Method for manufacturing a group III nitride semiconductor crystal and method for manufacturing a group III nitride semiconductor substrate

1. A method for manufacturing a group III nitride semiconductor crystal, the method comprising the steps of:

preparing a seed crystal; and

performing a convex surface-growing step including growing the group III nitride semiconductor crystal, wherein a growth surface of the group III nitride semiconductor crystal is constituted only by a plurality of surfaces not vertical to a growth direction, and wherein the group III nitride semiconductor crystal grows while forming a convex shape as a whole by the growth surface constituted of the plurality of surfaces.

2. The method for manufacturing a group III nitride semiconductor crystal according to claim 1 , wherein growth is progressed such that concave-shaped portions are not formed in the growth surface composed of the plurality of surfaces.

3. The method for manufacturing a group III nitride semiconductor crystal according to claim 1 , wherein the growth direction is set in a C-axis direction, and each of the plurality of surfaces is a plane excluding a c-plane.

4. The method for manufacturing a group III nitride semiconductor crystal according to claim 1 , wherein each of the plurality of surfaces is a plane excluding a c-plane and the plurality of surfaces includes six equivalent (10-1m) planes, in which m is a natural number.

5. The method for manufacturing a group III nitride semiconductor crystal according to claim 3 , wherein the plurality of surfaces includes six equivalent (1-12n) planes, in which n is a natural number.

6. The method for manufacturing a group III nitride semiconductor crystal according to claim 3 , wherein the plurality of surfaces includes a total of twelve planes, wherein six of the twelve planes are six equivalent (10-1m) planes, in which m is a natural number and six of the twelve planes are six equivalent (1-12n) planes, in which n is a natural number.

7. The method for manufacturing a group III nitride semiconductor crystal according to claim 1 , wherein in the convex surface-growing step the seed crystal is obtained by cutting a top part of the group III nitride semiconductor, the top part having the convex shape.

8. The method for manufacturing a group III nitride semiconductor crystal according to claim 1 , wherein a diameter of the group III nitride semiconductor crystal that grows by performing the convex surface-growing step is 10 mm or more.

9. The method for manufacturing a group III nitride semiconductor crystal according to claim 1 , wherein growth of the group III nitride semiconductor crystal during the convex surface-growing step is 300 μm/hour or more.

10. The method for manufacturing a group III nitride semiconductor crystal according to claim 1 , wherein the group III nitride semiconductor crystal is gallium nitride (GaN).

11. The method for manufacturing a group III nitride semiconductor crystal according to claim 1 , further comprising a flat surface-vanishing growth step performed prior to the convex surface-growing step, the flat surface-vanishing growth step including:

forming a growth surface inclined to a main surface of a seed crystal substrate, in an outer peripheral part of a group III nitride semiconductor crystal that grows on the main surface of a seed crystal substrate, by using the seed crystal substrate as a seed crystal, then growing the inclined growth surface so as to expand to a center side of the seed crystal substrate, and vanishing a flat surface of the group III nitride semiconductor crystal which is parallel to the main surface of the seed crystal substrate and exists at the center side of the seed crystal substrate,

wherein after the flat surface-vanishing growth step is performed, the convex surface-growing step is performed, in which the group III nitride semiconductor crystal is grown on a growth surface having a convex surface shape composed of only the inclined growth surface.

12. The method for manufacturing a group III nitride semiconductor crystal according to claim 11 , wherein a seed crystal substrate having a side wall surface inclined to the main surface is used as the seed crystal substrate.

13. The method for manufacturing a group III nitride semiconductor crystal according to claim 11 , wherein a mask having an opening is superposed on the main surface, the main surface being the growth surface of the seed crystal substrate, such that the opening is aligned in a prescribed crystal orientation of the main surface, and the flat surface-vanishing growth step is performed by growing the group III nitride semiconductor crystal on the main surface of an opening part.

14. The method for manufacturing a group III nitride semiconductor crystal according to claim 11 , wherein in the flat surface-vanishing growth step, crystal growth is carried out at a low growth rate so as not to generate a crack in the group III nitride semiconductor crystal during growth, and in the convex surface-growing step, crystal growth is carried out at a high growth rate of 300 μm/h or more.

15. A method for manufacturing a group III nitride semiconductor substrate, the method comprising the steps of:

preparing a seed crystal;

performing a convex surface-growing step including growing the group III nitride semiconductor crystal, wherein a growth surface of the group III nitride semiconductor crystal is constituted only by a plurality of surfaces not vertical to a growth direction and wherein the group III nitride semiconductor crystal grows while forming a convex shape as a whole by the growth surface constituted by the plurality of surfaces; and

manufacturing a group III nitride semiconductor substrate by cutting the group III nitride semiconductor crystal obtained by performing the convex surface-growing step.

16. The method for manufacturing a group III nitride semiconductor substrate according to claim 15 , wherein the group III nitride semiconductor substrate is a gallium nitride (GaN) substrate.

17. The method for manufacturing a group III nitride semiconductor crystal according to claim 1 , further comprising preparing a seed crystal substrate as the seed crystal and growing the group III nitride semiconductor crystal such that one convex shape is formed on the seed crystal substrate as a whole.

18. The method for manufacturing a group III nitride semiconductor crystal according to claim 1 , wherein when growing the group III nitride semiconductor crystal a surface vertical to the growth direction is not formed.

19. The method for manufacturing a group III nitride semiconductor crystal according to claim 11 , wherein when growing the group III nitride semiconductor crystal a surface vertical to the growth direction is not formed.