Methods of fabricating vertical JFET limited silicon carbide metal-oxide semiconductor field effect transistors

1. A method of fabricating a silicon carbide metal-oxide semiconductor field effect transistor unit cell comprising:

providing an n-type silicon carbide drift layer;

providing a first p-type silicon carbide region adjacent the drift layer;

providing a first n-type silicon carbide region within the first p-type silicon carbide region;

providing an oxide layer adjacent the drift layer; and

providing an n-type silicon carbide limiting region between the drift layer and a portion of the first p-type silicon carbide region, wherein the n-type limiting region comprises a first portion laterally extending along a floor of the first p-type silicon carbide region and a second portion disposed adjacent to a sidewall of the first p-type silicon carbide region,

wherein the n-type limiting region has a carrier concentration that is greater than a carrier concentration of the drift layer, and wherein the first portion has a carrier concentration greater than a carrier concentration of the second portion.

2. A method according to claim 1 , wherein providing a first p-type silicon carbide region further comprises:

implanting aluminum in the p-type silicon carbide region; and

annealing the p-type silicon carbide region at a temperature of at least 1500° C.

3. A method according to claim 1 , further comprising:

providing a gate contact on the oxide layer;

providing a source contact on the first n-type silicon carbide region; and

providing a drain contact on the drift layer opposite the oxide layer.

4. A method according to claim 1 , wherein providing an n-type limiting region comprises:

providing an n-type epitaxial layer of silicon carbide on the n-type silicon carbide drift layer;

providing a mask on the epitaxial layer;

patterning the epitaxial layer to form the n-type limiting region.

5. A method according to claim 1 , wherein providing an n-type limiting region comprises implanting n-type regions in the drift layer.

6. A method according to claim 1 , wherein the n-type limiting region is formed to a thickness of from about 0.5 μm to about 1.5 μm and a carrier concentration of from about 1×10 15 to about 5×10 17 cm −3 .

7. A method according to claim 1 , further comprising providing an n-type epitaxial layer on the first p-type region and a portion of the first n-type region, and between the first n-type region and the first p-type region and the oxide layer.

8. A method according to claim 1 , further comprising providing a second p-type silicon carbide region within the first p-type silicon carbide region and adjacent the first n-type silicon carbide region.

9. A method according to claim 3 , wherein the gate contact comprises polysilicon or metal.

10. A method according to claim 3 , further comprising providing an n-type silicon carbide substrate between the drift layer and the drain contact.

11. A method according to claim 4 , wherein providing a first p-type region comprises providing the first p-type region in but not through the epitaxial layer of silicon carbide.

12. The method of claim 1 , wherein the first portion of the n-type limiting region is confined beneath the first p-type silicon carbide region.

13. A method of fabricating a silicon carbide metal-oxide semiconductor field effect transistor, comprising the steps of:

providing a drift layer of n-type silicon carbide;

providing first regions of p-type silicon carbide adjacent the drift layer;

providing a first region of n-type silicon carbide between peripheral edges of the first regions of p-type silicon carbide;

providing second regions of n-type silicon carbide in the first regions of p-type silicon carbide, wherein the second regions of n-type silicon carbide have a carrier concentration greater than a carrier concentration of the drift layer and are spaced apart from the peripheral edges of the first regions of p-type silicon carbide;

providing an oxide layer on the drift layer, the first region of n-type silicon carbide and the second regions of n-type silicon carbide; and

providing third regions of n-type silicon carbide laterally extending along respective floors of the first regions of p-type silicon carbide and between the first regions of p-type silicon carbide and the drift layer, wherein the first and third regions of n-type silicon carbide define an n-type limiting region having a carrier concentration greater than the carrier concentration of the drift layer, wherein the first region of n-type silicon carbide has a higher carrier concentration than a carrier concentration of the drift layer and has a lower carrier concentration than the carrier concentration of the third regions of n-type silicon carbide;

providing source contacts on portions of the second regions of n-type silicon carbide;

providing a gate contact on the oxide layer; and

providing a drain contact on the drift layer opposite the oxide layer.

14. A method according to claim 13 , wherein providing third regions of n-type silicon carbide further comprises providing the third regions of n-type silicon carbide adjacent the peripheral edges of the first regions of p-type silicon carbide.

15. A method according to claim 13 , further comprising providing an n-type silicon carbide epitaxial layer on the drift layer, wherein the first region of n-type silicon carbide and the third regions of n-type silicon carbide are formed from the epitaxial layer, and wherein the first regions of p-type silicon carbide are formed in the epitaxial layer.

16. A method according to Claim 13 , wherein providing third regions of n-type silicon carbide comprises providing the third regions of n-type silicon carbide by implanting n-type regions in the drift layer.

17. A method according to claim 13 , further comprising providing an n-type epitaxial layer of silicon carbide on the first p-type regions and the first region of n-type silicon carbide.

18. A method according to claim 13 , further comprising providing an n-type silicon carbide layer between the drift layer and the drain contact, wherein the n-type silicon carbide layer has a higher carrier concentration than the carrier concentration of the drift layer.

19. A method according to claim 13 , further comprising providing second p-type silicon carbide regions within the first p-type silicon carbide regions.

20. A method according to claim 13 , wherein the third regions of n-type silicon carbide have a thickness of from about 0.5 μm to about 1.5 μm.

21. A method according to claim 13 , wherein the third regions of n-type silicon carbide have a carrier concentration of from about 1×10 15 to about 5×10 17 cm −3 .

22. The method of claim 13 , wherein the third regions of n-type silicon carbide are confined beneath the first regions of p-type silicon carbide.

23. A method according to claim 18 , wherein the n-type silicon carbide layer comprises an n-type silicon carbide substrate.

24. A method of fabricating a silicon carbide metal-oxide semiconductor field effect transistor comprising:

providing an n-type silicon carbide drift layer;

providing spaced apart p-type silicon carbide well regions; and

providing an n-type silicon carbide limiting region between the well regions and the drift layer, wherein the n-type limiting region comprises a first portion laterally extending along respective floors of the well regions and a second portion adjacent to respective sidewalls of the well regions,

wherein the n-type limiting region has a carrier concentration higher than a carrier concentration of the drift layer, and wherein the first portion has a carrier concentration higher than a carrier concentration of the second portion.

25. A method according to claim 24 , wherein providing an n-type limiting region comprises providing an epitaxial layer of silicon carbide on the drift layer, and wherein providing spaced apart p-type well regions comprises providing spaced apart p-type well regions in but not through the epitaxial layer.

26. The method of claim 24 , wherein the first portion of the n-type limiting region is confined beneath the well regions.