Inspection device and inspection method

Abstract

To ensure the quality of a wafer 20 to be processed into a full-cut state.SOLUTION: An inspection device 1 includes a laser irradiation unit 3, an imaging unit 4, and a control unit 8. The control unit 8 is configured to execute: treatment processing of controlling a laser irradiation unit 3 with a recipe set into a full-cut state in which a plurality of modified regions 12 is formed inside a wafer 20 when the wafer 20 is irradiated with a laser beam, and a crack 14 extending from the modified regions 12 reaches a back surface 21b and a front surface 21a; identifying processing of identifying the state of the crack 14 extending from the modified region 12 on the back surface 21b and at least one of the states of the modified region 12 and the crack 14 inside the wafer 20 on the basis of a signal output from the imaging unit 4; and determination processing of determining whether dividing force for the wafer 20 according to the recipe is appropriate on the basis of the information identified in the identifying processing.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an inspection device and an inspection method. [Background technology]

[0002] In order to cut a wafer having a semiconductor substrate and a functional element layer formed on one surface of the semiconductor substrate along each of a plurality of lines, an inspection device is known that irradiates a laser beam onto the wafer from the other surface side of the semiconductor substrate to form a plurality of rows of modified regions inside the semiconductor substrate along each of the plurality of lines. The inspection device described in Patent Document 1 is equipped with an infrared camera, and is capable of observing 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 inspection device as described above, the modified region may be formed in response to a user's request so that the crack extending from the modified region extends to both end faces of the wafer (full cut state). Whether or not the wafer is in the full cut state is determined, for example, by observing the state of both end faces of the wafer. Here, although it is possible to determine whether or not the wafer is in the full cut state by observing the state of both end faces of the wafer, it is not possible to determine during inspection whether or not the inside of the wafer in the full cut state is in an appropriate state (maintains quality). As a result, it may not be possible to fully guarantee the quality of the wafer to be processed into the full cut state.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide an inspection apparatus and an inspection method capable of guaranteeing the quality of wafers to be processed into a full-cut state. [Means for solving the problem]

[0006] An inspection device according to one embodiment of the present invention includes an irradiation unit that irradiates a wafer with laser light from the 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, and the control unit is configured to execute a first process of controlling the irradiation unit under processing conditions that are set so that the laser light is irradiated onto the wafer to form one or more modified regions inside the wafer and a full cut state is achieved in which cracks extending from the modified regions reach the first surface and the second surface; a second process of identifying the state of the cracks extending from the modified regions on the first surface and the state of at least one of the modified regions and cracks inside the wafer based on a signal output from the imaging unit that detects the light; and a third process of determining whether the dividing force on the wafer is appropriate according to the processing conditions based on the information identified in the second process.

[0007] In an inspection device according to one aspect of the present invention, a laser beam is irradiated under processing conditions set so that a full cut state is reached in which a crack extending from a modified region reaches the first surface and the second surface of the wafer. Then, the state of the crack on the first surface and at least one state of the modified region and the crack inside the wafer are specified, and based on the specified information, it is determined whether the dividing force for the wafer according to the processing conditions is appropriate or not. In this way, by specifying at least one state of the modified region and the crack inside the wafer in addition to the state of the crack on the first surface, which is the incident surface of the laser beam, the appropriateness of the dividing force for the wafer to be in the full cut state is determined taking into account not only the information on the edge surface (first surface) of the wafer but also the information on the inside of the wafer. This makes it possible to determine that the dividing force is not appropriate, for example, when the quality of the inside of the wafer has deteriorated even though the wafer is in the full cut state. This makes it possible to guarantee the quality of the wafer to be processed into the full cut state.

[0008] The control unit may specify the width of the meandering of the crack in the wafer in the second process in a direction intersecting the wafer thickness direction, and may determine in the third process that the dividing force is beyond the appropriate range and is not appropriate when the specified meandering width of the crack is greater than a predetermined value. If the dividing force is too large, the crack may meander significantly in the wafer in the direction intersecting the wafer thickness direction. The portion where the crack meanders in this way becomes an uneven portion on the end surface after the wafer is cut. For this reason, by determining that the dividing force is too large when the meandering width of the crack becomes large and correcting the dividing force as necessary, the occurrence of uneven portions on the end surface can be suppressed, and the quality of the wafer to be processed into a full cut state can be appropriately guaranteed.

[0009] In the second process, the control unit may determine a position inside the wafer where it is assumed that the crack is likely to meander, according to the wafer information, and specify the width of the crack's meander at the determined position. For example, the location where the crack is likely to meander can be predicted to some extent depending on the wafer thickness, etc. Therefore, by specifying the width of the crack's meander at a position inside the wafer where it is assumed that the crack is likely to meander, taking into account the wafer information such as the wafer thickness and the laser processing conditions such as the laser focusing position, it is possible to efficiently and appropriately determine the width of the crack's meander.

[0010] The control unit may specify the clarity of the laser light mark on the modified region in the second process, and in the third process, when the clarity of the specified mark is higher than a predetermined value, determine that the cutting force does not reach the appropriate range and is not appropriate. When the full cut state is reached, the mark on the modified region is observed vaguely and the clarity is low. On the other hand, when the full cut state is not reached, the mark on the modified region is observed clearly and the clarity is high. Therefore, when the clarity of the mark is high, the cutting force is determined to be small and a correction or the like is performed to increase the cutting force as necessary, thereby reliably achieving the full cut state and appropriately ensuring the quality of the wafer to be processed into the full cut state.

[0011] The control unit may specify the state of the crack on the first surface in the second process, and in the third process, when the specified state of the crack is a stealth state in which the crack has not reached the first surface, determine that the dividing force has not reached the appropriate range and is not appropriate. If the crack has not reached the first surface and is not in a half-cut state (stealth state), it is naturally not in a full-cut state. For this reason, when the half-cut state is not reached, the dividing force is determined to be small and a correction such as increasing the dividing force is performed as necessary, thereby reliably achieving the full-cut state and appropriately guaranteeing the quality of the wafer to be processed into the full-cut state.

[0012] The control unit may, in the second process, specify the width of the meandering of the crack in a direction intersecting the thickness direction of the wafer on the first surface, and in the third process, determine that the dividing force is outside the appropriate range and is not appropriate if the specified meandering width of the crack is greater than a predetermined value. If the crack on the first surface meanders significantly in a direction intersecting the thickness direction of the wafer, it is considered that the dividing force is too large. Therefore, if the meandering width of the crack on the first surface is greater than a predetermined value, the dividing force is determined to be large, and corrections such as reducing the dividing force are performed as necessary, thereby appropriately ensuring the quality of the wafer to be processed into a full cut state.

[0013] The control unit may specify the state of the crack on the second surface in the second process, and in the third process, when the specified state of the crack is a stealth state in which the crack has not reached the second surface, determine that the dividing force has not reached the appropriate range and is not appropriate. If the crack has not reached the second surface and is not in a BHC state (stealth state), it is naturally not in a full cut state. For this reason, if the BHC state is not reached, the dividing force is determined to be small and a correction such as increasing the dividing force is performed as necessary, thereby reliably achieving the full cut state and appropriately ensuring the quality of the wafer to be processed into the full cut state.

[0014] The control unit is configured to further execute a fourth process to correct the machining conditions so that the cutting force is within an appropriate range when it is determined in the third process that the cutting force is not appropriate, and may execute the first process, the second process, and the third process again under the machining conditions corrected in the fourth process. In this way, by executing each process again under the machining conditions corrected so that the cutting force is within the appropriate range, it is possible to determine whether the corrected machining conditions are appropriate and to reliably derive appropriate machining conditions.

[0015] The control unit may control the irradiation unit to form a plurality of modified regions in the first process, and execute the second process and the third process after the last modified region is formed in the first process. This makes it possible to determine whether or not the dividing force applied to the wafer to achieve the full cut state is appropriate based on the state of the wafer after all modified regions are formed (i.e., the state that should be the full cut state).

[0016] The inspection device according to one aspect of the present invention includes an irradiation unit that irradiates a wafer with laser light from the 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 propagated through the wafer, and a control unit. The control unit is configured to execute a first process that controls the irradiation unit under processing conditions set so that the wafer is irradiated with the laser light to form a plurality of modified regions inside the wafer and a full cut state in which cracks extending from the modified regions reach the first surface and the second surface, a pre-identification process that identifies information related to the modified regions and the cracks extending from the modified regions based on a signal output from the imaging unit that detects the light before the modified region that is finally formed in the first process is formed, and a pre-determination process that determines whether the state before the modified region that is finally formed is appropriate based on the information identified in the pre-identification process. In the full cut state, it may be difficult to observe the detailed state inside the wafer. In this regard, before the modified region that is finally formed is formed, details of the modified regions and information related to the cracks (such as the modified layer position and the crack length) can be observed (identified), making it possible to make a more detailed determination compared to the determination in the full cut state. Then, by determining whether the state before the finally formed modified region is formed is appropriate or not, the quality of the wafer to be processed into a full cut state can be guaranteed.

[0017] The control unit is configured to further execute a pre-correction process to correct the processing conditions when the pre-determination process determines that the state before the finally formed modified region is formed is not appropriate, and may execute the first process, the pre-identification process, and the pre-determination process again under the processing conditions corrected in the pre-correction process. In this way, by correcting the processing conditions when the pre-determination process determines that the state is not appropriate, the quality of the wafer to be processed into the full cut state can be guaranteed.

[0018] An inspection method according to one embodiment of the present invention includes a first step of irradiating laser light from the first surface side of a wafer having a first surface and a second surface under processing conditions set so that one or more modified regions are formed inside the wafer and cracks extending from the modified regions reach the first surface and the second surface to create a full cut state; a second step of outputting light that is transparent to the wafer in which a modified region has been formed by the first step, and identifying the state of the crack extending from the modified region on the first surface and the state of at least one of the modified region and the crack inside the wafer based on a signal output by detecting the light that has propagated through the wafer; and a third step of determining whether the cutting force applied to the wafer is appropriate according to the processing conditions based on the information identified in the second step. Effect of the Invention

[0019] According to the present invention, the quality of the wafers processed into a fully cut state can be guaranteed. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a configuration diagram of an inspection device according to an 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 the state of a wafer according to a cutting force applied to the wafer. [Figure 14] 1A and 1B are diagrams for explaining the reason why internal observation is necessary when performing laser processing under full-cut conditions. [Figure 15] 1A to 1C are diagrams illustrating the observation results for each state of a wafer. [Figure 16] FIG. 13 is a diagram illustrating the observation of the width of a meandering crack. [Figure 17] 1A and 1B are diagrams for explaining regions where end surface irregularities occur for each thickness of a wafer. [Figure 18] 11A and 11B are diagrams illustrating a machining condition derivation process. [Figure 19] 13 is a screen image relating to a machining condition derivation process. [Figure 20] 13 is a screen image relating to a machining condition derivation process. [Figure 21] 13 is a screen image relating to a machining condition derivation process. [Figure 22] 13 is a screen image relating to a machining condition derivation process. [Diagram 23] 13 is a screen image relating to a machining condition derivation process. [Figure 24] 13 is a screen image relating to a machining condition derivation process. [Diagram 25] 1 is a flowchart of an inspection method (processing condition derivation process). [Figure 26] 13A to 13C are diagrams illustrating a machining condition derivation process according to a modified example. [Figure 27] 13 is a screen image relating to a machining condition derivation process according to a modified example. [Figure 28] 13 is a screen image relating to a machining condition derivation process according to a modified example. [Figure 29] 13 is a flowchart of an inspection method (processing condition derivation process) according to a modified example. [Diagram 30] FIG. 13 is a diagram illustrating crack detection. [Diagram 31] FIG. 13 is a diagram illustrating crack detection. [Diagram 32] FIG. 13 is a diagram illustrating a scratch detection. [Diagram 33] FIG. 13 is a diagram illustrating a scratch detection. [Diagram 34] FIG. 13 is a diagram illustrating a scratch detection. [Diagram 35] 11A and 11B are diagrams illustrating differences in imaging sections depending on processing methods. [Diagram 36] 13 is a flowchart of a luminance calibration process. [Figure 37] 13 is a flowchart of a shading correction process. [Figure 38] 13 is a flowchart of a laser processing method (processing condition derivation process) when various correction processes are performed. [Figure 39] This is an image that has been subjected to various correction processes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] 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. [Inspection equipment configuration]

[0022] 1, the inspection device 1 includes a stage 2, a laser irradiation unit 3 (irradiation section), a plurality of imaging units 4, 5, and 6, a drive unit 7, a control section 8, and a display 150 (input section, display section). The inspection device 1 is a device that forms a modified region 12 in an object 11 by irradiating the object 11 with laser light L.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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 .

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] [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.

[0033] 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.

[0034] [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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] [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.

[0040] 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.

[0041] 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.

[0042] [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.

[0043] 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.

[0044] 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.

[0045] [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.

[0046] 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.

[0047] 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.

[0048] 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)).

[0049] 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).

[0050] [Processing condition derivation process] The following describes a cleaving force determination process in a processing condition derivation process, which 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 following describes an example of the cleaving force determination process in the processing condition derivation process, but the cleaving force determination process may be executed in a process 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 under what conditions and procedures the wafer 20 is processed.

[0051] The dividing force is a force applied to the wafer 20 by irradiation with a laser beam, which is related to dividing (cutting) the wafer 20. FIG. 13 is a diagram for explaining the state of the wafer 20 according to the dividing force applied to the wafer 20. In FIG. 13(a) to FIG. 13(d), the upper diagrams show the actual state (observed state) of the cross section of the wafer 20, and the lower diagrams show the cross section shown in the upper diagram. As shown in the lower diagrams of FIG. 13(a) to FIG. 13(d), five rows of modified regions 12a to 12e are formed on each wafer 20, starting from the side close to the surface 21a, which is the opposite side to the laser beam incident surface. In the example shown in FIG. 13, the dividing force applied to the wafer 20 increases in the order of FIG. 13(d), FIG. 13(c), FIG. 13(b), and FIG. 13(a). In the state of FIG. 13(a) where the dividing force is the smallest, the cracks 14 do not occur above or below the modified region (SD layer), and the cracks 14 do not reach either the back surface 21b or the front surface 21a, which is an ST (Stealth) state. In the state of FIG. 13(b), the cracks 14 occur above and below at least the modified regions 12a, 12d, and 12e, and the cracks 14 reach the back surface 21b, which is a half-cut (HC) state. In FIG. 13(b), the cracks 14 do not reach the front surface 21a (ST state). In the state of FIG. 13(c), the cracks 14 occur above and below all the modified regions 12a to 12e, and the cracks 14 reach the back surface 21b, which is an HC state, and the cracks 14 reach the front surface 21a, which is a BHC (Bottom side half-cut) state. Thus, the state of FIG. 13(c) is a full-cut state in which the cracks 14 reach the back surface 21b and the front surface 21a. Even if there are very small areas inside the wafer 20 where the cracks 14 are not connected, the state is considered to be a full cut state if the unconnected areas can be connected by standard tape expand (e.g., tape expand with an expansion amount of 15 mm and an expansion speed of 5 mm / sec) to a level that allows the wafer 20 to be divided. Areas where the cracks 14 are not connected very small include resolidified areas in the modified layer (areas that resolidify after melting during laser irradiation) or black streak areas where the cracks 14 are not connected intentionally to improve chip quality.

[0052] Similarly, even in the state of FIG. 13(d) where the dividing force is the largest, the crack 14 reaches the back surface 21b and the front surface 21a, resulting in a full cut state. Here, as shown in the lower diagram of FIG. 13(d), in the example of FIG. 13(d), the crack 14 meanders in a direction intersecting the thickness direction (Z direction) of the wafer 20 due to the excessively large dividing force. In this way, when the dividing force is too large, it is considered that the crack 14 will greatly meander in a direction intersecting the Z direction inside the wafer 20. The portion where the crack 14 meanders becomes an end surface uneven portion after the wafer 20 is cut. As described above, even when laser processing is performed for the purpose of achieving a full cut state, for example, and a full cut state is achieved, the quality of the inside of the wafer 20 may be deteriorated depending on the dividing force. In this embodiment, the inside of the wafer 20 is observed to determine whether the dividing force is within an appropriate range, and if it is not within the appropriate range, a correction process of the recipe (processing conditions) is performed so that the dividing force is within the appropriate range. In this manner, by executing the separation force determination process and the correction process, it is possible to derive an appropriate recipe (processing conditions) that takes the separation force into consideration.

[0053] The reason why the inside of the wafer 20 needs to be observed will be further explained with reference to FIG. 14. As described above, when laser processing is performed for the purpose of achieving a full cut state, even if it is confirmed that the crack 14 has reached the back surface 21b, which is the laser incident surface, if the crack condition inside the wafer 20 is poor, the device quality will be NG. An example of a poor crack condition is, for example, the occurrence of the above-mentioned uneven edge portion. The occurrence of the uneven edge portion may cause defects such as defective chip size, reduced chip flexural strength, and particle generation, resulting in NG device quality. In the example of the cross section shown in FIG. 14(a), the crack 14 generated inside the wafer 20 stops on the way to the back surface 21b, so that the crack 14 near the back surface 21b extends straight, but in the center part of the wafer 20 in the Z direction, the crack 14 is formed in a curved (meandering) manner. Thus, depending on the processing method, the crack condition near the back surface 21b can be normalized by stopping the extension of the crack 14, but the crack condition inside the wafer 20 may deteriorate. Considering such a case, the inside of the wafer 20 needs to be observed. Furthermore, as shown in the schematic cross-sectional view of FIG. 14(b), when the quality of the incident surface is particularly important, a reverse SD method may be adopted in which the modified region (SD1) closest to the rear surface 21b, which is the incident surface, is formed first, and then the other modified regions (SD2 to SD4) are formed. Even in this case, although the crack state of the rear surface 21b is normal, problems such as the crack 14 not continuing inside the wafer 20 may occur, for example, as shown in FIG. 14(b). Considering such a case, it is necessary to observe the inside of the wafer 20.

[0054] FIG. 15 is a diagram showing a schematic diagram of the internal observation results for each state of the wafer 20. FIG. 15(a) to FIG. 15(d) are the internal observation results corresponding to the states of FIG. 13(a) to FIG. 13(d). That is, FIG. 15(a) is the internal observation result of the ST state in which the crack 14 has not reached both the back surface 21b and the front surface 21a, FIG. 15(b) is the internal observation result of the HC state in which the crack 14 has reached only the back surface 21b, FIG. 15(c) is the internal observation result of the full cut state (good internal state) in which the crack 14 has reached the back surface 21b and the front surface 21a, and FIG. 15(d) is the internal observation result of the full cut state (poor internal state) in which the crack 14 has reached the back surface 21b and the front surface 21a. FIG. 15(a) to FIG. 15(d) show the observation results of the back surface 21b (incident surface), the modified region 12d (SD4), and the modified region 12c (SD3) in each state. Each internal observation result is obtained by focusing F on each point from the rear surface 21b side using the imaging unit 4 (based on a signal output from the imaging unit 4 that detects light from each point).

[0055] Regarding the incident surface, the crack 14 is not observed in the ST state of FIG. 15(a), but is observed in each state of FIG. 15(b) to FIG. 15(d). Regarding the modified region 12d (SD4), the sag De is clearly observed in the ST state of FIG. 15(a) and the HC state of FIG. 15(b), but is vaguely observed in the full cut state of FIG. 15(c) and FIG. 15(d). Regarding the modified region 12c (SD3), the sag De is clearly observed in the ST state of FIG. 15(a) and the HC state of FIG. 15(b), but is vaguely observed in the full cut state (good internal condition) of FIG. 15(c). Moreover, in the full cut state (poor internal condition) of FIG. 15(d), when the focus F is focused on the modified region 12c (SD3), the meandering portion of the crack 14, which becomes the end surface unevenness portion after cutting, is observed.

[0056] FIG. 16 is a diagram for explaining the observation of the width of the meandering crack 14. FIG. 16(a) shows an example of observing the tip of the crack 14 extending in the vertical direction from the modified regions 12a and 12b, and FIG. 16(c) shows an example of observing the width (width of the shadow of the crack 14) of the meandering crack 14 between the modified regions 12c and 12d. In the state shown in FIG. 16(a), when the focal point F is moved from the back surface 21b side toward the front surface 21a side, the tip of the crack 14 extending from the modified region 12b to the back surface 21b side is observed as shown in the upper diagram of FIG. 16(b). In addition, by moving the focal point F to the tip of the crack 14 extending from the modified region 12a to the front surface 21a side (or a point symmetrical to the tip of the crack 14 with respect to the front surface 21a), the tip of the crack 14 extending from the modified region 12b to the front surface 21a side is observed as shown in the lower diagram of FIG. 16(b). Similarly, when observing the width of the meandering crack 14 as shown in Fig. 16(c), the focus F is moved in the Z direction from the back surface 21b side toward the front surface 21a side. Then, as shown in Fig. 16(d), when the focus F reaches the meandering portion of the crack 14, a region in which the width of the shadow of the crack 14 is not constant is observed. In this way, by observing the width of the shadow of the crack 14, the meandering portion of the crack 14 can be identified.

[0057] Fig. 17 is a diagram illustrating an area where end surface irregularities occur (the meandering portion of the crack 14) for each thickness of the wafer 20. Fig. 17(a) shows a cross section of the wafer 20 having a thickness of 500 μm and in which the meandering portion of the crack 14 occurs, Fig. 17(b) shows a cross section of the wafer 20 having a thickness of 500 μm and in which the meandering portion of the crack 14 does not occur, Fig. 17(c) shows a cross section of the wafer 20 having a thickness of 400 μm and in which the meandering portion of the crack 14 occurs, and Fig. 17(d) shows a cross section of the wafer 20 having a thickness of 400 μm and in which the meandering portion of the crack 14 does not occur. As shown in FIG. 17(a), in the wafer 20 having a thickness of 500 μm, a meandering portion of the crack 14 (region where end surface irregularities are generated) occurs between SD2 and SD3, which are modified regions, whereas as shown in FIG. 17(c), in the wafer 20 having a thickness of 400 μm, a meandering portion of the crack 14 (region where end surface irregularities are generated) occurs between SD3 and SD4, which are modified regions. In this manner, the region where the meandering portion of the crack 14 occurs differs depending on the thickness of the wafer 20. For this reason, the control unit 8 may determine a position inside the wafer 20 where the meandering of the crack 14 is likely to occur according to information on the wafer 20 (e.g., the thickness of the wafer 20) and laser processing conditions (e.g., the laser focusing position inside the wafer 20, etc.), and determine whether or not the meandering width of the crack 14 is greater than a predetermined value at the determined position, thereby determining the crack state inside the wafer 20.

[0058] In the processing condition derivation process, the control unit 8 is configured to execute a determination process for determining a recipe (processing conditions) including the irradiation conditions of the laser light by the laser irradiation unit 3 based on the information received by the display 150; a processing process (first process) for controlling the laser irradiation unit 3 with a recipe (processing conditions) set so that the wafer 20 is irradiated with laser light to form multiple modified regions 12 inside the wafer 20 and a full cut state in which the cracks 14 extending from the modified regions 12 reach the back surface 21b and the front surface 21a; a specification process (second process) for identifying the state of the cracks 14 extending from the modified regions 12 on the back surface 21b and at least one state of the modified regions 12 and the cracks 14 inside the wafer 20 based on a signal output from the imaging unit 4 that detects the light; a judgment process (third process) for determining whether the dividing force for the wafer 20 according to the recipe is appropriate based on the information identified in the specification process; and a correction process (fourth process) for correcting the recipe so that the dividing force is within an appropriate range if it is determined in the judgment process that the dividing force is not appropriate.

[0059] FIG. 18 is a diagram for explaining an outline of the processing condition derivation process. In the processing condition derivation process, as described above, the processing of the wafer 20 is performed with a recipe (processing conditions) set to obtain a full cut state, and whether or not the dividing force for the wafer 20 (dividing force under full cut conditions) is appropriate is determined based on the state of the crack 14 on the back surface 21b and the internal state of the wafer 20. In determining whether or not the dividing force is appropriate, specifically, as shown in FIG. 18, the observation results of the incident surface state, the scratch state, the meandering state of the crack, and the incident back surface state are referenced. FIG. 18(a) shows a schematic diagram of the wafer 20 in a full cut state in which the crack 14 has reached the back surface 21b and the front surface 21a. For such a wafer 20, the incident surface state (state of the back surface 21b) is observed as shown in FIG. 18(b), and it is determined whether or not the wafer 20 is in an HC state in which the crack 14 has reached the back surface 21b, and whether or not the width of the crack 14 in the direction intersecting the Z direction, which is the thickness direction of the wafer 20, on the back surface 21b is larger than a predetermined value. The state of the sag is also observed to determine whether the sag is clear and sharp (see FIG. 18(c)) or vague and unclear (see FIG. 18(d)). The width of the shadow of the crack 14 between the modified regions (for example, between SD3 and SD4) (see FIG. 18(e)) is also observed to determine whether the width of the crack is larger than a predetermined value. The state of the incident back surface (state of the front surface 21a) is also observed to determine whether the crack 14 has reached the front surface 21a and is in a BHC state. Each step of the processing condition derivation process will be described below.

[0060] (Decision making process) The determination process will be described with reference to Figs. 19 to 21. In the determination process, first, the display 150 accepts user input of wafer processing information. The wafer processing information is information for deciding a recipe (processing conditions). Fig. 19 is an example of a setting screen (user input receiving screen) of wafer processing information displayed on the display 150. As shown in Fig. 19, "FC determination", "wafer thickness", "device type", and "processing setting" are displayed on the display 150. "FC determination" is information indicating that a determination regarding a dividing force under full cut conditions is performed after a modified region (modified region to be formed last) that is expected to be in a full cut state is formed. In the example shown in Fig. 19, "FC determination" is set to "execute", and this setting screen does not accept user input (change of the determination mode by the user). "Wafer thickness" is information indicating the thickness of the wafer 20. "Wafer thickness" is input by, for example, a user selecting from a plurality of options. "Device type" is information indicating the type of the wafer 20. "Device type" is indicated by, for example, a type such as a "0°" product or a "45°" product depending on the position of the notch. "Device type" is input by, for example, the user selecting from a number of options. "Processing settings" are setting information related to the laser processing desired by the user. "Processing settings" are input by, for example, the user selecting from a number of options. At least one of "wafer thickness," "device type," and "processing settings" needs to be input. When input is completed on the setting screen of FIG. 19, the screen transitions to the screen of FIG. 20.

[0061] FIG. 20 is an example of a judgment content confirmation screen displayed on the display 150. The judgment content confirmation screen is a screen for displaying information related to the judgment (judgment after processing) performed based on the contents inputted in the setting screen of FIG. 19. As shown in FIG. 20, the judgment content confirmation screen mainly displays the judgment content and the judgment criteria. The judgment content displays the contents of "FC judgment", "wafer thickness", "device type", and "processing setting" set (or derived from the set information) in the setting screen of FIG. 19. The judgment criteria displays the pass criteria in the judgment process, and the pass criteria of "crack state of the incidence surface" and "HC straightness" are displayed as the pass criteria of the laser incidence surface inspection (inspection of the state of the crack 14 extending from the modified region 12 on the back surface 21b), and the pass criteria of "crack state of the incidence back surface", "end surface unevenness position", "end surface unevenness width", and "scratch observation" are displayed as the pass criteria of the wafer internal inspection (inspection of the state of the modified region 12 and the crack 14 inside the wafer 20). The "crack state of the incident surface" is information indicating whether or not the crack 14 has reached the rear surface 21b, which is the incident surface of the laser light. In order to judge the dividing force under the full cut condition, the pass criterion for the "crack state of the incident surface" is the HC state. The "HC straightness" is information indicating the width of the meandering of the crack 14 in the direction intersecting the Z direction, observed on the rear surface 21b. The pass criterion for the "HC straightness" can be input (selected) by the user. The "crack state of the incident rear surface" is information indicating whether or not the crack 14 has reached the front surface 21a. In order to judge the dividing force under the full cut condition, the pass criterion for the "crack state of the incident rear surface" is the BHC. The "end surface unevenness position" is information indicating the position at which the judgment regarding the end surface unevenness (the meandering of the crack 14) is made. The "end surface unevenness position" is defined as the position between the modified regions, for example, "between SD3 and SD4". ​​The information for the "end surface unevenness position" can be input (selected) by the user. "End surface irregularity width" is information indicating the width of the meandering of the crack 14 in a direction intersecting the Z direction, observed at the position specified by "end surface irregularity position." The pass criteria for "end surface irregularity width" can be input (selected) by the user. "Scratch observation" is information indicating the observation results regarding the clarity of the scars related to each modified area.In order to judge the cutting force under full-cut conditions, the pass criterion for "mark observation" is set to "vague." When the input and confirmation on the confirmation screen of FIG. 20 are completed, the screen of FIG. 21 will be displayed.

[0062] FIG. 21 is an example of a processing condition confirmation screen displayed on the display 150. The processing condition confirmation screen is a screen for displaying a recipe (processing conditions) determined by the control unit 8 based on the contents inputted on the setting screen of FIG. 19. As shown in FIG. 21, the processing condition confirmation screen displays "number of processing", "ZH (Z height)", "VD", "number of focal points", "pulse energy", "focus state parameter", "processing speed", "frequency", and "pulse width". The Z height is information indicating the processing depth (height) when performing laser processing. The VD is the Z interval between the SD layers during multi-focus processing. The focus state parameter is a parameter for varying the laser focus state such as spherical aberration and astigmatism. Each piece of information displayed on the processing condition confirmation screen can be corrected by user input. Note that the optimal focus correction amount (for example, spherical aberration) differs between a shallow position and a deep position inside the silicon of the wafer 20. In the full cut process, the amount of scanning in the Z direction is large, so that more detailed imaging is possible by changing the focus correction amount for each Z position.

[0063] (Processing) In the processing, the control unit 8 controls the laser irradiation unit 3 according to the recipe (processing conditions) determined in the determination process and set. The set recipe is a recipe that is set so that the wafer 20 is irradiated with laser light to form multiple modified regions 12 inside the wafer 20 and to form a full cut state in which cracks 14 extending from the modified regions 12 reach the back surface 21b and the front surface 21a. In the processing, the control unit 8 controls the laser irradiation unit 3 so that multiple modified regions 12 are formed.

[0064] (Specific processing) In the identification process, the control unit 8 identifies the state of the crack 14 extending from the modified region 12 on the back surface 21b, and at least one of the states of the modified region 12 and the crack 14 inside the wafer 20, based on a signal output from the imaging unit 4 that detects light. That is, the control unit 8 identifies the state of the crack 14 extending from the modified region 12 on the back surface 21b, and at least one of the states of the modified region 12 and the crack 14 inside the wafer 20, based on the observation results of the back surface 21b and the inside of the wafer 20 by the imaging unit 4. In this embodiment, the control unit 8 executes the identification process after all modified regions 12 (the modified region 12 formed last) are formed.

[0065] The control unit 8 specifies the state of the crack 14 on the back surface 21b based on the observation result of the back surface 21b by the imaging unit 4. Specifically, the control unit 8 specifies whether the state is an ST state in which the crack 14 has not reached the back surface 21b, or an HC state in which the crack 14 has reached the back surface 21b. Based on the observation result of the back surface 21b by the imaging unit 4, the control unit 8 specifies the width of the meandering of the crack 14 on the back surface 21b in a direction intersecting the thickness direction (Z direction) of the wafer 20.

[0066] The control unit 8 determines the width of the meandering of the crack 14 in the direction intersecting the thickness direction (Z direction) of the wafer 20, inside the wafer 20, based on the observation results of the inside of the wafer 20 (e.g., between the multiple modified regions 12) by the imaging unit 4. The control unit 8 may determine a position inside the wafer 20 where the meandering of the crack 14 is likely to occur, based on information of the wafer 20 input (or estimated) by the user, such as the thickness of the wafer 20, or laser processing conditions (e.g., the laser focusing position, etc.), and may determine the width of the meandering of the crack 14 based on the observation results at the determined position. Alternatively, the control unit 8 may obtain the observation results over the entire thickness direction (Z direction) of the wafer 20, and determine the maximum value of the meandering width of the crack 14.

[0067] The control unit 8 determines the clarity of the laser light mark De on the modified region 12 based on the observation result of the inside of the wafer 20 (e.g., each modified region 12) by the imaging unit 4. Specifically, the control unit 8 determines that the mark De is clear when it is clearer than a predetermined clarity, and determines that the mark De is vague when it is not clearer than the predetermined clarity. The control unit 8 determines the reach state of the crack 14 on the surface 21a based on the observation result of the surface 21a by the imaging unit 4. Specifically, the control unit 8 determines whether the state is an ST state in which the crack 14 has not reached the surface 21a, or a BHC state in which the crack 14 has reached the surface 21a.

[0068] (Decision making process) In the determination process, the control unit 8 determines whether the dividing force for the wafer 20 according to the recipe is appropriate (appropriate as a dividing force under full cut conditions) based on the information identified in the identification process. When the identified reached state of the crack 14 is the ST state in which the crack 14 has not reached the back surface 21b, the control unit 8 determines that the dividing force does not reach the appropriate range and is not appropriate. When the identified meandering width of the crack 14 on the back surface 21b is larger than a predetermined value (for example, several μm to several tens of μm), the control unit 8 determines that the dividing force exceeds the appropriate range and is not appropriate.

[0069] When the identified meandering width of the crack 14 inside the wafer 20 is greater than a predetermined value (e.g., several μm to several tens of μm), the control unit 8 determines that the dividing force exceeds the appropriate range and is inappropriate. When the identified sharpness of the crease is higher than a predetermined sharpness and the crease is clear, the control unit 8 determines that the dividing force does not reach the appropriate range and is inappropriate. When the identified reached state of the crack 14 is the ST state in which the crack 14 has not reached the surface 21a, the control unit 8 determines that the dividing force does not reach the appropriate range and is inappropriate.

[0070] FIG. 22 is an example of a judgment result confirmation screen displayed on the display 150. The judgment result confirmation screen is a screen that displays the judgment result in the judgment process and accepts user input related to recipe correction. In the example shown in FIG. 22, the judgment item, the standard (pass standard), and the result are shown as the judgment result. Now, in the item of "end face unevenness" (width of the crack 14 inside the wafer), the pass standard is 6 μm, while the judgment result is 11 μm, and it is considered that the dividing force was too large. In this case, since the recipe correction is recommended, a message is displayed saying "Do you want to correct the conditions and perform reprocessing and re-judgment?", and it is possible to perform correction to reduce the dividing force according to the user input. In addition, the judgment result confirmation screen may display an observation image of the incident surface (an image showing whether it is HC or ST) and an image showing the width of the crack 14 inside the wafer, as shown in FIG. 22.

[0071] (Correction process) In the correction process, when the control unit 8 determines that the cutting force is not appropriate in the judgment process, the control unit 8 corrects the recipe so that the cutting force is within the appropriate range. The control unit 8 corrects the recipe so that the cutting force increases or decreases. The control unit 8 performs corrections to adjust, for example, the number of processed lines, ZH (Z height), VD, number of focal points, pulse energy, focusing state parameters, processing speed, frequency, pulse width, and the like in the recipe. FIG. 23 is an example of a processing condition correction screen displayed on the display 150. In the example shown in FIG. 23, a correction is performed to reduce the pulse width of each pass (a correction to reduce the pulse width from the initial recipe shown in FIG. 21) in order to reduce the cutting force. Such a correction may be performed by accepting a user input on the display 150, or may be performed automatically.

[0072] After performing the correction process, the control unit 8 executes the processing process, the identification process, and the judgment process again using the corrected recipe. FIG. 24 is an example of a judgment result confirmation screen displayed on the display 150 when the processing process, the identification process, and the judgment process are executed again after the correction process. The judgment result confirmation screen after the correction process displays the judgment result before the correction process (1'st result in FIG. 24) and the judgment result after the correction process (2'nd result in FIG. 24). In the judgment result after the correction process shown in FIG. 24, all judgment items meet the pass criteria, and the pass / fail judgment is "pass". Note that even if the pass / fail judgment is "pass", a correction may be performed to adjust the cutting force based on a user input according to the judgment result.

[0073] [Inspection method] The inspection method of this embodiment will be described with reference to Fig. 25. Fig. 25 is a flowchart of the inspection method. Fig. 25 is a flowchart showing a processing condition derivation process performed as a pre-processing of a process for forming a modified region on the wafer 20, among the inspection methods performed by the inspection apparatus 1. Note that the processes of steps S4, S6, and S8 may be performed in an order other than that shown in the flowchart.

[0074] 25, in the processing condition derivation process, first, the display 150 accepts a user input of wafer processing information (step S1). Specifically, the display 150 accepts a user input of various information shown in FIG.

[0075] Next, the control unit 8 determines a recipe (processing conditions) including the conditions for irradiating the laser light by the laser irradiation unit 3 based on the information received by the display 150. Specifically, the control unit 8 determines a recipe as shown in Fig. 21 (step S2). This recipe is set so that the laser light is irradiated onto the wafer 20 to form a plurality of modified regions 12 inside the wafer 20 and to form a full-cut state in which the cracks 14 extending from the modified regions 12 reach the rear surface 21b and the front surface 21a.

[0076] Next, the control unit 8 controls the laser irradiation unit 3 based on the determined recipe to process the wafer 20 (step S3). The control unit 8 controls the laser irradiation unit 3 so that a plurality of modified regions 12 are formed in the processing.

[0077] Next, the control unit 8 identifies the state of the crack 14 on the back surface 21b based on the observation result of the laser incident surface (back surface 21b) by the imaging unit 4, and judges whether the back surface 21b is in the HC state (step S4). If it is judged in step S4 that the back surface 21b is not in the HC state, the control unit 8 corrects the recipe so that the cutting force is increased (step S5). In this case, the process from step S2 onwards is executed again.

[0078] If it is determined in step S4 that the crack is in the HC state, the control unit 8 identifies the straightness of the crack 14 on the back surface 21b (the meandering width of the crack 14) based on the observation result of the laser incident surface (back surface 21b) by the imaging unit 4, and determines whether the meandering width of the crack 14 is smaller than a predetermined value (e.g., several μm to several tens of μm) (straightness is OK) (step S6). If it is determined in step S6 that the straightness is NG, the control unit 8 corrects the recipe so that the cutting force is reduced (step S7). In this case, the processes from step S2 onwards are executed again.

[0079] If the straightness is judged to be OK in step S6, the control unit 8 judges whether the internal inspection of the wafer 20 is OK or not (step S8). The internal inspection being OK means, for example, that the meandering width of the crack 14 inside the wafer 20 is smaller than a predetermined value (for example, several μm to several tens of μm), the trace De is vague, and the crack 14 reaches the surface 21a, which is a BHC state. If the internal inspection is judged to be NG in step S8, the control unit 8 corrects the recipe so that the parting force is decreased or increased according to the reason for NG (step S9). In this case, the process from step S2 onward is executed again. On the other hand, if the internal inspection is judged to be OK in step S8, the recipe is confirmed (confirmed to the determined recipe) (step S10), and the processing condition derivation process is terminated.

[0080] [Effects] Next, the effects of the inspection device 1 according to this embodiment will be described.

[0081] The inspection device 1 according to this embodiment includes a laser irradiation unit 3 that irradiates laser light onto the wafer 20 from the back surface 21b side of the wafer 20 having a back surface 21b and a front surface 21a, an imaging unit 4 that outputs light that is transparent to the wafer 20 and detects the light that has propagated through the wafer 20, and a control unit 8. The control unit 8 is configured to execute a processing process that controls the laser irradiation unit 3 with a recipe that is set so that the wafer 20 is irradiated with laser light to form multiple modified regions 12 inside the wafer 20 and to form a full cut state in which cracks 14 extending from the modified regions 12 reach the back surface 21b and the front surface 21a; a specification process that specifies the state of the cracks 14 extending from the modified regions 12 on the back surface 21b, and at least one state of the modified regions 12 and the cracks 14 inside the wafer 20, based on a signal output from the imaging unit 4 that detects the light; and a determination process that determines whether the dividing force for the wafer 20 according to the recipe is appropriate, based on information specified in the specification process.

[0082] In the inspection device 1, the laser light is irradiated according to a recipe set so that the crack 14 extending from the modified region 12 reaches the back surface 21b and the front surface 21a of the wafer 20 to be in a full cut state. Then, the state of the crack on the back surface 21b and at least one state of the modified region 12 and the crack 14 inside the wafer 20 are specified, and based on the specified information, it is determined whether the dividing force for the wafer 20 according to the recipe is appropriate or not. In this way, by specifying at least one state of the modified region 12 and the crack 14 inside the wafer 20 in addition to the state of the crack 14 on the back surface 21b, which is the incident surface of the laser light, the appropriateness of the dividing force for the wafer 20 to be in the full cut state is determined taking into account not only the information on the end face (back surface 21b) of the wafer 20 but also the information on the inside of the wafer 20. This makes it possible to determine that the dividing force is not appropriate, for example, when the quality of the inside of the wafer 20 has deteriorated even though the wafer 20 is in the full cut state. This makes it possible to guarantee the quality of the wafer 20 to be processed into the full cut state.

[0083] In the identification process, the control unit 8 may identify the width of the meandering of the crack 14 in the direction intersecting the thickness direction of the wafer 20 inside the wafer 20, and in the determination process, if the identified meandering width of the crack 14 is greater than a predetermined value, determine that the dividing force exceeds the appropriate range and is not appropriate. If the dividing force is too large, it is considered that the crack 14 will meander significantly in the direction intersecting the thickness direction of the wafer 20 inside the wafer 20. In this way, the portion where the crack 14 meanders becomes an uneven portion on the end surface after the wafer 20 is cut. For this reason, if the meandering width of the crack 14 becomes large, it is determined that the dividing force is too large, and correction of the dividing force is performed as necessary, thereby suppressing the occurrence of uneven portions on the end surface and appropriately ensuring the quality of the wafer 20 to be processed into a full cut state.

[0084] In the identification process, the control unit 8 may determine a position inside the wafer 20 where it is assumed that the meandering of the crack 14 is likely to occur, according to the information of the wafer 20, and identify the width of the meandering of the crack 14 at the determined position. For example, the location where the meandering of the crack 14 is likely to occur can be predicted to some extent depending on the thickness of the wafer 20, the laser focusing position in the wafer 20, etc. Therefore, by identifying the width of the meandering of the crack 14 at a position inside the wafer 20 where it is assumed that the meandering of the crack 14 is likely to occur, taking into account the information of the wafer 20 such as the thickness of the wafer 20, it is possible to efficiently and appropriately determine the width of the meandering of the crack 14.

[0085] In the identification process, the control unit 8 may identify the clarity of the laser light mark on the modified region 12, and in the determination process, when the clarity of the identified mark is higher than a predetermined value, it may be determined that the dividing force does not reach the appropriate range and is not appropriate. In the case of a full cut state, the mark on the modified region 12 is observed vaguely and the clarity is low. On the other hand, in the case of a non-full cut state, the mark on the modified region 12 is observed clearly and the clarity is high. For this reason, when the clarity of the mark is high, the dividing force is determined to be small and a correction or the like is performed to increase the dividing force as necessary, thereby reliably achieving a full cut state and appropriately ensuring the quality of the wafer 20 to be processed into a full cut state.

[0086] In the identification process, the control unit 8 may identify the state of the crack 14 on the back surface 21b, and in the determination process, if the identified state of the crack 14 is the ST state in which the crack 14 has not reached the back surface 21b, it may determine that the dividing force has not reached the appropriate range and is not appropriate. If the crack 14 has not reached the HC state (ST state) in which the crack 14 has reached the back surface 21b, it is naturally not in the full cut state. For this reason, if the HC state is not reached, the dividing force is determined to be small and a correction such as increasing the dividing force is performed as necessary, thereby reliably achieving the full cut state and appropriately ensuring the quality of the wafer 20 to be processed into the full cut state.

[0087] In the identification process, the control unit 8 may identify the meandering width of the crack 14 in a direction intersecting the thickness direction of the wafer 20 on the back surface 21b, and in the determination process, if the identified meandering width of the crack 14 is greater than a predetermined value, it may be determined that the dividing force is beyond the appropriate range and is not appropriate. If the crack 14 significantly meanders in a direction intersecting the thickness direction of the wafer 20 on the back surface 21b, it is considered that the dividing force is too large. For this reason, if the meandering width of the crack 14 on the back surface 21b is greater than a predetermined value, it is determined that the dividing force is large, and corrections such as reducing the dividing force are performed as necessary, thereby appropriately ensuring the quality of the wafer 20 to be processed into a full cut state.

[0088] In the identification process, the control unit 8 may identify the state of the crack 14 on the surface 21a, and in the determination process, if the identified state of the crack 14 is the ST state in which the crack 14 has not reached the surface 21a, it may determine that the dividing force has not reached the appropriate range and is not appropriate. If the crack 14 has not reached the surface 21a and is not in the BHC state (ST state), in which the crack 14 has reached the surface 21a, it is naturally not in the full cut state. For this reason, if the BHC state is not reached, the dividing force is determined to be small, and a correction such as increasing the dividing force is performed as necessary, thereby reliably achieving the full cut state and appropriately guaranteeing the quality of the wafer 20 to be processed into the full cut state.

[0089] The control unit 8 is configured to further execute a correction process for correcting the recipe so that the cutting force is within an appropriate range when it is determined in the determination process that the cutting force is not appropriate, and may execute the processing process, the identification process, and the determination process again with the recipe corrected in the correction process. In this way, by executing each process again with the recipe corrected so that the cutting force is within the appropriate range, it is possible to determine whether the corrected recipe is appropriate and to reliably derive an appropriate recipe.

[0090] The control unit 8 may control the laser irradiation unit 3 to form a plurality of modified regions 12 in the processing, and execute the identifying process and the determining process after the last modified region 12 in the processing is formed. This makes it possible to determine whether the dividing force applied to the wafer 20 to achieve the full cut state is appropriate, based on the state of the wafer after all modified regions 12 are formed (i.e., the state that should be the full cut state).

[0091] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, the control unit 8 may be configured to further execute a pre-identification process for identifying information related to the modified region 12 and the crack 14 extending from the modified region 12 based on a signal output from the imaging unit 4 that detects light before the modified region 12 to be formed last is formed, and a pre-determination process for determining whether the information identified in the pre-identification process is appropriate as a state before the modified region 12 to be formed last is formed. In a full cut state (a state in which the modified region 12 to be formed last is formed), it may be difficult to observe the detailed state inside the wafer 20. In this regard, before the modified region 12 to be formed last is formed, information related to the modified region 12 and the crack 14 is observed (identified) and whether the information is appropriate as a state before the modified region 12 to be formed last is determined, so that the observation result of the detailed state inside the wafer 20 can be taken into consideration, and the quality of the wafer 20 to be processed into a full cut state can be guaranteed.

[0092] FIG. 26 is a diagram for explaining an outline of the judgment of the suitability of the parting force in the processing condition derivation process according to the modified example. As shown in FIG. 26(a), in this modified example, the above-mentioned pre-specifying process and pre-judging process are executed before the modified region 12e (SD5) to be formed in the final pass is formed. In the pre-specifying process, as shown in FIG. 26(a), in addition to the incident surface state, the state of the dent inside the wafer 20, the position of the modified region (SD layer), and the state of the incident back surface are specified. In the judgment (FC judgment) after the last modified region 12e is formed, the passing criterion for the judgment (the passing criterion for the full cut state) is that the dent is vague (see FIG. 26(b)), but in the pre-judgment (FC-1) before the last modified region 12e is formed, the passing criterion for the judgment is that the dent is clear (see FIG. 26(c)). This difference is due to the fact that the full cut state is normal in the FC judgment, whereas the state that is not the full cut state is normal in the FC-1 judgment. That is, if the crease is vague in the FC-1 judgment, it is considered that there is an unevenness of the crack 14 inside the wafer, and the crease of the modified region below the unevenness is difficult to see due to the unevenness, and since it is expected that the end face unevenness will occur when the final modified region 12e is formed, it is judged as a failure (pre-judgment NG). As described above, when making the FC-1 judgment, the detailed state of the inside of the wafer 20 can be observed compared to the case of a full cut state, so in addition to the above-mentioned items, the presence or absence of black streaks, the position of the black streaks, BHC inspection, crack amount inspection, etc. may be performed.

[0093] FIG. 27 is an example of a confirmation screen for the pre-determination (FC-1 determination) displayed on the display 150. The criteria for the determination (pass criteria for the FC-1 determination) include, for example, the pass criteria for "end surface unevenness," "finger mark observation," "number of black streaks," "position of black streaks," "BHC inspection," "position of each SD layer," and "incident surface state." FIG. 28 is an example of a confirmation screen for the determination result displayed on the display 150. In the example shown in FIG. 28, the pass criteria are not met for "number of black streaks," "position of black streaks," and "BHC inspection," and the result is "failed," indicating that the dividing force is too low. In this case, it is possible to perform a correction to increase the dividing force according to a user input. That is, the control unit 8 is configured to further perform a pre-correction process to correct the recipe when it is determined in the pre-determination process that the state before the modified region 12 to be finally formed is not appropriate. Then, the control unit 8 performs the processing process, the pre-identification process, and the pre-determination process again with the recipe corrected in the pre-correction process. In this way, by correcting the recipe when the state is determined to be inappropriate in the pre-determination process, the quality of the wafer to be processed into the full cut state can be guaranteed.

[0094] FIG. 29 is a flowchart of an inspection method (processing condition derivation process) according to a modified example. Specifically, it is a flowchart of a process for executing a full cut state determination (FC determination) after performing a preliminary determination (FC-1 determination). As shown in FIG. 29, first, the display 150 accepts a user input of wafer processing information (step S101). Next, the control unit 8 determines a recipe (processing conditions) including the irradiation conditions of the laser light by the laser irradiation unit 3 based on the information accepted by the display 150 (step S102). Next, the control unit 8 controls the laser irradiation unit 3 based on the determined recipe, and processes the wafer 20 so that the modified region 12 is formed except for the final pass (step S103).

[0095] Next, the control unit 8 executes a preliminary identification process and a preliminary judgment process to judge whether the state before the modified region 12 to be finally formed is appropriate (whether the various inspections are OK) (step S104). If the various inspections are judged to be NG in step S104, the control unit 8 corrects the recipe so that the dividing force is increased or decreased (step S105). If the various inspections are judged to be OK in step S104, the control unit 8 processes the wafer 20 so that the modified region 12 of the final pass is formed (step S106). Then, the control unit 8 executes a process related to FC judgment (the process of steps S4 to S9 in FIG. 25) (step S107). After the process related to FC judgment, the control unit 8 finalizes the recipe (step S108).

[0096] (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.

[0097] 30 and 31 are diagrams for explaining crack detection. In FIG. 30, 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 30 as shown in FIG. 30(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.

[0098] 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. 31. 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. 31. 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.

[0099] 32 to 34 are diagrams for explaining the detection of scratches. In FIG. 32, 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. 32(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.

[0100] Here, as shown in FIG. 33, the dent 280 has a strong characteristic as a corner, since shapes such as circles and rectangles are arranged at regular intervals. Therefore, by aggregating 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. 34, 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 aggregating the feature amounts in this way, it is possible to estimate not only the dent position but also the pulse pitch.

[0101] (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. 35 is a diagram for explaining the difference in the imaging zone depending on the processing method. FIG. 35(a) shows the imaging zone when full cut processing is performed, and FIG. 35(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. 35(a) and (b), the lower half SD layer is the area related to the virtual focal point. As shown in FIG. 35, 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] In the brightness calibration process, as shown in FIG. 36, 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.

[0106] 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.

[0107] In the shading correction process, as shown in FIG. 37(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. 37(b). Then, for each internal observation position, difference data (see FIG. 37(c)) between the image after SD processing and the image for shading 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.

[0108] A laser processing method (processing condition derivation process) in the case where the above-mentioned aberration correction process, brightness calibration process, and shading correction process are performed will be described with reference to Fig. 38. Note that Fig. 38 shows a simplified description of the processing process and the determination process. As shown in Fig. 38, first, the display 150 accepts a user input of wafer processing information (step S51). Specifically, the display 150 accepts an input of at least information on the wafer thickness. As a result, the processing conditions are automatically and provisionally determined.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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. 38, 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] Fig. 39 is a diagram for explaining the effect of performing the aberration correction process, the brightness value calibration process, and the shading correction process. Fig. 39(a) is an image that has not been subjected to any of these processes, Fig. 39(b) is an image that has been subjected to only the aberration correction process, Fig. 39(c) is an image that has been subjected to the aberration correction process and the brightness value calibration process, and Fig. 39(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. 39, it can be seen that the sharpness of the crack 14 and the like in the image is greatly improved by performing these processes.

[0118] (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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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]

[0123] 1... inspection device, 3... laser irradiation unit, 4... imaging unit, 8... control unit, 20... wafer, 150... display.

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 processing conditions set so that one or more modified regions are formed inside the wafer by irradiating the wafer with the laser light and a full cut state is formed in which cracks extending from the modified regions reach the first surface and the second surface; a second process for identifying a state of a crack extending from the modified region on the first surface and a state of at least one of the modified region and the crack inside the wafer based on a signal output from the imaging unit that detects the light; and a third process for determining whether or not a dividing force applied to the wafer according to the processing conditions is appropriate based on the information identified in the second process. The control unit is In the second process, a meandering width of the crack in a direction intersecting a thickness direction of the wafer inside the wafer is identified; In the third process, if the width of the meandering of the identified crack is greater than a predetermined value, the inspection device determines that the dividing force exceeds an appropriate range and is inappropriate.

2. The control unit is The inspection device of claim 1, wherein in the second process, a position inside the wafer where the crack is likely to meander is determined based on the information about the wafer, and the width of the crack's meandering is identified at the determined position.

3. An irradiation unit that irradiates a laser beam onto a wafer having a first surface and a second surface 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 processing conditions set so that one or more modified regions are formed inside the wafer by irradiating the wafer with the laser light and a full cut state is formed in which cracks extending from the modified regions reach the first surface and the second surface; a second process for identifying a state of a crack extending from the modified region on the first surface and a state of at least one of the modified region and the crack inside the wafer based on a signal output from the imaging unit that detects the light; and a third process for determining whether or not a dividing force applied to the wafer according to the processing conditions is appropriate based on the information identified in the second process. The control unit is In the second process, a degree of visibility of a mark of the laser light on the modified region is determined; In the third process, if the clarity of the identified crease is higher than a predetermined value, the inspection device determines that the separating force does not reach an appropriate range and is not appropriate.

4. An irradiation unit that irradiates a laser beam onto a wafer having a first surface and a second surface 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 processing conditions set so that one or more modified regions are formed inside the wafer by irradiating the wafer with the laser light and a full cut state is formed in which cracks extending from the modified regions reach the first surface and the second surface; a second process for identifying a state of a crack extending from the modified region on the first surface and a state of at least one of the modified region and the crack inside the wafer based on a signal output from the imaging unit that detects the light; and a third process for determining whether or not a dividing force applied to the wafer according to the processing conditions is appropriate based on the information identified in the second process. The control unit is In the second process, a meandering width of the crack in a direction intersecting a thickness direction of the wafer on the first surface is identified; In the third process, if the width of the identified meandering crack is greater than a predetermined value, the inspection device determines that the dividing force exceeds an appropriate range and is inappropriate.

5. The control unit is In the second process, a state of arrival of the crack on the first surface is identified; An inspection device as described in any one of claims 1 to 4, wherein, in the third process, when the identified crack reach state is a stealth state in which the crack has not reached the first surface, it is determined that the shear force does not reach an appropriate range and is inappropriate.

6. The control unit is In the second process, a state of arrival of the crack on the second surface is identified; An inspection device as described in any one of claims 1 to 5, wherein in the third process, when the identified crack reach state is a stealth state in which the crack has not reached the second surface, it is determined that the shear force does not reach the appropriate range and is inappropriate.

7. The control unit is When it is determined that the separating force is not appropriate in the third process, a fourth process is further executed to correct the processing conditions so that the separating force is within an appropriate range, 7. The inspection device according to claim 1, further comprising: a step of executing the first process, the second process, and the third process again under the processing conditions corrected in the fourth process.

8. The control unit is In the first process, the irradiation unit is controlled so as to form a plurality of the modified regions; 8. The inspection apparatus according to claim 1, wherein the second process and the third process are carried out after the modified region that is formed last in the first process is formed.

9. 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 processing conditions set so that the wafer is irradiated with the laser light to form a plurality of modified regions inside the wafer and to form cracks extending from the modified regions in a full cut state by reaching the first surface and the second surface; A pre-identification process for identifying information related to the modified region and a crack extending from the modified region based on a signal output from the imaging unit that detects the light before the modified region that is to be formed last in the first process is formed; and a pre-determination process for determining whether the state before the last modified region is formed is appropriate based on the information identified in the pre-determination process.

10. The control unit is a pre-correction process is further executed to correct the processing conditions when it is determined in the pre-determination process that the processing conditions are not appropriate as a state before the modified region to be finally formed is formed, The inspection apparatus according to claim 9 , further comprising: a step of executing the first process, the pre-identification process, and the pre-determination process again under the processing conditions corrected in the pre-correction process.

11. a first step of irradiating a laser beam from a first surface side of a wafer having a first surface and a second surface under processing conditions set so that one or more modified regions are formed inside the wafer and a full cut state is achieved in which cracks extending from the modified regions reach the first surface and the second surface; a second step of outputting light having transparency to the wafer on which the modified region has been formed by the first step, and identifying a state of a crack extending from the modified region on the first surface and at least one state of the modified region and the crack inside the wafer based on a signal output by detecting the light propagating through the wafer; and a third step of determining whether or not a cutting force applied to the wafer is appropriate according to the processing conditions based on the information identified in the second step, In the second step, a meandering width of the crack in a direction intersecting a thickness direction of the wafer inside the wafer is identified; In the third step, when the width of the identified meandering of the crack is greater than a predetermined value, it is determined that the splitting force exceeds an appropriate range and is not appropriate.

12. A first step of irradiating laser light from a first surface side of a wafer having a first surface and a second surface under processing conditions set so that one or more modified regions are formed inside the wafer and cracks extending from the modified regions reach the first surface and the second surface to form a full cut state; a second step of outputting light having transparency to the wafer on which the modified region has been formed by the first step, and identifying a state of a crack extending from the modified region on the first surface and at least one state of the modified region and the crack inside the wafer based on a signal output by detecting the light propagating through the wafer; and a third step of determining whether or not a cutting force applied to the wafer is appropriate according to the processing conditions based on the information identified in the second step, In the second step, a degree of visibility of the laser light mark on the modified region is determined, In the third step, when the clarity of the identified crease is higher than a predetermined value, it is determined that the separating force does not reach an appropriate range and is therefore inappropriate.

13. A first step of irradiating a laser beam from a first surface side of a wafer having a first surface and a second surface under processing conditions set so that one or more modified regions are formed inside the wafer and cracks extending from the modified regions reach the first surface and the second surface to form a full cut state; a second step of outputting light having transparency to the wafer on which the modified region has been formed by the first step, and identifying a state of a crack extending from the modified region on the first surface and at least one state of the modified region and the crack inside the wafer based on a signal output by detecting the light propagating through the wafer; and a third step of determining whether or not a cutting force applied to the wafer is appropriate according to the processing conditions based on the information identified in the second step, In the second step, a width of the meandering of the crack in a direction intersecting a thickness direction of the wafer on the first surface is identified; In the third step, when the width of the identified meandering of the crack is greater than a predetermined value, it is determined that the dividing force exceeds an appropriate range and is not appropriate.

14. A first step of irradiating a laser beam from a first surface side of a wafer having a first surface and a second surface under processing conditions set so that one or more modified regions are formed inside the wafer and cracks extending from the modified regions reach the first surface and the second surface to form a full cut state; a pre-identification step of outputting light that is transparent to the wafer before the last modified region is formed in the first step, and identifying information related to the modified region and cracks extending from the modified region based on a signal output from an imaging unit that detects the light that has propagated through the wafer; and a pre-determination step of determining whether the state before the last modified region is formed is appropriate based on the information identified in the pre-determination step.

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