Crack detection device and method

Abstract

To provide a crack detection device and method capable of detecting an inclined state of a crack with respect to a thickness direction of a workpiece.SOLUTION: A crack detection device 10 includes oblique illumination means for irradiating a workpiece having a crack formed therein with first detection light and second detection light from a mutually different oblique direction, and a crack inclination state detection unit 550 for detecting an inclination state of the crack with respect to a thickness direction of the workpiece based on respective reflected light of the first detection light and the second detection light.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a crack detection device and method, and more particularly to a crack detection device and method for non-destructively detecting the depth position of a crack formed inside a workpiece. [Background technology]

[0002] Conventionally, there is known a laser processing device (also called a laser dicing device) that irradiates a workpiece such as a semiconductor wafer with a laser beam along a planned dividing line by focusing the laser beam on the inside of the workpiece, thereby forming a laser processing area that serves as a starting point for cutting within the workpiece along the planned dividing line. The workpiece with the laser processing area formed therein is then divided along the planned dividing line by a dividing process such as expanding or breaking, and separated into individual chips (see, for example, Patent Document 1).

[0003] When a laser processing area is formed on a workpiece using a laser processing device, a crack propagates from the laser processing area in the thickness direction of the workpiece. The crack formed inside the workpiece becomes the starting point when the workpiece is divided, so the degree of crack propagation affects the quality of the chips after the workpiece is divided.

[0004] Therefore, after forming the laser processing area using a laser processing device, by detecting the depth (depth position) of the crack formed inside the workpiece before the cutting process, it is possible to predict whether the workpiece will be successfully divided into chips during the cutting process.

[0005] Patent document 1 discloses a crack detection device that detects the depth of a crack formed inside a workpiece by illuminating the workpiece with detection light in an oblique manner and receiving light reflected from the workpiece. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-133997 Summary of the Invention [Problem to be solved by the invention]

[0007] When forming a crack, the processing line may meander due to vibrations of the laser processing device itself, resulting in the crack being inclined relative to the thickness direction of the workpiece. If the crack that serves as the starting point for the separation is significantly inclined, the workpiece will be separated at a significantly inclined angle relative to the thickness direction along the crack. As a result, the thickness of the resulting chips may be uneven, which can lead to problems such as chipping. Therefore, in order to successfully separate the workpiece, it is desirable for the crack that serves as the starting point for the separation to be formed linearly along the thickness direction of the workpiece.

[0008] However, although the crack detection device described in Patent Document 1 can detect the depth (depth position) of a crack, it does not take into consideration the fact that a crack formed inside a workpiece may be inclined. Therefore, even if a crack formed inside a workpiece is inclined, it is difficult to grasp the crack state of the crack. Therefore, there is a problem in that it is not possible to accurately predict whether the workpiece will be successfully divided into chips during the cleaving process.

[0009] The present invention has been made in consideration of these circumstances, and aims to provide a crack detection device and method capable of detecting the inclination state of a crack in the thickness direction of a workpiece, and ultimately to make it possible to more accurately predict whether or not the workpiece will be successfully divided into chips during the cutting process. [Means for solving the problem]

[0010] In order to solve the above problem, a crack detection device according to a first aspect of the present invention comprises an oblique illumination means for irradiating a workpiece having a crack formed therein with first detection light and second detection light from different oblique directions, a first crack detection means for detecting a first crack length, which is the length of the crack in the thickness direction of the workpiece, based on a first reflected light of the first detection light from the workpiece, a second crack detection means for detecting a second crack length, which is the length of the crack in the thickness direction of the workpiece, based on a second reflected light of the second detection light from the workpiece, and a crack inclination state detection means for detecting the inclination state of the crack relative to the thickness direction of the workpiece based on the first crack length and the second crack length.

[0011] The crack length is detected using first reflected light and second reflected light of first detection light and second detection light irradiated from different oblique directions onto the workpiece, and a first crack length and a second crack length are obtained, respectively. If the crack is inclined toward the irradiation direction of either the first detection light or the second detection light, a difference will occur between the detected first crack length and the detected second crack length. By utilizing this, the crack detection device according to the first aspect can detect the inclination of the crack relative to the thickness direction of the workpiece based on the first crack length and the second crack length. This ultimately makes it possible to more accurately predict whether the workpiece will be successfully divided into chips during the cleaving process.

[0012] Preferably, the crack inclination state detection means compares the first crack length with the second crack length and determines the inclination direction of the crack based on the comparison result. For example, if the crack is inclined toward the irradiation direction of the first detection light out of the first and second detection lights, the detected first crack length will be shorter than the detected second crack length. Utilizing this, the crack inclination state detection means can determine the inclination direction of the crack based on the comparison result of the first crack length with the second crack length.

[0013] Preferably, the crack inclination state detection means determines that the crack is inclined when a difference between the first crack length and the second crack length is greater than a first threshold value. Preferably, the crack inclination state detection means determines that the crack is not inclined when a difference between the first crack length and the second crack length is smaller than a second threshold value.

[0014] Preferably, when the incident angle of the first detection light is α degrees, the incident angle of the second detection light is β degrees, the first crack length is KL(B), and the second crack length is KL(C), the crack inclination state detection means calculates the inclination angle θ of the crack using the following equation (1).

[0015]

number

[0016] Preferably, when the incident angle of the first detection light and the incident angle of the second detection light are the same angle α degrees, the tilt state detection means calculates the tilt angle θ of the crack by the following formula (2).

[0017]

number

[0018] In this way, when the incident angles of the first detection light and the second detection light are known, the crack inclination state detection means can calculate the inclination angle θ of the crack from Equation (1) or Equation (2) using the first crack length and the second crack length, which in turn makes it possible to more accurately predict whether the cutting into chips will be successful in the cutting process.

[0019] In order to solve the above problem, a crack detection method according to a second aspect of the present invention includes an oblique illumination step of irradiating a workpiece having a crack formed therein with first and second detection lights from different oblique directions, a first crack detection step of detecting a first crack length, which is the length of the crack in the thickness direction of the workpiece, based on a first reflection of the first detection light from the workpiece, a second crack detection step of detecting a second crack length, which is the length of the crack in the thickness direction of the workpiece, based on a second reflection of the second detection light from the workpiece, and a crack inclination detection step of detecting an inclination of the crack with respect to the thickness direction of the workpiece based on the first and second crack lengths. The crack detection method according to the second aspect can also achieve the same effects as the crack detection device according to the first aspect. [Effects of the Invention]

[0020] According to the present invention, since the inclination state of the crack can be detected, it becomes possible to more accurately predict whether the separation into chips in the cleaving process will be successful. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a block diagram showing a crack detection device according to one embodiment of the present invention. [Figure 2] FIG. 2 is an explanatory diagram showing a state in which the workpiece is subjected to oblique illumination with detection light. [Figure 3] FIG. 3 is an explanatory diagram showing a state in which the workpiece is subjected to oblique illumination with detection light. [Figure 4] FIG. 4 is an explanatory diagram showing a state in which the workpiece is subjected to oblique illumination with detection light. [Figure 5] FIG. 5 is a diagram showing the state of reflected light received by the photodetector (corresponding to FIG. 2). [Figure 6] FIG. 6 is a diagram showing the state of reflected light received by the photodetector (corresponding to FIG. 3). [Figure 7] FIG. 7 is a diagram showing the state of reflected light received by the photodetector (corresponding to FIG. 4). [Figure 8] FIG. 8 is a diagram for explaining the path of light reflected from the workpiece and reaching the pupil of the objective lens. [Figure 9] FIG. 9 is a functional block diagram of the control unit. [Figure 10] FIG. 10 is a diagram illustrating the principle of detecting the inclination angle of a crack. [Figure 11] FIG. 11 is a diagram illustrating the principle of detecting the inclination angle of a crack. [Figure 12] FIG. 12 is a diagram showing the relationship between the length of a crack detected in the first region, the length of a crack detected in the second region, and the inclination angle of the crack. [Figure 13] FIG. 13 is a flowchart showing the flow of a method for detecting the tilt state of a crack K formed inside a wafer W. [Figure 14] FIG. 14 is a graph showing an example of the results of actual crack detection in the cases where the crack K is not inclined with respect to the thickness direction of the wafer W and where it is inclined. DETAILED DESCRIPTION OF THE INVENTION

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A crack detection device and method according to an embodiment of the present invention will now be described with reference to the accompanying drawings. First, an overview of the crack detection device will be described.

[0023] [Crack detection device] FIG. 1 is a block diagram showing a crack detection device according to one embodiment of the present invention.

[0024] The crack detection device 10 is a device used in combination with a laser processing device (not shown) that forms a laser processing area inside a wafer W, which is a workpiece, and is provided, for example, so as to be movable integrally with the processing head of the laser processing device. In the following explanation, the components related to the crack detection device 10 will be explained, and the configuration of the laser processing device will not be explained.

[0025] The crack detection device 10 according to this embodiment detects the depth of a crack K formed inside a wafer W, such as a silicon wafer, by irradiating a detection light L1 onto the wafer W and detecting reflected light L2 from the wafer W. In the following description, a three-dimensional Cartesian coordinate system is used in which a stage 510 on which the wafer W is placed is a plane parallel to the XY plane and the Z direction is the thickness direction of the wafer W. In addition, in FIG. 1, the wafer W is placed on the stage 510 so that the bottom surface Wa of the wafer W (the surface in contact with the stage 510) is the top surface (device surface) of the wafer W and the top surface Wb of the wafer W is the back surface (the surface opposite the device surface) of the wafer W.

[0026] As shown in Figure 1, the crack detection device 10 of this embodiment includes a light source unit 100, an illumination optical system 200, an interface detection optical system 300, a crack detection optical system 400, a control unit 500, a focal point position moving mechanism 502, an objective lens 504, an operation unit 506, and a display unit 508.

[0027] The light source unit 100 emits detection light L1. The detection light L1 is used to detect the interface position of the wafer W and to detect cracks K formed inside the wafer W. Here, when the wafer W is a silicon wafer, light that is transparent to the wafer W, for example, infrared light with a wavelength of 1,000 nm or more, is used as the detection light L1.

[0028] The light source unit 100 includes light sources 102A, 102B, and 102C and a half mirror 104. The light sources 102A, 102B, and 102C and the half mirror 104 are arranged along a main optical axis AX that is coaxial with the lens optical axis of the objective lens 504.

[0029] The light sources 102A, 102B, and 102C emit detection light L1 along a main optical axis AX. As the light sources 102A, 102B, and 102C, for example, a laser light source (infrared laser light source, laser diode) or an LED (Light Emitting Diode) light source can be used.

[0030] The light source 102A has a laser aperture capable of illuminating substantially the entire surface of the objective lens pupil 504a of the objective lens 504. The light source 102A is used for interface detection, which will be described later.

[0031] The light sources 102B and 102C each have a laser aperture capable of illuminating only a portion of the objective lens pupil 504a of the objective lens 504 that is decentered from the main optical axis AX (lens optical axis). The light sources 102B and 102C are used for crack detection, which will be described later.

[0032] In this embodiment, the aperture for interface detection (light source 102A) and the aperture for crack detection (light sources 102B and 102C) are provided separately, but the present invention is not limited to this. For example, one aperture may be used for both purposes, and a light blocking means may be used to switch between the aperture for interface detection and the aperture for crack detection.

[0033] The half mirror 104 reflects the detection light L1 emitted from the light source 102A for interface detection and transmits the detection light L1 emitted from the light sources 102B and 102C for crack detection. Although not shown in the drawings, the detection light L1 emitted from the light sources 102A, 102B, and 102C will be referred to as L1(A), L1(B), and L1(C), respectively.

[0034] In this embodiment, a total reflection mirror or a dichroic mirror can be used instead of the half mirror 104. In this case, a mirror is inserted in the optical path at the position of the half mirror 104 during interface detection, and the mirror is removed from the optical path during crack detection.

[0035] The light sources 102A, 102B, and 102C are each connected to a control unit 500, and the control unit 500 controls the emission of the light sources 102A, 102B, and 102C.

[0036] The control unit 500 is realized by, for example, a personal computer, a workstation, a PLC (Programmable Logic Controller), etc. The control unit 500 includes a CPU (Central Processing Unit) that controls the operation of each part of the crack detection device 10, a ROM (Read Only Memory), a storage device (e.g., an HDD (Hard Disk Drive) or an SSD (Solid State Drive)) that stores a control program, and an SDRAM (Synchronous Dynamic Random Access Memory) that can be used as a working area for the CPU. The control unit 500 accepts operation input from an operator via an operation unit 506, and transmits control signals corresponding to the operation input to each part of the crack detection device 10 to control the operation of each part.

[0037] The operation unit 506 is a means for accepting operation inputs from an operator, and includes, for example, a keyboard, a mouse, or a touch panel.

[0038] The display unit 508 is a device that displays an operation GUI (Graphical User Interface) and images (for example, crack detection results) for operating the crack detection device 10. As the display unit 508, for example, a liquid crystal display can be used.

[0039] The illumination optical system 200 guides the detection light L1 emitted from the light source unit 100 to the objective lens 504. The illumination optical system 200 includes relay lenses 202 and 206 and a mirror 204 (for example, a total reflection mirror).

[0040] The detection light L1 emitted from the light source unit 100 passes through the relay lens 202 and is reflected by the mirror 204, thereby bending the optical path. The detection light L1 reflected by the mirror 204 passes through the relay lens 206, and is then reflected by the half mirror 304 and the half mirror 302 in this order, before being emitted toward the objective lens 504.

[0041] The return light (observation light) reflected by the wafer W and transmitted through the half mirror 302 can be observed using an observation optical system 600 (for example, a photodetector, etc.). When the observation optical system 600 is not used, a dichroic mirror or a total reflection mirror can be used instead of the half mirror 302.

[0042] The objective lens 504 collects (focuses) the detection light L1 emitted from the illumination optical system 200 onto the wafer W. The objective lens 504 is disposed at a position facing the wafer W, and is disposed coaxially with the main optical axis AX.

[0043] The focal point position moving mechanism 502 changes the position of the focal point of the detection light L1 in the Z direction (the optical axis direction of the objective lens 504). The focal point position moving mechanism 502 includes an actuator (not shown) that moves the objective lens 504 in the Z direction. Here, a case where a piezoelectric actuator is used will be described as an example, but any actuator can be used. The focal point position moving mechanism 502 moves the objective lens 504 in the Z direction by driving the piezoelectric actuator under the control of the control unit 500. This changes the relative distance in the Z direction between the objective lens 504 and the wafer W, making it possible to adjust (fine-tune) the position of the focal point of the detection light L1 in the Z direction.

[0044] The focal point position moving mechanism 502 may also include a Z drive mechanism that moves the crack detection device 10 in the Z direction relative to the stage 510. The Z drive mechanism moves the crack detection device 10 in the Z direction, thereby performing Z-direction alignment (coarse adjustment) between the objective lens 504 and the wafer W with a larger adjustment range than the piezoelectric actuator.

[0045] As described above, when the position adjustment (coarse adjustment) of the focal point by the Z drive mechanism and the position adjustment (fine adjustment) of the focal point by the piezoelectric actuator are combined, the degree of freedom (adjustment range) in adjusting the position of the focal point of the detection light L1 in the Z direction is increased compared to when only the piezoelectric actuator is used, which makes it possible to detect cracks in wafers W of various thicknesses.

[0046] The Z drive mechanism may be a mechanism that drives the stage 510 in the Z direction, or a mechanism that drives both the crack detection device 10 and the stage 510 in the Z direction. The Z drive mechanism may also serve as a drive mechanism that moves the processing head of the laser processing device.

[0047] The reflected light L2 collected by the objective lens 504 and reflected by the wafer W is guided to the interface detection optical system 300 and the crack detection optical system 400, and is used to detect the interface and cracks of the wafer W, respectively.

[0048] [Crack detection procedure] In this embodiment, an example is described in which the interface position of the underside Wa of the wafer W (the surface in contact with the stage 510, for example, the front surface (device surface) of the wafer W) is detected, and then the crack depth is detected based on the interface position of the underside Wa of the wafer W.

[0049] In this embodiment, the crack depth is detected based on the lower surface Wa of the wafer W, but the present invention is not limited to this. For example, the crack depth may be detected based on the upper surface Wb of the wafer W (the back surface of the wafer W), or the average value of the crack depths detected based on the interface positions of both the lower surface Wa and the upper surface Wb of the wafer W may be calculated.

[0050] [Interface detection optical system] First, an outline of wafer W interface detection using a confocal focus mechanism will be described, which will be described in more detail later.

[0051] The interface detection optical system 300 is an optical system for detecting the interface (lower surface Wa or upper surface Wb) of the wafer W, and includes a half mirror 302, a half mirror 304, a relay lens 306, a half mirror 308, and a photodetector 310.

[0052] When detecting the lower surface Wa of the wafer W as the interface of the wafer W, the control unit 500 causes the light source 102A to emit light and irradiate the detection light L1(A) onto the wafer W. Here, the control unit 500 and the interface detection optical system 300 each function as a part of the interface detection means.

[0053] The detection light L1(A) (first detection light) from the light source 102A is laser light having an aperture of approximately the same size as the objective lens pupil 504a of the objective lens 504, and is reflected successively by the half mirror 304 and the half mirror 302 and guided to the objective lens 504. The detection light L1(A) is irradiated onto approximately the entire surface of the objective lens pupil 504a of the objective lens 504.

[0054] Here, the reflected light of the detection light L1(A) reflected by the wafer W is referred to as L2(A) (first reflected light). The reflected light L2(A) is reflected by the half mirror 302, passes through the half mirror 304, and is then guided to the relay lens 306. The reflected light L2(A) that has passed through the relay lens 306 is reflected by the half mirror 308 and is then guided to the photodetector 310.

[0055] The photodetector 310 is a device for receiving reflected light L2(A) from the wafer W and detecting the interface of the wafer W, and includes a detector body 310A and a pinhole panel 310B.

[0056] As the detector main body 310A, a photodetector (for example, a photodiode) that converts received light into an electrical signal and outputs it to the control unit 500, an infrared camera, or the like can be used.

[0057] The pinhole panel 310B has a pinhole formed therein for transmitting a portion of the incident light. The pinhole panel 310B is disposed upstream of the light receiving surface of the detector body 310A, and is disposed so that the pinhole of the pinhole panel 310B is positioned on the optical axis of the reflected light L2(A). The position of the pinhole of the pinhole panel 310B is optically conjugate with the focal point (front focal position) of the objective lens 504 (confocal pinhole). The size of the pinhole of the pinhole panel 310B is adjusted to approximately the diffraction limit of the objective lens 504.

[0058] The reflected light L2(A) reflected by the wafer W is focused at the position of a pinhole in the pinhole panel 310B, which is optically conjugate with the focusing point of the objective lens 504. When the focusing point of the objective lens 504 coincides with the lower surface Wa of the wafer W, which serves as the reflecting surface, the light beam of the detection light L1(A) is reflected by the lower surface Wa of the wafer W, becomes a parallel light beam, and returns after passing through the objective lens 504. Therefore, the signal S output from the detector main body 310A has a sharp peak when the focusing point of the objective lens 504 coincides with the position of the lower surface Wa of the wafer W, which serves as the reflecting surface.

[0059] The control unit 500 changes the relative distance between the objective lens 504 and the wafer W using the focal point position moving mechanism 502 while irradiating the wafer W with the detection light L1(A) from the light source 102A, thereby moving the position of the focal point of the detection light L1(A) (i.e., the front focal position of the objective lens 504) in the Z direction. This causes the focal point of the detection light L1(A) to be scanned in the Z direction. The control unit 500 detects the reflected light L2(A) from the wafer W when the focal point of the detection light L1(A) is scanned in the Z direction using the photodetector 310, and detects the interface position Z(0) of the underside Wa of the wafer W by detecting the peak of the signal from this photodetector 310.

[0060] In this embodiment, the interface of the wafer W is detected using the confocal method, but the present invention is not limited to this. For example, other focus detection methods such as the astigmatism method and the white light interferometry may be used.

[0061] [Crack detection optical system] Next, a description will be given of the detection of a crack K formed inside the wafer W. For ease of understanding, the description will be given here without taking into consideration the inclination of the crack K relative to the thickness direction of the wafer W.

[0062] The crack detection optical system 400 includes a relay lens 402 and photodetectors 404 and 406 .

[0063] When detecting a crack K formed inside the wafer W, the control unit 500 causes the light sources 102B and 102C to emit light and irradiate the wafer W with detection light L1(B) and L1(C) (second detection light). Here, the control unit 500 and the crack detection optical system 400 each function as part of a crack detection means. The light sources 102B and 102C each have a laser aperture at a position offset from the main optical axis AX. As a result, the detection light L1(B) and L1(C) that are eccentric with respect to the main optical axis AX are irradiated onto the wafer W. The light source unit 100, the illumination optical system 200, and the objective lens 504 are an example of an oblique illumination means.

[0064] The detection lights L1(B) and L1(C) are reflected by the wafer W, resulting in reflected lights L2(B) and L2(C) (second reflected lights). After being reflected by the half mirror 302, the reflected lights L2(B) and L2(C) are transmitted through the half mirror 304, the relay lens 306, and the half mirror 308 in this order, and then enter the relay lens 402. The reflected lights L2(B) and L2(C) transmitted through the relay lens 402 are received by the photodetectors 404 and 406.

[0065] In the interface detection optical system 300, a total reflection mirror or a dichroic mirror can be used instead of the half mirror 308. In this case, a mirror is inserted in the optical path at the position of the half mirror 308 during interface detection, and the mirror is removed from the optical path during crack detection.

[0066] The photodetectors 404 and 406 are devices that receive reflected light L2(B) and L2(C) from the wafer W and detect cracks K inside the wafer W. As the photodetectors 404 and 406, a photodetector (e.g., a photodiode) that converts the received light into an electrical signal and outputs it to the control unit 500, an infrared camera, or the like can be used.

[0067] The photodetectors 404 and 406 are arranged at positions conjugate with the objective lens pupil 504a, and are further arranged at positions offset from the optical axis of the objective lens 504 so as to receive the detection light beams L1(B) and L1(C).

[0068] 2 to 4 are explanatory diagrams showing the state when the detection light L1 is obliquely illuminated onto the wafer W. Fig. 2 shows a case where a crack K is present at the focal point of the objective lens 504, Fig. 3 shows a case where the crack K is not present at the focal point of the objective lens 504, and Fig. 4 shows a case where the focal point of the objective lens 504 coincides with the crack depth (position of the bottom end of the crack) of the crack K.

[0069] 5 to 7 are diagrams showing the state of the reflected light L2 received by the photodetectors 404 and 406, and correspond to the cases shown in FIGS. 2 to 4, respectively.

[0070] 8 is a diagram for explaining the path of reflected light L2 from the wafer W reaching the objective lens pupil 504a. Note that here, a case will be described in which detection light L1 passes through a first region G1 on one side (the right side in FIG. 8) of the objective lens pupil 504a, and oblique illumination is performed on the wafer W.

[0071] 2, if a crack K is present at the focal point of the objective lens 504, the detection light L1 is totally reflected by the crack K, and the reflected light L2 travels along a path on the same side of the optical path of the detection light L1 with respect to the main optical axis AX, and becomes a component that reaches an area of ​​the objective lens pupil 504a on the same side as the detection light L1. That is, as shown in Fig. 8, if the path of the detection light L1 when the detection light L1 from the light source unit 100 is irradiated onto the wafer W via the objective lens 504 is R1, the reflected light L2 that is totally reflected by the crack K inside the wafer W travels along a path R2 on the same side of the main optical axis AX as the path R1 of the detection light L1 (the right side in Fig. 8), and passes through a first area G1 of the objective lens pupil 504a.

[0072] 3, when no crack K is present at the focal point of the objective lens 504, the detection light L1 is reflected by the underside Wa of the wafer W, and the reflected light L2 is a component that reaches a region of the objective lens pupil 504a on the opposite side to the detection light L1. That is, as shown in Fig. 8, the reflected light L2 reflected by the underside Wa of the wafer W follows a path R3 on the opposite side of the main optical axis AX (the left side in Fig. 8) from the path R1 of the detection light L1, and passes through a second region G2 of the objective lens pupil 504a.

[0073] 4, when the focal point of the objective lens 504 coincides with the lower end position of the crack K, the detection light L1 is split into a reflected light component L2a and a non-reflected light component L2b. The reflected light component L2a is totally reflected by the crack K, then reflected by the lower surface Wa, and reaches an area of ​​the objective lens pupil 504a on the same side as the detection light L1, while the non-reflected light component L2b is not totally reflected by the crack K, but is reflected by the lower surface Wa of the wafer W, and reaches an area of ​​the objective lens pupil 504a on the opposite side to the detection light L1. That is, as shown in Figure 8, of the reflected light L2, the reflected light component L2a that is totally reflected by the crack K inside the wafer W follows a path R2 on the same side of the main optical axis AX (the right side in Figure 8) as the path R1 of the detection light L1 and passes through a first region G1 of the objective lens pupil 504a, while the non-reflected light component L2b that is not totally reflected by the crack K and is reflected by the underside Wa of the wafer W follows a path R3 on the opposite side of the main optical axis AX (the left side in Figure 8) from the path R1 of the detection light L1 and passes through a second region G2 of the objective lens pupil 504a.

[0074] The photodetectors 404 and 406 are disposed at positions optically conjugate with the first region G1 and the second region G2 of the objective lens pupil 504a, respectively, so that the photodetectors 404 and 406 can selectively receive light that has passed through the first region G1 and the second region G2 of the objective lens pupil 504a, respectively.

[0075] 2 (where crack K is present at the focal point of objective lens 504), reflected light L2 is incident on light receiving surface 404C of photodetector 404, out of photodetectors 404 and 406. Therefore, as shown in FIG. 5, the level of the detection signal output from light receiving surface 404C of photodetector 404 becomes higher than the level of the detection signal output from light receiving surface 406C of photodetector 406.

[0076] 3 (where crack K is not present at the focal point of objective lens 504), the reflected light is incident on light-receiving surface 406C of photodetector 406, of photodetectors 404 and 406. Therefore, as shown in FIG. 6, the level of the detection signal output from light-receiving surface 406C of photodetector 406 is higher than the level of the detection signal output from light-receiving surface 404C of photodetector 404.

[0077] 4 (where the focal point of the objective lens 504 coincides with the lower end position of the crack K), the components L2a and L2b of the reflected light L2 are incident on the light receiving surfaces 404C and 406C of the photodetectors 404 and 406, respectively. Therefore, as shown in FIG. 7, the levels of the detection signals output from the light receiving surfaces 404C and 406C of the photodetectors 404 and 406 become approximately equal.

[0078] In this way, the amount of light received by the light receiving surfaces 404C and 406C of the photodetectors 404 and 406 changes depending on whether or not a crack K is present at the focal point of the objective lens 504. In this embodiment, this property is utilized to detect the crack depth (the crack bottom end position or the crack top end position) of a crack K formed inside the wafer W.

[0079] Specifically, when the detection signal outputs from the light receiving surfaces 404C and 406C of the photodetectors 404 and 406 are D1 and D2, respectively, the evaluation value S for determining the presence of a crack K at the focal point of the objective lens 504 can be expressed by the following equation:

[0080] S = (D1 - D2) / (D1 + D2) ... (1) In equation (1), when the condition S=0 is satisfied, that is, when the amount of light received by the light receiving surfaces 404C and 406C of the photodetectors 404 and 406 is the same, the focal point of the objective lens 504 and the bottom end position of the crack (or the top end position of the crack) are coincident.

[0081] The control unit 500 (see Figure 1) controls the focal point position moving mechanism 502 (focal point changing means) to move the focal point of the detection light L1 in the Z direction, sequentially changing it from the interface position of the underside Wa of the wafer W to the thickness direction (Z direction) of the wafer W, while sequentially acquiring detection signals output from the light receiving surfaces 404C and 406C of the photodetectors 404 and 406, and calculating the evaluation value S shown in equation (1) based on these detection signals.By evaluating this evaluation value S and the focal point position information, the crack depth (bottom end position or top end position of the crack) of the crack K can be detected.

[0082] The crack depth may be detected based on either surface of the wafer W. For example, the crack depth may be detected based on the top surface Wb of the wafer W, or based on the bottom surface Wa of the wafer W. It is also possible to take the average value of the crack depths detected based on the interface positions of both the top surface Wb and the bottom surface Wa of the wafer W.

[0083] [Controller function configuration] 9 is a functional block diagram of the control unit 500. As shown in FIG. 9, the control unit 500 includes an interface detection unit 520, a first crack detection unit 530, a second crack detection unit 540, and a crack inclination state detection unit 550.

[0084] The interface detection unit 520 detects the peak of the detection signal level from the detection signal (focus signal; light intensity signal of reflected light L2(A) from the wafer W) output from the photodetector 310 when the focal point of the detection light L1(A) is scanned in the Z direction, and detects the position of the objective lens 504 corresponding to the peak value as the position of the interface of the wafer W.

[0085] The first crack detection unit 530 detects the positions of the upper and lower ends (both ends) Kt and Kb of the crack K based on a change in the level of the detection signal output from the photodetector 404. This detection result corresponds to the positions of the upper and lower ends Kt and Kb of the crack K detected on the first region G1 side. Furthermore, the first crack detection unit 530 detects the length of the crack K in the thickness direction of the wafer W (first crack length) based on the positions of the upper and lower ends Kt and Kb of the crack K detected on the first region G1 side.

[0086] The second crack detection unit 540 detects the positions of the upper and lower ends Kt and Kb of the crack K based on a change in the level of the detection signal output from the photodetector 406. This detection result corresponds to the positions of the upper and lower ends Kt and Kb of the crack K detected on the second region G2 side. Furthermore, the second crack detection unit 540 detects the length of the crack K in the thickness direction of the wafer W (second crack length) based on the positions of the upper and lower ends Kt and Kb of the crack K detected on the second region G2 side.

[0087] The crack inclination state detection unit 550 detects the inclination state of the crack K relative to the thickness direction of the wafer W based on the first crack length detected by the first crack detection unit 530 and the second crack length detected by the second crack detection unit 540.

[0088] More specifically, the crack inclination state detection unit 550 is equipped with an inclination direction determination unit 552 that compares the first crack length detected by the first crack detection unit 530 with the second crack length detected by the second crack detection unit 540, and determines the inclination direction of the crack K relative to the thickness direction of the wafer W based on the comparison result.

[0089] Furthermore, the crack inclination state detection unit 550 is equipped with an inclination angle calculation unit 554 that calculates the inclination angle of the crack K relative to the thickness direction of the wafer W based on the incident angle of the detection light L1 (L1(B) and L1(C)) relative to the main optical axis AX, the length of the crack K detected on the first region G1 side, and the length of the crack K detected on the second region G2 side.

[0090] The inclination state (inclination direction and inclination angle) of the crack K detected by the crack inclination state detection unit 540 (inclination direction determination unit 552 and inclination angle calculation unit 554 ) is output to the display unit 508 .

[0091] [Detection principle of crack inclination angle] Next, the principle of detecting the inclination angle and inclination direction of the crack K performed by the crack inclination state detection unit 540 and the method of calculating the inclination angle will be described in detail. First, the principle of detecting the inclination angle of the crack will be outlined using Figures 10 and 11. Figure 10 is a diagram showing the geometric positional relationship between the crack K and the detection lights L1(B) and L1(B) when the crack K is not inclined with respect to the thickness direction of the wafer W (Z direction, parallel to the main optical axis AX).

[0092] 10, reference numeral 10A indicates the overall positional relationship of the crack K, the detection light L1(B), and L1(B) relative to the objective lens 504, reference numeral 10B indicates in more detail the positional relationship between the crack K and the detection light L1(B) relative to the objective lens 504 (the positional relationship with respect to the first region G1 side of the objective lens pupil 504a), and reference numeral 10C indicates in more detail the positional relationship between the crack K and the detection light L1(C) relative to the objective lens 504 (the positional relationship with respect to the second region G2 side of the objective lens pupil 504a). It is assumed that the detection light L1(B) is irradiated at a known angle of incidence α (degrees) with respect to the main optical axis AX (which overlaps with the optical axis of the objective lens 504), and the detection light L1(C) is irradiated at a known angle of incidence β (degrees) with respect to the main optical axis AX.

[0093] 2 to 4, in crack detection, the objective lens 504 and the wafer W are aligned so that the crack K is on the main optical axis AX, and then the wafer W is irradiated with detection light L1 (L1(B) and L1(C)) that is decentered with respect to the main optical axis AX. Then, the control unit 500 moves the objective lens 504 in the thickness direction (Z direction) of the wafer W, and detects reflected light L2 (L2(B) and L2(C)) at the position of the focal point of each objective lens 504.

[0094] 10, when the crack K is not inclined with respect to the thickness direction of the wafer W, the upper and lower ends Kt and Kb of the crack K formed inside the wafer W are located on the main optical axis AX, and the entire crack K almost completely overlaps with the main optical axis AX. Therefore, as shown by the reference symbols 10B and 10C, the positions Pt(B) and Pb(B) of the upper and lower ends of the crack K detected on the first region G1 side coincide with the positions Pt(C) and Pb(C) of the upper and lower ends of the crack K detected on the second region G2 side.

[0095] Therefore, the distance KL(B) between the positions Pt(B) and Pb(B) of the upper and lower ends of the crack K detected on the first region G1 side (which is the length of the crack K detected on the first region G1 side and corresponds to the first crack length) is the same as the distance KL(C) between the positions Pt(C) and Pb(C) of the upper and lower ends of the crack K detected on the second region G2 side (which is the length of the crack K detected on the second region G2 side and corresponds to the second crack length).

[0096] Fig. 11 shows the geometric positional relationship of the crack K and the detection lights L1(B) and L1(B) with respect to the objective lens 504 when the crack K is inclined toward the first region G1 at an inclination angle θ (degrees) with respect to the thickness direction of the wafer W. As in Fig. 10, in Fig. 11, reference numeral 11A indicates the overall positional relationship of the crack K and the detection lights L1(B) and L1(B) with respect to the objective lens 504, reference numeral 11B indicates the positional relationship with respect to the first region G1 side of the objective lens pupil 504a, and reference numeral 11C indicates the positional relationship with respect to the second region G2 side of the objective lens pupil 504a.

[0097] In Fig. 11, the geometric positional relationship between the objective lens 504, the detection light L1(B), and the detection light L1(C) is the same as in Fig. 10, and therefore a description thereof will be omitted. In Fig. 11, it is assumed that the objective lens 504 and the wafer W are aligned so that the bottom end Kb of the crack K is on the main optical axis AX.

[0098] First, the first region G1 side will be described using reference numeral 11B. When the crack K is inclined with respect to the thickness direction of the wafer W, as shown in reference numeral 11B in Fig. 11, if the position of the intersection of the detection light L1(B) passing through the upper end Kt of the crack K and the main optical axis AX (the optical axis of the objective lens 504) is Pt(B), when crack detection is performed in this embodiment, the position Pt(B) on the main optical axis AX is detected as the position of the upper end Kt of the crack K detected using the detection light L1(B) on the first region G1 side. The detected position Pt(B) at this time is lower than the actual position of the upper end Kt of the crack K.

[0099] As shown by the reference symbol 11C, when the crack K is inclined with respect to the thickness direction of the wafer W on the second region G2 side as on the first region G1 side, if the position of the intersection of the detection light L1(C) passing through the upper end Kt of the crack K and the main optical axis AX is Pt(C), when crack detection is performed in this embodiment, the position Pt(C) on the main optical axis AX is detected as the position of the upper end Kt of the crack K detected using the detection light L1(C) on the second region G2 side. The detected position Pt(C) at this time is higher than the actual position of the upper end Kt of the crack K.

[0100] Furthermore, since the lower end Kb of the crack K is aligned on the main optical axis AX, the Z-direction position Pb(B) of the lower end Kb of the crack K detected on the first region G1 side is approximately the same as the position Pb(C) of the lower end Kb of the crack K detected on the second region G2 side.

[0101] Therefore, when the crack K is inclined toward the first region G1 in the thickness direction of the wafer W, the distance KL(B) between the positions Pt(B) and Pb(B) of the upper and lower ends of the crack K detected on the first region G1 side is shorter than the distance KL(C) between the positions Pt(C) and Pb(C) of the upper and lower ends of the crack K detected on the second region G2 side.

[0102] Conversely, KL(B) will be longer than KL(C) if the crack K is inclined toward the second region G2 with respect to the thickness direction of the wafer W. This is self-evident, so a description of this case will be omitted.

[0103] In this way, when the crack K is inclined with respect to the thickness direction of the wafer W, a difference occurs between the crack length KL(B) detected on the first region G1 side and the crack length KL(C) detected on the second region G2 side. The control unit 500 can use this difference to detect the inclination state (inclination direction and inclination angle) of the crack K.

[0104] [Calculation method for crack inclination angle] Next, a method for calculating the inclination angle of crack K will be specifically described using Fig. 12. When crack K and detection lights L1(B) and L1(B) have the geometric positional relationship shown in Fig. 11 with respect to objective lens 504, it is possible to create a triangle as shown in Fig. 12 from the lengths KL(B) and KL(C) of the detected crack and the angles α, β, and θ.

[0105] Based on the triangle shown in FIG. 12, the inclination angle θ of the crack K can be expressed by the following equation (2) using the sine law.

[0106]

number

[0107] Therefore, the inclination angle calculation unit 554 (see FIG. 9) of the crack inclination state detection unit 550 can calculate the inclination angle θ by substituting the known incident angles α and β and the detected crack lengths KL(C) and KL(B) into equation (2). Also, as described above, the inclination direction determination unit 552 (see FIG. 9) of the crack inclination state detection unit 550 can detect whether the crack K is inclined toward the first region G1 side or the second region G2 side by determining which of the crack lengths KL(B) and KL(C) is longer.

[0108] Here, when the incident angle α of the detection light L1(B) is the same as the incident angle β of L1(C) (α=β), equation (2) can be simplified to the following equation (3).

[0109]

number

[0110] From this equation (3), it can be seen that when the length of the crack K detected on the first region G1 side and the length of the crack K detected on the second region G2 side are the same, θ = 0 (zero), and therefore it can be confirmed that the crack K is not inclined in the thickness direction.

[0111] [Method for detecting the inclination of a crack] Next, a method (one example of a crack detection method) for detecting the inclination state of a crack K formed inside the wafer W will be described using the crack detection device 10 of this embodiment. Fig. 13 is a flowchart showing the flow of the method for detecting the inclination state of a crack K formed inside the wafer W.

[0112] First, as described using Figures 2 to 8, the interface detection unit 520 detects the position of the interface that serves as a reference for the height position, for example, the position of the underside Wa of the wafer W, based on the detection signal output from the photodetector 310 when the focal point of the detection light L1(A) is scanned in the Z direction (step S10).

[0113] Subsequently, detection lights L1(B) and L1(C) that are decentered with respect to the main optical axis AX are irradiated onto the wafer W from the light sources 102B and 102C, respectively (step S12).

[0114] Next, the first crack detection unit 520 sequentially moves the focal point of the detection light L1(B) relative to the position of the underside Wa in the thickness direction of the wafer W, while detecting the reflected light L2(B) of the detection light L1(B) reflected by the wafer W with each photodetector 404 of the crack detection optical system 400. At this time, the first crack detection unit 520 detects the positions Pt(B) and Pb(B) of the upper and lower ends of the crack K as the amount of movement (piezo movement amount, objective lens movement amount) from the wafer underside, which is the reference, based on the change in the level of the detection signal. Furthermore, the first crack detection unit 520 detects the crack length KL(B), which is the length of the crack K in the thickness direction of the wafer W, from the positions Pt(B) and Pb(B) (step S14).

[0115] Similarly, the second crack detection unit 530 sequentially moves the focal point of the detection light L1(C) relatively in the thickness direction of the wafer W using the position of the lower surface Wa as a reference, and detects the reflected light L2(C) of the detection light L1(C) reflected by the wafer W with each photodetector 406 of the crack detection optical system 400. Then, the second crack detection unit 530 detects the positions Pt(C) and Pt(C) of the upper and lower ends of the crack K based on the level of the detection signal, and further detects the crack length KL(C), which is the length of the crack K in the thickness direction of the wafer W from the positions Pt(C) and Pb(C) (step S16).

[0116] Furthermore, the crack inclination state detection unit 550 detects the inclination state of the crack K relative to the thickness direction of the wafer W based on the crack length KL(B) detected by the first crack detection unit 520 and the crack length KL(C) detected by the second crack detection unit 530 (step S18).

[0117] More specifically, the crack inclination state detection unit 550 determines that the crack K is inclined with respect to the thickness direction when the difference between the crack length KL(B) and the crack length KL(C) is greater than a predetermined threshold (first threshold).

[0118] Alternatively, the crack inclination state detection unit 550 may determine that the crack K is not inclined relative to the thickness direction when the difference between the crack length KL(B) and the crack length KL(C) is smaller than a predetermined threshold (second threshold).

[0119] In addition, according to the embodiment in which the inclination state of the crack K is determined using the first threshold value and the second threshold value as described above, it is possible to perform accurate determination even for a state in which the inclination of the crack K is so small that it can be considered that there is no inclination (i.e., a level that does not affect the quality of the chip after division), compared to an embodiment in which whether or not there is a difference between the crack length KL(B) and the crack length KL(C) is simply compared. Furthermore, the first threshold value and the second threshold value may be the same value or different values.

[0120] In addition, the inclination direction determination unit 552 of the crack inclination state detection unit 550 compares the crack length KL(B) with the crack length KL(C), and based on the comparison result, determines the inclination direction of the crack K, that is, whether the crack K is inclined toward the first region G1 side or the second region G2 side.

[0121] Furthermore, if the crack K is inclined, the inclination angle calculation unit 554 of the crack inclination state detection unit 550 can calculate the inclination angle θ of the crack K by substituting the detected lengths KL(B) and KL(C) of the crack K into equation (2) or equation (3).

[0122] When the crack K is inclined, the position Pt(B) of the upper end Kt of the crack K detected on the first region G1 side does not coincide with the position Pt(C) of the upper end Kt of the crack K detected on the second region G2 side, but the crack inclination state detection unit 550 can easily calculate the actual position of the upper end Kt of the crack K using trigonometric functions from the detected length KL(B) or KL(C) of the crack K and the inclination angle θ (see the triangle shown in FIG. 12). Therefore, even when the crack K is inclined, the actual depth position and length of the crack K can be accurately calculated.

[0123] [Specific example] 14, a specific example of crack detection will be described for the cases where the crack K is not inclined and where it is inclined with respect to the thickness direction of the wafer W. In the graphs indicated by reference numerals 14A and 14B in FIG. 14, the horizontal axis represents the movement amount of the objective lens 504 (the piezoelectric movement amount of the focal point position moving mechanism 502) indicating the position of the focal point of the detection light L1(B) and L1(C) (the focal point of the objective lens 504), and the vertical axis represents the level (intensity) of the detection signal of each of the photodetectors 404 and 406.

[0124] The solid line indicates the detection signal by the photodetector 404, which corresponds to the detection result obtained on the first region G1 side. The dotted line indicates the detection signal by the photodetector 406, which corresponds to the detection result obtained on the second region G2 side.

[0125] In crack detection, half of the detection light L1(B) and L1(C) are blocked by the upper and lower ends Kt and Kb of the crack K, so the position of the objective lens 504 when the level of the detection signal of the photodetectors 404 and 406 is halved (i.e., the difference between the maximum signal level and the minimum signal level is halved) corresponds to the positions of the upper and lower ends Kt and Kb of the crack.

[0126] Reference numeral 14A in Fig. 14 is a graph showing the results of crack detection when the crack K is not inclined with respect to the thickness direction of the wafer W, as shown in Fig. 10. As shown by reference numeral 14A, when the crack K is not inclined with respect to the thickness direction of the wafer W, the positions Pt(B) and Pb(B) of the upper and lower ends of the crack K detected on the first region G1 side are approximately the same as the positions Pt(C) and Pb(C) of the upper and lower ends of the crack K detected on the second region G2 side.

[0127] Therefore, the length KL(B) of the crack K detected on the first region G1 side is approximately equal to the length KL(C) of the crack K detected on the second region G2 side. As a result, the crack inclination state detection unit 550 can detect that the crack K is not inclined with respect to the thickness direction of the wafer W (the inclination angle θ is approximately 0 degrees).

[0128] Reference numeral 14B in Fig. 14 is a graph showing the results of crack detection when the crack K is inclined toward the first region G1 at an inclination angle θ with respect to the thickness direction of the wafer W, as shown in Fig. 11. Even when the crack K is inclined with respect to the thickness direction of the wafer W, the lower end Kb of the crack K is aligned on the main optical axis AX (the optical axis of the objective lens 504), and therefore, as shown by reference numeral 14B, the Z-direction position Pb(B) of the lower end Kb of the crack K detected on the first region G1 side substantially coincides with the position Pb(C) of the lower end Kb of the crack K detected on the second region G2 side.

[0129] However, the position Pt(B) of the upper end Kt of the crack K detected on the first region G1 side does not match the position Pt(C) of the upper end Kt of the crack K detected on the second region G2 side. Therefore, the length KL(B) of the crack K detected on the first region G1 side does not match the length KL(C) of the crack K detected on the second region G2 side. As a result, the crack inclination state detection unit 550 can determine that the crack K is inclined with respect to the thickness direction of the wafer W, for example, because the difference between the lengths KL(B) and KL(C) is greater than a predetermined value (first threshold value).

[0130] Furthermore, the length KL(B) of the crack K detected on the first region G1 side is shorter than the length KL(C) of the crack K detected on the second region G2 side. Therefore, the inclination direction determination unit 552 of the crack inclination state detection unit 550 can detect that the crack K is inclined toward the first region G1 side.

[0131] Furthermore, the inclination angle calculation unit 554 of the crack inclination state detection unit 550 can calculate the inclination angle θ of the crack K by substituting the lengths KL(B) and KL(C) of the detected crack K into equation (2) or equation (3).

[0132] Furthermore, when the crack K is inclined, the position Pt(B) of the upper end Kt of the crack K detected on the first region G1 side does not coincide with the position Pt(C) of the upper end Kt of the crack K detected on the second region G2 side, but the crack inclination state detection unit 550 can easily calculate the actual position of the upper end Kt of the crack K using trigonometric functions from the detected length KL(B) or KL(C) of the crack K and the inclination angle θ.

[0133] The control unit 500 outputs the depth position, inclination direction, and inclination angle of the detected crack K to the display unit 508. The user can determine whether the crack K has been successfully formed based on the information output to the display unit 508. For example, the user can accurately predict whether the chip will be successfully divided in the cleaving process by taking into account the inclination angle θ in addition to the depth position of the crack K.

[0134] For example, the user can predict the position and shape of the cut surface when the wafer W is cut from the depth position, inclination direction, and inclination angle θ of the crack K. Furthermore, for example, the user can predict that even if the depth position of the crack K is appropriate, the wafer W cannot be cut well because the inclination angle θ is too large.

[0135] [Variations] In the above description, it is assumed that crack detection is performed with the lower end Wb of the crack K aligned with the main optical axis AX when the crack K is inclined relative to the thickness direction, but crack detection may also be performed with the upper end Wt of the crack K aligned with the main optical axis AX.

[0136] [Effects of the invention] As described above, according to this embodiment, when a crack is detected, not only the depth position of the crack K but also the inclination state of the crack K with respect to the thickness direction of the wafer W can be detected. In particular, in this embodiment, it is possible to detect the inclination direction and inclination angle of the crack K as the inclination state of the crack K. This makes it possible to accurately predict whether the chip will be successfully divided in the cleaving process.

[0137] According to this embodiment, it is possible to detect the inclination state of the crack K using the crack detection optical system 400 without adding a new detector, so it is possible to realize the crack detection device and method of this embodiment at low cost.

[0138] According to this embodiment, the crack detection optical system 400 can be used to detect the inclination direction and inclination angle θ of the crack K in a non-destructive and non-contact manner, making it possible to efficiently evaluate the processing quality.

[0139] When the incident angles of the detection lights L1(B) and L1(C) are set to the same angle, it is possible to calculate the inclination angle θ of the crack K using equation (3). Even when the incident angles of the detection lights L1(B) and L1(C) are set to different angles, it is possible to calculate the inclination angle θ of the crack K using equation (2).

[0140] Although examples of the present invention have been described above, it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0141] 10...crack detection device, 100...light source unit, 102A, 102B, 102C...light source, 104...half mirror, 200...illumination optical system, 202...relay lens, 204...mirror, 206...relay lens, 300...interface detection optical system, 302...half mirror, 304...half mirror, 306...relay lens, 308...half mirror, 310...photodetector, 400...crack detection optical system, 402...relay lens, 404, 406...photodetector, 500...control unit, 502...focus point position moving mechanism, 504 ...Objective lens, 506...Operation unit, 508...Display unit, 510...Stage, 520...Interface detection unit, 530...First crack detection unit, 540...Second crack detection unit, 550...Crack inclination state detection unit, 552...Inclination direction detection unit, 554...Inclination angle calculation unit, K...Crack, Kt...Upper end of crack, Kb...Lower end of crack, KL(B), KL(C)...Detected crack length, Pt(B), Pt(C)...Detected position of upper end, Pb(B), Pb(C)...Detected position of lower end, Wb...Upper surface, Wa...Lower surface, α, β, θ...Angle

Claims

1. an oblique illumination means for irradiating a workpiece having a crack formed therein with a first detection light and a second detection light from different oblique directions; a crack inclination state detection means for detecting an inclination state of the crack with respect to the thickness direction of the workpiece based on the position of the end of the crack detected by the first detection light and the position of the end of the crack detected by the second detection light; A crack detection device comprising:

2. an oblique illumination step of irradiating a workpiece having a crack formed therein with first detection light and second detection light from different oblique directions; a crack inclination state detection step of detecting an inclination state of the crack with respect to a thickness direction of the workpiece based on the position of the end of the crack detected by the first detection light and the position of the end of the crack detected by the second detection light; A crack detection method comprising:

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