JP3692452B2 - Method for producing gallium nitride single crystal thick film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a gallium nitride single crystal thick film, and in particular, by detaching a single crystal layer of gallium nitride grown by a hydride vapor phase epitaxial growth method (hereinafter referred to as a hydride VPE method) from a substrate. The present invention relates to a method for obtaining a single crystal thick film.
[0002]
[Prior art]
Recently, a gallium nitride (GaN) semiconductor has attracted attention as a blue light emitting material.
[0003]
Conventionally, since a GaN semiconductor cannot be obtained as a large single crystal ingot, it can be obtained by vapor phase epitaxial growth on a substrate made of another material. A technique has also been proposed in which a gallium nitride single crystal film is obtained by peeling off the epitaxially grown gallium nitride layer from a substrate.
[0004]
For example, in Japanese Patent Laid-Open No. 61-7621, an aluminum nitride layer and a gallium nitride layer are sequentially stacked on a sapphire substrate, and then the gallium nitride crystal is peeled off from the substrate by selectively dissolving and removing the aluminum nitride layer. Such a method is disclosed.
[0005]
In Japanese Patent Publication No. 61-2635, a gallium nitride layer having a weak bonding force to a substrate is grown by doping an impurity such as Zn at the start of epitaxial growth, and then a gallium nitride layer containing no impurity is grown. Discloses a method in which a gallium nitride crystal is peeled off from a substrate after the growth is completed.
[0006]
Further, Japanese Patent Application Laid-Open No. 51-3379 discloses a high-resistance gallium nitride crystal by sequentially laminating a non-doped gallium nitride layer and a Zn-doped high-resistance gallium nitride layer on a substrate and then dissolving and removing the non-doped gallium nitride layer. A method is disclosed in which the substrate is peeled off from the substrate.
[0007]
Further, a ZnO buffer layer is formed on the sapphire substrate by sputtering, and after the gallium nitride layer is epitaxially grown on the sapphire substrate, the ZnO layer is etched away to remove the gallium nitride crystal from the substrate. Akazaki et al. Have reported on the method (Elevenh Recordof Alloy Semiconductor Physics and Electronics Symposium, 307-312 (1992)).
[0008]
[Problems to be solved by the invention]
However, each of the above conventional techniques has the following problems.
[0009]
That is, in the method disclosed in Japanese Patent Laid-Open No. 61-7621, an aluminum nitride layer must be formed by metal organic chemical vapor deposition (MOCVD). If the gallium nitride layer is also grown by the MOCVD method, the growth rate is slow (growth rate: 1 to 5 μm / hour), so it takes a lot of time to obtain a gallium nitride crystal with an appropriate thickness, and it is not produced. Is. Therefore, it is conceivable to grow the gallium nitride layer by a hydride VPE method having a high growth rate of 20 to 80 μm per hour. In this case, however, the growth method differs between the aluminum nitride layer and the gallium nitride layer. Has the disadvantage of becoming complicated.
[0010]
The method disclosed in Japanese Patent Publication No. 61-2635 has a problem that the gallium nitride film peeled off from the substrate is contaminated by impurities doped at the start of growth.
[0011]
In the method disclosed in Japanese Patent Application Laid-Open No. 51-3379, the gallium nitride film obtained by peeling off from the substrate has a high resistance, so that the film is not suitable for use as a substrate for manufacturing an LED. There is a point.
[0012]
In the above method reported by Akasaki et al., Since the thickness of the ZnO buffer layer is as thin as 1000 or less, the etchant liquid does not sufficiently contact the ZnO buffer layer during etching, and the gallium nitride film is easily removed from the substrate. There is a problem that does not peel off.
[0013]
The present invention has been made to solve the above problems, and provides a method for easily obtaining a gallium nitride single crystal thick film with good detachability of a gallium nitride layer epitaxially grown on a substrate. For the purpose.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the present inventor has conducted extensive research and as a result, substrates having a perovskite crystal structure containing gallium or aluminum as a constituent element (hereinafter referred to as a Ga perovskite substrate and an Al perovskite substrate, respectively). It was found that when a gallium nitride single crystal layer was epitaxially grown on the gallium nitride layer, the gallium nitride layer was easily separated from the substrate, and the present invention was completed.
[0015]
That is, the present invention is characterized in that after a gallium nitride single crystal layer is epitaxially grown on a Ga perovskite substrate or an Al perovskite substrate, the grown layer is peeled off from the substrate to obtain a gallium nitride single crystal thick film. To do.
[0016]
The present invention is characterized in that the gallium nitride single crystal layer is grown on the substrate by a hydride VPE method in which gallium chloride and nitrogen hydride are reacted on the substrate, and the nitride is formed on the substrate. The gallium single crystal layer is grown to have a thickness of 100 μm or more, preferably 200 μm or more.
[0017]
Furthermore, the gallium nitride single crystal layer is grown on the {101} plane or {011} plane of the substrate.
[0018]
Here, the reason for adopting the hydride VPE method is that, as described above, the hydride VPE method has a growth rate of 20 to 80 μm / hour, and a growth rate (1-2 μm / hour) of the MBE (molecular beam epitaxy) method or MOCVD. It is much faster than the growth rate of the method (1-5 μm / hour), and it is advantageous to obtain a film with a thickness of several hundred μm within a film formation time (several hours to several tens of hours) allowed for industrial production. Because.
[0019]
The reason why the thickness of the gallium nitride single crystal layer grown on the substrate is 100 μm or more, preferably 200 μm or more is that if the thickness is less than 100 μm, the strength is insufficient and it will collapse when peeled off. It is. If thickness is 200 micrometers or more, there exists an advantage that it is hard to be broken by the process of light emitting element preparation. The upper limit of the thickness of the gallium nitride single crystal layer to be grown is naturally determined from the viewpoints of industrial productivity and economic efficiency, and is not particularly limited, but is preferably 500 μm or less from those viewpoints.
[0020]
Further, since the {101} or {011} plane substrate has good lattice matching with the gallium nitride film, a high-quality gallium nitride single crystal film can be grown. The {101} plane or the {011} plane represents a plane equivalent to the (101) plane or the (011) plane, respectively, (1￣01) plane, (101￣) plane, (1￣01￣) It is a plane, or (01-1) plane, (011-1) plane, (01-1) plane. The index with “￣” on the right shoulder is a negative index. Further, a substrate slightly off-angled from the {101} plane or the {011} plane may be used.
[0021]
The reason why the gallium nitride film easily peels from the Ga perovskite substrate or the Al perovskite substrate is not clear, but is estimated as follows. For example, neodymium gallate (NdGaO ₃ ), which is a kind of Ga perovskite, will be specifically described. In the arrangement of Ga atoms on the (011) plane of neodymium gallate shown in FIG. 1, the lattice spacing indicated by dotted lines is the length of the a-axis. The coefficient of thermal expansion is equal to 6.6 × 10 ⁻⁶ cm / ° C., and the lattice spacing indicated by the solid lines is the sum of the squares of the lengths la, lb and lc of the a-axis, b-axis and c-axis, respectively. Its coefficient of thermal expansion is 7.1 × 10 ⁻⁶ cm / ° C. equal to half the length of the square root of. That is, since the thermal expansion coefficient of the substrate is anisotropic, the gallium nitride layer is considered to be easily peeled off. Alternatively, it is considered that the surface of neodymium gallate is nitrided at the start of epitaxial growth of gallium nitride to form a nitride layer of neodymium gallate, so that the gallium nitride layer is easily peeled off. The same cause can be considered for Ga perovskite substrates and Al perovskite substrates other than neodymium gallate and the (101) plane.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
An example of an embodiment of the present invention will be described.
[0023]
A substrate made of Ga perovskite or Al perovskite and a Ga raw material are placed in a hydride VPE apparatus (not shown), and the substrate portion and the Ga raw material portion are kept at a predetermined temperature, and N ₂ (nitrogen gas) is used as a carrier. Flow as gas. At that time, the plane orientation of the substrate to be used is a {101} plane or a {011} plane.
[0024]
In this state, HCl (hydrogen chloride) gas diluted with N ₂ is flowed from the upstream side of the Ga raw material to transport GaCl, which is a reaction product of the Ga raw material and HCl, to the substrate portion, and the Ga raw material portion is bypassed. Then, NH ₃ (ammonia) gas is allowed to flow immediately before the substrate. The NH ₃ gas and GaCl are reacted to epitaxially grow a gallium nitride single crystal layer on the substrate until the thickness becomes 100 μm or more, preferably 200 μm or more.
[0025]
After completion of the growth, the substrate is taken out slowly from the hydride VPE apparatus and the gallium nitride single crystal layer is peeled off to obtain a thick gallium nitride single crystal film. At that time, the gallium nitride layer can be easily peeled off from the substrate by vibrating the substrate with an apparatus such as an ultrasonic cleaner without performing an etching process.
[0026]
【Example】
Hereinafter, the features of the present invention will be clarified by giving examples. In addition, this invention is not limited at all by the following examples.
[0027]
A circular substrate made of neodymium gallate having a thickness of 500 μm, a diameter of 35 mm, and a plane orientation (011) was washed with an organic solvent, and then placed in a hydride VPE apparatus together with a Ga raw material, and epitaxial growth of a gallium nitride layer was performed for 10 hours. At that time, the temperatures of the substrate portion and the Ga material portion were 950 ° C. and 850 ° C., respectively. The flow rate of carrier gas N ₂ was 6 liter / min, and the flow rates of HCl gas and NH ₃ gas were 50 cc / min and 250 cc / min, respectively. After cooling, the substrate was taken out from the hydride VPE apparatus, and the substrate and the epitaxially grown layer were separated by ultrasonic cleaning to obtain a gallium nitride single crystal thick film having a thickness of 200 μm.
[0028]
When the obtained gallium nitride single crystal thick film was analyzed with an X-ray diffractometer, only diffraction of GaN (0002) and GaN (0004) was observed. When the electrical characteristics were evaluated by Hall measurement, the carrier concentration was 5 × 10 ¹⁸ cm ^{−3 for} n-type, and the mobility was 100 cm ² / V · s.
[0029]
In the above embodiment, the substrate material is neodymium gallate, but other Ga perovskites or Al perovskites may be used. The plane orientation of the substrate is (011), which is equivalent to each plane orientation of (01￣1), (011￣), (01￣1￣), or (101) and equivalent thereof. (1￣01), (101￣), and (1￣01￣) may be the orientations of the surfaces, or may be slightly off-angled from these orientations.
[0030]
In order to produce a high-quality gallium nitride single crystal thick film, the above-described thick film may be grown after a gallium nitride buffer layer is formed at a low temperature of about 500 ° C.
[0031]
Furthermore, a surface treatment such as flowing ammonia gas, GaCl gas, HCl gas, or the like may be performed on the substrate immediately before growing the thick film.
[0032]
【The invention's effect】
According to the method for manufacturing a gallium nitride single crystal thick film according to the present invention, after a single crystal layer of gallium nitride is epitaxially grown on a Ga perovskite or Al perovskite substrate, the growth layer is peeled off from the substrate and the gallium nitride single crystal is grown. Since a thick film of crystal is obtained, a single crystal thick film of gallium nitride can be easily obtained. At that time, since the mutual bonding force between the constituent atoms at the interface between the surface of the Ga perovskite substrate or Al perovskite substrate and the gallium nitride layer laminated on the substrate is weak and the gallium nitride layer is easy to peel off, Therefore, it is not necessary to interpose a layer for peeling between the substrate and the gallium nitride layer or to perform an etching process for peeling. Therefore, the process for producing a thick film is simplified, and a gallium nitride single crystal thick film that is not contaminated with impurities or the like can be obtained. In addition, if an impurity is not doped during epitaxial growth, an n-type gallium nitride layer grows, so that the obtained gallium nitride single crystal thick film has conductivity and is suitable as a substrate for LEDs and LDs. . Note that the conductivity can be improved by doping Si or the like during the growth.
[0033]
Further, by growing a gallium nitride single crystal layer on a substrate by a hydride VPE method, a gallium nitride layer having a thickness of 100 μm or more can be grown in a few hours to a few dozen hours.
[Brief description of the drawings]
FIG. 1 is a diagram showing the arrangement of Ga atoms on the (011) plane of neodymium gallate.

Claims (4)

After epitaxially growing a single crystal layer of gallium nitride on a {101} plane or {011} plane of a substrate having a perovskite crystal structure containing gallium or aluminum as a constituent element, the growth layer is peeled off from the substrate. A method for producing a gallium nitride single crystal thick film, comprising obtaining a gallium nitride single crystal thick film.  2. The gallium nitride single crystal according to claim 1, wherein the gallium nitride single crystal layer is grown on the substrate by a hydride vapor phase epitaxial growth method in which gallium chloride and nitrogen hydride are reacted on the substrate. Thick film manufacturing method.  3. The method for producing a gallium nitride single crystal thick film according to claim 1, wherein the gallium nitride single crystal layer is grown on the substrate so as to have a thickness of 100 μm or more, preferably 200 μm or more. . 4. The gallium nitride single crystal thick film manufacturing method according to claim 1, wherein the gallium nitride growth layer is peeled off from the substrate by applying vibration to the substrate on which the gallium nitride single crystal layer is grown. Method.

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