Junction field-effect transistor formed in silicon carbide

• US 5,264,713 A
• Filed: 06/14/1991
• Issued: 11/23/1993
• Est. Priority Date: 06/14/1991
• Status: Expired due to Term

• Current Assignee: Wolfspeed, Inc.
• Original Assignee: Cree Research, Inc.
• Inventors: Palmour, John W.
• Primary Examiner(s): Hille, Rolf
• Assistant Examiner(s): SAADAT, MAHSHID D
• Application Number:
  US07/715,400
• Time in Patent Office: 893 Days
• Field of Search: 357/22 I, 357/22 K, 357/22 C, 357/22 D, 357/23.2, 357/56, 357/61, 257/76, 257/77, 257/267, 437/100
• US Class Current: 257/77
• CPC Class Codes: H01L 29/1608 Silicon carbide
• CPC Class Codes: H01L 29/66068 the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
• CPC Class Codes: H01L 29/808 with a PN junction gate , e.g. PN homojunction gate H01L29/7725, H01L29/775, H01L29/778, H01L29/806 take precedence
• CPC Class Codes: Y10S 438/931 Silicon carbide semiconductor

Abstract

A junction field-effect transistor is disclosed that comprises a bulk single crystal silicon carbide substrate having respective first and second surfaces opposite one another, the substrate having a single polytype and having a concentration of suitable dopant atoms so as to make the substrate a first conductivity type. A first epitaxial layer of silicon carbide is formed on the first surface of the substrate, and having a concentration of suitable dopant atoms that give the first epitaxial layer the first conductivity type. A second epitaxial layer of silicon carbide is formed on the first epitaxial layer, the second epitaxial layer having a concentration of suitable dopant atoms to give the second epitaxial layer a second conductivity type opposite from the first conductivity type. A higher conductivity region of silicon carbide is formed on the second epitaxial layer, A trench is formed in the second epitaxial layer and higher conductivity region extending entirely through the higher conductivity region and partially into the second epitaxial layer toward the first surface of the substrate for defining a gate region in the second epitaxial layer between the trench and the first epitaxial layer. The trench divides the second epitaxial layer and higher conductivity region into respective first and second regions with the trench therebetween.

Claims

1. A junction field-effect transistor formed in silicon carbide comprising:

a bulk single crystal silicon carbide substrate having respective first and second surfaces opposite one another, said substrate having a single polytype and having a concentration of suitable dopant atoms for making said substrate a first conductivity type;

an epitaxial layer of silicon carbide on said first surface of said substrate, said epitaxial layer having a concentration of suitable dopant atoms for making said epitaxial layer a second conductivity type opposite said first conductivity type;

a higher conductivity region of silicon carbide of said second conductivity type on said epitaxial layer, said higher conductivity region having a greater concentration of said dopant atoms than said epitaxial layer for making said higher conductivity region more conductive than said epitaxial layer;

a trench formed in said epitaxial layer and in said higher conductivity region and extending entirely through said higher conductivity region and partially into said epitaxial layer toward said first surface of said substrate for defining a gate region in said epitaxial layer between said trench and said substrate, said trench dividing said epitaxial layer and said higher conductivity region into respective first and second regions with said trench therebetween; and

a metal gate contact on said second surface of said substrate for forming an active channel layer in said epitaxial layer between said first region and said second region when a bias is applied to said metal gate contact.

2. A junction field effect transistor according to claim 1 and further comprising:

ohmic contacts on said higher conductivity region for respectively defining one of aid first and second regions as the source region and the other of said ohmic contacts defining the other of said first and second regions as the drain region.

3. A junction field-effect transistor according to claim 1 wherein said epitaxial layers have the same polytype as said single crystal substrate.

4. A junction field-effect transistor according to claim 1 wherein said first conductivity type is p-type conductivity and said second conductivity type is n-type conductivity.

5. A junction field-effect transistor according to claim 1 where said first conductivity type is n-type conductivity and said second conductivity type is p-type conductivity.

6. A junction field-effect transistor according to claim 1 where said epitaxial layer and said higher conductivity region comprise a mesa for defining the periphery of said transistor and for confining the flow of current to said epitaxial layer and said higher conductivity region.

7. A junction field-effect transistor formed in silicon carbide comprising:

a bulk single crystal silicon carbide substrate having respective first and second surfaces opposite one another, said substrate having a single polytype and having a concentration of suitable dopant atoms for making said substrate a first conductivity type;

a first epitaxial layer of silicon carbide on said first surface of said substrate, said first epitaxial layer having a concentration of suitable dopant atoms for making said first epitaxial layer a first conductivity type;

a second epitaxial layer of silicon carbide on said first surface of said substrate, said second epitaxial layer having a concentration of suitable a dopant atoms for making said second epitaxial layer a second conductivity type opposite said first conductivity type;

a higher conductivity region of silicon carbide formed on said second epitaxial layer, said higher conductivity region having a concentration of suitable dopant atoms for making said higher conductivity region said second conductivity type, said higher conductivity region having a greater concentration of said dopant atoms than said second epitaxial layer for making said higher conductivity region more conductive than said second epitaxial layer; and

a trench formed in said second epitaxial layer and said higher conductivity region extending entirely through said higher conductivity region and partially into said second epitaxial layer, toward said first surface of said substrate for defining a gate region in said second epitaxial layer between said trench and said substrate, said trench dividing said second epitaxial layer and said higher conductivity region into respective first and second regions with said trench therebetween; and

a metal gate contact on said second surface of said substrate for forming an active channel layer in said second epitaxial layer between said first region and said second region when a bias is applied to said metal gate contact.

8. A junction field effect transistor according to claim 7 and further comprising:

ohmic contacts on said higher conductivity region for respectively defining one of said first and second regions as the source region and the other of said ohmic contacts defining the other of said first and second regions as the drain region.

9. A junction field-effect transistor according to claim 7 where said substrate is of a polytype selected from the group consisting of:

6H, 15R, 4H and 3C and said epitaxial layers are 15R SiC.

10. A junction field-effect transistor according to claim 7 where said substrate is of a polytype selected from the group consisting of:

6H, 4H, 15R and 3C and said epitaxial layers are 4H SiC.

11. A junction field-effect transistor according to claim 7 where said substrate is of a polytype selected from the group consisting of:

4H, 15R, and 3C and said epitaxial layers are 3C SiC.

12. A junction field-effect transistor according to claim 7 where said substrate is of a polytype selected from the group consisting of:

4H, 15R, 6H and 3C and said epitaxial layers are 6H SiC.

13. A junction field-effect transistor according to claim 7 wherein said epitaxial layers have the same polytype as said single crystal substrate.

14. A junction field-effect transistor according to claim 7 wherein said first conductivity type is p-type conductivity and said second conductivity type is n-type conductivity.

15. A junction field-effect transistor according to claim 7 where said first conductivity type is n-type conductivity and said second conductivity type is p-type conductivity.

16. A junction field-effect transistor according to claim 7 where said second epitaxial layer and said higher conductivity region form a mesa and thereby defining the periphery of said transistor and confining the flow of current to said epitaxial layer and higher conductivity region.

17. A junction field-effect transistor according to claim 7 where said substrate has a carrier concentration of dopant atoms greater than about 3×

10¹⁵ cm^-3.

18. A junction field-effect transistor according to claim 7 where said first epitaxial layer has a carrier concentration of dopant atoms greater than about 1×

10¹⁷ cm^-3.

19. A junction field-effect transistor according to claim 7 where said second epitaxial layer has a carrier concentration of dopant atoms of between about 1×

10¹⁶ and 2 ×

10¹⁸ cm^-3.

20. A junction field-effect transistor according to claim 7 wherein the length of said trench is minimized to maximize the electric field beneath said channel and thereby minimize the effect of low electron mobility of silicon carbide.

21. A junction field-effect transistor according to claim 7 having an operating range of up to 10 GHz.

22. A junction field-effect transistor according to claim 7 wherein said trench formed in said second epitaxial layer and said higher conductivity region forms a serpentine pattern of interdigitated regions of said second epitaxial layer and higher conductivity region.

23. A transistor according to claim 16 further comprising a passivating layer on the sidewalls of said mesa and said trench.

24. A junction field-effect transistor formed in silicon carbide comprising:

a bulk single crystal silicon carbide substrate having respective first and second surfaces opposite one another, said substrate having a single polytype and having a concentration of suitable dopant atoms for making said substrate a first conductivity type;

a first epitaxial layer of silicon carbide formed on said first surface of said substrate, said first epitaxial layer having a concentration of suitable dopant atoms so as to make said first epitaxial layer said first conductivity type;

a second epitaxial layer of silicon carbide formed on said first epitaxial layer, said second epitaxial layer having a concentration of suitable dopant atoms for making said second epitaxial layer a second conductivity type opposite said first conductivity type;

a higher conductivity region of said second polytype silicon carbide formed on said second epitaxial layer, said higher conductivity region having a concentration of suitable dopant atoms for making said higher conductivity region said second conductivity type, said higher conductivity region having a conductivity greater than said second epitaxial layer;

a trench formed in said higher conductivity region and said second epitaxial layer, said trench forming a serpentine pattern in said second epitaxial layer and higher conductivity region and extending entirely through said higher conductivity region and partially into said second epitaxial layer towards said first surface of said substrate for defining a gate region in said second epitaxial layer between said trench and said first epitaxial layer, said trench dividing said second epitaxial layer and higher conductivity region into a first region and a second region;

ohmic contacts formed on said higher conductivity region, said ohmic contacts being interdigitated between said serpentine pattern of said trench, one of said ohmic contacts having a plurality of digits and defining said first region as the source region and the other of said ohmic contacts having a plurality of digits and defining said second region as the drain region with said serpentine trench separating said digits of said source region from said digits of said drain region;

a metal gate contact formed on said second surface of said substrate for forming an active channel in said second epitaxial layer between said source region and said drain region when a bias is applied to said metal gate contact.

25. A junction field-effect transistor according to claim 24 wherein said substrate and said epitaxial layers have a polytype selected from the group consisting of:

6H, 15R, 4H and 3C.

26. A junction field-effect transistor according to claim 25 wherein said substrate and epitaxial layers are the same polytype.

27. A junction field-effect transistor according to claim 24 where said first conductivity type is p-type conductivity and said second conductivity type is n-type conductivity.

28. A junction field-effect transistor according to claim 24 where said first conductivity type is n-type conductivity and said second conductivity type is p-type conductivity.

29. A junction field-effect transistor according to claim 24 wherein said second epitaxial layer and said higher conductivity region form a mesa for defining the periphery of said transistor and confining the flow of current to said second epitaxial layer and higher conductivity region.

30. A junction field-effect transistor according to claim 29 further comprising an insulative layer formed on said first surface of said substrate and extending outward from said mesa, said source and drain ohmic contacts extending beyond said mesa on said insulative layer thereby minimizing the gate capacitance of said transistor.