METHOD FOR MANUFACTURING SiC SINGLE CRYSTAL INGOT, SiC SINGLE CRYSTAL INGOT AND MODIFIED LAYER FORMATION DEVICE

Abstract

To provide a method for manufacturing a SiC single crystal ingot having a reduced micro pipe density and capable of preventing impurities from mixing.SOLUTION: A method for manufacturing a SiC single crystal ingot comprises the first step of forming a SiC modified layer on the main surface of a SiC seed crystal and the second step of growing a SiC single crystal on the SiC modified layer by a sublimation method.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a SiC single crystal ingot. This application claims priority based on Japanese Patent Application No. 2019-098445, filed on May 27, 2019, the contents of which are incorporated herein by reference. [Background technology]

[0002] Silicon carbide (SiC) has properties such as an electric breakdown field that is one order of magnitude larger than that of silicon (Si), a band gap that is three times larger, and a thermal conductivity that is approximately three times higher. Because of these properties, silicon carbide is expected to be used in power devices, high-frequency devices, high-temperature operating devices, etc.

[0003] For semiconductor devices, SiC epitaxial wafers, which are made by forming an epitaxial film on a SiC wafer, are used. The epitaxial film formed on the SiC wafer by chemical vapor deposition (CVD) becomes the active region of the SiC semiconductor device. SiC wafers are obtained by processing SiC single crystal ingots.

[0004] SiC single crystal ingots can be produced by methods such as sublimation recrystallization (hereinafter referred to as sublimation). Sublimation is a method for obtaining large single crystals by recrystallizing raw material gas sublimated from a raw material on a SiC seed crystal. To obtain high-quality SiC single crystal ingots, a method is needed to suppress defects and heterogeneous polymorphism (the mixing of crystals with different polytypes).

[0005] Patent Document 1 describes a method for producing a SiC single crystal ingot with the aim of producing a high-quality SiC single crystal ingot with a low defect density, in which a SiC seed crystal and a SiC raw material are placed in a crucible and the ratio of C to Si in the raw material gas is adjusted by adjusting the heating temperature.

[0006] Patent Document 2 describes a method for producing a SiC single crystal, in which a SiC single crystal is brought into contact with a molten liquid obtained by melting Si heated in a graphite crucible and a SiC single crystal is grown on a substrate, and a SiC single crystal ingot is precipitated and grown from the molten liquid to which Cr and Ce or Nd have been added. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-275166 [Patent Document 2] Patent No. 4450075 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the method for producing a SiC single crystal ingot described in Patent Document 1 generates defects called micropipes, which are hollow pipe-shaped defects with diameters ranging from several μm to several tens of μm, and in some cases, diameters of 100 μm or more. Micropipes are killer defects in the fabrication of electronic devices. Therefore, there is a need for a method for producing a SiC single crystal ingot that suppresses the generation of micropipes.

[0009] In the method for producing a SiC single crystal ingot described in Patent Document 2, Cr and Ti are contained in the melt to improve the growth rate. To produce a SiC single crystal ingot with an industrially sufficient throughput, it is necessary to contain a large amount of Cr and Ti in the melt, and it is unavoidable that these impurities will be incorporated into the SiC single crystal ingot being grown. Impurities in a SiC single crystal ingot are undesirable because they may adversely affect processes such as epitaxial film formation and device fabrication, as well as device characteristics.

[0010] The present invention has been made in consideration of the above problems, and aims to provide a method for producing a SiC single crystal ingot in which the micropipe density is reduced and the incorporation of impurities is suppressed. [Means for solving the problem]

[0011] As a result of extensive research, the present inventors have found that by forming a SiC modified layer with reduced micropipes and growing a SiC single crystal ingot on the SiC modified layer by sublimation, it is possible to provide a SiC single crystal ingot with reduced micropipe density and suppressed impurity contamination.

[0012] (1) A method for producing a SiC single crystal ingot according to a first aspect of the present invention includes a first step of forming a SiC modified layer having a reduced micropipe density on a main surface of a SiC seed crystal, and a second step of growing a SiC single crystal on the SiC modified layer by sublimation.

[0013] (2) In the method for producing a SiC single crystal ingot according to the above aspect, the first step may form the SiC modified layer on a main surface of the SiC seed crystal using a solution process.

[0014] (3) In the method for producing a SiC single crystal ingot according to the above aspect, the first step may include spraying a gas containing Si onto a main surface of the SiC seed crystal to form the SiC modified layer on the main surface of the SiC seed crystal. The first step may also include spraying a gas containing C onto the main surface of the SiC seed crystal in addition to the gas containing Si.

[0015] (4) In the method for manufacturing a SiC single crystal ingot according to the above aspect, the first step may be performed while the SiC seed crystal is fixed to a pedestal having an attachment means, and after the first step is completed, the SiC seed crystal may be removed together with the pedestal from an apparatus in which the first step is performed, and then attached together with the pedestal to an apparatus in which the second step is performed using the attachment means.

[0016] (5) In the method for producing a SiC single crystal ingot according to the above aspect, the pedestal may be made of graphite.

[0017] (6) In the method for producing a SiC single crystal ingot according to the above aspect, the second step may be performed in a state in which the SiC modified layer formed in the first step is cut out from the SiC seed crystal and fixed to the inside of a lid of a crystal growth apparatus.

[0018] (7) In the method for producing a SiC single crystal ingot according to the above aspect, the SiC modified layer may have a thickness of 100 μm or more.

[0019] (8) In the method for producing a SiC single crystal ingot according to the above aspect, a SiC single crystal plate cut from a SiC single crystal ingot produced by any of the methods for producing a SiC single crystal ingot according to the above aspect may be used as the SiC seed crystal.

[0020] (9) In the method for producing a SiC single crystal ingot according to the above aspect, the first step may be carried out two or more times.

[0021] (10) In the method for producing a SiC single crystal ingot according to the above aspect, the first step may use a solution containing Si, C, and a transition metal as the raw material.

[0022] (11) The method for producing a SiC single crystal ingot according to the above aspect may include a step of polishing the main surface of the SiC modified layer between the first step and the second step.

[0023] (12) In the method for producing a SiC single crystal ingot according to the above aspect, a SiC single crystal ingot is obtained in the second step, and a micropipe density of a SiC wafer formed from the SiC single crystal ingot is 0 / cm. 2 More than 0.1 pieces / cm 2 It may be less than one. [Effects of the Invention]

[0024] According to the method for manufacturing a SiC single crystal ingot according to the above aspect, it is possible to reduce micropipes and suppress the incorporation of impurities.

Brief Description of the Drawings

[0025] [Figure 1] It is a schematic cross-sectional view of a preferable example of a modification layer forming apparatus that can be used in the method for manufacturing a SiC single crystal ingot according to the first embodiment. [Figure 2A] It is a schematic perspective view showing a preferable example of a pedestal that can be used in the method for manufacturing a SiC single crystal ingot according to the first embodiment. [Figure 2B] It is a schematic cross-sectional view showing a preferable example of a pedestal that can be used in the method for manufacturing a SiC single crystal ingot according to the first embodiment. [Figure 3] It is a schematic cross-sectional view showing a preferable example of a crystal manufacturing apparatus that can be used in the method for manufacturing a SiC single crystal ingot according to the first embodiment. [Figure 4] It is a schematic cross-sectional view showing a preferable example of a modification layer forming apparatus that can be used in the method for manufacturing a SiC single crystal ingot according to the second embodiment.

Modes for Carrying Out the Invention

[0026] Hereinafter, examples of preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The drawings used in the following description may show, for the sake of convenience, the characteristic parts enlarged in order to make the features of the present invention easier to understand, and the dimensional ratios of each component may be different from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and it can be appropriately modified and implemented without changing the gist thereof. For example, within the scope not departing from the invention, changes, additions, and omissions such as numbers, positions, sizes, numerical values, materials, shapes, ratios, etc. can be made.

[0027] <Method for Manufacturing a SiC Single Crystal Ingot> (First Embodiment) The method for producing a SiC single crystal ingot according to this embodiment includes a first step of forming a SiC modified layer with a reduced micropipe density on the main surface of a SiC seed crystal, and a second step of growing a SiC single crystal on the SiC modified layer by sublimation. The reduction rate of micropipes in the SiC modified layer obtained by the manufacturing method of the present invention varies depending on the conditions, but may be, for example, 10% or more, 50% or more, or 90% or more, etc. However, it is not limited to these examples. From the SiC single crystal ingot obtained by the present invention, the micropipe density is 0 pieces / cm 2 More than 0.1 pieces / cm 2 It is possible to form less than 100 SiC wafers.

[0028] (1st step) In the first step, a SiC modified layer with a reduced micropipe density is formed on the main surface of the SiC seed crystal. That is, a high-quality SiC single crystal layer with reduced hollow pipe-shaped defects is formed on the main surface of the SiC seed crystal. The SiC modified layer here refers to a SiC single crystal that serves as the starting point for growing the SiC single crystal by sublimation in the second step. Although not described in this specification, it is necessary to prepare a SiC seed crystal before performing the first step. The SiC seed crystal is made of a SiC single crystal and is prepared by a known method. In conventional methods, SiC single crystals cut from SiC single crystal ingots produced by sublimation deposition have often been used as seed crystals. However, conventional seed crystals have many micropipes. Compared to conventional seed crystals, the SiC modified layer produced by performing the first step of this embodiment has significantly fewer micropipes. Therefore, the present invention can produce excellent SiC single crystal ingots.

[0029] In the first step, a SiC modified layer is formed on the main surface of the SiC seed crystal, for example, using a solution method. In this embodiment, the formation of the SiC modified layer using the solution method can be performed using a known method. For example, the solution method using the slow cooling method described in Japanese Patent No. 4450075 can be used. Specifically, silicon carbide may be grown on a single crystal substrate from a melt, and after the growth time has elapsed, the grown crystal may be completely pulled out of the melt and the crucible may be slowly cooled to room temperature to obtain a silicon carbide single crystal. Alternatively, a solution method such as a solvent transfer crystal growth method, a vapor-gas-solid method, or a seeded solution growth method may be used. The solution method can be performed using, for example, the apparatus shown in FIG. 1. The SiC modified layer produced in this embodiment is a SiC single crystal with a reduced micropipe density.

[0030] Fig. 1 is a cross-sectional schematic diagram showing a preferred example of a modified layer forming apparatus 1. The modified layer forming apparatus 1 includes, for example, a crucible 10, a graphite rod 11, and a high-frequency coil 12. For ease of explanation, Fig. 1 shows a state in which a pedestal 2 is fixed to the graphite rod 11, a SiC seed crystal SD is fixed to the pedestal 2, and a SiC modified layer 4 is formed on the SiC seed crystal SD.

[0031] The crucible 10 includes a graphite crucible 101 and a heat insulating material 102 that covers the graphite crucible 101. The crucible 10 preferably has a hole 10Aa in an upper portion 10A through which a graphite rod 11 can pass. A raw material M for the SiC modified layer 4 is stored in a lower portion 10B of the crucible 10.

[0032] The raw material M is a known raw material used in the production of SiC single crystals (SiC modified layer) by the solution method. For example, a Si-C-based solution can be used as the raw material M. Furthermore, a solution containing not only Si and C but also transition metals, such as a Si-C-Cr solution or a Si-C-Ti solution, can also be used as the raw material M. That is, a solution containing Si, C, and a transition metal can also be used as the raw material M. Using a solution containing a transition metal, etc., as the raw material M can facilitate the dissolution of C into Si. In other words, the solubility of C in Si increases. Furthermore, using a solution containing a transition metal as the raw material M can improve the growth rate of the SiC modified layer 4.

[0033] The graphite rod 11 can be inserted into and removed from the crucible 10 through a hole 10Aa provided in the top 10A of the crucible 10. A SiC seed crystal SD is attached to the tip 11A of the graphite rod 11 directly or via a pedestal 2. A SiC modified layer 4 is formed on the main surface of the SiC seed crystal SD. The tip 11A is the tip of the graphite rod 11. During growth of the SiC modified layer 4 by the modified layer forming device 1, the graphite rod 11 with the SiC seed crystal SD attached to the tip 11A is placed inside the crucible 10, and after growth, it is pulled out to the outside of the crucible 10 and the SiC seed crystal SD is removed. The SiC seed crystal SD may be provided by being directly attached to the graphite rod 11, or may be provided on the graphite rod 11 via a pedestal 2 attached to the tip of the graphite rod 11 as shown in FIG. 1.

[0034] The pedestal 2 preferably has an attachment means 21 that can be attached to the graphite rod 11. The pedestal 2 is attached to the graphite rod 11 via the attachment means 21. The pedestal 2 has the attachment means 21 and a base 20 that is perpendicular to the axial direction of the attachment means 21. The base 20 is, for example, disk-shaped and has surfaces 20a and 20b that are perpendicular to the axial direction of the attachment means 21. Of the surfaces 20a and 20b, the surface that is away from the graphite rod 11 is referred to as the first surface 20a, and the surface that is in contact with the graphite rod 11 is referred to as the second surface 20b. The pedestal 2 fixes the SiC seed crystal SD to the first surface 20a. The SiC seed crystal SD is fixed to the first surface 20a using, for example, an adhesive. A known adhesive can be used as the adhesive. In the manufacturing method of this embodiment, after the SiC modified layer 4 is formed on the main surface of the SiC seed crystal SD, the SiC seed crystal SD and the SiC modified layer 4 can be removed together with the pedestal 2 from the graphite rod 11. Furthermore, the removed SiC seed crystal SD and the SiC modified layer 4 can be attached together with the pedestal 2 to a crystal growth apparatus that performs the second step. In other words, in the manufacturing method of this embodiment, the step of removing the SiC seed crystal SD and the SiC modified layer 4 from the pedestal 2 is not necessary. The base 2 can be made of, for example, graphite. Using graphite as the material for the base 2 is preferable because it prevents impurities from being mixed into the SiC modified layer 4. Different materials may be used for different parts of the base 2. For example, only the base 20, which may come into contact with the solution, may be made of graphite.

[0035] The configuration of the pedestal 2 is not particularly limited, and may be arbitrarily selected as long as it can stably fix the SiC seed crystal SD (or the SiC seed crystal SD and the SiC reforming layer 4) and can be stably fixed to and detached from the graphite rod 11. FIGS. 2A and 2B are perspective views showing a preferred example of the pedestal 2 having an attachment means 21 (21'). FIG. 2A shows the pedestal 2 having a pin structure. The pedestal 2 has the attachment means 21, a pin 22, and a base 20. The SiC seed crystal SD is fixed to the first surface 20a of the attachment means. The attachment means 21 is inserted into the graphite rod 11 up to the height of the second surface 20B of the base 20 and is fixed to the graphite rod 11 via the pin 22. After the SiC reforming layer 4 is formed, the pin 22 can be removed from the pedestal 2, and the attachment means 21 can be removed from the graphite rod 11. FIG. 2B shows the pedestal 2' in which the attachment means 21' has a screw structure. 2B is fixed to the graphite rod 11 or the like by the mounting means 21' having a screw structure. The shape of the graphite rod 11 is changed appropriately to match the shape of the base 2. For example, if the base has a male screw structure as the mounting means 21' like the base 2', the graphite rod 11 has a female screw structure that screws into the male screw structure mounting means 21'. By configuring base 2 to have mounting means 21 or mounting means 21', it is possible to improve the throughput in the production of SiC single crystal ingots.

[0036] The first step includes heating the raw material M with the high-frequency coil 13 to form a solution. In the first step, the raw material M for the SiC single crystal in the modified layer forming apparatus 1 is turned into a solution by heating with the high-frequency coil 13. The temperature at which the SiC seed crystal SD is immersed in the solution is preferably a temperature at which C from the graphite crucible 101 is sufficiently dissolved, the SiC concentration approaches its saturation concentration, and the concentration remains constant. For example, a preferred temperature is 1600 to 2100°C, more preferably 1950 to 2050°C. Other examples include 1700 to 1750°C and 1850 to 1900°C. However, since the temperature varies depending on the composition of the solution, it is not limited to these temperatures. The heating time is preferably 1 to 50 hours, more preferably 10 to 40 hours. Other examples include 5 to 10 hours and 30 to 50 hours. However, since the temperature varies depending on the composition and temperature of the solution, it is not limited to these times. With the SiC seed crystal SD in contact with the solution, the SiC modified layer 4 is formed on the main surface of the SiC seed crystal SD by, for example, a temperature gradient method in which a temperature gradient of about 5 to 100°C / cm is established, or a cooling method in which the solution is cooled by operating a heating device. That is, the first step includes a step of forming the SiC modified layer 4 on the main surface of the SiC seed crystal SD by using a solution.

[0037] The temperature gradient method is a method of creating a temperature gradient such that the temperature increases with increasing distance from the surface of the seed crystal SD (conversely, a temperature gradient such that the temperature decreases with increasing distance from the surface of the seed crystal SD). Such a temperature gradient can be obtained by controlling the heating position of the graphite crucible 101, for example, by the position of a high-frequency coil. The temperature gradient can be, for example, about 5 to 100°C / cm, and preferably about 5 to 50°C / cm. By setting the temperature gradient in this range, the SiC modified layer can be grown uniformly and quickly. Furthermore, in the case of the temperature gradient method, it is preferable to maintain the surface of the seed crystal SD (or the SiC modified layer 4 being grown) at approximately the same position as the liquid surface of the solution of raw material M, from the viewpoint of efficiently growing the SiC modified layer 4.

[0038] In the cooling method, for example, the solution around the SiC seed crystal SD is preferably cooled to 2100°C or less, more preferably to a temperature of about 1600 to 1800°C. The temperature range to which the solution is cooled is preferably 30 to 200°C, more preferably 50 to 150°C. However, since this varies depending on the composition and temperature of the solution, it is not limited to the above and may be 10 to 50°C, 100 to 250°C, etc. The cooling rate of the solution is preferably 0.3 to 2.0°C / h, more preferably 0.5 to 1.5°C / h. It may also be 0.1 to 50°C / h, 1.0 to 2.5°C / h, etc. Cooling the solution makes the SiC dissolved in the solution supersaturated, and a SiC modified layer 4 is formed on the main surface of the SiC seed crystal SD.

[0039] Various conditions can be applied to the heating means, atmosphere, heating time, graphite crucible shape, heating rate, cooling rate, etc., depending on the thickness of the SiC modified layer 4 to be formed. In the solution method, the thickness of the SiC modified layer 4 is determined by the product of the growth rate and the growth time. In this embodiment, the SiC modified layer 4 is grown under conditions that result in a thickness of 100 μm or more.

[0040] The thickness of the SiC modified layer 4 is, for example, 100 μm or more, preferably 150 μm or more, and more preferably 300 μm or more. By setting the thickness of the SiC modified layer 4 within this range, the micropipe density can be sufficiently reduced. Furthermore, if the SiC modified layer 4 is too thin, handling problems such as cracking may occur, but by setting the thickness within this range, cracking and the like can be sufficiently suppressed. The micropipe density of the SiC modified layer 4 produced by the first step is 10% or less of the micropipe density of the SiC seed crystal SD. Increasing the thickness of the SiC modified layer 4 can increase the reduction rate from the micropipe density of the SiC seed crystal SD. Specifically, by making the thickness of the SiC modified layer 4 150 μm or more, the reduction rate can be 95% or more, and by making the thickness of the SiC modified layer 4 300 μm or more, the reduction rate can be 99% or more. Here, the reduction rate is an index that indicates the percentage reduction in the micropipe density of the SiC modified layer 4 compared to the micropipe density of the SiC seed crystal SD, when comparing the micropipe densities of the SiC seed crystal SD and the SiC modified layer 4. In other words, when the reduction rate is 99%, the ratio of the micropipe densities of the SiC seed crystal SD and the SiC modified layer 4 is 100:1. The micropipe density in the SiC seed crystal SD refers to the micropipe density on the main surface of the SiC seed crystal SD. The micropipe density of the SiC modified layer 4 refers to the micropipe density on the main surface of the SiC modified layer 4. Conventionally, when forming a SiC single crystal by a solution method, excessive dissolution of the graphite crucible C has been a concern, as it can hinder single crystal growth due to the formation of SiC polycrystals, and thus can cause problems in stable growth over long periods of time. However, the formation of the SiC modified layer 4 according to this embodiment allows growth to be carried out in a short period of time. Therefore, the above-mentioned problems in stable growth of the SiC single crystal do not arise.

[0041] In the method for producing a SiC single crystal ingot according to this embodiment, the first step can form a SiC modified layer 4 on the main surface of the SiC seed crystal SD. The SiC modified layer 4 is a high-quality SiC single crystal with reduced micropipes. Performing the first step multiple times allows for the growth of a higher-quality SiC modified layer 4, so it is preferable to perform the first step two or more times. When the first step is performed two or more times, it is preferable to treat only the SiC single crystal grown in the last first step as the SiC modified layer 4. For example, if the first step is performed three times, it is preferable to refer to the SiC single crystal grown in the third step as the SiC modified layer 4, and the SiC single crystals grown up to the second step as the SiC seed crystal SD. Alternatively, all of the SiC single crystals grown in the first step from the first step to the last may be referred to as the SiC modified layer 4. Performing the second sublimation step using a SiC modified layer 4 with reduced micropipes can dramatically reduce the micropipe density in the SiC single crystal ingot produced by sublimation. Furthermore, the manufacturing method of this embodiment can also prevent impurities from being mixed into the SiC single crystal ingot, for reasons that will be described in detail later.

[0042] In the method for producing a SiC single crystal ingot according to this embodiment, the first step is performed using a solution method, thereby forming the SiC modified layer 4. The area where the raw material M for the SiC single crystal is stored is an area surrounded by a graphite crucible 101, and the pedestal 2 to which the SiC seed crystal SD is fixed and the graphite rod 11 to which the SiC seed crystal SD is fixed are both made of graphite. Therefore, the area where the SiC modified layer 4 is formed contains as few components as possible other than Si and C, thereby preventing impurities from entering the SiC modified layer 4.

[0043] After forming the SiC modified layer 4 on the main surface of the SiC seed crystal SD in the first step, the method may further include a step of flattening the surface of the SiC modified layer 4. The step of flattening the surface of the SiC modified layer can be performed by processing the surface of the SiC single crystal to be flat. For example, the surface of the SiC modified layer 4 can be flattened by polishing. By flattening the surface of the SiC modified layer 4, the growth surface of the SiC single crystal ingot grown in the second step becomes flat, allowing for the production of a higher quality SiC single crystal ingot.

[0044] (2nd process) The second step is a step of growing a SiC single crystal ingot on the SiC modified layer 4 formed on the main surface of the SiC seed crystal SD by sublimation.

[0045] FIG. 3 is a cross-sectional schematic diagram showing an example of a crystal growth apparatus 5 capable of carrying out the second step in the method for producing a SiC single crystal ingot according to this embodiment.

[0046] 3 includes a crucible 50 and a heating means 51 arranged around the crucible 50. The crucible 50 has a lid 501 and a main body 502.

[0047] The crucible 50 has a mounting portion 510 on the inner surface 501A of the lid 501. The SiC modified layer 4 is fixed to the mounting portion 510. More specifically, the pedestal 2 and the SiC seed crystal SD are fixed to the mounting portion 510 together with the SiC modified layer 4 formed on the main surface of the SiC seed crystal SD. When the SiC modified layer 4 is fixed to the mounting portion 510 together with the pedestal 2 and the SiC seed crystal SD, the pedestal 2 is preferably attached to the mounting portion 510 via an attachment means 21. When the attachment is performed via the attachment means 21, the mounting portion 510 can have a configuration that allows the pedestal 2 to be stably fixed by the attachment means 21. The SiC modified layer 4 may be peeled off from the SiC seed crystal SD and directly fixed to the mounting portion 510. When the SiC modified layer 4 is directly fixed to the mounting portion 510, it can be attached using a material selected as needed, such as an adhesive. Note that the use of an adhesive is not necessarily required. For example, a notch or the like may be formed in the base 2, and the SiC modified layer 4 may be disposed using the notch or the like.

[0048] The single crystal raw material M2 used in the sublimation method is accommodated in the main body 502, which is located opposite the lid 501. The accommodated single crystal raw material M2 can be a powdered SiC raw material. The single crystal raw material M2 is heated by a heating means 51 arranged around the crucible 50. The interior of the crucible 50 is then depressurized, causing the single crystal raw material M2 to sublimate. The temperature to which the single crystal raw material M2 is heated is, for example, 2200 to 2600°C, more preferably 2300 to 2500°C, and even more preferably 2350 to 2450°C. However, this is not limiting. Other conditions can be selected as needed. When the single crystal raw material M2 sublimes, it grows as a SiC single crystal on the SiC modification layer 4, forming a SiC single crystal ingot. The number of micropipes in this ingot is reduced compared to when a conventional seed crystal is used. Furthermore, when producing a SiC single crystal ingot by a solution method, transition metals added to the solution are incorporated into the SiC single crystal ingot. However, the method for producing a SiC single crystal ingot according to this embodiment includes a second step of growing the SiC single crystal ingot by sublimation, thereby preventing the transition metals from being mixed into the SiC single crystal ingot.

[0049] After the SiC single crystal ingot is formed, the base 2 can be removed from the lid 501 of the crucible 50 and the SiC single crystal ingot can be recovered.

[0050] (SiC wafer manufacturing) SiC wafers can be manufactured by cutting the SiC single crystal ingot manufactured by the method for manufacturing a SiC single crystal ingot according to this embodiment to an appropriate thickness.

[0051] Furthermore, by cutting the single crystal ingot produced by the method for producing a SiC single crystal ingot according to this embodiment into SiC single crystal plates of an appropriate thickness, the SiC single crystal plates can be used as SiC seed crystal SD. By performing the first and second steps according to this embodiment using this SiC seed crystal SD, a higher quality SiC single crystal ingot can be produced.

[0052] The method for manufacturing a SiC single crystal ingot according to this embodiment can grow a SiC single crystal ingot with a reduced micropipe density. For example, in a SiC wafer with a diameter of 100 mm or more cut from a SiC single crystal ingot, the micropipe density is 0.1 / cm. 2 The SiC single crystal ingot grown by the method for manufacturing a SiC single crystal ingot according to this embodiment has reduced impurities. In other words, it is possible to manufacture a high-quality SiC single crystal ingot and improve the yield in subsequent processes. (Method for evaluating micropipes) Micropipes are hollow pipe-shaped defects with diameters of several μm to several tens of μm, and in some cases, diameters of 100 μm or more. Micropipes can be evaluated as follows. The following method may be used to evaluate micropipes in SiC modified layers. After polishing the surface of a single crystal, micropipes can be detected by taking an X-ray topographic image. It is preferable to use either a transmission image or a reflection image depending on the output of the X-ray source and the thickness of the single crystal. Generally, the time required to obtain a transmission image is shorter than the time required to obtain a reflection image. For this reason, a reflection image is used when the thickness of the single crystal is large and the amount of X-ray that can penetrate is small. The micropipe density can be obtained by counting the number of micropipes visible in the topographic image and dividing by the area of ​​the topographic image.

[0053] (Second embodiment) FIG. 4 is a cross-sectional schematic diagram of a preferred example of a modified layer forming apparatus 1A according to the second embodiment. The method for producing a SiC single crystal ingot according to the second embodiment differs from the first embodiment in the first step. Specifically, the second embodiment differs from the first embodiment in that, in the first step, a gas containing Si is sprayed onto the main surface of the SiC seed crystal SD to form a SiC modified layer 4 on the main surface of the SiC seed crystal SD. In FIG. 4, the same components as those shown in FIG. 1 are designated by the same reference numerals, and their description will be omitted. The examples and conditions of the first embodiment can be preferably used in this embodiment unless there are particular problems.

[0054] 4, the modified layer forming apparatus 1A includes a crucible 6, a gas introduction section 631 that supplies gas G into the crucible 6, a first insulating section 71 that surrounds the periphery of the crucible 6, a second insulating section 72 that is located outside the first insulating section 71, a heating means 64 that is located outside the second insulating section 72, and a support mechanism 8 that supports the crucible 6 and is movable up and down and rotatable. For ease of explanation, FIG. 4 also shows the gas G introduced into the crucible 6 and the flow path of the gas G, but the present embodiment is not limited to this example.

[0055] In the method for producing a SiC single crystal ingot according to this embodiment, a gas containing Si is sprayed onto the main surface of the SiC seed crystal SD, and a SiC modified layer 4 can be formed on the main surface of the SiC seed crystal SD. The crucible 6 includes a ceiling portion 61 and a main body portion 63. A gas inlet portion 631 is formed on the bottom surface of the crucible main body portion 63, which serves as a flow path for the gas G introduced into the crucible 6. The ceiling portion 61 includes an outlet portion 611 that discharges the gas G inside the crucible 6 to the outside of the crucible 6, and a mounting portion 65. The mounting portion 65 can mount the pedestal 2 or a SiC seed crystal SD. The pedestal 2 is attached to the mounting portion 65 via mounting means 21, so that the pedestal 2 is stably fixed.

[0056] The crucible 6 is supported by a support mechanism 8. The support mechanism 8 includes a rotation / up / down mechanism 81 and a support base 82. With the crucible 6 supported by the support base 82, the support mechanism 8 can rotate and move the crucible 6 up and down using the rotation / up / down mechanism 81. A gas inlet for introducing gas G into the crucible 6 is located at the axial center of the support mechanism 8.

[0057] The outer periphery and top surface of the crucible 6 are surrounded by a first insulating section 71. The first insulating section 71 has a ceiling section 711 and a side periphery section 712. The ceiling section 711 covers the top surface of the crucible 6. The side periphery section 712 surrounds the side periphery of the crucible 6. The ceiling section 711 has a through-hole in a location located directly above the gas outlet section 611 of the crucible 6. Gas introduced into the crucible is discharged to the outside of the crucible 6 via the gas outlet section 611 and the through-hole. The outer periphery of the side peripheral portion 712 is surrounded by the second insulating portion 72, and the heating means 64 is located on the outer periphery of the second insulating portion 72. The length of the second insulating portion 72 in the axial direction is preferably equal to or greater than the length of the first insulating portion 71, and may be the same length as the length of the first insulating portion 71.

[0058] Gas G, which is a raw material for the SiC modified layer 4, is introduced into the crucible 6 via the gas inlet 631. The gas G to be introduced may be a gas containing Si. For example, silane (SiH4), SiH2Cl2, SiHCl3, SiCl4, etc. may be introduced. Furthermore, a gas G containing C, such as propane (C3H8), may be introduced together with the gas containing Si.

[0059] The gas G introduced into the crucible 6 is heated by the heating means 64 and further insulated by the first and second insulating sections 71 and 72, forming a SiC modified layer 4 on the main surface of the SiC seed crystal SD. The temperature inside the crucible 6 during the formation of the SiC modified layer 4 is preferably 1500°C or higher, more preferably 1600°C or higher. It is also preferably 2400°C or lower, more preferably 2350°C or lower. Gas that does not contribute to the formation of the SiC modified layer 4 is discharged to the outside of the crucible 6 via the gas discharge section 611. The gas discharge section 611 and the through-hole may be connected to a pump (not shown). The pressure inside the crucible 6 may be changed as appropriate. For example, the inside of the crucible 6 may be in a reduced pressure environment. Alternatively, the pressure inside the crucible 6 may be made higher than the pressure outside the crucible 6, and the gas introduced into the crucible 6 may be discharged to the outside of the crucible 6. It is preferable to change the pressure inside the crucible 6 as appropriate according to the type of gas used, the growth temperature, and the like.

[0060] The crucible 6 is rotated by the rotary up-down mechanism 81, thereby forming a highly symmetrical SiC modified layer 4. The thickness of the formed SiC modified layer 4 is, for example, 100 μm or more, preferably 200 μm or more, and more preferably 300 μm or more. By setting the thickness of the SiC modified layer 4 within this range, the micropipe density can be sufficiently reduced. Furthermore, cracking of the SiC modified layer can be sufficiently suppressed. In this embodiment, a SiC single crystal ingot can be grown on the SiC modified layer 4 formed in the first step using the same means as in the first embodiment.

[0061] The method for producing a SiC single crystal ingot according to this embodiment can grow a SiC single crystal ingot with reduced micropipes, can grow a SiC single crystal ingot with reduced impurity contamination, and can improve yields in subsequent device fabrication processes.

[0062] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Industrial Applicability]

[0063] As described above, the method for producing a SiC single crystal ingot according to the present invention can produce a high-quality SiC single crystal ingot with reduced micropipes, and can therefore be used to improve the quality and throughput of SiC devices. [Explanation of symbols]

[0064] 1. 1A modified layer forming device 10 Crucible 101 Graphite crucible 102 Insulation 11 Graphite rod 12 High frequency coil 2, 2' base 20 Foundation 20a Page 1 20b 2nd side 21, 21' mounting means 22-pin 4 SiC modified layer 5 Crystal growth equipment 50 Crucible 51 Heating means 501 Lid 502 Main body M Raw material M2 Single crystal raw material SD SiC seed crystal

Claims

1. a first step of forming a SiC modified layer on a main surface of a SiC seed crystal; a second step of growing a SiC single crystal on the SiC modified layer by sublimation.

2. The method for producing a SiC single crystal ingot according to claim 1 , wherein in the first step, the SiC modified layer is formed on the main surface of the SiC seed crystal using a solution method.

3. 3. The method for producing a SiC single crystal ingot according to claim 2, wherein the first step uses a solution containing Si, C, and a transition metal as a raw material.

4. 2. The method for producing a SiC single crystal ingot according to claim 1, wherein in the first step, a gas containing Si is sprayed onto a main surface of the SiC seed crystal to form the SiC modified layer on the main surface of the SiC seed crystal.

5. 5. The method for producing a SiC single crystal ingot according to claim 4, wherein the first step comprises spraying a gas containing C in addition to a gas containing Si onto a main surface of the SiC seed crystal.

6. The first step is performed while the SiC seed crystal is fixed to a pedestal having an attachment means; 6. The method for producing a SiC single crystal ingot according to claim 1, wherein, after the first step is completed, the SiC seed crystal and the SiC modified layer are removed together with the pedestal from an apparatus in which the first step is performed, and the SiC seed crystal and the SiC modified layer are attached together with the pedestal to an apparatus in which the second step is performed using the attachment means, and the second step is then performed.

7. The method for producing a SiC single crystal ingot according to claim 6 , wherein the pedestal is made of graphite.

8. 6. The method for producing a SiC single crystal ingot according to claim 1, wherein the second step is performed in a state in which the SiC modified layer formed in the first step is cut out from the SiC seed crystal and fixed to the inside of a lid of a crystal growth apparatus.

9. The method for producing a SiC single crystal ingot according to any one of claims 1 to 8, wherein the SiC modification layer has a thickness of 100 µm or more.

10. 10. The method for producing a SiC single crystal ingot according to claim 1, wherein a SiC single crystal substrate cut from a SiC single crystal ingot produced by the method for producing a SiC single crystal ingot according to claim 1 is used as the SiC seed crystal.

11. The method for producing a SiC single crystal ingot according to any one of claims 1 to 10, wherein the second step is carried out after the first step is carried out two or more times.

12. The method for producing a SiC single crystal ingot according to any one of claims 1 to 11, further comprising a step of polishing the main surface of the SiC modified layer between the first step and the second step.

13. In the second step, a SiC single crystal ingot is obtained, The density of micropipes in the SiC wafer formed from the SiC single crystal ingot is 0 pieces / cm ２ More than 0.1 pieces / cm ２ The method for producing a SiC single crystal ingot according to any one of claims 1 to 12, wherein the number of crystals is not more than 1.

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