Method for designing crystal growth device

Abstract

To provide a crystal growth device designing method for manufacturing an ingot with a desired shape.SOLUTION: A crystal growth device designing method has: a step (a) of acquiring correlation to a ratio between an index value including first information relating to a clearance in a vertical direction between a shielding plate and a seed crystal and second information relating to an opening diameter of the shielding plate, and a growth rate at a different position on a single crystal to be grown; a step (b) of calculating a target ratio of the growth rate at the different position on the single crystal from a target shape of an ingot serving as a manufacturing object; a step (c) of deriving a target index value corresponding to the target ratio calculated in the step (b) based on the correlation; and a step (d) of determining the clearance in the vertical direction between the shielding plate and the seed crystal and the opening diameter of the shielding plate from the target index value.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a method for designing a crystal growth apparatus that produces an ingot by growing a single crystal from a seed crystal using a raw material sublimation gas obtained by heating the raw material. [Background technology]

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

[0003] Patent Document 1 discloses a container for a crystal growth apparatus used in a sublimation recrystallization method. The document describes a container having a silicon carbide powder raw material and a seed crystal fixed to a pedestal, and uses the container to grow a single crystal on the seed crystal to produce an ingot. The document further describes the placement of a shielding plate with an opening between the raw material and the seed crystal to reduce polycrystals adhering to the container and to allow the single crystals to deposit intensively on the seed crystal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-295595 Summary of the Invention [Problem to be solved by the invention]

[0005] The single crystal growth rate on the crystal surface is not necessarily uniform, and often varies locally. The local crystal growth rate affects the local thickness of the ingot. In other words, since the crystal growth rate varies locally, the shape of the ingot obtained by growth is often not columnar with a uniform thickness. In addition, if the crystal growth rate varies significantly locally during the single crystal growth process, polytypes may be mixed into the single crystal, making it difficult to obtain a high-quality single crystal.

[0006] On the other hand, the ingot to be manufactured has a target shape and dimensions as a product (in this specification, the "target shape and dimensions" are simply referred to as the "target shape"). To bring the ingot closer to the target shape, it is necessary to precisely control the local crystal growth rate on the crystal surface. In order to precisely control the local crystal growth rate, control of the temperature distribution inside the container has been considered. However, there are limitations to bringing the ingot closer to the target shape simply by controlling the temperature distribution inside the container.

[0007] Therefore, the inventors focused on controlling the flow of the sublimated raw material gas, rather than controlling the temperature distribution in the vessel, in order to obtain an ingot of a desired shape. In order to control the flow of the sublimated raw material gas, it is necessary to reconsider the design of the vessel, which is a crystal growth apparatus. The problem to be solved by the present invention is to provide a method for designing a crystal growth apparatus for precisely controlling the local crystal growth rate and manufacturing an ingot of a target shape. [Means for solving the problem]

[0008] The present inventors focused on the shielding plate arranged between the raw material and the seed crystal as a factor affecting the flow of the sublimated raw material gas, and started to study the relationship between the design parameters related to the shielding plate and the parameters related to the local crystal growth rate. As a result of intensive research, the present inventors found that an index value including first information related to the vertical distance between the shielding plate and the seed crystal and second information related to the diameter of the opening of the shielding plate in a crystal growth apparatus equipped with a shielding plate has a correlation with the ratio of the growth rates at different positions on the single crystal. As described above, the local crystal growth rate affects the shape of the ingot. Then, the present inventors realized that by utilizing the correlation found, it is possible to design a crystal growth apparatus suitable for manufacturing an ingot of the target shape by back-calculating the design parameters related to the shielding plate from the target shape of the ingot.

[0009] The present invention provides a method for designing a crystal growth apparatus for growing a single crystal from a seed crystal to produce an ingot by utilizing a raw material sublimation gas obtained by heating the raw material, comprising the steps of: The crystal growth apparatus comprises: A raw material storage section that stores the raw material; a base that is installed vertically above the raw material storage unit and that fixes the seed crystal; a shielding plate disposed between the raw material storage unit and the base and having an opening at its center; (a) acquiring a correlation between an index value including first information related to a vertical distance between the shielding plate and the seed crystal and second information related to a diameter of the opening of the shielding plate and a ratio of growth rates at different positions on the single crystal; (b) calculating a target ratio of growth rates at different positions on the single crystal from a target shape of an ingot to be manufactured; (c) deriving a target index value, which is the index value corresponding to the target ratio calculated in (b), based on the correlation; and (d) determining a distance between the shielding plate and the seed crystal in the vertical direction and a diameter of the opening of the shielding plate from the target index value. By designing a crystal growth apparatus using this design method, it is possible to produce an ingot with a target shape.

[0010] In the method for designing a crystal growth apparatus, The different positions on the single crystal include a first position where a reference line that passes through an end of the opening and intersects a surface of the seed crystal at a right angle intersects with the surface of the single crystal, and a second position that is radially outward of the first position and located on the surface; The index value may be the cosine value (cos θ) of an angle θ between an imaginary line extending from the end toward the second position and the reference line.

[0011] The correlation may be expressed by the same function even if the diameter of the opening changes.

[0012] In step (d), the distance between the shielding plate and the raw material may be determined so as to satisfy equation (1) with respect to the sublimation rate Sa of the raw material when the single crystal ingot is produced using the crystal growth apparatus and the sublimation rate Sv of the raw material when the single crystal ingot is produced using a crystal growth apparatus without the shielding plate. Sa ≧ 0.7 × Sv (1)

[0013] The step (d) may include designing the distance between the shielding plate and the raw material and the diameter of the opening of the shielding plate so as to satisfy formula (2). Sa ≧ 0.9 × Sv (2) [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view of one embodiment of a crystal growing apparatus positioned within a manufacturing system. [Diagram 2] 2 is a cross-sectional view taken along the P1 plane in FIG. 1. [Diagram 3] FIG. [Figure 4] FIG. 2 is a cross-sectional view showing an example of a produced ingot. [Diagram 5] FIG. 2 is a partially enlarged cross-sectional view of a vessel that is a crystal growth apparatus. [Figure 6A] FIG. 1 is a scatter plot showing the relationship between cos θ, which is one of the index values, and the growth rate ratio Jx / J0. [Figure 6B] FIG. 1 is a scatter plot showing the relationship between cos θ, which is one of the index values, and the growth rate ratio Jx / J0. [Figure 6C] FIG. 1 is a scatter plot showing the relationship between cos θ, which is one of the index values, and the growth rate ratio Jx / J0. [Figure 6D] 6A to 6C are combined into one graph. [Figure 7] FIG. 1 is a diagram showing a flow of a method for designing a crystal growth apparatus. [Figure 8] FIG. 13 is a diagram showing a crystal growth apparatus without a shield plate as a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The design method of a crystal growth apparatus according to the present invention will be described with reference to the drawings. Note that the drawings disclosed in this specification are schematic illustrations, except for graphs and flow diagrams. In other words, the dimensional ratios in the drawings do not necessarily match the actual dimensional ratios, and the dimensional ratios between the drawings do not necessarily match.

[0016] In this specification, the XYZ coordinate system is appropriately referred to for explanation. In this specification, when a direction is expressed and a positive or negative direction is to be distinguished, it is described with a positive or negative sign, such as "+X direction" and "-X direction". In addition, when a direction is expressed without distinguishing between positive and negative directions, it is simply described as "X direction". In other words, in this specification, when it is 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 direction of gravity.

[0017] [Outline of the crystal growth equipment] FIG. 1 is a perspective view of one embodiment of a crystal growth apparatus disposed in a manufacturing system. The crystal growth apparatus is a container 10 having a space therein used as a raw material storage section 2. Hereinafter, the crystal growth apparatus may be referred to as a "container 10". The manufacturing system includes a heating chamber. The heating chamber has a floor 20, a wall 21, and a ceiling (not shown). The container 10 is placed in the heating chamber. At least one of the floor 20, the wall 21, and the ceiling radiates heat to heat the container 10. The raw material stored in the raw material storage section 2 is heated by heating the container 10. In other words, the container 10 functions as a crucible for heating the raw material. As shown in FIG. 1, in this embodiment, the container 10 has a cylindrical shape, but the container 10 is not limited to a cylindrical shape and may have other shapes.

[0018] Fig. 2 is a cross-sectional view of Fig. 1 taken along a P1 plane parallel to the XZ plane. The internal structure of the vessel 10 will be described with reference to Fig. 2. The vessel 10 includes a raw material storage section 2 for storing raw material 1, a pedestal 4 for fixing a seed crystal 3, and a shielding plate 5 located between the space of the raw material storage section 2 and the space near the pedestal 4 and for shielding both spaces. The raw material storage section 2 is located below in the vertical direction (-Z side), and the pedestal 4 is located above in the vertical direction (+Z side). The raw material 1 itself is not a component of the vessel 10 (crystal growth apparatus).

[0019] 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 downward (-Z side). The shielding plate 5 having an opening OP in the center blocks the sublimation gas close to the inner wall of the container 10 among the sublimation gas sublimated from the raw material 1. The dashed arrows in FIG. 2 indicate the flow of the sublimation gas. The sublimation gas passes through the opening OP of the shielding plate 5 and heads toward the seed crystal 3.

[0020] Although not provided in the vessel 10 of this embodiment, a spacer may be disposed between the shielding plate 5 and the seed crystal 3 so as to block at least a part of the space formed between the inner wall of the vessel 10 and the outer edge of the seed crystal 3. The spacer provides at least one of the functions of fixing the seed crystal 3 and controlling the diameter of the growing single crystal, for example. The spacer is one of the additional components of the crystal growth apparatus of the present invention.

[0021] In this embodiment, the raw material 1 is a solid material. In this embodiment, a powdered solid material is used as the raw material 1. When the container 10 is heated by the heating chamber, the solid material sublimes into gas. The sublimated gas recrystallizes on the surface of the seed crystal 3, causing the crystal to grow.

[0022] In this embodiment, silicon carbide (SiC) powder is used as the raw material 1. The seed crystal 3 fixed to the pedestal 4 is a SiC crystal. A single crystal 12 of SiC is grown on the seed crystal 3 to obtain an ingot. SiC has electrical properties such as a dielectric breakdown field strength value that is approximately one order of magnitude larger than that of silicon (Si) and a band gap value that is approximately three times larger. SiC also has a thermal conductivity that is approximately three times higher than that of Si. Due to these excellent properties, substrates cut from SiC ingots are used in power devices, high-frequency devices, devices that operate even at high temperatures, and the like.

[0023] Although not shown in FIG. 2, the container 10 is composed of a body and a lid. The lid can be opened to put in the raw material 1. When the lid is closed, the inside of the container 10 is isolated from the outside of the container 10. The sublimation gas is trapped in the container 10. However, since the container 10 itself is made of graphite and is a porous material, some of the gas permeates 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 body. The base 4 is located inside the lid.

[0024] The shielding plate 5 will now be described. FIG. 3 is a diagram showing the shielding plate 5. The central opening OP is annular. The diameter D1 of the shielding plate 5 is equal to the inner diameter of the container 10. The diameter D2 of the opening OP is related to the local crystal growth rate and the overall sublimation rate, as will be described in detail later. As the container 10 is heated, the shielding plate 5 is also heated and emits radiant heat. The thickness T1 of the shielding plate 5 is preferably, for example, 1.5 mm or more and 10 mm or less.

[0025] [ingot] FIG. 4 shows an example of an ingot 13. In FIG. 4, as indicated by the dashed line and arrow on the right side of the axis C1, the single crystal 12 in the middle of growth grows in the order of N1, N2, and N3. In this specification, for convenience, a single crystal in the middle of growth is referred to as a "single crystal 12", and a single crystal whose crystal growth (manufacturing) is completed is referred to as an "ingot 13". The seed crystal 3 has a disk shape of a certain thickness centered on the axis C1. In contrast, the ingot 13 has a shape that is rotationally symmetrical about the axis C1. The thickness of the ingot 13 is the thickest on the axis C1, and the thickness becomes thinner as it moves away from the axis C1 in the radial direction.

[0026] The shape shown in FIG. 4 is due to the local crystal growth rate being higher closer to the axis C1. For example, 10 The crystal growth rate at the position of thickness T 11 This indicates that, conversely, if the difference in growth rate at different positions on the single crystal can be intentionally controlled, the shape of the ingot 13 can be made closer to the target shape.

[0027] 4 shows only one example of the target shape of the ingot 13. For example, the target shape may be set to a shape whose thickness does not change in the radial direction of the ingot 13. In order to obtain a cylindrical ingot 13 whose thickness does not change in the radial direction, the difference in crystal growth rate at different positions on the single crystal is made small.

[0028] [Parameters related to the shielding plate and local crystal growth rate] The correlation between the parameters related to the shielding plate 5 and the local crystal growth rate, which the present inventors have found, will be described. Fig. 5 is an enlarged view showing only the upper part of the raw material 1 accommodated in the raw material accommodation section 2 in the vessel 10 of Fig. 2, the shielding plate 5, the seed crystal 3, and the single crystal 12 in the middle of growing on the seed crystal 3. In Fig. 5, the vessel 10 and the base 4 are omitted from the illustration.

[0029] The parameters shown in FIG. 5 are defined as follows: Distance H1: The distance between the seed crystal 3 and the shielding plate 5 in the Z direction. Distance H2: The distance between the raw material 1 and the shielding plate 5 in the Z direction. Reference line L1: a line that passes through the edge of the opening OP of the shielding plate 5 and intersects at a right angle with the surface of the seed crystal 3 (the boundary surface between the seed crystal 3 and the single crystal 12), and in this embodiment, is a line parallel to the Z axis. First position P1: The position where the reference line L1 intersects with the surface of the single crystal 12. Second position P2: An arbitrary position on the surface of the single crystal 12, located radially outward (in the X direction) from the first position P1. Distance D3: The distance between the first position P1 and the second position P2 in the radial direction (X direction). Diameter D4: the outer diameter of the raw material storage section 2, which is equal to the inner diameter of the container 10. Thickness T2: The thickness of the single crystal 12 at the second position P2. Imaginary line L2: An imaginary line extending from the edge of the opening OP toward the second position P2. Angle θ: the angle between an imaginary line L2 extending from the edge of the opening OP toward the second position P2 and the reference line L1. Velocity J0: Local crystal growth velocity in the normal direction (-Z direction) of the seed crystal 3 at the first position P1. Velocity Jx: local crystal growth velocity in the normal direction (−Z direction) of the seed crystal 3 at the second position P2.

[0030] As a result of extensive research, the inventors have found that the ratio Jx / J0 of the growth rates at positions P1 and P2 on the single crystal 12 is related to an index value including first information related to the vertical separation distance H1 between the shielding plate 5 and the seed crystal 3, and second information related to the diameter D2 of the opening OP of the shielding plate 5 (see Figure 2).

[0031] The index value will now be described. An example of the index value is cosθ, which is the cosine value of the angle θ defined above. cosθ can be expressed by the following equation (3).

number

[0032] As shown in formula (3), cos θ is a function including the separation distance H1 and the interval D3. The interval D3 is the interval between the first position P1 and the second position P2 on a reference line passing through the end of the opening OP of the shielding plate 5. Therefore, cos θ includes first information related to the separation distance H1 in the vertical direction between the shielding plate 5 and the seed crystal 3, and second information related to the diameter D2 (see FIG. 2) of the opening OP of the shielding plate 5.

[0033] The growth rate ratio Jx / J0 at the position (P1, P2) when cos θ is used as the index value will be described with reference to FIGS. 6A to 6D.

[0034] 6A is a scatter diagram showing the relationship between cosθ, which is the cosine value of the angle θ, and the growth speed ratio Jx / J0 of the second position P2 to the first position P1. This scatter diagram shows the growth speed ratio Jx / J0 of the second position P2 to the first position P1 when cosθ is changed by changing D3 (the distance between the first position P1 and the second position P2) and / or T2 (the thickness of the single crystal at the second position P2). This scatter diagram is based on actual measurement data obtained by actual experiments. From FIG. 6A, it can be seen that there is a certain correlation between cosθ and the growth speed ratio Jx / J0.

[0035] The contents of the experiment for obtaining the measured data will be described. In order to confirm the effect of the shielding plate 5, an experiment was performed using the growth of a single crystal of SiC as a model. First, a number of containers 10 were prepared. Three types of shielding plates 5 with different diameters D2 of the openings OP (diameters D2 of 80 mm, 100 mm, and 120 mm) were placed inside each container 10. The material of all the shielding plates 5 was graphite. The material of all the containers 10 was graphite. Since the containers 10 were porous, gas passed through the containers 10 even when the lids of the containers 10 were closed. The same amount (for example, 2 to 3 kg) of SiC raw material powder was contained in each container 10. A seed crystal of SiC was fixed to the pedestal 4 of each container 10.

[0036] The temperature of the heat source of the heating chamber was kept at 2300°C to 2400°C, and the inside of the heating chamber was reduced from atmospheric pressure to an environment, thereby growing the SiC single crystal for a predetermined time. While the single crystal was growing, the timing of increasing the nitrogen gas supplied to the heating chamber was set multiple times at regular time intervals. When the nitrogen gas supplied to the heating chamber was increased, the nitrogen gas passed through the container 10 and nitrogen atoms entered the growing single crystal. In the single crystal, the area with a high nitrogen concentration appears discolored. When the cross section of the grown single crystal is observed, the discolored area is represented as multiple lines. The discolored lines are called nitrogen markers. The interval between adjacent nitrogen markers represents the thickness grown during the time interval of the timing of increasing the nitrogen gas. Thus, the growth rate at any time elapsed from the start of processing can be calculated by dividing the interval between the nitrogen markers by the time interval of the timing of increasing the nitrogen gas. This calculation of the growth rate can be performed at any position in the single crystal. Therefore, the growth rate at each of the first position P1 and the second position P2 can be obtained using the nitrogen marker.

[0037] Fig. 6B is a scatter diagram showing the relationship between cos θ, which is the cosine value of the angle θ, and the growth speed ratio Jx / J0 of the second position P2 to the first position P1, similar to Fig. 6A. However, the diameter D2 of the interval OP is set to 100 mm. Fig. 6B shows that there is a certain correlation between cos θ and the growth speed ratio Jx / J0.

[0038] Fig. 6C is a scatter diagram showing the relationship between cos θ, which is the cosine value of the angle θ, and the growth speed ratio Jx / J0 of the second position P2 to the first position P1, similar to Fig. 6A. However, the diameter D2 of the interval OP is set to 120 mm. Fig. 6C shows that there is a certain correlation between cos θ and the growth speed ratio Jx / J0.

[0039] FIG. 6D is a graph that combines the plots shown in the scatter diagrams of FIG. 6A to FIG. 6C. The circle mark plot corresponds to the plot when the diameter D2 of the opening OP is 80 mm (FIG. 6A). The cross mark plot corresponds to the plot when the diameter D2 of the opening OP is 100 mm (FIG. 6B). The square mark plot corresponds to the plot when the diameter D2 of the opening OP is 120 mm (FIG. 6C). As can be seen in FIG. 6D, regarding the relationship between cosθ and the growth rate ratio Jx / J0, even if the diameter D2 of the opening OP changes, it is found that there is a common correlation that can be expressed by the same function f(cosθ).

[0040] [Crystal growth equipment design using correlation] As described above, the shape of the ingot 13 is related to the local crystal growth rate. Therefore, the growth rate ratio Jx / J0 at different positions on the single crystal can be obtained from the target shape of the ingot 13. If the above correlation is known in advance, it is possible to obtain cos θ corresponding to the obtained growth rate ratio Jx / J0, that is, the target index value, by utilizing the correlation. In other words, it is possible to back-calculate the parameters related to the shielding plate 5 from the target shape of the ingot 13 and design the design parameters related to the shielding plate 5 by utilizing the correlation between the growth rate ratio Jx / J0 and the parameters related to the shielding plate 5.

[0041] 7 is a diagram showing a flow of a method for designing a crystal growth apparatus for approximating the shape of the ingot 13 to a target shape. This design method includes the following steps (a) to (d).

[0042] Step (a) is a step of acquiring a correlation between an index value including first information related to the vertical distance between the shielding plate 5 and the seed crystal 3 and second information related to the diameter D2 of the opening OP of the shielding plate 5, and the ratio of the growth rates at different positions on the single crystal 12. The correlation is as described above. A specific example of the index value is cosθ.

[0043] Before carrying out step (a), it is advisable to calculate the correlation between the index value and the growth rate ratio and store the calculated correlation as a database. Alternatively, it is advisable to check whether the correlation has already been stored. As described above, the correlation may be provided in the form of a function or a graph. The correlation may also be provided in the form of a data table. The correlation database may be stored in a storage medium of a computer used to design the crystal growth apparatus, or in a server or cloud storage device connected via a telecommunication line such as the Internet.

[0044] Step (b) is a step of calculating a target ratio of growth rates at different positions on the single crystal 12 from the target shape of the ingot 13 to be manufactured. For example, the target shape of the ingot 13 is prepared, and two arbitrary points (a first position P1 and a second position P2) arranged radially (in the X direction) from the center are selected on the surface of the ingot 13 opposite to the seed crystal 3, and the target ratio (Jx / J0) of the growth rates at the two points (P1, P2) derived from the target shape is calculated. Since the first position P1 is also related to the diameter D2 of the opening OP, the sublimation rate may be taken into consideration. This point will be described in detail later.

[0045] In step (c), a target index value corresponding to the target ratio (Jx / J0) calculated in step (b) is derived based on the correlation obtained in step (a). The target index value is the same type of value as the index value. In this embodiment, the target index value is the cosine value (cos θ) of the angle θ.

[0046] Step (d) is a step of determining the vertical separation distance H1 between the shielding plate 5 and the seed crystal 3 and the diameter D2 of the opening OP of the shielding plate 5 from the target index value (e.g., cosθ) derived in step (c) and formula (3). The parameter D3 (the distance between the positions P1 and P2) in formula (3) can be calculated at the time of selecting the two points in step (b). The thickness T2 of the single crystal 12 in formula (3) is known. T2 may be set to zero. The shielding plate 5 is designed based on the diameter D2 of the opening OP of the shielding plate 5 determined in this manner, and the container 10 is designed so that the shielding plate 5 is disposed so as to obtain the separation distance H1.

[0047] Although the case has been described in which the index value and the target index value are the cosine value (cos θ) of the angle θ between the virtual line L2 and the reference line L1, the index value and the target index value do not have to be cos θ as long as they are values ​​that include first information related to the separation distance H1 and second information related to the diameter D2 of the opening OP of the shielding plate 5.

[0048] [Design of crystal growth equipment taking sublimation rate into account] While the shielding plate 5 is expected to have a positive effect of concentrating the deposition of the single crystal 12 on the seed crystal 3, it may also have a negative effect in that the gas sublimated from the raw material 1 is blocked by the shielding plate 5, making it difficult for it to reach the seed crystal 3 (or the single crystal 12 being grown).

[0049] For example, if there is a shield plate 5, if the area of ​​the opening OP is too small, the sublimation gas will not easily pass through the shield plate 5, and there is a concern that the sublimation rate will decrease. If the shield plate 5 is close to the raw material 1, the crystals attached to the shield plate 5 will narrow the flow path of the sublimation gas, and there is a concern that the sublimation rate will decrease. In this specification, the sublimation rate refers to the amount of sublimation gas generated in the entire container 10 per unit time. The sublimation rate can be obtained, for example, by the following method. The weight of the raw material 1 before the crystal growth process and the weight of the raw material 1 after the crystal growth process are measured. The weight difference before and after the process corresponds to the sublimation amount of the raw material 1. The sublimation rate is then set by dividing the weight difference before and after the process by the processing time.

[0050] Therefore, as design parameters related to the shielding plate 5, containers S1 to S6 containing the raw material 1 with different separation distance H2 and aperture ratios of the shielding plate 5 were prepared, and the sublimation rate ratios of the containers S1 to S6 were obtained. The aperture ratio is a value obtained by dividing the diameter D2 of the opening OP by the diameter D1 of the shielding plate 5 (see FIG. 3). The sublimation rate of the container 10 with the shielding plate 5 (see FIG. 2) is Sa. FIG. 8 shows a container 90 without a shielding plate as a comparative example. The sublimation rate of the container 90 without a shielding plate is Sv. The ratio of the sublimation rate Sa of the container 10 with the shielding plate 5 to the sublimation rate Sv of the container 90 without a shielding plate is the sublimation rate ratio (Sa / Sv). The closer the sublimation rate ratio (Sa / Sv) is to 1, the closer it is to the sublimation rate of the container 90 without the shielding plate 5, and it can be said that the sublimation gas is not affected by the shielding plate 5.

[0051] Table 1 shows the parameters of the containers S1 to S6 containing the raw material 1 and the experimental results of the containers S1 to S6. The separation distance H2 between the containers S1 to S5 is expressed as a numerical range of 2 to 3 mm, because the height of the raw material powder is not necessarily uniform, but has a height range of 2 to 3 mm. When the separation distance H2 of the container S6 is zero, the shielding plate 5 is in contact with the raw material powder.

[0052] [Table 1]

[0053] The evaluations were ranked from best to worst as S, A, and B. Evaluation S indicates that the effect of the decrease in sublimation rate due to the installation of the shielding plate 5 can be ignored. Evaluation A indicates that the effect of the decrease in sublimation rate due to the installation of the shielding plate 5 is relatively small. Evaluation B indicates that the effect of the decrease in sublimation rate due to the installation of the shielding plate 5 needs to be taken into consideration. To obtain an evaluation of A or higher, the sublimation rate ratio needs to be 0.7 or higher, i.e., formula (1) needs to be satisfied. To obtain an evaluation of S, the sublimation rate ratio needs to be 0.9 or higher, i.e., formula (2) needs to be satisfied. Sa ≧ 0.7 × Sv (1) Sa ≧ 0.9 × Sv (2)

[0054] For the containers S1 to S3, the sublimation rate ratio was 0.9 or more, and therefore the most excellent S rating was given. For the containers S4 to S5, the sublimation rate ratio was 0.7 or more and less than 0.9, and therefore the second excellent A rating was given. For the container S6, the sublimation rate ratio was reduced to 0.6. A high sublimation rate ratio means that crystal growth is fast even when the shielding plate 5 is used. In this way, if the crystal growth apparatus is designed taking the sublimation rate into consideration, high productivity can be maintained. Note that even if the container is rated B, the productivity is lower than when the shielding plate 5 is not used, but it is possible to obtain a desired ingot close to the target shape.

[0055] Based on the results shown in Table 1, in order to suppress the decrease in the sublimation rate, it is advisable to design the container 10 so that the distance H2 from the surface of the raw material to the shielding plate is at least 5 mm or more. More preferably, it is advisable to design the container 10 so that the distance H2 from the surface of the raw material to the shielding plate is at least 10 mm or more, and the opening ratio of the shielding plate is 60% or more.

[0056] The present invention is not limited to the above-described embodiment, and various improvements and modifications are possible without departing from the spirit of the present invention. Although the above mainly describes the case of producing a single crystal ingot of silicon carbide, the present invention can also be applied to the case of producing an ingot other than silicon carbide. [Explanation of symbols]

[0057] 1: Raw materials 2: Raw material storage section 3: Seed crystal 4: Pedestal 5: Shielding plate 10: Container 12: Single crystal 13: Ingot 20: (Manufacturing system) floor 21: (Manufacturing System) Wall 90: Container D1: Diameter of the shielding plate D2: Diameter of the opening of the shielding plate D3: Distance between the first and second positions D4: Outer diameter of raw material container H1: Distance between seed crystal and shield H2: Distance between the raw material and the shielding plate J0: Crystal growth rate at the first position Jx: Crystal growth rate at the second position L1: Reference line L2: Virtual line OP: Opening in the shielding plate P1 :First position P2 :Second position

Claims

1. A method for designing 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 a raw material, comprising the steps of: The crystal growth apparatus comprises: A raw material storage section that stores the raw material; a base that is installed vertically above the raw material storage unit and that fixes the seed crystal; a shielding plate disposed between the raw material storage unit and the base and having an opening at its center; (a) acquiring a correlation between an index value including first information related to a vertical distance between the shielding plate and the seed crystal and second information related to a diameter of the opening of the shielding plate and a ratio of growth rates at different positions on the single crystal; (b) calculating a target ratio of growth rates at different positions on the single crystal from a target shape of an ingot to be manufactured; (c) deriving a target index value, which is the index value corresponding to the target ratio calculated in the step (b), based on the correlation; and (d) determining a distance between the shielding plate and the seed crystal in the vertical direction and a diameter of the opening of the shielding plate from the target index value.

2. The different positions on the single crystal include a first position where a reference line that passes through an end of the opening and intersects a surface of the seed crystal at a right angle intersects with the surface of the single crystal, and a second position that is radially outward of the first position and located on the surface; 2. The method for designing a crystal growth apparatus according to claim 1, wherein the index value and the target index value are a cosine value (cos θ) of an angle θ between a virtual line extending from the end toward the second position and the reference line.

3. 3. The method for designing a crystal growing apparatus according to claim 1, wherein the correlation can be expressed by the same function even if the diameter of the opening changes.

4. 3. The method for designing a crystal growth apparatus according to claim 1 or 2, characterized in that in the step (d), the distance between the shielding plate and the raw material is determined so as to satisfy equation (1) for the sublimation rate Sa of the raw material when the single crystal ingot is produced using the crystal growth apparatus and the sublimation rate Sv of the raw material when the single crystal ingot is produced using a crystal growth apparatus without the shielding plate. Sa ≧ 0.7 × Sv (1)

5. 5. The method for designing a crystal growth apparatus according to claim 4, wherein the step (d) includes designing a distance between the shielding plate and the source material and a diameter of the opening of the shielding plate so as to satisfy formula (2). Sa ≧ 0.9 × Sv (2)

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