Laser processing methods, semiconductor device manufacturing methods, and inspection devices

Abstract

A camera device for capturing images of a modified region formed on an object by irradiating it with laser light and / or cracks extending from the modified region; characterized in that it comprises: a first camera unit for capturing images of the object by light penetrating the object; and a first control unit for controlling the first camera unit; the first control unit performs image processing when switching between the formation of the modified region along a first line and the formation of the modified region along a second line intersecting the first line, the image processing controlling the first camera unit in a manner that captures images of the modified region formed along the first line and / or the region including the cracks extending from the modified region.

Description

Laser processing method, semiconductor device manufacturing method, and inspection device One aspect of the present disclosure relates to an imaging device, a laser processing device, and an imaging method. A laser processing device is known that irradiates the wafer with laser light from the back side of the semiconductor substrate to cut a wafer having a semiconductor substrate and a functional element layer formed on the surface of the semiconductor substrate along a plurality of lines, thereby forming a plurality of rows of modified regions along the plurality of lines within the semiconductor substrate. The laser processing device described in Patent Document 1 is equipped with an infrared camera that can observe the modified regions formed within the semiconductor substrate and processing damage to the functional element layer from the back side of the semiconductor substrate. [Prior Art Document] [Patent Document] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-64746 [Technical Problem to be Solved by the Invention] As in the laser processing apparatus described in Patent Document 1, there is a need for non-destructive identification of modified regions formed within a wafer. In response to this, the infrared camera of the laser processing apparatus described in Patent Document 1 is positioned on a straight line downstream of the wafer processing position of the processing optical system in the wafer's travel direction. Therefore, an infrared camera captures the wafer at the same planned cutting line as the wafer processing position in the processing optical system, enabling immediate confirmation and measurement of the formation position of the modified region or processing damage formed within the wafer. However, confirming and measuring the modified region using an infrared camera takes a considerable amount of time. Therefore, if the laser processing device described in Patent Document 1 attempts to simultaneously form and confirm the modified region, the speed of forming the modified region will be limited, potentially reducing processing efficiency. Therefore, one aspect of the present disclosure is to provide an imaging device, a laser processing device, and an imaging method that can suppress a decrease in processing efficiency and enable non-destructive verification. [Technical Solution to Problem] One aspect of the present disclosure is: a camera device for capturing images of a modified region formed on an object by irradiating laser light and / or cracks extending from the modified region; the device is characterized by comprising: a first camera unit for capturing images of the object by light penetrating the object; and a first control unit for controlling the first camera unit; the first control unit performs a camera process at the timing of switching between forming a modified region along a first line and forming a modified region along a second line intersecting the first line, the camera process controlling the first camera unit in a manner of capturing images of the modified region formed along the first line and / or a region including cracks extending from the modified region. In the device, the first control unit performs the first imaging process, which is to control the first imaging unit to capture the modified area of ​​the object and / or the area including the cracks extending from the modified area by light penetrating the object. Therefore, without destroying the object, it is possible to obtain an image of the modified area, etc. (the modified area and / or the cracks extending from the modified area (the same below)) and to confirm it. In particular, in the device, the first control unit performs the aforementioned imaging process at the timing of switching between forming the modified area along the first line and forming the modified area along the second line intersecting the first line. Therefore, the modified area, etc. can be confirmed without affecting the speed of forming the modified area. That is, according to the device, it is possible to suppress the reduction in processing efficiency and to perform confirmation in a non-destructive manner. One form of the laser processing device disclosed herein comprises: the aforementioned camera device; a laser irradiation unit for irradiating an object with laser light; and a drive unit in which the laser irradiation unit is mounted and drives the laser irradiation unit in a direction intersecting an incident plane of the laser light on the object; the first camera unit is mounted on the drive unit together with the laser irradiation unit. This device includes the aforementioned imaging device. Therefore, this device can suppress reductions in processing efficiency and enable non-destructive verification. Furthermore, the device includes a drive unit that drives the laser irradiation unit in a direction (incident direction) that intersects the incident plane of the laser light on the object. Furthermore, the first imaging unit is attached to the drive unit together with the laser irradiation unit. Therefore, positional information regarding the incident direction can be easily shared during the formation of the modified region by irradiation with laser light and during imaging processing. A laser processing device according to one aspect of the present disclosure may also include: a second imaging unit for capturing an image of an object using light that passes through the object; and a second control unit for controlling the laser irradiation unit and the second imaging unit; the first imaging unit including a first lens for transmitting the light that passes through the object; and a first light detection unit for detecting the light that has passed through the first lens; the second imaging unit including a second lens for transmitting the light that passes through the object; and a second light detection unit for detecting the light that has passed through the second lens; and the second control unit for performing an alignment process for controlling the laser irradiation unit and the second imaging unit so as to align the irradiation position of the laser light based on the detection result of the second light detection unit. In this manner, by using the second imaging unit for aligning the irradiation position of the laser light in addition to the first imaging unit for capturing an image of the modified region, etc., it is possible to use appropriate optical systems for each. In one aspect of the laser processing apparatus disclosed herein, the numerical aperture of the first lens may be larger than that of the second lens. In this case, alignment can be more accurately performed by observing with a relatively small numerical aperture, while the modified region, etc., can be imaged with a relatively large numerical aperture. One aspect of the present disclosure is: a camera method for capturing images of a modified region formed on an object by irradiating a laser beam and / or cracks extending from the modified region; the method is characterized by comprising: a camera step of capturing images of the modified region formed along the first line and / or a region including cracks extending from the modified region by light penetrating the object when switching between forming the modified region along the first line and forming the modified region along the second line intersecting the first line. In this method, the modified area of ​​the object and / or the area including the cracks extending from the modified area are photographed by light that penetrates the object. Therefore, it is possible to obtain an image of the modified area, etc., and to confirm it without destroying the object. In particular, in this method, the aforementioned photography is performed at the timing of switching between forming the modified area along the first line and forming the modified area along the second line that intersects the first line. Therefore, it is possible to confirm the modified area, etc. without affecting the speed of forming the modified area. That is, according to this method, it is possible to suppress the reduction in processing efficiency and to confirm it in a non-destructive manner. [Effects of the Invention] According to one aspect of the present disclosure, an imaging device, a laser processing device, and an imaging method are provided that can suppress a decrease in processing efficiency and enable non-destructive confirmation. The following describes the embodiments in detail with reference to the drawings. In the drawings, identical or equivalent components are given the same reference numerals and repeated descriptions are omitted. Furthermore, the drawings show a rectangular coordinate system defined by the X-axis, Y-axis, and Z-axis. As shown in FIG1 , a laser processing apparatus 1 includes a stage 2, a laser irradiation unit 3, a plurality of imaging units 4, 5, and 6, a drive unit 7, and a control unit 8. The laser processing apparatus 1 irradiates an object 11 with laser light L, thereby forming a modified region 12 on the object 11. The stage 2 supports the object 11 by, for example, sucking a thin film attached to the object 11. The stage 2 is movable in the X and Y directions and rotatable about an axis parallel to the Z direction. The X and Y directions are first and second horizontal directions perpendicular to each other, while the Z direction is a vertical direction. Laser irradiation unit 3 focuses laser light L, which has penetrating properties, on object 11 and irradiates object 11. When laser light L is focused into object 11 supported by stage 2, it is particularly absorbed by the portion corresponding to focal point C of laser light L, forming a modified region 12 within object 11. The modified region 12 is a region whose density, refractive index, mechanical strength, or other physical properties differ from those of the surrounding unmodified region. Examples of the modified region 12 include a melt-processed region, a cracked region, a dielectric breakdown region, and a region with a changed refractive index. The modified region 12 exhibits properties such that cracks easily extend from the modified region 12 to both the incident side and the opposite side of the laser beam L. These properties of the modified region 12 are utilized to cut the object 11. For example, by moving the stage 2 in the X direction and the focal point C relative to the object 11 in the X direction, a plurality of modified spots 12s are formed in a row along the X direction. Each modified spot 12s is formed by irradiation with a single pulse of laser light L. A row of modified regions 12 is a collection of the plurality of modified spots 12s arranged in a row. Adjacent modified spots 12s may be connected or separated, depending on the relative movement speed of the focal point C relative to the object 11 and the repetition rate of the laser light L. The imaging unit (first imaging unit) 4, under the control of the control unit (first control unit) 8, uses light that penetrates the object 11 to capture an image of the object 11 supported by the stage 2. More specifically, the imaging unit 4 captures images of the modified region 12 formed in the object 11 and the leading ends of the cracks extending from the modified region 12. In this embodiment, the imaging unit 4 and the control unit 8 that controls the imaging unit 4 function as the imaging device 10. The imaging unit (second imaging unit) 5 and the imaging unit 6 capture an image of the object 11 supported by the stage 2 using light that penetrates the object 11 under the control of the control unit (second control unit) 8. The images captured by the imaging units 5 and 6 are used, for example, to align the irradiation position of the laser beam L. The drive unit 7 supports the laser irradiation unit 3 and the plurality of imaging units 4, 5, and 6. In other words, the laser irradiation unit 3 is mounted on the drive unit 7. Furthermore, the imaging units 4, 5, and 6 are mounted on the drive unit 7 together with the laser irradiation unit 3. The drive unit 7 moves the laser irradiation unit 3 and the plurality of imaging units 4, 5, and 6 in the Z direction. Here, the Z direction intersects the incident surface of the laser light L on the object 11 (e.g., the rear surface 21b described later). The control unit 8 controls the operation of the stage 2, the laser irradiation unit 3, the plurality of imaging units 4, 5, 6, and the drive unit 7. The control unit 8 is configured as a computer device including a processor, memory, storage, and a communication device. In the control unit 8, the processor executes the software (program) read from the memory, reads and writes data from the memory and storage, and controls the communication performed by the communication device. [Composition of the Object] The object 11 of this embodiment is a wafer 20, as shown in Figures 2 and 3. Wafer 20 includes a semiconductor substrate 21 and a functional element layer 22. Semiconductor substrate 21 has a surface 21a and a back surface 21b. Semiconductor substrate 21 is, for example, a silicon substrate. Functional element layer 22 is formed on surface 21a of semiconductor substrate 21. Functional element layer 22 includes a plurality of functional elements 22a arranged two-dimensionally along surface 21a. Functional elements 22a include, for example, light-receiving elements such as photodiodes, light-emitting elements such as laser diodes, and circuit elements such as memory. Functional elements 22a may be stacked in a three-dimensional manner. Furthermore, although grooves 21c indicating crystal orientation are provided in semiconductor substrate 21, orientation flats may be provided in place of grooves 21c. The wafer 20 is cut along a plurality of lines 15 into individual functional elements 22a. The plurality of lines 15, when viewed in the thickness direction of the wafer 20, pass between each of the plurality of functional elements 22a. More specifically, the plurality of lines 15, when viewed in the thickness direction of the wafer 20, pass through the center (the center in the width direction) of the grid region 23. The grid region 23 extends in the functional element layer 22 so as to pass between adjacent functional elements 22a. In this embodiment, the plurality of functional elements 22a are arranged in a matrix along the surface 21a, and the plurality of lines 15 are arranged in a grid pattern. Furthermore, although the lines 15 are imaginary lines, they may also be actually drawn lines. The line 15 includes a plurality of first lines 15a and a plurality of second lines 15b that intersect (are orthogonal to) the first lines 15a. Here, the first lines 15a are parallel to each other, and the second lines 15b are parallel to each other. Thus, a rectangular functional element 22a is defined by a pair of adjacent first lines 15a and a pair of adjacent second lines 15b. In other words, the wafer 20 (object 11), when viewed from the Z direction, includes a plurality of functional elements 22a defined by the first lines 15a and the second lines 15b. The intersection of the first line 15a and the second line 15b defines the corner of the functional element 22a, and the first line 15a and the second line 15b each define the side of the functional element 22a. [Composition of the laser irradiation unit] As shown in Figure 4, the laser irradiation unit 3 includes a light source 31, a spatial light modulator 32, and a focusing lens 33. The light source 31 outputs laser light L, for example, by pulse oscillation. The spatial light modulator 32 modulates the laser light L output from the light source 31. The spatial light modulator 32 is, for example, a reflective liquid crystal on silicon (LCOS) spatial light modulator (SLM). The focusing lens 33 focuses the laser light L modulated by the spatial light modulator 32. In this embodiment, the laser irradiation unit 3 irradiates the wafer 20 with laser light L along a plurality of lines 15 from the rear surface 21b side of the semiconductor substrate 21, thereby forming two rows of modified regions 12a and 12b within the semiconductor substrate 21 along the plurality of lines 15. The modified region (first modified region) 12a is the modified region closest to the surface 21a of the two rows of modified regions 12a and 12b. The modified region (second modified region) 12b is the modified region closest to the modified region 12a of the two rows of modified regions 12a and 12b, and is also the modified region closest to the rear surface 21b. The two rows of modified regions 12a and 12b are adjacent to each other in the thickness direction (Z direction) of the wafer 20. These two rows of modified regions 12a and 12b are formed by moving two focal points C1 and C2 relative to the semiconductor substrate 21 along a line 15. The laser light L is modulated by the spatial light modulator 32, for example, so that the focal point C2 is positioned behind the focal point C1 in the direction of travel and on the incident side of the laser light L. The laser irradiation unit 3 irradiates the wafer 20 with laser light L along a plurality of lines 15 from the rear surface 21b side of the semiconductor substrate 21, so that the cracks 14 spanning the two rows of modified regions 12a and 12b reach the surface 21a of the semiconductor substrate 21. For example, for a semiconductor substrate 21 having a thickness of 775 μm, the two focal points C1 and C2 are focused at positions 54 μm and 128 μm from the surface 21a, respectively. The laser light L is then irradiated along the plurality of lines 15 from the rear surface 21b side of the semiconductor substrate 21. The wavelength of the laser light L is 1099 nm, the pulse width is 700 nanoseconds, and the repetition frequency is 120 kHz. Furthermore, the output of the laser light L at the focal point C1 is 2.7 W, the output of the laser light L at the focal point C2 is 2.7 W, and the relative moving speed of the two focal points C1 and C2 with respect to the semiconductor substrate 21 is 800 mm / sec. The formation of two rows of modified regions 12a and 12b and cracks 14 is carried out as follows. That is, in a subsequent step, the back surface 21b of the semiconductor substrate 21 is ground to thin the semiconductor substrate 21, exposing the cracks 14 on the back surface 21b, and the wafer 20 is then cut along a plurality of lines 15 into a plurality of semiconductor devices. [Composition of the Inspection Camera Unit] As shown in Figure 5, the imaging unit 4 includes a light source 41, a mirror 42, an objective lens (first lens) 43, and a light detection unit (first light detection unit) 44. The light source 41 outputs light I1 that is transparent to the semiconductor substrate 21. The light source 41 is composed of, for example, a halogen lamp and a filter, and outputs light I1 in the near-infrared region. The light I1 output from the light source 41 is reflected by the mirror 42, passes through the objective lens 43, and irradiates the wafer 20 from the rear surface 21b of the semiconductor substrate 21. At this time, the stage 2 supports the wafer 20 having two rows of modified regions 12a and 12b formed thereon, as described above. The objective lens 43 allows the light I1 reflected by the surface 21a of the semiconductor substrate 21 to pass through. In other words, the objective lens 43 allows the light I1 that propagates (passes through) the semiconductor substrate 21 to pass through. The numerical aperture (NA) of the objective lens 43 is 0.45 or greater. The objective lens 43 has a correction ring 43a. The correction ring 43a corrects the aberration caused by the light I1 in the semiconductor substrate 21, for example, by adjusting the distance between the multiple lenses constituting the objective lens 43. The light detection unit 44 detects the light I1 that has passed through the objective lens 43 and the mirror 42. The light detection unit 44 is composed of, for example, an InGaAs camera and detects the light I1 in the near-infrared region. The imaging unit 4 is capable of capturing images of the two rows of modified regions 12a and 12b, as well as the leading ends of a plurality of cracks 14a, 14b, 14c, and 14d (details will be described later). Cracks 14a extend from the modified region 12a to the surface 21a side. Cracks 14b extend from the modified region 12a to the back surface 21b side. Cracks 14c extend from the modified region 12b to the surface 21a side. Cracks 14d extend from the modified region 12b to the back surface 21b side. The control unit 8 controls the laser irradiation unit 3 to irradiate the laser beam L (see FIG4 ) under the condition that the crack 14 spanning the two rows of modified regions 12a and 12b reaches the surface 21a of the semiconductor substrate 21. However, if the crack 14 does not reach the surface 21a due to an abnormality, a plurality of cracks 14a, 14b, 14c, and 14d will be formed. [Configuration of the Alignment Correction Imaging Unit] As shown in Figure 6, the imaging unit 5 includes a light source 51, a mirror 52, a lens (second lens) 53, and a light detection unit (second light detection unit) 54. The light source 51 outputs light I2 that is transparent to the semiconductor substrate 21. The light source 51 is composed of, for example, a halogen lamp and a filter, and outputs light I2 in the near-infrared region. The light source 51 can also be shared with the light source 41 of the imaging unit 4. The light I2 output from the light source 51 is reflected by the mirror 52, passes through the lens 53, and irradiates the wafer 20 from the rear surface 21b of the semiconductor substrate 21. Lens 53 transmits light I2 reflected by surface 21a of semiconductor substrate 21. That is, lens 53 transmits light I2 that has passed through semiconductor substrate 21. The numerical aperture of lens 53 is 0.3 or less. That is, the numerical aperture of objective lens 43 of imaging unit 4 is larger than that of lens 53. Light detection unit 54 detects light I2 that has passed through lens 53 and mirror 52. Light detection unit 55 is comprised of, for example, an InGaAs camera and detects light I2 in the near-infrared region. The imaging unit 5 irradiates the wafer 20 with light I2 from the inner side 21b under the control of the control unit 8 (second control unit), and detects the light I2 returned from the surface 21a (functional element layer 22), thereby capturing an image of the functional element layer 22. Furthermore, the imaging unit 5 also irradiates the wafer 20 with light from the inner side 21b under the control of the control unit 8, and detects the light I2 returned from the formation position of the modified regions 12a and 12b of the semiconductor substrate 21, thereby obtaining an image of the region including the modified regions 12a and 12b. These images are used to align the irradiation position of the laser light L. The imaging unit 6 has the same structure as the imaging unit 5, except that the magnification is lower than that of the lens 53 (for example, 6 times in the imaging unit 5 and 1.5 times in the imaging unit 6), and is used for alignment in the same manner as the imaging unit 5. [Imaging principle of the inspection imaging unit] Using the imaging unit 4 shown in FIG5 , as shown in FIG7 , the focus F (the focus of the objective lens 43) is moved from the back surface 21b side to the surface 21a side of the semiconductor substrate 21, where the crack 14 extending from the two rows of modified regions 12a and 12b reaches the surface 21a. In this case, if the focus F is adjusted from the back surface 21b side to the front end 14e of the crack 14 extending from the modified region 12b to the back surface 21b side, the front end 14e can be confirmed (the image on the right side of FIG7 ). However, even if the focus F is adjusted from the back surface 21b side to the crack 14 itself and the front end 14e of the crack 14 reaching the surface 21a, no confirmation is possible (the image on the left side of FIG7 ). Alternatively, if the focus F is adjusted from the back surface 21b side to the surface 21a of the semiconductor substrate 21, the functional element layer 22 can be confirmed. Furthermore, using the imaging unit 4 shown in FIG5 , as shown in FIG8 , a focus F is moved from the rear surface 21b side toward the surface 21a side of a semiconductor substrate 21 having a crack 14 spanning two rows of modified regions 12a and 12b, where the crack 14 does not reach the surface 21a. In this case, if the focus F is focused from the rear surface 21b side on the leading edge 14e of the crack 14 extending from the modified region 12a to the surface 21a, the leading edge 14e can be observed (the image on the left side of FIG8 ). However, if the focus F is focused from the rear surface 21b side on the region opposite the rear surface 21b side relative to the surface 21a (i.e., the region on the functional device layer 22 side relative to the surface 21a), and a virtual focus Fv symmetrical to the focus F with respect to the surface 21a is positioned at the leading edge 14e, the leading edge 14e can be observed (the image on the right side of FIG8 ). The virtual focus Fv is a point symmetrical to the focus F with respect to the surface 21a, taking into account the refractive index of the semiconductor substrate 21. As described above, the reason why cracks 14 cannot be confirmed is presumably because their width is smaller than the wavelength of the illumination light I1. Figures 9 and 10 show SEM (Scanning Electron Microscope) images of the modified region 12 and cracks 14 formed within the semiconductor substrate 21, which is a silicon substrate. Figure 9(b) is an enlarged image of area A1 shown in Figure 9(a), Figure 10(a) is an enlarged image of area A2 shown in Figure 9(b), and Figure 10(b) is an enlarged image of area A3 shown in Figure 10(a). Thus, the width of cracks 14 is approximately 120 nm, which is smaller than the wavelength of the near-infrared light I1 (e.g., 1.1 to 1.2 μm). The imaging principle envisioned in accordance with the above considerations is as follows. As shown in FIG11(a), if the focal point F is positioned in the air, light I1 will not be reflected, resulting in a dark image (the image on the right side of FIG11(a)). As shown in FIG11(b), if the focal point F is positioned inside the semiconductor substrate 21, light I1 reflected from the surface 21a will be reflected, resulting in a white image (the image on the right side of FIG11(b)). As shown in FIG11(c), if the focal point F is focused on the modified region 12 from the back surface 21b, a portion of the light I1 reflected from the surface 21a and returned will be absorbed or scattered by the modified region 12, resulting in an image showing the dark modified region 12 against a white background (the image on the right side of FIG11(c)). As shown in (a) and (b) of Figure 12, if the focus F is focused on the front end 14e of the crack 14 from the inside 21b side, the light will be confined near the front end 14e due to, for example, optical characteristics (stress concentration, distortion, discontinuity in atomic density, etc.) generated near the front end 14e, thereby causing a portion of the light I1 reflected and returned by the surface 21a to be scattered, reflected, interfered, absorbed, etc., so that an image showing the dark front end 14e against a white background is obtained (the images on the right side of (a) and (b) of Figure 12). As shown in (c) of Figure 12, if the focus F is focused on a portion other than the vicinity of the front end 14e of the crack 14 from the inside 21b side, at least a portion of the light I1 reflected by the surface 21a will return, so a white image is obtained (the image on the right side of (c) of Figure 12). [Inspection principle of the inspection camera unit] The control unit 8 controls the laser irradiation unit 3 to irradiate the laser beam L under conditions such that the crack 14 spanning the two rows of modified regions 12a and 12b reaches the surface 21a of the semiconductor substrate 21. As expected, when the crack 14 spanning the two rows of modified regions 12a and 12b reaches the surface 21a, the state of the front end 14e of the crack 14 is as described below. Specifically, as shown in FIG13 , the front end 14e of the crack 14 does not appear in the region between the modified region 12a and the surface 21a, or in the region between the modified region 12a and the modified region 12b. The position of the front end 14e of the crack 14 extending from the modified region 12b to the rear surface 21b (hereinafter simply referred to as the "front end position") is located on the rear surface 21b side relative to the reference position P between the modified region 12b and the rear surface 21b. In contrast, the control unit 8 controls the laser irradiation unit 3 to irradiate the laser beam L under conditions such that the crack 14 spanning the two rows of modified regions 12a and 12b reaches the surface 21a of the semiconductor substrate 21. However, if a problem occurs, such that the crack 14 spanning the two rows of modified regions 12a and 12b fails to reach the surface 21a, the state of the front end 14e of the crack 14 will be as follows. Specifically, as shown in FIG14 , the front end 14e of the crack 14a extending from the modified region 12a to the surface 21a side appears in the region between the modified region 12a and the surface 21a. The front end 14e of the crack 14b extending from the modified region 12a to the rear surface 21b side and the front end 14e of the crack 14c extending from the modified region 12b to the surface 21a side appear in the region between the modified region 12a and the modified region 12b. The tip of the crack 14 extending from the modified region 12b to the rear surface 21b is located on the surface 21a relative to the reference position P between the modified region 12b and the rear surface 21b. Based on the above, if the control unit 8 performs at least one of the following first, second, third, and fourth inspections, it is possible to evaluate whether the cracks 14 spanning the two rows of modified regions 12a and 12b have reached the surface 21a of the semiconductor substrate 21. The first inspection determines whether the front end 14e of the crack 14a extending from the modified region 12a to the surface 21a side exists in the inspection region R1, using the region between the modified region 12a and the surface 21a as the inspection region R1. The second inspection determines whether the front end 14e of the crack 14b extending from the modified region 12a to the rear surface 21b side exists in the inspection region R2, using the region between the modified region 12a and the modified region 12b as the inspection region R2. The third inspection determines whether the front end 14e of the crack 14c extending from the modified region 12b to the surface 21a side exists in the inspection region R2. The fourth inspection is to use the area extending from the reference position P to the inner side 21b but not reaching the inner side 21b as the inspection area R3, and to determine whether the front end position of the crack 14 extending from the modified area 12b to the inner side 21b is located in the inspection area R3. Inspection area R1, inspection area R2, and inspection area R3 can be set by focusing the two focal points C1 and C2 on the position of the semiconductor substrate 21 before forming the two rows of modified areas 12a and 12b. When the crack 14 spanning the two rows of modified areas 12a and 12b reaches the surface 21a of the semiconductor substrate 21, the front end position of the crack 14 extending from the modified area 12b to the back 21b side is stable, so the reference position P and inspection area R3 can be set based on the results of the measurement processing. In addition, the camera unit 4, as shown in Figures 13 and 14, can respectively capture the two modified areas 12a and 12b. Therefore, after forming the two rows of modified areas 12a and 12b, the inspection area R1, inspection area R2, and inspection area R3 can also be set based on the positions of the two modified areas 12a and 12b. [Laser processing method and semiconductor device manufacturing method] The semiconductor device manufacturing method of this embodiment will be described with reference to Fig. 15. The semiconductor device manufacturing method of this embodiment includes a laser processing method performed by the laser processing apparatus 1. First, a wafer 20 is prepared and placed on stage 2 of laser processing apparatus 1. Next, laser processing apparatus 1 irradiates wafer 20 with laser light L along a plurality of lines 15 from the rear surface 21b of semiconductor substrate 21, thereby forming two rows of modified regions 12a and 12b along the plurality of lines 15 within semiconductor substrate 21 (S01, first step). In this step, laser processing apparatus 1 irradiates wafer 20 with laser light L along the plurality of lines 15 from the rear surface 21b of semiconductor substrate 21, such that cracks 14 spanning the two rows of modified regions 12a and 12b reach the surface 21a of semiconductor substrate 21. Next, the laser processing device 1 inspects the area between the modified region 12a and the modified region 12b, serving as the inspection region R2, to determine whether the leading end 14e of the crack 14b extending from the modified region 12a to the rear surface 21b is present (S02, step 2). In this step, the laser processing device 1 focuses the focal point F on the inspection region R2 from the rear surface 21b and detects light I1 propagating (passing) through the semiconductor substrate 21 from the surface 21a toward the rear surface 21b. This detects whether the leading end 14e of the crack 14b is present in the inspection region R2. In this manner, in this embodiment, the laser processing device 1 performs the second inspection. More specifically, the objective lens 43 of the imaging unit 4 focuses the focal point F within the inspection region R2 from the rear surface 21b side. The light detection unit 44 of the imaging unit 4 detects the light I1 that propagates (passes through) the semiconductor substrate 21 from the surface 21a side toward the rear surface 21b side. At this time, the driving unit 7 moves the imaging unit 4 in the Z direction, causing the focal point F to move relatively in the Z direction within the inspection region R2. This allows the light detection unit 44 to acquire image data at various locations in the Z direction. Consequently, the control unit 8 inspects the inspection region R2 for the presence of the leading end 14e of the crack 14b based on the signal output from the light detection unit 44 (i.e., the image data at various locations in the Z direction). Next, the control unit 8 evaluates the processing results of step S01 based on the inspection results of step S02 (step S03, the third step). In this step, if the front end 14e of the crack 14b is not present in the inspection region R2, the control unit 8 evaluates that the crack 14 spanning the two rows of modified regions 12a and 12b has reached the surface 21a of the semiconductor substrate 21. On the other hand, if the front end 14e of the crack 14b is present in the inspection region R2, the control unit 8 evaluates that the crack 14 spanning the two rows of modified regions 12a and 12b has not reached the surface 21a of the semiconductor substrate 21. Next, if the crack 14 spanning the two rows of modified regions 12a and 12b reaches the surface 21a of the semiconductor substrate 21, the control unit 8 performs a pass process (S04). In this pass process, the control unit 8 causes the display of the laser processing apparatus 1 to display the pass status, displays image data on the display, stores the pass status in the memory unit of the laser processing apparatus 1 (as a log), and stores the image data in the memory unit. In this way, the display of the laser processing apparatus 1 functions as a notification unit, notifying the operator of the pass status. On the other hand, if the crack 14 spanning the two rows of modified regions 12a and 12b does not reach the surface 21a of the semiconductor substrate 21, the control unit 8 performs a failure process (S05). In this step, as a failure process, the control unit 8 causes a lamp included in the laser processing device 1 to illuminate to indicate failure, displays the failure status on a display included in the laser processing device 1, and stores the failure status in a memory included in the laser processing device 1 (as a log). In this way, at least one of the lamp and display included in the laser processing device 1 functions as a notification unit, notifying the operator of the failure status. The above steps S01 to S05 are the laser processing method implemented by the laser processing device 1 . In the case of performing qualified processing of step S04 (i.e., in step S03, evaluating whether the cracks 14 spanning the two rows of modified regions 12a and 12b reach the surface 21a of the semiconductor substrate 21), the inner surface 21b of the semiconductor substrate 21 is ground by a grinding device to expose the cracks 14 spanning the two rows of modified regions 12a and 12b on the inner surface 21b, and the wafer 20 is cut into a plurality of semiconductor devices along a plurality of lines 15 (S06, step 4). Steps S01 to S06 described above constitute a semiconductor device manufacturing method including a laser processing method performed by the laser processing apparatus 1. Furthermore, if a failure is detected in step S05 (i.e., if the crack 14 spanning two rows of modified regions 12a and 12b does not reach the surface 21a of the semiconductor substrate 21 in step S03), the laser processing apparatus 1 is inspected and adjusted, and the wafer 20 is laser processed again (recovery processing). Here, the grinding and cutting of wafer 20 in step S06 will be described in more detail. As shown in Figure 16 , grinding device 200 grinds (polishes) back surface 21b of semiconductor substrate 21 to thin it, exposing cracks 14 on back surface 21b. Wafer 20 is then cut along a plurality of lines 15 into a plurality of semiconductor devices 20a. In this step, grinding device 200 grinds back surface 21b of semiconductor substrate 21 to a fourth inspection reference position P. As described above, when the cracks 14 spanning two rows of modified regions 12a and 12b reach the surface 21a of the semiconductor substrate 21, the tip of the cracks 14 extending from the modified regions 12b to the rear surface 21b is located on the rear surface 21b side relative to the reference position P. Therefore, by grinding the rear surface 21b of the semiconductor substrate 21 to the reference position P, the cracks 14 spanning two rows of modified regions 12a and 12b can be exposed on the rear surface 21b. In other words, with the grinding completion position as the reference position P, and the cracks 14 spanning two rows of modified regions 12a and 12b reaching the surface 21a of the semiconductor substrate 21 and the reference position P, the wafer 20 is irradiated with laser light L along a plurality of lines 15 from the rear surface 21b side of the semiconductor substrate 21. Next, as shown in Figure 17, an expansion device 300 expands the expansion tape 201 attached to the back surface 21b of the semiconductor substrate 21, thereby separating the plurality of semiconductor devices 20a from each other. The expansion tape 201 is, for example, a DAF (die attach film) composed of a base material 201a and an adhesive layer 201b. In this case, the expansion of the expansion tape 201 severs the adhesive layer 201b disposed between the back surface 21b of the semiconductor substrate 21 and the base material 201a, along with the semiconductor devices 20a. The severed adhesive layer 201b is then picked up along with the semiconductor devices 20a. Here, as described above, imaging of the wafer 20 is performed while inspecting whether the front ends 14e of the cracks 14b are present in a predetermined region. Imaging of the wafer 20 is performed by the imaging device 10 comprising the imaging unit 4 and the control unit 8. In the example described above, imaging of the wafer 20 is performed after two rows of modified regions 12a and 12b are formed within the semiconductor substrate 21 along all the lines 15. However, the timing of the second inspection (imaging of the wafer 20) is not limited to this. For example, the second inspection may be performed at a timing when the modified regions 12a and 12b are formed along the first line 15a and the modified regions 12a and 12b are formed along the second line 15b. This will be described in detail below. The laser processing method shown in Figure 18 includes an imaging method. As shown in Figure 18 , the laser processing apparatus 1 first performs alignment of the processing start position with the wafer 20 mounted on the stage 2 ( S11 ). In this step, for example, the imaging unit 5 performs alignment by imaging the wafer 20 under the control of the control unit 8 . More specifically, in this step, the control unit 8 controls the imaging unit 5 to capture an image of the functional device layer 22 . On the other hand, initial information including the dimensions of the functional element 22a (tool dimensions), the workpiece dimensions of the wafer 20 (the dimensions of the processing area), and a reference image of the functional element layer 22 is pre-registered in the laser processing apparatus 1 (e.g., the control unit 8). The control unit 8 then aligns the irradiation position of the laser beam L (the position of the laser irradiation unit 3 in the X and Y directions) based on the image captured by the imaging unit 5 and this initial information. In the next step, the control unit 8 controls the drive unit 7 to set the processing height (Z-direction position) of the laser irradiation unit 3 (S12). The control unit 8 then begins forming the modified regions 12a and 12b (S13). Here, as an example, processing is performed along the first line 15a. That is, in this step, the laser processing apparatus 1 irradiates the wafer 20 with laser light L along the first line 15a from the back surface 21b of the semiconductor substrate 21, thereby forming two rows of modified regions 12a and 12b within the semiconductor substrate 21 along the first line 15a. Next, after processing a single first thread 15a, the control unit 8 determines whether the position of the first thread 15a is at the pre-set alignment position (S14). This alignment is a realignment to correct for the displacement caused by the alignment performed in step S11. This realignment can be performed after each first thread 15a is processed, but it is more efficient to perform it after processing multiple first threads 15a. In other words, the alignment position can be set individually for each first thread 15a, but it is more efficient to set a single alignment for multiple first threads 15a. If the position of the first line 15a processed in step S13 is not the alignment position, the process returns to step S13 and continues to form the modified regions 12a and 12b along the remaining first lines 15a. On the other hand, if the position of the first line 15a processed in step S13 is the alignment position, re-alignment is then performed. In other words, in this case, the formation of the modified regions 12a and 12b is temporarily suspended to allow alignment. In the next step, realignment is performed as described above (the control unit 8 performs alignment processing) (S15). An example of this alignment is as follows. That is, the control unit 8 controls the camera unit 5 to thereby capture the image of the functional element layer 22 at the alignment correction position. Furthermore, the control unit 8 controls the camera unit 5 to thereby capture the area including the modified regions 12a and 12b at this position. Next, the control unit 8 detects the offset of the modified regions 12a and 12b relative to the predetermined position (for example, the center position) of the grid area 23 based on the two images. The control unit 8 realigns the irradiation position of the laser light L based on the detected offset. Alternatively, another example of alignment is as follows. Specifically, the control unit 8 controls the imaging unit 5 to capture an image of the functional element layer 22 at the alignment calibration position. The control unit 8 then performs pattern matching between an image of the functional element layer 22 at the alignment calibration position, acquired before processing, and the image of the functional element layer 22 acquired in this step to detect the amount of offset between characteristic points such as alignment marks. The control unit 8 adjusts the irradiation position of the laser beam L based on the detected offset. In the next step, the control unit 8 determines whether the formation of the modified regions 12a, 12b has been completed along all of the first lines 15a (S16). If the result of this determination is that the formation of the modified regions 12a, 12b has not been completed along all of the first lines 15a, the process returns to step S13 and continues to form the modified regions 12a, 12b along the remaining first lines 15a. On the other hand, if the result of this determination is that the formation of the modified regions 12a, 12b has been completed along all of the first lines 15a, the formation of the modified regions 12a, 12b along the second lines 15b begins. In other words, in this case, the formation of the modified regions 12a, 12b is temporarily suspended, and the timing of forming the modified regions 12a, 12b along the first lines 15a and the timing of forming the modified regions 12a, 12b along the second lines 15b are switched. The second inspection is performed at this time. That is, in the next step, the control unit 8 controls the imaging unit 4 to capture an image of the wafer 20 (S17, imaging step). Here, the control unit 8 moves the imaging unit 4 in the Z direction, thereby relatively moving the focal point F within the wafer 20 in the Z direction. This allows the imaging unit 4 to capture images at various locations in the Z direction. Consequently, the images obtained may include only the modified regions 12a and 12b, the modified regions 12a and 12b and the cracks 14, or only the cracks 14. Specifically, here, the control unit 8 performs an imaging process (imaging step) at the timing of switching between forming the modified regions 12a, 12b along the first line 15a and forming the modified regions 12a, 12b along the second line 15b. This imaging process controls the imaging unit 4 to capture images of the modified regions 12a, 12b formed along the first line 15a and / or the region including the cracks 14 extending from the modified regions 12a, 12b. The image obtained in this step is provided to the control unit 8. Therefore, the control unit 8 can perform the second inspection based on the supplied image data and the aforementioned method and principles. In the next step, the laser processing device 1 irradiates the wafer 20 with laser light L along a second line 15b from the back side 21b of the semiconductor substrate 21, thereby forming two rows of modified regions 12a and 12b inside the semiconductor substrate 21 along the second line 15b (S18). Next, after processing a single second thread 15b, the control unit 8 determines whether the position of the second thread 15b is at the pre-set alignment position (S19). This alignment is a realignment to correct for the displacement caused by the alignment performed in step S16. This realignment can be performed after each second thread 15b is processed, but it is more efficient to perform it after processing multiple second threads 15b. In other words, the alignment position can be set individually for each second thread 15b, but setting a single alignment position for multiple second threads 15b is more efficient. If the position of the second line 15b processed in step S18 is not the alignment position, the process returns to step S18 and continues to form the modified regions 12a and 12b along the other second lines 15b. On the other hand, if the position of the second line 15b processed in step S18 is the alignment position, re-alignment is then performed. In other words, in this case, the formation of the modified regions 12a and 12b is temporarily suspended to allow alignment. In the next step, re-alignment (S20) is performed as described above. The alignment here is the same as in step S15. In the next step, the control unit 8 determines whether the formation of the modified regions 12a and 12b is complete along all the second lines 15b (S21). If the result of this determination is that the formation of the modified regions 12a and 12b is not complete along all the second lines 15b, the process returns to step S18 and continues to form the modified regions 12a and 12b along the remaining second lines 15b. On the other hand, if the result of this determination is that the formation of the modified regions 12a and 12b is complete along all the second lines 15b, the process is completed. Furthermore, the location for the second inspection (i.e., the imaging area when viewed from the Z direction) can be set to at least one location among the plurality of lines 15 in the grid pattern, but as an example, it can be the edge of the functional element 22a. As described above, the functional element 22a is defined by the first line 15a and the second line 15b when viewed from the Z direction. Therefore, the location for the second inspection can be the area of ​​the functional element 22a corresponding to the edge of the first line 15a and / or the second line 15b when viewed from the Z direction. In other words, the location for the second inspection can be the area of ​​the functional element 22a excluding the area at the corner of the intersection of the first line 15a and the second line 15b when viewed from the Z direction. 18 , the second inspection is exemplified as the inspection of the cracks 14 . However, the second inspection is not limited to the second inspection, and the first inspection, the third inspection, or the fourth inspection may also be performed. [Functions and Effects of Laser Processing Method and Semiconductor Device Manufacturing Method] In the aforementioned laser processing method, a focal point F is focused from the rear surface 21b side of the semiconductor substrate 21 to the inspection region R2 between the modified regions 12a and 12b, and light I1 propagating from the surface 21a side toward the rear surface 21b side of the semiconductor substrate 21 is detected. By detecting this light I1, if the front end 14e of a crack 14b extending from the modified region 12a toward the rear surface 21b exists in the inspection region R2, the front end 14e of the crack 14b can be confirmed. Furthermore, if the front end 14e of the crack 14b exists in the inspection region R2, it is assumed that the crack 14 spanning the two rows of modified regions 12a and 12b has not reached the surface 21a of the semiconductor substrate 21. Thus, the aforementioned laser processing method can confirm whether the crack 14 spanning the two rows of modified regions 12a and 12b has reached the surface 21a of the semiconductor substrate 21. Furthermore, in the aforementioned laser processing method, if the front end 14e of the crack 14b is absent in the inspection region R2, it is estimated that the crack 14 spanning the two rows of modified regions 12a and 12b has reached the surface 21a of the semiconductor substrate 21. If the front end 14e of the crack 14b is present in the inspection region R2, it is estimated that the crack 14 spanning the two rows of modified regions 12a and 12b has not reached the surface 21a of the semiconductor substrate 21. Thus, the implementation of subsequent steps can be determined based on the evaluation results. Furthermore, in the aforementioned laser processing method, two rows of modified regions 12a and 12b are formed as the plurality of rows of modified regions 12. This allows efficient formation of the plurality of rows of modified regions 12 and inspection of cracks 14 spanning the plurality of rows of modified regions 12. Furthermore, according to the aforementioned semiconductor device manufacturing method, if it is assessed that the cracks 14 spanning two rows of modified regions 12a and 12b have not reached the surface 21a of the semiconductor substrate 21, grinding of the back surface 21b of the semiconductor substrate 21 is not performed. This prevents the wafer 20 from being reliably cut along the plurality of lines 15 after the grinding step. [Imaging Device, Imaging Method, and Function and Effect of Laser Processing Device] The aforementioned imaging device 10 images the modified regions 12a and 12b formed on the object 11 (the semiconductor substrate 21 of the wafer 20) by irradiation with laser light L, and / or the cracks 14 extending from the modified regions 12a and 12b. The imaging device 10 includes an imaging unit 4 for capturing an image of the wafer 20 using light I1 that penetrates at least the semiconductor substrate 21 of the wafer 20, and a control unit 8 for controlling the imaging unit 4. The control unit 8 performs imaging processing when switching between forming the modified regions 12a, 12b along the first line 15a and forming the modified regions 12a, 12b along the second line 15b. The imaging processing controls the imaging unit 4 in a manner of imaging the modified regions 12a, 12b formed along the first line 15a and / or the regions including the cracks 14 extending from the modified regions 12a, 12b. In the imaging device 10, the control unit 8 controls the imaging unit 4 to execute an imaging process. This imaging process uses light I1 that penetrates the semiconductor substrate 21 to capture images of the modified regions 12a, 12b and / or the regions including the cracks 14 extending from the modified regions 12a, 12b. Therefore, images of the modified regions 12a, 12b (modified regions 12a, 12b and / or the cracks 14 extending from the modified regions 12a, 12b (hereinafter referred to as the same)) can be acquired and confirmed without destroying the wafer 20. In particular, in the imaging device 10, the control unit 8 executes the aforementioned imaging process at the timing of switching between forming the modified regions 12a, 12b along the first line 15a and forming the modified regions 12a, 12b along the second line 15b intersecting the first line 15a. Therefore, the modified regions 12a, 12b can be confirmed without affecting the speed of forming the modified regions 12a, 12b. That is, according to the imaging device 10, it is possible to suppress a decrease in processing efficiency and to perform confirmation in a non-destructive manner. The laser processing apparatus 1 includes the aforementioned imaging device 10; a laser irradiation unit 3 for irradiating a wafer 20 with laser light L; and a drive unit 7 to which the laser irradiation unit 3 is mounted for driving the laser irradiation unit 3 in the Z direction. The imaging unit 4 is mounted on the drive unit 7 together with the laser irradiation unit 3. The laser processing apparatus 1 includes the aforementioned imaging device 10. Therefore, according to the laser processing apparatus 1, it is possible to suppress a decrease in processing efficiency and enable non-destructive verification. Furthermore, the laser processing apparatus 1 includes a drive unit 7 that drives the laser irradiation unit 3 in the Z direction. Furthermore, the imaging unit 4 is attached to the drive unit 7 together with the laser irradiation unit 3. Therefore, positional information regarding the incident direction can be easily shared during the formation of the modified regions 12a and 12b by irradiation with laser light L and during the imaging process. The laser processing apparatus 1 further includes an imaging unit 5 for capturing an image of the wafer 20 using light I2 that has passed through the semiconductor substrate 21, and a control unit 8 for controlling the laser irradiation unit 3 and the imaging unit 5. The imaging unit includes an objective lens 43 for transmitting the light I1 that has passed through the semiconductor substrate 21, and a light detection unit 54 for detecting the light I1 that has passed through the objective lens 43. The imaging unit 5 includes a lens 53 for transmitting the light I2 that has passed through the semiconductor substrate 21, and a light detection unit 54 for detecting the light I2 that has passed through the lens 53. The control unit 8 performs an alignment process that controls the laser irradiation unit 3 and the imaging unit 5 to align the irradiation position of the laser light L based on the detection results of the light detection unit 54. Therefore, by using the imaging unit 5 for aligning the irradiation position of the laser light L, in addition to the imaging unit 4 for capturing images of the modified regions 12a and 12b, appropriate optical systems can be used. Furthermore, in the laser processing apparatus 1, the numerical aperture of the objective lens 43 is larger than that of the lens 53. Therefore, alignment can be performed more reliably by observation with a relatively small numerical aperture, and the modified regions 12a, 12b, etc. can be imaged with a relatively large numerical aperture. The imaging method described above is used to image modified regions 12a, 12b and / or cracks 14 extending from the modified regions 12a, 12b formed on a semiconductor substrate 21 by irradiation with laser light L. The imaging method includes an imaging step of imaging the modified regions 12a, 12b formed along the first line 15a and / or a region including the cracks 14 extending from the modified regions 12a, 12b using light that penetrates the semiconductor substrate 21 at a timing when switching between forming the modified regions 12a, 12b along the first line 15a and forming the modified regions 12a, 12b along the second line 15b. In this method, the modified regions 12a, 12b of the semiconductor substrate 21 and / or the regions including the cracks 14 extending from the modified regions 12a, 12b are imaged by light I1 that penetrates the semiconductor substrate 21. Therefore, it is possible to obtain images of the modified regions 12a, 12b, etc. and to perform confirmation without destroying the wafer 20. In particular, in this method, the aforementioned imaging is performed at the timing of switching between forming the modified regions 12a, 12b along the first line 15a and forming the modified regions 12a, 12b along the second line 15b that intersects the first line 15a. Therefore, the modified regions 12a, 12b, etc. can be confirmed without affecting the speed of forming the modified regions 12a, 12b. That is, according to this method, it is possible to suppress a decrease in processing efficiency and to perform confirmation in a non-destructive manner. [Variation Example] One aspect of the present disclosure is not limited to the aforementioned embodiment. For example, in the aforementioned embodiment, the laser processing apparatus 1 forms two rows of modified regions 12a and 12b within the semiconductor substrate 21 along a plurality of lines 15. However, the laser processing apparatus 1 may also form one row, or three or more rows of modified regions 12 within the semiconductor substrate 21 along a plurality of lines 15. The number and position of the rows of modified regions 12 formed per line 15 can be appropriately determined based on the thickness of the semiconductor substrate 21 of the wafer 20 or the thickness of the semiconductor substrate 21 of the semiconductor device 20a. Furthermore, multiple rows of modified regions 12 may be formed by relatively moving the focal point C of the laser light L multiple times along a single line 15. Furthermore, in the grinding and cutting step of step S06 shown in FIG15 , the grinding apparatus 200 may grind the back surface 21b of the semiconductor substrate 21 beyond the reference position P. The predetermined grinding end position can be appropriately set depending on whether or not the modified region 12 is to remain on the side surface (cut surface) of the semiconductor device 20a. Furthermore, if the semiconductor device 20a is, for example, a DRAM (Dynamic Random Access Memory), the modified region 12 may also remain on the side surface of the semiconductor device 20a. Furthermore, as shown in FIG19 , the imaging device 10 may be configured as a separate entity from the laser processing device 1. The imaging device 10 shown in FIG19 includes, in addition to the imaging unit 4, a stage 101, a drive unit 102, and a control unit (first control unit) 103. The stage 101 is configured similarly to the aforementioned stage 2, and supports a wafer 20 having a plurality of rows of modified regions 12 formed thereon. The drive unit 102 supports the imaging unit 4 and moves the imaging unit 4 along the Z direction. The control unit 103 is configured similarly to the aforementioned control unit 8. The laser processing system shown in FIG19 is located between the laser processing device 1 and the imaging device 10, and the wafer 20 is transported by a transport device such as a robotic arm. Furthermore, the irradiation conditions for laser light L when irradiating wafer 20 with laser light L along the plurality of lines 15 from the rear surface 21b of semiconductor substrate 21 are not limited to those described above. For example, the irradiation conditions for laser light L may be such that, as described above, cracks 14 spanning a plurality of rows of modified regions 12 (e.g., two rows of modified regions 12a and 12b) reach the interface between semiconductor substrate 21 and functional element layer 22. Alternatively, the irradiation conditions for laser light L may be such that cracks 14 spanning a plurality of rows of modified regions 12 reach the surface of functional element layer 22 opposite to semiconductor substrate 21. Alternatively, the irradiation conditions for laser light L may be such that cracks 14 spanning a plurality of rows of modified regions 12 reach near surface 21a within semiconductor substrate 21. In this manner, the irradiation conditions for laser light L may be such that cracks 14 spanning a plurality of rows of modified regions 12 are formed. In any case, it is possible to confirm whether the cracks 14 spanning the plurality of rows of modified regions 12 have sufficiently extended to the surface 21 a side of the semiconductor substrate 21 . Furthermore, the various components of the aforementioned embodiments are not limited to the aforementioned materials and shapes, but can be applied to various materials and shapes. Furthermore, the various components of one of the aforementioned embodiments or variations can be arbitrarily applied to the various components of other embodiments or variations. [Industrial Applicability] Provided are an imaging device, a laser processing device, and an imaging method that can suppress a decrease in processing efficiency and perform confirmation in a non-destructive manner. 1: Laser processing device 3: Laser irradiation unit 4: Imaging unit (first imaging unit) 5: Imaging unit (second imaging unit) 7: Drive unit 8: Control unit (first control unit, second control unit) 10: Imaging device 12, 12a, 12b: Modified region 11: Object 14: Crack 15a: First line 15b: Second line [Figure 1] is a block diagram of a laser processing device including an inspection device according to one embodiment. [Figure 2] is a top view of a wafer according to one embodiment. [Figure 3] is a cross-sectional view of a portion of the wafer shown in Figure 2. [Figure 4] is a block diagram of the laser irradiation unit shown in Figure 1. [Figure 5] is a block diagram of the inspection imaging unit shown in Figure 1. [Figure 6] is a block diagram of the alignment correction imaging unit shown in Figure 1. [Figure 7] is a cross-sectional view of a wafer illustrating the imaging principle of the inspection imaging unit shown in Figure 5, and images of various portions thereof obtained by the inspection imaging unit. [Figure 8] is a cross-sectional view of a wafer illustrating the imaging principle of the inspection imaging unit shown in Figure 5, and images of various portions thereof obtained by the inspection imaging unit. [Figure 9] is a SEM (Scanning Electron Microscope) image of a modified region and cracks formed within a semiconductor substrate. [Figure 10] is an SEM image of a modified region and cracks formed within a semiconductor substrate. [Figure 11] is an optical path diagram for illustrating the imaging principle of the inspection camera unit shown in Figure 5, and a schematic diagram showing an image at the focal point of the inspection camera unit. [Figure 12] is an optical path diagram for illustrating the imaging principle of the inspection camera unit shown in Figure 5, and a schematic diagram showing an image at the focal point of the inspection camera unit. [Figure 13] is a cross-sectional view of a wafer, an image of a cut surface of the wafer, and images of various locations captured by the inspection camera unit, for illustrating the inspection principle of the inspection camera unit shown in Figure 5. [Figure 14] is a cross-sectional view of a wafer, an image of a cut surface of the wafer, and images of various locations captured by the inspection camera unit, for illustrating the inspection principle of the inspection camera unit shown in Figure 5. [Figure 15] is a flow chart of a semiconductor device manufacturing method according to one embodiment. FIG16 is a cross-sectional view of a portion of a wafer during the grinding and slicing steps of the semiconductor device manufacturing method shown in FIG15. FIG17 is a cross-sectional view of a portion of a wafer during the grinding and slicing steps of the semiconductor device manufacturing method shown in FIG15. FIG18 is a flow chart illustrating a laser processing method and an imaging method according to one embodiment. FIG19 is a block diagram of a laser processing system including an imaging device according to a modified example.

Claims

1. A laser processing method comprising: a first step of preparing a wafer, the wafer comprising: a semiconductor substrate having a surface and an inner surface, a functional element layer formed on the surface, and irradiating the wafer with laser light from the inner surface along a plurality of lines, thereby forming modified regions along the plurality of lines inside the semiconductor substrate; a second step of inspecting, in an inspection area between the modified regions and the inner surface, the leading edge position of a crack extending from the modified regions to the inner surface; and a third step of evaluating the processing result of the first step based on the inspection result of the second step; wherein in the second step, a focal point is focused on the inspection area from the inner surface, and while the focal point is moved relative to the wafer along the thickness direction within the inspection area, light propagating from the surface to the inner surface along the semiconductor substrate is detected, thereby acquiring image data at various locations in the thickness direction, and checking whether the leading edge position is located within the inspection area based on the image data. In the first step mentioned above, to ensure that the aforementioned cracks reach the aforementioned surface, the aforementioned laser light is irradiated onto the aforementioned wafer from the aforementioned inside side along the aforementioned plurality of lines. In the third step mentioned above, if the aforementioned front end position is located on the aforementioned inside side relative to the aforementioned modified region and the aforementioned inside, it is evaluated that the aforementioned cracks have reached the aforementioned surface. If the aforementioned front end position is located on the aforementioned surface side relative to the aforementioned reference position, it is evaluated that the aforementioned cracks have not reached the aforementioned surface.

2. The laser processing method as described in claim 1, wherein, The aforementioned inspection area extends from the aforementioned reference position to the aforementioned inner side, but does not reach the aforementioned inner area. In the aforementioned third step, if the aforementioned front end position is located in the aforementioned inspection area, it is assessed that the aforementioned crack has reached the aforementioned surface. If the aforementioned front end position is not located in the aforementioned inspection area, it is assessed that the aforementioned crack has not reached the aforementioned surface.

3. A method for manufacturing a semiconductor device, comprising: the aforementioned first step, the aforementioned second step, and the aforementioned third step as described in claim 1 or 2; and a fourth step, wherein in the aforementioned third step, if it is determined that the aforementioned cracks have reached the aforementioned surface, the aforementioned wafer is cut into a plurality of semiconductor devices along the aforementioned plurality of lines respectively.

4. An inspection apparatus comprising: a stage for supporting a wafer, the wafer having a semiconductor substrate having a surface and a interior, and a functional element layer formed on the surface, and modified regions formed along a plurality of lines inside the semiconductor substrate; a light source for emitting light that is transmissive to the semiconductor substrate; an objective lens for transmitting the light emitted from the light source and propagating the light through the semiconductor substrate; a light detection unit for detecting the light passing through the objective lens; and an inspection unit for inspecting, based on a signal emitted from the light detection unit, the leading edge position of a crack extending from the modified region toward the interior in an inspection area between the modified region and the interior, and evaluating the crack on the wafer based on the inspection result; the objective lens for focusing the light from the interior onto the inspection area; and the light detection unit for detecting the light propagating from the surface to the interior in the semiconductor substrate. The aforementioned inspection unit uses the aforementioned object lens to focus the aforementioned focal point on the aforementioned inspection area from the aforementioned inner side. While moving the aforementioned focal point relative to the aforementioned wafer thickness direction within the aforementioned inspection area, the aforementioned light detection unit detects the aforementioned light propagating from the aforementioned surface side to the aforementioned inner side of the aforementioned semiconductor substrate, thereby acquiring image data at various locations in the aforementioned thickness direction. Based on the aforementioned image data, it checks whether the aforementioned front end position is located within the aforementioned inspection area. If the aforementioned front end position is located on the aforementioned inner side relative to the aforementioned reference position between the aforementioned modified area and the aforementioned inner side, it is assessed that the aforementioned crack has reached the aforementioned surface. If the aforementioned front end position is located on the aforementioned surface side relative to the aforementioned reference position, it is assessed that the aforementioned crack has not reached the aforementioned surface.

5. The inspection device as described in claim 4, wherein, The numerical aperture of the aforementioned objective lens is 0.45 or greater.

6. The inspection device as described in claim 4 or 5, wherein, The aforementioned objective lens has a correction ring.

Images