Silicon-rich nickel-silicide ohmic contacts for SiC semiconductor devices

• US 7,875,545 B2
• Filed: 01/28/2008
• Issued: 01/25/2011
• Est. Priority Date: 07/06/2004
• Status: Active Grant

• Current Assignee: Wolfspeed, Inc.
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Wieber, Keith Dennis, Henning, Jason Patrick, Ward, Allan III, Hagleitner, Helmut
• Primary Examiner(s): HO, HOANG QUAN TRAN
• Application Number:
  US12/020,731
• Publication Number:
  US 20080116464A1
• Time in Patent Office: 1,093 Days
• Field of Search: None
• US Class Current: 438/602
• CPC Class Codes: H01L 21/0455 Making n or p doped regions or layers, e.g. using diffusion
• CPC Class Codes: H01L 21/0485 Ohmic electrodes
• CPC Class Codes: H01L 29/1608 Silicon carbide
• CPC Class Codes: H01L 29/45 Ohmic electrodes
• CPC Class Codes: Y10S 438/931 Silicon carbide semiconductor

Abstract

A method of producing an ohmic contact and a resulting ohmic contact structure are disclosed. The method includes the steps of forming a deposited film of nickel and silicon on a silicon carbide surface at a temperature below which either element will react with silicon carbide and in respective proportions so that the atomic fraction of silicon in the deposited film is greater than the atomic fraction of nickel, and heating the deposited film of nickel and silicon to a temperature at which nickel-silicon compounds will form with an atomic fraction of silicon greater than the atomic fraction of nickel but below the temperature at which either element will react with silicon carbide. The method can further include the step of annealing the nickel-silicon compound to a temperature higher than the heating temperature for the deposited film, and within a region of the phase diagram at which free carbon does not exist.

Claims

1. A method of producing an ohmic contact to silicon carbide comprising:

providing a film of nickel and silicon on a silicon carbide surface in respective proportions so that the atomic fraction of silicon in the film is greater than the atomic fraction of nickel;

heating the film of nickel and silicon at a temperature between about 200 and 500°

C. to form a nickel-silicon compound; and

annealing the nickel-silicon compound to a temperature higher than the heating temperature for the film, and within a region of a phase diagram at which free carbon does not exist.

2. A method according to claim 1 comprising:

forming the film with an atomic fraction of silicon that is greater than 0.50 and no more than about 0.67; and

heating the film to form a nickel-silicon compound with an atomic fraction of silicon that is greater than 0.50 and no more than about 0.67.

3. A method according to claim 1 wherein the step of heating the film comprises heating the film to form a compound having the formula Ni_1-xSi._x where 0.5<

x<

0.67.

4. A method according to claim 1 comprising depositing the film on the silicon carbide surface.

5. A method according to claim 1 comprising annealing the nickel-silicon compound to a temperature of between about 500 and 850°

C.

6. A method according to claim 4 comprising doping the silicon carbide to a concentration of about 10¹⁹ cm⁻

3 prior to the step of depositing the nickel and the silicon.

7. A method according to claim 1 wherein the step of providing the film comprises depositing a plurality of nickel layers and a plurality of silicon layers in respective proportional thicknesses to produce the greater atomic fraction of silicon in the deposited film.

8. A method according to claim 7 comprising depositing the respective nickel and silicon layers in a ratio of total thickness of silicon to total thickness of nickel of between about 1.81 and 3.65.

9. A method according to claim 7 comprising depositing the silicon layer on the silicon carbide surface and thereafter depositing the nickel layer on the silicon layer.

10. A method according to claim 1 wherein the step of providing the film comprises sputter depositing a nickel-silicon layer in the desired proportion of nickel and silicon on the silicon carbide surface.

11. A method according to claim 10 comprising forming the deposited film on a doped silicon carbide surface.

12. A method according to claim 1 comprising providing the film on a silicon carbide surface selected from the group consisting of bulk single crystals of silicon carbide and epitaxial layers of silicon carbide.

13. A method according to claim 1 comprising providing the film on a silicon carbide surface having a polytype selected from the group consisting of the 4H and 6H polytypes of silicon carbide.

14. A method of producing an ohmic contact to silicon carbide comprising:

depositing a layer of nickel and a layer of silicon in respective proportional thicknesses on a silicon carbide surface so that the atomic fraction of silicon in the deposited layers is greater than the atomic fraction of nickel in the deposited layers;

depositing the layers of nickel and silicon at a temperature below which either element will react with silicon carbide; and

thereafter heating the deposited layers of nickel and silicon to a temperature at which nickel-silicon compounds will form with an atomic fraction of silicon greater than the atomic fraction of nickel but below the temperature at which either element will react with silicon carbide.

15. A method according to claim 14 comprising annealing the nickel-silicon compound to a temperature of between about 500 and 850°

C.

16. A method according to claim 14 comprising depositing the nickel and silicon in a ratio of silicon layer thickness to nickel layer thickness of between about 1.81 and 3.65.

17. A method according to claim 14 comprising depositing the silicon layer on the silicon carbide surface and thereafter depositing the nickel layer on the silicon layer.

18. A method of producing an ohmic contact to silicon carbide comprising:

providing a film of nickel and silicon on a silicon carbide surface in respective proportions so that the atomic fraction of silicon in the film is greater than the atomic fraction of nickel;

heating the film at a temperature below 500°

C.; and

thereafter annealing the film at a temperature of between 500 and 900°

C.

19. A method according to claim 18 wherein the step of providing the nickel and silicon film comprises forming the film with an atomic fraction of silicon that is greater than 0.50 and no more than about 0.67.