Defect reduction in seeded aluminum nitride crystal growth

• US 9,670,591 B2
• Filed: 08/13/2014
• Issued: 06/06/2017
• Est. Priority Date: 01/17/2007
• Status: Active Grant

• Current Assignee: Crystal IS, Inc. (Asahi Kasei Corporation)
• Original Assignee: Crystal IS, Inc. (Asahi Kasei Corporation)
• Inventors: Slack, Glen A., Bondokov, Robert T., Morgan, Kenneth E., Schowalter, Leo J.
• Primary Examiner(s): Kunemund, Robert M
• Application Number:
  US14/458,825
• Publication Number:
  US 20150013592A1
• Time in Patent Office: 1,028 Days
• CPC Class Codes: C30B 23/00 Single-crystal growth by condensing evaporated or sublimed materials
• CPC Class Codes: C30B 23/025 characterised by the substrate
• CPC Class Codes: C30B 29/403 AIII-nitrides
• CPC Class Codes: H01L 21/02389 Nitrides
• CPC Class Codes: Y10T 428/2982 Particulate matter [e.g., sphere, flake, etc.]

Abstract

Bulk single crystal of aluminum nitride (AlN) having an areal planar defect density ≦100 cm⁻². Methods for growing single crystal aluminum nitride include melting an aluminum foil to uniformly wet a foundation with a layer of aluminum, the foundation forming a portion of an AlN seed holder, for an AlN seed to be used for the AlN growth. The holder may consist essentially of a substantially impervious backing plate.

Claims

1. A method for growing single-crystal aluminum nitride (AlN), the method comprising:

providing a backing plate sized and shaped to receive an AlN seed;

disposing an AlN seed and a substantially impervious foil on the backing plate with the foil between the AlN seed and the backing plate; and

depositing aluminum and nitrogen onto the AlN seed under conditions suitable for growing single-crystal AlN originating at the AlN seed.

2. The method of claim 1, wherein the foil is substantially impervious to aluminum transport.

3. The method of claim 2, wherein the foil is substantially impervious to nitrogen.

4. The method of claim 1, wherein the foil is substantially impervious to nitrogen.

5. The method of claim 1, wherein the backing plate is substantially impervious to aluminum transport.

6. The method of claim 1, wherein a surface of the AlN seed facing the backing plate has a total thickness variance of less than 5 μ

m.

7. The method of claim 1, wherein a surface of the AlN seed facing the backing plate has a root mean square roughness less than 1 nm in a 10 μ

m×

10 μ

m square area.

8. The method of claim 1, wherein providing the backing plate comprises exposing the backing plate to an Al vapor.

9. The method of claim 1, wherein the backing plate comprises multiple layers of grains, at least some of which are swollen to inhibit diffusion therebetween.

10. The method of claim 1, wherein the backing plate consists essentially of a polycrystalline material.

11. The method of claim 1, wherein the backing plate is mechanically flexible.

12. The method of claim 1, wherein the backing plate comprises tungsten.

13. The method of claim 1, wherein the backing plate consists essentially of tungsten.

14. The method of claim 1, wherein the foil comprises tungsten.

15. The method of claim 1, wherein the foil consists essentially of tungsten.

16. The method of claim 1, wherein the foil comprises aluminum.

17. The method of claim 1, wherein the foil consists essentially of aluminum.

18. The method of claim 1, wherein the foil is single-crystalline.

19. The method of claim 1, wherein the foil is single-crystalline tungsten.

20. The method of claim 1, further comprising disposing a barrier layer over at least a portion of a surface of the AlN seed.

21. The method of claim 20, wherein the barrier layer comprises at least one of tungsten, Hf, HfN, HfC, W—

Re, W—

Mo, BN, Ta, TaC, TaN, Ta₂N, or carbon.

22. The method of claim 20, wherein the barrier layer consists essentially of tungsten.

23. The method of claim 1, wherein the AlN seed is a wafer having a diameter of at least 20 mm.

24. The method of claim 1, wherein the grown single-crystal AlN comprises a boule having a diameter approximately the same as a diameter of the AlN seed.

25. The method of claim 1, wherein the AlN seed is substantially free of planar defects.

26. The method of claim 1, wherein the AlN seed is substantially free of subsurface damage.

27. The method of claim 1, further comprising, prior to disposing the AlN seed on the backing plate, polishing a surface of the AlN seed to at least one of reduce a surface roughness of the AlN seed or remove subsurface damage from the AlN seed.

28. The method of claim 1, further comprising applying an adhesive to at least a portion of the backing plate.

29. The method of claim 1, wherein the grown single-crystal AlN has a diameter greater than 20 mm, a thickness greater than 0.1 mm, and an areal planar defect density ≦

100 cm<sup>−

2</sup>.

30. The method of claim 29, wherein the areal planar defect density is ≦

1 cm<sup>−

2</sup>.

31. The method of claim 1, wherein (i) the deposition on the AlN seed occurs within a crystal growth crucible, and (ii) the backing plate is a portion of the crystal growth crucible.

32. The method of claim 1, wherein at least a portion of the foil melts before and/or during the aluminum and nitrogen deposition.

33. The method of claim 1, further comprising minimizing or substantially eliminating any gap between the AlN seed and the foil.

34. The method of claim 1, further comprising disposing a weight over the backing plate.

35. The method of claim 1, wherein the grown single-crystal AlN comprises a boule having a diameter larger than a diameter of the AlN seed.

36. The method of claim 1, wherein the grown single-crystal AlN comprises a boule having a diameter that increases along at least a portion of a length of the boule.

37. The method of claim 1, further comprising, during at least a portion of the deposition on the AlN seed, applying heat to form (i) a radial thermal gradient of less than 50°

C./cm and (ii) a vertical thermal gradient greater than 1°

C./cm and less than 50°

C./cm.

38. The method of claim 37, further comprising controlling a diameter of at least a portion of the single-crystal AlN at least in part by controlling at least one of the radial thermal gradient or the vertical thermal gradient.