JP4565042B1 - Method for manufacturing group III nitride crystal substrate - Google Patents

Abstract

Disclosed is a method for producing a Group III nitride crystal substrate that is useful as a base substrate for Group III nitride single crystal growth, which is prevented from breaking, cracking and warping and has a large diameter.
A single crystal substrate having a thermal expansion coefficient smaller than that of a group III nitride single crystal layer, such as single crystal silicon, is selected, and a growth portion of the group III nitride single crystal is at least 5 mm inside from the outer periphery of the single crystal substrate. In this region, the laminate is manufactured so that the thickness of the group III nitride crystal layer is 100 μm or more, and the laminate is cooled to cause cracks in the single crystal substrate to separate the group III nitride crystal layer. Then, the single crystal substrate attached to the separated group III nitride crystal layer is dissolved and removed with hydrofluoric acid or the like.
[Selection] Figure 1

Description

  The present invention relates to a crystal substrate containing a group III nitride single crystal such as aluminum nitride, and a method for producing a group III nitride single crystal substrate.

  Aluminum nitride (AlN) has a large forbidden band width of 6.2 eV and is a direct transition type semiconductor. Therefore, the same group III nitride as gallium nitride (GaN) and indium nitride (InN) is used. It is expected as a material for ultraviolet light emitting devices including mixed crystals, particularly mixed crystals in which the proportion of Al in group III elements is 50 atomic% or more (hereinafter also referred to as Al group III nitride single crystal).

  In order to form a semiconductor device such as an ultraviolet light emitting device, a cladding layer, an active layer, etc. are provided between an n-type semiconductor layer electrically bonded to the n-electrode and a p-type semiconductor layer electrically bonded to the p-electrode. It is necessary to form a laminated structure including it, and from the viewpoint of light emission efficiency, it is important that any layer has high crystallinity, that is, few crystal dislocations and point defects.

  The semiconductor stacked structure is formed on a single crystal substrate (hereinafter, also referred to as “self-supporting substrate”) having sufficient mechanical strength to exist independently. The self-supporting substrate needs to have a small difference in lattice constant and difference in thermal expansion coefficient from the Al-based group III nitride single crystal forming the laminated structure, in order to suppress the dislocation density of crystal and the introduction density of point defects. Furthermore, it is required that the thermal conductivity is high from the viewpoint of preventing the deterioration of the element. Therefore, in order to fabricate a semiconductor element containing aluminum nitride, it is advantageous to form the above semiconductor stacked structure on an Al-based group III nitride single crystal substrate.

  As for an Al-based group III nitride single crystal free-standing substrate, a gas phase is usually formed on a dissimilar single crystal substrate such as sapphire (hereinafter, a substrate used for growing a single crystal is also referred to as a “base substrate”). An attempt has been made to form an Al-based group III nitride single crystal thick film by a growth method and to separate the thick film layer from a base substrate.

  Such vapor phase growth methods include the hydride vapor phase epitaxy (HVPE) method, the molecular beam epitaxy (MBE) method, and the metalorganic vapor phase epitaxy (MOVPE) method. Sublimation recrystallization method is adopted. As another growth method, a growth method through a metal melt is also used.

  Above all, the HVPE method is not always useful for the crystal laminated structure formation of semiconductor light emitting devices because it is difficult to control the film thickness precisely compared with the MOVPE method and MBE method, but a single crystal with good crystallinity is fast. Since it can be obtained at a deposition rate, it is frequently used as a vapor phase growth method for the purpose of forming a single crystal thick film.

  However, when a group III nitride single crystal such as GaN or Al group III nitride is produced by a vapor phase growth method such as the HVPE method, a lattice between the base substrate and the group III nitride single crystal to be grown is used. It is difficult to prevent the occurrence of dislocation from the interface due to mismatch. Furthermore, in the vapor phase growth method, a group III nitride single crystal is grown at a high temperature of 1000 ° C. or higher. Therefore, when a thick film of the single crystal is grown, a difference in thermal expansion coefficient between the base substrate and the single crystal. As a result, warping occurs after growth, and there is a problem that dislocation increases due to strain, cracks, and eventually breaks. By avoiding the occurrence of such breakage and separating the base substrate and the single crystal thick film, it is possible to obtain a free-standing substrate (a separated single crystal thick film portion) made of a group III nitride single crystal. Even if it is possible, the free-standing substrate has a large warp, and it has been necessary to perform a treatment for smoothing the surface in order to actually use it.

  As a method of separating the above-mentioned freestanding substrate from the base substrate, there are a method of dissolving and removing by chemical etching, a method of cutting and separating by dicing, a method of removing the base substrate by polishing, etc. There has also been proposed a method for facilitating separation by introducing a gap into the interface of a free-standing substrate (Patent Document 1).

  In the group III nitride single-crystal free-standing substrate such as GaN, the following methods have been proposed as means for solving the problems of the above-mentioned free-standing substrate. That is, a group III nitride single crystal such as GaN is grown on a base substrate such as gallium arsenide (GaAs) that can be dissolved in an acid or alkali solution, and then a group III nitride polycrystal is grown on the single crystal. Then, a method is proposed in which the base substrate is removed with an acid or alkali solution and then a group III nitride single crystal layer is further grown on the first formed group III nitride single crystal layer. (Patent Document 2).

Specifically, after a 200 nm GaAs buffer layer and a 20 nm GaN buffer layer are sequentially grown on a GaAs (111) substrate having a SiO ₂ layer as a protective layer formed on the back surface in accordance with the method, an additional 2 μm crystalline layer is formed. A good GaN layer and a 100 μm crystallinity-oriented GaN layer (polycrystalline in the vicinity of the surface) are grown sequentially, and then GaAs is dissolved and removed to obtain a GaN substrate. When a 15 μm GaN single crystal layer was grown on the surface that was in contact with the substrate, the resulting GaN single crystal layer had no cracks, and the number of dislocations was 10 ⁵ / cm ² . It is described that there was.

  The above method is an excellent method, but since the GaAs substrate (base substrate) must be completely dissolved, the larger the diameter of the GaN single crystal layer, the larger the amount of acid or alkali solution that must be used. There is a problem.

  Further, when the above method is applied as it is to the production of an Al-based group III nitride single crystal free-standing substrate such as AlN as it is, in a series of steps of producing a laminate having the same layer structure and then removing the base substrate, It is difficult to avoid the occurrence of cracks, and even when a self-supporting substrate can be obtained by avoiding the occurrence of breakage and cracks, warping may not be sufficiently suppressed.

  The inventors of the present invention have the reason that the method described in the above-mentioned Patent Document 2 cannot always be suitably applied to the production of an Al-based Group III nitride single crystal free-standing substrate. The Al-based Group III nitride crystal has an Al content. Since it is high, it was hard and inferior in elasticity compared to GaN, and it was considered that the temperature during vapor phase growth was also high. That is, when a group III nitride single crystal is grown using a base substrate such as sapphire, silicon carbide (SiC), silicon, etc., a difference in lattice constant or thermal expansion coefficient between the base substrate and the group III nitride single crystal. As a result, stress (hereinafter referred to as “lattice mismatch stress” or “thermal stress”) occurs in the group III nitride single crystal. In the case of a material having a relatively high elastic force such as GaN, cracks and fractures are unlikely to occur even if a lattice mismatch stress occurs, but in the case of a hard material such as an Al group III nitride crystal, a crack is not generated. And breakage is likely to occur. In addition, when the crystal growth temperature is as high as 1200 to 1600 ° C., for example, the thermal stress increases due to shrinkage in the cooling process after the growth of the group III nitride single crystal. did.

JP 2006-069814 A Japanese Patent No. 3350855

  As described above, in the conventional dissolution and removal method, a group III nitride single crystal free-standing substrate cannot be manufactured unless the entire base substrate is dissolved with an acid or alkaline solution. A large amount of acid or alkali solution waste was generated. Further, when the group III nitride single crystal is an Al group III nitride single crystal, a sufficiently satisfactory Al group III nitride single crystal free-standing substrate could not be manufactured even by the conventional method.

  Accordingly, an object of the present invention is to provide a method for producing a high-quality group III nitride single crystal substrate that can reduce the amount of acid or alkali used, and a method for producing a free-standing substrate using the substrate. In particular, an object of the present invention is to provide a manufacturing method that can be applied even to a hard material such as an Al-based group III nitride single crystal.

  The inventors of the present application pay attention to the stress generated in the single crystal substrate which is the base substrate during crystal growth or cooling after the growth, or the grown group III nitride crystal, and the group III nitride by relaxing the stress Instead of preventing the breakage of the crystal, a method of preventing the breakage of the group III nitride crystal by attracting the breakage point to a place other than the group III nitride crystal was considered. As a result of diligent research based on this completely different idea, the selection of the single crystal substrate that is the base substrate to be used, the identification of the growth region of the group III nitride single crystal on the base substrate, and the group III nitride crystal layer By controlling the thickness, a group III nitride single crystal substrate that has a novel concept and a simple method that has never been achieved, and that is easy to remove the base substrate and that is prevented from being broken, cracked and warped. The inventors have found a method capable of producing a group III nitride crystal substrate particularly useful as a substrate for producing the present invention, and have completed the present invention.

  That is, the present invention provides a layer obtained by growing a group III nitride single crystal including a group III nitride single crystal layer by growing a group III nitride single crystal on a single crystal substrate by a vapor phase growth method. In a method for producing a group III nitride crystal substrate comprising a group III nitride crystal layer by removing the single crystal substrate from the body, the substrate has a smaller thermal expansion coefficient than the group III nitride single crystal layer as the single crystal substrate The group III nitride single crystal growth part is a region at least 5 mm or more from the outer periphery of the single crystal substrate, and the laminate is manufactured so that the thickness of the group III nitride crystal layer is 100 μm or more, The laminated body is cooled to cause a crack in the single crystal substrate to separate the group III nitride crystal layer, and then the single crystal substrate attached to the separated group III nitride crystal layer is removed. The present invention relates to a method for manufacturing a group III nitride crystal substrate.

In the manufacturing method of the group III nitride crystal substrate,
(1) The group III nitride crystal layer is a crystal layer having a two-layer structure in which a group III nitride polycrystalline layer is formed on a group III nitride single crystal layer.
(2) The thickness of the single crystal substrate on which the group III nitride single crystal is grown is 600 μm or more,
(3) It is suitable for the case where the single crystal substrate is single crystal silicon and the group III nitride is aluminum nitride or a combination thereof.

  In another invention, a Group III nitride crystal substrate is manufactured by the above-described manufacturing method, the surface of the substrate on which the Group III nitride single crystal is exposed is used as a base, and a Group III nitride single crystal is further formed on the single crystal. The present invention relates to a method for producing a group III nitride single crystal substrate characterized by growing a crystal.

  In the present invention, the group III nitride crystal substrate is particularly useful as a substrate for producing a group III nitride single crystal substrate (a self-supporting substrate), and, if necessary, on the group III nitride crystal substrate. A group III nitride single crystal can be grown on a group III nitride single crystal substrate. Further, the present invention is based on the essence of the invention, and not only an Al group III nitride crystal substrate, but also a method for producing a group III nitride crystal substrate and a group III nitride single crystal substrate made of GaN, InN, and mixed crystals thereof. It is also useful.

  Provided is a method for efficiently producing a large-diameter group III nitride crystal substrate and a group III nitride single crystal substrate (a free-standing substrate) free from cracks and warpage. The former substrate is useful as a substrate for growing and stacking a group III nitride single crystal on the surface of the single crystal, and the latter substrate is useful as a substrate material for producing an ultraviolet light emitting device.

  In addition, according to the present invention, when a large-diameter group III nitride crystal substrate and a group III nitride single crystal substrate are manufactured, the amount of acid or alkali solution used can be reduced. Further, the surface treated with the acid or alkali solution has a shape as if the surface shape before the growth of the base substrate was transferred. Therefore, when grown using a base substrate that has been subjected to CMP treatment on the surface, the group III nitride crystal substrate and the group III nitride single crystal substrate have a surface equivalent to the CMP treatment and require high flatness. The polishing process for the subsequent process can be omitted.

  Furthermore, an Al-based group III nitride single crystal substrate (especially an aluminum nitride single crystal substrate), which has been difficult with the conventional method, and an Al-based group III nitride crystal substrate (especially a nitrided substrate) for producing the single crystal substrate. The present invention can be suitably applied to a method for producing an aluminum crystal substrate. Therefore, the present invention has high industrial utility value.

It is a flowchart which shows an example of the manufacturing process of this invention. It is the schematic which shows an example of the laminated body structure in each manufacturing process of this invention. It is the schematic which shows an example of the vapor phase growth apparatus used for the growth of a group III nitride crystal, and the substrate holding susceptor which limited the growth part. It is a figure which shows an example of the cross-section of the group III nitride crystal laminated body before cooling. It is a figure which shows an example of the cross-section of the group III nitride crystal laminated body before cooling. 1 is a schematic external view from the top of a base substrate showing a range in which a group III nitride crystal can be stacked on a rectangular base substrate. 1 is a schematic external view from the top of a base substrate showing a range in which a group III nitride crystal can be stacked on a circular base substrate. 1 is a schematic external view from the top of a base substrate showing an example of a range when a plurality of group III nitride crystals are stacked on a circular base substrate. FIG. 5 is an example of a member for controlling a growth portion of a group III nitride crystal on the base substrate. It is the schematic diagram which showed the distribution and the direction of the thermal stress concerning the inside of the group III nitride crystal laminated body under cooling with the arrow.

  The method for producing a group III nitride crystal substrate of the present invention will be described with reference to the drawings. 1 and 2 are diagrams showing an example of a specific manufacturing process of the present invention.

In the present invention, a group III nitride single crystal including a group III nitride single crystal layer 12 is grown on a base substrate 11 that is a single crystal by growing a group III nitride single crystal by a vapor phase growth method, A method for producing a group III nitride crystal substrate 18 comprising a group III nitride crystal layer 14 by collecting a group III nitride crystal body 17 from the obtained laminate 15, comprising:
1) A substrate having a smaller coefficient of thermal expansion than the group III nitride single crystal layer 12 is selected as the base substrate 11 that is a single crystal,
2) The growth portion 16 of the group III nitride single crystal layer 12 is set to an area at least 5 mm or more from the outer periphery of the base substrate 11;
3) A laminate 15 is manufactured so that the thickness of the group III nitride crystal layer 14 is 100 μm or more,
4) The laminated body 15 is cooled to cause cracks in the base substrate 11 to separate the group III nitride crystal 17,
5) Next, the group III nitride crystal substrate 18 is manufactured by removing the fragments of the base substrate 11 attached to the separated group III nitride crystal body 17.

Hereinafter, the manufacturing method of the present invention will be described in order.
The growth method of the group III nitride crystal layer 14 on the base substrate 11 which is a single crystal is easy to form a single crystal layer and easy to control the film thickness, and is further laminated on it as necessary. From the viewpoint that a polycrystalline layer can be formed only by slight changes in conditions such as temperature and raw material supply conditions, a vapor phase growth method is employed. Specific examples of the method include known vapor phase growth methods such as the sputtering method, PLD (Pulse Laser Deposition) method, and sublimation recrystallization method in addition to the HVPE method, MOVPE method, and MBE method described above. .

  In the present invention, the group III nitride includes not only single metal nitrides such as AlN, GaN, and InN but also composite nitrides such as AlGaN and InAlGaN.

In the HVPE method, a halide of a group III metal atom and a nitrogen source gas, which are raw materials, are introduced, a reaction is caused on the base substrate, and a target crystal is grown. As halides of group III metal atoms, halogen metal compounds such as aluminum halides such as AlCl ₃ , AlCl and AlBr ₃ and gallium halides such as GaCl ₃ are used, but mixed nitrides of composite nitrides such as AlGaN are used. When these are obtained, these halogen metal compounds are appropriately mixed and used in accordance with the composition of the target crystal. As the nitrogen source gas, ammonia, hydrazine, or the like is used.

  These source gases are usually mixed with a gas called a carrier gas and supplied onto the base substrate for the purpose of controlling the residence time in the vicinity of the base substrate and preventing turbulent flow. As carrier species, nitrogen, hydrogen, rare gases such as helium and argon, and mixed gases thereof are generally used, and the volume ratio is generally in the range of about 10 to several thousand times that of the source gas. Is done.

  In the MOVPE method, an organic metal is used as a raw material to supply group III atoms, ammonia, hydrazine, amines, etc. are used as a nitrogen source gas, and both are gasified and mixed into a carrier gas to cause a reaction on a base substrate. , Grow the desired crystals. Various molecular structures of organic metals are conceivable, and an appropriate raw material is selected according to the reaction rate predicted from the boiling point, chemical stability, etc., and the compatibility of the device design. Recently, trimethylaluminum is often used as an organic aluminum raw material, and trimethylgallium is used as an organic gallium raw material.

  In the MBE method, the Group III raw material is left alone and is put into a cell placed around a high vacuum chamber and supplied into the chamber by opening and closing the shutter. In many cases, nitrogen raw materials excite nitrogen gas at a high frequency to generate radical nitrogen atoms, which are supplied by opening and closing the shutter.

  The sputtering method is a method in which ionized argon or nitrogen atoms are implanted into a metal target in a vacuum chamber to repel the metal atoms and form a film at a predetermined location. Group III nitride crystals are produced by a method that targets group III nitride itself, or a reactive sputtering method in which a group III metal is used as a target and a nitrogen-containing gas is supplied to react before deposition on the base substrate. Industrial methods are being considered.

  The sublimation recrystallization method is a method in which a gas phase of group III nitride is generated at a high temperature portion in a furnace where a temperature gradient is formed, and is deposited on a seed crystal or a base substrate installed in the low temperature portion. When this process is functioning, the group III nitride is also thermally decomposed and moved in the state of group III metal vapor and nitrogen at the same time. Therefore, this process is generally called a chemical transport method.

  In the present invention, the selection of the base substrate 11 and the group III nitride single crystal layer 12 grown on the base substrate, the determination of the growth portion 16 on the base substrate 11, and the thickness of the group III nitride crystal layer 14 are limited. Any of the vapor phase growth methods described above may be employed. In particular, considering the growth rate of the group III nitride crystal layer 14, the ease of growth of the group III nitride crystal layer 14, and the ease of selection of the base substrate 11 and the group III nitride single crystal layer 12, HVPE The method is preferred.

Hereinafter, an example will be described in which an AlN crystal, which is a typical group III nitride crystal, is vapor-phase grown on a base substrate by the HVPE method.
A typical apparatus used in the HVPE method is an apparatus schematically shown in FIG. Specifically, as described in JP-A-2006-290662, a reactor main body 21 composed of a cylindrical quartz glass reaction tube, an external heating means 23 disposed outside the reaction tube, The apparatus includes a local heating device 22 and a holding susceptor 25 disposed inside the reaction tube.

  In this apparatus, the carrier gas and the raw material gas are supplied from one end of the reaction tube, and the carrier gas and the unreacted reaction gas are discharged from the opening provided in the side wall near the other end. ing. Specifically, two gas supply lines 26 and 27 are provided on the gas supply side of the reaction tank, and aluminum trichloride gas and carrier gas are supplied from one channel outlet (also referred to as a halide gas supply nozzle). And a mixed gas of ammonia gas as nitrogen source gas and hydrogen gas as carrier gas is supplied from the other channel outlet (also referred to as nitrogen source gas supply nozzle). . The external heating means is not intended to heat the base substrate, but is mainly used to maintain the temperature of the reaction gas in the reaction zone at a predetermined temperature, and is not necessarily essential. As this external heating means, a resistance heating heater, a high frequency heating device, a high frequency induction heating device, a lamp heater, or the like can be used. Further, the local heating device and the holding susceptor can hold the base substrate 24 and heat it to about 1600 ° C.

  In the present invention, it is important to select a single crystal substrate as a base substrate for growing the group III nitride crystal layer including the group III nitride single crystal layer. That is, a substrate having a smaller thermal expansion coefficient than the group III nitride single crystal layer must be selected as the single crystal substrate. The present invention is not intended for the case where the single crystal substrate and the group III nitride crystal layer have the same thermal expansion coefficient, for example, the case where the single crystal substrate and the group III nitride crystal layer are made of the same material. When the single crystal substrate and the group III nitride crystal layer have the same thermal expansion coefficient, the problem of the present invention does not occur. Therefore, the present invention is directed to the case where the single crystal substrate and the group III nitride crystal layer have different thermal expansion coefficients, for example, the case where the single crystal substrate and the group III nitride crystal layer are made of different materials.

  In order to obtain the effects of the present invention, it is desirable that the thermal expansion coefficient of the single crystal substrate is 95% or less of the thermal expansion coefficient of the group III nitride single crystal layer. The lower limit of the thermal expansion coefficient of the single crystal substrate is not particularly limited, but for the purpose of avoiding excessive thermal stress, the thermal expansion coefficient of the single crystal substrate is the thermal expansion coefficient of the group III nitride single crystal layer. It is desirable to be 50% or more.

  When the thermal expansion coefficient of the single crystal substrate is larger than that of the group III nitride single crystal layer, tensile stress is applied to the single crystal substrate, and stress concentration due to a mechanism described later does not occur. As a result, the single crystal substrate is broken from random positions, and it becomes difficult to collect the group III nitride crystal in a large area.

  As an example of a single crystal substrate that satisfies the above conditions, when the group III nitride single crystal layer is AlN (thermal expansion coefficient = 4.2 ppm / ° C.), single crystal silicon (thermal expansion coefficient = 2.4 ppm / ° C.) Or single crystal silicon carbide (thermal expansion coefficient = 2.8 ppm / ° C.) is used, and when the group III nitride single crystal layer is GaN (thermal expansion coefficient = 5.6 ppm / ° C.), single crystal silicon is used. In addition, single crystal gallium phosphide (thermal expansion coefficient = 5.3 ppm / ° C.), single crystal aluminum arsenide (thermal expansion coefficient = 5.2 ppm / ° C.), or the like can be used. In the case of a complex group III nitride crystal such as AlGaN, it is difficult to predict the change in physical property value due to the composition ratio, and therefore a material conforming to AlN should be adopted. The single crystal substrate to be used preferably has a smooth surface to be stacked in order to directly stack a group III nitride single crystal of good quality and controlled orientation on the single crystal substrate. Therefore, a general single crystal substrate for epitaxial growth is preferably used.

  The thickness of the single crystal substrate to be used is arbitrarily selected without any particular limitation, but in order to suppress deformation caused by lattice constant mismatch while laminating group III nitride crystals, the single crystal substrate is small. It is desirable that the thickness provides sufficient rigidity. From this viewpoint, the thickness is preferably 600 μm or more, and particularly preferably 800 μm or more. The upper limit of the thickness of the single crystal substrate to be used is not particularly limited, but is 5000 μm in consideration of industrial production.

  In the present invention, it is further important to select the growth region of the group III nitride crystal layer on the base substrate. That is, as shown in FIG. 4 or FIG. 5, the group III nitride single crystal growth portion needs to be an area at least 5 mm inside from the outer periphery of the base substrate.

  When the growth region extends to an area less than 5 mm from the outer periphery of the base substrate, stress concentration at the boundary between the portion where the group III nitride single crystal layer of the base substrate has grown and the portion where it has not grown is due to the mechanism described later. It does not occur sufficiently, and the selective crack inside the base substrate, which is the effect of the present invention, does not occur and the group III nitride single crystal layer is cracked. In the present invention, the region at least 5 mm or more from the outer periphery refers to a region on the substrate center side where a substrate surface of at least 5 mm or more from the outer periphery is left.

6, 7, and 8 show desirable examples of the relationship between the base substrate 31 and the group-III nitride crystal layer growth portion 32.
In the case of a square base substrate, the region 32 in FIG. 6 is referred to as a growth portion, and in the case of a disc-shaped base substrate, the region 32 in FIG. 7 is referred to as a growth portion. It is not limited at all. Further, the number of growth portions is not limited as long as it is in the above-described region, and a plurality of portions can be provided according to the size of the target base substrate as in the region 32 of FIG. However, in this case, it is essential for the same reason that the distance between the growth part is 5 mm or more.

  As a specific method for setting the growth portion of the group III nitride single crystal to a region at least 5 mm or more from the outer periphery of the base substrate, a method of depositing a mask material using a lithography technique is the most reliable. A method of covering a part of the surface of the base substrate with a member having resistance to the temperature and the source gas is simple. That is, the above-described object can be achieved by preparing a member capable of covering at least the entire base substrate, and then placing the growth portion in accordance with its shape on the base substrate (FIG. 9). With a similar idea, in a vapor phase growth apparatus in which the growth surface is directed downward or sideways, a susceptor in which the reaction part area of the fixing part necessary for fixing is expanded so that the growth part region satisfies the above conditions is provided. It may be prepared (25 in FIG. 3).

  The lower limit of the growth region is not particularly limited, but in order to efficiently use the base substrate and increase the productivity of the group III nitride crystal layer, the total area of the growth region is The design is preferably 10% or more with respect to the area of the entire main surface of the base substrate.

  In the present invention, it is essential that the thickness of the group III nitride crystal layer 14 grown and laminated on the base substrate 11 is 100 μm or more. The group III nitride crystal layer 14 will be described in detail below, but may be composed of only the group III nitride single crystal 12 as shown in FIG. 4, or the group III nitride as shown in FIG. The group III nitride polycrystalline layer 13 may be laminated on the single crystal 12.

  When this thickness is less than 100 μm, the rigidity of the group III nitride crystal layer becomes insufficient and stress relaxation due to deformation occurs, so that the group III nitride single crystal layer of the base substrate grew by the mechanism described later. Stress concentration is unlikely to occur at the boundary between the part and the part that has not grown. As a result, breakage propagates to the group III nitride crystal or cracks are introduced. Even if these adverse effects are avoided, the group III nitride crystal to be collected and the group III nitride crystal substrate obtained by processing the same have large warpage, so that the group III nitride single crystal vapor phase growth can be performed. The quality of the substrate (hereinafter referred to as a substrate for manufacturing a self-supporting substrate) is not sufficient. The upper limit of the thickness of group III nitride crystal layer 14 is not particularly limited, but is 500 μm in view of industrial production.

  The structure of the group III nitride crystal layer having a thickness of 100 μm or more is that if the layer directly in contact with the base substrate is a group III nitride single crystal layer, the crystal layer on the layer is a single crystal or a polycrystal. Also good. When it consists of only a single crystal, the layer will be 100 micrometers or more. When a polycrystalline layer is laminated on a single crystal layer, the total thickness needs to be 100 μm or more. In the latter case, it is preferable to set the thickness of the single crystal layer to 0.1 μm or more and 0.3 μm or less because crack introduction can be avoided almost certainly regardless of the conditions for polycrystalline deposition. In the case of the thickness within this range, even if a large stress is applied, a phenomenon peculiar to a thin film that achieves stress relaxation occurs by introducing a large number of fine defects instead of breaking or cracking. When a single crystal thicker than 0.3 μm and thinner than 100 μm is laminated, the above effect cannot be obtained. Therefore, unless a polycrystalline layer that effectively relieves stress is grown, it tends to be difficult to avoid breakage and cracks. .

  When the group III nitride crystal layer is composed of only a single crystal, it is possible to obtain a group III nitride crystal substrate made of a group III nitride single crystal by simply removing the base substrate after separation. The growth temperature may be limited from the viewpoint of the melting point of the substrate and the reaction between the base substrate and the group III nitride single crystal, and it tends to take a very long time to achieve a thickness of 100 μm or more with only the single crystal. On the other hand, when the group III nitride crystal layer has a double-layer structure of single crystal and polycrystal, generally, in the vapor phase growth method, the growth of the polycrystal is performed under a lower temperature condition than that of the single crystal as described later. Since it can be grown at high speed, it can be manufactured in a short time, and the energy cost can be reduced accordingly. Furthermore, in the case of a two-layer structure, defects are easily generated and moved at the grain boundaries formed in the polycrystalline layer, so that the obtained group III nitride crystal substrate is difficult to break, and the yield after the next step is high. It also has the advantage of improving. For the above reasons, the group III nitride crystal layer preferably has a two-layer structure in which a polycrystalline layer is stacked on a single crystal layer.

  Note that when an attempt is made to grow a polycrystal under extremely low temperature conditions, it takes a so-called amorphous form that does not take the form of crystal grains. In this embodiment, the same effect can be obtained, but the chemical resistance is relatively low. Therefore, when the single crystal substrate is removed by chemical treatment, it is necessary to examine the conditions so as not to disappear together.

  In the present invention, a group III nitride crystal layer may be grown on the base substrate so as to satisfy the above conditions. The conditions for growing the group III nitride crystal layer may be adjusted by adjusting the supply conditions of the source gas, the temperature during the growth, etc. in each vapor phase growth method. Even when the group III nitride crystal layer is composed of a group III nitride single crystal layer and a group III nitride polycrystalline layer, the manufacturing conditions may be adjusted in each vapor phase growth method. Hereinafter, a method for growing a group III nitride crystal layer by the HVPE method suitably employed in the method of the present invention will be described. The group III nitride will be described using a typical example of aluminum nitride (AlN).

  In order to form an AlN single crystal layer on a base substrate, first, the base substrate is heated for about 10 minutes at a high temperature of about 1100 ° C. for the purpose of removing organic substances adhering to the surface of the base substrate, and then thermal cleaning is performed. Is preferred. More desirably, it is preferably performed at 1200 ° C. or higher for 30 minutes or longer. Thermal cleaning may be performed by either an external heating device or a heating support. After the thermal cleaning, the base substrate temperature is heated to 800 ° C. to the substrate melting point, preferably 1000 ° C. to 100 ° C. lower than the substrate melting point, and supply of various source gases is started to form an AlN single crystal layer on the base substrate. . The reason why the temperature slightly lower than the melting point of the substrate is preferable is that the atoms constituting the base substrate are very easy to move near the melting point, so that the atomic arrangement on the surface is disturbed or the group III nitride crystal is grown. This is because an adverse effect of diffusing into the surface and disturbing the shape of the interface occurs.

  The supply amount of the aluminum trichloride gas is appropriately determined in consideration of the crystal growth rate on the base substrate. The nitrogen source gas is supplied so that the number of nitrogen atoms is 1 or more times the supply amount of aluminum atoms (hereinafter, this magnification is also referred to as V / III ratio).

  Aluminum trichloride gas can be obtained by reacting aluminum metal with hydrogen halide or chlorine. Specifically, for example, it can be produced by the method described in JP-A-2003-303774. Moreover, it can also manufacture by heating and vaporizing solid aluminum trichloride itself. In this case, it is preferable to use aluminum trichloride which is an anhydrous crystal and has few impurities. When impurities are mixed in the source gas, not only defects are generated in the formed crystal, but also changes in physical and chemical characteristics are required. Therefore, it is necessary to use a high-purity product as the gas source material.

  As the nitrogen source gas, a reactive gas containing nitrogen is adopted, but ammonia gas is preferable in terms of cost and ease of handling.

  Preferably, the aluminum halide gas and the nitrogen source gas are each diluted to a desired concentration with a carrier gas and introduced into the reaction vessel. At this time, hydrogen, nitrogen, helium, or a single gas of argon, or a mixed gas thereof can be used as a carrier gas, and an impurity gas component such as oxygen, water vapor, carbon monoxide, or carbon dioxide using a purifier in advance. Is preferably removed.

  When an AlN single crystal layer alone is used as an AlN crystal layer (when the AlN single crystal layer 12 is 100 μm or more), it is preferable to select conditions for increasing the growth rate of the single crystal among the above conditions. In order to increase the growth rate of the AlN single crystal, a high temperature of preferably 1250 ° C. or higher, more preferably 1350 ° C. or higher is desirable. In addition, when the reaction vessel is made of quartz, the service temperature is only about 1150 ° C. Therefore, when heating above this temperature, the reaction vessel is heated as disclosed in JP-A-2006-290662. It is preferable to employ a mechanism for heating only the growing AlN single crystal film. In addition, the upper limit of the temperature at the time of growing the AlN single crystal is 1700 ° C. in consideration of operability and the thermal decomposition reaction rate of the AlN single crystal and the substrate holding member. High speed growth of an AlN single crystal can be realized by performing the procedure taught in JP-A Nos. 2006-114845 and 2008-88048 after satisfying the above requirements.

  When only the AlN single crystal layer is used as the group III nitride crystal layer, a group III nitride crystal laminate in which the group III nitride crystal layer is laminated on the base substrate can be manufactured by the above method. Next, a growth method when the group III nitride crystal layer has a two-layer structure of a single crystal layer and a polycrystalline layer will be described.

  When forming a group III nitride crystal layer consisting of a single crystal and a polycrystalline two-layer structure, the conditions must generally be determined in consideration of the growth thickness of the single crystal and the growth efficiency in that case. When the growth thickness of the crystal layer is in the range of 0.1 μm to 0.3 μm described above, it is not always necessary to use conditions suitable for high-speed growth.

  The lamination of the group III nitride polycrystalline layer on the group III nitride single crystal layer is performed under the condition that deviates from the above-mentioned single crystal growth conditions. However, shifting to the high temperature condition side is not appropriate because it leads to melting of the base substrate. Effective operations include a method of lowering the temperature at which single crystal growth is difficult, or increasing the amount of raw material supply to several to several tens of times. In particular, an increase in the raw material supply amount is preferable because it leads to an improvement in the growth rate of the polycrystalline layer.

  When an AlN polycrystal layer is formed on an AlN single crystal layer by the HVPE method, the raw material supply amount is adjusted so that the growth rate is at least 20 μm / Hr at 1000 ° C. and at least 10 μm / Hr at 800 ° C. Switching from crystal growth to polycrystalline growth is realized. As another method, it is possible to switch from single crystal to polycrystalline growth by increasing the carrier flow rate to cause turbulent flow in the reaction vessel or changing the V / III ratio.

  According to the above method, an AlN polycrystal layer can be formed on an AlN single crystal layer, and a laminate in which a group III nitride crystal layer having a two-layer structure is laminated on a base substrate can be manufactured. it can.

Next, a method for cooling the laminate will be described.
For example, in the case of an AlN single crystal, the laminated body is generally manufactured at a temperature of 1100 ° C. or higher, although depending on the conditions of the vapor phase growth method. In the present invention, by cooling the laminated body manufactured at such a temperature, the boundary between the portion where the group III nitride single crystal layer has grown and the portion where it has not grown is selectively introduced into the base substrate. Cracks occur and group III nitride crystals separate spontaneously. This separation mechanism is considered as follows.

<1> By forming a growth part and a non-growth part of a group III nitride single crystal layer each having a certain area on a continuous base substrate, a compressive stress is applied to the base substrate surface of the growth part, and no growth occurs. No stress is applied to the surface of the base substrate.
<2> At this time, at the boundary between the growth part and the non-growth part, a tensile stress is applied toward the center of the group III nitride single crystal layer on the growth part side, and the non-growth part tries to stay there. Stress is applied.
<3> Since this tensile stress increases as the cooling progresses, the fracture occurs at a certain point exceeding the breaking strength of the base substrate.
<4> Inside the base substrate, thermal stress is generated by the group III nitride single crystal layer in the direction indicated by the arrow in FIG. 10 and the size indicated by the length of the arrow, so that the fracture occurs along this stress distribution. Proceeds and eventually spontaneously separates.

  The method for cooling the laminate is not particularly limited, and examples thereof include a method for cooling the inside of the reaction tube, for example, a method for stopping heating of crystal growth and flowing a carrier gas into the reaction apparatus. . In particular, when hydrogen is used as a carrier gas, in order to prevent re-decomposition of the group III nitride crystal grown on the base substrate, the nitrogen source gas may flow through the reaction vessel until the temperature of the substrate falls below 800 ° C. desirable.

  The cooling rate of the laminate is appropriately selected depending on the difference in thermal expansion coefficient and the breaking strength between the base substrate and the group III nitride crystal, but prevents the thermal shock cracking of the group III nitride crystal, and also within the base substrate. In order to effectively cause a crack, the temperature is preferably 5 ° C./min to 50 ° C./min, more preferably 10 ° C./min to 30 ° C./min. Furthermore, in order to ensure the reproducibility of the breakage of the base substrate, the laminated body has a constant cooling rate within the cooling rate range until it reaches a temperature range of 300 to 500 ° C. from the temperature range during growth. It is preferable to cool while keeping.

  Since the group III nitride crystal obtained by cooling is cracked and separated inside the base substrate, a part of the base substrate is adhered. The adhered base substrate can be removed by a conventionally known method, for example, a dissolution removal method by selective dissolution with an acid or alkali solution, or a polishing removal method by polishing with a diamond grindstone or diamond slurry.

  In the present invention, since only a part of the base substrate adheres to the group III nitride crystal layer, the base substrate is easily separated as compared with the conventional method to manufacture the group III nitride crystal substrate. be able to.

  In addition, in a method in which an external force such as a polishing removal method is applied, there is a risk that breakage or cracking may occur due to the stress remaining between the base substrate and the group III nitride crystal layer. Since the stress is partially released by the separation during cooling of the group nitride crystal, the probability of the occurrence of breakage and cracks can be reduced as compared with the case where the entire base substrate is separated. Further, in order to suppress the occurrence of breakage and cracks, it is preferable to employ a dissolution and removal method when there is a drug that can selectively dissolve only the base substrate. However, in the present invention, the entire base substrate is dissolved and removed. Since it is not necessary, the amount of medicine used can be reduced, and the base substrate can be separated in a short time. Hereinafter, the dissolution removal method will be described as an example.

  When the base substrate is single crystal silicon, an acid solution such as a mixed acid of hydrofluoric acid and nitric acid, or an alkaline solution such as a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, or a tetramethylammonium hydroxide aqueous solution is used as the solution. However, since these alkali solutions also dissolve group III nitrides in general, attention must be paid to the immersion method and concentration. The dissolution time depends on the concentration of the chemical solution and the amount of the attached base substrate, but 48 mass% hydrofluoric acid, 70 mass% nitric acid, high purity acetic acid, and ultrapure water are mixed at a volume ratio of 2: 1: 1: 1. In the case of using the obtained chemical solution, the group III nitride crystal of the present invention may be usually dissolved for about 0.5 to 2 hours.

  In any of the removal methods, in the production method of the present invention, it is only necessary to remove the fragment of the base substrate attached to the group III nitride crystal, so that the removal operation is easy and advantageous in terms of cost.

  The group III nitride crystal substrate of the present invention is obtained by removing the base substrate attached to the group III nitride crystal. Since the substrate effectively suppresses thermal stress generated during growth and cooling by various devices, a substrate for manufacturing a self-supporting substrate having a single crystal portion with no warping and no warping or cracking, or self-supporting Can be a substrate.

  For the measurement and management of the thickness of the laminated body, a method of performing contact type measurement with a micrometer on the group III nitride crystal substrate after removal of the base substrate is simple. Since the contact-type measurement may damage the crystal surface, a three-dimensional shape measuring apparatus capable of measuring the thickness after irradiating laser from both sides and excluding the influence of warpage may be used.

  For breaks and cracks, a differential interference microscope is used to make the step visible, and if it is not visually recognized, there will be no hindrance to the use described later. The amount of warpage can be easily measured with an optical interference microscope, a laser interferometer, or the like, and is generally evaluated by a radius of curvature or its reciprocal. The group III nitride crystal substrate obtained by the present invention is considered to be applicable to uses described later as long as the radius of curvature is 1 m or more, and it is possible to produce a substrate exceeding 10 m.

  Therefore, the group III nitride crystal substrate obtained by the present invention can be used as a self-supporting substrate for stacking ultraviolet light emitting elements, but the group III nitride single crystal of the substrate is exposed. A thick group III nitride single crystal substrate having excellent crystallinity can be obtained by growing a group III nitride single crystal on the single crystal using the surface thus formed as a base. Next, a method for manufacturing the group III nitride single crystal substrate (free-standing substrate) will be described.

  As a method for growing a group III nitride single crystal in the production of the group III nitride single crystal substrate, the above-described various vapor phase growth methods and conditions are employed. The underlying substrate used for single crystal growth originally needs a planarization step corresponding to the CMP polishing process, but according to the step of the present invention, the RMS value already shows a value on the order of nm when the fragment of the base substrate is removed. Since a good surface has already been obtained, conventional processes can be omitted.

  After the single crystal is grown to the required thickness, if the group III nitride crystal substrate as the base substrate has a single-crystal / polycrystalline double-layer structure, the polycrystalline layer portion can be formed by a known method, for example, a wire saw Or a cutting method using a diamond cutter, or a grinding method using a surface grinder or the like, to obtain a group III nitride single crystal substrate composed only of a group III nitride single crystal.

  The group III nitride crystal substrate and the group III nitride single crystal substrate made of only the group III nitride single crystal of the present invention thus obtained can withstand handling as a free-standing substrate if the thickness is 100 μm or more. Has strength. Therefore, the obtained group III nitride single crystal substrate having a thickness of several hundred μm or more is further thinly cut to produce a plurality of group III nitride single crystal substrates (substrate for self-standing substrate production), or A thinly cut substrate can be used as a self-supporting substrate. Although the existing non-oxide ceramic processing technology can be used without limitation for the method of cutting the group III nitride single crystal substrate, a method that reduces the amount of wear during processing is desirable, and a cutting method using a wire saw or a diamond cutter is preferable. is there.

  The obtained group III nitride single crystal substrate is self-supported for stacking an ultraviolet light emitting element after heat treatment in a nitrogen atmosphere or a reducing atmosphere or after performing post-treatment such as surface cleaning with aqua regia. It can be used as a substrate or a substrate for regrowing a group III nitride single crystal (a substrate for producing a self-supporting substrate).

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples. In addition, not all combinations of features described in the embodiments are essential to the solution means of the present invention.

Example 1
In this example, an aluminum nitride single crystal and a polycrystal were grown using the reactor shown in FIG. 3, and then an aluminum nitride crystal substrate was obtained after cooling.

  Here, the group III compound supply pipe (26) is provided with a reaction furnace in which metal aluminum pellets are placed upstream and heated to 500 ° C., and hydrogen chloride gas is supplied to generate aluminum trichloride gas. Ammonia was supplied from the nitrogen raw material supply pipe (27), and both pipes were heated to 200 ° C. or higher while the raw material was flowing. In this example, the external heating device (23) was not used as a heat source.

  A silicon single crystal substrate having a {1 1 1} plane as a main surface was used as the base substrate. The dimensions are 50.8 mm (2 inches) in diameter and 1.0 mm in thickness. The surface that was subjected to the CMP polishing treatment was defined as a group III nitride growth surface. This base substrate was immersed in a 5 mass% hydrofluoric acid aqueous solution for 30 seconds to remove the oxide film and to perform a hydrogen termination treatment.

  The base substrate is fixed at position 24 in FIG. 3 with a holding susceptor (25) made of pyrolytic boron nitride having a circular shape with a diameter of 26 mm, with the opening positioned in the center, with the growth surface facing downward. did. That is, the distance from the base substrate end to the opening end is 12.4 mm. In this state, the pressure was once reduced to 1 Torr or lower, and after returning to atmospheric pressure with nitrogen gas, the pressure was again reduced to 1 Torr or lower to discharge air. Then, hydrogen was introduced from the group III compound supply pipe and the nitrogen material supply pipe, the pressure was restored to atmospheric pressure, the local heating device (22) was energized, and heating was started at 20 ° C./min. During heating and growth, the internal pressure of the vessel and the gas flow rate from both pipes were fixed to form a steady flow. The gas flow rate here refers to the total of the hydrogen flow rate during heating and cooling, the hydrogen flow rate during growth, and the raw material gas flow rate.

After reaching the AlN single crystal growth temperature of 1200 ° C., the temperature distribution was stabilized and the raw material was held for 40 minutes without flowing to perform thermal cleaning, and then supply of aluminum trichloride gas and ammonia gas was started. The supply amount is 5.0 × 10 ⁻⁴ atm for aluminum trichloride gas and 16 times that for ammonia gas, mixed with hydrogen as a carrier gas and sprayed onto the base substrate, and both are applied onto the base substrate. By reacting, an aluminum nitride single crystal was synthesized. After maintaining in this state for 5 minutes, the supply of aluminum trichloride gas was stopped, and the flow was continued without changing the supply amount of only ammonia gas, and the mixture was cooled to 1000 ° C. at 20 ° C./min.

At 1000 ° C., the raw material was held without flowing for 5 minutes to stabilize the temperature distribution, and then the supply of aluminum trichloride gas was resumed to start growth. Here, the supply rate was 1.0 × 10 ⁻² atm for both aluminum trichloride gas and ammonia gas to promote high-speed growth. After maintaining in this state for 90 minutes, the supply of aluminum trichloride gas was stopped again and cooling was started at 20 ° C./min.

  When the temperature dropped to 800 ° C., the supply of ammonia gas and hydrogen gas was stopped, and the cooling was continued by switching to nitrogen gas at the same flow rate. After cooling to 500 ° C., the output of the local heating device was turned off and the system was allowed to cool without changing the flow rate of nitrogen gas.

  When the laminate was recovered after cooling to room temperature, it was confirmed that the aluminum nitride crystal was separated from the base substrate together with a part of the base substrate. As described above, crystal growth was performed with the growth surface facing downward, but the spontaneously separated aluminum nitride crystal body had almost the same shape as the opening of the holding susceptor. This is immersed in a chemical solution in which 48 mass% hydrofluoric acid, 70 mass% nitric acid, high-purity acetic acid, and ultrapure water are mixed at a volume ratio of 2: 1: 1: 1 for 1 hour, and the amount adhered to the base substrate is chemically treated. To obtain an aluminum nitride crystal substrate comprising a combination of a single crystal layer and a polycrystalline layer. There was no evidence of cracks or breaks on the surface of the single crystal layer that appeared after the removal, and it was glossy as if the original polished surface of CMP of silicon was transferred. When the surface roughness was evaluated with a scanning probe microscope, the RMS value was 2.6 nm.

  The glossy surface from which the silicon was removed was subjected to three-dimensional shape measurement using an optical interference microscope, and the curvature radius was calculated. Here, it is assumed that the sign of the curved surface is expressed by positive sign when the surface forming the interface with silicon forms a concave surface and negative sign when forming a convex surface. The curvature radius of the aluminum nitride crystal substrate obtained in this example was -2.7 m. The thickness was 213 μm, and the growth rate of the polycrystalline layer in this example was 141.8 μm / hour. The weight was 0.3127 g, and silicon adhering during spontaneous separation was 0.2913 g. To completely dissolve the adhered silicon, 14 mL of hydrofluoric acid was required, and the time required for dissolution was 50 minutes.

Example 2
In this example, the central opening of the susceptor is made larger than that in Example 1, and a large-area aluminum nitride crystal substrate is manufactured. The other experimental conditions were the same as in Example 1.

  As the base substrate, a silicon single crystal substrate having a {1 1 1} plane as a main surface was used. The dimensions are 50.8 mm (2 inches) in diameter and 1.0 mm in thickness. Here, a treatment for enlarging the growth region was performed with the opening located at the center of the pyrolytic boron nitride susceptor holding the substrate having a diameter of 40 mm. The distance from the base substrate end to the opening end is 5.4 mm.

  In the crystal stack after cooling, the aluminum nitride crystal including a part of the base substrate was recovered in the same manner as in Example 1 while maintaining the shape of φ40 mm in the growth part. The base substrate side had a recess that matched the shape of the silicon peeled off accompanying the aluminum nitride laminate, and the substrate was recovered without breaking into multiple pieces. The aluminum nitride crystal substrate after the base substrate was dissolved by the mixed acid had no evidence of cracks or breaks on the surface of the single crystal layer, and formed a flat surface having gloss as in Example 1.

  The radius of curvature of the aluminum nitride crystal substrate obtained in this example was -3.6 m in the central diameter range of 20 mm, and a distribution of -1.9 m at the outer periphery. However, conditions sufficient for practical use were satisfied, and the flatness of the surface was sufficiently secured at 2.2 nm in terms of RMS value. The thickness was 225 μm at the center, 190 μm near the outer periphery, the weight was 0.7732 g, and the silicon deposited during spontaneous separation was 0.6006 g. In order to completely dissolve the adhered silicon, 50 mL of hydrofluoric acid was required, and the time required for dissolution was 95 minutes.

Example 3
In this example, an aluminum nitride crystal substrate was manufactured using a base substrate that was thinner than the base substrate used in Example 1, and the other experimental conditions were the same as in Example 1.

  As the base substrate, a silicon single crystal substrate having a {1 1 1} plane as a main surface was used. The dimensions are 50.8 mm (2 inches) in diameter and 0.28 mm in thickness.

  In the laminated body after cooling, the aluminum nitride crystal body including a part of the base substrate was recovered in the same manner as in Example 1, with the growth portion having a diameter of 26 mm. However, since the base substrate was thin, it was not a rupture that peeled off from the base substrate as in Example 1, but a shape in which a crack penetrated the base substrate and was cut into a circle. The outer peripheral base substrate had radial cracks and was broken into eight.

  The aluminum nitride crystal substrate after the base substrate was dissolved by the mixed acid had no evidence of cracks or breaks on the surface of the single crystal layer, and formed a flat surface having gloss as in Example 1. However, since the rigidity of the base substrate is small and greatly deformed due to thermal stress, the radius of curvature of the aluminum nitride crystal substrate obtained in this example was −1.2 m, which was more distorted than in Example 1. . However, the flatness of the surface was ensured, and the RMS value was 2.9 nm. The thickness was 215 μm, the weight was 0.3195 g, and the silicon deposited during spontaneous separation was 0.3411 g. To completely dissolve the adhered silicon, 30 mL of hydrofluoric acid was required, and the time required for dissolution was 70 minutes.

Example 4
In this embodiment, the aluminum nitride crystal substrate obtained in Example 1 is used as a base substrate, and an aluminum nitride single crystal is further grown thereon. After the growth, the polycrystalline portion is removed to produce an aluminum nitride single crystal substrate. This is an example.

  The underlying substrate used for single crystal growth requires a planarization step corresponding to the conventional CMP polishing process. However, as described in Example 1, a good surface exhibiting an RMS value on the order of nm has already been obtained. The conventional process was omitted.

The same apparatus as used in Example 1 was used for crystal growth, and the holding susceptor made of pyrolytic boron nitride was changed to one having an opening of 22 mm in diameter to prevent the growth substrate from falling. The supply method such as generation method of aluminum trichloride gas and pipe temperature control was the same. The heating rate was the same, but the gas supplied during the heating was mixed with ammonia having a partial pressure of 5.0 × 10 ⁻⁴ atm in addition to hydrogen gas. This prevents the thermal decomposition of the aluminum nitride and preserves the aluminum nitride single crystal layer on the surface.

The AlN single crystal growth temperature was heated to 1400 ° C., and the aluminum trichloride gas was held without flowing for 40 minutes to stabilize the temperature distribution, and then the supply of aluminum trichloride gas was started. Nitrogen trichloride gas and ammonia gas are mixed with hydrogen as a carrier gas and sprayed onto the base substrate so that both the aluminum trichloride gas and ammonia gas are 5.0 × 10 ⁻³ atm, and both are reacted on the base substrate to perform nitriding Aluminum single crystals were synthesized.

  After maintaining in this state for 1200 minutes, the supply of aluminum trichloride gas was stopped, and the flow was continued without changing the supply amount of only ammonia gas, and the mixture was cooled to 800 ° C. at 20 ° C./min. When the temperature dropped to 800 ° C., the supply of ammonia gas and hydrogen gas was stopped as in Example 1, and the cooling was continued by switching to nitrogen gas at the same flow rate. After cooling to 500 ° C., the output of the local heating device was turned off and the system was allowed to cool without changing the flow rate of nitrogen gas.

  The growth surface after cooling had a shape in which hexagonal pyramids were spread, and the directions were uniform. When the three-dimensional shape measurement was performed on the laminated body with an optical interference microscope and the overall warpage was measured, the result was changed from −2.7 m, which is the result of Example 1, to +4.5 m. This is considered to be a phenomenon that occurs because the polycrystalline layer of the base substrate has an a-axis and a c-axis of aluminum nitride that are irregular, and has a slightly larger coefficient of thermal expansion than the a-axis direction of the single crystal layer. The occurrence of breakage and cracks due to this difference in thermal expansion coefficient was not confirmed. The total thickness of the base substrate and the growth layer measured with a micrometer was 1033 μm, and the average growth rate over 20 hours was 41 μm per hour.

  The laminated body was embedded in an epoxy resin, and the polycrystalline layer side was ground together with the epoxy resin with a surface grinder to remove the polycrystalline layer. Thereafter, polishing with diamond slurry was performed on both sides to prepare the shape as a substrate. The thickness of the aluminum nitride single crystal substrate after this step was 340 μm.

Example 5
In this example, an aluminum nitride crystal substrate was manufactured by replacing the base substrate with a material other than single crystal silicon, and the other experimental conditions were the same as in Example 1.

  As the base substrate, a silicon carbide single crystal substrate having a {0 0 0 1} plane as a main surface was used. The dimensions are 50.8 mm (2 inches) in diameter and 0.26 mm in thickness. Whereas the thermal expansion coefficient of aluminum nitride = 4.2 ppm / ° C., the thermal expansion coefficient of silicon carbide is 2.8 ppm / ° C., which satisfies the conditions of the base substrate required in the present invention.

  In the crystal stack after cooling, the aluminum nitride crystal including a part of the base substrate was recovered in the same manner as in Example 1 while maintaining the shape of φ26 mm in the growth portion. On the base substrate side, a portion having a recess matching the shape of the silicon carbide peeled off accompanying the aluminum nitride laminate was cut out in a circular shape, and the outer peripheral base substrate was cracked in three with radial cracks. The silicon carbide adhering at the time of spontaneous separation was 0.0627 g. In order to remove silicon carbide from the crystal laminate, a three-stage treatment was performed. First, after embedding and reinforcing in a thermoplastic resin, a polishing process was performed to remove a step of several μm or more. Subsequently, carbon tetrafluoride and oxygen were supplied in a reactive ion etching apparatus to generate reactive plasma, and etching was performed until the remaining silicon carbide was 0.0050 g or less. Finally, the surface oxidation treatment for supplying only oxygen and the oxide film removal treatment by 48 mass% hydrofluoric acid immersion were repeated to expose the aluminum nitride single crystal layer. The radius of curvature of the aluminum nitride crystal substrate obtained in this example was −1.3 m, which was the same as that obtained when single crystal silicon having substantially the same shape was used as the base substrate. However, the flatness of the surface was impaired by the damage of the plasma treatment, and the RMS value was 30.8 nm.

Comparative Example 1
In this example, the base substrate is an example in which an aluminum nitride crystal substrate is collected in place of a material whose thermal expansion coefficient relationship with the group III nitride crystal to be grown does not satisfy the present invention, and other experimental conditions are Same as Example 1.

  As the base substrate, an α-alumina single crystal substrate (sapphire substrate) having a {0 0 0 1} plane as a main surface was used. The dimensions are 50.8 mm (2 inches) in diameter and 0.43 mm thickness. Compared to the physical properties of aluminum nitride (coefficient of thermal expansion = 4.2 ppm / ° C.), the coefficient of thermal expansion of sapphire is 7.0 ppm / ° C., which is opposite to the base substrate conditions required in the present invention.

  The laminated body after cooling was recovered in a shape broken to 6 pieces from the center together with the sapphire substrate. The sapphire substrate has a larger coefficient of thermal expansion than aluminum nitride, and because the compressive stress is applied to the sapphire substrate side at the boundary between the growth part and the non-growth part that started breaking in Example 1, it failed to induce the breakage point. It is thought that random fracture occurred on the entire substrate. Further, since sapphire has a very high chemical resistance, the surface after separation of the base substrate could not be confirmed.

Comparative Example 2
In this example, the growth region was expanded to a region within 5 mm from the outer periphery, and the other experimental conditions were the same as in Example 1.

  As the base substrate, a silicon single crystal substrate having a {1 1 1} plane as a main surface was used. The dimensions are 50.8 mm (2 inches) in diameter and 1.0 mm in thickness. Here, a treatment for enlarging the growth region was performed with the opening located in the center of the pyrolytic boron nitride susceptor holding the substrate having a diameter of 48 mm. At this time, the non-growth part on the base substrate is an area from the outer periphery to 1.4 mm.

  The laminated body after cooling was recovered in such a manner that the spontaneous separation of the base substrate and the aluminum nitride crystal, which had been completed in Example 1, was stopped halfway. The starting points of the cracks for spontaneous separation varied from the main surface of the substrate to the side surface of the substrate, and these cracks stopped near the center of the substrate. On the side where no cracks occurred, there was no escape site for thermal stress, so cracks occurred on both the base substrate and the aluminum nitride crystal.

  When trying to dissolve the base substrate with mixed acid in this shape, the base substrate at the place where the cracks for spontaneous separation progressed and the place where it did not progress soon separated and became spontaneously separated locally. . The single crystal layer surface of the aluminum nitride crystal substrate after dissolution of the base substrate was flat as in Example 1, but breakage occurred at the position of the crack generated at the time of recovery, and the disk with a maximum diameter of 48 mm was almost halved. Only a semi-circular aluminum nitride crystal was collected. Since it was necessary to dissolve the entire base substrate having a thickness of 1.0 mm, 110 mL of hydrofluoric acid was required to completely dissolve the silicon of this laminate, and the time required for dissolution was It was 11 hours.

Comparative Example 3
In this example, the thickness of the growth crystal part of the aluminum nitride laminate was set to 100 μm or less, and the other experimental conditions were the same as in Example 1.

  As the base substrate, a silicon single crystal substrate having a {1 1 1} plane as a main surface was used. The dimensions are 50.8 mm (2 inches) in diameter and 1.0 mm in thickness. The equipment used, the method of generating aluminum trichloride gas, the piping temperature control, etc. were also the same. The conditions necessary for AlN single crystal growth and the conditions for cooling to 1000 ° C. for growing a polycrystalline layer were the same as in Example 1.

At 1000 ° C., the raw material was held without flowing for 5 minutes to stabilize the temperature distribution, and then the supply of aluminum trichloride gas was resumed to start growth. Here, the supply rate was 1.0 × 10 ⁻² atm for both aluminum trichloride gas and ammonia gas to promote high-speed growth. From the growth rate confirmed in Example 1, the growth time when the stack thickness becomes 100 μm or less is calculated, and after maintaining for 30 minutes in this state, the supply of aluminum trichloride gas is stopped again at 20 ° C./min. Cooling started. When the temperature dropped to 800 ° C., the supply of ammonia gas and hydrogen gas was stopped, and the cooling was continued by switching to nitrogen gas at the same flow rate. After cooling to 500 ° C., the output of the local heating device was turned off and the system was allowed to cool without changing the flow rate of nitrogen gas.

  The laminated body after cooling was cracked while adhering to the base substrate, and was not spontaneously separated. It is considered that the base substrate was broken by the tensile stress applied to the aluminum nitride laminate before the base substrate started to break.

  The aluminum nitride crystal substrate after the base substrate was dissolved by the mixed acid was separated along the cracks confirmed immediately after cooling, and recovered as seven pieces. There were no evidence of cracks or breaks on the surface of each single crystal layer, and a flat surface having gloss was formed as in Example 1. The thickness of the aluminum nitride crystal substrate was 76 μm and the total weight was 0.1140 g. Since it was necessary to dissolve the entire base substrate having a thickness of 1.0 mm, 250 mL of hydrofluoric acid was required to completely dissolve the silicon of this laminate, and the time required for dissolution was 13 hours. .

  The group III nitride single crystal substrate of the present invention is suitable as a material for a semiconductor device manufacturing substrate material such as an ultraviolet light emitting device or a material for a package component or heat sink component of a device having a high heat generation density such as a central processing unit (CPU) of a computer. Can be used for

11 Base substrate (single crystal substrate)
12 Group III Nitride Single Crystal Layer 13 Group III Nitride Polycrystalline Layer 14 Group III Nitride Crystal Layer 15 Group III Nitride Crystal Stack 16 Group III Nitride Crystal Growth Section 17 Group III Nitride Crystal 18 Group III Nitride Material crystal substrate 19 Group III nitride single crystal substrate 21 Reaction vessel 22 Local heating device 23 External heating device 24 Base substrate 25 Base substrate holding susceptor 26 Group III material supply piping 27 Nitrogen material supply piping 31 Base substrate 32 Group III nitride crystal Layer growth part 41 Base substrate 42 Raw material shielding member

Claims (6)

A group III nitride single crystal including a group III nitride single crystal layer is laminated on a single crystal substrate by growing a group III nitride single crystal by a vapor phase growth method, and the single crystal substrate is obtained from the obtained laminate. In the method for producing a group III nitride crystal substrate comprising a group III nitride crystal layer by removing
Select a substrate having a smaller coefficient of thermal expansion than the group III nitride single crystal layer as the single crystal substrate,
The growth part of the group III nitride single crystal is set to an area at least 5 mm or more from the outer periphery of the single crystal substrate,
A laminate is manufactured so that the thickness of the group III nitride crystal layer is 100 μm or more,
The laminated body is cooled to cause a crack inside the single crystal substrate to separate the group III nitride crystal layer,
Next, the single crystal substrate attached to the separated group III nitride crystal layer is removed.   The group III nitride crystal layer according to claim 1, wherein the group III nitride crystal layer is a crystal layer having a two-layer structure in which a group III nitride polycrystalline layer is formed on a group III nitride single crystal layer. A method for manufacturing a nitride crystal substrate.   The method for producing a group III nitride crystal substrate according to claim 1 or 2, wherein the thickness of the single crystal substrate on which the group III nitride single crystal is grown is 600 µm or more.   The method for producing a group III nitride crystal substrate according to any one of claims 1 to 3, wherein the single crystal substrate is single crystal silicon, and the group III nitride is aluminum nitride.   A group III nitride crystal substrate is manufactured by the manufacturing method according to claim 1, and a surface of the substrate on which the group III nitride single crystal is exposed is used as a base, and further on the single crystal. A method for producing a group III nitride single crystal substrate, comprising growing a group III nitride single crystal.   6. The method for producing a group III nitride single crystal substrate according to claim 5, wherein the group III nitride single crystal is aluminum nitride.

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