Vertical gate LDMOS device
Described here are transistors and fabrication methods thereof. In one implementation, a transistor includes an n-well region implanted into a surface of a substrate, and a trench in the n-well region. The trench extends from the surface to a first depth. The trench includes a gate of conductive material in the trench, and dielectric material filling a volume of the trench not filled by the conductive material. The transistor also includes a p-type material in a first region extending from a second depth to a third depth, the second depth and the third depth being greater than the first depth. The transistor further includes a source region and a drain region.
1. A transistor comprising:
an n-well region implanted into a surface of a substrate;
a trench in then-well region, the trench having a first side and an opposing second side, the trench extending from the surface to a first depth, the trench comprising
a gate of conductive material in the trench, and
dielectric material filling a volume of the trench not filled by the conductive material;
a p-type material in a first region extending from a second depth to a third depth in then-well region, wherein each of the second depth and the third depth is greater than the first depth;
a source region on the first side of the trench, the source region including a p-body region wherein an n+ region and a p+ region is implanted in the p-body region; and
a drain region on the second side of the trench, the drain region comprising an n+ region.
2. The transistor of claim 1 wherein a distance of the gate from the first side of the trench is less than a distance of the gate from the second side of the trench.
3. The transistor of claim 1 wherein a breakdown voltage of the transistor is substantially between a range 10V-100V.
4. The transistor of claim 1 wherein the conductive material is polysilicon.
5. The transistor of claim 1 wherein the dielectric material is an oxide.
6. The transistor of claim 1 , wherein the first region is below the trench and a width of the first region is more than a width of the trench.
7. The transistor of claim 1 , wherein the first region and the source region define a channel through which a current flows around the trench from the source region to the drain region.
8. The transistor of claim 1 , wherein a concentration of the p-type material in the first region is lower than a concentration of the p-type material in the p-body region.
9. The transistor of claim 8 , wherein the p-body region includes a deep p-body region and a shallow p-body region, the shallow p-body region being closer to the surface and having a higher concentration of the p-type material than the deep p-body region.
10. The transistor of claim 1 , wherein the p-body region extends from the surface to the first region.
11. The transistor of claim 1 comprising a gate electrode in electrical contact with the gate of conductive material in the trench.
12. The transistor of claim 11 comprising a layer of silicide between the gate electrode and the gate of conductive material in the trench.
13. A transistor comprising:
an n-well region implanted into a surface of a substrate;
a trench in then-well region, the trench having a first side and an opposing second side, the trench extending from the surface to a first depth, the trench comprising
a gate of conductive material in the trench, and
dielectric material filling a volume of the trench not filled by the conductive material;
a source region on the first side of the trench, the source region including a p-body region wherein an n+ region and a p+ region is implanted in the p-body region;
a drain region on the second side of the trench, the drain region comprising an n+ region, the n+ region abutting the trench, and
a p-type material in a first region extending from a second depth to a third depth in the n-well region, wherein each of the second depth and the third depth is greater than the first depth.
14. A transistor comprising:
an n-well region implanted into a surface of a substrate;
a trench in then-well region, the trench having a first side and an opposing second side, the trench extending from the surface to a first depth, the trench comprising
a first dielectric material abutting the n-well on the first side and the opposing second side of the trench,
a source side dielectric liner on the first dielectric material on a source side of the trench,
a drain side dielectric liner on the first dielectric material on a drain side of the trench,
a gate of conductive material filling a first volume in the trench between the source side dielectric liner and the source side dielectric liner and abutting the source side dielectric liner, and
wherein the first dielectric material fills a second volume of the trench between the source side dielectric liner and the source side dielectric liner not filled by the conductive material;
a source region on the first side of the trench, the source region including a p-body region wherein an n+ region and a p+ region is implanted in the p-body region; and
a drain region on the second side of the trench, the drain region comprising an n+ region.
15. The transistor of claim 14 , wherein the source-side dielectric liner and the drain side dielectric liner comprise silicon nitride.
16. The transistor of claim 14 , wherein the first dielectric material comprises silicon oxide.