Crystal growth apparatus and crystal growth method

Abstract

To provide a crystal growth apparatus capable of forming high-quality grown crystals in a short time. [Solution] A crystal growth apparatus for producing an ingot by growing a single crystal from a seed crystal using a raw material sublimation gas obtained by heating the raw material, wherein the crystal growth apparatus comprises a raw material storage section for storing the raw material, a shielding plate installed at a position vertically above the raw material storage section and having a single opening in the center, and a base installed at a position vertically above the shielding plate at least 30 mm away for fixing the seed crystal, wherein the distance between the raw material storage section and the shielding plate is L1 (L1>0) (mm), and the diameter of the opening is D1 (mm), satisfying D1 > -4L1 + 140.

Description

Technical Field

[0001] The present invention relates to a crystal growth apparatus for manufacturing an ingot by growing a single crystal from a seed crystal using a raw material sublimation gas obtained by heating a raw material, and a crystal growth method using the crystal growth apparatus.

Background Art

[0002] Single crystal substrates are used for manufacturing semiconductor devices. A single crystal substrate is manufactured by cutting out a single crystal ingot. There are various manufacturing methods for manufacturing such an ingot. As a manufacturing method in the case of manufacturing a silicon carbide (SiC) ingot, a sublimation recrystallization method is used in which a raw material of the ingot and a seed crystal are arranged in a container of a crystal growth apparatus, the container is heated to heat-sublimate the raw material, and a single crystal is grown on the seed crystal to manufacture an ingot.

[0003] Patent Document 1 discloses a crystal growth apparatus used for the sublimation recrystallization method. This document describes a container having a raw material of silicon carbide powder and a seed crystal fixed to a pedestal, and using this container, a single crystal is grown on the seed crystal to manufacture an ingot.

[0004] This document also describes that in order to reduce defects caused by impurities and the like in the grown crystal, a shielding plate having a number of small openings is arranged between the raw material and the seed crystal in the container of the crystal growth apparatus.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] When using a crystal growth apparatus, using a shielding plate with numerous small openings, as disclosed in Patent Document 1, presents a problem in that it excessively obstructs the flow of sublimation gas, resulting in a significant decrease in the crystal growth rate.

[0007] However, to reduce impurities in the growing crystal, it is useful to place a shielding plate between the raw material and the seed crystal to obstruct the flow of sublimation gas. Therefore, the inventors have worked to design a shielding plate that reduces impurities in the growing crystal, but that does not obstruct the flow of sublimation gas as much as possible. The present invention aims to provide a crystal growth apparatus and a crystal growth method that can form high-quality growing crystals with few impurities in a short time. [Means for solving the problem]

[0008] As a result of diligent research, we have created a crystal growth apparatus and crystal growth method equipped with shielding plates of the following shape and arrangement. The crystal growth apparatus is a crystal growth apparatus that uses raw material sublimation gas obtained by heating the raw materials to grow single crystals from seed crystals and produce ingots. The crystal growth apparatus is A raw material storage section for storing the aforementioned raw materials, A shielding plate is installed at a position vertically above the raw material storage section and has a single opening in the center, It is installed at a position at least 30 mm vertically above the shielding plate and comprises a base for fixing the seed crystal, When the distance between the raw material storage section and the shielding plate (the height of the shielding plate from the raw material) is L1 (L1>0) (mm) and the diameter of the opening (hole diameter) is D1 (mm), equation (1) is satisfied. D1> -4L1+140 ···(1)

[0009] A crystal growth method for producing ingots by growing single crystals from seed crystals in a crystal growth apparatus using raw material sublimation gas obtained by heating raw materials, The crystal growth apparatus is A raw material storage section for storing the aforementioned raw materials, A shielding plate is installed at a position vertically above the raw material storage section and has a single opening in the center, It is installed at a position at least 30 mm vertically above the shielding plate and comprises a base for fixing the seed crystal, When the distance between the raw material storage section and the shielding plate (the height of the shielding plate from the raw material) is L1 (L1>0) (mm) and the diameter of the opening (hole diameter) is D1 (mm), equation (1) is satisfied. D1> -4L1+140 ···(1)

[0010] First, let's explain the terminology used in this specification. A single crystal grown on a seed crystal is called a "growth crystal." A growth crystal that has grown to the target size, or a growth crystal that has been removed from its base, is called an "ingot."

[0011] As a result of diligent research, the inventors first found that a shielding plate having a single opening in the center can reduce impurities in the growing crystal and does not easily obstruct the flow of sublimation gas. Second, they found that the distance L1 between the raw material containment section and the shielding plate, and the diameter D1 of the opening are factors that affect the flow method and velocity of the sublimation gas when a shielding plate having a single opening in the center is used. The inventors then focused on the relationship between the distance L1 and the diameter D1 of the opening in the shielding plate.

[0012] Experiments using crystal growth apparatuses with different spacing L1 and pore diameter D1 revealed that when equation (1) above is satisfied, it is possible to reduce impurities in the grown crystal while minimizing obstruction to the flow of the impurity sublimation gas, thereby achieving a suitable sublimation gas flow pattern and velocity. In other words, the crystal growth apparatus can produce high-quality single crystals with few impurities at a constant growth rate.

[0013] The crystal growth method may be terminated before the grown single crystal reaches the shielding plate. [Effects of the Invention]

[0014] This makes it possible to provide a crystal growth apparatus and crystal growth method that can form high-quality grown crystals in a short amount of time. [Brief Description of the Drawings]

[0015] [Figure 1] It is a perspective view of one form of a crystal growth apparatus arranged in a manufacturing system. [Figure 2] It is a cross-sectional view taken on the P1 plane of FIG. 1. [Figure 3] It is a view showing a shielding plate. [Figure 4] It is a scatter diagram regarding the design parameters of the shielding plate. [Embodiments of the Invention]

[0016] A design method of a crystal growth apparatus according to the present invention will be described with reference to the drawings. Note that each drawing disclosed in this specification is schematically illustrated except for graphs. That is, the dimensional ratios on the drawings do not necessarily match the actual dimensional ratios, and the dimensional ratios are not necessarily the same between the drawings.

[0017] In this specification, the XYZ coordinate system is appropriately referred to for explanation. In this specification, when expressing a direction, when distinguishing between positive and negative directions, it is described with positive and negative signs such as “+X direction” and “-X direction”. When expressing a direction without distinguishing between positive and negative directions, it is simply described as “X direction”. That is, in this specification, when simply described as “X direction”, both “+X direction” and “-X direction” are included. The same applies to the Y direction and the Z direction. In this embodiment, the X direction and the Y direction are horizontal directions, and the -Z direction is the gravitational direction.

[0018] [Overview of the Crystal Growth Apparatus] Figure 1 is a perspective view of one embodiment of a crystal growth apparatus placed within a manufacturing system 100. The crystal growth apparatus is a container 10 that includes a space used as a raw material storage section 2 and a crystal growth space. The manufacturing system 100 includes a heating chamber. The heating chamber has a floor 20, walls 21 and a ceiling (not shown). The container 10 is placed inside the heating chamber. At least one of the floor 20, walls 21 and ceiling supplies a high-frequency magnetic field or heat to heat the container 10. As the container 10 is heated, the raw material (not shown in Figure 1) stored in the raw material storage section 2 is heated. In other words, the container 10 functions as a crucible for heating the raw material.

[0019] Regarding the shape of the container 10, in this embodiment the container 10 is cylindrical, but the container 10 is not limited to a cylindrical shape and may have other shapes. The diameter of the container 10 is preferably between 100 mm and 500 mm, and more preferably between 150 mm and 400 mm. The height of the container 10 in the Z direction is preferably between 100 mm and 600 mm, and more preferably between 150 mm and 500 mm.

[0020] The raw material storage section 2 is the space in which the raw material 1 is stored. In other words, when a specified amount of raw material 1 is stored in the container 10, the space in which the specified amount of raw material 1 is filled becomes the raw material storage section 2. If there is a line on the inner wall of the container 10 that serves as a guide for storing raw materials, the location of that line may be used as a guide for determining which area of ​​the internal space of the container 10 is the raw material storage section 2. Alternatively, if the manual for the container 10 contains data such as the weight and volume of the raw materials that can be stored, the area of ​​the raw material storage section 2 within the internal space may be determined based on that data.

[0021] Figure 2 is a cross-sectional view of Figure 1 in the P1 plane parallel to the XZ plane. The internal structure of the container 10 will be described with reference to Figure 2. The container 10 includes a raw material storage section 2 for containing the raw material 1, a base 4 for fixing the seed crystal 3, and a shielding plate 5 located between the space of the raw material storage section 2 and the space near the base 4, shielding both spaces. The raw material storage section 2 is located vertically downward (-Z side). The base 4 is located vertically upward (+Z side). The raw material 1 and seed crystal 3 are not components of the crystal growth apparatus (container 10) itself.

[0022] In this embodiment, the raw material storage section 2 is a cylindrical space. The base 4 is installed so that the surface in contact with the seed crystal 3 faces downwards (-Z side). The shielding plate 5, which has an opening OP in the center, blocks the sublimation gas that rises near the inner wall of the container 10 from the raw material 1, thereby changing the path of the sublimation gas. The dashed arrows in Figure 2 represent the flow of sublimation gas. The sublimation gas passes through the single opening OP in the center of the shielding plate 5 and heads towards the seed crystal 3. With a shielding plate 5 that has a single opening OP in the center, impurities in the growing crystal can be reduced by appropriately lowering the flow velocity of the sublimation gas and changing its flow pattern.

[0023] Although not present in the container 10 of this embodiment, a spacer may be placed between the shielding plate 5 and the seed crystal 3, and to block at least a portion of the space formed between the inner wall of the container 10 and the outer edge of the seed crystal 3. The spacer provides at least one of the following functions: fixing the seed crystal 3 and controlling the diameter of the growing crystal. The spacer is one of the additional components in the crystal growth apparatus of the present invention.

[0024] In this embodiment, raw material 1 is a solid material. In this embodiment, a powdered solid material is used as raw material 1. When the container 10 is heated by the heating chamber, the solid material sublimes into a gas. This sublimated gas derived from the solid material recrystallizes on the surface of the seed crystal 3, causing the crystal to grow.

[0025] In this embodiment, silicon carbide (SiC) powder is used as the raw material 1. The seed crystal 3 fixed to the base 4 is a SiC crystal. An ingot is obtained by growing a SiC single crystal 12 on the seed crystal 3. SiC has electrical properties that are about an order of magnitude larger in dielectric breakdown field strength and about three times larger in band gap compared to silicon (Si). In addition, SiC has a thermal conductivity that is about three times higher than Si. Due to these excellent properties, substrates cut from SiC ingots are used in power devices, high-frequency devices, devices that operate at high temperatures, etc.

[0026] Although not shown in Figure 2, the container 10 includes a container body and a lid. The lid can be opened to place the raw material 1 into the container body. When the lid is closed, the inside of the container 10 is isolated from the outside. The sublimation gas is trapped in the container 10. However, since the container 10 in this embodiment is made of a material mainly composed of graphite, and the container 10 is a porous material in a broad sense, some of the gas permeates through the container 10 and leaks out of the container 10. The raw material storage section 2 and the shielding plate 5 are located inside the main body. The base 4 is located inside the lid. The base 4 and the lid may be formed integrally.

[0027] [Shielding plate] The shielding plate 5 will now be described. The shielding plate 5 of this embodiment is made of a material mainly composed of graphite. In this specification, "main component" means that the carbon content of the graphite is 90 wt% or more of the total mass. Various types of graphite can be used, and either anisotropic extruded material or isotropic CIP material may be used.

[0028] As described above, the shielding plate 5 affects the flow and velocity of the sublimation gas. A disc with a single opening in the center was adopted as the shielding plate 5. When carbon powder contained in the sublimation gas is incorporated into the growing crystal, it becomes an impurity in the growing crystal called an inclusion, and dislocation defects are more easily introduced starting from the location where the carbon powder is present. In addition, when sublimation gas with an excessively Si-rich composition is cooled, Si atoms condense on the single crystal growth surface, forming unstable cluster-like foreign matter called Si droplets, which induce dislocations and lead to defect introduction. However, by using the shielding plate 5, the flow of sublimation gas in the space below the shielding plate 5 inside the crucible is disturbed, causing stagnation in that space and increasing the supersaturation of the sublimation gas. When the supersaturation of the sublimation gas increases, recrystallization becomes easier in the cooled areas of the inner wall of the container 10 and the top surface of the raw material, and in this recrystallization process, some of the carbon powder, which is the source of inclusions, is trapped. The polycrystalline material that recrystallizes on the inner wall of the container 10 or on the cooled surface of the raw material can function as a filter to remove inclusion sources (carbon powder) contained in the sublimation gas.

[0029] Furthermore, when the main component of the shielding plate 5 is a carbonaceous material such as graphite, the sublimation gas with an excessively Si-rich composition readily reacts with the carbon components on the surface of the shielding plate 5, changing the gas composition to a more C-rich one. In this way, the shielding plate 5 captures carbon nanoparticles and excess Si that are heading toward the growing crystal along with the sublimation gas, preventing them from being incorporated into the growing crystal.

[0030] Figure 3 shows the shielding plate 5. The shielding plate 5 is generally disc-shaped and has a central opening OP, so the shielding plate 5 has an annular plate shape. The outer diameter D2 of the shielding plate 5 is the same as the inner diameter of the container 10. The thickness of the container 10 is preferably 3 mm to 20 mm, and preferably 5 mm to 15 mm. A thickness of 3 mm or more makes it difficult for sublimation gas to leak out of the container 10, and can withstand stresses generated due to differences in thermal expansion coefficients, especially during cooling. The diameter (pore diameter) D1 of the opening OP varies depending on the diameter of the seed crystal, and D1 is preferably 60% to 95% of the diameter of the seed crystal. If the diameter of the seed crystal is 150 mm, the diameter (pore diameter) D1 of the opening OP may be 40 mm to 160 mm, and preferably 100 mm to 140 mm.

[0031] As the container 10 heats up, the shielding plate 5 also heats up and emits radiant heat. The thickness T1 of the shielding plate 5 is preferably between 0.5 mm and 10 mm, and more preferably between 1 mm and 5 mm. The distance L2 (see Figure 2) between the shielding plate 5 and the base 4 in the Z direction is preferably 30 mm or more. In other words, the base 4 is preferably installed at a position 30 mm or more vertically above the shielding plate 5. This enables a smooth flow of sublimation gas around the seed crystal 3.

[0032] [Overview of crystal growth methods] A SiC single crystal is grown using the crystal growth apparatus described above. If the crystal is grown until the tip of the growing crystal is below the shielding plate 5, the shielding plate 5 will no longer be able to capture carbon nanoparticles, increasing the risk of impurity contamination. Therefore, it is best to complete the sublimation recrystallization process before the growing crystal reaches the shielding plate 5.

[0033] As described above, the inventors have been working to design a shielding plate that reduces impurities in the growing crystal while minimizing obstruction to the flow of sublimation gas. As a result, the inventors have focused on the following design parameters for the shielding plate 5: the distance between the raw material 1 (raw material storage section) and the shielding plate 5 (i.e., the height of the shielding plate 5 from the raw material) L1 (see Figure 2), which determines the position of the shielding plate 5, and the diameter D1 of the opening OP (i.e., the hole diameter D1, see Figure 3), and have conducted the following experiments.

[0034] A crystal growth experiment was conducted using 13 crystal growth apparatuses with different spacing L1 and diameter D1, and one crystal growth apparatus without a shielding plate 5 as a comparative example. The experimental results are shown in Table 1 and Figure 4.

[0035] [Table 1]

[0036] Sample numbers 1 to 13 in Table 1 all represent data from crystal growth apparatuses equipped with a shielding plate 5. In Table 1, "Height from raw material L1" represents the distance L1 between the raw material 1 (raw material storage section) and the shielding plate 5, and "Shielding plate hole diameter D1" represents the diameter of the opening OP of the shielding plate 5. Sample number 14 represents data from a crystal growth apparatus without a shielding plate 5. The "Result" column shows the percentage of sublimation recrystallization amount in the crystal growth apparatus with a shielding plate 5, where the "Height from raw material L1" and "Shielding plate hole diameter D1" are set to the conditions in question, compared to the sublimation recrystallization amount when using a crystal growth apparatus without a shielding plate 5. For example, when the "Result" column is 60%, it means that the sublimation recrystallization amount in the crystal growth apparatus of that sample number reaches 60% of the sublimation recrystallization amount when using a crystal growth apparatus without a shielding plate 5. The sublimation recrystallization amount is expressed in terms of the mass (unit: g) of the grown crystal.

[0037] In calculating the aforementioned ratio, the amount of sublimation and recrystallization in a crystal growth apparatus with a shielding plate 5, where height L1 and pore diameter D1 were set to the respective conditions, and the amount of sublimation and recrystallization in a crystal growth apparatus without a shielding plate 5 were determined by actually conducting experiments. In all samples, the experimental conditions were standardized except for the presence or absence of the shielding plate 5 and the parameters of height L1 and pore diameter D1.

[0038] A value below 100% in the "Results" column indicates that the sublimation and recrystallization rate of the crystal growth apparatus with the shielding plate 5 set for each condition is lower than that of the crystal growth apparatus without the shielding plate 5. This indicates that the crystal growth rate of the crystal growth apparatus with the shielding plate 5 set for each condition is slower than that of the crystal growth apparatus without the shielding plate 5. However, the decrease in crystal growth rate due to the provision of the shielding plate 5 is not necessarily a problem. This is because, considering the objective of achieving both high-quality grown crystals and formation in a short time, if the amount of impurities in the grown crystal is reduced by providing the shielding plate 5, then a slight decrease in crystal growth rate due to the use of the shielding plate 5 can be tolerated.

[0039] However, we want to avoid a situation where the sublimation and recrystallization rate of a crystal growth apparatus with a shielding plate 5 set for each condition is less than 60% of the sublimation and recrystallization rate of a crystal growth apparatus without a shielding plate 5. In light of this, the "Judgment" column in Table 1 was established. Specifically, a ○ (good) is indicated when the "Result" is 60% or more, and a × (bad) is indicated when it is less than 60%. Hereafter, this judgment with a threshold of 60% may be referred to as the "60% judgment".

[0040] This section describes a method for identifying foreign matter in growing crystals. The growing crystal is split with a hammer, and UV light is shone onto the cleavage plane. The reflected and diffracted light from the cleavage plane is then observed using a microscope. Defects in the cleavage plane appear to be colored. By analyzing the intensity of the color in localized areas of the cleavage plane, the defect distribution within the cleavage plane, i.e., the size and number of inclusions, can be determined.

[0041] Although not shown in Table 1, when we examined the foreign matter contained in the grown crystals produced by each of the crystal growth apparatuses for samples 1 to 13 using the method described above, we found that the size and number of inclusions in the grown crystals produced by any of the crystal growth apparatuses were smaller than the size and number of inclusions in the grown crystals produced by the crystal growth apparatus without shielding plate 5 (sample number 14), confirming that the quality of the grown crystals was improved with samples 1 to 13.

[0042] Figure 4 shows the data from Table 1 as a scatter plot. The plots in the scatter plot are indicated as "○" and "×" with a 60% probability of success. The scatter plot shows that the boundary between the distribution area of ​​"○" and the distribution area of ​​"×" lies on the straight line D1 = -4L1 + 140. When the data is located above this line (i.e., D1 > -4L1 + 140), the "result" is "○" (good), and when D1 ≤ -4L1 + 140, it is "×" (bad). This indicates that in the crystal growth apparatus, when both parameters (L1, D1) related to the shielding plate 5 satisfy the equation D1 > -4L1 + 140, it is possible to reduce impurities in the growing crystal while minimizing obstruction to the flow of the impurity sublimation gas, thereby enabling the crystal growth apparatus to produce high-quality single crystals with few impurities at a constant growth rate.

[0043] Furthermore, the design may satisfy both parameters (L1, D1) such that D1 > -4L1 + 150, or both parameters (L1, D1) such that D1 > -4L1 + 160. The height L1 from the raw material is preferably 3 mm or more and 50 mm or less, preferably 4 mm or more and 40 mm or less, and more preferably 5 mm or more and 30 mm or less. The pore diameter D1 is preferably 80 mm or more and 160 mm or less, preferably 90 mm or more and 150 mm or less, and more preferably 100 mm or more and 140 mm or less.

[0044] The present invention is not limited in any way to the embodiments described above, and various improvements and modifications are possible without departing from the spirit of the invention. Although the above mainly describes the case of manufacturing silicon carbide single crystal ingots, it can also be applied to the case of manufacturing ingots other than silicon carbide. [Explanation of symbols]

[0045] 1: Raw materials 2: Raw material storage section 3: Seed crystal 4: Pedestal 5: Shielding plate 10: Container 12: Single crystal 20: (Floor of the manufacturing system) 21: (Walls in the manufacturing system) 100: Manufacturing System D1: Hole diameter of the shielding plate, or diameter of the opening of the shielding plate D2: Outer diameter of shielding plate L1: Height of the shielding plate from the raw material, or the distance in the Z direction between the raw material storage section and the shielding plate. L1: Distance between the shielding plate and the base in the Z direction. OP: Opening (of a shielding plate) T1: Thickness (of the shielding plate)

Claims

1. A crystal growth apparatus that uses raw material sublimation gas obtained by heating the raw materials to grow single crystals from seed crystals and produce ingots, The crystal growth apparatus is A raw material storage section for storing the aforementioned raw materials, A shielding plate is installed at a position vertically above the raw material storage section and has a single opening in the center, It is installed at a position at least 30 mm vertically above the shielding plate and comprises a base for fixing the seed crystal, The distance between the raw material storage section and the shielding plate is L １ (L １ Let >0) (mm), and set the diameter of the opening to D １ When (mm), the following conditions satisfy equation (1): D １ > -4, １ +140 ・・・(1) A crystal growth apparatus characterized by the following features.

2. A crystal growth method for producing ingots by growing single crystals from seed crystals in a crystal growth apparatus using raw material sublimation gas obtained by heating raw materials, The crystal growth apparatus is A raw material storage section for storing the aforementioned raw materials, A shielding plate is installed at a position vertically above the raw material storage section and has a single opening in the center, It is installed at a position at least 30 mm vertically above the shielding plate and comprises a base for fixing the seed crystal, The distance between the raw material storage section and the shielding plate is L １ (L １ Let >0) (mm), and set the diameter of the opening to D １ When (mm), the following conditions satisfy equation (1): D １ > -4, １ +140 ・・・(1) A method for growing crystals, characterized by the features described above.

3. The crystal growth method according to claim 2, characterized in that the crystal growth method is terminated before the grown single crystal reaches the shielding plate.

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