Inspection device and inspection method

Abstract

To improve inspection accuracy.SOLUTION: A control part 8 of a laser processing device 1 executes steps of: control of a laser irradiation unit 3 to form one or more modified regions 12 inside a wafer 20 by irradiating a laser beam along respective forward and backward paths in an X direction about each of a plurality of lines of the wafer 20; determining whether a crack extending from the modified regions 12 related to respective forward and backward paths of the plurality of lines is a BHC reaching a surface 21a side on the basis of a signal outputted from an imaging unit 4 that detects the beam; and determining the passing or failing of an irradiation condition of the laser beam on the basis of an average crack amount of forward and backward paths in which processing depth of the laser beam related to formation of the modified regions 12 is the shallowest, and information on difference of crack amounts of the forward and backward paths within the forward and backward paths determined to be the BHC.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] 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-121338 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[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 for irradiating the wafer with laser light using the second surface as an incident surface; an imaging unit for outputting light that is transparent to the semiconductor substrate and detecting 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 cracks extending from the modified regions on each of the outbound paths of the plurality of lines have 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 of 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 processing performance of the laser processing for achieving 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 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.

[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 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 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 from 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 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 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 on the average crack amount in the round trip and the difference between the crack amounts 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 considering 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 consideration, 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 described in any one of (1) to (8) above, 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 embodiment of the present invention includes a first step of preparing a wafer having a semiconductor substrate with 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 or not a crack extending from the modified region has reached the first surface side of the semiconductor substrate; and a fourth step of determining whether or not 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 the crack amount between the round trip paths, among the round trip paths determined to be in the crack reaching state. [Effects of the Invention]

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

[0018] [Figure 1] 1 is a configuration diagram of a laser processing apparatus equipped with an inspection 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 a modified region and cracks formed inside a semiconductor substrate. [Figure 10] 1 is an SEM image of a modified region 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 schematic diagram showing an image of forming a modified region for inspection. [Figure 14] 10 is a flowchart showing a processing procedure. [Figure 15] FIG. 10 is a diagram showing an example of a processing result. [Figure 16] FIG. 10 is a diagram showing a cross-sectional state of a wafer after processing. [Figure 17] 1 is a table showing an example of processing conditions and inspection standards. [Figure 18] FIG. 10 is a diagram illustrating rules for weighting, score derivation, and adjustment processing. [Figure 19] FIG. 10 is a diagram illustrating a processing and derivation loop. [Figure 20] FIG. 10 is a diagram illustrating a processing and derivation loop. [Figure 21] 1 is a flowchart showing an inspection method. DETAILED DESCRIPTION OF THE INVENTION

[0019] 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 duplicated explanations will be omitted. [Laser processing equipment configuration]

[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 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.

[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 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 propagate 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 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 an image 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 obtained 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 the reading and writing of data from and to the memory and storage, as well as communication via the communication device.

[0029] [Object Configuration] The object 11 of this embodiment 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 21a (first surface) and a back surface 21b (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 21a of the semiconductor substrate 21. The functional device layer 22 includes a plurality of functional devices 22a arranged two-dimensionally along the front surface 21a. The functional devices 22a are, for example, light-receiving devices such as photodiodes, light-emitting devices such as laser diodes, circuit devices such as memories, etc. The functional devices 22a 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 virtual lines, but may also be actually drawn lines.

[0031] [Laser irradiation unit configuration] 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.

[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 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 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 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] [Configuration of the inspection imaging unit] 5, the imaging unit 4 includes a light source 41, a mirror 42, an objective lens 43, and a photodetector 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 light I1 reflected by the surface 21a of the semiconductor substrate 21. In other words, the objective lens 43 passes 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 light I1 that has passed through the objective lens 43 and the mirror 42. The light detection unit 44 is formed, for example, by an InGaAs camera, and detects 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 that extends from the modified region 12a toward the front surface 21a. The crack 14b is a crack that extends from the modified region 12a toward the back surface 21b. The crack 14c is a crack that extends from the modified region 12b toward the front surface 21a. The crack 14d is a crack that extends 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 that allow the cracks 14 spanning the two rows of modified regions 12a and 12b to 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 kind of defect or the like, multiple cracks 14a, 14b, 14c, and 14d are formed. In this embodiment, as a pre-processing 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 aforementioned defect or the like. Specifically, as the pre-processing 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). Note that the pre-processing 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] [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 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 (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.

[0042] [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 back surface 21b toward the front surface 21a of a semiconductor substrate 21 in which cracks 14 extending across two rows of modified regions 12a and 12b reach the front surface 21a, as shown in FIG. 7. In this case, when the focal point F is aligned from the back surface 21b on the tip 14e of the crack 14 extending from the modified region 12b to the back 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 back surface 21b on the crack 14 itself or the tip 14e of the crack 14 reaching the front surface 21a, they cannot be seen (the image on the left in FIG. 7). Note that when the focal point F is aligned from the back surface 21b on the front surface 21a of the semiconductor substrate 21, the functional element layer 22 can be seen.

[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 to 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 focus Fv symmetrical to the focus F with respect to the front surface 21a at the tip 14e, the tip 14e could be seen (the image on the right side of FIG. 8). The virtual focus Fv is a point symmetrical with the focus F with respect to the front surface 21a, taking into account the refractive index of the semiconductor substrate 21.

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

[0045] 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 I1 does not return, resulting in a dark image (the image on the right in FIG. 11(a)). As shown in FIG. 11(b), 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. 11(b)). As shown in FIG. 11(c), when the focal point F is aligned with 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 returned, resulting in an image in which the modified region 12 appears dark against a whitish background (the image on the right in FIG. 11(c)).

[0046] 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 back 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 I1 reflected from 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 (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 back surface 21b side, at least a portion of the light I1 reflected from the front surface 21a returns, resulting in a whitish image (the image on the right in (c) of Figure 12).

[0047] The following describes the inspection and adjustment process of the laser light irradiation conditions, which is performed as a preprocessing for the process of forming a modified region for the purpose of cutting the wafer 20. The control unit 8 is configured to perform the following operations: 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 21a 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 amount, etc. (second determination process); and adjust the laser light irradiation conditions based on the average crack amount, etc. if the laser light irradiation conditions are unacceptable (adjustment process).

[0048] (Formation 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, 12b may be formed as described above. The number of focal points may be a single focal point, two focal points, 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 along the outward and return 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, on the outward path, the lines from "Z178" to "Z174," which have the deepest processing depth (Z height), are BHC, and the lines with a processing depth (Z height) shallower than "Z173" are ST. Additionally, for the return journey, the deepest Z-height lines, "Z178" to "Z175," are BHC, while lines shallower than "Z174" are ST. Below, among the BHC lines, "Z174," which has the shallowest Z-height on the outbound journey, may be referred to as the shallowest BHC line for the outbound journey, and "Z175," which has the shallowest Z-height on the return journey, may be referred to as the shallowest BHC line for the return journey.

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

[0055] Information regarding the difference in crack volume between the shallowest BHC line on the outbound pass and the shallowest BHC line on the return pass is an important indicator of whether the same laser processing state can be achieved on both passes. Information indicating the difference in crack volume between the shallowest BHC line on the outbound pass and the shallowest BHC line on the return pass is information that evaluates the difference in crack volume between the outbound and return passes based on actual values. For example, if the crack volume of the shallowest BHC line on the outbound pass is 60 μm and the crack volume of the shallowest BHC line on the return pass is 40 μm, the information indicating the difference in crack volume between the shallowest BHC line on the outbound pass and the shallowest BHC line on the return pass is 20 μm. Hereinafter, information indicating the difference in crack volume between the shallowest BHC line on the outbound pass and the shallowest BHC line on the return pass may be simply referred to as the "difference in crack volume between the outbound and return passes."

[0056] The information indicating the difference in laser beam machining depth between the outbound and return passes is information that evaluates the difference in crack volume between the two passes based on Z-height information, i.e., the dicer input value. By taking into account this information evaluating the difference in crack volume based on the dicer input value, it is possible to perform the adjustment process described below to avoid a situation where the machining results differ between the two 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 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 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 actual values ​​are to the target values, 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 beam irradiation conditions are acceptable by taking into consideration sub-parameters in addition to the main parameters consisting of the aforementioned 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 beam 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, as the closer the center of the coordinates of the aberration correction pattern in the spatial light modulator 32 is to the center of the pupil plane in the condenser lens 33 (closer to the mechanical center), the more resistant it is to changes over time in laser beam 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 subparameters) used in evaluating 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 becomes 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 requests 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 wafer 20 after processing. FIG. 16 is a diagram showing the cross-sectional state of the wafer 20 after processing. The control unit 8 may assign a lower score when there are gouged portions or black streaks, for example, as shown in FIG. 16(a). The control unit 8 may assign a higher score when the cross-section is clean, for example, as shown in FIG. 16(b).

[0062] (Adjustment processing) If the laser light irradiation conditions are unacceptable 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, if 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, if 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 between two paths or the difference in ZH between two paths is larger than the target value specified 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 between two paths or the difference in ZH between two paths. The control unit 8 reduces the difference in crack amount between two paths or the difference in ZH between two paths 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 initial conditions of the light focus correction amount and the offset amount (offset X) in the X direction of the modulation pattern are shown as processing conditions. The initial condition of the light focus correction amount is set to a reference value (light focus correction level ±0), and the initial condition of the offset X is also set to a reference value (X = ±0). In the adjustment process, the values ​​of the light focus correction amount 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 made; when it is greater than 50 μm at 5 points, the light concentration correction level is −2; when it is less than 50 μm at 5 points, the light concentration correction level is +2; when it is greater than 50 μm at 0 points, the light concentration correction level is −4; and when it is less than 50 μm at 0 points, the light concentration correction level is +4. Note that "Level +" indicates an adjustment of the amount of light concentration correction in the direction of increasing the amount of cracking, and "Level -" indicates an adjustment of the amount of light concentration correction in the direction of decreasing the amount of cracking, with 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 volume during round trips. In the example shown in Fig. 18(b), when the difference in crack volume 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 total score of the difference in crack amount between the outbound and return paths and the difference in ZH between the outbound and return paths is 10, no adjustment is made, if the outbound path is larger at 7 points then the offset is X+1, if the outbound path is smaller at 7 points then the offset is X-1, if the outbound path is larger at 4 points then the offset is X+2, if the outbound path is smaller at 4 points then the offset is X-2, if the outbound path is larger at 0 points then the offset is X+3, and if the outbound path is smaller at 0 points then the offset is X-3. Note that "offset X+" is an offset adjustment in the direction in which the crack amount on the outbound path becomes smaller and the crack amount on the return path becomes larger, and "offset X-" is an offset adjustment in the direction in which the crack amount on the outbound path becomes larger and the crack amount 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 volume of 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 volume on the two-way path is 50 μm, the difference in crack volume on the two-way path is 20 μm, and the ZH difference on the two-way path is 4. When compared with the conditions in Figure 18 described above, the weighted score for the average crack volume on the two-way path is 10, the weighted score for the difference in crack volume on the two-way path is 0, and the ZH difference is 0. Therefore, the total score is 10, and the result is determined to be unacceptable. Now, the score for the average crack amount in the two-way path is high and no adjustment is required, but the difference in the crack amount in the two-way path and the difference in ZH in the two-way path require adjustment, and an adjustment process of offset X+3 is performed.

[0069] Next, the processing of loop 2 shown in Figures 19(d) to (f) is performed. 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 formation processing is performed for the second time (loop 2), 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 of the shallowest BHC line on the outbound path is 45 μm, and the crack amount of 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 average crack amount during the round trip is 10, the weighted score for the difference in crack amount during the round trip is 2, and the score for the ZH difference during the round trip is 5, resulting in a total score of 17 points and a failure judgment. Now, the score for the average crack amount during the round trip is high and no adjustment is required, but the difference in crack amount during the round trip and the ZH difference during the round trip do require adjustment, so adjustment processing for offset X-1 is performed.

[0070] Next, the processing of loop 3 shown in Figures 20(d) to (f) is performed. 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 formation processing is performed for the third time (loop 3), and as shown in Figure 20(e), the results of internal observation 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 return path is Z174, and 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 return 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, and the total score is 20 (full score), so it 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 for highly accurate adjustment of the laser beam irradiation conditions. Therefore, the maximum number of loops may be set to nine for important inspections such as basic verification and the shipment of a new engine, or when deriving optimal processing conditions. On the other hand, if the maximum number of loops is set to two, the takt time is shortened but it becomes difficult to derive optimal irradiation conditions. Specifically, it may be difficult to distinguish whether the reason for failure is a problem with the target object's hardware or the irradiation 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. On the other hand, 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 irradiation 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 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 light 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 with respect to the laser light 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 in the round trip path, the difference in the crack amount in the round trip path, and the ZH difference in the round trip path are derived (step S107).

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

[0076] Then, it is determined whether the designated number of loops has been reached (step S109), and if not, the adjustment process of the irradiation conditions of the laser light, specifically, the change of the focusing correction level and the change of the offset X, is performed (step S110), and the process from step S105 onwards is 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 or not cracks extending from the modified regions 12 on each of the return paths of the plurality of lines reach the front surface 21a, based on a signal output from the imaging unit 4 that detects the light; and determine whether or not the laser light irradiation conditions are acceptable based on information about the average crack volume of the return path with the shallowest processing depth of the laser light for forming the modified regions 12, among the return paths determined to be BHC, and the difference in the crack volumes of the return paths.

[0081] In the laser processing apparatus 1 according to this embodiment, laser light is irradiated along each of the multiple linear paths to form the modified regions 12, and it is determined whether cracks extending from the modified regions 12 along each of the multiple linear paths have reached the surface 21a (whether the path is a BHC) 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 a BHC. The average crack volume for the path with the shallowest laser processing depth that results in a BHC 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 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.

[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 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 them, 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 on 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 by further considering additional parameters used in the evaluation of 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 better for thin materials. In this regard, by considering the additional parameters used in the evaluation of the average crack amount, the average crack amount can be appropriately evaluated, and the inspection accuracy can be further improved.

[0089] The control unit 8 may determine whether the laser beam irradiation conditions are acceptable by further considering information indicating the cross-sectional state of the processed wafer 20. By considering the cross-sectional state after the actual processing, it is possible to improve the inspection accuracy related to the laser beam irradiation conditions. [Explanation of symbols]

[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 stage 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; a control unit, 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. The inspection device according to claim 1 , wherein the information regarding the difference in the amount of cracks in the forward and backward paths includes information indicating the difference in the amount of cracks in the forward and backward paths and information indicating the difference in the processing depth of the laser light in the forward and backward paths.

3. 3. The inspection device according to 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. 4. The inspection device according to claim 3, wherein the control unit weights and scores 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.

5. 2. The inspection device of claim 1, wherein the control unit is further configured to adjust the laser light irradiation conditions based on information about 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. 6. The inspection apparatus according to claim 5, wherein a series of inspections are performed using only one of said wafers.

7. the laser irradiation unit includes 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; The inspection device according to any one of claims 1 to 6, wherein the control unit further takes into consideration information indicating the coordinates of the aberration correction pattern in the spatial light modulator and the position of the pupil plane in the focusing lens, and determines whether the irradiation conditions of the laser light are acceptable.

8. 7. The inspection device according to claim 1, wherein the control unit determines whether the laser light irradiation conditions are acceptable or not, further taking into consideration additional parameters used in the evaluation of the average crack volume.

9. 7. The inspection device according to claim 1, wherein the control unit determines whether the laser light irradiation conditions are acceptable by further taking into consideration information indicating a cross-sectional state of the wafer after processing.

10. a first step of preparing a wafer including a semiconductor substrate having a first surface and a second surface, and irradiating a laser beam along a forward path and a backward 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, thereby forming one or a plurality of modified regions inside the semiconductor substrate; a second step of outputting light that is transparent to the semiconductor substrate on which the modified region has been formed by the first step and detecting the light that has propagated through the semiconductor substrate; a third step of determining whether or not a crack extending from the modified region has reached a first surface side of the semiconductor substrate based on the light detected in the second step; 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, among the round trip paths determined to be in the crack reaching state, and the difference in the crack amount of the round trip paths.

Images