Substrate, epitaxial layer provided substrate, method for producing substrate, and method for producing epitaxial layer provided substrate
The present invention provides a substrate formed at a low cost and having a controlled plate shape, an epitaxial layer provided substrate obtained by forming an epitaxial layer on the substrate, and methods for producing them. The method for producing the substrate according to the present invention includes an ingot growing step serving as a step of preparing an ingot formed of gallium nitride (GaN); and a slicing step serving as a step of obtaining a substrate formed of gallium nitride, by slicing the ingot. In the slicing step, the substrate thus obtained by the slicing has a main surface with an arithmetic mean roughness Ra of not less than 0.05 μm and not more than 1 μm on a line of 10 mm.
1. A method for producing a substrate, comprising the steps of:
preparing an ingot formed of gallium nitride; and
obtaining a substrate formed of gallium nitride by slicing said ingot,
in the step of obtaining said substrate, said substrate obtained by the slicing having a main surface with an arithmetic mean roughness Ra of not less than 0.05 μm and not more than 1 μm on a line of 10 mm,
wherein in the step of obtaining said substrate, said ingot is sliced using a wire saw, and
wherein in the step of obtaining said substrate, said ingot is sliced using the wire saw and abrasive grains having an average grain size of not less than 6.5 μm and not more than 40 μm.
2. The method for producing a substrate according to claim 1 , wherein in the main surface of said substrate obtained in the step of obtaining said substrate, a region constituting a Ga atomic plane and a region constituting a N atomic plane are disposed on the same flat plane.
3. The method for producing a substrate according to claim 1 , wherein:
in the step of obtaining said substrate,
said substrate obtained by the slicing has a shape warped to project at the main surface of said substrate, the main surface of said substrate being mainly constituted by a region of a Ga atomic plane, and
said substrate obtained by the slicing has the warpage with a height of more than 0 μm and not more than 50 μm.
4. The method for producing a substrate according to claim 1 , wherein a ratio of a length of a longer side of a widest surface of each of said abrasive grains with respect to a length of a shorter side crossing said longer side thereof is not less than 1.3.
5. The method for producing a substrate according to claim 4 , wherein said ratio is not less than 1.4 and not more than 2.0.
6. The method for producing a substrate according to claim 1 , wherein in the step of obtaining said substrate, on the main surface of said substrate obtained by the slicing, there is formed a damaged layer having a maximum depth of not more than 10 μm and an average depth of not more than 5 μm.
7. A method for producing an epitaxial layer provided substrate, comprising the steps of:
preparing a substrate using the method for producing a substrate as recited in claim 6 ;
removing said damaged layer from the main surface of said substrate by vapor-phase etching; and
forming an epitaxial layer formed of a gallium nitride based semiconductor, on the main surface of said substrate, from which said damaged layer has been removed.
8. An epitaxial layer provided substrate, produced using the method for producing an epitaxial layer provided substrate as recited in claim 7 .
9. A method for producing an epitaxial layer provided substrate, comprising the steps of:
preparing a substrate using the method for producing a substrate as recited in claim 1 ;
removing a damaged layer from the main surface of said substrate; and
forming an epitaxial layer formed of a gallium nitride based semiconductor, on the main surface of said substrate, from which said damaged layer has been removed.
10. A method for producing an epitaxial layer provided substrate, comprising the steps of:
preparing a substrate using the method for producing a substrate as recited in claim 1 ;
polishing said substrate; and
forming an epitaxial layer formed of a gallium nitride based semiconductor, on the main surface of said substrate thus polished.
11. A substrate, produced using the method for producing a substrate as recited in claim 1 .