Defect inspection device

Abstract

To provide a defect inspection device and a defect inspection method capable of discriminating BPD in a SiC epitaxial wafer.SOLUTION: A defect inspection device 1 according to this embodiment includes a radiation optical system 10 that radiates excitation light EL onto a sample 50 including a SiC substrate 51, a buffer layer 52 formed on the SiC substrate 51, and a drift layer 53 formed on the buffer layer 52, a filter section 20 that controls a wavelength band that transmits photoluminescence light PL generated from the sample 50, a detection optical system 30 that detects the photoluminescence light PL that has transmitted through the filter section 20, and an image processing section 40 that forms an image from the detected photoluminescence light PL and discriminates a defect captured in the formed image. The image processing section discriminates the defect on the basis of whether the length of the defect is L1=(D1+D2) / tan θ or L2=D2 / tan θ.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a defect inspection apparatus and a defect inspection method. [Background technology]

[0002] Silicon carbide (hereinafter referred to as SiC) has excellent physical and thermal properties, and is therefore useful for manufacturing semiconductor devices with high breakdown voltage and low loss. A SiC epitaxial wafer is a wafer in which an epitaxial layer containing SiC is formed on a SiC substrate. In the manufacturing process of semiconductor devices using SiC epitaxial wafers, it is extremely important to detect defects present in the epitaxial layer and classify the detected defects in order to improve the manufacturing yield. In particular, basal plane dislocations (hereinafter referred to as BPDs) are killer defects that have a fatal adverse effect on the performance of semiconductor devices when semiconductor devices are manufactured on SiC epitaxial wafers. For this reason, there is a strong demand for distinguishing and detecting BPDs from other defects.

[0003] In a SiC epitaxial wafer in which a drift layer containing SiC is formed on a SiC substrate, a buffer layer doped with a high concentration of impurities may be sandwiched between the drift layer and the SiC substrate to prevent the occurrence of BPDs in the drift layer. With such a structure, BPDs in the buffer layer can be converted to threading edge dislocations (hereinafter referred to as TEDs) at the interface between the buffer layer and the drift layer. Generally, it is BPDs in the drift layer that become killer defects. Therefore, by converting BPDs in the buffer layer to TEDs in the drift layer, the occurrence of killer defects in the drift layer can be suppressed.

[0004] However, in consideration of long-term reliability, it is desirable to also detect BPDs present only in the buffer layer that have been converted into TEDs at the interface between the buffer layer and the drift layer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2015-119056 A [Patent Document 2] Patent No. 6999212 [Patent Document 3] JP 2019-099438 A Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 describes a defect inspection device that irradiates an SiC epitaxial wafer with ultraviolet light and detects defects from the generated photoluminescence light. The defect inspection device of Patent Document 1 detects BPDs in the drift layer from an image of the near-infrared wavelength band of the photoluminescence light. However, the defect inspection device of Patent Document 1 has difficulty detecting BPDs in the buffer layer.

[0007] Patent Document 2 describes a method of converting BPDs in the drift layer and buffer layer into Shockley type stacking faults (hereinafter referred to as SSFs) and detecting the BPDs by photoluminescence light from the converted SSFs. The method of Patent Document 2 can detect BPDs in the buffer layer, but it is necessary to convert the BPDs into SSFs, making the inspection process very complicated.

[0008] Patent Document 3 describes the detection of BPDs in a high-concentration epitaxial layer by photoluminescence light transmitted in a wavelength band of 430 nm or less. The defect inspection device in Patent Document 3 can detect BPDs in a high-concentration epitaxial layer as black linear defects compared to the surroundings. However, there is no description of the relationship between the detected BPDs and the TEDs in the drift layer.

[0009] In a SiC epitaxial wafer, it is desirable to determine whether BPDs extend from the buffer layer to the drift layer or exist only in the buffer layer.

[0010] The present disclosure has been made in consideration of such problems, and provides a defect inspection apparatus and a defect inspection method capable of identifying BPDs in SiC epitaxial wafers. [Means for solving the problem]

[0011] A defect inspection apparatus according to one aspect of the present embodiment includes an irradiation optical system that irradiates excitation light onto a sample including a silicon carbide substrate, a buffer layer formed on the silicon carbide substrate, and a drift layer formed on the buffer layer, a filter unit that controls a wavelength band through which photoluminescent light generated from the sample is transmitted, a detection optical system that detects the photoluminescent light that has transmitted through the filter unit, and an image processing unit that forms an image from the detected photoluminescent light and identifies defects captured in the formed image, wherein the filter unit transmits the wavelength band including 420 nm or more and 430 nm or less of the photoluminescent light, and when a thickness of the drift layer is D1, a thickness of the buffer layer is D2, an offset angle is θ, and a first length and a second length are L1 and L2 shown below, respectively, L1 = (D1 + D2) / tan θ L2=D2 / tanθ When the length of the defect falls within a predetermined first range including the first length, the image processing unit distinguishes the defect as the defect including a basal plane dislocation connecting from the buffer layer to the drift layer, and when the length of the defect falls within a predetermined second range including the second length and different from the first range, the image processing unit distinguishes the defect as the defect including the basal plane dislocation in the buffer layer and an edge dislocation in the drift layer.

[0012] In the above defect inspection device, the filter unit changes the wavelength band to be transmitted from the wavelength band including 420 nm or more and 430 nm or less to the wavelength band including near-infrared light, the detection optical system detects the near-infrared light transmitted through the changed filter unit, and the image processing unit forms a near-infrared image from the detected near-infrared light. When the third length is L3 as shown below, L3=D1 / tanθ When the length of the defect falls within a predetermined third range including the third length and different from the first range and the second range, the defect may be identified as the defect including the basal plane dislocation in the drift layer.

[0013] In the above defect inspection device, the image processing unit may calculate the accuracy of the determined defects by comparing the number of defects having the length that belongs to the first range with the number of defects having the length that belongs to the third range.

[0014] In the above-mentioned defect inspection device, the image processing unit may identify the defects captured in the image by using an algorithm that has been machine-trained in advance using a plurality of the defects belonging to the first range and a plurality of the defects belonging to the second range as learning data.

[0015] In the above defect inspection apparatus, the impurity concentration of the drift layer is 1×10 15 cm -3 5×10 or more 17 cm -3and the impurity concentration of the buffer layer is less than 5×10 17 cm -3 More than 1×10 19 cm -3 The following is also fine.

[0016] A defect inspection method according to one aspect of the present embodiment includes the steps of: irradiating a sample including a silicon carbide substrate, a buffer layer formed on the silicon carbide substrate, and a drift layer formed on the buffer layer with excitation light; transmitting photoluminescent light generated from the sample through a filter unit that controls a wavelength band to be transmitted; detecting the photoluminescent light transmitted through the filter unit; forming an image from the detected photoluminescent light; and identifying a defect imaged in the formed image. In the step of transmitting the photoluminescent light, the filter unit transmits the wavelength band including 420 nm or more and 430 nm or less in the photoluminescent light. In the step of identifying the defect, when a thickness of the drift layer is D1, a thickness of the buffer layer is D2, an offset angle is θ, and a first length and a second length are L1 and L2 shown below, respectively, L1 = (D1 + D2) / tan θ L2=D2 / tanθ If the length of the defect falls within a predetermined first range including the first length, the defect is identified as a defect including a basal plane dislocation connecting from the buffer layer to the drift layer, and if the length of the defect falls within a predetermined second range including the second length, the second range being different from the first range, the defect is identified as a defect including the basal plane dislocation in the buffer layer and an edge dislocation in the drift layer.

[0017] The above defect inspection method further includes, after the step of identifying the defect, a step of changing the wavelength band transmitted by the filter unit from the wavelength band including 420 nm or more and 430 nm or less to the wavelength band including near-infrared light, a step of detecting the near-infrared light transmitted through the changed filter unit, a step of forming a near-infrared image from the detected near-infrared light, and a step of identifying the defect captured in the formed near-infrared image, wherein, in the step of identifying the defect captured in the near-infrared image, when a third length is defined as L3 as shown below, L3=D1 / tanθ When the length of the defect captured in the near-infrared image is within a predetermined third range including the third length and is different from the first range and the second range, the defect may be identified as a defect including the basal plane dislocation in the drift layer.

[0018] The above defect inspection method may further include a step of calculating the accuracy of the determined defects by comparing the number of defects having the length belonging to the first range with the number of defects having the length belonging to the third range.

[0019] In the above defect inspection method, the defects captured in the image may be identified by using an algorithm that has been machine-trained in advance using a plurality of the defects belonging to the first range and a plurality of the defects belonging to the second range as learning data.

[0020] In the defect inspection method, the impurity concentration of the drift layer is 1×10 15 cm -3 5×10 or more 17 cm -3 and the impurity concentration of the buffer layer is less than 5×10 17 cm -3 More than 1×10 19 cm -3 The following is also fine. Effect of the Invention

[0021] According to the present disclosure, it is possible to provide a defect inspection apparatus and a defect inspection method capable of identifying BPDs in SiC epitaxial wafers. [Brief description of the drawings]

[0022] [Figure 1] 1 is a configuration diagram illustrating a defect inspection device according to a first embodiment. [Diagram 2] 1 is a cross-sectional view illustrating a sample to be inspected in the defect inspection device according to the first embodiment. [Diagram 3] 3 is a schematic diagram illustrating an image formed by an image processing unit in the defect inspection device according to the first embodiment. FIG. [Figure 4] FIG. 2 is a flow chart illustrating a defect inspection method according to the first embodiment. [Diagram 5] FIG. 11 is a configuration diagram illustrating a defect inspection device according to a second embodiment. [Figure 6] 11 is a schematic diagram illustrating an image formed by an image processing unit in the defect inspection device according to the second embodiment. FIG. [Figure 7] 1A to 1C are diagrams illustrating examples of how BPDs appear in defects imaged by the defect inspection device according to the first embodiment and the defect inspection device according to the second embodiment. [Figure 8] FIG. 11 is a flow chart illustrating a defect inspection method according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. The following description shows a preferred embodiment of the present disclosure, and the scope of the present disclosure is not limited to the following embodiment. In the following description, parts with the same reference numerals indicate substantially the same contents.

[0024] (Embodiment 1) A defect inspection device and a defect inspection method according to embodiment 1 will be described. Fig. 1 is a configuration diagram illustrating a defect inspection device 1 according to embodiment 1. As shown in Fig. 1, the defect inspection device 1 according to this embodiment includes an irradiation optical system 10, a filter unit 20, a detection optical system 30, and an image processing unit 40.

[0025] The irradiation optical system 10 irradiates the sample 50 placed on the stage 60 with excitation light EL. The irradiation optical system 10 may include a light source 11. The irradiation optical system 10 may also include optical members such as a filter, a mirror, and a lens. The irradiation optical system 10 irradiates the excitation light EL toward a SiC epitaxial wafer serving as the sample 50. The excitation light EL may include, for example, ultraviolet light that generates photoluminescence light PL from the SiC epitaxial wafer. That is, the excitation light EL has energy greater than the energy of the forbidden band width of SiC.

[0026] For example, the excitation light EL may be a laser light having a wavelength of 320 nm generated from a He-Cd laser, or a fourth harmonic laser light having a wavelength of 266 nm generated from a YAG laser. The excitation light EL may be ultraviolet light generated from a mercury xenon lamp. The irradiation optical system 10 may transmit a predetermined wavelength band in the excitation light EL by a filter. For example, when the light source 11 is a mercury xenon lamp, the excitation light EL may include a beam having a wavelength of 313 nm transmitted through a filter. The irradiation optical system 10 may have optical members such as a mirror and a lens on the optical path until the excitation light EL emitted from the light source 11 irradiates the sample 50. For example, the inspection surface of the sample 50 may be scanned with the excitation light EL by using a galvanometer mirror or the like. Alternatively, the inspection surface of the sample 50 may be scanned with the excitation light EL by moving the stage 60.

[0027] Here, for convenience in explaining the defect inspection apparatus 1, an XYZ Cartesian coordinate system is introduced. The direction perpendicular to the upper surface of the stage 60 is the Z-axis direction, and the plane parallel to the upper surface of the stage 60 is the XY plane. For example, the +Z-axis direction is the upward direction, and the -Z-axis direction is the downward direction. Note that upward and downward are directions for convenience in explaining the defect inspection apparatus 1, and do not indicate the directions in which the actual defect inspection apparatus 1 is disposed.

[0028] The filter section 20 controls the wavelength band that transmits the photoluminescent light PL generated from the sample 50. Specifically, for example, the filter section 20 may have a filter 21 that transmits a wavelength band including 420 nm or more and 430 nm or less in the photoluminescent light PP. The filter 21 transmits a wavelength band including 420 nm or more and 430 nm or less in the photoluminescent light P1. For example, the filter 21 may transmit a wavelength band including a central wavelength of 425±13 nm, or may transmit a wavelength band including a central wavelength of 425±5 nm.

[0029] The filter unit 20 may also include a filter 22 that transmits a wavelength band including near-infrared light. The filter 22 transmits a wavelength band including, for example, 700 nm to 1100 nm. The filter unit 20 may select the filter 21 or the filter 22 depending on the wavelength band to be detected.

[0030] The detection optical system 30 includes a detector 31. The detection optical system 30 detects the photoluminescence light P1 transmitted through the filter unit 20. In addition to the detector 31, the detection optical system 30 may include optical members such as a lens and a mirror that guide the photoluminescence light P1 transmitted through the filter unit 20 to the detector 31.

[0031] The detector 31 may include 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, or may include a line sensor in which multiple imaging elements are arranged in a row.

[0032] The image processing unit 40 forms an image from the photoluminescence light PL detected by the detection optical system 30. Then, the image processing unit 40 determines defects captured in the formed image. The image processing unit 40 is, for example, a computer having a CPU, memory, storage, etc. The image processing unit 40 may have an input / output unit including a display for displaying the image.

[0033] 2 is a cross-sectional view illustrating a sample 50 to be inspected in the defect inspection device 1 according to the first embodiment. As shown in FIG. 2, the sample 50 includes a SiC substrate 51, a buffer layer 52, and a drift layer 53. The sample 50 has a structure in which the SiC substrate 51, the buffer layer 52, and the drift layer 53 are stacked. The buffer layer 52 is formed on the SiC substrate 51, and the drift layer 53 is formed on the buffer layer 52. Thus, the buffer layer 52 is disposed between the SiC substrate 51 and the drift layer 53.

[0034] The SiC substrate 51 serves as a base for manufacturing thin films of the buffer layer 52 and the drift layer 53 by epitaxial growth. The SiC substrate 51 is a substrate including a SiC single crystal (4H-SiC). There is no particular limit to the method for manufacturing the SiC substrate 51. For example, the SiC substrate 51 can be obtained by slicing a SiC ingot obtained by a sublimation method or the like. The SiC substrate 51 may have BPDs along the (0001) plane (c-plane).

[0035] The buffer layer 52 and the drift layer 53 are thin films including SiC single crystal (4H-SiC) deposited on the SiC substrate 51 by epitaxial growth. Specifically, the epitaxial layer including the buffer layer 52 and the drift layer 53 may be formed on the SiC substrate 51 having a growth plane that is offset from the (0001) plane in the <11-20> direction. The epitaxial layer may be 4H-SiC grown on the SiC substrate 51 by step-flow growth (lateral growth from atomic steps).

[0036] The buffer layer 52 is a layer formed by epitaxially growing an epitaxial layer containing a high concentration of impurities on the SiC substrate 51. The doped impurity may be nitrogen, boron, titanium, vanadium, aluminum, gallium, phosphorus, or the like. The buffer layer 52 functions to suppress minority carriers from reaching the drift layer 53 in a power device, for example. By stacking the buffer layer 52, when a current flows in the forward direction of a bipolar device having BPDs, the minority carriers can be prevented from reaching the BPDs present in the SiC substrate 51.

[0037] The drift layer 53 is a layer obtained by epitaxially growing an epitaxial layer containing a low concentration of impurities on the buffer layer 52. The impurities to be doped may be nitrogen, boron, titanium, vanadium, aluminum, gallium, phosphorus, or the like, as in the above-mentioned buffer layer 52. The drift layer 53 is doped with impurities at a lower concentration than the buffer layer 52, and functions as, for example, a drift layer of a SiC-MOSFET.

[0038] The impurity concentration of the buffer layer 52 is 1×10 18 cm -3 For example, the impurity concentration of the buffer layer 52 is preferably 5×10 17 cm -3 More than 1×10 19 cm -3 The impurity concentration of the drift layer is 1×10 16 cm -3 For example, the impurity concentration of the drift layer is about 1×10 15 cm -3 5×10 or more 17 cm -3 is less than.

[0039] The thickness D2 of the buffer layer 52 is, for example, 1 μm. Note that the thickness D2 of the buffer layer 52 is not limited to 1 μm. The thickness D1 of the drift layer 53 is, for example, 10 μm. Note that the thickness D1 of the drift layer 53 is not limited to 10 μm. It is desirable that the thickness D1 of the drift layer 53 is different from the thickness D2 of the buffer layer 52. For example, it is desirable that the thickness D1 of the drift layer 53 is larger than the thickness D2 of the buffer layer 52, but this is not restrictive.

[0040] In the sample 50, a part of the BPD is inherited to the drift layer 53. That is, the defect K1 formed in the sample 50 includes, for example, a BPD that connects from the buffer layer 52 to the drift layer 53. Specifically, the defect K1 includes a BPD that passes from the SiC substrate 51 through the buffer layer 52 to reach the drift layer 53. In such a defect K1, the angle formed between the direction in which the BPD extends and the upper surface (called the basal surface) of the SiC substrate 51 is an offset angle θ. That is, the BPD extends in a direction at the offset angle θ with respect to the basal surface. The BPD inherited to the drift layer 53 emits photoluminescence light PL with a wavelength of 710 nm due to recombination of carriers generated by irradiation of the sample 50 with the excitation light EL.

[0041] On the other hand, BPDs may be converted to TEDs at the interface 54 between the buffer layer 52 and the drift layer 53. In this case, the defect K2 formed in the sample 50 includes the BPDs in the buffer layer 52 and the TEDs in the drift layer 53. Specifically, the defect K2 includes the BPDs in the buffer layer 52 and the TEDs converted from the BPDs at the interface 54 between the buffer layer 52 and the drift layer 53. In the defect K2, the angle between the extension direction of the BPDs in the buffer layer 52 and the basal plane is an offset angle θ. The BPDs in the buffer layer 102 before being converted at the interface 54 have a short carrier lifetime in the buffer layer 52, and therefore do not emit photoluminescence light PL even when the sample 50 is irradiated with excitation light EL.

[0042] Fig. 3 is a schematic diagram illustrating an image formed by the image processing unit 40 in the defect inspection apparatus 1 according to the embodiment 1. Fig. 3 is an image captured from the +Z axis direction formed from the photoluminescence light PL of the sample 50. For example, Fig. 3 shows one field of view during inspection, which is 1.75 mm square or 1.5 mm square.

[0043] As shown in Figure 3, when an image is formed from photoluminescence light PL that transmits a wavelength band including 420 nm or more and 430 nm or less, long and short linear defects that are darker (black) than the surroundings are observed in the image. For example, the black linear defect extends in the Y-axis direction. In the Y-axis direction, the length of the long linear defect is called the first length L1. The length of the short linear defect is called the second length L2.

[0044] Here, the thickness of the drift layer 53 is D1, the thickness of the buffer layer 52 is D2, the offset angle is θ, and the first length and the second length are L1 and L2 shown in the following formulas (1) and (2), respectively. Note that it is preferable that the thickness D1 of the drift layer 53 and the thickness D2 of the buffer layer 52 are different, but they may be the same thickness.

[0045] L1 = (D1 + D2) / tan θ (1) L2=D2 / tanθ (2)

[0046] In this case, the defect having a length of the first length L1 corresponds to defect K1 including a BPD connecting from the buffer layer 52 to the drift layer 53. The defect having a length of the second length L2 corresponds to defect K2 including a BPD in the buffer layer 52 and a TED in the drift layer 53. Therefore, when the length of the defect captured in the image is the first length L1, the image processing unit 40 determines the defect as defect K1 including a BPD connecting from the buffer layer 52 to the drift layer 53. On the other hand, when the length of the defect captured in the image is the second length, the image processing unit 40 determines the defect as defect K2 including a BPD in the buffer layer 52 and a TED in the drift layer 53.

[0047] The length of the defect K1 is not limited to the first length L1, but may include the first length L1 including an unavoidable error due to thickness variations and the like that occur when forming the buffer layer 52 and the drift layer 53. Similarly, the length of the defect K2 is not limited to the second length L2, but may include the second length L2 including an unavoidable error. The unavoidable error depends on conditions such as the thicknesses of the buffer layer 52 and the drift layer 53 when they are formed, and may be, for example, ±10% or ±5% of the first length L1 and the second length L2.

[0048] Therefore, when the length of the defect captured in the image falls within a predetermined first range including the first length L1, the image processing unit 40 determines the defect as a defect K1 including a BPD connecting from the buffer layer 52 to the drift layer 53. When the length of the defect captured in the image falls within a predetermined second range including the second length L2, which is different from the first range, the image processing unit 40 determines the defect as a defect K2 including a BPD in the buffer layer 52 and a TED in the drift layer 53. The first range is a range of the first length L1 including an unavoidable error, for example, a range from (first length - unavoidable error) to (first length L1 + unavoidable error). The second range is a range of the second length L2 including an unavoidable error, for example, a range from (second length L2 - unavoidable error) to (second length L2 + unavoidable error).

[0049] The length of the defect may be calculated from the number of pixels in the area detected as a defect by the image processing unit 40. The image processing unit 40 may also determine the defect captured in the image by using an algorithm that has been machine-trained in advance using the plurality of defects K1 belonging to the first range and the plurality of defects K2 belonging to the second range as learning data.

[0050] Next, the defect inspection method of this embodiment will be described. Fig. 4 is a flow chart illustrating the defect inspection method according to the embodiment 1. As shown in Fig. 4, the defect inspection method of this embodiment includes step S11 of irradiating the sample 50 with excitation light EL, step S12 of transmitting the photoluminescence light PL through the filter section 20, step S13 of detecting the photoluminescence light PL, step S14 of forming an image from the photoluminescence light PL, and step S15 of identifying defects captured in the image.

[0051] First, as shown in step S11, excitation light EL is irradiated onto the sample 50. The sample 50 includes a SiC substrate 51, a buffer layer 52 formed on the SiC substrate 51, and a drift layer 53 formed on the buffer layer 52. The impurity concentration of the drift layer is, for example, 1×10 15 cm -3 5×10 or more 17 cm -3 The impurity concentration of the buffer layer is, for example, less than 5×10 17 cm -3 More than 1×10 19 cm -3 The impurity concentration of the buffer layer 52 is therefore greater than the impurity concentration of the drift layer 53. The excitation light EL is irradiated by the irradiation optical system 10. The irradiation optical system 10 may scan the sample 50 with the excitation light EL. The sample 50 may be scanned with the excitation light EL by moving the stage 60. The sample 50 irradiated with the excitation light EL generates photoluminescence light PL.

[0052] Next, as shown in step S12, the photoluminescent light PL generated from the sample 50 is transmitted through the filter section 20. Specifically, the photoluminescent light PL generated from the sample 50 is transmitted through the filter section 20, which controls the wavelength band to be transmitted. For example, the filter section 20 transmits a wavelength band including 420 nm or more and 430 nm or less in the photoluminescent light PL by the filter 21.

[0053] Next, as shown in step S13, the photoluminescence light P1 transmitted through the filter unit 20 is detected. For example, the detector 31 in the detection optical system 30 detects the photoluminescence light PL transmitted through the filter .

[0054] Next, as shown in step S14, an image is formed from the detected photoluminescence light PL. Specifically, the image processing unit 40 forms an image from the photoluminescence light PL detected by the detection optical system 30 including the detector 31.

[0055] Next, as shown in step S15, the defect captured in the formed image is identified. For example, when the length of the defect captured in the image belongs to a predetermined first range including the first length L1, the image processing unit 40 may identify the defect as a defect K1 including a BPD connecting from the buffer layer 52 to the drift layer 53. When the length of the defect captured in the image belongs to a predetermined second range including the second length L2, which is different from the first range, the image processing unit 40 may identify the defect as a defect K2 including a BPD in the buffer layer 52 and a TED in the drift layer 53. In this manner, defects in the SiC epitaxial wafer can be inspected.

[0056] Next, the effects of this embodiment will be described. The defect inspection device 1 of this embodiment forms an image from photoluminescence light P1 having a wavelength band including 420 nm or more and 430 nm or less that is transmitted through the filter 21. Therefore, the image processing unit 40 can detect the BPD formed in the epitaxial layer as a black line-shaped defect in the formed image. In addition, the image processing unit 40 can identify the defect based on the length of the defect captured in the image. This makes it possible to identify defects in the SiC epitaxial wafer.

[0057] Furthermore, the defect inspection device 1 can identify BPDs in the buffer layer 52. Therefore, it is possible to identify BPDs present only in the buffer layer 52 that have been converted into TEDs at the interface 54 between the buffer layer 52 and the drift layer 53, and it is possible to improve the device characteristics of the drift layer 53.

[0058] (Embodiment 2) Next, a defect inspection device according to a second embodiment will be described. The defect inspection device of this embodiment changes the wavelength band of the photoluminescence light P1 transmitted by the filter section 20 from a wavelength band including 420 nm or more and 430 nm or less to a wavelength band including near-infrared light. FIG. 5 is a configuration diagram illustrating a defect inspection device according to the second embodiment. As shown in FIG. 5, the defect inspection device 2 of this embodiment changes the filter 21 in the filter section 20 to a filter 22, as compared to the above-mentioned defect inspection device 1.

[0059] The detection optical system 30 detects the photoluminescence light PL including near-infrared light that has passed through the modified filter unit 20. The image processing unit 40 forms an image from the detected photoluminescence light PL including near-infrared light. The image formed from the photoluminescence light PL including near-infrared light is called a near-infrared image. The image processing unit 40 identifies defects captured in the near-infrared image.

[0060] FIG. 6 is a schematic diagram illustrating an image formed by the image processing unit 40 in the defect inspection device 2 according to the second embodiment. FIG. 6 is a diagram in which the same position as FIG. 3 on the sample 50 is imaged. As shown in FIG. 6, the image processing unit 40 forms a near-infrared image from the photoluminescence light PL that transmits a wavelength band including near-infrared light. In this case, a linear defect is observed in the near-infrared image. The length of the linear defect is referred to as a third length L3. In FIG. 6, for convenience of explanation, the linear defect in the near-infrared image is shown by a black line as in FIG. 3.

[0061] The BPDs in the buffer layer 52 are not captured in the near-infrared image. The TEDs in the drift layer 53 are not captured in the near-infrared image. On the other hand, the BPDs in the drift layer 53 are captured in the near-infrared image.

[0062] Here, the thickness of drift layer 53 is D1, the thickness of buffer layer 52 is D2, the offset angle is θ, and the third length is L3 shown in the following formula (3). Note that it is desirable that the thickness D1 of drift layer 53 and the thickness D2 of buffer layer 52 are different.

[0063] L3=D1 / tanθ (3)

[0064] In this case, a defect having a length of the third length L3 corresponds to a defect K3 including a BPD in the drift layer 53. When the length of the defect is the third length L3, the image processing unit 40 determines that the defect is a defect K3 including a BPD in the drift layer 53. The length of the defect K3 is not limited to the third length L3, and may include the third length L3 including an unavoidable error due to thickness variations and the like that occur when forming the buffer layer 52 and the drift layer 53. Therefore, when the length of the defect captured in the near-infrared image is within a predetermined third range including the third length L3 and belongs to a third range different from the first range and the second range, the image processing unit 40 determines that the defect is a defect K3 including a BPD in the drift layer 53.

[0065] FIG. 7 is a diagram illustrating the appearance of BPD in defects K1 to K2 imaged by the defect inspection device 1 according to the first embodiment and the defect inspection device 2 according to the second embodiment. As shown in FIGS. 3 and 7, when a wavelength band including 420 nm or more and 430 nm or less is transmitted, both defects K1 and K2 are imaged in the image. On the other hand, as shown in FIGS. 6 and 7, when a wavelength band including near-infrared light is transmitted, defect K3 is imaged in the near-infrared image. Defects K1 and K2 are not imaged in the near-infrared image. Note that defect K3 is obtained by subtracting the portion of defect K2 from defect K1. Therefore, the third length L3 is the difference between the first length L1 and the second length L2.

[0066] The image processor 40 may also calculate the accuracy of the identified defects by comparing the number of defects K1 having a length that belongs to the first range with the number of defects K3 having a length that belongs to the third range. The closer the number of defects K1 and K3 are to each other, the higher the accuracy of the defect identification.

[0067] Next, the defect inspection method of this embodiment will be described. Fig. 8 is a flow chart illustrating a defect inspection method according to embodiment 2. As shown in Fig. 8, in addition to the above-mentioned steps S11 to S15, the defect inspection method of this embodiment includes step S16 of changing the wavelength band transmitted by filter section 20 to near-infrared light, step S17 of detecting near-infrared light, step S18 of forming a near-infrared image from the near-infrared light, and step S19 of identifying defects displayed in the image.

[0068] As shown in step S16, after step S15 of determining defects, the wavelength band transmitted through the filter unit 20 is changed from the wavelength band including 420 nm or more and 430 nm or less to a wavelength band including near-infrared light.

[0069] Next, as shown in step S17, the near-infrared light transmitted through the changed filter unit 20 is detected. Specifically, the detector 31 in the detection optical system 30 detects the near-infrared light transmitted through the filter 22 in the filter unit 20.

[0070] Next, as shown in step S18, the image processing unit 40 forms a near-infrared image from the near-infrared light detected by the detection optical system 30.

[0071] Next, as shown in step S19, the image processing unit 40 identifies the defect captured in the near-infrared image. Specifically, when the length of the defect captured in the near-infrared image falls within a predetermined third range including the third length L3, the image processing unit 40 identifies the defect as a defect K3 including a BPD in the drift layer 53. In this manner, the defect is identified, whereby the SiC epitaxial wafer can be inspected.

[0072] In addition, after step S19, the method may further include a step of calculating the accuracy of the determined defects by comparing the number of defects K1 having lengths belonging to the first range with the number of defects K3 having lengths belonging to the third range.

[0073] According to this embodiment, the defect inspection device 2 can distinguish the defect K3 captured in the near-infrared image. This makes it possible to detect BPD in the drift layer 53. In addition, it is possible to compare the defect K1 captured in the image through which a wavelength band including 420 nm or more and 430 nm or less is transmitted with the defect K3 captured in the near-infrared image, thereby improving the defect detection rate. Other configurations and effects are included in the description of the first embodiment.

[0074] Although the embodiments of the present disclosure have been described above, the present disclosure includes appropriate modifications that do not impair the objects and advantages thereof, and is not limited to the above-mentioned embodiments. In addition, combinations of the configurations of the first and second embodiments are also within the scope of the technical idea of ​​the present disclosure. [Explanation of symbols]

[0075] 1, 2 Defect inspection equipment 10 Irradiation optical system 11 Light source 20 Filter section 21, 22 Filter 30 Detection optical system 31 Detector 40 Image processing section 50 samples 51 SiC substrate 52 Buffer Layer 53 Drift Layer 54 Interface 60 Stages D1, D2 thickness EL excitation light K1, K2, K3 Defects L1 First length L2 Second length PL photoluminescence light

Claims

1. an irradiation optical system that irradiates an excitation light onto a sample including a silicon carbide substrate, a buffer layer formed on the silicon carbide substrate, and a drift layer formed on the buffer layer; a detection optical system for detecting photoluminescence light generated from the sample; an image processing unit that forms an image from the detected photoluminescence light and identifies defects captured in the formed image; an optical element that selectively guides light in a wavelength band including 420 nm or more and 430 nm or less in the photoluminescence light to the detection optical system; Equipped with the image processing unit determines whether the defect is the defect including a basal plane dislocation connecting from the buffer layer to the drift layer or the defect including the basal plane dislocation in the buffer layer and an edge dislocation in the drift layer based on a comparison between a length of the defect and a reference length based on the thickness and offset angle of the buffer layer. Defect inspection equipment.

2. When the thickness of the buffer layer is D2, the offset angle is θ, and the reference length is L2 as shown below, L2=D2 / tan θ When a length of the defect is longer than a length corresponding to the reference length, the image processing unit determines that the defect is the defect including a basal plane dislocation connecting from the buffer layer to the drift layer. The defect inspection device according to claim 1 .

3. When the thickness of the buffer layer is D2, the offset angle is θ, and the reference length is L2 as shown below, L2=D2 / tan θ When a length of the defect corresponds to the reference length, the image processing unit determines that the defect is the defect including the basal plane dislocation in the buffer layer and the edge dislocation in the drift layer. The defect inspection device according to claim 1 .

4. When the thickness of the drift layer is D1, the thickness of the buffer layer is D2, the offset angle is θ, and the reference length is L1 as shown below, L1=(D1+D2) / tanθ When a length of the defect is shorter than a length corresponding to the reference length, the image processing unit determines that the defect is the defect including the basal plane dislocation in the buffer layer and the edge dislocation in the drift layer. The defect inspection device according to claim 1 .

5. When the thickness of the drift layer is D1, the thickness of the buffer layer is D2, the offset angle is θ, and the reference length is L1 as shown below, L1=(D1+D2) / tanθ When a length of the defect corresponds to the reference length, the image processing unit determines that the defect is the defect including a basal plane dislocation connecting from the buffer layer to the drift layer. The defect inspection device according to claim 1 .

6. an irradiation optical system that irradiates an excitation light onto a sample including a silicon carbide substrate, a buffer layer formed on the silicon carbide substrate, and a drift layer formed on the buffer layer; a detection optical system for detecting photoluminescence light generated from the sample; an image processing unit that forms an image from the detected photoluminescence light and identifies defects captured in the formed image; an optical element that selectively guides light in a wavelength band including 420 nm or more and 430 nm or less in the photoluminescence light to the detection optical system; Equipped with When the thickness of the buffer layer is D2, the offset angle is θ, and the reference length is L2 shown below, L2=D2 / tan θ When a length of the defect is longer than a length corresponding to the reference length, the image processing unit determines that the defect is the defect including a basal plane dislocation connecting from the buffer layer to the drift layer. Defect inspection equipment.

7. an irradiation optical system that irradiates an excitation light onto a sample including a silicon carbide substrate, a buffer layer formed on the silicon carbide substrate, and a drift layer formed on the buffer layer; a detection optical system for detecting photoluminescence light generated from the sample; an image processing unit that forms an image from the detected photoluminescence light and identifies defects captured in the formed image; an optical element that selectively guides light in a wavelength band including 420 nm or more and 430 nm or less in the photoluminescence light to the detection optical system; Equipped with When the thickness of the buffer layer is D2, the offset angle is θ, and the reference length is L2 shown below, L2=D2 / tan θ When a length of the defect corresponds to the reference length, the image processing unit determines that the defect includes a basal plane dislocation in the buffer layer and an edge dislocation in the drift layer. Defect inspection equipment.

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