GaN substrate, method for producing GaN substrate, method for producing GaN crystal, and method for manufacturing semiconductor device

• US 10,655,244 B2
• Filed: 07/13/2018
• Issued: 05/19/2020
• Est. Priority Date: 01/17/2014
• Status: Active Grant

• Current Assignee: Mitsubishi Chemical Corporation (Mitsubishi Chemical Group Corp.)
• Original Assignee: Mitsubishi Chemical Corporation (Mitsubishi Chemical Group Corp.)
• Inventors: Tsukada, Yusuke, Nagao, Satoru, Kamada, Kazunori, Tashiro, Masayuki, Fujito, Kenji, Fujisawa, Hideo, Mikawa, Yutaka, Kajimoto, Tetsuharu, Fukada, Takashi
• Primary Examiner(s): Kunemund, Robert M
• Application Number:
  US16/034,953
• Publication Number:
  US 20180334758A1
• Time in Patent Office: 676 Days
• CPC Class Codes: C30B 23/025 characterised by the substrate
• CPC Class Codes: C30B 25/20 the substrate being of the same materials as the epitaxial layer
• CPC Class Codes: C30B 29/406 Gallium nitride
• CPC Class Codes: C30B 7/005 Epitaxial layer growth
• CPC Class Codes: C30B 7/105 using ammonia as solvent, i.e. ammonothermal processes
• CPC Class Codes: H01L 21/02389 Nitrides
• CPC Class Codes: H01L 21/02433 Crystal orientation
• CPC Class Codes: H01L 21/0254 Nitrides
• CPC Class Codes: H01L 21/0262 Reduction or decomposition of gaseous compounds, e.g. CVD
• CPC Class Codes: H01L 21/02642 Mask materials other than SiO2 or SiN
• CPC Class Codes: H01L 21/02647 Lateral overgrowth
• CPC Class Codes: H01L 29/2003 Nitride compounds
• CPC Class Codes: H01L 33/0075 comprising nitride compounds
• CPC Class Codes: H01L 33/32 containing nitrogen

Abstract

A disc-like GaN substrate is a substrate produced by a tiling method and having an angel between the normal line and m-axis on the main surface of the substrate of 0 to 20° inclusive and a diameter of 45 to 55 mm, to 4 or less. In a preferred embodiment, a disc-like GaN substrate has a first main surface and a second main surface that is opposite to the first main surface, and which has an angle between the normal line and m-axis on the first main surface of 0 to 20° inclusive and a diameter of 45 mm or more. The disc-like GaN substrate comprises at least four crystalline regions each being exposed to both of the first main surface and the second main surface, wherein the four crystalline regions are arranged in line along the direction of the orthogonal projection of c-axis on the first main surface.

Claims

1. A GaN substrate, comprising:

a first main surface; and

a second main surface provided on an opposite side from the first main surface, wherein

an angle between a normal line of the first main surface and an m-axis is 0°

to 20°

, and

when the first main surface is divided into an outer peripheral portion measuring 3 mm or less from an edge and a central portion surrounded by the outer peripheral portion, and the central portion is divided into a plurality of square partitions each having a 5 mm side, at least one square region, which has a 100 μ

m side and in which no dark spots are detected in a CL measurement, is observed within each of the partitions.

2. The GaN substrate according to claim 1, which is a (10-10) substrate, a (20-21) substrate, a (20-2-1) substrate, a (30-31) substrate or a (30-3-1) substrate.

3. The GaN substrate according to claim 1, wherein an RMS roughness of the first main surface as measured by AFM is smaller than 5 nm in a measurement area of 10 μ

m×

10 μ

m.

4. The GaN substrate according to claim 3, wherein the second main surface is a mirror surface.

5. The GaN substrate according to claim 3, wherein the second main surface is a matte surface.

6. The GaN substrate according to claim 3, wherein a ratio of an intensity of a yellow band with respect to an intensity of a peak of wavelength corresponding to a band gap of GaN is lower than ⅕

in an emission spectrum of the first main surface obtained by a photoluminescence measurement.

7. The GaN substrate according to claim 4, wherein a ratio of an intensity of a yellow band with respect to an intensity of a peak of wavelength corresponding to a band gap of GaN is lower than ⅕

in an emission spectrum of the second main surface obtained by a photoluminescence measurement.

8. The GaN substrate according to claim 5, wherein a ratio of an intensity of a yellow band with respect to an intensity of a peak of wavelength corresponding to a band gap of GaN is lower than ⅕

in an emission spectrum of the second main surface obtained by a photoluminescence measurement.

9. The GaN substrate according to claim 1, wherein the first main surface has a circular shape.

10. The GaN substrate according to claim 1, wherein the first main surface has a rectangular shape.

11. The GaN substrate according to claim 1, wherein an area of the first main surface is comparable to or greater than an area of a circle having a diameter of 2 inches.

12. The GaN substrate according to claim 1, which is made up of a single crystal region.

13. The GaN substrate according to claim 1, which is made up of a plurality of crystal regions each exposed at both the first main surface and the second main surface.

14. The GaN substrate according to claim 13, wherein the plurality of crystal regions are arrayed in one row in a direction of an orthogonal projection of a c-axis on the first main surface.

15. The GaN substrate according to claim 13, wherein the plurality of crystal regions are arrayed in two rows in a direction of an orthogonal projection of a c-axis on the first main surface.

16. The GaN substrate according to claim 13, wherein the plurality of crystal regions are arrayed in three rows in a direction of an orthogonal projection of a c-axis on the first main surface.

17. The GaN substrate according to claim 1, which comprises a GaN crystal having an alkali metal concentration lower than 1×

10¹⁵ cm<sup>−

3</sup> and an absorption coefficient at 450 nm of 2 cm<sup>−

1</sup> or smaller.

18. A method for producing a GaN crystal, the method comprising a step of preparing the GaN substrate according to claim 1, and epitaxially growing GaN thereon.

19. A method for producing a semiconductor device, the method comprising:

preparing the GaN substrate according to claim 1, and growing thereon one or more types of nitride semiconductor layer.