Method for manufacturing silicon carbide substrate, and apparatus for manufacturing silicon carbide substrate

Abstract

Provided is a method for manufacturing a silicon carbide substrate 100 that has a substrate layer 101 and an epitaxial layer 102, the method comprising: a detection step for detecting a basal plane dislocation (BPD) present in the epitaxial layer 102 by irradiating the silicon carbide substrate 100 with inspection light L1; an expansion step for irradiating the area in which the basal plane dislocation (BPD) detected in the detection step is present with expansion light L3 for expanding a Shockley type stacking fault (SSF) from the basal plane dislocation (BPD); and a contraction step for irradiating the Shockley type stacking fault (SSF) expanded from the basal plane dislocation (BPD) in the expansion step with contraction light L4 for contracting the Shockley type stacking fault (SSF). In cases where a plurality of basal plane dislocations (BPD) are detected in the detection step, in the expansion step, after irradiating one region in which a basal plane dislocation (BPD) is present with expansion light, another region in which a basal plane dislocation (BPD) is present is irradiated with expansion light L3 concurrently with the contraction step, and this operation is repeated for all regions in which a basal plane dislocation (BPD) is present.

Description

Silicon carbide substrate manufacturing method and silicon carbide substrate manufacturing apparatus

[0001] The present invention relates to a method for manufacturing a silicon carbide substrate having a substrate layer and an epitaxial layer, and to an apparatus for manufacturing a silicon carbide substrate.

[0002] Silicon carbide is a wide-gap semiconductor and has recently attracted attention in the field of power devices. Silicon carbide substrates used in power devices are typically manufactured by epitaxial growth, in which an epitaxial layer is grown on a substrate. However, due to the large difference in atomic radii between carbon and silicon atoms, silicon carbide is more susceptible to crystal defects in the epitaxial layer than gallium nitride, another wide-gap semiconductor. These crystal defects cause forward current degradation, which affects device performance, and are therefore problematic in the manufacture of power devices.

[0003] The occurrence of forward current degradation in power devices is thought to be due to carrier trapping at basal plane dislocations (hereinafter referred to as "BPDs") in the epitaxial layer, and the recombination energy of the trapped carriers causes the expansion of Shockley stacking faults (hereinafter referred to as "SSFs"). Therefore, technologies have been developed to suppress the formation of BPDs in epitaxial layers during the film formation process using epitaxial growth. For example, by setting the off-angle to 4°, more than 95% of the crystal defects inherited from BPDs in the substrate layer to the epitaxial layer formed by the epitaxial growth method can be structurally converted into threading edge dislocations (hereinafter referred to as "TEDs").

[0004] However, in power devices for automotive applications, a large current exceeding the rated current may flow due to special circumstances, such as when the vehicle derails. In such cases, SSFs may expand from BPDs that penetrate the epitaxial layer (BPDs present in the epitaxial layer) without being converted to TEDs in the epitaxial layer. Furthermore, even if the current density is low, SSFs may expand due to long-term use. Therefore, in order to further improve the stability of power devices for automotive applications, it is desirable to eliminate BPDs present in the epitaxial layer in the manufacture of silicon carbide substrates.

[0005] Conventionally, a method for manufacturing a silicon carbide substrate that prevents the expansion of SSFs has been proposed (see, for example, Patent Document 1). The method for manufacturing a silicon carbide substrate described in Patent Document 1 prevents the expansion of SSFs by including a step of expanding SSFs in an epitaxial layer by irradiating ultraviolet light and a step of reducing the SSFs by heating.

[0006] JP 2019-140184 A

[0007] The method for manufacturing a silicon carbide substrate disclosed in Patent Document 1 requires irradiation of the entire surface of the silicon carbide substrate with ultraviolet light to expand the SSFs, which results in the problem that it takes time to prevent the expansion of the SSFs. Furthermore, the method for manufacturing a silicon carbide substrate disclosed in Patent Document 1 shrinks the SSFs by heating the entire silicon carbide substrate, so the step of expanding the SSFs and the step of shrinking the SSFs cannot be performed simultaneously. Therefore, when the manufacturing method disclosed in Patent Document 1 is applied to large-diameter silicon carbide substrates, which have been in increasing demand in recent years, it results in an increase in manufacturing time.

[0008] On the other hand, silicon carbide substrates have made progress in terms of quality improvement, and in particular, BPDs present in the epitaxial layer are reduced to 1 cm ２ It is possible to suppress the occurrence of BPDs to approximately one or less per silicon carbide substrate (several BPDs in a 6-inch wafer). In this regard, the manufacturing method of Patent Document 1 assumes that many BPDs are present even in a high-quality silicon carbide substrate that actually has only a few BPDs in the epitaxial layer, and expands and contracts SSFs over the entire surface of the silicon carbide substrate. For this reason, ultraviolet light is irradiated to expand SSFs even in areas where no BPDs are present, which is inefficient.

[0009] The present invention has been made in view of the above problems, and has an object to provide a method and apparatus for manufacturing a silicon carbide substrate that can efficiently manufacture silicon carbide substrates.

[0010] A characteristic configuration of the method for manufacturing a silicon carbide substrate according to the present invention for solving the above problems is a method for manufacturing a silicon carbide substrate having a substrate layer and an epitaxial layer, in which basal plane dislocations (BPDs) present in the epitaxial layer are reduced or eliminated, the method comprising: a detection step of irradiating the silicon carbide substrate with inspection light to detect basal plane dislocations (BPDs) present in the epitaxial layer; an expansion step of irradiating areas where the basal plane dislocations (BPDs) detected in the detection step are present with expanding light that expands Shockley stacking faults (SSFs) from the basal plane dislocations (BPDs); and a contraction step of irradiating the Shockley stacking faults (SSFs) expanded from the basal plane dislocations (BPDs) in the expansion step with shrinkage light that shrinks the Shockley stacking faults (SSFs), If there are multiple basal plane dislocations (BPDs) detected in the detection process, the expansion process involves irradiating the expanding light onto one region where the basal plane dislocations (BPDs) exist, and then irradiating the expanding light onto another region where the basal plane dislocations (BPDs) exist, simultaneously with the contraction process, and repeating this process for all regions where the basal plane dislocations (BPDs) exist.

[0011] According to the method for manufacturing a silicon carbide substrate having this configuration, the detection step involves irradiating the silicon carbide substrate with inspection light to detect BPDs present in the epitaxial layer, and the expansion step involves irradiating the region where the BPDs detected in the detection step are present with expansion light that expands SSFs from the BPDs, thereby capturing the generated carriers in the BPDs present in the epitaxial layer and expanding the SSFs from the BPDs in a short period of time. Next, the contraction step involves irradiating the SSFs expanded from the BPDs in the expansion step with contraction light that contracts the SSFs, thereby contracting the SSFs expanded from the BPDs and ultimately converting them to TEDs. By performing the expansion and contraction steps in this manner, the BPDs present in the epitaxial layer are converted to TEDs, thereby eliminating or reducing the BPDs present in the epitaxial layer. Furthermore, a silicon carbide substrate in which the BPDs present in the epitaxial layer are eliminated or reduced has a high yield, and a wider region of the substrate can be used for the manufacture of power devices. In the case where multiple BPDs are detected in the detection step, the expansion step involves irradiating one region where the BPDs are present with expanding light, and then simultaneously and in parallel with the contraction step, irradiating another region where the BPDs are present with expanding light, and by repeating this process for all regions where the BPDs are present, the BPDs present in the epitaxial layer can be sequentially eliminated or reduced. In this way, according to the present invention, it is possible to efficiently manufacture high-quality silicon carbide substrates in which BPDs are reduced or eliminated.

[0012] In the method for manufacturing a silicon carbide substrate according to the present invention, the inspection light has a wavelength of 365 nm or less and an illuminance of 1 W / cm ２ It is preferable that:

[0013] According to the method for manufacturing a silicon carbide substrate having this configuration, the inspection light has a wavelength of 365 nm or less and an illuminance of 1 W / cm ２ By satisfying the condition (above), the silicon carbide substrate can be excited and PL light can be emitted from the BPDs present in the epitaxial layer without further expanding the SSF from the BPDs, thereby enabling appropriate detection of the BPDs present in the epitaxial layer.

[0014] In the method for manufacturing a silicon carbide substrate in accordance with the present invention, the extended light preferably has a wavelength and illuminance that can reach at least the interface between the substrate layer and the epitaxial layer.

[0015] According to the method for manufacturing a silicon carbide substrate of this configuration, the expanded light has a wavelength and irradiance that reaches at least the interface between the substrate layer and the epitaxial layer, so that when expanding SSFs from BPDs present in the epitaxial layer, the SSFs can be expanded to the fullest extent until the epitaxial layer is filled. Furthermore, SSFs can also be expanded from BPDs converted to TEDs at (or near) the interface between the substrate layer and the epitaxial layer. In this way, by generating sufficient carriers in the epitaxial layer, SSFs can be expanded from BPDs present in the epitaxial layer, and then the expanded SSFs can be contracted and efficiently converted to TEDs. Therefore, according to the present invention, it is possible to efficiently manufacture high-quality silicon carbide substrates in which BPDs are reduced or eliminated.

[0016] In the method for manufacturing a silicon carbide substrate according to the present invention, the extended light has a wavelength of 325 to 365 nm and an illuminance of 10 W / cm ２ It is preferable that this is equal to or greater than this.

[0017] According to the method for manufacturing a silicon carbide substrate of this configuration, the extended light has a wavelength of 325 to 365 nm and an illuminance of 10 W / cm ２ For the above reasons, sufficient carriers can be generated in the epitaxial layer, and SSFs can be sufficiently expanded from BPDs present in the epitaxial layer. By sufficiently expanding the SSFs and then contracting the expanded SSFs, the BPDs present in the epitaxial layer are efficiently converted into TEDs, making it possible to efficiently manufacture high-quality silicon carbide substrates in which BPDs are reduced or eliminated.

[0018] In the method for manufacturing a silicon carbide substrate in accordance with the present invention, the shrinking light preferably has a wavelength of 975 to 1095 nm, or 487 to 548 nm.

[0019] According to the method for manufacturing a silicon carbide substrate having this configuration, the contraction light has a wavelength of 975 to 1095 nm or 487 to 548 nm, so that the SSF can be contracted without further expanding the SSF from the BPD. Therefore, the silicon carbide substrate in which the BPDs present in the epitaxial layer have been eliminated or reduced can be cut to any size and used as a product.

[0020] In the method for manufacturing a silicon carbide substrate in accordance with the present invention, it is preferable that in the expanding step and the contracting step, the expanding light and the contracting light are irradiated using a galvano scanner.

[0021] According to the method for manufacturing a silicon carbide substrate having this configuration, the expansion light and contraction light are irradiated using a galvanometer scanner, so that the silicon carbide substrate can be irradiated with the expansion light and contraction light with high precision. Furthermore, by irradiating the expansion light and contraction light using a galvanometer scanner, the expansion process and the contraction process can be performed simultaneously. Therefore, it is possible to efficiently convert BPDs present in the epitaxial layer into TEDs, thereby eliminating or reducing the BPDs.

[0022] The method for manufacturing a silicon carbide substrate according to the present invention preferably further comprises an additional detection step of irradiating the silicon carbide substrate with the inspection light again after performing the expansion step and the contraction step for all basal plane dislocations (BPDs) detected in the detection step, and performing the expansion step and the contraction step if any basal plane dislocations (BPDs) are detected in the additional detection step.

[0023] According to the method for manufacturing a silicon carbide substrate having this configuration, even if BPDs remain in the epitaxial layer, they can be detected by performing the additional detection step, and the expansion step and contraction step can be performed again to convert the BPDs present in the epitaxial layer into TEDs, thereby reliably eliminating the BPDs. Therefore, a high-quality silicon carbide substrate having no BPDs present in the epitaxial layer can be manufactured.

[0024] A characteristic configuration of the silicon carbide substrate manufacturing apparatus according to the present invention for solving the above problems is a silicon carbide substrate manufacturing apparatus having a substrate layer and an epitaxial layer, in which basal plane dislocations (BPDs) present in the epitaxial layer are reduced or eliminated, the apparatus comprising: a detection means for irradiating the silicon carbide substrate with inspection light to detect basal plane dislocations (BPDs) present in the epitaxial layer; an expansion means for irradiating an area where the basal plane dislocations (BPDs) detected by the detection means exist with expanding light that expands Shockley stacking faults (SSFs) from the basal plane dislocations (BPDs); and a contraction means for irradiating the Shockley stacking faults (SSFs) expanded from the basal plane dislocations (BPDs) by the expansion means with contraction light that contracts the Shockley stacking faults (SSFs), When there are multiple basal plane dislocations (BPDs) detected by the detection means, the expansion means irradiates the expanded light onto one region where the basal plane dislocations (BPDs) exist, and then irradiates the expanded light onto another region where the basal plane dislocations (BPDs) exist, simultaneously with the shrinkage of the Shockley stacking faults (SSFs) by the shrinkage means, and repeats this for all regions where the basal plane dislocations (BPDs) exist.

[0025] In the silicon carbide substrate manufacturing apparatus of this configuration, the detection means irradiates the silicon carbide substrate with inspection light to detect BPDs present in the epitaxial layer, and the expansion means irradiates the region where the BPDs detected by the detection means are present with expansion light that expands SSFs from the BPDs, thereby capturing the generated carriers in the BPDs present in the epitaxial layer and expanding the SSFs from the BPDs in a short period of time. Next, the contraction means irradiates the SSFs expanded from the BPDs by the expansion means with contraction light that contracts the SSFs, thereby contracting the SSFs expanded from the BPDs and ultimately converting them to TEDs. In this way, by irradiating the expansion light and contraction light, the BPDs present in the epitaxial layer are converted to TEDs, and the BPDs present in the epitaxial layer can be eliminated or reduced. Silicon carbide substrates in which the BPDs present in the epitaxial layer are eliminated or reduced have a high yield, and a wider region of the substrate can be used for the manufacture of power devices. In the case where a plurality of BPDs are detected by the detection means, the expansion means irradiates one region where the BPDs are present with the expanded light, and then irradiates another region where the BPDs are present with the expanded light simultaneously with the contraction of the SSF by the contraction means. By repeating this process for all regions where the BPDs are present, the BPDs present in the epitaxial layer can be sequentially eliminated or reduced. In this way, according to the present invention, it is possible to efficiently manufacture high-quality silicon carbide substrates in which BPDs are reduced or eliminated.

[0026] FIG. 1 is a cross-sectional view schematically showing a silicon carbide substrate. FIG. 2 is an explanatory diagram schematically showing the expansion of SSFs, where (a) is a perspective view showing the expansion of SSFs from BPDs present in an epitaxial layer, and (b) is a perspective view showing the expansion of SSFs from BPDs converted to TEDs at the interface between the substrate layer and the epitaxial layer. FIG. 3 is an explanatory diagram schematically showing the process of converting BPDs present in an epitaxial layer to TEDs, where (a) shows a silicon carbide substrate having BPDs present in the epitaxial layer, (b) shows the silicon carbide substrate of (a) after irradiating it with expanding light at a wavelength and illuminance that reaches the interface between the substrate layer and the epitaxial layer, and (c) shows the silicon carbide substrate of (b) after irradiating it with contracting light. FIG. 4 is a schematic diagram of a silicon carbide substrate manufacturing apparatus of the present invention. FIG. 5 is a flowchart showing the steps of a silicon carbide substrate manufacturing method of the present invention. FIG. 6 is a time chart showing a specific example of the expansion step and contraction step of S5 in the flowchart of FIG.

[0027] Hereinafter, embodiments of a method for manufacturing a silicon carbide substrate and an apparatus for manufacturing a silicon carbide substrate according to the present invention will be described in detail with reference to the drawings. However, the present invention is not intended to be limited to the configurations described below. Note that the thickness relationships of the layer structures of the silicon carbide substrate shown in Figures 1 to 3 have been appropriately exaggerated or simplified for ease of explanation, and do not strictly reflect the relative thicknesses of the actual layers.

[0028] [Silicon Carbide Substrate] Before describing the method for manufacturing a silicon carbide substrate and the apparatus for manufacturing a silicon carbide substrate of the present invention, a silicon carbide substrate used in the manufacture of a power device will be described. Fig. 1 is a cross-sectional view schematically showing a silicon carbide substrate 100.

[0029] The silicon carbide substrate 100 has a structure in which a substrate layer 101 and an epitaxial layer 102 are stacked. The substrate layer 101 is a silicon carbide single crystal (4H-SiC) substrate that serves as a base for thin film manufacturing by epitaxial growth. The epitaxial layer 102 is a thin film made of silicon carbide single crystal (4H-SiC) deposited on the substrate layer 101 by epitaxial growth. An interface I exists between the substrate layer 101 and the epitaxial layer 102. If BPDs present in the substrate layer 101 cross the interface I, they either penetrate the epitaxial layer 102 as they are or are converted to TEDs at the interface I or in the epitaxial layer 102 near the interface I (hereinafter simply referred to as "interface I").

[0030] 2A and 2B are explanatory diagrams schematically illustrating the extension of SSFs, in which (a) is a perspective view showing the extension of SSFs from BPDs present in the epitaxial layer 102, and (b) is a perspective view showing the extension of SSFs from BPDs converted to TEDs at the interface I between the substrate layer 101 and the epitaxial layer 102. In FIGS. 2A and 2B, a portion of the silicon carbide substrate 100 is cut away to illustrate a plane parallel to the basal plane. The basal plane is a plane perpendicular to the c-axis

[0001] used to identify a crystal structure. In FIG. 2B, the TEDs present in the cut-away region are illustrated by dashed lines. The mechanism by which forward current degradation occurs in a power device manufactured using the silicon carbide substrate 100 is that carriers generated by current flow are captured by BPDs and recombined, causing SSFs to extend from the BPDs, resulting in a change in device characteristics. At this time, in the epitaxial layer 102, the SSFs expand from the BPDs formed parallel to the basal plane along a plane parallel to the basal plane, forming a triangular shape, as shown in Fig. 2(a). Also, from the BPDs converted to TEDs at the interface I between the substrate layer 101 and the epitaxial layer 102, the SSFs become band-shaped, as shown in Fig. 2(b).

[0031] Here, as shown in FIG. 2( b), the conversion point from BPD to TED is located deep below the surface of the silicon carbide substrate 100 (at the interface I between the substrate layer 101 and the epitaxial layer 102). Therefore, the conversion point from BPD to TED does not move at room temperature. However, the conversion point from BPD to TED can be moved by raising the temperature. In this case, by expanding SSFs from the BPD present in the epitaxial layer and the BPD converted to TED at the interface I between the substrate layer 101 and the epitaxial layer 102, the BPD that has penetrated from the substrate layer 101 to the epitaxial layer 102 can be efficiently converted to TED at the interface I between the substrate layer 101 and the epitaxial layer 102.

[0032] 3A and 3B are explanatory diagrams schematically illustrating the process by which BPDs present in the epitaxial layer 102 are converted to TEDs, in which (a) shows a silicon carbide substrate 100a having BPDs present in the epitaxial layer 102, (b) shows a silicon carbide substrate 100b after the silicon carbide substrate 100a in (a) is irradiated with expanding light at a wavelength and illuminance that reaches the interface I between the substrate layer 101 and the epitaxial layer 102, and (c) shows a silicon carbide substrate 100c after the silicon carbide substrate 100b in (b) is irradiated with contracting light. As shown in FIG. 3A, most of the BPDs present in the substrate layer 101 are converted to TEDs at the interface I between the substrate layer 101 and the epitaxial layer 102, but some of the BPDs are inherited to the epitaxial layer 102. BPDs that penetrate from the substrate layer 101 to the epitaxial layer 102 (BPDs present in the epitaxial layer 102) emit PL light with a wavelength of 710 nm due to recombination of carriers generated by irradiating the silicon carbide substrate 100 with excitation light. Therefore, if BPDs are present in the epitaxial layer 102, a linear defect image that is brighter than the surrounding area can be confirmed in a PL emission image taken of the silicon carbide substrate 100 through a filter that transmits light with a wavelength of 700 nm or more. When an area in the PL image where BPDs are determined to exist is irradiated with expanding light at a wavelength and illuminance that reaches the interface I between the substrate layer 101 and the epitaxial layer 102, triangular SSFs (SSFs shown in light colors) expand from the BPDs present in the epitaxial layer 102, as shown in FIG. 3B. Also, band-shaped SSFs (SSFs shown in dark colors) are generated from the BPDs present in the same area that have been converted to TEDs at the interface I between the substrate layer 101 and the epitaxial layer 102. It is preferable that these SSFs are expanded to their fullest extent until the epitaxial layer is filled. When the expanded SSFs are irradiated with contracting light at a wavelength that does not further expand the SSFs, the triangular and band-shaped SSFs contract, and the BPDs present in the epitaxial layer 102 are converted to TEDs at the interface I, as shown in FIG. 3C. In this way, the BPDs present in the epitaxial layer 102 can be eliminated or reduced.

[0033] Based on this knowledge, the present inventor has come to create a method for manufacturing a silicon carbide substrate and an apparatus for manufacturing a silicon carbide substrate, in which BPDs present in the epitaxial layer 102 are reduced or eliminated at the wafer stage before power devices are manufactured.

[0034] [Silicon carbide substrate manufacturing apparatus] Figure 4 is a schematic configuration diagram of silicon carbide substrate manufacturing apparatus 1 of the present invention. Silicon carbide substrate manufacturing apparatus 1 is an apparatus that reduces or eliminates BPDs present in epitaxial layer 102 of silicon carbide substrate 100 placed on mounting table 10. As shown in Figure 4, silicon carbide substrate manufacturing apparatus 1 includes detection means 2, expansion means 3, and contraction means 4. The operations of detection means 2, expansion means 3, and contraction means 4 are controlled by control means 5. Each component of silicon carbide substrate manufacturing apparatus 1 will be described in detail below.

[0035] <Detection Unit> The detection unit 2 is a unit that irradiates the silicon carbide substrate 100 with inspection light L1 to detect BPDs present in the epitaxial layer 102. The detection unit 2 has an inspection light irradiation unit 21, an imaging unit 22, and a determination unit 23.

[0036] The inspection light irradiating unit 21 irradiates the entire silicon carbide substrate 100 with inspection light L1. The inspection light L1 has a wavelength of 365 nm or less and an illuminance of 1 W / cm ２ It is preferable that the following condition is satisfied. Under the above irradiation conditions, the inspection light L1 can excite the silicon carbide substrate 100 without further expanding the SSF from the BPDs. By irradiating the entire silicon carbide substrate 100 with the inspection light L1 by the inspection light irradiating unit 21, PL light L2 can be emitted from the BPDs present in the epitaxial layer 102, and the BPDs present in the epitaxial layer 102 can be appropriately detected. As the light source of the inspection light irradiating unit 21, for example, an ultraviolet laser, a mercury-xenon lamp, etc. can be used.

[0037] The photographing unit 22 photographs the silicon carbide substrate 100 emitting PL light. The photographing unit 22 has an image sensor in which solid-state imaging elements such as CCDs (Charged-Coupled Devices) and CMOSs ​​(Complementary Metal-Oxide-Semiconductors) are arranged in a two-dimensional array, and a digital camera that detects incident light on the photographing unit 22 with the image sensor can be used. The photographing unit 22 is preferably configured to be movable so that any position on the silicon carbide substrate 100 can be photographed from the normal direction of the substrate surface. The photographing unit 22 has a filter 22a that transmits light with a wavelength of 700 nm or more. The filter 22a that transmits light with a wavelength of 700 nm or more selectively transmits PL light with a wavelength of 710 nm emitted from BPD. For example, a high-pass filter with a transmission band of 700 nm or more can be used. After the inspection light L1 is emitted from the inspection light irradiation unit 21, the photographing unit 22 transmits PL light L2 emitted from the silicon carbide substrate 100 through the filter 22a to photograph a PL light emission image. In the PL light emission image photographed in this manner, bright linear defect images appear at positions where BPDs exist in the epitaxial layer 102. The photographing unit 22 records the photographed image in a storage device (not shown), such as a hard disk.

[0038] The determination unit 23 determines whether or not a BPD is present by referring to the PL light emission image captured by the imaging unit 22. The determination unit 23 is implemented as a computer having a CPU, memory, storage, etc., and the CPU reads and executes a program recorded in the memory, thereby realizing its determination function. Specifically, the determination unit 23 extracts a BPD defect image, which is a bright linear defect image, by image analysis of the PL light emission image, and determines that a BPD is present. The extraction of the defect image can be performed, for example, by edge detection processing. When the determination unit 23 determines that a BPD is present, the detection means 2 detects the area where the defect image extracted by the determination unit 23 occurs as an area where a BPD is present.

[0039] <Expansion Means> The expansion means 3 is a means for irradiating an area where a BPD detected by the detection means 2 exists with expanded light L3 that expands the SSF from the BPD. By irradiating an area where a BPD detected by the detection means 2 exists with expanded light L3 that expands the SSF from the BPD, carriers generated by the irradiation of expanded light L3 are captured by the BPD present in the epitaxial layer 102, expanding the SSF from the BPD. Therefore, because the expanded light L3 is not irradiated onto an area where a BPD does not exist, the SSF can be expanded from the BPD in a short time without taking extra time. The expanded light L3 preferably has a wavelength and illuminance that can reach at least the interface I between the substrate layer 101 and the epitaxial layer 102. Since the expanded light L3 has a wavelength and illuminance that reach at least the interface between the substrate layer 101 and the epitaxial layer 102, when expanding SSF from BPDs present in the epitaxial layer 102, SSF can also be expanded from BPDs converted to TEDs at the interface I between the substrate layer 101 and the epitaxial layer 102. In this way, by generating sufficient carriers in the epitaxial layer 102, the SSF can be expanded to the fullest extent to fill the epitaxial layer 102, and when the SSF is contracted, the BPDs present in the epitaxial layer 102 can be efficiently converted to TEDs.

[0040] The extended light L3 has a wavelength of 325 to 365 nm and an illuminance of 10 W / cm ２ It is preferable that the wavelength is 355 nm and the illuminance is 100 W / cm or more. ２ It is more preferable that the wavelength of the extended light L3 is 325 to 365 nm and the illuminance is 10 W / cm or more. ２ As a result, sufficient carriers can be generated in the epitaxial layer 102, and the SSF can be sufficiently extended from the BPDs present in the epitaxial layer 102. Note that the illuminance of the extended light L3 is 10 W / cm ２If the SSF is smaller than this, the SSF expansion speed will be slow, and it may not be possible to perform the rapid inspection desired in the power device manufacturing process. The expansion means 3 may be of any type as long as it can irradiate expanded light L3 having a wavelength and illuminance that reaches at least the interface I between the substrate layer 101 and the epitaxial layer 102, and examples thereof include a YAG laser, a He—Cd laser, and an InGaN laser. Among these, it is preferable to use the third harmonic (355 nm) of a YAG laser.

[0041] <Contraction Means> The contraction means 4 is a means for irradiating the SSF expanded from the BPD by the expansion means 3 with contraction light L4 that contracts the SSF. By irradiating the SSF expanded from the BPD by the expansion means 3 with contraction light L4 that contracts the SSF, the SSF expanded from the BPD can be contracted and ultimately converted into TED. As a result, the BPDs present in the epitaxial layer 102 are converted into TEDs, so that the BPDs present in the epitaxial layer 102 can be eliminated or reduced, and a wider area of ​​the silicon carbide substrate 100 can be used for manufacturing power devices.

[0042] The wavelength of the contraction light L4 is preferably 975 to 1095 nm or 487 to 548 nm, and more preferably 1064 nm or 532 nm. By using a wavelength of the contraction light L4 of 975 to 1095 nm or 487 to 548 nm, the SSF can be contracted without further expanding the SSF from the BPD. The type of contraction means 4 is not limited as long as it can irradiate contraction light L4 with a wavelength equal to or greater than the absorption edge wavelength at which SSF expansion does not occur, or equal to or less than the absorption edge wavelength, and examples thereof include a YAG laser, a He—Cd laser, and an InGaN laser. Among these, it is preferable to use the fundamental wavelength (1064 nm) or the second harmonic (532 nm) of a YAG laser.

[0043] <Control means> The control means 5 is a computer having a CPU, memory, storage, etc., and the CPU reads and executes a program recorded in the memory, thereby realizing the function of controlling the operations of the detection means 2, expansion means 3, and contraction means 4.

[0044] The control unit 5 controls the expansion unit 3 and the contraction unit 4 so that, when multiple BPDs are detected by the detection unit 2, the expansion unit 3 first irradiates one region where a BPD is present with the expanding light L3, and then, simultaneously with the contraction of the SSF by the contraction unit 4, irradiates another region where a BPD is present with the expanding light L3, repeating this process for all regions where a BPD is present. For example, when three BPDs (A, B, and C) are detected by the detection unit 2, the expansion unit 3 first irradiates A with the expanding light L3 to expand the SSF. Next, the contraction unit 4 irradiates the SSF generated from A with the contraction light L4 to contract the SSF, and simultaneously, the expansion unit 3 irradiates B with the expanding light L3 to expand the SSF. Next, the contraction unit 4 irradiates the SSF generated from B with the contraction light L4 to contract the SSF, and simultaneously, the expansion unit 3 irradiates C with the expanding light L3 to expand the SSF. Finally, the contraction means 4 irradiates the contraction light L4 onto the SSF generated from C to contract the SSF. In this way, when there are multiple BPDs detected by the detection means 2, the expansion means 3 irradiates one region where the BPDs exist with the expanding light L3, and then irradiates another region where the BPDs exist with the expanding light L3 simultaneously with the contraction of the SSF by the contraction means 4. By repeating this process for all regions where the BPDs exist, it is possible to efficiently eliminate or reduce the BPDs present in the epitaxial layer 102.

[0045] The expanded light L3 and the contracted light L4 are preferably irradiated using a galvanometer scanner. In this embodiment, as shown in FIG. 4 , the expansion means 3 includes a light source 31, a focusing unit 32, and a galvanometer scanner 33. The galvanometer scanner 33 includes an X-axis galvanometer mirror 33x, a Y-axis galvanometer mirror 33y, and an actuator (not shown) that rotates the X-axis galvanometer mirror 33x and the Y-axis galvanometer mirror 33y. The light source 31 generates the expanded light L3. The focusing unit 32 focuses the expanded light L3 output from the light source 31 and adjusts it to a desired spot diameter. The galvanometer scanner 33 irradiates the expanded light L3 onto the silicon carbide substrate 100 while changing the irradiation direction of the expanded light L3 output from the focusing unit 32. Similarly, the contraction means 4 includes a light source 41, a focusing unit 42, and a galvanometer scanner 43. The galvanometer scanner 43 includes an X-axis galvanometer mirror 43x, a Y-axis galvanometer mirror 43y, and an actuator (not shown) that rotates the X-axis galvanometer mirror 43x and the Y-axis galvanometer mirror 43y. The light source 41 generates the contraction light L4. The focusing unit 42 focuses the contraction light L4 output from the light source 41 and adjusts the spot diameter to a desired value. The galvanometer scanner 43 irradiates the contraction light L4 onto the silicon carbide substrate 100 while changing the irradiation direction of the contraction light L4 output from the focusing unit 42. In this way, the expansion means 3 and the contraction means 4 irradiate the expansion light L3 and the contraction light L4 onto the silicon carbide substrate 100 using the galvanometer scanners 33 and 43. Therefore, the expansion light L3 and the contraction light L4 can be irradiated onto the silicon carbide substrate 100 with high precision, and the expansion and contraction of the SSF can be performed simultaneously. Therefore, it is possible to efficiently convert BPDs present in the epitaxial layer 102 into TEDs and eliminate or reduce the BPDs. In this embodiment, one galvanometer scanner is used for each of the expansion means 3 and the contraction means 4, but if, for example, expansion takes longer than contraction of the SSF, the expansion light L3 may be irradiated using multiple galvanometer scanners, and multiple BPDs can be irradiated with the expansion light L3 simultaneously in parallel. By irradiating the contraction light L4 first to the SSF that has been fully expanded, it is possible to efficiently eliminate or reduce the BPDs present in the epitaxial layer 102 in a shorter time.

[0046] <Placement Table> The placement table 10 has a built-in heater and heats the silicon carbide substrate 100 placed on its upper surface. When the expansion means 3 and contraction means 4 irradiate the silicon carbide substrate 100 with the expanding light L3 and the contraction light L4, the placement table 10 is preferably heated so that the temperature of the silicon carbide substrate 100 reaches 100 to 200°C, and more preferably 100 to 150°C. Heating the silicon carbide substrate 100 to 100 to 200°C improves carrier generation efficiency, and when the silicon carbide substrate 100 is irradiated with the expanding light L3 and the contraction light L4, the SSF can be expanded and contracted in a short time, thereby shortening the manufacturing time.

[0047] [Method for manufacturing silicon carbide substrate] Figure 5 is a flowchart showing the steps of a method for manufacturing a silicon carbide substrate of the present invention. In the method for manufacturing a silicon carbide substrate of the present invention, a detection step, an expansion step, and a contraction step are performed in order using silicon carbide substrate manufacturing apparatus 1 of Figure 4, and an additional detection step is further performed as an optional step. In the flowchart of Figure 5, the symbol "S" in the figure represents a step.

[0048] <Detection Step: S1 to S4> In the detection step, the detection means 1 irradiates the silicon carbide substrate 100 with the inspection light L1 to detect BPDs present in the epitaxial layer 102.

[0049] In S1, the inspection light irradiating unit 21 irradiates the entire silicon carbide substrate 100 with inspection light L1, thereby exciting the silicon carbide substrate 100 and causing it to emit PL light L2. In the detection step, the inspection light L1 has a wavelength of 365 nm or less and an illuminance of 1 W / cm ２ By irradiating the inspection light L1 under the above irradiation conditions, the silicon carbide substrate 100 can be excited and PL light L2 can be emitted from the BPDs present in the epitaxial layer 102 without further expanding the SSF from the BPDs. Therefore, the BPDs present in the epitaxial layer 102 can be appropriately detected.

[0050] In S2, while the silicon carbide substrate 100 is emitting PL light L2, the imaging unit 22 transmits the PL light L2 through a filter 22a that transmits light with a wavelength of 700 nm or more, and captures a PL light emission image. Generally, in power devices such as SiC-MOSFETs, the epitaxial layer 102 is formed to a thickness of approximately 0.5 to 20 μm and has an off-angle of 4°. Therefore, the length of BPDs in the epitaxial layer 102 captured from the normal direction of the substrate surface is approximately 7 to 286 μm. Therefore, the PL light emission image captures BPDs with lengths of approximately 7 to 286 μm, each of which corresponds to a size of multiple pixels. In the imaging process, the entire silicon carbide substrate 100 may be imaged at once, or the silicon carbide substrate 100 may be divided into multiple regions and imaged.

[0051] In S3, the determination unit 23 extracts a BPD defect image, which is a bright linear defect image, from the PL light emission image captured by the imaging unit 22, and determines whether a BPD is present. The defect image extraction can be performed, for example, by edge detection processing. The PL light emission image is subjected to image analysis to extract a BPD defect image, which is a bright linear defect image, and determine whether a BPD is present. If it is determined that a BPD is present (S3: YES), the region in which the BPD defect image, which is a bright linear defect image extracted by the determination unit 23, occurs is detected as a region in which a BPD is present (S4). If it is determined that a BPD is not present (S3: NO), the manufacture of the silicon carbide substrate 100 is terminated.

[0052] <Expansion Process / Contraction Process: S5> In S5, in the expansion process, the expansion means 3 irradiates the region where the BPDs detected in the detection process are present with expansion light L3 that expands the SSF from the BPDs, and in the contraction process, the contraction means 4 irradiates the SSF expanded from the BPDs in the expansion process with contraction light L4 that contracts the SSF. By irradiating the region where the BPDs detected in the detection process are present with expansion light L3 that expands the SSF from the BPDs, carriers generated by the irradiation of expansion light L3 are captured by the BPDs present in the epitaxial layer 102, allowing the SSF to expand from the BPDs in a short period of time. Next, in the contraction process, the SSF expanded from the BPDs in the expansion process is irradiated with contraction light L4 that contracts the SSF, thereby contracting the SSF expanded from the BPDs and ultimately converting it into TED. In this way, by performing the expansion step and the contraction step, BPDs present in the epitaxial layer 102 are converted to TEDs, and it is possible to eliminate or reduce the BPDs present in the epitaxial layer 102. Then, silicon carbide substrate 100 in which the BPDs present in epitaxial layer 102 have been eliminated or reduced has a high yield, and a larger region of silicon carbide substrate 100 can be used for manufacturing power devices.

[0053] The expanded light L3 in the expansion step preferably has a wavelength and illuminance that reach at least the interface I between the substrate layer 101 and the epitaxial layer 102. By using the expanded light L3 with a wavelength and illuminance that reach at least the interface I between the substrate layer 101 and the epitaxial layer 102, when expanding SSFs from BPDs present in the epitaxial layer 102, the SSFs can be expanded to the fullest extent until the epitaxial layer 102 is filled. Furthermore, SSFs can also be expanded from BPDs converted to TEDs at the interface I between the substrate layer 101 and the epitaxial layer 102. In this way, by generating sufficient carriers in the epitaxial layer 102, SSFs can be expanded from the BPDs present in the epitaxial layer 102, and then the expanded SSFs can be contracted and efficiently converted to TEDs. Therefore, it is possible to efficiently manufacture a high-quality silicon carbide substrate 100 in which BPDs are reduced or eliminated.

[0054] The expansion light L3 in the expansion step has a wavelength of 325 to 365 nm and an illuminance of 10 W / cm ２ By irradiating the epitaxial layer 102 with the extended light L3 under the above irradiation conditions, sufficient carriers can be generated in the epitaxial layer 102, and SSFs can be sufficiently expanded from the BPDs present in the epitaxial layer 102. By sufficiently expanding the SSFs and then contracting the expanded SSFs, the BPDs present in the epitaxial layer 102 are efficiently converted into TEDs, making it possible to efficiently manufacture a high-quality silicon carbide substrate 100 in which BPDs are reduced or eliminated.

[0055] The wavelength of the shrinking light L4 used in the shrinking step is preferably 975 to 1095 nm, or 487 to 548 nm. By irradiating the shrinking light L4 under the above irradiation conditions, the SSF can be shrunk without further expanding the SSF from the BPD. Therefore, silicon carbide substrate 100 in which the BPDs present in epitaxial layer 102 have been eliminated or reduced can be cut to any size and used as a product.

[0056] If multiple BPDs are detected in the detection process, the expansion process involves irradiating expansion light L3 onto one area where the BPDs are present, and then, simultaneously with the contraction process, irradiating expansion light L3 onto another area where the BPDs are present.By repeating this process for all areas where the BPDs are present, the BPDs present in the epitaxial layer 102 can be eliminated or reduced in sequence.

[0057] 6 is a time chart showing a specific example of the expansion step and contraction step of S5 in the flowchart of FIG. 5. FIG. 6 shows a case where n regions in which BPDs are present are detected in the detection step. First, at time t ０ At time t, the expansion step is started for the first BPD (the region where the BPD exists), and the expansion unit 3 irradiates the first BPD with the expansion light L3. Next, after the SSF is sufficiently expanded from the first BPD by the expansion step, at time t １ At time t, the contraction process is started, and the contraction means 4 irradiates the SSF expanded from the first BPD with contraction light L4 to contract the SSF. １At time t, the expansion process is started for the second BPD in parallel, and the expansion unit 3 irradiates the second BPD with expansion light L3. The expansion process and contraction process are repeated in the same manner, and finally, at time t ｎ In this embodiment, the contraction process is started, and the SSF expanded from the nth BPD is irradiated with contraction light L4, which contracts the SSF. In this embodiment, the contraction process of the nth BPD and the expansion process of the n+1th BPD are started simultaneously, but if the contraction process takes a long time, for example, the expansion process of the n+1th BPD and the expansion process of the n+2th BPD may be performed during the contraction process of the nth BPD, and the start timing of the expansion process and contraction process can be set appropriately.

[0058] In the expansion process and the contraction process, the expansion light L3 and the contraction light L4 are preferably irradiated using a galvanometer scanner 33. By using the galvanometer scanner 33 for irradiation, the expansion light L3 and the contraction light L4 can be irradiated onto the silicon carbide substrate 100 with high precision. Furthermore, by irradiating the expansion light L3 and the contraction light L4 using separate galvanometer scanners, the expansion process and the contraction process can be performed simultaneously. Therefore, the BPDs present in the epitaxial layer 102 can be efficiently converted into TEDs, thereby eliminating or reducing the BPDs. Furthermore, in each of the expansion process and the contraction process, the expansion light L3 and the contraction light L4 can be irradiated using multiple galvanometer scanners. For example, when the expansion light L3 is irradiated using two galvanometer scanners, the expansion processes of the nth BPD and the n+1th BPD can be performed simultaneously and in parallel, thereby expanding the SSF from the BPDs in a shorter time. In S5, the control unit 5 controls, for example, a galvanometer scanner to irradiate an arbitrary region with the expanding light L3 and the contracting light L4 at an arbitrary timing.

[0059] <Additional Detection Step: S6> The additional detection step is a step of confirming whether BPDs remain in the epitaxial layer. If the additional detection step is to be performed (S6: YES), the process returns to S1 and performs the additional detection step of irradiating the silicon carbide substrate 100 with the inspection light L1 again. The additional detection step is similar to the detection step, and S1 to S4 are performed in order. If BPDs are detected in the additional detection step, the expansion step and contraction step (S5) are performed. If the additional detection step is not to be performed (S6: NO), the manufacture of the silicon carbide substrate 100 is terminated. By performing the additional detection step, even if BPDs remain in the epitaxial layer 102, they can be detected by the additional inspection step. Therefore, the expansion step and contraction step can be performed again to convert the BPDs present in the epitaxial layer 102 into TEDs, thereby reliably eliminating the BPDs. Therefore, a high-quality silicon carbide substrate 100 can be manufactured in which no BPDs exist in the epitaxial layer 102.

[0060] As described above, in the silicon carbide substrate manufacturing method and silicon carbide substrate manufacturing apparatus of the present invention, when multiple BPDs are detected in the detection process, the expansion process involves irradiating expansion light onto one area where the BPDs are present, and then irradiating expansion light onto another area where the BPDs are present simultaneously with the contraction process, and this process is repeated for all areas where the BPDs are present, making it possible to efficiently manufacture high-quality silicon carbide substrates in which BPDs are reduced or eliminated.

[0061] The method and apparatus for manufacturing a silicon carbide substrate according to the present invention can be used in the manufacturing process of power device elements such as SiC-MOSFETs.

[0062] REFERENCE SIGNS LIST 1 Silicon carbide substrate manufacturing apparatus 2 Detection means 3 Expanding means 4 Contracting means 33, 43 Galvano scanner 100 Silicon carbide substrate 101 Substrate layer 102 Epitaxial layer L1 Inspection light L3 Expanding light L4 Contracting light I Interface

Claims

1. A method for manufacturing a silicon carbide substrate having a substrate layer and an epitaxial layer, in which basal plane dislocations (BPDs) present in the epitaxial layer are reduced or eliminated, the method comprising: a detection step of irradiating the silicon carbide substrate with inspection light to detect basal plane dislocations (BPDs) present in the epitaxial layer; an expansion step of irradiating areas where the basal plane dislocations (BPDs) detected in the detection step are present with expanding light that expands Shockley stacking faults (SSFs) from the basal plane dislocations (BPDs); and a contraction step of irradiating the Shockley stacking faults (SSFs) expanded from the basal plane dislocations (BPDs) in the expansion step with contraction light that contracts the Shockley stacking faults (SSFs), When multiple basal plane dislocations (BPDs) are detected in the detection process, the expansion process involves irradiating the expanding light onto one region where the basal plane dislocations (BPDs) exist, and then irradiating the expanding light onto another region where the basal plane dislocations (BPDs) exist, simultaneously with the contraction process, and repeating this process for all regions where the basal plane dislocations (BPDs) exist.

2. The inspection light has a wavelength of 365 nm or less and an illuminance of 1 W / cm ２ The method for manufacturing a silicon carbide substrate according to claim 1 , wherein:

3. The method for manufacturing a silicon carbide substrate according to claim 1, wherein the extended light has a wavelength and illuminance that allows it to reach at least the interface between the substrate layer and the epitaxial layer.

4. The expanded light has a wavelength of 325 to 365 nm and an illuminance of 10 W / cm ２ The method for manufacturing a silicon carbide substrate according to claim 3 .

5. The method for manufacturing a silicon carbide substrate according to claim 1, wherein the shrinking light has a wavelength of 975 to 1095 nm or 487 to 548 nm.

6. The method for manufacturing a silicon carbide substrate according to claim 1, wherein in the expansion step and the contraction step, the expanding light and the contraction light are irradiated using a galvano scanner.

7. A method for manufacturing a silicon carbide substrate according to any one of claims 1 to 6, further comprising an additional detection step of irradiating the silicon carbide substrate with the inspection light again after performing the expansion step and the contraction step for all basal plane dislocations (BPDs) detected in the detection step, wherein the expansion step and the contraction step are performed if a basal plane dislocation (BPD) is detected in the additional detection step.

8. An apparatus for manufacturing a silicon carbide substrate having a substrate layer and an epitaxial layer, in which basal plane dislocations (BPDs) present in the epitaxial layer are reduced or eliminated, comprising: a detection means for irradiating the silicon carbide substrate with inspection light to detect basal plane dislocations (BPDs) present in the epitaxial layer; an expansion means for irradiating an area where the basal plane dislocations (BPDs) detected by the detection means exist with expanding light that expands Shockley stacking faults (SSFs) from the basal plane dislocations (BPDs); and a contraction means for irradiating the Shockley stacking faults (SSFs) expanded from the basal plane dislocations (BPDs) by the expansion means with contraction light that contracts the Shockley stacking faults (SSFs), When there are multiple basal plane dislocations (BPDs) detected by the detection means, the expansion means irradiates the expanded light onto one region where the basal plane dislocations (BPDs) exist, and then irradiates the expanded light onto another region where the basal plane dislocations (BPDs) exist, simultaneously with the contraction of Shockley stacking faults (SSFs) by the contraction means, and repeats this process for all regions where the basal plane dislocations (BPDs) exist.

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