JP5735420B2 - Method for producing group III metal nitride single crystal - Google Patents

Description

  The present invention relates to a method for growing a group III metal nitride single crystal.

  Gallium nitride thin film crystals are attracting attention as an excellent blue light-emitting device, put into practical use in light-emitting diodes, and expected as a blue-violet semiconductor laser device for optical pickups.

  In Japanese Patent Application Laid-Open No. 2004-247711, a template substrate with a concavo-convex shape formed as a seed substrate is used as a seed substrate, and after GaN crystal growth by the Na flux method, flux method growth is performed in the vicinity of the void formed in the recess. The part is separated (peeled) from the template.

  In Japanese Patent Application Laid-Open No. 2005-12171, a gap is provided in the seed crystal film on the surface of the template substrate, and a group III metal nitride single crystal is grown on the seed crystal by a flux method.

  In JP 2008-239365, an island portion is formed on the surface of a sapphire substrate by processing, a seed crystal film is formed on the surface of the island portion, and a group III metal nitride single crystal is fluxed onto the seed crystal film. It is described that it is formed by a method.

  In Japanese Unexamined Patent Application Publication No. 2009-120465, a mask having a width (or diameter) of 10 to 100 μm is formed on a base substrate at intervals of 250 to 2000 μm, and then a GaN crystal is grown on the substrate by a vapor phase growth method.

  In JP-A-2004-182551, a large number of seed crystal portions are formed on the surface of a base substrate, and then a gallium nitride single crystal is grown by a vapor phase method.

JP2004-247711 JP2005-12171 JP2008-239365 JP2009-120465 JP2004-182551

  As described above, for example, a band-shaped seed crystal film is formed on a substrate, a substrate non-growing surface is formed between adjacent seed crystal films, and then a group III metal nitride single crystal is formed by a flux method. JP-A-2004-247711, JP-A-2005-12171, JP-A-2008-239365. In JP2009-120465 and JP2004-182551, a group III metal nitride single crystal is formed on a seed crystal film by a vapor phase method.

  However, as a result of further investigation by the present inventors, when a group III metal nitride single crystal is grown and cooled, the single crystal often does not peel off from the substrate, and it is particularly difficult to peel off the entire surface of the single crystal. there were. When this reason was examined, when the substrate had a crack, the single crystal was firmly bonded to the substrate, the area to be peeled was reduced, and the entire surface was not peeled off.

  An object of the present invention is to form a non-growth surface that is not covered with a seed crystal film on a substrate and grow the group III metal nitride single crystal on the seed crystal film by a flux method. It is to make it easy to peel off naturally.

The present invention provides a seed crystal film production step of forming a group III metal nitride single crystal seed crystal film on a substrate, and forming a non-growth surface not covered with the seed crystal film on the substrate; and seed crystal A growth process for growing a single crystal on the film by a flux method;
A method comprising:
The thickness of the substrate is 0.8mm or more, 1.2 mm Ri der hereinafter, the substrate is made of sapphire, III group metal nitride is grown by the flux method single crystal gallium nitride single crystal, an aluminum single crystal or nitride nitride characterized Rukoto such aluminum gallium single crystal.

  The inventor paid attention to a crack generated in the substrate when the seed crystal film was cooled. That is, it is considered that when a crack occurs in the substrate during cooling, the stress near the interface between the substrate and the single crystal is released to the substrate side, and the entire surface is not peeled off at the interface between the substrate and the single crystal.

  In order to confirm the validity of this hypothesis, the cause of the occurrence of cracks on the substrate side was examined. As a result, it has been found that it is effective to set the thickness of the substrate to 0.8 mm or more in order to further increase the strength of the substrate and make it difficult for cracks to propagate to the surface. As a result, it has been found that the release of stress due to the occurrence of cracks on the substrate side can be prevented, and the natural peeling at the interface between the substrate and the single crystal can be promoted. Conventionally, the specifications of the thickness of the substrate material are 0.43 mm and 0.63 mm, and there is no knowledge that increasing the thickness of the substrate increases the cost and that the substrate thickness is related to the natural peeling of the single crystal. Therefore, it is considered that there was no motivation to thicken the substrate.

  On the other hand, it has been found that if the thickness of the substrate is excessively increased, cracks are generated in the substrate, which hinders peeling at the interface between the substrate and the single crystal. The reason for this is not clear, but it is considered that the temperature distribution inside the substrate increases. From this point of view, the substrate thickness must be 1.2 mm or less.

FIG. 1A is a cross-sectional view schematically showing a state in which a seed crystal film 2 is formed on the surface 1a of the substrate 1, and FIG. 1B shows that the seed crystal films 3 separated from each other are formed. It is sectional drawing which shows a state typically. 2A is a cross-sectional view schematically showing a state in which a group III metal nitride single crystal 4 is grown on the seed crystal film 3 of FIG. 1 by a flux method, and FIG. It is sectional drawing which shows typically the state which peeled the single crystal 4 from. 3A is a cross-sectional view schematically showing a state in which the seed crystal film 2 is formed on the surface 1a of the substrate 1. FIG. 3B shows the recess 5 and the seed crystal film 3 separated from each other. It is sectional drawing which shows the formed state typically. FIG. 4A is a cross-sectional view schematically showing a state in which a group III metal nitride single crystal 4 is grown on the seed crystal film 3 of FIG. 3 by a flux method. FIG. It is sectional drawing which shows typically the state which peeled the single crystal 4 from. FIG. 5 is a plan view showing a planar shape of the substrate used in the example. FIG. 6 is a graph showing the relationship between the thickness of the substrate and the overall peel rate.

Hereinafter, the present invention will be described in more detail with reference to the drawings.
As shown in FIG. 1A, the surface 1a of the substrate 1 is processed smoothly, and a well-oriented seed crystal film 2 is formed on the surface 1a.

  Next, the seed crystal film 2 is processed to form a plurality of seed crystal films 3 spaced apart from each other as shown in FIG. The planar shape of the seed crystal film 3 is not limited, but is, for example, a band shape. A non-growing surface 1b is formed between adjacent seed crystal films 3.

  The non-growing surface is a surface on which the single crystal 4 does not grow. Specifically, the non-growing surface is an exposed surface of the substrate or the surface of another film (for example, an oxide thin film layer) formed on the substrate.

  Next, as shown in FIG. 2A, a group III metal nitride single crystal 4 is formed on the seed crystal film 3 by a flux method. In this step, the single crystals 4 formed on the adjacent seed crystal films 3 are connected to cover the substrate 1.

  Next, in the temperature lowering process after the growth of the single crystal 4, as shown in FIG. 2B, the single crystal 4 is peeled off from the substrate 1 naturally or with little effort, so that the productivity is improved. Extremely high.

  3 and 4 show another embodiment. As shown in FIG. 3A, the surface 1a of the substrate 1 is processed smoothly, and the seed crystal film 2 is formed on the surface 1a. Next, the surface 1a of the substrate 1 is processed to form a plurality of seed crystal films 3 spaced apart from each other as shown in FIG. However, in this example, the recess 5 is formed by further processing from the substrate surface 1a toward the inside. Therefore, the seed crystal film 3 remains on the protrusions 8 between the recesses 5. On the protrusion 8, the film formation surface 1a remains and a side wall surface 8a is formed. The side wall surface 8a and the recess bottom surface 1b are processed surfaces formed by processing. The planar shape of the seed crystal film 3 is not limited, but is, for example, a band shape.

  Next, as shown in FIG. 4A, a group III metal nitride single crystal 4 is formed on the seed crystal film 3 by a flux method. In this step, the single crystals 4 formed on the adjacent seed crystal films 3 are connected to cover the substrate 1.

  Next, in the temperature lowering process after the growth of the single crystal 4, as shown in FIG. 4B, the single crystal 4 is peeled off from the template substrate naturally or with little effort as shown in FIG. Extremely high.

  In accordance with the present invention, the thickness T (see FIGS. 1 and 3) of the substrate 1 is set to 0.8 mm or more and 1.2 mm or less. From the viewpoint of promoting natural peeling from a single crystal substrate, the thickness T of the substrate is more preferably 0.9 mm or more, and further preferably 1.1 mm or less.

  An interval (width of a non-growth surface) G (see FIGS. 1 and 3) between adjacent seed crystal films 3 is preferably 550 μm or more from the viewpoint of promoting natural separation from a single crystal substrate, and 1 mm. The following is preferred.

  The width W of the various crystal films is preferably 50 μm or more and preferably 1 mm or less from the viewpoint of promoting natural peeling from the single crystal substrate.

  Preferably, the angle θ formed by the longitudinal direction of the side wall surface 8a of the protrusion 8 and the a-axis of the substrate is 25 ° or less, more preferably 20 ° or less, and even more preferably 10 ° or less. Most preferably, the longitudinal direction of the side wall surface of the protrusion is parallel to the a-axis of the substrate body.

  Here, the a-axis indicates <1 1 -2 0> of a hexagonal single crystal. Since both sapphire and gallium nitride are hexagonal, a1, a2, and a3 are equivalent, [2 -1 -1 0], [1 1 -2 0], [-1 2 -1 0], [-2 [1 1 0], [-1 -1 2 0], [1 -2 1 0] are equivalent. Of these six, the a-axis often uses [1 1 -2 0] by convention, and the a-axis in this application means all of these equivalent axes and is expressed as [1 1 -2 0] Even when doing so, all of the equivalent axes are included.

The material of the substrate is a sapphire.

  The formation method of the non-growing surface 1b is not limited. In particular, by grooving by sandblasting, it is possible to produce a deep groove (depth of 10 microns or more) that is difficult to produce by lithography at a low cost. Further, it is sufficient that the processed surface is smooth, the processing strain remains, and is not epi-ready (that is, a surface state where the GaN thin film does not grow), for example, laser processing, plasma etching, dicing (diamond blade) may be used. .

The depth d of the recess 5 in FIGS. 3B and 4B is 100 from the viewpoint of promoting the peeling of the grown single crystal according to the present invention and preventing the substrate 1 from cracking from the recess.
μm or less is preferable, 1 μm or less is more preferable, and 0.1 μm or less is most preferable. In sandblasting, when the 600-800th alumina abrasive grains are used, the processing speed of the sapphire substrate is several tens times slower than that of the GaN thin film, which is suitable for adjusting the depth of the recess.

  The group III metal nitride single crystal constituting the seed crystal film is a nitride of one or more metals selected from Ga, Al, and In, such as GaN, AlN, GaAlN, and GaAlInN. Of these, GaN, AlN, and GaAlN are preferable.

  The formation method of the seed crystal film is preferably the MOCVD method from the viewpoint of controllability of impurity concentration and film thickness uniformity.

  The thickness of the seed crystal film is not particularly limited. From the viewpoint of suppressing the meltback of the seed crystal film, the thickness is preferably 1 μm or more, and more preferably 5 μm or more. In addition, when the base film is thick, it takes time to form the base film, so that the film thickness is preferably as thin as possible so as not to melt back. From this viewpoint, the thickness of the seed crystal film can be 30 μm or less.

  The planar shape of each protrusion and various crystal films is not limited to a stripe shape, and may be a triangle, a hexagon, or the like. However, in this case, the angle formed by the longitudinal direction of the side wall surface on each side of the protrusion and the a-axis of the substrate body is preferably 30 ° or less. Moreover, it is preferable that the angle which the longitudinal direction of the side wall surface in each side of a processus | protrusion and the a axis | shaft of a base film make is 5 degrees-30 degrees.

  It is also possible to form a large number of protrusions or seed crystal films on the substrate at regular intervals. For example, a large number of protrusions having various shapes such as a circular shape, an elliptical shape, a triangular shape, and a polygonal shape such as a quadrilateral shape can be formed on the substrate body vertically and horizontally at regular intervals.

  Next, a group III metal nitride single crystal is grown on the seed crystal film by a flux method.

  The type of flux is not particularly limited as long as a group III metal nitride single crystal can be produced. In a preferred embodiment, a flux containing at least one of sodium metal and calcium metal is used, and a flux containing sodium metal is particularly preferred.

  In the flux, the raw material of the target group III metal nitride single crystal is mixed and used. This group III metal nitride single crystal is GaN, AlN, or GaAlN. GaN and GaAlN are preferable.

  The raw material constituting the flux is selected according to the target group III metal nitride single crystal.

  As the gallium source material, a gallium simple metal, a gallium alloy, and a gallium compound can be applied, but a gallium simple metal is also preferable in terms of handling.

  As the aluminum raw material, an aluminum simple metal, an aluminum alloy, and an aluminum compound can be applied, but an aluminum simple metal is also preferable in terms of handling.

  The growth temperature and the holding time during the growth of the group III metal nitride single crystal are not particularly limited, and are appropriately changed according to the type of the target group III metal nitride single crystal and the composition of the flux. In one example, when a gallium nitride single crystal is grown using sodium or lithium-containing flux, the growth temperature can be set to 800 to 1000 ° C.

  In a preferred embodiment, the group III metal nitride single crystal is grown in an atmosphere composed of a mixed gas containing nitrogen gas. The total pressure of the atmosphere is not particularly limited, but is preferably 10 atm or more, and more preferably 30 atm or more from the viewpoint of preventing evaporation of the flux. However, since the apparatus becomes large when the pressure is high, the total pressure of the atmosphere is preferably 200 atm or less, and more preferably 100 atm or less.

Also, the nitrogen partial pressure in the atmosphere is not particularly limited, but when growing a gallium nitride single crystal, 10 to 200 atmospheres is preferable, and 30 to 100 atmospheres is more preferable. When growing an aluminum nitride single crystal, 0.1 to 50 atm is preferable, and 1 to 10 atm is more preferable.
A gas other than nitrogen in the atmosphere is not limited, but an inert gas is preferable, and argon, helium, and neon are particularly preferable. The partial pressure of a gas other than nitrogen is a value obtained by subtracting the nitrogen gas partial pressure from the total pressure.

  The actual training method in the present invention is not particularly limited. For example, the template substrate can be immersed in a flux in a crucible, the crucible can be accommodated in a pressure resistant container, and heated while supplying a nitrogen-containing atmosphere in the pressure resistant container. In addition, the flux can be brought into contact with the surface of the seed crystal film by fixing the template substrate at a predetermined position and raising the crucible containing the flux upward.

Example 1
In accordance with the method described with reference to FIGS. 3 and 4, a gallium nitride single crystal was produced.

  Specifically, a GaN low-temperature buffer layer is first deposited to a thickness of 70 nm at 550 ° C. on the surface of a c-plane sapphire substrate 1 having a diameter of 4 inches and a thickness of 0.8 mm, and then a GaN thin film 2 having a thickness of 30 microns is formed. A film was formed at 1050 ° C. by a vapor phase method. Striped grooves 5 having a depth d = 30 microns, a width G = 600 microns, and a period of 650 microns were formed on the entire surface of the surface of the GaN template except for the outer peripheral portion of 1.5 mm. The width W of the seed crystal film 3 is 50 microns. At this time, as shown in FIG. 5, the direction X of the stripe groove was set to be perpendicular to the a-axis of the GaN thin film crystal. The groove was formed by sand blasting. Further, the GaN thin film in the outer peripheral area of 1.5 mm was simultaneously removed by sandblasting.

  Next, the gallium nitride single crystal 4 was grown on the template substrate by a flux method. Specifically, first, in a glove box in an argon atmosphere, a φ4 inch GaN template grooved as a seed crystal substrate was placed at the center of the bottom in a growth vessel having an inner diameter of φ120 mm. Furthermore, 130 g of metallic sodium, 90 g of metallic gallium, and 350 mg of carbon were filled in the growth vessel. The growth vessel was placed in a refractory metal vessel and sealed, and then placed on a table where the crystal growth furnace can be swung and rotated. Crystals were grown by increasing the pressure to 4.5 MPa with nitrogen gas while raising the temperature to 870 ° C., and maintaining the flux solution for 100 hours with stirring by shaking and rotation. Thereafter, it was gradually cooled to room temperature over 30 hours. Thereafter, the growth vessel was taken out from the crystal growth furnace, the flux was removed using ethanol, and the grown gallium nitride crystal plate was recovered.

  The obtained gallium nitride crystal plate 4 had a diameter of 4 inches and a thickness of about 1.5 mm. As a result of growing 10 crystals under the same conditions, the grown gallium nitride crystal 4 was peeled from the sapphire substrate in the 3 sheets.

(Example 2)
A gallium nitride single crystal was grown in the same manner as in Example 1. However, the thickness T of the sapphire substrate was 0.9 mm. The obtained gallium nitride crystal plate 4 had a diameter of 4 inches and a thickness of about 1.5 mm. As a result of growing 10 crystals under the same conditions, the grown gallium nitride crystal 4 was peeled off from the sapphire substrate in 8 sheets.

(Example 3)
A gallium nitride single crystal 4 was grown in the same manner as in Example 1. However, the thickness of the substrate 1 was 1.0 mm. The obtained gallium nitride crystal plate had a diameter of 4 inches and a thickness of about 1.5 mm. As a result of performing 10-crystal growth under the same conditions, the grown gallium nitride crystal 4 was peeled from the entire surface of the 9 substrates.

Example 4
A gallium nitride single crystal was grown in the same manner as in Example 1. However, the thickness of the substrate 1 was 1.1 mm. The obtained gallium nitride crystal plate 4 had a diameter of 4 inches and a thickness of about 1.5 mm. As a result of growing 10 crystals under the same conditions, the grown gallium nitride crystal 4 was peeled off from the sapphire substrate in 8 sheets.

(Example 5)
A gallium nitride single crystal was grown in the same manner as in Example 1. However, the thickness of the substrate 1 was 1.2 mm. The obtained gallium nitride crystal plate had a diameter of 4 inches and a thickness of about 1.5 mm. As a result of growing 10 crystals under the same conditions, the grown gallium nitride crystal 4 was peeled from the entire surface from the sapphire substrate 1 in 4 sheets.

(Comparative Example 1)
A gallium nitride single crystal was grown in the same manner as in Example 1. However, the sapphire thickness was 0.6 mm. A gallium nitride crystal having a size of 4 inches and a thickness of about 1.5 mm was grown on the template substrate. As a result of growing 10 crystals under the same conditions, many sapphire substrates 1 were cracked, and 20 to 60% of sapphire by area ratio remained attached to the gallium nitride single crystal. It did not peel.

(Comparative Example 2)
A gallium nitride single crystal was grown in the same manner as in Example 1. However, the thickness of the substrate 1 was 0.7 mm. A gallium nitride crystal having a size of 4 inches and a thickness of about 1.5 mm was grown on the template substrate. As a result of growing 10 crystals under the same conditions, many sapphire substrates 1 had many cracks, and 10 to 50% of sapphire by area ratio remained attached to the gallium nitride single crystal, and the substrate 1 was entirely It did not peel.

(Comparative Example 3)
A gallium nitride single crystal was grown in the same manner as in Example 1. However, the thickness of the sapphire substrate 1 was 1.3 mm. A gallium nitride crystal having a size of 4 inches and a thickness of about 1.5 mm was grown on the template substrate. As a result of growing 10 crystals under the same conditions, many sapphire substrates 1 had many cracks, and 10 to 50% of sapphire by area ratio remained attached to the gallium nitride single crystal, and the substrate 1 was entirely It did not peel.

(Comparative Example 4)
A gallium nitride single crystal was grown in the same manner as in Example 1. However, the thickness of the sapphire substrate 1 was 1.4 mm. A gallium nitride crystal having a size of 4 inches and a thickness of about 1.5 mm was grown on the template substrate. As a result of growing 10 crystals under the same conditions, a large number of cracks occurred in all the substrates 1, and the substrate 1 was peeled off entirely while 20 to 60% of the sapphire was adhered to the gallium nitride single crystal. I didn't.
The data of Examples 1-5 and Comparative Examples 1-4 are shown in FIG.

  Although specific embodiments of the present invention have been described, the present invention is not limited to these specific embodiments and can be implemented with various changes and modifications without departing from the scope of the claims.

Claims (9)

Forming a seed crystal film of a group III metal nitride single crystal on the substrate, and forming a non-growth surface not covered by the seed crystal film on the substrate; and on the seed crystal film; A growth process for growing a group III metal nitride single crystal by a flux method;
A method comprising:
The thickness of the substrate is 0.8mm or more, 1.2 mm Ri der hereinafter, the substrate is made of sapphire, the group III metal nitride single crystal gallium nitride single crystal is grown by the flux method, the aluminum nitride single characterized Rukoto such a crystal or aluminum gallium nitride single crystal, manufacturing method of a group III metal nitride single crystal.   2. The method according to claim 1, wherein a plurality of rows of the seed crystal films have a band shape, and the non-growth surface is formed between the adjacent seed crystal films.   The method according to claim 1, wherein a concave portion is formed in the substrate, and the non-growing surface is formed in the concave portion.   4. The method according to claim 2, wherein in the growing step, a-planes of group III metal nitride single crystals grown from the adjacent seed crystal films are associated with each other.   5. The method according to claim 2, wherein a width of the seed crystal film is 50 μm to 1 mm, and a width of the non-growth surface is 550 μm to 1 mm.   The method according to claim 2, wherein a side surface of the seed crystal film is a {1 1 −2 0} plane.   The method according to any one of claims 1 to 6, wherein the group III metal nitride single crystal to be grown is a gallium nitride single crystal or an aluminum nitride single crystal.   8. The group III metal nitride single crystal constituting the seed crystal film is a gallium nitride single crystal, an aluminum nitride single crystal, or an aluminum nitride-gallium nitride solid solution crystal. A method according to one claim. The method according to claim 1, wherein the grown group III metal nitride single crystal is naturally separated from the seed crystal film.

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