Method for producing modified aluminum nitride raw material, modified aluminum nitride raw material, method for producing aluminum nitride crystal, collapse suppression method

Abstract

An object of the present invention is to provide a modified AlN raw material that suppresses collapse. A method for producing a modified aluminum nitride raw material includes a heat treatment step of heat treating an aluminum nitride raw material and producing an aluminum nitride sintered body.

Description

Technical Field

[0001] This invention relates to a method for manufacturing modified aluminum nitride raw materials, a method for manufacturing modified aluminum nitride raw materials and aluminum nitride crystals, and a method for suppressing collapse. Background Technology

[0002] Aluminum nitride (AlN) has high thermal conductivity and excellent electrical insulation properties, and is widely used in various applications, primarily as semiconductor substrates and semiconductor packaging substrates.

[0003] In recent years, AlN's wide bandgap (6.28eV) has attracted attention, with the expectation of its application in light-emitting diodes (LEDs) that output deep ultraviolet (UV-C).

[0004] However, since AlN monomer substrates are small in diameter and expensive, heterogeneous substrates obtained by forming AlN films on substrates made of other materials are often used as large-diameter and inexpensive substrates.

[0005] For example, Patent Document 1 describes a substrate comprising: a sapphire substrate, a first AlN film formed on a first main surface of the sapphire substrate, and an AlN film formed on a second main surface of the sapphire substrate opposite to the first main surface.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2019-151520 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] Because AlN is a high-melting-point material, it is difficult to grow single crystals using melting methods that can easily produce large-diameter, high-quality single crystals like silicon. Therefore, single crystal growth centered on vapor-phase methods is required.

[0011] However, the diameter of sufficiently high-quality aluminum nitride single-crystal wafers used as semiconductor substrates is currently limited to 2 inches.

[0012] Anisotropy during AlN crystal growth is one of the reasons why high-quality, large-diameter AlN single crystals cannot be manufactured.

[0013] For AlN, thermodynamically, growth in the c-direction (perpendicular to the growth surface) is better than growth in the m-direction (parallel to the growth surface), and there is a problem that growth is difficult in the direction of increasing wafer diameter.

[0014] Thus, since it is difficult to increase the wafer diameter in the homogeneous growth of AlN single crystals, a method is considered to perform heterogeneous growth of AlN crystals on SiC substrate with a larger wafer diameter and a smaller lattice mismatch with AlN.

[0015] However, as Figure 1 As shown, the thermal expansion coefficients of AlN growth layer 10 and SiC substrate 20 are very different. During the cooling process of AlN crystal growth, the shrinkage rate of AlN is higher than that of SiC, which leads to the problem of many cracks in AlN growth layer 10.

[0016] To address this problem, the inventors have proposed a method that reduces the stress on AlN during cooling caused by the difference in thermal expansion coefficients between AlN and SiC by using a brittle SiC substrate 21 obtained through processing such as through-processing to reduce the strength of the SiC substrate and increase its expansion and contraction rates. (This is filed on the same day as this application, see reference 1). Figure 2 ).

[0017] By implementing processing to improve the expansion and contraction rate of the SiC substrate, cracks are generated in the brittle SiC substrate 21 during cooling. In the AlN growth layer 10A, crack generation can be suppressed.

[0018] Thus, the inventors have discovered a method for suppressing crack generation during AlN heterogeneous growth, but further challenges remain in applying this method to practical applications.

[0019] Because the mechanical strength of the aforementioned brittle SiC substrate 21 is significantly reduced, the conventional face-down method (where the growth surface of the substrate faces down and the AlN growth material 40 is placed at a position opposite to the growth surface) suffers from the problem of bending due to weight and substrate breakage because only the edge of the brittle SiC substrate 21 is supported. Figure 3 ).

[0020] To address this problem, the inventors have explored a method of changing the conventional face-down method to a face-up method (where the growth surface of the substrate faces upward and the AlN growth material 40 is disposed at a position opposite to the growth surface). Figure 4 ).

[0021] In the face-up configuration, since the entire SiC brittle substrate 21 can be supported, bending will not occur even when the strength of the SiC brittle substrate 21 is significantly low.

[0022] On the other hand, since the AlN growth material 40 is located on top, it adheres to the SiC substrate in a solid state (collapse). This collapse becomes the starting point of defects and a major factor in the polycrystalline formation of the AlN growth crystal. Figure 4 ).

[0023] Therefore, the object of the present invention is to provide a modified AlN raw material that suppresses collapse.

[0024] Problem-solving methods

[0025] The present invention, which solves the above problems, is a modified aluminum nitride raw material, which has a bulk density of 2.0 g / cm³. 3 It consists of aluminum nitride sintered bodies with an open porosity of less than 10%.

[0026] This modified aluminum nitride material suppresses collapse and is suitable as a source material for face-down crystal growth.

[0027] In a preferred embodiment of the present invention, the carbon content is less than 1000 ppm and the oxygen content is less than 10000 ppm.

[0028] In a preferred embodiment of the present invention, the modified aluminum nitride raw material is used as a source material for the crystal growth of aluminum nitride.

[0029] The present invention, which solves the above problems, is also a method for manufacturing modified aluminum nitride raw materials, including a heat treatment step of heating the aluminum nitride raw materials to generate an aluminum nitride sintered body.

[0030] By heating the aluminum nitride raw material, even when AlN crystals are grown in an upward-facing configuration, modified aluminum nitride raw materials with suppressed collapse can be produced.

[0031] In a preferred embodiment of the present invention, an etching step for etching the aluminum nitride sintered body is also included.

[0032] Etching aluminum nitride sintered bodies can produce raw materials with better collapse suppression effects.

[0033] In a preferred embodiment of the present invention, the etching step is a chemical etching step.

[0034] In a preferred embodiment of the present invention, the heat treatment step is a pressure sintering step.

[0035] In a preferred embodiment of the present invention, the heat treatment step is a discharge plasma sintering step.

[0036] In a preferred embodiment of the present invention, the heat treatment step is a pressureless sintering step, and includes a forming step prior to the heat treatment step of shaping the aluminum nitride raw material to form an aluminum nitride molded body.

[0037] In a preferred embodiment of the present invention, the modified aluminum nitride raw material is a source material for the crystal growth of aluminum nitride.

[0038] Furthermore, the present invention that solves the above problems is a modified aluminum nitride raw material, which is manufactured by the aforementioned manufacturing method.

[0039] Furthermore, the present invention, which solves the above problems, is also a method for manufacturing aluminum nitride crystals, including a crystal growth step of using a modified aluminum nitride raw material generated by heating aluminum nitride raw material as a source material for growing aluminum nitride crystals and growing aluminum nitride crystals on a substrate.

[0040] According to the method for manufacturing aluminum nitride crystals of the present invention, aluminum nitride crystals with fewer defects and suppressed collapse during the manufacturing process can be manufactured.

[0041] In a preferred embodiment of the present invention, the substrate and the modified aluminum nitride material are arranged with their faces facing upwards.

[0042] In a preferred embodiment of the present invention, the modified aluminum nitride raw material has a bulk density of 2.0 g / cm³. 3 Aluminum nitride sintered bodies with an open porosity of 0-10% are described above.

[0043] Furthermore, the present invention, which solves the above problems, is also an aluminum nitride crystal, manufactured by the aforementioned manufacturing method.

[0044] The aluminum nitride crystals of the present invention have low defects, particularly low particle density caused by collapse.

[0045] Furthermore, the present invention, which solves the above problems, is a method for suppressing the collapse of aluminum nitride raw materials in the crystal growth of aluminum nitride, wherein the method uses modified aluminum nitride raw materials generated by heat treatment of aluminum nitride raw materials as the source raw materials for growing aluminum nitride crystals on a substrate.

[0046] In a preferred embodiment of the present invention, the substrate and the modified aluminum nitride raw material are configured with their faces facing upwards.

[0047] In a preferred embodiment of the present invention, the modified aluminum nitride raw material has a bulk density of 2.0 g / cm³. 3 Aluminum nitride sintered bodies with an open porosity of 0-10% are described above.

[0048] The effects of the invention

[0049] According to the present invention, collapse during the growth of aluminum nitride crystals can be suppressed, and low-defect aluminum nitride single crystals can be manufactured. Attached Figure Description

[0050] Figure 1 This diagram illustrates the crack formation mechanism in an AlN growth layer with SiC as the substrate.

[0051] Figure 2 This diagram illustrates the mechanism for suppressing crack formation in an AlN growth layer with SiC as the substrate having through holes.

[0052] Figure 3 This diagram shows the state of a SiC substrate with through-holes configured face down.

[0053] Figure 4 This is a diagram showing the collapse state of AlN powder raw material when it is held face up.

[0054] Figure 5 This is an explanatory diagram illustrating the difference between apparent density and bulk density.

[0055] Figure 6 This is an explanatory diagram illustrating the crystal growth steps in the manufacturing method of AlN crystals using modified AlN raw materials.

[0056] Figure 7 This is a graph showing the apparent density and bulk density of each modified AlN raw material.

[0057] Figure 8 This is a diagram showing the apparatus structure in the AlN crystal growth process.

[0058] Figure 9 The graph shows the relationship between particle density and annealing time on the AlN crystal growth surface, as well as SEM and optical microscope images of the AlN crystal growth surface. Detailed Implementation

[0059] (1) AlN raw materials

[0060] This invention relates to a method for manufacturing modified AlN raw materials by heat treatment of aluminum nitride (AlN) raw materials.

[0061] In this invention, AlN raw material refers to raw material that generates AlN sintered body through heat treatment, including not only AlN powder, granules (powder-granules), and shaped bodies, but also Al powder-granules and Al shaped bodies. Al powder-granules and Al shaped bodies are heated under a nitrogen atmosphere to undergo a nitriding reaction, thereby generating AlN sintered body.

[0062] When using powdered particles as AlN raw materials, the median particle size (d50) of the powdered particles is preferably 50 μm or less, more preferably 30 μm or less, even more preferably 10 μm or less, particularly preferably 5 μm or less, more preferably 3 μm or less, and most preferably 1 μm or less.

[0063] By using powder particles with small median particle size as AlN raw materials, modified AlN raw materials with better collapse inhibition can be manufactured efficiently.

[0064] As an AlN raw material, the impurity content is preferably 10,000 ppm or less. More preferably, the impurity content of the AlN raw material is 8,000 ppm or less, even more preferably 6,000 ppm or less, and particularly preferably 5,000 ppm or less.

[0065] Furthermore, even among the impurities contained in the AlN raw material, the content of carbon atoms (C) is preferably 1000 ppm or less, more preferably 800 ppm or less, even more preferably 600 ppm or less, particularly preferably 400 ppm or less, even more preferably 200 ppm or less, and most preferably 100 ppm or less.

[0066] Furthermore, even among the impurities contained in the AlN raw material, the content of oxygen atoms (O) is preferably 10,000 ppm or less, more preferably 8,000 ppm or less, even more preferably 6,000 ppm or less, and particularly preferably 5,000 ppm or less.

[0067] When AlN raw materials containing a large number of impurities are used as raw materials for AlN crystal growth, defects caused by the impurities may be introduced into the AlN crystal. Therefore, it is preferable to use AlN raw materials with fewer impurities.

[0068] AlN feedstock is preferably produced by direct nitriding of aluminum. This method produces AlN feedstock with low impurity content.

[0069] (2) Heat treatment steps

[0070] The heat treatment method for AlN raw materials is not particularly limited, except for so-called pressureless sintering and pressure sintering, and also includes heat treatment performed under conditions that result in the formation of AlN sintered bodies.

[0071] As a form of pressureless sintering, examples include atmosphere sintering, thermal plasma sintering, and microwave / millimeter-wave sintering. Reaction sintering can also be performed when Al powder particles are used as the AlN raw material.

[0072] As a type of pressure sintering, examples include hot pressing sintering (HP), vacuum hot pressing sintering (VHP), and discharge plasma sintering (pulse energizing method, pulse energizing pressure sintering method, SPS), etc.

[0073] In this invention, the AlN sintered body is preferably manufactured by pressure sintering, and more preferably by discharge plasma sintering.

[0074] Discharge plasma sintering is a method that directly applies pulsed voltage and current to a graphite sintering mold and the material to be sintered, utilizing self-heating and pressure as the driving force for sintering. Compared to atmosphere heating using electric furnaces or similar methods, it enables rapid heating and cooling. Therefore, it can efficiently manufacture dense sintered bodies that suppress grain growth.

[0075] In the manufacture of AlN sintered bodies, sintering aids can be added as needed. Calcium oxide (CaO), aluminum oxide (Al2O3), yttrium oxide (Y2O3), etc., can be used as sintering aids.

[0076] The sintering temperature for manufacturing AlN sintered bodies varies depending on the presence and type of sintering aids, but sintering can be carried out at a temperature of 1400°C or higher and less than 2400°C. Furthermore, a sintering temperature of 1600°C or higher is more preferred, 1700°C or higher is even more preferred, 1800°C or higher is particularly preferred, and 1850°C or higher is most preferred.

[0077] Furthermore, the ambient temperature is more preferably below 2100°C, even more preferably below 2000°C, and particularly preferably below 1950°C.

[0078] The heating time of AlN raw materials can be appropriately set by the sintering method.

[0079] When pressure sintering is used as the heat treatment method, the heat treatment time can be from 1 minute to about 2 hours, or from 5 minutes to about 1 hour.

[0080] When pressureless sintering is used as the heat treatment method, the heat treatment time can be more than 1 hour, more than 3 hours, more than 5 hours, more than 10 hours, more than 20 hours, more than 30 hours, more than 40 hours, more than 50 hours, more than 60 hours, more than 70 hours, or more than 80 hours.

[0081] The heat treatment can be carried out in an inert gas atmosphere or in an atmosphere such as nitrogen.

[0082] In this case, the flow rate of the inert gas is not particularly limited, preferably 0.5 to 20 slm, more preferably 1 to 10 slm, even more preferably 1 to 5 slm, and particularly preferably 2 to 4 slm.

[0083] As a fixture used in heat treatment, specifically a container, support, mold, or pressure bar for holding AlN raw materials, it is preferable to use a fixture with a carbon content of 1% by mass or less. More preferably, the carbon content of the fixture is 0.5% by mass or less, further preferably 0.1% by mass or less, particularly preferably 0.01% by mass or less, further preferably 0.001% by mass or less, and most preferably carbon-free.

[0084] When the fixture used for heat treatment contains carbon, supplying carbon to the AlN raw material through the fixture during heat treatment may increase the carbon content of the modified AlN raw material. By minimizing the carbon content used as fixture material, the carbon content, i.e., the amount of impurities, in the modified AlN raw material can be reduced.

[0085] Examples of heat-resistant materials used for clamps include boron nitride, tungsten, tungsten carbide, tantalum, tantalum carbide, molybdenum, and molybdenum carbide.

[0086] If the AlN sintered body obtained by the heat treatment step is to be used, it is preferable to undergo annealing treatment to remove oxygen and / or sintering aids.

[0087] The annealing temperature is preferably 1800°C or higher, and more preferably 1900°C or higher.

[0088] The annealing time is preferably 3 hours or more, more preferably 5 hours or more, even more preferably 7 hours or more, and particularly preferably 10 hours or more.

[0089] Annealing is preferably performed in a non-oxidizing atmosphere. Examples of non-oxidizing atmospheres include inert gas atmospheres such as nitrogen, argon, or helium (He), as well as vacuum atmospheres.

[0090] (3) Molding steps

[0091] When pressureless sintering is used as the heat treatment method, there may also be a forming step that shapes the AlN raw material and manufactures the AlN molded body before the heat treatment step.

[0092] There are no particular restrictions on the molding method for AlN molded parts; conventional ceramic molding methods can be used.

[0093] Examples of molding methods include mechanical pressing, hydrostatic pressing, extrusion molding, injection molding, and casting.

[0094] (4) Etching Step

[0095] The AlN sintered body generated by the above heat treatment steps is preferably further etched. Etching yields a modified AlN raw material with better collapse suppression effect.

[0096] Chemical etching is the preferred etching method.

[0097] Examples of chemical etching include thermal etching and wet etching in a reactive gas atmosphere.

[0098] Examples of thermal etching in a reactive gas atmosphere include hydrogen etching and etching using halide gases.

[0099] As an example of wet etching, wet etching using KOH can be shown.

[0100] Etching of AlN sintered bodies yields modified AlN raw materials with superior collapse suppression effects.

[0101] (5) Modified AlN raw materials

[0102] Furthermore, the present invention relates to a modified AlN raw material manufactured by the above-described manufacturing method.

[0103] The inventors have discovered that the AlN sintered bodies obtained through the above heat treatment can be roughly classified into three groups. Table 1 summarizes the physical properties and characteristics of the three groups.

[0104] [Table 1]

[0105]

[0106] Figure 5 An explanatory diagram is shown to illustrate the difference between apparent density and bulk density.

[0107] like Figure 5 As shown in (a), the apparent density is the density obtained by adding the volume of the closed pores 41 to the volume occupied by the raw material 40 for AlN growth (the material itself), and using the volume for density calculation.

[0108] On the other hand, the volume density is the density obtained by adding the volume of the open pores 42 to the volume occupied by the AlN growth raw material 40 itself, in addition to the volume of the closed pores 41.

[0109] The AlN sintered bodies of Group 1 and Group II show almost no difference between apparent density and bulk density. That is, since the difference between apparent density and bulk density can be said to be the difference in porosity, the AlN sintered bodies of Group I and Group II can be said to have few or almost no porosity.

[0110] On the other hand, compared with Group II, Group I has lower absolute values ​​of apparent density and bulk density. Therefore, it can be concluded that Group I has a larger volume than Group II. As mentioned above, the AlN sintered bodies of Group I and Group II have fewer open pores, so it can be said that the difference in volume is the difference in the volume of closed pores. That is, it can be said that Group I has a larger proportion of closed pores compared with Group II.

[0111] On the other hand, it can be said that Group II has a smaller volume compared to Group I, that is, a smaller proportion of closed pores.

[0112] Group III differs between apparent density and bulk density; specifically, bulk density is lower than apparent density.

[0113] As mentioned above, since the difference between apparent density and bulk density can be said to be the difference in the volume of open pores, it can be said that the volume of open pores in the AlN sintered body of Group III is large.

[0114] The physical properties of AlN sintered bodies belonging to each group are described in more detail below. Furthermore, the AlN sintered bodies of groups I to III are respectively referred to as modified AlN raw material I to modified AlN raw material III.

[0115] (Modified AlN raw material I)

[0116] The apparent density of modified AlN raw material I is preferably less than 3.2 g / cm³. 3 More preferably, less than 3.15 g / cm³. 3 Furthermore, the apparent density of modified AlN raw material I is preferably 2.0 g / cm³. 3 The above, more preferably 2.5 g / cm³ 3 The above is further optimized to 2.7 g / cm³. 3 The above. For example, the apparent density of the modified AlN raw material in group I can be 2.9 g / cm³. 3 The above can also be 3.0 g / cm³. 3 above.

[0117] The preferred bulk density of modified AlN raw material I is less than 3.2 g / cm³. 3 More preferably, less than 3.15 g / cm³. 3 Furthermore, the bulk density of modified AlN raw material I is preferably 2.0 g / cm³. 3 The above, more preferably 2.5 g / cm³ 3 The above is further optimized to 2.7 g / cm³. 3 That's all. Furthermore, the bulk density of the modified AlN raw material in Group I can be 2.9 g / cm³. 3 The above can also be 3.0 g / cm³. 3 above.

[0118] The absolute value of the difference between the apparent density and the bulk density of the modified AlN raw material I is preferably 0 to 0.1, more preferably 0 to 0.05, and even more preferably 0 to 0.01.

[0119] The porosity of the modified AlN raw material I is preferably 0-10%, more preferably 0-5%, further preferably 0-3%, particularly preferably 0-1%, more preferably 0-0.5%, and most preferably 0-0.1%.

[0120] Furthermore, the closed porosity of the modified AlN raw material I is preferably 0.8-25%, more preferably 1-20%, further preferably 1-18%, particularly preferably 2-16%, and most preferably 4-14%.

[0121] Modified AlN raw material I can be estimated to be manufactured by applying excessive pressure to the AlN powder particles or by using AlN powder particles with large particle sizes to prevent the particle distances from becoming too close and by applying a large amount of heat energy. The specific pressure and energy vary depending on the particle size of the AlN powder particles or the manufacturing method used. Examples of methods for manufacturing modified AlN raw material I include spark plasma sintering using coarse-sized AlN powder particles and hot pressing using coarse-sized AlN powder particles.

[0122] In addition, one method is to perform annealing after pressing AlN powder particles into shape.

[0123] Furthermore, if modified AlN raw material I has a high closed porosity, as the AlN crystal growth reaction described later proceeds, the originally closed pores will be exposed and become open pores, and there is a possibility that it can obtain the same properties as modified AlN raw material III.

[0124] (Modified AlN raw material I)

[0125] The apparent density of modified AlN raw material II is preferably less than 3.2 g / cm³. 3 Furthermore, the apparent density of modified AlN raw material I is preferably 3.26 g / cm³. 3 the following.

[0126] The bulk density of modified AlN raw material II is 3.2 g / cm³. 3 That's all. Furthermore, the preferred bulk density of the modified AlN raw material is 3.26 g / cm³. 3 the following.

[0127] The absolute value of the difference between the apparent density and the bulk density of the modified AlN raw material II is preferably 0 to 0.1, more preferably 0 to 0.05, and even more preferably 0 to 0.01.

[0128] The porosity of the modified AlN raw material II is preferably 0-10%, more preferably 0-5%, further preferably 0-3%, particularly preferably 0-1%, more preferably 0-0.5%, and most preferably 0-0.1%.

[0129] Furthermore, the closed porosity in the modified AlN raw material II is preferably 0-4%, more preferably 0-3%, further preferably 0-2%, particularly preferably 0-1%, more preferably 0-0.8%, and most preferably 0-0.7%.

[0130] Modified AlN raw material II is estimated to be manufactured by applying strong pressure or by using small-sized AlN powder particles to reduce the distance between particles and applying a large amount of heat.

[0131] The specific pressure and energy vary depending on the particle size of the AlN powder or the manufacturing method used. As a means of manufacturing modified AlN raw material II, methods for manufacturing AlN sintered bodies include sintering by spark plasma sintering, vacuum hot pressing, and hot pressing.

[0132] (Modified AlN Raw Material III)

[0133] The apparent density of modified AlN raw material III is preferably 3.26 g / cm³. 3 The preferred value is 3.2 g / cm³. 3 The following is a further preferred value: 3.1 g / cm³ 3 The following is a summary of the above. Furthermore, the apparent density of modified AlN raw material III is preferably 2.2 g / cm³. 3 The above, more preferably 2.5 g / cm³ 3 The above is further optimized to 2.7 g / cm³. 3 The above, especially preferred, is 2.9 g / cm³. 3 above.

[0134] The preferred bulk density of modified AlN raw material III is 2.5 g / cm³. 3 The preferred value is 2.3 g / cm³. 3 The following is a further preferred value: 2.2 g / cm³ 3 The following is a summary of the above. Furthermore, the bulk density of modified AlN raw material III is preferably 1 g / cm³. 3 The above, more preferably 1.2 g / cm³ 3 The above is further preferred to be 1.5 g / cm³. 3 above.

[0135] Furthermore, as another embodiment, the bulk density of modified AlN raw material III is preferably 1.6 g / cm³. 3 The above, more preferably 1.8 g / cm³ 3The above is further preferred to be 2.0 g / cm³. 3 above.

[0136] In addition, the bulk density of modified AlN raw material III is lower than its apparent density.

[0137] The difference between the apparent density and the bulk density of modified AlN raw material III is preferably 0.5–2.5 g / cm³. 3 More preferably 0.7–2 g / cm³ 3 Further preferably 1–1.5 g / cm³ 3 .

[0138] The porosity of the modified AlN raw material III is preferably 10-60%, more preferably 20-60%, further preferably 25-60%, particularly preferably 25-55%, and most preferably 25-50%.

[0139] Furthermore, the closed porosity of the modified AlN raw material III is preferably 2-10%, more preferably 2-8%, further preferably 4-8%, and particularly preferably 4-6%.

[0140] Modified AlN raw materials with low collapse incidence are preferably modified AlN raw material I and modified AlN raw material II, and more preferably modified AlN raw material II.

[0141] Therefore, as a modified AlN raw material, it is preferable to use a modified AlN raw material classified as either modified AlN raw material I or modified AlN raw material II (modified AlN raw material I-II). Examples of such modified AlN raw materials are as follows.

[0142] The apparent density of modified AlN raw material I-II is preferably 2.5 g / cm³. 3 The above, more preferably 2.6 g / cm³ 3 The above is further optimized to 2.7 g / cm³. 3 The above, especially preferred, is 2.8 g / cm³. 3 That's all. Furthermore, the apparent density of modified AlN raw materials I-II is preferably 3.26 g / cm³. 3 the following.

[0143] The preferred bulk density of modified AlN raw materials I-II is 2.5 g / cm³. 3 The above, more preferably 2.6 g / cm³ 3 The above is further optimized to 2.7 g / cm³. 3 The above, especially preferred, is 2.8 g / cm³. 3 That's all. Furthermore, the preferred bulk density of modified AlN raw materials I-II is 3.26 g / cm³. 3 the following.

[0144] The absolute value of the difference between the apparent density and the bulk density of the modified AlN raw materials I-II is preferably 0 to 0.8, more preferably 0 to 0.6, further preferably 0 to 0.4, particularly preferably 0 to 0.2, more preferably 0 to 0.1, and most preferably 0 to 0.01.

[0145] The open porosity of the modified AlN raw materials I-II is preferably 0-10%, more preferably 0-5%, further preferably 0-3%, particularly preferably 0-1%, more preferably 0-0.5%, and most preferably 0-0.1%.

[0146] Furthermore, the closed porosity of the modified AlN raw materials I-II is preferably 0-25%, more preferably 0-20%, further preferably 0-18%, particularly preferably 0-16%, and most preferably 0-14%.

[0147] The apparent density and bulk density mentioned above can be determined using distilled water via Archimedes' method.

[0148] In addition, the open porosity and closed porosity can be calculated using the following formula.

[0149] [Equation 1]

[0150]

[0151] W1: Dry weight of the sample

[0152] W2: The weight of the sample after it has been suspended and immersed in the liquid (weight in water).

[0153] ρ1: Density of the liquid

[0154] [Equation 2]

[0155]

[0156] W3: Weight after removing surface liquid (weight of water saturated in air)

[0157] [Equation 3]

[0158]

[0159] [Equation 4]

[0160]

[0161] [Equation 5]

[0162] Relative density + total porosity = 100 (5)

[0163] [Equation 6]

[0164] Total porosity = Open porosity + Closed porosity (6)

[0165] [Equation 7]

[0166] Closed porosity = 100 - (relative density + open porosity) (7)

[0167] In addition, the theoretical density of AlN is 3.26 g / cm³. 3 .

[0168] The modified AlN raw material of the present invention is preferably used as a source material (supply source) for AlN crystal growth. Furthermore, it is preferably used as a source material in crystal growth by a so-called face-up manner, in which the growth surface of the crystal growth substrate is facing upward, and the source material for crystal growth is disposed at a position opposite to the growth surface.

[0169] The modified AlN raw material of the present invention hardly collapses even when used as a source material in the face-up manner, and can produce AlN single crystals with low defects.

[0170] Furthermore, the preferred range of impurity content in the modified AlN raw material of the present invention can be directly applied to the preferred range of impurity content in the AlN raw material described above.

[0171] (6) Methods to suppress collapse of AlN raw materials

[0172] Furthermore, the present invention relates to a method for suppressing the collapse of AlN raw materials during the AlN crystal growth step.

[0173] The collapse suppression method of the present invention uses the above-mentioned modified AlN raw material as the source material (supply source).

[0174] The collapse suppression method of the present invention is particularly effective in AlN crystal growth via the face-up method described above.

[0175] The preferred AlN crystal growth method for which the method of the present invention is applied is vapor phase growth.

[0176] The growth temperature in the AlN crystal growth method can be set to a temperature known as the AlN crystal growth temperature, for example, it can be set to around 1600℃~2200℃.

[0177] Furthermore, the method of the present invention is preferably applied when performing heteroepitaxial growth of AlN crystals. The heteroepitaxial substrate used in the heteroepitaxial growth is not particularly limited, and semiconductor substrates commonly used in the manufacture of semiconductor substrates can be used. Examples include: sapphire substrates, group IV semiconductor substrates such as Si, germanium (Ge), and diamond (C), group II-VI semiconductor substrates such as zinc selenide (ZnSe), cadmium sulfide (CdS), and zinc oxide (ZnO), group III-V semiconductor substrates such as GaAs, GaN, and AlN, group IV compound semiconductor substrates such as SiC and silicon germanide (SiGe), and gallium oxide (Ga2O3) substrates, etc.

[0178] From the perspective of lattice mismatch and thermal expansion coefficient, SiC substrate is preferred.

[0179] As a SiC substrate, a SiC brittle-processed substrate that has undergone brittle processing is preferred.

[0180] In this specification, brittle processing is a process that reduces the strength of a substrate. In other words, a brittle processing step is a process that makes the substrate more susceptible to deformation or damage by external forces. Furthermore, the term "strength" in this specification refers to the durability against physical forces such as compression and tension, and includes the concept of mechanical strength.

[0181] As a brittle processing method, forming through holes in a substrate can be cited. However, by forming through holes in a substrate, it is easily deformed or damaged by external forces.

[0182] (7) Methods for manufacturing AlN crystals

[0183] Furthermore, the present invention relates to a method for manufacturing AlN crystals using the modified AlN raw material.

[0184] That is, the manufacturing method of the present invention can produce AlN crystals with fewer defects by using modified AlN raw materials as the source raw materials for AlN crystal growth.

[0185] The AlN crystal is preferably an AlN semiconductor substrate.

[0186] Furthermore, the AlN crystal is preferably a single crystal.

[0187] The AlN crystal manufacturing method of the present invention preferably manufactures AlN crystals by using epitaxial growth on a substrate. In particular, it is preferred to manufacture AlN crystals by heteroepitaxial growth.

[0188] In the manufacturing method of the present invention, the aforementioned substrate can be used as the base substrate, and a SiC substrate is preferred. In particular, a SiC brittle-processed substrate that has undergone brittle processing is preferred.

[0189] Furthermore, the AlN crystal manufacturing method of the present invention is preferably a method of manufacturing AlN crystals in a so-called face-up manner, which means that the crystal growth surface of the substrate is facing upward (opposite to the direction of gravity), and the source material is arranged in a direction opposite to the crystal growth surface of the substrate.

[0190] Figure 6 An explanatory diagram illustrating the AlN crystal growth steps is shown.

[0191] The AlN crystal growth step involves arranging the SiC substrate 20 and the AlN growth material 40 opposite each other and heating them. The AlN growth material 40 is the modified AlN material described above.

[0192] By heating the SiC substrate 20 and AlN growth material 40 configured in this way, the material is transported from the AlN growth material 40 to the SiC substrate 20 through the material transport space 51.

[0193] The driving force for transporting raw materials can be a temperature gradient or the chemical potential difference between the SiC substrate 20 and the AlN growth material 40.

[0194] Specifically, vapor composed of elements sublimated from the AlN growth feedstock 40 is transported by diffusion in the feedstock transport space 51 and reaches supersaturation and condenses on the SiC substrate 20, where the temperature is set 40°C lower than that of the AlN growth feedstock. Alternatively, it reaches supersaturation and condenses on the SiC substrate 20 where the chemical potential is lower than that of the AlN growth feedstock 40. As a result, an AlN growth layer 10 is formed on the SiC substrate 20.

[0195] Alternatively, a doping gas can be used to adjust the doping concentration of the AlN growth layer 10 during this crystal growth step. Furthermore, the doping concentration of the AlN growth layer 10 can also be adjusted by using an AlN growth raw material 40 with a different doping concentration than the SiC substrate 20.

[0196] use Figure 6 An embodiment of forming an AlN growth layer 10 by means of PVT method is shown, but the AlN crystal manufacturing method of the present invention can of course be used as long as it is a method that can form an AlN growth layer 10.

[0197] As a substrate, the SiC brittle processing substrate described above is preferred.

[0198] By using a SiC brittle substrate, cracks can be suppressed at the AlN crystal during cooling after crystal growth.

[0199] Furthermore, according to the present invention, since the modified AlN material described above is used as the material for AlN growth, even if the substrate and the modified AlN material are arranged face-up, the collapse of the modified AlN material onto the growth surface of the substrate can be suppressed. As a result, AlN crystals with very few defects can be manufactured.

[0200] Example

[0201] (Experimental Example 1) Preparation of Modified AlN Raw Material

[0202] Two types of AlN powder particles (fine powder: median diameter (d50) = 1 μm, coarse powder: median diameter (d50) = 10 μm) were prepared, and 10 modified AlN raw materials were manufactured using the processing methods described in Table 2. Details of each processing method are summarized in Table 3.

[0203] For each modified AlN raw material, the apparent density and bulk density were measured using the Archimedes method (using distilled water). Furthermore, the open porosity and closed porosity were calculated for each modified AlN raw material. The results are shown in Table 4 and... Figure 7 middle.

[0204] [Table 2]

[0205]

[0206] [Table 3]

[0207]

[0208] [Table 4]

[0209]

[0210] As shown in Table 4 and Figure 7 As shown, raw materials 1, 2, 4, 5, 6, 7, and 8 have the same apparent density and bulk density. Among them, the density of any one of raw materials 1, 2, 5, and 7 is 3.20 g / cm³. 3 In the above cases, the density is higher than that of raw materials 4, 6, and 8, and they belong to Group II as described above. On the other hand, raw materials 4, 6, and 8 belong to Group I as described above.

[0211] In addition, the bulk density of raw materials 3, 9 and 10 is lower than their apparent density, and they belong to group III above.

[0212] (Experimental Example 2) Collapse Suppression Effect Verification Test

[0213] Figure 8 The structure of the device used in the collapse suppression effect verification test is shown.

[0214] Use fixture 50 (material: tantalum carbide, tungsten), such as Figure 8 As shown, a SiC substrate 20 (4H-SiC, substrate size: 10mm) with a substrate size of 10mm is configured with the growth surface facing upwards.

[0215] Next, AlN growth material 40 (modified AlN material 2 in Tables 1 to 4) is placed at a position opposite to the growth surface of the SiC substrate 20.

[0216] In addition, the modified AlN raw material 2 was wet-etched under the following conditions beforehand.

[0217] (Etching conditions)

[0218] Etching temperature: 500℃

[0219] Etching time: 10 seconds

[0220] Etching agent: KOH:NaOH = 1:1

[0221] Inside the assembled fixture 50, there is a material transport space 51 between the SiC substrate 20 and the AlN growth material 40, through which the growth material is transported from the AlN growth material 40 to the SiC substrate 20.

[0222] With the above configuration, the SiC substrate and AlN growth material 40 are placed in a heating furnace and subjected to heat treatment under the following conditions (Example 1).

[0223] (Heating conditions)

[0224] Heating temperature: 1900℃

[0225] Heating time: 8 hours

[0226] N2 gas pressure: 30 kPa

[0227] In addition, AlN crystal growth was carried out on SiC substrate 20 under the same conditions as in Example 1 (Examples 2 to 4), except that the raw materials obtained by further heating the modified AlN raw material 2 for 18 hours (1900°C, 50 kPa, N2 (3 slm), the same below), the raw materials obtained by heating AlN powder particles (fine particles) for 23 hours, and the raw materials obtained by heating AlN powder particles (fine particles) for 80 hours were configured as AlN growth raw material 40.

[0228] The growth surfaces of the AlN crystals in Example 1 and Example 3 were observed using an optical microscope, and the growth surfaces of the AlN crystals in Example 3 and Example 4 were observed using a scanning electron microscope. Figure 9 Then, the particle density (particles / mm²) is calculated by counting the number of particles across the entire surface of the growth region of each AlN crystal. 2 ).

[0229] Table 5 and Figure 9 The results are shown.

[0230] [Table 5]

[0231] Example 1 Modified AlN raw material 2 Group II 0 Example 2 Modified AlN raw material 2 Group II 18 hours 0 Example 3 AlN fine-particle heat-treated raw material Group III 23 hours 53 Example 4 AlN fine-particle heat-treated raw material Group III 80 hours 11

[0232] As shown in Table 5 and Figure 9 As shown, it can be confirmed that the AlN crystals in Examples 1 and 2 are completely free of particles (small flakes).

[0233] AlN crystals were obtained by crystal growth using the modified AlN raw material that underwent heat treatment for 23 hours as described in Example 3. Figure 9 The particle density is 53 particles / mm². 2 On the other hand, when using the modified AlN raw material of Example 4, which was subjected to a longer heat treatment of 80 hours compared to Example 3, it was found that the particle density of AlN crystals was 11 particles / mm². 2 It has been reduced to about one-fifth.

[0234] The results show that by using the modified AlN raw material manufactured by the manufacturing method of the present invention as the source material, the collapse of the source material is suppressed, and AlN crystals with low defects can be manufactured.

[0235] (Experimental Example 3) Collapse Suppression Effect Verification Experiment 2

[0236] Using raw materials 1, 3 to 5, and 8 to 10 from the raw materials listed in Table 3, AlN crystals were grown using the same method as in Experimental Example 2. Then, the particle density (particles / mm²) was calculated by counting the number of particles across the entire surface of the growth region of each AlN crystal. 2 In addition, raw materials 1, 3 to 5 and 8 were pre-etched using the same method as shown in Test Example 2.

[0237] Table 6 shows the results.

[0238] [Table 6]

[0239]

[0240]

[0241] As shown in Table 6, it can be confirmed that the AlN crystals using raw materials 1, 4, 5, and 8 as growth materials have fewer particles (small pieces).

[0242] On the other hand, it was confirmed that needle-like crystals formed on the surface of AlN crystals using raw materials 3, 9, and 10. It is believed that these needle-like crystals were formed due to numerous particles falling onto the surface of the AlN crystals.

[0243] This result shows that the bulk density is 2.0 g / cm³. 3 The modified aluminum nitride raw material composed of aluminum nitride sintered bodies with an open porosity of 0-10% exhibits excellent collapse suppression effect and is suitable as a source material for crystal growth by face-up method.

[0244] Industrial applicability

[0245] This invention can be applied to AlN crystal growth technology.

[0246] Explanation of reference numerals in the attached figures

[0247] 10 AlN growth layer

[0248] 20 SiC substrate

[0249] 21 SiC brittle processing substrate

[0250] 22 Through holes

[0251] 30 Retainer

[0252] 40 AlN growth raw materials

[0253] 50 clamps

[0254] 51 Raw material conveying space

[0255] G gravity

Claims

1. A modified aluminum nitride raw material, which has a bulk density of 2.8 g / cm³ 3 The above-mentioned aluminum nitride sintered bodies are composed of open porosity of 0-0.1% and closed porosity of 0-14%. It is also used as a source material for the crystal growth of aluminum nitride.

2. The modified aluminum nitride raw material according to claim 1, wherein, The carbon content is below 1000 ppm and the oxygen content is below 10000 ppm.

3. The method for manufacturing the modified aluminum nitride raw material according to claim 1, comprising: The heat treatment steps for heating aluminum nitride raw materials to produce aluminum nitride sintered bodies; as well as The etching step of etching the aluminum nitride sintered body.

4. The method for manufacturing the modified aluminum nitride raw material according to claim 3, wherein, The etching step is a chemical etching step.

5. The method for manufacturing the modified aluminum nitride raw material according to claim 3 or 4, wherein, The heat treatment step is a pressure sintering step.

6. The method for manufacturing the modified aluminum nitride raw material according to claim 3 or 4, wherein, The heat treatment step is a discharge plasma sintering step.

7. The method for manufacturing the modified aluminum nitride raw material according to claim 3 or 4, wherein, The heat treatment step is a pressureless sintering step, and includes a forming step prior to the heat treatment step to form an aluminum nitride molded body by shaping the aluminum nitride raw material.

8. The method for manufacturing the modified aluminum nitride raw material according to claim 3 or 4, wherein, The modified aluminum nitride raw material is the source material for the crystal growth of aluminum nitride.

9. A method for manufacturing aluminum nitride crystals, comprising heating aluminum nitride raw materials to form a crystal with a bulk density of 2.8 g / cm³. 3 The modified aluminum nitride raw material with an open porosity of 0-0.1% and a closed porosity of 0-14% is used as the source material for aluminum nitride crystal growth, and the crystal growth step is performed to grow aluminum nitride crystals on a substrate. In the crystal growth step, the substrate and the modified aluminum nitride raw material are arranged with their faces facing upwards.

10. A method for suppressing aluminum nitride feedstock collapse during aluminum nitride crystal growth, wherein the feedstock for growing aluminum nitride crystals on a substrate is a material with a bulk density of 2.8 g / cm³ generated by sintering aluminum nitride feedstock. 3 The modified aluminum nitride raw material with an open porosity of 0-0.1% and a closed porosity of 0-14% is arranged with the substrate and the modified aluminum nitride raw material facing upwards.

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