EPITAXIAL SUBSTRATE FOR SEMICONDUCTOR ELEMENT, SEMICONDUCTOR ELEMENT, AND METHOD FOR PRODUCING EPITAXIAL SUBSTRATE FOR SEMICONDUCTOR ELEMENT

• US 20120211765A1
• Filed: 04/27/2012
• Published: 08/23/2012
• Est. Priority Date: 11/06/2009
• Status: Active Grant

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: MIYOSHI, Makoto, Sumiya, Shigeaki, Ichimura, Mikiya, Tanaka, Mitsuhiro
• Granted Patent: US 8,415,690 B2
• Time in Patent Office: Days
• US Class Current: 257/76
• CPC Class Codes: C23C 16/0272 Deposition of sub-layers, e.g. to promote the adhesion of the main coating
• CPC Class Codes: C23C 16/029 Graded interfaces
• CPC Class Codes: C23C 16/303 Nitrides
• CPC Class Codes: C30B 25/02 Epitaxial-layer growth
• CPC Class Codes: C30B 29/403 AIII-nitrides
• CPC Class Codes: C30B 29/68 Crystals with laminate structure, e.g. "superlattices"
• CPC Class Codes: H01L 21/0237 Materials
• CPC Class Codes: H01L 21/02381 Silicon, silicon germanium, germanium
• CPC Class Codes: H01L 21/02458 Nitrides
• CPC Class Codes: H01L 21/02494 Structure
• CPC Class Codes: H01L 21/02505 consisting of more than two layers
• CPC Class Codes: H01L 21/02507 Alternating layers, e.g. superlattice
• CPC Class Codes: H01L 21/0251 Graded layers
• CPC Class Codes: H01L 21/0254 Nitrides
• CPC Class Codes: H01L 29/1075 of field-effect transistors
• CPC Class Codes: H01L 29/2003 Nitride compounds
• CPC Class Codes: H01L 29/7786 with direct single heterostructure, i.e. with wide bandgap layer formed on top of active layer, e.g. direct single heterostructure MIS-like HEMT
• CPC Class Codes: H01L 29/872 Schottky diodes

Abstract

Provided is an epitaxial substrate using a silicon substrate as a base substrate. An epitaxial substrate, in which a group of group-III nitride layers are formed on a (111) single crystal Si substrate such that a (0001) crystal plane of the group of group-III nitride layers is substantially in parallel with a surface of the substrate, includes: a first group-III nitride layer made of AlN with many defects configured of at least one kind from a columnar or granular crystal or domain; a second group-III nitride layer whose interface with the first group-III nitride layer is shaped into a three-dimensional concave-convex surface; and a third group-III nitride layer epitaxially formed on the second group-III nitride layer as a graded composition layer in which the proportion of existence of Al is smaller in a portion closer to a fourth group-III nitride.

Claims

1. An epitaxial substrate for a semiconductor element, in which a group of group-III nitride layers are formed on a base substrate made of (111)-oriented single crystal silicon such that a (0001) crystal plane of said group of group-III nitride layers is substantially in parallel with a substrate surface of said base substrate, said epitaxial substrate comprising:

a first group-III nitride layer made of AlN and formed on said base substrate;

a second group-III nitride layer made of Al_pGa_1-pN (0≦

p≦

1) and formed on said first group-III nitride layer;

a third group-III nitride layer expressed by a composition formula of Al_qGa_1-qN (0≦

q≦

1) and epitaxially formed on said second group-III nitride layer; and

at least one fourth group-III nitride layer epitaxially formed on said third group-III nitride layer,

wherein

said first group-III nitride layer is a layer with many crystal defects configured of at least one kind from a columnar or granular crystal or domain,

an interface between said first group-III nitride layer and said second group-III nitride layer is shaped into a three-dimensional concave-convex surface,

said third group-III nitride layer is formed as a graded composition layer in which the proportion of existence of Al in a group-III element continuously decreases progressively from a first boundary portion at a boundary with said second group-III nitride layer toward a second boundary portion at a boundary with said fourth group-III nitride layer.

3. The epitaxial substrate for a semiconductor element according to claim 1, wherein

t2<

40e^0.0017t1 is satisfied,

when the thickness of said third group-III nitride layer is defined as t1 (nm), and the thickness of said fourth group-III nitride is defined as t2 (nm).

4. The epitaxial substrate for a semiconductor element according to claim 1, wherein

the thickness of said third group-III nitride layer is 1 μ

m or more and 3 μ

m or less.

5. The epitaxial substrate for a semiconductor element according to claim 1, wherein

said fourth group-III nitride layer includes a layer made of GaN, as a layer adjacent to said third group-III nitride layer,

said second boundary portion of said third group-III nitride layer is made of GaN.

6. The epitaxial substrate for a semiconductor element according to claim 1, wherein

when q=qa is established in said first boundary portion of said third group-III nitride layer, 0.8≦

qa≦

1 is satisfied.

7. The epitaxial substrate for a semiconductor element according to claim 6, wherein

said first boundary portion of said third group-III nitride layer is made of AlN.

8. The epitaxial substrate for a semiconductor element according to claim 1, wherein

a plurality of said third group-III nitride layers are laminated.

9. The epitaxial substrate for a semiconductor element according to claim 1, further comprising

a layer made of AlN and provided between said third group-III nitride layer and said fourth group-III nitride layer.

10. The epitaxial substrate for a semiconductor element according to claim 1, further comprising

a superlattice structure layer provided between said second group-III nitride layer and said third group-III nitride layer, said superlattice structure layer being formed by periodically laminating two or more kinds of group-III nitride layers having different compositions.

11. The epitaxial substrate for a semiconductor element according to claim 1,

an acceptor element is doped in said third group-III nitride layer.

12. The epitaxial substrate for a semiconductor element according to claim 11, wherein

said acceptor element is Mg.

13. The epitaxial substrate for a semiconductor element according to claim 1, wherein

a donor element is doped in said second group-III nitride layer.

14. The epitaxial substrate for a semiconductor element according to claim 13, wherein

said donor element is Si.

15. A semiconductor element prepared by using the epitaxial substrate according to claim 1.

2. The epitaxial substrate for a semiconductor element according to claim wherein

the rate of change of the proportion of existence of Al in said third nitride layer is 0.13%/nm or less.

16. A method for manufacturing an epitaxial substrate for a semiconductor element in which a group of group-III nitride layers are formed on a base substrate made of (111)-oriented single crystal silicon such that a (0001) crystal plane of said group of group-III nitride layers is substantially in parallel with a substrate surface of said base substrate, said method comprising:

a first formation step for forming, on said base substrate, a first group-III nitride layer made of AlN;

a second formation step for forming, on said second group-III nitride layer, a second group-III nitride layer made of Al_pGa_1-pN (0≦

p<

1);

a third formation step for epitaxially forming, on said second group-III nitride layer, a third group-III nitride layer expressed by a composition formula of Al_qGa_1-pN (0≦

q≦

1); and

a fourth formation step for epitaxially forming at least one fourth group-III nitride layer on said third group-III nitride layer,

wherein

in said first formation step, said first group-III nitride layer is formed as a layer with many crystal defects configured of at least one kind from a columnar or granular crystal or domain and having a surface thereof shaped into a three-dimensional concave-convex surface,

in said third formation step, said third group-III nitride layer is formed as a graded composition layer in which the proportion of existence of Al in a group-III element continuously decreases progressively from a first boundary portion at a boundary with said second group-III nitride layer toward a second boundary portion at a boundary with said fourth group-III nitride layer.

17. The method for manufacturing an epitaxial substrate for a semiconductor element according to claim 16, wherein

in said third formation step, said third group-III nitride layer is formed such that the rate of change of the proportion of existence of Al is 0.13%/nm or less.

18. The method for manufacturing an epitaxial substrate for a semiconductor element according to claim 16, wherein

said third group-III nitride layer and said fourth group-III nitride Layer are formed so as to satisfy

t2≦

40e^0.0017t1

when the thickness of said third group-III nitride layer is defined as t1 (nm), and the thickness of said fourth group-III nitride is defined as t2 (nm).

19. The method for manufacturing an epitaxial substrate for a semiconductor element according to claim 16, wherein

in said third formation step, said third group-III nitride layer is formed with a thickness of 1 μ

m or more and 3 μ

m or less.

20. The method for manufacturing an epitaxial substrate for a semiconductor element according to claim 16, herein

in said third formation step, said second boundary portion of said third group-III nitride layer is formed of GaN,

in said fourth formation step, a layer adjacent to said third group-III nitride layer is formed of GaN.

21. The method for manufacturing an epitaxial substrate for a semiconductor element according to claim 16, wherein

in said third formation step, said third group-III nitride layer is formed so as to satisfy 0.8≦

qa≦

1, when q=qa is established in said first boundary portion of said third group-III nitride layer.

22. The method for manufacturing an epitaxial substrate for a semiconductor element according to claim 21, wherein

in said third formation step, said first boundary portion of said third group-III nitride layer is formed of AlN.

23. The method for manufacturing an epitaxial substrate for a semiconductor element according to claim 16, wherein

in said third formation step, a plurality of said third group-III nitride layers are laminated.

24. The method for manufacturing an epitaxial substrate for a semiconductor element according to claim 16, wherein

after said third formation step, a layer made of AlN is formed on said third group-III nitride layer, and in said fourth formation step, said fourth group-III nitride layer is formed on said layer made of AlN.

25. The method for manufacturing an epitaxial substrate for a semiconductor element according to claim 16, wherein

after said second formation step, a superlattice structure layer is formed on said second group-III nitride layer, said superlattice structure layer being formed by periodically laminating two or more kinds of group-III nitride layers having different compositions,

in said third formation step, said third group-III nitride layer is formed on said superlattice structure layer.

26. The method for manufacturing an epitaxial substrate for a semiconductor element according to claim 16, wherein

in said third formation step, said third group-III nitride layer is formed while being doped with an acceptor element.

27. The method for manufacturing an epitaxial substrate for a semiconductor element according to claim 26, wherein

said acceptor element is Mg.

28. The method for manufacturing an epitaxial substrate for a semiconductor element according to claim 16, wherein

in said second formation step, said second group-III nitride layer is formed while being doped with a donor element.

29. The method for manufacturing an epitaxial substrate for a semiconductor element according to claim 28, wherein

said donor element is Si.