Method for producing nitride semiconductor crystal, and nitride semiconductor wafer and nitride semiconductor device

• US 20030183160A1
• Filed: 03/26/2003
• Published: 10/02/2003
• Est. Priority Date: 03/26/2002
• Status: Active Grant

• Current Assignee: Sumitomo Chemical Company Limited
• Original Assignee: Hitachi Cable Limited (Proterial Ltd.)
• Inventors: Iizuka, Kazuyuki, Fujikura, Hajime
• Granted Patent: US 7,294,200 B2
• Time in Patent Office: Days
• US Class Current: 117/86
• CPC Class Codes: C30B 25/02 Epitaxial-layer growth
• CPC Class Codes: C30B 25/18 characterised by the substrate
• CPC Class Codes: C30B 29/403 AIII-nitrides
• CPC Class Codes: C30B 29/406 Gallium nitride

Abstract

A method for producing a nitride semiconductor crystal comprising a step (a) for forming fine crystal particles made of a nitride semiconductor on a substrate; a step (b) for forming a nitride semiconductor island structure having a plurality of facets inclined relative to a surface of the substrate with the fine crystal particles as nuclei; and a step (c) for causing the nitride semiconductor island structure to grow in a direction parallel with a surface of the substrate to merge a plurality of the nitride semiconductor island structures with each other, thereby forming a nitride semiconductor crystal layer having a flat surface; the steps (a)-(c) being continuously conducted in the same growing apparatus.

Claims

1. A method for producing a nitride semiconductor crystal comprising a step (a) for forming fine crystal particles made of a nitride semiconductor on a substrate;

a step (b) for forming a nitride semiconductor island structure having a plurality of facets inclined relative to a surface of said substrate with said fine crystal particles as nuclei; and

a step (c) for causing said nitride semiconductor island structure to grow in a direction parallel with a surface of said substrate to merge a plurality of said nitride semiconductor island structures with each other, thereby forming a nitride semiconductor crystal layer having a flat surface;

said steps (a)-(c) being continuously conducted in the same growing apparatus.

2. The method for producing a nitride semiconductor crystal according to claim 1, wherein said substrate is made of a nitride semiconductor, sapphire, silicon carbide, silicon, zinc oxide, LiGaO₂ or LiAlO₂.

3. The method for producing a nitride semiconductor crystal according to claim 1, wherein said step (a) comprises a step for forming a nitride semiconductor crystal buffer layer on said substrate at a lower temperature than a crystal-growing temperature in said steps (b) and (c), and a step for heat-treating said nitride semiconductor crystal buffer layer at a higher temperature than its crystal-growing temperature to form said fine crystal particles.

4. The method for producing a nitride semiconductor crystal according to claim 3, wherein a temperature, at which said nitride semiconductor crystal buffer layer is formed, is 400 to 800°

C.

5. The method for producing a nitride semiconductor crystal according to claim 3, wherein the heat-treating temperature of said nitride semiconductor crystal buffer layer is 800 to 1200°

C.

6. The method for producing a nitride semiconductor crystal according to claim 1, wherein said substrate is a composite substrate having a nitride semiconductor layer formed on a surface of a substrate body made of a nitride semiconductor, sapphire, silicon carbide, silicon, zinc oxide, LiGaO₂ or LiAlO₂.

7. The method for producing a nitride semiconductor crystal according to claim 6, wherein a nitride semiconductor crystal is caused to grow on said composite substrate having fine roughness on a surface on the side of said nitride semiconductor layer, to form said fine crystal particles.

8. The method for producing a nitride semiconductor crystal according to claim 7, wherein a nitride semiconductor layer surface of said composite substrate is exposed to an ozone atmosphere, to form fine roughness on a surface of said composite substrate.

9. The method for producing a nitride semiconductor crystal according to claim 7, wherein a nitride semiconductor layer surface of said composite substrate is heat-treated to form fine roughness on a surface of said composite substrate.

10. The method for producing a nitride semiconductor crystal according to claim 7, wherein a nitride semiconductor layer surface of said composite substrate is brought into contact with an etching gas to form fine roughness on a surface of said composite substrate.

11. The method for producing a nitride semiconductor crystal according to claim 6, wherein said nitride semiconductor crystal is caused to grow on said composite substrate partially covered by a material hindering interactions between atoms constituting the nitride semiconductor layer of said composite substrate, and atoms constituting the nitride semiconductor crystal growing in said step (a), thereby forming said fine crystal particles.

12. The method for producing a nitride semiconductor crystal according to claim 11, wherein said material hindering interactions between said atoms is silicon, oxygen, silicon nitride, silicon oxide or a metal.

13. The method for producing a nitride semiconductor crystal according to claim 6, wherein said step (a) comprises placing said composite substrate in a growing apparatus, and introducing a starting material gas into said growing apparatus to form said fine crystal particles made of a nitride semiconductor.

14. The method for producing a nitride semiconductor crystal according to claim 1, wherein part or all of the growing of said nitride semiconductor crystal is conducted by an MOVPE method or an HVPE method.

15. The method for producing a nitride semiconductor crystal according to claim 1, wherein the conditions of growing said nitride semiconductor crystal are different in said steps (a)-(c).

16. The method for producing a nitride semiconductor crystal according to claim 15, wherein at least one of a temperature, an atmosphere pressure, a speed and an atmosphere composition for crystal growth is different among said steps (a)-(c).

17. The method for producing a nitride semiconductor crystal according to claim 16, wherein said nitride semiconductor crystal is caused to grow, by selecting at least one of a crystal growth condition (1) that a crystal-growing temperature in said step (b) is lower than that in said step (c), a crystal growth condition (2) that the hydrogen concentration in a crystal-growing atmosphere in said step (b) is higher than that in said step (c), a crystal growth condition (3) that a crystal-growing atmosphere pressure in said step (b) is higher than that in said step (c), and a crystal growth condition (4) that a crystal-growing speed in said step (b) is lower than that in said step (c).

18. The method for producing a nitride semiconductor crystal according to claim 17, wherein the crystal-growing temperature is 800 to 1050°

C. in said step (b) and 1050 to 1200°

C. in said step (c).

19. The method for producing a nitride semiconductor crystal according to claim 17, wherein the hydrogen concentration in the crystal-growing atmosphere is 50% or more in said step (b) and 0 to 30% in said step (c).

20. The method for producing a nitride semiconductor crystal according to claim 17, wherein the crystal-growing atmosphere pressure is 300 to 800 Torr in said step (b) and 70 to 150 Torr in said step (c).

21. The method for producing a nitride semiconductor crystal according to claim 17, wherein the crystal-growing speed is 0.1 to 4 μ

m/hr in said step (b) and 2 to 8 μ

m/hr in said step (c).

22. The method for producing a nitride semiconductor crystal according to claim 1, wherein said fine crystal particles of a nitride semiconductor are made of In_nGa₁₋

nN (0<

n≦

0.3).

23. The method for producing a nitride semiconductor crystal according to claim 1, wherein said nitride semiconductor island structure is made of GaN.

24. The method for producing a nitride semiconductor crystal according to claim 1, wherein said nitride semiconductor crystal layer formed in said step (c) is made of GaN.

25. The method for producing a nitride semiconductor crystal according to claim 1, wherein said nitride semiconductor island structure, and said nitride semiconductor crystal layer growing from said nitride semiconductor island structure in a direction parallel with said substrate surface have different compositions.

26. The method for producing a nitride semiconductor crystal according to claim 25, wherein any of said nitride semiconductor island structure and said nitride semiconductor crystal layer has a composition represented by In_xAl_yGa_zN (x 0, y 0, z 0, and x+y+z=1), though they have different contents of In and/or Al.

27. The method for producing a nitride semiconductor crystal according to claim 26, wherein said nitride semiconductor crystal layer is constituted by a layer having a composition represented by Al_yGa₁₋

yN (0<

y≦

1) and a layer having a composition represented by GaN.

28. The method for producing a nitride semiconductor crystal according to claim 1, wherein said nitride semiconductor island structure is formed by a nitride semiconductor crystal, to which In, Al or Si is added, in said step (b).

29. The method for producing a nitride semiconductor crystal according to claim 1, wherein said nitride semiconductor crystal layer is caused to grow by a nitride semiconductor crystal, to which Mg is added, in said step (c).

30. A nitride semiconductor wafer having a plurality of semiconductor layers formed on a nitride semiconductor crystal obtained by the method according to claim 1.

31. The nitride semiconductor wafer .according to claim 30, wherein a dislocation density is 1×

10⁹ cm<sup>−

2</sup> or less on the entire surface of said nitride semiconductor crystal.

32. A nitride semiconductor device constituted with the nitride semiconductor wafer according to claim 30.