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 from the other surface of the semiconductor substrate with laser light, thereby forming a plurality of rows of modified regions inside 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, and makes it possible to observe the modified regions formed inside the semiconductor substrate and processing damage formed in the functional element layer from the back surface side of the semiconductor substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-64746 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the laser processing device as described above, the processing layer may be formed while forming a plurality of focal points of the laser light, thereby improving the formation speed of the processing layer. On the other hand, according to the knowledge of the present inventors, when a plurality of focal points are simultaneously formed in the thickness direction of the 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 the other focal point and the progress of the crack, and as a result, the amount of cracks (length of the cracks) may become unstable. Such a problem may occur even when a plurality of focal points are not simultaneously formed (when there is one focus). That is, for example, in a case where a modified region far from the incident surface is formed first with one focus, and then a modified region close to the incident surface is formed, the modified region close to the incident surface may be processed in a state where the crack far from the incident surface has not fully extended, and the total amount of cracks may become unstable. When the amount of cracks becomes unstable, the quality of the cut surface (i.e., the processing quality) when the object is cut at the crack as a boundary is reduced.

[0005] In order to prevent the amount of cracks from becoming unstable, it is possible to form, in advance, a plurality of modified regions that are sufficiently separated so that the cracks do not join together, and then form modified regions between the plurality of modified regions (between them in the thickness direction of the wafer), and finally form a crack that spans all of the modified regions, so that the cracks extending from simultaneously formed modified regions (or from a plurality of modified regions formed continuously at one focus) do not join together. In this way, the processing method of forming an inner modified region after forming an outer modified region is complicated, 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 with laser light from a first surface side of the wafer having a first surface and a second surface, 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 located on the laser light incident side of the first modified region are formed inside the wafer by irradiating the wafer with the laser light, and 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 after the first process, and The system is configured to execute a second process of determining whether or not the first processing conditions are appropriate based on the information set in the first process; a third process of 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 of identifying, after the third process, states relating to 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 or not the second processing conditions are appropriate based on the identified information.

[0008] In the laser processing apparatus according to one embodiment of the present invention, in the third process, outer modified regions (first modified region and second modified region) in the thickness direction of the wafer and an inner modified region therebetween (third modified region) are formed based on the second processing conditions, and in the fourth process, the state of each modified region is identified based on the signal output from the imaging unit, and based on the identification result, it is determined whether the second processing conditions are appropriate or not. In this way, the outer modified region and the inner modified region are processed so as to actually be formed, and the suitability of the processing conditions is determined based on the state of each modified region after processing, so that the suitability of the processing conditions is determined based on the final processed state of the wafer. In this way, the suitability of the processing conditions can be accurately determined, and the quality of the processed wafer can be guaranteed. Furthermore, in the laser processing apparatus according to one aspect of the present invention, in the first process, only the outer modified region (first modified region and second modified region) in the thickness direction of the wafer is formed based on the first processing conditions, and in the second process, the state of the outer modified region is identified based on the signal output from the imaging unit, and whether the first processing conditions are appropriate or not is determined based on the identification result. 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 region extend to both end faces of the wafer), there is little information related to the modified region 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, in a state in which only a part of the modified region (the outer modified region) is formed, the appropriateness of the processing conditions (first processing conditions) related to the formation of the part of the modified region is determined based on information related to the part of the modified region, so that the appropriateness of the processing conditions can be determined with high accuracy based on the processed state of the wafer from which more information (information related to the modified region) is obtained 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 considered to have a greater effect on the quality and divisibility of the processed wafer. In this regard, by determining in the second process whether the processing conditions (first processing conditions) related to the formation of the outer modified region are appropriate, the quality of the processed wafer can be more appropriately guaranteed.

[0009] The control unit may specify 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 specified, and the suitability of the processing conditions to be determined with higher accuracy. This makes it possible to more appropriately guarantee 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 position. The processing conditions can be appropriately determined by determining whether the processing conditions are appropriate depending on whether the modified region is positioned at the desired position. This makes it possible to more appropriately ensure the quality of the processed wafer.

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

[0012] The control unit may determine that the first processing conditions are not appropriate when the crack has propagated to at least one of the first surface and the second surface in the second process. This ensures that the processing state before the final processing state is in the ST state (a state in which the internal observation is easy) in which the crack has not reached the front and back surfaces. This makes it possible to obtain appropriate and abundant information related to the processing state. Even if the final processing state is a full cut state, if the crack has reached the front and back surfaces in an earlier state (a state in which processing is still performed thereafter), it is considered that the chip quality and divisibility will deteriorate in the final processing state. For this reason, by setting the ST state in the processing state before the final processing state as a condition in which the processing conditions are appropriate, the chip quality and divisibility can be guaranteed.

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

[0014] The control unit may specify the width of the meandering of the crack in a direction intersecting the thickness direction of the wafer, and judge whether the processing conditions are appropriate based on the width of the meandering. If the processing conditions are not appropriate, the width of the meandering of the crack may be large. By judging the suitability of the processing conditions from the width of the meandering of the crack, the processing conditions can be judged appropriately. This makes it possible to more appropriately guarantee the quality of the processed wafer.

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

[0016] The control unit may be further configured to execute a fifth process of controlling the irradiating unit under third processing conditions set so that a third modified region is formed inside the wafer by irradiating the wafer with the laser light, and a sixth process of identifying a state related to the third modified region based on a signal output from the imaging unit that detects the light after the fifth process, and judging whether the third processing conditions are appropriate or not based on the identified information. According to such a configuration, in a state in which only the inner modified region is formed, the suitability of the processing conditions related to the formation of the inner modified region (third processing conditions) is judged based on the information related to the inner modified region. In addition to the case in which the outer and inner modified regions are formed and the case in which only the outer modified region is formed, the suitability of the processing conditions can be judged with higher accuracy from the information related to the modified region.

[0017] The control unit may determine that the third processing conditions are not appropriate when the crack has propagated to at least one of the first surface and the second surface in the sixth process. This ensures that the processing state before the final processing state is in the ST state (a state in which the inside is easily observed) in which the crack has not reached the front and back surfaces. This makes it possible to obtain appropriate and abundant information related to the processing state. Even if the final processing state is a full cut state, if the crack has reached the front and back surfaces in an earlier state (a state in which processing is still performed thereafter), it is considered that the chip quality and divisibility will deteriorate in the final processing state. For this reason, by setting the ST state in the processing state before the final processing state as a condition in which the processing conditions are appropriate, the chip quality and divisibility can be guaranteed.

[0018] The control unit may determine that the first processing conditions are inappropriate when a crack has propagated 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 when a crack has propagated to at least one of the first surface and the second surface in the sixth process. This ensures that the processing state before the final processing state is in the ST state (a state in which the inside is easily observed) in which the crack has not reached the front and back surfaces. This makes it possible to obtain appropriate and abundant information related to the processing state. Even if the final processing state is a full cut state, if the crack has reached the front and back surfaces in an earlier state (a state in which processing is still performed thereafter), it is considered that the chip quality and divisibility will deteriorate in the final processing state. For this reason, by setting the ST state in the processing state before the final processing state as a condition in which the processing conditions are deemed appropriate, the chip quality and divisibility can be guaranteed.

[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, and the quality of the processed wafer can be more appropriately guaranteed.

[0020] The control unit may be further configured to execute a brightness calibration process for controlling the imaging unit so that the imaging unit outputs light with an amount of light according to the position of each region in the thickness direction of the wafer, so that the imaging unit can capture each region in the thickness direction of the wafer with a predetermined brightness. With this configuration, the amount of light of the imaging unit can be determined so that each imaging region in the thickness direction (depth direction) of the wafer has a constant or optimal brightness. This makes it possible to appropriately identify the state of each modified region.

[0021] The control unit is configured to control the imaging unit to capture a shading image for each region in the thickness direction of the wafer, which is imaged by the imaging unit, before processing the modified region, and to further execute a shading correction process to identify difference data between the image of each region captured by the imaging unit and the shading image of the corresponding region after processing the modified region, and the second process and the fourth process may identify 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 brightness of the screen has been removed, and is image data of 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 is 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 execute an aberration correction process for controlling 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 in which the imaging unit performs imaging. For example, when full cut processing is performed, the interval between each modified region is narrow and the extension amount of the crack is also small, so that clear observation is not possible unless aberration correction is applied to each position in the thickness direction of the wafer. In this regard, as described above, by performing aberration correction according to the thickness of the wafer for each region in the thickness direction of the wafer, clear observation is possible and the state related to the modified region can be more appropriately identified.

[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 relating to the first modified region and the second modified region based on an imaging result of the wafer processed based on the first processing conditions, and determining whether or not the first processing conditions are appropriate based on the identified information; processing the wafer based on second processing conditions that are set so that the wafer is irradiated with laser light to form the first modified region and the second modified region inside the wafer, and a third modified region is formed between the first modified region and the second modified region in a thickness direction of the wafer; and identifying states relating to the first modified region, the second modified region, and the third modified region based on an imaging result of the wafer processed based on the second processing conditions, and determining whether or not the second processing conditions are appropriate based on the identified information. Effect of the Invention

[0024] According to the present invention, it is possible to provide a laser processing apparatus and a laser processing method 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 description of the drawings]

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

[0026] Hereinafter, an embodiment 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), a plurality of imaging units 4, 5, 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 direction and the Y direction, and is rotatable about an axis parallel to the Z direction. The X direction and the Y direction are a first horizontal direction and a second horizontal direction that are perpendicular to each other, and the Z direction is a vertical direction.

[0029] The laser irradiation unit 3 focuses laser light L, which is transparent to the object 11, and irradiates the object 11. When the laser light L is focused inside the object 11 supported by the stage 2, the laser light L is particularly absorbed in a portion corresponding to a 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 that differs from the surrounding non-modified region in terms of density, refractive index, mechanical strength, and other physical properties. Examples of the modified region 12 include a melting treatment region, a crack region, a dielectric breakdown region, and a refractive index change region. The modified region 12 has a 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. Such a property of the modified region 12 is utilized for cutting the target 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. One 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 by 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, a memory, a 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 in the memory and storage, as well as communication by 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 composition] The object 11 in this embodiment is a wafer 20, as shown in FIG. 2 and FIG. 3. The wafer 20 includes a semiconductor substrate 21 and a functional device layer 22. In this embodiment, the wafer 20 is described as having the functional device layer 22, but the wafer 20 may or may not have the functional device layer 22, and may be a bare wafer. The semiconductor substrate 21 has a front surface 21a (second surface) and a back surface 21b (first surface). The semiconductor substrate 21 is, for example, a silicon substrate. The functional device layer 22 is formed on the front surface 21a of the semiconductor substrate 21. The functional device layer 22 includes a plurality of functional devices 22a arranged two-dimensionally along the front surface 21a. The functional device 22a is, for example, a light receiving device such as a photodiode, a light emitting device such as a laser diode, a circuit device such as a memory, or the like. The functional device 22a 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 functional elements 22a along each of the lines 15. The lines 15 pass between the functional elements 22a when viewed from the thickness direction of the wafer 20. More specifically, the lines 15 pass through the center (the center in the width direction) of the street region 23 when viewed from the thickness direction of the wafer 20. The street region 23 extends in the functional element layer 22 so as to pass between adjacent functional elements 22a. In this embodiment, the functional elements 22a are arranged in a matrix along the surface 21a, and the lines 15 are set in a lattice pattern. The lines 15 are virtual lines, but may be lines that are actually drawn.

[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 a pulse oscillation method. 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: Spatial Light Modulator). The condenser lens 33 condenses the laser light L modulated by the spatial light modulator 32. The condenser lens 33 may be a correction ring lens.

[0040] In this embodiment, 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, thereby forming two rows of modified regions 12a, 12b inside the semiconductor substrate 21 along each of the multiple lines 15. The modified region 12a is the modified region closest to the front surface 21a among the two rows of modified regions 12a, 12b. The modified region 12b is the modified region closest to the modified region 12a among the two rows of modified regions 12a, 12b, and is the modified region 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 the two focusing points C1, C2 along the line 15 relative to the semiconductor substrate 21. The laser light L is modulated by the spatial light modulator 32, for example, so that the focusing point C2 is located on the rear side of the focusing 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 may be formed 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, a single crystal silicon <100> Two focusing points C1 and C2 are aligned at positions 54 μm and 128 μm from the front surface 21a of the semiconductor substrate 21, respectively, and the laser light L is irradiated from the back surface 21b of the semiconductor substrate 21 along each of the multiple lines 15 to the wafer 20. At this time, for example, when the condition is that the cracks 14 across the 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. The output of the laser light L at the focusing point C1 is 2.7 W, the output of the laser light L at the focusing point C2 is 2.7 W, and the relative moving speed of the two focusing points C1 and C2 with respect to the semiconductor substrate 21 is 800 mm / sec. In addition, for example, when the number of processing passes is 5, ZH80 (position 328 μm from the surface 21a), ZH69 (position 283 μm from the surface 21a), ZH57 (position 234 μm from the surface 21a), ZH26 (position 107 μm from the surface 21a), and ZH12 (position 49.2 μm from the surface 21a) 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 12a, 12b and the cracks 14 is performed in the following case: That is, in a later process, for example, by grinding the back surface 21b of the semiconductor substrate 21 to thin the semiconductor substrate 21 and expose the cracks 14 on the back surface 21b, and then cutting the wafer 20 into a plurality of semiconductor devices along each of the plurality of lines 15.

[0044] [Configuration of the inspection imaging unit] As shown in FIG. 5, the imaging unit 4 (imaging section) has 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 composed of, for example, a halogen lamp and a filter, and outputs light I1 in the near-infrared region. The light I1 output from the light source 41 is reflected by the mirror 42, passes through the objective lens 43, and 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 are formed as described above.

[0045] The objective lens 43 passes the light I1 reflected by the surface 21a of the semiconductor substrate 21. That is, the objective lens 43 passes the light I1 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 occurring in the light I1 in the semiconductor substrate 21, for example, by adjusting the distances between the multiple lenses constituting the objective lens 43. Note that the means for correcting the aberrations is not limited to the correction collar 43a, and may be other correction means such as a spatial light modulator. The light detection unit 44 detects the light I1 transmitted through the objective lens 43 and the mirror 42. The light detection unit 44 is, for example, configured by 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, and may be any other imaging means that captures images in a transmission type, such as a transmission confocal microscope.

[0046] The imaging unit 4 can capture images of each of the two rows of modified regions 12a, 12b and the tips of each of the multiple cracks 14a, 14b, 14c, and 14d (details will be described later). The crack 14a is a crack that extends from the modified region 12a to the front surface 21a. The crack 14b is a crack that extends from the modified region 12a to the back surface 21b. The crack 14c is a crack that extends from the modified region 12b to the front surface 21a. The crack 14d is a crack that extends from the modified region 12b to 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 composed of, for example, 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. That is, the lens 53 passes the light I2 propagated through the semiconductor substrate 21. The numerical aperture of the lens 53 is 0.3 or less. That is, 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] The imaging unit 5, under the control of the control unit 8, irradiates the wafer 20 with light I2 from the back surface 21b side and detects the light I2 returning from the front surface 21a (functional element layer 22), thereby capturing an image of the functional element layer 22. Similarly, under the control of the control unit 8, the imaging unit 5, under the control of the control unit 8, irradiates the wafer 20 with light I2 from the back surface 21b side and detects the light I2 returning from the positions where the modified regions 12a and 12b are formed in the semiconductor substrate 21, thereby acquiring an image of the region including the modified regions 12a and 12b. These images are used for alignment of 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 manner 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 side to the front surface 21a side with respect to the semiconductor substrate 21 in which the cracks 14 extending across the 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 adjusted from the back surface 21b side to the tip 14e of the crack 14 extending from the modified region 12b to the back surface 21b side, the tip 14e can be confirmed (the image on the right side in FIG. 7). However, even if the focal point F is adjusted from the back surface 21b side to the cracks 14 themselves and the tip 14e of the cracks 14 reaching the front surface 21a, they cannot be confirmed (the image on the left side in FIG. 7). It should be noted that when the focal point F is adjusted from the back surface 21b side to the front surface 21a of the semiconductor substrate 21, the functional element layer 22 can be confirmed.

[0051] 5, the focal point F is moved from the back surface 21b side to the front surface 21a side for the semiconductor substrate 21 in which the cracks 14 extending across the two rows of modified regions 12a, 12b have not yet reached the front surface 21a, as shown in FIG. 8. In this case, even if the focal point F is aligned from the back surface 21b side to the tip 14e of the crack 14 extending from the modified region 12a to the front surface 21a side, the tip 14e cannot be confirmed (the image on the left side in FIG. 8). However, when the focal point F is aligned from the back surface 21b side to the region on the opposite side of the back surface 21b with respect to the front surface 21a (i.e., the region on the functional element layer 22 side with respect to the front surface 21a) and a virtual focal point Fv symmetrical to the focal point F with respect to the front surface 21a is positioned at the tip 14e, the tip 14e can be confirmed (the image on the right side in FIG. 8). The virtual focal point Fv is a point symmetrical with respect to the front surface 21a to the focal point F 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 assumed to be because the width of the crack 14 is smaller than the wavelength of the light I1, which is the illumination light. 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. (b) of Figure 9 is an enlarged image of the region A1 shown in (a) of Figure 9, (a) of Figure 10 is an enlarged image of the region A2 shown in (b) of Figure 9, and (b) of Figure 10 is an enlarged image of the region A3 shown in (a) of Figure 10. Thus, the width of the crack 14 is about 120 nm, which is smaller than the wavelength (e.g., 1.1 to 1.2 μm) of the light I1 in the near-infrared region.

[0053] Based on the above, the imaging principle is assumed as follows. As shown in FIG. 11(a), when the focal point F is located in air, the light I1 does not return, and a dark image is obtained (the image on the right side of FIG. 11(a)). As shown in FIG. 11(b), when the focal point F is located inside the semiconductor substrate 21, the light I1 reflected by the front surface 21a returns, and a whitish image is obtained (the image on the right side of FIG. 11(b)). As shown in FIG. 11(c), when the focal point F is aligned with the modified region 12 from the rear surface 21b side, the modified region 12 absorbs, scatters, or the like a part of the light I1 reflected by the front surface 21a and returned, and an image is obtained in which the modified region 12 appears dark against a whitish background (the image on the right side of FIG. 11(c)).

[0054] As shown in (a) and (b) of FIG. 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, distortion, discontinuity of atomic density, etc.) occurring near the tip 14e, light confinement occurring near the tip 14e, etc., scattering, reflection, interference, absorption, etc. occur for a part of the light I1 reflected by the surface 21a and returned, so an image is obtained in which the tip 14e appears dark on a whitish background (the right image in (a) and (b) of FIG. 12). As shown in (c) of FIG. 12, when the focal point F is focused on a part other than the vicinity of the tip 14e of the crack 14 from the back surface 21b side, at least a part of the light I1 reflected by the surface 21a returns, so a whitish image is obtained (the right image in (c) of FIG. 12).

[0055] [Processing condition derivation process] The following describes a processing condition derivation process that is executed as a pre-processing of a process 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 for explaining a processing example by the laser irradiation unit 3. As shown in Fig. 13, the laser irradiation unit 3 forms a modified region while forming a plurality of focusing points of the laser light, thereby improving the forming speed of the modified region. In the example shown in Fig. 13, a branching pattern for branching at least the laser light L into a plurality (here, two) 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 lights L1 and L2 in the spatial light modulator 32, and is focused by the focusing lens 33 to form the focusing 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 the Z direction intersecting with 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 laser light so that a plurality of focal points are simultaneously formed in the thickness direction of the wafer 20. For this reason, 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 at different positions in the Z direction as the modified region 12. 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 with respect to 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 changing 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 the 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 forward of the focusing point C2 in the X direction (machining progress direction).

[0058] Here, when the laser beam is irradiated so as to simultaneously form a plurality of focal points C1, C2 in the thickness direction of the 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 the wafer 20 is cut at the crack as a boundary, i.e., the processing quality, will decrease.

[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 to be 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 are not connected 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. Crack 122c and crack 121c further extend as crack 123c is formed, and as a whole, crack 12c extends from front surface 21a to back surface 21b.

[0060] In this way, according to the processing method in which the outer SD layers (modified regions 121, 122) are formed so as to be sufficiently separated from each other so that the cracks do not connect to each other, and then the 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 modified region does not affect the formation of the other modified region and the extension of the crack, and the wafer 20 can be appropriately put into a full cut state while suppressing a decrease in processing quality. The full cut state is a state in which the cracks in the wafer 20 reach the back surface 21b and the front surface 21a. Note that even if there are very small parts inside the wafer 20 where the cracks 14 are not connected, the state where the unconnected parts are connected by a standard tape expand (for example, a tape expand 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 places where the cracks 14 are not connected very slightly include resolidified places in the modified layer (places that resolidify after melting during laser irradiation) or black streak places where the cracks 14 are not connected intentionally to improve the chip quality. However, the above-mentioned processing method involves complicated steps, and it is difficult to appropriately set processing conditions suitable for the processing method. Below, a processing condition derivation process will be described for processing the wafer 20 by the above-mentioned processing method (a processing method in which outer SD layers are formed that are sufficiently spaced from each other so that the cracks do not connect to each other, and then an inner SD layer is formed between the outer SD layers). Below, a processing condition derivation process will be described for the case where the wafer 20 is in a full cut state by the above-mentioned processing method. Note that the full cut processing may be performed by irradiating the laser light from the back surface 21b side of the wafer 20 as described above, or may be performed by irradiating the laser light from the front surface 21a side of the wafer 20.

[0061] In the above-mentioned processing method, the outer SD layers are formed, and then the inner SD layers are formed between the outer SD layers. As such a processing method, for example, as shown in FIG. 15(a), a pattern in which a pair of outer SD layers (SD1, SD1) are first formed at two focal points, and then a pair of inner SD layers (SD2, SD2) are formed, or a pattern in which the outer SD layer (SD1) on the front surface 21a side, the outer SD layer (SD2) on the back surface 21b side, the inner SD layer (SD3) on the front surface 21a side, and the inner SD layer (SD4) on the back surface 21b side are formed in this order at one focal point, etc. are conceivable. In any of the patterns, the inner SD layer is formed after the outer SD layer is formed. In such a processing method, for example, the processing conditions for forming the outer SD layer and the processing conditions for forming the inner SD layer must be set separately. 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 processing conditions are derived based on the suitability determination results of each processing condition.

[0062] Specifically, the control unit 8 sequentially executes an outer SD layer forming process (first process) in which the laser irradiation unit 3 is controlled under a first processing condition set to form only the outer SD layer, a process (second process) in which the first processing condition is judged to be appropriate based on the state of the outer SD layer formed in the outer SD layer forming process, an inner SD layer forming process (fifth process) in which the laser irradiation unit 3 is controlled under a third processing condition set to form only the inner SD layer, a process (sixth process) in which the third processing condition is judged to be appropriate based on the state of the inner SD layer formed in the inner SD layer forming process, a total SD layer forming process (third process) in which the laser irradiation unit 3 is controlled under a second processing condition set to form both the outer SD layer and the inner SD layer, and a process (fourth process) in which the second processing condition is judged to be appropriate based on the state of the outer SD layer and the inner SD layer formed in the total SD layer forming process. Then, the control unit 8 determines the final processing condition based on the judgment result of each processing condition (details will be described later). Each process by the control unit 8 will be described in detail below.

[0063] (Outer SD layer formation process and process to judge suitability of first processing conditions) The control unit 8 performs an outer SD layer forming process that controls the laser irradiation unit 3 under first processing conditions set so that the wafer 20 is irradiated with laser light to form a modified region 121 (first modified region) and a modified region 122 (second modified region) located on the back surface 21b side, which is the incident surface of the laser light, inside the wafer 20 as shown in FIG. 16 and the like. The control unit 8 provisionally determines first processing conditions including the irradiation conditions of the laser light by the laser irradiation unit 3 based on information received, for example, by the display 150 (see FIG. 25). The processing conditions are, 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, and the like. The information received by the display 150 (see FIG. 25) is, for example, the wafer thickness, the final processing target (full cut, etc.), and the like.

[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 layer, 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] Fig. 16 is a diagram for explaining the state of the wafer 20 according to the processing state of the outer SD layer. In Fig. 16(a) to Fig. 16(c), the upper part shows the state of the cross section of the wafer 20 when only the outer SD layer is formed, and the lower part shows the state of the cross section of the wafer 20 when an inner SD layer is further formed from the state in the upper part. Fig. 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, Fig. 16(b) shows a state in which the dividing force is optimal, and Fig. 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, the crack 14 in the wafer 20 reaches the back surface 21b and the front surface 21a, resulting in a full cut state, as shown in the lower part of FIG. 16(b). In addition, the width of the meandering of the crack 14 in the 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) so that no crack remains after processing. For this reason, when the state of the modified region 121 and the modified region 122, which are the outer SD layer, is the state shown in the upper part of FIG. 16(b), the control unit 8 judges that the first processing conditions are appropriate (details of the judgment method will be described later).

[0067] On the other hand, when the dividing force for forming the outer SD layer is weak, for example as shown in the upper part of FIG. 16(a), the extension amount of the crack 14 extending from the modified region 121 and the modified region 122 becomes short, and as shown in the lower part of FIG. 16(a), even if the inner SD layer (modified region 123a, 123b) is formed thereafter, the crack 14 in the wafer 20 does not reach the back surface 21b and the front surface 21a to reach a full cut state. In this case, the crack remains after processing (for example, about 30% remains cracked), and the processing quality cannot be guaranteed. For this reason, when the state of the modified region 121 and the modified region 122, which are the outer SD layer, is the state shown in the upper part of FIG. 16(a), the control unit 8 judges that the first processing conditions are not appropriate (details of the judgment method will be described later). Also, for example, as shown in the upper part of FIG. 16(c), when the dividing force for forming the outer SD layer is strong, the extension amount of the crack 14 becomes excessively large, and even before the formation of the inner SD layer, the crack 14 reaches the back surface 21b in a half-cut (HC) state, and the crack 14 reaches the front surface 21a in a bottom side half-cut (BHC) state. In this case, the meandering amount of the crack 14 also becomes large. Then, as shown in the lower part of FIG. 16(c), the crack 14 in the outer SD layer, which has a large extension amount, inhibits the formation of the inner SD layer, making it difficult to achieve a full cut state, and cracks remain after processing (for example, about 10% remain cracked), 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 the state shown in the upper part of FIG. 16(c), the control unit 8 judges that the first processing conditions are not appropriate (details of the judgment method will be described later).

[0068] Details of the determination method for the first processing conditions will be described with reference to Fig. 18(a) and Fig. 19(a). The control unit 8 determines whether the first processing conditions are appropriate based on the internal observation results acquired by adjusting the focus F to each point from the back surface 21b side by the imaging unit 4. As shown in Fig. 18(a), the control unit 8 specifies information such as information on whether the crack 14 extends to the back surface 21b (whether it is in a HC state or not), the amount of cracks (amount of extension of the crack 14) inside the wafer 20, the presence or absence of unevenness of 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 side, is observed), the modified layer position (positions of the modified regions 121, 122), and whether the crack 14 extends to the front surface 21a (whether it is in a BHC state or not), based on the internal observation results. FIG. 19(a) shows a part of the internal observation result (including the observation result of the back surface 21b which is the incident surface) of the wafer 20 when the outer SD layer is formed. The upper part of FIG. 19(a) shows the observation result 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 does not reach 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 reaches the back surface 21b may be determined based on whether or not the tip of the crack 14 extending from the modified region 122 in the upward direction (toward the back surface 21b) is observed. That is, when the tip of the crack 14 extending from the modified region 122 toward the rear surface 21b is observed, it may be determined that the state is ST and the crack 14 has not reached the rear 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 rear surface 21b. The middle part of FIG. 19(a) shows the observation result 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 FIG. 19(a), based on the observation result, it is possible to distinguish between a case with a black streak (a case in which the tip of the upper crack, which is the crack 14 extending from the modified region 121 toward the rear surface 21b, is confirmed) and a case without a black streak (a case in which the tip of the upper crack is not confirmed).The lower part of Fig. 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 Fig. 19(a), based on the observation results, it is possible to distinguish between a case in which 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 (the case of the BHC state) and a case in which the crack 14 has not reached the surface 21a and the tip of the crack 14 is observed (the case of the 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 when 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 when the state is 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 front surface 21a) even though only the outer SD layer has been formed, the dividing force of the first processing conditions is too strong."

[0070] The control unit 8 may specify 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 an optimum value ±5 μm, for example. The control unit 8 may also specify the presence or absence of unevenness of the crack 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 is no unevenness of the crack 14 inside the wafer 20.

[0071] The control unit 8 may specify 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 to the back surface 21b, is observed. The 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 specify 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 not appropriate 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 the cracks in the outer SD layer are connected to each other, the cracks affect each other's crack extension, etc., and therefore the dividing 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 position. Specifically, the control unit 8 may determine that the first processing conditions are appropriate when the modified layer position is within about ±4 μm of the optimal value, for example.

[0073] (Process for forming the inner SD layer and process for determining suitability of the third processing conditions) The control unit 8 performs an inner SD layer formation process in which the laser irradiation unit 3 is controlled under third processing conditions set so that the wafer 20 is irradiated with laser light to form modified regions 123a and 123b (third modified regions) that are inner SD layers inside the wafer 20 as shown in FIG. 17 and other figures. The control unit 8 provisionally determines third processing conditions including the irradiation conditions of the laser light by the laser irradiation unit 3 based on information received, for example, by the display 150 (see FIG. 25). The processing conditions are, 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, and the like. The information received by the display 150 (see FIG. 25) is, for example, the wafer thickness, the final processing target (full cut, etc.), and the like.

[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] Fig. 17 is a diagram for explaining the state of the wafer 20 according to the processing state of the inner SD layer. In Fig. 17(a) to Fig. 17(d), the upper part shows the state of the cross section of the wafer 20 when only the inner SD layer is formed, and the lower part shows the cross section of the wafer 20 when an outer SD layer is further formed in addition to the state in the upper part. Fig. 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 a positional deviation related to the formation of the inner SD layer occurs, Fig. 17(b) shows a state in which the dividing force (force related to cutting) is weak, Fig. 17(c) shows a state in which the dividing force is optimal, and Fig. 17(d) shows a state in which the dividing force is strong.

[0076] When the dividing force of the laser light for forming the inner SD layer as shown in FIG. 17(c) is appropriate, when 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 state, as shown in the lower part of FIG. 17(c). In addition, the width of the meandering of the crack 14 in the 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) so that no crack remains after processing. Therefore, when the state of the modified regions 123a, 123b, which are the inner SD layer, is the state shown in the upper part of FIG. 17(c), the control unit 8 judges that the third processing conditions are appropriate (details of the judgment method will be described later).

[0077] Here, under the condition where the crack state of the outer SD layer is optimal, the crack state of the inner SD layer has a comparatively 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 SD layer and the inner SD layer may be in an appropriate full cut state and the meandering width of the crack 14 may be suppressed to a predetermined value or less (for example, 2 μm or less) when the outer SD layer and the inner SD layer are formed. In this case, the wafer 20 can be completely divided (cut) so that no crack remains after processing. For this reason, the control unit 8 may determine that the third processing conditions are appropriate when the state of the modified regions 123a, 123b, which are the inner SD layer, is the state 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 of the crack state of the inner SD layer is wide, if the dividing force is too weak and the final full cut state is not achieved, 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, the full cut will not be achieved, and some of the cracks will remain after processing (for example, about 80% will remain), making it impossible to ensure processing quality. In such a case, the control unit 8 will determine that the third processing conditions are not appropriate (details of the determination method will be described later).

[0079] Details of the determination method for the third processing condition will be described with reference to Fig. 18(b) and Fig. 19(b). The control unit 8 determines whether the third processing condition is appropriate based on the internal observation result acquired by focusing F on each point from the back surface 21b side by the imaging unit 4. As shown in Fig. 18(b), the control unit 8 specifies information such as whether the crack 14 extends to the back surface 21b (whether it is in a HC state), the amount of cracks (amount of 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 (position of the modified regions 123a, 123b), and whether the crack 14 extends to the front surface 21a (whether it is in a BHC state) based on the internal observation result. Fig. 19(b) shows a part of the internal observation result of the wafer 20 when the inner SD layer is formed. As shown in Fig. 19(b), the size of unevenness of the crack inside the wafer 20 is specified based on the internal observation result. The left diagram in FIG. 19(b) shows an example where the unevenness of the crack is 2 μm or less, and the right diagram in FIG. 19(b) shows an example where the unevenness of the crack 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 when 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 when the state is 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 front surface 21a) despite the state in which only the inner SD layer has been formed, the dividing force of the third processing conditions is too strong."

[0081] The control unit 8 may specify 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 an optimum value ±5 μm, for example. The control unit 8 may also specify the presence or absence of unevenness of the crack 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 crack 14 inside the wafer 20 (for example, 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 position. Specifically, the control unit 8 may determine that the third processing conditions are appropriate when the modified layer position is within about ±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 in which the laser irradiation unit 3 is controlled under second processing conditions set so that an outer SD layer (modified regions 121, 122) is formed inside the wafer 20 by irradiating the wafer 20 with laser light, and an inner SD layer (modified regions 123a, 123b) is 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 irradiation conditions of the laser light by the laser irradiation unit 3 based on information received, for example, by the display 150 (see FIG. 25). The processing conditions are, 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) is, for example, the wafer thickness, the final processing target (full cut, etc.), etc.

[0084] After the entire SD layer formation process, the control unit 8 identifies the states of the outer SD layer (modified regions 121, 122) and the inner SD layer (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 the entire SD layer 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] Details of the determination method for the second processing conditions will be described with reference to Fig. 18(c) and Fig. 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 adjusting the focus F to each point from the back surface 21b side. As shown in Fig. 18(c), the control unit 8 specifies information on whether the crack 14 extends to the back surface 21b (whether it is in the HC state or not), the meandering amount (HC meandering amount) of the crack 14 on the back surface 21b, the clarity of the modified layer and the crack tip, and information on whether the crack 14 extends to the front surface 21a (whether it is in the BHC state or not), based on the internal observation results. Fig. 19(c) shows a part 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 FIG. 19(c), the meandering amount (HC meandering amount) of the crack 14 on the back surface 21b is specified. The meandering amount here is 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 FIG. 19(c) shows an example in which the HC meandering amount is 2 μm or less, and the right diagram of FIG. 19(c) shows an example in which the HC meandering amount is 5.2 μm. The middle diagram of FIG. 19(c) shows the result of internal observation of the wafer 20. As shown in the middle diagram of FIG. 19(c), it is possible to distinguish whether the modified layer and the crack tip are clear or unclear inside the wafer 20 based on the observation result. The lower diagram of FIG. 19(c) shows the result 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 in which the crack 14 has reached the surface 21a and the tip of the crack 14 is not observed (BHC state) and a case in which 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. 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 determine whether the second processing conditions are appropriate based on whether the back surface 21b is in an BHC state in which the crack 14 has propagated. Specifically, the control unit 8 may determine that the second processing conditions are appropriate when the back surface 21b is in an 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 parting force of the second processing conditions is appropriate."

[0087] The control unit 8 may determine the meandering amount (HC meandering amount) of the crack 14 on the back surface 21b, and may 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 visibility 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 visibility. 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, a full cut state is not achieved when the modified layer or the crack tip is clear, and the dividing force of the second processing conditions is too weak."

[0089] (Algorithm for determining whether or not something is based on internal observation results) Concerning 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 for explaining crack detection. In FIG. 20, an internal observation result (image inside the wafer 20) is shown. The control unit 8 first detects a group of straight lines 140 from an image inside the wafer 20 as shown in FIG. 20(a). For the detection of the group of straight lines 140, an algorithm such as Hough transformation or LSD (Line Segment Detector) is used. The Hough transformation is a method of detecting straight lines by detecting all straight lines passing through a point on an image and weighting the straight lines that pass through more characteristic points. The LSD is a method of detecting straight lines by calculating the gradient and angle of the brightness value in the image to estimate an area that will be a line segment, and approximating the area to a rectangle.

[0091] Next, the control unit 8 detects the crack 14 from the straight line group 140 by calculating the similarity between the straight line group 140 and the crack line as shown in FIG. 21. The crack line has a characteristic that the front and rear of the crack line are very bright in the Y direction compared to the luminance value on the line, as shown in the upper diagram of FIG. 21. For this reason, the control unit 8, for example, compares the luminance values ​​of all pixels of the detected straight line group 140 with the front and rear in the Y direction, and determines the number of pixels whose difference is equal to or greater than a threshold both before and after as the similarity score. Then, the one with the highest similarity score to the crack line among the detected multiple straight line groups 140 is determined as the representative value in the image. The higher the representative value, the more likely the crack 14 is to exist. The control unit 8 determines the one with a relatively high score as a crack image candidate by comparing the representative values ​​in multiple images.

[0092] 22 to 24 are diagrams for explaining the detection of scratches. In FIG. 22, an internal observation result (image of the inside of the wafer 20) is shown. The control unit 8 detects corners (concentration of edges) in the image of the inside of the wafer 20 as shown in FIG. 22(a) as key points, and detects the 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, AKAZE, and the like.

[0093] Here, as shown in FIG. 23, the dent 280 has a strong characteristic as a corner, since shapes such as circles and rectangles are arranged at regular intervals. Therefore, by collecting the feature amounts of the feature points 250 in the image, it is possible to detect the dent 280 with high accuracy. As shown in FIG. 24, when comparing the total feature amounts of the images captured by shifting in the depth direction, a change in a mountain indicating the amount of crack rows for each modified layer can be confirmed. The control unit 8 estimates the peak of the change as the position of the dent 280. By collecting the feature amounts in this way, it is 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 judgment results of each of the above-mentioned processing conditions. The control unit 8 changes the first processing conditions (provisionally determined first processing conditions) related to the formation of the outer SD layer based on the judgment results of the first processing conditions based on the state of the outer SD layer formed under the first processing conditions, if the first processing conditions are not appropriate. When changing the first processing conditions, the control unit 8 executes a correction process (seventh process) for correcting the first processing conditions according to the judgment results. In the correction process, new first processing conditions are set in which, for example, the pulse energy of the laser light (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 under the newly set first processing conditions, and determines whether or not the first processing conditions are to be the processing conditions for the outer SD layer based on the judgment results of the first processing conditions. The control unit 8 repeats the correction process, reprocessing, and judgment 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) related to the formation of 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 not appropriate. When changing the third processing conditions, the control unit 8 executes a correction process (seventh process) to correct the third processing conditions according to the judgment results. The control unit 8 performs processing again under the newly set third processing conditions, and determines whether or not to set 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, re-processing, and judgment until the third processing conditions become appropriate processing conditions.

[0096] The control unit 8 provisionally determines the second processing conditions (processing conditions related to the formation of the outer SD layer and the inner SD layer) in consideration of the first processing conditions and the third processing conditions optimized by the above-mentioned processing. Then, the control unit 8 changes the second processing conditions if the second processing conditions are not appropriate based on the judgment result 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. When changing the second processing conditions, the control unit 8 executes a correction process (seventh process) for correcting the second processing conditions according to the judgment result. 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 among the second processing conditions according to the judgment result. The control unit 8 performs processing again under the newly set second processing conditions, and determines whether the second processing conditions are to be the final processing conditions based on the judgment result of the second 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 judging the outer SD layer, the inner SD layer, and the outer and inner SD layers, but the processing condition derivation process is not limited to this. For example, the final processing conditions may be derived by processing and judging only the outer SD layer and the outer and inner SD layers without processing and judging the inner SD layer alone.

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

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

[0100] The judgment content displays information related to the judgment to be performed, and displays "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 judgment is made on the processing conditions 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 from a number of options, for example.

[0101] The processing quality indicates the quality desired for the processed wafer 20, and includes the "crack state," "HC straightness," and "edge unevenness width." "Crack state" is information on the crack, such as the full cut state or ST state. "HC straightness" is information on the amount of HC meandering. "Edge unevenness width" is information on the unevenness width of the crack on the edge face.

[0102] The judgment method and criteria display the pass criteria in the judgment process of the processing conditions, and the pass criteria of "backside crack state", "SD1 (modified area 121) crack amount", "SD2 (modified area 122) crack amount", "SD1 bottom end position", "SD2 bottom end position", "end surface unevenness width", "black streak", and "surface crack state" are displayed as the pass criteria of the first processing condition related to the formation of the outer SD layer. Since these are the pass criteria of the first processing condition, the "backside crack state" is set to ST, "black streak" is set to present, and "surface crack state" is set to ST. In addition, the pass criteria of "backside crack state", "HC meandering amount", "modified layer image state", "surface crack state", and "crack state" are displayed as the pass criteria of the second processing condition related to the formation of the outer SD layer and the inner SD layer. Since these are the pass criteria of the second processing condition, the "backside crack state" is set to HC, the "modified layer image state" (clarity of the modified layer) is set to unclear, the "surface crack state" is set to BHC, and the "crack state" (overall crack state) 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 condition) and accepts a user input related to the correction of the first processing condition. In the example shown in Fig. 26, the judgment content, processing quality, and judgment result are displayed on the display 150. The judgment content and processing quality are information set on the above-mentioned wafer processing information setting screen (Fig. 25). In detail, on the processing result confirmation screen, in addition to the information set on the wafer processing information setting screen (Fig. 25), the processing position (here, the outer SD layer) is displayed as an item of the judgment content.

[0104] In the example shown in FIG. 26, the left part of the area where the judgment result is displayed displays the judgment item, the standard (pass standard), the result, and pass / fail. In addition, in the center part of the area where the judgment result is displayed, a diagram (estimated processing result) depicting the outer SD layer and cracks when the processing result is assumed to be the standard value, and a diagram depicting the outer SD layer and cracks of the actual processing result are displayed. In addition, in the right part of the area where the judgment result is displayed, the observation result of the tip of the upper crack, which is the crack 14 extending from SD1 (modified area 121) to the back surface 21b side, and the observation result of the tip of the lower crack, which is the crack 14 extending from SD1 (modified area 121) to the front surface 21a side, are displayed. Now, in the items of SD1 crack amount and SD2 crack amount, the pass standard of 60±5 μm is not met, and specifically, the crack amount is smaller than the pass standard, and the result is fail (NG pass / fail). In this case, correction of the first processing condition is recommended, so a message saying "Reprocessing is recommended. Do you want to perform it?" is displayed, and it is possible to correct the first processing condition and perform reprocessing according to the user's input. In this case, it is assumed that 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 of the outer SD layer and the inner SD layer shown in Figure 27 is displayed.

[0105] Fig. 27 is an example of a processing result screen for the outer SD layer and the inner SD layer. The processing result confirmation screen is a screen that displays the judgment result after processing (here, the judgment result of the second processing condition) and 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 FIG. 27, the left part of the area where the judgment result is displayed displays the judgment item, the standard (pass standard), the result, and pass / fail. In addition, in the center part of the area where the judgment result is displayed, a diagram of the outer SD layer and the inner SD layer and their cracks when the processing result is assumed to be the standard value, and a diagram of the outer SD layer and the inner SD layer and their cracks as the actual processing result are displayed. In addition, in the right part of the area where the judgment result is displayed, the observation results of the HC straightness (HC meandering amount) on the back surface 21b and the end face unevenness width of the crack 14 are displayed. Now, the item of the HC meandering amount does not meet the pass standard of within 5 μm, and it is rejected (NG). In this case, since the correction of the second processing condition is recommended, the message "We recommend reprocessing the outer SD layer. Do you want to do it?" is displayed. Depending on the content of the rejection, the user can select whether to correct the first processing condition for the outer SD layer and reprocess it, or to correct the third processing condition for the inner SD layer and reprocess it. Then, in response to a user input, it is possible to correct and re-machine the first machining conditions, or correct and re-machine the third machining conditions.

[0107] [Laser processing method] The laser processing method of this embodiment will be described with reference to Fig. 28 and Fig. 29. Fig. 28 and Fig. 29 are both flow charts of the laser processing method. Fig. 28 shows a process of deriving the final processing conditions by performing processing and judgment on the outer SD layer, processing and judgment on the inner SD layer, and processing and judgment on the outer SD layer and the inner SD layer. Fig. 29 shows a process of deriving the final processing conditions by performing only processing and judgment on the outer SD layer, and processing and judgment on the outer SD layer and the inner SD layer, without performing processing and judgment on 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 processed wafer 20 is imaged by the imaging unit 4 (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 result, and judges 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 carried out again. On the other hand, if the first processing conditions are appropriate, the control unit 8 decides that the first processing conditions are the first processing conditions. Then, 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 condition 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 imaging 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 result, and judges 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 carried out again. On the other hand, if the third processing conditions are appropriate, the control unit 8 decides that the third processing conditions are the third processing conditions. Then, 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 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 so that the imaging result is displayed on the display 150 (step S13).

[0114] Next, the control unit 8 specifies the state of the outer SD layer and the inner SD layer based on the imaging result, and judges whether the processing is appropriate (i.e., whether the second processing condition is appropriate) based on the specified information (step S14). If the second processing condition is not appropriate, the control unit 8 judges whether to readjust the first condition related to the formation of the outer SD layer (or readjust the third processing condition related to the formation of the inner SD layer) according to the judgment result (step S15). The control unit 8 may make the judgment according to a user input. When the first processing condition is readjusted, the control unit 8 accepts the input of a new first processing condition (step S1), and the processing from step S2 onwards is performed again. When the third processing condition is readjusted, the control unit 8 accepts the input of a new third processing condition (step S16), and the processing from step S6 onwards is performed again. On the other hand, when the second processing condition is appropriate, the control unit 8 finally decides on the second processing condition as the final processing condition.

[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, a first processing condition for forming the outer SD layer is 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 processed wafer 20 is imaged by the imaging unit 4 (step S23). Then, the control unit 8 controls the display 150 to display the imaging 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 result, and judges 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 carried out again. On the other hand, if the first processing conditions are appropriate, the control unit 8 decides that the first processing conditions are the first processing conditions. Then, 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 provisionally determined based on the first processing conditions finally determined, 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 so that the imaging result is displayed 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 result, 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 not appropriate, the control unit 8 accepts input of new first processing conditions (step S1), and the processing from step S2 onwards is carried out 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] [Effects] 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 region 121 and the modified region 122 are formed inside the wafer 20 by irradiating the wafer 20 with the laser light, and after the first process, identifies the states related to the modified regions 121 and 122 based on a signal output from the imaging unit 4 that detects the light, and based on the identified information, The system is configured to execute a second process of determining whether the first processing conditions are appropriate or not, 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 states 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 or not based on the identified information.

[0122] In the laser processing device 1 according to the present embodiment, in the third process, the outer SD layer (modified regions 121, 122) in the thickness direction of the wafer 20 and the inner SD layer (modified regions 123a, 123b) therebetween are formed based on the second processing conditions, and in the fourth process, the states of the outer SD layer and the inner SD layer are specified based on the signal output from the imaging unit 4, and based on the specified result, it is determined whether the second processing conditions are appropriate or not. In this way, the outer SD layer and the inner SD layer are processed so as to be actually formed, and the suitability of the processing conditions is determined based on the state of the outer SD layer and the inner SD layer after processing, so that the suitability of the processing conditions is determined based on the final processed state of the wafer 20. In this way, the suitability of the processing conditions is accurately determined, and the quality of the wafer 20 after processing can be guaranteed. Furthermore, in the laser processing device 1 according to the present embodiment, in the first process, only the outer SD layer is formed based on the first processing conditions, and in the second process, the state of the outer SD layer is specified based on the signal output from the imaging unit 4, and based on the specified result, it is determined whether the first processing conditions are appropriate or not. For example, in a case where the final processed state of the wafer 20 is processed to a full cut state (a state where cracks extending from the modified region extend to both end faces of the wafer 20), there is little information on the modified region obtained from the final processed state of the wafer 20, and it may be difficult to determine the suitability of the processing conditions with high accuracy. In this regard, in a state where only a part of the modified region (outer SD layer) is formed, the suitability of the processing conditions (first processing conditions) related to the formation of the part of the modified region is determined based on the information related to the part of the modified region, so that the suitability of the processing conditions can be determined with high accuracy based on the processed state of the wafer 20 where more information (information related to the modified region) is obtained than the final processed state of the wafer 20. According to the findings of the inventors, in a case where the outer SD layer and the inner SD layer are formed in the thickness direction of the wafer 20, it is considered that the state related to the outer SD layer has a greater influence on the quality of the processed wafer 20. In this regard, the suitability of the processing conditions (first processing conditions) related to the formation of the outer SD layer is determined in the second process, so that the quality of the processed wafer 20 can be more suitably guaranteed.

[0123] The control unit 8 specifies 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 specified, and the suitability of the processing conditions to be determined with higher accuracy. This allows the quality of the wafer 20 to be more appropriately guaranteed.

[0124] The control unit 8 identifies the position of the modified region, and judges 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 position. The processing conditions can be appropriately judged by judging whether the processing conditions are appropriate depending on whether the modified region is positioned at the desired position. This makes it possible to more appropriately guarantee the quality of the processed wafer 20.

[0125] The control unit 8 specifies whether the crack 14 has extended to at least one of the back surface 21b and the front surface 21a, and judges whether the processing conditions are appropriate based on whether the crack 14 has extended. As a result, when it is desired to process the wafer 20 into a full-cut state in the final processing state, for example, it is possible to appropriately determine the processing conditions by judging that the crack has not extended to the back surface 21b and the front surface 21a at the stage of the second processing where only the outer SD layer is formed, and that the crack 14 has extended to the back surface 21b and the front surface 21a at the stage of the fourth processing where the outer SD layer and the inner SD layer are formed. As a result, the quality of the wafer 20 after processing can be more appropriately guaranteed.

[0126] The control unit 8 identifies the extension amount of the crack 14, and judges 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 be the desired length. By judging the appropriateness of the processing conditions from the extension amount of the crack 14, the processing conditions can be judged appropriately. This makes it possible to more appropriately guarantee the quality of the wafer 20 after processing.

[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 judges whether the processing conditions are appropriate based on the meandering width. If the processing conditions are not appropriate, the meandering width of the crack 14 may be large. By judging the suitability of the processing conditions from the meandering width of the crack 14, the processing conditions can be judged appropriately. This makes it possible to more appropriately guarantee the quality of the wafer 20 after processing.

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

[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 specifying a state related to the inner SD layer based on a signal output from the imaging unit 4 that detects the light after the fifth process, and judging whether the third processing conditions are appropriate or not based on the specified information. With this configuration, in a state in which only the inner SD layer is formed, the suitability of the processing conditions related to the formation of the inner SD layer (third processing conditions) is judged based on the information related to the inner SD layer. In addition to the case in which the outer SD layer and the inner SD layer are formed and the case in which only the outer SD layer is formed, the suitability of the processing conditions is judged from the information related to the modified region, so that the suitability of the processing conditions can be judged with higher accuracy even in the case in which only the inner SD layer is formed.

[0130] The control unit 8 may determine that the first processing conditions are inappropriate when the crack 14 extends to at least one of the back surface 21b and the front surface 21a when deriving the first processing conditions, and may determine that the third processing conditions are inappropriate when the crack 14 extends to at least one of the back surface 21b and the front surface 21a when deriving the third processing conditions. This ensures that the processing state before the final processing state is in the ST state (a state in which the inside is easily observed). This makes it possible to obtain appropriate and abundant information related to the processing state. 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 thereafter), it is considered that the chip quality and divisibility will deteriorate in the final processing state. For this reason, by setting the ST state in the processing state before the final processing state as a condition in which the processing conditions are deemed appropriate, the chip quality and divisibility can be guaranteed.

[0131] The control unit 8 is configured to further execute a seventh process of correcting the processing conditions in accordance with the judgment result of the processing conditions when the processing conditions are judged to be inappropriate. With such a configuration, the processing conditions are corrected based on the judgment result, and the quality of the processed wafer 20 can be more appropriately guaranteed.

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

[0133] In addition, for example, after a laser beam is irradiated to the wafer 20 along a first direction (X direction) to form a modified region or the like, a modified region may be formed by irradiating the laser beam along a second direction (Y direction) different from the first direction so as to straddle the modified region that has already been formed. In such a case, 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 are different in the X and Y directions (e.g., 0.2 mm × 15 mm), when the quality required by the user is different in the X and Y directions (e.g., the crack meandering is within 2 μm in the X direction and within 10 μm in the Y direction), when the chip size is very small such as 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 the X direction processing (pre-processing) and the Y direction processing (post-processing).

[0134] (Adjusting settings for internal observation) Also, for example, the laser processing device may adjust the settings for internal observation of the wafer in more detail. FIG. 30 is a diagram for explaining the difference in the imaging zone 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 (for example, BHC processing) is performed. In either processing, imaging is also performed for the virtual focal point symmetrical with respect to the surface 21a. That is, in the wafers in FIGS. 30(a) and (b), the lower half SD layer is the area related to the virtual focal point. 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. Also, when full cut processing is performed, the intervals between the modified regions (SD1 to SD4) become narrower, and the extension amount of the crack 14 becomes smaller. For this reason, 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 are adjusted in more detail in the thickness direction of the wafer 20.

[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 for controlling the imaging unit 4 so that aberration correction (optimum 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 according to the position in the thickness direction of the wafer 20. 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.

[0137] Secondly, the control unit 8 is configured to further execute a brightness calibration process for controlling the imaging unit 4 so that the imaging unit 4 outputs light with a light amount corresponding to the position in the thickness direction of the wafer 20 of each region in which imaging is performed by the imaging unit 4, so that imaging is performed by the imaging unit 4 with a predetermined (for example, constant or optimal) brightness for each region in the thickness direction of the wafer 20. In internal observation, the deeper the observation depth, the more light is required to ensure sufficient brightness. That is, the amount of light required for each depth changes. Therefore, it is necessary to grasp the amount of light required to obtain the optimal brightness value for each depth before observation or each time the laser device is started up or the device is changed. In the brightness calibration process, the amount of light when observing each position in the thickness direction is determined, and the imaging unit 4 is set to output light with the determined amount of light when observing each position.

[0138] In the brightness calibration process, as shown in FIG. 31, first, an input related to the brightness calibration is accepted (step S71). The input related to the brightness calibration may be, for example, an input of a wafer thickness input for derivation of processing conditions. Next, the control unit 8 determines a calibration implementation section according to the input related to the brightness calibration (for example, a wafer thickness). The calibration implementation section here is, for example, information on a plurality of ZHs in which the brightness calibration is performed. The calibration implementation section 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 section (step S73). Then, the light amount of the light source 41 is adjusted so that the luminance imaged at the ZH becomes an optimal luminance (step S74), and the ZH and the light amount are stored in correspondence with each other (step S75). The light source 41 is adjusted using an aperture stop or the like. The processes of steps S73 to S75 are performed until the adjustment of the light amount is completed for all ZHs. The amount of light thus adjusted is output from the light source 41 of the imaging unit 4 during observation at each position, so that observation at each position can be performed with appropriate brightness.

[0139] Thirdly, 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 to determine difference data between the image of each region imaged by the imaging unit 4 and the shading image of the corresponding region after processing the modified region. In this case, the control unit 8 determines 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 obtained at each internal observation position (determination position). Then, SD processing is performed, and an image after SD processing is obtained for each internal observation position (determination position) as shown in FIG. 32(b). Then, for each internal observation position, difference data between the image after SD processing and the image for shading (see FIG. 32(c)) is obtained (shading correction is performed). Note that, if there is a positional deviation between the image after SD processing and the image for shading, a correction may be performed according to the amount of deviation. Items that are shaded by shading correction include, for example, device patterns, point defects, uneven brightness of the screen, etc.

[0141] A laser processing method (processing condition derivation process) in the case of performing the above-mentioned aberration correction process, brightness calibration process, and shading correction process will be described with reference to Fig. 33. In Fig. 33, the processing process and the 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 distinguishing). 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 the imaging unit 4 outputs light 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 captures 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). For example, 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.

[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 specifies the state of the SD layer based on the imaging result, and judges whether the processing is appropriate (i.e., whether the processing conditions are appropriate) based on the specified information (step S59). The control unit 8 performs this judgment 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 the processing process is performed again. In this case, as shown in FIG. 33, the process may start from the brightness calibration process (step S52) again, or from the SD processing (step S54). On the other hand, if the processing conditions are appropriate, the control unit 8 determines the processing conditions as the processing conditions, and the process ends.

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

[0148] 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 where the imaging unit 4 captures an image before the modified region is processed, and to further execute a shading correction process to identify difference data between the image of each region captured by the imaging unit 4 and the shading image of the corresponding region after the modified region is processed, and to identify the state of the modified region based on the difference data in the determination process. The difference data acquired by the shading correction process is image data from which noise such as device patterns, point defects, and uneven brightness of the screen has been removed, and is image data of only the modified region and crack state to be observed. The state of the modified region is identified based on such difference data, and the state of the processed wafer 20 is 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 for controlling 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 the modified regions are narrow and the extension amount of the crack is also small, so that clear observation is not possible unless aberration correction is applied to 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 is possible and the state related to the modified region can be more appropriately specified.

[0150] Fig. 34 is a diagram for explaining the effect of performing the aberration correction process, the brightness value calibration process, and the shading correction process. Fig. 34(a) is an image that has not been subjected to any of these processes, Fig. 34(b) is an image that has been subjected to only the aberration correction process, Fig. 34(c) is an image that has been subjected to the aberration correction process and the brightness value calibration process, and Fig. 34(d) is an image that has been subjected to the aberration correction process, the brightness value calibration process, and the shading correction process. As shown in Fig. 34, it can be seen that the sharpness of the crack 14 and the like in the image is greatly improved by performing these processes.

[0151] (Automating the process of deriving processing conditions) In the above-mentioned embodiment, the wafer processing information is input, and the tentative processing conditions are automatically derived, and an estimated processing result image is automatically derived and displayed based on the processing conditions, and an actual processing result image is 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 a processing condition derivation process does not have to be performed entirely automatically.

[0152] For example, in the first step for automating the processing condition derivation process, the user may manually generate and set processing conditions (tentative processing conditions) based on the wafer processing information. Then, the actual processing results under the generated processing conditions may be acquired, and the actual processing results may be stored in the database in association with 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 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 analysis method. Specifically, analysis 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 processing conditions may be adjusted for the input wafer processing information and input (simulated) into the regression model to search for optimal processing conditions for outputting a target processing result. As such an optimization method, for example, a grid search, a random search, a Bayesian optimization, or the like may be used.

[0155] Furthermore, in the fourth step, the simulation result (estimated machining result) is compared with the actual machining result, and if the conditions need to be corrected, the data is stored in a database, and the 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 result and the actual machining result, the accuracy of the regression model can be improved by feeding back the actual machining result. [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 transmissive to the wafer and detects the light that has propagated through the wafer; A control unit, The control unit is 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 detects 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 image each region in the thickness direction of the wafer at a predetermined brightness.

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. The control unit, in the luminance calibration process, Receiving an input related to luminance calibration; determining a calibration execution interval in response to the input; and adjusting an amount of light output from the imaging unit so that a desired luminance is obtained when the imaging unit captures an image for each region in the calibration implementation section.

4. The control unit is In the first process, the irradiation unit is controlled under the first processing conditions set so that a second modified region located closer to the incident surface of the laser light than the first modified region is further formed; The laser processing apparatus according to claim 1 , wherein in the second process, a state relating to the second modified region is further specified, and whether or not the first processing conditions are appropriate is determined based on the specified information.

5. The control unit is 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 a thickness direction of the wafer; and The laser processing apparatus of claim 4, further configured to execute a fourth process after the third process, in which conditions relating to the first modified region, the second modified region, and the third modified region are identified based on a signal output from the imaging unit that detects the light, and whether or not the second processing conditions are appropriate is determined based on the identified information.

6. The laser processing device according to claim 5 , wherein the control unit specifies at least one of a state of the modified region and a state of a crack extending from the modified region as the state related to the modified region.

7. The laser processing device according to claim 6 , wherein the control unit identifies a position of the modified region, and determines whether or not the processing conditions are appropriate based on the specified position.

8. The laser processing apparatus of claim 6 or 7, wherein 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.

9. The laser processing apparatus of claim 8, wherein the control unit determines that the first processing conditions are inappropriate when the crack propagates to at least one of the first surface and the second surface during the second process.

10. 8. The laser processing apparatus according to claim 6, wherein the control unit specifies an extension amount of the crack, and determines whether the processing conditions are appropriate based on the extension amount.

11. 8. The laser processing apparatus according to claim 6, wherein the control unit identifies a meandering width of the crack in a direction intersecting a thickness direction of the wafer, and determines whether the processing conditions are appropriate based on the meandering width.

12. The laser processing apparatus according to claim 6 or 7, wherein the control unit identifies whether or not cracks extending from different modified regions are connected to each other, and determines whether or not the processing conditions are appropriate based on whether or not the cracks are connected to each other.

13. The control unit is 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 6, further configured to execute a sixth process after the fifth process, which identifies a state relating to the third modified region based on a signal output from the imaging unit that detects the light, and determines whether the third processing conditions are appropriate based on the identified information.

14. The laser processing apparatus according to claim 13, 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.

15. The control unit is 6. The laser processing apparatus according to claim 5, further comprising: a seventh process for correcting the processing conditions in accordance with a result of the determination of the processing conditions when the processing conditions are determined to be inappropriate.

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

17. The control unit is 2. The laser processing apparatus according to claim 1, further configured to execute an aberration correction process for controlling at least one of the irradiation unit and the imaging unit so that aberration correction according to a 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.

18. processing the wafer under first processing conditions set so that a first modified region is formed inside the wafer by irradiating the wafer with laser light; Identifying a state related to the first modified region based on an imaging result of the wafer processed based on the first processing conditions; and performing a brightness calibration process that outputs light for imaging with an amount of light corresponding to a position of each region in the thickness direction of the wafer, so that imaging is performed at a predetermined brightness for each region in the thickness direction of the wafer.

Images