Inspection device and inspection method

Abstract

To eliminate the effects of noise in internal observation after laser processing and achieve an improvement in estimation accuracy of a wafer processing state.SOLUTION: A laser processing device 1 includes: an imaging unit 4 outputting transparent light to a wafer 20 and imaging the inside of the wafer 20 by detecting light propagating through the wafer 20; a drive unit 7 moving the imaging unit 4 along the Z direction of a vertical direction; and a control unit 8. The control unit 8 performs to: control the drive unit 7 so that the imaging unit 4 sequentially moves in a position where each imaging area along the Z direction in a predetermined imaging range of the wafer 20 can be imaged; control the imaging unit 4 so that each imaging area is imaged; and determine the adequacy of internal observation after laser processing, in the imaging range based on a captured image output from the imaging unit 4 that detects light associated with each imaging area.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One aspect of the present invention relates to an inspection apparatus and an inspection method. [Background technology]

[0002] An inspection device is known that includes a semiconductor substrate and cuts a wafer, the back surface of which is provided with a functional device layer, along a plurality of lines by irradiating the wafer from the front side of the semiconductor substrate with laser light to form a plurality of rows of modified regions within the semiconductor substrate along each of the plurality of lines. The inspection device described in Patent Document 1 includes an infrared camera, which makes it possible to observe the modified regions formed within the semiconductor substrate and the processing damage formed in the functional device layer from the front side of the semiconductor substrate. For example, the inspection device estimates the state of cracks in the wafer after processing based on the results of such internal observation, and determines whether the processing is successful (whether the desired processing was performed under the set processing conditions) based on the estimated crack state. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-64746 Summary of the Invention [Problem to be solved by the invention]

[0004] In the internal observation described above, for example, the position of a modified layer, the position of a crack, etc. are estimated based on the feature quantities of feature points shown in the captured image for internal observation. Here, various structures such as TEGs and films in the device pattern of the wafer may affect (become noise) the detection of the above-mentioned feature quantities. In this case, the position of the modified layer, the position of a crack, etc. may not be estimated appropriately. Potential noise in detecting feature quantities is not limited to the device pattern described above, but may also include, for example, grinding marks on the incident surface (surface) of the laser light, foreign matter adhering to the surface of the wafer, or foreign matter adhering to the observation optical system.

[0005] One aspect of the present invention has been made in consideration of the above-described circumstances, and relates to an inspection device and an inspection method that can eliminate the influence of noise in internal observation after laser processing and improve the estimation accuracy of the processed state of a wafer. [Means for solving the problem]

[0006] An inspection device according to one embodiment of the present invention includes an imaging unit that outputs light that is transparent to the wafer and captures an image of the inside of the wafer by detecting the light that has propagated through the wafer, a drive unit that moves the imaging unit along the vertical Z direction, and a control unit. The control unit is configured to control the drive unit so that the imaging unit sequentially moves to a position where each imaging area along the Z direction in a predetermined imaging range of the wafer can be imaged, control the imaging unit so that each imaging area is imaged, and determine the suitability of the imaging range for internal observation after laser processing based on the image output from the imaging unit that detects the light related to each imaging area.

[0007] In an inspection device according to one aspect of the present invention, an imaging unit moving along the Z direction captures images of each imaging region along the Z direction in a predetermined imaging range of a wafer. Then, in this inspection device, the suitability of the imaging region for internal observation after laser processing is determined based on the captured images of each imaging region. In this way, by taking into account the captured images of each imaging region along the Z direction of the wafer, the influence of potential noise in internal observation after laser processing can be identified along the Z direction. Then, after identifying the influence of potential noise in each region along the Z direction of the imaging range, the suitability of the imaging region for internal observation can be determined, thereby determining with high accuracy whether the imaging region is suitable for internal observation. With this configuration, after laser processing, internal observation can be performed in an imaging region suitable for internal observation, thereby eliminating the influence of noise in internal observation after laser processing and improving the estimation accuracy of the processed state of the wafer.

[0008] The control unit may determine the suitability of the imaging range for internal observation based on the feature amounts of the feature points shown in the captured images for each imaging region. By taking the feature amounts of the feature points shown in the captured images into consideration, the magnitude of the influence on detection of the feature amounts in internal observation after laser processing can be appropriately identified, and it can be determined with higher accuracy whether the imaging range is suitable for internal observation.

[0009] The control unit may determine the suitability of the imaging range for internal observation based on the feature amounts of processing range feature points, which are feature points in a range corresponding to an area where internal observation after laser processing is desired, among the feature points shown in the captured image of each imaging range. With this configuration, only the feature amounts of feature points (processing range feature points) in a range that is likely to affect detection of feature amounts in internal observation after laser processing are taken into consideration, making it possible to more accurately determine whether the imaging range is suitable for internal observation.

[0010] The control unit may compare, for an area where internal observation is desired after laser processing, the feature amounts of the processing range feature points with assumed feature amounts that are assumed to be feature amounts of feature points caused by the laser processing, and determine that the imaging range is more suitable for internal observation the smaller the feature amounts of the processing range feature points are compared with the assumed feature amounts. In this way, the feature amounts of the processing range feature points are compared with the feature amounts (assumed feature amounts) of the feature points caused by the laser processing, and if the feature amounts of the processing range feature points are relatively small and have little effect on detection of the feature amounts in internal observation after laser processing, the imaging range is determined to be suitable for internal observation, thereby making it possible to more accurately determine whether the imaging range is suitable for internal observation.

[0011] The control unit may be further configured to output a result of determining whether internal observation is appropriate, thereby allowing the user to confirm the result and determine the area for internal observation based on the result.

[0012] The control unit may determine the suitability of internal observation for each of a plurality of different imaging ranges and output the determination results for each of the plurality of imaging ranges so that the user can select the imaging range for the area where internal observation will be performed after laser processing. In this way, the suitability of internal observation for each of the plurality of imaging ranges is determined and each determination result is output, so that the user can select the area where internal observation will be performed while comparing each determination result.

[0013] The control unit may store at least one of the captured image and position information for the imaging range selected by the user as information related to internal observation after laser processing. This ensures that the information on the imaging range selected by the user is registered as information related to internal observation after laser processing, and allows internal observation to be performed with an imaging range that takes into account the user's selection (i.e., an imaging range that is less susceptible to noise).

[0014] The wafer may have a device pattern on the surface opposite to the surface irradiated with the laser, and the control unit may determine the suitability of the imaging range for internal observation based on captured images of the imaging areas excluding the device pattern. The area in which the device pattern is formed has a large feature value of the feature points in the captured image, but is not an area in which a modified layer or cracks will be formed. Therefore, by excluding the captured image of the area in which the device pattern is formed and determining the suitability of the internal observation from only the other captured images, it is possible to more accurately determine whether the imaging range is suitable for internal observation based on the captured image of the area in which the internal observation will actually be performed.

[0015] An inspection method according to one embodiment of the present invention includes taking images of a predetermined imaging range inside a wafer while changing the imaging area along the Z direction, which is the vertical direction, and determining the suitability of the imaging range for internal observation after laser processing based on the captured images of each imaging area. [Effects of the Invention]

[0016] According to one aspect of the present invention, it is possible to eliminate the influence of noise in internal observation after laser processing, and improve the accuracy of estimating the processed state of a wafer. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a configuration diagram of a laser processing apparatus according to an embodiment; [Figure 2] FIG. 2 is a plan view of a wafer according to an embodiment. [Figure 3] FIG. 3 is a cross-sectional view of a portion of the wafer shown in FIG. 2. [Figure 4] FIG. 2 is a configuration diagram of a laser irradiation unit shown in FIG. [Figure 5] FIG. 2 is a configuration diagram of an inspection imaging unit shown in FIG. [Figure 6] FIG. 2 is a configuration diagram of an imaging unit for alignment correction shown in FIG. [Figure 7]6A and 6B are cross-sectional views of a wafer for explaining the imaging principle of the inspection imaging unit shown in FIG. 5, and images at various locations taken by the inspection imaging unit. [Figure 8] 6A and 6B are cross-sectional views of a wafer for explaining the imaging principle of the inspection imaging unit shown in FIG. 5, and images at various locations taken by the inspection imaging unit. [Figure 9] 1 is an SEM image of modified regions and cracks formed inside a semiconductor substrate. [Figure 10] 1 is an SEM image of modified regions and cracks formed inside a semiconductor substrate. [Figure 11] 6 is a light path diagram for explaining the imaging principle of the inspection imaging unit shown in FIG. 5, and a schematic diagram showing an image at a focal point of the inspection imaging unit. FIG. [Figure 12] 6 is a light path diagram for explaining the imaging principle of the inspection imaging unit shown in FIG. 5, and a schematic diagram showing an image at a focal point of the inspection imaging unit. FIG. [Figure 13] FIG. 10 is a diagram illustrating crack detection. [Figure 14] FIG. 10 is a diagram illustrating crack detection. [Figure 15] FIG. 10 is a diagram illustrating the detection of a scratch. [Figure 16] FIG. 10 is a diagram illustrating the detection of a scratch. [Figure 17] FIG. 10 is a diagram illustrating the detection of a scratch. [Figure 18] 1A and 1B are diagrams illustrating internal observation of a mirror wafer. [Figure 19] FIG. 10 is a diagram illustrating noise factors in feature detection. [Figure 20] FIG. 2 is a diagram illustrating a device pattern on a wafer. [Figure 21] 10A and 10B are diagrams illustrating feature detection influenced by a device pattern. [Figure 22] FIG. 10 is a diagram illustrating the determination of the suitability of internal observation. [Figure 23] 10 is a flowchart illustrating an example of an inspection method. [Figure 24]FIG. 10 is a diagram illustrating an example of noise determination processing. [Figure 25] 10 is a flowchart illustrating an example of a noise determination process. [Figure 26] FIG. 10 is a diagram illustrating an example of a noise determination result. [Figure 27] FIG. 10 is a diagram illustrating an example of noise determination processing. [Figure 28] 10 is a flowchart illustrating an example of a noise determination process. [Figure 29] FIG. 10 is a diagram illustrating an example of a noise determination result. [Figure 30] 10A and 10B are diagrams illustrating an example of detection of BG marks according to a comparative example. [Figure 31] 10A to 10C are diagrams illustrating an example of detection of a BG mark according to the present embodiment. [Figure 32] FIG. 10 is a diagram illustrating an example of noise determination processing. [Figure 33] 10 is a flowchart illustrating an example of a noise determination process. [Figure 34] FIG. 10 is a diagram illustrating an example of a noise determination result. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be omitted. [Laser processing equipment configuration]

[0019] 1, the laser processing apparatus 1 includes a stage 2, a laser irradiation unit 3, a plurality of imaging units 4 (imaging sections), 5, and 6, a drive unit 7 (drive section), a control section 8, and a display 150. The laser processing apparatus 1 is an apparatus that forms a modified region 12 in an object 11 by irradiating the object 11 with laser light L.

[0020] The stage 2 is a suction table that supports the object 11, for example, by suctioning a film attached to the object 11. Although not shown in FIG. 1, a holding member 600 that holds the wafer 20 may be provided between the wafer 20, which is the object 11, and the stage 2, as shown in FIG. 19. The stage 2 is movable along both the X and Y directions, and is rotatable about an axis parallel to the Z direction. The X and Y directions are first and second horizontal directions that are perpendicular to each other, and the Z direction is the vertical direction.

[0021] The laser irradiation unit 3 focuses laser light L, which is transparent to the object 11, and irradiates the object 11 with the focused laser light. When the laser light L is focused inside the object 11 supported by the stage 2, the laser light L is particularly absorbed in a portion corresponding to the focusing point C of the laser light L, and a modified region 12 is formed inside the object 11.

[0022] The modified region 12 is a region whose density, refractive index, mechanical strength, and other physical properties differ from those of the surrounding unmodified region. Examples of the modified region 12 include a melt-treated region, a crack region, a dielectric breakdown region, and a refractive index change region. The modified region 12 has the property that cracks tend to extend from the modified region 12 to the incident side of the laser light L and to the opposite side. These properties of the modified region 12 are utilized to cut the object 11.

[0023] As an example, when the stage 2 is moved along the X direction and the focal point C is moved along the X direction relative to the object 11, multiple modified spots 12s are formed in a row along the X direction. One modified spot 12s is formed by irradiating one pulse of laser light L. A row of modified regions 12 is a collection of multiple modified spots 12s lined up in a row. Adjacent modified spots 12s may be connected to each other or separated from each other depending on the relative moving speed of the focal point C with respect to the object 11 and the repetition frequency of the laser light L.

[0024] The imaging unit 4 captures an image of the modified region 12 formed in the object 11 and the tip of the crack extending from the modified region 12 .

[0025] Under the control of the control unit 8, the imaging units 5 and 6 capture an image of the object 11 supported on the stage 2 using light transmitted through the object 11. The images obtained by the imaging units 5 and 6 are used, for example, to align the irradiation position of the laser light L.

[0026] The drive unit 7 supports the laser irradiation unit 3 and the multiple imaging units 4, 5, and 6. The drive unit 7 moves the laser irradiation unit 3 and the multiple imaging units 4, 5, and 6 along the Z direction.

[0027] The control unit 8 controls the operations of the stage 2, the laser irradiation unit 3, the multiple imaging units 4, 5, and 6, and the drive unit 7. The control unit 8 is configured as a computer device including a processor, memory, storage, a communication device, etc. In the control unit 8, the processor executes software (programs) loaded into the memory, etc., and controls the reading and writing of data from and to the memory and storage, as well as communication via the communication device.

[0028] The display 150 functions as an input unit that accepts information input from the user, and as a display unit that displays information to the user.

[0029] [Object Configuration] As shown in FIGS. 2 and 3 , the object 11 in this embodiment is a wafer 20. The wafer 20 includes a semiconductor substrate 21 and a functional device layer 22. While this embodiment describes the wafer 20 as having the functional device layer 22, the wafer 20 may or may not include the functional device layer 22, and may be a bare wafer. The semiconductor substrate 21 has a back surface 21a and a front surface 21b. The semiconductor substrate 21 is, for example, a silicon substrate. The functional device layer 22 is formed on the back surface 21a of the semiconductor substrate 21. The functional device layer 22 includes a plurality of functional devices 22a arranged two-dimensionally along the back surface 21a. The functional devices 22a may be, for example, light-receiving devices such as photodiodes, light-emitting devices such as laser diodes, or circuit devices such as memories. The functional devices 22a may be three-dimensionally configured by stacking multiple layers. The semiconductor substrate 21 has a notch 21c indicating the crystal orientation, but an orientation flat may be provided instead of the notch 21c.

[0030] The wafer 20 is cut into individual functional elements 22a along each of the multiple lines 15. When viewed in the thickness direction of the wafer 20, the multiple lines 15 pass between each of the multiple functional elements 22a. More specifically, when viewed in the thickness direction of the wafer 20, the lines 15 pass through the center of the street region 23 (the center in the width direction). The street region 23 extends in the functional element layer 22 so as to pass between adjacent functional elements 22a. In this embodiment, the multiple functional elements 22a are arranged in a matrix along the back surface 21a, and the multiple lines 15 are set in a lattice pattern. Note that the lines 15 are virtual lines, but may also be actually drawn lines.

[0031] [Laser irradiation unit configuration] As shown in Fig. 4, the laser irradiation unit 3 has a light source 31, a spatial light modulator 32, and a condenser 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 (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM). The condenser lens 33 condenses the laser light L modulated by the spatial light modulator 32. Note that the condenser lens 33 may be a correction collar lens.

[0032] In this embodiment, the laser irradiation unit 3 irradiates the wafer 20 with laser light L from the front surface 21b of the semiconductor substrate 21 along each of the multiple lines 15, thereby forming two rows of modified regions 12a, 12b inside the semiconductor substrate 21 along each of the multiple lines 15. Of the two rows of modified regions 12a, 12b, the modified region 12a is the modified region closest to the back surface 21a. Of the two rows of modified regions 12a, 12b, the modified region 12b is the modified region closest to the modified region 12a and closest to the front surface 21b.

[0033] The two rows of modified regions 12a, 12b are adjacent to each other in the thickness direction (Z direction) of the wafer 20. The two rows of modified regions 12a, 12b are formed by moving two focal points C1, C2 along a line 15 relative to the semiconductor substrate 21. The laser light L is modulated by the spatial light modulator 32 so that the focal point C2 is located behind the focal point C1 in the traveling direction and on the incident side of the laser light L. The modified regions may be formed by a single focus or multiple focuses, and by one pass or multiple passes.

[0034] The laser irradiation unit 3 irradiates the wafer 20 with laser light L from the front surface 21b side of the semiconductor substrate 21 along each of the multiple lines 15. As an example, <100> Two focal points C1 and C2 are aligned with the semiconductor substrate 21 at positions 54 μm and 128 μm from the back surface 21a, respectively, and laser light L is irradiated onto the wafer 20 from the front surface 21b of the semiconductor substrate 21 along each of a plurality of lines 15. At this time, for example, if the conditions are such that the cracks 14 spanning two rows of modified regions 12a and 12b reach the back surface 21a of the semiconductor substrate 21, the wavelength of the laser light L is 1099 nm, the pulse width is 700 ns, 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 movement speed of the two focal points C1 and C2 with respect to the semiconductor substrate 21 is 800 mm / s. Note that, for example, when the number of processing passes is 5, ZH80 (position 328 μm from the back surface 21 a), ZH69 (position 283 μm from the back surface 21 a), ZH57 (position 234 μm from the back surface 21 a), ZH26 (position 107 μm from the back surface 21 a), and ZH12 (position 49.2 μm from the back surface 21 a) may be set as processing positions for the above-mentioned wafer 20. In this case, for example, the wavelength of the laser light L may be 1080 nm, the pulse width may be 400 nsec, the repetition frequency may be 100 kHz, and the moving speed may be 490 mm / sec.

[0035] [Configuration of the inspection imaging unit] As shown in FIG. 5, the imaging unit 4 (imaging section) includes a light source 41, a mirror 42, an objective lens 43, and a light detection section 44. The imaging unit 4 outputs light that is transparent to the wafer 20 and detects the light that has propagated through the wafer 20, thereby capturing an image of the interior of the wafer 20. The light source 41 outputs light l1 that is transparent to the semiconductor substrate 21. The light source 41 is configured, for example, with a halogen lamp and a filter, and outputs light l1 in the near-infrared region. The light l1 output from the light source 41 is reflected by the mirror 42, passes through the objective lens 43, and is irradiated onto the wafer 20 from the front surface 21b side of the semiconductor substrate 21. At this time, the stage 2 supports the wafer 20 on which the two rows of modified regions 12a and 12b have been formed as described above.

[0036] The objective lens 43 passes the light l1 reflected by the back surface 21a of the semiconductor substrate 21. In other words, the objective lens 43 passes the light l1 propagating through the semiconductor substrate 21. The numerical aperture (NA) of the objective lens 43 is, for example, 0.45 or more. The objective lens 43 has a correction collar 43a. The correction collar 43a corrects aberrations occurring in the light l1 within the semiconductor substrate 21, for example, by adjusting the distances between the multiple lenses that make up the objective lens 43. Note that the means for correcting the aberrations is not limited to the correction collar 43a, and other correction means such as a spatial light modulator may also be used. The light detection unit 44 detects the light l1 that has passed through the objective lens 43 and the mirror 42. The light detection unit 44 is, for example, configured with an InGaAs camera, and detects light l1 in the near-infrared region. The means for detecting (capturing) the light l1 in the near-infrared region is not limited to an InGaAs camera, but may be any other imaging means that captures images in a transmission type, such as a transmission type confocal microscope.

[0037] The imaging unit 4 can capture images of each of the two rows of modified regions 12a and 12b and the tips of each of the multiple cracks 14a, 14b, 14c, and 14d (details will be described later). The crack 14a is a crack that extends from the modified region 12a toward the back surface 21a. The crack 14b is a crack that extends from the modified region 12a toward the front surface 21b. The crack 14c is a crack that extends from the modified region 12b toward the back surface 21a. The crack 14d is a crack that extends from the modified region 12b toward the front surface 21b.

[0038] [Configuration of the imaging unit for alignment correction] 6, the imaging unit 5 has a light source 51, a mirror 52, a lens 53, and a light detection unit 54. The light source 51 outputs light I2 that is transparent to the semiconductor substrate 21. The light source 51 is configured, for example, with a halogen lamp and a filter, and outputs light I2 in the near-infrared region. The light source 51 may 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 and passes through the lens 53, and is irradiated onto the wafer 20 from the front surface 21b side of the semiconductor substrate 21.

[0039] The lens 53 passes the light I2 reflected by the back surface 21a of the semiconductor substrate 21. In other words, the lens 53 passes the light I2 that has propagated through the semiconductor substrate 21. The numerical aperture of the lens 53 is 0.3 or less. In other words, the numerical aperture of the objective lens 43 of the imaging unit 4 is larger than the numerical aperture of the lens 53. The light detection unit 54 detects the light I2 that has passed through the lens 53 and the mirror 52. The light detection unit 54 is configured, for example, by an InGaAs camera, and detects the light I2 in the near-infrared region.

[0040] Under the control of the control unit 8, the imaging unit 5 irradiates the wafer 20 with light I2 from the front surface 21b and detects light I2 returning from the back surface 21a (functional device layer 22), thereby capturing an image of the functional device layer 22. Similarly, under the control of the control unit 8, the imaging unit 5 irradiates the wafer 20 with light I2 from the front surface 21b and detects light I2 returning from the positions where the modified regions 12a and 12b are formed on the semiconductor substrate 21, thereby capturing an image of the region including the modified regions 12a and 12b. These images are used for aligning the irradiation position of the laser light L. The imaging unit 6 has a similar configuration to the imaging unit 5, except that the lens 53 has a lower magnification (for example, 6x in the imaging unit 5 and 1.5x in the imaging unit 6), and is used for alignment in the same way as the imaging unit 5.

[0041] [Principle of imaging by inspection imaging unit] Using the imaging unit 4 shown in FIG. 5, the focal point F (the focal point of the objective lens 43) is moved from the front surface 21b toward the back surface 21a of a semiconductor substrate 21 in which cracks 14 spanning two rows of modified regions 12a, 12b reach the back surface 21a, as shown in FIG. 7. In this case, when the focal point F is aligned from the front surface 21b to the tip 14e of the crack 14 extending from the modified region 12b to the front surface 21b, the tip 14e can be seen (the image on the right in FIG. 7). However, when the focal point F is aligned from the front surface 21b to the tip 14e of the crack 14 reaching the back surface 21a, the crack 14 itself and the tip 14e of the crack 14 reaching the back surface 21a cannot be seen (the image on the left in FIG. 7). Note that when the focal point F is aligned from the front surface 21b to the back surface 21a of the semiconductor substrate 21, the functional element layer 22 can be seen.

[0042] 5, the imaging unit 4 was used to move the focal point F from the front surface 21b toward the back surface 21a of a semiconductor substrate 21 in which cracks 14 spanning two rows of modified regions 12a and 12b did not reach the back surface 21a, as shown in FIG. 8. In this case, even if the focal point F was aligned from the front surface 21b to the tip 14e of the crack 14 extending from the modified region 12a to the back surface 21a, the tip 14e could not be seen (the image on the left side of FIG. 8). However, by aligning the focal point F from the front surface 21b to the region on the opposite side of the back surface 21a from the front surface 21b (i.e., the region on the functional device layer 22 side of the back surface 21a) and positioning a virtual focal point Fv symmetrical to the focal point F with respect to the back surface 21a at the tip 14e, the tip 14e could be seen (the image on the right side of FIG. 8). The virtual focal point Fv is a point symmetrical with the focal point F with respect to the back surface 21a, taking into account the refractive index of the semiconductor substrate 21.

[0043] As described above, the reason why the crack 14 itself cannot be confirmed is presumably because the width of the crack 14 is smaller than the wavelength of the illumination light 11. Figures 9 and 10 are SEM (Scanning Electron Microscope) images of the modified region 12 and the crack 14 formed inside the semiconductor substrate 21, which is a silicon substrate. Figure 9(b) is an enlarged image of region A1 shown in Figure 9(a), Figure 10(a) is an enlarged image of region A2 shown in Figure 9(b), and Figure 10(b) is an enlarged image of region A3 shown in Figure 10(a). As such, the width of the crack 14 is approximately 120 nm, which is smaller than the wavelength of the near-infrared light 11 (e.g., 1.1 to 1.2 μm).

[0044] Based on the above, the imaging principle assumed is as follows. As shown in FIG. 11(a), when the focal point F is positioned in air, the light l1 does not return, resulting in a dark image (the image on the right side of FIG. 11(a)). As shown in FIG. 11(b), when the focal point F is positioned inside the semiconductor substrate 21, the light l1 reflected by the back surface 21a returns, resulting in a whitish image (the image on the right side of FIG. 11(b)). As shown in FIG. 11(c), when the focal point F is aligned with the modified region 12 from the front surface 21b side, the modified region 12 absorbs, scatters, or otherwise causes a portion of the light l1 reflected by the back surface 21a and returned, resulting in an image in which the modified region 12 appears dark against a whitish background (the image on the right side of FIG. 11(c)).

[0045] As shown in (a) and (b) of Figure 12, when the focal point F is focused on the tip 14e of the crack 14 from the surface 21b side, for example, optical singularities (stress concentration, strain, discontinuity in atomic density, etc.) occurring near the tip 14e, light confinement occurring near the tip 14e, etc., cause scattering, reflection, interference, absorption, etc. of a portion of the light l1 reflected by the back surface 21a and returned, resulting in an image in which the tip 14e appears dark against a whitish background (the images on the right in (a) and (b) of Figure 12). As shown in (c) of Figure 12, when the focal point F is focused on a portion of the crack 14 other than the vicinity of the tip 14e from the surface 21b side, at least a portion of the light l1 reflected by the back surface 21a returns, resulting in a whitish image (the image on the right in (c) of Figure 12).

[0046] [Detection algorithm for internal observation] With regard to the internal observation of the wafer 20 described above, an algorithm for detecting (identifying) the cracks 14 and an algorithm for detecting (identifying) the scars related to the modified region will be described in detail.

[0047] 13 and 14 are diagrams illustrating crack detection. FIG. 13 shows the results of internal observation (image of the inside of the wafer 20). The control unit 8 first detects a group of straight lines 140 from the image of the inside of the wafer 20 as shown in FIG. 13(a). To detect the group of straight lines 140, an algorithm such as Hough transform or LSD (Line Segment Detector) is used. The Hough transform is a method of detecting straight lines by detecting all straight lines passing through a point on an image and weighting the lines that pass through more characteristic points. The LSD is a method of detecting straight lines by calculating the gradient and angle of brightness values ​​in an image to estimate an area that will become a line segment, and approximating the area to a rectangle.

[0048] Next, the control unit 8 detects a crack 14 from the group of straight lines 140 by calculating the similarity between the group of straight lines 140 and the crack line, as shown in FIG. 14. As shown in the upper diagram of FIG. 14, a crack line has a characteristic in that the brightness values ​​on the line are very bright in the Y direction. For this reason, the control unit 8, for example, compares the brightness values ​​of all pixels in the detected group of straight lines 140 with the brightness values ​​on the line before and after the line in the Y direction, and determines the number of pixels whose difference is equal to or greater than a threshold value both before and after as a similarity score. Then, the detected group of straight lines 140 with the highest similarity score to the crack line is determined as a representative value for that image. A higher representative value is an indicator that the possibility of the presence of a crack 14 is higher. By comparing the representative values ​​in multiple images, the control unit 8 determines those with relatively high scores as crack image candidates.

[0049] 15 to 17 are diagrams illustrating the detection of creases. FIG. 15 shows the results of internal observation (images of the inside of the wafer 20). The control unit 8 detects corners (concentrations of edges) in the image of the inside of the wafer 20 as shown in FIG. 15(a) as key points, and detects their positions, sizes, and directions to detect feature points 250. Known methods for detecting feature points in this way include Eigen, Harris, Fast, SIFT, SURF, STAR, MSER, ORB, and AKAZE.

[0050] As shown in FIG. 16, the dent 280 has a distinctive corner feature, as it is made up of circles, rectangles, and other shapes arranged at regular intervals. Therefore, by aggregating the feature quantities of the feature points 250 in the image, the dent 280 can be detected with high accuracy. As shown in FIG. 17, by comparing the total feature quantities for each image captured by shifting the image depthwise, a change in the peaks, indicating the number of crack rows for each modified layer, can be confirmed. The control unit 8 estimates the peak of this change as the position of the dent 280. By aggregating the feature quantities in this way, it becomes possible to estimate not only the dent position but also the pulse pitch.

[0051] [Process to determine internal observation position] The process of determining the internal observation position will be described in detail below. The process of determining the internal observation position is performed on the wafer 20 before the modified region is formed (the wafer 20 before laser processing). Here, when forming a modified region for the purpose of cutting the wafer 20, processing conditions for forming the modified region are derived in advance. These processing conditions are derived based on the results of internal observation of the wafer 20 after laser processing. Here, depending on the structure of the wafer 20, if internal observation is not performed at an appropriate position, it may not be possible to perform internal observation after laser processing with high accuracy.

[0052] FIG. 18 is a diagram illustrating internal observation of a mirror wafer 520, an example of a wafer 20. The mirror wafer 520 does not have a functional element layer on its back surface 521a, and does not have a device pattern (details will be described later) in the street region of the back surface 521a. As shown in FIG. 18(a), the imaging range for internal observation of the mirror wafer 520 includes a direct observation region imaged by shifting the focus from the front surface 521b toward the back surface 521a, and a back surface reflection region imaged by focusing from the front surface 521b to the region on the opposite side of the back surface 521a. FIG. 18(b) is a diagram illustrating feature amounts for each feature point in multiple images captured by shifting the focus in the depth direction. In FIG. 18(b), the horizontal axis represents feature amount, and the vertical axis represents imaging depth. The results shown in Figure 18(b) are the results of internal observation when the mirror wafer 520 is laser-processed to create a bottom-side half-cut (BHC) state in which the crack 14 reaches the back surface 521a. As shown in Figure 18(b), feature amount data 901 of the modified region SD1 on the back surface 521a, feature amount data 902 of the modified region SD2 on the front surface 521b, and feature amount data 910 of the tip of the upper crack are detected in the direct observation area. Furthermore, feature amount data 903 of the modified region SD1 on the back surface 521a and feature amount data 904 of the modified region SD2 on the front surface 521b are detected in the back surface reflection area. Note that the numerical values ​​of the feature amount data in Figure 18(b) (e.g., the numerical value "396" for feature amount data 901) indicate the total value of the aggregated features. In this way, for a mirror wafer 520 that does not have a device pattern and does not have other noise factors (described later), modified areas, etc. can be appropriately identified from the internal observation results without any special adjustment of the internal observation position, and processing conditions can be appropriately derived from the internal observation results.

[0053] On the other hand, for a wafer 20 that has some noise factor in feature detection, internal observation after laser processing may not be performed with high accuracy unless internal observation is performed at an appropriate position. FIG. 19 is a diagram illustrating noise factors in feature detection. The noise factors here refer to factors that affect the above-mentioned feature. FIG. 19 illustrates, as noise factors, device pattern F1, noise F2 on the front surface 21b (incident surface), foreign matter F3 adhering to the front surface 21b, foreign matter F4 adhering to the light detection unit 44, noise F5 on the front surface of the stage 2, and noise F6 on the back surface of the holding member 600.

[0054] FIG. 20 is a diagram illustrating a device pattern F1 on a wafer 20. The device pattern F1 is disposed on a street region 23 and can include various structures such as a TEG or a film. In the example shown in FIG. 20, structures such as a TEG indicated by "1-A" to "3-F" are shown as the device pattern F1 in the region of one channel (CH1) in the pattern shot of the wafer 20. Hereinafter, the structures such as a TEG indicated by "1-A" to "3-F" may be referred to as device patterns 1-A to 3-F. Note that while FIG. 20 only shows the device pattern F1 in the region of one direction (CH1) in the lattice-shaped street region 23, a device pattern F1 may also exist in the region of the orthogonal CH2.

[0055] FIG. 21 is a diagram illustrating feature detection affected by device pattern F1. FIG. 21(a) shows the internal observation results (feature detection results) at a position where device pattern F1 is not present. FIGS. 21(b) to 21(d) show the internal observation results (feature detection results) at positions where device patterns 1-A, 1-C, and 1-F (see FIG. 20) are present, respectively. In FIGS. 21(a) to 21(d), the horizontal axis represents feature amount, and the vertical axis represents imaging depth. The results shown in FIGS. 21(a) to 21(d) are the results of internal observation when wafer 20 is laser processed to create a bottom side half-cut (BHC) state in which cracks reach the backside, for example.

[0056] 21(a), when the device pattern F1 is not present, similar to the internal observation results of the mirror wafer 520 described above (see FIG. 18(b)), feature amount data 901 of the modified region SD1 on the back surface 21a, feature amount data 902 of the modified region SD2 on the front surface 21b, and feature amount data 910 of the tip of the upper crack are detected in the direct observation area, and feature amount data 903 of the modified region SD1 on the back surface 21a and feature amount data 904 of the modified region SD2 on the front surface 21b are detected in the back surface reflected area. Because the device pattern F1 is not present, only feature amounts related to the formation of the modified region are detected in the internal observation after laser processing.

[0057] On the other hand, as shown in Figures 21(b) to 21(d), when a device pattern F1 is present, the feature amount of the device pattern F1 affects the feature amount of the modified region. For example, in the internal observation results at the position where the device pattern 1-A is present as shown in Figure 21(b), feature amount data 950 and 960 due to the device pattern 1-A are detected near the position of the dent in the modified region SD1. Due to these feature amount data 950 and 960, the position of the dent in the modified region SD1 is detected as being shifted (shifted from the feature amount data 901 and 903 shown in Figure 21(a)). This results in an erroneous detection.

[0058] 21(c), the internal observation result at the position where the device pattern 1-C is present detects feature amount data 970 due to the device pattern 1-C. However, since the feature amount of the feature amount data 970 is sufficiently small compared with the feature amounts of the feature amount data 901, etc. of the modified region, in such a case, even if the feature amount data 970 due to the device pattern 1-C is detected, it can be distinguished from the feature amount data 901, etc. of the modified region, and false detection does not occur.

[0059] 21(d), the internal observation result at the position where the device pattern 1-F is present shows that the feature amount data 980 of the device pattern 1-F is detected near the back surface 21a (at a position deeper than the modified region SD1), and the feature amount data 980 detects a dent at a position even deeper than the modified region SD1, resulting in a false detection.

[0060] As described above, depending on the type of device pattern F1, the detection of the feature amount related to the formation of the modified region may be affected, resulting in erroneous detection. Therefore, when performing internal observation after laser processing on a wafer 20 having the device pattern F1, it is necessary to determine the internal observation position in advance so as to prevent erroneous detection. Note that, when determining the internal observation position so as not to be affected by the device pattern F1, it is possible to consider, for example, an exclusion setting that does not perform internal observation in at least one of the Z direction and the X and Y directions.

[0061] Another noise factor, noise F2 on the surface 21b (incident surface) shown in FIG. 19 , is noise caused by, for example, grinding marks (background grain marks) on the surface 21b or unevenness in the film on the surface 21b. The wafer 20 is ground using a grinding device to thin the wafer from its original thickness, and grinding marks may remain. Grinding marks have various shapes on the surface 21b of the wafer 20. Depending on the shape of the grinding marks, detection of feature quantities related to the formation of modified regions may be affected, resulting in false positives. Therefore, when performing internal observation after laser processing on a wafer 20 having noise F2 on the surface 21b, it is necessary to determine the internal observation position in advance to prevent false positives. To determine the internal observation position so as not to be affected by noise F2 on the surface 21b, it is possible to perform an exclusion setting that does not perform internal observation in at least one of the Z direction and the X and Y directions, for example.

[0062] 19, the foreign matter F3 adhering to the surface 21b is, for example, a foreign matter such as dust adhering to the surface 21b. Such foreign matter F3 may affect the detection of feature quantities related to the formation of modified regions and cause erroneous detection. Therefore, when performing internal observation after laser processing on a wafer 20 having foreign matter F3 adhering to the surface 21b, it is necessary to determine the internal observation position in advance so as to prevent erroneous detection. Note that, when determining the internal observation position so as not to be affected by the foreign matter F3 adhering to the surface 21b, it is possible to consider, for example, an exclusion setting that does not perform internal observation in at least one of the Z direction and the X and Y directions.

[0063] 19, a foreign substance F4 adhering to the light detection unit 44 is, for example, dust or other foreign substance adhering to the light detection unit 44. Such foreign substance F4 may affect the detection of feature quantities related to the formation of modified regions and cause erroneous detection. Therefore, when performing internal observation after laser processing in an environment where foreign substance F4 is adhering to the light detection unit 44, it is necessary to determine the internal observation position in advance so as to prevent erroneous detection. Note that, when determining the internal observation position so as not to be affected by foreign substance F4 adhering to the light detection unit 44, it is possible to perform an exclusion setting that does not perform internal observation in the Z direction, for example.

[0064] Another noise factor shown in FIG. 19 is noise F5 on the surface of stage 2, which is noise caused by, for example, the porous structure of the surface of stage 2. Such noise F5 may affect the detection of feature quantities related to the formation of modified regions and result in false positives. Therefore, when performing internal observation after laser processing in an environment where noise F5 on the surface of stage 2 is present, it is necessary to determine the internal observation position in advance to prevent false positives. When determining the internal observation position to avoid the influence of noise F5 on the surface of stage 2, it is possible to perform an exclusion setting that does not perform internal observation in the Z direction, for example.

[0065] Another noise factor shown in FIG. 19 is noise F6 on the rear surface of the holding member 600, which is noise caused by, for example, embossing the rear surface of the holding member 600. Such noise F6 may affect the detection of feature quantities related to the formation of the modified region, resulting in erroneous detection. Therefore, when performing internal observation after laser processing in an environment where noise F6 on the rear surface of the holding member 600 is present, it is necessary to determine the internal observation position in advance so as to prevent erroneous detection. Note that, when determining the internal observation position so as not to be affected by noise F6 on the rear surface of the holding member 600, it is possible to perform an exclusion setting that does not perform internal observation in the Z direction, for example.

[0066] Next, the process of the control unit 8 for determining the internal observation position taking the above-mentioned noise factors into consideration will be described. The control unit 8 performs the process for determining the internal observation position before laser processing. That is, the control unit 8 determines the internal observation position for the wafer 20 before laser processing is performed. The control unit 8 is configured to execute the following three controls: first control for controlling the drive unit 7 to sequentially move the imaging unit 4 to a position where each imaging region along the Z direction in a predetermined imaging range of the wafer 20 can be imaged; second control for controlling the imaging unit 4 to image each imaging region; third control for determining the appropriateness of the internal observation for the imaging range after laser processing based on the captured image output from the imaging unit 4 that detected light corresponding to each imaging region; and fourth control for outputting a determination result indicating the appropriateness of the internal observation.

[0067] In the first control, the control unit 8 first controls the drive unit 7 to move the imaging unit 4 to an imaging start position within the imaging range based on information indicating the imaging range set (input) as an inspection condition. More specifically, the control unit 8 controls the drive unit 7 to move the imaging unit 4 to the imaging start position based on the height set positions of the front surface 21b and the back surface 21a of the wafer 20, the coordinate position of the wafer 20 in the Z direction, and the information indicating the imaging range. The imaging range here includes a direct observation region (see, for example, FIG. 24 ) that is imaged by moving the focus from the front surface 21b side toward the back surface 21a side, and a back surface reflection region (see, for example, FIG. 24 ) that is imaged by focusing from the front surface 21b side to an area on the opposite side of the back surface 21a from the front surface 21b and that captures light reflected by the back surface 21a. The control unit 8 then controls the drive unit 7 to move the imaging unit 4 along the Z direction from the imaging start position to the imaging end position.

[0068] In the second control, the control unit 8 controls the imaging unit 4 so that imaging is continuously performed by the imaging unit 4 moving in the Z direction in the first control so that each imaging area is imaged. Each imaging area is an area included in the imaging range, and is determined by, for example, the moving speed and imaging cycle of the imaging unit 4.

[0069] In the third control, the control unit 8 determines the suitability of the imaging range for internal observation based on the captured image of each imaging region. The control unit 8 determines the suitability of the imaging range for internal observation based on, for example, feature amounts of feature points shown in the captured image of each imaging region. The control unit 8 may determine the suitability of the imaging range for internal observation based on feature amounts of processing range feature points, which are feature points of a range corresponding to a region where internal observation is desired after laser processing, among the feature points shown in the captured image of each imaging region. Furthermore, the control unit 8 may compare the feature amounts of the processing range feature points with assumed feature amounts assumed as feature amounts of feature points resulting from laser processing for a region where internal observation is desired after laser processing, and determine that the imaging range is more suitable for internal observation when the feature amounts of the processing range feature points are smaller than the assumed feature amounts.

[0070] Figure 22 is a diagram for explaining the determination of the adequacy of the internal observation at the position where device pattern F1 exists. Figure 22(a) shows the result of the internal observation before laser processing at the position where device pattern 1-A exists, Figure 22(b) shows the result of the internal observation before laser processing at the position where device pattern 1-C exists, and Figure 22(c) shows the result of the internal observation before laser processing at the position where device pattern 1-F exists. In Figures 22(a) to 22(c), the horizontal axis shows the feature amount, and the vertical axis shows the imaging depth.

[0071] In the example shown in FIG. 22(a), the presence of device pattern 1-A results in the detection of feature data 950 and 960 corresponding to device pattern 1-A. When such feature data 950 and 960 are detected, the control unit 8 may first determine whether these feature points are processing range feature points, which are feature points of a range corresponding to an area where internal observation is desired after laser processing. Assume now that the feature points associated with the feature data 950 and 960 are processing range feature points. In this case, the control unit 8 compares the feature data 950 and 960 of the processing range feature points with the assumed feature values ​​assumed as feature values ​​of the feature points resulting from laser processing. As shown in FIG. 21(b), the feature data 950 and 960 of the processing range feature points are significantly larger than the assumed feature values ​​assumed as feature values ​​of the feature points resulting from laser processing (e.g., the feature data 902 of the modified region SD2 on the surface 21b side and the feature data 904 of the modified region SD2 on the surface 521b side). In this case, the control unit 8 determines that the imaging range is not suitable for internal observation. In the example shown in Fig. 22(a), the control unit 8 sets the result of the determination of the imaging range as "X" and the score indicating suitability for internal observation as "25 points."

[0072] In the example shown in FIG. 22(b), the presence of device pattern 1-C results in the detection of feature data 970 corresponding to device pattern 1-C. When such feature data 970 is detected, the control unit 8 may first determine whether these feature points are processing range feature points, which are feature points of a range corresponding to an area where internal observation is desired after laser processing. Assume now that the feature points associated with the feature data 970 are processing range feature points. In this case, the control unit 8 compares the feature data 970 of the processing range feature points with the assumed feature values ​​assumed as feature values ​​of feature points resulting from laser processing. As shown in FIG. 21(c), the feature data 970 of the processing range feature points is significantly smaller than the assumed feature values ​​assumed as feature values ​​of feature points resulting from laser processing (e.g., feature data 901 of the modified region SD1 on the surface 21b side and feature data 903 of the modified region SD1 on the surface 521b side). In this case, the control unit 8 determines that the imaging range is suitable for internal observation. In the example shown in FIG. 22(b), the control unit 8 determines the imaging range as "OK" and assigns a score of "90 points" indicating the appropriateness of the internal observation. When comparing feature amount data of the processed range feature points with the assumed feature amounts assumed to be feature amounts of feature points resulting from laser processing, the comparison is performed at equivalent imaging depths. For example, the feature amount data 970 shown in FIG. 22(c) is compared with feature amount data 901 of the modified region SD1 on the front surface 21b side and feature amount data 903 of the modified region SD1 on the front surface 521b side (see FIG. 21(c)), which have equivalent detected imaging depths.

[0073] In the example shown in FIG. 22(c), the presence of device pattern 1-F allows feature amount data 980 corresponding to device pattern 1-F to be detected. Here, as shown in FIG. 22(d), the Z-direction position of the feature amount data 980 corresponding to device pattern 1-F does not overlap with any of the following positions in the direct observation area: the position of feature amount data 901 for the modified region SD1 on the back surface 21a side, the position of feature amount data 902 for the modified region SD2 on the front surface 21b side, and the position of feature amount data 910 for the tip of the upper crack. Furthermore, the Z-direction position of the feature amount data 980 does not overlap with any of the positions of feature amount data 903 for the modified region SD1 on the back surface 21a side and the position of feature amount data 904 for the modified region SD2 on the front surface 21b side in the back surface reflection area. In other words, the feature point of the feature amount data 980 is not a processing range feature point. In this case, the feature point of the feature amount data 980 does not affect internal observation, so the control unit 8 determines that the imaging range is suitable for internal observation. In the example shown in Fig. 22(c), the control unit 8 sets the result of the determination of the imaging range as "◯" and the score indicating the suitability of internal observation as "85 points." In this way, the control unit 8 may set the area in which the device pattern F1 is formed in the Z direction as the judgment exclusion area. Then, the control unit 8 may determine the suitability of internal observation for the imaging range only from the captured image related to the imaging area excluding the judgment exclusion area (here, the area in which the device pattern F1 is formed).

[0074] The control unit 8 may determine the suitability of internal observation for each of a plurality of different imaging ranges. That is, for example, the control unit 8 may sequentially determine the suitability of internal observation for each of the imaging ranges shown in Figures 22(a) to 22(c) (the imaging ranges corresponding to the device patterns 1-A to 1-F).

[0075] In the fourth control, the control unit 8 outputs the judgment result of the judgment of the suitability of the internal observation to the display 150 in a displayable manner. For example, when the control unit 8 has obtained judgment results for each of a plurality of imaging ranges, the control unit 8 outputs the judgment results for each of the plurality of imaging ranges so that the user can select the imaging range related to the area where internal observation will be performed after laser processing. For example, when the control unit 8 has obtained judgment results for three device patterns 1-A to 1-F as shown in Figures 22(a) to 22(c), the control unit 8 may output this information so that a diagram showing the respective feature data, the judgment result, and a score indicating suitability are displayed side by side.

[0076] The control unit 8 stores at least one of the captured image and position information for the imaging range selected by the user as information related to internal observation after laser processing. As a result, when internal observation after laser processing is performed on the same wafer 20, internal observation will be performed in the imaging range selected by the user.

[0077] Fig. 23 is a flowchart showing an example of an inspection method for determining an internal observation position. As shown in Fig. 23, in this inspection method, first, the laser processing apparatus 1 is started (step S1) and warmed up (step S2).

[0078] Next, the imaging units 5 and 6 are controlled to perform wafer alignment regarding the irradiation position of the laser light L (step S3), and a height setting process is performed to set the Z-height, which is the processing depth (height) during laser processing (step S4). In the height setting process, the height setting position of the front surface 21b of the wafer 20 is set, and the height setting position of the back surface 21a is also set. Note that information from the wafer alignment and height setting processes is used not only in the noise determination process described below, but also when observing the interior of the stealth diced wafer 20, so the information may be carried over for the interior observation process. Also, if the wafer alignment and height setting processes have already been completed in processing the stealth diced wafer 20, the completed information may be carried over, and the processes of steps S3 and S4 may be omitted. Also, the processes of steps S3 and S4 may be incorporated into the noise determination process (step S6) described below, as necessary.

[0079] Next, a judgment position (position in the X and Y directions) for judging the suitability of the internal observation is specified (step S5). The position in the X and Y directions may be linked to the planned processing line for stealth dicing, for example. In this case, for example, index movement in the Y direction may be performed for each planned processing line, and the X direction may be determined by the user while viewing the IR camera image. Furthermore, the position in the X and Y directions may be checked at equal intervals by automatic processing.

[0080] Next, a noise determination process (a process for determining whether the internal observation is appropriate) is performed (step S6). The noise determination process is performed on the wafer 20 before a modified region is formed inside. Then, it is determined whether or not it is necessary to change the designated location to change the imaging range (step S7), and if it is necessary, the determination position (position in the X and Y directions) is designated again (step S5). If it is not necessary, the process is completed.

[0081] Next, the above-mentioned noise determination process (step S6) will be described in detail with reference to Figs. 24 to 34. Figs. 24 to 26 are diagrams illustrating a first example of the noise determination process. Figs. 27 to 29 are diagrams illustrating a second example of the noise determination process. Figs. 30 to 34 are diagrams illustrating a third example of the noise determination process.

[0082] A first example of the noise determination process will be described. FIG. 24 is a diagram illustrating the first example of the noise determination process. FIG. 25 is a flowchart according to the first example. FIG. 26 is a diagram illustrating an example of a noise determination result of the first example. In the first example, as shown in FIG. 24, when a recipe (processing conditions) for SDBG (Stealth Dicing Before Grinding) processing of a wafer having a device pattern and a thickness t=775 μm is derived by internal observation, a position for internal observation is determined as a preliminary step. In the first example, first, information indicating an imaging range and a noise determination exclusion area is set. Now, as shown in FIG. 24, it is assumed that the imaging range is set to ±400 μm from the height set position of the back surface 21 a (i.e., 400 μm toward the direct observation area and 400 μm toward the back surface reflection area), and the noise determination exclusion area is set to ±20 μm from the height set position of the back surface 21 a. Such a noise determination exclusion area is set to include, for example, an area where a device pattern is formed, but not to include an area where internal observation is desired (for example, the vicinity of the positions Va and Vb where the modified area is to be formed).

[0083] The imaging range may be set by specifying a numerical value, or may be set automatically based on a processing method such as SDBG or a processing recipe. The noise determination exclusion area may be set by specifying a numerical value, or may be automatically assigned by setting it as a "device area" (area of ​​device patterns).

[0084] 25, in a first example of the noise determination process, first, an imaging start position is calculated based on the height set positions of the front surface 21b and the back surface 21a of the wafer 20, the coordinate position in the Z direction on the wafer 20, and information indicating the imaging range, and the drive unit 7 is controlled to move the imaging unit 4 to the imaging start position (step S101). Then, imaging is repeatedly performed while the imaging unit 4 moves along the Z direction from the imaging start position to the imaging end position (step S102). In the first example, imaging is performed from the imaging start position to the imaging end position, including the noise determination exclusion region. Imaging is repeatedly performed, for example, by focusing on the device pattern region.

[0085] Next, factors that may cause noise in internal observation are detected based on the captured image captured by the imaging unit 4 (step S103), and the suitability of internal observation in this imaging range is determined (noise determination) based on the detected information (step S104). The noise determination is performed excluding a range of ±20μ from the height set position of the back surface 21a, which is the noise determination exclusion area.

[0086] Then, the noise determination result is displayed on the display 150 (step S105). In FIG. 26, the feature amount is shown on the horizontal axis and the imaging depth on the vertical axis, and the feature amount of each imaging region is shown. In the example of the noise determination result shown in FIG. 26, the feature amount is large only in the noise determination exclusion region, and the feature amount is not large in the region to be determined. For this reason, as shown in FIG. 26, the noise determination result is determined to be "o" (suitable for internal observation). Note that, as described above, in the first example, although the noise determination exclusion region is excluded from the target of noise determination, imaging is performed. For this reason, the determination exclusion region can be changed as necessary based on the feature amount detected from the captured image of the noise determination exclusion region.

[0087] Finally, at least one of the captured image and the position information is registered as information related to the internal observation after laser processing. The registration of the internal observation position, etc. may be performed at the discretion of the user or automatically. A plurality of internal observation positions, etc. may be registered. Information on the internal observation position, etc. may be linked to data such as auto-alignment, and the internal observation position may be moved to the registered position automatically (or by button operation, etc.) during internal observation.

[0088] A second example of the noise determination process will be described. FIG. 27 is a diagram illustrating the second example of the noise determination process. FIG. 28 is a flowchart according to the second example. FIG. 29 is a diagram illustrating an example of a noise determination result of the second example. In the second example, as shown in FIG. 27, when a recipe (processing conditions) for SDBG (Stealth Dicing Before Grinding) processing of a wafer having a device pattern and a thickness t=775 μm is derived by internal observation, a position for internal observation is determined as a preliminary step. In the second example, first, information indicating an imaging range and a noise determination exclusion area is set. Now, as shown in FIG. 27, it is assumed that the imaging range is set to ±400 μm from the height set position of the back surface 21 a (i.e., 400 μm toward the direct observation area and 400 μm toward the back surface reflection area), and the noise determination exclusion area is set to ±20 μm from the height set position of the back surface 21 a.

[0089] Here, in the first example described above, the noise determination exclusion area is included in the imaging range, whereas in the second example, the noise determination exclusion area is excluded from the imaging range. For example, in cases where the device pattern area is known (known noise), the imaging time can be reduced by not imaging the noise determination exclusion area in this way.

[0090] 28, in the second example of the noise determination process, first, an imaging start position is calculated based on the height set positions of the front surface 21b and the back surface 21a of the wafer 20, the coordinate position in the Z direction on the wafer 20, and information indicating the imaging range, and the drive unit 7 is controlled to move the imaging unit 4 to the imaging start position (step S201). Then, imaging is repeatedly performed while the imaging unit 4 moves along the Z direction from the imaging start position to the imaging end position (step S202). In the second example, imaging is performed from the imaging start position to the imaging end position for each region except for the noise determination exclusion region.

[0091] Next, factors that may cause noise in internal observation are detected based on the captured image captured by the imaging unit 4 (step S203), and the suitability of internal observation in this imaging range is determined (noise determination) based on the detected information (step S204). The noise determination is performed for all imaging regions.

[0092] The noise determination result is then displayed on the display 150 (step S205). In FIG. 29, the horizontal axis represents the feature amount and the vertical axis represents the imaging depth, showing the feature amount of each imaging region. In the second example, the determination exclusion region is not imaged, so the feature amount of the determination exclusion region is not shown in FIG. 29. In the example of the noise determination result shown in FIG. 29, the feature amount is not large in the region to be determined, so the noise determination result is determined to be "o" (suitable for internal observation). Note that, based on the noise determination result, the determination exclusion region can be changed (mainly by widening the range) as necessary. Finally, at least one of the captured image and the position information is registered as information related to internal observation after laser processing.

[0093] A third example of noise determination processing will be described. In the third example, noise determination will be described for a case where grinding marks (BG marks) on the surface 21b can be a problem as a noise factor in addition to the device pattern. For example, when performing FC (full cut) processing in which cracks reach the surface 21b after laser processing, the surface 21b is also observed, and therefore the grinding marks (BG marks) can be a noise factor. First, an example of detecting BG marks according to a comparative example will be described with reference to FIG. 30.

[0094] FIG. 30(a) is a diagram showing an example of a BG mark formed on the surface 21b. The BG mark can be formed in various directions relative to the planned processing line. For example, in an area where the BG mark is formed perpendicular or oblique to the planned processing line, the BG mark is unlikely to be erroneously detected as a crack, etc., but in an area where the BG mark is formed horizontally to the planned processing line, the BG mark may be erroneously detected as a crack, etc. In a BG mark detection method according to a comparative example, for example, the crack detection position is determined based on the reflectance (brightness value) in the captured image. FIG. 30(b) shows the brightness value at each position on the XY plane. However, such a detection method based on reflectance (brightness value) may not be able to properly distinguish between BG marks that are unlikely to be erroneously detected and BG marks that are prone to be erroneously detected.

[0095] FIG. 31 is a diagram illustrating an example of BG mark detection according to this embodiment. The detection method according to this embodiment can appropriately distinguish at which positions on the wafer surface (in the XY plane) BG marks become noise. That is, BG marks that are nearly perpendicular to the processing direction as shown in FIG. 31(a) are not detected as line segments (noise that may be erroneously detected as cracks) as shown in FIG. 31(b), and BG marks that are nearly horizontal to the processing direction as shown in FIG. 31(c) can be detected as line segments 700 as shown in FIG. 31(d). This makes it possible to determine that an imaging range containing BG marks that may be detected as line segments and thus result in erroneous detection is not suitable for internal observation.

[0096] FIG. 32 is a diagram illustrating a third example of the noise determination process. FIG. 33 is a flowchart according to the third example. FIG. 34 is a diagram illustrating an example of a noise determination result of the third example. In the third example, as shown in FIG. 32, when a recipe (processing conditions) for FC (full cut) processing of a wafer having a device pattern and a thickness t=400 μm is derived by internal observation, a position for internal observation is determined as a preliminary step. In the third example, first, information indicating the imaging range and the noise determination exclusion area is set. Now, as shown in FIG. 32, it is assumed that the imaging range is set to ±420 μm from the height set position of the back surface 21a (i.e., 420 μm toward the direct observation area and 420 μm toward the back surface reflection area), and the noise determination exclusion area is set to ±20 μm from the height set position of the back surface 21a. In the third example, similar to the second example, the noise determination exclusion area is excluded from the imaging range. The device pattern area in the Z direction (the area of ​​the back surface 21a) is included in the determination exclusion area. On the other hand, the region of the BG marks in the Z direction (region of the surface 21b) is also a region where cracks are detected after processing, and therefore is not included in the judgment exclusion region in the Z direction, but is included in the imaging range.

[0097] 33, in the third example of the noise determination process, first, an imaging start position is calculated based on the height set positions of the front surface 21b and the back surface 21a of the wafer 20, the coordinate position in the Z direction on the wafer 20, and information indicating the imaging range, and the drive unit 7 is controlled to move the imaging unit 4 to the imaging start position (step S301). Then, imaging is repeatedly performed while the imaging unit 4 moves along the Z direction from the imaging start position to the imaging end position (step S302). In the third example, imaging is performed from the imaging start position to the imaging end position for each area except for the noise determination exclusion area.

[0098] Next, factors that may cause noise in internal observation are detected based on the captured image captured by the imaging unit 4 (step S303), and the suitability of internal observation in this imaging range is determined (noise determination) based on the detected information (step S304). The noise determination is performed for all imaging regions.

[0099] In Figures 34(a) and 34(b), the horizontal axis represents the feature amount and the vertical axis represents the imaging depth, showing the feature amount for each imaging region. As shown in Figure 34(a), it is assumed that feature amount data 990 related to a BG mark is detected near the surface 21b. In this case, there is a risk that the line segment related to the BG mark may be erroneously detected as a crack during internal observation, so the noise determination result is determined to be "x" (not suitable for internal observation). In a third example, noise determination is performed at multiple locations on the XY plane. That is, after the noise determination is completed, the XY position of the imaging range is moved as shown in Figure 33 (step S305), and the processes of steps S301 to S304 are performed again. As shown in Figure 34(b), it is assumed that in the noise determination performed after the XY position is changed, feature amount data related to the BG mark is not detected, and only feature amount data 971 related to the device pattern is detected. In the example of the noise determination result shown in FIG. 34(b), the feature amount is not large in the region to be determined, so the noise determination result is determined to be "Good" (suitable for internal observation). Based on the noise determination result, the determination exclusion region can be changed (mainly by widening the range) as necessary. Finally, at least one of the captured image and the position information is registered as information related to internal observation after laser processing. As described above, in the third example, a position where no false detection occurs is searched for while changing the XY position.

[0100] Here, for each of the above-mentioned noise factors, it may be possible to distinguish between those that can be noise and those that cannot be noise based on the device type, etc. For example, noise factors include noise caused by device patterns, noise caused by BG marks, and noise inside the silicon of the wafer 20 caused by foreign matter adhering to the light detection unit 44. In this case, depending on the device type, the user may know in advance whether noise caused by device patterns and noise caused by BG marks are present. Also, the user may know in advance from past performance that there is no noise inside the silicon. In such cases, the GUI (Graphical User Interface) of the display 150 may be configured so that the user can specify to exclude judgment areas for noise factors that do not require noise judgment. That is, the user may specify a combination of judgment areas for noise judgment using the GUI. For example, for a wafer with a mirror-finished front surface and a device pattern on the back surface, it is known in advance that judgment of noise caused by BG marks is unnecessary, so the user may specify in the GUI to perform a combination of judgment of noise caused by Device patterns and judgment of noise inside the silicon. Furthermore, if the area where noise occurs inside the silicon is known in advance, the user may specify via the GUI that a combination of noise determination due to Debye patterns and noise determination due to BG marks be performed. This can increase the speed of noise determination. In addition to specifying a combination of the three noise determination methods described above, a GUI may also be set that allows specification of performing noise determination only in the vicinity of the modified area, for example.

[0101] Next, the effects of the laser processing device 1 according to this embodiment will be described.

[0102] The laser processing apparatus 1 of this embodiment includes an imaging unit 4 that outputs light that is transparent to the wafer 20 and captures images of the interior of the wafer 20 by detecting the light that has propagated through the wafer 20, a drive unit 7 that moves the imaging unit 4 along the vertical Z direction, and a control unit 8. The control unit 8 is configured to control the drive unit 7 so that the imaging unit 4 sequentially moves to a position where each imaging area along the Z direction in a predetermined imaging range of the wafer 20 can be imaged, control the imaging unit 4 so that each imaging area is imaged, and determine the suitability of internal observation after laser processing for the imaging range based on the image output from the imaging unit 4 that detects the light related to each imaging area.

[0103] In the laser processing apparatus 1 according to this embodiment, the imaging unit 4, which moves along the Z direction, captures images of each imaging region along the Z direction in a predetermined imaging range of the wafer 20. Then, in the laser processing apparatus 1, the suitability of the imaging region for internal observation after laser processing is determined based on the captured image of each imaging region. In this way, by taking into account the captured images of each imaging region along the Z direction of the wafer 20, the influence of potential noise in internal observation after laser processing can be identified along the Z direction. Then, after identifying the influence of potential noise in each region along the Z direction of the imaging range, the suitability of the imaging region for internal observation can be determined, thereby determining with high accuracy whether the imaging region is suitable for internal observation. With this configuration, after laser processing, internal observation can be performed in an imaging region suitable for internal observation, thereby eliminating the influence of noise in internal observation after laser processing and improving the estimation accuracy of the processed state of the wafer.

[0104] The control unit 8 may determine the suitability of the imaging range for internal observation based on the feature amounts of the feature points shown in the captured image for each imaging region. By taking the feature amounts of the feature points shown in the captured image into consideration, the magnitude of the influence on the detection of the feature amounts in internal observation after laser processing can be appropriately identified, and it can be determined with higher accuracy whether the imaging range is suitable for internal observation.

[0105] The control unit 8 may determine the suitability of the imaging range for internal observation based on the feature amounts of processing range feature points, which are feature points in a range corresponding to an area where internal observation after laser processing is desired, among the feature points shown in the captured image of each imaging range. With this configuration, only the feature amounts of feature points (processing range feature points) in a range that is likely to affect detection of feature amounts in internal observation after laser processing are taken into consideration, making it possible to more accurately determine whether the imaging range is suitable for internal observation.

[0106] The control unit 8 may compare, for an area where internal observation is desired after laser processing, the feature amounts of the processing range feature points with assumed feature amounts that are assumed to be feature amounts of feature points caused by the laser processing, and determine that the imaging range is more suitable for internal observation the smaller the feature amounts of the processing range feature points are compared with the assumed feature amounts. In this way, the feature amounts of the processing range feature points are compared with the feature amounts (assumed feature amounts) of the feature points caused by the laser processing, and if the feature amounts of the processing range feature points are relatively small and have little effect on detection of the feature amounts in internal observation after laser processing, the imaging range is determined to be suitable for internal observation, thereby making it possible to more accurately determine whether the imaging range is suitable for internal observation.

[0107] The control unit 8 may further be configured to output the result of the determination of the suitability of internal observation, allowing the user to confirm the result and determine the area for internal observation based on the result.

[0108] The control unit 8 may determine the suitability of internal observation for each of a plurality of different imaging ranges and output the determination results for each of the plurality of imaging ranges so that the user can select the imaging range for the area where internal observation will be performed after laser processing. In this way, the suitability of internal observation for each of a plurality of imaging ranges is determined and each determination result is output, allowing the user to select the area where internal observation will be performed while comparing each determination result.

[0109] The control unit 8 may store at least one of the captured image and position information for the imaging range selected by the user as information related to internal observation after laser processing. This ensures that the information on the imaging range selected by the user is registered as information related to internal observation after laser processing, and allows internal observation to be performed with an imaging range that takes into account the user's selection (i.e., an imaging range that is less susceptible to the influence of noise).

[0110] The wafer 20 has a device pattern on the surface opposite to the surface irradiated with the laser, and the control unit 8 may determine the suitability of the imaging range for internal observation based on captured images of the imaging areas excluding the device pattern. The area where the device pattern is formed has a large feature value of the feature points in the captured image, but is not an area where a modified layer or cracks will be formed. Therefore, by excluding the captured image of the area where the device pattern is formed and determining the suitability of the internal observation from only the other captured images, it is possible to more accurately determine whether the imaging range is suitable for internal observation based on the captured image of the area where the internal observation will actually be performed. [Explanation of symbols]

[0111] 1...laser processing device (inspection device), 4...imaging unit (imaging section), 7...driving unit (driving section), 8...control section, 20...wafer

Claims

1. an imaging unit that outputs light that is transmissive to the wafer and detects the light that has propagated through the wafer, thereby imaging the inside of the wafer; a drive unit that moves the imaging unit along a Z direction that is a vertical direction; a control unit, The control unit controlling the driving unit so that the imaging unit sequentially moves to a position where each imaging region along the Z direction in a predetermined imaging range of the wafer can be imaged; controlling the imaging unit so that each imaging area is imaged; determining whether the imaging range is suitable for internal observation after laser processing based on the captured image output from the imaging unit that detected the light related to each imaging region; is configured to run the control unit determines the suitability of the internal observation for the imaging range based on a feature amount of a feature point shown in the captured image for each of the imaging regions; The control unit determines the suitability of the internal observation for the imaging range based on the feature amounts of processing range feature points, which are feature points in a range corresponding to an area where internal observation is desired after laser processing, among the feature points shown in the captured image for each imaging range.

2. 2. The inspection device according to claim 1, wherein the control unit compares, for an area where internal observation is desired after the laser processing, a feature amount of the processing range feature point with an assumed feature amount that is assumed to be a feature amount of a feature point resulting from the laser processing, and determines that the imaging range is more suitable for the internal observation as the feature amount of the processing range feature point is smaller than the assumed feature amount.

3. 3. The inspection device according to claim 1, wherein the control unit is further configured to output a determination result of whether the internal observation is appropriate.

4. The control unit determining the suitability of the internal observation for each of the plurality of imaging ranges that are different from one another; 4. The inspection device according to claim 3, wherein the judgment results for each of the plurality of imaging ranges are output so that a user can select the imaging range relating to an area for internal observation after laser processing.

5. 5. The inspection device according to claim 4, wherein the control unit stores at least one of the captured image and position information for the imaging range selected by a user as information related to internal observation after laser processing.

6. the wafer has a device pattern on a surface opposite to the surface irradiated with the laser; The inspection device according to any one of claims 1 to 5, wherein the control unit determines the suitability of the internal observation for the imaging range based on the captured image relating to the imaging area excluding the device pattern among the imaging areas.

7. An imaging unit that outputs light that is transparent to the wafer and detects the light that has propagated through the wafer, thereby imaging the inside of the wafer; a drive unit that moves the imaging unit along a Z direction that is a vertical direction; a control unit, The control unit controlling the driving unit so that the imaging unit sequentially moves to a position where each imaging region along the Z direction in a predetermined imaging range of the wafer can be imaged; controlling the imaging unit so that each imaging area is imaged; determining whether the imaging range is suitable for internal observation after laser processing based on the captured image output from the imaging unit that detected the light related to each imaging region; is configured to run The control unit is further configured to output a determination result of whether the internal observation is appropriate, The control unit determining the suitability of the internal observation for each of the plurality of imaging ranges that are different from one another; An inspection device that outputs a determination result for each of the plurality of imaging ranges so that a user can select the imaging range relating to an area for internal observation after laser processing.

8. taking an image of a predetermined imaging range inside the wafer while changing an imaging region along a Z direction which is a vertical direction; and determining suitability of the imaging range for internal observation after laser processing based on the captured image of each imaging region, determining the suitability of the internal observation for the imaging range based on feature amounts of feature points shown in the captured images for each of the imaging regions; An inspection method for determining the suitability of the internal observation for each imaging area based on the feature amounts of processing area feature points, which are feature points in a range corresponding to an area where internal observation is desired after laser processing, among the feature points shown in the captured image for each imaging area.

9. Taking an image of a predetermined imaging range inside a wafer while changing the imaging area along the Z direction, which is the vertical direction; and determining suitability of the imaging range for internal observation after laser processing based on the captured image of each imaging region, and outputting a determination result of the suitability of the internal observation. determining the suitability of the internal observation for each of the plurality of imaging ranges that are different from one another; An inspection method, comprising: outputting a judgment result for each of the plurality of imaging ranges so that a user can select the imaging range relating to an area for internal observation after laser processing.

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