Method for manufacturing nitride crystal substrate and substrate for crystal growth

1. A method for manufacturing a nitride crystal substrate, comprising: arranging a plurality of seed crystal substrates made of a nitride crystal in a planar appearance, so that their main surfaces are parallel to each other and their lateral surfaces are in contact with each other; growing a first crystal film using a vapor-phase growth method on a surface of the plurality of seed crystal substrates arranged in the planar appearance, and preparing a combined substrate formed by combining the adjacent seed crystal substrates with each other by the first crystal film; growing a second crystal film using a liquid-phase growth method on a main surface of the combined substrate so as to be embedded in a groove that exists at a combined part of the seed crystal substrates, and preparing a substrate for crystal growth having a smoothened main surface, wherein a thickness of the second crystal film is set to a minimum necessary thickness to grow the smoothened main surface of the substrate for crystal growth by embedding the second crystal film in the groove; and growing a third crystal film using the vapor-phase growth method, on the smoothed main surface of the substrate for crystal growth.

2. The method for manufacturing a nitride crystal substrate according to claim 1 , wherein the seed crystal substrates are made of GaN crystals, the main surface of the seed crystal substrates is a c-plane, and all lateral surfaces of the seed crystal substrates in contact with lateral surfaces of other seed crystal substrates are a-planes.

3. The method for manufacturing a nitride crystal substrate according to claim 1 , wherein preparing the combined substrate is performed in a state of holding the plurality of seed crystal substrates on a holding plate, a thickness of the first crystal film is set to a minimum necessary thickness for maintaining a combined state of the adjacent seed crystal substrates even when the combined substrate is removed from the holding plate.

4. The method for manufacturing a nitride crystal substrate according to claim 3 , wherein the thickness of the first crystal film is set to a minimum necessary thickness for maintaining a combined state of the adjacent seed crystal substrates, even when the combined substrate removed from the holding plate is immersed in a raw material melt or a raw material solution when preparing the substrate for crystal growth.

5. The method for manufacturing a nitride crystal substrate according to claim 1 , wherein when an outer diameter of the combined substrate is set to D cm, the thickness of the first crystal film is set in a range of 30D μm or more and 100D μm or less.

6. The method for manufacturing a nitride crystal substrate according to claim 1 , wherein the second crystal film is formed on the surface of the combined substrate on the side where the first crystal film is formed.

7. The method for manufacturing a nitride crystal substrate according to claim 1 , wherein the first crystal film and the third crystal film are grown using a vapor-phase growth method which is Hydride Vapor-phase Epitaxy method, and different processing conditions are set between when growing the first crystal film, and when growing the third crystal film.

8. The method for manufacturing a nitride crystal substrate according to claim 1 , wherein the second crystal film is set to have a prescribed thickness in a range of 0.8 times or more and 1.2 times or less of a size of a larger one of a depth or an opening width of the groove.

9. The method for manufacturing a nitride crystal substrate according to claim 1 , wherein the third crystal film is set to be thick enough to obtain a plurality of nitride crystal substrates from the third crystal film.