Schottky diode structure with silicon mesa and junction barrier Schottky wells

• US 8,384,181 B2
• Filed: 02/09/2007
• Issued: 02/26/2013
• Est. Priority Date: 02/09/2007
• Status: Active Grant

• Current Assignee: Wolfspeed, Inc.
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Zhang, Qingchun, Ryu, Sei-Hyung
• Primary Examiner(s): Rizkallah, Kimberly
• Assistant Examiner(s): Karimy, Timor
• Application Number:
  US11/673,117
• Publication Number:
  US 20080191304A1
• Time in Patent Office: 2,209 Days
• Field of Search: 257/E31.065, 257/E31.066, 257/E29.338, 257/E27.04, 257/E27.068, 257/E29.041, 257/471, 438/570
• US Class Current: 257/471
• CPC Class Codes: H01L 27/0814 Diodes only
• CPC Class Codes: H01L 29/1608 Silicon carbide
• CPC Class Codes: H01L 29/6606 the devices being controllable only by variation of the electric current supplied or the electric potential applied, to one or more of the electrodes carrying the current to be rectified, amplified, oscillated or switched, e.g. two-terminal devices
• CPC Class Codes: H01L 29/872 Schottky diodes

Abstract

A power diode having a silicon mesa atop the drift region includes a first contact positioned on the silicon mesa. The silicon mesa is highly doped p-type or n-type, and the anode may be formed on the mesa. The mesa may include two separate silicon layers, one of which is a Schottky barrier height layer. Under a forward bias, the silicon mesa provides carriers to achieve desirable forward current characteristics. The substrate has a significantly reduced thickness. The diode achieves reverse voltage blocking capability by implanting junction barrier Schottky wells within the body of the diode. The diode utilizes a deeper portion of the drift region to support the reverse bias. The method of forming the diode with a silicon mesa includes forming the mesa within a window on the diode or by thermally or mechanically bonding the silicon layer to the drift region.

Claims

1. A Schottky diode comprising:

a first semiconductor layer of a first conductivity type forming a drift region, said drift region having a first surface and a second surface;

at least one doped well within a conductive channel in said drift region and adjacent said first surface, said doped well having an opposite conductivity type as said drift region; and

a silicon mesa on said first surface of said drift region adjacent said doped well.

2. A Schottky diode according to claim 1, wherein said silicon mesa comprises a silicon Schottky barrier layer on said drift region and a second layer of silicon on said barrier layer.

3. A Schottky diode according to claim 1, wherein said drift region is N−

type silicon carbide, said well is p+ type silicon carbide, and said mesa is n type silicon.

4. A Schottky diode according to claim 1, wherein said drift region is N−

type silicon carbide, said well is p+ type silicon carbide, and said mesa is p+ type silicon.

5. A Schottky diode according to claim 1, wherein said drift region further comprises termination wells at said first surface and adjacent edges of said mesa, said termination wells arresting current flow at said edges.

6. A Schottky diode according to claim 1, further comprising a conductive substrate on said second surface of said drift region.

7. A Schottky diode according to claim 6, wherein said substrate is less than about 100 microns thick.

8. A Schottky diode according to claim 7, wherein said substrate is less than about 25 microns thick.

9. A Schottky diode according to claim 6, further comprising a cathode contact on a surface of said substrate opposite said drift region.

10. A Schottky diode according to claim 1, further comprising an anode contact on said mesa.

11. A Schottky diode according to claim 1, further comprising a passivation layer covering sides of said mesa and the first surface of said drift region adjacent said mesa.

12. A Schottky diode according to claim 1, wherein said drift region is about 25 microns thick.

13. A Schottky diode according to claim 1, wherein said drift region is doped to about 3×

10¹⁵ cm<sup>−

3</sup>.

14. A Schottky diode comprising:

a drift region of a first conductivity type, said drift region having a first surface and a second surface;

at least one doped well within a conductive channel in said drift region and adjacent said first surface;

said doped well having an opposite conductivity type as said drift region;

a silicon mesa on said first surface of said drift region adjacent said doped well, wherein said drift region supports a maximum electric field without breakdown throughout a thickness of more than one micron in said drift region.

15. A Schottky diode according to claim 14, wherein said maximum electric field is greater than 1.4 x 10⁶ V/cm.

16. A Schottky diode according to claim 14, wherein said diode has a current density that is greater than 50 amps/cm² at an anode voltage of 2 volts.

17. A Schottky diode according to claim 14, wherein the maximum reverse blocking voltage is greater than 2800 V.

18. Schottky diode according to claim 14, wherein said drift region is n—

type silicon carbide, said well is p+ type silicon carbide, and said mesa is n type_silicon.

19. A Schottky diode according to claim 14, wherein said drift region is n—

type silicon carbide, said well is p+ type silicon carbide, and said mesa is p+ type silicon.

20. A Schottky diode according to claim 14, wherein said drift region further comprises termination wells at said first surface and adjacent edges of said mesa, said termination wells arresting current flow at said edges.

21. A Schottky diode according to claim 14, further comprising a conductive substrate on said second surface of said drift region.

22. A Schottky diode according to claim 21, wherein said substrate is less than about 100 microns thick.

23. A Schottky diode according to claim 22, further comprising a cathode contact on a surface of said substrate opposite said drift region.

24. A Schottky diode according to claim 14, further comprising an anode contact on said mesa.

25. A Schottky diode according to claim 14, further comprising a passivation layer covering sides of said mesa and the first surface of said drift region adjacent said mesa.

26. A Schottky diode according to claim 14, wherein said drift region is about 25 microns thick.

27. A Schottky diode according to claim 14, wherein said drift region is doped to about 3×

10¹⁵ cm<sup>−

3</sup>.

28. A Schottky diode according to claim 14, wherein said silicon mesa comprises a silicon Schottky barrier layer on said drift region and a second layer of silicon on said barrier layer.

29. A Schottky diode comprising:

a first silicon carbide layer of a first conductivity type forming a drift region, said drift region having a first surface and a second surface;

at least one doped well substantially within a conductive channel in said drift region and adjacent said first surface, said doped well having an opposite conductivity type as said drift region; and

a silicon mesa on said first surface of said drift region adjacent said doped well.

30. A Schottky diode according to claim 29, wherein said silicon mesa comprises a silicon Schottky barrier layer on said drift region and a second layer of silicon on said barrier layer.

31. A Schottky diode according to claim 29, wherein said silicon mesa has the same conductivity type as said drift region.

32. A Schottky diode according to claim 29, wherein said silicon mesa has the opposite conductivity type of said drift region.

33. A Schottky diode according to claim 29, wherein said drift region further comprises termination wells at said first surface and adjacent edges of said mesa, said termination wells arresting current flow at said edges.

34. A Schottky diode according to claim 29, further comprising a conductive substrate on said second surface of said drift region.

35. A Schottky diode according to claim 34, wherein said substrate is less than about 100 microns thick.

36. A Schottky diode according to claim 35, wherein said substrate is less than about 25 microns thick.

37. A Schottky diode according to claim 35, further comprising a cathode contact on a surface of said substrate opposite said drift region.

38. A Schottky diode according to claim 29, further comprising an anode contact on said mesa.

39. A Schottky diode according to claim 29, further comprising a passivation layer covering sides of said mesa and the first surface of said drift region adjacent said mesa.

40. A Schottky diode according to claim 29, wherein said drift region is about 25 microns thick.

41. A Schottky diode according to claim 29, wherein said drift region is doped to about 3×

10¹⁵ cm<sup>−

3</sup>.