said N type buried layer is non selective and is located over selective regions of the oxide layer;
e) wherein said N type buried layer comprises a majority N type dopant having a first coefficient of diffusion;
f) wherein said P type buried layer is selective;
g) wherein said P type buried layer comprises a majority P type dopant having a coefficient of diffusion greater than said first coefficient of diffusion; and
h) an N type layer extending over said non selective N type buried layer and said selective P type buried layer, the N type layer having a doping concentration less than the doping concentration of the non selective N type buried layer.
9. The semiconductor device set forth in claim 8 wherein said P type buried layer over compensates completely through said N type buried layer is places where said P type buried layer is formed.
10. The semiconductor device set forth in claim 8 wherein said P type buried layer does not over compensate completely through the thickness of said N type buried layer.
11. The semiconductor device set forth in claim 8 wherein a majority dopant in said N type buried layer is one of arsenic or antimony and a majority dopant in said P type buried layer is boron.
12. The semiconductor device set forth in claim 8 wherein a maximum concentration of an N type majority dopant of said N type buried layer is less than a maximum concentration of a P type majority dopant of said P type buried layer.
13. The semiconductor device set forth in claim 8 further including:
a P well extending from said P type buried layer through said N type layer.
14. The semiconductor device set forth in claim 13 wherein an N type majority dopant in said N type buried layer has a maximum concentration greater than a maximum P type majority dopant concentration in a P well extending from said P type buried layer through an N type layer.
15. A semiconductor device comprising:
a non selective N type buried layer extending over a first layer;
at least one selective P type buried layer having its entire lateral extent formed in a selected portion of the N type buried layer;
a semiconductor layer extending over the N and P type buried layers, the semiconductor layer having a doping concentration lower than the N type buried layer and is totally separated from the first layer by the non selective N type buried layer and the P type buried layer;
the P type buried layer extending from the N type buried layer into the semiconductor layer; and
a P well extending from the P type buried layer through the semiconductor layer.
16. The semiconductor device set forth in claim 15 in which the semiconductor layer is N type.
17. The semiconductor device set forth in claim 15 , wherein the first layer is an insulator.
18. The semiconductor device set forth in claim 15 , wherein the first layer is a semiconductor substrate.
19. The semiconductor device set forth in claim 15 , wherein non selective N type buried layer covers the total surface of the first layer.