Radiation hardened isolation structures and fabrication methods
Semiconductor devices can be fabricated using conventional designs and process but including specialized structures to reduce or eliminate detrimental effects caused by various forms of radiation. Such semiconductor devices can include one or more parasitic isolation devices and/or buried layer structures disclosed in the present application. The introduction of design and/or process steps to accommodate these novel structures is compatible with conventional CMOS fabrication processes, and can therefore be accomplished at relatively low cost and with relative simplicity.
1. A semiconductor device comprising: a substrate having a substrate impurity concentration and a substrate resistivity no greater than 20 ohm-cm, having a top surface, and having a conductive bottom surface for providing electrical connection to a device package contact;
a first plurality of wells having a first conductivity type;
a second plurality of wells having a second conductivity type opposite the first conductivity type;
a first plurality of transistors formed proximate to the top surface of the substrate, said first plurality of transistors including a respective transistor disposed in each of the first plurality of wells;
a second plurality of transistors formed proximate to the top surface of the substrate, said second plurality of transistors including a respective transistor disposed in each of the second plurality of wells;
a buried layer formed via ion-implantation, having the first conductivity type and comprising a buried layer impurity concentration greater than the substrate impurity concentration, said buried layer extending substantially continuously beneath and vertically spaced apart from both the first and second plurality of wells;
and a vertical conductive path between the buried layer and the conductive bottom surface of the substrate, said vertical conductive path traversing through the substrate.
2. The semiconductor device of claim 1 wherein the substrate is formed from a bulk silicon wafer having the first conductivity type.
3. The semiconductor device of claim 1 further comprising:
an epitaxial layer formed on the top surface of the substrate; wherein the first and second plurality of transistors further comprise a plurality of source and drain regions formed in the epitaxial layer.
4. The semiconductor device of claim 3 wherein the epitaxial layer has the first conductivity type.
5. The semiconductor device of claim 3 wherein an epitaxial layer impurity concentration is less than the substrate impurity concentration.
6. The semiconductor device of claim 3 wherein the buried layer is located one of:
above the top surface of the substrate;
below the top surface of the substrate; and
overlapping the top surface of the substrate.
7. The semiconductor device of claim 1 further comprising:
at least one package contact electrode formed on the conductive bottom surface.
8. The semiconductor device of claim 1 wherein at least one transistor of the first or second plurality of transistors is a field effect transistor including:
a source region having a first width;
a drain region having a second width;
a channel region located between the source region and the drain region, wherein the channel region has a channel length and a third width greater than each of the first width and the second width, thereby forming at least one channel extension, and wherein the at least one channel extension provides a net channel edge length between the source region and the drain region that is greater than the channel length.
9. The semiconductor device of claim 8 , wherein the at least one channel extension further comprises:
a channel extension impurity region along the length of the at least one channel extension and spaced apart from the source and drain regions.
10. The semiconductor device of claim 9 wherein the channel extension impurity region extends to a depth greater than a depth of at least one of the source region and the drain region.
11. The semiconductor device of claim 9 wherein the channel extension impurity region has an impurity concentration greater than the substrate impurity concentration.
12. The semiconductor device of claim 9 wherein the channel extension impurity region has a second conductivity type.
13. The semiconductor device of claim 1 wherein the buried layer is sufficiently beneath the second plurality of wells so as to substantially avoid counter-doping the second plurality of wells.
14. A semiconductor device comprising:
a substrate having a substrate impurity concentration, having a top surface, and having a conductive bottom surface for providing electrical connection to a device package contact;
a first plurality of wells having a first conductivity type;
a second plurality of wells having a second conductivity type opposite the first conductivity type;
a first plurality of transistors formed proximate to the top surface of the substrate, said first plurality of transistors including a respective transistor disposed in each of the first plurality of wells;
a second plurality of transistors formed proximate to the top surface of the substrate, said second plurality of transistors including a respective transistor disposed in each of the second plurality of wells;
a buried layer formed via ion-implantation, having the first conductivity type and comprising a buried layer impurity concentration greater than the substrate impurity concentration, said buried layer extending substantially continuously beneath and vertically spaced apart from both the first and second plurality of wells; and
and a vertical conductive path between the buried layer and the conductive bottom surface of the substrate, said vertical conductive path traversing through the substrate;
wherein at least one transistor of the first or second plurality of transistors is a field effect transistor including:
a source region having a first width;
a drain region having a second width; and
a channel region located between the source region and the drain region, wherein the channel region has a channel length and a third width greater than each of the first width and the second width, thereby forming at least one channel extension, and wherein the at least one channel extension provides a net channel edge length between the source region and the drain region that is greater than the channel length.
15. The semiconductor device of claim 14 wherein the substrate is formed from a bulk silicon wafer having the first conductivity type.
16. The semiconductor device of claim 14 further comprising: an epitaxial layer formed on the top surface of the substrate; wherein the first and second plurality of transistors further comprise a plurality of source and drain regions formed in the epitaxial layer.
17. The semiconductor device of claim 16 wherein the epitaxial layer has the first conductivity type.
18. The semiconductor device of claim 16 wherein an epitaxial layer impurity concentration is less than the substrate impurity concentration.
19. The semiconductor device of claim 16 wherein the buried layer is located one of: above the top surface of the substrate; below the top surface of the substrate; and overlapping the top surface of the substrate.
20. The semiconductor device of claim 14 further comprising: at least one package contact electrode formed on the conductive bottom surface.
21. The semiconductor device of claim 14 , wherein the at least one channel extension further comprises: a channel extension impurity region along the length of the at least one channel extension and spaced apart from the source and drain regions.
22. The semiconductor device of claim 21 wherein the channel extension impurity region extends to a depth greater than a depth of at least one of the source region and the drain region.
23. The semiconductor device of claim 21 wherein the channel extension impurity region has an impurity concentration greater than the substrate impurity concentration.
24. The semiconductor device of claim 21 wherein the channel extension impurity region has a second conductivity type.
25. The semiconductor device of claim 14 wherein the buried layer is sufficiently beneath the second plurality of wells so as to substantially avoid counter-doping the second plurality of wells.