Inspection device and inspection method

Abstract

A control unit of a laser processing device according to the present invention is configured to execute: controlling of a laser irradiation unit such that each of a plurality of lines on a wafer is irradiated with laser light along a forward path and a return path in an X direction, and one or a plurality of modified regions are thereby formed inside the wafer; determining, on the basis of a signal output from an imaging unit that has detected light, whether or not a crack extending from the modified region associated with each of the reciprocating paths of the plurality of lines is BHC that has reached the surface side; and determining whether the irradiation condition of the laser light is acceptable or not on the basis of the average crack amount of reciprocating paths of which the processing depth of the laser light related to the formation of the modified region is the shortest among the reciprocating paths determined to be BHC, and information on the difference in the crack amounts of the reciprocating paths.

Description

Inspection device and inspection method

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

[0002] Patent Document 1 discloses a laser processing device that includes an evaluation unit that generates an evaluation value indicating processing quality corresponding to each of a plurality of processing defect modes using feature values ​​based on an image of a cut surface cut by laser cutting processing, and outputs a combination pattern that is a plurality of evaluation values ​​corresponding to each of the plurality of processing defect modes, and a correction amount calculation unit that calculates a correction amount for processing parameters of the laser cutting processing based on the combination pattern.

[0003] Japanese Patent Application Laid-Open No. 2020-121338

[0004] For the laser processing device as described above, actual processing is performed at the time of shipment or delivery, or during periodic inspection by the end user to check whether the processing results satisfy specified conditions, and if they do not, the processing parameters may be adjusted.

[0005] An object of one aspect of the present invention is to provide an inspection device and an inspection method that can improve inspection accuracy.

[0006] (1) An inspection device according to one aspect of the present invention includes a stage for supporting a wafer having a semiconductor substrate with a first surface and a second surface; a laser irradiation unit that irradiates the wafer with laser light using the second surface as an incident surface; an imaging unit that outputs light that is transparent to the semiconductor substrate and detects the light that has propagated through the semiconductor substrate; and a control unit. The control unit is configured to: control the laser irradiation unit so that, for each of a plurality of lines on the wafer that extend in a first direction and are adjacent to each other in a second direction, one or more modified regions are formed inside the semiconductor substrate by irradiating the laser light along each of the outbound and inbound paths in the first direction; determine, based on a signal output from the imaging unit that detects the light, whether or not a crack extending from the modified region on each of the outbound paths of the plurality of lines has reached the first surface side of the semiconductor substrate; and determine whether or not the laser light irradiation conditions are acceptable based on information regarding the average crack amount of the outbound path in which the laser light has been processed to the shallowest depth for forming the modified region, and the difference in the crack amount of the outbound path.

[0007] In an inspection device according to one aspect of the present invention, laser light is irradiated along each of a plurality of linear paths to form a modified region, and whether cracks extending from the modified regions along each of the linear paths have reached the first surface (whether the crack has reached the first surface) is determined based on the detection results from the imaging unit. The pass / fail of the laser light irradiation conditions is then determined based on information regarding the average crack volume and the difference in the crack volume for the path with the shallowest laser processing depth among the paths determined to be in the crack-reached state. The average crack volume for the path with the shallowest processing depth that is in the crack-reached state is an important indicator of the laser processing performance required to achieve the crack-reached state. Furthermore, information regarding the difference in the crack volume for the paths is an important indicator of whether the same laser processing state can be achieved across the paths. By evaluating these indicators in a comprehensive manner to determine whether the laser light irradiation conditions are pass / fail, the accuracy of the pass / fail determination can be improved. This improves the inspection accuracy of the laser light irradiation conditions.

[0008] (2) In the inspection device described in (1) above, the information regarding the difference in crack amount between the two passes may include information indicating the difference in crack amount between the two passes and information indicating the difference in processing depth of the laser beam between the two passes. The information indicating the difference in crack amount between the two passes is information evaluating the difference in crack amount based on real values. The information indicating the difference in processing depth of the laser beam between the two passes is information evaluating the difference in crack amount based on dicer input values. By taking into account such information evaluating the difference in crack amount based on dicer input values ​​when making a pass / fail judgment, it is possible to avoid a situation where discrepancies occur in the processing results even when the same numerical values ​​are input for the dicer input. As described above, by including the above two pieces of information as information regarding the difference in crack amount between the two passes, inspection accuracy can be further improved.

[0009] (3) In the inspection device described in (2) above, the control unit may assign scores to the average crack volume in the forward and backward passes, the information indicating the difference in the crack volume in the forward and backward passes, and the information indicating the difference in the processing depth of the laser beam in the forward and backward passes, and may determine whether the laser beam irradiation conditions are acceptable or not based on the total score. This configuration allows the above three pieces of information to be quantitatively evaluated and the evaluation to be standardized. This improves the accuracy of the pass / fail determination.

[0010] (4) In the inspection device described in (2) or (3) above, the control unit may weight and score the average crack volume in the forward and backward passes, the information indicating the difference in the crack volume in the forward and backward passes, and the information indicating the difference in the processing depth of the laser light in the forward and backward passes, and determine whether the laser light irradiation conditions are acceptable or not from the total value. With this configuration, optimal evaluation can be performed by weighting in accordance with the evaluation policy.

[0011] (5) In the inspection device described in any one of (1) to (4) above, the control unit may be configured to further adjust the laser light irradiation conditions based on information about the average crack amount in the round trip and the difference in the crack amount in the round trip when the laser light irradiation conditions are unacceptable. With this configuration, the laser light irradiation conditions can be repeatedly adjusted based on the average crack amount in the round trip until the laser light irradiation conditions are acceptable, and the laser light irradiation conditions can be appropriately set.

[0012] (6) The inspection device described in any one of (1) to (5) above may perform a series of inspections using only one wafer. By performing a series of inspections using only one wafer, it is possible to eliminate evaluation variations due to individual differences between wafers, perform accurate pass / fail judgments, and appropriately adjust the laser light irradiation conditions.

[0013] (7) In the inspection device described in any one of (1) to (6) above, the laser irradiation unit may include a light source that emits laser light, a spatial light modulator that modulates the laser light output from the light source, and a condenser lens that condenses the laser light modulated by the spatial light modulator onto the wafer, and the control unit may determine whether the laser light irradiation conditions are acceptable by further taking into account information indicating the coordinates of the aberration correction pattern in the spatial light modulator and the position of the pupil plane in the condenser lens. It is believed that the closer the center coordinates of the aberration correction pattern in the spatial light modulator are to the center of the condenser lens, the more resistant the laser light irradiation to changes over time. Therefore, by taking such information into account, the inspection accuracy can be further improved.

[0014] (8) In the inspection device described in any one of (1) to (7) above, the control unit may determine whether the laser light irradiation conditions are acceptable by further considering additional parameters used in evaluating the average crack amount. For example, the evaluation of the average crack amount may change depending on requirements, such as whether a smaller crack amount is preferable for thin materials. In this regard, by considering the additional parameters used in evaluating the average crack amount, the average crack amount can be appropriately evaluated, thereby further improving inspection accuracy.

[0015] (9) In the inspection device according to any one of (1) to (8), the control unit may determine whether the laser beam irradiation conditions are acceptable by further considering information indicating the cross-sectional state of the wafer after processing. By considering the cross-sectional state after actual processing, the inspection accuracy related to the laser beam irradiation conditions can be improved.

[0016] (10) An inspection method according to one aspect of the present invention includes a first step of preparing a wafer including a semiconductor substrate having a first surface and a second surface, and forming one or more modified regions inside the semiconductor substrate by irradiating laser light along both an outward path and a return path in the first direction on each of a plurality of lines on the wafer that extend in a first direction and are adjacent to each other in a second direction; a second step of outputting light that is transparent to the semiconductor substrate in which the modified regions have been formed by the first step and detecting the light that has propagated through the semiconductor substrate; a third step of determining, based on the light detected in the second step, whether a crack extending from the modified region has reached the first surface side of the semiconductor substrate; and a fourth step of determining whether the laser light irradiation conditions are acceptable based on information regarding the average crack amount of the round trip path in which the processing depth of the laser light for forming the modified region is shallowest, and the difference in the crack amount between the round trip paths, among the round trip paths determined to be in the crack reaching state.

[0017] According to one aspect of the present invention, it is possible to improve inspection accuracy.

[0018] 1 is a configuration diagram of a laser processing apparatus equipped with an inspection apparatus of one embodiment. FIG. 2 is a plan view of a wafer of one embodiment. FIG. 3 is a cross-sectional view of a portion of the wafer shown in FIG. 2. FIG. 4 is a configuration diagram of a laser irradiation unit shown in FIG. 1. FIG. 5 is a configuration diagram of an inspection imaging unit shown in FIG. 1. FIG. 6 is a configuration diagram of an alignment correction imaging unit shown in FIG. 1. FIG. 7 is a cross-sectional view of a wafer for explaining the imaging principle by the inspection imaging unit shown in FIG. 5, and images at various locations taken by the inspection imaging unit. FIG. 8 is a cross-sectional view of a wafer for explaining the imaging principle by the inspection imaging unit shown in FIG. 5, and images at various locations taken by the inspection imaging unit. FIG. 9 is an SEM image of a modified region and a crack formed inside a semiconductor substrate. FIG. 10 is an SEM image of a modified region and a crack formed inside a semiconductor substrate. FIG. 11 is a schematic diagram showing an optical path diagram for explaining the imaging principle by the inspection imaging unit shown in FIG. 5, and an image at a focus taken by the inspection imaging unit. FIG. 12 is a schematic diagram showing an optical path diagram for explaining the imaging principle by the inspection imaging unit shown in FIG. 5, and an image at a focus taken by the inspection imaging unit. FIG. 13 is a schematic diagram showing an image of a formed modified region for inspection. FIG. 14 is a flowchart showing a processing procedure. FIG. 1 is a diagram showing an example of a processing result; FIG. 2 is a diagram showing a cross-sectional state of a wafer after processing; FIG. 3 is a table showing an example of processing conditions and inspection standards; FIG. 4 is a diagram showing rules for weighting, score derivation, and adjustment processing; FIG. 5 is a diagram explaining a processing and derivation loop; FIG. 6 is a diagram explaining a processing and derivation loop; and FIG. 7 is a flowchart showing an inspection method.

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present invention will be described in detail below with reference to the accompanying drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be omitted. [Configuration of the laser processing device]

[0020] 1, the laser processing apparatus 1 (inspection apparatus) includes a stage 2, a laser irradiation unit 3, a plurality of imaging units 4, 5, and 6, a drive unit 7, and a control unit 8. The laser processing apparatus 1 is an apparatus that forms a modified region 12 in an object 11 by irradiating the object 11 with laser light L.

[0021] The stage 2 supports the object 11, for example, by adsorbing a film attached to the object 11. The stage 2 is movable along both the X direction (first direction) and the Y direction (second direction), and is rotatable about an axis parallel to the Z direction. The X direction and the Y direction are horizontal directions perpendicular to each other, and the Z direction is a vertical direction.

[0022] The laser irradiation unit 3 focuses laser light L, which is transparent to the object 11, and irradiates the object 11. 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.

[0023] 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 melting treatment 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.

[0024] 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 lined up 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.

[0025] The imaging unit 4 captures images of the modified region 12 formed in the object 11 and the tip of the crack extending from the modified region 12 .

[0026] 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 captured by the imaging units 5 and 6 are used, for example, to align the irradiation position of the laser light L.

[0027] 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.

[0028] 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 reading and writing of data from and to the memory and storage, as well as communication via the communication device.

[0029] [Configuration of Object] In this embodiment, the object 11 is a wafer 20, as shown in FIGS. 2 and 3 . 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 front surface 21 a (first surface) and a back surface 21 b (second surface, incident surface). The semiconductor substrate 21 is, for example, a silicon substrate. The functional device layer 22 is formed on the front surface 21 a of the semiconductor substrate 21. The functional device layer 22 includes a plurality of functional devices 22 a arranged two-dimensionally along the front surface 21 a. The functional devices 22 a 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 22 a may be three-dimensionally configured by stacking multiple layers. Although the semiconductor substrate 21 has a notch 21c indicating the crystal orientation, 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 surface 21a, and the multiple lines 15 are set in a lattice pattern. Note that the lines 15 are imaginary lines, but may also be actually drawn lines.

[0031] 4, the laser irradiation unit 3 includes 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.

[0032] In this embodiment, the laser irradiation unit 3 irradiates the wafer 20 with laser light L from the back 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. The modified region (first modified region) 12a is the modified region closest to the front surface 21a of the two rows of modified regions 12a, 12b. The modified region (second modified region) 12b is the modified region closest to the modified region 12a and closest to the back surface 21b of the two rows of modified regions 12a, 12b.

[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 relative to the semiconductor substrate 21 along a line 15. The laser light L is modulated by a 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 back surface 21b of the semiconductor substrate 21 along each of the multiple lines 15 under the condition that the cracks 14 spanning the two rows of modified regions 12a, 12b reach the front surface 21a of the semiconductor substrate 21. As an example, for the semiconductor substrate 21, which is a single-crystal silicon substrate with a thickness of 775 μm, two focusing points C1, C2 are aligned at positions 54 μm and 128 μm from the front surface 21a, respectively, and the laser light L is irradiated from the back surface 21b of the semiconductor substrate 21 along each of the multiple lines 15. At this time, the wavelength of the laser light L is 1099 nm, the pulse width is 700 ns, and the repetition frequency is 120 kHz. The output of the laser light L at the focal point C1 is 2.7 W, the output of the laser light L at the focal point C2 is 2.7 W, and the relative moving speed of the two focal points C1 and C2 with respect to the semiconductor substrate 21 is 800 mm / sec.

[0035] The formation of the two rows of modified regions 12 a, 12 b and the cracks 14 is performed in the following case: in a later process, the back surface 21 b of the semiconductor substrate 21 is ground to thin the semiconductor substrate 21 and expose the cracks 14 on the back surface 21 b, and the wafer 20 is cut into a plurality of semiconductor devices along each of the plurality of lines 15.

[0036] 5, the imaging unit 4 includes a light source 41, a mirror 42, an objective lens 43, and a light detection unit 44. The light source 41 outputs light I1 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 I1 in the near-infrared region. The light I1 output from the light source 41 is reflected by the mirror 42, passes through the objective lens 43, and is irradiated onto the wafer 20 from the back 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, 12b have been formed as described above.

[0037] The objective lens 43 passes the light I1 reflected by the surface 21a of the semiconductor substrate 21. In other words, the objective lens 43 passes the light I1 that has propagated through the semiconductor substrate 21. The numerical aperture (NA) of the objective lens 43 is 0.45 or greater. The objective lens 43 has a correction collar 43a. The correction collar 43a corrects aberrations that occur in the light I1 within the semiconductor substrate 21, for example, by adjusting the distances between the multiple lenses that make up the objective lens 43. The light detection unit 44 detects the light I1 that has passed through the objective lens 43 and the mirror 42. The light detection unit 44 is, for example, an InGaAs camera, and detects the light I1 in the near-infrared region.

[0038] The imaging unit 4 can capture images of each of the two rows of modified regions 12a, 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 extending from the modified region 12a toward the front surface 21a. The crack 14b is a crack extending from the modified region 12a toward the back surface 21b. The crack 14c is a crack extending from the modified region 12b toward the front surface 21a. The crack 14d is a crack extending from the modified region 12b toward the back surface 21b. The control unit 8 controls the laser irradiation unit 3 to irradiate the laser beam L under conditions such that the cracks 14 extending across the two rows of modified regions 12a and 12b reach the surface 21a of the semiconductor substrate 21 (see FIG. 4 ). However, if the cracks 14 do not reach the surface 21a due to some defect or other reason, multiple cracks 14a, 14b, 14c, and 14d are formed. In this embodiment, as a preprocessing step for irradiating the wafer 20 with the laser beam L from the laser irradiation unit 3 to cut the wafer 20 into multiple semiconductor devices, the length of the cracks and the like are inspected and the laser beam irradiation conditions are adjusted according to the inspection results to address the defect or other problem. Specifically, as the preprocessing step, a modified region for inspection is formed on the wafer 20, and the pass / fail of the laser beam irradiation conditions is determined according to the length of the cracks extending from the modified region and the like, and the laser beam irradiation conditions are adjusted as necessary (details will be described later). The preprocessing step may be performed, for example, at the time of shipment or delivery of the laser processing apparatus or during a periodic inspection by the end user.

[0039] 6 , the imaging unit 5 includes 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 back surface 21b side of the semiconductor substrate 21.

[0040] The lens 53 passes the light I2 reflected by the 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 55 is configured, for example, by an InGaAs camera, and detects the light I2 in the near-infrared region.

[0041] Under the control of the control unit 8, the imaging unit 5 irradiates the wafer 20 with light I2 from the back surface 21b side and detects light I2 returning from the front 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 back surface 21b side 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 (e.g., 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.

[0042] [Principle of Imaging Using Inspection Imaging Unit] Using the imaging unit 4 shown in Figure 5, the focal point F (the focal point of the objective lens 43) is moved from the back surface 21b toward the front surface 21a of a semiconductor substrate 21 on which cracks 14 extending across two rows of modified regions 12a and 12b reach the front surface 21a, as shown in Figure 7. In this case, when the focal point F is aligned from the back surface 21b to the tip 14e of the crack 14 extending from the modified region 12b to the back surface 21b, the tip 14e can be confirmed (image on the right in Figure 7). However, when the focal point F is aligned from the back surface 21b to the tip 14e of the crack 14 reaching the front surface 21a, they cannot be confirmed (image on the left in Figure 7). Note that when the focal point F is aligned from the back surface 21b to the front surface 21a of the semiconductor substrate 21, the functional element layer 22 can be confirmed.

[0043] 5, the imaging unit 4 was used to move the focal point F from the back surface 21b toward the front surface 21a of a semiconductor substrate 21 in which a crack 14 spanning two rows of modified regions 12a and 12b had not yet reached the front surface 21a, as shown in FIG. 8. In this case, even if the focal point F was aligned from the back surface 21b to the tip 14e of the crack 14 extending from the modified region 12a toward the front 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 back surface 21b to the region on the opposite side of the front surface 21a from the back surface 21b (i.e., the region on the functional device layer 22 side of the front surface 21a) and positioning a virtual focal point Fv symmetrical to the focal point F with respect to the front surface 21a, 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, which takes into account the refractive index of the semiconductor substrate 21, with respect to the front surface 21a.

[0044] 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 I1. 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). Thus, the width of the crack 14 is approximately 120 nm, which is smaller than the wavelength of the near-infrared light I1 (e.g., 1.1 to 1.2 μm).

[0045] Based on the above, the imaging principle assumed is as follows. As shown in FIG. 11A, when the focal point F is positioned in air, the light I1 does not return, resulting in a dark image (the image on the right in FIG. 11A). As shown in FIG. 11B, when the focal point F is positioned inside the semiconductor substrate 21, the light I1 reflected by the front surface 21a returns, resulting in a whitish image (the image on the right in FIG. 11B). As shown in FIG. 11C, when the focal point F is positioned on the modified region 12 from the rear surface 21b side, the modified region 12 absorbs, scatters, or otherwise causes a portion of the light I1 reflected by the front surface 21a and returns, resulting in an image in which the modified region 12 appears dark against a whitish background (the image on the right in FIG. 11C).

[0046] 12(a) and 12(b), when the focal point F is focused on the tip 14e of the crack 14 from the back surface 21b side, for example, optical peculiarities (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 I1 reflected by the front 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 FIG. 12(a) and 12(b)). As shown in FIG. 12(c), when the focal point F is focused on a portion of the crack 14 other than the vicinity of the tip 14e from the back surface 21b side, at least a portion of the light I1 reflected by the front surface 21a returns, resulting in a whitish image (the image on the right in FIG. 12(c)).

[0047] The following describes the inspection and adjustment process of the laser light irradiation conditions, which is performed as a preprocessing step for forming a modified region for the purpose of, for example, cutting the wafer 20. The control unit 8 is configured to perform the following steps: control the laser irradiation unit 3 so that one or more modified regions 12 for inspection are formed inside the semiconductor substrate 21 by irradiating the wafer 20 with laser light L (forming process); determine whether or not cracks 14 extending from the modified regions 12 have reached the surface 21 a of the semiconductor substrate 21 based on an image acquired by the imaging unit 4 (a signal output from the imaging unit 4) (first determination process); determine whether or not the laser light irradiation conditions are acceptable based on the average crack volume, etc. (second determination process); and adjust the laser light irradiation conditions based on the average crack volume, etc. if the laser light irradiation conditions are unacceptable (adjustment process).

[0048] (Forming Process) As shown in FIG. 13 , in the forming process, the control unit 8 controls the laser irradiation unit 3 to form modified regions 12 along each of a plurality of lines on the wafer 20. FIG. 13 shows a plurality of lines extending in the X direction and adjacent to each other in the Y direction. The control unit 8 controls the laser irradiation unit 3 to irradiate each of the plurality of lines on the wafer 20 with laser light along both the forward and backward paths in the X direction, thereby forming one or more modified regions 12 within the wafer 20. The control unit 8 controls the laser irradiation unit 3 to form modified regions 12 with different formation depths between the plurality of lines. In the example shown in FIG. 13 , the modified region 12 is shallowest along the line marked "Z167," and the modified region 12 gradually becomes deeper as it moves away from the line marked "Z167" in the Y direction, with the modified region being deepest along the line marked "Z178." Such differences in the depth at which the modified regions are formed are caused by differences in the Z-height, which is the processing depth (height) in the laser processing device 1. In order to change the depth at which the modified regions 12 are formed for each line, the set value of the Z-height is changed for each line.

[0049] The modified regions 12 of each line are formed by moving the wafer 20 in the X direction relative to the laser light L output from the laser irradiation unit 3. The movement of the wafer 20 in the X direction includes an outward movement (forward path) and a return movement (return path), and for each line, a modified region 12 is formed on the outward path and a modified region 12 on the return path. In the determination process described below, a determination is made for each outward path and each return path as to whether or not the crack has reached the crack. This is because, for example, the optical axis of the laser light L is not the same on the outward path and the return path, so it is preferable to make a determination for each path. Note that while only one modified region is shown for each modified region 12 in FIG. 13, in reality, two modified regions 12a and 12b may be formed as described above. The number of foci may be a single focus, two foci, or more.

[0050] Fig. 14 is a flowchart showing the processing procedure for the forming process (the processing procedure for the example of the forming process shown in Fig. 13). In the example shown in Fig. 14, first, laser processing is performed on the outgoing path of "Z178" where the processing depth (Z height) is the deepest (step S1). Then, index feed is performed so that the processing position is changed in the Y direction (step S2), and laser processing is performed on the returning path of "Z178" (step S3).

[0051] Next, the Z-height is reset and index feed is performed so that laser processing of the outbound path of "Z177", which is the line adjacent to "Z178", becomes possible (step S4), and laser processing of the outbound path of "Z177" is performed (step S5). Then, index feed is performed so that laser processing of the return path of "Z178" becomes possible (step S6), and laser processing of the return path of "Z177" is performed (step S7). Thereafter, similar resetting of the Z-height and index feed are repeated until laser processing of the return path of "Z167", which has the shallowest processing depth (Z-height), is performed (step S8).

[0052] (First Determination Process) In the first determination process, the control unit 8 determines whether the crack 14 extending from the modified region 12 on each of the multiple lines in the forward and backward paths has reached the surface 21a of the wafer 20 (bottom side half-cut (BHC)) based on the signal output from the imaging unit 4 that detected the light, i.e., the image acquired by the imaging unit 4. The process of determining whether the crack 14 has reached the surface 21a of the wafer 20 may be performed using, for example, the technology disclosed in Japanese Patent Application Laid-Open No. 2021-048235. Note that hereinafter, the state in which the crack 14 has not reached the surface 21a of the wafer 20 may be referred to as ST (Stealth). In the example shown in FIG. 13, as shown in FIG. 15, for the forward path, the lines from "Z178" to "Z174" with the deepest processing depth (Z height) are BHC, and lines with a processing depth (Z height) shallower than "Z173" are ST. Additionally, for the return journey, the lines with the deepest Z-height (Z-height), "Z178" to "Z175," are BHC, while lines with a shallower Z-height than "Z174" are ST. Hereinafter, among the BHC lines, "Z174," with the shallowest Z-height on the outbound journey, may be referred to as the outbound shallowest BHC line, and "Z175," with the shallowest Z-height on the return journey, may be referred to as the return shallowest BHC line.

[0053] (Second Determination Process) In the second determination process, the control unit 8 determines whether the laser beam irradiation conditions are acceptable based on information about the average crack amount of the shallowest BHC line on the outbound path and the shallowest BHC line on the return path, which have the shallowest processing depth (Z-height) of the laser beam used to form the modified region 12 among the outbound paths determined to be BHC, and the difference in the crack amount between the shallowest BHC line on the outbound path and the shallowest BHC line on the return path. The information about the difference in the crack amount between the shallowest BHC line on the outbound path and the shallowest BHC line on the return path specifically includes information indicating the difference in the crack amount between the shallowest BHC line on the outbound path and the shallowest BHC line on the return path, and information indicating the difference in the processing depth of the laser beam between the shallowest BHC line on the outbound path and the shallowest BHC line on the return path.

[0054] The average crack volume of the shallowest BHC line on the outbound path and the shallowest BHC line on the return path is an important indicator of the processing performance of the laser processing for forming a BHC. For example, if the crack volume of the shallowest BHC line on the outbound path is 60 μm and the crack volume of the shallowest BHC line on the return path is 40 μm, the average crack volume of the shallowest BHC line on the outbound path and the shallowest BHC line on the return path will be 50 μm. Hereinafter, the average crack volume of the shallowest BHC line on the outbound path and the shallowest BHC line on the return path may be simply referred to as the "average crack volume on the two-way path."

[0055] Information regarding the difference in crack amount between the shallowest BHC line on the outbound path and the shallowest BHC line on the return path is an important indicator of whether the same laser processing state can be achieved on the outbound path. Information indicating the difference in crack amount between the shallowest BHC line on the outbound path and the shallowest BHC line on the return path is information that evaluates the difference in crack amount between the outbound path and the return path on a real value basis. For example, if the crack amount of the shallowest BHC line on the outbound path is 60 μm and the crack amount of the shallowest BHC line on the return path is 40 μm, the information indicating the difference in crack amount between the shallowest BHC line on the outbound path and the shallowest BHC line on the return path is 20 μm. Hereinafter, information indicating the difference in crack amount between the shallowest BHC line on the outbound path and the shallowest BHC line on the return path may be simply referred to as the "difference in crack amount between the outbound and return paths."

[0056] The information indicating the difference in the laser beam machining depth between the outbound pass shallowest BHC line and the return pass shallowest BHC line is information that evaluates the difference in the amount of cracking between the outbound and return passes based on Z-height information, i.e., dicer input values. By taking into account this information that evaluates the difference in the amount of cracking based on the dicer input values, it is possible to perform the adjustment process described below to avoid a situation in which the machining results differ between the outbound and return passes even when the same value is entered in the dicer input (the same Z-height is set). For example, if the machining depth of the outbound pass shallowest BHC line is "Z174" and the machining depth of the return pass shallowest BHC line is "Z175," the difference in the laser beam machining depth between the outbound pass shallowest BHC line and the return pass shallowest BHC line is "1" (175 - 174 = 1). Hereinafter, the information indicating the difference in the laser beam machining depth between the outbound pass shallowest BHC line and the return pass shallowest BHC line may be simply referred to as the "outbound pass ZH difference."

[0057] The control unit 8 may assign scores to each of the two-way path average crack amount, the two-way path crack amount difference, and the two-way path ZH difference, and may determine whether the laser light irradiation conditions are acceptable or not based on the total score. The control unit 8 may assign scores by comparing the actual values ​​of the two-way path average crack amount, the two-way path crack amount difference, and the two-way path ZH difference with target values ​​predetermined as inspection standards. The control unit 8 may assign scores so that the closer the target values ​​and the actual values ​​are to each other, the higher the score. The target value of the two-way path average crack amount is a predetermined reference value, and the target values ​​of the two-way path crack amount difference and the two-way path ZH difference are, for example, 0.

[0058] The control unit 8 may assign a weight to each of the two-way path average crack amount, the two-way path crack amount difference, and the two-way path ZH difference, and then assign the above scores, and determine whether the laser light irradiation conditions are acceptable or not from the total value. The control unit 8 may assign the above scores by increasing the weight of an index that is considered important in accordance with an evaluation policy.

[0059] The control unit 8 may determine whether the laser light irradiation conditions are acceptable by taking into consideration sub-parameters in addition to the main parameters consisting of the above-mentioned round-trip path average crack amount, round-trip path crack amount difference, and round-trip path ZH difference. The control unit 8 may determine whether the laser light irradiation conditions are acceptable by further taking into consideration, for example, information (an example of a sub-parameter) indicating the coordinates of the aberration correction pattern in the spatial light modulator 32 and the position of the pupil plane in the condenser lens 33. In this case, the control unit 8 may assign a higher score, for example, to a condition where the center of the coordinates of the aberration correction pattern in the spatial light modulator 32 is closer to the center of the pupil plane in the condenser lens 33 (closer to the mechanical center), since this condition is more resistant to changes over time in laser light irradiation.

[0060] The control unit 8 may determine whether the laser light irradiation conditions are acceptable or unacceptable by further considering additional parameters (an example of sub-parameters) used to evaluate the average crack amount. Such additional parameters may be set according to the end user's requests or targets. For example, in the case of laser processing for thin materials, since it is difficult to assemble the conditions if the crack amount is large, information indicating a higher score when the crack amount is small may be used as the additional parameter. For example, in the case of laser processing of an SD engine for memory, since the end user desires a larger crack amount, information indicating a higher score when the crack amount is large may be used as the additional parameter.

[0061] The control unit 8 may determine whether the laser light irradiation conditions are acceptable by further considering information (an example of a subparameter) indicating the cross-sectional state of the processed wafer 20. Figure 16 is a diagram showing the cross-sectional state of the processed wafer 20. The control unit 8 may assign a lower score when there are gouged portions or black streaks, as shown in Figure 16(a), for example. The control unit 8 may assign a higher score when the cross-section is clean, as shown in Figure 16(b), for example.

[0062] (Adjustment Process) When the laser light irradiation conditions fail in the second process, the control unit 8 adjusts the laser light irradiation conditions based on information about the round-trip path average crack amount, the round-trip path crack amount difference, and the round-trip path ZH difference. For example, when the round-trip path average crack amount is smaller than the target value specified in the inspection standard, the control unit 8 adjusts the light concentration correction amount of the spatial light modulator 32 so that the crack amount increases in accordance with the degree of deviation from the target value. For example, when the round-trip path average crack amount is larger than the target value specified in the inspection standard, the control unit 8 adjusts the light concentration correction amount of the spatial light modulator 32 so that the crack amount decreases in accordance with the degree of deviation from the target value.

[0063] For example, when the difference in crack amount during round-trip path or the difference in ZH during round-trip path is larger than a target value defined by the inspection standard, the control unit 8 adjusts the modulation pattern of the spatial light modulator 32 so as to reduce the difference in crack amount during round-trip path or the difference in ZH during round-trip path. The control unit 8 reduces the difference in crack amount during round-trip path or the difference in ZH during round-trip path by offsetting the modulation pattern in the X direction.

[0064] Next, specific examples of the above-mentioned processes will be described with reference to FIGS.

[0065] FIG. 17 is a table showing an example of processing conditions ( FIG. 17( a) ) and inspection specifications ( FIG. 17( b) ). As shown in FIG. 17( a) , the processing conditions include initial conditions for the amount of light focus correction and the offset amount (offset X) in the X direction of the modulation pattern. The initial condition for the amount of light focus correction is set to a reference value (light focus correction level ±0), and the initial condition for the offset X is also set to a reference value (X = ±0). In the adjustment process, the values ​​of the amount of light focus correction and the offset X are adjusted. In the example shown in FIG. 17( b) , the following inspection specifications are preset: target crack length: 50 μm, target crack length (specification): 50 μm ±8 μm, target ZH: Z174, and round-trip ZH difference: within 3.

[0066] FIG. 18 is a diagram illustrating predetermined rules for weighting, score derivation, and adjustment processing. FIG. 18( a) is a table illustrating rules related to the round-trip path average crack amount. In the example shown in FIG. 18( a), when the round-trip path average crack amount is the target value of 50 μm, the weighted score is 10 points, when it is 50±4 μm, the weighted score is 5 points, and when it exceeds 50±4 μm, the weighted score is 0 points. In the adjustment processing, when the round-trip path average crack amount score is 10 points, no adjustment is performed; when it is greater than 50 μm with 5 points, the light concentration correction level is −2; when it is less than 50 μm with 5 points, the light concentration correction level is +2; when it is greater than 50 μm with 0 points, the light concentration correction level is −4; and when it is less than 50 μm with 0 points, the light concentration correction level is +4. Note that "Level +" is an adjustment of the amount of light concentration correction in the direction of increasing the amount of cracking, and "Level -" is an adjustment of the amount of light concentration correction in the direction of decreasing the amount of cracking, and the larger the number after + (or -) the larger the adjustment amount.

[0067] FIG. 18(b) is a table showing rules relating to the difference in crack amount during round trips. In the example shown in FIG. 18(b), when the difference in crack amount during round trips is 0 to 4 μm, the weighted score is 5 points, when it is 5 to 12 μm, the weighted score is 2 points, and when it exceeds 13 μm, the weighted score is 0 points. FIG. 18(c) is a table showing rules relating to the difference in ZH during round trips. In the example shown in FIG. 18(c), when the difference in ZH during round trips is 0 to 1, the weighted score is 5 points, when it is 2 to 3, the weighted score is 2 points, and when it exceeds 4, the weighted score is 0 points. In the adjustment process, if the sum of the score for the difference in crack amount between the outbound and return paths and the score for the difference in ZH between the outbound and return paths is 10 points, no adjustment is made, if the outbound path is large at 7 points then the offset is X+1, if the outbound path is small at 7 points then the offset is X-1, if the outbound path is large at 4 points then the offset is X+2, if the outbound path is small at 4 points then the offset is X-2, if the outbound path is large at 0 points then the offset is X+3, and if the outbound path is small at 0 points then the offset is X-3. Note that "offset X+" is an offset adjustment in the direction in which the amount of cracking on the outbound path becomes smaller and the amount of cracking on the return path becomes larger, and "offset X-" is an offset adjustment in the direction in which the amount of cracking on the outbound path becomes larger and the amount of cracking on the return path becomes smaller, and the larger the number after + (or -) the larger the adjustment amount.

[0068] Under these assumptions, for example, assume that the first (loop 1) formation process is performed with the initial conditions of the light concentration correction level and offset X as shown in Figure 19(a). As a result of internal observation as shown in Figure 19(b), the Z-height of the shallowest BHC line on the outbound path is Z172, the Z-height of the shallowest BHC line on the return path is Z176, and the crack amount on the shallowest BHC line on the outbound path is 60 μm and 40 μm. In this case, as shown in Figure 19(c), it is derived that the average crack amount on the return path is 50 μm, the difference in crack amount on the return path is 20 μm, and the ZH difference on the return path is 4. When compared with the conditions in Figure 18 described above, it is derived that the weighted score for the average crack amount on the return path is 10, the weighted score for the difference in crack amount on the return path is 0, and the ZH difference on the return path is 0. Therefore, the total score is 10, and the result is determined to be unacceptable. Now, the score for the average crack amount during the two-way path is high and no adjustment is required, but the difference in crack amount during the two-way path and the difference in ZH during the two-way path require adjustment, and an adjustment process of offset X+3 is performed.

[0069] Next, loop 2 processing is performed, as shown in Figures 19(d) to 19(f). As shown in Figure 19(d), after the adjustment processing of loop 1, the light collection correction level remains at the initial condition, and the offset X is set to the initial condition +3. In this state, the second (loop 2) formation processing is performed, and as shown in Figure 19(e), the results of internal observation show that the Z-height of the shallowest BHC line on the outbound path is Z174, the Z-height of the shallowest BHC line on the return path is Z174, the crack amount on the shallowest BHC line on the outbound path is 45 μm, and the crack amount on the shallowest BHC line on the return path is 55 μm. In this case, as shown in Figure 19(f), it is derived that the average crack amount on the round trip path is 50 μm, the difference in crack amount on the round trip path is 10 μm, and the ZH difference on the round trip path is 0. 18, the weighted score for the round-trip average crack amount is 10, the weighted score for the round-trip crack amount difference is 2, and the score for the round-trip ZH difference is 5, resulting in a total score of 17 points and a failure judgment. Now, the score for the round-trip average crack amount is high and no adjustment is required, whereas the round-trip crack amount difference and the round-trip ZH difference require adjustment, and an adjustment process for offset X-1 is performed.

[0070] Next, loop 3 processing is performed, as shown in Figures 20(d) to (f). As shown in Figure 20(d), after the adjustment processing of loop 2, the light collection correction level remains at the initial condition, and the offset X is set to the initial condition +2. In this state, the third (loop 3) formation processing is performed, and as shown in Figure 20(e), the internal observation results show that the Z-height of the shallowest BHC line on the outbound path is Z173, the Z-height of the shallowest BHC line on the inbound path is Z174, the crack amount of the shallowest BHC line on the outbound path is 50 μm, and the crack amount of the shallowest BHC line on the inbound path is 50 μm. In this case, as shown in Figure 20(f), it is derived that the average crack amount on the round trip path is 50 μm, the crack amount difference on the round trip path is 0 μm, and the ZH difference on the round trip path is 1. 18, the weighted score for the round-trip average crack amount is 10, the weighted score for the round-trip crack amount difference is 5, and the score for the round-trip ZH difference is 5. The total score is 20 (full score), and the wafer is determined to be pass. In this case, no adjustment process is performed, and the series of inspection processes ends. Note that such a series of inspections may be performed using only one wafer 20.

[0071] The number of loops may be predetermined. The process of adjusting the laser beam irradiation conditions may be terminated when the number of loops is reached. For example, if the maximum number of loops is set to nine, it takes time but allows the laser beam irradiation conditions to be adjusted with high precision. Therefore, the maximum number of loops may be set to nine for important inspections such as basic verification or when deriving optimal processing conditions, such as when deriving basic inspections or new engines upon shipping. Furthermore, if the maximum number of loops is set to two, the takt time is shortened but it becomes difficult to derive optimal processing conditions. Specifically, there is a risk that it may be difficult to determine whether the reason for a failure is a hardware problem with the target object or a problem with the processing conditions. Therefore, the maximum number of loops may be set to two for periodic processing inspections, etc., when processing conditions have already been derived and a pass / fail determination is sufficient. Furthermore, if the maximum number of loops is set to three, it is possible to achieve a good balance between the takt time and the accuracy of the derived results for the processing conditions. The maximum number of loops may be set to three for shipping inspections or start-up inspections.

[0072] FIG. 21 is a flowchart showing the inspection method.

[0073] As shown in FIG. 21 , a reference focus correction level and offset X (initial center of LBA) are set as the initial conditions for the inspection and processing conditions, and an inspection standard (processing inspection standard) is also set (step S101). The inspection standard may include the pass score for each inspection item and the number of loops for the inspection process. The inspection standard may also include the score allocation for each inspection item. In this case, weighting is performed based on the score allocation. Next, the wafer 20 is loaded (step S102), wafer alignment is performed (step S103), and the Z-height is set (step S104). Setting the Z-height (performing height setting) refers to projecting a reticle onto the laser beam irradiation surface of the wafer 20, moving the laser processing head so that the reticle is focused on the image captured by the imaging unit, and aligning the position of the focusing lens in the optical axis direction relative to the laser beam incident surface to a reference position.

[0074] Then, while changing the Z-height, the modified region 12 is formed on the round trip path of each line (step S105). Subsequently, the inside of the processed wafer 20 is observed (step S106), and the average crack amount, the difference in the crack amount, and the ZH difference are derived (step S107).

[0075] Next, a score is assigned based on each piece of derived information (step S108). The score may be weighted or may be assigned taking into account sub-parameters.

[0076] Then, it is determined whether the designated number of loops has been reached (step S109). If the designated number of loops has not been reached, the irradiation conditions of the laser light are adjusted, specifically, the focus correction level and the offset X are changed (step S110), and the processes from step S105 onwards are performed again.

[0077] On the other hand, if the specified number of loops has been reached, the loop with the highest score among the loops is identified, and the score and irradiation conditions for that loop are extracted (step S111).Then, it is determined whether the extracted score meets the processing inspection standard (step S112).

[0078] If the test result is a failure, the failure data is displayed and recorded (step S113), and the process of step S110 is performed again. On the other hand, if the test result is a pass, the pass data is displayed and recorded (step S114), and the process of the inspection method ends.

[0079] Next, the effects of the laser processing device 1 according to this embodiment will be described.

[0080] The laser processing apparatus 1 according to this embodiment includes a stage 2 that supports a wafer 20, a laser irradiation unit 3 that irradiates the wafer 20 with laser light, an imaging unit 4 that outputs light that is transparent to the wafer 20 and detects the light that has propagated through the wafer 20, and a control unit 8. The control unit 8 is configured to control the laser irradiation unit 3 so that one or more modified regions 12 are formed inside the wafer 20 by irradiating each of a plurality of lines on the wafer 20 with laser light along each of an outbound path and a return path in the X direction, determine whether cracks extending from the modified regions 12 on each of the outbound paths of the plurality of lines are BHCs that have reached the surface 21a, based on a signal output from the imaging unit 4 that detected the light, and determine whether the laser light irradiation conditions are acceptable based on information about the average crack volume of the outbound path with the shallowest processing depth of the laser light for forming the modified regions 12, and the difference in the crack volumes of the outbound paths.

[0081] In the laser processing apparatus 1 according to this embodiment, laser light is irradiated along each of the multiple line paths to form the modified regions 12, and it is determined whether cracks extending from the modified regions 12 along each of the multiple line paths have reached the surface 21a (whether the modified regions 12 are BHCs) based on the detection results from the imaging unit 4. The pass / fail of the laser light irradiation conditions is then determined based on information regarding the average crack volume and the difference in the crack volume for the path with the shallowest laser processing depth among the paths determined to be BHCs. The average crack volume for the path with the shallowest BHC processing depth is an important indicator of the laser processing performance required to achieve a BHC. Furthermore, information regarding the difference in the crack volume for the paths is an important indicator of whether the same laser processing state can be achieved for each path. By evaluating these indicators in a comprehensive manner to determine the pass / fail of the laser light irradiation conditions, the accuracy of the pass / fail determination can be improved. This improves the inspection accuracy of the laser light irradiation conditions.

[0082] The information regarding the difference in crack amount between the two passes may include information indicating the difference in crack amount between the two passes and information indicating the difference in processing depth of the laser light between the two passes. The information indicating the difference in crack amount between the two passes is information evaluating the difference in crack amount based on real values. The information indicating the difference in processing depth of the laser light between the two passes is information evaluating the difference in crack amount based on dicer input values. By making a pass / fail judgment taking into account such information evaluating the difference in crack amount based on dicer input values, it is possible to avoid a situation where discrepancies occur in the processing results even when the same numerical values ​​are input in the dicer input. As described above, by including the above two pieces of information as information regarding the difference in crack amount between the two passes, inspection accuracy can be further improved.

[0083] The control unit 8 may assign scores to the average crack volume in the forward and backward passes, the information indicating the difference in the crack volume in the forward and backward passes, and the information indicating the difference in the processing depth of the laser beam in the forward and backward passes, and may determine whether the laser beam irradiation conditions are acceptable or not from the total score. With this configuration, the above three pieces of information can be quantitatively evaluated and the evaluation can be standardized. This can improve the accuracy of the pass / fail determination.

[0084] The control unit 8 may assign weights to each of the average crack amount in the forward and backward passes, the information indicating the difference in the crack amount in the forward and backward passes, and the information indicating the difference in the processing depth of the laser light in the forward and backward passes, and may assign scores to each of the weighted scores, and may determine whether the laser light irradiation conditions are acceptable or not from the total value. With this configuration, optimal evaluation can be performed by weighting in accordance with the evaluation policy.

[0085] The control unit 8 may be further configured to adjust the laser beam irradiation conditions based on information about the average crack amount in the round trip and the difference in the crack amount in the round trip when the laser beam irradiation conditions are unacceptable. With this configuration, the laser beam irradiation conditions can be repeatedly adjusted based on the average crack amount in the round trip until the laser beam irradiation conditions are acceptable, and the laser beam irradiation conditions can be appropriately set.

[0086] The laser processing apparatus 1 may perform a series of inspections using only one wafer 20. By performing a series of inspections using only one wafer 20, it is possible to eliminate evaluation variations due to individual differences between wafers 20 (such as deviations in inspection values ​​due to differences in the thickness of the wafer 20), accurately determine pass / fail, and appropriately adjust the laser light irradiation conditions. Furthermore, with this configuration, processing is performed at the same time, making it less susceptible to the effects of the laser state and changes over time, and improving inspection accuracy.

[0087] The control unit 8 may determine whether the laser light irradiation conditions are acceptable by further considering information indicating the coordinates of the aberration correction pattern in the spatial light modulator 32 and the position of the pupil plane in the condenser lens 33. It is considered that the closer the central coordinates of the aberration correction pattern in the spatial light modulator 32 are to the center of the condenser lens 33, the more resistant it is to changes over time in laser light irradiation. Therefore, by taking such information into consideration, it is possible to further improve the inspection accuracy.

[0088] The control unit 8 may determine whether the laser light irradiation conditions are acceptable or unacceptable, taking into account additional parameters used in the evaluation of the average crack amount. For example, the evaluation of the average crack amount may vary depending on requirements, such as whether a smaller crack amount is preferable for thin materials. In this regard, by taking into account the additional parameters used in the evaluation of the average crack amount, the average crack amount can be appropriately evaluated, thereby further improving inspection accuracy.

[0089] The control unit 8 may determine whether the laser beam irradiation conditions are acceptable or not, further taking into consideration information indicating the cross-sectional state of the processed wafer 20. By taking into consideration the cross-sectional state after actual processing, it is possible to improve the inspection accuracy related to the laser beam irradiation conditions.

[0090] 1...laser processing device, 2...stage, 3...laser irradiation unit (laser irradiation section), 4...imaging unit (imaging section), 8...control section, 12...modified region, 20...wafer, 21...semiconductor substrate, 21a...front surface (first surface), 21b...back surface (second surface), 31...light source, 32...spatial light modulator, 33...condensing lens

Claims

1. A laser irradiation unit that irradiates the wafer with laser light using the second surface as an incident surface, an imaging unit that outputs light that is transparent to the semiconductor substrate and detects the light that has propagated through the semiconductor substrate, and a control unit, wherein the control unit: an inspection device configured to perform the following operations: controlling the laser irradiation unit so that one or more modified regions are formed inside the semiconductor substrate by irradiating the laser light along each of the outbound and inbound paths in the first direction for each of a plurality of lines on the wafer that extend in a first direction and are adjacent to each other in a second direction; determining, based on a signal output from the imaging unit that detects the light, whether or not cracks extending from the modified regions on each of the outbound paths of the plurality of lines are in a crack reach state in which they have reached the first surface side of the semiconductor substrate; and determining whether or not the irradiation conditions of the laser light are acceptable based on information regarding the average crack amount of the outbound path in which the processing depth of the laser light for forming the modified region is shallowest, among the outbound paths determined to be in the crack reach state, and the difference in crack amount between the outbound paths.

2. An inspection device as described in claim 1, wherein the information regarding the difference in the amount of cracks on the return path includes information indicating the difference in the amount of cracks on the return path and information indicating the difference in the processing depth of the laser light on the return path.

3. The inspection device of claim 2, wherein the control unit assigns a score to each of the average crack amount in the round trip path, information indicating the difference in the crack amount in the round trip path, and information indicating the difference in the processing depth of the laser light in the round trip path, and determines whether the laser light irradiation conditions are acceptable or not from the total value.

4. An inspection device as described in claim 2 or 3, wherein the control unit weights and scores the average crack amount for the round trip, the information indicating the difference in the crack amount for the round trip, and the information indicating the difference in the processing depth of the laser light for the round trip, and determines whether the laser light irradiation conditions are acceptable or not from the total value.

5. An inspection device as claimed in any one of claims 1 to 4, wherein the control unit is further configured to adjust the laser light irradiation conditions based on information relating to the average crack amount in the round trip path and the difference in the crack amount in the round trip path when the laser light irradiation conditions are unacceptable.

6. The inspection device according to any one of claims 1 to 5, wherein a series of inspections is performed using only one of the wafers.

7. An inspection device according to any one of claims 1 to 6, wherein the laser irradiation unit comprises a light source that emits laser light, a spatial light modulator that modulates the laser light output from the light source, and a focusing lens that focuses the laser light modulated by the spatial light modulator onto the wafer, and the control unit determines whether the irradiation conditions of the laser light are acceptable, further taking into consideration information indicating the coordinates of an aberration correction pattern in the spatial light modulator and the position of the pupil plane in the focusing lens.

8. An inspection device according to any one of claims 1 to 7, wherein the control unit determines whether the laser light irradiation conditions are acceptable by further taking into consideration additional parameters used in evaluating the average crack volume.

9. An inspection device according to any one of claims 1 to 8, wherein the control unit determines whether the laser light irradiation conditions are acceptable by further taking into consideration information indicating the cross-sectional state of the wafer after processing.

10. An inspection method comprising: a first step of preparing a wafer comprising a semiconductor substrate having a first surface and a second surface, and irradiating a plurality of lines on the wafer that extend in a first direction and are adjacent to each other in a second direction with laser light along both an outward path and a return path in the first direction, thereby forming one or more modified regions inside the semiconductor substrate; a second step of outputting light that is transparent to the semiconductor substrate in which the modified regions have been formed by the first step, and detecting the light that has propagated through the semiconductor substrate; a third step of determining, based on the light detected in the second step, whether a crack extending from the modified region has reached the first surface side of the semiconductor substrate; and a fourth step of determining whether the irradiation conditions of the laser light are acceptable based on information regarding the average crack amount of the round trip path in which the processing depth of the laser light for forming the modified region is shallowest, and the difference in crack amount between the round trip paths, among the round trip paths determined to be in the crack reach state.

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