Silicon carbide crystal growth method

Abstract

The silicon carbide crystal growth does not require precise control of temperature gradients or gas flow paths, and the occurrence of crystal defects and thermal distortion is suppressed, thereby increasing the efficiency of use of silicon carbide raw materials, thereby improving the productivity of silicon carbide substrates and reducing manufacturing costs. [Solution] By sublimating raw material molecules from the silicon carbide sublimation surface of the source substrate and applying gravitational acceleration to transport them stably and uniformly to the silicon carbide growth surface of the growth substrate, it is possible to simultaneously form a large number of silicon carbide growth layers without the need for a temperature gradient. Furthermore, by preventing leakage of the silicon carbide raw material from the back surface of the growth substrate or the gap between the growth substrate and the source substrate, the efficiency of use of the silicon carbide raw material is improved, thereby enabling improved productivity and reduced manufacturing costs.

Description

[Technical Field]

[0001] The present invention relates to a method for producing silicon carbide crystal substrates used as substrate materials for semiconductor devices, and in particular to a method for inexpensively producing a large number of large-area silicon carbide substrates simultaneously by sublimation. [Background technology]

[0002] Typical methods for producing single-crystal silicon carbide substrates include liquid phase epitaxy, vapor phase epitaxy, and sublimation. Among these, the most common method for producing silicon carbide is the modified Lely process, a type of sublimation process. However, the modified Lely process requires precise control of the amount of source molecules (one or more types of molecules composed of carbon and silicon) supplied to the surface of the seed crystal (the substrate on which silicon carbide crystals are grown). This requires delicate adjustments of the placement of the seed crystal and source materials (substrates or powders generated by sublimation of source molecules) within the furnace, the temperature gradient from the source materials to the seed crystal, and the gas flow path. Furthermore, reproducibly obtaining high-quality silicon carbide crystals requires extensive adjustment of the conditions based on empirical rules. Furthermore, the power and consumable parts required for crystal growth, as well as the labor required for substrate contour processing, make it difficult to significantly reduce production costs. Additionally, the temperature gradient during crystal growth can cause thermal distortion within the growing silicon carbide layer, which can lead to crystal defects and result in poor crystal quality.

[0003] Unlike the modified Lely process, a simpler method for producing silicon carbide substrates has been devised: the proximity sublimation method, described in Materials Science Forum Vol. 264-268 (1998) pp. 143-146 (Non-Patent Document 1). The proximity sublimation method involves placing a seed crystal and a source material in close proximity in a vessel, heating the source material to sublimate silicon carbide, which is then recrystallized on the seed crystal to obtain a growth layer. However, because a temperature difference is created between the source material and the seed crystal in a typical proximity sublimation method, the occurrence of crystal defects due to thermal distortion cannot be suppressed, as with the modified Lely process. Furthermore, only one single-crystal silicon carbide substrate can be produced per operation, and significant reductions in production costs compared to the modified Lely process cannot be expected.

[0004] Japanese Patent Publication No. 6720436 (Patent Document 1) proposes a method for growing silicon carbide crystals by placing silicon carbide with different polarity faces (carbon and silicon faces) facing each other and maintaining a uniform temperature between 1600°C and 2600°C. The method transports source molecules from the source surface (carbon face), which has a relatively high saturated vapor pressure, to the seed crystal surface (silicon face), which has a relatively low saturated vapor pressure. This method achieves crystal growth in a uniform temperature atmosphere, enabling the simultaneous growth of multiple silicon carbide crystals. Furthermore, because it does not require a temperature gradient from the source surface to the seed crystal surface, the occurrence of crystal defects associated with thermal strain, as in the modified Lely process, is suppressed. Furthermore, it has been shown that by ensuring that the solid angle of any point on the seed crystal surface looking out at the silicon carbide surface with a high saturated vapor pressure is 2π steradians, silicon carbide is uniformly supplied to the seed crystal surface, improving the film thickness uniformity of the recrystallized silicon carbide. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6720436 [Patent Document 2] U.S. Patent No. 4,912,064 [Patent Document 3] U.S. Patent No. 5,011,549 [Non-patent literature]

[0006] [Non-Patent Document 1] Materials Science Forum Vol 264-268(1998) pp.143-146 Summary of the Invention [Problem to be solved by the invention]

[0007] Despite the above-mentioned technological advances, close-range sublimation has not yet been used for industrial production of silicon carbide. For example, in Non-Patent Document 1 (Materials Science Forum Vol. 264-268 (1998) pp. 143-146), it is difficult to simultaneously grow crystals on multiple substrates due to the need for a temperature gradient. Alternatively, the method proposed in Patent Document 1 (Japanese Patent No. 6720436) requires a difference in saturated vapor pressure between the source material and the seed crystal, limiting the polarity combinations of the source material and the seed crystal surface. Specifically, the source material surface must be a carbon surface with a high saturated vapor pressure, while the seed crystal surface must be a silicon surface with a low saturated vapor pressure. Furthermore, to ensure that the seed crystal surface has a solid angle of 2π steradians looking into the source material surface, silicon carbide must be deposited not only on the source material surface but also on the surrounding furnace walls. This results in a problem of poor source material utilization efficiency (the rate at which silicon carbide lost from the source material is converted into silicon carbide crystals in the growth layer).

[0008] The present invention has been developed in consideration of the above circumstances, and enables a reduction in manufacturing costs by minimizing the consumption of consumable parts and silicon carbide raw material required for crystal growth without requiring the delicate gas distribution, temperature gradient control, gas flow path adjustment, etc., and empirical adjustment of growth conditions required in the modified Lely process.Furthermore, the present invention provides a manufacturing method for simultaneously manufacturing a large number of high-quality silicon carbide substrates with any crystal plane at low cost, eliminating restrictions on the crystal orientation exposed on the surface of the raw material and the seed crystal surface. [Means for solving the problem]

[0009] As a result of extensive research into solving the above problems, the inventors noticed that applying gravitational acceleration to a source substrate (a substrate for sublimating source molecules formed by bonding carbon and silicon) in the direction of a growth substrate (corresponding to the seed crystal in conventional technology, a substrate for growing silicon carbide crystals on the growth surface) causes a certain amount of source molecules to move uniformly, and discovered that this is the driving force for crystal growth on the growth surface of the growth substrate, thereby completing the present invention.

[0010] Next, the means for solving the problems according to the present invention will be described. [1] A plate-shaped source substrate for sublimating source molecules consisting of molecules in which carbon and silicon are bonded from a sublimation surface made of silicon carbide, and a plate-shaped growth substrate for growing silicon carbide crystals by crystallizing the source molecules on a growth surface made of silicon carbide are used. The growth substrate is arranged so that the growth surface faces vertically upward in a gravitational field, and the source substrate is arranged so that the sublimation surface opposite the growth surface faces vertically downward. The entire vertically downward side of the growth substrate is covered with carbon, boron nitride (BN), aluminum oxide (Al2O3), zirconium oxide (ZrO2), yttrium oxide (Y2O2), A silicon carbide crystal growth method in which a protective film of 10 μm or more in thickness made of either tantalum carbide (TaC) is tightly adhered without any gaps, the distance between the opposing sublimation surface and growth surface is set to a constant distance of 0.1 mm or more and 3 mm or less, the space between the growth surface and the sublimation surface is filled 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, and the temperature is maintained at a uniform temperature of 1900°C or more and 2300°C or less to grow silicon carbide crystals on the growth surface. [2] A method for growing silicon carbide crystals according to [1], characterized in that single-crystal silicon carbide is exposed on the growth surface, and the angle between the growth surface and the basal plane of the crystal lattice is set to be 1 degree or more and 12 degrees or less. [3] The silicon carbide crystal growth method according to either [1] or [2], wherein the source substrate is composed of silicon carbide microcrystals or fine powder, and the specific gravity of the source substrate (JIS R 1634) is 1.6 g / cm 3 or more and 3.1g / cm 3 A method for growing silicon carbide crystals, characterized by: [4] A method for growing silicon carbide crystals according to [2], characterized in that single-crystal silicon carbide is exposed on the sublimation surface of the source substrate, and the angle at which the sublimation surface intersects with the basal plane of the crystal lattice is at least 2 degrees higher than the angle at which the growth surface opposite the sublimation surface intersects with the basal plane of the crystal lattice. [5] The silicon carbide crystal growth method according to [4], wherein a raw material substrate made of single crystal silicon carbide is used, and a raw material auxiliary substrate is placed vertically above the raw material substrate, and the raw material auxiliary substrate is made of silicon carbide microcrystals or fine powder, and its specific gravity (JIS R 1634) is 1.6 g / cm 3 or more and 3.1g / cm 3 A method for growing silicon carbide crystals, characterized by: [6] A method for growing silicon carbide crystal according to any one of [1], [2], [4] or [5], characterized in that the growth substrate and source substrate are disk-shaped and arranged coaxially, and the diameter of the source substrate is 1.1 times or more the diameter of the growth substrate. [7] A method for growing silicon carbide crystal according to [3], characterized in that the growth substrate and source substrate are disk-shaped and arranged coaxially, and the diameter of the source substrate is at least 1.1 times the diameter of the growth substrate. [Effects 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, a source substrate (S) and a growth substrate (G) are held horizontally so that the gravitational acceleration (g) of the gravitational field acts in the vertical direction. However, the source substrate (S) is placed above the growth substrate (G). When the space containing the source substrate and the growth substrate is heated to 1900°C or higher, source molecules sublimated from the sublimation surface (Fs), which is the vertically downward surface of the source substrate (S), are subjected to gravitational acceleration (g) and transported to the growth surface (Fg), which is the vertically upward surface of the growth substrate (G), where they contribute to crystal growth. Because gravitational acceleration (g) acts almost uniformly on Earth, the transport of source molecules is also uniform, and a highly uniform silicon carbide crystal growth layer can be obtained on the growth surface (Fg).

[0012] In the present invention, the distance (d) is adjusted to a range of 0.1 mm to 3 mm while maintaining the parallelism between the sublimation surface (Fs) and the growth surface (Fg). This prevents the leakage of source molecules from the distance between the sublimation surface (Fs) and the growth surface (Fg), and most of the source molecules contribute to crystal growth, thereby increasing the utilization efficiency of the source substrate.

[0013] On the other hand, vertically downward gravitational acceleration (g) also acts on the back surface (Rg) of the growth substrate (G). When silicon carbide is exposed on the back surface (Rg), precursor molecules fall off the growth substrate (G), offsetting the amount of silicon carbide crystals grown on the growth surface (Fg). To avoid this, in the present invention, the back surface (Rg) of the growth substrate is coated with a protective film (Gb) with a thickness of 10 μm or more. The components of the protective film, carbon, boron nitride (BN), aluminum oxide (Al2O3), zirconium oxide (ZrO2), yttrium oxide (YO2O2), and tantalum carbide (TaC), all have lower vapor pressures than silicon carbide at temperatures above 1900°C. This prevents silicon carbide from sublimating from the back surface (Rg) of the growth substrate and prevents precursor molecules from falling off. As a result, the thickness of the growth substrate (G) can be increased in proportion to the growth time.

[0014] The source molecules exist as gases near the sublimation surface (Fs) and the growth surface (Fg), 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 can maintain the equilibrium vapor pressure near the sublimation surface (Fs) higher than that near the growth surface (Fg) by exposing a silicon carbide crystal surface with a higher surface tension than the growth surface (Fg) to the sublimation surface (Fs) or by reducing the crystal grain size exposed to the sublimation surface (Fs). Adding a source material transport mechanism using gravitational acceleration (g) to this allows for a uniform crystal growth rate higher than that of the method described in Patent Document 1 (Japanese Patent No. 6720436).

[0015] The saturated vapor pressure at the silicon carbide crystal surface increases exponentially as the temperature rises. 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 source molecules is generated near the sublimation surface (Fs). Furthermore, for every 100°C increase in temperature, the partial pressure of the source molecules increases by approximately 9 times, and at 2200°C, the partial pressure of the source molecules is approximately 700 Pa, dramatically increasing the silicon carbide crystal growth rate. However, as the temperature increases, the difference with the partial pressure of the vapor sublimating from the growth surface (Fg) narrows, reducing the efficiency of source material use. Therefore, the upper limit of the temperature for achieving the effects of the present invention is 2300°C.

[0016] Since the temperature when carrying out the present invention is maintained at a specific temperature (growth temperature) in the range of 1900°C or higher and 2300°C or lower, it is possible to improve productivity by using a unit structure in which a source substrate (S) and a growth substrate (G) face each other as shown in the cross-sectional view of Fig. 1 and stacking multiple unit structures to form a multi-layer structure as shown in the cross-sectional view of Fig. 2. In this case, if the source substrate (S) and the growth substrate (G) are disk-shaped, aligning their respective centers on the same axis makes it possible to improve the uniformity of the thickness of the growth layer within the plane of the growth surface (Fg).

[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 (N), argon (Ar), and krypton (Kr), thereby suppressing oxidation of the source substrate, growth substrate, and source molecules. Furthermore, because the pressure is kept below 1300 hPa, the buoyancy effect acting on the source molecules sublimated from the sublimation surface (Fs) is minimal, and vertical downward transport due to gravitational acceleration is not impeded. The transport capacity of source molecules due to gravitational acceleration (g) increases as the surrounding gas pressure is lowered, but at the same time, the mean free path of the source molecules increases, leading to leakage from the space between the growth surface (Fs) and the sublimation surface (Fg), resulting in reduced source utilization efficiency. To avoid this, the present invention suppresses source molecule leakage by setting the lower limit of the gas pressure to 700 hPa. Therefore, as shown in Patent Document 1 (Japanese Patent No. 6720436), it is not necessary to maintain the solid angle of the sublimation surface on the growth surface at 2π steradians.

[0018] The main component of the source substrate (S) used in the present invention is silicon carbide. However, there are no limitations on the crystalline structure exposed on its sublimation surface (Fs). It is possible to expose silicon carbide of any crystalline structure, whether single crystal or polycrystalline. In other words, unlike Patent Document 1 (Japanese Patent No. 6720436), there is no need to impose specific limitations on the surface polarity of the silicon carbide exposed on the growth surface or sublimation surface. Silicon carbide with the desired crystalline 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 crystallites and their voids. In fact, the more voids the source 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 source molecules increases, accelerating crystal growth on the growth surface (Fg). For this reason, in the present invention, the density of the source substrate (S) is set to 3.1 g / cm. 3 By keeping the voids contained therein at 3% or more of the total volume, it also provides a means for increasing the amount of raw material molecules supplied to the growth surface (Fg).

[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 sintered silicon carbide is exposed, certain crystal grains may grow over time due to merging, and some of these grains may detach during crystal growth and fall to the growth surface (Fg) due to gravitational acceleration. As a result, it is impossible to eliminate the possibility of silicon carbide with a crystal structure different from that originally intended to be exposed on the growth surface (Fg). To address this issue, the silicon carbide crystal growth method of the present invention also provides a means for growing a crystal 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 growing and falling is eliminated.

[0020] However, the vapor pressure (σs) of the sublimation plane (Fs) where the single-crystal silicon carbide is exposed does not necessarily exceed the vapor pressure (σg) of the growth plane (Fg), which may result in a silicon carbide growth layer not being obtained on the growth plane (Fg). To avoid this, the present invention provides a method for maintaining a higher inclination angle of the sublimation plane (Fs) where the single-crystal silicon carbide is exposed with respect to the close-packed plane (CPP) of the crystal lattice than the inclination angle of the growth plane (Fg) where the single-crystal silicon carbide is exposed with respect to the close-packed plane (CPP) of the crystal lattice, as shown in the cross-sectional view of Figure 3.

[0021] As shown in the microscopic cross-sectional view of the substrate surface in Figure 4, the inclination of the single crystal surface relative to the close-packed planes of the crystal lattice results in the formation of microscopic terraces (Cp) and microscopic steps (Np) on the surface. The surface of the microscopic terraces (Np) corresponds to the close-packed planes (CPP) of the crystal lattice, and the microscopic steps (Np) expose nonpolar or semipolar planes with relatively high surface energy, increasing their vapor pressure. Therefore, the vapor pressure increases as the angle of the single crystal surface relative to the close-packed planes (CPP) of the crystal lattice increases. In this invention, we provide a method in which the angle between the sublimation plane (Fs) of the single crystal and the close-packed planes (CPP) of the crystal lattice is defined as θs, and the angle between the growth plane (Fg) of the single crystal and the close-packed planes (CPP) of the crystal lattice is defined as θg, and θs is set to an angle of at least 2 degrees relative to θg. In this case, the vapor pressure (σg) of the growth plane reflects the step density and is proportional to Sin(θg). Similarly, the vapor pressure (σs) of the sublimation surface reflects the density of the steps and is proportional to Sin(θs). Therefore, the growth rate on the growth surface is proportional to the value obtained by subtracting Sin(θg) from Sin(θs). In the present invention, θs is more than 2 degrees higher than θg, so the value of σs relative to σg is more than 1.03 times, and the crystal growth rate on the growth surface (Fg) is accelerated.

[0022] Exposing the growth surface (Fg) of single-crystal silicon carbide and tilting the surface from the close-packed plane (CPP) of the crystal lattice is also effective in preventing the incorporation of polymorphic crystals into the growth layer. As described with reference to the cross-sectional view shown in Figure 4, on the growth surface (Fg) tilted from the close-packed plane (CPP) of the crystal lattice, microscopic terraces (Cp) and microscopic steps (Np) consisting of close-packed planes are formed depending on the tilt angle (θg). The crystal growth in this case is step-controlled epitaxy, in which the microscopic steps (Np) grow laterally, as shown in Patent Document 2 (U.S. Patent No. 4,912,064) and Patent Document 3 (U.S. Patent No. 5,011,549). Step-controlled epitaxy preserves the layered structure of silicon carbide exposed on the initial growth surface and prevents the development of a different crystal structure. Furthermore, step-controlled epitaxy also seals dislocations exposed on the initial growth surface, thereby reducing the defect density in the growth layer of the silicon carbide layer. In the present invention, step-controlled epitaxy is achieved by setting the tilt angle (θg) to 1 degree or more. However, to avoid step bunching, which increases the surface roughness of the grown layer, the tilt angle (θg) must be kept to 12 degrees or less.

[0023] However, when the silicon carbide crystal growth method of the present invention is carried out using single-crystal silicon carbide as the source substrate (S) and obtaining a growth layer of single-crystal silicon carbide on the growth surface (Fg), an amount of single-crystal silicon carbide equal to or greater than the growth layer is consumed from the source substrate, which does not fundamentally reduce manufacturing costs. However, in the present invention, as shown in Figure 5, a source support substrate (SS) made of polycrystalline silicon carbide or sintered silicon carbide is placed vertically above the back surface (Rs) of the source substrate, and source molecules sublimated from the source substrate (SS) are supplied to the source 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 produced on the back surface (Rs). Even if the source auxiliary substrate (SS) comes into contact with the source substrate (S), single-crystal silicon carbide is always exposed on the sublimation surface (Fs) opposite the growth surface (Fg), so the properties of the source auxiliary substrate (SS) do not affect the growth conditions or the quality of the grown layer. Here, if a quantity of single-crystal silicon carbide is grown on the back surface (Rs) of the source substrate that exceeds the amount of silicon carbide sublimated on the sublimation surface (Fs), consumption of the source substrate (S) is eliminated. To achieve this, in the present invention, the source auxiliary substrate (SS) placed on the back surface (Rs) of the source substrate is made of silicon carbide microcrystals or fine powder, and its specific gravity is 1.6 g / cm 3 or more and 3.1g / cm 3 By setting the above, it is possible to supply single crystal silicon carbide to the back surface (Rs) side in excess of the amount consumed on the sublimation surface (Fs) side.

[0024] There is no particular restriction on the distance between the rear surface (Rs) of the source substrate and the source supplementary substrate (SS), but it is desirable to set the distance to 1 mm or less so that the source molecules sublimated from the source supplementary substrate (SS) are reliably incorporated into the source substrate. Alternatively, the source substrate (S) and the source supplementary substrate (SS) may be brought into close contact with each other. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a cross-sectional view showing the effects of the present invention and the arrangement of a source substrate, a growth substrate, and a protective film in an embodiment. [Figure 2]1 is a cross-sectional view showing the effects of the present invention and the arrangement when source substrates and growth substrates are multi-layered in an embodiment. [Figure 3] 1 is a cross-sectional view showing the effects of the present invention and the arrangement of a source substrate made of single-crystal silicon carbide and a growth substrate made of single-crystal silicon carbide in an embodiment. [Figure 4] 1A and 1B are cross-sectional views showing the microscopic surface structures of a source substrate made of single-crystal silicon carbide and a growth substrate made of single-crystal silicon carbide in the effect of the present invention. [Figure 5] 1 is a cross-sectional view showing the arrangement of a source substrate made of single-crystal silicon carbide, a growth substrate made of single-crystal silicon carbide, and a source auxiliary substrate in the effect of the present invention. [Figure 6] FIG. 2 is a diagram showing the relationship between the ratio of the diameter (Ds) of the source substrate to the diameter (Dg) of the growth substrate and the film thickness distribution of the growth layer in an embodiment of the present invention. [Figure 7] FIG. 2 is a diagram showing the film thickness distribution of a growth layer relative to the distance (d) between the growth surface and the sublimation surface in an embodiment of the present invention. [Figure 8] 1 is a cross-sectional view showing a state in which a source substrate and a growth substrate are placed in a container in an embodiment of the present invention. [Figure 9] 1 is a cross-sectional view showing an arrangement when containers in which source substrates and growth substrates are placed are stacked in multiple layers in an embodiment of the present invention. [Figure 10] 1 is a cross-sectional view showing an arrangement when a plurality of source substrates and a plurality of growth substrates are alternately stacked in a container in an embodiment of the present invention. [Figure 11] 1 is a cross-sectional view showing an arrangement when a plurality of source substrates and a plurality of growth substrates are alternately stacked in a container in an embodiment of the present invention. [Figure 12] FIG. 2 is a cross-sectional view showing the arrangement when a source substrate and a growth substrate are placed opposite each other in a container in Examples 1 and 2 of the present invention. [Figure 13] FIG. 10 is a cross-sectional view showing an arrangement when a plurality of source substrates and a plurality of growth substrates are alternately stacked in a container in Example 3 of the present invention. [Figure 14]FIG. 10 is a cross-sectional view showing an arrangement when a plurality of source substrates, a plurality of growth substrates, and source auxiliary substrates are alternately stacked in a container in Example 4 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

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

[0027] (growth substrate) There is no limit to the area of ​​the growth substrate (G); its maximum width can be 1 cm or 30 cm, and similar results can be achieved. To grow single-crystal silicon carbide with a specific crystal structure on a growth substrate, a single-crystal silicon carbide with the same crystal structure must be exposed on the growth surface. For example, if single-crystal 4H-SiC is to be grown as a growth layer using the substrate configuration 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 exposed on the growth surface (Fg) is a (0001) silicon-polar plane, the surface of the growth layer will also be a 4H-SiC (0001) silicon-polar plane. If the surface orientation of the 4H-SiC exposed on the growth surface is a (000-1) carbon-polar plane, the surface of the growth layer will also be a 4H-SiC (000-1) carbon-polar plane. On the other hand, if the (0001) silicon polarity plane of single-crystal 6H-SiC is exposed on the growth surface (Fg), the surface of the growth layer will also be a 6H-SiC (0001) silicon polarity plane. Similarly, if the (111) silicon plane of single-crystal 3C-SiC is exposed on the growth surface (Fg), the surface of the growth layer will also be a 3C-SiC (111) silicon polarity plane. When multiple source substrates (S) and growth substrates (G) are stacked as shown in the cross-sectional view of Figure 2, growth substrates with different crystal structures may be mixed.

[0028] In this case, 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 close-packed plane (CPP) of the crystal lattice, as shown in the cross-sectional view of Figure 3, step-controlled epitaxy will occur, as shown in Patent Document 2 (U.S. Patent No. 4,912,064) and Patent Document 3 (U.S. Patent No. 5,011,549), and it will be possible to prevent the incorporation of heterogeneous crystal structures. However, in order to prevent an increase in the density of crystal defects that accompanies the formation of macrosteps, θg must be kept to 12 degrees or less.

[0029] When 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; it is sufficient that at least the growth surface (Fg) is a specific single-crystal silicon carbide. Therefore, it is also possible to use a substrate made of polycrystalline silicon carbide or amorphous silicon carbide as the growth substrate (G) and obtain the 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] Since the back surface (Rg) of the growth surface (Fg) faces vertically downward, if the entire growth substrate (G) is made of silicon carbide, the vapor containing silicon carbide sublimated from the back surface (Rg) will sink due to gravitational acceleration and be lost from the growth substrate (G). To prevent this, in the present invention, as shown in the cross-sectional views of Figures 1, 2, and 3, a protective film (Gb) made of carbon, boron nitride (BN), aluminum oxide (Al2O3), zirconium oxide (ZrO2), yttrium oxide (YO2O2), or tantalum carbide (TaC) is adhered to the back surface (Rg) of the growth substrate to suppress sublimation. The vapor pressure of the protective film components is lower than that of silicon carbide at temperatures above 1900°C, 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 is at least 10 μm or more, and more preferably is greater than the thickness of the silicon carbide growth layer to be obtained on the growth surface (Fg).

[0031] The protective film (Gb) must adhere tightly to the entire backside (Rg) of the growth substrate without any gaps. Simply placing the growth substrate (G) on a carbon or tantalum carbide plate, as is typically done in semiconductor substrate heat treatment, is undesirable because it creates voids on the backside (Rg) due to warpage of the growth substrate (G), which prevents complete sublimation of silicon carbide. PVD methods such as sputtering and ion plating, chemical vapor deposition, and plasma CVD can be used to form a protective film (Gb) that adheres tightly to the backside (Rg) of the growth substrate. A simpler and more inexpensive method is to apply a commercially available carbon coating material to the backside (Rg) of the growth substrate to a thickness of approximately 100 μm and dry it to use as the protective film (Gb). Alternatively, if a single-crystal growth surface is not required, polycrystalline or amorphous silicon carbide can be deposited on the protective film (Gb) using chemical vapor deposition, sputtering, laser ablation, ion plating, or plasma CVD.

[0032] (Raw material substrate) There are no restrictions on the crystalline structure of silicon carbide exposed on the sublimation surface (Fs) of the source substrate (S); it is sufficient to generate an equilibrium vapor pressure (σs) equal to or greater than 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 Figures 1 and 2, the source molecules are transported by the gravitational acceleration (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 identical to 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) relative to the crystal grain size of the silicon carbide exposed on the growth surface (Fg), the more σs becomes dominant over σg, making it possible to achieve a higher crystal growth rate. For this reason, it is desirable that the average particle size (ds) of the silicon carbide microparticles exposed on the sublimation surface (Fs) be 10 μm or less, and by further setting ds to 1 μm or less, it is possible to obtain a crystal growth rate of over 30 μm / hour. However, if ds falls below 0.1 μm, polynuclear silicon carbide crystals will form on the growth surface (Fg) at temperatures below 1900°C, increasing the crystal defect density, so ds must be kept at 0.1 μm or more.

[0033] As mentioned above, while the source substrate (S) is primarily composed of silicon carbide, it does not necessarily have to be single crystal, and its density does not have to be the same as that of single crystal silicon carbide. Rather, by including voids in the source substrate and increasing the surface roughness of the sublimation surface (Fs), the effective surface area can be expanded and the equilibrium vapor pressure (σs) can be increased. Such low-density source substrates can be produced by sintering silicon carbide particles and processing them into wafers. There is no limit to the thickness of the source substrate in this case; the thicker it is, the greater its mechanical strength, but its specific gravity (JIS R 1634) is 3.1 g / cm. 3 It is desirable that the density of the raw material substrate is 3% or more of the total volume of voids. This is because the effective surface area of ​​the sublimation surface increases, making it possible to increase the vapor pressure of the raw material molecules. However, as the density of the raw material substrate decreases, the mechanical strength decreases and the substrate becomes more susceptible to breakage, so the lower limit of the specific gravity should be 1.6 g / cm. 3 It is necessary to do so.

[0034] It is preferable to minimize the variation in the size of the silicon carbide microparticles that make up the source substrate. This is because, when microparticles of different sizes are adjacent, the smaller microparticles have a higher vapor pressure, and are transported by the vapor pressure difference with the larger microparticles adjacent to them, contributing to the increase in their size (this phenomenon is referred to as coalescence in this specification). Once coalescence occurs, the uniformity of the microparticle size further deteriorates, and eventually, the enlarged crystal grains cover the sublimation surface, reducing the equilibrium vapor pressure and resulting in a decrease in the crystal growth rate on the growth surface. To prevent this coalescence, the standard deviation of the silicon carbide crystal grain size that makes up the source substrate is preferably 50% or less of the average grain size, and even more preferably 30% or less if the growth time exceeds 24 hours.

[0035] (area ratio of source substrate to growth substrate) The sizes of the source substrate (S) and the growth substrate (G) do not necessarily need to be identical, and increasing the area ratio of the source substrate to the growth substrate improves the growth rate and uniformity of the growth layer. Figure 6 shows the results of a simulation based on statics and the diffusion equation for the thickness distribution of the silicon carbide growth layer as a function of the ratio of the diameter (Dg) of the growth substrate to the diameter (Ds) of the source substrate, assuming the substrate arrangement shown in Figure 1. The simulation assumes that the growth substrate and source substrate are both disk-shaped and arranged coaxially. The distance (d) between the growth surface and the sublimation surface is 1 mm, and the diameter (Dg) of the growth substrate is 200 mm. Figure 6 shows that the growth rate distribution improves as the Ds / Dg value increases. It can be seen that if the Ds / Dg ratio is 1.1 or greater, the film thickness variation within the growth surface can be kept below 1.3% of the average film thickness.

[0036] (Arrangement of growth surface and sublimation surface) When implementing 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) must be oriented vertically upward, and the opposing sublimation surface (Fs) must be oriented vertically downward, maintaining a constant distance (d) and maintaining them as parallel as possible. One reason for this is that source molecules are unevenly distributed on a growth surface tilted relative to gravity. Another reason is that in-plane variations occur in the gap between the growth surface (Fg) and the sublimation surface (Fs), resulting in an in-plane distribution of the 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 growth layer on the growth surface (Fg). For this reason, it is desirable to mechanically hold the source substrate (S) and growth substrate (G) and keep the normal axes of the sublimation surface (Fs) and growth surface (Fg) within 2 degrees of the vertical.

[0037] Furthermore, it is desirable to set the distance (d) between the growth surface (Fg) and the sublimation surface (Fs) to 3 mm or less. This is because a narrower distance (d) increases the number of growth substrates (G) that can be processed simultaneously, improving productivity, and also improves the silicon carbide growth rate on the growth surface (Fg) by reducing the amount of source molecules that escape through the distance (d). Figure 7 shows the simulation results of the thickness distribution of the silicon carbide growth layer obtained on the growth surface when the distance (d) between the sublimation surface and the growth surface is changed when a growth substrate and source substrate of the same diameter are placed facing each other. The simulation results show that narrowing the distance (d) increases the growth layer thickness and improves its uniformity within the surface. In particular, a distance (d) of 1 mm or less increases the growth layer thickness, increases the number of substrates that can be processed simultaneously, and improves productivity. However, to prevent the growth surface (Fg) and the sublimation surface (Fs) from fusing together due to unevenness or warping within the surface of the source substrate (S) and the growth substrate (G), the distance (d) must be kept at 0.1 mm or more.

[0038] (holding the growth substrate and sublimation substrate) When implementing the silicon carbide crystal growth method provided by the present invention, it is desirable to hold a pair of growth substrates (G) and source substrates (S) in a container (CT) as shown in the cross-sectional view of Figure 8 to prevent source molecules from escaping from the gap between the growth surface (Fg) and sublimation surface (Fs). The container must be able to withstand temperatures of 2300°C or higher, be clean enough not to release impurities into the vapor phase, and have the mechanical strength to stably hold all of the growth substrates (G) and source 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 substrates (G) and source substrates (S) are placed in this container (CT) so that the growth surface (Fg) faces vertically upward and the sublimation surface (Fs) faces 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 floor of the container (CT), and the back side of the source substrate (S) may be attached to the top plate 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 of the present invention, stacking and heating multiple containers (CT) each with a pair of source substrates and a growth substrate facing each other, as shown in the cross-sectional view of Figure 9, makes it possible to simultaneously obtain a large number of growth layers. Alternatively, as shown in the cross-sectional view of Figure 10, multiple source substrates (S) and growth substrates (G) can be stacked alternately and placed in the same container (CT). Furthermore, as shown in the cross-sectional view of Figure 11, attaching the back side (Rg) of the growth substrate (G) via a protective film (Gb) to the vertically upward surface (Rs) of the source substrate located vertically below increases the number of growth substrates per unit volume of the container (CT), prevents source molecules from sublimating on the vertically upward surface (Rs) of the source substrate, and further improves the utilization efficiency of the source substrates.

[0040] (Heating mechanism) A container (CT) containing the source substrate (S) and growth substrate (G) placed at a predetermined distance is placed inside an electric furnace. The heating method of the electric furnace may be resistance heating or induction heating, but it is desirable to keep the temperature difference inside the container within 5°C. If a significant temperature difference occurs inside the container, the source 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, it is desirable to arrange the heating mechanism of the electric furnace concentrically, with the container (CT) located at the center, so that uniform heat radiation can be supplied to the outer periphery of the container.

[0041] (Atmosphere during silicon carbide crystal growth) Prior to heating the container (CT), the electric furnace must be filled with a specified high-purity inert gas to remove oxygen and moisture from the container and suppress oxidation of the silicon carbide. The inert gas to be filled into the electric furnace can be one or more of helium (He), neon (Ne), nitrogen (N2), argon (Ar), and krypton (Kr). However, argon (Ar) is the most preferable gas to suppress the buoyancy acting on the source molecules sublimated from the sublimation surface and to reduce gas production costs. Furthermore, donor impurities can be added to the silicon carbide growth layer by mixing an appropriate amount of nitrogen (N2) or phosphine (PH3) with argon (Ar). Acceptor impurities can also be added by mixing an appropriate amount of diborane (B2H6) or trimethylaluminum (Al(CH3)3) with argon (Ar). Prior to introducing the gases, evacuating the electric furnace to a vacuum of 1 Pa or less can reduce the partial pressure of residual gases such as oxygen and moisture, thereby improving the quality of the silicon carbide grown by the present 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 is preferably set to 1100 hPa or higher to avoid the inclusion of ambient air. However, as the inert gas pressure inside the electric furnace increases, the effect of buoyancy acting on the source molecules increases, suppressing the transport of source molecules from the sublimation surface to the growth surface. Therefore, it is desirable to set the upper limit of the pressure inside the electric furnace to 1300 hPa. The pressure inside the electric furnace is measured with a capacitance type pressure gauge, and the pressure can be adjusted by adjusting the opening of a throttle valve installed in the exhaust section of the electric furnace so that the pressure is at a predetermined value.

[0043] (growth temperature) In the present invention, silicon carbide crystal is grown by supplying source molecules from a source substrate to a growth substrate at a specific temperature (growth temperature) in the temperature range of 1900°C or higher and 2300°C or lower. At temperatures below 1900°C, the partial pressure of the source molecules is low, making it impossible to supply a sufficient amount of source molecules to the growth surface. As the growth temperature increases, the partial pressure of the source molecules increases, improving the growth rate of silicon carbide crystals on the growth surface. However, when the growth temperature exceeds 2300°C, the vapor pressure of the source molecules increases not only on the sublimation surface but also on the growth surface, slowing the temperature dependence of the growth rate. As a result, the utilization efficiency of the source substrate (the ratio of the weight increase of the growth substrate to the weight loss of the source substrate) decreases. To achieve a growth rate of 1 μm / hour or higher, the growth temperature is preferably 2100°C or higher, and to maintain a source utilization efficiency of 80% or higher, the growth temperature is preferably 2200°C or lower.

[0044] (heating rate) Although there are no strict limitations on the heating rate when raising the temperature of the electric furnace to the specified growth temperature, if the heating rate is low, raw material molecules sublimated from the sublimation surface in the temperature range below 1900°C may form multiple nuclei on the growth surface, destabilizing the crystal structure of the growth layer. Therefore, if it is necessary to prevent the incorporation of polymorphs into the silicon carbide growth layer or an increase in defect density, it is desirable to raise the temperature at a rate of 10°C / min or more. However, if the heating rate is too high, thermal distortion can cause deformation or damage to the growth substrate, so it is desirable to keep it at 100°C / min or less.

[0045] (crystal growth time) Once the temperature inside the electric furnace reaches the desired growth temperature, a silicon carbide growth layer can be formed on the growth surface (Fg) by maintaining the temperature constant for a desired period of time. For example, the typical growth rate at 2200°C is 11.1 μm / hour, so to obtain a 500 μm thick growth layer, the temperature must be maintained for approximately 45 hours. At 2100°C, the typical growth rate is 2.4 μm / hour, so the temperature must be maintained for approximately 208 hours.

[0046] (cooling process) After the temperature has been maintained for the specified time, 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 the rate of temperature reduction must not exceed 100°C / hour to prevent deformation of the growth layer due to thermal strain and the occurrence of crystal defects. Furthermore, if the rate of temperature reduction is too slow, an amorphous silicon carbide layer will grow on the growth layer at low temperatures below 1900°C, so the rate of temperature reduction must be greater than 10°C / hour.

[0047] Once the temperature of the container has dropped below 100°C, the source substrate and growth substrate are removed into the atmosphere. The edges of the removed growth substrate are ground to form the desired wafer shape, and the surface of the growth layer is then mirror-polished to complete the production of a silicon carbide substrate that can be used for wafers used in semiconductor manufacturing. If the source substrate removed together with the growth substrate is 1 mm or thicker, it can be reused.

[0048] [Example 1] To verify the effectiveness of the present invention, a crystal growth experiment was conducted using 100 mm-diameter disk-shaped single-crystal silicon carbide substrates as source and growth substrates. As shown in the cross-sectional view of Figure 12, in this experiment, the substrates were fixed coaxially in a cylindrical container made of high-purity carbon so that the normal axes of their surfaces were within 2 degrees of the vertical. The container had an inner diameter of 105 mm. The source substrate (S) was attached to the container top with its sublimation surface (Fs) facing downward, and the growth substrate (G) was attached to the container floor with its growth surface (Fg) facing upward. G-Coat, a carbon coating material manufactured by Nippon Carbon Co., Ltd., was used as the adhesive layer for attaching the substrates. The thickness of the G-Coat layer (Gr) was adjusted to maintain a gap of 0.5 mm ± 0.1 mm between the substrates. The G-Coat layer (Gr) and the container bottom also function as the protective film (Gb) described in claim 1 of the present invention.

[0049] The container containing the source substrate and growth substrate was placed in the center of an electric furnace with concentric resistance heaters. After evacuation, the container was replaced with argon gas at 1100 hPa. The container was then heated at a rate of 40 °C / min until it reached the desired growth temperature (Tg) of 2200 °C. After the container reached 2200 °C, the growth time was set to 2 hours, during which the container temperature was maintained constant. The container was then naturally cooled in an argon atmosphere at 1100 hPa until the temperature dropped below 100 °C. The container was removed from the electric furnace, the substrates were separated from the container, and the G-coat residue on the backside 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 weight change of the substrate before and after the present invention is implemented, the growth rate of silicon carbide on the growth substrate (r g ) and the sublimation rate (r s ) was calculated. Furthermore, the utilization efficiency (η) of the source substrate was calculated by dividing the weight change of the growth substrate by the weight change of the sublimation substrate. Table 1 shows the growth rate (r g ) and sublimation rate (r s), and the utilization efficiency of the raw substrate (η).

[0051] [Table 1]

[0052] From the results of the verification using containers No. 1 to No. 4 in Table 1, it was found that the source substrate (S) made of single-crystal silicon carbide, which is located relatively higher, had a positive sublimation rate (r s ), and the growth substrate (G) made of single-crystal silicon carbide located relatively below exhibits a positive growth rate (r g ) It is clear that the source molecules were transported by gravity from the source substrate located above to the growth substrate located below. It is also clear that the sublimation rate of the sublimation surface made of carbon exceeds that of the sublimation surface made of silicon, and the growth rate on the growth surface made of silicon exceeds that on the growth surface made of carbon. In other words, it is clear that the vapor pressure of the source 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, the results of testing using containers No. 5 to No. 7 and container No. 1 demonstrated that the greater the angle at which the sublimation surface of single-crystal silicon carbide is tilted relative to the close-packed plane, the greater the sublimation rate, thereby increasing the growth rate of silicon carbide on the opposing growth surface. A crystal growth rate of more than 5 μm / hour can be achieved when the angle at which the sublimation surface is tilted relative to the close-packed plane is 2 degrees or more compared to the angle at which the growth surface is tilted relative to the close-packed plane.

[0054] [Example 2] To verify the effects of the present invention, a silicon carbide growth experiment was carried out using a 100 mm diameter disk-shaped single crystal silicon carbide substrate as the growth substrate (G) and a 100 mm diameter disk-shaped polycrystalline cubic silicon carbide substrate, a hexagonal silicon carbide sintered body, or a single crystal silicon carbide substrate as the source substrate (S). The substrate arrangement, heating atmosphere, temperature rise process, temperature fall process, and weight measurement method were the same as in Example 1, and therefore will not be described here.

[0055] [Table 2]

[0056] Table 2 shows the growth rate (r g ) and sublimation rate (r s ), and the utilization efficiency (η) of the source substrate. From the results shown in Table 2, it can be seen that regardless of the type of source substrate, the sublimation rate (r s ) increases. g ) and the sublimation rate (r s ) and shows an increasing tendency with increasing growth temperature (Tg) in the range of 1900°C to 2300°C. However, growth hardly occurs below 1900°C, and the raw material utilization efficiency (η) drops significantly at temperatures above 2300°C. Therefore, it has been confirmed that the practical range of growth temperature (Tg) for implementing the present invention is 1900°C or higher and 2300°C or lower.

[0057] On the other hand, focusing on the properties of the raw material substrate, the sublimation rate (r s ) and growth rate (r g ), the lower the specific gravity, the faster the growth rate (r g ) and sublimation rate (r s ) is found to be 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 / cm 3 It was confirmed from this example that the growth rate was improved by 1.3 times or more by using the following polycrystalline silicon carbide substrate or sintered silicon carbide as the raw material substrate.

[0058] [Example 3] To verify the effects of the present invention, a verification experiment was conducted using a disk-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° inclination 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) made of a 50 μm thick G coat was applied to the surfaces other than the growth surface (Fg) except for growth substrate G32. A disk-shaped hexagonal silicon carbide sintered body with a diameter of 100 mm and a thickness of 1 mm was used as the source substrate (S) facing the growth substrate. The hexagonal silicon carbide sintered body had an average grain size of 5.6 μm and a specific gravity of 2.2 g / cm. 3 These growth substrates (G31, G32, G33) and source substrate (S) 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 of the vertical direction, as shown in the cross-sectional view in Figure 13. To maintain a gap of 0.5 mm ± 0.1 mm between the source substrate (S) and each growth substrate (G31, G32, G33), a 0.5 mm thick donut-shaped disk (CS) made of high-purity carbon was inserted between each substrate. The outer diameter of the donut-shaped disk (CS) was 104 mm, and the inner diameter was 98 mm. The inner diameter of the container was 105 mm.

[0059] The container holding the source substrate (S) and growth substrates (G31, G32, and G33) was placed in the center of an electric furnace with concentric resistance heaters. The electric furnace was evacuated and then filled with argon gas at 1100 hPa. The temperature was then increased at a rate of 40 °C / min until the growth temperature (Tg) reached 2200 °C. After the temperature inside the electric furnace reached 2200 °C, the container was maintained at 2200 °C for 2 hours. The container was then allowed to cool 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. The G-coat residues on the backsides of the growth substrates (G31, G32, and G33) were 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 g ) was sought.

[0060] Table 3 shows the growth rate (r g ) is shown. As is clear from the table, the growth substrates (G31, G33) with a protective film (Gb) formed on the backside exhibit a growth rate three times or more faster than the growth substrate (G32) on which no protective film was formed. Therefore, it has become clear that the protective film (Gb) in the silicon carbide crystal growth method of the present invention prevents silicon carbide from sublimating from the surface vertically below the growth substrate, significantly improving the utilization efficiency of the source substrate.

[0061] [Table 3]

[0062] [Example 4] To verify the effectiveness of the present invention, we conducted experiments using 100 mm diameter, 0.36 mm thick, circular single-crystal 4H-SiC silicon carbide substrates as source and growth substrates. The growth surface (Fg) of the growth substrate was exposed at a 4° angle from the 4H-SiC (0001) silicon surface toward the [11-20] direction, and the sublimation surface (Fs) of the source substrate was exposed at a 8° angle from the 4H-SiC (000-1) carbon surface toward the [-1-120] direction. These growth and source substrates were fixed in a cylindrical container (CT) made of high-purity carbon, as shown in the cross-sectional view in Figure 14, so that the normal axis of the substrate surface was within 2° of the vertical direction. The growth substrates are designated G41 and G42 in Figure 14. A 50 μm thick protective film (Gb) made of G-coat was applied to the surface of each growth substrate other than the growth surface (Fg). The raw material substrates are shown as S41 and S42 in Fig. 14, and a raw material support substrate (SS) made of a disk-shaped hexagonal silicon carbide sintered body with a diameter of 100 mm and a thickness of 1 mm was placed vertically above the raw material substrate S41 so as to be coaxial. The hexagonal silicon carbide sintered body constituting the raw material support substrate (SS) had an average grain size of 5.6 µm and a specific gravity of 2.2 g / cm 3To maintain the spacing between the source substrates (S41, S42), growth substrates (G41, G42), and source support substrate (SS) at 0.5 mm ± 0.1 mm, a 0.5 mm thick donut-shaped disk (CS) made of high-purity carbon was inserted between each substrate. The outer diameter of the donut-shaped disk was 104 mm, and the inner diameter was 98 mm. The inner diameter of the container was 105 mm.

[0063] The atmosphere in the container in which each substrate was placed and the heating method were the same as in Example 3, so a detailed description will be omitted. After heating, the container was cooled to below 100°C and removed from the electric furnace. The substrates were then separated from the container, and the G-coat residues on the backside of the growth substrates were removed by heating at 900°C for 120 minutes in air. The weight change was then measured using an electronic balance, and the growth rate (r g ) and the sublimation rate (r s ) was sought.

[0064] Table 4 shows the growth rate (r g ) and sublimation rate (r s As is clear from the table, the growth rate (r) on both growth substrates (G41 and G42) was greater than 5 μm / hour. g ) can be achieved. s ) is 7.7 μm / hour, while the sublimation rate (r s ) is a negative value, indicating that the growth rate of silicon carbide crystals exceeds the sublimation rate. In other words, it can be determined that the source material supplementary substrate (SS) supplies source material molecules to the source material substrate S41, thereby increasing its thickness. As described above, it has been verified that the present invention eliminates the consumption of source material substrates made of single-crystal silicon carbide and reduces the manufacturing costs of single-crystal silicon carbide substrates.

[0065] [Table 4]

[0066] Although the present invention has been described above using the embodiments and examples shown in the drawings, the present invention is not limited thereto, and the crystal structure of the silicon carbide constituting the source substrate and growth substrate can be selected arbitrarily. Furthermore, there is no limit to the thickness of each substrate, and it can be determined taking into account the number of substrates required for processing and the thickness of the silicon carbide growth layer. The source substrate and growth substrate do not necessarily have to be perfectly circular; as long as they are stacked coaxially, they may have orientation flats at their edges to indicate the crystal orientation.

[0067] Normally, when a Miller index indicating the plane orientation of a SiC crystal is a negative value, a horizontal line (bar) should be written above the corresponding number. However, since this is not possible, in this specification and claims, the corresponding number is expressed by adding a minus sign "-" before it. [Industrial Applicability]

[0068] The silicon carbide crystal growth method of the present invention can be used to form substrate materials and epitaxially grown layers in the manufacture of semiconductor devices such as power MOSFETs. Taking advantage of its high productivity and low manufacturing costs, it can also be used to manufacture substrates for mold optics, high-temperature and pressure-resistant sensors, and 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 backside Rs Back side of raw substrate θg Inclination angle of the growth plane relative to the close-packed plane of the crystal lattice θs: Inclination angle of the sublimation plane relative to the close-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 diameter of growth substrate Ds diameter of raw substrate SS raw material auxiliary substrate CT Container d Distance between the growth surface and the sublimation surface g gravitational acceleration Close-packed plane of CPP crystal lattice Np microscopic terraces Cp microscopic step

Claims

1. The present invention uses a plate-shaped source substrate for sublimating source molecules, which are 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 growing silicon carbide crystals by crystallizing the source molecules on a growth surface made of silicon carbide. The growth substrate is arranged so that the growth surface faces vertically upward in a gravitational field, and the source substrate is arranged so that the sublimation surface opposite to the growth surface faces vertically downward. The entire vertically downward side of the growth substrate is coated with carbon, boron nitride (BN), aluminum oxide (Al ２ O ３ ), zirconium oxide (ZrO ２ ), yttrium oxide (Y ２ O ２ a protective film of 10 μm or more made of either tantalum carbide (TaC) or tantalum carbide (TaC) is tightly attached without any gaps, and the distance between the opposing sublimation surface and growth surface is set to a constant distance of 0.1 mm or more and 3 mm or less, and the distance between the growth surface and the sublimation surface is filled with helium (He), neon (Ne), nitrogen (N ２ a silicon carbide crystal growth method in which one or more inert gases selected from the group consisting of nitrogen (N), argon (Ar), and krypton (Kr) are filled at a pressure of 1300 hPa or less and 700 hPa or more, and then the temperature is maintained at a uniform temperature of 1900°C or more and 2300°C or less, thereby growing silicon carbide crystals on the growth surface.

2. 2. The method for growing silicon carbide crystal according to claim 1, wherein the single crystal silicon carbide is exposed on a growth surface, and the angle between the growth surface and the basal plane of the crystal lattice is set to be 1 degree or more and 12 degrees or less.

3. 3. The silicon carbide crystal growth method according to claim 1, wherein the source substrate is made of silicon carbide microcrystals or fine powder, and the specific gravity of the source substrate (JIS R 1634) is 1.6 g / cm ３ or more and 3.1 g / cm ３ A method for growing silicon carbide crystals, characterized by:

4. 3. A method for growing silicon carbide crystals according to claim 2, wherein single-crystal silicon carbide is exposed on the sublimation surface of the source substrate, and the angle at which the sublimation surface intersects with the basal plane of the crystal lattice is set to be at least 2 degrees higher than the angle at which the growth surface opposite the sublimation surface intersects with the basal plane of the crystal lattice.

5. 5. The silicon carbide crystal growth method according to claim 4, wherein a source substrate made of single crystal silicon carbide is used, and a source auxiliary substrate is placed vertically above the source substrate, and the source auxiliary substrate is made of silicon carbide microcrystals or fine powder, and its specific gravity (JIS R 1634) is 1.6 g / cm ３ or more and 3.1 g / cm ３ A method for growing silicon carbide crystals, characterized by:

6. 6. A silicon carbide crystal growth method according to claim 1, 2, 4 or 5, wherein the growth substrate and source substrate are disk-shaped and arranged coaxially, and the diameter of the source substrate is at least 1.1 times the diameter of the growth substrate.

7. 4. A silicon carbide crystal growth method according to claim 3, wherein the growth substrate and source substrate are disk-shaped and arranged coaxially, and the diameter of the source substrate is at least 1.1 times the diameter of the growth substrate.

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