JP2002316898A - Method for manufacturing nitride semiconductor substrate and nitride semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a nitride semiconductor substrate which is easy in peeling from a starting substrate and is good in reproducibility, and the nitride semiconductor substrate. SOLUTION: An aluminum nitride layer 2 and a nitride semiconductor layer 3 which turns to the self-standing type nitride semiconductor substrate 3a after the removal of a sapphire substrate 1 as the starting substrate and is different from the aluminum nitride layer 2 are successively epitaxially grown on the sapphire substrate 1. The resulted epitaxial substrate is treated with water or an aqueous hydroxide solution of an alkaline metal to hydrolyze the aluminum oxide layer 2, by which the sapphire substrate 1 can be easily removed and the nitride semiconductor substrate 3a of the self-standing type is obtained with good reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a nitride semiconductor substrate and a nitride semiconductor substrate.

[0002]

2. Description of the Related Art As a method of manufacturing a free-standing nitride semiconductor substrate, a nitride semiconductor thick film is formed on a sapphire substrate by HVPE.
There is a method (e.g., M) in which a sapphire substrate is removed after epitaxial growth by a method (a hydride vapor phase epitaxy method) to remove a sapphire substrate.
ichael K .; Kelly et al, Jpn.
J. Appl. Phys. 38 (1999) Pt. 2,
No. 3A, pp. L217).

[0003]

However, the prior art described above has a problem that there is no practical method for removing the sapphire substrate.

[0004] A technique for separating GaN grown on a sapphire substrate by etching has not been developed at present. Attempts have been made to remove all the sapphire substrate by polishing, but the warpage of the substrate increases during the polishing process, the defect rate of breaking the substrate is high, and sapphire is very hard, and the time required for polishing is increased. The cost is enormous and not realistic. Further, a method of irradiating a laser from the sapphire substrate side of the epitaxial growth substrate to separate the sapphire substrate (for example, Jpn.J. Appl.P.
hys. Vol. 38 (1999) Pt. 2, No. 3
A) has been attempted, but since heating occurs locally, in most cases, the nitride semiconductor layer is broken during the peeling. Even if the substrate does not crack, it takes a very long time to scan a laser beam to remove a large-area substrate, which is not practical.

As a method of using a substrate which can be easily removed, Japanese Patent Application Laid-Open No. 2000-012900 discloses a method in which H is formed on a GaAs substrate.
A method is disclosed in which GaN is grown thick by a VPE method and then the GaAs substrate is removed by etching. By using this method, a large GaN substrate can be obtained with a relatively high yield, but there is a problem that the GaAs substrate is decomposed during GaN crystal growth, and As is mixed into GaN as an impurity. there were.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a method of manufacturing a nitride semiconductor substrate which can be easily separated from a starting substrate and has good reproducibility, and a nitride semiconductor substrate.

[0007]

In order to achieve the above object, a method of manufacturing a nitride semiconductor substrate according to the present invention comprises the steps of sequentially forming an aluminum nitride layer and a nitride semiconductor layer different from the aluminum nitride layer on a starting substrate. The self-standing nitride semiconductor substrate is obtained by epitaxially growing and hydrolyzing the aluminum nitride layer to peel and remove the starting substrate.

In the method for manufacturing a nitride semiconductor substrate according to the present invention, in addition to the above structure, it is preferable to use a sapphire substrate as a starting substrate.

In addition to the above structure, in the method for manufacturing a nitride semiconductor substrate of the present invention, the aluminum nitride layer may be hydrolyzed with water vapor.

In addition to the above structure, in the method for manufacturing a nitride semiconductor substrate of the present invention, the aluminum nitride layer may be hydrolyzed with hot water.

[0011] In addition to the above structure, the method for manufacturing a nitride semiconductor substrate according to the present invention further comprises the steps of:
The hydrolysis may be carried out with an aqueous solution containing at least one of the group consisting of sodium hydroxide, potassium hydroxide, and hydrogen peroxide.

[0012] A nitride semiconductor substrate of the present invention is obtained by any one of the manufacturing methods described above.

According to the present invention, an aluminum nitride layer is formed on a sapphire substrate as a starting substrate, and a nitride semiconductor layer different from aluminum nitride, which becomes a free-standing nitride semiconductor substrate after removal of the sapphire substrate, is sequentially epitaxially grown. The sapphire substrate can be easily removed by treating the obtained epitaxial substrate with water or an aqueous solution of an alkali metal hydroxide to hydrolyze the aluminum nitride layer, and a self-supporting nitride semiconductor substrate with good reproducibility can be obtained. can get.

[0014]

Embodiments of the present invention will be described below in detail.

The method for manufacturing a nitride semiconductor substrate according to the present invention comprises:
On a starting substrate, an aluminum nitride layer and a nitride semiconductor layer different from the aluminum nitride layer are sequentially epitaxially grown, and the aluminum nitride layer is hydrolyzed to peel and remove the substrate to obtain a free-standing nitride semiconductor substrate. It is. It is preferable to use a sapphire substrate as a starting substrate. The aluminum nitride layer may be hydrolyzed with steam or hot water, and the aluminum nitride layer is hydrolyzed with an aqueous solution containing at least one of the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, and hydrogen peroxide. May be.

With such a structure, the sapphire substrate can be easily removed, and a nitride semiconductor substrate can be obtained with good reproducibility.

[0017]

Next, the present invention will be described with reference to specific numerical values, but the present invention is not limited thereto.

FIGS. 1A to 1D are process diagrams showing one example of a method for manufacturing a nitride semiconductor substrate according to the present invention. Example 1 A metal-organic vapor phase epitaxy (M) was performed on a sapphire substrate having a diameter of 50.8 mm (2 inches) as a starting substrate.
AlN and GaN were sequentially stacked using the OVPE method.
A horizontal normal-pressure MOVPE furnace was used as a growth furnace, ammonia gas, trimethylgallium and trimethylaluminum were used as raw materials, and a mixed gas of hydrogen and nitrogen was used as a carrier gas. Step 1 First, the sapphire substrate 1 is placed in a hydrogen atmosphere for 110
It was heated to 0 ° C. to clean oxides and the like on the surface (FIG. 1A). Step 2 The temperature of the sapphire substrate 1 is reduced to 550 ° C., an AlN layer 2 is grown on the sapphire substrate 1 to a thickness of 20 nm, and the temperature of the sapphire substrate 1 is further raised to 1050 ° C. Was sequentially grown at 2 μm each (FIG. 1B). Step 3 Put H on the obtained GaN epitaxial growth substrate.
A GaN layer was epitaxially grown on the single crystal 3a having a thickness of 300 μm by using the VPE method. The device has horizontal normal pressure H
A VPE furnace was used. GaCl obtained by reacting ammonia gas and metal Ga with HCl gas at 850 ° C. was used as a raw material, and hydrogen gas was used as a carrier gas. The growth temperature is 1050 ° C. and the growth rate is 80 μm
/ H (FIG. 1 (c)). Step 4 When the epitaxial growth substrate taken out of the HVPE furnace was boiled with hot water at 90 ° C. for 6 hours, the sapphire substrate 1 was peeled off, and a free-standing nitride semiconductor substrate 3a was obtained (FIG. 1D). Example 2 Instead of Step 3 of Example 1, when the epitaxial growth substrate was exposed to water vapor at 500 ° C. for about 1 hour, the sapphire substrate was peeled off, and a freestanding nitride semiconductor substrate was obtained. Example 3 Instead of Step 3 of Example 1, the epitaxial growth substrate was pressurized to 20 atm to increase the boiling point.
After boiling for about 2 hours in hot water at ℃, the sapphire substrate was peeled off, and a free-standing nitride semiconductor substrate was obtained. Example 4 Instead of Step 3 of Example 1, when the epitaxial growth substrate was boiled in a 3 mol / l aqueous sodium hydroxide solution at 80 ° C. for about 1 hour, the sapphire substrate was peeled off, and the freestanding nitride semiconductor substrate was removed. was gotten.

Here, the higher the temperature, the faster the hydrolysis reaction between the aluminum nitride layer and water proceeds. Therefore, the higher the temperature of water, the better. However, when the boiling point is reached, water that has entered between the nitride semiconductor layer and the sapphire substrate rapidly generates bubbles (bumping), and the nitride semiconductor layer and the sapphire substrate are broken, so that no bubbles are generated. Processing at a temperature below the boiling point is preferred.

In the above embodiment, the case where the MOVPE method is used as the epitaxial growth method of the nitride semiconductor has been described. However, the present invention is not limited to these.
Various known methods such as the HVPE method and the MBE method may be used. Also, a two-step growth method using a low-temperature buffer layer such as gallium nitride or aluminum nitride, a method of directly growing at a high temperature, and an ELO method (O) for reducing dislocations to lateral growth using microfabrication and regrowth during growth. .H.N
am et al, Appl. phys. Lett. 7
1 (1997) 2472), the FIELO method (A. Sak
ai et al, Appl. Phys. Lett. 7
1 (1997) 2259) can be used.

In the above embodiment, only the case where the aluminum nitride layer and the gallium nitride layer are sequentially laminated directly on the sapphire substrate has been described. However, an aluminum nitride layer as a peeling layer is provided between the sapphire substrate and the gallium nitride layer. If it exists, any multilayer structure may be provided between the sapphire substrate and the gallium nitride layer. Further, another substrate such as SiC may be used instead of the sapphire substrate.

The aluminum nitride layer may be hydrolyzed by jetting hot water or steam from the side surface of the epitaxial wafer in addition to the method described in the above embodiment. Also, instead of water, lithium hydroxide, sodium hydroxide,
By using an aqueous alkali solution such as potassium hydroxide or hydrogen peroxide, the decomposition rate of the aluminum nitride layer can be increased.

[0023]

In summary, according to the present invention, the following excellent effects are exhibited.

A method of manufacturing a nitride semiconductor substrate which can be easily separated from a starting substrate and has high reproducibility and a nitride semiconductor substrate can be provided.

[Brief description of the drawings]

FIGS. 1A to 1D are process diagrams showing one example of a method for manufacturing a nitride semiconductor substrate of the present invention.

[Explanation of symbols]

 Reference Signs List 1 sapphire substrate 2 AlN layer 3 GaN layer 3a single crystal (self-supporting nitride semiconductor substrate)

Claims (6)

[Claims] 1. An aluminum nitride layer on a starting substrate,
The nitride characterized in that a self-standing nitride semiconductor substrate is obtained by sequentially growing the aluminum nitride layer and a different nitride semiconductor layer epitaxially, hydrolyzing the aluminum nitride layer, and peeling and removing the starting substrate. A method for manufacturing a semiconductor substrate. 2. The method for manufacturing a nitride semiconductor substrate according to claim 1, wherein a sapphire substrate is used as said starting substrate. 3. The method according to claim 1, wherein the aluminum nitride layer is hydrolyzed with water vapor. 4. The method for manufacturing a nitride semiconductor substrate according to claim 1, wherein said aluminum nitride layer is hydrolyzed with hot water. 5. The nitride semiconductor substrate according to claim 1, wherein the aluminum nitride layer is hydrolyzed with an aqueous solution containing at least one kind selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, and hydrogen peroxide. Production method. 6. A nitride semiconductor substrate obtained by the method according to claim 1.