Polarizing microscope, crystal defect evaluation device, and crystal defect evaluation method

Abstract

A polarizing microscope (1) is provided with: a sample stage (4) on which a sample (8) is placed; a polarizer (3) provided on the light source side of the sample (8); and an analyzer (6) provided on the observation side of the sample (8). At least one of the polarizer (3) and the analyzer (6) is provided such that the polarization direction is inclined with respect to the optical main axis of the sample (8), or such that the included angle between the polarization direction of the analyzer (6) and the polarization direction of the polarizer (3) deviates from a right angle.

Description

Technical Field

[0001] The present invention relates to a technique for evaluating crystal defects using a polarizing microscope. Background Art

[0002] Power devices, which are semiconductor devices that convert and control electric power, are widely used in the fields of home appliances, industrial equipment, automobiles, railways, high-voltage direct current transmission, wind power generation, solar power generation, etc. Currently, silicon (Si) is mainly used in semiconductors for power devices, but with the goal of higher performance, silicon carbide (SiC) is attracting attention as a semiconductor material for next-generation power devices.

[0003] (Prior art literature)

[0004] (Patent Document)

[0005] Patent Document 1: "Polytype Control in SiC Crystal Growth - Proposal of a Dynamic Polytype Control Method (Taking 3C-SiC Solution Growth as an Example)", Journal of the Crystal Growth Society of Japan, Vol. 40, No. 4, pp. 253-260 Summary of the invention

[0006] (Problems to be solved by the invention)

[0007] With the advancement of SiC crystal growth technology, macroscopic defects have been greatly suppressed, but there are still many microscopic defects such as edge dislocation, screw dislocation, basal plane dislocation, etc., which have an adverse effect on the long-term reliability and characteristics of the device. It is necessary to accurately evaluate the defects of semiconductor crystals.

[0008] The present disclosure has been made in view of such problems, and an object of the present disclosure is to improve a technique for evaluating defects in a crystal.

[0009] (Measures taken to solve the problem)

[0010] In order to solve the above problem, a polarizing microscope of a certain aspect of the present disclosure comprises: a loading portion for loading a sample; a polarizer disposed on the light source side of the sample; and an analyzer disposed on the observation side of the sample. At least one of the polarizer and the analyzer is configured such that the polarization direction is tilted relative to the optical principal axis of the sample, or the angle between the polarization direction of the analyzer and the polarization direction of the polarizer deviates from a right angle.

[0011] Another aspect of the present disclosure is a crystal defect evaluation device including: an image acquisition unit that acquires an image observed by the polarizing microscope; and a defect evaluation unit that evaluates defects included in a sample based on the image acquired by the image acquisition unit.

[0012] Yet another aspect of the present disclosure is a method for evaluating crystal defects, including: obtaining an image observed by the polarizing microscope; and evaluating defects contained in a sample based on the obtained image.

[0013] Yet another aspect of the present disclosure is a method for evaluating crystal defects. The method includes: a step of obtaining an image of a sample observed by a polarizing microscope; and a step of evaluating defects contained in the sample based on the obtained image, wherein the obtained image is an image whose contrast is clear due to the deviation of the polarization direction of at least one of the polarizer and the analyzer of the polarizing microscope from the optical principal axis of the sample or the deviation from the orthogonal polarization of the polarizer of the analyzer.

[0014] Furthermore, any combination of the above components and conversion of the expression of the present disclosure among methods, apparatuses, systems, storage media, computer programs, etc. are also valid as modes of the present disclosure.

[0015] (Effects of the Invention)

[0016] According to the present disclosure, it is possible to improve the technology for evaluating defects in crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a diagram schematically showing the structure of a polarizing microscope according to an embodiment.

[0018] Figure 2 It is a diagram showing the structure of the control device involved in the embodiment.

[0019] Figure 3 It is a diagram showing the structure of a crystal defect evaluation device according to an embodiment.

[0020] Figure 4 The diagram shows polarization observation images of threading edge dislocations with different Burgers vector directions and polarization microscope images calculated in consideration of shear stress distribution in the XY plane.

[0021] Figure 5 The diagram shows a polarization observation image (a) actually measured of threading edge dislocations contained in a crystal and a polarization microscope image (b) calculated by also taking into account the shear stress distribution in the Z direction caused by the threading edge dislocations.

[0022] Figure 6 This is a diagram showing an actually measured polarization observation image of threading edge dislocations contained in a crystal.

[0023] Figure 7 This figure shows a polarizing microscope image calculated by also taking into account the shear stress distribution in the Z direction caused by the threading edge dislocation.

[0024] Figure 8 Graph showing the inclination angle of a threading edge dislocation.

[0025] Fig. 9 It is a flowchart showing the steps of the crystal defect evaluation method involved in the embodiment. DETAILED DESCRIPTION

[0026] In the present disclosure, a technique for evaluating defects in a crystal such as SiC using a polarizing microscope is described.

[0027] Figure 1 The structure of the polarization microscope according to the embodiment is schematically shown. The polarization microscope 1 includes a light source 2 , a polarizer 3 , a sample stage 4 , an objective lens 5 , an analyzer 6 , and an eyepiece 7 .

[0028] Light from the light source 2 passes through a sample 8 placed on a sample stage 4 and is observed through an objective lens 5 and an eyepiece 7. The polarizer 3 and the analyzer 6 are respectively disposed in front of and behind the sample stage 4, and transmit linearly polarized light whose electric field vibrates in only one direction. In the present embodiment, the sample 8 is observed in a state where the transmission axes of the polarizer 3 and the analyzer 6 are orthogonal to each other (crossed polarization).

[0029] When an optically isotropic sample having no anisotropy in refractive index is placed on the sample stage 4, the polarization state of the linearly polarized light emitted from the polarizer 3 does not change when passing through the sample, and therefore, the light that has passed through the sample does not pass through the analyzer 6 whose transmission axis is set to be orthogonal to the polarizer 3. Therefore, the image observed from the eyepiece 7 becomes a dark field.

[0030] When an optically anisotropic sample having birefringence in which the refractive index differs depending on the polarization direction is placed on the sample stage 4, when the vibration direction of the linearly polarized light emitted from the polarizer 3 coincides with the optical axis of the sample, the polarization state of the linearly polarized light does not change when passing through the sample, and thus, the image observed from the eyepiece 7 becomes a dark field, similar to the case of an optically isotropic sample. On the other hand, when the vibration direction of the linearly polarized light emitted from the polarizer 3 is different from the optical axis of the sample, the light emitted from the polarizer 3 is separated into two polarization components due to the birefringence of the sample when passing through the sample, and these polarization components interfere to change the polarization state, and thus, the light passing through the sample passes through the analyzer 6. Therefore, the image observed from the eyepiece 7 becomes a bright field, and a contrast of polarization intensity corresponding to the optical path difference (retardation) of the light separated into two is observed.

[0031] When a crystal contains defects, the stress generated by the defects causes birefringence, so contrast is observed using a polarizing microscope 1. Using this phenomenon, defects contained in crystals such as SiC can be observed non-destructively. Observation of dislocations in a crystal material using birefringence caused by stress is usually performed along the principal optical axis.

[0032] However, according to the research of the present inventors, it is clear that due to the deviation of the polarizer 3 from the extinction angle and the deviation of the analyzer 6 from the orthogonal polarization, a clearer contrast can be obtained in the polarization observation image. It is also clear that the result of theoretical calculation of the polarization microscope image of the crystal taking into account the shear stress distribution caused by defects in the crystal corresponds to the contrast observed by the polarization microscope 1. Therefore, by observing the sample with the polarization microscope 1 in which the polarizer 3 and the analyzer 6 are slightly offset from the extinction angle and the orthogonal polarization, and comparing the observed contrast with the calculation result of the polarization microscope image of the crystal taking into account the shear stress distribution caused by defects in the crystal, the defects in the crystal can be evaluated more accurately.

[0033] In the polarizing microscope 1 of the present embodiment, at least one of the polarizer 3 and the analyzer 6 is set so that the polarization direction is inclined relative to the optical principal axis of the sample 8, or the angle between the polarization direction of the analyzer 6 and the polarization direction of the polarizer 3 deviates from a right angle. According to the type, crystal structure, thickness of the sample 2, the type, size, number, orientation, etc. of the defects to be observed, the angle (deviation) between the polarization direction of the polarizer 3 or the analyzer 6 and the optical principal axis of the sample 8, and the angle (deviation) between the polarization direction of the polarizer 3 and the polarization direction of the analyzer 6 are adjusted so that a clearer contrast can be observed. The polarizer 3 and the analyzer 6 can be fixed at a predetermined angle, or the polarizer 3 and the analyzer 6 can be set to a variable angle. In the latter case, the polarizing microscope 1 is provided with a control device 10 for controlling the angle of the polarizer 3 or the analyzer 6.

[0034] Figure 2 The configuration of the control device according to the embodiment is shown. The control device 10 includes an input device 11 , a storage device 30 , and a processing device 20 .

[0035] The input device 11 transmits the instruction input input by the user of the polarizing microscope 1 to the processing device 20. The input device 11 can be a mouse, a keyboard, a touch pad, etc.

[0036] The storage device 30 stores programs, data, etc. used by the processing device 20. The storage device 30 may be a semiconductor memory, a hard disk, etc. The storage device 30 includes an angle information storage unit 31.

[0037] The angle information storage unit 31 is used to store the correspondence between the type, crystal structure, thickness, type, size, number, orientation of defects to be observed, and other information related to the sample 2 and the angle of the polarizer 3 or the analyzer 6.

[0038] The processing device 20 includes: a sample information acquisition unit 21, an angle determination unit 22, and an angle adjustment unit 23. These structures are implemented in hardware by arbitrary circuits, a CPU of a computer, a memory, other LSIs, etc., and in software by programs loaded into the memory, etc., but are described here by functional blocks implemented by these combinations. Therefore, it can be understood by those skilled in the art that these functional blocks can be implemented in various ways such as hardware alone or a combination of hardware and software.

[0039] The sample information acquisition unit 21 acquires information related to the sample 2 from the user via the input device 11. The sample information acquisition unit 21 acquires information such as the type, crystal structure, thickness, type, size, number, and orientation of defects to be observed of the sample 2.

[0040] The angle determination unit 22 determines the angle of the polarizer 3 or the analyzer 6 by referring to the angle information storage unit 31 based on the information on the sample 2 acquired by the sample information acquisition unit 21 .

[0041] The angle adjustment unit 23 controls a drive unit such as a motor for changing the angle of the polarizer 3 or the analyzer 6 to adjust the angle of the polarizer 3 or the analyzer 6 so that the angle of the polarizer 3 or the analyzer 6 becomes the angle determined by the angle determination unit 22 .

[0042] Thus, the angle of the polarizer 3 or the analyzer 6 can be adjusted according to the sample 2 so that the contrast corresponding to the defect in the sample 8 can be observed more clearly, thereby improving the accuracy of evaluating the defect.

[0043] Figure 3 The structure of the crystal defect evaluation device involved in the embodiment is shown. The crystal defect evaluation device 50 includes: a communication device 51, a display device 52, an input device 53, a storage device 70, and a processing device 60. The crystal defect evaluation device 50 can be a server device, a device such as a personal computer, or a mobile terminal such as a mobile phone terminal, a smart phone, or a tablet terminal.

[0044] The communication device 51 controls the communication with the polarizing microscope 1 and the like. The communication device 51 can communicate by any wired or wireless communication method. The display device 52 displays the image generated by the processing device 60. The display device 52 can be a liquid crystal display device, an OLED display device, etc. The input device 53 transmits the instruction input input by the user of the crystal defect evaluation device 50 to the processing device 60. The input device 53 can be a mouse, a keyboard, a touch pad, etc. The display device 52 and the input device 53 can be assembled as a touch panel.

[0045] The storage device 70 stores programs, data, etc. used by the processing device 60. The storage device 70 may be a semiconductor memory, a hard disk, etc. The storage device 70 includes a stress distribution storage unit 71.

[0046] The calculated image storage unit 71 stores information related to defects in the sample in association with polarized light microscope images calculated by taking into account the shear stress distribution generated in the sample due to the defects. The information related to the defects may be, for example, the type, number, size, position, shape, direction, angle, etc. of the defects. In order to evaluate the type, number, size, position, shape, direction, angle, etc. of the defects, the candidate image storage unit 71 stores a plurality of polarized light microscope images (hereinafter also referred to as "calculated images") calculated by changing at least one of the type, number, size, position, shape, direction, and angle of the defects.

[0047] The processing device 60 includes an image acquisition unit 61, a defect evaluation unit 62, and a polarization microscope image calculation unit 63. These structures are implemented in hardware by any circuit, a CPU of a computer, a memory, other LSIs, etc., and in software by a program loaded into the memory, etc., but the functional blocks implemented by these combinations are described here. Therefore, it can be understood by those skilled in the art that these functional blocks can be implemented in various ways such as hardware alone or a combination of hardware and software.

[0048] The image acquisition unit 61 acquires a polarization microscope image (hereinafter, may also be referred to as a “measured image”) of the crystal from the polarization microscope 1 and stores it in the storage device 70 .

[0049] The defect evaluation unit 62 evaluates defects contained in the sample 2 based on the polarizing microscope image obtained by the image acquisition unit 61. The defect evaluation unit 62 compares the measured image observed by the polarizing microscope 1 and the calculated image stored in the calculated image storage unit 71 to determine the calculated image similar to the measured image, and obtains information on defects corresponding to the determined calculated image. The defect evaluation unit 62 displays the information related to the obtained defects on the display device 52.

[0050] In order to retrieve a calculated image similar to the measured image, the defect evaluation unit 62 can use artificial intelligence that has undergone machine learning, etc. The defect evaluation unit 62 can determine the calculated image with high similarity to the measured image by calculating the sum of the absolute values ​​of the differences between the brightness values ​​of the measured image and the brightness values ​​of the calculated image, the sum of the squares of the differences, the normalized cross correlation, etc. The distribution of the brightness values ​​of the measured image varies depending on the measurement conditions, etc. Therefore, the defect evaluation unit 62 can normalize the brightness values ​​of the measured image and then compare it with the calculated image. The defect evaluation unit 62 can use the input measured image and use an evaluator for outputting the type, size, number, direction, etc. of the defect to evaluate the defect. In this case, the crystal defect evaluation device 50 can have a learning unit for artificial intelligence and an evaluator for machine learning image retrieval.

[0051] In order to improve the accuracy of defect evaluation based on polarizing microscope images, polarizing microscope images containing defects of various types, numbers, sizes, positions, shapes, directions, and angles are calculated and stored in the calculated image storage unit 71 as calculated images.

[0052] The polarizing microscope image calculation unit 63 calculates the polarizing microscope image of the sample in consideration of the shear stress distribution caused by the defects in the sample, and associates the calculation result with the information related to the defects and stores it in the calculated image storage unit 71. The calculated image may be obtained from another device and stored in the calculated image storage unit 71. In this case, the crystal defect evaluation device 50 may not include the polarizing microscope image calculation unit 63.

[0053] The polarizing microscope image calculation unit 63 calculates the refractive index of polarized light propagating in a crystal to which shear stress caused by defects is applied by solving theoretical formulas such as the refractive index ellipsoid equation, thereby calculating the polarizing microscope image of the sample. In the case where it is impossible or difficult to solve the theoretical formula analytically, the polarizing microscope image calculation unit 63 can use a numerical analysis method such as the finite element method to calculate the polarizing microscope image of the sample.

[0054] The following is a method for calculating a polarizing microscope image of a SiC crystal in consideration of the shear stress distribution caused by edge dislocations contained in the SiC crystal.

[0055] In the SiC substrate for power devices, a 4-degree off-angle is set from the (0001) plane to [11-20], and the substrate has optical anisotropy in the plane. If the direction parallel to the observation direction perpendicular to the substrate is set as the Z axis, the [1-100] in the plane perpendicular to the off-angle is set as the X axis, and the direction perpendicular to the X axis in the plane is set as the Y axis, the equation of the refractive index ellipsoid in the plane is as follows.

[0056] B1 0 X 2 +B2 0 Y 2 +2B6 0 XY=1

[0057] Among them, B1 0 =n n -2 、B2 0 =n e -2 、B6 0 =0,n n 、n e are the refractive indices of normal light and extraordinary light respectively.

[0058] Here, when stress is applied due to threading dislocation or the like, the equation of the refractive index ellipsoid is as follows.

[0059] B1 0 X 2+B2 0 Y 2 +2B6 0 XY=1

[0060] Among them, B m =B m 0 +Π mn σ n (m=1,2,6), mn , σ n They are the photoelastic tensor and stress tensor expressed by the following formulas respectively.

[0061] [Number 1]

[0062]

[0063] B1=B1 0 +p 11 σ xx +p 12 σ yy +p 13 σ zz

[0064] B2=B2 0 +p 12 σ xx +p 11 σ yy +p 13 σ zz

[0065] B6=(p 11 -p 12 )σ xy

[0066] Here, for simplicity, it is assumed that the stress caused by the defect is uniform in the Z direction. In addition, the method of calculating the polarization microscope image of the crystal taking into account the shear stress distribution in the Z direction is described later. The refractive index of the crystal to which stress is applied is obtained as the solution of the following characteristic equation.

[0067] [Number 2]

[0068]

[0069] The phase difference δ is proportional to the difference between the two refractive indices and can be expressed as follows.

[0070] [Number 3]

[0071]

[0072] Where, Δl is the thickness of the substrate, B aveis the arithmetic average of B1 and B2. In addition, the angle α between the optical principal axis direction and the X-axis satisfies the following formula.

[0073] 2α=tan -1 (2B6 / (B2-B1))

[0074] Here, the angle between the polarization direction of the polarizer 3 and the X-axis is set to β, and the angle between the polarization directions of the polarizer 3 and the analyzer 6 is set to π / 2+ε, considering the deviation of the polarizer 3 from β and the deviation of the analyzer 6 from the orthogonal polarization from ε. In this case, if the incident intensity is set to I0, the polarization intensity is as follows.

[0075] [Number 4]

[0076]

[0077] (1) Case ε = 0

[0078] When the deviation ε from the orthogonal polarization of the analyzer 6 is 0, the polarization intensity is as follows.

[0079] [Number 5]

[0080]

[0081] [Number 6]

[0082]

[0083] Among them, assuming that the birefringence caused by stress is sufficiently small compared to the birefringence caused by the deviation angle and β is close to 0, since B2-B1≒B2 0 -B1 0 , sin2β≒2β, cos2β≒1, therefore,

[0084] [Number 7]

[0085]

[0086] Since B2 0 -B1 0 >>B6, therefore,

[0087] [Number 8]

[0088]

[0089] The only thing that causes the contrast to change is the first term on the right, whose intensity is proportional to B6. The change in the background of the second term on the right is proportional to σ xy The contrast is inversely proportional to β. In the state of complete extinction with β = 0, the same as B6 is generated.2 Proportional contrast.

[0090] (2) When β = 0

[0091] When the deviation β of the polarization direction of the polarizer 3 from the X-axis is 0, the polarization intensity is as follows.

[0092] [Number 9]

[0093]

[0094] Among them, assuming that the birefringence caused by stress is sufficiently small compared to the birefringence caused by the deviation angle and β is close to 0, since B2-B1≒B2 0 -B1 0 , sinε≒ε, cos2ε≒1, so

[0095] [Number 10]

[0096]

[0097] Since B2 0 -B1 0 >>B6, therefore,

[0098] [Number 11]

[0099]

[0100] The first term on the right side is expressed as a constant value regardless of stress, and the second term on the right side is proportional to B6 (ie, the shear stress within the plane).

[0101] (3) ε≠0, β≠0

[0102] When both the deviation ε of the analyzer 6 from the orthogonal polarization and the deviation β of the polarization direction of the polarizer 3 from the X-axis are not 0, the polarization intensity is as follows.

[0103] [Number 12]

[0104]

[0105] When the conditions assumed in the above calculation are satisfied, it is considered that the contrast of the polarization intensity calculated as described above is observed in the image observed by the polarization microscope 1 .

[0106] The polarizing microscope image calculation unit 63 sets the type, number, size, position, shape, direction, angle, etc. of defects contained in the crystal, and calculates the shear stress distribution generated in the crystal due to the set defects. The polarizing microscope image calculation unit 63 calculates the polarizing microscope image as described above in consideration of the calculated shear stress distribution. The polarizing microscope image calculation unit 63 associates the calculated polarizing microscope image with the information related to the defect and stores it in the calculated image storage unit 71.

[0107] Next, a method for calculating a polarizing microscope image by further considering the shear stress distribution in the Z direction is described. By calculating a polarizing microscope image by considering not only the shear stress distribution in the XY plane caused by the defect but also the shear stress distribution in the Z direction, and comparing the calculated polarizing microscope image with the measured image observed by the polarizing microscope 1, it is possible to evaluate not only the XY shape of the defect contained in the crystal but also the three-dimensional shape.

[0108] The polarizing microscope image calculation unit 63 divides the crystal of the observation object into a plurality of regions in the Z direction, and calculates the propagation of polarized light when the polarized light passes through each region in stages. The number and thickness of the regions can be determined according to the type, number, size, position, shape, direction, angle, etc. of the defects to be evaluated, the required accuracy, etc.

[0109] The polarizing microscope image calculation unit 63 may discretely calculate the change in the refractive index of polarized light inside the sample, assuming that the stress distribution in the thickness direction of each region is uniform and birefringence occurs only at the boundary of the region. In this way, the calculation load can be suppressed and the three-dimensional shape of the defect can be evaluated with good accuracy. In this case, for each region, the birefringence generated at the boundary of the region is calculated based on the shear stress distribution in the surface of the boundary surface, as described above. First, the polarized light incident on the surface of the first layer is divided into normal light E0 and extraordinary light E1 due to birefringence. e The polarization microscope image calculation unit 63 calculates the normal light E0 and the extraordinary light E0 when the polarized light passes through the first layer by using the formula of equation 3. e Next, the normal light E0 incident on the boundary surface between the first layer and the second layer is divided into the normal light E' 0，1 and abnormal light E' e，1 , abnormal light E e Divided into normal light E' 0，2 and abnormal light E' e，2 The polarization microscope image calculation unit 63 synthesizes the light having the same refractive index as normal light E'0 (=E' 0，1 +E' 0，2 ) and abnormal light E' e (=E' e，1 +E'e，2 ). The polarization microscope image calculation unit 63 calculates the normal light E'0 and the extraordinary light E'0 when the polarized light passes through the second layer by using the formula of equation 3. e The polarization microscope image calculation unit 63 repeats the above calculation until the last layer, thereby calculating the phase difference accumulated in each layer. The polarization microscope image calculation unit 63 calculates the polarization microscope image of the crystal to be observed by calculating the polarization intensity of the polarized light passing through the analyzer 6 as described above. The polarization microscope image calculation unit 63 associates the calculated polarization microscope image with the information related to the defect and stores it in the calculated image storage unit 71.

[0110] [Example]

[0111] Polarized observation images of SiC crystals obtained using a polarizing microscope 1 were investigated. For the observation sample, a 4H-SiC substrate produced by chemical vapor deposition was used. As the polarizing microscope 1, a SiC crystal dislocation high-sensitivity visualization device XS-1 manufactured by Mipox Co., Ltd. was used. In addition to polarized observation, dislocations were evaluated by X-ray morphology observation using radiated light. In the X-ray morphology image, it can be seen that the contrast of the through-edge dislocation shows different contrasts depending on the direction of the Burgers vector. By observing the same position, the correspondence between the direction of the Burgers vector of the through-edge dislocation and the contrast of the polarized observation image was investigated.

[0112] Figure 4 The measured polarization observation images of the through-edge dislocation with different Burgers vector directions and the polarization microscope images calculated by assuming that the shear stress distribution in the Z direction is uniform as described above are shown. It can be seen that the measured polarization observation images of the edge dislocation correspond to the calculated polarization microscope images, and the Burgers vector of the through-edge dislocation can be determined from the polarization observation images. In addition, the SiC substrate contains a dislocation line

[0001] and a Burgers vector <0001> The +1 / 3<-1-120> dislocation (threading mixed dislocation) suggests that the blade-shaped component of the Burgers vector of the threading mixed dislocation can also be determined by polarization observation. Thus, it can be seen that by comparing the measured polarization observation image and the calculated polarization observation image, the blade-shaped component of the threading dislocation can be determined based on the observation image.

[0113] Figure 5 The polarization observation image (a) of the measured threading dislocations contained in the crystal and the polarization microscope image (b) calculated by considering the shear stress distribution in the Z direction caused by the threading dislocations. The tilt direction and angle of each threading dislocation use the values ​​reported in the published paper (R. Tanuma, et al. J. Appl. Phys. 124 (2018) 125703). Figure 5As shown, the contrast intensity of the measured image changes according to the direction of the Burgers vector, but the calculated image also reproduces the same contrast intensity tendency as the measured image. In addition, the contrast boundary of the measured image is tilted in b=1 / 3[11-20] and 1 / 3[-1-120], but the calculated image also reproduces the same contrast boundary direction and angle as the measured image. From the above results, it can be seen that the above calculation method can show the changes in the polarization image caused by the tilt direction and angle of the penetrating dislocation. By comparing the calculated image and the measured image, not only the Burgers vector of the penetrating dislocation can be evaluated, but also the tilt direction and angle of the penetrating dislocation can be evaluated.

[0114] Figure 6 Shown is a polarization observation image of actually measured threading edge dislocations contained in a crystal. Figure 7 The polarizing microscope image calculated by also considering the shear stress distribution in the Z direction caused by the threading edge dislocation is shown. Figure 8 As shown, the x and y coordinates of the direction vector ξ that tilts the unit vector of length 1 toward the dislocation line of the edge dislocation are ξ1 and ξ2, respectively. That is, the direction vector ξ is rotated from

[0001] to [11-20] by θ, and thus the x and y coordinates when rotated by ψ about

[0001] are [ξ1, ξ2] = [sinθcosψ, sinθsinψ]. Figure 7 The calculated image shown is an image calculated by changing ξ1 by 0.03 in the range of 0.09 to 0.27 and by changing ξ2 by 0.02 in the range of -0.04 to 0.04. If the measured image and the calculated image are compared, the calculated image corresponding to ξ1=0.04, ξ2=0.12 is most similar to the measured image. Therefore, ξ1 and ξ2 of the through-edge dislocation can be evaluated as ξ1=0.04, ξ2=0.12. Based on ξ1 and ξ2 and the above formula, the inclination angles θ and ψ of the through-edge dislocation can be calculated. As described above, the calculated image that is most similar to the measured image can also be automatically determined based on normalized cross-correlation, etc.

[0115] Fig. 9 This is a flowchart showing the steps of the crystal defect evaluation method involved in the embodiment. When the angle of the polarizer 3 or the analyzer 6 of the polarizing microscope 1 is variable, the control device 10 adjusts the angle of the polarizer 3 or the analyzer 6 according to the sample 2 (S10). When the angle of the polarizer 3 or the analyzer 6 of the polarizing microscope 1 is not variable, step S10 is omitted.

[0116] The image acquisition unit 61 of the crystal defect evaluation device 50 acquires a polarization microscope image of the crystal from the polarization microscope 1 (S12). The defect evaluation unit 62 evaluates defects included in the sample 2 based on the acquired polarization microscope image (S14). The defect evaluation unit 62 outputs the evaluation result (S20).

[0117] The present disclosure is described above based on the embodiment. It can be understood by those skilled in the art that the embodiment is an example, and the combination of each component and each processing process can produce various variations, and these variations all belong to the scope of the present disclosure.

[0118] The technology of this embodiment can also be used to evaluate defects in crystals of semiconductor materials other than silicon carbide.

[0119] (Industrial Applicability)

[0120] The present invention relates to a technique for evaluating defects in a crystal using a polarizing microscope.

[0121] (Explanation of Reference Numerals)

[0122] 1: polarizing microscope; 2: light source; 2: sample; 3: polarizer; 4: sample stage;

[0123] 5: objective lens; 6: analyzer; 7: eyepiece; 8: sample; 10: control device;

[0124] 21: sample information acquisition unit; 22: angle determination unit; 23: angle adjustment unit;

[0125] 31: Angle information storage unit; 50: Crystal defect evaluation device; 61: Image acquisition unit;

[0126] 62: Defect evaluation unit; 63: Polarization microscope image calculation unit; 71: Calculation image storage unit.

Claims

1. A polarizing microscope, characterized in that: have: A loading portion for loading a sample; a polarizer disposed on the light source side of the sample; and an analyzer, which is disposed on the observation side of the sample, At least one of the polarizer and the analyzer is configured such that the polarization direction is tilted relative to the optical principal axis of the sample, or such that the angle between the polarization direction of the analyzer and the polarization direction of the polarizer deviates from a right angle.

2. The polarizing microscope according to claim 1, wherein: The polarization direction of at least one of the polarizer and the analyzer is changeable, The polarizing microscope further includes a control device for controlling a polarization direction of at least one of the polarizer and the analyzer.

3. The polarizing microscope according to claim 2, wherein: The control device controls the polarization direction of at least one of the polarizer and the analyzer based on the type, crystal structure, thickness and orientation of the sample and at least one of the type, size, number and orientation of defects to be observed.

4. A crystal defect evaluation device, wherein: have: An image acquisition unit that acquires an image observed by the polarizing microscope according to any one of claims 1 to 3; and The defect evaluation unit evaluates defects included in the sample based on the image acquired by the image acquisition unit.

5. The crystal defect evaluation device according to claim 4, wherein: The defect evaluation unit compares a polarization microscope image of the sample calculated in consideration of stress distribution caused by a defect included in the sample with the image acquired by the image acquisition unit, thereby evaluating the defect included in the sample.

6. The crystal defect evaluation device according to claim 5, wherein: The defect evaluation unit determines a polarizing microscope image similar to the image acquired by the image acquisition unit from among multiple polarizing microscope images of the sample calculated by changing at least one of the type, size, shape, direction, and angle of the defects contained in the sample, thereby evaluating at least one of the type, size, direction, and angle of the defects contained in the sample.

7. The crystal defect evaluation device according to claim 5 or 6, wherein: The crystal defect evaluation device further includes a polarization microscope image calculation unit that calculates a polarization microscope image of the sample in consideration of stress distribution caused by defects included in the sample.

8. The crystal defect evaluation device according to claim 7, wherein: The polarizing microscope image calculation unit sets information on defects contained in the sample, and calculates propagation of polarized light inside the sample in consideration of stress distribution caused by the set defects, thereby calculating a polarizing microscope image of the sample containing the set defects.

9. The crystal defect evaluation device according to claim 7 or 8, wherein: The polarization microscope image calculation unit divides the sample into a plurality of regions in the thickness direction and calculates the propagation of polarized light in each region in stages, thereby calculating a polarization microscope image of the sample.

10. The crystal defect evaluation device according to claim 9, wherein: The polarization microscope image calculation unit calculates the propagation of polarized light inside the sample on the assumption that stress distribution in the thickness direction of each region is uniform and birefringence occurs only at the boundary of the region.

11. The crystal defect evaluation device according to claim 10, wherein: The polarization microscope image calculation unit calculates a change in refractive index due to birefringence generated at a boundary of a region based on an in-plane stress distribution of the boundary surface.

12. The crystal defect evaluation device according to any one of claims 9 to 11, wherein: The defect evaluation unit evaluates a three-dimensional shape of a defect included in the sample.

13. The crystal defect evaluation device according to any one of claims 4 to 12, wherein: The image acquisition unit acquires an image of a silicon carbide (SiC) crystal having an off angle, The defect evaluation unit evaluates defects included in the crystal of the silicon carbide.

14. A crystal defect evaluation method, characterized in that: have: A step of obtaining an image observed by a polarizing microscope according to any one of claims 1 to 3; and The step of evaluating defects contained in the sample based on the acquired image.

15. A crystal defect evaluation method, characterized in that: have: The step of obtaining an image of the sample observed by a polarizing microscope; and a step of evaluating defects contained in the sample based on the acquired image, The acquired image is an image with clear contrast due to the deviation of the polarization direction of at least one of the polarizer and the analyzer of the polarizing microscope from the optical principal axis of the sample or the deviation of the orthogonal polarization of the polarizer from the analyzer.

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