RF SiC MOSFET with recessed gate dielectric
A Field Effect Transistor (FET) may include a semiconductor substrate having a first conductivity type, a semiconductor layer of the first conductivity type formed over the substrate, and a pair of doped bodies of a second conductivity type opposite the first conductivity type formed in the semiconductor layer. A trench filled with a trench dielectric is formed within a region between the doped bodies. The FET may be a Vertical Metal-Oxide-Semiconductor FET (VMOSFET) including a gate dielectric disposed over the region between the doped bodies and the trench, and a gate electrode disposed over the gate dielectric, wherein the trench operates to prevent breakdown of the gate dielectric, or the FET may be a Junction FET. The FET may be designed to operate at radio frequencies or under heavy-ion bombardment. The semiconductor substrate and the semiconductor layer may comprise a wide band-gap semiconductor such as silicon carbide.
1. A semiconductor device comprising:
a semiconductor substrate having a first conductivity type;
a semiconductor layer formed over the substrate and having the first conductivity type;
a pair of doped bodies formed in the semiconductor layer and having a second conductivity type opposite the first conductivity type;
a trench formed within a region between the doped bodies;
a trench dielectric disposed within the trench;
a polysilicon fill formed within the trench dielectric and separated from the gate electrode by a gate dielectric; and
a gate electrode disposed over the region between the doped bodies and over the trench.
2. The semiconductor device of claim 1 , wherein the trench penetrates the semiconductor layer to a depth greater than a depth of a metallurgical junction between the bottom of one of the doped bodies and the semiconductor layer.
3. The semiconductor device of claim 1 , wherein the trench penetrates an entire thickness of the semiconductor layer.
4. The semiconductor device of claim 1 , further comprising:
the gate dielectric disposed over the region between the doped bodies and over the trench,
wherein the gate electrode is disposed over the gate dielectric.
5. The semiconductor device of claim 4 , wherein the trench operates to provide the gate dielectric with immunity to dielectric breakdown caused by heavy-ion bombardment.
6. The semiconductor device of claim 1 , further comprising:
a shield region formed within the region between the doped bodies and having the second conductivity type,
wherein the trench is disposed within the shield region.
7. The semiconductor device of claim 6 , further comprising:
a source region disposed in one of the doped bodies and having the first conductivity type,
wherein the shield region is electrically connected to the source region.
8. The semiconductor device of claim 1 , further comprising:
a liner oxide formed over surfaces of the trench before the trench dielectric is disposed within the trench,
wherein the trench dielectric is disposed within the liner oxide.
9. The semiconductor device of claim 8 , wherein a composition of the liner oxide is different from a composition of the trench dielectric.
10. The semiconductor device of claim 1 , wherein the semiconductor substrate comprises silicon carbide and the semiconductor layer comprises silicon carbide.
11. A semiconductor device comprising:
a semiconductor substrate having a first conductivity type;
a semiconductor layer formed over the substrate and having the first conductivity type;
a pair of doped bodies formed in the semiconductor layer and having a second conductivity type opposite the first conductivity type;
a trench formed within a region between the doped bodies;
a trench dielectric disposed within the trench;
a raised dielectric disposed over the trench and not over the doped bodies; and
a gate electrode disposed over the region between the doped bodies and over the trench,
wherein the gate electrode is disposed over a gate dielectric and the raised dielectric, and
wherein an elevation over the substrate of a portion of the gate electrode over the raised dielectric is greater than an elevation over the substrate of a portion of the gate electrode not over the raised dielectric.
12. The semiconductor device of claim 11 , wherein the trench penetrates the semiconductor layer to a depth greater than a depth of a metallurgical junction between the bottom of one of the doped bodies and the semiconductor layer.
13. A method of manufacturing a semiconductor device, the method comprising:
forming a semiconductor layer of a first conductivity type on a semiconductor substrate of the first semiconductor type;
forming a pair of doped bodies having a second conductivity type opposite the first conductivity type in the semiconductor layer;
forming a trench in a region between the doped bodies;
forming a trench dielectric within the trench;
forming a cavity in the trench dielectric;
forming a polysilicon fill within the cavity in the trench dielectric; and
forming a gate electrode over the region between the doped bodies including over the trench.
14. The method of claim 13 , further comprising:
forming a sacrificial oxide over surfaces of the trench; and
removing the sacrificial oxide from the surfaces of the trench before forming the trench dielectric.
15. The method of claim 13 , wherein the trench penetrates the semiconductor layer to a depth greater than a depth of a metallurgical junction between the bottom of one of the doped bodies and the semiconductor layer.
16. The method of claim 13 , wherein the trench penetrates an entire thickness of the semiconductor layer.
17. The method of claim 13 , further comprising:
forming a gate dielectric over the region between the doped bodies including over the trench; and
forming the gate electrode over the gate dielectric.
18. The method of claim 17 , wherein the trench operates to provide the gate dielectric with immunity to dielectric breakdown caused by heavy-ion bombardment.
19. The method of claim 13 , further comprising:
forming a shield region within the region between the doped bodies and having the second conductivity type before forming the trench; and
forming the trench in the shield region.
20. The method of claim 19 , further comprising:
forming a source region in one of the doped bodies and having the first conductivity type,
wherein the shield region is electrically connected to the source region.
21. The method of claim 13 , further comprising:
forming liner oxide over surfaces of the trench before forming the trench dielectric; and
forming the trench dielectric within the liner oxide.
22. The method of claim 13 , wherein the semiconductor substrate comprises silicon carbide and the semiconductor layer comprises silicon carbide.
23. A method of manufacturing a semiconductor device, the method comprising:
forming a semiconductor layer of a first conductivity type on a semiconductor substrate of the first semiconductor type;
forming a pair of doped bodies having a second conductivity type opposite the first conductivity type in the semiconductor layer;
forming a trench in a region between the doped bodies;
forming a trench dielectric within the trench;
forming a gate electrode over the region between the doped bodies including over the trench;
forming a gate dielectric over the region between the doped bodies including over the trench;
forming a raised dielectric disposed over the trench and not over the bodies; and
forming a gate electrode over the gate dielectric and over the raised dielectric,
wherein an elevation over the substrate of a portion of the gate electrode over the raised dielectric is greater than an elevation over the substrate of a portion of the gate electrode not over the raised dielectric.
24. The semiconductor device of claim 23 , wherein the trench penetrates the semiconductor layer to a depth greater than a depth of a metallurgical junction between the bottom of one of the doped bodies and the semiconductor layer.