# US 8,785,943 B2 · Nitride semiconductor device, nitride semiconductor wafer, and method for manufacturing nitride semiconductor layer

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- Number: US 8,785,943 B2
- Document ID: US8785943B2
- Status: Granted
- Kind: B2
- Application number: 13/407,169
- Filed: 2012-02-28
- Published: 2013-03-14
- Granted: 2014-07-22
- Earliest claimed: 2011-09-08
- Assignees: Kabushiki Kaisha Toshiba
- Applicants: Tomonari Shioda; Hung Hung; Jongil Hwang; Hisashi Yoshida; Naoharu Sugiyama; Shinya Nunoue
- Inventors: Tomonari Shioda; Hung Hung; Jongil Hwang; Hisashi Yoshida; Naoharu Sugiyama; Shinya Nunoue
- Web page: https://patentgrep.com/patent/US8785943B2

## CPC

- H10P 14/3416: {Nitrides}
- H10H 20/01335: {the light-emitting regions comprising nitride materials}
- H10H 20/815: having stress relaxation structures, e.g. buffer layers
- H10H 20/825: containing nitrogen, e.g. GaN
- H10P 14/2905: {Silicon, silicon germanium or germanium}
- H10P 14/3216: {Nitrides}
- H10P 14/3251: {consisting of three or more layers}
- H10P 14/3254: {Graded layers}
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
- H10H: INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS

## Abstract

According to one embodiment, a nitride semiconductor device includes a foundation layer, a first stacked intermediate layer, and a functional layer. The foundation layer includes an AlN buffer layer formed on a substrate. The first stacked intermediate layer is provided on the foundation layer. The first stacked intermediate layer includes a first AlN intermediate layer provided on the foundation layer, a first AlGaN intermediate layer provided on the first AlN intermediate layer, and a first GaN intermediate layer provided on the first AlGaN intermediate layer. The functional layer is provided on the first stacked intermediate layer. The first AlGaN intermediate layer includes a first step layer in contact with the first AlN intermediate layer. An Al composition ratio in the first step layer decreases stepwise in a stacking direction from the first AlN intermediate layer toward the first step layer.

## Claims

### Claim 1

A nitride semiconductor device comprising:
a foundation layer including an AlN buffer layer formed on a substrate;
a first stacked intermediate layer provided on the foundation layer, the first stacked intermediate layer including:
a first AlN intermediate layer including Al provided on the foundation layer;
a first AlGaN intermediate layer provided on the first AlN intermediate layer; and
a first GaN intermediate layer provided on the first AlGaN intermediate layer; and
a functional layer provided on the first stacked intermediate layer,
the first AlGaN intermediate layer being in contact with the first AlN intermediate layer, and
an Al composition ratio in the first AlGaN intermediate layer being lower than an Al composition ratio in the first AlN intermediate layer.

### Claim 2 (depends on 1)

The device according to claim 1, wherein
the first AlGaN intermediate layer includes a first layer and a second layer, the first layer being in contact with the first AlN intermediate layer, the second layer being provided on the first layer,
an Al composition ratio in the first layer decreases stepwise relative to an Al composition ratio in the first AlN intermediate layer, and
an Al composition ratio in the second layer gradually decreases from the first layer.

### Claim 3 (depends on 1)

The device according to claim 1, further comprising:
a second stacked intermediate layer provided between the first stacked intermediate layer and the functional layer, the second stacked intermediate layer including:
a second AlN intermediate layer including Al provided on the first GaN intermediate layer;
a second AlGaN intermediate layer provided on the second AlN intermediate layer; and
a second GaN intermediate layer provided on the second AlGaN intermediate layer,
the second AlGaN intermediate layer being in contact with the second AlN intermediate layer, and
an Al composition ratio in the second AlGaN intermediate layer being lower than an Al composition ratio in the second AlN intermediate layer.

### Claim 4 (depends on 1)

The device according to claim 1, wherein the first AlGaN intermediate layer has a thickness of 5 nanometers or more and 2000 nanometers or less.

### Claim 5 (depends on 1)

The device according to claim 1, wherein the first AlN intermediate layer has a thickness of 5 nanometers or more and 100 nanometers or less.

### Claim 6 (depends on 1)

The device according to claim 1, wherein the first AlN intermediate layer is formed at a temperature being 80° C. or more lower than a temperature at which the first GaN intermediate layer is formed.

### Claim 7 (depends on 1)

The device according to claim 1, wherein the first AlN intermediate layer is formed at a temperature of 500° C. or more and 1050° C. or less.

### Claim 8 (depends on 1)

The device according to claim 1, wherein the first AlN intermediate layer is formed at a temperature being 80° C. or more lower than a temperature at which the first AlGaN intermediate layer is formed.

### Claim 9

A nitride semiconductor device comprising:
a foundation layer including an AlN buffer layer formed on a substrate;
a first stacked intermediate layer provided on the foundation layer, the first stacked intermediate layer including:
a first AlGaN-based intermediate layer provided on the foundation layer; and
a first GaN intermediate layer provided on the first AlGaN-based intermediate layer; and
a functional layer provided on the first stacked intermediate layer,
absolute value of difference between an a-axis lattice constant of the first AlGaN-based intermediate layer and an a-axis lattice constant of GaN being larger than absolute value of difference between the a-axis lattice constant of the first AlGaN-based intermediate layer and an a-axis lattice constant of AlN.

### Claim 10 (depends on 9)

The device according to claim 9, wherein
the first AlGaN-based intermediate layer includes
a first AlN intermediate layer having a thickness of 5 nanometers or more and 100 nanometers or less,
a first AlGaN intermediate layer having a thickness of 5 nanometers or more and 2000 nanometers or less.

### Claim 11 (depends on 9)

The device according to claim 9, further comprising: a second stacked intermediate layer provided between the first stacked intermediate layer and the functional layer,
the second stacked intermediate layer including:
a second AlGaN-based intermediate layer provided on the first GaN intermediate layer; and
a second GaN intermediate layer provided on the second AlGaN-based intermediate layer,
absolute value of difference between an a-axis lattice constant of the second AlGaN-based intermediate layer and the a-axis lattice constant of the GaN being larger than absolute value of difference between the a-axis lattice constant of the second AlGaN-based intermediate layer and the a-axis lattice constant of the AlN,
a RMS value of surface height of the second AlGaN-based intermediate layer being 1 nanometer or less.

### Claim 12 (depends on 1)

The device according to claim 1, wherein a surface of the first AlGaN intermediate layer is flatter than a surface of the first AlN intermediate layer.

### Claim 13 (depends on 1)

The device according to claim 1, wherein a RMS value of surface height of the first AlGaN intermediate layer is 1 nanometer or less.

### Claim 14

A nitride semiconductor wafer comprising:
a substrate;
a foundation layer including an AlN buffer layer provided on the substrate;
a stacked intermediate layer provided on the foundation layer, the stacked intermediate layer including:
an AlN intermediate layer including Al provided on the foundation layer;
an AlGaN intermediate layer provided on the AlN intermediate layer; and
a GaN intermediate layer provided on the AlGaN intermediate layer; and
a functional layer provided on the stacked intermediate layer,
the AlGaN intermediate layer being in contact with the AlN intermediate layer, and
an Al composition ratio in the AlGaN intermediate layer being lower than an Al composition ratio in the AlN intermediate layer.

### Claim 15 (depends on 14)

The wafer according to claim 14, wherein
the AlGaN intermediate layer includes a first layer and a second layer, the first layer being in contact with the AlN intermediate layer, the second layer being provided on the first layer,
an Al composition ratio in the first layer decreases stepwise relative to an Al composition ratio in the AlN intermediate layer, and
an Al composition ratio in the second layer gradually decreases from the first layer.

### Claim 16 (depends on 14)

The wafer according to claim 14, wherein the AlN intermediate layer is formed at a temperature being 80° C. or more lower than a temperature at which the GaN intermediate layer is formed.

### Claim 17 (depends on 14)

The wafer according to claim 14, wherein the AlGaN intermediate layer has a thickness of 5 nanometers or more and 2000 nanometers or less.

### Claim 18 (depends on 14)

The wafer according to claim 14, wherein the AlN intermediate layer is formed at a temperature of 500° C. or more and 1050° C. or less.

### Claim 19 (depends on 14)

The wafer according to claim 14, wherein the AlN intermediate layer is formed at a temperature being 80° C. or more lower than a temperature at which the AlGaN intermediate layer is formed.

### Claim 20 (depends on 14)

The wafer according to claim 14, wherein the AlN intermediate layer is formed at a temperature being 200° C. or more lower than a temperature at which the GaN intermediate layer is formed.

### Claim 21

A nitride semiconductor wafer comprising:
a substrate;
a foundation layer including an AlN buffer layer formed on the substrate;
a stacked intermediate layer provided on the foundation layer, the stacked intermediate layer including:
an AlGaN-based intermediate layer provided on the foundation layer; and
a GaN intermediate layer provided on the AlGaN-based intermediate layer; and
a functional layer provided on the stacked intermediate layer,
absolute value of difference between an a-axis lattice constant of the AlGaN-based intermediate layer and an a-axis lattice constant of GaN being larger than absolute value of difference between the a-axis lattice constant of the AlGaN-based intermediate layer and an a-axis lattice constant of AlN.

### Claim 22 (depends on 21)

The wafer according to claim 21, wherein
the AlGaN-based intermediate layer includes
an AlN intermediate layer having a thickness of 5 nanometers or more and 100 nanometers or less,
an AlGaN intermediate layer having a thickness of 5 nanometers or more and 2000 nanometers or less.

### Claim 23 (depends on 22)

The wafer according to claim 22, wherein a surface of the AlGaN intermediate layer is flatter than a surface of the AlN intermediate layer.

### Claim 24 (depends on 22)

The wafer according to claim 22, wherein a RMS value of surface height of the AlGaN intermediate layer is 1 nanometer or less.

### Claim 25

A method for manufacturing a nitride semiconductor layer, comprising:
a first step to form a foundation layer including an AlN buffer layer on a silicon substrate;
a second step to form a stacked intermediate layer by:
forming an AlN intermediate layer on the foundation layer at 500° C. or more and 1050° C. or less;
forming an AlGaN intermediate layer on the AlN intermediate layer at a temperature being 80° C. or more higher than a temperature for forming the AlN intermediate layer, the AlGaN intermediate layer including a step layer in contact with the AlN intermediate layer; and
forming a GaN intermediate layer on the AlGaN intermediate layer at a temperature being 80° C. or more higher than the temperature for forming the AlN intermediate layer; and
a third step to form a functional layer on the stacked intermediate layer,
an Al composition ratio in the step layer being decreased stepwise in a stacking direction from the AlN intermediate layer toward the step layer.

### Claim 26 (depends on 25)

The method according to claim 25, wherein in the second step, a gradient layer is further formed between the step layer and the GaN intermediate layer, and an Al composition ratio in the gradient layer is gradually decreased in the stacking direction.

### Claim 27 (depends on 25)

The method according to claim 25, wherein the second step is repeated a plurality of times between the first step and the third step.

### Claim 28 (depends on 25)

The method according to claim 25, wherein a thickness of the AlGaN intermediate layer is set to 5 nanometers or more and 2000 nanometers or less.

### Claim 29 (depends on 25)

The method according to claim 25, wherein a thickness of the AlN intermediate layer is set to 5 nanometers or more and 100 nanometers or less.

### Claim 30

A method for manufacturing a nitride semiconductor layer, comprising:
a first step to form a foundation layer including an AlN buffer layer on a silicon substrate;
a second step to form a stacked intermediate layer by:
forming an AlN intermediate layer on the foundation layer;
forming an AlGaN intermediate layer on the AlN intermediate layer, the AlGaN intermediate layer including a step layer in contact with the AlN intermediate layer; and
forming a GaN intermediate layer on the AlGaN intermediate layer; and
a third step to form a functional layer on the stacked intermediate layer,
absolute value of difference between an a-axis lattice constant of the AlGaN-based intermediate layer and an a-axis lattice constant of GaN being set to be larger than absolute value of difference between the a-axis lattice constant of the AlGaN-based intermediate layer and an a-axis lattice constant of AlN.

### Claim 31 (depends on 30)

The method according to claim 30, wherein
a thickness of the AlN intermediate layer is set to be 5 nanometers or more and 100 nanometers or less, and
a thickness of the AlGaN intermediate layer is set to be 5 nanometers or more and 2000 nanometers or less.

### Claim 32 (depends on 30)

The method according to claim 30, wherein a surface of the AlGaN intermediate layer is set to be flatter than a surface of the AlN intermediate layer.

### Claim 33 (depends on 30)

The method according to claim 30, wherein a RMS value of surface height of the AlGaN intermediate layer is set to be 1 nanometer or less.