EPITAXIAL SUBSTRATE FOR SEMICONDUCTOR ELEMENTS, SEMICONDUCTOR ELEMENT, AND MANUFACTURING METHOD FOR EPITAXIAL SUBSTRATES FOR SEMICONDUCTOR ELEMENTS

• US 20180247809A1
• Filed: 04/27/2018
• Published: 08/30/2018
• Est. Priority Date: 11/02/2015
• Status: Active Grant

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: ICHIMURA, Mikiya, MAEHARA, Sota, KURAOKA, Yoshitaka
• Granted Patent: US 10,410,859 B2
• Time in Patent Office: Days
• CPC Class Codes: C23C 16/303 Nitrides
• CPC Class Codes: C23C 16/34 Nitrides C23C16/303 takes precedence
• CPC Class Codes: C30B 19/02 using molten solvents, e.g. flux
• CPC Class Codes: C30B 29/406 Gallium nitride
• CPC Class Codes: H01L 21/02389 Nitrides
• CPC Class Codes: H01L 21/02458 Nitrides
• CPC Class Codes: H01L 21/0251 Graded layers
• 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 29/2003 Nitride compounds
• CPC Class Codes: H01L 29/201 including two or more compounds , e.g. alloys H01L29/2006 takes precedence
• CPC Class Codes: H01L 29/205 in different semiconductor regions , e.g. heterojunctions
• CPC Class Codes: H01L 29/207 further characterised by the doping material H01L29/2006 takes precedence
• CPC Class Codes: H01L 29/401 Multistep manufacturing processes
• CPC Class Codes: H01L 29/66007 Multistep manufacturing processes
• CPC Class Codes: H01L 29/66462 with a heterojunction interface channel or gate, e.g. HFET, HIGFET, SISFET, HJFET, HEMT
• CPC Class Codes: H01L 29/778 with two-dimensional charge carrier gas channel, e.g. HEMT ; with two-dimensional charge-carrier layer formed at a heterojunction interface H01L29/803 takes precedence
• 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 29/7787 with wide bandgap charge-carrier supplying layer, e.g. direct single heterostructure MODFET
• CPC Class Codes: H01L 29/812 with a Schottky gate H01L29/7725, H01L29/775, H01L29/778, H01L29/806 take precedence; with Schottky contact on top of heterojunction gate H01L29/802

Abstract

Provided is an epitaxial substrate for semiconductor elements which suppresses an occurrence of current collapse. The epitaxial substrate for the semiconductor elements includes: a semi-insulating free-standing substrate formed of GaN being doped with Zn; a buffer layer being adjacent to the free-standing substrate; a channel layer being adjacent to the buffer layer; and a barrier layer being provided on an opposite side of the buffer layer with the channel layer therebetween, wherein the buffer layer is a diffusion suppressing layer that suppresses diffusion of Zn from the free-standing substrate into the channel layer.

Claims

1. An epitaxial substrate for semiconductor elements, comprising:

a semi-insulating free-standing substrate formed of GaN being doped with Zn;

a buffer layer being adjacent to said free-standing substrate and being a group 13 nitride layer that is doped with C at a concentration equal to or higher than 1×

10¹⁸ cm<sup>−

3</sup> in at least part of said buffer layer in a thickness direction;

a channel layer being adjacent to said buffer layer; and

a barrier layer being provided on an opposite side of said buffer layer with said channel layer therebetween, wherein

said buffer layer is a diffusion suppressing layer that suppresses diffusion of Zn from said free-standing substrate into said channel layer, and

a concentration of Zn in said channel layer is equal to or lower than 1×

10¹⁸ cm<sup>−

3</sup>.

2. The epitaxial substrate for the semiconductor elements according to claim 1, wherein

said group 13 nitride layer is a GaN layer.

3. The epitaxial substrate for the semiconductor elements according to claim 1, wherein

said group 13 nitride layer is either of

a multi-layered buffer layer, which is formed by laminating two or more group 13 nitride layers having different compositions, at least one of said two or more group 13 nitride layers being doped with C at a concentration of 1×

10¹⁸ cm<sup>−

3</sup> or more, or

a composition gradient buffer layer formed of group 13 nitride containing two or more group 13 elements each having an existence ratio being changed in a thickness direction.

4. The epitaxial substrate for the semiconductor elements according to claim 1, wherein

said channel layer is formed of GaN, and said barrier layer is formed of AlGaN.

14. The epitaxial substrate for the semiconductor elements according to claim 2, wherein

said channel layer is formed of GaN, and said barrier layer is formed of AlGaN.

15. The epitaxial substrate for the semiconductor elements according to claim 3, wherein

said channel layer is formed of GaN, and said barrier layer is formed of AlGaN.

5. A semiconductor element, comprising:

a semi-insulating free-standing substrate formed of GaN being doped with Zn;

a buffer layer being adjacent to said free-standing substrate and being a group 13 nitride layer that is doped with C at a concentration equal to or higher than 1×

10¹⁸ cm<sup>−

3</sup> in at least part of said buffer layer in a thickness direction;

a channel layer being adjacent to said buffer layer;

a barrier layer being provided on an opposite side of said buffer layer with said channel layer therebetween; and

a gate electrode, a source electrode, and a drain electrode being provided on said barrier layer, wherein

said buffer layer is a diffusion suppressing layer that suppresses diffusion of Zn from said free-standing substrate into said channel layer, and

a concentration of Zn in said channel layer is equal to or lower than 1×

10¹⁶ cm<sup>−

3</sup>.

6. The semiconductor element according to claim 5, wherein

said group 13 nitride layer is a GaN layer.

7. The semiconductor element according to claim 5, wherein

said group 13 nitride layer is either of

a multi-layered buffer layer, which is formed by laminating two or more group 13 nitride layers having different compositions, at least one of said two or more group 13 nitride layers being doped with C at a concentration of 1×

10¹⁸ cm<sup>−

3</sup> or more, or

a composition gradient buffer layer formed of group 13 nitride containing two or more group 13 elements each having an existence ratio being changed in a thickness direction.

8. The semiconductor element according to claim 5, wherein

said channel layer is formed of GaN, and said barrier layer is formed of AlGaN.

16. The semiconductor element according to claim 6, wherein

said channel layer is formed of GaN, and said barrier layer is formed of AlGaN.

17. The semiconductor element according to claim 7, wherein

said channel layer is formed of GaN, and said barrier layer is formed of AlGaN.

9. A method of manufacturing an epitaxial substrate for semiconductor elements, comprising:

a) a preparation step of preparing a semi-insulating free-standing substrate formed of GaN being doped with Zn;

b) a buffer layer formation step of forming a buffer layer to be adjacent to said free-standing substrate;

c) a channel layer formation step of forming a channel layer to be adjacent to said buffer layer; and

d) a barrier layer formation step of forming a barrier layer in a position opposite to said buffer layer with said channel layer therebetween, wherein

in said buffer layer formation step, said buffer layer is formed as a diffusion suppressing layer, which is a group 13 nitride layer that is doped with C at a concentration equal to or higher than 1×

10¹⁸ cm<sup>−

3</sup> in at least part of said buffer layer in a thickness direction, that suppresses diffusion of Zn from said free-standing substrate into said channel layer, so that a concentration of Zn in said channel layer is equal to or lower than 1×

10¹⁶ cm<sup>−

3</sup>.

10. The method of manufacturing the epitaxial substrate for the semiconductor elements according to claim 9, wherein

said group 13 nitride layer is formed of GaN.

11. The method of manufacturing the epitaxial substrate for the semiconductor elements according to claim 9, wherein

said group 13 nitride layer is formed as either of

a multi-layered buffer layer by laminating two or more group 13 nitride layers having different compositions, at least one of said two or more group 13 nitride layers being doped with C at a concentration of 1×

10¹⁸ cm<sup>−

3</sup> or more, or

a composition gradient buffer layer formed of group 13 nitride containing two or more group 13 elements each having an existence ratio being changed in a thickness direction.

12. The method of manufacturing the epitaxial substrate for the semiconductor elements according to claim 9, wherein

said channel layer is formed of GaN, and said barrier layer is formed of AlGaN.

13. The method of manufacturing the epitaxial substrate for the semiconductor elements according to claim 9, wherein

said free-standing substrate is manufactured by a flux method.

18. The method of manufacturing the epitaxial substrate for the semiconductor elements according to claim 10, wherein

said free-standing substrate is manufactured by a flux method.

19. The method of manufacturing the epitaxial substrate for the semiconductor elements according to claim 11, wherein

said free-standing substrate is manufactured by a flux method.

20. The method of manufacturing the epitaxial substrate for the semiconductor elements according to claim 12, wherein

said free-standing substrate is manufactured by a flux method.