Avalanche-protected transistors using a bottom breakdown current path and methods of forming the same
An avalanche-protected field effect transistor includes, within a semiconductor substrate, a body semiconductor layer and a doped body contact region having a doping of a first conductivity type, and a source region a drain region having a doping of a second conductivity type. A buried first-conductivity-type well may be located within the semiconductor substrate. The buried first-conductivity-type well underlies, and has an areal overlap in a plan view with, the drain region, and is vertically spaced apart from the drain region, and has a higher atomic concentration of dopants of the first conductivity type than the body semiconductor layer. The configuration of the field effect transistor induces more than 90% of impact ionization electrical charges during avalanche breakdown to flow from the source region, to pass through the buried first-conductivity-type well, and to impinge on a bottom surface of the drain region.
1. A field effect transistor comprising:
a body semiconductor layer located in a semiconductor substrate and having a doping of a first conductivity type;
a source region and a drain region formed in an upper portion of the semiconductor substrate, having a doping of a second conductivity type that is an opposite of the first conductivity type, and laterally spaced apart by a channel region;
a doped body contact region formed in the upper portion of the semiconductor substrate, having a doping of the first conductivity type, and spaced from the source region;
a buried first-conductivity-type well located within the semiconductor substrate, underlying, and having an areal overlap in a plan view with, the drain region, vertically spaced apart from the drain region, and having a higher atomic concentration of dopants of the first conductivity type than the body semiconductor layer; and
a source-side first-conductivity-type well located within the semiconductor substrate, wherein the source-side first-conductivity-type well is in direct contact with the source region to provide a first p-n junction having a periphery located entirely within a top surface of the semiconductor substrate, and in direct contact with the body semiconductor layer along an interface that extends from the top surface of the semiconductor substrate to a top surface of the buried first-conductivity-type well, and having a higher atomic concentration of dopants of the first conductivity type than the body semiconductor layer.
2. The field effect transistor of claim 1 , wherein the source-side first-conductivity-type well connects the doped body contact region and a planar top surface of the buried first-conductivity-type well.
3. The field effect transistor of claim 2 , wherein
the channel region underlies a gate dielectric and laterally extends through an upper portion of the source-side first-conductivity-type well and through an upper portion of the body semiconductor layer.
4. The field effect transistor of claim 2 , wherein the source-side first conductivity type well is laterally spaced from the buried first-conductivity-type well by a portion of the body semiconductor layer that underlies a gate dielectric.
5. The field effect transistor of claim 1 , wherein the source region and the drain region have asymmetric extension regions such that a drain extension region has a greater areal overlap with a gate electrode in the plan view than a source extension region has with the gate electrode in the plan view.
6. The field effect transistor of claim 1 , wherein the drain region forms a second p-n junction with the body semiconductor layer or a drain-side first-conductivity-type well that overlies the buried first-conductivity-type well and having a lower atomic concentration of dopants of the first conductivity type than the buried first-conductivity-type well.
7. The field effect transistor of claim 1 , wherein the field effect transistor has a configuration that causes more than 90% of impact ionization electrical charges during avalanche breakdown to flow from the source region, to pass through the buried first-conductivity-type well, and to impinge on a horizontal surface of a second p-n junction that is a bottom surface of the drain region, and less than 10% of the impact ionization electrical charges to impinge on a sidewall surface of the second p-n junction.
8. The field effect transistor of claim 1 , wherein the buried first-conductivity-type well has an areal overlap with an entirety of areas of the source region, the drain region, and the doped body contact region in the plan view.
9. The field effect transistor of claim 1 , further comprising a shallow trench isolation structure that laterally surrounds the source region, the drain region, and the doped body contact region, wherein an entirety of a closed periphery of an interface between a top surface of the buried first-conductivity-type well and the body semiconductor layer contacts sidewalls of the shallow trench isolation structure.
10. The field effect transistor of claim 1 , wherein the buried first-conductivity-type well has an areal overlap with an entirety of an area of the drain region in the plan view, and does not overlap with an area of the doped body contact region in the plan view.
11. The field effect transistor of claim 1 , further comprising a buried second-conductivity-type well underlying the buried first-conductivity-type well and forming an additional p-n junction with the buried first-conductivity-type well.
12. A semiconductor chip comprising at least one avalanche-protected field effect transistor located in a semiconductor substrate, wherein each of the at least one avalanche-protected field effect transistor comprises:
a body semiconductor layer located in a semiconductor substrate and having a doping of a first conductivity type;
a source region and a drain region formed in an upper portion of the semiconductor substrate, having a doping of a second conductivity type that is an opposite of the first conductivity type, and laterally spaced apart by a channel region;
a buried first-conductivity-type well located within the semiconductor substrate, underlying, and having an areal overlap in a plan view with, the drain region, vertically spaced apart from the drain region, and having a higher atomic concentration of dopants of the first conductivity type than the body semiconductor layer; and
a source-side first-conductivity-type well located within the semiconductor substrate, wherein the source-side first-conductivity-type well is in direct contact with the source region to provide a first p-n junction having a periphery located entirely within a top surface of the semiconductor substrate, in direct contact with the body semiconductor layer along an interface that extends from the top surface of the semiconductor substrate to a top surface of the buried first-conductivity-type well, and having a higher atomic concentration of dopants of the first conductivity type than the body semiconductor layer,
wherein each of the at least one avalanche-protected field effect transistor has a configuration that induces more than 90% of impact ionization electrical charges during avalanche breakdown to flow from the source region, to pass through the buried first-conductivity-type well, and to impinge on a horizontal surface of a second p-n junction that is a bottom surface of the drain region, and less than 10% of the electrical charges to impinge on a sidewall surface of the second p-n junction.
13. The semiconductor chip of claim 12 , wherein each of the at least one avalanche-protected field effect transistor comprises a doped body contact region formed in the upper portion of the semiconductor substrate, having a doping of the first conductivity type, and spaced from the source region.
14. The semiconductor chip of claim 13 , wherein the source-side first-conductivity-type well of each of the at least one avalanche-protected field effect transistor has a higher atomic higher atomic concentration of dopants of the first conductivity type than the body semiconductor layer.
15. The semiconductor chip of claim 14 , wherein the source-side first-conductivity-type well connects the doped body contact region and the buried first-conductivity-type well within each of the at least one avalanche-protected field effect transistor.
16. The semiconductor chip of claim 12 , wherein each of the at least one avalanche-protected field effect transistor comprises a buried second-conductivity-type well underlying, and forming an additional p-n junction with, the buried first-conductivity-type well of a respective avalanche-protected field effect transistor.
17. A field effect transistor comprising:
a body semiconductor layer located in a semiconductor substrate and having a doping of a first conductivity type;
a source-side first-conductivity-type well located within the semiconductor substrate, having a higher atomic concentration of dopants of the first conductivity type than the body semiconductor layer, and in contact with the body semiconductor layer;
a source region and a drain region formed in an upper portion of the semiconductor substrate, having a doping of a second conductivity type that is an opposite of the first conductivity type, and laterally spaced apart by a channel region;
a doped body contact region having a doping of the first conductivity type, spaced from the source region, and laterally surrounded by, and contacting, the source-side first-conductivity-type well; and
a buried first-conductivity-type well located within the semiconductor substrate, having a higher atomic concentration of dopants of the first conductivity type than the body semiconductor layer; and in contact with the body semiconductor layer and in contact with the source-side first-conductivity-type well,
wherein the source-side first-conductivity-type well is in direct contact with the source region to provide a first p-n junction having a periphery located entirely within a top surface of the semiconductor substrate, and is in direct contact with the body semiconductor layer along an interface that extends from the top surface of the semiconductor substrate to a top surface of the buried first-conductivity-type well.
18. The field effect transistor of claim 17 , wherein the source region and the drain region have asymmetric extension regions such that a drain extension region has a greater areal overlap with a gate electrode in a plan view than a source extension region has with the gate electrode in the plan view.
19. The field effect transistor of claim 18 , wherein:
the source extension region and the drain extension region have a respective bottom surface at a first depth from a top surface of the semiconductor substrate; and
a deep source region of the source region and a deep drain region of the drain region have a respective bottom surface at a second depth from the top surface of the semiconductor substrate, the second depth being greater than the first depth and being less than a depth of a top surface of the buried first-conductivity-type well from the top surface of semiconductor substrate.
20. The field effect transistor of claim 1 , wherein:
the drain region comprises a drain extension region having a bottom surface located at a first depth from a top surface of the semiconductor substrate, and a deep drain region having a bottom surface located at a second depth from the top surface of the semiconductor substrate that is greater than the first depth and having a greater atomic concentration of dopants of the second conductivity type than the drain extension region; and
an entirety of the bottom surface of the drain extension region and an entirety of the bottom surface of the drain region are in contact with surfaces of the body semiconductor layer to provide a second p-n junction having an entirety of a periphery within a horizontal plane including the top surface of the semiconductor substrate.