Power silicon carbide based MOSFET transistors with improved short circuit capabilities and methods of making such devices
A power MOSFET includes a silicon carbide drift region having a first conductivity type, first and second well regions located in upper portions of the silicon carbide drift region that are doped with second conductivity dopants, and a channel region in a side portion of the first well region, an upper portion of the channel region having the first conductivity type, wherein a depth of the first well region is at least 1.5 microns and the depth of the first well region exceeds a distance between the first and second well regions.
1. A power MOSFET, comprising:
a silicon carbide drift region having a first conductivity type;
a first well region located in an upper portion of the silicon carbide drift region and extending to an upper surface of the silicon carbide drift region, the first well region doped with second conductivity dopants and at least a lower portion of the first well region having a second conductivity type, where the second conductivity type is different than the first conductivity type;
a second well region located in the upper portion of the silicon carbide drift region and extending to the upper surface of the silicon carbide drift region, the second well region spaced apart from the first well region to define a JFET region of the silicon carbide drift region, the second well region doped with second conductivity dopants and at least a lower portion of the second well region having the second conductivity type; and
a channel region in a side portion of the first well region, an upper portion of the channel region having the first conductivity type,
wherein a depth of the first well region is at least 1.5 microns, and
wherein the depth of the first well region exceeds a distance between the first and second well regions.
2. The power MOSFET of claim 1 , further comprising:
a first source/drain contact on a lower surface of the silicon carbide drift region;
a first conductivity type region in an upper portion of the first well region and extending to an upper surface of the first well region;
a second source/drain contact on an upper surface of the first conductivity type region;
a gate insulating layer directly on the first well region; and
a gate electrode on the gate insulating layer.
3. The power MOSFET of claim 1 , wherein the first and second well regions comprise implanted regions that are implanted with the second conductivity type dopants.
4. The power MOSFET of claim 1 , wherein a doping concentration of the JFET region is between 1×10 16 cm 3 and 5×10 17 /cm 3 .
5. The power MOSFET of claim 1 , wherein at least the upper 0.2 microns of the first well region has the first conductivity type.
6. The power MOSFET of claim 1 , wherein the first and second well regions each have a depth of at least 2.5 microns.
7. The power MOSFET of claim 1 , wherein the channel region and a central portion of the first well region have substantially the same doping profile of second conductivity type dopants as a function of depth from the upper surface of the silicon carbide drift region.
8. The power MOSFET of claim 1 , wherein a concentration of second conductivity type dopants in the first well region varies by less than a factor of three at depths between 1.0 and 2.0 microns from the upper surface of the silicon carbide drift region.
9. The power MOSFET of claim 1 , wherein a lower portion of the channel region has the second conductivity type.
10. The power MOSFET of claim 1 , wherein a distance between the first and second well regions is at least 2.0 microns and a depth of the first well region is at least 2.5 microns.
11. The power MOSFET of claim 1 , wherein the power MOSFET exhibits a negative temperature coefficient for the drain current for at least temperatures in the range of 25−150° C. at drain-source currents of less than 40 Amps.
12. A power MOSFET, comprising:
a silicon carbide drift region having a first conductivity type;
a first well region located in an upper portion of the silicon carbide drift region and extending to an upper surface of the silicon carbide drift region, the first well region doped with second conductivity dopants and at least a lower portion of the first well region having a second conductivity type, where the second conductivity type is different than the first conductivity type;
a second well region located in the upper portion of the silicon carbide drift region and extending to an upper surface of the silicon carbide drift region, the second well region doped with second conductivity dopants and at least a lower portion of the second well region having a second conductivity type, the first and second well regions defining a JFET region therebetween;
a gate insulating layer on the upper surface of the first well region; and
a channel region under the gate insulating layer in a side portion of the first well region, an upper portion of the channel region having the first conductivity type,
wherein a doping density of the silicon carbide drift region, a width of the JFET region, a doping density of the channel region and/or a depth of the first well region are selected to produce a negative temperature coefficient for the drain current for at least temperatures in the range of 25−150° C. at drain-source currents of less than 40 Amps.
13. The power MOSFET of claim 12 , wherein a depth of the first well region is at least 1.5 microns and wherein the depth of the first well region exceeds a distance between the first well region and a second well region that is adjacent the first well region.
14. The power MOSFET of claim 13 , wherein the first and second well regions comprise implanted regions that are implanted with the second conductivity type dopants.
15. The power MOSFET of claim 14 , wherein at least the upper 0.3 microns of the first well region has the first conductivity type.
16. The power MOSFET of claim 15 , wherein the first and second well regions each have a depth of at least 2.5 microns.
17. The power MOSFET of claim 12 , wherein the channel region and a central portion of the first well region have substantially the same doping profile of second conductivity type dopants as a function of depth from the upper surface of the silicon carbide drift region.
18. The power MOSFET of claim 1 , wherein at least the upper 0.4 microns of the first well region has the first conductivity type.
19. The power MOSFET of claim 12 , wherein a concentration of second conductivity type dopants in the first well region varies by less than a factor of three at depths between 1.0 and 2.0 microns from the upper surface of the silicon carbide drift region.