Defect reduction in seeded aluminum nitride crystal growth

• US 9,771,666 B2
• Filed: 04/13/2015
• Issued: 09/26/2017
• 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: Bondokov, Robert T., Schowalter, Leo J., Morgan, Kenneth, Slack, Glen A., Rao, Shailaja P., Gibb, Shawn Robert
• Primary Examiner(s): Kunemund, Robert M
• Application Number:
  US14/684,754
• Publication Number:
  US 20150275393A1
• Time in Patent Office: 897 Days
• Field of Search: 117 80- 83
• 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: 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:

mounting an AlN seed on a seed holder, thereby forming a seed-seed holder assembly;

disposing the seed-seed holder assembly within a crystal-growth crucible;

heating the crystal-growth crucible to apply thereto (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; 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, further comprising disposing AlN source material within the crystal-growth crucible, the deposited aluminum and nitrogen evolving from the AlN source material during heating of the crystal-growth crucible.

3. The method of claim 2, wherein the AlN source material is polycrystalline.

4. The method of claim 1, wherein the seed-seed holder assembly is affixed to a lid of the crystal-growth crucible.

5. The method of claim 1, wherein mounting the AlN seed on the seed holder comprises disposing a foil between the AlN seed and the seed holder.

6. The method of claim 5, wherein the foil is substantially impervious to aluminum transport.

7. The method of claim 6, wherein the foil is substantially impervious to nitrogen.

8. The method of claim 5, wherein the foil is substantially impervious to nitrogen.

9. The method of claim 5, wherein the foil comprises tungsten.

10. The method of claim 5, wherein the foil is single-crystalline tungsten.

11. The method of claim 5, wherein the foil comprises aluminum.

12. The method of claim 1, wherein the seed holder is substantially impervious to aluminum transport.

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

14. The method of claim 13, wherein the barrier layer comprises at least one of tungsten, Hf, HfN, HfC, W—

Re, W—

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

15. The method of claim 13, wherein the barrier layer consists essentially of tungsten.

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

17. 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>.

18. The method of claim 17, wherein the areal planar defect density is ≦

1 cm<sup>−

2</sup>.

19. The method of claim 1, further comprising minimizing or substantially eliminating any gap between the AlN seed and the seed holder by positioning a weight on the seed-seed holder assembly.

20. The method of claim 19, wherein the weight is positioned on the AlN seed.

21. The method of claim 19, wherein the weight comprises tungsten.

22. The method of claim 19, further comprising removing the weight from the seed-seed holder assembly prior to depositing aluminum and nitrogen onto the AlN seed.

23. The method of claim 1, wherein a ratio of the vertical thermal gradient to the radial thermal gradient is less than 10.

24. The method of claim 1, wherein a ratio of the vertical thermal gradient to the radial thermal gradient is less than 5.5.

25. The method of claim 1, wherein a ratio of the vertical thermal gradient to the radial thermal gradient is less than 3.

26. The method of claim 1, wherein a ratio of the vertical thermal gradient to the radial thermal gradient is greater than 1.2.

27. The method of claim 1, wherein the radial thermal gradient is larger than 4°

C./cm.

28. The method of claim 1, wherein the vertical thermal gradient is larger than 5°

C./cm.

29. The method of claim 1, wherein applying the radial thermal gradient comprises arranging a plurality of thermal shields outside the crystal-growth crucible.

30. The method of claim 29, wherein each of the thermal shields comprises a refractory material.

31. The method of claim 29, wherein each of the thermal shields comprises tungsten.

32. The method of claim 29, wherein each thermal shield defines an opening therethrough.

33. The method of claim 32, wherein the openings of the thermal shields are substantially equal in size to each other.

34. The method of claim 32, wherein the opening of each thermal shield ranges from approximately 10 mm to approximately 2 mm less than a dimension of the growth chamber substantially perpendicular to a growth direction along which the single-crystal AlN grows.

35. The method of claim 32, wherein the openings of at least two of the thermal shields are different in size.

36. The method of claim 32, wherein a first thermal shield having a first opening is disposed between the crucible and a second thermal shield, the second thermal shield having a second opening larger than the first opening.

37. The method of claim 29, wherein at least two of the thermal shields have different thicknesses.

38. The method of claim 29, wherein a thickness of each of the thermal shields ranges from approximately 0.125 mm to approximately 0.5 mm.

39. The method of claim 29, wherein the thermal shields are arranged with substantially equal spacings therebetween.

40. The method of claim 29, wherein spacings between at least two pairs of the thermal shields are different.