Patent Publication Number: US-2023154774-A1

Title: Inspection device and inspection method

Description:
TECHNICAL FIELD 
     One aspect of the present invention relates to an inspection device and an inspection method. 
     BACKGROUND ART 
     There has been known an inspection device that, in order to cut a wafer including a semiconductor substrate and a functional element layer along each of a plurality of lines, irradiates the wafer with a laser beam 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 functional element layer being formed on one surface of the semiconductor substrate. An inspection device disclosed in Patent Literature 1 includes an infrared camera, and can observe modified regions formed inside a semiconductor substrate, processing damage formed in a functional element layer, and the like from a back surface side of the semiconductor substrate. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Publication No. 2017-64746 
     SUMMARY OF INVENTION 
     Technical Problem 
     The inspection device described above may form the modified regions to attain a state where cracks extending from the modified regions extend to both end surfaces of the wafer (full-cut state), in respect to a user&#39;s request. For example, the states of both the end surfaces of the wafer are observed to determine whether or not the full-cut state is attained. Here, for example, the states of both the end surfaces of the wafer are observed to determine whether or not the full-cut state is attained, but at the time of inspection, it cannot be determined whether or not the inside of the wafer in the full-cut state is in an appropriate state (whether or not the quality is maintained). Therefore, it may not be possible to sufficiently ensure the quality of the wafer to be processed into the full-cut state. 
     One aspect of the present invention is conceived in view of the above circumstances, and an object of the present invention is to provide an inspection device and an inspection method that can ensure the quality of a wafer to be processed into a full-cut state. 
     Solution to Problem 
     An inspection device according to one aspect of the present invention includes: an irradiation unit that irradiates a wafer having a first surface and a second surface with a laser beam from a first surface side of the wafer; an imaging unit that outputs light having a property of transmitting through the wafer, and that detects the light that has propagated through the wafer; and a control unit. The control unit is configured to execute a first process of controlling the irradiation unit according to a processing condition set such that one or a plurality of modified regions are formed inside the wafer by irradiating the wafer with the laser beam and a full-cut state where cracks extending from the modified regions have reached the first surface and the second surface is attained; a second process of identifying a state of the crack on the first surface extending from the modified region, and a state of at least one of the modified regions and the cracks inside the wafer, based on a signal output from the imaging unit that has detected the light; and a third process of determining whether or not a dicing force applied to the wafer according to the processing condition is proper, based on information identified in the second process. 
     The inspection device according to one aspect of the present invention applies the laser beam according to the processing condition set to attain the full-cut state where the cracks extending from the modified regions have reached the first surface and the second surface of the wafer. Then, the state of the crack on the first surface and the state of at least one of the modified regions and the cracks inside the wafer are identified, and it is determined whether or not the dicing force applied to the wafer according to the processing condition is proper, based on the identified information. As described above, since in addition to the state of the crack on the first surface that is an incident surface of the laser beam, the state of at least one of the modified regions and the cracks inside the wafer are identified, in consideration of not only information regarding an end surface (first surface) of the wafer but also information regarding the inside of the wafer, it is determined whether or not the dicing force applied to the wafer to attain the full-cut state is proper. Therefore, for example, when the full-cut state is attained but the internal quality of the wafer decreases, it can be determined that the dicing force is not proper. Accordingly, the quality of the wafer to be processed into the full-cut state can be ensured. 
     The control unit may identify a meandering width of the crack in a direction intersecting a thickness direction of the wafer inside the wafer in the second process, and determine that the dicing force is out of a proper range and is not proper, when the identified meandering width of the crack is larger than a predetermined value, in the third process. When the dicing force is too large, it is considered that the crack greatly meanders in the direction intersecting the thickness direction of the wafer inside the wafer. A spot where the crack meanders as described above becomes an end surface uneven spot after the wafer is cut. For this reason, when the meandering width of the crack is large, it is determined that the dicing force is too large, and the correction of the dicing force or the like is executed as necessary, so that the occurrence of an uneven spot in the end surface can be suppressed, and the quality of the wafer to be processed into the full-cut state can be appropriately ensured. 
     In the second process, the control unit may decide a position inside the wafer at which meandering of the crack is assumed to be likely to occur, according to information regarding the wafer, and identify a meandering width of the crack at the decided position. The spot where the meandering of the crack is likely to occur can be predicted to some extent by, for example, a thickness of the wafer or the like. For this reason, the meandering width of the crack at the position inside the wafer at which the meandering of the crack is assumed to be likely to occur is identified in consideration of the information regarding the wafer such as the thickness of the wafer or laser processing conditions such as a laser condensing position, so that a determination related to the meandering width of the crack can be efficiently and appropriately performed. 
     The control unit may identify a clearness of a mark of the laser beam related to the modified region in the second process, and determine that the dicing force has not reached a proper range and is not proper, when the identified clearness of the mark is higher than a predetermined value, in the third process. When the full-cut state is attained, the mark related to the modified region is vaguely observed and the clearness is low. On the other hand, when the full-cut state is not attained, the mark related to the modified region is distinctly observed and the clearness is high. For this reason, when the clearness of the mark is high, it is determined that the dicing force is small, and correction or the like to increase the dicing force is executed as necessary, so that the full-cut state can be reliably attained, and the quality of the wafer to be processed into the full-cut state can be appropriately ensured. 
     The control unit may identify a reach state of the crack on the first surface in the second process, and determine that the dicing force has not reached a proper range and is not proper, when the identified reach state of the crack is a stealth state where the crack has not reached the first surface, in the third process. When a half-cut state where the crack has reached the first surface is not attained (the stealth state is attained), naturally, the full-cut state is not attained. For this reason, when the half-cut state is not attained, it is determined that the dicing force is small, and correction or the like to increase the dicing force is executed as necessary, so that the full-cut state can be reliably attained, and the quality of the wafer to be processed into the full-cut state can be appropriately ensured. 
     The control unit may identify a meandering width of the crack on the first surface in a direction intersecting a thickness direction of the wafer in the second process, and determine that the dicing force is out of a proper range and is not proper, when the identified meandering width of the crack is larger than a predetermined value, in the third process. When the crack on the first surface greatly meanders in the direction intersecting the thickness direction of the wafer, it is considered that the dicing force is too large. For this reason, when the meandering width of the crack on the first surface is larger than the predetermined value, it is determined that the dicing force is large, and correction or the like to reduce the dicing force is executed as necessary, so that the quality of the wafer to be processed into the full-cut state can be appropriately ensured. 
     The control unit may identify a reach state of the crack on the second surface in the second process, and determine that the dicing force has not reached a proper range and is not proper, when the identified reach state of the crack is a stealth state where the crack has not reached the second surface, in the third process. When a BHC state where the crack has reached the second surface is not attained (the stealth state is attained), naturally, the full-cut state is not attained. For this reason, when the BHC state is not attained, it is determined that the dicing force is small, and correction or the like to increase the dicing force is executed as necessary, so that the full-cut state can be reliably attained, and the quality of the wafer to be processed into the full-cut state can be appropriately ensured. 
     The control unit may be configured to further execute a fourth process of correcting the processing condition to set the dicing force within a proper range, when it is determined in the third process that the dicing force is not proper, and may execute the first process, the second process, and the third process again according to the processing condition corrected in the fourth process. As described above, since each process is executed again according to the processing condition corrected to set the dicing force within the proper range, it can be determined whether or not the corrected processing condition is proper, and the proper processing condition can be reliably derived. 
     The control unit may control the irradiation unit to form the plurality of modified regions in the first process, and execute the second process and the third process after the modified region to be formed last in the first process is formed. Accordingly, it can be determined whether or not the dicing force applied to the wafer to attain the full-cut state is proper, based on a state of the wafer after all the modified regions are formed (namely, a state that should be the full-cut state). 
     An inspection device according to one aspect of the present invention includes: an irradiation unit that irradiates a wafer having a first surface and a second surface with a laser beam from a first surface side of the wafer; an imaging unit that outputs light having a property of transmitting through the wafer, and that detects the light that has propagated through the wafer; and a control unit. The control unit is configured to execute a first process of controlling the irradiation unit according to a processing condition set such that a plurality of modified regions are formed inside the wafer by irradiating the wafer with the laser beam and a full-cut state where cracks extending from the modified regions have reached the first surface and the second surface is attained; a pre-identification process of identifying information related to the modified regions and to the cracks extending from the modified regions, based on a signal output from the imaging unit that has detected the light, before the modified region to be formed last in the first process is formed; and a pre-determination process of determining whether or not a state before the modified region to be formed last is formed is proper, based on the information identified in the pre-identification process. In the full-cut state, it may be difficult to observe a detailed internal state of the wafer. In this respect, since details of the information related to the modified regions and to the cracks (a modified layer position, a crack length, or the like) can be observed (identified) before the modified region to be formed last is formed, a more detailed determination can be performed compared to the determination in the full-cut state. Then, since it is determined whether or not the state before the modified region to be formed last is formed is proper, the quality of the wafer to be processed into the full-cut state can be ensured. 
     The control unit may be configured to further execute a pre-correction process of correcting the processing condition when it is determined in the pre-determination process that the state before the modified region to be formed last is formed is not proper, and may execute the first process, the pre-identification process, and the pre-determination process again according to the processing condition corrected in the pre-correction process. As described above, the processing condition is corrected when it is determined in the pre-determination process that the state is not proper, so that the quality of the wafer to be processed into the full-cut state can be ensured. 
     An inspection method according to one aspect of the present invention includes: a first step of irradiating a wafer having a first surface and a second surface with a laser beam from a first surface side according to a processing condition set such that one or a plurality of modified regions are formed inside the wafer and a full-cut state where cracks extending from the modified regions have reached the first surface and the second surface is attained; a second step of outputting light having a property of transmitting through the wafer in which the modified regions are formed by the first step, and of identifying a state of the crack on the first surface extending from the modified region and a state of at least one of the modified regions and the cracks inside the wafer, based on a signal output when the light that has propagated through the wafer is detected; and a third step of determining whether or not a dicing force applied to the wafer according to the processing condition is proper, based on information identified in the second step. 
     Advantageous Effects of Invention 
     According to one aspect of the present invention, the quality of the wafer to be processed into the full-cut state can be ensured. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a configuration view of an inspection device of one embodiment. 
         FIG.  2    is a plan view of a wafer of one embodiment. 
         FIG.  3    is a cross-sectional view of a portion of the wafer shown in  FIG.  2   . 
         FIG.  4    is a configuration view of a laser irradiation unit shown in  FIG.  1   . 
         FIG.  5    is a configuration view of an imaging unit for inspection shown in  FIG.  1   . 
         FIG.  6    is a configuration view of an imaging unit for alignment correction shown in  FIG.  1   . 
         FIG.  7    is a cross-sectional view of a wafer for describing an imaging principle of the imaging unit for inspection shown in  FIG.  5   , and shows images captured at each spot by the imaging unit for inspection. 
         FIG.  8    is a cross-sectional view of a wafer for describing the imaging principle of the imaging unit for inspection shown in  FIG.  5   , and shows images captured at each spot by the imaging unit for inspection. 
         FIG.  9    shows SEM images of a modified region and a crack formed inside a semiconductor substrate. 
         FIG.  10    shows SEM images of the modified region and the crack formed inside a semiconductor substrate. 
         FIG.  11    shows optical path views for describing the imaging principle of the imaging unit for inspection shown in  FIG.  5   , and schematic views showing images captured at a focus by the imaging unit for inspection. 
         FIG.  12    shows optical path views for describing the imaging principle of the imaging unit for inspection shown in  FIG.  5   , and schematic views showing images captured at a focus by the imaging unit for inspection. 
         FIG.  13    shows views for describing states of wafers according to a dicing force applied to the wafers. 
         FIG.  14    shows views for describing the reason for the necessity of an internal observation when laser processing is performed under a full-cut condition. 
         FIG.  15    shows views schematically showing observation results of each state of wafers. 
         FIG.  16    shows views for describing the observation of a width of a crack that meanders. 
         FIG.  17    shows views for describing an end surface unevenness occurrence region for each thickness of wafers. 
         FIG.  18    shows views for describing a processing condition derivation process. 
         FIG.  19    is a screen image related to the processing condition derivation process. 
         FIG.  20    is a screen image related to the processing condition derivation process. 
         FIG.  21    is a screen image related to the processing condition derivation process. 
         FIG.  22    is a screen image related to the processing condition derivation process. 
         FIG.  23    is a screen image related to the processing condition derivation process. 
         FIG.  24    is a screen image related to the processing condition derivation process. 
         FIG.  25    is a flowchart of an inspection method (processing condition derivation process). 
         FIG.  26    shows views for describing a processing condition derivation process according to a modification example. 
         FIG.  27    is a screen image related to the processing condition derivation process according to the modification example. 
         FIG.  28    is a screen image related to the processing condition derivation process according to the modification example. 
         FIG.  29    is a flowchart of an inspection method (processing condition derivation process) according to the modification example. 
         FIG.  30    shows views for describing crack detection. 
         FIG.  31    shows views for describing crack detection. 
         FIG.  32    shows views for describing mark detection. 
         FIG.  33    shows views for describing mark detection. 
         FIG.  34    shows views for describing mark detection. 
         FIG.  35    shows views for describing a difference in an imaging section depending on a processing method. 
         FIG.  36    is a flowchart of a brightness calibration process. 
         FIG.  37    is a flowchart of a shading correction process. 
         FIG.  38    is a flowchart of a laser processing method (processing condition derivation process) when various correction processes are performed. 
         FIG.  39    shows images on which various correction processes are performed. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Incidentally, in the drawings, the same or corresponding portions will be denoted by the same reference signs, and a duplicated description will not be repeated. 
     Configuration of Inspection Device 
     As shown in  FIG.  1   , an inspection device  1  includes a stage  2 , a laser irradiation unit  3  (irradiation unit), a plurality of imaging units  4 ,  5 , and  6 , a drive unit  7 , a control unit  8 , and a display  150  (an input unit and a display unit). The inspection device  1  is a device that irradiates an object  11  with a laser beam L to form a modified region  12  in the object  11 . 
     The stage  2  supports the object  11 , for example, by suctioning a film attached to the object  11 . The stage  2  is movable in each of an X direction and a Y direction, and is rotatable around an axis parallel to a Z direction as a center line. Incidentally, the X direction and the Y direction are a first horizontal direction and a second horizontal direction perpendicular to each other, and the Z direction is a vertical direction. 
     The laser irradiation unit  3  condenses the laser beam L having a property of transmitting through the object  11 , and irradiates the object  11  with the laser beam L. When the laser beam L is condensed inside the object  11  supported by the stage  2 , the laser beam L is absorbed particularly at a portion corresponding to a condensing point C of the laser beam L, and the modified region  12  is formed inside the object  11 . 
     The modified region  12  is a region of which the density, the refractive index, the mechanical strength, and other physical characteristics are different from those of a surrounding non-modified region. Examples of the modified region  12  include a melting region, a crack region, a dielectric breakdown region, a refractive index change region, and the like. The modified region  12  has a characteristic that cracks easily extend from the modified region  12  to an incident side of the laser beam L and to a side opposite the incident side. Such a characteristic of the modified region  12  is used for the cutting of the object  11 . 
     As one example, when the stage  2  is moved along the X direction to move the condensing point C relative to the object  11  along the X direction, a plurality of modified spots  12   s  are formed to be arranged in one row along the X direction. One modified spot  12   s  is formed by irradiating the object  11  with the laser beam L of one pulse. 
     One row of the modified regions  12  are a set of a plurality of the modified spots  12   s  arranged in one row. The modified spots  12   s  adjacent to each other may be connected to each other or separated from each other depending on a relative movement speed of the condensing point C with respect to the object  11  and on a repetition frequency of the laser beam L. 
     The imaging unit  4  captures an image of the modified regions  12  formed in the object  11 , and an image of tips of cracks extending from the modified regions  12 . 
     The imaging units  5  and  6  capture images of the object  11  supported by the stage  2 , with light transmitting through the object  11  under control of the control unit  8 . As one example, the images obtained by the imaging units  5  and  6  are used for the alignment of an irradiation position of the laser beam L. 
     The drive unit  7  supports the laser irradiation unit  3  and the plurality of imaging units  4 ,  5 , and  6 . The drive unit  7  moves the laser irradiation unit  3  and the plurality of imaging units  4 ,  5 , and  6  along the Z direction. 
     The control unit  8  controls operations of the stage  2 , the laser irradiation unit  3 , the plurality of 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, and the like. In the control unit  8 , the processor executes software (program) read into the memory or the like, and controls the reading and writing of data from and to the memory and the storage and communication by the communication device. 
     The display  150  has a function as an input unit that receives an input of information from a user, and a function as a display unit that displays information for the user. 
     Configuration of Object 
     The object  11  of the present embodiment is a wafer  20  as shown in  FIGS.  2  and  3   . The wafer  20  includes a semiconductor substrate  21  and a functional element layer  22 . Incidentally, in the present embodiment, the wafer  20  will be described as including the functional element layer  22 , but the wafer  20  may or may not include the functional element layer  22  and may be a bare wafer. The semiconductor substrate  21  includes a surface  21   a  (second surface) and a back surface  21   b  (first surface). The semiconductor substrate  21  is, for example, a silicon substrate. The functional element layer  22  is formed on the surface  21   a  of the semiconductor substrate  21 . The functional element layer  22  includes a plurality of functional elements  22   a  that are two-dimensionally arranged along the surface  21   a.  The functional element  22   a  is, for example, a light-receiving element such as a photodiode, a light-emitting element such as a laser diode, a circuit element such as a memory, or the like. The functional element  22   a  may be three-dimensionally configured such that a plurality of layers are stacked. Incidentally, the semiconductor substrate  21  is provided with a notch  21   c  indicating a crystal orientation, but an orientation flat may be provided instead of the notch  21   c.    
     The wafer  20  is cut for each functional element  22   a  along each of a plurality of lines  15 . The plurality of lines  15  pass between the plurality of respective functional elements  22   a  when viewed in a thickness direction of the wafer  20 . More specifically, each of the lines  15  passes through a center of a street region  23  (center in a width direction) when viewed in the thickness direction of the wafer  20 . The street region  23  extends to pass between the functional elements  22   a  adjacent to each other in the functional element layer  22 . In the present embodiment, the plurality of functional elements  22   a  are arranged in a matrix pattern along the surface  21   a,  and the plurality of lines  15  are set in a grid pattern. Incidentally, the lines  15  are imaginary lines but may be lines that are actually drawn. 
     Configuration of Laser Irradiation Unit 
     As shown in  FIG.  4   , the laser irradiation unit  3  includes a light source  31 , a spatial light modulator  32 , and a condenser lens  33 . The light source  31  outputs the laser beam L according to, for example, a pulse oscillation method. The spatial light modulator  32  modulates the laser beam L output from the light source  31 . The spatial light modulator  32  is, for example, a liquid crystal on silicon (LCOS) spatial light modulator (SLM). The condenser lens  33  condenses the laser beam L modulated by the spatial light modulator  32 . Incidentally, the condenser lens  33  may be a correction ring lens. 
     In the present embodiment, the laser irradiation unit  3  irradiates the wafer  20  with the laser beam L from a back surface  21   b  side of the semiconductor substrate  21  along each of the plurality of lines  15  to form two rows of modified regions  12   a  and  12   b  inside the semiconductor substrate  21  along each of the plurality of lines  15 . Of the two rows of modified regions  12   a  and  12   b,  the modified region  12   a  is a modified region closest to the surface  21   a.  Of the two rows of modified regions  12   a  and  12   b,  the modified region  12   b  is a modified region closest to the modified region  12   a,  and is a modified region closest to the back surface  21   b.    
     The two rows of modified regions  12   a  and  12   b  are adjacent to each other in the thickness direction (Z direction) of the wafer  20 . The two rows of modified regions  12   a  and  12   b  are formed by moving two condensing points C 1  and C 2  relative to the semiconductor substrate  21  along the line  15 . For example, the laser beam L is modulated by the spatial light modulator  32  such that the condensing point C 2  is located behind the condensing point C 1  in a traveling direction and on the incident side of the laser beam L. Incidentally, regarding the formation of the modified regions, a single focus or a multi-focus may be used, and a single pass or a plurality of passes may be used. 
     The laser irradiation unit  3  irradiates the wafer  20  with the laser beam L from the back surface  21   b  side of the semiconductor substrate  21  along each of the plurality of lines  15 . As one example, the two condensing points C 1  and C 2  are aligned with a position of 54 μm and with a position of 128 μm from the surface  21   a  in the semiconductor substrate  21  that is a single-crystal silicon &lt;100&gt; substrate having a thickness of 400 μm, respectively, and the wafer  20  is irradiated with the laser beam L from the back surface  21   b  side of the semiconductor substrate  21  along each of the plurality of lines  15 . In this case, for example, in order to satisfy a condition where a crack  14  across the two rows of modified regions  12   a  and  12   b  reaches the surface  21   a  of the semiconductor substrate  21 , the laser beam L is set to have a wavelength of 1099 nm, a pulse width of 700 nsec, and a repetition frequency of 120 kHz. In addition, an output of the laser beam L at the condensing point C 1  is set to 2.7 W, an output of the laser beam L at the condensing point C 2  is set to 2.7 W, and a relative movement speed of the two condensing points C 1  and C 2  with respect to the semiconductor substrate  21  is set to 800 mm/sec. Incidentally, for example, when the number of processing passes is set to 5, for example, ZH80 (a position of 328 μm from the surface  21   a ), ZH69 (a position of 283 μm from the surface  21   a ), ZH57 (a position of 234 μm from the surface  21   a ), ZH26 (a position of 107 μm from the surface  21   a ), and ZH12 (a position of 49.2 μm from the surface  21   a ) may be set as processing positions in the wafer  20  described above. In this case, for example, the laser beam L may have a wavelength of 1080 nm, a pulse width of 400 nsec, and a repetition frequency of 100 kHz, and the movement speed of the condensing points C 1  and C 2  may be 490 mm/sec. 
     Such formation of the two rows of modified regions  12   a  and  12   b  and of the crack  14  is executed in the following case. Namely, such a case is, for example, a case where, in a post-step, the back surface  21   b  of the semiconductor substrate  21  is ground to thin the semiconductor substrate  21  and to expose the crack  14  on the back surface  21   b,  and the wafer  20  is cut into a plurality of semiconductor devices along each of the plurality of lines  15 . 
     Configuration of Imaging Unit for Inspection 
     As shown in  FIG.  5   , the imaging unit  4  (imaging unit) includes a light source  41 , a mirror  42 , an objective lens  43 , and a light detection unit  44 . The imaging unit  4  captures an image of the wafer  20 . The light source  41  outputs light I 1  having a property of transmitting through the semiconductor substrate  21 . The light source  41  includes, for example, a halogen lamp and a filter, and outputs the light I 1  in a near-infrared region. The light I 1  output from the light source  41  is reflected by the mirror  42 , passes through the objective lens  43 , and is applied to the wafer  20  from the back surface  21   b  side of the semiconductor substrate  21 . At this time, the stage  2  supports the wafer  20  in which the two rows of modified regions  12   a  and  12   b  are formed as described above. 
     The objective lens  43  passes the light I 1  reflected by the surface  21   a  of the semiconductor substrate  21 . Namely, the objective lens  43  passes the light I 1  that has propagated through the semiconductor substrate  21 . A numerical aperture (NA) of the objective lens  43  is, for example, 0.45 or more. The objective lens  43  includes a correction ring  43   a.  For example, the correction ring  43   a  adjusts a distance between a plurality of lenses forming the objective lens  43 , to correct an aberration generated in the light I 1  inside the semiconductor substrate  21 . Incidentally, means for correcting an aberration is not limited to the correction ring  43   a,  and may be other correction means such as a spatial light modulator. The light detection unit  44  detects the light I 1  that has transmitted through the objective lens  43  and through the mirror  42 . The light detection unit  44  is configured as, for example, an InGaAs camera, and detects the light I 1  in the near-infrared region. Incidentally, means for detecting (capturing an image) the light I 1  in the near-infrared region is not limited to the InGaAs camera, and may be other imaging means such as a transmission confocal microscope as long as the other imaging means can capture a transmissive image. 
     The imaging unit  4  can capture an image of each of the two rows of modified regions  12   a  and  12   b  and of a tip of each of a plurality of cracks  14   a,    14   b,    14   c,  and  14   d  (details will be described later). The crack  14   a  is a crack extending from the modified region  12   a  toward a surface  21   a  side. The crack  14   b  is a crack extending from the modified region  12   a  toward the back surface  21   b  side. The crack  14   c  is a crack extending from the modified region  12   b  toward the surface  21   a  side. The crack  14   d  is a crack extending from the modified region  12   b  toward the back surface  21   b  side. 
     Configuration of Imaging Unit for Alignment Correction 
     As shown in  FIG.  6   , the imaging unit  5  includes a light source  51 , a mirror  52 , a lens  53 , and a light detection unit  54 . The light source  51  outputs light  12  having a property of transmitting through the semiconductor substrate  21 . The light source  51  includes, for example, a halogen lamp and a filter, and outputs the light  12  in the near-infrared region. The light source  51  and the light source  41  of the imaging unit  4  may be common to each other. The light  12  output from the light source  51  is reflected by the mirror  52 , passes through the lens  53 , and is applied to the wafer  20  from the back surface  21   b  side of the semiconductor substrate  21 . 
     The lens  53  passes the light  12  reflected by the surface  21   a  of the semiconductor substrate  21 . Namely, the lens  53  passes the light  12  that has propagated through the semiconductor substrate  21 . A numerical aperture of the lens  53  is 0.3 or less. Namely, 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  12  that has passed through the lens  53  and through the mirror  52 . The light detection unit  54  is configured as, for example, an InGaAs camera and detects the light  12  in the near-infrared region. 
     Under control of the control unit  8 , the imaging unit  5  irradiates the wafer  20  with the light  12  from the back surface  21   b  side and detects the light  12  returning from the surface  21   a  (functional element layer  22 ), to capture an image of the functional element layer  22 . In addition, similarly, under control of the control unit  8 , the imaging unit  5  irradiates the wafer  20  with the light  12  from the back surface  21   b  side and detects the light  12  returning from formation positions of the modified regions  12   a  and  12   b  in the semiconductor substrate  21 , to acquire images of regions including the modified regions  12   a  and  12   b . These images are used for the alignment of the irradiation position of the laser beam L. The imaging unit  6  has the same configuration as that of the imaging unit  5  except that the lens  53  has a lower magnification (for example, the lens  53  of the imaging unit  5  has a magnification of  6 , and a lens of the imaging unit  6  has a magnification of 1.5), and is used for alignment similarly to the imaging unit  5 . 
     Imaging Principle of Imaging Unit for Inspection 
     As shown in  FIG.  7   , the imaging unit  4  shown in  FIG.  5    is used to move a focus F (a focus of the objective lens  43 ) from the back surface  21   b  side toward the surface  21   a  side in the semiconductor substrate  21  in which the crack  14  across the two rows of modified regions  12   a  and  12   b  reaches the surface  21   a.  In this case, when the focus F is aligned with a tip  14   e  of the crack  14  from the back surface  21   b  side, the crack  14  extending from the modified region  12   b  toward the back surface  21   b  side, the tip  14   e  can be checked (a right image in  FIG.  7   ). However, even when the focus F is aligned with the crack  14  itself and with the tip  14   e  of the crack  14  reaching the surface  21   a,  from the back surface  21   b  side, the crack  14  and the tip  14   e  of the crack  14  cannot be checked (left images in  FIG.  7   ). Incidentally, when the focus F is aligned with the surface  21   a  of the semiconductor substrate  21  from the back surface  21   b  side, the functional element layer  22  can be checked. 
     In addition, as shown in  FIG.  8   , the imaging unit  4  shown in  FIG.  5    is used to move the focus F from the back surface  21   b  side toward the surface  21   a  side in the semiconductor substrate  21  in which the crack  14  across the two rows of modified regions  12   a  and  12   b  does not reach the surface  21   a.  In this case, even when the focus F is aligned with the tip  14   e  of the crack  14  extending from the modified region  12   a  toward the surface  21   a  side, from the back surface  21   b  side, the tip  14   e  cannot be checked (a left image in  FIG.  8   ). However, when the focus F is aligned with a region opposite the back surface  21   b  with respect to the surface  21   a  (namely, a region on a functional element layer  22  side with respect to the surface  21   a ), from the back surface  21   b  side, and an imaginary focus Fv that is symmetric to the focus F with respect to the surface  21   a  is located at the tip  14   e,  the tip  14   e  can be checked (a right image in  FIG.  8   ). Incidentally, the imaginary focus Fv is a point that is symmetric to the focus F with respect to the surface  21   a  and that is set in consideration of a refractive index of the semiconductor substrate  21 . 
     It is assumed that the reason the crack  14  itself cannot be checked as described above is that a width of the crack  14  is smaller than a wavelength of the light I 1  that is illumination light.  FIGS.  9  and  10    show scanning electron microscope (SEM) images of the modified region  12  and of the crack  14  formed inside the semiconductor substrate  21  that is a silicon substrate.  FIG.  9 ( b )  is an enlarged image of a region A 1  shown in  FIG.  9 ( a ) ,  FIG.  10 ( a )  is an enlarged image of a region A 2  shown in  FIG.  9 ( b ) , and  FIG.  10 ( b )  is an enlarged image of a region A 3  shown in  FIG.  10 ( a ) . As described above, the width of the crack  14  is approximately 120 nm, and is smaller than the wavelength (for example, 1.1 to 1.2 μm) of the light I 1  in the near-infrared region. 
     An imaging principle assumed based on the above is as follows. 
     As shown in  FIG.  11 ( a ) , when the focus F is located in the air, the light I 1  does not return, so that a blackish image is obtained (a right image in  FIG.  11 ( a ) ). As shown in  FIG.  11 ( b ) , when the focus F is located inside the semiconductor substrate  21 , the light I 1  reflected by the surface  21   a  returns, so that a whitish image is obtained (a right image in  FIG.  11 ( b ) ). As shown in  FIG.  11 ( c ) , when the focus F is aligned with the modified region  12  from the back surface  21   b  side, the absorption, the scattering, or the like of some of the light I 1  that is reflected by the surface  21   a  to return is caused by the modified region  12 , so that an image is obtained in which the modified region  12  appears blackish in the whitish background (a right image in  FIG.  11 ( c ) ). 
     As shown in  FIGS.  12 ( a ) and  12 ( b ) , when the focus F is aligned with the tip  14   e  of the crack  14  from the back surface  21   b  side, the scattering, the reflection, the interference, the absorption, or the like of some of the light I 1  that is reflected by the surface  21   a  to return is caused, for example, by optical singularities (stress concentration, strain, a discontinuity of atomic density, and the like) occurring in the vicinity of the tip  14   e,  and by light confinement occurring in the vicinity of the tip  14   e,  so that images are obtained in which the tip  14   e  appears blackish in the whitish background (right images in  FIGS.  12 ( a ) and  12 ( b ) ). As shown in  FIG.  12 ( c ) , when the focus F is aligned with a portion other than the vicinity of the tip  14   e  of the crack  14  from the back surface  21   b  side, at least some of the light I 1  reflected by the surface  21   a  returns, so that a whitish image is obtained (a right image in  FIG.  12 ( c ) ). 
     Processing Condition Derivation Process 
     Hereinafter, a dicing force determination process in a processing condition derivation process will be described, which is to be executed as a pre-process of a process of forming modified regions for the purpose of cutting the wafer  20  or the like. Incidentally, hereinafter, the dicing force determination process in the processing condition derivation process will be described as one example, but the dicing force determination process may be executed in processes other than the processing condition derivation process, for example, in various inspection processes to be executed after a processing condition is derived. The processing condition is a recipe related to processing that indicates in which conditions and procedures the wafer  20  is processed. 
     A dicing force is a force related to the dicing (cutting) of the wafer  20  that is applied to the wafer  20  when the wafer  20  is irradiated with the laser beam.  FIG.  13    shows views for illustrating states of the wafers  20  according to a dicing force applied to the wafers  20 . In  FIGS.  13 ( a ) to  13 ( d ) , upper views are views showing actual states (observed states) of cross-sections of the wafers  20 , and lower views are views schematically showing the cross-sections shown in the upper views. As shown in the lower views of  FIGS.  13 ( a ) to  13 ( d ) , five rows of modified regions  12   a  to  12   e  are formed in each of the wafers  20  from a side close to the surface  21   a,  the side being opposite an incident surface of the laser beam. In the examples shown in  FIG.  13   , the dicing force applied to the wafers  20  decreases in order of  FIG.  13 ( d ) ,  FIG.  13 ( c ) ,  FIG.  13 ( b ) , and  FIG.  13 ( a ) . In the state of  FIG.  13 ( a )  where the dicing force is the smallest, the crack  14  does not occur above and below the modified regions (SD layers), and a stealth (ST) state where the crack  14  has not reached both the back surface  21   b  and the surface  21   a  is attained. In the state of  FIG.  13 ( b ) , the cracks  14  occur above and below at least modified regions  12   a,    12   d,  and  12   e,  and a half-cut (HC) state where the crack  14  has reached the back surface  21   b  is attained. In  FIG.  13 ( b ) , the crack  14  has not reached the surface  21   a  (ST state). In the state of  FIG.  13 ( c ) , the cracks  14  occur above and below all the modified regions  12   a  to  12   e,  the HC state where the crack  14  has reached the back surface  21   b  is attained, and a bottom side half-cut (BHC) state where the crack  14  has reached the surface  21   a  is attained. As described above, the state of  FIG.  13 ( c )  is a full-cut state where the cracks  14  have reached the back surface  21   b  and the surface  21   a.  Incidentally, a state where, even when there are very few spots inside the wafer  20  where the cracks  14  are not connected to each other, the spots where the cracks  14  are connected to each other are at a level at which the wafer  20  can be diced by a standard expand tape (for example, an expand tape having an expansion distance of 15 mm and an expansion rate of 5 mm/sec) is regarded as the full-cut state. The very few spots where the cracks  14  are not connected to each other are a resolidified spot (spot that is resolidified after being melt when laser irradiation is performed) in a modified layer portion, a black streak spot where the cracks  14  are not intentionally connected to each other to improve chip quality, and the like. 
     Similarly, even in the state of  FIG.  13 ( d )  where the dicing force is the largest, the full-cut state where the cracks  14  have reached the back surface  21   b  and the surface  21   a  is attained. Here, as shown in the lower view of  FIG.  13 ( d ) , since the dicing force is too large, in the example of  FIG.  13 ( d ) , the crack  14  meanders in a direction intersecting the thickness direction (Z direction) of the wafer  20 . When the dicing force is too large as described above, it is considered that the crack  14  greatly meanders in the direction intersecting the Z direction inside the wafer  20 . A spot where the crack  14  meanders becomes an end surface uneven spot after the wafer  20  is cut. As described above, for example, even when laser processing is performed for the purpose of attaining the full-cut state and the full-cut state is attained, the internal quality of the wafer  20  may decrease depending on the dicing force. In the present embodiment, an internal observation of the wafer  20  is performed to determine whether or not the dicing force is within a proper range, and when the dicing force is not within the proper range, a recipe (processing condition) correction process is executed such that the dicing force is within the proper range. An appropriate recipe (processing condition) taking the dicing force into consideration can be derived by executing the dicing force determination process and the correction process as described above. 
     The reason for the necessity of an internal observation of the wafer  20  will be further described with reference to  FIG.  14   . As described above, when laser processing is performed for the purpose of attaining the full-cut state, even though it is confirmed that the crack  14  has reached the back surface  21   b  that is a laser incident surface, if a crack state inside the wafer  20  is poor, the device quality is NG. For example, the occurrence of the above-described end surface uneven spot is considered as an example of a poor crack state. Since it is considered that a defect such as an incorrect chip size, a reduction in chip transverse strength, or particle dust generation is caused by the occurrence of end surface unevenness, the device quality is NG. In the cross-section example shown in  FIG.  14 ( a ) , since the crack  14  occurring inside the wafer  20  stops on the way toward the back surface  21   b,  the crack  14  in the vicinity of the back surface  21   b  extends straight, but the crack  14  at a central portion of the wafer  20  in the Z direction is formed to be bent (meander). As described above, depending on the method, a crack state in the vicinity of the back surface  21   b  can be normalized by stopping the extension of the crack  14 , but a crack state inside the wafer  20  may become poor. In consideration of such a case, it is necessary to perform internal observation of the wafer  20 . In addition, as shown in a schematic view of the cross-section shown in  FIG.  14 ( b ) , when the incident surface quality is of particular concern, a reversed SD method may be adopted in which first, a modified region (SD 1 ) closest to the back surface  21   b  that is an incident surface is formed, and then other modified regions (SD 2  to SD 4 ) are formed. Even in this case, the crack state of the back surface  21   b  is normal, but for example, as shown in  FIG.  14 ( b ) , there is a possibility of the occurrence of a problem such as the crack  14  discontinuing inside the wafer  20 . In consideration of such a case, it is necessary to perform internal observation of the wafer  20 . 
       FIG.  15    shows views schematically showing internal observation results of each state of wafers  20 .  FIGS.  15 ( a ) to  15 ( d )  show internal observation results corresponding to the states of  FIGS.  13 ( a ) to  13 ( d ) , respectively. Namely,  FIG.  15 ( a )  shows internal observation results in the ST state where the cracks  14  have not reached both the back surface  21   b  and the surface  21   a,    FIG.  15 ( b )  shows internal observation results in the HC state where the crack  14  has reached only the back surface  21   b,    FIG.  15 ( c )  shows internal observation results in the full-cut state (inside is good) where the crack  14  has reached the back surface  21   b  and the surface  21   a,  and  FIG.  15 ( d )  shows internal observation results in the full-cut state (inside is poor) where the crack  14  has reached the back surface  21   b  and the surface  21   a .  FIGS.  15 ( a ) to  15 ( d )  show an observation result of the back surface  21   b  (incident surface), an observation result of the modified region  12   d  (SD 4 ), and an observation result of the modified region  12   c  (SD 3 ) in each state. Each internal observation result is acquired by aligning the focus F with each point from the back surface  21   b  side through the imaging unit  4  (based on a signal output from the imaging unit  4  that has detected light from each point). 
     On the incident surface, the crack  14  is not observed in the ST state of  FIG.  15 ( a ) , and the crack  14  is observed in each of the states of  FIGS.  15 ( b ) to  15 ( d ) . In the modified region  12   d  (SD 4 ), marks De are distinctly observed in the ST state of  FIG.  15 ( a )  and in the HC state of  FIG.  15 ( b ) , but the marks De are vaguely observed in the full-cut states of  FIGS.  15 ( c ) and  15 ( d ) . In the modified region  12   c  (SD 3 ), the marks De are distinctly observed in the ST state of  FIG.  15 ( a )  and in the HC state of  FIG.  15 ( b ) , but the mark De is vaguely observed in the full-cut state (inside is good) of  FIG.  15 ( c ) . In addition, in the full-cut state (inside is poor) of  FIG.  15 ( d ) , when the focus F is aligned with the modified region  12   c  (SD 3 ), a meandering portion of the crack  14  which becomes an end surface uneven spot after cutting is observed. 
       FIG.  16    shows views for illustrating the observation of a width of the crack  14  that meanders.  FIG.  16 ( a )  shows an example in which tips of the cracks  14  extending from the modified regions  12   a  and  12   b  in an up-down direction are observed, and  FIG.  16 ( c )  shows an example in which a width of the crack  14  (width of the shadow of the crack  14 ) meandering between the modified regions  12   c  and  12   d  is observed. In the state shown in  FIG.  16 ( a ) , when the focus F is moved from the back surface  21   b  side toward the surface  21   a  side, the tip of the crack  14  extending from the modified region  12   b  toward the back surface  21   b  side is observed as shown in an upper view of  FIG.  16 ( b ) . In addition, when the focus F is moved to the tip of the crack  14  extending from the modified region  12   a  toward the surface  21   a  side (or a point symmetric to the end of the crack  14  with respect to the surface  21   a ), the tip of the crack  14  extending from the modified region  12   b  toward the surface  21   a  side is observed as shown in a lower view of  FIG.  16 ( b ) . Even when the width of the crack  14  meandering as shown in  FIG.  16 ( c )  is observed, similarly, the focus F is moved from the back surface  21   b  side toward the surface  21   a  side in the Z direction. Then, as shown in  FIG.  16 ( d ) , when the focus F reaches the meandering portion of the crack  14 , a region where the width of the shadow of the crack  14  is not constant is observed. The meandering portion of the crack  14  can be identified by observing the width of the shadow of the crack  14  is observed as described above. 
       FIG.  17    shows views for illustrating an end surface unevenness occurrence region (meandering portion of the crack  14 ) for each thickness of the wafers  20 .  FIG.  17 ( a )  shows a cross-section of the wafer  20  which has a thickness of 500 μm and in which a meandering portion of the crack  14  is generated,  FIG.  17 ( b )  shows a cross-section of the wafer  20  which has a thickness of 500 μm and in which a meandering portion of the crack  14  is not generated,  FIG.  17 ( c )  shows a cross-section of the wafer  20  which has a thickness of 400 μm and in which a meandering portion of the crack  14  is generated, and  FIG.  17 ( d )  shows a cross-section of the wafer  20  which has a thickness of 400 μm and in which a meandering portion of the crack  14  is not generated. As shown in  FIG.  17 ( a ) , in the wafer  20  having a thickness of 500 μm, the meandering portion (end surface unevenness occurrence region) of the crack  14  is generated between SD 2  and SD 3  that are modified regions, whereas as shown in  FIG.  17 ( c ) , in the wafer  20  having a thickness of 400 μm, the meandering portion of the crack  14  (end surface unevenness occurrence region) is generated between SD 3  and SD 4  that are modified regions. As described above, a region where the meandering portion of the crack  14  is generated varies depending on the thickness of the wafer  20 . For this reason, the control unit  8  may decide a position inside the wafer  20  at which the meandering of the crack  14  is assumed to be likely to occur, according to information regarding the wafer  20  (for example, the thickness of the wafer  20 ) or to laser processing conditions (for example, a laser condensing position inside the wafer  20  and the like), determine whether or not a meandering width of the crack  14  at the decided position is larger than a predetermined value, and determine a crack state inside the wafer  20 . 
     In the processing condition derivation process, the control unit  8  is configured to execute: a decision process of deciding a recipe (processing conditions) including laser beam irradiation conditions of the laser irradiation unit  3 , based on information received by the display  150 ; a processing process (first process) of controlling the laser irradiation unit  3  according to the recipe (processing conditions) set such that a plurality of the modified regions  12  are formed inside the wafer  20  by irradiating the wafer  20  with the laser beam and a full-cut state where the cracks  14  extending from the modified regions  12  have reached the back surface  21   b  and the surface  21   a  is attained; an identification process (second process) of identifying a state of the crack  14  on the back surface  21   b  which extends from the modified region  12 , and a state of at least one of the modified regions  12  and the cracks  14  inside the wafer  20 , based on a signal output from the imaging unit  4  that has detected light; a determination process (third process) of determining whether or not a dicing force applied to the wafer  20  according to the recipe is proper, based on information identified in the identification process; and a correction process (fourth process) of correcting the recipe to set the dicing force within a proper range when it is determined in the determination process that the dicing force is not proper. 
       FIG.  18    shows views for illustrating an outline of the processing condition derivation process. In the processing condition derivation process, as described above, the processing process of the wafer  20  is performed according to the recipe (processing condition) set to attain the full-cut state, and it is determined whether or not the dicing force (dicing force under a full-cut condition) applied to the wafer  20  is proper, based on the state of the crack  14  on the back surface  21   b  and on the internal state of the wafer  20 . Specifically, as shown in  FIG.  18   , observation results of an incident surface state, a mark state, a meandering state of cracks, and an incident back surface state are referred to in the determination as to whether or not the dicing force is proper.  FIG.  18 ( a )  schematically shows the wafer  20  in the full-cut state where the cracks  14  have reached the back surface  21   b  and the surface  21   a.  In the wafer  20 , the incident surface state (state of the back surface  21   b ) is observed as shown in  FIG.  18 ( b )  to determine whether or not the HC state where the crack  14  has reached the back surface  21   b  is attained, and whether or not a width of the crack  14  on the back surface  21   b  in the direction intersecting the Z direction that is the thickness direction of the wafer  20  is larger than a predetermined value. In addition, the mark state is observed to determine whether the mark is distinct and clear (refer to  FIG.  18 ( c ) ) or the mark is vague and unclear (refer to  FIG.  18 ( d ) ). In addition, a width of the shadow of the crack  14  between the modified regions (for example, between SD 3  and SD 4 ) (refer to  FIG.  18 ( e ) ) is observed to determine whether or not the width of the crack is larger than a predetermined value. In addition, the incident back surface state (state of the surface  21   a ) is observed to determine whether or not the BHC state where the crack  14  has reached the surface  21   a  is attained. Hereinafter, each process of the processing condition derivation process will be described. 
     (Decision Process) 
     The decision process will be described with reference to  FIGS.  19  to  21   . In the decision process, first, the display  150  receives a user&#39;s input of wafer processing information. The wafer processing information is information for deciding a recipe (processing condition).  FIG.  19    is one example of a setting screen for wafer processing information (user input reception screen) to be displayed on the display  150 . As shown in  FIG.  19   , the display  150  displays “FC determination”, “wafer thickness”, “device type”, and “processing setting”. The “FC determination” is information indicating that after a modified region (modified region to be formed last) assumed to be in the full-cut state is formed, a determination related to the dicing force under the full-cut condition is performed. In the example shown in  FIG.  19   , the “FC determination” is set to “execution”, and a user&#39;s input (a change in determination mode made by a user) is not received on this setting screen. The “wafer thickness” is information indicating a thickness of the wafer  20 . For example, the “wafer thickness” is selected from a plurality of options and is input by the user. The “device type” is information indicating a type of the wafer  20 . The “device type” is indicated by, for example, a type such as a “0°” product or a “45°” product according to the position of the notch. For example, the “device type” is selected from a plurality of options and is input by the user. The “processing setting” is setting information related to laser processing desired by the user. For example, the “processing setting” is selected from a plurality of options and is input by the user. At least one of the “wafer thickness”, the “device type”, and the “processing setting” may be input. When the input on the setting screen of  FIG.  19    is completed, the display  150  transitions to the screen of  FIG.  20   . 
       FIG.  20    is one example of a determination content confirmation screen to be displayed on the display  150 . The determination content confirmation screen is a screen for displaying information related to determinations (determinations after processing) to be executed based on contents input on the setting screen of  FIG.  19   . As shown in  FIG.  20   , determination contents and determination criteria are mainly displayed on the determination content confirmation screen. In the determination contents, contents of the “FC determination”, the “wafer thickness”, the “device type”, and the “processing setting” set on the setting screen of  FIG.  19    (or derived from the set information) are displayed. In the determination criteria, pass criteria in the determination process are displayed, pass criteria for “crack state of the incident surface” and “HC straightness” are displayed as pass criteria of a laser incident surface inspection (inspection of a state of the crack  14  on the back surface  21   b  which extends from the modified region  12 ), and pass criteria for “crack state of the incident back surface”, “end surface unevenness position”, “end surface unevenness width”, and “mark observation” are displayed as pass criteria of a wafer internal inspection (inspect of states of the modified region  12  and of 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 back surface  21   b  that is an incident surface of the laser beam. In order to perform a determination related to the dicing force under the full-cut condition, the pass criterion for the “crack state of the incident surface” is set to the HC state. The “HC straightness” is information indicating a meandering width of the crack  14  in the direction intersecting the Z direction, the crack  14  being observed on the back surface  21   b.  The pass criterion for the “HC straightness” can be input (selected) by the user. The “crack state of the incident back surface” is information indicating whether or not the crack  14  has reached the surface  21   a.  In order to perform a determination on the dicing force under the full-cut condition, the pass criterion for the “crack state of the incident back surface” is set to the BHC. The “end surface unevenness position” is information indicating a position where a determination related to end surface unevenness (meandering of the crack  14 ) is performed. The “end surface unevenness position” is defined to be, for example, a position between the modified regions such as “between SD 3  and SD 4 ”. Information of the “end surface unevenness position” can be input (selected) by the user. The “end surface unevenness width” is information indicating a meandering width of the crack  14  in the direction intersecting the Z direction, the crack  14  being observed at the position defined as the “end surface unevenness position”. The pass criterion for the “end surface unevenness width” can be input (selected) by the user. The “mark observation” is information indicating an observation result related to the clearness of a mark in each modified region. In order to perform a determination related to the dicing force under the full-cut condition, the pass criterion for the “mark observation” is set to “being vague”. When the input and the confirmation on the confirmation screen of  FIG.  20    are completed, the display  150  transitions to the screen of  FIG.  21   . 
       FIG.  21    is one example of a processing condition confirmation screen to be displayed on the display  150 . The processing condition confirmation screen is a screen for displaying the recipe (processing condition) decided by the control unit  8  based on the contents input on the setting screen of  FIG.  19   . As shown in  FIG.  21   , the processing condition confirmation screen displays “processing number”, “Z height (ZH)”, “VD”, “number of focuses”, “pulse energy”, “condensing state parameter”, “processing speed”, “frequency”, and “pulse width”. The Z height is information indicating a processing depth (height) when laser processing is performed. The VD is a Z interval between the SD layers when multi-focus processing is performed. The condensing state parameter is a parameter for varying a laser condensing state such as a spherical aberration or an astigmatism. Each information to be displayed on the processing condition confirmation screen can be corrected by a user&#39;s input. Incidentally, an optimum condensing correction amount (for example, a spherical aberration) differs between a shallow position and a deep position inside the silicon of the wafer  20 . In a full-cut process, since the amount of scanning in the Z direction is large, a more detailed image can be captured by changing the condensing correction amount for each Z position. 
     (Processing Process) 
     In the processing process, the control unit  8  controls the laser irradiation unit  3  according to the recipe (processing condition) decided and set in the decision process. The set recipe is a recipe set such that the plurality of modified regions  12  are formed inside the wafer  20  by irradiating the wafer  20  with the laser beam and the full-cut state where the cracks  14  extending from the modified regions  12  have reached the back surface  21   b  and the surface  21   a  is attained. In the processing process, the control unit  8  controls the laser irradiation unit  3  to form the plurality of modified regions  12 . 
     (Identification Process) 
     In the identification process, the control unit  8  identifies a state of the crack  14  on the back surface  21   b  which extends from the modified region  12 , and a state of at least one of the modified regions  12  and the cracks  14  inside the wafer  20 , based on a signal output from the imaging unit  4  that has detected light. Namely, the control unit  8  identifies a state of the crack  14  on the back surface  21   b  which extends from the modified region  12 , and a state of at least one of the modified regions  12  and the cracks  14  inside the wafer  20 , based on observation results of the back surface  21   b  and of the inside of the wafer  20  obtained by the imaging unit  4 . In the present embodiment, the control unit  8  executes the identification process after all the modified regions  12  (modified region  12  to be formed last) are formed. 
     The control unit  8  identifies a reach state of the crack  14  on the back surface  21   b  based on an observation result of the back surface  21   b  obtained by the imaging unit  4 . Specifically, the control unit  8  identifies whether the ST state where the crack  14  has not reached the back surface  21   b  is attained or the HC state where the crack  14  has reached the back surface  21   b  is attained. The control unit  8  identifies a meandering width of the crack  14  on the back surface  21   b  in the direction intersecting the thickness direction (Z direction) of the wafer  20 , based on an observation result of the back surface  21   b  obtained by the imaging unit  4 . 
     The control unit  8  identifies a meandering width of the crack  14  in the direction intersecting the thickness direction (Z direction) of the wafer  20  inside the wafer  20 , based on an observation result of the inside of the wafer  20  (for example, between the plurality of modified regions  12 ) obtained by the imaging unit  4 . The control unit  8  may decide a position inside the wafer  20  at which the meandering of the crack  14  is assumed to be likely to occur, according to the information regarding the wafer  20  (for example, the thickness of the wafer  20 ) or to laser processing conditions (for example, a laser condensing position and the like) input by the user (or estimated), and identify a meandering width of the crack  14  based on an observation result at the decided position. Alternatively, the control unit  8  may acquire observation results over the entire range in the thickness direction (Z direction) of the wafer  20 , and identify a maximum value of the meandering width of the crack  14 . 
     The control unit  8  identifies a clearness of the mark De of the laser beam related to the modified region  12 , based on an observation result of the inside of the wafer  20  (for example, each of the modified regions  12 ) obtained by the imaging unit  4 . Specifically, when the mark De is clearer than a predetermined clearness, the control unit  8  identifies that the mark De is distinct, and when the mark De is not clearer than the predetermined clearness, the control unit  8  identifies that the mark De is vague. The control unit  8  identifies a reach state of the crack  14  on the surface  21   a  based on an observation result of the surface  21   a  obtained by the imaging unit  4 . Specifically, the control unit  8  identifies whether the ST state where the crack  14  has not reached the surface  21   a  is attained or the BHC state where the crack  14  has reached the surface  21   a  is attained. 
     (Determination Process) 
     In the determination process, the control unit  8  determines whether or not the dicing force applied to the wafer  20  according to the recipe is proper (proper as a dicing force under the full-cut condition), based on the information identified in the identification process. When the identified reach state of the crack  14  is the ST state where the crack  14  has not reached the back surface  21   b,  the control unit  8  determines that the dicing force has not reached a proper range and is not proper. When the identified meandering width of the crack  14  on the back surface  21   b  is larger than a predetermined value (for example, several μm to several tens of μm), the control unit  8  determines that the dicing force is out of the proper range and is not proper. 
     When the identified meandering width of the crack  14  inside the wafer  20  is larger than a predetermined value (for example, several μm to several tens of μm), the control unit  8  determines that the dicing force is out of the proper range and is not proper. When the identified clearness of the mark is higher than a predetermined clearness and the mark is distinct, the control unit  8  determines that the dicing force has not reached the proper range and is not proper. When the identified reach state of the crack  14  is the ST state where the crack  14  has not reached the surface  21   a,  the control unit  8  determines that the dicing force has not reached the proper range and is not proper. 
       FIG.  22    is one example of a determination result confirmation screen to be displayed on the display  150 . The determination result confirmation screen is a screen that displays determination results in the determination process, and that receives a user&#39;s input related to the correction of the recipe. In the example shown in  FIG.  22   , as determination results, determination items, criteria (pass criteria), and results are shown. Now, regarding an item of “end surface unevenness” (width of the crack  14  inside the wafer), the pass criterion is 6 μm whereas the determination result is 11 μm, and it is considered that the dicing force is too large. In this case, since the correction of the recipe is recommended, a message “will the conditions be corrected and reprocessing and redetermination be executed?” is displayed, and correction can be executed to decrease the dicing force according to a user&#39;s input. Incidentally, as shown in  FIG.  22   , the determination result confirmation screen may display an observation image of the incident surface (image indicating whether the HC is attained or the ST is attained) and an image showing the width of the crack  14  inside the wafer. 
     (Correction Process) 
     In the correction process, when it is determined in the determination process that the dicing force is not proper, the control unit  8  corrects the recipe to set the dicing force within a proper range. The control unit  8  corrects the recipe to increase or decrease the dicing force. The control unit  8  performs correction to adjust, for example, the processing number, the Z height (ZH), the VD, the number of focuses, the pulse energy, the condensing state parameter, the processing speed, the frequency, the pulse width, or the like in the recipe.  FIG.  23    is one example of a processing condition correction screen to be displayed on the display  150 . In the example shown in  FIG.  23   , in order to decrease the dicing force, correction to reduce the pulse width of each pass (correction to make the pulse width smaller than that of the initial recipe shown in  FIG.  21   ) is executed. Such correction may be executed by receiving a user&#39;s input on the display  150  or may be automatically executed. 
     After the correction process is performed, the control unit  8  executes the processing process, the identification process, and the determination process again according to the corrected recipe.  FIG.  24    is one example of a determination result confirmation screen to be displayed on the display  150  when the processing process, the identification process, and the determination process are executed again after the correction process. The determination result confirmation screen after the correction process displays a determination results before the correction process (a first result in  FIG.  24   ) and a determination result after the correction process (a second result in  FIG.  24   ). In the determination result after the correction process shown in  FIG.  24   , all determination items satisfy the pass criteria, and the pass/fail determination is set to “pass”. Incidentally, even when the pass/fail determination is “pass”, correction may be performed to adjust the dicing force based on a user&#39;s input according to the determination result. 
     [Inspection Method] 
     An inspection method of the present embodiment will be described with reference to  FIG.  25   .  FIG.  25    is a flowchart of the inspection method.  FIG.  25    is a flowchart showing the processing condition derivation process to be executed as a pre-process of the process of forming modified regions in the wafer  20 , in the inspection method to be executed by the inspection device  1 . Incidentally, processes of steps S 4 , S 6 , and S 8  may be executed in an order other than the order in the flowchart. 
     As shown in  FIG.  25   , in the processing condition derivation process, initially, the display  150  receives a user&#39;s input of wafer processing information (step S 1 ). Specifically, the display  150  receives a user&#39;s input of various information shown in  FIG.  19   . 
     Subsequently, the control unit  8  decides a recipe (processing condition) including laser beam irradiation conditions of the laser irradiation unit  3 , based on the information received by the display  150 . Specifically, the control unit  8  decides the recipe as shown in  FIG.  21    (step S 2 ). The recipe is a recipe set such that the plurality of modified regions  12  are formed inside the wafer  20  by irradiating the wafer  20  with the laser beam and the full-cut state where the cracks  14  extending from the modified regions  12  have reached the back surface  21   b  and the surface  21   a  is attained. 
     Subsequently, the control unit  8  controls the laser irradiation unit  3  based on the decided recipe, to process the wafer  20  (step S 3 ). In the processing process, the control unit  8  controls the laser irradiation unit  3  to form the plurality of modified regions  12 . 
     Subsequently, the control unit  8  identifies a reach state of the crack  14  on the back surface  21   b  based on an observation result of the laser incident surface (back surface  21   b ) obtained by the imaging unit  4 , and determines whether or not the back surface  21   b  is in the HC state (step S 4 ). When it is determined in step S 4  that the HC state is not attained, the control unit  8  corrects the recipe to increase the dicing force (step S 5 ). In this case, the processes after step S 2  are executed again. 
     When it is determined in step S 4  that the HC state is attained, the control unit  8  identifies the straightness of the crack  14  (meandering width of the crack  14 ) on the back surface  21   b  based on an observation result of the laser incident surface (back surface  21   b ) obtained by the imaging unit  4 , and determines whether or not the meandering width of the crack  14  is smaller than a predetermined value (for example, several μm to several tens of μm) (whether or not the straightness is OK) (step S 6 ). When it is determined in step S 6  that the straightness is NG, the control unit  8  corrects the recipe to decrease the dicing force (step S 7 ). In this case, the processes after step S 2  are executed again. 
     When it is determined in step S 6  that the straightness is OK, the control unit  8  determines whether or not the internal inspection of the wafer  20  is OK (step S 8 ). The fact that the internal inspection is OK refers to satisfying, for example, a condition that the meandering width of the crack  14  inside the wafer  20  is smaller than the predetermined value (for example, several μm to several tens of μm), the mark De is vague, and the BHC state where the crack  14  has reached the surface  21   a  is attained. When it is determined in step S 8  that the internal inspection is NG, the control unit  8  corrects the recipe to increase or decrease the dicing force according to an NG reason (step S 9 ). In this case, the processes after step S 2  are executed again. On the other hand, when it is determined in step S 8  that the internal inspection is OK, the recipe is finalized (the decided recipe is finalized) (step S 10 ), and the processing condition derivation process ends. 
     Actions and Effects 
     Next, actions and effects of the inspection device  1  according to the present embodiment will be described. 
     The inspection device  1  according to the present embodiment includes the laser irradiation unit  3  that irradiates the wafer  20  with a laser beam from the back surface  21   b  side of the wafer  20  having the back surface  21   b  and the surface  21   a;  the imaging unit  4  that outputs light having a property of transmitting through the wafer  20 , and that detects the light that has propagated through the wafer  20 ; and the control unit  8 . The control unit  8  is configured to execute: the processing process of controlling the laser irradiation unit  3  according to the recipe set such that the plurality of modified regions  12  are formed inside the wafer  20  by irradiating the wafer  20  with the laser beam and the full-cut state where the cracks  14  extending from the modified regions  12  have reached the back surface  21   b  and the surface  21   a  is attained; the identification process of identifying a state of the crack  14  on the back surface  21   b  which extends from the modified region  12 , and a state of at least one of the modified regions  12  and the cracks  14  inside the wafer  20 , based on a signal output from the imaging unit  4  that has detected light; and the determination process of determining whether or not a dicing force applied to the wafer  20  according to the recipe is proper, based on information identified in the identification process. 
     The inspection device  1  applies the laser beam according to the recipe set to attain the full-cut state where the cracks  14  extending from the modified regions  12  have reached the back surface  21   b  and the surface  21   a  of the wafer  20 . Then, the state of the crack on the back surface  21   b  and the state of at least one of the modified regions  12  and the cracks  14  inside the wafer  20  are identified, and it is determined whether or not the dicing force applied to the wafer  20  according to the recipe is proper, based on the identified information. As described above, since in addition to the state of the crack  14  on the back surface  21   b  that is an incident surface of the laser beam, the state of at least one of the modified regions  12  and the cracks  14  inside the wafer  20  are identified, in consideration of not only information regarding an end surface (back surface  21   b ) of the wafer  20  but also information regarding the inside of the wafer  20 , it is determined whether or not the dicing force applied to the wafer  20  to attain the full-cut state is proper. Therefore, for example, when the full-cut state is attained but the internal quality of the wafer  20  decreases, it can be determined that the dicing force is not proper. Accordingly, the quality of the wafer  20  to be processed into the full-cut state can be ensured. 
     In the identification process, the control unit  8  may identify a meandering width of the crack  14  in the direction intersecting the thickness direction of the wafer  20  inside the wafer  20 , and in the determination process, when the identified meandering width of the crack  14  is larger than the predetermined value, the control unit  8  may determine that the dicing force is out of the proper range and is not proper. When the dicing force is too large, it is considered that the crack  14  greatly meanders in the direction intersecting the thickness direction of the wafer  20  inside the wafer  20 . A spot where the crack  14  meanders as described above becomes an end surface uneven spot after the wafer  20  is cut. For this reason, when the meandering width of the crack  14  is large, it is determined that the dicing force is too large, and the correction of the dicing force or the like is executed as necessary, so that the occurrence of an uneven spot in the end surface can be suppressed, and the quality of the wafer  20  to be processed into the full-cut state can be appropriately ensured. 
     In the identification process, the control unit  8  may decide a position inside the wafer  20  at which the meandering of the crack  14  is assumed to be likely to occur, according to the information regarding the wafer  20 , and identify a meandering width of the crack  14  at the decided position. The spot where the meandering of the crack  14  is likely to occur can be predicted to some extent by, for example, the thickness of the wafer  20 , the laser condensing position inside the wafer  20 , or the like. For this reason, the meandering width of the crack  14  at the position inside the wafer  20  at which the meandering of the crack  14  is assumed to be likely to occur is identified in consideration of the information regarding the wafer  20  such as the thickness of the wafer  20 , so that a determination related to the meandering width of the crack  14  can be efficiently and appropriately performed. 
     In the identification process, the control unit  8  may identify a clearness of the mark of the laser beam related to the modified region  12 , and in the determination process, when the identified clearness of the mark is higher than the predetermined value, the control unit  8  may determine that the dicing force has not reached a proper range and is not proper. When the full-cut state is attained, the mark related to the modified region  12  is vaguely observed and the clearness is low. On the other hand, when the full-cut state is not attained, the mark related to the modified region  12  is distinctly observed and the clearness is high. For this reason, when the clearness of the mark is high, it is determined that the dicing force is small, and correction or the like to increase the dicing force is executed as necessary, so that the full-cut state can be reliably attained, and the quality of the wafer  20  to be processed into the full-cut state can be appropriately ensured. 
     In the identification process, the control unit  8  may identify a reach state of the crack  14  on the back surface  21   b,  and in the determination process, when the identified reach state of the crack  14  is the ST state where the crack  14  has not reached the back surface  21   b , the control unit  8  may determine that the dicing force is out of a proper range and is not proper. When the HC state where the crack  14  has reached the back surface  21   b  is not attained (the ST state is attained), naturally, the full-cut state is not attained. For this reason, when the HC state is not attained, it is determined that the dicing force is small, and correction or the like to increase the dicing force is executed as necessary, so that the full-cut state can be reliably attained, and the quality of the wafer  20  to be processed into the full-cut state can be appropriately ensured. 
     In the identification process, the control unit  8  may identify a meandering width of the crack  14  on the back surface  21   b  in the direction intersecting the thickness direction of the wafer  20 , and in the determination process, when the identified meandering width of the crack  14  is larger than the predetermined value, the control unit  8  may determine that the dicing force is out of a proper range and is not proper. When the crack  14  on the back surface  21   b  greatly meanders in the direction intersecting the thickness direction of the wafer  20 , it is considered that the dicing force is too large. For this reason, when the meandering width of the crack  14  on the back surface  21   b  is larger than the predetermined value, it is determined that the dicing force is large, and correction or the like to reduce the dicing force is executed as necessary, so that the quality of the wafer  20  to be processed into the full-cut state can be appropriately ensured. 
     In the identification process, the control unit  8  may identify a reach state of the crack  14  on the surface  21   a,  and in the determination process, when the identified reach state of the crack  14  is the ST state where the crack  14  has not reached the surface  21   a,  the control unit  8  may determine that the dicing force has not reached a proper range and is not proper. When the BHC state where the crack  14  has reached the surface  21   a  is not attained (the ST state is attained), naturally, the full-cut state is not attained. For this reason, when the BHC state is not attained, it is determined that the dicing force is small, and correction or the like to increase the dicing force is executed as necessary, so that the full-cut state can be reliably attained, and the quality of the wafer  20  to be processed into the full-cut state can be appropriately ensured. 
     The control unit  8  is configured to further execute the correction process of correcting the recipe to set the dicing force within a proper range when it is determined in the determination process that the dicing force is not proper, and may execute the processing process, the identification process, and the determination process again according to the recipe corrected in the correction process. As described above, since each process is executed again according to the recipe corrected to set the dicing force within the proper range, it can be determined whether or not the corrected recipe is proper, and the proper recipe can be reliably derived. 
     The control unit  8  may control the laser irradiation unit  3  to form the plurality of modified regions  12  in the processing process, and execute the identification process and the determination process after the modified region  12  to be formed last in the processing process is formed. Accordingly, it can be determined whether or not the dicing force applied to the wafer  20  to attain the full-cut state is proper, based on a state of the wafer after all the modified regions  12  are formed (namely, a state that should be the full-cut state). 
     The embodiment of the present invention has been described above, but the present invention is not limited to the embodiment. For example, the control unit  8  may be configured to further execute a pre-identification process of identifying information related to the modified regions  12  and to the cracks  14  extending from the modified regions  12  before the modified region  12  to be formed last is formed, based on a signal output from the imaging unit  4  that has detected light; and a pre-determination process of determining whether or not a state before the modified region  12  to be formed last is formed is proper, based on the information identified in the pre-identification process. In the full-cut state (state where the modified region  12  to be formed last is formed), it may be difficult to observe a detailed internal state of the wafer  20 . In this respect, the information related to the modified regions  12  and to the cracks  14  before the modified region  12  to be formed last is formed is observed (identified), and it is determined whether or not the state before the modified region  12  to be formed last is formed is proper, so that an observation result of the detailed internal state of the wafer  20  can be taken into consideration, and the quality of the wafer  20  to be processed into the full-cut state can be ensured. 
       FIG.  26    shows views for illustrating an outline of a determination as to whether or not the dicing force is proper in a processing condition derivation process according to a modification example. As shown in  FIG.  26 ( a ) , in the present modification example, before the modified region  12   e  (SD 5 ) scheduled to be formed in a final pass is formed, the pre-identification process and the pre-determination process described above are executed. In the pre-identification process, as shown in  FIG.  26 ( a ) , in addition to an incident surface state, a mark state, the positions of the modified regions (SD layers), an incident back surface state, and the like inside the wafer  20  are identified. In a determination (FC determination) after the final modified region  12   e  is formed, the pass criterion for the determination (pass criterion of being the full-cut state) is that the mark is vague (refer to  FIG.  26 ( b ) ), but in a pre-determination (FC- 1 ) before the final modified region  12   e  is formed, the pass criterion for the determination is that the mark is distinct (refer to  FIG.  26 ( c ) ). This difference is due to the fact that a state of being the full-cut state is normal in the FC determination whereas a state of not being the full-cut state is normal in the FC- 1  determination. Namely, in the FC- 1  determination, when the mark is vague, it is considered that an uneven portion of the crack  14  exists inside the wafer and it is difficult to visually recognize the mark of the modified region under the uneven portion because of the uneven portion, and when the final modified region  12   e  is formed, the occurrence of end surface unevenness is expected, so that a determination result is a fail (the pre-determination is NG). As described above, when the FC- 1  determination is performed, a detailed internal state of the wafer  20  can be better observed compared to the case of the full-cut state, so that in addition to the above-described items, an inspection for the presence or absence of a black streak, an inspection for a black streak position, a BHC inspection, a crack amount inspection, and the like may be executed. 
       FIG.  27    is one example of a determination content confirmation screen related to the pre-determination (FC- 1  determination) which is to be displayed on the display  150 . In a determination criteria (pass criteria for the FC- 1  determination), for example, pass criteria for “end surface unevenness”, “mark observation”, “number of black streaks”, “black streak position”, “BHC inspection”, “each SD layer position”, and “incident surface state” are displayed.  FIG.  28    is one example of a determination result confirmation screen to be displayed on the display  150 . In the example shown in  FIG.  28   , a case is shown in which the “number of black streaks”, the “black streak position”, and the “BHC inspection” do not satisfy the respective pass criteria and are determined as a fail and the dicing force is too low. In this case, correction to increase the dicing force can be executed according to a user&#39;s input. Namely, the control unit  8  is configured to further execute a pre-correction process of correcting the recipe when it is determined in the pre-determination process that the state before the modified region  12  to be formed last is formed is not proper. Then, the control unit  8  executes the processing process, the pre-identification process, and the pre-determination process again according to the recipe corrected in the pre-correction process. As described above, the recipe is corrected when it is determined in the pre-determination process that the state is not proper, so that the quality of the wafer to be processed into the full-cut state can be ensured. 
       FIG.  29    is a flowchart of an inspection method (processing condition derivation process) according to the modification example. Specifically,  FIG.  29    is a flowchart of a process of executing a determination (FC determination) as to the full-cut state after the pre-determination (FC- 1  determination) is executed. As shown in  FIG.  29   , initially, the display  150  receives a user&#39;s input of wafer processing information (step S 101 ). Subsequently, the control unit  8  decides a recipe (processing condition) including laser beam irradiation conditions of the laser irradiation unit  3 , based on the information received by the display  150  (step S 102 ). Subsequently, the control unit  8  controls the laser irradiation unit  3  based on the decided recipe, to process the wafer  20  such that the modified regions  12  except for a final pass are formed (step S 103 ). 
     Subsequently, the control unit  8  executes the pre-identification process and the pre-determination process to determine whether or not a state before the modified region  12  to be formed last is formed is proper (whether or not various inspections are OK) (step S 104 ). When it is determined in step S 104  that the various inspections are NG, the control unit  8  corrects the recipe to increase or decrease the dicing force (step S 105 ). When it is determined in step S 104  that the various inspections are OK, the control unit  8  causes the wafer  20  to be processed such that the modified region  12  of the final pass is formed (step S 106 ). Then, the control unit  8  executes the processes related to the FC determination (processes of steps S 4  to S 9  in  FIG.  25   ) (step S 107 ). After the processes related to the FC determination, the control unit  8  finalizes the recipe (step S 108 ). 
     (Algorithm Related to Determination Based on Internal Observation Result) 
     Regarding various determinations based on internal observation results described above, an algorithm for detecting (identifying) the crack  14  and an algorithm for detecting (identifying) the mark related to the modified region will be described in detail. 
       FIGS.  30  and  31    are views for illustrating crack detection.  FIG.  30    shows internal observation results (images of the inside of the wafer  20 ). First, the control unit  8  detects a straight line group  140  in an image of the inside of the wafer  30  as shown in  FIG.  30 ( a ) . For example, an algorithm such as Hough transform or line segment detector (LSD) is used for the detection of the straight line group  140 . The Hough transform is a technique in which as for points on an image, all straight lines passing through the points are detected and a straight line is detected while weighting the straight lines passing through more feature points. The LSD is a technique in which a region that becomes a line segment is estimated by calculating a gradient and an angle of brightness values in an image and a straight line is detected by approximating the region to a rectangular shape. 
     Subsequently, the control unit  8  detects the crack  14  from the straight line group  140  by calculating a similarity of the straight line group  140  to a crack line as shown in  FIG.  31   . As shown in an upper view of  FIG.  31   , the crack line has a characteristic that the front and the rear in the Y direction with respect to a brightness value on the line are very bright. For this reason, for example, the control unit  8  compares brightness values of all pixels of the detected straight line group  140  to those in the front and in the rear in the Y direction, and sets the number of pixels, of which the difference both in the front and in the rear is a threshold value or more, as a score of the similarity. Then, the straight line group  140  having a highest score of the similarity to the crack line among a plurality of the detected straight line groups  140  is taken as a representative value in the image. An index that the higher the representative value is, the higher the crack  14  is likely to exist is obtained. The control unit  8  compares representative values of a plurality of images to each other to take an image having a relatively high score, as a crack image candidate. 
       FIGS.  32  to  34    are views for illustrating mark detection.  FIG.  32    shows internal observation results (images of the inside of the wafer  20 ). In an image of the inside of the wafer  20  as shown in  FIG.  32 ( a ) , the control unit  8  detects corners (concentration of edges) in the image as key points, and detects the positions, the sizes, and the directions thereof to detect feature points  250 . As a technique of detecting the feature points in such a manner, Eigen, Harris, Fast, SIFT, SURF, STAR, MSER, ORB, AKAZE, and the like are known. 
     Here, as shown in  FIG.  33   , since marks  280  each having a circular shape, a rectangular shape, or the like are arranged at regular intervals, each of the marks  280  has a strong feature as a corner. For this reason, it is possible to detect the marks  280  with high accuracy by summing up feature amounts of the feature points  250  in the image. As shown in  FIG.  34   , when totals of feature amounts for each image that is captured while shifting the focus in a depth direction are compared to each other, a change in a mountain indicating a crack row amount for each modified layer can be confirmed. The control unit  8  estimates a peak of the change as the position of the mark  280 . It is possible to estimate not only the positions of the marks but also a pulse pitch by summing up the feature amounts as described above. 
     (Adjustment of Setting Related to Internal Observation) 
     In addition, for example, a laser processing device may adjust a setting for performing the internal observation of the wafer in more detail.  FIG.  35    shows views for illustrating a difference in an imaging section depending on a processing method.  FIG.  35 ( a )  shows an imaging section when full-cut processing is performed, and  FIG.  35 ( b )  shows an imaging section when other processing (for example, BHC processing) is performed. In both the processing, an image of an imaginary focus that is symmetric to the surface  21   a  is also captured. Namely, in the wafers of  FIGS.  35 ( a ) and  35 ( b ) , the SD layers in a lower half are regions related to the imaginary focus. As shown in  FIG.  35   , when the full-cut processing is performed, the total imaging section is widened in the thickness direction of the wafer  20 . In addition, when the full-cut processing is performed, the interval between the modified regions (SD 1  to SD 4 ) becomes narrow, and the extension amount of the crack  14  is also reduced. For this reason, when the full-cut processing is performed, it is considered that unless the adjustment of the setting related to internal observation in the thickness direction of the wafer  20  in more detail or the like is executed, the modified regions and the cracks cannot be clearly observed. 
     Specifically, the control unit  8  performs the following processes to clearly observe the modified regions and the like even when the full-cut processing is performed. 
     Firstly, the control unit  8  is configured to further execute an aberration correction process of controlling the imaging unit  4  such that aberration correction according to a position in the thickness direction of the wafer  20  (optimum aberration correction in each thickness direction) is performed in each region in the thickness direction of the wafer  20  of which an image is captured by the imaging unit  4 . For example, the control unit  8  executes an optimum aberration correction by adjusting the spatial light modulator  32  or the correction ring  43   a  of the objective lens  43  in each region corresponding to an SD processing position (modified region formation position) estimated from the processing condition. 
     Secondarily, the control unit  8  is configured to further execute a brightness calibration process of controlling the imaging unit  4  such that the imaging unit  4  captures an image with a predetermined (for example, constant or optimum) brightness in each region in the thickness direction of the wafer  20  of which an image is captured by the imaging unit  4 , and such that the imaging unit  4  outputs light of a light amount corresponding to a position of each region in the thickness direction of the wafer  20 . In the internal observation, the deeper the observation depth is, the larger the light amount required to secure sufficient brightness is. Namely, the light amount required for each depth changes. For this reason, it is necessary to figure out a light amount required to obtain an optimum brightness value for each depth each time before observation is performed, when the laser device is started up, or the device is changed. In the brightness calibration process, a light amount when each position in the thickness direction is observed is decided, and setting is done such that the imaging unit  4  outputs light of the light amount during observation of each position. 
     In the brightness calibration process, as shown in  FIG.  36   , initially, an input related to brightness calibration is received (step S 71 ). The input related to brightness calibration may be, for example, an input of a wafer thickness to be input related to the derivation of the processing condition, or the like. Subsequently, the control unit  8  decides a calibration execution section according to the input (for example, the wafer thickness) related to brightness calibration. The calibration execution section referred to here is, for example, information of a plurality of ZHs at which brightness calibration is executed. Incidentally, the calibration execution section may be decided and input by the user. Subsequently, an imaging position of the imaging unit  4  is set to one ZH of the calibration execution section (step S 73 ). Then, the light amount of the light source  41  is adjusted such that the brightness with which an image at the ZH is captured is an optimum brightness (step S 74 ), and the ZH and the light amount are stored in association with each other (step S 75 ). An aperture diaphragm or the like is used for the adjustment of the light source  41 . The processes of steps S 73  to S 75  are executed until the adjustment of the light amount for all the ZHs is completed. Then, the light amount adjusted in such a manner is output from the light source  41  of the imaging unit  4  during observation of each position, so that the observation of each position can be performed with an appropriate brightness. 
     Thirdly, the control unit  8  is configured to further execute a shading correction process of controlling the imaging unit  4  to capture an image for shading in each region in the thickness direction of the wafer  20  of which an image is captured by the imaging unit  4 , before the modified regions are processed, and of identifying difference data between the image of each region and the image for shading of the corresponding region captured by the imaging unit  4 , after the modified regions are processed. In this case, the control unit  8  identifies a state related to each modified region based on the difference data. 
     In the shading correction process, as shown in  FIG.  37 ( a ) , an image for shading at each internal observation position (determination position) is acquired before SD processing (processing of the modified regions). Then, the SD processing is performed, and an image after the SD processing as shown in  FIG.  37 ( b )  is acquired at each internal observation position (determination position). Then, difference data between the image after the SD processing and the image for shading (refer to  FIG.  37 ( c ) ) is acquired at each internal observation position (shading correction is executed). Incidentally, when there is a positional offset between the image after the SD processing and the image for shading, correction may be executed according to an offset amount. Things to be shaded by the shading correction are, for example, a device pattern, point defects, uneven screen brightness, and the like. 
     A laser processing method (processing condition derivation process) in the case of executing the aberration correction process, the brightness calibration process, and the shading correction process described above will be described with reference to  FIG.  38   . Incidentally, in  FIG.  38   , the processing process and the determination process are described in a simplified manner. As shown in  FIG.  38   , initially, the display  150  receives a user&#39;s input of wafer processing information (step S 51 ). Specifically, the display  150  receives an input of information of at least the wafer thickness. Accordingly, the processing condition is automatically and provisionally decided. 
     Subsequently, the control unit  8  executes the brightness calibration process (step S 52 ). Specifically, the control unit  8  sets the imaging unit  4  such that the imaging unit  4  captures an image with a predetermined (for example, constant or optimum) brightness in each region in the thickness direction of the wafer  20  of which an image is captured by the imaging unit  4 , and such that the imaging unit  4  outputs light of a light amount corresponding to a position of each region in the thickness direction of the wafer  20 . 
     Subsequently, the control unit  8  acquires an image for shading correction (image for shading) (step S 53 ). Specifically, the control unit  8  acquires an image at each internal observation position before SD processing, as the image for shading. 
     Subsequently, the control unit  8  controls the laser irradiation unit  3  based on the processing condition, to process SD layers in the wafer  20  (step S 54 ). Subsequently, the control unit  8  executes aberration correction according to the position in the thickness direction of the wafer  20  (step S 55 ). For example, the control unit  8  executes an optimum aberration correction by adjusting the spatial light modulator  32  or the correction ring  43   a  of the objective lens  43  in each region corresponding to an SD processing position (modified region formation position) estimated from the processing condition. 
     Subsequently, an image of the processed wafer  20  is captured by the imaging unit  4  (step S 56 ). The control unit  8  executes shading correction (step S 57 ). Specifically, the control unit  8  acquires difference data between the image of each region and the image for shading of the corresponding region captured by the imaging unit  4 . 
     Then, the control unit  8  controls the display  150  such that imaging results are displayed on the display  150  (step S 58 ). Subsequently, the control unit  8  identifies a state related to each SD layer based on the imaging results, and determines whether or not the processing is proper (namely, whether or not the processing condition is proper), based on the identified information (step S 59 ). The control unit  8  performs the determination process referred to here, using difference data after the shading correction. When it is determined in step S 59  that the processing condition is not proper, the control unit  8  receives an input of a new processing condition, and executes the processing process again. In this case, as shown in  FIG.  38   , the processing process may be executed from the brightness calibration process (step S 52 ) again or may be executed from the SD processing (step S 54 ) again. On the other hand, when the processing condition is proper, the control unit  8  finally decides the processing condition as a processing condition, and the process ends. 
     As described above, the control unit  8  is configured to further execute the brightness calibration process of controlling the imaging unit  4  such that the imaging unit  4  captures an image with a predetermined brightness in each region in the thickness direction of the wafer  20  of which an image is captured by the imaging unit  4 , and such that the imaging unit  4  outputs light of a light amount corresponding to a position of each region in the thickness direction of the wafer  20 . According to such a configuration, the light amount of the imaging unit  4  can be decided such that a constant or optimum brightness is obtained for each imaging region in the thickness direction (depth direction) of the wafer  20 . Accordingly, the state related to each modified region can be appropriately identified. 
     The control unit  8  is configured to further execute the shading correction process of controlling the imaging unit  4  to capture an image for shading in each region in the thickness direction of the wafer  20  of which an image is captured by the imaging unit  4 , before the modified regions are processed, and of identifying difference data between the image of each region and the image for shading of the corresponding region captured by the imaging unit  4 , after the modified regions are processed. In the determination process, the state related to each modified region is identified based on the difference data. The difference data acquired by the shading correction process is image data from which noise such as a device pattern, point defects, or uneven screen brightness is removed, and is image data of only modified regions, a crack state, and the like that are desired to be observed. The state related to each modified region is identified based on such difference data, so that a state of the wafer  20  after the processing is appropriately identified. Accordingly, the quality of the wafer  20  after the processing can be more suitably ensured. 
     The control unit  8  is configured to further execute the aberration correction process of controlling the imaging unit  4  such that aberration correction according to a position in the thickness direction of the wafer  20  is performed in each region in the thickness direction of the wafer  20  of which an image is captured by the imaging unit  4 . For example, when full-cut processing is performed, the interval between the modified regions becomes narrow, and the extension amount of the crack is also reduced, so that clear observation cannot be performed unless aberration correction is performed for each position in the thickness direction of the wafer  20 . In this respect, as described above, since aberration correction according to the thickness of the wafer  20  is performed in each region in the thickness direction of the wafer  20 , clear observation can be performed, and a state related to each modified region can be more appropriately identified. 
       FIG.  39    shows images for illustrating effects obtained by executing the aberration correction process, the brightness value calibration process, and the shading correction process.  FIG.  39 ( a )  is an image when none of these processes is performed,  FIG.  39 ( b )  is an image when only the aberration correction process is performed,  FIG.  39 ( c )  is an image when the aberration correction process and the brightness value calibration process are performed, and  FIG.  39 ( d )  is an image when the aberration correction process, the brightness value calibration process, and the shading correction process are performed. As shown in  FIG.  39   , it can be seen that the clearness of the cracks  14  and the like are greatly improved by performing these processes. 
     (Regarding Automation of Processing Condition Derivation Process) 
     In the above-described embodiment, a final processing condition is derived by automatically deriving a provisional processing condition through inputting wafer processing information, by automatically deriving and displaying an image of an estimated processing result based on the processing condition, by displaying an image of an actual processing result, and by performing correction on the processing condition until the actual processing result coincides with the estimated processing result. However, all of such a processing condition derivation process may not be automatically executed. 
     For example, in a first step for automating the processing condition derivation process, the user may manually generate and set a processing condition (provisional processing condition) based on wafer processing information. Then, an actual processing result under the generated processing condition may be acquired, and each combination of the input wafer processing information and the processing condition that is manually generated may be stored in a database in association with the actual processing result. 
     Furthermore, in a second step, a model for deriving an estimated processing result from the wafer processing information and from the processing condition may be generated by learning information stored in the database. Then, a regression model for deriving an optimum (the most accurate) estimated processing result from the wafer processing information and from the processing condition may be generated by analyzing data in the above-described database. In this case, multivariate analysis or machine learning may be used as an analysis technique. Specifically, analysis techniques such as simple regression, multiple regression, SGD regression, Lasso regression, Ridge regression, decision tree, support vector regression, Bayesian linear regression, deep machine learning, and k-nearest neighbors method may be used. 
     Furthermore, in a third step, a regression model for automatically deriving an optimum processing condition (recipe) for obtaining a target processing result, from the input wafer processing information may be generated. Namely, parameters of the processing condition may be input to the regression model while being adjusted with respect to the input wafer processing information, and the optimum processing condition that outputs the target processing result may be searched. For example, techniques such as grid search, random search, and Bayesian optimization can be used as such an optimization technique. 
     Furthermore, in a fourth step, when the needs for the correction of the conditions are determined by comparing a simulation result (estimated processing result) and an actual processing result to each other, the data may be stored in the database, and a regression model (active learning) may be generated again, so that the accuracy of the regression model is improved through actual operation. As described above, the accuracy of the regression model can be improved by feedbacking the actual processing result through correcting the processing condition from a difference between the estimated processing result and the actual processing result. 
     REFERENCE SIGNS LIST 
       1 : inspection device,  3 : laser irradiation unit,  4 : imaging unit,  8 : control unit,  20 : wafer,  150 : display.