Method for producing nitride semiconductor, semiconductor wafer and semiconductor device

1. A method for producing a nitride semiconductor comprising growing at least first to third nitride semiconductor layers on a substrate; said first nitride semiconductor layer being grown at 400–600° C.; and said second and third nitride semiconductor layers being grown on said first nitride semiconductor layer at 700–1,300° C. after heat-treating said first nitride semiconductor layer at 700–1,300° C.; using a carrier gas supplied near said substrate together with a starting material gas, the carrier gas being a hydrogen/nitrogen mixture gas containing 63% or more by volume of hydrogen during growing said second nitride semiconductor layer, and a hydrogen/nitrogen mixture gas containing 50% or more by volume of nitrogen during growing said third nitride semiconductor layer; and said second nitride semiconductor layer being formed to a thickness of more than 1 μm.

2. The method for producing a nitride semiconductor according to claim 1 , wherein the thickness of said second nitride semiconductor layer is 2.25 μm or more.

3. The method for producing a nitride semiconductor according to claim 1 or 2 , wherein a carrier gas used to grow said second nitride semiconductor layer is a hydrogen/nitrogen mixture gas containing 82% or more by volume of hydrogen.

4. The method for producing a nitride semiconductor according to any one of claims 1 to 3 , wherein a carrier gas used to grow said third nitride semiconductor layer is a hydrogen/nitrogen mixture gas containing 70% or more by volume of nitrogen.

5. The method for producing a nitride semiconductor according to any one of claims 1 to 4 , wherein the growing speed of said second nitride semiconductor layer is 4.8 μm/hour or less.

6. The method for producing a nitride semiconductor according to any one of claims 1 to 5 , wherein the growing speed of said third nitride semiconductor layer is 2.2 to 10.9 μm/hour.

7. The method for producing a nitride semiconductor according to any one of claims 1 to 6 , wherein the pressure during the growth of said third nitride semiconductor layer is 112 to 800 Torr.

8. The method for producing a nitride semiconductor according to any one of claims 1 to 7 , wherein the pressure during the growth of said first and second nitride semiconductor layers is 615 Torr or more.

9. The method for producing a nitride semiconductor according to any one of claims 1 to 8 , wherein the thickness of said first nitride semiconductor layer is 5 to 42 nm.

10. The method for producing a nitride semiconductor according to any one of claims 1 to 9 , wherein the thickness of said third nitride semiconductor layer is 500 to 10,000 nm.

11. The method for producing a nitride semiconductor according to any one of claims 1 to 10 , wherein the difference in a growing temperature between said second nitride semiconductor layer and said third nitride semiconductor layer is 100° C. or less.

12. The method for producing a nitride semiconductor according to any one of claims 1 to 11 , wherein a flow rate of ammonia supplied as a nitrogen source to grow said second nitride semiconductor layer is equal to or less than that of ammonia supplied to grow said third nitride semiconductor layer.

13. The method for producing a nitride semiconductor according to any one of claims 1 to 12 , wherein said substrate is made of a single crystal of sapphire, silicon carbide, silicon, ZrB 2 , ZnO, LiGaO 2 or LiAlO 2 .

14. The method for producing a nitride semiconductor according to any one of claims 1 to , wherein each of said first to third nitride semiconductor layers is made of In x Al y Ga z N (x≧0, y≧0, z≧0, x+y+z=1).

15. The method for producing a nitride semiconductor according to any one of claims 1 to 14 , wherein at least one of said first to third nitride semiconductor layers is undoped, or doped with silicon, oxygen, iron, zinc or magnesium at a doping concentration of 5×10 19 atoms or less per 1 cm 3 .