JP2002161000A - Method for producing gallium nitride single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce defects of a gallium nitride single crystal and to develop a method for reducing a warpage of a single crystal substrate. SOLUTION: The method for producing a gallium nitride single crystal (comprises thickly growing gallium nitride by a hydride vapor phase epitaxy(HVPE) growing method on a sapphire substrate having fine asperities of which the projecting part size is >=30 nm and <=200 nm, and peeling the same from the sapphire substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a gallium nitride single crystal substrate used for a blue laser diode or the like.

[0002]

2. Description of the Related Art A single crystal of gallium nitride (GaN, hereinafter referred to as GaN) is formed on a sapphire substrate by a selective growth method such as a lateral growth method by a chloride vapor phase growth method (hereinafter, referred to as an HVPE method). A thick GaN film is deposited, and then the sapphire substrate and the thick GaN are separately formed. Also Ga
A GaN bulk crystal is grown at a temperature of about 1500 ° C. under a high pressure of about 1.5 × 10 ⁹ Pa so that N is not decomposed. These growing methods require complicated facilities or expensive equipment. Further, these crystals have a large etch pit density indicating the degree of crystal defects, and the half width of the X-ray rocking curve of the asymmetrical reflection on the (10-10) plane is 400.
arcsec. In addition, a substrate having a diameter of 50 mm and a thickness of 300 microns (μ) has a warpage of about 20 μ, and the characteristics and yield of a device formed on the substrate are poor.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to develop a GaN single crystal having a small defect density in a crystal and a small warpage.

[0004]

Means for Solving the Problems In order to solve the above problems, a method of growing GaN thickly on a sapphire substrate having fine irregularities by a vapor phase method is adopted.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a method for growing a GaN layer on a sapphire substrate having irregularities whose surface is controlled at a nano-level and manufacturing a GaN single crystal with few defects and little warpage at low cost. It is.

The unevenness controlled at the nano level is created by a chemical or physical method. As a chemical method, there is a method of etching the sapphire substrate surface with phosphoric acid or pyrophosphoric acid, or adding a material having a lattice constant close to the crystal lattice constant of sapphire to the sapphire substrate surface by a spray method or a sol-gel method. Also, there is a combined method of adding by a sol-gel method and then etching with phosphoric acid or pyrophosphoric acid or etching with hydrogen. As a physical method, there is a method in which a material having a lattice constant close to the crystal lattice constant of sapphire is added to the surface by vacuum deposition, ion plating, sputtering, or a plasma method. A chemical solution and hydrogen gas treatment may be combined with these physical methods.

In order for GaN to grow two-dimensionally, it is necessary that the object to be added has an orientation having a certain relationship with the orientation of the sapphire substrate, and preferably has the same orientation. For this reason, a material having a lattice constant close to the crystal lattice constant of sapphire can be optimally used, and alumina (Al ₂ O ₃ ) or spinel (MgA) of the same material as sapphire can be used.
l ₂ O ₄ ) and the like are preferable.

The average size (approximate diameter) of the convex portion of the sapphire substrate is measured with a three-dimensional surface structure analysis microscope, and is 30 n
It is preferably from m to 200 nm, particularly preferably from 50 nm to 100 nm. The height is preferably such that the lateral growth of AlGaN on the convex portion is not hindered by AlGaN grown from the concave portion, and is preferably substantially the same. Height is AlGa
It is determined by the growth rate of N and the density of the projections. About 1 size
In the case of 00 nm, the height is about 50 nm with a three-dimensional surface structure analysis microscope. The unevenness may be present in a state where the protrusions are connected or in contact with each other at a grain boundary. However, it is preferable that the protrusions are separated from each other like an island and exist at a high density. If the size of the convex portion is 100 nm,
It is preferably 10 ¹⁰ or less per 1 cm ^{2 of the} sapphire substrate, and about 10 ¹¹ or less per 1 cm ² if the size is 30 nm.

Film formation on a sapphire substrate having fine irregularities is performed by a gas phase method such as HVPE or MOCVD. Ga
The temperature for growing the N layer is 900 ° C., which facilitates two-dimensional growth.
When the temperature is 1150 ° C. or higher, the decomposition of GaN becomes severe. Therefore, the temperature is preferably 1150 ° C. or lower. GaN
The growth rate of the film may be changed during the film formation by controlling the supply of a raw material such as trimethylgallium during the growth of the film. MOCVD
After the low-temperature buffer layer is stacked by the HVPE method, a thick film may be formed by the HVPE method.

[0010] To remove GaN grown on the sapphire substrate, a rapid heating from 500 to 1000 ° C or
This is done by gradually applying a load with a press.

The improvement in the crystallinity of GaN grown on a sapphire substrate having fine irregularities is due to the fact that the GaN grown at the beginning of growth
The size of aN is not more than the size of the convex portion, the distortion of the GaN growth film is reduced due to the space of the concave portion, and the orientation of the side portion of the convex portion is the treatment of phosphoric acid, high temperature hydrogen, etc. It is considered that the crystallinity of the grown film is improved because AlGaN is more likely to grow in a certain direction because of the uniformity, and the twist of AlGaN is reduced.

[0012]

Example 1 An alumina seed component was added to an alumina sol having an alumina component concentration of 20% and mixed with a stirrer.
The viscosity was 10 centipoise. The method of preparing the alumina seed component was as follows. High-purity alumina balls and pure water were placed in an alumina pot mill and rotated for 3 days, and then the liquid was centrifuged at 15,000 rpm.
The supernatant was used as an alumina seed component. The seeded alumina sol was placed on a c-plane smooth, 50 mm diameter, 350 micron thick sapphire substrate,
Thin coating was performed with a spin coater at 1500 rpm for 15 seconds. This was placed in a heating furnace at 70 ° C. for 5 hours for 12 hours.
5 hours at 0 ° C, 3 hours at 250 ° C, 5 hours at 350 ° C,
Heat treatment was performed at 450 ° C. for 5 hours, at 650 ° C. for 3 hours, and at 750 ° C. for 3 hours.
Rapid heating was performed so as to be maintained in a heating furnace at a temperature of 200 ° C. for 3 minutes, and rapid cooling was performed at 200 ° C./min. Mixed acid taken out of the furnace and heated to 110 ° C (sulfuric acid: phosphoric acid = 3: 1)
In water for 30 minutes and then immersed in phosphoric acid at 230 ° C. for 15 minutes, washed well with pure water and dried. The average size of the protrusions was about 75 nm, and the height was about 40 nm, which was almost hexagonal and island-like.

This sapphire substrate having irregularities at the nanometer level is set on a substrate holder inside a horizontal HVPE apparatus, and the substrate surface temperature is set to 1150 while flowing hydrogen gas.
The substrate surface was cleaned by holding at 5 ° C. for 5 minutes.

Then, the substrate surface temperature is lowered to 1030 ° C., and in this state, hydrogen chloride is supplied while flowing 18 l / min of nitrogen gas, 2 l / min of hydrogen gas, and 2 l / min of ammonia as the main carrier gas. The flow rate was 0.2 liter / min, and was maintained for 3 hours. The reaction between gallium metal and hydrogen chloride was performed at 850 ° C., and the hydrogen chloride was diluted with hydrogen eight times. GaN having a thickness of 300 μ was obtained.

The grown sapphire substrate with GaN is
When rapidly heated to 00 ° C. for 2 minutes, peeling occurred at the interface. The peeled surface was smooth by visual observation.

In order to evaluate the degree of defect of the peeled GaN substrate, that is, the crystallinity, (10-1)
0) The half width of the X-ray rocking curve of the asymmetric reflection on the plane was measured. The half width was 250 arcsec. The warpage height at the center of the substrate was measured with a surface profiler and found to be 5 μm.

[0017]

Example 2 Nitric acid was added to the seeded alumina sol of Example 1 to adjust the viscosity of the sol to 20 centipoise.
A projection was formed on a sapphire substrate in the same manner as described in Example 1. The average size was about 200 nm and the height was about 60 nm with the projections partially connected.

Then, 300 μm of a GaN layer was stacked in the same manner as described in the first embodiment.

The grown sapphire substrate with GaN is
When rapidly heated to 00 ° C. for 2 minutes, peeling occurred at the interface. The peeled surface was smooth by visual observation.

The half width of the X-ray rocking curve of the asymmetrical reflection on the (10-10) plane of the peeled GaN layer was measured.
The half width was 400 arcsec. The warpage height at the center of the substrate was measured with a surface profiler and found to be 15 μm.

[0021]

Example 3 Nitric acid was added to the seeded alumina sol of Example 1 to adjust the viscosity of the sol to 5 centipoise. Except that the sintering temperature was changed from 1200 ° C to 1150 ° C,
Protrusions were formed on a sapphire substrate in the same manner as described in Example 1. The average size of the protrusions is about 3
At 0 nm, it was in contact with the grain boundary.

Next, GaN was prepared by the same method as that described in the first embodiment. That is, the sapphire substrate having the nanometer-level unevenness is formed by a horizontal HVP.
E was set inside the apparatus, cleaned with hydrogen, and a 300 μm GaN layer was stacked.

The grown sapphire substrate with GaN was
When rapidly heated to 00 ° C. for 2 minutes, peeling occurred at the interface. The peeled surface was smooth by visual observation.

The half width of the X-ray rocking curve of the asymmetric reflection on the (10-10) plane of the peeled GaN layer was measured.
The half width was 400 arcsec. The warpage height at the center of the substrate was measured with a surface profiler and found to be 15 μm.

[0025]

[Comparative Example 1] A smooth sapphire substrate was placed inside a horizontal HVPE apparatus, and was cleaned with hydrogen gas.
In the same manner as described in the first embodiment,
00μ was piled up.

The grown sapphire substrate with GaN was opaque. When this was rapidly heated to 500 ° C. for 2 minutes, it was partially cracked and peeled off at the interface in an uneven state.

(10-1) of the GaN layer peeled off at a part of the interface
0) The half width of the X-ray rocking curve of the asymmetric reflection on the plane was measured. The half width was 1500 arcsec.

[0028]

According to the present invention, a GaN substrate can be manufactured by a simple process, not by a complicated process as in the prior art. Further, the substrate has few defects, and the sapphire substrate and the GaN substrate can be easily separated. It has great industrial value in terms of cost and performance.

Claims (1)

[Claims] 1. The method according to claim 1, wherein the size of the projection is 30 nanometers or more.
A method for producing a gallium nitride single crystal, comprising forming a gallium nitride film on a sapphire substrate having fine irregularities of not more than 00 nanometers by a chloride vapor phase epitaxy method.