Silicon carbide crystal growth method

Abstract

In silicon carbide crystal growth, this method eliminates the need for precise control of temperature gradients and gas flow paths, suppresses the occurrence of crystal defects and thermal distortion, and improves the efficiency of silicon carbide raw material utilization, thereby increasing the productivity of silicon carbide substrates and reducing manufacturing costs. [Solution] By sublimating the silicon carbide sublimation surface of the raw material substrate and applying gravitational acceleration to transport the silicon carbide growth surface of the growth substrate stably and uniformly, it is possible to form multiple silicon carbide growth layers simultaneously without requiring a temperature gradient. Furthermore, by preventing the silicon carbide raw material from leaking from the back surface of the growth substrate or from the gap between it and the raw material substrate, the utilization efficiency of the silicon carbide raw material is increased, thereby enabling improved productivity and reduced manufacturing costs.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing silicon carbide crystal substrates used as substrate materials for semiconductor devices, and more particularly to a method for inexpensively manufacturing a large number of large-area silicon carbide substrates simultaneously by sublimation. [Background technology]

[0002] Typical methods for manufacturing single-crystal silicon carbide substrates include liquid phase growth, vapor phase growth, and sublimation. Of these, the most common method for manufacturing silicon carbide is the modified Rayleigh process, a type of sublimation method. However, the modified Rayleigh process requires precise control of the amount of raw material molecules (one or more molecules composed of carbon and silicon) supplied to the surface of the seed crystal (the substrate from which the silicon carbide crystal grows). This necessitates delicate adjustments to the arrangement of the seed crystal and raw materials (substrate or powder generated by the sublimation of raw material molecules) within the furnace space, the temperature gradient from the raw materials to the seed crystal, and the gas flow path. Furthermore, obtaining high-quality silicon carbide crystals with good reproducibility requires numerous condition adjustments based on empirical rules. Moreover, the significant power consumption, consumable parts, and effort required for substrate shaping make it difficult to significantly reduce manufacturing costs. In addition, the temperature gradient during crystal growth causes thermal strain within the growing silicon carbide layer, which can lead to crystal defects and a deterioration in crystal quality.

[0003] Unlike the improved Rayleigh method, a simpler method for manufacturing silicon carbide substrates has been devised, such as the proximity sublimation method described in Materials Science Forum Vol 264-268 (1998) pp.143-146 (Non-Patent Literature 1). The proximity sublimation method involves placing a seed crystal and raw material in close proximity in a container, heating the raw material to sublimate the silicon carbide, and then recrystallizing it on the seed crystal to obtain a grown layer. However, in the general proximity sublimation method, a temperature difference is created between the raw material and the seed crystal, so, like the improved Rayleigh method, it is not possible to suppress the occurrence of crystal defects due to thermal strain. Furthermore, only one single-crystal silicon carbide substrate can be manufactured in a single operation, and a significant reduction in manufacturing costs compared to the improved Rayleigh method cannot be expected.

[0004] Japanese Patent Publication No. 6720436 (Patent Document 1) provides a method for growing silicon carbide crystals by facing opposite polar surfaces (carbon surface and silicon surface) of silicon carbide and maintaining a uniform temperature between 1600°C and 2600°C, while transporting raw material molecules from the raw material surface (carbon surface) with a relatively high saturated vapor pressure to the seed crystal surface (silicon surface) with a relatively low saturated vapor pressure. This method enables crystal growth under a uniform temperature atmosphere, allowing for the simultaneous growth of multiple silicon carbide crystals. Furthermore, since it does not require a temperature gradient from the raw material surface to the seed crystal surface, the occurrence of crystal defects due to thermal strain, as seen in the improved Rayleigh method, is suppressed. In addition, it has been shown that if the solid angle of the silicon carbide surface with a high saturated vapor pressure at any point on the seed crystal surface is 2π steradians, silicon carbide is uniformly supplied to the seed crystal surface, improving the uniformity of the film thickness of the recrystallized silicon carbide. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6720436 [Patent Document 2] U.S. Patent No. 4912064 [Patent Document 3] U.S. Patent No. 5011549 [Non-patent literature]

[0006] [Non-Patent Document 1] Materials Science Forum Vol 264-268(1998) pp.143-146 [Overview of the project] [Problems that the invention aims to solve]

[0007] Despite the aforementioned technological achievements, proximity sublimation has not yet led to an industrial method for producing silicon carbide. For example, in Non-Patent Document 1 (Materials Science Forum Vol 264-268 (1998) pp. 143-146), it is difficult to perform crystal growth on multiple substrates simultaneously in order to create a temperature gradient. Alternatively, the method provided in Patent Document 1 (Japanese Patent No. 6720436) requires a difference in the saturated vapor pressure of the raw material and the seed crystal, which limits the combination of polarities of the raw material and seed crystal surfaces. That is, the raw material surface must be a carbon surface with a high saturated vapor pressure, and the seed crystal surface must be a silicon surface with a low saturated vapor pressure. Furthermore, in order to make the solid angle of the seed crystal surface that includes the raw material surface 2π steradians, silicon carbide must be deposited not only on the raw material surface but also on the surrounding furnace wall, which leads to a problem of poor raw material utilization efficiency (the rate at which the amount of silicon carbide lost from the raw material is converted into the amount of silicon carbide crystals in the growth layer).

[0008] This invention was made in view of the above circumstances and eliminates the need for delicate gas distribution and temperature gradient control, gas flow path adjustments, and empirical adjustments to growth conditions required in the improved Rayleigh process. By minimizing the consumption of consumable parts and silicon carbide raw materials required for crystal growth, it enables a reduction in manufacturing costs. Furthermore, it eliminates restrictions on the crystal orientation exposed on the raw material surface and seed crystal surface, providing a manufacturing method for simultaneously producing a large number of high-quality silicon carbide substrates with arbitrary crystal planes at low cost. [Means for solving the problem]

[0009] As a result of intensive studies to solve the above problems, the inventors focused on the fact that by applying a gravitational acceleration in the direction of the growth substrate (a substrate corresponding to the seed crystal of the prior art and for growing a silicon carbide crystal on the growth surface) with respect to the raw material substrate (a substrate for sublimating raw material molecules in which carbon and silicon are bonded), a certain amount of raw material molecules move uniformly, and found that this becomes the driving force for crystal growth on the growth surface of the growth substrate, thereby completing the present invention.

[0010] Next, means for solving the problems according to the present invention will be described. [1] A plate-shaped raw material substrate for sublimating raw material molecules composed of molecules in which carbon and silicon are bonded from a sublimation surface made of silicon carbide, and a plate-shaped growth substrate for crystallizing the raw material molecules on a growth surface made of silicon carbide to grow a silicon carbide crystal are used. The growth substrate is arranged in a gravitational field such that the growth surface faces vertically upward, and the raw material substrate is arranged such that the sublimation surface facing the growth surface faces vertically downward. A protective film with a thickness of 10 μm or more made of any one of carbon, boron nitride (BN), aluminum oxide (Al2O3), zirconium oxide (ZrO2), yttrium oxide (Y2O2), and tantalum carbide (TaC) is adhered to the entire vertically downward side of the growth substrate without gaps. The distance between the opposing sublimation surface and the growth surface is set to a constant distance within the range of 0.1 mm or more and 3 mm or less. After filling the space between the growth surface and the sublimation surface with one or more inert gases selected from helium (He), neon (Ne), nitrogen (N2), argon (Ar), and krypton (Kr) at a pressure of 1300 hPa or less and 700 hPa or more, the temperature is maintained at a uniform temperature of 1900 °C or more and 2300 °C or less to grow a silicon carbide crystal on the growth surface. A method for growing a silicon carbide crystal. [2] The method for growing a silicon carbide crystal according to [1], wherein single-crystalline silicon carbide is exposed on the growth surface, and the angle at which the growth surface intersects the basal plane of the crystal lattice is 1 degree or more and 12 degrees or less. A method for growing a silicon carbide crystal. [3] The method for growing silicon carbide crystals according to any one of [1] or [2], wherein the raw material substrate is composed of microcrystals or fine powders of silicon carbide, and the specific gravity (JIS R 1634) of the raw material substrate is 1.6 g / cm 3 or more and 3.1 g / cm 3 or less. A method for growing silicon carbide crystals, characterized by this. [4] The method for growing silicon carbide crystals according to [2], wherein single crystal silicon carbide is exposed on the sublimation surface of the raw material substrate, and the angle at which the sublimation surface intersects the basal plane of the crystal lattice is 2 degrees or more higher than the angle at which the growth surface facing the sublimation surface intersects the basal plane of the crystal lattice. A method for growing silicon carbide crystals, characterized by this. [5] The method for growing silicon carbide crystals according to [4], wherein a raw material substrate made of single crystal silicon carbide is used, a raw material auxiliary substrate is arranged directly above the raw material substrate in the vertical direction, the raw material auxiliary substrate is composed of microcrystals or fine powders of silicon carbide, and the specific gravity (JIS R 1634) of the raw material auxiliary substrate is 1.6 g / cm 3 or more and 3.1 g / cm 3 or less. A method for growing silicon carbide crystals, characterized by this. [6] The method for growing silicon carbide crystals according to any one of [1] to [5], wherein the growth substrate and the raw material substrate are in the shape of disks and are arranged coaxially, and the diameter of the raw material substrate is 1.1 times or more the diameter of the growth substrate. A method for growing silicon carbide crystals, characterized by this.

Advantages of the Invention

[0011] The effects of the present invention will be explained below with reference to the cross-sectional view shown in Figure 1. In the present invention, the raw material substrate (S) and the growth substrate (G) are held horizontally so that the gravitational acceleration (g) of the gravitational field acts in the vertical direction. However, the raw material substrate (S) is placed above the growth substrate (G). When the space containing the raw material substrate and the growth substrate is heated to 1900°C or higher, raw material molecules sublimated from the sublimation surface (Fs), which is the vertically downward surface of the raw material substrate (S), are subjected to the gravitational acceleration (g) and transported to the growth surface (Fg), which is the vertically upward surface of the growth substrate (G), thereby contributing to crystal growth. Since the gravitational acceleration (g) acts almost uniformly on Earth, the transport of raw material molecules is also uniform, and a silicon carbide crystal growth layer with extremely high uniformity can be obtained on the growth surface (Fg).

[0012] In this invention, the gap (d) is adjusted within a range of 0.1 mm or more and 3 mm or less while maintaining parallelism between the sublimation surface (Fs) and the growth surface (Fg). As a result, leakage of raw material molecules from the gap between the sublimation surface (Fs) and the growth surface (Fg) is suppressed, and most of the raw material molecules contribute to crystal growth, thereby increasing the efficiency of using the raw material substrate.

[0013] On the other hand, a vertically downward gravitational acceleration (g) also acts on the back surface (Rg) of the growth substrate (G). If silicon carbide is exposed on the back surface (Rg), raw material molecules will detach from the growth substrate (G), offsetting the amount of silicon carbide crystals grown on the growth surface (Fg). To avoid this, the present invention coats the back surface (Rg) of the growth substrate with a protective film (Gb) of 10 μm or more in thickness. The components of the protective film—carbon, boron nitride (BN), aluminum oxide (Al2O3), zirconium oxide (ZrO2), yttrium oxide (Y2O2), and tantalum carbide (TaC)—all have lower vapor pressures than silicon carbide at temperatures above 1900°C. Therefore, they prevent the sublimation of silicon carbide from the back surface (Rg) of the growth substrate and prevent the detachment of raw material molecules. As a result, it becomes possible to increase the thickness of the growth substrate (G) in proportion to the growth time.

[0014] In the vicinity of both the sublimation surface (Fs) and the growth surface (Fg), raw material molecules exist as a gas, and their equilibrium vapor pressure is determined according to the Kelvin-Thomson equation as a function of temperature, the surface tension of the substrate, and the silicon carbide crystal grain size constituting each substrate. The silicon carbide crystal growth method provided by the present invention makes it possible to maintain an equilibrium vapor pressure near the sublimation surface (Fs) higher than the equilibrium vapor pressure near the growth surface (Fg) by exposing a silicon carbide crystal surface with high surface tension relative to the growth surface (Fg) to the sublimation surface (Fs), or by making the crystal grain size exposed to the sublimation surface (Fs) relatively small. By adding a raw material transport mechanism due to gravitational acceleration (g) to this, it is possible to maintain a uniform crystal growth rate higher than that described in Patent Document 1 (Japanese Patent No. 6720436).

[0015] The saturated vapor pressure on the surface of a silicon carbide crystal increases exponentially with increasing temperature. At 1900°C, the lower limit of the growth temperature in the silicon carbide crystal growth method provided by the present invention, a partial pressure of approximately 1 Pa of raw material molecules is generated near the sublimation surface (Fs). Furthermore, for every 100°C increase in temperature, the partial pressure of the raw material molecules increases by approximately nine times, reaching approximately 700 Pa at 2200°C, significantly increasing the crystal growth rate of silicon carbide. However, as the temperature increases, the difference between the partial pressure of the vapor sublimating from the growth surface (Fg) narrows, worsening the efficiency of raw material utilization. Therefore, the upper limit of the temperature for obtaining the effects of the present invention is 2300°C.

[0016] When implementing the present invention, the temperature is maintained at a specific temperature (growth temperature) in the range of 1900°C or higher and 2300°C or lower. Therefore, the configuration in which the raw material substrate (S) and growth substrate (G) face each other, as shown in the cross-sectional view of Figure 1, can be used as a unit structure, and productivity can be increased by stacking many of these unit structures in layers to form the multilayer structure shown in the cross-sectional view of Figure 2. In this case, if the raw material substrate (S) and growth substrate (G) are disc-shaped, the uniformity of the growth layer thickness within the plane of the growth surface (Fg) can be improved by making their respective center positions coaxial.

[0017] The space between the opposing growth surface (Fs) and sublimation surface (Fg) is filled with one or more gases selected from helium (He), neon (Ne), nitrogen (N2), argon (Ar), and krypton (Kr), thereby suppressing oxidation of the raw material substrate, growth substrate, and raw material molecules. Furthermore, since the pressure is maintained below 1300 hPa, the buoyant effect acting on the raw material molecules sublimated from the sublimation surface (Fs) is minimal, and vertical downward transport due to gravitational acceleration is not hindered. The transport capacity of raw material molecules due to gravitational acceleration (g) increases as the surrounding gas pressure decreases, but at the same time, the mean free path of the raw material molecules increases, and leakage from the space between the growth surface (Fs) and sublimation surface (Fg) deteriorates the efficiency of raw material use. To avoid this, the lower limit of the gas pressure in this invention is set to 700 hPa to suppress leakage of raw material molecules. Therefore, as shown in Patent Document 1 (Japanese Patent No. 6720436), it is not necessary to maintain a solid angle of 2π steradians in the growth surface that accounts for the sublimation surface.

[0018] The main component of the raw material substrate (S) used in this invention is silicon carbide, but there are no restrictions on the crystal structure exposed on its sublimation surface (Fs). It is possible to expose silicon carbide of any crystal structure, whether single-crystal or polycrystalline. In other words, as in Patent Document 1 (Japanese Patent No. 6720436), there is no need to impose specific restrictions on the plane polarity of the silicon carbide exposed on the growth surface or sublimation surface, and silicon carbide with the required crystal plane can be obtained on the growth surface (Fg). Furthermore, the sublimation surface (Fs) does not necessarily have to be dense silicon carbide; it may contain carbon, silicon, and silicon carbide microcrystals and their voids. Rather, the more voids the raw material substrate contains, the greater the surface roughness of the sublimation surface (Fs) and the greater its effective surface area. As a result, the equilibrium vapor pressure of the raw material molecules increases, accelerating crystal growth on the growth surface (Fg). For this reason, in this invention, the density of the raw material substrate (S) is 3.1 g / cm³. 3 The following is also provided as a means to increase the amount of raw material molecules supplied to the growth surface (Fg) by maintaining the voids contained therein at 3% or more of the total volume.

[0019] Exposing single-crystal silicon carbide on the sublimation surface (Fs) is extremely effective in reducing the crystal defect density of the silicon carbide growth layer formed on the growth surface (Fg). This is because, on the sublimation surface where polycrystalline silicon carbide or silicon carbide sintered bodies are exposed, certain crystal grains may expand over time due to merging, and some of these may detach during crystal growth and fall onto the growth surface (Fg) due to gravitational acceleration. As a result, it is impossible to eliminate the possibility of generating silicon carbide with a structure different from the crystal structure that should be exposed on the growth surface (Fg). To address this problem, the silicon carbide crystal growth method of the present invention also provides a means of performing crystal growth by exposing single-crystal silicon carbide on both the sublimation surface (Fs) and the growth surface (Fg). Since no crystal grains exist on the sublimation surface (Fs) made of single-crystal silicon carbide, the problem of crystal grains expanding and falling is eliminated.

[0020] However, the vapor pressure (σs) of the sublimation surface (Fs) where single-crystal silicon carbide is exposed does not necessarily exceed the vapor pressure (σg) of the growth surface (Fg), which may result in the failure to obtain a silicon carbide growth layer on the growth surface (Fg). To avoid this, the present invention provides a method, as shown in the cross-sectional view in Figure 3, in which the angle at which the sublimation surface (Fs) where single-crystal silicon carbide is exposed is inclined with respect to the closest-packed plane (CPP) of the crystal lattice is kept high compared to the angle at which the growth surface (Fg) where single-crystal silicon carbide is exposed is inclined with respect to the closest-packed plane (CPP) of the crystal lattice.

[0021] As shown in the microscopic structural cross-section of the substrate surface in Figure 4, the inclination of the single crystal surface with respect to the closest-packed plane of the crystal lattice means the formation of microscopic terraces (Cp) and microscopic steps (Np) on that surface. The surface of the microscopic terraces (Np) corresponds to the closest-packed plane (CPP) of the crystal lattice, but the microscopic steps (Np) expose non-polar and semi-polar surfaces with relatively high surface energy, increasing their vapor pressure. Therefore, the greater the angle at which the single crystal surface is inclined with respect to the closest-packed plane (CPP), the greater the vapor pressure. In this invention, the angle between a sublimation surface (Fs) made of a single crystal and its closest-packed plane (CPP) is defined as θs, and the angle between a growth surface (Fg) made of a single crystal and its closest-packed plane (CPP) is defined as θg, and θs is set to an angle of 2 degrees or more relative to θg. In this case, the vapor pressure (σg) of the growth surface is proportional to Sin(θg), reflecting the step density. Similarly, the vapor pressure (σs) on the sublimation surface is proportional to Sin(θs), reflecting the step density. Therefore, the growth rate on the growth surface is proportional to the value obtained by subtracting Sin(θg) from Sin(θs). In this invention, since θs is at least 2 degrees higher than θg, the value of σs relative to σg is at least 1.03 times, and the crystal growth rate on the growth surface (Fg) is accelerated.

[0022] Exposing single-crystal silicon carbide on the growth surface (Fg) and tilting its surface away from the closest-packed plane (CPP) of the crystal lattice is effective in preventing the inclusion of crystalline polymorphs in the growth layer. As described with reference to the cross-sectional view shown in Figure 4, microscopic terraces (Cp) and microscopic steps (Np) consisting of the closest-packed plane are formed on the growth surface (Fg) tilted from the closest-packed plane (CPP) of the crystal lattice, depending on the tilt angle (θg). In this case, the crystal growth becomes a step-controlled epitaxy in which the microscopic steps (Np) grow laterally, as shown in Patent Document 2 (U.S. Patent No. 4912064) and Patent Document 3 (U.S. Patent No. 5011549). In step-controlled epitaxy, the layered structure of silicon carbide exposed on the initial growth surface is maintained, and the generation of different crystalline structures is prevented. Furthermore, dislocations exposed on the initial growth surface are also sealed by step-controlled epitaxy, making it possible to reduce the defect density contained in the growth layer of the silicon carbide layer. In this invention, step-controlled epitaxy is made possible by setting the tilt angle (θg) to 1 degree or more. However, in order to avoid an increase in the surface roughness of the growth layer due to step bunching, the tilt angle (θg) must be kept to 12 degrees or less.

[0023] By the way, if the silicon carbide crystal growth method provided by the present invention is carried out using single-crystal silicon carbide as the raw material substrate (S), and a growth layer made of single-crystal silicon carbide is obtained on the growth surface (Fg), then an amount of single-crystal silicon carbide equal to or greater than the amount of the growth layer will be consumed from the raw material substrate, so it will not lead to a fundamental reduction in manufacturing costs. However, in the present invention, as shown in Figure 5, a raw material auxiliary substrate (SS) made of polycrystalline silicon carbide or a silicon carbide sintered body is placed vertically above the back surface (Rs) of the raw material substrate, and raw material molecules sublimated from the raw material substrate (SS) are supplied to the raw material substrate (S) to increase the thickness of the single-crystal silicon carbide. In this case, single-crystal silicon carbide is consumed on the sublimation surface (Fs), but new single-crystal silicon carbide is generated on its back surface (Rs). Even if the raw material auxiliary substrate (SS) comes into contact with the raw material substrate (S), single-crystal silicon carbide is always exposed on the sublimation surface (Fs) facing the growth surface (Fg), so the properties of the raw material auxiliary substrate (SS) do not affect the growth conditions or the quality of the grown layer. Here, if an amount of single-crystal silicon carbide exceeding the amount of silicon carbide sublimation on the sublimation surface (Fs) is grown on the back surface (Rs) of the raw material substrate, the consumption of the raw material substrate (S) is eliminated. To achieve this, in this invention, the raw material auxiliary substrate (SS) placed on the back surface (Rs) of the raw material substrate is composed of fine crystals or fine powder of silicon carbide, and its specific gravity is 1.6 g / cm³. 3 The above, and 3.1 g / cm³ 3 By doing the following, it is possible to supply single-crystal silicon carbide to the back side (Rs) in excess of the amount consumed on the sublimation side (Fs).

[0024] There are no particular restrictions on the distance between the back surface (Rs) of the raw material substrate and the raw material auxiliary substrate (SS), but it is desirable to keep the distance to 1 mm or less so that the raw material molecules sublimated from the raw material auxiliary substrate (SS) are reliably incorporated into the raw material substrate. Alternatively, the raw material substrate (S) and the raw material auxiliary substrate (SS) may be placed in close contact. [Brief explanation of the drawing]

[0025] [Figure 1] This is a cross-sectional view showing the arrangement of the raw material substrate, growth substrate, and protective film in the effects and embodiments of the present invention. [Figure 2]This is a cross-sectional view showing the effects of the present invention and the arrangement of the raw material substrate and growth substrate when stacking multiple layers in an embodiment. [Figure 3] This is a cross-sectional view showing the arrangement of a raw material substrate made of single-crystal silicon carbide and a growth substrate made of single-crystal silicon carbide in the effects and embodiments of the present invention. [Figure 4] This is a cross-sectional view showing the microscopic surface structure of a raw material substrate made of single-crystal silicon carbide and a growth substrate made of single-crystal silicon carbide in the effects of the present invention. [Figure 5] This is a cross-sectional view showing the arrangement of a raw material substrate made of single-crystal silicon carbide, a growth substrate made of single-crystal silicon carbide, and a raw material auxiliary substrate in the effects of the present invention. [Figure 6] This figure shows the relationship between the thickness distribution of the growth layer and the ratio of the diameter of the raw material substrate (Ds) to the diameter of the growth substrate (Dg) in an embodiment of the present invention. [Figure 7] This figure shows the film thickness distribution of the growth layer with respect to the distance (d) between the growth surface and the sublimation surface in an embodiment of the present invention. [Figure 8] This is a cross-sectional view of an embodiment of the present invention showing a raw material substrate and a growth substrate arranged inside a container. [Figure 9] This is a cross-sectional view showing the arrangement when multiple containers, each containing a raw material substrate and a growth substrate, are stacked in an embodiment of the present invention. [Figure 10] This is a cross-sectional view showing the arrangement of multiple raw material substrates and multiple growth substrates when they are alternately stacked in a container according to an embodiment of the present invention. [Figure 11] This is a cross-sectional view showing the arrangement of multiple raw material substrates and multiple growth substrates when they are alternately stacked in a container according to an embodiment of the present invention. [Figure 12] This is a cross-sectional view showing the arrangement of the raw material substrate and the growth substrate when they are placed facing each other inside the container in Examples 1 and 2 of the present invention. [Figure 13] This is a cross-sectional view showing the arrangement of multiple raw material substrates and multiple growth substrates when they are alternately stacked in a container in Embodiment 3 of the present invention. [Figure 14]This is a cross-sectional view showing the arrangement of multiple raw material substrates, multiple growth substrates, and raw material auxiliary substrates when they are alternately stacked in a container in Embodiment 4 of the present invention. [Modes for carrying out the invention]

[0026] (Substrate material) As shown in the cross-sectional views of Figures 1 and 2, the substrate arrangement required for carrying out silicon carbide crystal growth as provided by the present invention consists of a growth substrate (G) and a raw material substrate (S). Raw material molecules sublimated from the sublimation surface (Fs) of the raw material substrate are transported to the growth surface (Fg) of the growth substrate, thereby achieving crystal growth. The raw material substrate (S) and the growth substrate (G) may be disc-shaped or rectangular, but considering the possibility of damage to the corners during handling and the use of general semiconductor manufacturing equipment in subsequent processes, it is preferable for each substrate to be disc-shaped. Furthermore, when setting up the disc-shaped growth substrate and raw material substrate, it is preferable to arrange them coaxially to improve the in-plane distribution of the film thickness and quality of the grown layer.

[0027] (Growth substrate) There is no limit to the area of ​​the growth substrate (G), and the same effect can be obtained whether its maximum width is 1 cm or 30 cm. When attempting to grow single-crystal silicon carbide with a specific crystal structure on the growth substrate, it is necessary to expose single-crystal silicon carbide with the same crystal structure on the growth surface. For example, when attempting to obtain a single-crystal 4H-SiC as a growth layer with the substrate arrangement shown in Figure 1, single-crystal 4H-SiC is exposed on the growth surface (Fg). If the surface orientation of the single-crystal 4H-SiC surface exposed on the growth surface (Fg) is a (0001) silicon polar plane, then the surface of the growth layer will also be a 4H-SiC (0001) silicon polar plane. If the surface orientation of the 4H-SiC surface exposed on the growth surface is a (000-1) carbon polar plane, then the surface of the growth layer will also be a 4H-SiC (000-1) carbon polar plane. On the other hand, if the polar surface of single-crystal 6H-SiC(0001) silicon is exposed on the growth surface (Fg), the surface of the growth layer will also become a polar surface of 6H-SiC(0001) silicon. Similarly, if the (111) silicon surface of single-crystal 3C-SiC is exposed on the growth surface (Fg), it is possible to obtain a polar surface of 3C-SiC(111) silicon on the surface of the growth layer. When multiple raw material substrates (S) and growth substrates (G) are stacked as shown in the cross-sectional view in Figure 2, growth substrates with different crystal structures may be mixed.

[0028] In this case, as shown in the cross-sectional view in Figure 3, if the single crystal surface exposed on the growth plane (Fg) has an inclination angle (θg) of 1 degree or more with respect to the closest packed plane (CPP) of its crystal lattice, step-controlled epitaxy will occur as described in Patent Document 2 (U.S. Patent No. 4912064) and Patent Document 3 (U.S. Patent No. 5011549), and it is possible to prevent the mixing of different crystal structures. However, in order to prevent an increase in crystal defect density due to macrostepping, θg must be kept below 12 degrees.

[0029] In carrying out the silicon carbide crystal growth method provided by the present invention, the entire growth substrate (G) does not need to be single-crystal silicon carbide; at least the growth surface (Fg) needs to be a specific single-crystal silicon carbide. Therefore, it is possible to use a substrate made of polycrystalline silicon carbide or amorphous silicon carbide as the growth substrate (G) and obtain a growth surface (Fg) by attaching a specific single-crystal thin film to its surface. If a silicon carbide crystal with a specific structure is not required as the growth layer, it is also possible to use a growth surface (Fg) made of amorphous silicon carbide or polycrystalline silicon carbide.

[0030] Incidentally, since the back surface (Rg) of the growth surface (Fg) is oriented vertically downward, if the entire growth substrate (G) is composed of silicon carbide, the silicon carbide-containing vapor sublimating from the back surface (Rg) will settle due to gravity and be lost from the growth substrate (G). To prevent this, in the present invention, as shown in the cross-sectional views in Figures 1, 2, and 3, a protective film (Gb) made of one of the following materials is tightly attached to the back surface (Rg) of the growth substrate to suppress sublimation. The vapor pressure of the above-mentioned protective film components is lower than the vapor pressure of silicon carbide at temperatures of 1900°C or higher, thereby suppressing sublimation of the back surface (Rg) of the growth substrate. The thickness of the protective film (Gb) depends on the growth time according to the present invention, but it is desirable to have a thickness of at least 10 μm, and more preferably, a thickness equal to or greater than the thickness of the silicon carbide growth layer to be obtained on the growth surface (Fg).

[0031] The protective film (Gb) needs to adhere seamlessly to the entire back surface (Rg) of the growth substrate. Simply placing it on a carbon plate or tantalum carbide plate, as is done in the heat treatment of typical semiconductor substrates, is undesirable because warping of the growth substrate (G) creates voids on the back surface (Rg), preventing complete suppression of silicon carbide sublimation. As a method for forming a protective film (Gb) with high adhesion to the back surface (Rg) of the growth substrate, PVD methods such as sputtering and ion plating, chemical vapor deposition, or plasma CVD can be used. Furthermore, as a simpler and less expensive method, it is also possible to use commercially available carbon coating material applied to the back surface (Rg) of the growth substrate to a thickness of approximately 100 μm and then dried, thereby using it as the protective film (Gb). Alternatively, if a growth surface made of single crystals is not required, it is also possible to form a growth substrate by depositing polycrystalline silicon carbide or amorphous silicon carbide on the protective film (Gb) using chemical vapor deposition, sputtering, laser ablation, ion plating, or plasma CVD.

[0032] (Raw material substrate) There is no restriction on the crystal structure of silicon carbide exposed on the sublimation surface (Fs) of the raw material substrate (S), and it is only necessary to generate an equilibrium vapor pressure (σs) of at least the equilibrium vapor pressure (σg) on the growth surface (Fg). Even if σs and σg are equal, as shown in the cross-sectional views of FIGS. 1 and 2, raw material molecules are transported by the acceleration due to gravity (g) acting vertically downward from the sublimation surface (Fs), and silicon carbide crystals grow on the growth surface (Fg). Therefore, the silicon carbide exposed on the sublimation surface (Fs) may be the same as the silicon carbide exposed on the growth surface (Fg). However, the smaller the crystal grain size of the silicon carbide exposed on the sublimation surface (Fs) compared to the crystal grain size of the silicon carbide exposed on the growth surface (Fg), the more σs predominates over σg, and it becomes possible to obtain a higher crystal growth rate. For this reason, it is desirable that the average value (ds) of the particle size of the silicon carbide fine particles exposed on the sublimation surface (Fs) is 10 μm or less, and by further setting ds to 1 μm or less, it is also possible to obtain a crystal growth rate exceeding 30 μm / hour. However, if ds is less than 0.1 μm, silicon carbide crystals will form multiple nuclei on the growth surface (Fg) at a temperature below 1900 °C, increasing the crystal defect density, so ds needs to be maintained at 0.1 μm or more.

[0033] As described above, the raw material substrate (S) has silicon carbide as the main component, but does not necessarily need to be a single crystal, and its density does not necessarily need to be equivalent to that of single crystal silicon carbide. Rather, by including voids in the raw material substrate and increasing the surface roughness of the sublimation surface (Fs), the substantial surface area can be expanded, and the equilibrium vapor pressure (σs) can be increased. Such a low-density raw material substrate can be produced by sintering silicon carbide fine particles and processing them into a wafer shape. There is no restriction on the thickness of the raw material substrate at this time. The thicker it is, the greater the mechanical strength, but its specific gravity (JIS R 1634) should be 3.1 g / cm 3 It is desirable to be as follows. This is because when the volume of the voids contained in the raw material substrate is 3% or more of the total volume, the substantial surface area of the sublimation surface increases, and it becomes possible to increase the vapor pressure of the raw material molecules. However, when the density of the raw material substrate decreases, the mechanical strength decreases and it becomes easier to break, so the lower limit value of its specific gravity is 1.6 g / cm 3 needs to be.

[0034] It is preferable to keep the variation in the silicon carbide particle size constituting the raw material substrate as low as possible. This is because, when particles of different sizes are adjacent, the vapor pressure of the smaller particles becomes dominant, and they are transported by the vapor pressure difference with the adjacent larger particles, contributing to their particle size expansion (in this specification, this phenomenon is called merging). Once merging occurs, the uniformity of the particle size deteriorates further, and eventually the enlarged crystal grains cover the sublimation surface, lowering the equilibrium vapor pressure and leading to a decrease in the crystal growth rate on the growth surface. To prevent this merging, it is desirable that the standard deviation of the silicon carbide crystal grain size constituting the raw material substrate be 50% or less of the average grain size, and it is even more desirable to be 30% or less if the growth time exceeds 24 hours.

[0035] (Area ratio of raw material substrate to growth substrate) The sizes of the raw material substrate (S) and the growth substrate (G) do not necessarily need to match; increasing the area ratio of the raw material substrate to the growth substrate improves both the growth rate and the uniformity of the grown layer. Figure 6 shows the results of a simulation of the silicon carbide grown layer thickness distribution as a function of the ratio of the diameter of the growth substrate (Dg) to the diameter of the raw material substrate (Ds), based on the static equation and the diffusion equation, assuming the substrate arrangement shown in Figure 1. However, it is assumed that both the growth substrate and the raw material substrate are disc-shaped and arranged coaxially. The distance (d) between the growth surface and the sublimation surface is 1 mm, and the diameter of the growth substrate (Dg) is 200 mm. Figure 6 shows that the distribution of the growth rate improves as the value of Ds / Dg increases, and it can be seen that if Ds / Dg is 1.1 or higher, the difference in thickness within the growth surface can be kept below 1.3% of the average thickness.

[0036] (Arrangement of growth and sublimation surfaces) In carrying out the silicon carbide crystal growth method provided by the present invention, as shown in the cross-sectional views of Figures 1 and 2, the growth surface (Fg) is oriented vertically upward, and the sublimation surface (Fs) opposite it is oriented vertically downward, maintaining a constant distance (d) between them and keeping them as parallel as possible. One reason for this is that raw material molecules become unevenly distributed on a growth surface tilted with respect to gravity, and another is that in-plane variation occurs in the gap between the growth surface (Fg) and the sublimation surface (Fs), resulting in an in-plane distribution of equilibrium vapor pressure. The more the normal direction of the growth surface is tilted from the vertical, the greater the film thickness distribution of the grown layer on the growth surface (Fg). For this reason, it is desirable to mechanically hold the raw material substrate (S) and the growth substrate (G) and keep the normal axis of the sublimation surface (Fs) and the growth surface (Fg) within 2 degrees from the vertical.

[0037] Furthermore, it is desirable that the gap (d) between the growth surface (Fg) and the sublimation surface (Fs) be 3 mm or less. This is because a narrower gap (d) not only increases the number of growth substrates (G) that can be processed simultaneously, thereby improving productivity, but also reduces the amount of raw material molecules escaping from the gap (d), thereby improving the silicon carbide growth rate on the growth surface (Fg). Figure 7 shows the simulation results of the film thickness distribution of the silicon carbide growth layer obtained on the growth surface when a growth substrate and a raw material substrate of the same diameter are placed opposite each other and the gap (d) between the sublimation surface and the growth surface is varied. These simulation results show that narrowing the gap (d) increases the film thickness of the growth layer and also improves the uniformity within the plane. In particular, setting the gap (d) to 1 mm or less increases the film thickness of the growth layer even more, increases the number of substrates that can be processed simultaneously, and improves productivity. However, in order to avoid fusion of the growth surface (Fg) and the sublimation surface (Fs) due to in-plane irregularities or warping of the raw material substrate (S) and the growth substrate (G), the gap (d) must be kept at 0.1 mm or more.

[0038] (Holding the growth substrate and sublimation substrate) In carrying out the silicon carbide crystal growth method provided by the present invention, it is desirable to hold the pair of growth substrate (G) and raw material substrate (S) inside a container (CT) as shown in the cross-sectional view in Figure 8, in order to prevent raw material molecules from escaping to the outside through the gap between the growth surface (Fg) and the sublimation surface (Fs). The container must withstand temperatures of 2300°C or higher, have a cleanliness that does not release impurities into the gas phase, and have the mechanical strength to stably hold all the growth substrates (G) and raw material substrates (S). For this reason, it is desirable to use a cylindrical container (CT) made of high-purity carbon with a thickness of 5 mm or more. The growth substrate (G) and raw material substrate (S) are placed inside this container (CT) such that the growth surface (Fg) is vertically upward and the sublimation surface (Fs) is vertically downward. In this case, a protective film (Gb) may be formed on the back side of the growth substrate (G) and then attached to the bottom surface of the container (CT), while the back side of the raw material substrate (S) may be attached to the top surface so that the sublimation surface (Fs) faces vertically downward.

[0039] Furthermore, when increasing the number of growth substrates processed by the silicon carbide crystal growth method according to the present invention, as shown in the cross-sectional view of Figure 9, multiple containers (CTs) with a pair of raw material substrates and growth substrates facing each other can be stacked and heat-treated to obtain a large number of growth layers simultaneously. Alternatively, as shown in the cross-sectional view of Figure 10, it is also possible to stack multiple raw material substrates (S) and growth substrates (G) alternately and place them in the same container (CT). Furthermore, as shown in the cross-sectional view of Figure 11, by attaching the back side (Rg) of the growth substrate (G) to the vertically upward surface (Rs) of the raw material substrate located vertically below it via a protective film (Gb), the number of growth substrates per unit volume of the container (CT) can be increased, and the sublimation of raw material molecules on the vertically upward surface (Rs) of the raw material substrate can be prevented, further improving the utilization efficiency of the raw material substrate.

[0040] (Heating mechanism) A container (CT) containing a raw material substrate (S) and a growth substrate (G) placed at predetermined intervals is installed inside an electric furnace. The electric furnace may use resistance heating or induction heating, but it is desirable to maintain the temperature difference within the container within 5°C. If a significant temperature difference occurs within the container, the raw material molecules will be transported from the high-temperature area to the low-temperature area due to the temperature gradient, and the effects of the present invention will not be obtained. Furthermore, in order to supply uniform heat radiation to the outer circumference of the container, it is desirable to arrange the heating mechanism of the electric furnace in concentric circles and install the container (CT) in the center.

[0041] (Atmosphere during silicon carbide crystal growth) Prior to heating the container (CT), it is necessary to fill the electric furnace with a predetermined high-purity inert gas to remove oxygen and moisture from inside the container and suppress the oxidation of silicon carbide. As the inert gas to fill the electric furnace, one or more gases can be selected from helium (He), neon (Ne), nitrogen (N2), argon (Ar), and krypton (Kr). However, considering the need to suppress the buoyancy acting on the raw material molecules sublimated from the sublimation surface and the need to reduce the cost of gas production, it is most preferable to use argon (Ar) as the primary gas. When adding donor impurities to the silicon carbide growth layer, it is sufficient to mix argon (Ar) with an appropriate amount of nitrogen (N2) or phosphine (PH3). On the other hand, when adding acceptor impurities, it is also possible to mix argon (Ar) with an appropriate amount of diborane (B2H6) or trimethylaluminum (Al(CH3)3). Prior to introducing the gas as described above, evacuating the electric furnace to a vacuum of 1 Pa or less can keep the partial pressure of residual gases such as oxygen and moisture low, thereby improving the quality of silicon carbide grown by this invention.

[0042] The pressure inside the electric furnace during silicon carbide crystal growth according to the present invention can be set to 700 hPa or higher and 1300 hPa or lower, but it is desirable to set it to 1100 hPa or higher to avoid mixing with ambient air. However, as the inert gas pressure inside the electric furnace increases, the effect of buoyancy acting on the raw material molecules increases, suppressing the transport of raw material molecules from the sublimation surface to the growth surface, so it is desirable to set the upper limit of the pressure inside the electric furnace to 1300 hPa. The pressure inside the electric furnace can be measured with a capacitive pressure gauge, and the pressure can be adjusted by opening a throttle valve installed in the exhaust section of the electric furnace so that the measured value reaches a predetermined value.

[0043] (growth temperature) In this invention, silicon carbide crystals are grown by supplying raw material molecules from a raw material substrate to a growth substrate at a specific temperature (growth temperature) within the temperature range of 1900°C or higher and 2300°C or lower. At temperatures below 1900°C, the partial pressure of the raw material molecules is low, making it impossible to supply a sufficient amount of raw material molecules to the growth surface. As the growth temperature increases, the partial pressure of the raw material molecules increases, and the growth rate of silicon carbide crystals on the growth surface improves. However, when the growth temperature exceeds 2300°C, the vapor pressure of the raw material molecules increases not only on the sublimation surface but also on the growth surface, slowing down the temperature dependence of the growth rate. As a result, the utilization efficiency of the raw material substrate (the ratio of the weight increase of the growth substrate to the weight decrease of the raw material substrate) decreases. To obtain a growth rate of 1 μm / hour or more, it is desirable that the growth temperature be 2100°C or higher, and to maintain a raw material utilization efficiency of 80% or more, it is desirable that the growth temperature be 2200°C or lower.

[0044] (Temperature of rise) While there are no strict restrictions on the heating rate when setting the electric furnace temperature to the predetermined growth temperature, a low heating rate may lead to polynucleation of raw material molecules sublimated from the sublimation surface in the temperature range below 1900°C, potentially destabilizing the crystal structure of the growth layer. Therefore, if it is necessary to prevent the inclusion of crystalline polymorphs in the silicon carbide growth layer and an increase in defect density, it is desirable to heat the material at a rate of 10°C / min or higher. However, if the heating rate is excessively high, thermal strain may cause deformation or damage to the growth substrate, so it is desirable to keep it below 100°C / min.

[0045] (Crystal growth time) Once the temperature inside the electric furnace reaches the predetermined growth temperature, it is possible to form a silicon carbide growth layer on the growth surface (Fg) by maintaining a constant temperature for a predetermined time. For example, the typical growth rate at 2200°C is 11.1 μm / hour, so to obtain a growth layer 500 μm thick, the temperature should be maintained for approximately 45 hours. The typical growth rate at 2100°C is 2.4 μm / hour, so the temperature needs to be maintained for approximately 208 hours.

[0046] (cooling process) After the predetermined temperature maintenance period is complete, the temperature inside the electric furnace is lowered to below 100°C while continuing to introduce inert gas. This process can be done by natural air cooling, but to suppress deformation of the growth layer due to thermal strain and the occurrence of crystal defects, the cooling rate must not exceed 100°C / hour. Furthermore, if the cooling rate is too low, an amorphous silicon carbide layer will grow on the growth layer in the low temperature range below 1900°C, so the cooling rate must exceed 10°C / hour.

[0047] After the container temperature drops below 100°C, the raw material substrate and growth substrate are removed into the atmosphere. The edges of the removed growth substrate are ground to form the predetermined wafer shape, and then the surface of the growth layer is mirror-polished to complete the production of a silicon carbide substrate that can be used as a wafer for semiconductor manufacturing. At this time, if the thickness of the raw material substrate removed along with the growth substrate is 1 mm or more, it can be reused.

[0048] [Example 1] To verify the effects of the present invention, crystal growth experiments were conducted using a 100 mm diameter disc-shaped single-crystal silicon carbide substrate as both the raw material substrate and the growth substrate. As shown in the cross-sectional view in Figure 12, in this embodiment, the substrates were fixed coaxially within a cylindrical container made of high-purity carbon so that the normal axis of each substrate surface was within 2 degrees vertically. The inner diameter of the container was 105 mm. The raw material substrate (S) was attached to the top of the container with the sublimation surface (Fs) facing downwards, and the growth substrate (G) was attached to the bottom of the container with the growth surface (Fg) facing upwards. G-coat, a carbon coating material manufactured by Nippon Carbon Co., Ltd., was used as the adhesive layer for attaching each substrate, and the gap between the substrates was adjusted to 0.5 mm ± 0.1 mm by adjusting the thickness of the G-coat layer (Gr). The G-coat layer (Gr) and the bottom of the container also function as the protective film (Gb) described in claim 1 of the present invention.

[0049] The container, with the raw material substrate and growth substrate attached, was placed in the center of an electric furnace where resistance-heating heaters were arranged concentrically. After vacuum evacuation, the furnace was replaced with argon gas at 1100 hPa. The container was then heated at a rate of 40°C / min until it reached the predetermined growth temperature (Tg) of 2200°C. After the container reached 2200°C, the growth time was set to 2 hours, and the container temperature was maintained constant. After that, the container was naturally air-cooled in an argon atmosphere at 1100 hPa until its temperature fell below 100°C. The container was removed from the electric furnace, the substrates were separated from the container, and any G-coat residue adhering to the back surface of each substrate was removed by heating in air at 900°C for 120 minutes. Finally, the weight of each substrate was measured using an electronic balance.

[0050] From the change in the weight of the substrate before and after the implementation of the present invention, the growth rate of silicon carbide on the growth substrate (r g ) and the sublimation rate (r) on the sublimation substrate s The growth rate (r) against the properties of the substrate in Example 1 was determined. Furthermore, the utilization efficiency (η) of the raw material substrate was determined by dividing the weight change of the growth substrate by the weight change of the sublimation substrate. Table 1 shows the growth rate (r) against the properties of the substrate in Example 1. g ) and sublimation rate (r s), and the utilization efficiency (η) of the raw material substrate are summarized.

[0051] [Table 1]

[0052] From the verification results using containers No. 1 to No. 4 listed in Table 1, the raw material substrate (S) made of single-crystal silicon carbide located relatively higher showed a positive sublimation rate (r s ) shows that the growth substrate (G) made of single-crystal silicon carbide located relatively below has a positive growth rate (r g It can be seen that ). Therefore, it is clear that the raw material molecules were transported by gravity from the raw material substrate located above to the growth substrate located below. Furthermore, it can be seen that the sublimation rate of the sublimation surface made of carbon is higher than that of the sublimation surface made of silicon, and the growth rate on the growth surface made of silicon is higher than that on the growth surface made of carbon. In other words, it can be seen that the vapor pressure of the raw material molecules is higher on the carbon surface, which has a higher surface energy, than on the silicon surface, which has a lower surface energy.

[0053] Furthermore, verification results using containers No. 5 to No. 7 and container No. 1 demonstrated that increasing the angle at which the surface of the sublimation surface, made of single-crystal silicon carbide, is inclined relative to the close-packed surface increases the sublimation rate, thereby increasing the growth rate of silicon carbide on the growth surface opposite it. A crystal growth rate exceeding 5 μm / hour can be obtained when the angle at which the surface of the sublimation surface is inclined relative to the close-packed surface is 2 degrees or more, relative to the angle at which the surface of the growth surface is inclined relative to the close-packed surface.

[0054] [Example 2] To verify the effects of the present invention, silicon carbide growth experiments were conducted using a 100 mm diameter disc-shaped single-crystal silicon carbide substrate as the growth substrate (G), and a 100 mm diameter disc-shaped polycrystalline cubic silicon carbide substrate, a hexagonal silicon carbide sintered body, or a single-crystal silicon carbide substrate as the raw material substrate (S). The arrangement method of these substrates, heating atmosphere, heating process, cooling process, and gravimetric measurement method are the same as in Example 1, so their description is omitted.

[0055] [Table 2]

[0056] Table 2 shows the properties of the substrate in Example 2 and the growth rate (r) relative to the growth temperature (Tg). g ) and sublimation rate (r s ), and the utilization efficiency (η) of the raw material substrate are shown. From the results shown in Table 2, regardless of the type of raw material substrate, the sublimation rate (r) on the raw material substrate increases as the growth temperature (Tg) increases. s It can be seen that the growth rate (r) on the growth substrate increases. g ) also sublimation rate (r s The growth rate (Tg) depends on the temperature and shows an increasing trend in the range of 1900°C to 2300°C as the growth temperature (Tg) increases. However, growth hardly occurs below 1900°C, and the raw material utilization efficiency (η) decreases significantly at temperatures above 2300°C. For this reason, it was confirmed that the practical growth temperature (Tg) range for implementing the present invention is between 1900°C and 2300°C.

[0057] On the other hand, focusing on the properties of the raw material substrate, the sublimation rate (r) at the same growth temperature (Tg) is considered. s ) and growth rate (r g When comparing the specific gravity, the lower the specific gravity, the faster the growth rate (r g ) and sublimation rate (r s It was found that the specific gravity improved. 3 Compared to the case where a raw material substrate made of single-crystal silicon carbide is used, the specific gravity is 3.1 g / cm³. 3 This embodiment confirmed that using the following polycrystalline silicon carbide substrates or silicon carbide sintered bodies as raw material substrates improves the growth rate by more than 1.3 times.

[0058] [Example 3] To verify the effects of the present invention, a verification experiment was conducted using a disc-shaped single-crystal 4H-SiC silicon carbide substrate with a diameter of 100 mm and a thickness of 0.36 mm as the growth substrate (G). However, the growth surface (Fg) of the growth substrate (G) was exposed at a 4-degree angle from the 4H-SiC(0001) silicon surface. The growth substrates are shown as G31, G32, and G33 in Figure 13, and a protective film (Gb) consisting of a 50 μm thick G-coat was applied to the surfaces other than the growth surface (Fg), except for growth substrate G32. A disc-shaped hexagonal silicon carbide sintered body with a diameter of 100 mm and a thickness of 1 mm was used as the raw material substrate (S) facing the growth substrate. The average particle size of the hexagonal silicon carbide sintered body was 5.6 μm, and its specific gravity was 2.2 g / cm³. 3 These growth substrates (G31, G32, G33) and the raw material substrate (S) were fixed inside a cylindrical container (CT) made of high-purity carbon, as shown in the cross-sectional view in Figure 13, such that the normal axis of the substrate surface was within 2 degrees vertically. To maintain a distance of 0.5 mm ± 0.1 mm between the raw material substrate (S) and each growth substrate (G31, G32, G33), a donut-shaped disc (CS) made of high-purity carbon with a thickness of 0.5 mm was inserted between each substrate. The outer diameter of the donut-shaped disc (CS) was 104 mm, and its inner diameter was 98 mm. The inner diameter of the container was 105 mm.

[0059] The container, in which the raw material substrate (S) and growth substrates (G31, G32, G33) were fixed, was placed in the center of an electric furnace with resistance heating elements arranged concentrically. After evacuating the electric furnace, the contents were replaced with argon gas at 1100 hPa and heated at a rate of 40°C / min until the growth temperature (Tg) reached 2200°C. After the electric furnace reached 2200°C, the container temperature was maintained at 2200°C for 2 hours. Subsequently, the container was air-cooled naturally in an argon atmosphere at 1100 hPa until the temperature dropped below 100°C. After removing the container from the electric furnace, all substrates were separated from the container, and the G-coat residue adhering to the back surface of the growth substrates (G31, G32, G33) was removed by heating in air at 900°C for 120 minutes. Finally, the weight change of the growth substrates was measured using an electronic balance, and the growth rate (r) on the growth substrates was determined. g ) was sought.

[0060] Table 3 shows the growth rate (r) on each growth substrate. g The table shows that the growth substrates (G31, G33) with a protective film (Gb) formed on their back surface exhibit a growth rate more than three times faster than the growth substrate (G32) without a protective film. Therefore, it has become clear that the protective film (Gb) in the silicon carbide crystal growth method of the present invention prevents the sublimation of silicon carbide from the vertically downward surface of the growth substrate, thereby significantly improving the utilization efficiency of the raw material substrate.

[0061] [Table 3]

[0062] [Example 4] To verify the effects of the present invention, verification was conducted using a disc-shaped single-crystal 4H-SiC silicon carbide substrate with a diameter of 100 mm and a thickness of 0.36 mm as both the raw material substrate and the growth substrate. However, the growth surface (Fg) of the growth substrate was exposed with a surface tilted 4 degrees in the [11-20] direction from the 4H-SiC(0001) silicon surface, and the sublimation surface (Fs) of the raw material substrate was exposed with a surface tilted 8 degrees in the [-1-120] direction from the 4H-SiC(000-1) carbon surface. These growth substrates and raw material substrates were fixed in a cylindrical container (CT) made of high-purity carbon so that the normal axis of the substrate surface was within 2 degrees in the vertical direction, as shown in the cross-sectional view in Figure 14. The growth substrates are shown as G41 and G42 in Figure 14. A protective film (Gb) consisting of a 50 μm thick G-coat was applied to the surface of each growth substrate that was different from the growth surface (Fg). The raw material substrates are shown as S41 and S42 in Figure 14. A raw material auxiliary substrate (SS), consisting of a disc-shaped hexagonal silicon carbide sintered body with a diameter of 100 mm and a thickness of 1 mm, is placed coaxially above the raw material substrate S41. The average particle size of the hexagonal silicon carbide sintered body constituting the raw material auxiliary substrate (SS) is 5.6 μm, and its specific gravity is 2.2 g / cm³. 3To maintain a spacing of 0.5 mm ± 0.1 mm between the raw material substrates (S41, S42), the growth substrates (G41, G42), and the raw material auxiliary substrate (SS), a donut-shaped disc (CS) made of high-purity carbon with a thickness of 0.5 mm was inserted between each substrate. The outer diameter of the donut-shaped disc is 104 mm, and the inner diameter is 98 mm. The inner diameter of the container is 105 mm.

[0063] The atmosphere and heating method inside the containers in which each substrate is placed are the same as in Example 3, so a detailed description is omitted. After heating, the containers are cooled to below 100°C and removed from the electric furnace. Each substrate is then separated from the container, and the G-coat residue adhering to the back surface of the growth substrate is removed by heating in air at 900°C for 120 minutes. The weight change is then measured using an electronic balance, and the growth rate (r) on the growth substrate is determined. g ) and the sublimation rate of the raw material substrate and raw material auxiliary substrate (r s ) was sought.

[0064] Table 4 shows the growth rate (r) on each growth substrate. g ) and sublimation rate (r s This shows that the growth rate (r) exceeds 5 μm / hour on all growth substrates (G41, G42). As is clear from the table, the growth rate (r) exceeds 5 μm / hour on all growth substrates (G41, G42). g ) can be achieved. Sublimation rate of raw material substrate S42 (r s ) is 7.7 μm / hour, while the sublimation rate (r) in the raw material substrate S41 is 7.7 μm / hour. s The negative value indicates that the growth rate of silicon carbide crystals exceeded the sublimation rate. In other words, it can be concluded that the raw material auxiliary substrate (SS) supplied raw material molecules to the raw material substrate S41, increasing its thickness. As described above, it has been verified that the present invention eliminates the consumption of raw material substrates made of single-crystal silicon carbide and reduces the manufacturing cost of single-crystal silicon carbide substrates.

[0065] [Table 4]

[0066] Although the present invention has been described so far with reference to the embodiments and examples shown in the drawings, the present invention is not limited thereto, and the crystal structure of silicon carbide constituting the raw material substrate and growth substrate can be arbitrarily selected. Furthermore, there are no restrictions on the thickness of each substrate, and it can be determined in consideration of the required number of processing sheets and the thickness of the silicon carbide growth layer. The raw material substrate and growth substrate do not necessarily have to be perfectly circular, and as long as they are stacked coaxially, orientation flats to indicate the crystal orientation may be provided at the edges.

[0067] In addition, while ideally a horizontal line (bar) should be placed above the number when the Miller index, which indicates the plane orientation of the SiC crystal, is negative, this is not possible. Therefore, in this specification and the claims, a minus sign "-" is placed before the number to indicate this. [Industrial applicability]

[0068] The silicon carbide crystal growth method of the present invention can be used for substrate materials and epitaxial growth layers in the manufacture of semiconductor devices, including power MOSFETs. Furthermore, taking advantage of its high productivity and low manufacturing cost, it can also be used for manufacturing substrates for mold optics, high-temperature and high-pressure resistant sensors, or X-ray mirrors. [Explanation of Symbols]

[0069] S, S41, S42 Raw material substrate G, G31, G32, G33, G41, G42 growth substrate Fs sublimation surface Fg growth surface r g growth rate r s Sublimation speed Rg growth substrate back surface Rs raw material substrate back surface θg: The inclination angle of the growth plane relative to the closest-packed plane of the crystal lattice. θs: Inclination angle of the sublimation plane relative to the closest-packed plane of the crystal lattice. σg Equilibrium vapor pressure on the growth surface σs Equilibrium vapor pressure on the sublimation surface Gb protective film Dg growth substrate diameter Ds raw material substrate diameter SS raw material auxiliary substrate CT container d. Spacing between the growth surface and the sublimation surface. g gravitational acceleration Closest-packed surfaces of CPP crystal lattices Np Microscopic Terrace Cp microscopic step

Claims

1. A plate-shaped raw material substrate is used for sublimating raw material molecules, which are molecules composed of carbon and silicon bonded together, from a sublimation surface made of silicon carbide, and a plate-shaped growth substrate is used for crystallizing the raw material molecules on a growth surface made of silicon carbide to grow silicon carbide crystals. The growth substrate is positioned in a gravitational field so that the growth surface is oriented vertically upward, and the raw material substrate is positioned so that the sublimation surface opposite the growth surface is oriented vertically downward. The entire vertically downward side of the growth substrate is covered with carbon, boron nitride (BN), and aluminum oxide (Al ２ O ３ ), zirconium oxide (ZrO ２ ), yttrium oxide (Y ２ O ２ A protective film of 10 μm or more in thickness, made of either , tantalum carbide (TaC), or is tightly adhered without any gaps, and the distance between the opposing sublimation surface and the growth surface is set to a constant interval of 0.1 mm or more and 3 mm or less, and helium (He), neon (Ne), nitrogen (N) is placed in the space between the growth surface and the sublimation surface. ２ A method for growing silicon carbide crystals, comprising filling a growth surface with one or more inert gases selected from argon (Ar) and krypton (Kr) at a pressure of 1300 hPa or less and 700 hPa or more, and then maintaining it at a uniform temperature of 1900°C or higher and 2300°C or lower.

2. A method for growing silicon carbide crystals according to claim 1, characterized in that a single-crystal silicon carbide is exposed on the growth surface, and the angle at which the growth surface intersects the base plane of the crystal lattice is 1 degree or more and 12 degrees or less.

3. A silicon carbide crystal growth method according to claim 1 or 2, wherein the raw material substrate is composed of silicon carbide microcrystals or fine powder, and the specific gravity of the raw material substrate (JIS R 1634) is 1.6 g / cm³. ３ The above, and 3.1 g / cm³ ３ A method for growing silicon carbide crystals, characterized by the following:

4. A silicon carbide crystal growth method according to claim 2, characterized in that single-crystal silicon carbide is exposed on the sublimation surface of the raw material substrate, and the angle at which the sublimation surface intersects the base plane of the crystal lattice is 2 degrees or more higher than the angle at which the growth surface opposite the sublimation surface intersects the base plane of the crystal lattice.

5. The method for growing a silicon carbide crystal according to claim 4, which uses a raw material substrate made of single crystal silicon carbide, arranges a raw material auxiliary substrate vertically above the raw material substrate, the raw material auxiliary substrate is composed of microcrystals or micropowders of silicon carbide, and its specific gravity (JIS R 1634) is 1.6 g / cm ３ or more and 3.1 g / cm ３ or less, and is characterized by the method for growing a silicon carbide crystal.

6. A silicon carbide crystal growth method according to any one of claims 1 to 5, characterized in that the growth substrate and the raw material substrate are disc-shaped and arranged coaxially, and the diameter of the raw material substrate is 1.1 times or more the diameter of the growth substrate.

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