Method for producing silicon carbide wafer

Abstract

The present invention comprises, after performing maintenance and before growing an epitaxial layer: performing a pre-start inspection including a defect inspection for forming a first inspection wafer on which a non-doped layer is grown, and determining whether or not a prescribed defect in the non-doped layer is equal to or greater than a threshold, and an effective C / Si ratio inspection for forming a second inspection wafer on which a buffer layer is grown, and determining whether or not the effective C / Si ratio is within the range of 0.53 to 0.68 on the basis of the dopant concentration of the buffer layer; and, in a case where it is determined that there is an abnormality as a result of the pre-start inspection, adjustment is performed so as to achieve an effective C / Si ratio of 0.53 to 0.68 and a prescribed defect of less than the threshold. The epitaxial layer is grown after it is determined that there is no abnormality as a result of the pre-start inspection, so that the effective C / Si ratio is 0.53 to 0.68 and the prescribed defect is less than the threshold.

Description

Method for manufacturing silicon carbide wafers CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Patent Application No. 2024-089236, filed on May 31, 2024, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a method for manufacturing a silicon carbide (hereinafter also simply referred to as SiC) wafer.

[0003] Conventionally, SiC wafers have been proposed in which an epitaxial layer is grown on a single crystal substrate made of SiC. It is known that if such SiC wafers contain basal plane dislocations (hereinafter simply referred to as BPDs (abbreviation of basal plane dislocations)) in the epitaxial layer, characteristics such as on-resistance tend to deteriorate when semiconductor devices such as transistors are formed thereon. However, it has been reported that when growing an epitaxial layer on a single crystal substrate, BPDs in the single crystal substrate can be converted to threading edge dislocations (hereinafter also referred to as TEDs (abbreviation of threading edge dislocations)) in the epitaxial layer by adjusting the growth conditions of the epitaxial layer. TEDs are defects that are less likely to degrade the characteristics of SiC semiconductor devices than BPDs.

[0004] For example, Patent Document 1 discloses that when growing an epitaxial layer on a single crystal substrate, the growth rate of the epitaxial layer is controlled to reduce the inclusion of BPDs in the epitaxial layer. When growing the epitaxial layer, the single crystal substrate is placed in a growth chamber of a SiC wafer manufacturing apparatus, and a reaction gas containing a silicon source gas and a carbon source gas is supplied to the single crystal substrate to grow the epitaxial layer. The growth rate of the epitaxial layer is adjusted by controlling the flow rate of the reaction gas that contributes to the growth of the epitaxial layer to a predetermined value.

[0005] Patent No. 6762484

[0006] Incidentally, when SiC wafers are continuously manufactured over a long period of time, polycrystalline deposits and the like may adhere to the growth chamber, resulting in a deterioration in quality. Therefore, when SiC wafers are continuously manufactured over a long period of time, it is preferable to periodically perform maintenance on the SiC wafer manufacturing apparatus. However, when maintenance is performed on the SiC wafer manufacturing apparatus, variations in the performance may occur due to factors such as the assembly of components. Therefore, depending on the performance of the SiC wafer manufacturing apparatus, it may not be possible to obtain the desired growth rate even if the reaction gas is supplied to the growth chamber at the same flow rate as before maintenance, or the carbon to silicon ratio during growth may not be consistent with the flow rate of the reaction gas, which may result in a deterioration in the quality of the SiC wafer due to the inclusion of BPDs, etc.

[0007] An object of the present disclosure is to provide a method for manufacturing SiC wafers that can suppress deterioration in quality even when maintenance is performed.

[0008] According to one aspect of the present disclosure, a method for manufacturing a SiC wafer includes: preparing a single crystal substrate made of SiC; placing the single crystal substrate in a growth chamber of a SiC wafer manufacturing apparatus; and supplying a reaction gas containing a silicon raw material-containing gas, a carbon raw material-containing gas, and a dopant gas into the growth chamber to grow an epitaxial layer on the single crystal substrate, the epitaxial layer including a buffer layer to which an impurity is added, and a drift layer disposed on the buffer layer and having a dopant concentration lower than that of the buffer layer; and maintaining the SiC wafer manufacturing apparatus, wherein the steps of growing the epitaxial layer and maintaining the SiC wafer manufacturing apparatus are repeated; after the maintenance but before growing the epitaxial layer, placing the single crystal substrate in the maintained SiC wafer manufacturing apparatus and supplying the silicon raw material-containing gas and the carbon raw material-containing gas to the single crystal substrate to grow an undoped layer to form a first inspection wafer; and determining whether or not predetermined defects in the undoped layer in the first inspection wafer are equal to or greater than a threshold value. and an effective C / Si ratio inspection in which a single crystal substrate is placed in a maintained SiC wafer manufacturing apparatus, a reactive gas is supplied to the single crystal substrate, and a buffer layer is grown on the single crystal substrate to form a second inspection wafer, and an effective C / Si ratio inspection is performed in which an effective C / Si ratio, which is the ratio of carbon contained in the carbon raw material-containing gas to silicon contained in the silicon raw material-containing gas that actually contributes to the growth of the buffer layer, is determined to be within a range of 0.53 to 0.68, based on the dopant concentration of the buffer layer in the second inspection wafer. If an abnormality is determined to exist as a result of the pre-start inspection, the flow rate of at least one of the silicon raw material-containing gas and the carbon raw material-containing gas supplied to the growth chamber is adjusted so that the effective C / Si ratio is 0.53 to 0.68 and the number of predetermined defects is less than a threshold value. Growth of an epitaxial layer is performed after the pre-start inspection has determined that no abnormality exists, and a reactive gas is supplied to the growth chamber so that the effective C / Si ratio is 0.53 to 0.68 and the number of predetermined defects is less than a threshold value.

[0009] According to this method, a pre-inspection is performed before performing maintenance and growing an epitaxial layer. Then, when growing the epitaxial layer, a reactive gas is supplied to the growth chamber so that the effective C / Si ratio is 0.53 to 0.68 and the number of predetermined defects is less than a threshold. This allows continuous production of SiC wafers over a long period of time, with quality degradation suppressed even when maintenance is performed.

[0010] Fig. 1 is a cross-sectional view showing a SiC wafer manufacturing apparatus in a first embodiment; Fig. 2 is a flowchart showing a manufacturing method of a SiC wafer; Fig. 3 is a diagram showing the relationship between an effective C / Si ratio, a through-hole BPD density, and a killer defect density; Fig. 4 is a diagram for explaining the relationship between a supply C / Si ratio and a flow rate; Fig. 5 is a diagram showing the relationship between a growth rate and a through-hole BPD density; Fig. 6 is a diagram showing the relationship between a supply C / Si ratio and a dopant concentration; Fig. 7 is a timing chart showing an effective C / Si ratio in a manufacturing method of a SiC wafer; Fig. 8 is a timing chart showing a through-hole BPD density in a manufacturing method of a SiC wafer.

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the following embodiments, identical or equivalent parts will be denoted by the same reference numerals.

[0012] First Embodiment A first embodiment will be described with reference to the drawings. First, a SiC wafer manufacturing apparatus 1 used in a method for manufacturing SiC wafers 12 will be described. In this embodiment, the SiC wafer manufacturing apparatus 1 will be described using, as an example, a downflow type gas supply structure in which a reaction gas is blown down toward the surface 10a of a single crystal substrate 10.

[0013] 1, the SiC wafer manufacturing apparatus 1 has a chamber 20 constituting a growth chamber 200 for growing an epitaxial layer 11 on the surface 10a side of a single crystal substrate 10 to manufacture a SiC wafer 12. The epitaxial layer 11 in this embodiment is arranged on the surface 10a side of the single crystal substrate 10 and includes an n-type buffer layer 11a having a predetermined dopant concentration, and an n-type buffer layer 11b arranged on the buffer layer 11a and having a lower dopant concentration than the buffer layer 11a. － The semiconductor device further includes a drift layer 11b.

[0014] The chamber 20 is made of quartz glass, stainless steel, carbon, SiC-coated carbon, or the like, and is generally cylindrical, having an upper portion 21, a lower portion 22, and a side portion 23 connecting the upper portion 21 and the lower portion 22. The chamber 20 is provided with first to third supply pipes 31 to 33 in the upper portion 21, which supply reactive gases for growing the epitaxial layer 11. The ends of the first to third supply pipes 31 to 33 opposite the chamber 20 are connected to first to third gas sources 41 to 43, respectively, and a mass flow controller (hereinafter simply referred to as an MFC) 34 is provided between the chamber 20 and the first to third gas sources 41 to 43. The reactive gas is introduced into the growth chamber 200 at a flow rate adjusted by the MFC 34.

[0015] The first gas source 41 contains monosilane (SiH ４ The second gas source 42 supplies a silicon raw material containing gas (hereinafter simply referred to as a Si raw material containing gas) containing silicon, such as propane (C ３ H ８ ) gas and ethylene (C ２ H ４ The third gas source 43 is a carbon raw material containing gas (hereinafter simply referred to as a C raw material containing gas) containing a carbon raw material such as ammonia (NH ３ A dopant gas containing n-type impurities, such as hydrogen chloride (HCl) gas, is supplied to the first to third supply pipes 31 to 33. An etching gas, such as hydrogen chloride (HCl) gas, and a carrier gas, such as hydrogen gas, argon gas, or helium gas, are supplied to the first to third supply pipes 31 to 33. The etching gas and the carrier gas may be supplied from a separate supply pipe (not shown) in addition to the first to third supply pipes 31 to 33. The etching gas and the carrier gas may also be supplied only from a supply pipe separate from the first to third supply pipes 31 to 33.

[0016] An external heating device 50 is provided around the chamber 20. The external heating device 50 heats the inside of the growth chamber 200 and is configured with a heating coil such as an induction heating coil or a direct heating coil, and is disposed so as to surround the periphery of the chamber 20.

[0017] A rotation device 60 on which single crystal substrate 10 is placed is disposed on the lower side of chamber 20. Single crystal substrate 10 is then placed on a susceptor 70 disposed on rotation device 60.

[0018] The rotation device 60 includes a cylindrical portion 61, a rotation shaft 62, and a drive unit 63. The cylindrical portion 61 is a bottomed cylindrical member that defines a hollow chamber 61a, and the susceptor 70 is disposed on the open end side. The open end side of the cylindrical portion 61 is disposed so as to face the upper side of the chamber 20 (i.e., the upper portion 21 side).

[0019] The rotating shaft 62 is a shaft that rotates by the output of a driving unit 63, and is connected to the cylindrical portion 61 so as to be rotatable integrally with the cylindrical portion 61. The driving unit 63 is composed of a motor or the like that outputs a rotational force, and rotates the rotating shaft 62. In the rotation device 60 configured in this manner, the rotating shaft 62 rotates by the output of the driving unit 63, and the cylindrical portion 61 and the susceptor 70 rotate integrally.

[0020] The susceptor 70 has an outer shape that matches the open end of the cylindrical portion 61, and is disposed at the open end of the cylindrical portion 61 to substantially close the cylindrical portion 61. This substantially closes the hollow chamber 61a of the cylindrical portion 61. Specifically, the susceptor 70 is plate-shaped having one surface 70a and the other surface 70b. A recess 71 for accommodating the single crystal substrate 10 is formed in the center of the one surface 70a. The susceptor 70 also has a step 72 formed at the outer edge of the other surface 70b to fit into the open end of the cylindrical portion 61. The susceptor 70 is disposed in the cylindrical portion 61 by fitting the step 72 into the open end of the cylindrical portion 61. The single crystal substrate 10 is mounted on the susceptor 70 such that the bottom surface 71a of the recess 71 in the susceptor 70 serves as a mounting surface, and the back surface 10b faces the bottom surface 71a.

[0021] The cylindrical portion 61, the susceptor 70, and the like disposed in the growth chamber 200 are made of, for example, graphite. However, the cylindrical portion 61, the susceptor 70, and the like may be made of polycrystalline SiC formed by sintering or a CVD method, or the surfaces may be coated with polycrystalline SiC or a high-melting-point metal carbide such as tantalum carbide or niobium carbide to make them resistant to thermal etching. CVD is an abbreviation for Chemical Vapor Deposition.

[0022] An internal heating device 80 for heating the single crystal substrate 10 (i.e., the growth chamber 200) is disposed in the hollow chamber 61a. The internal heating device 80 is configured by, for example, a resistance heater or the like.

[0023] Furthermore, an exhaust pipe 90 for exhausting reacted gases and unreacted gases is provided on the lower side of the chamber 20. The exhaust pipe 90 is connected to a vacuum pump (not shown) on the side opposite to the chamber 20. This allows the growth chamber 200 to be maintained at a predetermined pressure.

[0024] Although not specifically shown, the SiC wafer manufacturing apparatus 1 is provided with an elevator or the like for assisting the transfer robot in carrying the susceptor 70, on which the single crystal substrate 10 is placed, into the growth chamber 200 and in carrying the susceptor 70 out of the growth chamber 200. The elevator has a function of, for example, lifting the susceptor 70 and separating it from the cylindrical portion 61 when carrying out the susceptor 70, thereby handing over the susceptor 70 to the transfer robot. However, the SiC wafer manufacturing apparatus 1 may not be one that carries in and out the susceptor 70 on which the single crystal substrate 10 is placed, but may instead carry in and out only the single crystal substrate 10 without moving the susceptor 70.

[0025] The above is the configuration of the SiC wafer manufacturing apparatus 1 in this embodiment. When manufacturing the SiC wafer 12, the SiC wafer 12 is manufactured using the above-described SiC wafer manufacturing apparatus 1. Next, a method for manufacturing the SiC wafer 12 in this embodiment will be described.

[0026] 2, when manufacturing SiC wafers 12, the SiC wafers 12 are continuously manufactured over a long period of time by repeatedly performing a maintenance process in step S101, a pre-inspection process in step S102, a growth process in step S105, and a post-inspection process in step S106, etc. The growth process is not particularly limited, but may be, for example, for about 10 to 20 days.

[0027] First, the growth step of step S105 will be described. The growth step of step S105 is a step of growing an epitaxial layer 11 on a single crystal substrate 10 to manufacture a SiC wafer 12. The epitaxial layer 11 is grown using the SiC wafer manufacturing apparatus 1 described above. Specifically, in this growth step, the single crystal substrate 10 is first placed on the susceptor 70, and the susceptor 70 is rotated by the rotation device 60 at, for example, 200 rpm, while the external heating device 50 and the internal heating device 80 are driven to maintain the growth chamber 200 at approximately 1650°C. The single crystal substrate 10 used has, for example, a surface 10a with an off-angle of 0.4 to 5° with respect to the (0001) plane and a diameter of 150 mm or more. The temperature of the growth chamber 200 is variable and is maintained at a predetermined temperature between approximately 1600 and 1750°C.

[0028] Then, reaction gases are supplied from the first to third supply pipes 31 to 33 toward the growth chamber 200. The flow rates of the Si raw material-containing gas supplied from the first supply pipe 31 and the C raw material-containing gas supplied from the second supply pipe 32 are adjusted so as to satisfy the effective C / Si ratio described below.

[0029] In growth chamber 200, ammonia gas is introduced while the Si raw material-containing gas and the C raw material-containing gas react with each other, and SiC wafer 12 is produced having epitaxial layer 11 in which buffer layer 11 a and drift layer 11 b are grown in this order on single crystal substrate 10. In this embodiment, the dopant concentration of buffer layer 11 a is set higher than the dopant concentration of drift layer 11 b, and the dopant concentration is adjusted by adjusting the flow rate of ammonia gas or nitrogen gas supplied from third supply pipe 33.

[0030] The above is the growth process in step S105. The growth process in step S105 is performed over a predetermined period of time to continuously manufacture SiC wafers 12. Here, although BPDs may be contained in the single crystal substrate 10, growing the epitaxial layer 11 under predetermined conditions facilitates the conversion of the BPDs in the single crystal substrate 10 to TEDs in the epitaxial layer 11, thereby preventing the inclusion of BPDs in the epitaxial layer 11. In addition to BPDs, defects such as stacking faults, particle inclusions, and polytype inclusions may also be introduced into the epitaxial layer 11 of the SiC wafer 12. Similarly to BPDs, stacking faults, particle inclusions, and polytype inclusions are defects that are likely to degrade characteristics such as on-resistance when semiconductor elements such as transistors are formed. Hereinafter, in this embodiment, defects such as stacking faults, particle inclusions, and polytype inclusions that are likely to degrade characteristics are collectively referred to as killer defects. In the following description, when the epitaxial layer 11 is grown on the single crystal substrate 10, BPDs that are not converted to TEDs in the epitaxial layer 11 and propagate from the single crystal substrate 10 to the epitaxial layer 11 are also referred to as penetrating BPDs.

[0031] The inventors then investigated the relationship between the effective C / Si ratio, the threading BPD density, and the killer defect density, and obtained the results shown in Figure 3. Note that, at present, the threading BPD density is 0.3 / cm ２ The killer defect density is required to be 0.50 / cm or less. ２ The effective C / Si ratio herein means the ratio of C contained in the C raw material containing gas to Si contained in the Si raw material containing gas, which actually contributes to the growth of epitaxial layer 11 when epitaxial layer 11 is grown on single crystal substrate 10.

[0032] As shown in FIG. 3, the through-hole BPD density is 0.3 / cm when the effective C / Si ratio is 0.53 or higher. ２ It is confirmed that the killer defect density is 0.50 / cm when the effective C / Si ratio is 0.68 or less. ２It is confirmed that the effective C / Si ratio is as follows: As described above, the effective C / Si ratio is the ratio of Si to C that actually contributes to the growth of epitaxial layer 11, and may differ from the supplied C / Si ratio, which is the ratio of C contained in the C raw material containing gas to Si contained in the Si raw material containing gas supplied to growth chamber 200. In the growth process of step S105, the flow rates of the Si raw material containing gas and the C raw material containing gas are adjusted so that the effective C / Si ratio is 0.53 or more and 0.68 or less.

[0033] The supply C / Si ratio supplied to the growth chamber 200 is adjusted by controlling the flow rates of the gases, as shown in Fig. 4. For example, when the Si raw material-containing gas is monosilane gas and the C raw material-containing gas is propane gas, the supply C / Si ratio supplied to the growth chamber 200 is calculated as (B x 3) / A, where A is the flow rate of the monosilane gas and B is the flow rate of the propane gas. Furthermore, when the Si raw material-containing gas is monosilane gas and the C raw material-containing gas is ethylene gas, the supply C / Si ratio supplied to the growth chamber 200 is calculated as (C x 2) / A, where A is the flow rate of the monosilane gas and C is the flow rate of the ethylene gas. Furthermore, for example, when the Si raw material-containing gas is monosilane gas and the C raw material-containing gas is a mixed gas of propane gas and ethylene gas, the supply C / Si ratio supplied to the growth chamber 200 is calculated as (B×3+C×2) / A, where A is the flow rate of the monosilane gas, B is the flow rate of the propane gas, and C is the flow rate of the ethylene gas. As described above, the supply C / Si ratio supplied to the growth chamber 200 may not coincide with the effective C / Si ratio.

[0034] The inventors also conducted extensive research into the relationship between the growth rate and the through-hole BPD density, and obtained the results shown in Fig. 5. Fig. 5 shows the results obtained by setting the temperature of the growth chamber 200 to 1650°C, adjusting the supply rates of the Si raw material-containing gas and the C raw material-containing gas so that the effective C / Si ratio becomes 0.6, and controlling the flow rates of the Si raw material-containing gas and the C raw material-containing gas to change the growth rate.

[0035] As shown in Figure 5, the penetration BPD density was 0.3 / cm when the growth rate was 35 μm / h or higher. ２Therefore, in the growth step of step S105, the flow rates of the Si raw material containing gas and the C raw material containing gas are preferably adjusted so that the growth rate becomes 35 μm / h.

[0036] Continuing the growth process in step S105 may result in the adhesion of foreign matter such as deposits to the SiC wafer manufacturing apparatus 1, which may change the environment in the growth chamber 200 and result in a deterioration in the quality of the SiC wafers 12. For this reason, in the maintenance process in step S101, maintenance of the SiC wafer manufacturing apparatus 1 is performed. In this embodiment, for example, a new SiC wafer manufacturing apparatus 1 is prepared by replacing the chamber 20, the rotation device 60, etc. with new ones and assembling them. However, when the maintenance process is performed to prepare a new SiC wafer manufacturing apparatus 1, errors during assembly, manufacturing errors of each component, etc. may cause deviations in the effective C / Si ratio even if the flow rates of the Si raw material-containing gas and the C raw material-containing gas supplied to the growth chamber 200 are the same as those before the maintenance process.

[0037] 2, after the maintenance step of step S101 is performed, a pre-start inspection step of step S102 is performed before the growth step of step S105 is performed. In the pre-start inspection step of this embodiment, two inspections, a defect inspection and an effective C / Si ratio inspection, are performed using the SiC wafer manufacturing apparatus 1 prepared in the maintenance step of step S101.

[0038] Specifically, the defect inspection is performed as follows. Specifically, a single crystal substrate 10 is placed on the susceptor 70 of a new SiC wafer manufacturing apparatus 1. A Si raw material-containing gas and a C raw material-containing gas are supplied to the growth chamber 200 with the supply of ammonia gas stopped, and a non-doped layer serving as the epitaxial layer 11 is grown on the single crystal substrate 10 to prepare a first inspection wafer. The flow rates of the Si raw material-containing gas and the C raw material-containing gas supplied to the growth chamber 200 (i.e., the supplied C / Si ratio) are set to the flow rates planned for the growth process in step S105. Then, in the defect inspection, predetermined defects in the epitaxial layer 11 of the first inspection wafer are confirmed using a PL (abbreviation for PhotoLuminescence) method or the like, and if the predetermined defects are equal to or greater than a threshold, an abnormality is determined. The predetermined defects can be appropriately selected and may be through-hole BPDs, killer defects, or other defects. The comparison between the predetermined defects and the threshold may be a comparison of the number or density.

[0039] The effective C / Si ratio inspection is performed as follows. Specifically, a single crystal substrate 10 is placed on the susceptor 70 of a new SiC wafer manufacturing apparatus 1, and a reaction gas is supplied to the growth chamber 200 to grow a buffer layer 11a on the single crystal substrate 10, thereby preparing a second inspection wafer. The flow rates of the Si raw material-containing gas and the C raw material-containing gas supplied to the growth chamber 200 (i.e., the supplied C / Si ratio) are set to the flow rates planned for the growth process in step S105. The flow rate of the ammonia gas is also set to the flow rate planned for the growth process in step S105. The dopant concentration of the buffer layer 11a in the second inspection wafer is then inspected using CV measurement, mass spectrometry, or the like, and the effective C / Si ratio is derived based on the dopant concentration. Note that when the above-described defect inspection is performed, the second inspection wafer has a high dopant concentration in the buffer layer 11a, making it difficult to determine the number of defects using PL or the like. For this reason, in this embodiment, a first inspection wafer is prepared in which a non-doped layer is grown on the single crystal substrate 10, and defect inspection is performed using this first inspection wafer.

[0040] The dopant concentration of the buffer layer 11 a (i.e., the epitaxial layer 11) varies depending on the effective C / Si ratio when the buffer layer 11 a is grown. The effective C / Si ratio can vary depending on an assembly error during the maintenance process, a manufacturing error of each component, etc., even if the C / Si ratio supplied to the growth chamber 200 is the same as that before the maintenance process.

[0041] For example, when the flow rate of ammonia gas is set to 8 sccm and the supply C / Si ratio supplied to the growth chamber 200 is changed, the dopant concentration of the ideal buffer layer 11a decreases as the supply C / Si ratio increases, as shown by the solid line in Figure 6. However, the inventors' investigations have confirmed that when manufacturing the second test wafer, the dopant concentration of the buffer layer 11a varies even when the supply C / Si ratio of the Si raw material-containing gas and the C raw material-containing gas supplied to the growth chamber 200 is kept constant at 0.6. Note that each sample in Figure 6 is a sample (i.e., a second test wafer) obtained using a different SiC wafer manufacturing apparatus 1 with a supply C / Si ratio of 0.6.

[0042] For example, in sample 1, the supply C / Si ratio is 0.6, but the effective C / Si ratio based on the dopant concentration is confirmed to be 0.54. Similarly, in sample 2, the effective C / Si ratio based on the dopant concentration is confirmed to be 0.56, and in sample 3, the effective C / Si ratio based on the dopant concentration is confirmed to be 0.59. In sample 4, the effective C / Si ratio based on the dopant concentration is confirmed to be 0.63. In sample 5, the effective C / Si ratio based on the dopant concentration is confirmed to be 0.48. In this example, if the result of the effective C / Si ratio test for sample 5 is obtained, even if the Si raw material-containing gas and the C raw material-containing gas are introduced into the growth chamber 200 in the growth process of step S105 so that the supply C / Si ratio is 0.6, the effective C / Si ratio will be 0.48, and there is a high possibility that a SiC wafer 12 containing many through-hole BPDs will be manufactured. Therefore, in the effective C / Si ratio inspection, if the effective C / Si ratio is not between 0.53 and 0.68, it is determined that there is an abnormality.

[0043] As shown in FIG. 2 , after the pre-start inspection process in step S102 is completed, a determination is made in step S103 as to whether or not an abnormality was detected in the pre-start inspection process. In this embodiment, if an abnormality is detected in at least one of the defect inspection and the effective C / Si ratio inspection in step S103 (i.e., step S103: YES), an adjustment process is performed in step S104. In the adjustment process in step S104, if an abnormality is detected in the effective C / Si ratio inspection, the flow rates of the Si raw material-containing gas and the C raw material-containing gas are adjusted so that the effective C / Si ratio is within a range of 0.53 to 0.68. For example, if the result of sample 5 is obtained, the flow rate of the Si raw material-containing gas supplied to the growth chamber 200 is reduced so that the effective C / Si ratio is increased. Furthermore, if an abnormality is detected in the defect inspection, the flow rates of the Si raw material-containing gas and the C raw material-containing gas are finely adjusted. After the adjustment process in step S104 is performed, the pre-start inspection process in S102 is performed again.

[0044] On the other hand, if it is determined in step S103 that there are no abnormalities (i.e., step S103: NO), the above-described growth process is performed in step S105. Note that in this growth process, since the pre-start inspection process of step S102 is performed, a Si raw material-containing gas and a C raw material-containing gas are supplied to the growth chamber 200 so that the effective C / Si ratio is within the range of 0.53 to 0.68 and the number of predetermined defects is less than the threshold value. Specifically, a flow rate corresponding to the flow rate of the reaction gas used to manufacture the inspection wafer determined to be normal is supplied to the growth chamber 200. Therefore, a SiC wafer 12 is manufactured that is suppressed from containing a large amount of through-hole BPDs and killer defects.

[0045] After the growth process of step S105 is performed for a predetermined period, a post-termination inspection process is performed in step S106. The post-termination inspection process of step S106 performs a defect inspection and an effective C / Si ratio inspection similar to those in the pre-initiation inspection process. After the post-termination inspection process of step S106 is completed, a determination is made in step S107 as to whether or not an abnormality has been found in the post-termination inspection process. In this embodiment, if it is determined in step S107 that both the defect inspection and the effective C / Si ratio inspection are normal (i.e., step S107: NO), a normal processing process is performed in step S108. In the normal processing process, a normal inspection of electrical characteristics and the like is performed.

[0046] On the other hand, if it is determined in step S107 that there is an abnormality in at least one of the defect inspection and the effective C / Si ratio inspection (i.e., step S107: YES), a special processing step is performed in step S109. In the special processing step, since there is a high possibility that the SiC wafer 12 manufactured in the growth step of step S105 contains a large number of through-hole BPDs and / or killer defects, more precise or multiple characteristic inspections than in the normal processing step are performed, or the manufactured SiC wafer 12 is discarded, or other processing is performed.

[0047] After the normal processing step of step S108 or the special processing step of step S109 is performed, the maintenance step of step S101 is performed, and a new SiC wafer manufacturing apparatus 1 is prepared to perform the steps from step S102 onwards. This allows SiC wafers 12 to be manufactured over a long period of time with reduced quality degradation even after the maintenance step is performed.

[0048] Here, in practice, the effective C / Si ratio when performing the maintenance process of step S101, the pre-inspection process of step S102, the growth process of step S105, and the post-inspection process of step S106 is, for example, as shown in FIG. 7 . Furthermore, in practice, the through-hole BPD density when performing the maintenance process of step S101, the pre-inspection process of step S102, the growth process of step S105, and the post-inspection process of step S106 is, for example, as shown in FIG. 8 . In FIG. 8 , the predetermined defects in the defect inspection are considered to be through-hole BPDs. In this example, in the post-inspection process of the portion indicated by arrow A1 in FIG. 7 and the post-inspection process indicated by arrow B1, it is confirmed that the effective C / Si is less than 0.53. Furthermore, in FIG. 8 , in the post-inspection process of the portion indicated by arrow A1 and the post-inspection process indicated by arrow B1, the through-hole BPD density is 0.3 / cm ２ Although the height is below 100 mm, it is confirmed that the height is higher than other portions. Therefore, the SiC wafers 12 obtained in the growth process after the end of arrow A1 and before the inspection process, and the SiC wafers 12 obtained in the growth process before the end of arrow B1 and before the inspection process, may be of low quality. Therefore, in this example, after the inspection processes after the end of arrows A1 and B1, a special processing process in step S109 is performed. Note that, although not shown in detail in these figures, a pre-start inspection process is performed before the maintenance process and the growth process are performed, and an adjustment process is performed if necessary.

[0049] According to the present embodiment described above, a pre-inspection step is performed before the maintenance step and the growth step. Then, in the growth step, a reactive gas is supplied to the growth chamber 200 so that the effective C / Si ratio is 0.53 or more and 0.68 or less, and the predetermined defects are less than the threshold. Therefore, it is possible to manufacture SiC wafers 12 in which deterioration in quality is suppressed even when the maintenance step is performed.

[0050] (1) In this embodiment, after the growth process is completed, a post-inspection process is performed before the maintenance process. If an abnormality is determined in the post-inspection process, a special processing process is performed on the SiC wafers 12 obtained in the growth process performed immediately before the post-inspection process. This makes it possible to prevent SiC wafers 12 with potentially degraded quality from being distributed.

[0051] (2) In this embodiment, the growth rate in the growth step is set to 35 μm / h, which further reduces the inclusion of through-hole BPDs.

[0052] (Other Embodiments) While the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

[0053] For example, in the first embodiment, the post-termination inspection step may not be performed. Even in this manufacturing method of the SiC wafer 12, by performing the pre-initiation inspection step after the maintenance step, it is possible to manufacture the SiC wafer 12 with reduced quality degradation.

[0054] In the first embodiment, SiC wafer manufacturing apparatus 1 may have an upflow type gas supply structure in which a reactive gas is blown up toward surface 10 a of single crystal substrate 10 .

[0055] Furthermore, in the first embodiment, the Si raw material containing gas may be dichlorosilane, trichlorosilane, or the like, and the C raw material containing gas may be acetylene, or the like.

[0056] Furthermore, in the first embodiment, Fourier transform infrared spectroscopy (i.e., FT-IR) or ellipsometry may be performed during the growth process to derive the effective C / Si ratio based on the concentration of the buffer layer 11a even during the growth process. When the effective C / Si ratio is derived during the growth process in this manner, the flow rates of the Si raw material-containing gas and the C raw material-containing gas may be adjusted according to the derived effective C / Si ratio. This allows the manufacture of SiC wafers 12 with further reduced quality degradation.

Claims

1. A method for manufacturing a silicon carbide wafer, comprising: preparing a single crystal substrate (10) made of silicon carbide; placing the single crystal substrate in a growth chamber (200) of a silicon carbide wafer manufacturing apparatus (1); and supplying a reaction gas containing a silicon raw material-containing gas, a carbon raw material-containing gas, and a dopant gas into the growth chamber to grow an epitaxial layer (11) on the single crystal substrate, the epitaxial layer including a buffer layer (11a) to which an impurity is added and a drift layer (11b) disposed on the buffer layer and having a dopant concentration lower than that of the buffer layer; and maintaining the silicon carbide wafer manufacturing apparatus, wherein growing the epitaxial layer and maintaining the silicon carbide wafer manufacturing apparatus are repeated, after performing the maintenance and before growing the epitaxial layer, a pre-start inspection is performed, including: a defect inspection in which the single crystal substrate is placed in the maintained silicon carbide wafer manufacturing apparatus, and the silicon feedstock-containing gas and the carbon feedstock-containing gas are supplied to the single crystal substrate to grow a non-doped layer, to form a first inspection wafer, and a predetermined defect in the non-doped layer in the first inspection wafer is determined to be equal to or greater than a threshold; and an effective C / Si ratio inspection in which the single crystal substrate is placed in the maintained silicon carbide wafer manufacturing apparatus, and the reaction gas is supplied to the single crystal substrate to grow the buffer layer, to form a second inspection wafer, and a dopant concentration of the buffer layer in the second inspection wafer is determined to be equal to or greater than 0.53 and equal to or less than 0.

68. If it is determined by the pre-start inspection that there is an abnormality, adjusting the flow rate of at least one of the silicon source-containing gas and the carbon source-containing gas supplied to the growth chamber so that the effective C / Si ratio is 0.53 or more and 0.68 or less and the predetermined defects are less than a threshold value;growing the epitaxial layer after it has been determined that there are no abnormalities in the pre-start inspection, and supplying the reaction gas to the growth chamber so that the effective C / Si ratio is 0.53 or more and 0.68 or less and the predetermined defects are less than a threshold value.

2. The method for producing a silicon carbide wafer according to claim 1, wherein after growing the epitaxial layer and before performing the maintenance, a post-processing inspection including the defect inspection and the effective C / Si ratio inspection is performed, and if the post-processing inspection determines that an abnormality is present, a predetermined process is performed on the silicon carbide wafer obtained by growing the epitaxial layer before the post-processing inspection.

3. The method for producing a silicon carbide wafer according to claim 1 or 2, wherein the reaction gas is supplied to the growth chamber so that the growth rate of the epitaxial layer is 35 μm / h.

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