Molybdenum barrier metal for SiC Schottky diode and process of manufacture

• US 9,627,552 B2
• Filed: 07/31/2007
• Issued: 04/18/2017
• Est. Priority Date: 07/31/2006
• Status: Active Grant

• Current Assignee: Vishay Siliconix
• Original Assignee: Vishay Siliconix
• Inventors: Richieri, Giovanni
• Primary Examiner(s): Malsawma, Lex
• Assistant Examiner(s): JONES, ERIC W
• Application Number:
  US11/888,452
• Publication Number:
  US 20080237608A1
• Time in Patent Office: 3,549 Days
• Field of Search: 438105, 438931, 438570, 438571, 438582, 257 77, 257471-473, 257483, 257484
• CPC Class Codes: H01L 29/0619 with a supplementary region doped oppositely to or in rectifying contact with the semiconductor containing or contacting region, e.g. guard rings with PN or Schottky junction
• CPC Class Codes: H01L 29/1608 Silicon carbide
• CPC Class Codes: H01L 29/47 Schottky barrier electrodes H01L29/435 takes precedence
• 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 method for fabricating a diode is disclosed. In one embodiment, the method includes forming a Schottky contact on an epitaxial layer of silicon carbide (SiC) and annealing the Schottky contact at a temperature in the range of 300° C. to 700° C. The Schottky contact is formed of a layer of molybdenum.

Claims

1. A method for fabricating a diode, said method comprising:

forming a Schottky contact on an epitaxial layer of silicon carbide (SiC) wherein a ring termination region is formed in said epitaxial layer of silicon carbide (SiC) below a passivation layer, and wherein said Schottky contact comprises a layer of molybdenum (Mo);

annealing said Schottky contact at a temperature in the range of 300°

C. to 700°

C.;

forming an ohmic contact that contacts said passivation layer and said Schottky contact and overlies portions of said ring termination region;

forming a layer of amorphous silicon that has a top surface that fully lies underneath and contacts a bottom surface of said ohmic contact and a side surface of said passivation layer wherein at least a portion of said bottom surface of said ohmic contact lies above a structure other than said amorphous silicon; and

forming a polyimide layer over said layer of amorphous silicon and over said Schottky contact wherein said layer of amorphous silicon contacts portions of said Schottky contact.

2. The method of claim 1 wherein said forming a Schottky contact that is comprised of Mo provides said diode with greater forward current conduction with less forward voltage applied than a similar diode with a Schottky contact that comprises titanium (Ti).

3. The method of claim 1 further comprising forming an ohmic contact above said layer of molybdenum wherein material used to form said ohmic contact is selected from the group consisting of aluminum (Al), nickel (Ni), titanium (Ti), tungsten (W), copper (Cu) and gold (Au).

4. The method of claim 3 wherein said ohmic contact is formed using a wire bonding process and comprises an aluminum top layer formed over a molybdenum barrier metal which are annealed together during the Schottky contact annealing step using a temperature in the range of 300-700°

C.

5. The method of claim 1 further comprising forming a boron termination implant in said epitaxial layer of SiC.

6. The method of claim 5 wherein said boron termination implant is formed using high temperature rapid thermal annealing (HTRTA) with temperature in excess of 1550°

C.

7. The method of claim 1 further comprising forming a backside phosphorous termination implant in said epitaxial layer of SiC.

8. The method of claim 1 wherein said layer of molybdenum (Mo) has a thickness that is between 500 angstroms and 2000 angstroms.

9. A method for fabricating a diode, said method comprising:

forming a substrate;

forming an epitaxial layer of silicon carbide on said substrate;

forming an edge termination implant in an edge termination region of said epitaxial layer of silicon carbide (SiC) below a passivation layer;

forming a Schottky contact on said epitaxial layer wherein said Schottky contact comprises a layer of molybdenum (Mo);

annealing said Schottky contact at a temperature in the range of 300°

C. to 700°

C.;

forming an ohmic contact layer above said Schottky contact that contacts said passivation layer and said Schottky contact and overlies portions of said edge termination implant;

forming a backside ohmic contact on a backside of said substrate;

forming a layer of amorphous silicon that has a top surface that fully lies underneath and contacts a bottom surface of said ohmic contact and a side surface of said passivation layer wherein at least a portion of said bottom surface of said ohmic contact lies above a structure other than said amorphous silicon; and

forming a polyimide layer to contact top and side surfaces of said ohmic contact and a surface of said layer of amorphous silicon and over said Schottky contact wherein said layer of amorphous silicon contacts portions of said Schottky contact.

10. The method of claim 9 wherein said forming said Schottky contact that is comprised of Mo provides said diode with greater forward current conduction with less forward voltage applied than a similar diode with a Schottky contact that comprises titanium (Ti).

11. The method of claim 9 wherein material used to form said ohmic contact is selected from the group consisting of aluminum (Al), nickel (Ni), titanium (Ti), tungsten (W), copper (Cu) and gold (Au).

12. The method of claim 11 wherein said ohmic contact is formed using a wire bonding process and comprises an aluminum top layer formed over a molybdenum barrier metal which are annealed together during the Schottky contact annealing step using a temperature in the range of 300-700°

C.

13. The method of claim 9 further comprising forming a boron (B) termination implant in said epitaxial layer of SiC.

14. The method of claim 13 wherein said boron (B) termination implant is formed by high temperature rapid thermal annealing activation (HTRTA).

15. The method of claim 9 further comprising forming a backside phosphorous (P) implant in said epitaxial layer of SiC.

16. The method of claim 9 wherein said layer of molybdenum (Mo) has a thickness that is between 500 angstroms and 2000 angstroms.

17. A Schottky diode comprising:

a substrate;

an epitaxial layer located adjacent to and above said substrate;

an edge termination implant formed in a termination region of said epitaxial layer below a passivation layer;

a Schottky contact formed on said epitaxial layer, wherein said Schottky contact comprises a layer of molybdenum;

an ohmic contact formed above said Schottky contact that contacts said passivation layer and said Schottky contact and overlies portions of said termination region;

a backside ohmic contact formed on a backside of said substrate;

forming a layer of amorphous silicon that has a top surface that fully lies underneath and contacts a bottom surface of said ohmic contact and a side surface of said passivation layer wherein at least a portion of said bottom surface of said ohmic contact lies above a structure other than said amorphous silicon; and

a polyimide layer formed to contact top and side surfaces of said ohmic contact and a surface of said layer of amorphous silicon and over said Schottky contact wherein said layer of amorphous silicon contacts portions of said Schottky contact.

18. The diode of claim 17 wherein said diode provides greater forward current conduction with less forward voltage applied than a similar diode comprising a Schottky contact made of titanium.

19. The diode of claim 17 further comprising an ohmic contact located above said layer of molybdenum wherein material used to form said ohmic contact is selected from the group consisting of aluminum (Al), nickel (Ni), titanium (Ti), tungsten (W), copper (Cu) and gold (Au).

20. The diode of claim 19 wherein said ohmic contact is formed using a wire bonding process and comprises an aluminum top layer formed over a molybdenum barrier metal which are annealed together during the Schottky contact annealing step using a temperature in the range of 300-700°

C.

21. The diode of claim 17 further comprising forming a boron (B) termination implant in said epitaxial layer of SiC.

22. The diode of claim 20 wherein said boron (B) termination implant is formed using (HTRTA) high temperature rapid thermal annealing with a temperature in excess of 1550°

C.

23. The diode of claim 17 further comprising forming a backside phosphorous (P) termination implant in said epitaxial layer of SiC.

24. The diode of claim 17 wherein said layer of molybdenum (Mo) has a thickness that is between 500 angstroms and 2000 angstroms.