Laser processing device and laser processing method

Abstract

To ensure the quality of a wafer when an outer modified region and an inner modified region are formed in the thickness direction of a wafer.SOLUTION: A laser processing device 1 includes a control unit 8. The control unit 8 executes: first processing of controlling a laser irradiation unit 3 under a first processing condition set such that a modified region 121 and a modified region 122 are formed inside a wafer 20; second processing of identifying a state related to the modified regions 121 and 122 and determining whether the first processing condition is appropriate, third processing of controlling the laser irradiation unit 3 under a second processing condition set such that the modified regions 121 and 122 are formed inside the wafer 20 and modified regions 123a and 123b are formed between the modified regions 121 and 122 in a thickness direction of the wafer 20, and fourth processing of identifying a state related to the modified regions 121, 122, 123a, 123b and determining whether the second processing condition is appropriate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laser processing apparatus and a laser processing method. [Background technology]

[0002] A laser processing device is known that cuts a wafer, which includes a semiconductor substrate and a functional element layer formed on one surface of the semiconductor substrate, along each of a plurality of lines by irradiating the wafer with laser light from the other surface of the semiconductor substrate, thereby forming a plurality of rows of modified regions within the semiconductor substrate along each of the plurality of lines. The laser processing device described in Patent Document 1 is equipped with an infrared camera, which makes it possible to observe the modified regions formed within the semiconductor substrate and processing damage formed in the functional element layer from the back surface of the semiconductor substrate. [Prior art documents] [Patent documents]

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

[0004] In the laser processing apparatus described above, the processing layer may be formed at multiple focal points while forming a processed layer, thereby improving the processing layer formation rate. However, according to the inventors' findings, when multiple focal points are simultaneously formed in the thickness direction of an object and laser light is irradiated, a crack extending from a modified region formed at one focal point may affect the formation of a modified region at another focal point and the propagation of the crack, resulting in unstable crack volume (crack length). This problem can also occur when multiple focal points are not simultaneously formed (single focal point). For example, when a modified region farther from the incident surface is formed first with a single focal point, followed by a modified region closer to the incident surface, the total crack volume may become unstable because the modified region closer to the incident surface is processed before the crack farther from the incident surface has fully extended. When the crack volume becomes unstable, the quality of the cut surface (i.e., processing quality) decreases when the object is cut along the crack.

[0005] To prevent the amount of cracks from becoming unstable, it is possible to first form multiple modified regions that are far enough apart so that the cracks do not connect to each other, so that the cracks extending from simultaneously formed modified regions (or multiple modified regions formed continuously at one focus) do not connect to each other, and then form modified regions between the multiple modified regions (between them in the thickness direction of the wafer), ultimately forming cracks that span all of the modified regions. In this way, the processing method of forming an inner modified region after forming an outer modified region is complex, and it is difficult to set appropriate processing conditions. If the processing conditions are not set appropriately, there is a risk that the quality of the processed wafer cannot be fully guaranteed.

[0006] The present invention has been made in consideration of the above-mentioned situation, and aims to provide a laser processing apparatus and a laser processing method that can ensure the quality of a wafer when forming an outer modified area and an inner modified area in the thickness direction of the wafer. [Means for solving the problem]

[0007] A laser processing apparatus according to one aspect of the present invention includes an irradiation unit that irradiates a wafer having a first surface and a second surface with laser light from the first surface side of the wafer, an imaging unit that outputs light that is transparent to the wafer and detects the light that has propagated through the wafer, and a control unit, wherein the control unit performs a first process of controlling the irradiation unit under first processing conditions that are set so that a first modified region and a second modified region that is located closer to the laser light incident surface side than the first modified region are formed inside the wafer by irradiating the wafer with the laser light, and after the first process, identifies states related to the first modified region and the second modified region based on a signal output from the imaging unit that detects the light, and determines the specific a second process for determining whether the first processing conditions are appropriate based on the information set therein; a third process for controlling the irradiation unit under the second processing conditions set so that a first modified region and a second modified region are formed inside the wafer by irradiating the wafer with laser light and a third modified region is formed between the first modified region and the second modified region in the thickness direction of the wafer; and a fourth process for identifying, after the third process, the states of the first modified region, the second modified region, and the third modified region based on a signal output from an imaging unit that detects the light, and determining whether the second processing conditions are appropriate based on the identified information.

[0008] In a laser processing apparatus according to one embodiment of the present invention, in a third process, outer modified regions (first modified region and second modified region) and an inner modified region (third modified region) between them in the thickness direction of the wafer are formed based on the second processing conditions. In a fourth process, the state of each modified region is identified based on the signal output from the imaging unit, and the appropriateness of the second processing conditions is determined based on the identification results. In this way, processing is performed so that the outer modified region and the inner modified region are actually formed, and the appropriateness of the processing conditions is determined based on the state of each modified region after processing, thereby determining the appropriateness of the processing conditions based on the final processed state of the wafer. This allows the appropriateness of the processing conditions to be determined with high accuracy, ensuring the quality of the processed wafer. Furthermore, in a laser processing apparatus according to one embodiment of the present invention, in the first process, only the outer modified regions (first and second modified regions) in the thickness direction of the wafer are formed based on the first processing conditions. In the second process, the state of the outer modified regions is identified based on the signal output from the imaging unit, and the appropriateness of the first processing conditions is determined based on the identification results. For example, in a case where the final processed state of the wafer is processed to a full cut state (a state in which cracks extending from the modified regions extend to both end surfaces of the wafer), there is little information regarding the modified regions obtained from the final processed state of the wafer, and the appropriateness of the processing conditions may not be determined with high accuracy. In this regard, when only a portion of the modified region (the outer modified region) is formed, the appropriateness of the processing conditions (first processing conditions) for forming the portion of the modified region is determined based on information regarding the portion of the modified region. This makes it possible to more accurately determine the appropriateness of the processing conditions based on the processed state of the wafer, which provides more information (information regarding the modified regions) than the final processed state of the wafer. According to the findings of the inventors, when an outer modified region and an inner modified region are formed in the thickness direction of the wafer, the state of the outer modified region is thought to have a greater impact on the quality and divisibility of the processed wafer. In this regard, by determining the suitability of the processing conditions (first processing conditions) for forming the outer modified region in the second process, the quality of the processed wafer can be more appropriately guaranteed.

[0009] The control unit may identify at least one of the state of the modified region and the state of a crack extending from the modified region as the state related to the modified region. This allows the state of the wafer after processing to be appropriately identified, and the appropriateness of the processing conditions to be determined with higher accuracy. This makes it possible to more appropriately ensure the quality of the wafer.

[0010] The control unit may identify the position of the modified region and determine whether the processing conditions are appropriate based on the position. If the processing conditions are inappropriate, the modified region may not be positioned at the desired location. By determining whether the processing conditions are appropriate depending on whether the modified region is positioned at the desired location, the processing conditions can be determined appropriately. This makes it possible to more appropriately ensure the quality of the processed wafer.

[0011] The control unit may determine whether a crack has propagated to at least one of the first surface and the second surface, and determine whether the processing conditions are appropriate based on whether the crack has propagated. This allows the processing conditions to be appropriately determined, for example, when processing a wafer to a full-cut state in the final processing state, by determining that the crack has not propagated to the first surface and the second surface in the second processing stage and that the crack has propagated to the first surface and the second surface in the fourth processing stage. This allows the quality of the processed wafer to be more appropriately guaranteed.

[0012] The control unit may determine that the first processing conditions are inappropriate if a crack propagates to at least one of the first surface and the second surface during the second process. This ensures that the processing state prior to the final processing state is in an ST state (a state where the crack has not reached the front and back surfaces) (a state where the internal observation is easy). This allows appropriate and abundant information regarding the processing state to be obtained. Even if the final processing state is a full-cut state, if a crack has reached the front and back surfaces in an earlier state (a state where processing is still to be performed after that), it is believed that chip quality and divisibility will deteriorate in the final processing state. Therefore, by determining that the ST state in a processing state prior to the final processing state is a condition where the processing conditions are appropriate, chip quality and divisibility can be ensured.

[0013] The control unit may identify the amount of crack extension and determine whether the processing conditions are appropriate based on the amount of extension. If the processing conditions are inappropriate, the crack may not extend to the desired length. By determining whether the processing conditions are appropriate from the amount of crack extension, the processing conditions can be determined appropriately. This makes it possible to more appropriately ensure the quality of the processed wafer.

[0014] The control unit may identify the width of the meandering crack in a direction intersecting the thickness direction of the wafer and determine whether the processing conditions are appropriate based on the width of the meandering. If the processing conditions are inappropriate, the width of the meandering crack may be large. By determining whether the processing conditions are appropriate from the width of the meandering crack, the processing conditions can be determined appropriately. This makes it possible to more appropriately ensure the quality of the processed wafer.

[0015] The control unit may identify whether cracks extending from different modified regions are connected to each other, and determine whether the processing conditions are appropriate based on whether they are connected. If the processing conditions are inappropriate, cracks may connect to each other when it is not desired that they be connected, or may not connect to each other when it is desired that they be connected. By determining whether the processing conditions are appropriate based on whether the cracks are connected to each other, the processing conditions can be determined appropriately. This makes it possible to more appropriately ensure the quality of the processed wafer.

[0016] The control unit may be further configured to perform a fifth process of controlling the irradiation unit under third processing conditions set so that a third modified region is formed inside the wafer by irradiating the wafer with laser light, and a sixth process of, after the fifth process, identifying a state of the third modified region based on a signal output from the imaging unit that detected the light and determining whether the third processing conditions are appropriate based on the identified information. With this configuration, when only an inner modified region is formed, the appropriateness of the processing conditions (third processing conditions) for forming the inner modified region is determined based on the information related to the inner modified region. When outer and inner modified regions are formed, the appropriateness of the processing conditions can be determined from the information related to the modified region not only when only an outer modified region is formed, but also when only an inner modified region is formed, thereby enabling the appropriateness of the processing conditions to be determined with higher accuracy.

[0017] The control unit may determine that the third processing conditions are inappropriate if, in the sixth process, a crack propagates to at least one of the first surface and the second surface. This ensures that the processing state prior to the final processing state is in the ST state (a state where the crack has not reached the front and back surfaces) (a state where the internal observation is easy). This allows appropriate and abundant information regarding the processing state to be obtained. Even if the final processing state is a full-cut state, if a crack has reached the front and back surfaces in an earlier state (a state where processing is still to be performed after that), it is believed that chip quality and divisibility will deteriorate in the final processing state. Therefore, by determining that the processing conditions are appropriate when the ST state is reached in a processing state prior to the final processing state, chip quality and divisibility can be ensured.

[0018] The control unit may determine that the first processing conditions are inappropriate if a crack propagates to at least one of the first surface and the second surface in the second process, and may determine that the third processing conditions are inappropriate if a crack propagates to at least one of the first surface and the second surface in the sixth process. This ensures that a processing state prior to the final processing state is in an ST state (a state in which the internal observation is easy) in which the crack has not reached the front and back surfaces. This allows for appropriate and abundant information regarding the processing state to be obtained. Even if the final processing state is a full-cut state, if a crack has reached the front and back surfaces in an earlier state (a state in which processing is still to be performed after that), it is believed that chip quality and divisibility will deteriorate in the final processing state. Therefore, by determining that the ST state in a processing state prior to the final processing state is a condition in which processing conditions are appropriate, chip quality and divisibility can be ensured.

[0019] The control unit may be configured to further execute a seventh process of correcting the processing conditions in accordance with the results of the determination of the processing conditions when the processing conditions are determined to be inappropriate. With this configuration, the processing conditions are corrected based on the results of the determination, thereby more appropriately ensuring the quality of the processed wafer.

[0020] The control unit may further be configured to perform a brightness calibration process to control the imaging unit so that the imaging unit outputs light at an amount corresponding to the position of each region in the wafer thickness direction, so that each region in the wafer thickness direction is imaged by the imaging unit at a predetermined brightness. This configuration allows the light amount of the imaging unit to be determined so that each imaging region in the wafer thickness direction (depth direction) has a constant or optimal brightness. This allows the state of each modified region to be appropriately identified.

[0021] The control unit is configured to control the imaging unit to capture shading images for each region in the wafer thickness direction imaged by the imaging unit before processing the modified region, and to further perform a shading correction process after processing the modified region to identify difference data between the image of each region imaged by the imaging unit and the shading image of the corresponding region. In the second and fourth processes, the state of the modified region may be identified based on the difference data. The difference data acquired by the shading correction process is image data from which noise such as device patterns, point defects, and uneven screen brightness has been removed, and is image data containing only the modified region and crack state to be observed. By identifying the state of the modified region based on such difference data, the state of the processed wafer can be appropriately identified. This makes it possible to more appropriately ensure the quality of the processed wafer.

[0022] The control unit may be further configured to perform an aberration correction process that controls at least one of the irradiation unit and the imaging unit so that aberration correction is performed according to the position in the wafer thickness direction for each region in the wafer thickness direction imaged by the imaging unit. For example, when full-cut processing is performed, the intervals between each modified region are narrow and the amount of crack extension is also small, so clear observation is not possible unless aberration correction is performed for each position in the wafer thickness direction. In this regard, as described above, performing aberration correction according to the wafer thickness for each region in the wafer thickness direction enables clear observation and more appropriately identifies the state of the modified region.

[0023] A laser processing method according to one embodiment of the present invention includes: processing a wafer based on first processing conditions that are set so that a first modified region and a second modified region located on the laser light incident side of the first modified region are formed inside the wafer by irradiating the wafer with laser light; identifying states related to the first modified region and the second modified region based on imaging results of the wafer processed based on the first processing conditions, and determining whether the first processing conditions are appropriate based on the identified information; processing the wafer based on second processing conditions that are set so that a first modified region and a second modified region are formed inside the wafer by irradiating the wafer with laser light, and a third modified region is formed between the first modified region and the second modified region in the thickness direction of the wafer; and identifying states related to the first modified region, the second modified region, and the third modified region based on imaging results of the wafer processed based on the second processing conditions, and determining whether the second processing conditions are appropriate based on the identified information. [Effects of the Invention]

[0024] According to the present invention, a laser processing apparatus and a laser processing method can be provided that can ensure the quality of a wafer when forming an outer modified region and an inner modified region in the thickness direction of the wafer. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a configuration diagram of a laser processing apparatus according to one embodiment; [Figure 2] FIG. 1 is a plan view of a wafer of one embodiment. [Figure 3] FIG. 3 is a cross-sectional view of a portion of the wafer shown in FIG. 2. [Figure 4] FIG. 2 is a configuration diagram of a laser irradiation unit shown in FIG. [Figure 5] FIG. 2 is a configuration diagram of an inspection imaging unit shown in FIG. [Figure 6] FIG. 2 is a configuration diagram of an imaging unit for alignment correction shown in FIG. [Figure 7] 6A and 6B are cross-sectional views of a wafer for explaining the imaging principle of the inspection imaging unit shown in FIG. 5, and images at various locations taken by the inspection imaging unit. [Figure 8] 6A and 6B are cross-sectional views of a wafer for explaining the imaging principle of the inspection imaging unit shown in FIG. 5, and images at various locations taken by the inspection imaging unit. [Figure 9] 1 is an SEM image of modified regions and cracks formed inside a semiconductor substrate. [Figure 10] 1 is an SEM image of modified regions and cracks formed inside a semiconductor substrate. [Figure 11] 6 is a light path diagram for explaining the imaging principle of the inspection imaging unit shown in FIG. 5, and a schematic diagram showing an image at a focal point of the inspection imaging unit. FIG. [Figure 12] 6 is a light path diagram for explaining the imaging principle of the inspection imaging unit shown in FIG. 5, and a schematic diagram showing an image at a focal point of the inspection imaging unit. FIG. [Figure 13] 10A and 10B are diagrams illustrating an example of processing using a laser irradiation unit. [Figure 14] 10A and 10B are diagrams illustrating an example of processing using a laser irradiation unit. [Figure 15] FIG. 10 is a diagram illustrating a processing condition derivation process. [Figure 16] 10A to 10C are diagrams illustrating the state of a wafer depending on the processing state of the outer SD layer. [Figure 17] 10A to 10C are diagrams illustrating the state of a wafer depending on the processing state of the inner SD layer. [Figure 18] FIG. 10 is a diagram illustrating a determination process. [Figure 19] FIG. 10 is a diagram illustrating a determination process. [Figure 20] FIG. 10 is a diagram illustrating crack detection. [Figure 21] FIG. 10 is a diagram illustrating crack detection. [Figure 22] FIG. 10 is a diagram illustrating the detection of a scratch. [Figure 23] FIG. 10 is a diagram illustrating the detection of a scratch. [Figure 24] FIG. 10 is a diagram illustrating the detection of a scratch. [Figure 25] 10 is a screen image relating to a processing condition derivation process. [Figure 26] 10 is a screen image relating to a processing condition derivation process. [Figure 27] 10 is a screen image relating to a processing condition derivation process. [Figure 28] 10 is a flowchart showing an example of a laser processing method (processing condition derivation process). [Figure 29] 10 is a flowchart according to another example of the laser processing method (processing condition derivation process). [Figure 30] 10A and 10B are diagrams illustrating differences in imaging sections depending on the processing method. [Figure 31] 10 is a flowchart of a luminance calibration process. [Figure 32] 10 is a flowchart of a shading correction process. [Figure 33] 10 is a flowchart of a laser processing method (processing condition derivation process) when various correction processes are performed. [Figure 34] This is an image that has undergone various correction processes. DETAILED DESCRIPTION OF THE INVENTION

[0026] 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]

[0027] 1, the laser processing apparatus 1 includes a stage 2, a laser irradiation unit 3 (irradiation section), multiple imaging units 4, 5, and 6, a drive unit 7, a control section 8, and a display 150 (input section, display section). 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.

[0028] 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 and Y directions, and is rotatable about an axis parallel to the Z direction. The X and Y directions are first and second horizontal directions that are perpendicular to each other, and the Z direction is the vertical direction.

[0029] 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.

[0030] The modified region 12 is a region whose density, refractive index, mechanical strength, and other physical properties differ from those of the surrounding unmodified region. Examples of the modified region 12 include a melt-treated region, a crack region, a dielectric breakdown region, and a refractive index change region. The modified region 12 has the property that cracks tend to extend from the modified region 12 to the incident side of the laser light L and to the opposite side. These properties of the modified region 12 are utilized to cut the object 11.

[0031] 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.

[0032] 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 .

[0033] 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.

[0034] 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.

[0035] 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.

[0036] The display 150 functions as an input unit that accepts information input from the user, and as a display unit that displays information to the user.

[0037] [Object Configuration] As shown in FIGS. 2 and 3 , the object 11 in this embodiment is a wafer 20. The wafer 20 includes a semiconductor substrate 21 and a functional device layer 22. While the present 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 (second surface) and a back surface 21 b (first 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 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 22 a may be configured three-dimensionally by stacking a plurality of 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.

[0038] 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 be actually drawn lines.

[0039] [Laser irradiation unit configuration] As shown in Fig. 4, the laser irradiation unit 3 has a light source 31, a spatial light modulator 32, and a condenser lens 33. The light source 31 outputs laser light L, for example, by pulse oscillation. The spatial light modulator 32 modulates the laser light L output from the light source 31. The spatial light modulator 32 is, for example, a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM). The condenser lens 33 condenses the laser light L modulated by the spatial light modulator 32. Note that the condenser lens 33 may be a correction collar lens.

[0040] 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. Of the two rows of modified regions 12a, 12b, the 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 12b is the modified region closest to the modified region 12a and closest to the back surface 21b.

[0041] 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.

[0042] The laser irradiation unit 3 irradiates the wafer 20 with laser light L from the back surface 21b side of the semiconductor substrate 21 along each of the multiple lines 15. As an example, <100> Two focal points C1 and C2 are aligned with positions 54 μm and 128 μm from the front surface 21a of the semiconductor substrate 21, respectively, and laser light L is irradiated onto the wafer 20 from the back surface 21b of the semiconductor substrate 21 along each of a plurality of lines 15. At this time, for example, if the conditions are such that the cracks 14 spanning two rows of modified regions 12a and 12b reach the front surface 21a of the semiconductor substrate 21, the wavelength of the laser light L is 1099 nm, the pulse width is 700 ns, and the repetition frequency is 120 kHz. Furthermore, the output of the laser light L at the focal point C1 is 2.7 W, the output of the laser light L at the focal point C2 is 2.7 W, and the relative movement speed of the two focal points C1 and C2 with respect to the semiconductor substrate 21 is 800 mm / s. Note that, for example, when the number of processing passes is 5, ZH80 (position 328 μm from the surface 21 a), ZH69 (position 283 μm from the surface 21 a), ZH57 (position 234 μm from the surface 21 a), ZH26 (position 107 μm from the surface 21 a), and ZH12 (position 49.2 μm from the surface 21 a) may be set as processing positions for the above-mentioned wafer 20. In this case, for example, the wavelength of the laser light L may be 1080 nm, the pulse width may be 400 nsec, the repetition frequency may be 100 kHz, and the moving speed may be 490 mm / sec.

[0043] The formation of the two rows of modified regions 12 a, 12 b and the cracks 14 is performed in the following case: that is, in a later process, for example, by grinding the back surface 21 b of the semiconductor substrate 21 to thin the semiconductor substrate 21 and expose the cracks 14 on the back surface 21 b, and then cutting the wafer 20 along each of the multiple lines 15 into multiple semiconductor devices.

[0044] [Configuration of the inspection imaging unit] As shown in FIG. 5, the imaging unit 4 (imaging section) includes a light source 41, a mirror 42, an objective lens 43, and a light detection section 44. The imaging unit 4 captures an image of the wafer 20. 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 and 12b have been formed as described above.

[0045] 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, for example, 0.45 or more. 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. Note that the means for correcting the aberrations is not limited to the correction collar 43a, and other correction means such as a spatial light modulator may also be used. The light detection unit 44 detects the light I1 that has passed through the objective lens 43 and the mirror 42. The light detection unit 44 is, for example, configured with an InGaAs camera, and detects the light I1 in the near-infrared region. The means for detecting (capturing) the light I1 in the near-infrared region is not limited to an InGaAs camera, but may be any other imaging means that captures images in a transmission type, such as a transmission type confocal microscope.

[0046] The imaging unit 4 can capture images of each of the two rows of modified regions 12a and 12b and the tips of each of the multiple cracks 14a, 14b, 14c, and 14d (details will be described later). The crack 14a is a crack that extends from the modified region 12a toward the 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.

[0047] [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.

[0048] 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 54 is configured by, for example, an InGaAs camera, and detects the light I2 in the near-infrared region.

[0049] 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.

[0050] [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 spanning two rows of modified regions 12a, 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.

[0051] 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 with respect to the front surface 21a, taking into account the refractive index of the semiconductor substrate 21.

[0052] 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 of the near-infrared light I1 (e.g., 1.1 to 1.2 μm).

[0053] 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)).

[0054] 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, due to optical singularities (stress concentration, strain, discontinuity in atomic density, etc.) occurring near the tip 14e, or light confinement occurring near the tip 14e, a portion of the light I1 reflected by the surface 21a and returned is scattered, reflected, interfered, absorbed, etc., resulting in an image in which the tip 14e appears dark against a whitish background (the right images 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 by the surface 21a is returned, resulting in a whitish image (the right image in (c) of Figure 12).

[0055] [Processing condition derivation process] The following describes a processing condition derivation process that is executed as a preprocessing step for forming a modified region for the purpose of cutting the wafer 20. Note that the processing condition determination process and other processes described below may be executed in processes other than the processing condition derivation process, for example, in various inspection processes after the processing conditions are derived. The processing conditions are a processing recipe that indicates the conditions and procedures under which the wafer 20 is processed.

[0056] First, a processing method for which processing conditions are derived will be described with reference to FIGS. 13 and 14. FIGS. 13 and 14 are diagrams illustrating a processing example using the laser irradiation unit 3. As shown in FIG. 13, the laser irradiation unit 3 forms a modified region while forming multiple focal points of the laser light, thereby improving the speed at which the modified region is formed. In the example shown in FIG. 13, a branching pattern for branching at least the laser light L into multiple beams (here, two beams) is displayed on the spatial light modulator 32. As a result, the laser light L incident on the spatial light modulator 32 is branched into two laser beams L1 and L2 by the spatial light modulator 32 and is then converged by the condenser lens 33 to form focal points C1 and C2.

[0057] The spatial light modulator 32 branches the laser light L so that the focal point C1 and the focal point C2 are formed at different positions in at least the Z direction intersecting the back surface 21b, which is the incident surface of the laser light L on the wafer 20. That is, the laser irradiation unit 3 irradiates the wafer 20 with laser light so that multiple focal points are simultaneously formed in the thickness direction of the wafer 20. Therefore, by moving the focal point C1 and the focal point C2 relative to the wafer 20, two rows of modified regions 121 and modified regions 122 are formed as the modified region 12 at different positions in the Z direction. The modified region 121 corresponds to the laser light L1 and its focal point C1, and the modified region 122 corresponds to the laser light L2 and its focal point C2. The focal point C1 and the modified region 121 are located on the opposite side of the back surface 21b from the focal point C2 and the modified region 122 (on the front surface 21a side of the wafer 20). The spatial light modulator 32 is capable of varying the distance Dz (vertical branching amount) between the focusing point C1 and the focusing point C2 in the Z direction by adjusting the branching pattern. Furthermore, the spatial light modulator 32 is capable of varying the distance Dx (horizontal branching amount) between the focusing point C1 and the focusing point C2 in the horizontal direction (X direction in the illustrated example) when branching the laser light L into laser lights L1 and L2. In the example of Fig. 13, the spatial light modulator 32 sets the distance Dx to be greater than 0 so that the focusing point C1 is located further forward than the focusing point C2 in the X direction (machining progress direction).

[0058] Here, when laser light is irradiated so as to simultaneously form multiple focal points C1 and C2 in the thickness direction of wafer 20, a crack extending from a modified region (e.g., modified region 121) formed at one focal point (e.g., focal point C1) may affect the formation of a modified region (e.g., modified region 122) at the other focal point (e.g., focal point C2) and the extension of the crack. In this case, the amount of crack at the other focal point becomes unstable, and there is a risk that the quality of the cut surface when wafer 20 is cut at the crack boundary, i.e., the processing quality, will be reduced.

[0059] In contrast, in the processing example shown in Fig. 14, for example, the distance Dz in the Z direction between the focal point C1 and the focal point C2 is set relatively large. As a result, as shown in Fig. 14(a) and (b), the laser beams L1 and L2 are irradiated so that the crack 121c extending from the modified region 121 and the crack 122c extending from the modified region 122 do not connect to each other. In the processing example shown in Fig. 14, as shown in Fig. 14(b) and (c), the laser beam L3 is irradiated so that the focal point C3 of the laser beam L3 is formed at a position between the focal points C1 and C2, thereby forming a crack 123c that extends from the modified region 123 formed at the third focal point C3 and spans the modified region 121 and the modified region 122. The crack 122c and the crack 121c further extend as a crack 123c is formed, and as a whole, form a crack 12c that extends from the front surface 21a to the back surface 21b.

[0060] In this way, according to the processing method in which outer SD layers (modified regions 121, 122) are formed so as to be sufficiently spaced apart from each other so that cracks do not connect to each other, and then an inner SD layer (modified region 123) is formed between the outer SD layers in the thickness direction of the wafer 20, a crack extending from one of the simultaneously formed modified regions does not affect the formation and extension of the other modified region, and the wafer 20 can be appropriately brought into a full-cut state while suppressing a deterioration in processing quality. The full-cut state is a state in which cracks in the wafer 20 have reached the back surface 21b and the front surface 21a. Note that even if there are very few unconnected cracks 14 inside the wafer 20, the state in which the unconnected portions can be connected by standard tape expanding (e.g., tape expanding with an expansion amount of 15 mm and an expansion speed of 5 mm / sec) and the wafer 20 can be divided is considered to be a full-cut state. The areas where the cracks 14 are slightly disconnected include resolidified areas in the modified layer (areas that resolidify after melting during laser irradiation) or black streaks where the cracks 14 are not connected to improve chip quality. However, the above-described processing method involves complex steps, making it difficult to appropriately set processing conditions suitable for the processing method. Below, we will explain the processing condition derivation process for processing the wafer 20 using the above-described processing method (a processing method in which outer SD layers are formed that are sufficiently spaced apart so that the cracks do not connect to each other, and then an inner SD layer is formed between the outer SD layers). Below, we will explain the processing condition derivation process for fully cutting the wafer 20 using the above-described processing method. Note that the full-cut processing may be performed by irradiating the laser beam from the back surface 21b of the wafer 20 as described above, or by irradiating the laser beam from the front surface 21a of the wafer 20.

[0061] In the above-described processing method, after the outer SD layers are formed, the inner SD layer is formed between the outer SD layers. Examples of such processing methods include a pattern in which a pair of outer SD layers (SD1, SD1) is first formed at two focal points, followed by a pair of inner SD layers (SD2, SD2), as shown in FIG. 15(a), and a pattern in which an outer SD layer (SD1) on the front surface 21a, an outer SD layer (SD2) on the back surface 21b, an inner SD layer (SD3) on the front surface 21a, and an inner SD layer (SD4) on the back surface 21b are formed in this order at one focal point. All of these patterns share the common feature that the inner SD layer is formed after the outer SD layer is formed. In such processing methods, for example, it is necessary to set separate processing conditions for forming the outer SD layer and for forming the inner SD layer. Therefore, in the processing condition derivation process according to this embodiment, as shown in FIG. 15(b), the suitability of the processing conditions is determined not only for the final processed state of the wafer 20, but also for the state in which only the outer SD layer has been processed and the state in which only the inner SD layer has been processed, and the processing conditions are derived based on the judgment results of the suitability of each processing condition.

[0062] Specifically, the control unit 8 sequentially executes the following processes: an outer SD layer formation process (first process) in which the laser irradiation unit 3 is controlled under first processing conditions set to form only the outer SD layer; a process (second process) in which the appropriateness of the first processing conditions is determined based on the state of the outer SD layer formed in the outer SD layer formation process; an inner SD layer formation process (fifth process) in which the laser irradiation unit 3 is controlled under third processing conditions set to form only the inner SD layer; a process (sixth process) in which the appropriateness of the third processing conditions is determined based on the state of the inner SD layer formed in the inner SD layer formation process; a total SD layer formation process (third process) in which the laser irradiation unit 3 is controlled under second processing conditions set to form both the outer and inner SD layers; and a process (fourth process) in which the appropriateness of the second processing conditions is determined based on the state of the outer and inner SD layers formed in the total SD layer formation process. The control unit 8 then determines the final processing conditions based on the results of the determination of each processing condition (details will be described later). Each process performed by the control unit 8 is described in detail below.

[0063] (Process for forming the outer SD layer and process for determining the suitability of the first processing conditions) The control unit 8 performs an outer SD layer formation process by controlling the laser irradiation unit 3 under first processing conditions set so that, by irradiating the wafer 20 with laser light, a modified region 121 (first modified region) and a modified region 122 (second modified region) located closer to the back surface 21b, which is the laser light incident surface, as shown in FIG. 16 and other figures are formed inside the wafer 20. The control unit 8 provisionally determines first processing conditions, including the conditions for irradiating the laser light by the laser irradiation unit 3, based on information received, for example, via the display 150 (see FIG. 25). The processing conditions include, for example, the pulse energy of the laser light (including output and frequency adjustment), aberration correction, pulse width, pulse pitch, the number of modified layers, the number of focusing points, etc. The information received via the display 150 (see FIG. 25) includes, for example, the wafer thickness and the final processing target (full cut, etc.).

[0064] After the outer SD layer formation process, the control unit 8 identifies the states of the modified regions 121 and 122, which are the outer SD layers, based on the signal (i.e., the imaging result) output from the imaging unit 4, and determines whether the first processing conditions (provisionally determined first processing conditions) for forming the outer SD layer are appropriate based on the identified information. The control unit 8 identifies the states of the modified regions 121, 122 and the state of the crack 14 extending from the modified regions 121, 122 as the states of the modified regions 121, 122.

[0065] Figure 16 is a diagram illustrating the state of the wafer 20 depending on the processing state of the outer SD layer. In Figures 16(a) to 16(c), the upper rows show the cross-sectional state of the wafer 20 when only the outer SD layer is formed, and the lower rows show the cross-sectional state of the wafer 20 when an inner SD layer is further formed from the state shown in the upper rows. Figure 16(a) shows a state in which the dividing force (force related to cutting) applied to the wafer 20 by the laser light irradiated to form the outer SD layer is weak, Figure 16(b) shows a state in which the dividing force is optimal, and Figure 16(c) shows a state in which the dividing force is strong.

[0066] When the dividing force of the laser beam for forming the outer SD layer is appropriate as shown in FIG. 16(b), when the inner SD layer (modified regions 123a, 123b) is formed following the outer SD layer, as shown in the lower part of FIG. 16(b), the crack 14 in the wafer 20 reaches the back surface 21b and the front surface 21a, resulting in a full cut. Furthermore, the meandering width of the crack 14 in a direction intersecting the thickness direction of the wafer 20 can be suppressed to a predetermined value or less (e.g., 2 μm or less). In this case, the wafer 20 can be completely divided (cut) without leaving any residual cracks after processing. Therefore, when the state of the modified regions 121 and 122, which are the outer SD layer, is as shown in the upper part of FIG. 16(b), the control unit 8 determines that the first processing conditions are appropriate (details of the determination method will be described later).

[0067] On the other hand, if the dividing force for forming the outer SD layer is weak, as shown in the upper part of FIG. 16(a), the extension of the crack 14 extending from the modified region 121 and the modified region 122 becomes short. As shown in the lower part of FIG. 16(a), even if the inner SD layer (modified region 123a, 123b) is subsequently formed, the crack 14 in the wafer 20 does not reach the back surface 21b and the front surface 21a, resulting in a full cut. In this case, some cracks remain after processing (for example, about 30% remain), making it impossible to ensure processing quality. For this reason, when the state of the modified region 121 and the modified region 122, which are the outer SD layer, is as shown in the upper part of FIG. 16(a), the control unit 8 determines that the first processing conditions are inappropriate (the determination method will be described in detail later). Furthermore, as shown in the upper part of FIG. 16(c), if the dividing force for forming the outer SD layer is strong, the crack 14 will extend excessively. This will result in a half-cut (HC) state where the crack 14 reaches the back surface 21b, or a bottom-side half-cut (BHC) state where the crack 14 reaches the front surface 21a, even before the inner SD layer is formed. In this case, the meandering amount of the crack 14 will also be large. As shown in the lower part of FIG. 16(c), the crack 14 in the outer SD layer, which extends significantly, will hinder the formation of the inner SD layer, making it difficult to achieve a full-cut state. This will result in residual cracks remaining after processing (e.g., about 10% of the cracks will remain), making it impossible to ensure processing quality. Therefore, when the state of the modified region 121 and the modified region 122, which are the outer SD layer, is as shown in the upper part of FIG. 16(c), the control unit 8 determines that the first processing conditions are inappropriate (the determination method will be described in detail later).

[0068] The details of the determination method for the first processing conditions will be described with reference to Figures 18(a) and 19(a). The control unit 8 determines whether the first processing conditions are appropriate based on the internal observation results acquired by the imaging unit 4 by adjusting the focus F to each point from the back surface 21b side. As shown in Figure 18(a), based on the internal observation results, the control unit 8 identifies information such as whether the crack 14 has extended to the back surface 21b (whether it is in the HC state), the amount of cracks inside the wafer 20 (the amount of extension of the crack 14), whether there are irregularities in the crack 14 inside the wafer 20, the presence or absence of black streaks (whether the tip of the upper crack, which is the crack 14 extending from the modified region 121 to the back surface 21b, is observed), the modified layer position (the position of the modified regions 121, 122), and whether the crack 14 has extended to the front surface 21a (whether it is in the BHC state). FIG. 19(a) shows a portion of the internal observation results (including the observation results of the back surface 21b, which is the incident surface) of the wafer 20 when an outer SD layer is formed. The upper part of FIG. 19(a) shows the observation results of the back surface 21b, which is the incident surface. As shown in the upper part of FIG. 19(a), when the crack 14 reaches the back surface 21b (HC state), the crack 14 is observed on the back surface 21b, which is the incident surface. On the other hand, when the crack 14 has not reached the back surface 21b (ST state), the crack 14 is not observed on the back surface 21b. Note that whether or not the crack 14 has reached the back surface 21b may be determined based on whether or not the tip of the crack 14 extending upward from the modified region 122 (toward the back surface 21b) is observed. That is, when the tip of the crack 14 extending from the modified region 122 toward the back surface 21b is observed, it may be determined that the state is ST and the crack 14 has not reached the back surface 21b, and when the tip of the crack 14 is not observed, it may be determined that the state is HC and the crack 14 has reached the back surface 21b. The middle part of Figure 19(a) shows the observation results of the region between the modified region 121 and the modified region 122 in the thickness direction of the wafer 20. As shown in the middle part of Figure 19(a), based on the observation results, it is possible to distinguish between a case where a black streak is present (when the tip of an upper crack, which is a crack 14 extending from the modified region 121 toward the back surface 21b, is confirmed) and a case where a black streak is not present (when the tip of the upper crack is not confirmed).The lower part of Figure 19(a) shows the observation results of the region between the modified region 121 and the surface 21a in the thickness direction of the wafer 20. As shown in the lower part of Figure 19(a), based on the observation results, it is possible to distinguish between a case where the crack 14 has reached the surface 21a and the tip of the crack 14 extending from the modified region 121 toward the surface 21a is not observed (BHC state), and a case where the crack 14 has not reached the surface 21a and the tip of the crack 14 is observed (ST state).

[0069] The control unit 8 may determine whether the state is an HC state in which the crack 14 extends to the back surface 21b, and determine whether the first processing conditions are appropriate based on whether the state is an HC state. Specifically, the control unit 8 may determine that the first processing conditions are inappropriate if the state is an HC state. The control unit 8 may also determine whether the state is a BHC state in which the crack 14 extends to the front surface 21a, and determine whether the first processing conditions are appropriate based on whether the state is a BHC state. Specifically, the control unit 8 may determine that the first processing conditions are inappropriate if the state is a BHC state. These determinations are based on the judgment that "if the crack 14 has reached the back surface 21b (or front surface 21a) even though only the outer SD layer has been formed when the final full cut state is to be achieved, the separating force of the first processing conditions is too strong."

[0070] The control unit 8 may identify the amount of cracks inside the wafer 20 and determine whether the first processing conditions are appropriate based on the amount of cracks. Specifically, the control unit 8 may determine that the first processing conditions are appropriate when the amount of cracks is within approximately ±5 μm of the optimal value, for example. The control unit 8 may also identify the presence or absence of unevenness of the cracks 14 inside the wafer 20 and determine whether the first processing conditions are appropriate based on the presence or absence of the unevenness. Specifically, the control unit 8 may determine that the first processing conditions are appropriate when there are no unevenness of the cracks 14 inside the wafer 20.

[0071] The control unit 8 may determine whether or not a black streak is present, specifically, whether or not the tip of an upper crack, which is a crack 14 extending from the modified region 121 toward the back surface 21b, is observed. Observation of the tip of the upper crack indicates that the cracks 14 extending from the modified region 121 and the modified region 122, which are different modified regions, are not connected to each other. In other words, the control unit 8 may determine whether or not the cracks 14 extending from the modified region 121 and the modified region 122, which are different modified regions, are connected to each other. Then, the control unit 8 may determine that the first processing conditions are inappropriate when the cracks 14 extending from the modified region 121 and the modified region 122 are connected to each other (when there is no black streak). This determination is based on the judgment that "when cracks in the outer SD layer are connected to each other, the connecting cracks affect the extension of each crack, and therefore the separating force of the first processing conditions is too strong."

[0072] The control unit 8 may identify the modified layer position (the position of the modified regions 121, 122) and determine whether the first processing conditions are appropriate based on the identified position. Specifically, the control unit 8 may determine that the first processing conditions are appropriate when the modified layer position is within approximately ±4 μm of the optimal value, for example.

[0073] (Process for forming the inner SD layer and process for determining the suitability of the third processing conditions) The control unit 8 performs an inner SD layer formation process by controlling the laser irradiation unit 3 under third processing conditions set so that modified regions 123a and 123b (third modified regions), which are inner SD layers, are formed inside the wafer 20 as shown in FIG. 17 and other figures by irradiating the wafer 20 with laser light. The control unit 8 provisionally determines the third processing conditions, including the conditions for irradiating the laser light by the laser irradiation unit 3, based on information received, for example, via the display 150 (see FIG. 25). The processing conditions include, for example, the pulse energy of the laser light (including output and frequency adjustment), aberration correction, pulse width, pulse pitch, the number of modified layers, the number of focusing points, etc. The information received via the display 150 (see FIG. 25) includes, for example, the wafer thickness and the final processing target (full cut, etc.).

[0074] After the inner SD layer formation process, the control unit 8 identifies the state of the modified regions 123a, 123b, which are the inner SD layer, based on the signal (i.e., the imaging result) output from the imaging unit 4, and determines whether the third processing conditions (provisionally determined third processing conditions) for forming the inner SD layer are appropriate based on the identified information. The control unit 8 identifies the state of the modified regions 123a, 123b and the state of the crack 14 extending from the modified regions 123a, 123b as the state of the modified regions 123a, 123b.

[0075] Figure 17 is a diagram illustrating the state of the wafer 20 depending on the processing state of the inner SD layer. In Figures 17(a) to 17(d), the upper rows show the cross-sectional state of the wafer 20 when only the inner SD layer is formed, and the lower rows show the cross-sectional state of the wafer 20 when an outer SD layer is also formed in addition to the state in the upper rows. Figure 17(a) shows a state in which the dividing force (force related to cutting) applied to the wafer 20 by the laser light irradiated to form the inner SD layer is weak and there is a positional misalignment related to the formation of the inner SD layer, Figure 17(b) shows a state in which the dividing force (force related to cutting) is weak, Figure 17(c) shows a state in which the dividing force is optimal, and Figure 17(d) shows a state in which the dividing force is strong.

[0076] When the dividing force of the laser beam for forming the inner SD layer is appropriate as shown in FIG. 17(c), once the outer and inner SD layers are formed, the crack 14 in the wafer 20 reaches the back surface 21b and the front surface 21a, resulting in a full cut, as shown in the lower part of FIG. 17(c). Furthermore, the meandering width of the crack 14 in a direction intersecting the thickness direction of the wafer 20 can be kept below a predetermined value (e.g., 2 μm or less). In this case, the wafer 20 can be completely divided (cut) without leaving any residual cracks after processing. Therefore, when the state of the modified regions 123a and 123b, which are the inner SD layers, is the state shown in the upper part of FIG. 17(c), the control unit 8 determines that the third processing conditions are appropriate (details of the determination method will be described later).

[0077] Here, under conditions where the crack state of the outer SD layer is optimal, the crack state of the inner SD layer has a relatively wide margin. For example, even when the dividing force for forming the inner SD layer is weak as shown in FIG. 17(b) or when the dividing force for forming the inner SD layer is strong as shown in FIG. 17(d), the outer and inner SD layers can be properly fully cut and the meandering width of the crack 14 can be kept below a predetermined value (e.g., 2 μm or less) after the outer and inner SD layers are formed. In this case, the wafer 20 can be completely divided (cut) without leaving any residual cracks after processing. Therefore, the control unit 8 may determine that the third processing conditions are appropriate when the state of the modified regions 123a and 123b, which are the inner SD layer, is as shown in the upper part of FIG. 17(b) or FIG. 17(d) (details of the determination method will be described later). However, even if the margin for the crack state of the inner SD layer is wide, if the dividing force is too weak and the final state is not fully cut, or if the dividing force is too strong and the amount of meandering of the crack 14 becomes large, the control unit 8 will naturally determine that the third processing conditions are inappropriate (details of the determination method will be described later).

[0078] 17(a), if the cutting force is weak and there is a positional misalignment related to the formation of the inner SD layer, the cracks 14 extending from the modified regions 123a, 123b will not connect to the cracks 14 in the outer SD layer, resulting in a failure to achieve a full cut. This will result in residual cracks remaining after processing (e.g., about 80% of the cracks will remain), making it impossible to guarantee processing quality. In such cases, the control unit 8 will determine that the third processing conditions are inappropriate (the determination method will be described in detail later).

[0079] The details of the determination method for the third processing conditions will be described with reference to FIGS. 18(b) and 19(b). The control unit 8 determines the appropriateness of the third processing conditions based on the internal observation results acquired by the imaging unit 4 by focusing F on each point from the back surface 21b side. As shown in FIG. 18(b), the control unit 8 determines, based on the internal observation results, information on whether the crack 14 has extended to the back surface 21b (whether it is in the HC state), the amount of cracks (extension of the crack 14) inside the wafer 20, the presence or absence of unevenness of the crack 14 inside the wafer 20, the position of the modified layer (the position of the modified regions 123a, 123b), and whether the crack 14 has extended to the front surface 21a (whether it is in the BHC state). FIG. 19(b) shows a portion of the internal observation results of the wafer 20 when an inner SD layer is formed. As shown in FIG. 19(b), the magnitude of unevenness of the cracks inside the wafer 20 is determined based on the internal observation results. The left diagram in FIG. 19(b) shows an example where the unevenness of the cracks is 2 μm or less, and the right diagram in FIG. 19(b) shows an example where the unevenness of the cracks is 5.6 μm.

[0080] The control unit 8 may determine whether the state is an HC state in which the crack 14 extends to the back surface 21b, and determine whether the third processing conditions are appropriate based on whether the state is an HC state. Specifically, the control unit 8 may determine that the third processing conditions are inappropriate if the state is an HC state. The control unit 8 may also determine whether the state is a BHC state in which the crack 14 extends to the front surface 21a, and determine whether the third processing conditions are appropriate based on whether the state is a BHC state. Specifically, the control unit 8 may determine that the third processing conditions are inappropriate if the state is a BHC state. These determinations are based on the judgment that "if the crack 14 has reached the back surface 21b (or front surface 21a) even though only the inner SD layer has been formed when the final full cut state is to be achieved, the separating force of the third processing conditions is too strong."

[0081] The control unit 8 may identify the amount of cracks inside the wafer 20 and determine whether the first processing conditions are appropriate based on the amount of cracks. Specifically, the control unit 8 may determine that the third processing conditions are appropriate when the amount of cracks is within approximately ±5 μm of the optimal value, for example. The control unit 8 may also identify the presence or absence of unevenness of the cracks 14 inside the wafer 20 and determine whether the first processing conditions are appropriate based on the presence or absence of the unevenness. Specifically, the control unit 8 may determine that the third processing conditions are appropriate when there is no unevenness of the cracks 14 inside the wafer 20 (for example, when the unevenness is 2 μm or less).

[0082] The control unit 8 may identify the modified layer position (the position of the modified regions 123a, 123b) and determine whether the third processing conditions are appropriate based on the identified position. Specifically, the control unit 8 may determine that the third processing conditions are appropriate when the modified layer position is within approximately ±4 μm of the optimal value, for example.

[0083] (Process for determining whether all SD layer formation processes and second processing conditions are appropriate) The control unit 8 performs a full SD layer formation process by controlling the laser irradiation unit 3 under second processing conditions set so that, by irradiating the wafer 20 with laser light, outer SD layers (modified regions 121, 122) are formed inside the wafer 20 and inner SD layers (modified regions 123a, 123b) are formed between the modified regions 121 and 122 in the thickness direction of the wafer 20. The control unit 8 provisionally determines second processing conditions, including the conditions for irradiating the laser light by the laser irradiation unit 3, based on information received, for example, via the display 150 (see FIG. 25). The processing conditions include, for example, the pulse energy of the laser light (including output and frequency adjustment), aberration correction, pulse width, pulse pitch, the number of modified layers, the number of focusing points, etc. The information received by the display 150 (see FIG. 25) includes, for example, the wafer thickness and the final processing target (full cut, etc.).

[0084] After the entire SD layer formation process, the control unit 8 identifies the states of the outer SD layers (modified regions 121, 122) and inner SD layers (123a, 123b) based on the signal (i.e., the imaging result) output from the imaging unit 4, and determines whether the second processing conditions (provisionally determined second processing conditions) for forming all SD layers are appropriate based on the identified information. The control unit 8 identifies the states of the modified regions 121, 122, 123a, 123b and the states of the cracks 14 extending from the modified regions 121, 122, 123a, 123b as the states of the modified regions 121, 122, 123a, 123b.

[0085] The details of the determination method for the second processing conditions will be described with reference to FIGS. 18(c) and 19(c). The control unit 8 determines whether the second processing conditions are appropriate based on the internal observation results acquired by the imaging unit 4 by focusing F on each point from the back surface 21b side. As shown in FIG. 18(c), the control unit 8 determines, based on the internal observation results, information on whether the crack 14 extends to the back surface 21b (whether it is in the HC state), the amount of meandering of the crack 14 on the back surface 21b (HC meandering amount), the clarity of the modified layer and the crack tip, and whether the crack 14 extends to the front surface 21a (whether it is in the BHC state). FIG. 19(c) shows a portion of the internal observation results (including the observation results of the back surface 21b, which is the incident surface) of the wafer 20 when the outer SD layer and the inner SD layer are formed. The upper end of FIG. 19(c) shows the observation results of the back surface 21b, which is the incident surface. As shown in the upper part of Figure 19(c), the meandering amount (HC meandering amount) of the crack 14 on the back surface 21b is identified. The meandering amount here refers to the width of the meandering of the crack 14 in a direction intersecting the thickness direction of the wafer 20 (a direction intersecting the back surface 21b). The left diagram of Figure 19(c) shows an example in which the HC meandering amount is 2 μm or less, and the right diagram of Figure 19(c) shows an example in which the HC meandering amount is 5.2 μm. The middle diagram of Figure 19(c) shows the results of internal observation of the wafer 20. As shown in the middle diagram of Figure 19(c), based on the observation results, it is possible to distinguish whether the modified layer and the crack tip are clear or unclear within the wafer 20. The bottom diagram of Figure 19(c) shows the results of internal observation of the wafer 20. As shown in the lower part of Figure 19(c), based on the observation results, it is possible to distinguish between a case where the crack 14 has reached the surface 21a and the tip of the crack 14 is not observed (BHC state) and a case where the crack 14 has not reached the surface 21a and the tip of the crack 14 is observed (ST state).

[0086] The control unit 8 may determine whether the second processing conditions are appropriate based on whether the back surface 21b is in an HC state, in which the crack 14 has propagated, and whether the second processing conditions are appropriate. Specifically, the control unit 8 may determine that the second processing conditions are appropriate when the back surface 21b is in an HC state. The control unit 8 may also determine whether the second processing conditions are appropriate based on whether the back surface 21b is in a BHC state, in which the crack 14 has propagated, and whether the second processing conditions are appropriate based on whether the back surface 21b is in a BHC state. Specifically, the control unit 8 may determine that the second processing conditions are appropriate when the back surface 21b is in a BHC state. These determinations are based on the judgment that "when the full cut state is finally achieved, if the crack 14 has reached the back surface 21b (or the front surface 21a) with all the SD layers formed, the separating force of the second processing conditions is appropriate."

[0087] The control unit 8 may identify the meandering amount (HC meandering amount) of the crack 14 on the back surface 21b and determine whether the second processing conditions are appropriate based on the HC meandering amount. Specifically, the control unit 8 may determine that the second processing conditions are appropriate when the HC meandering amount is within about 5 μm, for example.

[0088] The control unit 8 may identify the degree of definition of the modified layer and the crack tip inside the wafer 20, and may determine whether the second processing conditions are appropriate based on the degree of definition. Specifically, the control unit 8 may determine that the second processing conditions are inappropriate when at least one of the modified layer and the crack tip is clear. This determination is based on the judgment that "when a full cut state should be achieved, if the modified layer or the crack tip is clear, the full cut state is not achieved, and the separating force of the second processing conditions is too weak."

[0089] (Algorithm for determining the results of internal observation) With regard to the above-mentioned various determinations based on the internal observation results, an algorithm for detecting (identifying) the cracks 14 and an algorithm for detecting (identifying) the scars related to the modified region will be described in detail.

[0090] 20 and 21 are diagrams illustrating crack detection. FIG. 20 shows the results of internal observation (image of the inside of the wafer 20). The control unit 8 first detects a group of straight lines 140 from the image of the inside of the wafer 20 as shown in FIG. 20(a). To detect the group of straight lines 140, an algorithm such as Hough transform or LSD (Line Segment Detector) is used. The Hough transform is a method of detecting straight lines by detecting all straight lines passing through a point on an image and weighting the lines that pass through more characteristic points. The LSD is a method of detecting straight lines by calculating the gradient and angle of brightness values ​​in an image to estimate an area that will become a line segment, and approximating the area to a rectangle.

[0091] Next, the control unit 8 detects a crack 14 from the group of straight lines 140 by calculating the similarity between the group of straight lines 140 and the crack line, as shown in FIG. 21 . As shown in the upper diagram of FIG. 21 , a crack line has a characteristic in that the brightness values ​​on the line are very bright in the Y direction. For this reason, the control unit 8, for example, compares the brightness values ​​of all pixels of the detected group of straight lines 140 with the brightness values ​​on the line before and after the line in the Y direction, and determines the number of pixels whose difference is equal to or greater than a threshold value both before and after as a similarity score. Then, the detected group of straight lines 140 with the highest similarity score to the crack line is determined as a representative value for that image. A higher representative value is an indicator that the possibility of the presence of a crack 14 is higher. The control unit 8 compares the representative values ​​in multiple images and determines those with relatively high scores as crack image candidates.

[0092] 22 to 24 are diagrams illustrating the detection of creases. FIG. 22 shows the results of internal observation (images of the inside of the wafer 20). The control unit 8 detects corners (concentrations of edges) in the image of the inside of the wafer 20 as shown in FIG. 22(a) as key points, and detects their positions, sizes, and directions to detect feature points 250. Known methods for detecting feature points in this way include Eigen, Harris, Fast, SIFT, SURF, STAR, MSER, ORB, and AKAZE.

[0093] As shown in FIG. 23, the dent 280 has a distinctive corner feature, as it is made up of circles, rectangles, and other shapes arranged at regular intervals. Therefore, by aggregating the feature quantities of the feature points 250 in the image, the dent 280 can be detected with high accuracy. As shown in FIG. 24, by comparing the total feature quantities for each image captured by shifting the image depthwise, a change in the peaks, which indicates the number of crack rows for each modified layer, can be confirmed. The control unit 8 estimates the peak of this change as the position of the dent 280. By aggregating the feature quantities in this way, it becomes possible to estimate not only the dent position but also the pulse pitch.

[0094] (Processing related to determining processing conditions) The control unit 8 determines the final processing conditions based on the evaluation results of each of the processing conditions described above. Regarding the first processing conditions (provisionally determined first processing conditions) for forming the outer SD layer, the control unit 8 changes the first processing conditions if the first processing conditions are inappropriate based on the evaluation results of the first processing conditions based on the state of the outer SD layer formed under the first processing conditions. When changing the first processing conditions, the control unit 8 executes a correction process (seventh process) to correct the first processing conditions in accordance with the evaluation results. In the correction process, new first processing conditions are set in which, for example, the pulse energy of the laser beam (including output and frequency adjustment), aberration correction, pulse width, pulse pitch, number of modified layers, number of focusing points, etc. are corrected. The control unit 8 performs processing again using the newly set first processing conditions and, based on the evaluation results of the first processing conditions, determines whether the first processing conditions will be used as the processing conditions for the outer SD layer. The control unit 8 repeats the correction process, reprocessing, and evaluation until the first processing conditions become appropriate processing conditions.

[0095] Similarly, the control unit 8 changes the third processing conditions (provisionally determined third processing conditions) for forming the inner SD layer based on the judgment results of the third processing conditions based on the state of the inner SD layer formed under the third processing conditions if the third processing conditions are inappropriate. When changing the third processing conditions, the control unit 8 executes a correction process (seventh process) to correct the third processing conditions in accordance with the judgment results. The control unit 8 performs processing again under the newly set third processing conditions, and determines whether or not to use the third processing conditions as the processing conditions for the inner SD layer based on the judgment results of the third processing conditions. The control unit 8 repeats the correction process, reprocessing, and judgment until the third processing conditions become appropriate processing conditions.

[0096] The control unit 8 provisionally determines second processing conditions (processing conditions related to the formation of the outer SD layer and the inner SD layer) taking into account the first processing conditions and the third processing conditions optimized by the above-described process. Then, based on the judgment results of the second processing conditions based on the state of the outer SD layer and the inner SD layer formed under the second processing conditions, the control unit 8 changes the second processing conditions if the second processing conditions are inappropriate. When changing the second processing conditions, the control unit 8 executes a correction process (seventh process) to correct the second processing conditions in accordance with the judgment results. When changing the second processing conditions, the control unit 8 determines whether to change the processing conditions related to the formation of the outer SD layer or the processing conditions related to the formation of the inner SD layer in accordance with the judgment results. The control unit 8 performs processing again under the newly set second processing conditions and, based on the judgment results of the second processing conditions, determines whether the second processing conditions will be the final processing conditions. The control unit 8 repeats the correction process, reprocessing, and judgment until the second processing conditions become appropriate processing conditions.

[0097] In the processing condition derivation process, the final processing conditions are derived by processing and determining the outer SD layer, the inner SD layer, and the outer and inner SD layers, but this is not limiting. For example, the processing condition derivation process may derive the final processing conditions by processing and determining only the outer SD layer and the outer and inner SD layers, without processing and determining the inner SD layer alone.

[0098] (Screen image related to processing condition derivation process) Next, an example of a GUI (Graphical User Interface) related to the processing condition derivation process will be described with reference to Figures 25 to 27. Below, an example will be described in which final processing conditions are derived by performing processing and judgment on the outer SD layer, and processing and judgment on the outer SD layer and the inner SD layer only (an example in which processing and judgment are not performed on the inner SD layer alone). Figures 25 to 27 are screen images of the display 150 related to the processing condition derivation process.

[0099] 25 is an example of a setting screen (user input reception screen) for wafer processing information. As shown in FIG. 25, the display 150 displays the judgment content, processing quality, and judgment method and criteria. At least each item of the judgment content is set based on user input. Note that each item of the judgment content may be set to a fixed value. Furthermore, each item of the processing quality and judgment method and criteria may be set based on user input, or may be automatically set based on the content set in the judgment content.

[0100] The determination content displays information related to the determination to be made, including "FC condition determination" and "wafer thickness." "FC condition determination" is information indicating that after a modified region that is expected to be in a full cut state is formed, a determination of the processing conditions is made and the processing conditions are determined (derived). In the example shown in FIG. 25, "FC condition determination" is set to "execute." "Wafer thickness" is information indicating the thickness of the wafer 20. "Wafer thickness" is input by the user selecting, for example, from multiple options.

[0101] The processing quality displays the quality required for the wafer 20 after processing, and includes "crack state," "HC straightness," and "edge surface irregularity width." "Crack state" is information on cracks such as full cut state or ST state. "HC straightness" is information on the amount of HC meandering. "Edge surface irregularity width" is information on the irregularity width of the crack on the edge surface.

[0102] The judgment method and criteria display the pass criteria for the processing condition judgment process. The pass criteria for the first processing condition related to the formation of the outer SD layer are displayed for "Backside crack condition," "SD1 (modified area 121) crack amount," "SD2 (modified area 122) crack amount," "SD1 bottom end position," "SD2 bottom end position," "Edge unevenness width," "Black streaks," and "Surface crack condition." Since these are pass criteria for the first processing condition, "Backside crack condition" is set to ST, "Black streaks" is set to present, and "Surface crack condition" is set to ST. Furthermore, the pass criteria for the second processing condition related to the formation of the outer and inner SD layers are displayed for "Backside crack condition," "HC meander amount," "Modified layer image condition," "Surface crack condition," and "Crack condition." Since these are pass criteria for the second processing condition, "Backside crack condition" is set to HC, "Modified layer image condition" (clearness of the modified layer) is set to unclear, "Surface crack condition" is set to BHC, and "Crack condition" (overall crack condition) is set to FC (full cut).

[0103] Fig. 26 is an example of a processing result screen for the outer SD layer. The processing result confirmation screen is a screen that displays the judgment result after processing (here, the judgment result of the first processing conditions) and accepts user input related to correction of the first processing conditions. In the example shown in Fig. 26, the display 150 displays the judgment content, processing quality, and judgment result. The judgment content and processing quality are information set in the wafer processing information setting screen (Fig. 25) described above. In detail, the processing result confirmation screen displays the processing position (here, the outer SD layer) as an item of the judgment content in addition to the information set in the wafer processing information setting screen (Fig. 25).

[0104] In the example shown in FIG. 26, the left part of the area displaying the judgment results displays the judgment item, criteria (pass criteria), result, and pass / fail. The center part of the area displaying the judgment results displays a diagram of the outer SD layer and cracks assuming the processing result is the reference value (estimated processing result) and a diagram of the outer SD layer and cracks resulting from the actual processing. The right part of the area displaying the judgment results displays the observation results of the tip of the upper crack, which is the crack 14 extending from SD1 (modified region 121) to the back surface 21b, and the observation results of the tip of the lower crack, which is the crack 14 extending from SD1 (modified region 121) to the front surface 21a. The SD1 crack volume and SD2 crack volume items do not meet the pass criteria of 60±5 μm. Specifically, the crack volume is smaller than the pass criteria, resulting in a fail (NG). In this case, correction of the first processing conditions is recommended, so a message is displayed saying, "Reprocessing is recommended. Do you want to perform it?" The user can then correct the first processing conditions and perform reprocessing according to their input. Here, after the correction of the first processing conditions and reprocessing are performed, the first processing conditions meet the pass criteria, and then the outer SD layer and the inner SD layer are processed, and the processing result screen for the outer SD layer and the inner SD layer shown in Figure 27 is displayed.

[0105] 27 shows an example of a processing result screen for the outer SD layer and the inner SD layer. The processing result confirmation screen displays the judgment result after processing (here, the judgment result of the second processing condition) and also accepts user input related to correction of the second processing condition. In the example shown in FIG. 27, the judgment content, processing quality, and judgment result are displayed on the display 150.

[0106] In the example shown in Figure 27, the left part of the area displaying the evaluation results displays the evaluation item, standard (pass standard), result, and pass / fail. The center part of the area displaying the evaluation results displays a diagram of the outer and inner SD layers and their cracks assuming the processing results are the standard value, as well as a diagram of the outer and inner SD layers and their cracks as actually processed. The right part of the area displaying the evaluation results displays the observation results of the HC straightness (HC meandering amount) on the back surface 21b and the unevenness width of the end surface of the crack 14. The HC meandering amount does not meet the pass standard of within 5 μm, resulting in a fail (NG). In this case, correction of the second processing conditions is recommended, and a message is displayed saying, "We recommend reprocessing the outer SD layer. Do you want to do this?" Depending on the nature of the failure, the user can choose to correct the first processing conditions for the outer SD layer and reprocess it, or correct the third processing conditions for the inner SD layer and reprocess it. Then, in response to a user input, it is possible to correct and reprocess the first processing conditions or correct and reprocess the third processing conditions.

[0107] [Laser processing method] The laser processing method of this embodiment will be described with reference to Figures 28 and 29. Figures 28 and 29 are both flowcharts of the laser processing method. Figure 28 shows a process for deriving final processing conditions by processing and determining the outer SD layer, processing and determining the inner SD layer, and processing and determining the outer and inner SD layers. Figure 29 shows a process for deriving final processing conditions by processing and determining only the outer SD layer and processing and determining the outer and inner SD layers, without processing and determining the inner SD layer alone.

[0108] 28, first, the display 150 accepts user input of wafer processing information (step S1). Specifically, the display 150 accepts input of at least information on the wafer thickness. As a result, for the processing method for processing the outer SD layer and the inner SD layer to a full-cut state, first processing conditions for forming the outer SD layer and third processing conditions for forming the inner SD layer are automatically and provisionally determined.

[0109] Next, the control unit 8 processes the outer SD layer on the wafer 20 by controlling the laser irradiation unit 3 based on the provisionally determined first processing conditions (step S2). Next, the imaging unit 4 captures an image of the processed wafer 20 (step S3). Then, the control unit 8 controls the display 150 to display the imaged result on the display 150 (step S4).

[0110] Next, the control unit 8 identifies the state of the outer SD layer based on the imaging results, and determines whether the processing is appropriate (i.e., whether the first processing conditions are appropriate) based on the identified information (step S5). If the first processing conditions are not appropriate, the control unit 8 accepts input of new first processing conditions (step S1), and the processing from step S2 onwards is performed again. On the other hand, if the first processing conditions are appropriate, the control unit 8 officially determines the first processing conditions as the first processing conditions. Next, the processing of step S6 is executed.

[0111] In the process of step S6, the laser irradiation unit 3 is controlled based on the provisionally determined third processing conditions to process the inner SD layer on the wafer 20 (step S6). Next, the imaging unit 4 captures an image of the processed wafer 20 (step S7). Then, the control unit 8 controls the display 150 to display the imaged result on the display 150 (step S8).

[0112] Next, the control unit 8 identifies the state of the inner SD layer based on the imaging results, and determines whether the processing is appropriate (i.e., whether the third processing conditions are appropriate) based on the identified information (step S9). If the third processing conditions are not appropriate, the control unit 8 accepts input of new third processing conditions (step S10), and the processing from step S6 onwards is performed again. On the other hand, if the third processing conditions are appropriate, the control unit 8 officially determines the third processing conditions as the third processing conditions. Next, the processing of step S11 is executed.

[0113] In the process of step S11, the laser irradiation unit 3 is controlled based on second processing conditions that are provisionally determined based on the first and third processing conditions, thereby processing the outer and inner SD layers on the wafer 20 (step S11). Next, the imaging unit 4 captures an image of the processed wafer 20 (step S12). Then, the control unit 8 controls the display 150 to display the imaged result on the display 150 (step S13).

[0114] Next, the control unit 8 identifies the states of the outer SD layer and the inner SD layer based on the imaging results, and determines whether the processing is appropriate (i.e., whether the second processing conditions are appropriate) based on the identified information (step S14). If the second processing conditions are not appropriate, the control unit 8 determines whether to readjust the first conditions for forming the outer SD layer (or readjust the third processing conditions for forming the inner SD layer) based on the determination result (step S15). The control unit 8 may make this determination based on user input. If the first processing conditions are to be readjusted, the control unit 8 accepts input of new first processing conditions (step S1), and the processing from step S2 onwards is performed again. If the third processing conditions are to be readjusted, the control unit 8 accepts input of new third processing conditions (step S16), and the processing from step S6 onwards is performed again. On the other hand, if the second processing conditions are appropriate, the control unit 8 finally determines the second processing conditions as the final processing conditions.

[0115] 29, first, the display 150 accepts user input of wafer processing information (step S21). Specifically, the display 150 accepts input of at least information on the wafer thickness. As a result, first processing conditions for forming the outer SD layer are automatically and provisionally determined for the processing method for processing the outer SD layer and the inner SD layer to a full-cut state.

[0116] Next, the control unit 8 processes the outer SD layer on the wafer 20 by controlling the laser irradiation unit 3 based on the provisionally determined first processing conditions (step S22). Next, the imaging unit 4 captures an image of the processed wafer 20 (step S23). Then, the control unit 8 controls the display 150 to display the imaged result on the display 150 (step S24).

[0117] Next, the control unit 8 identifies the state of the outer SD layer based on the imaging results, and determines whether the processing is appropriate (i.e., whether the first processing conditions are appropriate) based on the identified information (step S25). If the first processing conditions are not appropriate, the control unit 8 accepts input of new first processing conditions (step S1), and the processing from step S2 onwards is performed again. On the other hand, if the first processing conditions are appropriate, the control unit 8 officially determines the first processing conditions as the first processing conditions. Next, the processing of step S26 is executed.

[0118] In the process of step S26, the laser irradiation unit 3 is controlled based on second processing conditions that are provisionally determined based on the first processing conditions, thereby processing the outer SD layer and the inner SD layer on the wafer 20 (step S26). Next, the imaging unit 4 captures an image of the processed wafer 20 (step S27). Then, the control unit 8 controls the display 150 to display the imaged result on the display 150 (step S28).

[0119] Next, the control unit 8 identifies the state of the outer SD layer and the inner SD layer based on the imaging results, and determines whether the processing is appropriate (i.e., whether the second processing conditions are appropriate) based on the identified information (step S29). If the second processing conditions are inappropriate, the control unit 8 accepts input of new first processing conditions (step S1), and the processing from step S2 onwards is performed again. On the other hand, if the second processing conditions are appropriate, the control unit 8 finally decides on the second processing conditions as the final processing conditions.

[0120] [Action and effect] Next, the effects of the laser processing device 1 according to this embodiment will be described.

[0121] The laser processing apparatus 1 according to this embodiment includes a laser irradiation unit 3 that irradiates the wafer 20 with laser light from the back surface 21b side of the wafer 20, 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 performs a first process of controlling the laser irradiation unit 3 under first processing conditions that are set so that the modified regions 121 and 122 are formed inside the wafer 20 by irradiating the wafer 20 with laser light, and after the first process, identifies the states of the modified regions 121 and 122 based on a signal output from the imaging unit 4 that detects the light, and performs a second process of detecting the modified regions 121 and 122 based on the identified information. The system is configured to execute a second process of determining whether the first processing conditions are appropriate; a third process of controlling the laser irradiation unit 3 under the second processing conditions set so that modified regions 121, 122 are formed inside the wafer 20 by irradiating the wafer 20 with laser light, and modified regions 123a, 123b are formed between the modified regions 121, 122 in the thickness direction of the wafer 20; and a fourth process of identifying, after the third process, the state of the modified regions 121, 122, 123a, 123b based on a signal output from the imaging unit 4 that detects the light, and determining whether the second processing conditions are appropriate based on the identified information.

[0122] In the laser processing apparatus 1 according to this embodiment, in the third process, outer SD layers (modified regions 121, 122) and inner SD layers (modified regions 123a, 123b) between them are formed in the thickness direction of the wafer 20 based on the second processing conditions. In the fourth process, the states of the outer SD layers and the inner SD layers are identified based on the signal output from the imaging unit 4, and the appropriateness of the second processing conditions is determined based on the identification results. In this way, the outer SD layers and the inner SD layers are processed so as to be actually formed, and the appropriateness of the processing conditions is determined based on the states of the outer SD layers and the inner SD layers after processing. This determines the appropriateness of the processing conditions based on the final processed state of the wafer 20. This allows the appropriateness of the processing conditions to be determined with high accuracy, ensuring the quality of the processed wafer 20. Furthermore, in the laser processing apparatus 1 according to this embodiment, in the first process, only the outer SD layers are formed based on the first processing conditions. In the second process, the states of the outer SD layers are identified based on the signal output from the imaging unit 4, and the appropriateness of the first processing conditions is determined based on the identification results. For example, in a case where the final processed state of the wafer 20 is a full-cut state (a state in which cracks extending from the modified region extend to both end surfaces of the wafer 20), there is little information regarding the modified region obtained from the final processed state of the wafer 20, and the appropriateness of the processing conditions may not be determined with high accuracy. In this regard, when only a portion of the modified region (outer SD layer) is formed, the appropriateness of the processing conditions (first processing conditions) for forming the portion of the modified region is determined based on information regarding the portion of the modified region. This allows the appropriateness of the processing conditions to be determined with high accuracy based on the processed state of the wafer 20, which provides more information (information regarding the modified region) than the final processed state of the wafer 20. According to the inventors' findings, when an outer SD layer and an inner SD layer are formed in the thickness direction of the wafer 20, the state of the outer SD layer is thought to have a greater impact on the quality of the processed wafer 20. In this regard, by determining the appropriateness of the processing conditions (first processing conditions) for forming the outer SD layer in the second process, the quality of the processed wafer 20 can be more appropriately guaranteed.

[0123] The control unit 8 identifies at least one of the state of the modified region and the state of the crack 14 extending from the modified region as the state related to the modified region. This allows the state of the wafer 20 after processing to be appropriately identified, and the appropriateness of the processing conditions to be determined with higher accuracy. This makes it possible to more appropriately ensure the quality of the wafer 20.

[0124] The control unit 8 identifies the position of the modified region and determines whether the processing conditions are appropriate based on that position. If the processing conditions are inappropriate, the modified region may not be positioned as desired. By determining whether the processing conditions are appropriate based on whether the modified region is positioned as desired, the processing conditions can be appropriately determined. This makes it possible to more appropriately ensure the quality of the processed wafer 20.

[0125] The control unit 8 determines whether the crack 14 has propagated to at least one of the back surface 21b and the front surface 21a, and determines whether the processing conditions are appropriate based on whether the crack 14 has propagated. For example, when processing the wafer 20 to a fully cut state in the final processing state, the control unit 8 can appropriately determine the processing conditions by determining whether the crack has not propagated to the back surface 21b and the front surface 21a at the second processing stage when only the outer SD layer is formed, and whether the crack 14 has propagated to the back surface 21b and the front surface 21a at the fourth processing stage when both the outer SD layer and the inner SD layer are formed. This more appropriately ensures the quality of the processed wafer 20.

[0126] The control unit 8 identifies the extension amount of the crack 14 and determines whether the processing conditions are appropriate based on the extension amount. If the processing conditions are inappropriate, the extension amount of the crack 14 may not reach the desired length. By determining whether the processing conditions are appropriate from the extension amount of the crack 14, the processing conditions can be determined appropriately. This makes it possible to more appropriately ensure the quality of the processed wafer 20.

[0127] The control unit 8 identifies the meandering width of the crack 14 in a direction intersecting the thickness direction of the wafer 20, and determines whether the processing conditions are appropriate based on the meandering width. If the processing conditions are inappropriate, the meandering width of the crack 14 may be large. By determining whether the processing conditions are appropriate from the meandering width of the crack 14, the processing conditions can be determined appropriately. This makes it possible to more appropriately ensure the quality of the processed wafer 20.

[0128] The control unit 8 determines whether cracks 14 extending from different modified regions are connected, and determines whether the processing conditions are appropriate based on whether they are connected. If the processing conditions are inappropriate, the cracks 14 may connect when it is not desired that they be connected, or may not connect when it is desired that they be connected. By determining whether the processing conditions are appropriate based on whether the cracks 14 are connected, the processing conditions can be determined appropriately. This makes it possible to more appropriately ensure the quality of the processed wafer 20.

[0129] The control unit 8 is configured to further execute a fifth process of controlling the laser irradiation unit 3 under third processing conditions set so that an inner SD layer is formed inside the wafer 20 by irradiating the wafer 20 with laser light, and a sixth process of identifying the state of the inner SD layer based on a signal output from the imaging unit 4 that detected the light after the fifth process and determining whether the third processing conditions are appropriate based on the identified information. With this configuration, when only the inner SD layer is formed, the appropriateness of the processing conditions (third processing conditions) for forming the inner SD layer is determined based on the information related to the inner SD layer. The appropriateness of the processing conditions can be determined more accurately from the information related to the modified region not only when both an outer SD layer and an inner SD layer are formed, or when only the outer SD layer is formed, but also when only the inner SD layer is formed.

[0130] When deriving the first processing conditions, the control unit 8 may determine that the first processing conditions are inappropriate if the crack 14 extends to at least one of the back surface 21b and the front surface 21a. When deriving the third processing conditions, the control unit 8 may determine that the third processing conditions are inappropriate if the crack 14 extends to at least one of the back surface 21b and the front surface 21a. This ensures that the ST state (a state in which internal observation is easy) is achieved in a processing state prior to the final processing state. This allows appropriate and abundant information regarding the processing state to be obtained. Even if the final processing state is a full-cut state, if the crack 14 reaches the back surface 21b or the front surface 21a in an earlier state (a state in which processing is still performed after that), it is considered that chip quality and separability will deteriorate in the final processing state. Therefore, by determining that the ST state in a processing state prior to the final processing state is a condition in which processing conditions are appropriate, chip quality and separability can be ensured.

[0131] When it is determined that the processing conditions are inappropriate, the control unit 8 is further configured to execute a seventh process of correcting the processing conditions in accordance with the determination result of the processing conditions. With this configuration, the processing conditions are corrected based on the determination result, and the quality of the processed wafer 20 can be more suitably guaranteed.

[0132] [Variations] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, in the embodiments, the processing method for which processing conditions are derived has been described as forming the outer SD layer followed by the inner SD layer, but the present invention is not limited to this. In the processing method for which processing conditions are derived, the outer and inner SD layers may be formed simultaneously, or the inner SD layer may be formed before the outer SD layer.

[0133] In addition, for example, after irradiating the wafer 20 with laser light along a first direction (X direction) to form a modified region, etc., a modified region may be formed by irradiating the wafer 20 with laser light along a second direction (Y direction) different from the first direction so as to straddle the already formed modified region. In such cases, different processing conditions may be derived for the X-direction processing (pre-processing) and the Y-direction processing (post-processing) based on the above-mentioned internal observation results (position of modified layer, presence or absence of black streaks) and back surface observation results (HC meandering / BHC meandering). Specifically, for example, when the lengths of the chip sides differ in the X and Y directions (e.g., 0.2 mm x 15 mm), when the quality desired by the user differs in the X and Y directions (e.g., the meandering of the crack must be within 2 μm in the X direction and within 10 μm in the Y direction), or when the chip size is very small, such as with RF-ID, and the quality is likely to differ depending on whether it is pre-processed or post-processed, different processing conditions may be derived for processing in the X direction (pre-processing) and processing in the Y direction (post-processing).

[0134] (Adjusting settings for internal observation) Furthermore, for example, the laser processing apparatus may be configured to adjust the settings for internal observation of the wafer in more detail. FIG. 30 illustrates the differences in imaging zones depending on the processing method. FIG. 30(a) shows the imaging zone when full-cut processing is performed, and FIG. 30(b) shows the imaging zone when other processing (e.g., BHC processing) is performed. In both processing methods, imaging is also performed at a virtual focus symmetrical with respect to the surface 21a. That is, the lower half SD layer of the wafer in FIGS. 30(a) and 30(b) is the region related to the virtual focus. As shown in FIG. 30, when full-cut processing is performed, the total imaging zone in the thickness direction of the wafer 20 becomes wider. Furthermore, when full-cut processing is performed, the spacing between the modified regions (SD1 to SD4) becomes narrower, and the extension of the crack 14 also becomes smaller. Therefore, when full-cut processing is performed, it is considered that the modified regions and cracks cannot be clearly observed unless the settings for internal observation in the thickness direction of the wafer 20 are adjusted in more detail.

[0135] Specifically, the control unit 8 performs the following in order to clearly observe the modified region and the like even when full cutting is performed.

[0136] First, the control unit 8 is configured to further execute an aberration correction process that controls the imaging unit 4 so that aberration correction according to the position in the thickness direction of the wafer 20 (optimal aberration correction in each thickness direction) is performed for each region in the thickness direction of the wafer 20 imaged by the imaging unit 4. The control unit 8 performs optimal aberration correction for each region according to, for example, the SD processing position (modified region formation position) estimated from the processing conditions by adjusting the spatial light modulator 32 or the correction collar 43a of the objective lens 43.

[0137] Second, the control unit 8 is configured to further execute a brightness calibration process to control the imaging unit 4 so that the imaging unit 4 outputs light at a light intensity corresponding to the position of each region in the thickness direction of the wafer 20, so that the imaging unit 4 captures each region in the thickness direction of the wafer 20 at a predetermined (e.g., constant or optimal) brightness. In internal observation, the deeper the observation depth, the greater the amount of light required to ensure sufficient brightness. That is, the amount of light required for each depth varies. Therefore, before observation, or whenever the laser device is started up or a device is changed, it is necessary to determine the amount of light required to achieve the optimal brightness value for each depth. In the brightness calibration process, the amount of light required for observing each position in the thickness direction is determined, and the imaging unit 4 is set to output light at that light intensity when observing each position.

[0138] In the brightness calibration process, as shown in FIG. 31, first, an input related to brightness calibration is accepted (step S71). The input related to brightness calibration may be, for example, an input of wafer thickness input for deriving processing conditions. Next, the control unit 8 determines a calibration implementation period according to the input related to brightness calibration (e.g., wafer thickness). The calibration implementation period here is, for example, information on multiple ZHs for which brightness calibration is to be performed. Note that the calibration implementation period may be determined and input by a user. Next, the imaging position of the imaging unit 4 is set to one ZH in the calibration implementation period (step S73). Then, the light intensity of the light source 41 is adjusted so that the luminance captured at the ZH becomes optimal (step S74), and the ZH and the light intensity are associated and stored (step S75). An aperture diaphragm or the like is used to adjust the light source 41. The processes of steps S73 to S75 are repeated until the adjustment of the light intensity for all ZHs is completed. The light amount adjusted in this way is output from the light source 41 of the imaging unit 4 when observing each position, so that each position can be observed with appropriate brightness.

[0139] Third, the control unit 8 is configured to control the imaging unit 4 to capture a shading image for each region in the thickness direction of the wafer 20 imaged by the imaging unit 4 before processing the modified region, and to further execute a shading correction process after processing the modified region to identify difference data between the image of each region imaged by the imaging unit 4 and the shading image of the corresponding region. In this case, the control unit 8 identifies the state of the modified region based on the difference data.

[0140] In the shading correction process, as shown in FIG. 32(a), before SD processing (processing of the modified region), a shading image is acquired at each internal observation position (determination position). Then, SD processing is performed, and an image after SD processing, as shown in FIG. 32(b), is acquired for each internal observation position (determination position). Then, for each internal observation position, difference data (see FIG. 32(c)) between the image after SD processing and the shading image is acquired (shading correction is performed). Note that if there is a positional deviation between the image after SD processing and the shading image, correction may be performed according to the amount of deviation. Examples of things that are shaded by shading correction include device patterns, point defects, and uneven screen brightness.

[0141] A laser processing method (processing condition derivation process) when the above-mentioned aberration correction process, brightness calibration process, and shading correction process are performed will be described with reference to FIG. 33. Note that in FIG. 33, the processing process and determination process are described in a simplified manner (processing related to the first processing condition, processing related to the second processing condition, etc. are described without distinction). As shown in FIG. 33, first, the display 150 accepts user input of wafer processing information (step S51). Specifically, the display 150 accepts input of at least information on the wafer thickness. As a result, the processing conditions are automatically and provisionally determined.

[0142] Next, the control unit 8 performs a brightness calibration process (step S52). Specifically, the control unit 8 sets the imaging unit 4 so that light is output from the imaging unit 4 with an amount of light according to the position of each region in the thickness direction of the wafer 20, so that the imaging unit 4 can capture an image of each region in the thickness direction of the wafer 20 with a predetermined (for example, constant or optimal) brightness.

[0143] Next, the control unit 8 acquires an image for shading correction (image for shading) (step S53). Specifically, the control unit 8 acquires an image at each internal observation position before SD processing as the image for shading.

[0144] Next, the control unit 8 processes an SD layer on the wafer 20 by controlling the laser irradiation unit 3 based on the processing conditions (step S54). Next, the control unit 8 performs aberration correction according to the position in the thickness direction of the wafer 20 (step S55). The control unit 8 performs optimal aberration correction by adjusting the spatial light modulator 32 or the correction collar 43a of the objective lens 43 for each region according to the SD processing position (modified region formation position) estimated from the processing conditions, for example.

[0145] Next, the processed wafer 20 is imaged by the imaging unit 4 (step S56). The control unit 8 performs shading correction (step S57). Specifically, the control unit 8 obtains difference data between the image of each region imaged by the imaging unit 4 and the shading image of the corresponding region.

[0146] Then, the control unit 8 controls the display 150 so that the imaging result is displayed on the display 150 (step S58). Next, the control unit 8 identifies the state of the SD layer based on the imaging result, and determines whether the processing is appropriate (i.e., whether the processing conditions are appropriate) based on the identified information (step S59). The control unit 8 performs this determination process using the difference data after shading correction. If the processing conditions are not appropriate in step S59, the control unit 8 accepts input of new processing conditions and performs the processing again. In this case, as shown in FIG. 33, the process may start again from the brightness calibration process (step S52) or from the SD processing (step S54). On the other hand, if the processing conditions are appropriate, the control unit 8 officially determines the processing conditions as the processing conditions, and the process ends.

[0147] As described above, the control unit 8 is further configured to execute a brightness calibration process to control the imaging unit 4 so that the imaging unit 4 outputs light with an amount of light corresponding to the position of each region in the thickness direction of the wafer 20, so that the imaging unit 4 captures the image at a predetermined brightness for each region in the thickness direction of the wafer 20. With this configuration, the light amount of the imaging unit 4 can be determined so that the brightness is constant or optimal for each imaging region in the thickness direction (depth direction) of the wafer 20. This makes it possible to appropriately identify the state of each modified region.

[0148] The control unit 8 is configured to control the imaging unit 4 to capture shading images for each region in the thickness direction of the wafer 20 that will be imaged by the imaging unit 4 before processing the modified region, and to further execute a shading correction process after processing the modified region to identify difference data between the image of each region captured by the imaging unit 4 and the shading image of the corresponding region. The determination process identifies the state of the modified region based on the difference data. The difference data acquired by the shading correction process is image data from which noise such as device patterns, point defects, and uneven screen brightness has been removed, and is image data containing only the modified region and crack state that is to be observed. By identifying the state of the modified region based on such difference data, the state of the processed wafer 20 can be appropriately identified. This makes it possible to more appropriately ensure the quality of the processed wafer 20.

[0149] The control unit 8 is further configured to execute an aberration correction process that controls the imaging unit 4 so that aberration correction is performed according to the position in the thickness direction of the wafer 20 for each region in the thickness direction of the wafer 20 imaged by the imaging unit 4. For example, when full-cut processing is performed, the intervals between each modified region are narrow and the amount of extension of the crack is also small, so clear observation is not possible unless aberration correction is performed for each position in the thickness direction of the wafer 20. In this regard, as described above, by performing aberration correction according to the thickness of the wafer 20 for each region in the thickness direction of the wafer 20, clear observation becomes possible and the state of the modified region can be more appropriately identified.

[0150] Fig. 34 is a diagram illustrating the effects of performing aberration correction processing, brightness value calibration processing, and shading correction processing. Fig. 34(a) is an image that has not undergone any of these processes, Fig. 34(b) is an image that has undergone only aberration correction processing, Fig. 34(c) is an image that has undergone aberration correction processing and brightness value calibration processing, and Fig. 34(d) is an image that has undergone aberration correction processing, brightness value calibration processing, and shading correction processing. As shown in Fig. 34, it can be seen that by performing these processes, the clarity of cracks 14 and the like in the image is significantly improved.

[0151] (Automation of processing condition derivation process) In the above-described embodiment, it has been explained that tentative processing conditions are automatically derived by inputting wafer processing information, an estimated processing result image is automatically derived and displayed based on the processing conditions, and an image of the actual processing result is also displayed, and the processing conditions are corrected until the actual processing result matches the estimated processing result, and the final processing conditions are derived. However, such processing condition derivation processing does not have to be performed entirely automatically.

[0152] For example, in the first step of automating the processing condition derivation process, a user may manually generate and set processing conditions (tentative processing conditions) based on wafer processing information. Then, actual processing results under the generated processing conditions may be acquired and stored in a database in association with the actual processing results for each combination of the input wafer processing information and the manually generated processing conditions.

[0153] Furthermore, in the second step, a model for deriving an estimated processing result from wafer processing information and processing conditions may be generated by learning the information stored in the database. Then, a regression model for deriving an optimal (most accurate) estimated processing result from the wafer processing information and processing conditions may be generated by analyzing the data in the database. In this case, multivariate analysis or machine learning may be used as an analytical method. Specifically, analytical methods such as simple regression, multiple regression, SGD regression, Lasso regression, Ridge regression, decision tree, support vector regression, Bayesian linear regression, deep learning, and k-nearest neighbor method may be used.

[0154] Furthermore, in the third step, a regression model may be generated that automatically derives optimal processing conditions (recipe) for obtaining a target processing result from the input wafer processing information. That is, parameters of the processing conditions may be adjusted for the input wafer processing information and input (simulated) into the regression model to search for optimal processing conditions that output a target processing result. Examples of such optimization methods include grid search, random search, and Bayesian optimization.

[0155] Furthermore, in the fourth step, the simulation results (estimated machining results) are compared with the actual machining results, and if it is necessary to modify the conditions, the data is stored in a database, and a regression model is generated again (active learning), thereby improving the accuracy of the regression model through actual operation. In this way, by correcting the machining conditions based on the difference between the estimated machining results and the actual machining results, the accuracy of the regression model can be improved by feeding back the actual machining results. [Explanation of symbols]

[0156] 1...laser processing device, 3...laser irradiation unit (irradiation section), 4...imaging unit (imaging section), 8...control section.

Claims

1. an irradiation unit that irradiates a wafer having a first surface and a second surface with laser light from the first surface side of the wafer; an imaging unit that outputs light that is transparent to the wafer and detects the light that has propagated through the wafer; a control unit, The control unit a first process of controlling the irradiation unit under first processing conditions set so that a first modified region is formed inside the wafer by irradiating the wafer with the laser light; a second process for identifying a state of the first modified region based on a signal output from the imaging unit that detected the light after the first process; and a brightness calibration process for controlling the imaging unit so that light is output from the imaging unit with an amount of light corresponding to the position of each region in the thickness direction of the wafer, so that the imaging unit can capture an image of each region in the thickness direction of the wafer at a predetermined brightness, the control unit identifies at least one of a state of the modified region and a state of a crack extending from the modified region as a state related to the modified region; The control unit determines whether the crack has propagated to at least one of the first surface and the second surface, and determines whether the processing conditions are appropriate based on whether the crack has propagated.

2. The laser processing apparatus according to claim 1 , wherein the control unit executes the brightness calibration process before observation, when the laser processing apparatus is started up, or whenever a device is changed.

3. In the brightness calibration process, the control unit Accepting input related to luminance calibration; determining a calibration execution interval in accordance with the input; and adjusting the amount of light output from the imaging unit so that the brightness when the imaging unit captures an image is a desired brightness for each region in the calibration execution section.

4. The control unit In the first process, the irradiation unit is controlled under the first processing conditions set so that a second modified region is further formed, the second modified region being located closer to the incident surface of the laser light than the first modified region; The laser processing device according to claim 1 , wherein the second processing further identifies a state of the second modified region, and determines whether the first processing conditions are appropriate based on the identified information.

5. The control unit a third process of controlling the irradiation unit under second processing conditions set so that the first modified region and the second modified region are formed inside the wafer by irradiating the wafer with the laser light, and a third modified region is formed between the first modified region and the second modified region in the thickness direction of the wafer; The laser processing apparatus of claim 4, further configured to execute a fourth process after the third process, which identifies the states of the first modified region, the second modified region, and the third modified region based on a signal output from the imaging unit that detected the light, and determines whether the second processing conditions are appropriate based on the identified information.

6. The laser processing device according to claim 1 , wherein the control unit identifies the position of the modified region and determines whether the processing conditions are appropriate based on the specified position.

7. The laser processing apparatus of claim 6, wherein the control unit determines that the first processing conditions are inappropriate when the crack extends to at least one of the first surface and the second surface during the second process.

8. 8. The laser processing device according to claim 1, wherein the control unit specifies an extension amount of the crack, and determines whether the processing conditions are appropriate based on the extension amount.

9. The control unit identifies the width of the meandering of the crack in a direction intersecting the thickness direction of the wafer, and determines whether the processing conditions are appropriate based on the width of the meandering. A laser processing apparatus as described in any one of claims 1 to 7.

10. The control unit determines whether cracks extending from different modified regions are connected, and determines whether the processing conditions are appropriate based on whether they are connected. A laser processing apparatus as described in any one of claims 1 to 7.

11. The control unit a fifth process of controlling the irradiation unit under third processing conditions set so that the third modified region is formed inside the wafer by irradiating the wafer with the laser light; and The laser processing apparatus of claim 5 is further configured to perform a sixth process after the fifth process, which identifies the state of the third modified region based on a signal output from the imaging unit that detected the light, and determines whether the third processing conditions are appropriate based on the identified information.

12. The laser processing apparatus according to claim 11, wherein the control unit determines that the third processing conditions are inappropriate when the crack extends to at least one of the first surface and the second surface in the sixth process.

13. The control unit The laser processing apparatus according to any one of claims 1 to 7, further configured to execute a seventh process to correct the processing conditions in accordance with the judgment result of the processing conditions when it is determined that the processing conditions are inappropriate.

14. The control unit before processing the modified region, the imaging unit is controlled to capture a shading image for each region in the thickness direction of the wafer, which is imaged by the imaging unit, and after processing the modified region, a shading correction process is further performed to identify difference data between the image of each region imaged by the imaging unit and the shading image of the corresponding region, The laser processing device according to claim 5 , wherein in the second process and the fourth process, a state of the modified region is identified based on the difference data.

15. The control unit The laser processing apparatus according to any one of claims 1 to 7, further configured to perform an aberration correction process that controls at least one of the irradiation unit and the imaging unit so that aberration correction according to the position in the thickness direction of the wafer is performed for each region in the thickness direction of the wafer imaged by the imaging unit.

16. Processing a wafer having a first surface and a second surface under first processing conditions set so that a first modified region is formed inside the wafer by irradiating the wafer with laser light from the first surface side of the wafer; Identifying a state of the first modified region based on an imaging result of the wafer processed under the first processing conditions; performing a brightness calibration process for outputting light for imaging with an amount of light corresponding to the position of each region in the thickness direction of the wafer so that the region in the thickness direction of the wafer where imaging is performed is imaged at a predetermined brightness; Identifying at least one of the state of the modified region and the state of a crack extending from the modified region as the state related to the modified region; A laser processing method that determines whether the crack has propagated to at least one of the first surface and the second surface, and determines whether the processing conditions are appropriate based on whether the crack has propagated.

Images