Crack detection device and crack detection method

Abstract

To provide a crack detection device and a crack detection method capable of improving crack detection accuracy.SOLUTION: A crack detection device according to an aspect of the present invention includes a light source unit that emits first detection light, a condenser lens that condenses the first detection light emitted from the light source unit inside a workpiece, a condenser lens moving unit that moves a focal point of the condenser lens in a thickness direction of the workpiece, a first detection unit that detects first multiple reflection light that is the first detection light multiply reflected inside the workpiece, and a crack detection unit that detects a crack formed in the workpiece on the basis of an intensity pattern of the first multiple reflection light.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a crack detection device and a crack detection method. [Background technology]

[0002] Conventionally, there is known a laser processing device (also called a laser dicing device) that focuses (converges) on the inside of a substrate such as a silicon wafer or a glass wafer (hereinafter referred to as a "workpiece"), irradiates the workpiece with laser light along a planned cutting line, and forms a laser processing area that serves as a starting point for cutting within the workpiece along the planned cutting line. The workpiece with the formed laser processing area is then cleaved along the planned cutting line by a cleaving process such as expanding or breaking, and divided into individual chips.

[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. If the crack reaches the surface (laser light incident surface) or the back surface of the workpiece, proper separation into chips can be achieved during the cutting process. This is because a crack formed inside the workpiece serves as the starting point for separating the workpiece, and the degree of crack propagation determines the separation rate of the workpiece. On the other hand, in the case of a thick workpiece, the crack may not reach the surface or back surface of the workpiece (inside cut), but the workpiece can still be properly separated. Therefore, simply determining whether the crack has reached the surface or back surface of the workpiece may not necessarily determine whether the laser processing area has been properly formed.

[0004] Therefore, after forming the laser processing area using the laser processing device, before the cutting process, it is possible to accurately predict whether the laser processing area, which serves as the starting point for dividing the workpiece, was properly formed, i.e., by detecting the crack depth of the crack formed inside the workpiece. Furthermore, if there is a portion inside the workpiece where the laser processing area was not properly formed, it is possible to reprocess only that portion using the laser processing device or change the cutting method in the cutting process. This eliminates the loss of chips in the subsequent cutting process. Furthermore, the processing conditions of the laser processing device can be modified based on the occurrence of defective portions, thereby reducing the occurrence of defective portions in the laser processing area on subsequent workpieces. When the defective laser processing area is reprocessed, reducing the occurrence of defective portions also reduces the time required for reprocessing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-10281 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 discloses a technique for non-destructively inspecting cracks formed inside a workpiece. The technique disclosed in Patent Document 1 involves obliquely illuminating the crack inside the workpiece, detecting light that does not hit the crack but is reflected by the back surface of the workpiece in the area where the crack is formed, and utilizing the decrease in the amount of detected light caused by the scattering or total reflection of the incident light by the crack to inspect the crack.

[0007] However, this technique has the problem that light reflected from the surface of the workpiece becomes disturbance light (noise). For example, if a crack occurs on the surface of a workpiece but does not reach the back surface (half-cut), ideally, the detected light intensity near the surface should be zero. This is because the measurement light is scattered or totally reflected by the crack near the surface, preventing it from being detected. However, in reality, when measuring near the surface, the reflected light from the surface of the workpiece cannot be completely removed and enters the detector as disturbance light. As a result, the detected intensity does not become zero. On the other hand, reflected light from the surface of the workpiece is detected even when there is no crack on the surface of the workpiece. Therefore, light is detected at a certain intensity in the detection light path regardless of whether there is a crack near the surface or not, making it difficult to determine whether a crack has formed on the surface of the workpiece.

[0008] Therefore, the technology disclosed in Patent Document 1 attempts to remove surface reflected light, which becomes disturbance light, by placing a branching mirror at or near a position (focal plane) that is optically conjugate with the front focal position (focal plane) of the focusing lens.

[0009] Although Patent Document 1 states that the splitting mirror can completely eliminate the surface reflected light, this is a calculation based on a geometrical optics simulation, and in actual operation, the surface reflected light is detected as disturbance light due to the diffraction phenomenon. Therefore, it is not possible to stably detect cracks, especially when the cracks are on or near the surface of the workpiece.

[0010] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a crack detection device and a crack detection method that can improve the accuracy of crack detection. [Means for solving the problem]

[0011] The gist of the present invention is as follows. (1) a light source unit that emits a first detection light; a condenser lens that condenses the first detection light emitted from the light source unit inside the workpiece; a condenser lens moving unit that moves the focus of the condenser lens in the thickness direction of the workpiece; a first detection unit that detects first multiple-reflected light, which is the first detection light that has been multiple-reflected within the workpiece; a crack detection unit that detects a crack formed in the workpiece based on the intensity pattern of the first multiple reflected light. (2) the first detection unit detects first back-surface reflected light, which is the first detection light reflected by a back surface of the workpiece; The crack detection device described in (1) is characterized in that the crack detection unit detects cracks formed in the workpiece based on the intensity pattern of the first back surface reflected light and the intensity pattern of the first multiple reflected light. (3) The crack detection device described in (2) is characterized in that the crack detection unit detects cracks formed in the workpiece based on the intensity pattern of the first back-surface reflected light, and further detects cracks formed in the workpiece based on the intensity pattern of the first multiple-reflected light, and compares the results. (4) The crack detection device described in (2) or (3) is characterized in that the crack detection unit detects the type of crack formed in the workpiece based on a combination of the intensity pattern of the first back surface reflected light and the intensity pattern of the first multiple reflected light. (5) emitting a first detection light; a step of focusing the first detection light emitted from a light source unit inside the workpiece using a focusing lens; moving the focus of the condenser lens in the thickness direction of the workpiece; detecting first multiple-reflected light, which is the first detection light that has been multiple-reflected within the workpiece; and detecting a crack formed in the workpiece based on the intensity pattern of the first multiple reflection light. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a crack detection device and a crack detection method that can improve the crack detection accuracy. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram showing the structure of a crack detection system according to an embodiment of the present invention; [Figure 2] 3 shows an example of a measurement graph obtained by the crack detection device according to the present embodiment. [Figure 3] FIG. 1 is a perspective view showing a half cut (HC), which is an example of a crack. [Figure 4] FIG. 1 is a perspective view showing a backside half cut (BHC), which is an example of a crack. [Figure 5] FIG. 1 is a perspective view showing an inside cut (IC), which is an example of a crack. [Figure 6] FIG. 1 is a perspective view showing a full cut (FC), which is an example of a crack. [Figure 7] 10(a) is a side view showing the optical path of the first multiple-reflected light when measuring a half cut, and FIG. 10(b) is an example of an assumed measurement graph. [Figure 8] 1A is a side view showing the optical path of the first multiple-reflected light when measuring a backside half cut, and FIG. 1B is an example of an assumed measurement graph. [Figure 9] 10(a) is a side view showing the optical path of the first multiple-reflected light when measuring a full cut, and FIG. 10(b) is an example of an assumed measurement graph. [Figure 10] 10(a) is a side view showing the optical path of the first multiple-reflected light when measuring the inside cut, and FIG. 10(b) is an example of an assumed measurement graph. [Figure 11] 4 is a flowchart showing a processing procedure performed by the crack detection device according to the present embodiment. [Figure 12] 1 is a table showing a list of results of examples. [Figure 13]FIG. 2 is a diagram for explaining an optical system in the crack detection device according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0015] <1. Crack detection system> First, the overall configuration of a crack detection system 1 according to this embodiment will be described with reference to FIG. 1. Note that FIG. 1 also shows the x-axis, y-axis, and z-axis. The crack detection system 1 includes a crack detection device 10 and a system control device 40. The crack detection device 10 includes a light source unit 10a, a condenser lens 10b, a first detection unit 10c, a second detection unit 10d, a crack detection unit 10e, an interface position detection unit 10f, an xy stage 10g, and a z-stage (condenser lens moving unit) 10h. The crack detection device 10 according to this embodiment has the structure shown in FIG. 13 (FIG. 2 of Patent Document 1). FIG. 13 is a diagram for explaining the optical system of the crack detection device according to this embodiment. Here, we will describe the configuration unique to this embodiment of the structure shown in FIG. 13. Note that in this embodiment, polarized light does not necessarily need to be used as the first detection light L1 and the second detection light L2. If polarized light is not used, the polarizing filters 60 and 62 shown in FIG. 13 are unnecessary.

[0016] The light source unit 10a emits a first detection light L1 and a second detection light L2. The structure of the light source unit 10a is not particularly limited, and any structure capable of emitting two types of probe light, i.e., the first detection light L1 and the second detection light L2, may be used. For example, two light sources may be provided, one light source may be split into two using a mask or a shutter, or two optical paths may be provided using a polarizing beam splitter (PBS) 34, as in the light source unit 14 shown in FIG. 13 .

[0017] The condenser lens 10b condenses the first detection light L1 and the second detection light L2 and irradiates the light onto a workpiece (work) 20 on an xy stage 10g. The focal plane of the condenser lens 10b within the workpiece can be moved up and down by moving a z stage 10h up and down.

[0018] The first detection unit 10c has a configuration corresponding to the photodetector 26A shown in FIG. 13 and detects first surface-reflected light L1′, which is the first detection light reflected from the surface 21 of the workpiece 20; first back-reflected light L1″, which is the first detection light reflected from the back surface 22 of the workpiece 20; and first multiple-reflected light L1′″, which is the first detection light reflected from the back surface 22 of the workpiece 20. The first detection unit 10c outputs the detected light to the crack detection unit 10e. Note that multiple-reflected light refers to reflected light that is reflected at least once from the surface 21 of the workpiece 20 and twice from the back surface 22 before emitting from the surface 21 of the workpiece 20 (see FIG. 7(a) and other figures). Since the first detection light L1 is actually reflected infinitely within the workpiece 20, multiple-reflected light exists infinitely. However, the intensity decreases as the number of reflections increases, making detection more difficult. Therefore, in this embodiment, the target of detection is multiple reflected light that is reflected once by the front surface 21 of the workpiece 20 and twice by the back surface 22 thereof and then exits from the front surface 21 of the workpiece 20.

[0019] The second detection unit 10d has a configuration corresponding to the photodetector 26B shown in Fig. 13, and detects second surface-reflected light L2', which is second detection light reflected from the surface of the workpiece 20, second back-reflected light L2'' which is second detection light reflected from the back surface 22 of the workpiece 20, and second multiple-reflected light L2''' which is multiple-reflected within the workpiece 20. The second detection unit 10d outputs the detected light to the crack detection unit 10e.

[0020] The crack detection unit 10e detects a crack 20a formed in the workpiece 20 based on the intensity pattern of the first multiple reflected light L1''' (multiple reflection region f in graph L10 described later) and the intensity pattern of the second multiple reflected light L2''' (multiple reflection region f in graph L20 described later). For example, the crack detection unit 10e detects the depth of the crack 20a. Note that the crack detection unit 10e may also detect a crack formed in the workpiece 20 based on the intensity pattern of the first back-surface reflected light L1'' (back-surface reflection region e in graph L10 described later), the intensity pattern of the second back-surface reflected light L2'' (back-surface reflection region e in graph L20 described later), the intensity pattern of the first multiple reflected light L1''', and the intensity pattern of the second multiple reflected light L2'''. For example, the intensities of the first multiple reflected light L1'" and the second multiple reflected light L2'" are lower than those of the first and second surface-reflected lights L1', L2' and the first and second back-reflected lights L1", L2", which may result in a poor signal-to-noise ratio. Therefore, the crack detection unit 10e may first detect a crack formed in the workpiece 20 based on the intensity pattern of the multiple reflected light L1'" and the intensity pattern of the second multiple reflected light L2'" and then detect the crack based on the intensity pattern of the first back-reflected light L1" and the intensity pattern of the second back-reflected light L2" to confirm whether the detection result is correct. Furthermore, the combination of the intensity pattern of the first back-reflected light L1" and the intensity pattern of the first multiple reflected light L1'" (i.e., graph L10 described later) and the combination of the intensity pattern of the second back-reflected light L2" and the intensity pattern of the second multiple reflected light L2'" (i.e., graph L20 described later) differ depending on the type of crack (see Table 1 described later). Therefore, the crack detection unit 10e may detect the type of crack based on these combinations. The crack detection unit 10e outputs the crack detection result to the system control device 40. A specific example of a crack detection method will be described later in <4. Relationship between crack types and measurement graphs>.

[0021] The crack detection unit 10e includes a hardware configuration including a CPU, a ROM, a RAM, a hard disk, etc., and performs the above-described processing using this hardware configuration. The processing performed by the crack detection unit 10e is recorded as a program in the ROM.

[0022] 13, and detects the interfaces of the workpiece 20, i.e., the front surface 21 and the back surface 22, using a portion of the reflected light incident on the first detection unit 10c and the second detection unit 10d. Note that the interface position detection unit 10f also detects a mirror image 21' of the front surface 21, as will be described in detail later.

[0023] The xy stage 10g moves the workpiece 20 along the xy plane (horizontal plane) under the control of the system control device 40. The z stage 10h moves the crack detection device 10 along the z-axis direction (vertical direction) under the control of the system control device 40. The z stage 10h has a built-in piezoelectric element, for example, and movement of the piezoelectric element causes the z stage 10h to move.

[0024] The system control device 40 includes a receiving unit 41, a transmitting unit 42, and a control unit 43, and controls the entire crack detection system 1 as well as correcting crack depth. The system control device 40 includes a hardware configuration including a CPU, ROM, RAM, a hard disk, various transmitting / receiving devices, various input devices, and various display devices, and this hardware configuration realizes the receiving unit 41, transmitting unit 42, and control unit 43. The processing performed by the control unit 43 is recorded as a program in the ROM.

[0025] <2. Example of measurement graph> 2 is a measurement graph showing an example of the detected intensity (V) of reflected light detected (measured) by the first detector 10c, the second detector 10d, and the interface position detector 10f. The horizontal axis represents the piezo movement amount (μm), which indicates the movement amount of the z-stage 10h, i.e., the focal plane of the focusing lens 10b, in the -z direction. The vertical axis represents the detected intensity (V) of reflected light detected (measured) by the first detector 10c, the second detector 10d, and the interface position detector 10f.

[0026] Graph L10 shows the correlation (Ch-A) between the amount of piezoelectric movement and the detected intensity (V) of the reflected light detected (measured) by the first detection unit 10c. In other words, graph L10 shows the intensity patterns of the first front-surface reflected light L1', the first back-surface reflected light L1", and the first multiple reflected light L1'". Graph L20 shows the correlation (Ch-B) between the amount of piezoelectric movement and the detected intensity (V) of the reflected light detected (measured) by the second detection unit 10d. In other words, graph L10 shows the intensity patterns of the second front-surface reflected light L2', the second back-surface reflected light L2", and the second multiple reflected light L2'". Graph L30 shows the correlation (Focus) between the amount of piezoelectric movement and the detected intensity (V) of the reflected light detected (measured) by the interface position detection unit 10f.

[0027] The measurement stroke lengths of graphs L10 to L30 are longer than conventional ones in order to obtain a multiple reflection region (a region where multiple reflected light is detected).

[0028] 2, point a indicates the surface position of the workpiece 20 obtained by interface detection, point b indicates the back surface position of the workpiece 20 obtained by interface detection, and point c indicates a mirror image (front surface mirror image) of the surface position of the workpiece 20 obtained by interface detection (mirror image 21' shown in FIG. 7(a) etc.). Details will be described later, but the mirror image 20' of the workpiece 20 is an image obtained by folding the workpiece 20 (turning it upside down) with the back surface 22 of the workpiece 20 as the plane of symmetry (see FIG. 7(a) etc.).

[0029] Region d is a surface reflection region for crack detection. Region e is a back surface reflection region for crack detection. Region f is a multiple reflection region for crack detection. In the surface reflection region d, the first detection unit 10c and the second detection unit 10d detect the first surface reflected light L1' and the second surface reflected light L2'. In the back surface reflection region e, the first detection unit 10c and the second detection unit 10d detect the first back surface reflected light L1'' and the second back surface reflected light L2''. In the multiple reflection region f, the first detection unit 10c and the second detection unit 10d detect the first multiple reflected light L1''' and the second multiple reflected light L2'''.

[0030] Point g is the center position of the rise of the surface reflection in crack detection. Point h is the center position of the rise of the back surface reflection in crack detection. Point i is the center position of the rise of the multiple reflection in crack detection. The center position of the rise is the position corresponding to the midpoint between the top and bottom of the rise of the graph (the point where the detection intensity increases with the movement of the piezo).

[0031] As shown in Figure 2, the more reflections there are within the workpiece 20, the lower the detected intensity, so the order of detected intensity is front-surface reflection > back-surface reflection > multiple reflection. Multiple reflections continue even deeper than point c (to the right of point c), but the detected intensity drops significantly. For this reason, in this embodiment, the measurement is performed up to point c, where the first front-surface specular image appears. That is, as described above, the target of detection is the multiple-reflected light that is reflected once by the front surface 21 of the workpiece 20 and twice by the back surface 22, and then emerges from the front surface 21 of the workpiece 20.

[0032] The back surface reflection region e in Figure 2 is the region where crack detection is performed in the prior art. While sufficient detection intensity can be ensured in this region, it is difficult to detect cracks 20a near the surface of the workpiece 20. This is because, even if the back surface reflected light is blocked by the crack 20a and the detection intensity decreases, the center position g of the front surface reflection rise exists near the surface position a, so in many cases the decrease in the detection intensity of the back surface reflected light is overshadowed by the increase in the detection intensity of the front surface reflected light (i.e., the presence or absence of a crack becomes unclear).

[0033] Therefore, in this embodiment, the crack 20a is detected using the multiple reflection region f. Note that the multiple reflection region f has a rear surface reflection rising center position h, but unlike the front surface reflection rising center position g, which does not respond to the crack 20a, the rear surface reflection rising center position h responds to the crack 20a. In other words, if the crack 20a exists near the rear surface position b, this rising will not appear and will not adversely affect the data analysis. A specific example will be described later.

[0034] <3. Types of cracks> 3 to 6 show types of cracks 20a. The crack 20a shown in FIG. 3 is a half cut (HC). In this case, the crack 20a is formed on the front surface 21 of the workpiece 20 but does not reach the back surface 22. The crack 20a shown in FIG. 4 is a backside half cut (BHC). In this case, the crack 20a is formed on the back surface 22 of the workpiece 20 but does not reach the front surface 21. The crack 20a shown in FIG. 5 is an inside cut (IC). In this case, the crack 20a is formed inside the workpiece 20 and does not reach either the front surface 21 or the back surface 22. The crack 20a shown in FIG. 6 is a full cut (FC). In this case, the crack 20a reaches from the front surface 21 to the back surface 22 of the workpiece 20.

[0035] <4. Relationship between crack type and measurement graph> 7 to 10, (a) is a side view showing the optical path of the first multiple-reflected light L1''' when measuring various cracks, and (b) is an example of an expected measurement graph. The symbols a to i have the same meanings as in FIG. 2.

[0036] The crack in Fig. 7 is a half cut. Specifically, Fig. 7(a) shows the optical path of the first multiple-reflected light L1''' and the mirror image 20' of the workpiece 20, and graph L10 in Fig. 7(b) shows the correlation (Ch-A) between the piezo movement amount and the detection intensity (V) of the reflected light detected (measured) by the first detection unit 10c.

[0037] The solid line in Figure 7(a) indicates the actual optical path L1'''-1 of the first multiple-reflected light L1''', and the dashed line indicates the apparent optical path L1'''-2. Furthermore, Figure 7(a) shows a mirror image 20' of the workpiece 20 folded back at the back surface 22. The mirror image 20' of the workpiece 20 has a mirror image 20a' of the crack 20a. In the apparent optical path L1'''-2, the first multiple-reflected light L1''' is reflected by the mirror image (surface mirror image) 21' of the surface 21 of the workpiece 20 and is emitted from the surface 21 of the workpiece 20. The optical paths L1'''-1 and L1'''-2 in Figure 7(a) are obtained when the focal plane of the focusing lens 10b is aligned with the mirror image (surface mirror image) 21' of the surface 21 of the workpiece 20. The detection (measurement) of the first multiple reflected light L1''' is synonymous with the detection of the mirror image 21' of the workpiece 20.

[0038] In Figure 7(b), region L10a is the location of the strength reduction due to the crack 20a, and points P1 and P1' (indicated by "x") are the crack bottom position (or a mirror image of the crack bottom position). The actual crack bottom position (or a mirror image of the crack bottom position) can be determined using the method shown in Figure 14 of JP 2022-117056 A. Generally, the center position of the output fluctuation location in region L10a is the crack bottom position or a mirror image of the crack bottom position (marked with an x ​​on the graph). Therefore, the crack detection unit 10e determines the distance from the interface (e.g., the back surface or the mirror image of the front surface) to the crack bottom position or the mirror image of the crack bottom position based on graph L10. Next, this distance (the distance determined from graph L10) is multiplied by the effective refractive index of the workpiece 20 to determine the actual crack bottom position or the mirror image of the crack bottom position. The difference between the back surface reflection region e and the multiple reflection region f is that the left and right of graph L10 are reversed when the piezoelectric movement is taken in the left-right direction. When the focusing position (measurement depth position) of the first detection light L1 or the second detection light L2 passes the back surface 22 of the workpiece 20 and enters the multiple reflection region f, the crack detection unit 10e measures a mirror image of the back surface reflection region e by the back surface 22. As a result, the shape of the detection intensity is reversed in the back surface reflection region e and the multiple reflection region f. Note that in Figure 7, the crack 20a reaches the surface 21 of the workpiece 20, so ideally the detection intensity would be 0 at point a on graph L10. However, in reality, point g (the center position of the rise of the surface reflection in crack detection) exists, and the detection intensity increases due to this. In contrast, in the multiple reflection region f that detects the mirror image 21', there is no rise at point c (the mirror image 21' of the surface 21 of the workpiece 20). In the measurement of point c, the measurement depth position and the surface 21 of the workpiece 20 are located far enough apart, and the state is similar to that of the measurement near the back surface 22 of the workpiece 20. For this reason, the reflected light from the surface 21 of the workpiece 20 can be removed as disturbance light. Therefore, it can be reliably recognized that the mirror image 20a' of the crack 20a has reached the mirror image 21' of the surface 21 of the workpiece 20, and it can be reliably determined that the crack 20a has reached the surface 21 of the workpiece 20. The depth of the mirror image 20a' of the crack 20a is the same as the depth of the crack 20a. The position of the mirror image 21' of the surface 21 of the workpiece 20 can be calculated using the following equation (1).The depth of the crack 20a can also be determined based on this formula (1) and the mirror image of the crack bottom end position. M=T+2(D / n) (1) In equation (1), M represents the position of the mirror image 21' of the surface 21 of the workpiece 20, T represents the position of the surface 21 of the workpiece 20 (which can be determined as the position of point a), D represents the thickness of the workpiece 20, and n represents the effective refractive index of the workpiece 20. There are two methods for determining the effective refractive index: experimental and theoretical. The former is disclosed in JP 2022-117056 A, and the latter is disclosed in JP 2021-156674 A. The latter can be briefly explained as "the effective refractive index for a focused beam of light with a certain width, when a certain NA is set." This "certain NA" is determined by the focusing lens 10b and the beam incident on the focusing lens 10b. In other words, the effective refractive index can be calculated using the NA and the incident beam.

[0039] In actual operation, the multiple reflection region f exhibits a large attenuation of light intensity and a poorer signal-to-noise ratio than the back surface reflection region e. Therefore, when attempting to determine the depth of a crack 20a using the multiple reflection region f of a workpiece 20 with a complex pattern or a workpiece 20 coated with an oxide film, accuracy is significantly reduced. Therefore, when a sufficient amount of light is not expected in the multiple reflection region f, it is preferable to also acquire the back surface reflection region e. In this case, the measurement stroke length doubles, extending the measurement time, but in exchange, the accuracy of determining the crack state is improved. This is because, depending on the type of crack 20a, the depth of the crack 20a can also be measured using the back surface reflection region e. In other words, a crack 20a that is not located near the front surface 21 of the workpiece 20 (such as a backside half cut) can be detected using the back surface reflection region e. However, in this case, it is preferable to determine the distance from the bottom end position of the crack to the back surface 22 of the workpiece 20 and then use this value to determine the depth of the crack 20a.

[0040] By measuring in this way, two depths of the crack 20a can be obtained. Then, by comparing these, the depth of the crack 20a can be double-checked. Of course, if multiple reflected light can be obtained stably, it is sufficient to measure only the multiple reflection region.

[0041] Although not shown here, the depth of the crack 20a can also be calculated for the graph L20 by a similar process. Therefore, the depth of the crack 20a can be calculated for each of the graphs L10 and L20, and the average value of these values ​​can be used as the depth of the crack 20a. The same applies to the following.

[0042] The crack in Fig. 8 is a backside half cut. Specifically, Fig. 8(b) shows the optical path of the first multiple-reflected light L1''' and the mirror image 20' of the workpiece 20, and graph L10 in Fig. 8(b) shows the correlation (Ch-A) between the piezo movement amount and the detection intensity (V) of the reflected light detected (measured) by the first detection unit 10c.

[0043] The solid line in Figure 8(a) indicates the actual optical path L1'''-1 of the first multiple-reflected light L1''', and the dashed line indicates the apparent optical path L1'''-2. Furthermore, Figure 8(a) shows a mirror image 20' of the workpiece 20 folded back at the back surface 22. The mirror image 20' of the workpiece 20 has a mirror image 20a' of the crack 20a. In the apparent optical path L1'''-2, the first multiple-reflected light L1''' is reflected by the mirror image (surface mirror image) 21' of the surface 21 of the workpiece 20 and is emitted from the surface 21 of the workpiece 20. The optical paths L1'''-1 and L1'''-2 in Figure 7(a) are obtained when the focal plane of the focusing lens 10b is aligned with the mirror image (surface mirror image) 21' of the surface 21 of the workpiece 20. The detection (measurement) of the first multiple reflected light L1''' is synonymous with the detection of the mirror image 21' of the workpiece 20.

[0044] In Figure 8(b), region L10a represents the location of strength reduction due to crack 20a and its mirror image 20a', and points P2 and P2' (marked with a star) represent the crack top (or its mirror image). The actual crack top (or its mirror image) can be determined using the method shown in Figure 14 of JP 2022-117056 A. The center position of the output fluctuation point in region L10a corresponds to the crack top or its mirror image (marked with a star on the graph). Based on graph L10, the crack detection unit 10e determines the distance from the interface (e.g., the back surface or the mirror image of the front surface) to the crack top or its mirror image. This distance (calculated from graph L10) is then multiplied by the effective refractive index of the workpiece 20 to determine the actual crack top or its mirror image. The difference between the back surface reflection region e and the multiple reflection region f is that the left and right of graph L10 are reversed when the piezoelectric movement is taken in the left-right direction. When the focusing position (measurement depth position) of the first detection light L1 or the second detection light L2 passes the back surface 22 of the workpiece 20 and enters the multiple reflection region f, the crack detection unit 10e measures a mirror image of the back surface reflection region e by the back surface 22. As a result, the shape of the detection intensity is reversed between the back surface reflection region e and the multiple reflection region f. Note that in FIG. 8, the crack 20a has reached the back surface 22 of the workpiece 20, so ideally, the detection intensity would be 0 at point b on graph L10. In graph L10, the intensity at point b is very low, and it can be determined that a nearly ideal graph has been obtained (the center position h of the back surface reflection rise does not exist). Therefore, it can be reliably recognized that the mirror image 20a' of the crack 20a has reached the back surface 22 of the workpiece 20, and it can be reliably determined that the crack 20a has reached the back surface 22 of the workpiece 20. The depth of the mirror image 20a' of the crack 20a is the same as the depth of the crack 20a. The position of the rear surface 22 of the workpiece 20 can be calculated by the formula (5) in JP 2022-117056 A.

[0045] In actual operation, it is preferable to use both the multiple reflection region f and the back surface reflection region e, and the depth of the crack 20a is calculated using graph L20, as described above. When calculating the depth of the crack 20a using the back surface reflection region e, the depth of the crack 20a can be found as the distance from the position of the back surface 22 of the workpiece 20 to the crack upper end position (point P2).

[0046] The crack in Fig. 9 is a full cut. Specifically, Fig. 9(a) shows the optical path of the first multiple-reflected light L1''' and the mirror image 20' of the workpiece 20, and graph L10 in Fig. 9(b) shows the correlation (Ch-A) between the piezo movement amount and the detection intensity (V) of the reflected light detected (measured) by the first detection unit 10c.

[0047] The solid line in Figure 9(a) indicates the actual optical path L1'''-1 of the first multiple-reflected light L1''', and the dashed line indicates the apparent optical path L1'''-2. Furthermore, Figure 9(a) shows a mirror image 20' of the workpiece 20 folded back at the back surface 22. The mirror image 20' of the workpiece 20 has a mirror image 20a' of the crack 20a. In the apparent optical path L1'''-2, the first multiple-reflected light L1''' is reflected by the mirror image (surface mirror image) 21' of the surface 21 of the workpiece 20 and is emitted from the surface 21 of the workpiece 20. The optical paths L1'''-1 and L1'''-2 in Figure 9(a) are obtained when the focal plane of the focusing lens 10b is aligned with the mirror image (surface mirror image) 21' of the surface 21 of the workpiece 20. The detection (measurement) of the first multiple reflected light L1''' is synonymous with the detection of the mirror image 21' of the workpiece 20.

[0048] In Figure 9(b), region L10a represents the intensity drop due to the crack 20a and its mirror image 20a'. The difference between the back surface reflection region e and the multiple reflection region f is that the left and right sides of graph L10 are reversed when the piezoelectric element travels horizontally. When the focusing position (measurement depth position) of the first detection light L1 or the second detection light L2 passes the back surface 22 of the workpiece 20 and enters the multiple reflection region f, the crack detection unit 10e measures the mirror image of the back surface reflection region e by the back surface 22. As a result, the shape of the detection intensity is reversed between the back surface reflection region e and the multiple reflection region f. In Figure 9, the crack 20a reaches the surface 21 of the workpiece 20, so ideally, the detection intensity would be 0 at point a on graph L10. However, in reality, point g (the center position of the rising edge of the surface reflection in crack detection) exists, and the detection intensity increases due to this. In contrast, in the multiple reflection region f where the mirror image 21' is detected, there is no rise at point c (the mirror image 21' of the surface 21 of the workpiece 20). In the measurement of point c, the measurement depth position and the surface 21 of the workpiece 20 are located far enough apart, resulting in a state similar to that of the measurement near the back surface 22 of the workpiece 20. Therefore, the reflected light from the surface 21 of the workpiece 20 can be removed as ambient light. Therefore, it is possible to reliably recognize that the mirror image 20a' of the crack 20a reaches the mirror image 21' of the surface 21 of the workpiece 20. Furthermore, because the detection intensity is sufficiently reduced at point b corresponding to the back surface 22 of the workpiece 20 (i.e., the center position h of the rise of the back surface reflection is not detected), it can be determined that the mirror image 20a' of the crack 20a reaches the back surface 22 of the workpiece 20. Therefore, it can be determined that the crack 20a is a full cut, and that the depth of the crack 20a matches the thickness of the workpiece 20.

[0049] In actual operation, it is preferable to use the multiple reflection area f and the back surface reflection area e in combination, and the depth of the crack 20a is calculated using the graph L20, as described above.

[0050] The crack in Fig. 10 is an inside cut. Specifically, Fig. 10(a) shows the optical path of the first multiple-reflected light L1''' and the mirror image 20' of the workpiece 20, and graph L10 in Fig. 10(b) shows the correlation (Ch-A) between the piezo movement amount and the detection intensity (V) of the reflected light detected (measured) by the first detection unit 10c.

[0051] The solid line in Figure 10(a) indicates the actual optical path L1'''-1 of the first multiple-reflected light L1''', and the dashed line indicates the apparent optical path L1'''-2. Furthermore, Figure 10(a) shows a mirror image 20' of the workpiece 20 folded back at the back surface 22. The mirror image 20' of the workpiece 20 has a mirror image 20a' of the crack 20a. In the apparent optical path L1'''-2, the first multiple-reflected light L1''' is reflected by the mirror image (surface mirror image) 21' of the surface 21 of the workpiece 20 and is emitted from the surface 21 of the workpiece 20. The optical paths L1'''-1 and L1'''-2 in Figure 10(a) are obtained when the focal plane of the focusing lens 10b is aligned with the mirror image (surface mirror image) 21' of the surface 21 of the workpiece 20. The detection (measurement) of the first multiple reflected light L1''' is synonymous with the detection of the mirror image 21' of the workpiece 20.

[0052] In Figure 10(b), region L10a represents the location of the intensity drop caused by the crack 20a and its mirror image 20a'. Points P1 and P1' (indicated by "x") represent the bottom end of the crack (or its mirror image), and points P2 and P2' (indicated by "☆") represent the top end of the crack (or its mirror image). The actual bottom and top end positions of the crack can be determined using the method described above. The difference between the back surface reflection region e and the multiple reflection region f is that the left and right sides of graph L10 are reversed when the piezoelectric actuator movement is taken as the horizontal direction. When the focusing position (measurement depth position) of the first detection light L1 or the second detection light L2 passes beyond the back surface 22 of the workpiece 20 and enters the multiple reflection region f, the crack detection unit 10e measures the mirror image of the back surface 22 of the back surface reflection region e. As a result, the shape of the detected intensity is reversed between the back surface reflection region e and the multiple reflection region f. The length of the crack can be determined as the distance from the crack upper end position P2 to the crack lower end position P1, or the distance from the mirror image P2' of the crack upper end position to the mirror image P1' of the crack lower end position.

[0053] In actual operation, it is preferable to use the multiple reflection area f and the back surface reflection area e in combination, and the depth of the crack 20a is calculated using the graph L20, as described above.

[0054] 7 to 10(b), the shape of graph L10 differs depending on the type of crack 20a (although not shown, the shape of graph L20 also differs). Specifically, the types of crack 20a can be classified as shown in Table 1 below depending on the presence or absence of a rise in the back surface reflection region e and the multiple reflection region f (note that a rise here refers to a point where the detection intensity increases as the amount of piezoelectric movement increases).

[0055] [Table 1]

[0056] Therefore, the type of crack 20a can be detected based on graph L10, i.e., the combination of the intensity pattern of the first back-surface reflected light L1" and the intensity pattern of the first multiple reflected light L1'", or graph L20, i.e., the combination of the intensity pattern of the second back-surface reflected light L2" and the intensity pattern of the second multiple reflected light L2'". Furthermore, the type of crack may be detected from both graph L10 and graph L20 and double-checked.

[0057] Therefore, the crack detection unit 10e can accurately detect a crack 20a formed in the workpiece 20 based on the intensity pattern of the first multiple reflected light L1''' (i.e., the multiple reflection region f of graph L10) and the intensity pattern of the second multiple reflected light L2''' (i.e., the multiple reflection region f of graph L20). For example, the crack detection unit 10e can accurately detect the depth of the crack 20a. Note that the crack detection unit 10e may also detect a crack formed in the workpiece 20 based on the intensity pattern of the first back-surface reflected light L1'' (i.e., the back-surface reflection region e of graph L10), the intensity pattern of the second back-surface reflected light L2'' (i.e., the back-surface reflection region e of graph L20), the intensity pattern of the first multiple reflected light L1''', and the intensity pattern of the second multiple reflected light L2''' (double check). Furthermore, the crack detection unit 10e can detect the type of crack based on the combination of the intensity pattern of the first back surface reflected light L1'' and the intensity pattern of the first multiple reflected light L1''' (i.e., graph L10), or the combination of the intensity pattern of the second back surface reflected light L2'' and the intensity pattern of the second multiple reflected light L2''' (i.e., graph L20).

[0058] <5. Processing using crack detection system> Next, the processing procedure by the crack detection system 1 will be explained with reference to the flowchart shown in Fig. 11. The workpiece 20 is placed on the xy stage 10g. A device pattern is formed on the back surface 22 of the workpiece 20.

[0059] In step S1, the control unit 43 of the system control device 40 adjusts the relative position between the workpiece 20 on the xy stage 10g and the condenser lens 10b. Specifically, the control unit 43 transmits a control signal to the xy stage 10g via the transmitter 42, and the xy stage 10g moves based on the control signal. Furthermore, the control unit 43 transmits a control signal to the z stage 10h via the transmitter 42, and the z stage 10h moves to a position where the piezoelectric movement amount is zero.

[0060] In step S2, the crack detection device 10 performs a preliminary measurement. In the preliminary measurement, the crack detection device 10 detects the patterns of the first detection light L1 and the second detection light L2 reflected by the device pattern. Specifically, first, the light source unit 10a emits the first detection light L1 and the second detection light L2 (first step). Next, the crack detection device 10 uses the condenser lens 10b to focus the first detection light L1 and the second detection light L2 emitted from the light source unit 10a inside the workpiece 20 (second step). Next, the first detection unit 10c detects the first detection light L1 reflected within the workpiece 20, and the second detection unit 10d detects the second detection light L2 reflected within the workpiece 20 (third step). Next, the crack detection device 10 repeatedly performs steps 1 to 3 while moving the z-stage 10h in the -z direction. As a result, the first detection unit 10c detects the first surface reflected light L1', the first back surface reflected light L1'', and the first multiple reflected light L1''' due to the device pattern. Similarly, the second detection unit 10d detects the second surface reflected light L2', the second back surface reflected light L2'', and the second multiple reflected light L2''' due to the device pattern (fourth step).

[0061] In step S3, a crack 20a is formed in the workpiece 20. Step S3 is performed using a laser processing device (not shown).

[0062] In step S4, the crack detection device 10 performs the actual measurement. Specifically, the crack detection device 10 performs the same steps as in step S2 described above. That is, steps 1 to 4 are performed. However, since a device pattern is formed on the rear surface of the workpiece 20, the intensity pattern of the first multiple reflected light L1''' (multiple reflection region f in graph L10) and the intensity pattern of the second multiple reflected light L2''' (multiple reflection region f in graph L20) are affected by the device pattern.

[0063] In step S5, the control unit 43 of the system control device 40 corrects the actual measurement data (data obtained in step S4) based on the pre-measurement data (data obtained in step S2) to remove the influence of the device pattern applied to the workpiece 20. A specific method of correction is disclosed in, for example, JP 2022-117055 A.

[0064] In step S6, the control unit 43 of the system control device 40 calculates the identification of the crack state (identification of the type of crack) and the crack position (crack depth) based on the corrected data. Specifically, the crack detection unit 10e detects the crack 20a formed in the workpiece 20 based on the intensity pattern of the first multiple reflected light L1''' (multiple reflection region f in graph L10) and the intensity pattern of the second multiple reflected light L2''' (multiple reflection region f in graph L20) (fifth step). Here, the crack detection unit 10e may further detect the crack 20a based on the intensity pattern of the first back-surface reflected light L1'' and the intensity pattern of the second back-surface reflected light L2'', and compare the detected cracks with the above-mentioned results (double check). The specific method for detecting the crack 20a is as described above. The crack detection unit 10e outputs the measurement results to the system control device 40. The receiving unit 41 of the system control device 40 outputs the received measurement results to the control unit 43.

[0065] As described above, according to this embodiment, the crack detection device 10 detects the crack 20a formed in the workpiece 20 based on the intensity pattern of the first multiple reflected light L1''' and the intensity pattern of the second multiple reflected light L2''', so that the crack 20a can be detected while eliminating the influence of the surface reflected light L1', L2'. Therefore, the crack detection accuracy is improved. [Example]

[0066] Four types of cracks 20a were formed in a 150 μm thick mirror wafer (workpiece 20), and the reflected light was detected and the depth of the cracks 20a was measured using the method described above. The results are shown in Figure 12. Figure 12 shows the types of cracks, graphs L10 to L30 of the back surface reflection region e, and graphs L10 to L30 of the multiple reflection region f (an enlarged view of a portion of the range of graphs L10 to L30 of the back surface reflection region e). It can be seen that all of these graphs are similar to the graphs shown in Figures 7 to 10(b).

[0067] Furthermore, for the half-cut, the crack bottom position was determined using both the back surface reflection region e and the multiple reflection region f. The difference in the results was within 8 μm, demonstrating that the multiple reflection region f can be used to determine the crack bottom position, and therefore the depth of the crack 20 a.

[0068] For the backside half cut, the crack top position was determined using both the back surface reflection region e and the multiple reflection region f. The difference in the results was within 7 μm, demonstrating that the multiple reflection region f can be used to determine the crack top position and, ultimately, the depth of the crack 20 a.

[0069] For the full cut, similar results were obtained for the back surface reflection region e and the multiple reflection region f. Therefore, it became clear that the multiple reflection region f can be used to confirm that the crack 20a is formed from the front surface 21 to the back surface 22 of the mirror wafer.

[0070] For the inside cut, the crack top and bottom positions were determined using the back surface reflection region e and the multiple reflection region f. The difference in the results for the crack top position was within 4 μm, and the difference in the results for the crack bottom position was within 3 μm, so it became clear that the crack top and bottom positions, and therefore the depth of the crack 20 a, could be determined using the multiple reflection region f.

[0071] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention. [Explanation of symbols]

[0072] 1. Crack detection system 10 Crack detection device 10a Light source section 10b Condenser lens 10c First detection unit 10d Second detection unit 10e Crack detection unit 10f Interface position detection unit 10g xy stage 10h z-stage 40 System Control Unit 41 Receiving unit 42 Transmitter 43 Control Unit L1 First detected light L2 Second detected light L1' 1st surface reflected light L2' 2nd surface reflected light L1'' First backside reflected light L2'' Second backside reflected light L1''' 1st multiple reflected light L2''' 2nd multiple reflected light

Claims

1. a light source unit that emits a first detection light; a condenser lens that condenses the first detection light emitted from the light source unit inside the workpiece; a condenser lens moving unit that moves the focus of the condenser lens in the thickness direction of the workpiece; a first detection unit that detects first multiple-reflected light, which is the first detection light that has been multiple-reflected within the workpiece; a crack detection unit that detects a crack formed in the workpiece based on the intensity pattern of the first multiple reflected light.

2. the first detection unit detects first back-surface reflected light, which is the first detection light reflected by a back surface of the workpiece; The crack detection device according to claim 1, characterized in that the crack detection unit detects a crack formed in the workpiece based on the intensity pattern of the first back-surface reflected light and the intensity pattern of the first multiple-reflected light.

3. The crack detection device described in claim 2, characterized in that the crack detection unit detects cracks formed in the workpiece based on the intensity pattern of the first back-surface reflected light, and further detects cracks formed in the workpiece based on the intensity pattern of the first multiple-reflected light, and compares the results.

4. The crack detection device described in claim 2 or 3, characterized in that the crack detection unit detects the type of crack formed in the workpiece based on a combination of the intensity pattern of the first back-surface reflected light and the intensity pattern of the first multiple-reflected light.

5. emitting a first detection light; a step of focusing the first detection light emitted from a light source unit inside the workpiece using a focusing lens; moving the focus of the condenser lens in the thickness direction of the workpiece; detecting first multiple-reflected light, which is the first detection light that has been multiple-reflected within the workpiece; and detecting a crack formed in the workpiece based on the intensity pattern of the first multiple reflection light.

Images