JP2021130585A - Method for manufacturing gallium nitride crystal - Google Patents

Abstract

To provide a manufacturing method capable of obtaining a high quality GaN crystal.SOLUTION: A method for manufacturing a gallium nitride crystal comprises steps of: (a) forming a bottom 220 dug from a main surface 201 constituted of the -c plane of a seed substrate 200 consisting of a gallium nitride single crystal by removing a part of the main surface 201 and a plurality of projections 210 projected from the bottom 220 and leaving the main surface 201, on the seed substrate 200; and (b) supplying a raw material gas including a gallium trihalide gas and a hydrogen nitride gas to the seed substrate 200. The (b) step includes epitaxially growing a plurality of growth crystals 230 consisting of a gallium nitride single crystal in a -c axis direction on the plurality of projections 210 while expanding a diameter in a direction along the main surface 201 to bond the plurality of growth crystals 230 to each other and growing a crystal grown from the bottom 220 to an extent without contacting the plurality of growth crystals 230.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for producing a gallium nitride (GaN) crystal.

As one of the chemical vapor deposition methods for GaN crystals, the THVPE method (Tri-halide Vapor Phase Epitaxy) is known (see Patent Document 1).

International Publication No. 2015/037322

An object of the present invention is to provide a technique capable of obtaining a high quality GaN crystal.

According to one aspect of the invention
(A) By removing a part of the main surface of the seed substrate made of a single crystal of gallium nitride, which is composed of the −c surface, on the seed substrate, the bottom portion dug down from the main surface and the bottom portion. A step of forming a plurality of convex portions that project and leave the main surface, and
(B) A step of supplying a raw material gas containing gallium trihalogenate gas and hydrogen nitride gas to the seed substrate, and
A method for producing a gallium nitride crystal having the above is provided.

According to the present invention, a high quality GaN crystal can be obtained.

FIG. 1 is a schematic configuration diagram of a GaN crystal crystal manufacturing apparatus 100 according to the first embodiment of the present invention. FIG. 2 is a flowchart showing an example of a method for producing a GaN crystal according to the first embodiment of the present invention. FIG. 3A is a schematic cross-sectional view schematically showing the seed substrate 200 in the seed substrate preparation step S101 according to the first embodiment of the present invention, and FIG. 3B is a plan view thereof. FIG. 3C is a schematic cross-sectional view schematically showing the seed substrate 200 in the convex portion forming step S102 according to the first embodiment of the present invention, and FIG. 3D is a plan view thereof. FIG. 3 (e) is a schematic cross-sectional view schematically showing the seed substrate 200 and the GaN crystal grown on the seed substrate 200 in the growth step S103 according to the first embodiment of the present invention, and FIG. 3 (f) is a schematic cross-sectional view. It is the plan view.

<Findings obtained by the inventor>
First, the findings obtained by the inventor will be described.

The THVPE method is known as one of the chemical vapor deposition methods for GaN crystals. The THVPE method is characterized in that the crystal grows epitaxially in the −c axis direction while expanding its diameter.

It is difficult for the penetrating dislocations of the seed substrate to propagate to the region (diameter-expanded portion) whose diameter has been expanded by the THVPE method. Therefore, it has been found by the inventor of the present application that the enlarged diameter portion is a high-quality region with a small dislocation density. The inventor of the present application has conducted diligent research in order to further expand such a high-quality area and develop a technology that can be utilized more effectively.

As a result, the inventor of the present application has found a new manufacturing method in which a plurality of GaN crystals are epitaxially grown in the −c axis direction while expanding the diameter and bonded to each other. By this manufacturing method, it is possible to obtain a GaN crystal having an enlarged region of high quality.

[Details of Embodiments of the present invention]
Next, an embodiment of the present invention will be described below with reference to the drawings. It should be noted that the present invention is not limited to these examples, and is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

<First Embodiment of the present invention>
(1) Configuration of Crystal Manufacturing Device for GaN Crystals First, the configuration of the GaN crystal crystal manufacturing device 100 according to the present embodiment will be described.

FIG. 1 is a schematic configuration diagram of the GaN crystal crystal manufacturing apparatus 100 of the present embodiment. As shown in FIG. 1, the GaN crystal crystal manufacturing apparatus 100 of the present embodiment includes, for example, a reaction vessel 110, a growth vessel 120, and a heating unit 130. Hereinafter, the left-right direction of FIG. 1 is referred to as a horizontal direction, and the vertical direction of FIG. 1 is referred to as a vertical direction.

The reaction vessel 110 is, for example, a straight tube made of quartz and is arranged in the horizontal direction. The growth vessel 120 is, for example, a straight tube made of quartz and is arranged in the vertical direction. A part of the reaction vessel 110 is inserted into the growth vessel 120 from the side surface of the growth vessel 120. The reaction vessel 110 and the growth vessel 120 are each airtight. Various gases used for producing GaN crystals can flow into the reaction vessel 110 and the growth vessel 120, respectively. One end of the reaction vessel 110 (the side not inserted into the growth vessel 120) is located upstream, and the lower end of the growth vessel 120 is located downstream.

In the reaction vessel 110, for example, a first zone Z11 and a second zone Z12 are provided. The first zone Z11 is located on the upstream side of the reaction vessel 110, and the second zone Z12 is located on the downstream side of the reaction vessel 110. For example, a raw material storage container 111 is installed in the first zone Z11. The raw material storage container 111 is made of, for example, quartz, and is configured to contain gallium 112 as a raw material for GaN crystals. The raw material container 111 is provided with an opening on the upper surface thereof, for example. The gallium 112 is housed in the raw material container 111 with its upper surface exposed.

The reaction vessel 110 has, for example, a gas introduction port 113, a gas introduction port 114, and a gas discharge port 115. The gas introduction port 113 is located at one end (upstream side) of the reaction vessel 110, for example, and is used for introducing _{chlorine (Cl 2) gas into the first zone Z11.} The gas introduction port 114 is located on the side surface of the reaction vessel 110, for example, near the boundary between the first zone Z11 and the second zone Z12, and is used to introduce _{Cl 2 gas into the second zone Z12.} The gas discharge port 115 is located, for example, on the downstream side of the reaction vessel 110, and is configured so that the gas generated in the second zone Z12 is transported into the growth vessel 120.

In the growth container 120, for example, a growth zone Z13 is provided below the gas discharge port 115. In the growth zone Z13, a susceptor 121 for holding the seed substrate 200, which will be described later, is installed at a position facing the gas discharge port 115. The gas transported from the gas discharge port 115 is supplied onto the seed substrate 200.

The susceptor 121 is made of, for example, a heat-resistant and corrosion-resistant boron nitride sintered body or carbon covered with a boron nitride sintered body, and is configured so that the seed substrate 200 can be held on the upper surface thereof. A rotating portion 122 is provided below the susceptor 121. The rotating portion 122 is configured to rotate the susceptor 121 in a horizontal posture. A substrate heating unit 123 such as a carbon heating element is provided in the susceptor 121. The substrate heating unit 123 is configured so that the seed substrate 200 can be heated to a predetermined temperature.

The growth container 120 has, for example, a gas introduction port 124 and a gas exhaust port 125. The gas introduction port 124 is located at the upper end of the growth vessel 120, for example, _{and is used for introducing ammonia (NH 3} ) gas or a carrier gas into the growth vessel 120. The gas exhaust port 125 is located, for example, at the lower side surface of the growth container 120. A pump 126 is provided at the gas exhaust port 125. The gas in the growth vessel 120 can be exhausted from the gas exhaust port 125 by using the pump 126.

A guide ring 127 is preferably provided on the inner wall of the growth container 120. The guide ring 127 can be made of, for example, a heat-resistant and corrosion-resistant boron nitride sintered body or carbon covered with a boron nitride sintered body. Since the guide ring 127 narrows the flow path of the gas in the growth vessel 120, the speed at which the gas in the growth vessel 120 flows into the gas exhaust port 125 can be adjusted.

The heating unit 130 is composed of, for example, a resistance heating type heater, a lamp heater, or the like, and is provided so as to cover the outer periphery of the reaction vessel 110. The heating unit 130 can heat the inside of the reaction vessel 110 to a predetermined temperature.

(2) Method for producing GaN crystal Next, the method for producing the GaN crystal of the present embodiment will be described.

FIG. 2 is a flowchart showing an example of the method for producing a GaN crystal of the present embodiment. As shown in FIG. 2, the method for producing a GaN crystal of the present embodiment includes, for example, a seed substrate preparation step S101, a convex portion forming step S102, a growth step S103, and a post-step S104.

FIG. 3A is a schematic cross-sectional view schematically showing the seed substrate 200 in the seed substrate preparation step S101 of the present embodiment, and FIG. 3B is a plan view thereof. FIG. 3C is a schematic cross-sectional view schematically showing the seed substrate 200 in the convex portion forming step S102 of the present embodiment, and FIG. 3D is a plan view thereof. FIG. 3 (e) is a schematic cross-sectional view schematically showing the seed substrate 200 and the GaN crystal grown on the seed substrate 200 in the growth step S103 of the present embodiment, and FIG. 3 (f) is a plan view thereof. ..

(Seed substrate preparation step S101)
In the seed substrate preparation step S101, as shown in FIGS. 3A and 3B, a seed substrate 200 made of a single crystal of GaN is prepared. The seed substrate 200 is, for example, a disk-shaped self-supporting substrate, preferably having a diameter of 50 mm or more. The thickness of the seed substrate 200 is, for example, 0.25 mm or more in order to prevent the mechanical strength of the seed substrate 200 from decreasing when the bottom portion 220 is formed in the convex portion forming step S102 described later. preferable. The seed substrate 200 can be produced, for example, by the HVPE method (Hydlide vapor phase epitaxy).

The main surface 201 of the seed substrate 200 is composed of the −c surface and serves as a ground for crystal growth. In the present specification, the “−c plane” includes a GaN crystal slightly inclined from the (000-1) plane. This angle of inclination is called the off angle and can be, for example, 5 ° or less.

(Convex forming step S102)
In the convex portion forming step S102, for example, as shown in FIGS. 3 (c) and 3 (d), the main surface 201 of the seed substrate 200 is irradiated with a laser beam to remove a part of the main surface 201. As a result, a bottom portion 220 dug down from the main surface 201 and a plurality of convex portions 210 protruding from the bottom portion 220 and leaving the main surface 201 left are formed on the seed substrate 200. As the laser beam, for example, a CO ₂ laser or a YAG laser can be used.

The shape of the plurality of convex portions 210 is preferably, for example, a cylinder or a hexagonal column. As a result, the GaN crystal can be grown isotropically in the growth step S103 described later. The upper surface of the plurality of convex portions 210 is the main surface 201. In the present specification, when the shape of the plurality of convex portions 210 is other than a cylinder, the diameter thereof means the longest diameter on the upper surface (main surface 201) of the convex portions 210.

The distance a between the plurality of convex portions 210 is preferably, for example, 200 μm or more and 1000 μm or less. If the interval a is less than 200 μm, a high-quality region may not be sufficiently wide in the grown GaN crystal. On the other hand, by setting the interval a to 200 μm or more, it is possible to obtain a sufficiently wide high-quality region in the grown GaN crystal. On the other hand, if the interval a exceeds 1000 μm, it may be difficult to bond the plurality of growth crystals 230 to each other in the growth step S103 described later. On the other hand, by setting the interval a to 1000 μm or less, it becomes easy to bond the plurality of growth crystals 230 to each other in the growth step S103 described later.

The diameter b of the plurality of convex portions 210 is preferably, for example, 20 μm or more and 100 μm or less. If the diameter b is less than 20 μm, it may be difficult to bond the plurality of growth crystals 230 to each other in the growth step S103 described later. On the other hand, by setting the diameter b to 20 μm or more, it becomes easy to bond the plurality of growth crystals 230 to each other in the growth step S103 described later. On the other hand, if the diameter b exceeds 100 μm, a high-quality region may not be sufficiently wide in the grown GaN crystal. On the other hand, by setting the diameter b to 100 μm or less, a high-quality region can be sufficiently widened in the grown GaN crystal.

The thickness c of the plurality of convex portions 210 is preferably, for example, 20 μm or more and 100 μm or less. If the thickness c is less than 20 μm, the crystals 240 grown from the bottom 220 may inhibit the growth of the plurality of grown crystals 230 in the growth step S103 described later. On the other hand, by setting the thickness c to 20 μm or more, it is possible to prevent the growth of the plurality of grown crystals 230 from being inhibited by the crystals 240 grown from the bottom 220. On the other hand, if the thickness c exceeds 100 μm, the mechanical strength of the plurality of convex portions 210 may decrease. On the other hand, by setting the thickness c to 100 μm or less, it is possible to suppress a decrease in the mechanical strength of the plurality of convex portions 210.

In the convex portion forming step S102, for example, when irradiating a laser beam to remove a part of the main surface 201, it is preferable that the surface of the bottom portion 220 is roughened. Specifically, it is preferable to form the bottom 220 so that the arithmetic mean roughness Ra of the surface of the bottom 220 is 0.5 μm or more and 10 μm or less. If the arithmetic mean roughness Ra of the surface of the bottom 220 is less than 0.5 μm, the growth of the crystals 240 growing from the bottom 220 may be accelerated in the growth step S103 described later, and the growth of the plurality of growth crystals 230 may be inhibited. There is sex. On the other hand, when the arithmetic mean roughness Ra of the surface of the bottom 220 is set to 0.5 μm or more, many surfaces other than the −c surface exist on the surface of the bottom 220. Therefore, in the growth step S103 described later. , The growth of the crystal 240 growing from the bottom 220 can be suppressed. On the other hand, when the arithmetic mean roughness Ra of the surface of the bottom 220 exceeds 10 μm, abnormal nucleation occurs in regions other than the plurality of convex portions 210, and crystals having poor crystal quality (hereinafter, also referred to as miscellaneous crystals) grow. Therefore, there is a possibility that the growth of the plurality of growth crystals 230 will be hindered. On the other hand, by setting the arithmetic mean roughness Ra of the surface of the bottom 220 to 10 μm or less, it is possible to reduce the possibility that the growth of the plurality of grown crystals 230 is hindered by miscellaneous crystals.

In the convex portion forming step S102, for example, it is preferable to form the plurality of convex portions 210 so that the m-planes of the plurality of grown crystals 230 in the growth step S103 described later are bonded to each other. Specifically, for example, as shown in FIG. 3D, it is preferable to form the plurality of convex portions 210 at the positions of the vertices of the equilateral triangle whose sides are the m-axis of the plurality of convex portions 210. .. As a result, in the growth step S103 described later, a plurality of growth crystals 230 can be bonded to the surface thereof without any gaps.

In the convex portion forming step S102, since a plurality of convex portions 210 are formed from the seed substrate 200 which is one GaN free-standing substrate, as shown in FIG. 3D, the m-axis of the plurality of convex portions 210 is formed. It is complete. That is, the crystal orientations of the plurality of convex portions 210 are aligned. As a result, in the growth step S103 described later, a plurality of growth crystals 230 can be bonded to the surface thereof without any gaps.

After forming the plurality of convex portions 210 and the bottom portion 220 on the seed substrate 200, the seed substrate 200 is arranged on the susceptor 121 with the main surface 201 exposed.

After the seed substrate 200 is arranged on the susceptor 121, the susceptor 121 may be rotated in advance by using the rotating portion 122 in order to uniformly grow the GaN crystal on the seed substrate 200.

(Growth step S103)
In the growth step S103, for example, a raw material gas containing _{gallium trichloride (GaCl 3} ) gas as gallium trihalide gas and NH _{3 gas as hydrogen nitride gas is supplied to the seed substrate 200.} First, the carrier gas is flowed into the reaction vessel 110 and the growth vessel 120, respectively, and the atmosphere in the reaction vessel 110 and the growth vessel 120 is defined as the carrier gas atmosphere, respectively. As the carrier gas, nitrogen (N ₂ ) gas or a rare gas, which is an inert gas, can be used. The carrier gas is introduced through, for example, the gas introduction port 113 and the gas introduction port 124.

NH ₃ gas is introduced into the growth vessel 120 through the gas inlet 124. The NH ₃ gas may be introduced at the same time as the carrier gas.

The pressure in the growth vessel 120 is adjusted to a predetermined processing pressure using the pump 126.

The inside of the reaction vessel 110 is heated to a predetermined temperature by using the heating unit 130.

The seed substrate 200 is heated by using the substrate heating unit 123. _{When the seed substrate 200 reaches a predetermined growth temperature, Cl 2} gas is introduced into the reaction vessel 110 from each of the gas introduction port 113 and the gas introduction port 114.

In the first zone Z11, the Cl ₂ gas introduced from the gas introduction port 113 is reacted with the gallium 112 in the raw material container 111 to generate gallium chloride (GaCl) gas. The reaction for producing GaCl gas is represented by the following reaction formula (1).

Ga (l) + 1 / 2Cl ₂ (g) → GaCl (g) ・ ・ ・ (1)

In the reaction formula (1), (l) and (g) indicate that the substances are liquid and gas, respectively. This point also applies to the following.

In the first zone Z11, in addition to GaCl gas, gallium chloride gas such as gallium dichloride _{(GaCl 2} ) gas and GaCl _{3 gas may be generated.} By setting the temperature of the first zone Z11 to a predetermined temperature, most of the gas generated in the first zone Z11 can be GaCl gas.

In the second zone Z12, the Cl ₂ gas introduced from the gas introduction port 114 is reacted with the GaCl gas generated in the first zone Z11 to generate a GaCl ₃ gas. The _{reaction for producing GaCl 3} gas is represented by the following reaction formula (2).

GaCl (g) + Cl ₂ (g) → GaCl ₃ (g) ・ ・ ・ (2)

In the second zone Z12, in _{addition to GaCl 3} gas, other gallium chloride gas may be generated. By setting the temperature of the second zone Z12 to a predetermined temperature, most of the gas generated in the second zone Z12 can be _{GaCl 3 gas.}

_{The GaCl 3} gas produced in the second zone Z12 is transported into the growth vessel 120 through the gas discharge port 115. As described above, the raw material gas containing _{GaCl 3} gas as gallium trihalide gas and NH _{3 gas as hydrogen nitride gas is supplied to the seed substrate 200.} The following are examples of other processing conditions in the growth step S103.
Temperature in reaction vessel 110: 400 ° C. or higher and 800 ° C. or lower Pressure in reaction vessel 110: 0.8 atm or higher and 1.2 atm or lower Partial pressure of Cl ₂ gas in reaction vessel 110: 1 × 10 ^-3 atm or higher 1 × 10 ^-2 atm or less

In the growth step S103, _{by reacting GaCl 3} gas and NH ₃ gas in the growth zone Z13, a plurality of growth crystals 230 composed of GaN single crystals are formed on the plurality of convex portions 210 (on the main surface 201). Epitaxially grows in the −c axis direction while increasing the diameter of the main surface 201 in the creeping direction. Since the penetrating dislocations of the seed substrate 200 are difficult to propagate in the expanded diameter region (diameter expanded portion), a high-quality GaN crystal having a small dislocation density can be obtained. Further, in the growth step S103, as shown in FIGS. 3 (e) and 3 (f), a plurality of growth crystals 230 are bonded to each other. This makes it possible to expand a high-quality region with a low dislocation density.

In the growth step S103, as shown in FIG. 3 (f), a plurality of growth crystals 230 are epitaxially grown in a hexagonal shape, for example, in a plan view. The m-planes of the plurality of grown crystals 230 correspond to each side of the hexagon. In the growth step S103, it is preferable to bond the m-planes of the plurality of growth crystals 230 to each other. Thereby, a plurality of grown crystals 230 can be bonded to the surface thereof without any gaps.

In the growth step S103, for example, it is preferable that the plurality of growth crystals 230 grown from the plurality of convex portions 210 block the supply of the raw material gas to the bottom portion 220 and suppress the crystal growth from the bottom portion 220. When the crystal 240 growing from the bottom 220 comes into contact with the plurality of growing crystals 230, stress is applied to the plurality of growing crystals 230, which may cause defects in the plurality of growing crystals 230. On the other hand, in the present embodiment, since the plurality of growth crystals 230 are bonded to each other above the bottom 220, the supply of the raw material gas to the bottom 220 can be blocked by the plurality of bonded growth crystals 230. As a result, it is possible to suppress the growth of the crystal 240 growing from the bottom 220 and suppress the occurrence of defects in the plurality of grown crystals 230.

In the growth step S103, the crystals 240 growing from the bottom 220 do not come into contact with the plurality of growth crystals 230 (that is, the heights of the plurality of convex portions 210 are not exceeded) until the plurality of growth crystals 230 are bonded to each other. It is preferable to grow to a degree). By growing the crystals 240 to such an extent that they do not come into contact with the plurality of grown crystals 230, the raw material gas is consumed at the bottom 220, so that the supply of the raw material gas to the back surfaces of the plurality of grown crystals 230 can be suppressed. Therefore, the growth of miscellaneous crystals on the back surface of the plurality of grown crystals 230 can be suppressed. When miscellaneous crystals grow on the back surface of the plurality of grown crystals 230, stress is applied to the plurality of grown crystals 230, which may cause defects. By suppressing the growth of miscellaneous crystals on the back surface of the plurality of grown crystals 230, it is possible to suppress the occurrence of defects and obtain a high-quality GaN crystal.

In the growth step S103, as shown in FIGS. 3 (e) and 3 (f), when a plurality of growth crystals 230 are viewed in a plan view from the normal direction of the main surface 201, they are directly above the plurality of convex portions 210. A first region 231 located and a second region 232 located in a region other than the first region 231 are grown, respectively. The second region 232 can also be rephrased as an enlarged diameter portion. In the growth step S103, it is preferable that the through-dislocation density of the second region 232 is smaller than the through-dislocation density of the first region 231. Specifically, for example, the first region 231 and the second region 232 can be grown so that the penetrating dislocations of the seed substrate 200 propagate to the first region 231 and not to the second region 232, respectively. preferable. As a result, the second region 232 can be a high-quality region with a small dislocation density. Further, it is more preferable that the penetrating dislocation density of the second region 232 is one digit or more smaller than the penetrating dislocation density of the first region 231, and the penetrating dislocation density of the second region 232 is set to 1 × 10 ⁴ cm- ² or less. Is even more preferable. The lower limit of the through-dislocation density of the second region 232 is not particularly limited, but is, for example, 1 × 10 ² cm- ² or more.

Further, in the growth step S103, the first region 231 and the second region 232 may be grown, respectively, so that the through dislocations of the seed substrate 200 propagate to the second region 232. Specifically, for example, by growing a plurality of grown crystals 230 to a thickness of 0.5 mm or more, the penetrating dislocations of the seed substrate 200 propagate so as to spread to the second region 232 as the crystals grow. Therefore, the penetrating dislocations propagating to the first region 231 can be reduced. As a result, the through-dislocation densities of the first region 231 and the second region 232 can be averaged, and both the first region 231 and the second region 232 can be made into high-quality regions. The upper limit of the thickness of the plurality of grown crystals 230 is not particularly limited.

In the growth step S103, as shown in FIG. 3E, it is preferable to form a gap 234 between the bonding portion 233 in which the plurality of growth crystals 230 are bonded to each other and the seed substrate 200. Thereby, the strain of the plurality of grown crystals 230 can be relaxed. Further, in the subsequent step S104, which will be described later, the plurality of grown crystals 230 can be easily peeled off from the seed substrate 200.

In the growth step S103, it is preferable that each of the plurality of growth crystals 230 is anisotropically grow in the a-axis direction and the m-axis direction. Specifically, for example, the V / III ratio, which is the ratio of the number of moles of _{NH 3} gas, which is a group V raw material gas, to the number of moles of _{GaCl 3} gas, which is a group III raw material gas, is 50 or more and 200 or less. It is preferable to adjust the value within the range. Normally, in the THVPE method, the GaN crystal tends to grow in the m-axis direction, but by adjusting the V / III ratio to a value within the above range, each of the plurality of grown crystals 230 tends to grow in the a-axis direction. It can be epitaxially grown isotropically in the m-axis direction. As a result, it becomes possible to grow each of the plurality of grown crystals 230 into a regular hexagonal shape in a plan view and bond them to the surface thereof without any gap.

The growth temperature of the GaN crystal in the growth step S103 is preferably 1200 ° C. or higher and 1400 ° C. or lower, for example. If the growth temperature is less than 1200 ° C., the epitaxial growth of the GaN crystal in the −c axis direction may become unstable. On the other hand, by setting the growth temperature to 1200 ° C. or higher, a plurality of growth crystals 230 can be stably epitaxially grown in the −c axis direction. On the other hand, if the growth temperature exceeds 1400 ° C., it may be difficult for the plurality of growth crystals 230 to grow epitaxially while increasing the diameter in the creeping direction of the main surface 201. On the other hand, by setting the growth temperature to 1400 ° C. or lower, the plurality of growth crystals 230 can be epitaxially grown while increasing the diameter in the creepage direction of the main surface 201.

In the growth step S103, the growth conditions may be changed before and after the plurality of growth crystals 230 are bonded to each other. Specifically, for example, before the plurality of growth crystals 230 are bonded to each other, the conditions for easily expanding the diameter (that is, the conditions for easily growing in the a-axis direction and the m-axis direction) are controlled, and the plurality of growth crystals 230 are controlled. After they are bonded to each other, the conditions may be controlled so that the diameter is difficult to expand (that is, the condition is easy to grow in the −c axis direction). As a result, a plurality of growth crystals 230 can be efficiently grown.

(Post-process S104)
In the post-step S104, after the plurality of growth crystals 230 are grown to a sufficient thickness, the growth of the GaN crystal is terminated by stopping the introduction _{of Cl 2 gas into the reaction vessel 110.} At the same time, heating of the reaction vessel 110 and the seed substrate 200 is stopped, and the temperature inside the reaction vessel 110 and the growth vessel 120 is raised to a temperature at which the GaN crystal containing the seed substrate 200 and the plurality of growth crystals 230 can be carried out. Lower each. At this time, in order to prevent decomposition of the plurality of growth crystals 230, it is preferable to flow a _{carrier gas or NH 3 gas into the growth container 120.}

After lowering the temperature inside the reaction vessel 110 and the inside of the growth vessel 120 to a temperature at which the GaN crystal containing the seed substrate 200 and the plurality of growth crystals 230 can be carried out, the GaN crystal is carried out from the inside of the growth vessel 120. ..

In the post-step S104, the plurality of grown crystals 230 may be peeled from the seed substrate 200. As described above, in the present embodiment, since the gap 234 is formed between the bonding portion 233 and the seed substrate 200, it is easy to peel off the plurality of grown crystals 230 from the seed substrate 200. The plurality of grown crystals 230 exfoliated from the seed substrate 200 are high-quality GaN crystals that are bonded to each other and have a low dislocation density.

Further, the GaN crystal obtained by the present embodiment may be sliced in the horizontal direction to obtain a GaN free-standing substrate made of a single crystal of GaN. The GaN crystal can be sliced using, for example, a wire saw, an inner peripheral blade slicer, or the like. Usually, the surface of the as-slice of the blank wafer obtained by slicing is flattened by mechanical polishing, and further etching is performed to remove the damaged layer accumulated on the surface by mechanical polishing. The GaN free-standing substrate thus obtained can be suitably used, for example, when manufacturing a semiconductor device such as a laser diode, an LED, or a high-speed transistor.

(3) Effects of the present embodiment According to the present embodiment, one or more of the following effects are exhibited.

(A) In the method for producing a GaN crystal of the present embodiment, by removing a part of the main surface 201 of the seed substrate 200, the bottom 220 and the bottom 220 dug down from the main surface 201 on the seed substrate 200 are used. It has a convex portion forming step S102 that protrudes and forms a plurality of convex portions 210 on which the main surface 201 is left. Therefore, a plurality of grown crystals 230 can be epitaxially grown on the plurality of convex portions 210 in the −c axis direction while increasing the diameter of the main surface 201 in the creeping direction. In the plurality of grown crystals 230, the penetrating dislocations of the seed substrate 200 are difficult to propagate in the expanded diameter region (second region 232), so that a high-quality GaN crystal having a small dislocation density can be obtained.

(B) In the growth step S103 of the present embodiment, a plurality of growth crystals 230 are bonded to each other. As a result, a high-quality region with a low dislocation density (second region 232) can be expanded. As a result, it is possible to obtain a GaN crystal having a large area having a high quality region having a small dislocation density.

(C) In the growth step S103 of the present embodiment, the plurality of growth crystals 230 grown from the plurality of convex portions 210 block the supply of the raw material gas to the bottom 220 and suppress the crystal growth from the bottom 220. This makes it possible to suppress the growth of the crystal 240 growing from the bottom 220 and suppress the occurrence of defects in the plurality of grown crystals 230. Further, in the convex portion forming step S102, when a part of the main surface 201 is removed, the same effect can be obtained by making the surface of the bottom portion 220 a rough surface.

(D) In the growth step S103 of the present embodiment, it is preferable that the crystals 240 growing from the bottom 220 are grown to such an extent that they do not come into contact with the plurality of growth crystals 230 until the plurality of growth crystals 230 are bonded to each other. By growing the crystals 240 to such an extent that they do not come into contact with the plurality of grown crystals 230, the raw material gas is consumed at the bottom 220, so that the supply of the raw material gas to the back surfaces of the plurality of grown crystals 230 can be suppressed. Therefore, the growth of miscellaneous crystals on the back surface of the plurality of grown crystals 230 can be suppressed. By suppressing the growth of miscellaneous crystals on the back surface of the plurality of grown crystals 230, it is possible to suppress the occurrence of defects and obtain a high-quality GaN crystal.

(E) In the growth step S103 of the present embodiment, the penetrating dislocation density of the second region 232 is made smaller than the penetrating dislocation density of the first region 231. As a result, the second region 232 can be a high-quality region with a small dislocation density.

(F) In the growth step S103 of the present embodiment, a gap 234 is formed between the bonding portion 233 in which the plurality of growth crystals 230 are bonded to each other and the seed substrate 200. Thereby, the strain of the plurality of grown crystals 230 can be relaxed. Further, in the subsequent step S104, it becomes easy to peel off the plurality of grown crystals 230 from the seed substrate 200.

(G) In the growth step S103 of the present embodiment, the m-planes of the plurality of growth crystals 230 are bonded to each other. Further, in the convex portion forming step S102 of the present embodiment, the plurality of convex portions 210 are formed at the positions of the vertices of the equilateral triangle with the m-axis of the plurality of convex portions 210 as each side. As a result, a plurality of grown crystals 230 can be bonded to the surface thereof without any gaps.

<Other Embodiments of the Present Invention>
Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist thereof.

_{In the above-described embodiment, GaCl 3} gas as gallium trihalide gas and NH ₃ gas as hydrogen nitride gas are used as the raw material gas for the GaN crystal, but gallium tribromide (gallium tribromide _{) is used instead of GaCl 3 gas.} It is also possible to use gallium trihalide gas such as GaBr ₃ ) gas or gallium triiodide (GaI ₃ ) gas, or use hydrogen nitride gas such as hydrazine (N ₂ H _{4 ) gas instead of NH 3 gas.} You can also.

Further, in the above-described embodiment, a case where a plurality of convex portions 210 and a bottom portion 220 are formed on the seed substrate 200 by irradiating a laser beam to remove a part of the main surface 201 has been described. The method of forming the convex portion 210 and the bottom portion 220 of the above is not limited to the above-described embodiment. For example, after masking a part of the main surface 201, a part of the main surface 201 is removed by etching to form a bottom 220 and a bottom portion dug down from the main surface 201 on the seed substrate 200. A plurality of convex portions 210 protruding from the 220 and leaving the main surface 201 may be formed. In this case, for example, potassium hydroxide melt can be used as the etchant. Since the main surface 201 is composed of the −c surface, it can be easily etched as compared with the + c surface. Further, after the bottom 220 is formed by etching, the surface of the bottom 220 can be roughened by treating the surface of the bottom 220 with, for example, a mixed solution of hydrochloric acid and hydrogen peroxide solution.

Further, in the above-described embodiment, the mode of _{supplying the GaCl 3} gas to the seed substrate 200 from the vertical direction has been described, but the mode of supplying the raw material gas can be variously changed. _{For example, GaCl 3} gas may be supplied to the seed substrate 200 from the horizontal direction. _{In this case, GaCl 3} gas may be selectively supplied to the plurality of convex portions 210 by adjusting the height of the seed substrate 200. _{By selectively supplying GaCl 3} gas to the plurality of convex portions 210 and _{making it difficult to supply GaCl 3} gas to the bottom portion 220, it is possible to suppress the growth of the crystal 240 growing from the bottom portion 220.

Further, in the above-described embodiment, the case where the seed substrate 200, which is a GaN free-standing substrate, is used has been described. However, the seed substrate 200 may be, for example, a template substrate in which a GaN single crystal is heteroepitaxially grown on a sapphire substrate. good. In this case, for example, the sapphire substrate is nitrided and then the GaN crystal is grown by the MOCVD method (Metalorganic Chemical Vapor Deposition) to make the main surface 201 the -c surface. Can be done. By using such a template substrate, it can be carried out at a lower cost than in the first embodiment. Further, in this case, when removing a part of the main surface 201 in the convex portion forming step S102, the bottom portion 220 may be formed by digging down to the surface of the sapphire substrate. As a result, the growth of the crystal 240 growing from the bottom 220 can be suppressed. However, from the viewpoint of suppressing the growth of miscellaneous crystals on the back surface of the plurality of grown crystals 230, the crystals 240 grown from the bottom 220 are grown to such an extent that they do not come into contact with the plurality of grown crystals 230, as in the first embodiment. Is preferable.

Further, in the above-described embodiment, the case where the m-planes of the plurality of grown crystals 230 are bonded to each other has been described, but the a-planes of the plurality of grown crystals 230 may be bonded to each other. That is, in the convex portion forming step S102, a plurality of convex portions 210 may be formed at the positions of the vertices of the equilateral triangle whose sides are the a-axis of the plurality of convex portions 210.

<Preferable Aspect of the Present Invention>
Hereinafter, preferred embodiments of the present invention will be added.

(Appendix 1)
According to one aspect of the invention
(A) By removing a part of the main surface of the seed substrate made of a single crystal of gallium nitride, which is composed of the −c surface, on the seed substrate, the bottom portion dug down from the main surface and the bottom portion. A step of forming a plurality of convex portions that project and leave the main surface, and
(B) A step of supplying a raw material gas containing gallium trihalogenate gas and hydrogen nitride gas to the seed substrate, and
A method for producing a gallium nitride crystal having the above is provided.

(Appendix 2)
The method for producing a gallium nitride crystal according to Appendix 1, wherein the gallium nitride crystal is produced.
In (b), a plurality of grown crystals composed of gallium nitride single crystals are expanded on the plurality of convex portions (on the main surface) in the creepage direction of the main surface and epitaxially grown in the −c axis direction. The plurality of grown crystals are bonded to each other.

(Appendix 3)
The method for producing a gallium nitride crystal according to Appendix 2, wherein the gallium nitride crystal is produced.
In (b), the plurality of grown crystals grown from the plurality of convex portions block the supply of the raw material gas to the bottom portion and suppress the crystal growth from the bottom portion.

(Appendix 4)
The method for producing a gallium nitride crystal according to Appendix 2 or Appendix 3, wherein the gallium nitride crystal is produced.
In (b), the crystal growing from the bottom is grown to the extent that it does not come into contact with the plurality of growing crystals (to the extent that the height of the plurality of convex portions is not exceeded).

(Appendix 5)
The method for producing a gallium nitride crystal according to any one of Supplementary note 2 to Supplementary note 4.
In the above (b), as the plurality of grown crystals, when viewed in a plan view from the normal direction of the main surface, the first region located immediately above the plurality of convex portions and the region other than the first region are formed. The second region located is grown, and the through-dislocation density of the second region is made smaller than the through-dislocation density of the first region.
More preferably, the penetrating dislocation density in the second region is made one digit or more smaller than the penetrating dislocation density in the first region.
More preferably, the penetration dislocation density in the second region is 1 × 10 ⁴ cm- ² or less.

(Appendix 6)
The method for producing a gallium nitride crystal according to any one of Supplementary note 2 to Supplementary note 5.
In the above (b), a gap is formed between the joint portion in which the plurality of grown crystals are bonded to each other and the seed substrate.

(Appendix 7)
The method for producing a gallium nitride crystal according to any one of Supplementary note 2 to Supplementary note 6.
In (b), the m-planes of the plurality of grown crystals are bonded to each other.
Preferably, in the above (a), the plurality of convex portions are formed at the positions of the vertices of the equilateral triangle whose sides are the m-axis of the plurality of convex portions.

(Appendix 8)
The method for producing a gallium nitride crystal according to any one of Supplementary note 2 to Supplementary note 7.
In (b), each of the plurality of grown crystals is anisotropically grown in the a-axis direction and the m-axis direction.
Preferably, the V / III ratio, which is the ratio of the number of moles supplied of the hydrogen nitride gas, which is a group V raw material gas, to the number of moles supplied of the gallium trihalogenate gas, which is a group III raw material gas, is 50 or more and 200 or less. Adjust to a value within the range.

(Appendix 9)
The method for producing a gallium nitride crystal according to any one of Supplementary note 1 to Supplementary note 8.
In the above (a), the surface of the bottom is made a rough surface.
Preferably, in the above (a), the bottom portion is formed so that the arithmetic mean roughness Ra of the surface of the bottom portion is 0.5 μm or more and 10 μm or less.

100 Crystal production equipment 110 Reaction vessel 111 Raw material storage vessel 112 Gallium 113 Gas inlet 114 Gas inlet 115 Gas outlet 120 Growth vessel 121 Suceptor 122 Rotating unit 123 Substrate heating unit 124 Gas inlet 125 Gas exhaust port 126 Pump 127 Guide ring 130 Heating part 200 type substrate 201 Main surface 210 Convex part 220 Bottom part 230 Growth crystal 231 First region 232 Second region 233 Coupling part 234 Void 240 Crystal S101 type Substrate preparation step S102 Convex part formation step S103 Growth step S104 Post-step Z11 1 zone Z12 2nd zone Z13 3rd zone

Claims (7)

(A) By removing a part of the main surface of the seed substrate made of a single crystal of gallium nitride, which is composed of the −c surface, on the seed substrate, the bottom portion dug down from the main surface and the bottom portion. A step of forming a plurality of convex portions that project and leave the main surface, and
(B) A step of supplying a raw material gas containing gallium trihalogenate gas and hydrogen nitride gas to the seed substrate, and
A method for producing a gallium nitride crystal having. In the above (b), a plurality of grown crystals composed of a single crystal of gallium nitride are epitaxially grown on the plurality of convex portions in the −c axis direction while expanding the diameter in the creeping direction of the main surface, and the plurality of growths are performed. The method for producing a gallium nitride crystal according to claim 1, wherein the crystals are bonded to each other. In (b), the gallium nitride crystal according to claim 2, wherein the plurality of grown crystals grown from the plurality of convex portions block the supply of the raw material gas to the bottom portion and suppress the crystal growth from the bottom portion. Manufacturing method. The method for producing a gallium nitride crystal according to claim 2 or 3, wherein in (b), the crystal growing from the bottom is grown to such an extent that it does not come into contact with the plurality of grown crystals. In the above (b), as the plurality of grown crystals, when viewed in a plan view from the normal direction of the main surface, the first region located directly above the plurality of convex portions and the region other than the first region are formed. The gallium nitride according to any one of claims 2 to 4, wherein the second region located is grown and the through-dislocation density of the second region is made smaller than the through-dislocation density of the first region. Crystal manufacturing method. In (b), the method for producing a gallium nitride crystal according to any one of claims 2 to 5, wherein a gap is formed between the bonded portion in which the plurality of grown crystals are bonded to each other and the seed substrate. .. In (b), the method for producing a gallium nitride crystal according to any one of claims 2 to 6, wherein the m-planes of the plurality of grown crystals are bonded to each other.

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