Deep N wells in triple well structures
A disclosed method for fabricating a structure in a semiconductor die comprises steps of implanting a deep N well in a substrate, depositing an epitaxial layer over the substrate, and forming a P well and a lateral isolation N well over the deep N well, wherein the lateral isolation N well and the P well are fabricated in the substrate and the epitaxial layer, and wherein the lateral isolation N well laterally surrounds the P well, and wherein the deep N well and the lateral isolation N well electrically isolate the P well. Implanting a deep N well can comprise steps of depositing a screen oxide layer over the substrate, forming a mask over the screen oxide layer, implanting the deep N well in the substrate, removing the mask, and removing the screen oxide layer. Depositing the epitaxial layer can comprise depositing a single crystal silicon over the substrate.
1. A structure in a semiconductor die comprising:
a P substrate;
an epitaxial layer situated above said P substrate;
at least one P substrate contact situated in said epitaxial layer, said at least one P substrate contact allowing a bias voltage to be applied to said P substrate;
a deep N well situated in said P substrate, said deep N well being situated at a depth below a top surface of said P substrate such that a portion of said P substrate is situated between said deep N well and said epitaxial layer;
a lateral isolation N well situated in said P substrate and said epitaxial layer, said lateral isolation N well being a lightly doped N type region extending from a top surface of said epitaxial layer to said deep N well;
an isolated P well situated over said deep N well, said isolated P well being laterally surrounded by said lateral isolation N well, said isolated P well extending completely through said epitaxial layer;
said isolated P well being electrically isolated from said P substrate by said deep N well and said lateral isolation N well.
2. The structure of claim 1 wherein said deep N well is a heavily doped N type region.
3. The structure of claim 1 wherein said isolated P well is a lightly doped P type region extending from said top surface of said epitaxial layer to said deep N well.
4. The structure of claim 3 wherein said isolated P well is defined by a P well mask.
5. The structure of claim 1 wherein said isolated P well comprises at least one NFET.
6. The structure of claim 1 wherein said isolated P well comprises at least one P well contact, wherein said at least one P well contact allows a bias voltage to be applied to said isolated P well.
7. A structure in a semiconductor die comprising:
a P substrate;
an epitaxial layer situated above said P substrate;
at least one P substrate contact situated in said epitaxial layer, said at least one P substrate contact allowing a bias voltage to be applied to said P substrate;
a deep N well situated in said P substrate, said deep N well being situated at a depth below a top surface of said P substrate such that a portion of said P substrate is situated between said deep N well and said epitaxial layer, said deep N well being a heavily doped N type region;
a lateral isolation N well situated in said P substrate and said epitaxial layer, said lateral isolation N well being a heavily doped N type region extending from a top surface of said epitaxial layer to said deep N well;
an isolated P well situated over said deep N well, said isolated P well being laterally surrounded by said lateral isolation N well, said isolated P well extending completely through said epitaxial layer;
said isolated P well being electrically isolated from said P substrate by said deep N well and said lateral isolation N well.
8. The structure of claim 7 wherein said isolated P well is a lightly doped P type region extending from said top surface of said epitaxial layer to said deep N well.
9. The structure of claim 7 wherein said isolated P well comprises at least one NFET.
10. The structure of claim 9 wherein said isolated P well is defined by a P well mask.
11. The structure of claim 7 wherein said epitaxial layer comprises single crystal silicon.
12. The structure of claim 7 wherein said lateral isolation N well comprises at least one N well contact, wherein said at least one N well contact allows a bias voltage to be applied to said lateral isolation N well.
13. The structure of claim 7 wherein said isolated P well comprises at least one P well contact, wherein said at least one P well contact allows a bias voltage to be applied to said isolated P well.