Nitride semiconductor substrate and method of producing same
A nitride semiconductor crystal substrate is produced by forming a network mask repeating a closed loop unit shape upon an undersubstrate, growing a nitride semiconductor crystal in vapor phase, producing convex facet hills covered with facets on exposed parts Π, forming outlining concavities on mask-covered parts , not burying the facets, maintaining the convex facet hills on Π and the network concavities on , excluding dislocations in the facet hills down to the outlining concavities on , forming a defect accumulating region H on , decreasing dislocations in the facet hills and improving the facet hills to low defect density single crystal regions Z, producing a rugged nitride crystal, and slicing and polishing the nitride crystal into mirror nitride crystal wafers. After the fabrication of devices on the nitride wafer, dry-etching or wet etching of hot KOH or NaOH divides the device-carrying wafer into chips by corroding the network defect accumulating region H.
1. A nitride semiconductor substrate comprising:
a top surface;
a bottom surface;
a plurality of isolated, polygonal low defect density single crystal regions Z extending from the top surface to the bottom surface;
a plurality of isolated, polygonal closed loop grain boundaries K enclosing the low defect density single crystal region Z and extending from the top surface and the bottom surface; and
a network of a defect accumulating region H which repeats a polygonal closed loop unit shape enclosing one of the grain boundaries K; the defect accumulating region H having a width T, accommodating dislocations and extending from the top surface to the bottom surface.
2. A nitride semiconductor substrate comprising:
a top surface;
a bottom surface;
a plurality of isolated, polygonal low defect density single crystal regions Z extending from the top surface to the bottom surface;
a plurality of isolated, polygonal closed loop grain boundaries K enclosing the low defect density single crystal region Z and extending the top surface and the bottom surface;
a network of a defect accumulating region H which repeats a polygonal closed loop unit shape enclosing one of the grain boundaries K; and
isolated C-plane growth regions Y existing in the low defect single crystal regions Z, the defect accumulating region H having a width T′, accommodating dislocations and extending from the top surface to the bottom surface.
3. The nitride semiconductor substrate as claimed in claim 1 , wherein the maximum diameter of the low defect single crystal regions Z is 0.1 mm to 20 mm and the width T′ of the defect accumulating region H is 0.03 mm to 0.2 mm.
4. The nitride semiconductor substrate as claimed in claim 2 , wherein the maximum diameter of the low defect single crystal regions Z is 0.1 mm to 20 mm and width T′ of the defect accumulating region H is 0.03 mm to 0.2 mm.
5. The nitride semiconductor substrate as claimed in claim 1 , wherein low defect density single crystal regions Z are separated from each other by the network defect accumulating region H.
6. The nitride semiconductor substrate as claimed in claim 2 , wherein the low defect density single crystal regions Z are separated from each other by the network defect accumulating region H.
7. The nitride semiconductor substrate as claimed in claim 1 , wherein the defect accumulating region H is single crystal having orientation inverse to the low defect density single crystal regions Z.
8. The nitride semiconductor substrate as claimed in claim 2 , wherein the defect accumulating region H is single crystal having orientation inverse to the low defect density single crystal regions Z.
9. The nitride semiconductor substrate as claimed in claim 1 , wherein the defect accumulating regions H are polycrystals.
10. The nitride semiconductor substrate as claimed in claim 5 , wherein the longest distance from the closed loop grain boundaries K to the center of gravity of the low defect density single crystal region Z is denoted by L2, the shortest distance from the closed loop grain boundaries K to the center of gravity of the low defect density single crystal region Z is denoted by L1, and a ratio L2/L1 is less than 5.
11. The nitride semiconductor substrate as claimed in claim 1 , wherein the defect accumulating region H and the closed loop grain boundaries K are regular polygons, the maximum of diameters of the regular polygon boundaries K is 0.1 mm to 5 mm and the width T′ of the defect accumulating region H is 0.01 mm to 0.1 mm.
12. The nitride semiconductor substrate as claimed in claim 2 , wherein the defect accumulating region H and the closed loop grain boundaries K are regular polygons, the maximum of diameters of the regular polygon boundaries K is 0.1 mm to 5 mm and the width T′ of the defect accumulating region H is 0.01 mm to 0.1 mm.
13. The nitride semiconductor substrate as claimed in claim 1 , wherein the defect accumulating region H and the closed loop grain boundaries K are hexagons with 120 degree inner angles and sides of the hexagon are parallel to <10-10> directions.
14. The nitride semiconductor substrate as claimed in claim 2 , wherein the defect accumulating region H and the closed loop grain boundaries K are hexagons with 120 degree inner angles and sides of the hexagon are parallel to <10-10> directions.
15. The nitride semiconductor substrate as claimed in claim 1 , wherein the defect accumulating region H and the closed loop grain boundaries K are hexagons with 120 degree inner angles and sides of the hexagon are parallel to <11-20> directions.
16. The nitride semiconductor substrate as claimed in claim 2 , wherein the defect accumulating region H and the closed loop grain boundaries K are hexagons with 120 degree inner angles and sides of the hexagon are parallel to <11-20> directions.
17. The nitride semiconductor substrate as claimed in claim 1 , wherein the defect accumulating region H and the closed loop grain boundaries K are rectangles with 90 degree inner angles and sides of the rectangle are parallel or orthogonal to <10-10> directions.
18. The nitride semiconductor substrate as claimed in claim 1 , wherein the defect accumulating region H and the closed loop grain boundaries K are rectangles with 90 degree inner angles and sides of the rectangle incline at 45 degrees to <10-10> directions.
19. The nitride semiconductor substrate as claimed in claim 1 wherein the defect accumulating region H and the closed loop grain boundaries K are equilateral triangles and sides of the triangle are parallel to <10-10> directions.
20. The nitride semiconductor substrate as claimed in claim 1 , wherein the nitride semiconductor is Al x In y Ga 1-x-y N (0≦x≦1, 0≦y≦1, x+y≦1).
21. The nitride semiconductor substrate as claimed in claim 2 , wherein the nitride semiconductor is Al x In y Ga 1-x-y N (0≦x≦1, 0≦y≦1, x+y≦1).
22. The nitride semiconductor substrate as claimed in claim 1 , wherein the full width at half maximum (FWHM) of X-ray diffraction at (0004) planes is less than 30 arcseconds.
23. The nitride semiconductor substrate as claimed in claim 1 , wherein the etch pit density (EPD) at the low defect density single crystal regions Z is less than 1×10 6 cm −2 .