Patent Publication Number: US-10758999-B2

Title: Machining object cutting method and machining object cutting device

Description:
TECHNICAL FIELD 
     One aspect of the present invention relates to an object to be processed cutting method and an object to be processed cutting device. 
     BACKGROUND ART 
     A technique is known that forms a cutting start point region along each of a plurality of lines to cut set in a grid pattern for an object to be processed including a substrate made of a crystalline material, and causes a crack to reach the front surface and the back surface of the object to be processed from the cutting start point region, to obtain a plurality of chips by cutting the object to be processed along each of the plurality of lines to cut (see Patent Literature 1, for example). Examples of the cutting start point region include a modified region formed inside the substrate, a groove formed on the front surface of the object to be processed, and the like. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Publication No. 2006-108459 
     SUMMARY OF INVENTION 
     Technical Problem 
     When the plurality of chips is obtained by cutting the object to be processed with the technique as described above, a level difference appears on the cut surface of the chip, and the yield of the chip is reduced, in some cases. Therefore, in the object to be processed cutting method, it is required to smooth the cut surface. 
     An object of one aspect of the present invention is to provide an object to be processed cutting method and an object to be processed cutting device capable of smoothing a cut surface. 
     Solution to Problem 
     An object to be processed cutting method according to one aspect of present invention is an object to be processed cutting method of cutting an object to be processed including a substrate made of a crystalline material and a plurality of functional devices arrayed on a front surface of the substrate, the object to be processed cutting method including: a crystal orientation identifying step of identifying a crystal orientation of the substrate; a line to cut setting step of setting, for the object to be processed, a line to cut passing through a street region formed between adjacent functional devices, after the crystal orientation identifying step; and a cutting step of cutting the object to be processed along the line to cut, after the line to cut setting step, in which, in the line to cut setting step, in a case where an extending direction of the street region does not match the crystal orientation, the line to cut parallel to the crystal orientation and inclined with respect to the extending direction of the street region, is set for the object to be processed. 
     An object to be processed cutting device according to one aspect of the present invention is an object to be processed cutting device configured to cut an object to be processed including a substrate made of a crystalline material and a plurality of functional devices arrayed on a front surface of the substrate, the object to be processed cutting device including: a crystal orientation identifying unit configured to identify a crystal orientation of the substrate; a line to cut setting unit configured to set, for the object to be processed, a line to cut passing through a street region formed between adjacent functional devices; and a cutting unit configured to cut the object to be processed along the line to cut, in which the line to cut setting unit, in a case where an extending direction of the street region does not match the crystal orientation, sets, for the object to be processed, the line to cut parallel to the crystal orientation and inclined with respect to the extending direction of the street region. 
     The inventors of the present invention have found that appearance of the level difference is caused by the fact that the line to cut is set to deviate with respect to a crystal orientation of the substrate of the object to be processed. Under this finding, in the object to be processed cutting method and the object to be processed cutting device of the present invention, in a case where the extending direction of the street region does not match the crystal orientation, the line to cut parallel to the crystal orientation and inclined with respect to the extending direction of the street region, is set for the object to be processed. Accordingly, even in a case where the extending direction of the street region does not match the crystal orientation, it is possible to inhibit the line to cut from deviating with respect to the crystal orientation and being set. It is possible to inhibit the level difference in the cut surface from appearing and to smooth the cut surface. 
     In the object to be processed cutting method according to one aspect of the present invention, in the line to cut setting step, the line to cut may be set at a position where the line to cut falls within the street region in a width direction of the street region. In the object to be processed cutting device according to one aspect of the present invention, the line to cut setting unit may set the line to cut at a position where the line to cut falls within the street region in a width direction of the street region. Accordingly, in a case where the plurality of chips is obtained by cutting the object to be processed, the number of defective chips can be reduced. 
     In the object to be processed cutting method according to one aspect of the present invention, in the line to cut setting step, in a case where the line to cut does not fall within the street region in a width direction of the street region, the line to cut may be set at a position where a number of the functional devices crossed by the line to cut protruding from the street region is equal to or less than a predetermined number. In the object to be processed cutting device according to one aspect of the present invention, the line to cut setting unit, in a case where the line to cut does not fall within the street region in a width direction of the street region, may set the line to cut at a position where a number of the functional devices crossed by the line to cut protruding from the street region is equal to or less than a predetermined number. Accordingly, in the case where the plurality of chips is obtained by cutting the object to be processed, even when the line to cut does not fall within the street region, the number of defective chips can be reduced. 
     In the object to be processed cutting method according to one aspect of the present invention, the crystal orientation identifying step may include: a first step of setting a plurality of candidate lines extending in mutually different directions, for the object to be processed; a second step of converging laser light at the object to be processed such that a modified region is formed inside the substrate along each of the plurality of candidate lines, and a crack reaches a front surface of the object to be processed from the modified region; and a third step of identifying the crystal orientation on the basis of a state of the crack. In the object to be processed cutting device according to one aspect of the present invention, the crystal orientation identifying unit may include: a support table configured to support the object to be processed; a laser light source configured to emit laser light; a converging optical system configured to converge the light emitted from the laser light source at the object to be processed supported by the support table; an imaging unit configured to image a front surface of the object to be processed supported by the support table; a candidate line setting unit configured to set, for the object to be processed, a plurality of candidate lines extending in mutually different directions; an operation controller configured to control operation of at least one of the support table, the laser light source, and the converging optical system such that a modified region is formed inside the substrate along each of the plurality of candidate lines, and a crack reaches the front surface of the object to be processed from the modified region; and an identifying unit configured to identify the crystal orientation on the basis of an image of the crack imaged by the imaging unit. 
     The inventors of the present invention have found that, in a case where the modified region is formed in the substrate along the candidate line and the crack reaching the front surface from the modified region is formed, the smaller the degree of deflection of the crack is, the smaller the angular deviation between the direction of the candidate line and the crystal orientation is. Under this finding, in the object to be processed cutting method and the object to be processed cutting device of the present invention, the crystal orientation is identified on the basis of the state of the crack reaching the front surface from the modified region formed in the substrate along the candidate line. In this case, the crystal orientation can be accurately identified. 
     In the object to be processed cutting method according to one aspect of the present invention, the crystal orientation identifying step may identify the crystal orientation on the basis of a reference mark formed on the object to be processed and indicating the crystal orientation. In the object to be processed cutting device according to one aspect of the present invention, the crystal orientation identifying unit may include: an imaging unit configured to image a reference mark formed on the object to be processed and indicating the crystal orientation; and an identifying unit configured to identify the crystal orientation on the basis of an image of the reference mark imaged by the imaging unit. In this case, the crystal orientation can be accurately identified by using the reference mark. 
     In the object to be processed cutting method according to one aspect of the present invention, in the cutting step, laser light may be converged inside the object to be processed, a modified region may be formed inside the object to be processed along the line to cut, and the object to be processed may be cut along the line to cut from the modified region as a start point of cutting. In the object to be processed cutting device according to one aspect of the present invention, the cutting unit may include: a support table configured to support the object to be processed; a laser light source configured to emit laser light; a converging optical system configured to converge the laser light emitted from the laser light source at the object to be processed supported by the support table; and an operation controller configured to control operation of at least one of the support table, the laser light source, and the converging optical system such that a modified region to be a start point of cutting is formed inside the object to be processed along the line to cut. In this case, the object to be processed can be accurately cut along the line to cut from the modified region formed inside the object to be processed as the start point of cutting. 
     Advantageous Effects of Invention 
     With one aspect of the present invention, it is possible to provide an object to be processed cutting method and an object to be processed cutting device capable of smoothing the cut surface. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic configuration diagram of a laser processing device used for forming a modified region. 
         FIG. 2  is a plan view of an object to be processed for which the modified region is formed. 
         FIG. 3  is a sectional view of the object to be processed taken along the line of  FIG. 2 . 
         FIG. 4  is a plan view of the object to be processed after laser processing. 
         FIG. 5  is a sectional view of the object to be processed taken along the line V-V of  FIG. 4 . 
         FIG. 6  is a sectional view of the object to be processed taken along the line VI-VI of  FIG. 4 . 
         FIG. 7  is a sectional view of the object to be processed for explaining laser processing along a candidate line. 
         FIG. 8( a )  is a plan view illustrating a first example of a substrate front surface on which a half cut is formed.  FIG. 8( b )  is a plan view illustrating a second example of the substrate front surface on which the half cut is formed. 
         FIG. 9( a )  is a graph illustrating an example of a relationship between a crank period and an angle formed by a candidate line with respect to a crystal orientation.  FIG. 9( b )  is a graph illustrating an example of a relationship between a length of the half cut and an appearance frequency of a crank shape. 
         FIG. 10( a )  is a plan view illustrating a third example of a substrate front surface on which a half cut is formed.  FIG. 10( b )  is a plan view illustrating a fourth example of the substrate front surface on which the half cut is formed. 
         FIG. 11( a )  is a photographic view illustrating the substrate front surface on which the half cut is formed in an enlarged manner.  FIG. 11( b )  is another plan view illustrating the substrate front surface on which the half cut is formed in an enlarged manner. 
         FIG. 12  is a schematic configuration diagram illustrating a laser processing device according to a first embodiment. 
         FIG. 13  is a flowchart illustrating a laser processing method according to the first embodiment. 
         FIG. 14  is a flowchart illustrating processing of setting a reference line in the laser processing method according to the first embodiment. 
         FIG. 15( a )  is a plan view illustrating an example of the candidate line and the reference line set by the processing of  FIG. 14 .  FIG. 15( b )  is a graph for explaining setting of the reference line in the processing of  FIG. 14 . 
         FIG. 16  is a plan view illustrating an example of the substrate front surface on which marking is performed. 
         FIG. 17  is a plan view illustrating an example of the line to cut set in a street region in an enlarged manner. 
         FIG. 18  is a flowchart illustrating processing of setting the reference line in a laser processing method according to a second embodiment. 
         FIG. 19( a )  is a plan view illustrating an example of the candidate line and the reference line set by the processing of  FIG. 18 .  FIG. 19( b )  is a graph for explaining setting of the reference line in the processing of  FIG. 18 . 
         FIG. 20  is a flowchart illustrating a laser processing method according to the third embodiment. 
         FIG. 21( a )  is a diagram for explaining a line to cut setting step.  FIG. 21( b )  is another diagram for explaining the line to cut setting step. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, embodiments of the present invention will be described in detail with reference to drawings. In the drawings, the same or equivalent parts will be denoted by the same reference signs, without redundant description. 
     In a laser processing device that is an object to be processed cutting device according to the embodiment and a laser processing method that is an object to be processed cutting method according to the embodiment, by converging laser light at an object to be processed, a modified region is formed on the object to be processed along a processing line (including a candidate line, a reference line, and a line to cut). Therefore, the forming of the modified region will be described at first with reference to  FIGS. 1 to 6 . 
     As illustrated in  FIG. 1 , a laser processing device  100  (object to be processed cutting device) includes a laser light source  101  for causing laser light L to oscillate in a pulsating manner, a dichroic mirror  103  arranged to change a direction of the optical axis (optical path) of the laser light L by 90°, and a converging lens  105  for converging the laser light L. The laser processing device  100  further includes a support table  107  for supporting an object to be processed  1  that is irradiated with the laser light L converged by the converging lens  105 , a stage  111  for moving the support table  107 , a laser light source controller  102  for regulating the laser light source  101  in order to adjust the output, pulse width, pulse waveform, and the like of the laser light L, and a stage controller  115  for regulating the movement of the stage  111 . 
     In the laser processing device  100 , the laser light L emitted from the laser light source  101  changes the direction of its optical axis by 90° with the dichroic mirror  103  and then is converged by the converging lens  105  inside the object to be processed  1  mounted on the support table  107 . At the same time, the stage  111  is moved, so that the object to be processed  1  moves with respect to the laser light L along a processing line  5 . Accordingly, the modified region along the processing line  5  is formed in the object to be processed  1 . While the stage  111  is moved here for relatively moving the laser light L, the converging lens  105  may be moved instead or together therewith. 
     Employed as the object to be processed  1  is a planar member (e. g., a substrate or a wafer), examples of which include semiconductor substrates formed of semiconductor materials and piezoelectric substrates formed of piezoelectric materials. As illustrated in  FIG. 2 , the line to cut is set for cutting the object to be processed  1 , as the processing line  5 , for the object to be processed  1 . The processing line  5  is a virtual line extending straight. In a case where the modified region is formed inside the object to be processed  1 , the laser light L is relatively moved along the processing line  5  (that is, in the direction of arrow A in  FIG. 2 ) while locating a converging point (converging position) P inside the object to be processed  1 , as illustrated in  FIG. 3 . Accordingly, as illustrated in  FIGS. 4, 5 and 6 , a modified region  7  is formed in the object to be processed  1  along the processing line  5 . In a case where the processing line  5  is the line to cut, the modified region  7  formed along the processing line  5  is a cutting start point region  8 . 
     A converging point P is a position at which the laser light L is converged. The processing line  5  may be curved instead of being straight, a three-dimensional one combining them, or one specified by coordinates. The processing line  5  may be one actually drawn on a front surface  3  of the object to be processed  1  without being restricted to the virtual line. The modified region  7  may be formed either continuously or intermittently. The modified region  7  may be formed in either rows or dots, and is only required to be formed at least inside the object to be processed  1 . The crack may be formed from the modified region  7  as a start point, and the crack and the modified region  7  may be exposed at an outer surface (the front surface  3 , a back surface  21 , or an outer peripheral surface) of the object to be processed  1 . A laser light entrance surface in forming the modified region  7  is not limited to the front surface  3  of the object to be processed  1  but may be the back surface  21  of the object to be processed  1 . 
     Incidentally, in a case where the modified region  7  is formed inside the object to be processed  1 , the laser light L passes through the object to be processed  1  and is absorbed especially near the converging point P located inside the object to be processed  1 . Accordingly, the modified region  7  is formed on the object to be processed  1  (that is, internal absorption type laser processing). In this case, the front surface  3  of the object to be processed  1  hardly absorbs the laser light L and thus does not melt. On the other hand, in a case where the modified region  7  is formed on the front surface  3  of the object to be processed  1 , the laser light L is particularly absorbed near the converging point P located on the front surface  3 , and removal portions such as holes and grooves are formed (surface absorption type laser processing) by being melted from the front surface  3  and removed. 
     The modified region  7  is a region in which density, refractive index, mechanical strength and other physical characteristics are different from the surroundings. Examples of the modified region  7  include molten processed regions (meaning at least one of regions resolidified after having being once molten, those in the molten state, and those in the process of resolidifying from the molten state), crack regions, dielectric breakdown regions, refractive index changed regions, and their mixed regions. Other examples of the modified region  7  include regions where the density of the modified region  7  has changed from that of an unmodified region and regions formed with a lattice defect in a material of the object to be processed  1  (which may also collectively be referred to as high dislocation density regions). 
     The molten processed regions, refractive index changed regions, regions where the modified region  7  has a density different from that of the unmodified region, and regions formed with a lattice defect may further incorporate a crack (cut or microcrack) therewithin or at an interface between the modified region  7  and the unmodified region. The incorporated crack may be formed over the whole surface of the modified region  7  or in only a part or a plurality of parts thereof. The object to be processed  1  includes a substrate made of a crystalline material having a crystal structure. For example, the object to be processed  1  includes a substrate formed of at least one of gallium nitride (GaN), silicon (Si), silicon carbide (SiC), LiTaO 3 , and sapphire (Al 2 O 3 ). In other words, the object to be processed  1  includes, for example, a gallium nitride substrate, a silicon substrate, a SiC substrate, a LiTaO 3  substrate, or a sapphire substrate. The crystalline material may be either an anisotropic crystal or an isotropic crystal. 
     In the embodiment, the modified region  7  can be formed by forming a plurality of modified spots (processing marks) along the processing line  5 . In this case, the plurality of modified spots gathers to be the modified region  7 . The modified spot is a modified portion formed by a shot of one pulse of pulsed laser light (that is, laser irradiation of one pulse: laser shot). Examples of the modified spots include crack spots, molten processed spots, refractive index changed spots, and those in which at least one of them is mixed. As for the modified spots, their sizes and lengths of cracks occurring therefrom can be controlled as necessary in view of the required cutting accuracy, the demanded flatness of cut surfaces, the thickness, kind, and crystal orientation of the object to be processed  1 , and the like. In addition, in the present embodiment, the modified spot can be formed as the modified region  7 , along the processing line  5 . 
     In the embodiment, the modified region  7  is formed along the candidate line inside the object to be processed  1 , and a crack (hereinafter referred to as “half cut”) reaching the front surface  3  or the back surface  21  from the modified region  7 , is formed along the candidate line. On the basis of a state of the half cut, the crystal orientation of the object to be processed  1  is identified, and the reference line is set that is a line indicating the crystal orientation. A principle of identifying the crystal orientation of the object to be processed  1  and setting the reference line will be described below. 
     As illustrated in  FIG. 7 , a candidate line  5 A is set for the object to be processed  1  including a substrate  12  of the crystalline material. The converging point P is aligned with the inside of the object to be processed  1 , and the laser light L is emitted to a front surface  12   a  of the substrate  12  as the laser light entrance surface, along the candidate line  5 A. Accordingly, one or more rows (two rows in the example illustrated) of modified regions  7  are formed inside the substrate  12  in the thickness direction; along the candidate line  5 A. Along with this, the half cut that is a surface crack extending from the modified region  7  to the front surface  12   a , is generated along the candidate line  5 A. Incidentally, the Z direction is a direction corresponding to the thickness direction of the object to be processed  1 , the X direction is a direction perpendicular to the Z direction, and the Y direction is a direction orthogonal to both the Z direction and the Y direction (the same applies hereinafter). 
       FIGS. 8( a ) and 8( b )  are diagrams each illustrating an example of a half cut Hc as viewed from the front surface  12   a . The example of  FIG. 8( b )  illustrates a case where an angular deviation Δθ that is an angle at which an extending direction of the candidate line  5 A deviates with respect to a direction of a crystal orientation K of the substrate  12  is larger than the angle of the example of  FIG. 8( a ) . For example, in a case where the substrate  12  is a SiC substrate, the crystal orientation K is the crystal orientation K of its m-plane. 
     As illustrated in  FIGS. 8( a ) and 8( b ) , the half cut Hc is constituted by periodically repeated shapes each extending in the circumferential direction to be deflected in one direction crossing the extending direction of the candidate line  5 A, as viewed from the front surface  12   a . The half cut Hc has a shape in which a crank shape that is a shape of deflection (that is, a sawtooth shape extending to be inclined with respect to the candidate line  5 A and then bending in a direction crossed by the candidate line  5 A) is periodically repeated. 
     It is found that, in a case where the angular deviation Δθ is large, a degree of deflection of the half cut Hc is smaller than in a case where the angular deviation Δθ is small. The degree of deflection is an index value representing an extent of deflection. The degree of deflection includes, for example, a period of deflection, a frequency of deflection, and an amount of deflection. Specifically, the degree of deflection includes a crank period (period of deflection) that is a length (interval) in a direction along the candidate line  5 A in one crank shape, and an appearance frequency (frequency of deflection) of the crank shape per predetermined length of the half cut Hc. 
     In a case where the angular deviation Δθ is large, the crank period is smaller, and the appearance frequency of the crank shape per predetermined length of the half cut Hc is higher than in a case where the angular deviation Δθ is small. Accordingly, it is found that a degree between a magnitude of the angular deviation Δθ and the half cut Hc has a certain correlation. Specifically, it is found that the smaller the angular deviation Δθ is (the closer the extending direction of the candidate line  5 A is to the crystal orientation K), the larger the crank period is, and the lower the appearance frequency of the crank shape is. 
       FIG. 9( a )  is a graph illustrating an example of a relationship between an angle formed by the candidate line  5 A with respect to the crystal orientation K, and the crank period that is the degree of deflection of the half cut Hc.  FIG. 9( b )  is a graph illustrating an example of a relationship between a coordinate of the candidate line  5 A, and the appearance frequency of the crank shape that is the degree of deflection of the half cut Hc. A distance between coordinates corresponding to a difference between the appearance frequencies of the crank shape corresponds to the length between the cranks, that is, the crank period. In the figure, the angle formed by the candidate line  5 A with respect to the crystal orientation K (hereinafter simply referred to as the “angle of the candidate line  5 A”) is the angle of when an angle of a standard processing line determined as the standard setting is 0°. The standard processing line is, for example, a line parallel to an orientation flat of the object to be processed  1 . The crank period here is an average value of a predetermined number of crank periods. The crank period is represented as a relative value based on a certain crank period as a reference. 
     As illustrated in  FIG. 9( a ) , by changing the angle of the candidate line  5 A, the crank period changes. Accordingly, considering the above finding that the angular deviation Δθ decreases as the crank period is larger and the direction of the processing line  5  approaches the direction of the crystal orientation K, it can be seen that the crystal orientation K can be obtained from the candidate line  5 A having a large crank period. In the example illustrated, the angle of the candidate line  5 A and the crank period are inversely proportional to each other. An optimum angle of the candidate line  5 A is −0.05°, and in this case, a direction rotated by −0.05° from a direction of the standard processing line can be identified as the crystal orientation K, and the candidate line  5 A rotated by −0.05° from the standard processing line can be set as a reference line  5 B. 
     As illustrated in  FIG. 9( b ) , the larger the angular deviation Δθ is, the higher the appearance frequency of the crank shape is (the shorter the crank period is), per predetermined length of the half cut Hc. Accordingly, it can be seen that the crystal orientation K can be obtained from the candidate line  5 A having a low appearance frequency of the crank shape. 
       FIGS. 10( a ) and 10( b )  are views each illustrating another example of the half cut Hc as viewed from the front surface  12   a . In the example of  FIG. 10( a )  and the example of  FIG. 10( b ) , directions of the angular deviation Δθ with respect to the candidate line  5 A are different from each other. In a case of being divided into one side and the other side by the candidate line  5 A, when the crank shape of the half cut Hc has a shape extending to be inclined to one side of the candidate line  5 A, as illustrated in  FIG. 10( a ) , the direction of the crystal orientation K is inclined to the one side with respect to the candidate line  5 A. When the crank shape of the half cut Hc has a shape extending to be inclined to the other side of the candidate line  5 A, as illustrated in  FIG. 10( b ) , the direction of the crystal orientation K is inclined to the other side with respect to the candidate line  5 A. 
       FIGS. 11( a ) and 11( b )  are photographic views each illustrating an example of the half cut Hc as viewed from the front surface  12   a  in an enlarged manner. In the example in the figure, the substrate  12  is a SiC substrate, and a street region  17  described later is illustrated. The candidate line  5 A is set, on the street region  17 , parallel to an extending direction of the street region  17 . The half cut Hc illustrated in FIG.  11 ( a ) has a shape in which the crank shape extends upward with respect to the candidate line  5 A. In this case, the direction of the crystal orientation K has a counterclockwise angular deviation Δθ with respect to the candidate line  5 A as viewed from the front surface  12   a . The half cut Hc illustrated in  FIG. 11( b )  has a shape in which the crank shape extends downward with respect to the candidate line  5 A. In this case, the direction of the crystal orientation K has a clockwise angular deviation Δθ with respect to the candidate line  5 A as viewed from the front surface  12   a.    
     As described above, in the embodiment, a direction of the candidate line  5 A can be identified as the crystal orientation K, in which the candidate line has the smallest degree of deflection of the half cut Hc (for example, the largest crank period, or the lowest appearance frequency of the crank shape) out of a plurality of the candidate lines  5 A. The candidate line  5 A can be set as the reference line  5 B indicating the direction of the crystal orientation K. 
     Search is performed for the candidate line  5 A in which the degree of deflection of the half cut Hc falls within a predetermined range (for example, the crank period is equal to or greater than the threshold value, or the appearance frequency of the crank shape is equal to or less than a certain value), and the direction of the candidate line  5 A found can be identified as the crystal orientation K. The candidate line  5 A can be set as the reference line  5 B. A direction of an angle of the crystal orientation K with respect to the candidate line  5 A can be identified from a direction of deflection of the half cut Hc (inclination direction of the crank shape with respect to the candidate line  5 A). In other words, on the basis of whether the half cut Hc extends upward or downward with respect to the candidate line  5 A, it can be identified whether the angular deviation Δθ of the crystal orientation K with respect to the candidate line  5 A is in the positive direction or the negative direction. 
     Next, a laser processing device (object to be processed cutting device) of a first embodiment will be described with reference to the schematic configuration diagram of  FIG. 12 . 
     A laser processing device (object to be processed cutting device)  300  converges the laser light L at the object to be processed  1  to form the modified region  7  in the object to be processed  1  along the processing line  5  (including the candidate line  5 A, the reference line  5 B, and the line to cut  5 C). In addition, the laser processing device  300  converges the laser light L at the front surface  12   a  of the substrate  12  in the object to be processed  1  to perform marking for forming marks M that are a plurality of dent marks along the processing line  5  (see  FIG. 16 ). The plurality of marks M along the processing line  5  is arranged side by side along the processing line  5  at intervals corresponding to, for example, a pulse pitch (relative speed of the pulse laser light to the object to be processed  1 /repetition period of the pulse laser light). The plurality of marks M is a reference mark indicating the crystal orientation K. The marks M here are constituted by a modified spot (modified region  7 ) formed to be exposed on the front surface  12   a.    
     The laser processing device  300  includes a laser light source  202 , a converging optical system  204 , and a surface observation unit (imaging unit)  211 . The laser light source  202 , the converging optical system  204 , and the surface observation unit (imaging unit)  211  are provided in a housing  231 . The laser light source  202  emits the laser light L having a wavelength that is transmitted through the object to be processed  1 . The wavelength is, for example, 532 nm to 1500 nm. The laser light source  202  is, for example, a fiber laser or a solid laser. The converging optical system  204  converges the laser light L emitted from the laser light source  202 , inside the object to be processed  1 . The converging optical system  204  includes a plurality of lenses. The converging optical system  204  is installed on a bottom plate  233  of the housing  231  via a drive unit  232  including a piezoelectric device and the like. 
     In the laser processing device  300 , the laser light L emitted from the laser light source  202  is sequentially transmitted through the dichroic mirrors  210  and  238  to enter the converging optical system  204 , and is converged by the converging optical system  204  into the object to be processed  1  mounted on the support table  107  on the stage  111 . 
     The surface observation unit  211  observes the laser light entrance surface of the object to be processed  1 . The surface observation unit  211  images the front surface  12   a  of the substrate  12  in the object to be processed  1  supported by the support table  107 . The surface observation unit  211  includes an observation light source  211   a  and a detector  211   b . The observation light source  211   a  emits the visible light VL 1 . The observation light source  211   a  is not particularly limited, and a known light source can be used. 
     The detector  211   b  detects reflected light VL 2  of the visible light VL 1  reflected by the laser light entrance surface of the object to be processed  1 , to acquire an image of the front surface  12   a  (hereinafter simply referred to as a “surface image”). The detector  211   b  acquires a surface image including the half cut Hc. In addition, the detector  211   b  acquires a surface image including the plurality of marks M. The detector  211   b  is not particularly limited, and a known imaging device such as a camera can be used. 
     In the surface observation unit  211 , the visible light VL 1  emitted from the observation light source  211   a  is reflected by or transmitted through a mirror  208  and dichroic mirrors  209 ,  210 , and  238 , to be converged by the converging optical system  204  toward the object to be processed  1 . The reflected light VL 2  reflected by the laser light entrance surface of the object to be processed  1  is converged by the converging optical system  204 , to be transmitted through or reflected by the dichroic mirrors  238  and  210 , and then transmitted through the dichroic mirror  209 , to be received by the detector  211   b.    
     The laser processing device  300  includes a display unit  240  for displaying the surface image imaged by the surface observation unit  211 , and a controller  250  for controlling the laser processing device  300 . As the display unit  240 , a monitor or the like can be used. 
     The controller  250  includes, for example, a CPU, ROM, RAM, and the like. The controller  250  controls the laser light source  202 , to adjust the output, pulse width, and the like of the laser light L emitted from the laser light source  202 . When forming the modified region  7 , the controller  250  controls at least one of the housing  231 , a position of the stage  111  (support table  107 ), and driving of the drive unit  232 , to position the converging point P of the laser light L on the front surface  3  (front surface  12   a ) of the object to be processed  1 , or at a position within the predetermined distance from the front surface  3  (or the back surface  21 ). When forming the modified region  7 , the controller  250  controls at least one of the housing  231 , the position of the stage  111 , and the driving of the drive unit  232 , to relatively move the converging point P along the processing line  5 . 
     The controller  250  sets the plurality of candidate lines  5 A extending in mutually different directions for the object to be processed  1 . The controller  250  controls operation of at least one of the stage  111  (support table  107 ), the laser light source  202 , and the drive unit  232  (converging optical system  204 ) such that the modified region  7  is formed inside the substrate  12  and the half cut Hc is formed, along each of the plurality of candidate lines  5 A. 
     The controller  250  controls operation of the surface observation unit  211  to image the surface image. The controller  250  determines the reference line  5 B on the basis of the surface image imaged by the surface observation unit  211 , and sets the reference line  5 B for the object to be processed  1 . Specifically, image recognition processing is performed to a plurality of the surface images including the half cut Hc, and the candidate line  5 A having the smallest degree of deflection of the half cut Hc out of a predetermined number of candidate lines  5 A is set as the reference line  5 B indicating the crystal orientation K of the substrate  12  for the object to be processed  1 . Here, the crank period of each of a plurality of the half cuts Hc is recognized from the surface images, and the candidate line  5 A corresponding to the half cut Hc having the largest crank period is set as the reference line  5 B. The image recognition processing performed by the controller  250  is not particularly limited, and well-known image recognition processing such as pattern recognition or the like can be adopted. 
     The controller  250  controls operation of at least one of the stage  111 , the laser light source  202 , and the drive unit  232  such that the plurality of marks M (see  FIG. 16 ) is formed on the object to be processed  1  along the reference line  5 B. 
     The controller  250  performs image recognition processing to the surface image including the plurality of marks M and recognizes an arrangement direction of the marks M. The controller  250  identifies the crystal orientation K on the basis of the arrangement direction of the marks M recognized and aligns the line to cut  5 C. For example, the controller  250  sets the line to cut  5 C or changes the existing line to cut  5 C such that the line to cut  5 C is parallel to the arrangement direction of the marks M (parallel to the crystal orientation K). 
     The controller  250  sets the line to cut  5 C passing through the street region  17  described later of the object to be processed  1 . In a case where the extending direction of the street region  17  does not match the crystal orientation K, the controller  250  sets, for the object to be processed  1 , the line to cut  5 C parallel to the crystal orientation K and inclined with respect to the extending direction of the street region  17 . 
     Next, a laser processing method (object to be processed cutting method) performed in the laser processing device  300  will be described with reference to the flowcharts of  FIGS. 13 and 14 . 
     The laser processing method of the present embodiment is used, for example, in a manufacturing method for manufacturing a semiconductor chip such as a light emitting diode. In the object to be processed cutting method according to the present embodiment, first, the object to be processed  1  is prepared. As illustrated in  FIG. 15( a ) , the object to be processed  1  is a bare wafer and includes the substrate  12 . On the substrate  12 , an orientation flat OF is provided. The substrate  12  includes an ineffective region  16   x  provided on an outer edge portion on the front surface  12   a  and an effective region  16   y  provided inside the ineffective region  16   x . The effective region  16   y  is a region where a functional device layer  15  described later is provided. The ineffective region  16   x  is a region where the functional device layer  15  is not provided. 
     Subsequently, the reference line  5 B is set for the object to be processed  1  (S 10 ). Specifically, first, the substrate  12  is mounted on the support table  107  of the stage  111 . The controller  250  sets the candidate line  5 A parallel to the orientation flat OF (or inclined by a reference angle in the θ direction) as the standard processing line (S 11 ). The controller  250  changes the angle of the candidate line  5 A in the θ direction such that the angle of the candidate line  5 A is deviated by a specified angle in the θ direction with respect to the standard processing line (S 12 ). The θ direction is a rotation direction with the Z direction as an axial direction. The reference angle and the specified angle are predetermined angles set in advance. The reference angle and the specified angle are not particularly limited. The reference angle and the specified angle can be obtained from, for example, the specification or state of the substrate  12 . 
     Subsequently, along the candidate line  5 A in the ineffective region  16   x , the laser light L is scanned one or multiple times while being converged inside the substrate  12 , and one or more rows of the modified region  7  are formed inside the substrate  12  in the ineffective region  16   x . Accordingly, the half cut Hc reaching the front surface  12   a  of the substrate  12  in the ineffective region  16   x , is formed along the candidate line  5 A (S 13 ). In scanning of multiple times of the laser light L, scanning of the laser light L in the same direction (so-called one way processing) is repeated multiple times. Then, the surface image including the half cut Hc is imaged by the surface observation unit  211  and stored in a storage unit (ROM or RAM) of the controller  250 . In the scanning of multiple times of the laser light L, the laser light L may be scanned to reciprocate along the candidate line  5 A (so-called reciprocating processing). 
     Subsequently, laser processing according to S 12  and S 13  is repeatedly executed until the number of times of processing reaches a predetermined number of times set in advance (here, five times) (S 14 ). In S 12 , which is repeated multiple times, the angle is changed such that the angle of the candidate line  5 A in the θ direction does not become the same, and as a result, the predetermined number of candidate lines  5 A extending in different predetermined directions are set. 
     Subsequently, the controller  250  performs image recognition processing to the plurality of surface images stored, and recognizes and evaluates a state of each of the plurality of half cuts Hc (S 15 ). The controller  250  selects the half cut Hc having the largest crank period out of a plurality of the crank periods recognized. The controller  250  selects the candidate line  5 A from the plurality of candidate lines  5 A, in which the candidate line  5 A is along the half cut Hc having the largest crank period (S 16 ). Then, the controller  250  sets the candidate line  5 A selected, as the reference line  5 B indicating the crystal orientation K of the substrate  12 , for the object to be processed  1  (S 17 ). A direction (crystal orientation K) of the reference line  5 B set is stored in the storage unit of the controller  250 . 
     For example, in S 16 , as illustrated in  FIG. 15( b ) , a candidate line  5 G having the largest crank period is selected out of the five candidate lines  5 A set in the ineffective region  16   x . In this case, in S 17 , a direction of the candidate line  5 G is determined as the crystal orientation K, and the reference line  5 B parallel to the candidate line  5 G is set in the ineffective region  16   x . The direction of the reference line  5 B can be represented as an angle (optimum angle) in the θ direction from a parallel direction of the orientation flat OF. The reference line  5 B is a line extending to deviate in the θ direction by the optimum angle from the parallel direction of the orientation flat OF, in the ineffective region  16   x.    
     Subsequently, the plurality of marks M arranged along the reference line  5 B is marked on the front surface  12   a  of the substrate  12  (S 20 ). In S 20 , the laser light L is scanned while being converged at the front surface  12   a  of the substrate  12  along the reference line  5 B in the ineffective region  16   x , and the plurality of marks M is formed along the reference line  5 B on the front surface  12   a  of the substrate  12  in the ineffective region  16   x  (see  FIG. 16 ). 
     Subsequently, the substrate  12  is removed from the stage  111 , and the functional device layer  15  is formed on the front surface  12   a  of the substrate  12  (S 30 ). The functional device layer  15  includes a plurality of functional devices  15   a  (for example, a light receiving device such as a photodiode, a light emitting device such as a laser diode, or a circuit device formed as a circuit) arrayed in a matrix in the effective region  16   y  of the front surface  12   a . The street region (dicing street)  17  is formed between the adjacent functional devices  15   a.    
     In S 30 , the functional device layer  15  is formed, using the orientation flat OF as a reference. Specifically, the plurality of functional devices  15   a  arranged in the parallel direction and a vertical direction of the orientation flat OF is arrayed in the effective region  16   y  of the front surface  12   a . The grid-like street region  17  extending in the parallel direction and the vertical direction of the orientation flat OF is formed between the plurality of functional devices  15   a.    
     Subsequently, an expand tape is attached to the back surface  21  of the object to be processed  1  including the substrate  12  and the functional device layer  15 , and the object to be processed  1  is mounted on the stage  111 . The surface image including the plurality of marks M is imaged by the surface observation unit  211 . The controller  250  recognizes the arrangement direction of the plurality of marks M from the surface image. The controller  250  identifies the arrangement direction of the plurality of marks M as the crystal orientation K. The controller  250  sets the line to cut  5 C parallel to the arrangement direction of the marks M and passing through the street region  17 , and the line to cut  5 C orthogonal to the arranging direction of the marks M and passing through the street region  17  (S 40 ). In other words, the grid-like line to cut  5 C passing through the street region  17  between the plurality of functional devices  15   a  is set to extend along the parallel direction and an orthogonal direction of the crystal orientation K identified, by adjusting the angle in the θ direction. 
       FIG. 17  is a plan view illustrating the functional device layer  15  in an enlarged manner. As illustrated in  FIG. 17 , for example, in S 40 , the line to cut  5 C is set to pass through the street region  17  of the object to be processed  1 . In addition, the line to cut  5 C is set, in the street region  17 , to be along the parallel direction and the orthogonal direction of the crystal orientation K. In the example illustrated, the extending direction of the street region  17  (the direction in which the functional devices  15   a  are arranged) does not match the crystal orientation K. In this case, in S 40 , the line to cut  5 C passing through the street region  17  is set to be inclined with respect to the extending direction of the street region  17  and to be parallel to the crystal orientation K as viewed from the Z direction. In addition, the line to cut  5 C passing through the street region  17  is set to be inclined with respect to the extending direction of the street region  17  and to be vertical to the crystal orientation K as viewed from the Z direction. 
     Subsequently, the object to be processed  1  is cut along the line to cut  5 C to form a plurality of semiconductor chips (for example, a memory, an IC, a light emitting device, and a light receiving device) (S 50 ). Specifically, the laser light L is scanned one or multiple times along the line to cut  5 C while being converged inside the object to be processed  1 . Accordingly, one or more rows of the modified region  7  are formed inside the object to be processed  1 , along the line to cut  5 C. Then, by expanding the expand tape, the object to be processed  1  is cut along the line to cut  5 C from the modified region  7  as a start point of cutting, to be separated from each other as the plurality of semiconductor chips. 
     Here, it is found that appearance of a level difference in the cut surface in a case where the object to be processed  1  is cut along the line to cut  5 C, is caused by the fact that the line to cut  5 C is set to deviate with respect to the crystal orientation K. Under this finding, in the present embodiment, in a case where the extending direction of the street region  17 , the line to cut  5 C parallel to the crystal orientation K and inclined with respect to the extending direction of the street region  17 , is set for the object to be processed  1 . Accordingly, even in a case where the extending direction of the street region  17  does not match the crystal orientation K, it is possible to inhibit the line to cut  5 C from deviating with respect to the crystal orientation K and being set. It is possible to inhibit the level difference in the cut surface from appearing, and to smooth the cut surface and eventually make a mirror surface. 
     In the present embodiment, the crystal orientation K is identified on the basis of the plurality of marks M formed on the front surface  12   a  of the object to be processed  1  and indicating the crystal orientation K. Accordingly, the crystal orientation K can be accurately identified by using the marks M formed on the front surface  12   a.    
     In the present embodiment, the laser light L is converged inside the object to be processed  1 , and the modified region  7  is formed inside the object to be processed  1  along the line to cut  5 C. From the modified region  7  as a start point for cutting, the object to be processed  1  is cut along the line to cut  5 C. Accordingly, from the modified region  7  formed inside the object to be processed  1  as the start point of cutting, the object to be processed  1  can be accurately cut along the line to cut  5 C. 
     Incidentally, it is found that the number of level differences increases that appears on the cut surface of the object to be processed  1  cut along the processing line  5 , as the degree of deflection of the half cut Hc increases that occurs in a case where the modified region  7  is formed along the processing line  5 . Under this finding, in the present embodiment, on the basis of the surface image including the half cut Hc along each of the plurality of candidate lines  5 A extending in mutually different directions, the reference line  5 B is set for the object to be processed  1 . 
     Accordingly, it is possible to set the line to cut  5 C extending in a direction parallel to the reference line  5 B. As a result, it is possible to inhibit the line to cut  5 C from deviating with respect to the crystal orientation K of the substrate  12  and being set. It is possible to inhibit the level difference from appearing in the cut surface (end surface) of the chip obtained by cutting the object to be processed  1 , and to smooth the cut surface of the chip and eventually make a mirror surface. Further, the yield of the chip can be improved. 
     Incidentally, in general, directions of the orientation flat OF and the crystal orientation K may deviate from each other by about 1° at the maximum. Therefore, as compared with a case where the line to cut  5 C is set parallel to the orientation flat OF, the present embodiment having the above-described effect is particularly effective. 
     In the present embodiment, the controller  250  sets the predetermined number of candidate lines  5 A extending in mutually different predetermined directions, and sets the candidate line  5 A having the smallest degree of deflection of the half cut Hc out of the predetermined number of candidate lines  5 A, as the reference line  5 B. Accordingly, it is sufficient that laser light L irradiation, confirmation of the state of the half cut Hc, and the like are performed only for the predetermined number of candidate lines  5 A, so that setting of the reference line  5 B can be simply performed. 
     In the present embodiment, the controller  250  sets, for the substrate  12 , the predetermined number of candidate lines  5 A extending in mutually different predetermined directions, using the orientation flat OF provided in the object to be processed  1  as a reference. That is, the standard processing line parallel to the orientation flat OF is set, and the predetermined number of candidate lines  5 A are set, using the standard processing line as a reference. Accordingly, fluctuation in settings of the candidate lines  5 A for each object to be processed  1  can be inhibited. In particular, in a case where matching accuracy is high between the direction of the orientation flat OF and the direction of the crystal orientation K, it is effective because the settings of the plurality of candidate lines  5 A can be made only by fine adjustment from the standard processing line. Further, it is effective in a case where the chips are mass-produced from the object to be processed  1 . 
     The present embodiment includes a display unit  260  that displays the surface image imaged by the surface observation unit  211 . Accordingly, an operator can perform confirmation of the state of the half cut Hc, and the like. 
     In the present embodiment, the plurality of marks M is formed on the object to be processed  1  along the reference line  5 B. Accordingly, it is possible to set, for the object to be processed  1 , the line to cut  5 C extending in the direction parallel to the reference line  5 B, using the plurality of marks M as a reference. 
     In the present embodiment, the line to cut  5 C, extending in the direction parallel to the reference line  5 B is set for the object to be processed  1 , and the modified region  7  is formed inside the substrate  12  along the line to cut  5 C. Accordingly, a series of steps such as laser light L irradiation along the candidate line  5 A, confirmation of the state of the half cut Hc, setting of the reference line  5 B, setting of the line to cut  5 C, and laser light L irradiation along the line to cut  5 C, can be performed on one laser processing device  300 . 
     In the present embodiment, the candidate line  5 A and the reference line  5 B are set in the ineffective region  16   x  of the substrate  12 , and the plurality of marks M is formed on the front surface  12   a  in the ineffective region  16   x  of the substrate  12 . Accordingly, when manufacturing the chip by cutting the object to be processed  1 , it is possible to effectively utilize a portion (ineffective region  16   x ) that is normally removed and discarded. The candidate line  5 A and the reference line  5 B may be set in the ineffective region  16   x . The plurality of marks M may be formed in the effective region  16   y.    
     In the present embodiment, when forming the plurality of rows of modified regions  7  along the candidate line  5 A to form the half cut Hc, the laser light L is not scanned to reciprocate along the candidate line  5 A, but the laser light L is repeatedly scanned multiple times in the same direction. Accordingly, the half cut Hc from the modified region  7  can suitably reach the front surface  12   a , and deflection of the half cut Hc (crank shape) can be caused to occur noticeably. 
     The present embodiment is not limited to the above, and may be configured as follows. 
     In the present embodiment, the plurality of marks M arranged along the reference line  5 B is formed as the reference mark; however, the reference mark to be formed is not particularly limited. For example, a new orientation flat (a plane formed on a part of the outer peripheral surface of the substrate  12 ) different from the orientation flat OF may be provided parallel to the reference line  5 B as a reference mark. A surface cut by using the half cut Hc of the optimum candidate line  5 A may be used as a new orientation flat as a reference mark. The modified region  7  may be formed inside the object to be processed  1  along the reference line  5 B by the laser light L irradiation, and the surface cut from the modified region  7  as a start point may be used as a new orientation flat as a reference mark. Incidentally, various known processing methods can be adopted for forming the new orientation flat. 
     The reference mark may be a crack reaching the front surface  12   a  from the modified region  7  in the substrate  12 . The reference mark may be constituted by a shape (including a two-dimensional shape and a three-dimensional shape) indicating a crystal orientation, a pattern, a color, a display, a one-dimensional code, a two-dimensional code, or the like, or a combination thereof. The reference mark may be a scribe line formed along the reference line  5 B. 
     In the present embodiment, the controller  250  performs image recognition processing to the surface image of the substrate  12  to automatically recognize the degree of deflection of the half cut Hc; however, the degree of deflection of the half cut Hc may be recognized from the surface image displayed on the display unit  240  or visually by the operator. In this case, for example, in an operation unit connected to the controller  250 , the operator may perform operation of setting the reference line  5 B on the basis of the degree of deflection of the half cut Hc, to set the reference line  5 B for the object to be processed  1 . 
     In the present embodiment, the controller  250  performs the image recognition processing to the surface image of the substrate  12  to automatically recognize the plurality of marks M; however, the plurality of marks M may be recognized from the surface image displayed on the display unit  240  or visually by the operator. In this case, for example, in the operation unit connected to the controller  250 , the operator may perform operation of setting the line to cut  5 C parallel to the arrangement direction of the plurality of marks M, to set the line to cut  5 C for the object to be processed  1 . 
     In the present embodiment, in S 30  in which the functional device layer  15  is formed on the front surface  12   a  of the substrate  12 , the functional device layer  15  is formed, using the orientation flat OF as a reference; however, the functional device layer  15  may be formed, using the plurality of marks M as a reference. Specifically, the plurality of functional devices  15   a  arranged in the arrangement direction and its vertical direction of the plurality of marks M may be arrayed in the effective region  16   y  of the front surface  12   a , and the grid-like street region  17  extending in the arrangement direction and its vertical direction of the plurality of marks M may be formed between the plurality of functional devices  15   a . Accordingly, the plurality of functional devices  15   a  and the street region  17  can be accurately arranged along the crystal orientation K. 
     In the present embodiment, after S 20  in which marking is performed on the substrate  12 , S 30  is performed in which the functional device layer  15  is performed; however, not limited thereto, the object to be processed  1  may be used in which the functional device  15   a  is formed in advance on the substrate  12  (so-called device-formed wafer). That is, after S 10  in which the reference line  5 B is set for the object to be processed  1  on which the functional device  15   a  is formed in advance on the substrate  12 , S 20  is performed in which marking is performed, and S 40  may be immediately performed in which the line to cut is set. In this case, the line to cut  5 C may be set to be parallel to the reference line  5 B set, in S 40 , without performing S 20  in which marking is performed. 
     Next, a second embodiment will be described. In the description of the second embodiment, points different from the first embodiment will be described. 
     In the present embodiment, on the basis of the surface image imaged by the surface observation unit  211 , the controller  250  sequentially sets the plurality of candidate lines  5 A for the object to be processed  1  until the degree of deflection of the half cut Hc falls within the predetermined range. The controller  250  sets the candidate line  5 A of which the degree of deflection of the half cut Hc falls within the predetermined range, as the reference line  5 B for the object to be processed  1 . Here, the candidate line  5 A is set as the reference line  5 B, in which the candidate line  5 A is along the half cut Hc having the crank period equal to or greater than the threshold value. 
     As illustrated in  FIG. 18 , in the laser processing method (object to be processed cutting method) according to the second embodiment, the reference line  5 B is set in S 10  as follows. That is, first, the substrate  12  is mounted on the support table  107  of the stage  111 . The candidate line  5 A parallel to the orientation flat OF (or inclined by the reference angle in the θ direction) is set as the standard processing line (S 61 ). 
     Subsequently, along the candidate line  5 A in the ineffective region  16   x , the laser light L is scanned one or multiple times while being converged inside the substrate  12 , and one or more rows of the modified region  7  are formed inside the substrate  12  of the ineffective region  16   x . Accordingly, the half cut Hc reaching the front surface  12   a  of the substrate  12  in the ineffective region  16   x  is formed along the candidate line  5 A (S 62 ). The surface image including the half cut Hc is imaged by the surface observation unit  211  and stored in the storage unit (ROM or RAM) of the controller  250 . 
     Subsequently, the controller  250  performs image recognition processing to the surface image stored, and recognizes and evaluates the state of the half cut Hc (S 63 ). It is determined whether or not the crank period of the half cut Hc is equal to or greater than the threshold value (S 64 ). In a case of NO in S 64  (in a case where the crank period is less than the threshold value), the angle in the θ direction of the candidate line  5 A is changed in accordance with the recognition result, and a new candidate line  5 A is set (S 65 ). 
     In S 65 , in the plan view, a direction in the θ direction (whether it is the positive direction or the negative direction) in which the candidate line  5 A rotates in the direction of deflection of the half cut Hc, is obtained as a specified rotation direction. A specified rotation angle is obtained from the crank period of the half cut Hc, using a data function or data table set in advance. The angle of the candidate line  5 A in the θ direction is changed to deviate by a specified angle in the specified rotation direction. After S 65 , the processing returns to S 62 . 
     The threshold value is a value that can be set on the basis of the crank period of when the angular deviation Δθ is sufficiently small between the direction of the crystal orientation K and the direction of the candidate line  5 A. The data function or data table is data relating to a correlation  66  (see  FIG. 19( b ) ) between the angle formed by the candidate line  5 A with respect to with respect to the crystal orientation K and the crank period (the degree of deflection of the half cut Hc). The threshold value and the data function or data table are stored in the storage unit (ROM) of the controller  250 . Rotating the processing line  5  to a deflection side of the crank shape in the θ direction is the same as rotating the object to be processed  1  to a side opposite to the deflection side of the crank shape in the θ direction. 
     In a case of YES in S 64  (in a case where the crank period is equal to or greater than the threshold value), the current candidate line  5 A is set as the reference line  5 B, and the direction of the reference line  5 B set is stored as the crystal orientation K in the storage unit of the controller  250  (S 66 ). 
     In the example illustrated in  FIGS. 19( a ) and 19( b ) , first, laser processing is performed along a candidate line  5 A 1  to form a half cut Hc. Since a crank period C 3  of the half cut Hc is less than a threshold value α, a candidate line  5 A 2  is newly set. Subsequently, laser processing is performed along the candidate line  5 A 2 , and a half cut Hc is formed. Since a crank period C 2  of the half cut Hc is still less than the threshold value α, a candidate line  5 A 3  is newly set. Subsequently, laser processing is performed along the candidate line  5 A 3 , and a half cut Hc is formed. A crank period C 3  of the half cut Hc is equal to or greater than the threshold value α, so that the candidate line  5 A 3  is set as the reference line  5 B. After that, in S 20 , the plurality of marks M is formed along the reference line  5 B. 
     As described above, also in the present embodiment, in a case where the plurality of chips is obtained by cutting the object to be processed  1  along the line to cut  5 C, the above effect is exerted that it is possible to smooth the cut surface and eventually make a mirror surface. 
     In the present embodiment, the controller  250  sequentially sets the plurality of candidate lines  5 A for the object to be processed  1  until the degree of deflection of the half cut Hc falls within the predetermined range (here, the crank period becomes the threshold value α). Then, the candidate line  5 A of which the degree of deflection of the half cut Hc falls within the predetermined range, is set as the reference line  5 B. Accordingly, it is possible to set the reference line  5 B for the object to be processed  1  with desired accuracy. For example, by setting the threshold value α to a value of when the crystal orientation K and the direction of the candidate line  5 A match each other, high matching accuracy can be realized between the crystal orientation K and the reference line  5 B. 
     In the present embodiment, the controller  250  sets the initial candidate line  5 A 1  for the object to be processed  1 , using the orientation flat OF provided on the object to be processed  1  as a reference. That is, the standard processing line parallel to the orientation flat OF is set, and the candidate line  5 A 1  is set, using the standard processing line as a reference. In this case, fluctuation in settings of the candidate lines  5 A for each object to be processed  1  can be inhibited. 
     The controller  250  of the present embodiment includes the storage unit that stores the correlation  66  (data function or data table) between the angle formed by the candidate line  5 A with respect to the crystal orientation K and the degree of deflection of the half cut Hc. Accordingly, when setting a new candidate line  5 A in S 65 , the correlation  66  can be used as an index. As a result, it is possible to reduce the number of candidate lines  5 A that are sequentially set before the reference line  5 B is set. 
     Next, a third embodiment will be described. In the description of the third embodiment, points different from the first embodiment will be described. 
     In the present embodiment, the controller  250  sets the line to cut  5 C at a position where the line to cut  5 C falls within the street region  17  in a width direction of the street region  17  (a direction orthogonal to the extending direction of the street region  17 , hereinafter referred to as a “street width direction”). In a case where the line to cut  5 C does not fall within the street region  17  in the street width direction, the controller  250  sets the line to cut  5 C at a position where the number of functional devices  15   a ′ (see  FIG. 21( b ) ) crossed by the line to cut  5 C protruding from the street region  17 , is equal to or less than a predetermined number or is the least. 
     The laser processing method (object to be processed cutting method) according to the present embodiment will be described with reference to the flowchart of  FIG. 20 . First, the object to be processed  1  is prepared (see  FIG. 21 ). The object to be processed  1  here is a device-formed wafer and includes the substrate  12  and the functional device layer  15  including the plurality of functional devices  15   a  arrayed on the front surface  12   a  of the substrate  12 . The street region  17  is formed between the adjacent functional devices  15   a . The plurality of functional devices  15   a  is arranged side by side in the parallel direction and the vertical direction of the orientation flat OF. The street region  17  extends in the parallel direction and the vertical direction of the orientation flat OF. 
     Subsequently, the crystal orientation K of the substrate  12  is identified (S 71 ). In S 71 , by performing the same processing as the processing of S 11  to S 17 , the crystal orientation K can be identified. That is, the object to be processed  1  is mounted on the support table  107  of the stage  111 . The candidate line  5 A parallel to the orientation flat OF is set as the standard processing line. The angle of the candidate line  5 A in the θ direction is changed such that the angle of the candidate line  5 A deviates by a specified angle in the θ direction with respect to the standard processing line. The laser light L is scanned one or more times while being converged inside the object to be processed  1 , along the candidate line  5 A. Accordingly, one or more rows of the modified regions  7  are formed inside the substrate  12 , and the half cut Hc is formed along the candidate line  5 A. The surface image including the half cut Hc is imaged by the surface observation unit  211  and stored in the storage unit (ROM or RAM) of the controller  250 . 
     Laser processing relating to changing the angle of the candidate line  5 A and forming the half cut Hc is repeatedly executed a predetermined number of times set in advance. Image recognition processing is performed to the plurality of surface images stored, and the crank period of each of the plurality of half cuts Hc is recognized. The half cut Hc having the largest crank period out of the crank periods is selected. The direction of the candidate line  5 A corresponding to the half cut Hc selected, is identified as the crystal orientation K. 
     Alternatively, in S 71 , by performing the same processing as the processing of S 61  to S 66 , the crystal orientation K can be identified. That is, the object to be processed  1  is mounted on the support table  107  of the stage  111 . The candidate line  5 A parallel to the orientation flat OF is set as the standard processing line. The laser light L is scanned one or more times while being converged inside the object to be processed  1 , along the candidate line  5 A. Accordingly, one or more rows of the modified regions  7  are formed inside the substrate  12 , and the half cut Hc is formed along the candidate line  5 A. The surface image including the half cut Hc is imaged by the surface observation unit  211  and stored in the storage unit (ROM or RAM) of the controller  250 . 
     Image recognition processing is performed to the surface image stored, and the crank period of the half cut Hc is recognized. Until the crank period recognized becomes equal to or greater than the threshold value, setting of a new candidate line  5 A in which the angle in the θ direction is changed, formation of the half cut Hc, imaging of the surface image, and recognition of the crank period are repeated. In a case where the crank period is equal to or greater than the threshold value α, the direction of the candidate line  5 A corresponding to the half cut Hc of this crank period is identified as the crystal orientation K. 
     Subsequently, it is determined whether or not the crystal orientation K and the extending direction of the street region  17  match each other (S 72 ). In a case of YES in S 72 , the standard processing line, that is, the grid-like line to cut  5 C extending in parallel and vertical directions with respect to the orientation flat OF, is set (S 73 ). In a case of NO in S 72 , the line to cut  5 C parallel to the crystal orientation K and inclined with respect to the extending direction of the street region  17 , is set for the object to be processed  1  (S 74 ). After S 73  or S 74 , the object to be processed  1  is cut along the line to cut  5 C, and the plurality f semiconductor chips is formed (S 75 ). 
       FIG. 21( a )  is a diagram illustrating an example of the line to cut  5 C set for the object to be processed  1 . In the figure, a state is illustrated of the front surface  3  of the object to be processed  1  viewed from the Z direction. As illustrated in  FIG. 21( a ) , in S 74 , the line to cut  5 C is set at the position where the line to cut  5 C falls within the street region  17 , in the street width direction. 
     For example, describing in detail setting related to one line to cut  5 C, first, the line to cut  5 C parallel to the crystal orientation K is moved along the street width direction, and a position where the line to cut  5 C does not protrude from the street region  17  (does not cross the functional device  15   a ) is determined as the position where the line to cut  5 C falls within the street region  17 . The line to cut  5 C is set at the position determined. 
       FIG. 21( b )  is a diagram illustrating another example of the line to cut  5 C set for the object to be processed  1 . In the figure, a state is illustrated of the front surface  3  of the object to be processed  1  viewed from the Z direction. As illustrated in  FIG. 21( b ) , in S 74 , in the case where the line to cut  5 C does not fall within the street region  17  in the street width direction, the line to cut  5 C is set at a position where the number of the functional devices  15   a ′ crossed by the line to cut  5 C protruding from the street region  17  (going outside the street region  17 ) is equal to or less than the predetermined number or is the least. 
     For example, describing in detail setting related to one line to cut  5 C, first, the line to cut  5 C parallel to the crystal orientation K is moved along the street width direction. When there is no position where the line to cut  5 C does not protrude from the street region  17 , it is determined that the line to cut  5 C does not fall within the street region  17 . Here, as the line to cut  5 C is moved in the street width direction, the number of the functional devices  15   a ′ crossed by the line to cut  5 C protruding from the street region  17  changes. Therefore, in a case where the line to cut  5 C does not fall within the street region  17 , a relationship is calculated between a position in the street width direction of the line to cut  5 C and the functional device  15   a ′ crossed by the line to cut  5 C. On the basis of the relationship calculated, a position is determined where the number of functional devices  15   a ′ crossed by the line to cut  5 C is equal to or less than the predetermined number or is the least. The line to cut  5 C is set at the position determined. The predetermined number is a value set in advance, and may be a fixed value or a variable value. The predetermined number is a value that can be set from a viewpoint of, for example, an experience, an experiment, or a required specification. 
     As described above, also in the present embodiment, in a case where the extending direction of the street region  17  does not match the crystal orientation K, the line to cut  5 C parallel to the crystal orientation K and inclined with respect to the extending direction of the street region  17 , is set for the object to be processed. Therefore, in the case where the plurality of chips is obtained by cutting the object to be processed  1  along the line to cut  5 C, the above effect is exerted that it is possible to smooth the cut surface and eventually make a mirror surface. 
     It is found that, in a case where the modified region  7  is formed in the substrate  12  along the candidate line  5 A and the half cut Hc is formed, the smaller the degree of deflection in the half cut Hc is, the smaller the angular deviation Δθ between the direction of the candidate line  5 A and the crystal orientation K is. Under this finding, in the present embodiment, the crystal orientation K is identified on the basis of the state of the half cut Hc along the candidate line  5 A. Accordingly, the crystal orientation K can be accurately identified. 
     In the present embodiment, the line to cut  5 C is set at a position where the line to cut  5 C falls within the street region  17  in the width direction of the street region  17 . Accordingly, in a case where the plurality of chips is obtained by cutting the object to be processed  1 , the number of defective chips can be reduced. 
     In the present embodiment, in a case where the line to cut  5 C does not fall within the street region  17  in the width direction of the street region  17 , the line to cut  5 C is set at a position where the number of the functional devices  15   a  crossed by the line to cut  5 C protruding from the street region  17  is equal to or less than the predetermined number. Accordingly, in the case where the plurality of chips is obtained by cutting the object to be processed  1 , even when the line to cut  5 C does not fall within the street region  17 , the number of defective chips can be reduced. 
     In the above, the preferred embodiments of the present invention have been described; however, the present invention is not limited to the above-described embodiments, and may be modified within the range not changing the gist described in each claim or applied to other things. 
     In the above embodiments, the object to be processed  1  is cut along the line to cut  5 C by forming the modified region  7  inside the object to be processed  1  along the line to cut  5 C; however, a step and a configuration for cutting the object to be processed  1  are not particularly limited. For example, it may have a step and a configuration for cutting the object to be processed  1  by performing blade dicing with a dicing blade along the line to cut  5 C. For example, it may have a step and a configuration for cutting the object to be processed  1  by performing ablation processing along the line to cut  5 C. Known steps and configurations (devices) can be adopted as long as the object to be processed  1  can be cut along the line to cut  5 C. 
     In the above embodiments, a step and a configuration for identifying the crystal orientation K are not limited. For example, it may be a step or a configuration for identifying the crystal orientation K by observing the cross section of the substrate  12 . Known steps and configurations (devices) can be adopted as the steps and configurations for identifying the crystal orientation K as long as the crystal orientation K can be identified. 
     In the above embodiments, only one row may be formed of the modified regions  7  in which the positions thereof in the thickness direction are different from each other inside the object to be processed  1 , or two or more rows may be formed. In the above embodiments, the “laser light entrance surface” is the front surface  3  (the front surface  12   a ) and an “opposite surface of the laser light entrance surface” is the back surface  21 ; however, in a case where the back surface  21  is the “laser light entrance surface”, the front surface  3  is the “opposite surface of the laser light entrance surface”. In the above embodiments, “match” includes not only an exact match but also a substantial match. The “match” includes a design error, a manufacturing error, and a measurement error. 
     The present invention can also be regarded as the chip manufactured by the object to be processed cutting device or the object to be processed cutting method. The present invention may be applied only to a case where the processing line  5  is set along the direction parallel to the orientation flat OF. The present invention may be applied only to a case where the processing line  5  is set along the direction vertical to the orientation flat OF. The present invention may be applied to a case where the processing line  5  is set along the directions parallel and vertical to the orientation flat OF. In the above, the controller  250  constitutes a line to cut setting unit. In addition, the controller  250  constitutes a candidate line setting unit, an operation controller, and an identifying unit in a crystal orientation identifying unit. In addition, the controller  250  constitutes an operation controller in a cutting unit. 
     INDUSTRIAL APPLICABILITY 
     With one aspect of the present invention, it is possible to provide an object to be processed cutting method and an object to be processed cutting device capable of smoothing the cut surface. 
     REFERENCE SIGNS LIST 
       1  . . . object to be processed,  3 ,  12   a  . . . front surface,  5 A . . . candidate line,  5 C . . . line to cut,  7  . . . modified region,  12  . . . substrate,  15   a ,  15   a ′ . . . functional device,  17  . . . street region,  100 ,  300  . . . Laser processing device (object to be processed cutting device),  107  . . . support table (crystal orientation identifying unit),  202  . . . laser light source (crystal orientation identifying unit),  204  . . . converging optical system (crystal orientation identifying unit),  211  . . . surface observation unit (imaging unit, crystal orientation identifying unit),  240  . . . display unit,  250  . . . Controller (crystal orientation identifying unit, line to cut setting unit, cutting unit, candidate line setting unit, operation controller, identifying unit), Hc . . . half cut (crack), K . . . crystal orientation, L . . . laser light, M . . . mark (reference mark).