Self-aligned methods of fabricating silicon carbide power devices by implantation and lateral diffusion

• US 6,107,142 A
• Filed: 06/08/1998
• Issued: 08/22/2000
• Est. Priority Date: 06/08/1998
• Status: Expired due to Term

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: Cree Research, Inc. (Wolfspeed, Inc.)
• Inventors: Singh, Ranbir, Suvorov, Alexander, Palmour, John W.
• Primary Examiner(s): TRINH, MICHAEL MANH
• Application Number:
  US09/093,207
• Time in Patent Office: 806 Days
• Field of Search: 438/285, 438/105, 438/138, 438/268, 438/931, 438/DIG. 148, 438/519, 438/522
• US Class Current: 438/285
• CPC Class Codes: H01L 21/046 using ion implantation
• 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 29/7801 DMOS transistors, i.e. MISFETs with a channel accommodating body or base region adjoining a drain drift region lateral high-voltage MISFETs with channel well and drain offset region H01L29/7835
• CPC Class Codes: H01L 29/7802 Vertical DMOS transistors, i.e. VDMOS transistors
• CPC Class Codes: H01L 29/7816 Lateral DMOS transistors, i.e. LDMOS transistors
• CPC Class Codes: Y10S 438/931 Silicon carbide semiconductor

Abstract

Silicon carbide power devices are fabricated by implanting p-type dopants into a silicon carbide substrate through an opening in a mask, to form a deep p-type implant. N-type dopants are implanted into the silicon carbide substrates through the same opening in the mask, to form a shallow n-type implant relative to the p-type implant. Annealing is then performed at temperature and time that is sufficient to laterally diffuse the deep p-type implant to the surface of the silicon carbide substrate surrounding the shallow n-type implant, without vertically diffusing the p-type implant to the surface of the silicon carbide substrate through the shallow n-type implant. Accordingly, self-aligned shallow and deep implants may be performed by ion implantation, and a well-controlled channel may be formed by the annealing that promotes significant diffusion of the p-type dopant having high diffusivity, while the n-type dopant having low diffusivity remains relatively fixed. Thereby, a p-base may be formed around an n-type source. Lateral and vertical power MOSFETs may be fabricated.

Claims

1. A method of fabricating a silicon carbide power device comprising the steps of:

masking a surface of a silicon carbide substrate to define an opening at the surface;

first implanting p-type dopants into the silicon carbide substrate through the opening at implantation energy and dosage that form a deep p-type implant;

then implanting n-type dopants into the silicon carbide substrate through the opening at implantation energy and dosage that form a shallow n-type implant relative to the deep p-type implant;

annealing at temperature and time that is sufficient to laterally diffuse the deep p-type implant to the surface of the silicon carbide substrate surrounding the shallow n-type implant, without vertically diffusing the deep p-type implant to the surface of the silicon carbide substrate through the shallow n-type implant; and

implanting a p-type well at the surface of the silicon carbide substrate, electrically contacting the laterally diffused deep p-type implant.

2. A method according to claim 1:

wherein the step of first implanting p-type dopants comprises the step of implanting p-type dopants into the silicon carbide substrate through the opening at a plurality of implantation energies and dosages that form a deep p-type implant; and

wherein the step of then implanting n-type dopants comprises the step of then implanting n-type dopants into the silicon carbide substrate through the opening at a plurality of implantation energies and dosages that form a shallow n-type implant relative to the deep p-type implant.

3. A method according to claim 2:

wherein the step of first implanting p-type dopants comprises the step of implanting boron into the silicon carbide substrate through the opening at a plurality of implantation energies and dosages that form a deep p-type implant; and

wherein the step of then implanting n-type dopants comprises the step of then implanting nitrogen into the silicon carbide substrate through the opening at a plurality of implantation energies and dosages that form a shallow n-type implant relative to the deep p-type implant.

4. A method according to claim 1 wherein the step of first implanting p-type dopants comprises the step of implanting boron, and wherein the step of then implanting n-type dopants comprises the step of implanting nitrogen.

5. A method according to claim 1 wherein the step of first implanting p-type dopants comprises the step of implanting beryllium, and wherein the step of then implanting n-type dopants comprises the step of implanting nitrogen.

6. A method according to claim 1 wherein the p-type well comprises an aluminum well.

45. A method according to claim 1 wherein the step of implanting a p-type well follows the step of first implanting p-type dopants.

7. A method of fabricating a silicon carbide power device comprising the steps of:

masking a surface of a silicon carbide substrate to define an opening at the surface;

first implanting n-type dopants into the silicon carbide substrate through the opening at implantation energy and dosage that form a shallow n-type implant;

electrically activating the n-type dopants;

then implanting p-type dopants into the silicon carbide substrate through the opening at implantation energy and dosage that form a deep p-type implant relative to the shallow n-type implant;

annealing at temperature and time that is sufficient to laterally diffuse the deep p-type implant to the surface of the silicon carbide substrate surrounding the shallow n-type implant, without vertically diffusing the deep p-type implant to the surface of the silicon carbide substrate through the shallow n-type implant; and

implanting a p-type well at the surface of the silicon carbide substrate, electrically contacting the laterally diffused deep p-type implant.

8. A method according to claim 7:

wherein the step of first implanting n-type dopants comprises the step of implanting n-type dopants into the silicon carbide substrate through the opening at a plurality of implantation energies and dosages that form a shallow n-type implant; and

wherein the step of then implanting p-type dopants comprises the step of then implanting p-type dopants into the silicon carbide substrate through the opening at a plurality of implantation energies and dosages that form a deep p-type implant relative to the shallow n-type implant.

9. A method according to claim 8:

wherein the step of first implanting n-type dopants comprises the step of implanting nitrogen into the silicon carbide substrate through the opening at a plurality of implantation energies and dosages that form a shallow n-type implant; and

wherein the step of then implanting p-type dopants comprises the step of then implanting boron into the silicon carbide substrate through the opening at a plurality of implantation energies and dosages that form a deep p-type implant relative to the shallow n-type implant.

10. A method according to claim 7 wherein the step of first implanting n-type dopants comprises the step of implanting nitrogen, and wherein the step of then implanting p-type dopants comprises the step of implanting boron.

11. A method according to claim 7 wherein the step of first implanting n-type dopants comprises the step of implanting nitrogen, and wherein the step of then implanting p-type dopants comprises the step of implanting beryllium.

12. A method according to claim 7 wherein the p-type well comprises an aluminum well.

46. A method according to claim 7 wherein the step of implanting a p-type well precedes the step of first implanting n-type dopants.

13. A method of fabricating a silicon carbide lateral power MOSFET comprising the steps of:

implanting an aluminum well into a drift region at a surface of a silicon carbide substrate;

masking the drift region at the surface of the silicon carbide substrate to define a first pair of openings on the drift region, a respective one of which is on a respective opposite side of the aluminum well;

first implanting p-type dopants into the silicon carbide substrate through the first pair of openings at implantation energy and dosage that form deep p-type implants;

then implanting n-type dopants into the silicon carbide substrate through the first pair of openings at implantation energy and dosage that form shallow n-type implant relative to the deep p-type implants;

masking the drift region at the surface of the silicon carbide substrate to define a second pair of openings on the drift region, a respective one of which is spaced apart from a respective shallow n-type implant and opposite the aluminum well;

implanting n-type dopants into the silicon carbide substrate through the second pair of openings to define a pair of drain regions;

annealing at temperature and time that is sufficient to laterally diffuse the respective deep p-type implants to the surface of the silicon carbide substrate surrounding the respective shallow n-type implants, without vertically diffusing the respective deep p-type implants to the surface of the silicon carbide substrate through the respective shallow n-type implants, to thereby form a pair of channel regions in the laterally diffused p-type implants at the surface of the silicon carbide substrate, a respective one of which is on a respective opposite side of the aluminum well;

forming a pair of gate insulating regions on the drift region at the surface of the silicon carbide substrate, a respective one of which contacts a respective one of the pair of channel regions; and

forming a common source contact, a pair of drain contacts and a pair of gate contacts on the shallow n-type implants and the aluminum well therebetween, on the drain regions, and on the pair of gate insulating regions, respectively.

14. A method according to claim 13:

wherein the step of first implanting p-type dopants comprises the step of implanting p-type dopants into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form deep p-type implants; and

wherein the step of then implanting n-type dopants comprises the step of then implanting n-type dopants into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form shallow n-type implants relative to the deep p-type implants.

15. A method according to claim 14:

wherein the step of first implanting p-type dopants comprises the step of implanting boron into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form deep p-type implants; and

wherein the step of then implanting n-type dopants comprises the step of then implanting nitrogen into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form shallow n-type implants relative to the deep p-type implants.

16. A method according to claim 14:

wherein the step of first implanting p-type dopants comprises the step of implanting beryllium into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form deep p-type implants; and

wherein the step of then implanting n-type dopants comprises the step of then implanting nitrogen into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form shallow n-type implants relative to the deep p-type implants.

17. A method according to claim 13 wherein the step of first implanting p-type dopants comprises the step of implanting boron and wherein the step of then implanting n-type dopants comprises the step of implanting nitrogen.

18. A method according to claim 13 wherein the step of first implanting p-type dopants comprises the step of implanting beryllium and wherein the step of then implanting n-type dopants comprises the step of implanting nitrogen.

19. A method according to claim 13 wherein the step of implanting an aluminum well follows the step of then implanting n-type dopants, such that the aluminum well is implanted between the shallow n-type implants.

20. A method according to claim 13 wherein the steps of first implanting p-type dopants and then implanting n-type dopants are performed after the step of implanting n-type dopants, such that a pair of drain regions are formed prior to forming the deep p-type implants and the shallow n-type implants.

21. A method according to claim 13 wherein the steps of then implanting n-type dopants and implanting n-type dopants are performed simultaneously, such that the shallow n-type dopants and the pair of drain regions are formed simultaneously.

22. A method of fabricating a silicon carbide lateral power MOSFET comprising the steps of:

implanting an aluminum well into a drift region at a surface of a silicon carbide substrate;

masking the drift region at the surface of the silicon carbide substrate to define a first pair of openings on the drift region, a respective one of which is on a respective opposite side of the aluminum well;

first implanting n-type dopants into the silicon carbide substrate through the first pair of openings at implantation energy and dosage that form shallow n-type implants;

electrically activating the n-type dopants;

then implanting p-type dopants into the silicon carbide substrate through the first pair of openings at implantation energy and dosage that form deep p-type implants relative to the shallow n-type implants;

masking the drift region at the surface of the silicon carbide substrate to define a second pair of openings on the drift region, a respective one of which is spaced apart from a respective shallow n-type implant and opposite the aluminum well;

implanting n-type dopants into the silicon carbide substrate through the second pair of openings to define a pair of drain regions;

annealing at temperature and time that is sufficient to laterally diffuse the respective deep p-type implants to the surface of the silicon carbide substrate surrounding the respective shallow n-type implants, without vertically diffusing the respective deep p-type implants to the surface of the silicon carbide substrate through the respective shallow n-type implants, to thereby form a pair of channel regions in the laterally diffused p-type implants at the surface of the silicon carbide substrate, a respective one of which is on a respective opposite side of the aluminum well;

forming a pair of gate insulating regions on the drift region at the surface of the silicon carbide substrate, a respective one of which contacts a respective one of the pair of channel regions; and

forming a common source contact, a pair of drain contacts and a pair of gate contacts on the shallow n-type implants and the aluminum well therebetween, on the drain regions, and on the pair of gate insulating regions, respectively.

23. A method according to claim 22:

wherein the step of first implanting n-type dopants comprises the step of implanting n-type dopants into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form shallow n-type implants; and

wherein the step of then implanting p-type dopants comprises the step of then implanting p-type dopants into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form deep p-type implants relative to the shallow n-type implants.

24. A method according to claim 23:

wherein the step of first implanting n-type dopants comprises the step of implanting nitrogen into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form shallow n-type implants; and

wherein the step of then implanting p-type dopants comprises the step of then implanting boron into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form deep p-type implants relative to the shallow n-type implants.

25. A method according to claim 23:

wherein the step of first implanting n-type dopants comprises the step of implanting nitrogen into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form shallow n-type implants; and

wherein the step of then implanting p-type dopants comprises the step of then implanting beryllium into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form deep p-type implants relative to the shallow n-type implants.

26. A method according to claim 22 wherein the step of first implanting n-type dopants comprises the step of implanting nitrogen and wherein the step of then implanting p-type dopants comprises the step of implanting boron.

27. A method according to claim 22 wherein the step of first implanting n-type dopants comprises the step of implanting nitrogen and wherein the step of then implanting p-type dopants comprises the step of implanting beryllium.

28. A method according to claim 22 wherein the step of implanting an aluminum well follows the step of then implanting n-type dopants, such that the aluminum well is implanted between the shallow n-type implants.

29. A method according to claim 22 wherein the steps of first implanting p-type dopants and then implanting n-type dopants are performed after the step of implanting n-type dopants, such that a pair of drain regions are formed prior to forming the deep p-type implants and the shallow n-type implants.

30. A method according to claim 22 wherein the steps of first implanting n-type dopants and implanting n-type dopants are performed simultaneously, such that the shallow n-type dopants and the pair of drain regions are formed simultaneously.

31. A method of fabricating a silicon carbide vertical power MOSFET comprising the steps of:

implanting a pair of spaced apart aluminum wells into a drift region at a surface of a silicon carbide substrate;

masking the drift region at the surface of the silicon carbide substrate to define a first pair of openings on the drift region, between the pair of the aluminum wells;

first implanting p-type dopants into the silicon carbide substrate through the first pair of openings at implantation energy and dosage that form deep p-type implants;

then implanting n-type dopants into the silicon carbide substrate through the first pair of openings at implantation energy and dosage that form shallow n-type implants relative to the deep p-type implants;

annealing at temperature and time that is sufficient to laterally diffuse the respective deep p-type implants to the surface of the silicon carbide substrate surrounding the respective shallow n-type implants, without vertically diffusing the respective deep p-type implants to the surface of the silicon carbide substrate through the respective shallow n-type implants, to thereby form a pair of channel regions in the laterally diffused p-type implants at the surface of the silicon carbide substrate, between the shallow n-type implants;

forming a gate insulating region at the surface of the silicon carbide substrate extending on and between the pair of channel regions;

forming a pair of source contacts, a gate contact and a drain contact on the respective shallow n-type implants and extending on the aluminum well adjacent thereto, on the gate insulating region, and on a second face of the silicon carbide substrate opposite the drift region, respectively.

32. A method according to claim 31:

wherein the step of first implanting p-type dopants comprises the step of implanting p-type dopants into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form deep p-type implants; and

wherein the step of then implanting n-type dopants comprises the step of then implanting n-type dopants into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form shallow n-type implants relative to the deep p-type implants.

33. A method according to claim 32:

wherein the step of first implanting p-type dopants comprises the step of implanting boron into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form deep p-type implants; and

wherein the step of then implanting n-type dopants comprises the step of then implanting nitrogen into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form shallow n-type implants relative to the deep p-type implants.

34. A method according to claim 32:

wherein the step of first implanting p-type dopants comprises the step of implanting beryllium into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form deep p-type implants; and

wherein the step of then implanting n-type dopants comprises the step of then implanting nitrogen into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form shallow n-type implants relative to the deep p-type implants.

35. A method according to claim 31 wherein the step of first implanting p-type dopants comprises the step of implanting boron and wherein the step of then implanting n-type dopants comprises the step of implanting nitrogen.

36. A method according to claim 31 wherein the step of first implanting p-type dopants comprises the step of implanting beryllium and wherein the step of then implanting n-type dopants comprises the step of implanting nitrogen.

37. A method according to claim 31 wherein the step of implanting a pair of spaced apart aluminum wells follows the step of then implanting n-type dopants, such that the aluminum wells are implanted outside the shallow n-type implants.

38. A method of fabricating a silicon carbide vertical power MOSFET comprising the steps of:

implanting a pair of spaced apart aluminum wells into a drift region at a surface of a silicon carbide substrate;

masking the drift region at the surface of the silicon carbide substrate to define a first pair of openings on the drift region, between the pair of the aluminum wells;

first implanting n-type dopants into the silicon carbide substrate through the first pair of openings at implantation energy and dosage that form shallow n-type implants;

electrically activating the n-type dopants;

then implanting p-type dopants into the silicon carbide substrate through the first pair of openings at implantation energy and dosage that form deep p-type implants relative to the shallow n-type implants;

annealing at temperature and time that is sufficient to laterally diffuse the respective deep p-type implants to the surface of the silicon carbide substrate surrounding the respective shallow n-type implants, without vertically diffusing the respective deep p-type implants to the surface of the silicon carbide substrate through the respective shallow n-type implants, to thereby form a pair of channel regions in the laterally diffused p-type implants at the surface of the silicon carbide substrate, between the shallow n-type implants;

forming a gate insulating region at the surface of the silicon carbide substrate extending one and between the pair of channel regions;

forming a pair of source contacts, a gate contact and a drain contact on the respective shallow n-type implants and extending on the aluminum well adjacent thereto, on the gate insulating region, and on a second face of the silicon carbide substrate opposite the drift region, respectively.

39. A method according to claim 38:

wherein the step of first implanting n-type dopants comprises the step of implanting n-type dopants into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form shallow n-type implants; and

wherein the step of then implanting p-type dopants comprises the step of then implanting p-type dopants into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form deep p-type implants relative to the shallow n-type implants.

40. A method according to claim 39:

wherein the step of first implanting n-type dopants comprises the step of implanting nitrogen into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form shallow n-type implants; and

wherein the step of then implanting p-type dopants comprises the step of then implanting boron into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form deep p-type implants relative to the shallow n-type implants.

41. A method according to claim 39:

wherein the step of first implanting n-type dopants comprises the step of implanting nitrogen into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form shallow n-type implants; and

wherein the step of then implanting p-type dopants comprises the step of then implanting beryllium into the drift region at the face of the silicon carbide substrate through the first pair of openings at a plurality of implantation energies and dosages that form deep p-type implants relative to the shallow n-type implants.

42. A method according to claim 38 wherein the step of first implanting n-type dopants comprises the step of implanting nitrogen and wherein the step of then implanting p-type dopants comprises the step of implanting boron.

43. A method according to claim 38 wherein the step of first implanting n-type dopants comprises the step of implanting nitrogen and wherein the step of then implanting p-type dopants comprises the step of implanting beryllium.

44. A method according to claim 38 wherein the step of implanting a pair of spaced apart aluminum wells follows the step of then implanting n-type dopants, such that the aluminum wells are implanted outside the shallow n-type implants.