Method for manufacturing SiC single crystal ingot

Abstract

This method for producing a SiC single crystal ingot includes: a first step for forming a SiC modified layer on the main surface of a SiC seed crystal; and a second step for growing a SiC single crystal on the SiC modified layer by means of a sublimation method.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a SiC single crystal ingot. This application claims priority based on Japanese Patent Application No. 2019-098445 filed in Japan on May 27, 2019, and incorporates its content herein by reference.

Background Art

[0002] Silicon carbide (SiC) has characteristics such as a breakdown electric field that is one order of magnitude larger than that of silicon (Si), a bandgap that is three times larger, and a thermal conductivity that is about three times higher. Because of these characteristics of silicon carbide, applications to power devices, high-frequency devices, high-temperature operation devices, etc. are expected.

[0003] For devices such as semiconductors, a SiC epitaxial wafer in which an epitaxial film is formed on a SiC wafer is used. The epitaxial film provided on the SiC wafer by the Chemical Vapor Deposition Method (CVD method) becomes the active region of the SiC semiconductor device. The SiC wafer is obtained by processing a SiC single crystal ingot.

[0004] A SiC single crystal ingot can be produced by a method such as the sublimation recrystallization method (hereinafter referred to as the sublimation method). The sublimation method is a method of obtaining a large single crystal by recrystallizing the raw material gas sublimated from the raw material on the SiC seed crystal. In order to obtain a high-quality SiC single crystal ingot, a method for suppressing defects and polytypes (the coexistence of crystals with different polytypes) is required.

[0005] Patent Document 1 describes a method for manufacturing a SiC single crystal ingot that aims to manufacture 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 growing a SiC single crystal on a substrate by bringing a SiC single crystal into contact with a melt obtained by melting Si heated in a graphite crucible, wherein a SiC single crystal ingot is precipitated and grown using a melt containing Cr and Ce or Nd in the melt.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in the method for manufacturing a SiC single crystal ingot described in Patent Document 1, defects in the shape of hollow pipes called micropipes, having a diameter of about several μm to several tens of μm, and in some cases, a diameter of 100 μm or more, are generated. Micropipes become killer defects in the production of electronic devices. Therefore, a method for manufacturing a SiC single crystal ingot that suppresses the generation of micropipes is required.

[0009] The method for manufacturing a SiC single crystal ingot described in Patent Document 2 contains Cr and Ti in the melt to improve the growth rate. In order to manufacture a SiC single crystal ingot with industrially sufficient throughput, it is necessary to include a large amount of Cr and Ti in the melt, and it is inevitable that these impurities are incorporated into the SiC single crystal ingot to be grown. Impurities in the SiC single crystal ingot may have an adverse effect on processes such as the formation of an epitaxial film and device manufacturing, and device characteristics, which is not preferable.

[0010] The present invention has been made in view of the above problems, and an object thereof is to provide a method for manufacturing a SiC single crystal ingot in which the micropipe density is reduced and the incorporation of impurities is suppressed.

Means for Solving the Problems

[0011] As a result of intensive studies, the present inventors have found that by forming a SiC modified layer with reduced micropipes and growing a SiC single crystal ingot thereon by the sublimation method, it is possible to provide a SiC single crystal ingot with a reduced micropipe density and suppressed incorporation of impurities. That is, in order to solve the above problems, the present invention provides the following means.

[0012] (1) The method for manufacturing a SiC single crystal ingot according to the first aspect of the present invention 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 by the sublimation method on the SiC modified layer.

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

[0014] (3) In the method for manufacturing a SiC single crystal ingot according to the above aspect, the first step may form the SiC modified layer on the main surface of the SiC seed crystal by injecting a gas containing Si onto the main surface of the SiC seed crystal. Further, in the first step, a gas containing C may be injected 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 SiC seed crystal is fixed to a pedestal having attachment means, and the first step is performed. After the first step is completed, the pedestal is removed together with the attachment means from the apparatus in which the first step is performed, and the pedestal is attached to the apparatus in which the second step is performed using the attachment means.

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

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

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

[0019] (8) The method for manufacturing a SiC single crystal ingot according to the above aspect may use a SiC single crystal plate cut out from a SiC single crystal ingot manufactured by any of the methods for manufacturing a SiC single crystal ingot according to the above aspect as the SiC seed crystal.

[0020] (9) The method for manufacturing a SiC single crystal ingot according to the above aspect may perform the first step two or more times.

[0021] (10) In the method for manufacturing 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 manufacturing 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 manufacturing a SiC single crystal ingot according to the above aspect, a SiC single crystal ingot is obtained in the second step, and the density of micropipes of the SiC wafer formed from the SiC single crystal ingot is 0 pieces / cm 2 or more and 0.1 pieces / cm 2 or less.

Advantages 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

Figure 2A

Figure 2B

Figure 3

Figure 4

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 clarity, the characteristic parts enlarged for convenience, 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 can be appropriately modified and implemented without changing the gist thereof. For example, changes, additions, and omissions in terms of numbers, positions, sizes, numerical values, materials, shapes, ratios, etc. can be made without departing from the invention.

[0027] <Method for Manufacturing a SiC Single Crystal Ingot> (First Embodiment) The method for manufacturing 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 the sublimation method. The reduction rate of micropipes in the SiC modified layer obtained by the manufacturing method of the present invention varies depending on conditions, but is, for example, 10% or more, and may be 50% or more, 90% or more, etc. However, it is not limited to only these examples. From the SiC single crystal ingot obtained in the present invention, a SiC wafer with a micropipe density of 0 pieces / cm 2 or more and 0.1 pieces / cm or less 2 can be formed.

[0028] (First 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 layer of high-quality SiC single crystal with reduced defects in the shape of hollow pipes is formed on the main surface of the SiC seed crystal. The SiC modified layer mentioned here is a SiC single crystal that serves as the starting point for the growth of a SiC single crystal by the sublimation method performed 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 the conventional method, a SiC single crystal cut out from a SiC single crystal ingot manufactured by the sublimation method was often used as a seed crystal. However, there were many micropipes in the conventional seed crystal. Compared with the conventional seed crystal, the SiC modified layer manufactured by performing the first step of this embodiment has a significantly reduced number of micropipes. Therefore, excellent SiC single crystal ingots can be manufactured by the present invention.

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

[0030] FIG. 1 is a schematic cross-sectional view showing a preferred example of the 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 convenience 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 covering the graphite crucible 101. The crucible 10 preferably has a hole 10Aa through which the graphite rod 11 can pass in the upper part 10A. The raw material M for the SiC modified layer 4 is stored in the lower part 10B of the crucible 10.

[0032] The raw material M is a known raw material used for the production of a SiC single crystal (SiC modified layer) by the solution method. As the raw material M, for example, a Si-C based solution or the like can be used. Further, a solution obtained by adding not only Si and C but also a transition metal or the like, such as a Si-C-Cr solution or a Si-C-Ti solution, may be used as the raw material M. That is, a solution containing Si, C, and a transition metal may be used as the raw material M. By using a solution containing a transition metal or the like as the raw material M, the dissolution of C into Si can be facilitated. That is, the solubility of C in Si increases. Further, by using a solution containing a transition metal as the raw material M, the growth rate of the SiC modified layer 4 can be improved.

[0033] The graphite rod 11 can be inserted into and removed from inside and outside the crucible 10 through a hole 10Aa provided in the upper part 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. Also, a SiC modification 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 the growth of the SiC modification layer 4 by the modification layer forming apparatus 1, the graphite rod 11 with the SiC seed crystal SD attached to the tip 11A is inserted into the crucible 10, removed from the outside of the crucible 10 after growth, 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 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 orthogonal to the axial direction of the attachment means 21. The base 20 has, for example, a disk shape and has surfaces 20a and 20b orthogonal to the axial direction of the attachment means 21. Of the surfaces 20a and 20b, the surface separated from the graphite rod 11 is referred to as the first surface 20a, and the surface 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. Fixing of the SiC seed crystal SD to the first surface 20a is performed using, for example, an adhesive. As the adhesive, known ones can be used. In the manufacturing method of the present embodiment, after the SiC modification layer 4 is formed on the main surface of the SiC seed crystal SD, the SiC seed crystal SD and the SiC modification layer 4 can be removed from the graphite rod 11 together with the pedestal 2. Also, the removed SiC seed crystal SD and SiC modification layer 4 can be attached to the crystal growth apparatus that performs the second step together with the pedestal 2. That is, in the manufacturing method of the present embodiment, the step of removing the SiC seed crystal SD and the SiC modification layer 4 from the pedestal 2 is unnecessary. The pedestal 2 can use, for example, graphite. Using graphite as the material of the pedestal 2 is preferable to suppress impurities from mixing into the SiC modification layer 4. The pedestal 2 may use different materials for each part. For example, only the base 20 that may come into contact with the solution may be made of graphite.

[0035] The configuration of the pedestal 2 only needs to be able to stably fix the SiC seed crystal SD (or the SiC seed crystal SD and the SiC modification layer 4), and stably fix and remove it from the graphite rod 11, and can be arbitrarily selected without particular limitation. FIGS. 2A and 2B are perspective views showing a preferred example of the pedestal 2 having the mounting means 21 (21'). FIG. 2A shows a pedestal 2 having a pin structure. The pedestal 2 has a mounting means 21, a pin 22, and a base 20. The SiC seed crystal SD is fixed to the first surface 20a of the mounting means. The mounting means 21 is inserted into the graphite rod 11 up to the height of the second surface 20B of the base 20 and fixed to the graphite rod 11 via the pin 22. After the formation of the SiC modification layer 4, the pedestal 2 can remove the pin 22 and remove the mounting means 21 from the graphite rod 11. FIG. 2B shows a pedestal 2' in which the mounting means 21' has a screw structure. The mounting means 21' as shown in FIG. 2B is fixed to the graphite rod 11 or the like by the screw-structured mounting means 21'. The shape of the graphite rod 11 is appropriately changed according to the shape of the pedestal 2. For example, when the pedestal has a male screw structure as the mounting means 21' like the pedestal 2', the graphite rod 11 has a female screw structure that engages with the male screw-structured mounting means 21'. Since the pedestal 2 has the configuration of having the mounting means 21 or the mounting means 21', the throughput in the production of the SiC single crystal ingot can be improved.

[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 of the reforming layer forming apparatus 1 becomes 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 is sufficiently dissolved from the graphite crucible 101 and the concentration is near the saturation concentration of SiC and the concentration is constant. For example, preferably, it is 1600 - 2100 °C, more preferably 1950 - 2050 °C, etc. In addition, 1700 - 1750 °C, 1850 - 1900 °C, etc. can be mentioned. However, since it also varies depending on the composition of the solution, it is not limited to only these temperatures. The heating time is preferably 1 h - 50 h, more preferably 10 h - 40 h, etc. In addition, 5 h - 10 h, 30 h - 50 h, etc. can be mentioned. However, since it also varies depending on the composition and temperature of the solution, it is not limited to only these times. With the SiC seed crystal SD in contact with the solution, the SiC reforming layer 4 is formed on the main surface of the SiC seed crystal SD by, for example, the temperature gradient method of providing a temperature gradient of about 5 - 100 °C / cm or the cooling method of operating the heating device to cool the solution. That is, the first step includes a step of forming the SiC reforming layer 4 on the main surface of the SiC seed crystal SD with the solution.

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

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

[0039] For the heating means, atmosphere, heating time, shape of the graphite crucible, heating rate, cooling rate, etc., various conditions can be applied according to the thickness of the SiC modification layer 4 to be formed. In the solution method, the thickness of the SiC modification layer 4 is determined by the product of the growth rate and the growth time. In the present embodiment, the condition that the thickness of the SiC modification layer 4 becomes 100 μm or more is applied for the growth.

[0040] The thickness of the SiC modification layer 4 is, for example, 100 μm or more. Preferably, it is 150 μm or more, and more preferably, it is 300 μm or more. By setting the thickness of the SiC modification layer 4 within the above range, the micropipe density can be sufficiently reduced. Also, if the SiC modification layer 4 is too thin, there is a risk of handling problems such as cracking, but by setting it within the above 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. By increasing the thickness of the SiC modified layer 4, the reduction rate from the micropipe density of the SiC seed crystal SD can be increased. Specifically, by setting the thickness of the SiC modified layer 4 to 150 μm or more, the reduction rate can be set to 95% or more, and by setting the thickness of the SiC modified layer 4 to 300 μm or more, the reduction rate can be set to 99% or more. Here, the reduction rate is an index indicating how many percent the micropipe density of the SiC modified layer 4 is reduced with respect to the micropipe density of the SiC seed crystal SD when comparing the micropipe density of the SiC seed crystal SD and the micropipe density of the SiC modified layer 4. In other words, when the reduction rate is 99%, the ratio of the micropipe density between the SiC seed crystal SD and the SiC modified layer 4 is 100:1. Note that the micropipe density in the SiC seed crystal SD refers to the micropipe density on the main surface of the SiC seed crystal SD. Also, 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, in the formation of SiC single crystals by the solution method, there have been concerns about problems in long-term stable growth such as inhibition of single crystal growth due to the formation of SiC polycrystals due to excessive dissolution of the graphite crucible C. However, the formation of the SiC modified layer 4 according to the present embodiment can be grown in a short time. Therefore, the problems in the long-term stable growth of SiC single crystals as described above do not occur.

[0041] In the method for manufacturing a SiC single crystal ingot according to this embodiment, by performing the first step, a SiC modified layer 4 can be formed 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. By performing the first step a plurality of times, a higher-quality SiC modified layer 4 can be grown. Therefore, 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 handle only the SiC single crystal grown in the last first step as the SiC modified layer 4. For example, when the first step is performed three times, it is preferable to refer to the SiC single crystal grown in the third time as the SiC modified layer 4, and the SiC single crystals grown up to the second time as the SiC seed crystal SD. Also, all of the SiC single crystals grown in the first step from the first time to the last time may be used as the SiC modified layer 4. When performing the sublimation method of the second step using the SiC modified layer 4 with reduced micropipes, the density of micropipes in the SiC single crystal ingot manufactured by the sublimation method can be dramatically reduced. Also, in the manufacturing method of this embodiment, due to reasons described in detail later, the incorporation of impurities into the SiC single crystal ingot can also be suppressed.

[0042] In the method for manufacturing a SiC single crystal ingot according to this embodiment, by performing the first step using the solution method, the SiC modified layer 4 can be formed. Also, the location where the raw material M for the SiC single crystal is stored is the area surrounded by the 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 made of graphite. Therefore, in the region where the SiC modified layer 4 is formed, the components other than Si and C are minimized, and the entry of impurities into the SiC modified layer 4 can be suppressed.

[0043] After forming the SiC modified layer 4 on the main surface of the SiC seed crystal SD in the first step, a step of flattening the surface of the SiC modified layer 4 may be further included. For the step of flattening the surface of the SiC modified layer, a method of processing the surface of the SiC single crystal to be flat can be used. 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, and a higher quality SiC single crystal ingot can be manufactured.

[0044] (Second step) 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 the sublimation method.

[0045] FIG. 3 is a cross-sectional schematic view showing an example of a crystal growth apparatus 5 capable of performing the second step in the method for manufacturing a SiC single crystal ingot according to the present embodiment.

[0046] The crystal growth apparatus 5 shown in FIG. 3 includes a crucible 50 and heating means 51 disposed around the crucible 50. The crucible 50 has a lid 501 and a main body portion 502.

[0047] On the inner side 501A of the lid 501 of the crucible 50, an installation portion 510 is provided. The SiC modification layer 4 is fixed to the installation portion 510. More specifically, with the SiC modification layer 4 formed on the main surface of the SiC seed crystal SD, the pedestal 2 and the SiC seed crystal SD as a whole are fixed to the installation portion 510. When the SiC modification layer 4 is fixed to the installation portion 510 together with the pedestal 2 and the SiC seed crystal SD, the pedestal 2 is preferably attached to the installation portion 510 via the attachment means 21. When the attachment is performed via the attachment means 21, the installation portion 510 can have a configuration capable of stably fixing the pedestal 2 by the attachment means 21. Incidentally, the SiC modification layer 4 may be peeled off from the SiC seed crystal SD and directly fixed to the installation portion 510. When the SiC modification layer 4 is directly fixed to the installation portion 510, it can be attached using a material selected as necessary, such as an adhesive. Note that an adhesive or the like is not necessarily used. For example, a notch or the like may be formed in the pedestal 2, and the SiC modification layer 4 may be installed using the notch or the like.

[0048] The single crystal raw material M2 used in the sublimation method is accommodated in the main body portion 502, which is a position facing the lid 501. As the single crystal raw material M2 to be accommodated, a powdery SiC raw material can be used. The single crystal raw material M2 is heated by heating means 51 arranged around the crucible 50. Then, by reducing the pressure inside the crucible 50, the single crystal raw material M2 sublimes. The temperature for heating the single crystal raw material M2 is, for example, 2200 to 2600 °C as an example, more preferably 2300 to 2500 °C, and even more preferably 2350 to 2450 °C. However, it is not limited to only these. Other environments can be arbitrarily selected as necessary. When the single crystal raw material M2 sublimes, it grows as a SiC single crystal on the SiC modification layer 4 to form a SiC single crystal ingot. The number of micropipes in this ingot is reduced compared to the case of using a conventional seed crystal. In addition, when manufacturing a SiC single crystal ingot by the solution method, the transition metal added to the solution is incorporated into the SiC single crystal ingot. However, in the method for manufacturing a SiC single crystal ingot according to the present embodiment, by having the second step of growing the SiC single crystal ingot by the sublimation method, it is possible to prevent the transition metal from being mixed into the SiC single crystal ingot.

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

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

[0051] In addition, by cutting the single crystal ingot manufactured by the method for manufacturing a SiC single crystal ingot according to the present embodiment into a SiC single crystal plate of an appropriate thickness, the SiC single crystal plate can be used as the SiC seed crystal SD. By performing the first step and the second step according to the present embodiment using this SiC seed crystal SD, a higher quality SiC single crystal ingot can be manufactured.

[0052] The method for manufacturing a SiC single crystal ingot according to the present 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 out from a SiC single crystal ingot, the micropipe density is less than 0.1 piece / cm 2 Furthermore, the SiC single crystal ingot grown by the method for manufacturing a SiC single crystal ingot according to the present embodiment has reduced impurities. That is, a high-quality SiC single crystal ingot can be manufactured, and the yield in subsequent steps can be improved. (Method for evaluating micropipes) A micropipe is a hollow pipe-shaped defect with a diameter of about several μm to several tens of μm, and in some cases, about 100 μm or more. The evaluation of micropipes can be performed as follows. The following method may also be used for the evaluation of micropipes in the SiC modified layer. After polishing the surface of a single crystal, micropipes can be detected by taking an X-ray topographic image. Depending on the output of the X-ray source and the thickness of the single crystal, it is preferable to use the transmission image and the reflection image appropriately. Generally, the time required to obtain a transmission image is shorter than that for a reflection image. Therefore, when the thickness of the single crystal is large and the X-ray dose that can penetrate is small, a reflection image is used. By counting the number of micropipes shown in the topographic image and dividing by the area of the topographic image, the density of micropipes can be obtained.

[0053] (Second Embodiment) FIG. 4 is a schematic cross-sectional view of a preferred example of the modified layer forming apparatus 1A according to the second embodiment. The manufacturing method of the SiC single crystal ingot according to the second embodiment is different from that of the first embodiment in the first step. Specifically, the second embodiment is different from the first embodiment in that, in the first step, a gas containing Si is injected 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 denoted by the same reference numerals, and the description thereof is omitted. The examples and conditions in the first embodiment can be preferably used in this embodiment as long as there are no particular problems.

[0054] As shown in FIG. 4, the modified layer forming apparatus 1A includes a crucible 6, a gas introduction unit 631 that supplies a gas G into the crucible 6, a first heat insulating unit 71 that surrounds the crucible 6, a second heat insulating unit 72 that is located outside the first heat insulating unit 71, a heating means 64 that is located outside the second heat insulating unit 72, and a support mechanism 8 that supports the crucible 6 and is capable of moving up and down and rotating. In FIG. 4, for convenience of explanation, the gas G introduced into the crucible 6 and the flow path of the gas G are shown together, but the present embodiment is not limited to this example.

[0055] The manufacturing method of the SiC single crystal ingot according to this embodiment can form a SiC modification layer 4 on the main surface of the SiC seed crystal SD by injecting a gas containing Si onto 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 introduction portion 631 serving as a flow path for the gas G introduced into the crucible 6 is formed on the bottom surface of the crucible main body portion 63. The ceiling portion 61 includes a discharge portion 611 for discharging the gas G in the crucible 6 to the outside of the crucible 6 and an installation portion 65. The installation portion 65 can install the pedestal 2 or the SiC seed crystal SD. By attaching the pedestal 2 to the installation portion 65 via the attachment means 21, the pedestal 2 is stably fixed.

[0056] The crucible 6 is supported by a support mechanism 8. The support mechanism 8 includes a rotary vertical mechanism 81 and a support base 82. The support mechanism 8 can rotationally drive and vertically move the crucible 6 with the rotary vertical mechanism 81 in a state where the crucible 6 is supported by the support base 82. Incidentally, a gas introduction portion for introducing the gas G into the crucible 6 is arranged at the axial center of the support mechanism 8.

[0057] The outer circumference and the upper surface of the crucible 6 are surrounded by a first heat insulating portion 71. The first heat insulating portion 71 has a ceiling portion 711 and a side peripheral portion 712. The ceiling portion 711 covers the upper surface of the crucible 6. The side peripheral portion 712 surrounds the side periphery of the crucible 6. A through hole is provided at a position of the ceiling portion 711 directly above the gas discharge portion 611 of the crucible 6. The gas introduced into the crucible is discharged to the outside of the crucible 6 through the gas discharge portion 611 and the through hole. Further, the outer circumference of the side peripheral portion 712 is surrounded by a second heat insulating portion 72, and a heating means 64 is located on the outer circumference of the second heat insulating portion 72. The length of the second heat insulating portion 72 in the axial direction is preferably equal to or greater than the length of the first heat insulating portion 71, and may be the same as the length of the first heat insulating portion 71.

[0058] Inside the crucible 6, a gas G that serves as a raw material for the SiC modification layer 4 is introduced through the gas introduction part 631. As the gas G to be introduced, a gas containing Si can be introduced. For example, silane (SiH4), SiH2Cl2, SiHCl3, SiCl4, etc. can be introduced. Further, 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 heat insulation part 71 and the second heat insulation part 72, and the SiC modification layer 4 is formed on the main surface of the SiC seed crystal SD. The temperature inside the crucible 6 during the formation of the SiC modification layer 4 is preferably 1500 °C or higher, more preferably 1600 °C or higher. Also, it is preferably 2400 °C or lower, more preferably 2350 °C or lower. The gas that did not contribute to the formation of the SiC modification layer 4 is discharged to the outside of the crucible 6 through the gas discharge part 611. The gas discharge part 611 and the through-hole may be connected to a pump (not shown). Further, the pressure inside the crucible 6 is appropriately changed. For example, the inside of the crucible 6 may be in a reduced pressure environment. Also, the pressure inside the crucible 6 may be made larger than the pressure outside the crucible 6, and the gas introduced into the crucible 6 may be exhausted to the outside of the crucible 6. The pressure inside the crucible 6 is preferably appropriately changed according to the type of gas used, the growth temperature, etc.

[0060] By rotating the crucible 6 by the rotation up-and-down mechanism 81, a highly symmetric SiC modification layer 4 is formed. The thickness of the SiC modification layer 4 to be formed is, for example, 100 μm or more. Preferably, it is 200 μm or more, more preferably 300 μm or more. By setting the thickness of the SiC modification layer 4 within this range, the micropipe density can be sufficiently reduced. Also, cracks in the SiC modification layer can be sufficiently suppressed. In the present embodiment, on the SiC modification layer 4 formed in the first step, a SiC single crystal ingot can be grown using the same means as in the first embodiment.

[0061] The method for manufacturing a SiC single crystal ingot according to this embodiment can grow a SiC single crystal ingot with reduced micropipes. Further, a SiC single crystal ingot with suppressed impurity incorporation can be grown. Moreover, the yield in subsequent device fabrication processes can be improved.

[0062] As described above in detail for the preferred embodiments of the present invention, the present invention is not limited to specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Industrial Applicability

[0063] As described above, according to the method for manufacturing a SiC single crystal ingot according to the present invention, a high-quality SiC single crystal ingot with reduced micropipes can be manufactured, and thus it can be used for improving the quality and throughput of SiC devices.

Explanation of Signs

[0064] 1, 1A Modification Layer Forming Apparatus 10 Crucible 101 Graphite Crucible 102 Heat Insulating Material 11 Graphite Rod 12 High Frequency Coil 2, 2′ Pedestal 20 Base 20a First Surface 20b Second Surface 21, 21′ Mounting Means 22 Pin 4 SiC Modification Layer 5 Crystal Growth Apparatus 50 Crucible 51 Heating Means 501 Lid 502 Main Body M Raw Material M2 Raw Material for Single Crystal SD SiC Seed Crystal

Claims

1. A first step of forming a SiC modification layer with a thickness of 100 μm or more on the main surface of a SiC seed crystal; A second step of growing a SiC single crystal by sublimation method on the SiC modification layer, and having, In the first step, a solution method using a solution containing Si, C, and a transition metal as raw materials is used to form the SiC modification layer on the main surface of the SiC seed crystal, In the second step, a SiC single crystal ingot is obtained, The manufacturing method of a SiC single crystal ingot, wherein the density of micropipes of a SiC wafer formed from the SiC single crystal ingot is 0 pieces / cm ２ or more and 0.1 pieces / cm ２ or less.

2. A first step of forming a SiC modification layer with a thickness of 100 μm or more on the main surface of a SiC seed crystal; A second step of growing a SiC single crystal by sublimation method on the SiC modification layer, and having, In the first step, a crucible provided with an annular gas discharge portion on the upper wall is used, and a gas containing Si is injected onto the main surface of the SiC seed crystal to form the SiC modification layer on the main surface of the SiC seed crystal. A method for manufacturing a SiC single crystal ingot.

3. The method for manufacturing a SiC single crystal ingot according to claim 2, wherein in the first step, in addition to the gas containing Si, a gas containing C is injected onto the main surface of the SiC seed crystal.

4. 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 or more and 0.1 pieces / cm ２ or less. The method for manufacturing a SiC single crystal ingot according to claim 2 or 3.

5. The first step is performed in a state where the SiC seed crystal is fixed to a pedestal having a mounting means, After the first step is completed, the SiC seed crystal and the SiC modification layer are removed together with the pedestal from the apparatus in which the first step is performed, and the SiC seed crystal and the SiC modification layer are attached together with the pedestal to the apparatus in which the second step is performed using the mounting means, and the second step is performed. The method for manufacturing a SiC single crystal ingot according to any one of claims 1 to 4.

6. The pedestal is made of graphite. The method for manufacturing a SiC single crystal ingot according to claim 5.

7. The second step is performed in a state where the SiC modification layer formed in the first step is cut out from the SiC seed crystal and fixed inside the lid of a crystal growth apparatus. The method for manufacturing a SiC single crystal ingot according to any one of claims 1 to 4.

8. A SiC single crystal substrate cut out from a SiC single crystal ingot manufactured by the method for manufacturing a SiC single crystal ingot according to any one of claims 1 to 7 is used as the SiC seed crystal. The method for manufacturing a SiC single crystal ingot according to any one of claims 1 to 7.

9. The method for manufacturing a single crystal ingot of SiC according to any one of claims 1 to 8, wherein the first step is performed two or more times, and then the second step is performed.

10. The method for manufacturing a single crystal ingot of SiC according to any one of claims 1 to 9, further comprising a step of polishing the main surface of the SiC modified layer between the first step and the second step.

Images