Diode having reduced on-resistance and associated method of manufacture

• US 8,138,583 B2
• Filed: 02/16/2007
• Issued: 03/20/2012
• Est. Priority Date: 02/16/2007
• Status: Active Grant

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Sriram, Saptharishi, Smith, Thomas J. Jr., Hagleitner, Helmut
• Primary Examiner(s): Louie, Wai Sing
• Assistant Examiner(s): Jahan, Bilkis
• Application Number:
  US11/675,658
• Publication Number:
  US 20080197360A1
• Time in Patent Office: 1,859 Days
• Field of Search: 257/656, 257/E29.336, 257/77, 257/623, 257/622, 257/601, 257603-606, 257/594, 257/482, 257/497, 257/498, 257/551
• US Class Current: 257/656
• CPC Class Codes: H01L 23/291 Oxides or nitrides or carbides, e.g. ceramics, glass
• CPC Class Codes: H01L 23/31 characterised by the arrangement or shape
• CPC Class Codes: H01L 29/0657 characterised by the shape of the body
• 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 29/6609 Diodes
• CPC Class Codes: H01L 29/861 Diodes
• CPC Class Codes: H01L 29/868 PIN diodes
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Abstract

A diode structure having a reduced on-resistance in the forward-biased condition includes semiconductor layers, preferably of silicon carbide. The anode and cathode of the device are located on the same side of the bottom semiconductor layer, providing lateral conduction across the diode body. The anode is positioned on a semiconductor mesa, and the sides of the mesa are covered with a nonconductive spacer extending from the anode to the bottom layer. An ohmic contact, preferably a metal silicide, covers the surface of the bottom layer between the spacer material and the cathode. The conductive path extends from anode to cathode through the body of the mesa and across the bottom semiconductor layer, including the ohmic contact. The method of forming the diode includes reacting layers of silicon and metal on the appropriate regions of the diode to form an ohmic contact of metal silicide.

Claims

1. A laterally conductive diode comprising:

a first doped semiconductor layer having a first surface;

a semiconductor mesa on said first surface of said first doped layer, said semiconductor mesa comprising an intrinsic semiconductor region and a region having a different conductivity type from said first doped layer, wherein said intrinsic semiconductor region is located between said first doped semiconductor layer and said region having a different conductivity type;

a top ohmic contact on said mesa;

a nonconductive mesa sidewall spacer only on a side of said mesa between said first surface of said first doped layer and the top of said mesa; and

a lateral ohmic contact extending across at least a portion of said first surface of said first doped layer, said lateral ohmic contact conducting a current from said top ohmic contact laterally across said first doped layer.

2. A laterally conductive diode according to claim 1, wherein said lateral ohmic contact extends from said sidewall spacer.

3. A laterally conductive diode according to claim 2, wherein said first doped layer is of n+ doping type.

4. A laterally conductive diode according to claim 3, wherein said region of different conductivity type is of p+ doping type.

5. A laterally conductive diode according to claim 1, wherein said top ohmic contact extends across said mesa to a position adjacent said sidewall spacer.

6. A laterally conductive diode according to claim 1, further comprising a conductive metal cathode on said lateral ohmic contact.

7. A laterally conductive diode according to claim 1, further comprising a conductive metal anode on said top ohmic contact.

8. A laterally conductive diode according to claim 1, wherein said top ohmic contact comprises a metal silicide.

9. A laterally conductive diode according to claim 8, wherein said metal silicide is selected from the group consisting of TiSi₂, CoSi₂, and Ni₂Si.

10. A laterally conductive diode according to claim 1, further comprising a conductive metal cathode on said lateral ohmic contact.

11. A laterally conductive diode according to claim 10, wherein said metal silicide is selected from the group consisting of TiSi₂, CoSi₂, and Ni₂Si.

12. A laterally conductive diode according to claim 1, wherein said first doped semiconductor layer comprises silicon carbide.

13. A laterally conductive diode according to claim 1, wherein said semiconductor mesa comprises silicon carbide.

14. A laterally conductive diode according to claim 1, wherein said first doped layer is on a semi-insulating substrate.

15. A laterally conductive diode according to claim 14, wherein said semi-insulating substrate is a silicon carbide substrate.

16. A laterally conductive diode according to claim 14, further comprising a bottom contact on the side of said substrate opposite said n+ layer for mounting the diode in a circuit.

17. A PIN diode comprising:

an n+ type doped semiconductor layer having a first surface;

an intrinsic semiconductor layer on said first surface of said n+ semiconductor layer for controlling the current through the diode;

a p+ semiconductor layer on said intrinsic layer opposite said n+ type doped semiconductor layer;

a top ohmic contact on said p+ type semiconductor layer;

a lateral ohmic contact on said first surface of said n+ type semiconductor layer, said lateral ohmic contact positioned proximate to said intrinsic layer and said p+ layer, wherein the PIN diode conducts a current from said top ohmic contact to said lateral ohmic contact across said n+ layer; and

a sidewall spacer on at least one side of both said intrinsic layer and said p+ layer, wherein said sidewall spacer is limited to the side or sides of both said intrinsic layer and said p+ layer and faces said lateral ohmic contact to prevent short circuiting between said top ohmic contact and said lateral ohmic contact.

18. A PIN diode according to claim 17, further comprising a cathode on said lateral ohmic contact.

19. A PIN diode according to claim 17, wherein said lateral ohmic contact is a metal silicide.

20. A PIN diode according to claim 19, wherein said metal silicide is selected from the group consisting of TiSi₂, CoSi₂, and Ni₂Si.

21. A PIN diode according to claim 17, wherein said top ohmic contact is a metal silicide.

22. A PIN diode according to claim 21, wherein said metal silicide is selected from the group consisting of TiSi₂, CoSi₂, and Ni₂Si.

23. A PIN diode according to claim 17, wherein said sidewall spacer is selected from the group consisting of silicon dioxide and silicon nitride.

24. A PIN diode according to claim 23, further comprising a bottom contact on the side of said substrate opposite said n+ layer for mounting the PIN diode in a circuit.

25. A laterally conductive diode according to claim 17, wherein said lateral ohmic contact extends from said sidewall spacer.

26. A laterally conductive diode according to claim 17, wherein said top ohmic contact extends across said mesa to a position adjacent said sidewall spacer.

27. A PIN diode according to claim 17, wherein said n+ type doped semiconductor layer comprises silicon carbide.

28. A PIN diode according to claim 17, wherein said intrinsic semiconductor layer comprises silicon carbide.

29. A PIN diode according to claim 17, wherein said p+ semiconductor layer comprises silicon carbide.

30. A PIN diode according to claim 17, wherein said n+ layer is on a silicon carbide substrate.

31. A laterally conductive diode comprising:

a first doped semiconductor layer having a first surface;

a semiconductor mesa on said first surface of said first doped layer;

a top ohmic contact on said mesa;

a nonconductive mesa sidewall spacer only on a side of said mesa between said first surface of said first doped layer and the top of said mesa; and

a lateral ohmic contact extending across at least a portion of said first surface of said first doped layer, said lateral ohmic contact conducting a current from said top ohmic contact laterally across said first doped layer.

32. A laterally conductive diode according to claim 31, wherein said lateral ohmic contact extends from said sidewall spacer.

33. A laterally conductive diode according to claim 31, wherein said top ohmic contact extends across said mesa to a position adjacent to from said sidewall spacer.

34. A laterally conductive diode according to claim 31, wherein said first doped semiconductor layer comprises an n+ type semiconductor and wherein said semiconductor mesa comprises an n−

doping type semiconductor.

35. A laterally conductive diode according to claim 31, wherein said first doped semiconductor layer comprises silicon carbide.

36. A laterally conductive diode according to claim 31, wherein said semiconductor mesa comprises silicon carbide.

37. A laterally conductive diode according to claim 31, wherein said semiconductor mesa comprises a region having less doping than said first doped semiconductor layer.