JP2006151805A - GaN SINGLE CRYSTAL SUBSTRATE, METHOD FOR MANUFACTURING GaN SINGLE CRYSTAL SUBSTRATE, LIGHT EMITTING ELEMENT FORMED ON GaN SINGLE CRYSTAL SUBSTRATE, AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a GaN single crystal substrate which is wide in area, has reduced warping, and is self-supportable. <P>SOLUTION: A mask having a zigzagged window and a striped window is formed on the GaAs (111) substrate. A GaN buffer layer is then formed at low temperature by an HVPE (hydride vapor phase epitaxy) method or MOC (metal organic chloride) method and a GaN epitaxial layer is formed at high temperature by the HVPE method and the GaAs substrate is removed. GaN is thickly deposited by the HVPE method with the self-supporting film of GaN as a seed crystal to produce a GaN ingot. This ingot is cut by a slicer and is polished and thereby the transparent and colorless GaN wafer having the reduced warping is created. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a GaN single crystal substrate for a blue light emitting element such as a light emitting diode (LED) or a laser diode (LD) using a III-V nitride compound semiconductor (GaN-based), a manufacturing method, and a GaN single crystal. It relates to the LED and LD used.

FIG. 1 shows the ratio of the lattice constant to the thermal expansion coefficient of GaN, which can be a substrate for GaN growth. Sapphire (Al ₂ O ₃ ), SiC, Si, GaAs, ZnO, and the like are weighed. A nitride-based semiconductor light-emitting device or a GaN-based light-emitting device has been conventionally produced by epitaxially growing a GaN thin film on a sapphire substrate. A sapphire (Al ₂ O ₃ ) substrate is chemically stable and heat resistant. By forming a buffer layer having a lattice constant different from that of GaN by about 16%, GaN is epitaxially grown thereon. Because of these advantages, a sapphire substrate is used. Even after a thin film such as GaN is attached, the sapphire substrate is still attached, and it is used as an LED or LD. In other words, it is a composite element of sapphire and GaN. This is a practical element, and GaN-based LEDs on a sapphire substrate are commercially available. It is also said that GaN-based LDs will be commercially available soon.

Sapphire and GaN have different lattice constants. Nevertheless, practical GaN elements grow on sapphire substrates. This is because the relaxation of the lattice constant occurs smoothly. FIG. 2 is a graph showing the relationship between the film thickness of GaN on sapphire and the change in lattice constant. The lattice constant changes slowly as the film thickness changes. Sapphire is still the most excellent substrate. All currently mass-produced products have a GaN / Al ₂ O ₃ structure. Such a structure is described in the following document, for example.
JP-A-5-183189 JP-A-6-260680

However, there are still problems with sapphire substrates. The defect density of the GaN epitaxial layer on the sapphire substrate is extremely high. Does this come from a lattice mismatch? There is a defect density as high as 10 ⁹ cm ⁻² . It may be said that it is full of defects. Nevertheless, GaN LEDs have a long life. It is a mysterious material. Therefore, it can be said that high-density defects may be a problem in crystallography, but not really a problem.

But sapphire has another mechanical difficulty. Sapphire (Al ₂ O ₃ ) is chemically stable and has high hardness. It seems good to be chemically stable, but it is not. GaN remains, and only the substrate cannot be removed by etching. The most troublesome is the lack of cleavage. Hard to it. Dicing when dividing the GaN / sapphire substrate into LED chips is difficult. Because there is no natural cleavage, the blade is pressed and cut. Yield is low due to damage.

In order to easily perform dicing, it was considered to use a material having a cleavage property such as SiC as a substrate. The SiC substrate GaN element is, for example,
Appl. Phys. Lett. Vol. 71, No. 17 (1997). However, there is a problem with SiC. It is chemically stable and the processing temperature for production is 1500 ° C. or higher. It is difficult to manufacture the SiC substrate itself. It is still at a level that has just gone out of the development stage. Therefore, it becomes an expensive substrate, and the cost of the GaN light emitting device becomes high. Actually, SiC is not widely used as a substrate for GaN light emitting devices. SiC / GaN devices are not manufactured on a mass production scale.

  In any case, the conventional GaN device is formed by growing GaN on a heterogeneous substrate and does not remove the substrate, so that the sapphire remains attached. It is a composite device.

  In order to epitaxially grow GaN on the substrate, the substrate must be heated to a high temperature of 1000 ° C. or higher. A gas phase reaction does not occur unless the temperature is high. When the temperature is lowered after growing an epitaxial layer such as GaN, an influence due to the difference in thermal expansion coefficient between the thin film and the substrate appears. The coefficient of thermal expansion is a function of temperature and is not constant. So it's not easy to compare, but a quick comparison is as follows. Assuming that the thermal expansion coefficient of GaN is 1, GaAs has a thermal expansion coefficient of approximately 1.08 times, SiC has a thermal expansion coefficient of 0.87 times, and sapphire has a thermal expansion coefficient of 1.36 times.

  The first problem due to the difference in the thermal expansion coefficient between the thin film and the substrate is that thermal stress is generated in the GaN thin film and defects or microcracks enter the GaN thin film. The second problem due to the difference in thermal expansion coefficient is that warpage occurs during cooling. The entire wafer is deformed by warping. The third problem is that a large composite GaN substrate is not possible. A composite in which a GaN thin film is placed on a sapphire substrate is not necessarily a GaN substrate. However, since the thermal stress and warpage due to the difference in thermal expansion coefficient between the thin film and the substrate are large, a large composite substrate cannot be obtained. Only a few mm square GaN / sapphire GaN composites have been reported. It is not a size that can be used industrially.

  There have been previous attempts to grow GaN using GaAs crystals as substrates. However, the GaAs substrate has drawbacks. As evaporates from the GaAs surface in a high temperature atmosphere during growth. GaAs reacts with ammonia. For these reasons, a high-quality GaN crystal could not be produced on a GaAs substrate. For this reason, GaN growth on a GaAs substrate (GaN / GaAs) has hardly been considered promising.

Only the GaN / sapphire elements still survive today. Therefore, one way of development would be to further refine the sapphire substrate method. Even if the dislocation density is high, the LED has a long life, but if the dislocation density is low, it may have a longer life. And blue LD is still not a satisfactory life. It may be due to the high density of defects. Further attempts are made to grow GaN with lower defects on sapphire substrates.
IEICE Transactions C-II, vol. J81-C-II, p58-64 This is a sapphire substrate with a striped (stripe) mask and a GaN film grown on it. GaN grows from the surfaces separated in the horizontal direction by the vertical stripes (stripes) and eventually coalesces beyond the stripes. It is reported that the defect density is greatly reduced by such stripe growth. If the defect density is reduced, it is one result. However, the stripe growth method on the sapphire substrate is silent against other problems. It is only a growth on sapphire, and the sapphire substrate remains attached. It does not solve the stubborn uncanny problem. Since it is not cleaved, the dicing process is difficult and the yield is poor. Since sapphire remains attached, many dislocations and microcracks are introduced into the GaN single crystal due to the difference in thermal expansion coefficient. Also, warping cannot be ignored. Another problem is that it is unsuitable for wafer processing due to warpage.

  The difference in coefficient of thermal expansion and the difference in lattice constant will always follow as long as different materials are used. The most ideal substrate is a GaN substrate. However, there is no wide GaN substrate. A wafer suitable for the semiconductor manufacturing process must have a diameter of 1 inch or more, preferably 2 inches or more. However, such a large GaN substrate was not available.

  For growing large crystals, there are a chocolate ski method and a Bridgman method, both of which solidify the solid from the raw material melt. Large single crystals can be produced because they can start from the melt. However, GaN cannot be melted only by heating. Sublimates and turns into gas. A small amount of GaN can be added to Ga and heated by applying an ultrahigh pressure of tens of thousands of atmospheres to obtain a Ga-GaN melt. However, the space where ultra-high pressure can be achieved is extremely narrow. Large crystals cannot be made in a small space. Manufacturing a large ultra-high pressure device is not practical because it is too costly. Since a method for producing a large crystal cannot be applied, a large GaN crystal has not been formed so far, and a GaN substrate has not existed.

The GaN thin film is made by a thin film growth method. These are all reactions from the gas phase to the solid phase. The following four methods are known for growing a GaN thin film on a sapphire substrate.
1. HVPE (Hydride Vapor Phase Epitaxy)
2. MOC method (metallorganic chloride method)
3. MOCVD (metallorganic chemical vapor deposition)
4). Sublimation method

In the MOC method, an organometallic metal such as trimethylgallium TMG and HCl gas are reacted in a hot wall type furnace to synthesize GaCl once and react with ammonia NH ₃ flowing in the vicinity of the substrate. A GaN thin film is grown thereon. In actuality, organometallic gas and HCl gas are transported using hydrogen as a carrier gas. Since an organic metal is used as a Ga raw material, carbon is mixed into GaN as an impurity. A colorless and transparent GaN crystal can be obtained, but depending on conditions, yellow may be exhibited due to carbon contamination. The carrier concentration (free electrons) increases due to carbon, and the electron mobility decreases. Due to the carbon, the electrical properties also deteriorate. The organometallic chloride vapor phase production method is an excellent method, but still has such drawbacks.

The MOCVD method is most frequently used as a GaN thin film growth method. In a cold-wall type reactor, an organometallic metal such as TMG and ammonia NH ₃ are sprayed onto a heated substrate together with hydrogen gas. TMG and NH ₃ react on the substrate to form a GaN thin film. Since this method uses a large amount of gas, the raw material gas yield is low. Although it is the most widely used technique as a GaN thin film growth method, there is a problem of carbon contamination like the MOC method. Colored yellow because of carbon. Carbon becomes an n-type impurity and emits electrons. If so, the mobility is low. Electrical characteristics are bad. There are such difficulties.
The HVPE method uses metallic Ga as a Ga raw material. A Ga reservoir is provided in a hot wall type reactor and Ga metal is placed therein. Since Ga has a low melting point, it becomes a Ga melt at 30 ° C. or higher. When hydrogen gas or HCl gas is sprayed there, gallium chloride GaCl is produced. GaCl is carried to the vicinity of the substrate by the carrier gas H ₂ and reacts with ammonia to deposit GaN on the substrate surface. This method uses metal Ga and does not contain carbon in the raw material. It does not color because carbon does not enter the thin film. There is an advantage that the electron mobility is not lowered.

  A GaN single crystal is most suitable as a substrate for producing a GaN light emitting device. Large GaN substrates have not existed so far. It is a first object of the present invention to provide a large GaN substrate having an area suitable for practical use that has not existed so far. It is a second object of the present invention to provide a GaN substrate with less warpage.

  A mask having windows arranged at equal intervals in the [11-2] direction and distributed at equal intervals in the [−110] direction is attached on a GaAs (111) single crystal substrate, and a GaN buffer is formed at a low temperature in the window portion of the mask. The layer is grown, and then the temperature is raised, and the GaN layer is epitaxially grown on the buffer layer and the mask by the HVPE method, and the GaAs substrate is removed to produce a GaN single crystal substrate. This is a method of making one substrate. Alternatively, this single crystal substrate is used as a seed crystal, and a GaN epitaxial layer is formed thickly thereon to form a GaN ingot having a thickness of at least 10 mm, which is cut or cleaved to form a plurality of GaN substrates. This is the GaN substrate manufacturing method of the present invention. The GaAs substrate can be removed by etching with aqua regia. Further, the surface of GaN is polished and smoothed. In this way, a large crystal is produced by using an epitaxial growth method which is a method for producing a thin film.

  The greatest characteristic of the GaN crystal of the present invention is its size. In the present invention, the diameter of the GaN substrate is 1 inch or more, preferably 2 inches or more. In order to manufacture light emitting elements such as LEDs at low cost industrially, a wider GaN substrate is better. Therefore, the diameter is 20 mm or more, preferably 1 inch (25 mm) or more, and more preferably 2 inches or more. If the starting material GaAs substrate is wide, a large-area GaN crystal can be manufactured.

  The present invention provides a large GaN single crystal wafer. Due to the lateral growth method through a mask with a window, there are few defects such as dislocations in the GaN crystal. Since there are few defects and the internal stress is small, warpage can be reduced. Further, since the substrate surface is flattened by polishing, warping is extremely small. It can be processed by a wafer process such as photolithography. In addition, the fluctuation of the crystal plane is within a practical range. There is no problem in device formation. LEDs and LDs can be manufactured using this wafer with low defects and small warpage. If it does so, the characteristic of LED can be improved and the lifetime of LD can be extended.

A GaN substrate manufactured by these methods is warped. Warpage occurs due to internal stress in the GaN substrate single crystal. Warpage is a significant obstacle in the wafer process for making devices. It is necessary to reduce the warpage of the substrate. The biggest problem of GaN fabrication by these methods is “reduction of warpage”. In order to reduce warpage, the present inventors propose to improve the growth process and newly polish the substrate.
(1) Growth process improvement: Lateral growth with a devised mask shape (2) Polishing: If there is some thickness, it can be flattened by polishing even if there is warping.
(3) Surface polishing: Since the warp is removed by polishing, the surface may deviate from a predetermined crystal orientation. Surface polishing is also necessary to correct the crystal orientation misalignment. Surface polishing is performed even when the surface roughness is still large. In this way, the present inventors have defined the deviation of the crystal orientation of the surface when the polishing process is originally performed in a state where a slight warp exists, and clarified the deviation of the crystal orientation which should be a GaN single crystal substrate.

  The HVPE method is adopted so that carbon is not included in the raw material. Since carbon is not contained in GaN, it hardly colors yellow. Carbon does not add electrons as carriers and lower the electron mobility. Since carbon does not enter, depending on conditions, GaN becomes a colorless and transparent wafer. Actually, when the GaN wafer of the present invention is placed on the letters, the letters on the base can be seen through. It looks like glass. However, light yellow, light brown, or dark gray may occur due to contamination of As or the like evaporated from the GaAs substrate side.

The GaN production of the present invention starts from a GaAs substrate. Not sapphire. The sapphire substrate cannot be removed later. However, the GaAs substrate can be removed with aqua regia over time. As described above, it was difficult to grow GaN on a GaAs substrate, which was once abandoned. However, the present inventors have established a method for growing a GaN crystal on a GaAs substrate. This is described in Japanese Patent Application No. 10-078333.

  GaN is hexagonal. The (0001) plane has sixfold symmetry. Since GaAs is cubic, the (100) and (110) planes do not have a three-fold symmetry. Therefore, the GaAs (111) A surface or B surface is used as a substrate. This is a plane orthogonal to an axis having threefold symmetry. The A plane is a plane where Ga atoms are exposed. The B surface is a surface where As atoms are exposed.

FIG. 3 shows a part of a mask used for lateral growth. The mask is preferably Si ₃ N ₄ or SiO ₂ that does not directly attach GaN. The mask thickness is 100 nm to several 100 nm. It is a mask having windows at equal intervals. The window is a small square. It is a small window with a diameter of several μm. This may be round, triangular, elliptical, hexagonal, etc. Sequence is important. The windows are arranged in a row in the [11-2] direction. Let L be the interval. The columns adjacent to the [−110] direction perpendicular to the same are shifted by a half pitch. Let d be the distance to the adjacent row. Preferably, d = 3 ^1/2 L / 2. In other words, it is best to arrange the window at the apex of the equilateral triangle. For example, the window may be a square with a side of 2 μm, the window pitch L may be 6 μm, and the column spacing d may be 5 μm. The reason why such an equilateral triangular distribution window is preferable is that GaN grown from adjacent windows simultaneously touches the boundary as shown in FIG. However, d and L may slightly deviate from the above formula. Such isolated windows arranged in parallel in a sequence of dots are called dot type and dot type.
Further, GaN can be grown even with a mask having stripe-like windows having parallel continuous windows.

  The lateral growth method of growing GaN through a mask with a window has the following meaning. Since the mask and GaN are not directly bonded, the underlying GaAs and thin film GaN are bonded only to the window portion. In the case of normal GaN growth, a large number of nuclei are formed on the buffer layer, and they grow by striking each other. In doing so, many defects are introduced. However, when there is a mask as in the present invention, there is nothing that hinders the portion that protrudes from the mask and grows laterally. It is thought that it grows almost without defects because there is no interference. Since the contact area is small, the thermal stress is relaxed even if the temperature is lowered after growth at a high temperature. The lateral growth layer connected only by the window is much smaller in thermal stress than in the case where the entire area is dense. With that alone, any array distribution window can be used. Instead, it is desirable to have a window distribution in which regular hexagonal pyramid-shaped crystals contact at the same time as shown in FIG. 5 and may grow to a uniform thickness thereafter. 4 and 5 indicate the shape of the bottom of the hexagonal pyramid crystal.

  To attach the mask, the entire GaAs substrate is coated with a mask material, and windows are opened at equal intervals by photolithography. The same state is shown in cross section in FIG.

  Thereafter, a thin GaN buffer layer of about several tens of nm to 100 nm is formed by HVPE at a relatively low temperature of about 450 ° C. to 500 ° C. Since it is thinner than the mask, the buffer layer is isolated in the window. FIG. 6 (2) shows this state.

  A GaN epitaxial layer is formed by HVPE at a high temperature of about 800 ° C. to 1050 ° C. At this time, the buffer layer crystallizes. As shown in FIG. 4, a GaN crystal nucleated in an isolated window usually forms a hexagonal pyramid. After nucleation, hexagonal pyramids gradually grow in the height direction and the bottom side. The bottom spreads in a hexagonal shape and fills the window. Eventually GaN spreads beyond the mask. It still retains the hexagonal pyramid shape. As shown in FIG. 5, the crystal grows in contact with the crystal from the adjacent window. The size of the substrate crystal is determined by the thickness of the epitaxial growth layer. Since one wafer has a thickness of 70 μm to 1 mm, it is sufficient if the thickness is about that level. This is the state of FIG. Since the growth process as described above is taken, the growth surface is rough and rubbed. To be transparent, it must be polished.

  Further, the GaAs portion is removed by etching with aqua regia. The mask portion is removed by polishing. The state shown in FIG. This is a single GaN crystal. Transparent and independent. If only one wafer is to be produced, this is the end.

  Further, if it is desired to manufacture a plurality of wafers, this substrate is used as a seed crystal for further epitaxial growth. FIG. 7 illustrates this. FIG. 7 (1) shows a GaN substrate epitaxially grown thicker by HVPE on a GaN substrate. It becomes a cylinder-shaped GaN ingot. The thickness is 10 mm or more. A support member is fixed to the side surface, and the wafer is cut into wafers one by one with an inner peripheral slicer or the like. FIG. 7 (2) shows this. The as-cut wafer is polished to obtain a transparent and smooth GaN wafer as shown in FIG. In this case, As is not mixed into the GaN crystal.

The HVPE method used for epitaxial growth in the present invention will be described with reference to FIG. A cylindrical heater 2 surrounds a vertically long reactor 1. There are source gas inlets 3 and 4 at the top of the reactor 1. A source gas of HCl + H ₂ is introduced from the source gas inlet 3. H ₂ is a carrier gas. Directly there is a Ga reservoir 5. Here, metal Ga is accommodated. Since it has a low melting point, it is heated by the heater 2 to become a Ga melt 6. Since HCl is sprayed onto the Ga melt, a reaction of Ga + HCl → GaCl occurs and gallium chloride GaCl is produced. The mixed gas of GaCl and carrier gas H ₂ is conveyed downward through the space in the reaction furnace. The raw material gas inlet 4 opens further downward. A mixed gas of ammonia NH ₃ + hydrogen H ₂ is introduced into the reactor from here. A reaction of GaCl + NH ₃ → GaN occurs due to GaCl and NH ₃ .

  The susceptor 7 is provided to be rotatable up and down by a shaft 8. On the susceptor 7, a GaAs substrate 9 or a GaN substrate is attached. Since the substrate is heated, the product GaN subjected to the gas phase reaction adheres to the substrate. The exhaust gas is discharged from the exhaust gas outlet 10. The HVPE method uses Ga metal as a raw material. GaCl is then made as an intermediate product. This is a feature.

  In epitaxial growth, the raw material must be gas, but there is no gas containing Ga. Ga itself is a liquid at 30 ° C. or higher. The MOC method and the MOCVD method use an organic metal to form a gas. In these methods, although it is a gas, it contains carbon, so carbon is mixed into the GaN crystal as an impurity. Unlike these, the HVPE method heats liquid Ga to react with HCl to form GaCl. GaCl is carried as a gas by the predominant hydrogen gas. The HVPE method has the advantage that carbon does not enter the crystal as an impurity because no organic metal is used.

A GaN single crystal substrate made according to the present invention is non-doped but n-type. The carrier concentration is about 1 × 10 ¹⁶ cm ⁻³ . The present inventor has found that what gives n-type conductivity is oxygen contained in a trace amount in the source gas. By controlling the oxygen partial pressure in the HVPE growth furnace, the carrier concentration can be controlled in the range of 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ . By controlling the oxygen partial pressure, the electron mobility can be adjusted in the range of 80cm ² / Vs~800cm ² / Vs. The specific resistance can be controlled in the range of 1 × 10 ⁻⁴ Ωcm to 1 × 10 Ωcm. The carrier concentration can also be changed depending on the growth conditions.

  The GaN substrate thus produced has excellent characteristics. The properties are wide, free-standing film, transparent, and colorless. However, it may be yellow, light brown or dark gray depending on the growth conditions. The substrate for an optical device is required to have little light absorption. Therefore, being colorless and transparent is important as a GaN substrate. However, that is not enough. There are still more problems. What is it? It is a problem of strain and internal stress. If the internal stress is large, the warpage becomes severe and the wafer process such as photolithography is hindered.

  GaN is grown on the heated GaAs substrate and cooled to room temperature, and the composite is taken out from the apparatus. Since the coefficient of thermal expansion is different, the strain varies with decreasing temperature. The GaN / GaAs composite is bent as shown in FIG. Stress is generated in GaN. Stress in the opposite direction is also generated in GaAs. There are two types of stress. Thermal stress and intrinsic stress. Thermal stress is generated by a temperature change when two different materials having different thermal expansion coefficients are bonded together.

  If only the thermal stress is present, the thermal stress disappears when the GaAs substrate is removed. Therefore, GaN should be flat as shown in FIG. This is not the case with intrinsic stress. Even when the GaAs substrate is removed, there is still residual stress in the GaN. Therefore, GaN itself is distorted as shown in FIG. This warp appears due to the difference in stress between the front and back surfaces and the gradient of stress in the thickness direction regardless of GaAs.

  In the past, GaN could not be skillfully grown on a GaAs substrate because of the high intrinsic stress. The internal stress including thermal stress was too large, and GaN had a lot of defects and was peeled off. The device for reducing the intrinsic internal stress is actually the lateral growth method using the mask described above. A large number of isolated windows are formed as masks, from which a GaN buffer layer is grown and an epitaxial layer is further grown. The cause of internal stress is considered to be a defect such as dislocation. In the lateral growth method, since the dislocation is separated from the dislocation by the mask, the portion grown on the mask is reduced in defects. Thereby, the internal stress of GaN can be reduced.

  That's fine, but some internal stress still remains. Therefore, the GaN substrate is warped. When warping is large, the wafer process is not affected. The warpage must be evaluated to determine the upper limit of allowable warpage.

  FIG. 12 shows the definition of the measurement method or expression method of warpage. A central ridge H is measured on a flat table on a wafer of constant diameter. For example, the center lift H is calculated in terms of a 2 inch diameter wafer. H is one measurement method and expression method.

The warpage can be defined and expressed by the curvature ξ or the curvature radius R of the curvature of the wafer. It can be converted by R = D ² / 8H or ξ = 8H / D ² . D is the diameter of the wafer. In the case of a 2-inch wafer, D = 50 mm.

  Since warping or bending is a phenomenon that appears outside, it can be measured directly. Internal stress cannot be easily measured because it is an intrinsic potential.

  The internal stress when the disk bends with a curvature δ is

Given by. σ is the internal stress, E is the rigidity, ν is the Poisson's ratio, b is the thickness of the substrate, d is the thickness of the thin film, I is the substrate diameter, and δ is the deflection (corresponds to H). When I = 50 mm, δ = H in the above definition. This is called Stoney's formula for calculating the internal stress of the thin film from the deflection. Since it is only a thin film (since it is a GaN single layer), d = b,

From this equation, σ was calculated from the deflection δ. This stress value σ can be interpreted as an internal stress value applied when the warped substrate is flattened. The relationship between warpage, radius of curvature and internal stress is as follows. When the substrate thickness is constant, the greater the internal stress, the greater the warp and the smaller the radius of curvature. When the internal stress is constant, the warpage decreases and the radius of curvature increases as the substrate thickness increases. Regarding the GaN substrate by the present inventors, considering the ease of device process on the substrate and the strength of the substrate, the allowable range of warpage, radius of curvature, and internal stress was studied. The appropriate value varies depending on the thickness of the wafer, but generally speaking,
1. Curvature radius R 600 mm or more (curvature is 1.67 × 10 ⁻³ mm ⁻¹ or less)
2. Warpage H (50mm diameter) 0.55mm or less
3. Internal stress σ
7 MPa or less In other words, the conditions imposed on the wafer by the present inventors are R ≧ 600 mm, H ≦ 0.55 mm, and σ ≦ 7 MPa. Furthermore, the internal stress σ is more preferably 3 MPa or less. More preferably, the radius of curvature is 750 mm or more.

In the present invention, in addition to a method of manufacturing a single GaN substrate, a method of manufacturing a single crystal ingot by using a GaN substrate as a seed crystal and epitaxially growing GaN thickly thereon is also employed. In that case, the thickness is 10 mm or more, and several tens of wafers are cut out. Warpage is small because the ingot is thick. Slicing with high accuracy because there is little warping. Lower dislocations are progressing because of the large thickness. Wafers sliced and cut out also have low dislocations. Therefore, there is little warp.
By adding a polishing step to the warped substrate described above, the warpage of the substrate itself can be greatly reduced. However, when polished, as shown in FIG. 15, the substrate is flattened by polishing while maintaining the fluctuation of the crystal orientation of the substrate itself. FIG. 15A shows a state before polishing. This is a GaN substrate having a convex warp upward. Since there is warping, the substrate normal is not parallel but has a fan-shaped distribution. Similarly, the normal of the crystal plane has a fan-shaped distribution. The crystal plane normal and the substrate surface normal match. When this is polished, the result is as shown in FIG. Only the top surface is flat. Even when flattened, the fan-shaped distribution in the direction of the crystal plane normal does not change. However, since the substrate surface is flattened, the normals are parallel. In the center, the substrate normal and the crystal plane normal coincide. However, the crystal plane normal is shifted from the substrate normal at the peripheral portion.

The angle between the normal of the substrate surface and the normal of the crystal plane is defined as θ. In the case of a simple convex distortion as shown in FIG. 15, the distance from the center is x and the substrate diameter is L, and when x = ± L / 2, θ takes the minimum value and the maximum value. This value is defined as ± Θ. That is, x = −L / 2 is −Θ, and x = + L / 2 is + Θ. When the disk is warped with a radius of curvature R, 2RΘ = D, where D is the diameter and ± Θ is the angle of warping at the end. Of course, the diameter of the substrate varies, but here, the relationship between the radius of curvature R and the end warp angle Θ is determined as 2 inches. If Θ is expressed as an angle, the above equation can be expressed as πRΘ = 90D. When D = 2 inches = 50 mm and Θ is expressed in angle, Θ = 1432 / R. This relationship is shown in FIG.

Just normalizing to a 2 inch size to give a relationship between curvature and edge angle does not mean that the wafer is always 2 inches in diameter. For an M inch diameter, only Θ = 1432 M / R. Such conversion is easy. In the following, it is described as normalized to 2 inches. In order to make the radius of curvature 600 mm or more in a 2-inch wafer, the deviation of the crystal plane normal line at the end must be within a range of ± 2 °. That is, the total misalignment angle between the crystal plane and the substrate flattened surface must be 4 ° or less.
The deviation angle Θ of the end must be ± 3 ° or less by adding ± 2 ° from the above-mentioned condition that the curvature radius is 600 mm or more to the alignment accuracy ± 1 ° during polishing. That is, the deviation between the main crystal plane normal and the substrate surface normal is within 3 °, which is a condition for the warp of the substrate.
In principle, as described above, the polished surface should be a mirror surface and flat. However, this is not always the case, and a new warp may occur after polishing. This seems to be due to internal stress in the GaN substrate. As a result of various studies, the warpage H (FIG. 12) after polishing can be suppressed to 0.2 mm or less (2 inch equivalent), which is a warpage amount that can withstand a device process for forming a fine pattern. found. Since the relationship between the radius of curvature and the curvature H is R = D ² / 8H as described above, the limit of H = 0.2 mm corresponds to about R = 1563 mm. Further, considering the suitability for the device process, the warp amount is preferably 0.1 mm or less. In this case, similarly, the value of H = 0.1 mm corresponds to about R = 3125 mm.

[Example 1 (Preparation of one GaN single crystal by HVPE lateral growth)]
A GaAs (111) A substrate was placed in the reaction vessel. The substrate size was a 30 mm diameter circular substrate. A Si ₃ N ₄ layer (mask layer) was formed to a thickness of 0.1 μm on a GaAs substrate with a plasma CVD apparatus. A window having a regular distribution was opened by photolithography. Three types of windows were used. There are three types: a staggered dot window shown in FIG. 3, a <11-2> stripe window, and a <1-10> stripe window.
1. Staggered dot window: As shown in FIGS. 3 to 5, adjacent windows arranged on a straight line parallel to GaAs <11-2> are shifted by a half pitch. d = 3.5 μm, L = 4 μm.
2. <11-2> Striped window A mask of a long window (striped) parallel to the <11-2> direction. The stripe width is 2 μm, the interval is 2 μm, and the pitch is 4 μm.
3. <1-10> Striped window A mask of a long window (striped) parallel to the <1-10> direction. The stripe width is 2 μm and the interval is 6 μm. The pitch is 8 μm.

A GaN buffer layer and an epitaxial layer are grown using Si ₃ N ₄ having such a window as a mask.
(1) Formation of GaN buffer layer A GaAs substrate covered with a mask having a periodic window was placed in an HVPE apparatus. The GaAs substrate was heated to about 500 ° C. in the HVPE apparatus. The quartz Ga reservoir is heated to 850 ° C. or higher to form a Ga melt. A mixed gas of hydrogen gas H ₂ and hydrogen chloride gas HCl was introduced into the Ga reservoir from the source gas inlet, and gallium chloride GaCl was synthesized. A mixed gas of hydrogen H ₂ and ammonia NH ₃ is introduced from another source gas inlet, and a reaction of GaCl + NH ₃ → GaN is caused in the vicinity of the substrate heated to 500 ° C. to deposit GaN on the GaAs substrate. As a result, a GaN buffer layer of about 70 nm is formed on the GaAs substrate. Si ₃ N ₄ has a GaN growth suppressing action, and GaN is not deposited on the Si ₃ N ₄ mask. The buffer layer (70 nm) is thinner than the mask (100 nm). Therefore, a GaN buffer layer is formed only on the GaAs portion of the window.

(2) Formation of GaN epitaxial layer The introduction of HCl was stopped. The substrate temperature was increased from 500 ° C. to about 1000 ° C. HCl is again introduced into the Ga reservoir. As in the previous step, gallium chloride GaCl is synthesized by the reaction of Ga and HCl. Since hydrogen gas flows as a carrier, GaCl flows downward. Ammonia NH ₃ and GaCl react in the vicinity of the heated substrate to form GaN. This grows epitaxially on the buffer layer in the window. When the mask thickness (100 nm) is exceeded, the GaN crystal spreads in a regular hexagonal shape on the mask. However, the GaN crystal is a hexagonal pyramid until the entire mask is covered with GaN. 4 and 5 schematically show the state of the bottom surface of the hexagonal pyramid. Since the window is located at the apex position of the equilateral triangle, the GaN spreading in a regular hexagonal shape touches the crystal spreading from the adjacent window exactly. Since the growth rate is equal, the regular hexagonal pyramid crystals are in good contact. When the GaN crystal layer completely covers the upper surface of the mask, GaN is deposited upwards. The growth rate is 50 μm / H. An epitaxial layer having a thickness of about 100 μm was grown. As described above, nucleation is independently generated from a myriad of small windows and crystal growth is performed (lateral growth), so that the internal stress in GaN can be greatly reduced. The surface was frosted glass.

(3) Removal of GaAs substrate Next, the sample was placed in an etching apparatus. Etched with aqua regia for about 10 hours. The GaAs substrate was completely removed. It became a crystal only of GaN. Both surfaces were polished to obtain a GaN single crystal substrate. This was a self-supporting membrane. Three samples were grown on GaN under almost the same conditions except that the window size and window pitch L of the mask and the distance d between adjacent rows were changed. Sample 1 was grown using a staggered dot window (window 2 μm square, L = 4 μm, d = 3.5 μm) mask. Sample 2 was grown using a <11-2> stripe mask. Sample 3 uses <1-10> stripe mask.

(4) Optical characteristics Although it is non-doped, it is an n-type electron conduction type. Considering the maintenance of crystallinity, the lower carrier concentration is better and the higher electron mobility is better. However, a higher specific resistance is better. These electrical characteristics vary depending on the growth conditions. The stripe mask is incomplete in terms of reducing internal stress. These samples are transparent light brown. Absorption coefficient at a wavelength 400nm~600nm was ^{40cm -1 ~80cm} -1 without correction by reflection.
(5) X-ray diffraction In this GaN substrate, the relationship between the angle between the substrate surface and the GaN (0001) plane was investigated using an X-ray diffractometer. As a result, it was found that the angle formed between the normal of the substrate surface and the normal of the GaN (0001) plane was 2.5 ° within the substrate. It was also found that the variation in the normal line of the GaN (0001) plane was 3.2 ° within the substrate. Further, when the amount of warpage of the substrate after polishing was measured for two samples, there were one 1 inch long (D = 25 mm) and about H = 25 μm and H = 48 μm. Since R = D ² / 8H, R = 3125 mm and R = 1628 mm. As mentioned above, the limit of photolithography on a 2-inch wafer is 0.2 mm and R = 1563 mm, but this embodiment is below this limit. This is a warp capable of pattern drawing by photolithography.

[Example 2 (HVPE laterally grown GaN seed crystal, HVPE method GaN thickening)]
A 2-inch diameter GaAs (111) A surface was used as the substrate. An SiO ₂ insulating film was formed thereon. A window as shown in FIG. 3 was provided by photolithography.
(1) Formation of GaN buffer layer

A GaAs substrate having a mask was placed in an HVPE apparatus. The Ga reservoir 5 was heated to 800 ° C. using the apparatus of FIG. As source gases, H ₂ + HCl was introduced into the Ga reservoir, and H ₂ + NH ₃ was introduced directly to the substrate. A GaN buffer layer was formed at a low temperature of about 500 ° C. (substrate temperature). The buffer layer thickness is 80 nm.
(2) Formation of epitaxial layer Next, the substrate temperature was raised to 1000 ° C. A GaN epitaxial layer of 80 μm was formed using the same source gas.
(3) Removal of GaAs The GaN / GaAs substrate was taken out from the HVPE apparatus. It was confirmed that a GaN continuous film was formed in a mirror shape. The GaAs substrate was removed by etching in aqua regia.

(4) Thickening of GaN This was thoroughly cleaned. The state shown in FIG. What was only GaN was set again in the HVPE apparatus. The substrate temperature was 1020 ° C., and GaN was thickened by the HVPE method to obtain a GaN ingot. This is the state shown in FIG. This ingot had a shape in which the central portion was slightly depressed. The ingot had a minimum height of about 20 mm and an outer diameter of 55 mm.

(5) Cutting out wafer with slicer The ingot was cut out in a direction perpendicular to the axial direction with an inner peripheral slicer. As shown in FIG. Twenty GaN single crystal substrates having an outer diameter of about 50 mm and a thickness of 350 μm were obtained. When GaN was analyzed, both As and carbon were at the background level. It can be seen that arsenic (As) and carbon are hardly contained in GaN.

(6) Polishing Further lapping polishing and final polishing were performed. This is a transparent wafer as shown in FIG. The substrate was not warped because it was machined.
(7) X-Ray Diffraction As in Example 1, this GaN substrate was examined for the angle relationship between the substrate surface and the GaN (0001) plane using an X-ray diffractometer. It was found that the angle formed between the normal line of the substrate surface and the normal line of the GaN (0001) plane was 0.6 ° at the maximum in the substrate. It was found that the variation in the normal direction of the GaN (0001) plane was 0.5 ° within the substrate. The warpage of the substrate after polishing was 2 inches long (D = 50 mm) and H = about 15 μm. Since R = D ² / 8H, R = 20000 mm or so. It is flat enough to allow photolithography to be applied.

(8) Measurement of electrical characteristics The electrical characteristics of the wafer taken from the upper end of the ingot (at the end of growth) were measured. The n-type carrier concentration was 5 × 10 ¹⁸ cm ⁻³ . The electron mobility was 200 cm ² / Vs. The specific resistance was 0.017 Ωcm.

The electrical characteristics of the wafer taken from the lower end of the ingot (early growth portion) were as follows. The n-type carrier concentration was 10 ¹⁸ cm ⁻³ and the electron mobility was 150 cm ² / Vs. The specific resistance was 0.01 Ωcm. This is the electrical property of the extremes. The middle part will be an intermediate value.

(9) Measurement of light absorption These wafers were transparent and dark gray or colorless. Absorption coefficient at a wavelength 400nm~600nm was ^{20cm -1 ~40cm} -1.
(10) Production of LED Since a GaN substrate was formed, an LED having InGaN as a light emitting layer was produced thereon. Compared with the conventional sapphire substrate, the light emission luminance is improved about 5 times. The reason why the luminance is improved is due to a decrease in dislocations. This is because many threading dislocations exist in the active layer in the conventional sapphire substrate LED, but the threading dislocations of the present invention on the GaN substrate greatly decrease.

[Example 3 (MOC laterally grown GaN seed crystal, HVPEGaN thickened)]
The GaAs (111) B surface was used as the substrate. SiO ₂ was attached to the substrate, and stripe windows extending in the [1-10] direction were formed by photolithography.

(1) Formation of GaN buffer layer A GaN buffer layer having a thickness of 90 nm was formed on a substrate at a low temperature of about 490 ° C. by an organic metal chloride vapor phase growth method (MOC method).

(2) Formation of GaN epitaxial layer In the same apparatus, the substrate temperature was raised to about 970 ° C., and the GaN epitaxial layer was formed to a thickness of 25 μm.
(3) Removal of GaAs substrate A GaN / GaAs sample was taken out from the MOC apparatus. A mirror-finished GaN single crystal was growing. The direction of the stripe mask was the [11-20] direction of GaN. That is, the [11-20] direction of GaN grows in the [1-10] direction of GaAs. The GaAs substrate was dissolved and removed with aqua regia.

(4) Thickening growth of GaN 25 μm-thick GaN was used as a seed crystal and set in an HVPE apparatus. GaN was thickly epitaxially grown by heating at 1000 ° C. by the HVPE method. A GaN ingot having a cylindrical shape and a minimum height of about 3 cm was grown.

(5) Wafer-cutting with inner peripheral blade slicer An ingot was cut into a thickness of 400 μm in the direction perpendicular to the axis with an inner peripheral blade slicer. 25 as-cut wafers could be cut out.

(6) Polishing The cut wafer was lapped and finished. A GaN single crystal wafer as a product was obtained.
(7) Measurement of electrical characteristics The electrical characteristics of the wafer were measured. It was n-type and had an electron mobility of 250 cm ² / Vs. The specific resistance was 0.05 Ωcm.
In the same manner as in Example 1, this GaN substrate was examined for the angle relationship between the substrate surface and the (0001) plane using an X-ray diffractometer. The maximum angle between the substrate surface normal and the (0001) plane normal was ± 1.1 ° within the substrate. R = 1300 mm. The variation in the normal direction of the GaN (0001) plane was 1.4 ° within the substrate. Further, the warped amount H of the substrate after polishing was 2 inches long and H = about 45 μm. R = about 6900 mm.

  In this embodiment, a GaN single crystal is grown thick using GaN itself as a seed crystal. Since thick single crystal GaN is grown and cut with a slicer, as many as 25 substrates can be fabricated at once. The manufacturing cost was reduced to 64% as compared with the case of growing from one piece of GaAs. The manufacturing cost of the substrate can be reduced. The production time per sheet including quality control could be greatly reduced. When GaN was analyzed, both arsenic (As) and carbon (C) were at the background level.

  As the mask window, a mask having a window at the apex of the equilateral triangle is best. However, it may have a striped window. There is a certain effect of reducing internal stress. Lateral growth on the mask leads to lower defects in the crystal, reducing internal stress and reducing the contact area between GaAs and GaN and mitigating internal stress. Therefore, it is possible to suppress the occurrence of warpage despite the large temperature change.

Example 4 (Relationship between Ga Partial Pressure and Surface Morphology / Internal Stress)
Using a [1-100] stripe mask, a [11-2] stripe mask, and a dot mask, a GaN wafer was fabricated by the HVPE method. The source gases are H ₂ + NH ₃ and H ₂ + HCl. Increasing the total flow of source gas improves the surface morphology. However, the internal stress tended to increase.

Of these, six (i), (b), (d), (d), (e), (d), (c), and (c) are group A, and (c) are five groups (c).
(A) The Ga partial pressure is 1 kPa (10 ⁻² atm). GaN was grown on the buffer layer / mask at 970 ° C. for 1 hour, and GaN was further grown at 1030 ° C. for 3 hours. Epitaxial growth for a total of 4 hours. The result is shown by white circles in FIG. There are six samples (I, B, D, E, G, H). These have a flat surface and good morphology. However, the internal stress is large. Some samples have cracks. In FIG. 13, the horizontal axis represents the film thickness (μm). The film thickness is distributed between 30 μm and 120 μm. The vertical axis represents internal stress (MPa). The white circle sample has an internal stress of 10 MPa to 30 MPa. Most exhibit internal stresses greater than 10 MPa. However, the internal stress is preferably 7 MPa or less (7 × 10 ⁻³ GPa).
(B) The Ga partial pressure is 2 kPa. GaN was epitaxially grown on the buffer layer / mask at 970 ° C. for 6 hours. The number of samples is ten. The same is shown in FIG. The film thickness is distributed between 120 μm and 300 μm. The surface of the GaN sample is rough. Rmax is about 20 μm. The GaN substrate size is 20 mm × 20 mm. Although the surface condition is poor, the internal stress is small. The internal stress is 1 MPa to 6 MPa as indicated by black circles in FIG. Since the target is 7 MPa or less, this can be satisfied. However, the film thickness varies widely (110 μm to 300 μm) even under the same conditions. The curvature radius R of the warp is R = 780 mm to 1500 mm.
(X-ray diffraction)
The relationship between the substrate surface and the normal line of the (0001) plane was examined using an X-ray diffractometer. The maximum angle of deviation in the substrate was ± 2.0 °. Further, the variation in the normal line of the GaN (0001) plane was 2.4 ° within the substrate. The warped amount of the substrate after polishing was 60 μm in terms of 2 inches long. This is R = 5200 mm.

[Example 5 (Relationship of radius of curvature)]
The relationship between the film thickness and the radius of curvature was examined for the six samples (A) and the five samples (B) as in the previous example. Warpage was evaluated by the stylus method. FIG. 14 shows the result. The horizontal axis is the film thickness (μm). The vertical axis is the radius of curvature. The radius of curvature is preferably 600 mm or more.
(A) Sample A grown at 970 ° C. for 1 hour + 1030 ° C. for 3 hours has a thin film thickness and a flat surface but a large warp. The curvature radius is 200 mm or less. A desirable range of the radius of curvature is 600 mm or more. All six samples do not reach the target.
(B) Sample B grown at 970 ° C. for 6 hours has a large film thickness and a roughened surface, but the internal stress is small and the warpage is small. All five B samples exceed the desirable range of 600 mm. In growth without a mask, the radius of curvature is extremely small and the warp is large. This is why the 1970s GaAs substrate attempts failed.

[Example 6 (polishing)]
Sample A failed to polish. Among samples B, a sample having a film thickness of 150 μm, an internal stress of 4 MPa, a curvature radius of 1030 mm, and a Rmax of 20 μm was polished. The film thickness was reduced to 80 μm by polishing. The radius of curvature is reduced to 650 mm after polishing. The surface roughness was reduced to Rmax 7.2 nm and Ra 2 nm by polishing. Polishing smoothes the surface, but may increase warpage.
(X-ray diffraction)
The relationship between the substrate surface normal and the (0001) plane normal was examined using an X-ray diffractometer. The maximum value of the angle formed between the substrate surface normal and the (0001) plane normal was ± 1.7 °. The variation in the normal direction of the GaN (0001) plane was 3.7 ° within the substrate. The warped amount of the substrate after polishing was 90 μm with a length of 2 inches. The radius of curvature is R = 3400 mm. This is also within the limits of photolithography.

The graph which shows the difference of the thermal expansion coefficient and lattice constant of the substrate material for growing a GaN crystal, and a GaN to x and ay coordinate. The graph which shows that a lattice constant changes smoothly when GaN epitaxial growth is carried out on a sapphire substrate, and GaN film thickness changes. The top view of what fixed the zigzag type dotted window mask to the GaAs (111) A surface. The top view of the state which grew the GaN buffer layer epitaxially in the part exposed from the mask window. The top view which shows a state, when GaN is further epitaxially grown on the mask and the buffer layer, and the crystal | crystallization from an adjacent window met | combined. The process figure which shows the process of mounting a mask on a GaAs substrate, growing a GaN buffer layer and a GaN epitaxial layer, and removing the GaAs substrate by etching. (1) is a diagram of a process in which a mask is formed on a GaAs (111) substrate. (2) is a diagram of a process in which a buffer layer is grown on a portion not covered with a mask. (3) is a diagram of a process in which a GaN epitaxial layer is grown on a buffer layer and a mask. (4) is a diagram showing a state in which the GaAs substrate is removed to form a free-standing film of GaN. The figure which shows the process of making a GaN ingot by further growing GaN thickly on a GaN substrate, and cutting this into a wafer. (1) is a diagram of a GaN ingot thickened on a GaN substrate. (2) is a figure which shows the condition which is cutting | disconnecting an ingot into an as-cut wafer with an internal peripheral slicer. (3) is a view of a cut wafer. The schematic sectional drawing of an HVPE apparatus. Sectional drawing which shows the state which the composite substrate which grew GaN on the GaAs substrate has warped because of thermal stress. Sectional drawing which shows that GaN after removing GaAs will be flat if internal stress is zero. Cross-sectional view showing that strain remains even if GaAs is removed if internal stress is present in GaN itself. The figure which shows the definition of the curvature of a GaN wafer. Warpage is expressed by a bulge H at the center of a 50 mm diameter wafer. The figure which shows distribution of the measured value of a film thickness and internal stress about a group of (A) 1 kPa and a group of (B) 2 kPa of Ga partial pressure. Black circles are rough and are group B. White circles are surface smooth and group A. The figure which shows distribution of a film thickness and a curvature radius about the same A group sample (5 sheets) and B group sample (6 sheets). Black circles are group B and white circles are group A. The figure which shows the definition of a substrate surface normal line and a crystal plane normal line in a warped GaN wafer. (A) shows that the substrate surface normal line and the crystal surface normal line in a warped state coincide with each other. (B) shows that since the convex surface is polished flat, the substrate surface normal is parallel, but the crystal surface normal is the original sector shape. (C) is the figure which showed the definition of the fluctuation | variation of the crystal plane normal in the board | substrate surface. The graph which shows the relationship between the curvature angle (theta) of the edge part of a 2 inch diameter wafer with curvature, and the curvature radius of curvature. The horizontal axis is the radius of curvature (mm), and the vertical axis is the corner of the end.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reactor 2 Heater 3 Source gas inlet 4 Source gas inlet 5 Ga reservoir 6 Ga melt 7 Susceptor 8 Shaft 9 GaAs substrate or GaN substrate 10 Gas outlet

Claims (11)

A method of a crystal plane having a diameter of 20 mm or more and a thickness of 0.07 mm or more, being self-supporting, and having a normal to the polished substrate surface and a low-index crystal plane having the highest parallelism with the polished substrate surface A GaN single crystal substrate, wherein an angle formed with a line is 3 degrees or less in the substrate, and at least one surface is polished. 2. The GaN single layer according to claim 1, wherein a normal variation between a polished substrate surface and a polished substrate surface having a highest parallelism and a low-plane index crystal plane is 4 degrees or less in the substrate. Crystal substrate. Carrier concentration of ^{1 × 10 16 ~1 × 10 20} cm -3, wherein the electron mobility is equal to or 80cm ² / Vs~800cm ² / Vs, the specific resistance is 1 × ¹⁰ -4 ~1 × 10Ωcm Item 2. A GaN single crystal substrate according to Item 1. The GaN single crystal substrate according to claim 2, wherein the dopant generating n-type carriers is oxygen. The light emitting element which is LED or LD produced on the GaN single crystal substrate in any one of Claims 1-4. After growing a GaN crystal using HVPE, lapping polishing and finishing polishing are performed on at least one surface of the obtained GaN crystal, so that it has a diameter of 20 mm or more and a thickness of 0.07 mm or more and is self-supporting. In addition, a GaN single crystal substrate having an angle formed by the normal of the polished substrate surface and the normal of the low-plane index crystal plane having the highest parallelism with the polished substrate surface is 3 ° or less in the substrate. A method for producing a GaN single crystal substrate. 7. The GaN single crystal substrate according to claim 6, wherein after the GaN crystal is grown, a plurality of GaN single crystals are obtained by slicing before at least one surface of the obtained GaN crystal is polished. Manufacturing method. The method for producing a GaN single crystal substrate according to claim 6, wherein the substrate is grown on a rotating susceptor. On a (111) plane GaAs substrate, a mask having dot windows arranged at a certain interval in the [11-2] direction and shifted by a half pitch in the [−110] direction, or a stripe extending in the [11-2] direction. Forming a mask having a rectangular window or a mask having a striped window extending in the [−110] direction, providing a GaN buffer layer, epitaxially growing GaN by the HVPE method, removing the GaAs substrate, and polishing at least one surface By doing so, it has a diameter of 20 mm or more and a thickness of 0.07 mm or more, is self-supporting, has a normal of the polished substrate surface, and a low surface index that has the highest parallelism with the polished substrate surface. A method for producing a GaN single crystal substrate, comprising obtaining a GaN single crystal substrate having an angle of 3 degrees or less in the substrate with a normal to a crystal plane. On a (111) plane GaAs substrate, a mask having dot windows arranged at a certain interval in the [11-2] direction and shifted by a half pitch in the [−110] direction, or a stripe extending in the [11-2] direction. Forming a mask having a rectangular window or a mask having a striped window extending in the [−110] direction, providing a GaN buffer layer, epitaxially growing GaN by the HVPE method, and removing the GaAs substrate to obtain a GaN substrate. A GaN single crystal is epitaxially grown on the GaN substrate by the HVPE method, and the epitaxially grown GaN ingot is divided by cutting or cleaving, and at least one surface is polished to have a diameter of 20 mm or more and a thickness of 0.07 mm or more. It is self-supporting and has the highest parallel to the normal of the polished substrate surface and the polished substrate surface. Method of manufacturing a GaN single crystal substrate angle between the normal of the crystal plane of the lower plane index is equal to or obtaining a GaN single crystal substrate is not more than 3 times within the substrate. A method for producing a light-emitting element, comprising producing a light-emitting element by laminating a light-emitting layer on the GaN single crystal substrate according to claim 9.

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