JP2003048800A - METHOD OF PRODUCING GaN-BASED COMPOUND SEMICONDUCTOR CRYSTAL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology for a method of producing a GaN-based compound semiconductor crystal using a rare earth group 13 (3B) perovskite as a substrate, which comprises improving the quality of a GaN thin film formed between the substrate and the GaN-based compound semiconductor crystal and by which the crystal quality of the GaN-based compound semiconductor crystal can be improved. SOLUTION: In a method for growing the GaN-based compound semiconductor crystal on the surface (1 main surface) of the substrate of the rare earth group 13 (3B) perovskite crystal containing one or more rare earth elements, a high quality GaN single crystal thin film having a uniform thickness is formed on the substrate of the rare earth group 13 (3B) perovskite crystal mentioned above by allowing Ga atom to adsorb on the substrate of the rare earth group 13 (3B) perovskite crystal so as to form several atomic layers and nitriding the adsorbed Ga atom, and then, the GaN-based compound semiconductor crystal is grown on the high quality GaN single crystal thin film mentioned above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for manufacturing semiconductor devices such as light emitting devices and electronic devices.
The present invention relates to a method for manufacturing an aN-based compound semiconductor crystal.

[0002]

2. Description of the Related Art GaN, InGaN, AlGaN, In
GaN-based compound such as GaAlN semiconductor _(In x _Ga y A
l _1−x−y N, where 0 ≦ x, y; x + y ≦ 1) is expected as a material for a semiconductor electronic device such as a light emitting device and a power device, and is noted as a material applicable in various other fields. There is.

Conventionally, it has been difficult to grow a bulk crystal of a GaN-based compound semiconductor. Therefore, in the above electronic device, a substrate on which a thin film single crystal such as GaN is formed by heteroepitaxy on a heterogeneous crystal such as sapphire. Was used.

However, since the lattice mismatch between the sapphire crystal and the GaN-based compound semiconductor crystal is large, the dislocation density of the GaN-based compound semiconductor crystal grown on the sapphire crystal becomes large and a crystal defect occurs. was there. Further, since sapphire has a small thermal conductivity and is difficult to radiate heat, there is a problem that a substrate on which a GaN-based compound semiconductor crystal is grown on a sapphire crystal is likely to reach a high temperature when used in an electronic device or the like with high power consumption.

Further, the hydride vapor phase epitaxy method (hereinafter, referred to as H
ELO (Epitaxial latera) using VPE
Growth of GaN-based compound semiconductor crystals has been attempted by a method such as an overgrowth method. Here, the ELO method means that, for example, an insulating film serving as a mask is formed on a sapphire substrate, an opening is provided in a part of the insulating film and the insulating film is used as a mask, and the exposed surface of the sapphire substrate is used as a seed for epitaxial growth. Is a method of growing a GaN-based compound semiconductor crystal having high crystallinity.

According to this method, the growth of the GaN-based compound semiconductor crystal starts from the surface of the sapphire substrate inside the opening provided in the mask and the growth layer spreads over the mask, so that the dislocation density in the crystal is suppressed to a small value. Therefore, a GaN-based compound semiconductor crystal with few crystal defects can be obtained.

However, since the GaN-based compound semiconductor crystal obtained by the ELO method has a large thermal strain, polishing is performed after the growth of the GaN crystal by the ELO method to separate the sapphire substrates and separate the GaN-based compound semiconductor crystal wafer. There was a problem that the wafer would bend due to residual strain when trying to obtain it.

Therefore, the present inventors have used a rare earth 13 (3B) group perovskite crystal as one of the materials for the heterogeneous crystal substrate, and have a GaN compound semiconductor with its {011} plane or {101} plane as a growth plane. A method of growing by heteroepitaxy has been proposed (WO95 / 278).
No. 15). The {011} plane or the {10}
The 1} plane represents a set of planes equivalent to the (011) plane and the (101) plane, respectively.

According to the growth technique of the prior application, for example, NdGa, which is one of the rare earth 13 (3B) group perovskites, is used.
Using O ₃ as a substrate, its {011} plane or {101}
When GaN is grown on the surface, the lattice mismatch is about 1.2%, which is extremely smaller than that when sapphire or SiC used as a substitute thereof is used as the substrate. Therefore, since the dislocation density in the crystal is low, it is possible to grow a GaN-based compound semiconductor crystal with few crystal defects.

Further, by further improving the above-mentioned prior art, N
A first GaN layer is formed on a dGaO ₃ substrate at a low temperature (400 to 750 ° C.), and then heated to a predetermined temperature in an inert gas (N ₂ gas) atmosphere to perform a heat treatment, and the first GaN layer is formed. An invention has been proposed in which the second GaN layer is grown on the GaN layer at a high temperature (800 to 1200 ° C.) (Japanese Patent Laid-Open No. 2000-4045). With this technology,
Since NdGaO ₃ substrate can be prevented from being reduced by reaction with NH ₃ or the like in GaN-based compound semiconductor growth temperature (800 to 1200 ° C.), GaN crystal degradation NdGaO ₃ substrate grew due to reduced You can avoid doing it.

[0011]

However, in the above prior art (Japanese Patent Laid-Open No. 2000-4045), GaN is used.
Since the thin film is formed by the hydride VPE method, which has a relatively high growth rate, it is difficult to control the thickness of the GaN thin film and the variation in film thickness becomes large. Also, Ga
The N thin film is made of GaN so that the NdGaO ₃ substrate is not reduced.
Temperature of system compound semiconductor crystal (800-1200 ℃)
The crystal quality is poor because it is formed at a much lower temperature (400 to 750 ° C.).

Therefore, NdGaO is produced by the method described above.
₃ It is possible to prevent the substrate from being reduced at the growth temperature of the GaN crystal, but the GaN thin film adversely affects the GaN-based compound semiconductor crystal grown on the GaN thin film and may deteriorate the crystal quality. There is a nature.

The present invention is to improve the quality of a GaN thin film formed between a substrate and a GaN-based compound semiconductor crystal in a method for producing a GaN-based compound semiconductor crystal using a rare earth 13 (3B) group perovskite as a substrate. By G
An object is to provide a technique for improving the crystal quality of an aN-based compound semiconductor crystal.

[0014]

In order to achieve the above object, the present invention uses a rare earth 13 (3B) group perovskite crystal containing one or more kinds of rare earth elements as a substrate on its surface (one main surface). In the method of growing a GaN-based compound semiconductor crystal, a step of adsorbing Ga atoms on the rare earth 13 (3B) group perovskite crystal substrate; a step of nitriding the adsorbed Ga atoms to form a GaN thin film; And a step of growing a GaN-based compound semiconductor crystal on the thin film.

As a result, the GaN thin film can be formed with a uniform thickness, so that the GaN thin film does not adversely affect the quality of the GaN-based compound semiconductor crystal grown thereon, and the crystal quality is improved. Further, the formation of the GaN thin film can prevent the substrate from being reduced at the growth temperature of the GaN-based compound semiconductor crystal.

Preferably, in the step of adsorbing Ga atoms on the rare earth 13 (3B) group perovskite crystal substrate, the temperature of the Ga atoms is set to 0.
It is better to lower the temperature in the range of 5 ° C to 5 ° C. This allows
Ga atoms can be efficiently adsorbed on the substrate, and
The thickness of the adsorption layer of GaN atoms can be controlled relatively easily.

Further, by adsorbing the Ga atoms to the substrate in a thickness of one to several molecular layers, it becomes possible to nitride all the adsorbed Ga atoms, and one to several molecules of the Ga atoms are formed on the substrate. The layer thickness forms a GaN thin film. Therefore, although the GaN thin film is formed at a temperature lower than the crystal growth temperature, the crystal quality of the GaN thin film is not significantly deteriorated. By thus improving the crystal quality of the GaN thin film, the crystal quality of the GaN-based compound semiconductor crystal grown thereon can be improved.

As the 13 (3B) group element, A
A rare earth 13 (3B) group perovskite crystal containing at least one of l, Ga and In, for example NdGaO
_It can be applied when ₃ crystals are used as a substrate.

The process leading to the completion of the present invention will be described below. Initially, the inventors of the present invention described the prior application
No. 000-4045), a GaN-based compound semiconductor crystal was grown according to the method for growing a GaN-based compound semiconductor crystal, but it was found that some of them had poor crystal quality. Therefore, in order to elucidate the cause of the deterioration of crystal quality, the crystal growth method of the previous application was repeatedly studied.

In the crystal growth method of the above-mentioned prior application, after the substrate is mirror-polished and washed, the substrate is placed at a predetermined site in the hydride VPE apparatus and the substrate temperature is set to 600 while introducing N ₂ gas. The temperature is raised to 0 ° C., and GaCl generated from Ga metal and HCl gas and NH ₃ gas are supplied onto the NdGaO ₃ substrate using the N ₂ carrier gas to form a GaN thin film of about 100 nm. Then, after raising the substrate temperature to 1000 ° C. in an atmosphere of N ₂ gas as an inert gas, a GaN-based compound semiconductor crystal was grown on the GaN thin film.

However, when the method of the above-mentioned prior application is applied,
Since the hydride VPE method has a relatively high growth rate,
It has been found that it is difficult to uniformly control the thickness of the N thin film, and the thickness of the formed GaN thin film varies. Also, the growth temperature (100 GaN films NdGaO ₃ substrate reduced so as not to GaN-based compound semiconductor crystal
Since it was formed at a temperature (620 ° C.) much lower than 0 ° C., it could be expected that the crystal quality was poor.

From the above, the inventors of the present invention can prevent the NdGaO ₃ substrate from being reduced at the crystal growth temperature in the GaN thin film formed according to the method of the prior application, but on the other hand, It is considered that the crystal quality of the grown GaN-based compound semiconductor crystal may be deteriorated.

When the GaN thin film is grown thicker, the quality of the GaN-based compound semiconductor crystal deteriorates. Therefore, the GaN thin film having poor crystal quality and unevenness is grown on the GaN-based compound semiconductor crystal. It was found to affect the crystal quality of. From this, it was convinced that the crystal quality of the GaN-based compound semiconductor crystal grown thereon could be further improved by making the GaN thin film formed on the substrate uniform in thickness.

Based on the above findings, the inventors of the present invention have earnestly studied a method of uniformly forming a GaN thin film on a rare earth 13 (3B) group perovskite crystal substrate, and as a result, completed the present invention.

Specifically, a step of adsorbing Ga atoms on the rare earth 13 (3B) group perovskite crystal substrate and a step of nitriding the adsorbed Ga atoms with NH ₃ or the like are performed to make the GaN thin film uniform. It could be formed with a thickness. As a result of Auger analysis of the sample after performing the above-mentioned two steps, N peak was observed in addition to Ga peak, which confirmed that GaN was formed on the substrate.

As mentioned above, the present invention provides NdGaO ₃
It has been discovered by an experiment of growing a GaN compound semiconductor crystal on a substrate, but similar effects can be obtained when a GaN compound semiconductor crystal such as InGaN or AlGaN is grown in addition to the GaN compound semiconductor crystal. it is conceivable that. Further, as the rare earth 13 (3B) group perovskite crystal substrate, in addition to NdGaO ₃ , NdAlO ₃ , N
dInO ₃ or the like can be used.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION A preferred embodiment of the present invention will be described below for the case of growing a GaN compound semiconductor crystal using an NdGaO ₃ crystal as a substrate. In this embodiment, an NdGaO ₃ ingot is sliced to form a substrate for crystal growth. At this time, the size of the NdGaO ₃ substrate was 50 mm in diameter and the thickness was 0.5 mm.

(Example) Applying the present invention, NdGaO ₃
A method of forming a GaN thin film on a substrate and growing a GaN compound semiconductor crystal on it will be described. First,
The mirror-polished NdGaO ₃ substrate was subjected to ultrasonic cleaning for 5 minutes in acetone, and then ultrasonic cleaning for 5 minutes with methanol. Then, it was blown with N ₂ gas to blow off the droplets and then naturally dried. Next, washed NdGaO
₃ substrate a sulfuric acid-based etchant (phosphoric acid: sulfuric acid = 1: 3, 8
Etching was performed at 0 ° C. for 5 minutes.

Next, the NdGaO ₃ substrate was hydride V
After arranging at a predetermined site in the PE device, the substrate temperature was raised to 724 ° C. while introducing N ₂ gas. Then, the Ga raw material was heated to 722 ° C. at a position 1.2 m away from the substrate, and the evaporated Ga atoms were supplied onto the substrate while introducing N ₂ gas at 2000 sccm to adsorb the Ga atoms on the substrate surface. .

In this example, this state was maintained for 15 minutes to supply Ga atoms onto the substrate. Where 722 of Ga
The time required to supply Ga atoms for one atomic layer is calculated to be 150 seconds based on the evaporation rate at ° C. Therefore, in this embodiment, Ga atoms for six atomic layers are supplied.
From this, it is considered that the film thickness of Ga atoms adsorbed on the substrate is equivalent to several atomic layers.

Next, NH ₃ gas was added at 1000 sccm for 3 times.
After being supplied onto the substrate for 0 minutes, Ga atoms adsorbed on the substrate were nitrided to form a GaN thin film. In this embodiment, since the thickness of Ga atoms to be adsorbed on the substrate is very thin, that is, several atomic layers, all the adsorbed Ga atoms can be nitrided, and a high-quality GaN thin film with a uniform film thickness can be obtained. Can be formed with.

Next, the substrate temperature is raised to 1000.degree.
GaCl generated from a metal and HCl gas, and NH
₃ gas was supplied onto the NdGaO ₃ substrate using N ₂ carrier gas. At this time, the GaCl partial pressure is 5.0 × 10
^-3 atm, NH ₃ partial pressure is controlled to about 3.0 × 10 ^-1 atm while controlling each gas introduction amount to about 40 μm.
A GaN compound semiconductor crystal was grown at a growth rate of m / h for 300 minutes.

Then, at a cooling rate of 5.3 ° C./min, 90
After cooling for a minute, a GaN compound semiconductor crystal having a film thickness of about 200 μm was obtained. It was confirmed that the obtained GaN compound semiconductor crystal had an X-ray rocking curve full width at half maximum (FWHM) of 100 seconds and had excellent crystal quality.

(Comparative Example) Next, as a comparative example, NdGa
A method of forming a GaN thin film on the O ₃ substrate by a conventional method and growing a GaN compound semiconductor crystal thereon will be described. Comparative examples are only the embodiments and the method of forming the thin film of GaN is different, the previous _{NdGaO 3} substrate processing and G
The growth conditions and the like of the aN compound semiconductor crystal were the same as in the example.

First, the mirror-polished NdGaO ₃ substrate was ultrasonically cleaned in acetone for 5 minutes, and subsequently, ultrasonically cleaned in methanol for 5 minutes. Then, it was blown with N ₂ gas to blow off the droplets and then naturally dried. next,
The washed NdGaO ₃ substrate was etched with a sulfuric acid-based etchant (phosphoric acid: sulfuric acid = 1: 3, 80 ° C.) for 5 minutes.

Next, after placing this NdGaO ₃ substrate at a predetermined site in the hydride VPE apparatus, the substrate temperature was raised to 620 ° C. while introducing N ₂ gas, and the NdGaO ₃ substrate was produced from Ga metal and HCl gas. GaCl and NH ₃ gas were supplied onto the NdGaO ₃ substrate using an N ₂ carrier gas to form a GaN thin film of about 100 nm.

Next, the substrate temperature is raised to 1000.degree.
GaCl generated from a metal and HCl gas, and NH
₃ gas was supplied onto the NdGaO ₃ substrate using N ₂ carrier gas. At this time, the GaCl partial pressure is 5.0 × 10
^-3 atm, NH ₃ partial pressure is controlled to about 3.0 × 10 ^-1 atm while controlling each gas introduction amount to about 40 μm.
A GaN compound semiconductor crystal was grown at a growth rate of m / h for 300 minutes.

Then, at a cooling rate of 5.3 ° C./min, 90
After cooling for a minute, a GaN compound semiconductor crystal having a film thickness of about 200 μm was obtained.

When a GaN compound semiconductor crystal was grown using this substrate, the obtained GaN compound semiconductor crystal had an X-ray rocking curve full width at half maximum (FWHM) of 30.
It was 0 second, and the crystal quality was inferior as compared with the GaN compound semiconductor crystal of the above example.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments. For example, NdGaO
The temperature of the substrate and the Ga atom when adsorbing GaN atoms on the ₃ substrate is not limited to the temperature applied in the above-mentioned embodiment, and G
Ga atoms can be adsorbed on the substrate by setting the temperature a to 0.5 ° C. to 5 ° C. lower than the substrate temperature.

Further, in the present embodiment, N ₂ was used as the carrier gas for supplying Ga atoms and NH ₃ onto the substrate in the GaN thin film forming step, but H ₂ was used instead of N _2.
2 can also be used. However, since a nitride compound is grown, it is desirable to use N ₂ as a carrier gas.

Further, as a growth condition of the Ga compound semiconductor crystal, the GaCl partial pressure is 1.0 × 10 ^{−3 to} 1.0 × 1.
0 ^-2 atm, NH ₃ partial pressure 1.0 × ¹⁰ -1 to 4.0
× 10 ⁻¹ atm, growth rate 30 to 100 μm / h,
Growth temperature 930-1050 ° C, cooling rate 4-10
C./min is desirable.

[0043]

According to the present invention, a method for growing a GaN-based compound semiconductor crystal on a surface (one main surface) of a rare earth 13 (3B) group perovskite crystal containing one or more kinds of rare earth elements as a substrate. , The rare earth 13
High-quality GaN is obtained by performing a step of adsorbing Ga atoms on a (3B) group perovskite crystal substrate and a step of nitriding the adsorbed Ga atoms to form a GaN thin film.
Since the single crystal thin film is formed to have a uniform thickness, G
The aN thin film is less likely to adversely affect the quality of the GaN-based compound semiconductor crystal grown on the aN thin film, and the crystal quality can be improved.

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Claims (5)

[Claims] 1. A method of growing a GaN-based compound semiconductor crystal on a surface of a rare earth 13 (3B) group perovskite crystal containing one or more kinds of rare earth elements as a substrate, wherein the rare earth 13 (3B) group perovskite crystal substrate is used. At least adsorbing Ga atoms thereon, nitriding the adsorbed Ga atoms to form a GaN thin film, and growing a GaN-based compound semiconductor crystal on the GaN thin film. Method for producing GaN-based compound semiconductor crystal. 2. In the step of adsorbing Ga atoms on the rare earth 13 (3B) group perovskite crystal substrate, the temperature of the Ga atoms is 0.5 ° C. to 5 ° C. below the temperature of the substrate.
The method for producing a GaN-based compound semiconductor crystal according to claim 1, wherein the temperature is lowered in the range of ° C. 3. The Ga atom is adsorbed on the substrate in a thickness of 1 to several molecular layers, and the GaN thin film is formed in a thickness of 1 to several molecular layers. Alternatively, the method for producing a GaN-based compound semiconductor crystal according to claim 2. 4. The rare earth 13 used as a substrate
13 (3B) that constitutes a (3B) group perovskite crystal
The method for producing a GaN-based compound semiconductor crystal according to claim 1, wherein the group element is at least one of Al, Ga, and In. 5. The method for producing a GaN-based compound semiconductor crystal according to claim 4, wherein the rare earth 13 (3B) group perovskite crystal is an NdGaO ₃ crystal.