JPH10321954A - Group III nitride semiconductor device and method of manufacturing the same - Google Patents

Abstract

(57) Abstract: current path without the high-resistance portion, provides little heat during operation _{Al x Ga y In 1-x-} y N Group III nitride semiconductor device and its manufacturing method. SOLUTION: Al _x Ga _y In _1-xy N (0
≦ x, y, and x + y ≦ 1). A group III nitride in which an electrode layer 8a is formed on a final group III nitride semiconductor thin film 3 to 7 In the semiconductor element, a buffer layer 2c made of a transition metal nitride exhibiting metal conductivity and having a rock salt type or hexagonal crystal structure is interposed between the substrate and the group III nitride semiconductor thin film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

Relates III nitride semiconductor device, such as a BACKGROUND OF THE INVENTION The _{Al x Ga y In 1-xy} N film laser diode or a light emitting diode using, in particular, III-nitride semiconductor having a low electrode of their resistance Related to the element.

[0002]

2. Description of the Related Art At present, single crystals of GaN or AlN having a large size have not been obtained. Therefore, a laser diode (hereinafter referred to as LD) or a light emitting diode (hereinafter referred to as LED) using an Al _x Ga _y In _{1- xy} N film. Group III nitride semiconductor devices such as sapphire (Al ₂ O ₃ ), spinel
It is formed on a single crystal substrate made of another material such as (MgAl ₂ O ₄ ), silicon (Si), and silicon carbide (SiC). Usually, an AlN buffer layer or a GaN low-temperature buffer layer is formed on the substrate surface, and various Al _x Ga _y In _1-xy N films are formed on the substrate surface in order to alleviate distortion due to lattice mismatch. I have.

[0003] Such Al _x Ga _y which has been put to practical use in the past.
In a semiconductor device such as an LED using an In _1-xy N film, a substrate, which is an insulating material, cannot be used as a current path, so that the following structure must be used. FIG. 5 is a sectional view of a light emitting diode formed on a conventional sapphire substrate. AlN buffer layer 2, n on sapphire substrate 1i
Contact layer 3 of n-type GaN, first cladding layer layer 4 of n-type AlGaN, GaN active layer 5, p-type AlGaN
A second contact layer 7 made of p-type GaN, an epitaxial layer side electrode layer 8a made of Al / Ti (hereinafter abbreviated as epi side electrode layer), and The nitride semiconductor layers 4 to 7 were removed by etching, and the substrate-side electrode 8b made of Au / Cr was formed on the remaining n-type GaN contact layer 3. That is, the contact layer 3 of n-type GaN is used as a conductive lead member, and the cross section of the current path is the product of the thickness and the width of the contact layer 3 (in the direction perpendicular to the plane of FIG. 5). Even if the resistance of the GaN contact layer is reduced, the lead tends to have high resistance.

However, if a substrate made of a low-resistance semiconductor material can be used, a substrate-side electrode can be formed on the back of the substrate to form a current path through the substrate. FIG. 6 is a cross-sectional view of a conventional light emitting diode formed on a semiconductor substrate. The semiconductor substrate is Si. The substrate-side electrode 8b is formed on the back side of the substrate, and the layer configuration of the group III nitride semiconductor layer is the same as that of FIG. 5 except that the substrate and the element have the same area, and thus the description of the layer configuration is omitted. Since the n-side electrode 8b is formed on the back side of the substrate 1, the cross section of the current path becomes the element area, so that the resistance of the current path can be expected to be low. Further, the effective area ratio of the material is increased, and the removal of the group III nitride semiconductor layer by etching is not required, and the number of manufacturing steps is reduced, which is suitable for mass production.

[0005]

However, in forming a group III nitride semiconductor layer on a semiconductor substrate, the AlN or GaN buffer layer conventionally used is an AlN insulator, and the resistance of GaN cannot be reduced too much. Therefore, the buffer layer is a factor that still increases the element resistance. Also, p
Conventionally, Au / Cr electrodes were used as the electrodes formed on the Al _x Ga _y In _1-xy N type, but the contact resistance was large, which also caused an increase in the element resistance. .

[0006] The portion where the element resistance is increased becomes a Joule heat generating portion, which is a cause of deteriorating the characteristics and reliability of the element. SUMMARY OF THE INVENTION It is an object of the present invention to provide an Al _x Ga _y In which has no high resistance portion in a current path and generates less heat during operation.
_An object of the present invention is to provide a group III nitride semiconductor device made of _1-xyN .

[0007]

In order to achieve the above object, Al _x Ga _y In _1-xy N (0 ≦ x,
y, and x + y ≦ 1). In a group III nitride semiconductor device in which an electrode layer is formed on a final group III nitride semiconductor thin film composed of A buffer layer made of a transition metal nitride exhibiting metal conductivity and having a rock salt type or hexagonal crystal structure is interposed between the group III nitride semiconductor thin films.

[0008] The transition metal nitride is titanium nitride (TiN).
), Vanadium nitride (VN), zirconium nitride (ZrN
), Niobium nitride (NbN) or hafnium nitride (HfN
), Or a mixed crystal composed of two of them, or tantalum nitride (TaN). The semiconductor substrate is preferably silicon, silicon carbide, gallium phosphide, or gallium arsenide.

Preferably, a second buffer layer is interposed between the buffer layer and the group III nitride semiconductor thin film to further reduce lattice mismatch. The second buffer layer is formed of the II
The same composition as the group I nitride semiconductor thin film, and
It is preferable that the low-temperature film formation layer is formed at a substrate temperature lower than the substrate temperature at the time of forming the group III nitride semiconductor thin film.

[0010] The substrate temperature of the low-temperature film-forming layer is at least 25 ° C and 5
The temperature is preferably not higher than 00 ° C. The second buffer layer is
It is preferable that the superlattice layer be a thin film having the same composition as the group III nitride semiconductor thin film and a plurality of double layers including the buffer layer. The thickness of the double layer is preferably 50 nm or less.
In addition, Al _x Ga _y In _1-xy N (0 ≦ x,
y, and x + y ≦ 1). In the group III nitride semiconductor device in which an electrode layer is formed on a final group III nitride semiconductor thin film, the group consisting of: Is a thin film made of a transition metal nitride having a metal salt conductivity and a rock salt type or hexagonal crystal structure.

The transition metal nitride is titanium nitride (TiN).
), Vanadium nitride (VN), zirconium nitride (ZrN
), Niobium nitride (NbN), hafnium nitride (HfN), a mixed crystal composed of two of them, or tantalum nitride (TaN). above
In the method for manufacturing a group III nitride semiconductor device, the layer made of the transition metal nitride may be formed by molecular beam epitaxy.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The present inventors have developed thin films of some of transition metal nitrides and their mixed crystals into silicon (Si), germanium (Ge), silicon carbide (SiC), gallium phosphide (GaP).
), Epitaxial growth on a semiconductor substrate such as gallium arsenide (GaAs), and an Al _x Ga _y In _1-xy It has been found that the lattice matching with the N film is good, and that a high-quality Al _x Ga _y In _1-xy N film can be easily epitaxially formed. Table 1 shows the crystal types and lattice constants of these transition metal nitrides.

[0013]

[Table 1]The metal nitrides listed in Table 1 are Si, Ge, SiC, GaAs, GaP
Epitaxial growth on semiconductor substrates such as
To the epitaxial layer._xGa_yIn _1-xy
The N film could be grown epitaxially. Also, TaN
With the exception of these, these are two types of transition metals
Nitride can form a mixed crystal in which only the lattice constant changes. Follow
And by choosing the lattice constant appropriately
 Al_xGa_yIn_1-xyFor any x and y in N
A buffer layer that can mitigate lattice mismatch
You. Although TaN is hexagonal, it also reduces lattice mismatch.
It can be a buffer layer that can be integrated.

Further, since these materials exhibit metal conductivity and low contact resistance with a semiconductor, they do not increase the resistance between the semiconductor element of the group III nitride laminate and the substrate. Further, for the same reason, when an electrode is formed on an n-type semiconductor substrate, it does not cause an increase in resistance. On the other hand, p-type Al _x Ga _y
The contact resistance is very low even for In _1-xy N and is useful as an electrode material.

Although the above-mentioned transition metal nitride buffer layer causes distortion due to lattice mismatch, the distortion can be further reduced by adding a second buffer layer. It is important that the second buffer layer includes a thin film having the same composition as the subsequent group III nitride semiconductor layer, and the presence of this thin film makes the change in lattice constant smooth. Example 1 FIG. 1 is a cross-sectional view of a group III nitride semiconductor device having a transition metal nitride buffer layer according to the present invention. The structure will be described according to the manufacturing process. n-type Si substrate 1s (substrate surface is (1
11) The surface was washed with an acid, and a TiN film was formed using a molecular beam epitaxy apparatus to form a buffer layer 2c having a thickness of 50 nm. The substrate temperature during film formation was 650 ° C., Ti was evaporated by electron beam irradiation, and nitrogen was supplied from an atomic nitrogen source utilizing rf discharge. This thin film was (111) oriented, and was an epitaxially grown film in which the <111> axes of the substrate and the film were parallel to each other.

Next, the substrate temperature is set to 800 ° C. and n-type GaN
A contact layer 3 having a thickness of 300 nm was formed. Hereinafter, at a substrate temperature of 800 ° C., a cladding layer 4 of n-type Al _x Ga _1-x N (x = 0.15) having a thickness of 500 nm and a thickness of 50 nm of GaN
Active layer 5 of p-type Al _x Ga ₁ -xN (x = 0.15) with a thickness of 500
A cladding layer 6 of nm and a cap layer 7 of p-type GaN having a thickness of 300 nm were sequentially formed. Finally, at a substrate temperature of 650 ° C., a 50 nm-thick TiN thin film is formed by molecular beam epitaxy.
An n-side electrode 8 b made of Al was formed on the back surface of the Si substrate 1.

The above substrate was cut into a die having an active layer area of 0.3 mm ² , and Au electrodes were bonded to both electrodes to produce an LED element. When the forward voltage-current characteristics of the device were measured, a forward current of 200 mA was obtained at an applied voltage of 3 V. For comparison, as a conventional buffer layer
Except for using AlN, an LED element having the same layer structure was prepared and the voltage-current characteristics were measured. The forward voltage-current characteristics were 50 mA forward current at an applied voltage of 3 V.

A conventional LE having the same layer structure except that AlN was used for the buffer layer and Au / Cr electrode was used for the p-side electrode.
When a D element was manufactured, the forward current was 10 mA at an applied voltage of 3 V. From this, it is understood that the TiN layer realized a buffer layer having low resistance, and also reduced the resistance as the p-side electrode. Example 2 In Example 1, the lattice mismatch between TiN and GaN used for the buffer layer was 6% (see Table 1), and the TiN layer still caused strain in the GaN layer and was grown on the GaN layer. Al _x Ga
_1-X N (X = 0.15) is also distorted. However, the transition metal nitride used for the buffer layer was mixed with Al _x Ga _1-x
The lattice mismatch with N (x = 0.15) can be reduced, and Ga
It is possible to omit the N contact layer.

FIG. 2 has a mixed crystal buffer layer according to the present invention.
1 is a cross-sectional view of a group III nitride semiconductor device. In the manufacturing process
Therefore, the structure will be described. n-type Si (111) substrate 1s with acid
Surface cleaning and molecular beam epitaxy at substrate temperature of 650 ° C
50nm thick V using_0.29Zr_0.71Conductive made of N thin film
The buffer layer 2c was formed. At this time, Ti and Zr
Vaporized by nitrogen and nitrogen is atomic nitrogen using rf discharge
Supplied by source. This thin film is (111) oriented,
Epitaxially grown film with <111> axes of plate and film parallel to each other
Met. This conductive buffer layer 2c is made of n-type Al_0.15
Ga_0.85Lattice matched with N, n-type at 800 ° C substrate temperature
Al _xGa_1-x500 nm thick cladding layer made of N (x = 0.15)
4 could be directly formed into a film.

In the same manner as in Example 1, the thickness of GaN
Active layer 5 of 50 nm, cladding layer 6 of p _- type Al _x Ga ₁ -xN (x = 0.15) of 500 nm, thickness of 300 nm of p-type GaN
Were sequentially formed. Finally, substrate temperature 650
A 300 nm thick ZrN thin film was formed as an epi-side electrode 8a at a temperature of .degree.

The substrate was cut into dies having an active layer area of 0.3 mm ² , and Au electrodes were bonded to both electrodes to form an LE.
A D element was produced. When the forward voltage-current characteristics of the obtained LED element were measured, the current was 200 mA at an applied voltage of 3 V, and a low-resistance LED element was obtained as in the case of Example 1.

As described above, by using a conductive buffer layer of a mixed crystal of VN and ZrN, the resistance of the device can be reduced and lattice matching can be achieved. Further, a contact layer is not required and the device structure can be simplified. Has become possible. Further, the manufacturing process can be shortened. Example 3 Al formed at a low temperature on a transition metal nitride buffer layer
By inserting the second buffer layer made of _0.15 Ga _0.85 N, it is possible to further relax the lattice strain of the buffer layer and the first cladding layer and subsequent Al _0.15 Ga _0.85 N layer transition metal nitride.

FIG. 3 shows a low-temperature film-forming layer according to the present invention.
FIG. 2 is a sectional view of a group I nitride semiconductor device. The structure will be described according to the manufacturing process. The surface of the n-type Si (111) substrate 1s was washed with an acid, and a 50 nm NbN thin film was formed at a substrate temperature of 650 ° C. using a molecular beam epitaxy apparatus to form a buffer layer 2c. At this time, Nb was evaporated by an electron beam, and nitrogen was supplied by an atomic nitrogen source using rf discharge. This film is (111)
The epitaxial film was oriented and the <111> axes of the substrate and the film were parallel to each other.

Next, at a low substrate temperature of 400 ° C., a 10 nm Al
_A low-temperature film formation layer 2t was formed as a second buffer layer composed of a _0.15 Ga _0.85 N layer. Thereafter, the substrate temperature is increased to 800 ° C., and each II from the cladding layer 4 to the contact layer 7 is increased.
A group I semiconductor layer was formed to form a double hetero structure as shown in FIG. In addition, the substrate temperature is changed from room temperature (25 ℃) to 500
When the temperature is between 0 ° C., the low-temperature film-forming layer 2t is in an amorphous state, which has been found to be useful for alleviating lattice mismatch.

Further, NbN was used for the electrode layer 8a. This substrate was cut to produce a 0.3 mm square LED with upper and lower electrodes. As a result of measuring the forward voltage-current characteristics of this element,
When the applied voltage was 3 V, the forward current was 150 mA, and characteristics according to the device manufactured in Example 1 were obtained. Example 4 A thin Al _x Ga _1-x N layer was formed on a transition metal nitride buffer layer.
By inserting a second buffer layer having a superlattice structure in which layers and thin transition metal nitride layers are alternately stacked, strain is concentrated between these layers, and a transition metal nitride buffer layer and a first cladding layer are formed. Lattice strain with the subsequent Al _0.15 Ga _0.85 N layer can be further reduced.

FIG. 4 shows a III having a superlattice layer according to the present invention.
It is sectional drawing of a group nitride semiconductor element. The structure will be described according to the manufacturing process. The surface of the n-type Si (111) substrate 1s was washed with acid, and a 50 nm HfN layer was formed at a substrate temperature of 650 ° C. using a molecular beam epitaxy apparatus. At this time, Hf was evaporated by an electron beam, and nitrogen was supplied by an atomic nitrogen source using rf discharge. This thin film was (111) oriented, and was an epitaxially grown film in which the <111> axes of the substrate and the film were parallel to each other.

On the buffer layer 2c, a substrate temperature of 70
At 0 ° C, a 10 nm thick Al _0.30 Ga _0.70 N layer and a 10 nm thick HfN
The layers were alternately formed four times to form a second buffer layer 2m having a superlattice structure. Thereafter, the substrate temperature is raised to 800 ° C., and each II from the cladding layer 4 to the contact layer 7 is heated.
Each group III semiconductor layer was formed as a group I semiconductor layer to form a double heterostructure as shown in FIG.

HfN was used for the electrode layer 8a on the epitaxial layer side. The substrate after this film formation was cut to produce an LED having upper and lower electrodes of 0.3 mm square. As a result of measuring the forward voltage-current characteristics of the device, when the applied voltage was 3 V, the forward current was 200 mA, and characteristics equivalent to those of the device manufactured in Example 1 were obtained.

[0029]

According to the present invention, Al _x Ga is formed on a semiconductor substrate.
_y In _1-xy N (0 ≦ x, y and x + y ≦ 1)
A group III nitride semiconductor thin film is laminated, and the final III
An electrode layer formed on a group III nitride semiconductor thin film III
In the group-III nitride semiconductor device, a thin-film buffer layer made of a transition metal nitride having metal conductivity and having a rock salt type or hexagonal crystal structure is provided between the substrate and the group-III nitride semiconductor thin film. The substrate and Al _x Ga _y In
Lattice matching with the _1-xy N film is improved, and strain due to lattice mismatch can be reduced. Al _x Ga _y In
The device resistance of a semiconductor laser diode and a light emitting diode using a _1-xy N film can be reduced.

The electrode layers are made of TiN, VN, ZrN, NbN, Hf
Since a thin film made of either N or tantalum nitride TaN or a thin film of a transition metal nitride such as a mixed crystal made of two different materials, Al _x Ga _y In
The device resistance of a semiconductor laser diode and a light emitting diode using a _1-xy N film can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a group III nitride semiconductor device having a transition metal nitride buffer layer according to the present invention.

FIG. 2 is a cross-sectional view of a group III nitride semiconductor device having a mixed crystal buffer layer according to the present invention.

FIG. 3 is a cross-sectional view of a group III nitride semiconductor device having a low-temperature film formation layer according to the present invention.

FIG. 4 is a sectional view of a group III nitride semiconductor device having a superlattice layer according to the present invention.

FIG. 5 is a cross-sectional view of a light emitting diode formed on a conventional sapphire substrate.

FIG. 6 is a cross-sectional view of a light emitting diode formed on a conventional Si substrate.

[Explanation of symbols]

 Reference Signs List 1i Sapphire substrate 1s Semiconductor substrate 2 Buffer layer 2c Buffer layer 2t Low-temperature deposition layer 2m Superlattice layer 3 First contact layer 4 First clad layer 5 Active layer 6 Second clad layer 7 Second contact layer 8a Epitaxial Layer side electrode layer 8b Substrate side electrode layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Kamijo 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (72) Inventor Hideaki Matsuyama 1st Tanabe Nitta, Kawasaki-ku, Kawasaki, Kanagawa No. 1 Fuji Electric Co., Ltd.

Claims (10)

[Claims] An Al _x Ga _y In _{1 -xy} N (0 ≦
x, y, and x + y ≦ 1), wherein the group III nitride semiconductor thin film is formed by laminating, and an electrode layer is formed on the final group III nitride semiconductor thin film. A group III nitride semiconductor layer comprising a buffer layer made of a transition metal nitride exhibiting metal conductivity and having a rock salt type or hexagonal crystal structure is interposed between the substrate and the group III nitride semiconductor thin film. Semiconductor semiconductor device. 2. The transition metal nitride is titanium nitride (TiN).
), Vanadium nitride (VN), zirconium nitride (ZrN
), Niobium nitride (NbN) or hafnium nitride (HfN
3. The group III nitride semiconductor semiconductor device according to claim 1, wherein the group III nitride semiconductor semiconductor device is a mixed crystal composed of any one of the above or two of them, or tantalum nitride (TaN). 3. The group III nitride semiconductor device according to claim 1, wherein said semiconductor substrate is silicon, silicon carbide, gallium phosphide, or gallium arsenide. 4. The group III according to claim 1, wherein a second buffer layer is interposed between the buffer layer and the group III nitride semiconductor thin film, and lattice mismatch is further alleviated. Nitride semiconductor device. 5. A low-temperature layer formed at a substrate temperature lower than the substrate temperature at the time of forming the group III nitride semiconductor thin film, wherein the second buffer layer has the same composition as the group III nitride semiconductor thin film. The group III nitride semiconductor device according to claim 4, which is a film formation layer. 6. The method for manufacturing a group III nitride semiconductor device according to claim 5, wherein the substrate temperature of said low-temperature film formation layer is 25.
A method for producing a group III nitride semiconductor device, wherein the temperature is not lower than 500C and not higher than 500C. 7. The semiconductor device according to claim 1, wherein said second buffer layer is a superlattice layer comprising a plurality of stacked layers of a thin film having the same composition as said group III nitride semiconductor thin film and said buffer layer. 5. The group III nitride semiconductor device according to item 4. 8. An Al _x Ga _y In _1-xy N (0 ≦
x, y, and x + y ≦ 1), wherein the group III nitride semiconductor thin film is formed by laminating, and an electrode layer is formed on the final group III nitride semiconductor thin film. A group III nitride semiconductor device, wherein the electrode layer has metal conductivity and is made of a transition metal nitride having a rock salt type or hexagonal crystal structure. 9. The transition metal nitride is titanium nitride (TiN).
), Vanadium nitride (VN), zirconium nitride (ZrN
), Niobium nitride (NbN), hafnium nitride (HfN), or a mixed crystal consisting of two of them;
9. The group III nitride semiconductor device according to claim 8, wherein said device is tantalum nitride (TaN). 10. The method of manufacturing a group III nitride semiconductor device according to claim 1, wherein the layer made of the transition metal nitride is formed by molecular beam epitaxy. A method for manufacturing a semiconductor device.