Group III nitride crystal and method for surface treatment thereof, group III nitride stack and manufacturing method thereof, and group III nitride semiconductor device and manufacturing method thereof
A method for surface treatment of a group III nitride crystal includes the steps of lapping a surface of a group III nitride crystal using a hard abrasive grain with a Mohs hardness higher than 7, and abrasive-grain-free polishing the lapped surface of the group III nitride crystal using a polishing solution without containing abrasive grain, and the polishing solution without containing abrasive grain has a pH of not less than 1 and not more than 6, or not less than 8.5 and not more than 14. Accordingly, the method for surface treatment of a group III nitride crystal can be provided according to which hard abrasive grains remaining at the lapped crystal can be removed to reduce impurities at the crystal surface.
1. A method for surface treatment of a group III nitride crystal, comprising the steps of:
lapping a surface of a group III nitride crystal using a hard abrasive grain with a Mohs hardness higher than 7; and
abrasive-grain-free polishing for polishing said lapped surface of said group III nitride crystal using a polishing solution without containing abrasive grain,
said polishing solution without containing abrasive grain having a pH of not less than 1 and not more than 6, or not less than 8.5 and not more than 14.
2. The method for surface treatment of a group III nitride crystal according to claim 1 , wherein
in said step of abrasive-grain-free polishing, polishing is performed using a polishing pad with a compressibility of not less than 1.5% and not more than 20% and at a polishing pressure of not less than 0.98 kPa and not more than 58.8 kPa.
3. The method for surface treatment of a group III nitride crystal according to claim 1 , further comprising the step of soft-abrasive-grain polishing for polishing said lapped surface of said group III nitride crystal using a polishing solution containing a soft abrasive grain with a Mohs hardness of not more than 7, after said step of lapping and before said step of abrasive-grain-free polishing.
4. The method for surface treatment of a group III nitride crystal according to claim 3 , wherein
in said step of soft-abrasive-grain polishing, polishing is performed using a polishing pad with a compressibility of not less than 0.8% and not more than 5% and at a polishing pressure of not less than 4.9 kPa and not more than 98 kPa.
5. A group III nitride crystal produced through the surface treatment as recited in claim 1 .
6. The group III nitride crystal according to claim 5 , wherein
a surface roughness Ra of the group III nitride crystal is not more than 2 nm.
7. The group III nitride crystal according to claim 5 , wherein
a work-affected layer of the group III nitride crystal has a thickness of not more than 50 nm.
8. The group III nitride crystal according to claim 5 , wherein
said group III nitride crystal includes a high dislocation density region and a low dislocation density region, and a difference in level between a surface of said low dislocation density region and a surface of said high dislocation density region is not more than 3 μm.
9. The group III nitride crystal according to claim 5 , wherein
said group III nitride crystal includes a high dislocation density region and a low dislocation density region, and a flat surface region of said low dislocation density region has an area of not less than 40% of the whole surface of said low dislocation density region.
10. A group III nitride stack comprising the group III nitride crystal as recited in claim 5 and at least one group III nitride layer epitaxially grown on a surface of said group III nitride crystal.
11. A method for manufacturing a group III nitride stack using the group III nitride crystal as recited in claim 5 , comprising the steps of:
preparing said group III nitride crystal; and
epitaxially growing at least one group III nitride layer ( 650 ) on a surface of said group III nitride crystal.
12. A group III nitride semiconductor device comprising:
the group III nitride crystal as recited in claim 5 ;
at least one group III nitride layer epitaxially grown on a surface of the group III nitride crystal; and
an electrode formed on at least one of a surface of an outermost layer of said group III nitride layer and a surface of said group III nitride crystal.
13. A method for manufacturing a group III nitride semiconductor device using the group III nitride crystal as recited in claim 5 , comprising the steps of:
preparing said group III nitride crystal;
epitaxially growing at least one group III nitride layer on a surface of said group III nitride crystal; and
forming an electrode on at least one of a surface of an outermost layer of said group III nitride layer and a surface of said group III nitride crystal.