Confirmation method

Abstract

A confirmation method is provided, which easily confirms the influence of irradiation of a laser beam on the front surface of a workpiece. Two linear processing marks (M1) and (M2) are formed on a metal foil of a confirmation wafer, and a modified layer (T) is formed by irradiating a laser beam to a reference position between them. Although the modified layer (T) formed inside the base material is not easily visually recognized, the linear processing marks (M1) and (M2) are clearly formed on the front surface of the metal foil (5), and thus can be easily visually recognized. Therefore, according to the linear processing marks (M1) and (M2), the position of the modified layer (T), that is, the irradiation position of the laser beam at the time of formation of the modified layer (T) can be grasped. Therefore, the user can acquire the positional relationship of the irradiation position of the laser beam and the front surface damage (LD) formed by the laser beam reaching the front surface of the base material (2), and thus can easily confirm the influence of irradiation of the laser beam on the front surface of the workpiece.

Description

TECHNICAL FIELD

[0001] The present application relates to a confirmation method for confirming an influence of a laser beam irradiated to a back surface of a work on a front surface of the work. BACKGROUND

[0002] A work for forming a chip has, for example, a device in each region divided by a plurality of spaced-apart streets (singulation predetermined lines) formed in a cross on a front surface thereof. The chip is formed by breaking the work along the streets. Therefore, there is a method of forming a modified layer along the streets in the inside of the work by irradiating a laser beam along the streets from a back surface of the work.

[0003] In this method, sometimes the device on the front surface is affected by the irradiation of the laser beam from the back surface. Therefore, it is required to confirm the presence or absence of such an influence or the degree of such an influence. A confirmation wafer for confirming the influence of such a laser beam is disclosed in Patent Literature 1, for example. By forming a modified layer by irradiating a laser beam from the back surface of the confirmation wafer, damage (hereinafter referred to as front surface damage) generated on the front surface of the confirmation wafer can be detected. Thereby, it is possible to confirm the influence of the laser beam on the front surface of the work, to select appropriate processing conditions, and to detect abnormalities of a processing device.

[0004] Patent Literature 1: Japanese Patent Application Publication No. 2017-37912

[0005] At the time of formation of the modified layer, the device is not formed in the street, so it is not a problem that the front surface damage is generated in the street on the front surface as the irradiation position of the laser beam. Therefore, it is important to know at what degree of position deviated from the irradiation position of the laser beam the front surface damage is generated.

[0006] However, in the confirmation wafer of Patent Literature 1, the street is not formed, so it is difficult to distinguish the irradiation position of the laser beam from the appearance thereof. In addition, it is also considered to distinguish the irradiation position of the laser beam from the modified layer. However, the modified layer is formed in the inside of the confirmation wafer, so it is not easy to distinguish from the appearance. In this way, in the confirmation wafer of Patent Literature 1, there is a problem that the irradiation position of the laser beam is not easy to grasp accurately. SUMMARY

[0007] Therefore, an object of the present application is to provide a confirmation method capable of distinguishing the irradiation position of a laser beam for forming a modified layer when the laser beam is irradiated to a confirmation wafer not having a street from a back surface, thereby being able to easily confirm the influence of the irradiation of the laser beam on the front surface of a work.

[0008] According to the present application, there is provided a confirmation method of confirming an influence on a front surface of a workpiece by irradiation of a laser beam when a modified layer is formed inside the workpiece by irradiating a laser beam having a wavelength that is transmissive to the workpiece from a back surface side of the workpiece with a laser processing apparatus, wherein the confirmation method has the steps of: a confirmation wafer preparation step of preparing a confirmation wafer in which a metal foil is stacked on a front surface of a substrate; a modified layer formation step of forming a modified layer inside the substrate by positioning a focal point inside the substrate of the confirmation wafer, irradiating a laser beam having a wavelength that is transmissive to the substrate from a back surface side of the substrate, and relatively moving the focal point and the confirmation wafer in a processing feed direction; a linear processing mark formation step of forming a linear processing mark on a front surface of the metal foil by positioning a focal point at an interface between the substrate and the metal foil of the confirmation wafer at a position that is a prescribed distance from a position of irradiation of the laser beam in the modified layer formation step in a indexing feed direction that is perpendicular to the processing feed direction, irradiating a laser beam having a wavelength that is transmissive to the substrate from a back surface side of the substrate in this state, and relatively moving the focal point and the confirmation wafer in the processing feed direction; and a confirmation step of confirming an influence on the front surface of the metal foil by the laser beam irradiated in the modified layer formation step based on a position of the linear processing mark after the modified layer formation step and the linear processing mark formation step are performed.

[0009] Preferably, the modified layer formation step is performed after the linear processing mark formation step is performed.

[0010] Preferably, the present confirmation method further has a reference position setting step of setting a position in the confirmation wafer at which the modified layer is to be formed as a reference position after the confirmation wafer preparation step is performed. Preferably, in the modified layer formation step, a laser beam is irradiated at the reference position, and in the linear processing mark formation step, a laser beam is irradiated at a position that is the prescribed distance from the reference position in the indexing feed direction.

[0011] According to the present application, although the modified layer formed inside the substrate of the confirmation wafer is not easily visually recognized, when the back surface of the metal foil is processed by the laser beam, the metal foil is molten in a thickness direction of the metal foil, discoloration also occurs on the front surface side, and a linear processing mark appears on the front surface side, so the user can easily visually recognize.

[0012] Accordingly, the user can easily grasp the position of the modified layer, i.e., the irradiation position of the laser beam at the time of formation of the modified layer, from the appearance of the confirmation wafer based on the linear processing mark. Accordingly, the user can acquire the positional relationship of the irradiation position of the laser beam at the time of formation of the modified layer and the front surface damage, and thus can appropriately confirm the generation state of the front surface damage, i.e., the influence of the laser beam on the front surface of the base material, which is formed on the metal foil by a portion of the laser beam that does not contribute to the formation of the modified layer directly reaching the front surface side of the base material or being reflected, scattered, refracted, or the like in a crack formed in the modified layer or the periphery of the modified layer. As a result, the user can easily confirm the influence of the irradiation of the laser beam on the front surface of the workpiece. Accordingly, the user can select appropriate processing conditions in the laser processing device, for example, and detect abnormalities in the laser processing device.

[0013] Preferably, in the present confirmation method, the linear processing mark formation step is implemented before the modified layer formation step. In this regard, depending on the relationship between the formation position of the modified layer and the formation position of the linear processing mark, when the modified layer is formed first, the irradiation of the laser beam for forming the linear processing mark can be hindered by the modified layer. By implementing the linear processing mark formation step first, such a situation can be prevented.

[0014] Preferably, in the present confirmation method, the reference position setting step described above is implemented before the linear processing mark formation step. Thereby, by setting the formation position of the modified layer as the reference position, the linear processing mark and the modified layer can be formed based on the reference position. Thereby, the positional relationship of the linear processing mark and the modified layer can be easily and appropriately set. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a perspective view of the confirmation wafer.

[0016] Figure 2 is a partially enlarged cross-sectional view of the confirmation wafer.

[0017] Figure 3 is a perspective view showing the structure of the laser processing device.

[0018] Figure 4 is a schematic view showing the structure of the processing head of the laser processing device.

[0019] Figure 5 is a plan view showing the reference position set in the confirmation wafer.

[0020] Figure 6 is a cross-sectional view showing the focal point of the laser beam in the linear processing mark formation step.

[0021] Figure 7 is an explanatory view showing the linear processing mark formed on the metal foil of the confirmation wafer by the linear processing mark formation step.

[0022] Figure 8 It is a cross-sectional view showing the converging point of the laser beam in the reforming layer forming step.

[0023] Figure 9 It is an explanatory diagram showing linear processing marks and damage formed on the front surface of the metal foil by the reforming layer forming step.

[0024] Figure 10 This is an explanatory diagram showing linear processing marks formed on a metal foil by another method of forming linear processing marks.

[0025] Description of labels

[0026] 1: Confirmation wafer; 2: Base material; 3: Front side; 4: Back side; 5: Metal foil; 9: Notch; 10: Laser processing device; 11: Base; 13: Wall portion; 12: Laser processing unit; 17: Arm portion; 18: Processing head; 53: Oscillation portion; 54: Focusing lens; L: Laser beam; P: Focusing point; B: Reference position; M1: First linear processing mark; M2: Second linear processing mark; LD: Front side damage; T: Modified layer; d: Offset distance; 14: Worktable moving mechanism for holding the worktable; 20: Indexing feed portion; 30: Processing feed portion; 40: Worktable holding portion; 43: Worktable holding; 51: Control unit. DETAILED DESCRIPTION

[0027] A confirmation method of one embodiment of the present invention (this confirmation method) is a confirmation method for confirming the effect of laser beam irradiation on the front side of the workpiece when a laser beam of a wavelength that is transparent to the workpiece is irradiated from the back side of the workpiece by a laser processing device to form a modified layer inside the workpiece.

[0028] The following describes the steps of this confirmation method.

[0029] (1) Confirmation wafer preparation steps

[0030] In this confirmation method, a confirmation wafer different from the workpiece actually used to manufacture a product (chip) is used to confirm the effect of laser beam irradiation on the front surface of the workpiece.

[0031] like Figure 1 and Figure 2 As shown in FIG. 1 , the confirmation wafer 1 includes a substrate 2 formed into a disk shape and a metal foil 5 provided on the front surface of the substrate 2. Figure 2 As shown, the substrate 2 has a front surface 3 and a back surface 4. A metal foil 5 is formed on the front surface 3 of the substrate 2. A notch 9 is provided on the outer periphery of the substrate 2 to indicate the crystal orientation of the confirmation wafer 1. The outer periphery of the substrate 2 is chamfered (see Figure 6 ).

[0032] In the confirmation wafer preparation step, for example, a circular as-cut wafer is ground and polished to a predetermined thickness after deformation elements including warping and undulation are removed, and notches 9 are formed on the outer periphery to obtain a substrate 2. Furthermore, a metal foil 5 is laminated on the front surface 3 of the substrate 2, for example, by vapor deposition. Thus, a confirmation wafer 1 is prepared.

[0033] The base material 2 is preferably made of silicon or other materials that are homogeneous with the workpiece used in actual product manufacturing. The metal foil 5 is preferably a tin film formed by depositing tin, for example, and has a thickness of several hundred nanometers.

[0034] (2) Reference position setting step, linear processing mark forming step, and modified layer forming step

[0035] Next, a reference position setting step is performed to set a reference position on the confirmation wafer 1, a linear processing mark forming step is performed to form a linear processing mark on the front surface of the metal foil 5, and a modified layer forming step is performed to form a modified layer inside the substrate 2. First, the structure of the laser processing apparatus used in these steps will be described.

[0036] like Figure 3 As shown, the laser processing apparatus 10 includes a rectangular parallelepiped base 11 , a vertical wall portion 13 erected at one end of the base 11 , and a control unit 51 that controls the components of the laser processing apparatus 10 .

[0037] A holding table moving mechanism 14 is provided on the upper surface of the base 11 to move the holding table 43. The holding table moving mechanism 14 includes a holding table unit 40 having the holding table 43; an indexing feed unit 20 to move the holding table 43 in an indexing feed direction (Y-axis direction); and a processing feed unit 30 to move the holding table 43 in a processing feed direction (X-axis direction).

[0038] The indexing and feeding section 20 includes a pair of guide rails 23 extending in the Y-axis direction, a Y-axis table 24 mounted on the guide rails 23 , a ball screw 25 extending parallel to the guide rails 23 , and a drive motor 26 for rotating the ball screw 25 .

[0039] A pair of guide rails 23 are arranged parallel to the Y-axis direction on the upper surface of the base 11. A Y-axis table 24 is provided on the pair of guide rails 23 so as to be slidable along these guide rails 23. A processing feed unit 30 and a holding table unit 40 are placed on the Y-axis table 24.

[0040] The ball screw 25 is screwed with a nut portion (not shown) provided on the lower surface side of the Y-axis table 24. The drive motor 26 is coupled to one end portion of the ball screw 25 to rotate and drive the ball screw 25. The Y-axis table 24, the machining feed portion 30, and the holding table portion 40 are moved in the indexing feed direction (Y-axis direction) along the guide rail 23 by the rotation and drive of the ball screw 25.

[0041] The machining feed portion 30 has a pair of guide rails 31 extending in the X-axis direction, an X-axis table 32 placed on the guide rails 31, a ball screw 33 extending in parallel with the guide rails 31, and a drive motor 35 rotating the ball screw 33. The pair of guide rails 31 are arranged in parallel with the X-axis direction on the upper surface of the Y-axis table 24. The X-axis table 32 is provided on the pair of guide rails 31 in a manner capable of sliding along the guide rails 31. The holding table portion 40 is placed on the X-axis table 32.

[0042] The ball screw 33 is screwed with a nut portion (not shown) provided on the lower surface side of the X-axis table 32. The drive motor 35 is coupled to one end portion of the ball screw 33 to rotate and drive the ball screw 33. The X-axis table 32 and the holding table portion 40 are moved in the machining feed direction (X-axis direction) along the guide rails 31 by the rotation and drive of the ball screw 33.

[0043] The holding table portion 40 has a holding table 43 attracting and holding the confirmation wafer 1 or the workpiece, four clamping portions 45 provided around the holding table 43, and a θ table 47 supporting the holding table 43. The θ table 47 is provided on the upper surface of the X-axis table 32 in a manner capable of rotating in the XY plane. The holding table 43 is formed in a circular plate shape and is provided on the θ table 47.

[0044] A holding surface including a porous ceramic material is formed on the upper surface of the holding table 43. The holding surface is communicated with a suction source (not shown). In a case where the holding table 43 holds the workpiece having a ring-shaped frame, the four clamping portions 45 clamp and fix the ring-shaped frame from four sides.

[0045] A laser machining unit 12 for laser machining the machined member is provided on the front surface of the standing wall portion 13 provided at the rear of the holding table moving mechanism 14. The laser machining unit 12 has a machining head 18 irradiating a laser beam to the confirmation wafer 1 or the like held by the holding table 43, and an arm portion 17 supporting the machining head 18.

[0046] An optical system of the laser machining unit 12 is provided in the arm portion 17 and the machining head 18. As shown in FIG. 2, the arm portion 17 is provided with a laser oscillator 19 and a laser beam expander 20. The laser oscillator 19 is a semiconductor laser oscillator, and emits a laser beam. The laser beam expander 20 expands the laser beam emitted from the laser oscillator 19. Figure 4As shown, the processing head 18 includes an oscillator 53 that generates laser light and a condenser lens 54 that focuses the laser beam oscillated by the oscillator 53. The processing head 18 focuses the laser beam L output from the oscillator 53 by the condenser lens 54 and irradiates the laser beam L onto the confirmation wafer 1 held by the holding stage 43.

[0047] The laser beam L emitted from the processing head 18 is, for example, a pulsed laser beam having a wavelength that is transparent to the verification wafer 1. The focused point P obtained by converging the laser beam L can be arranged at any height (position along the Z-axis direction).

[0048] The control unit 51 performs integrated control of the components of the laser processing apparatus 10. The control unit 51 includes a processor for executing various processes. Detection results from various detectors (not shown) are input to the control unit 51.

[0049] (2-1) Reference position setting steps

[0050] Next, a description will be given of a reference position setting step using the laser processing apparatus 10. This step is performed after the confirmation wafer preparation step.

[0051] In this step, the user first follows Figure 2 The confirmation wafer 1 is placed on the holding table 43 with the exposed back surface 4 of the substrate 2 facing upward. Accordingly, the control unit 51 controls the suction source to suction-hold the metal foil 5 of the confirmation wafer 1 on the holding table 43 .

[0052] Then, if Figure 5 As shown, the control unit 51 sets the position of the confirmation wafer 1 where the modified layer is to be formed as the reference position B. Since no streets or devices are formed on the confirmation wafer 1, the reference position B can be set at any position, and the angle adjustment of the confirmation wafer 1 using the θ stage 47 is unnecessary.

[0053] For example, the control unit 51 controls the index feed unit 20 to set the position of the holding table 43 holding the confirmation wafer 1 in the index feed direction (Y-axis direction) to a predetermined first position. Furthermore, the position at which the laser beam L from the processing head 18 irradiates the confirmation wafer 1 at this time becomes the reference position B.

[0054] (2-2) Linear processing mark formation step

[0055] In this step, the laser beam L is positioned at a position a predetermined distance from the reference position B in the index feed direction perpendicular to the machining feed direction.

[0056] That is, the control unit 51 controls the index feed unit 20 to move the holding table 43 holding the confirmation wafer 1, thereby setting the irradiation position of the laser beam L from the processing head 18 on the confirmation wafer 1 to be a predetermined offset distance d (refer to the reference position B) on the positive side (+Y axis direction) of the index feed direction. Figure 7 ) location.

[0057] In this state, if Figure 6 As shown, the control unit 51 controls the optical system of the processing head 18 to position the focal point P of the processing head 18 at the interface between the substrate 2 and the metal foil 5 in the confirmation wafer 1. Furthermore, the control unit 51 irradiates the laser beam L from the processing head 18 toward the confirmation wafer 1 from the back side 4, and controls the processing feed unit 30 to move the holding table 43 holding the confirmation wafer 1 along the processing feed direction as shown by the arrow A, so that the processing head 18 moves relative to the confirmation wafer 1 along the processing feed direction. As a result, the back side of the metal foil 5 is processed by the laser beam, causing the metal foil to melt in the thickness direction of the metal foil 5, as shown in FIG. Figure 7 As shown, a first linear processing mark M1 , which is a mark of melting of the metal foil 5 by irradiation with the laser beam L, is formed on the +Y axis direction side of the reference position B on the front surface of the metal foil 5 .

[0058] Next, the control unit 51 sets the irradiation position of the laser beam L from the processing head 18 on the confirmation chip 1 to a position that is offset by a distance d from the reference position B on the - side (-Y axis direction) of the indexing feed direction, and performs irradiation of the laser beam L and processing feed of the workbench 43 in the same manner as when the first linear processing mark M1 is formed.

[0059] As a result, a second linear processing mark M2 is formed on the -Y-axis side of the reference position B on the front surface of the metal foil 5. Thus, in the linear processing mark forming step, two linear processing marks M1 and M2 are formed on both sides of the reference position B, approximately parallel to the reference position B. Irradiation with the laser beam L causes the metal foil 5 to melt in the thickness direction of the metal foil 5, discoloring the front surface, allowing them to be identified from the front surface of the metal foil 5.

[0060] Furthermore, the distance between the processing marks M1 and M2 is preferably equal to the width of the actual lane of the workpiece where the modified layer is to be formed. This allows for easy understanding of whether the laser beam irradiation affects the front surface of the workpiece within the lane.

[0061] In the linear processing mark forming step, the wavelength of the laser beam L is, for example, 1064 nm, the output is, for example, 0.2 W, and the moving speed of the processing feed unit 30 is, for example, 500 mm / sec.

[0062] (2-3) Modified layer formation step

[0063] In this step, the control unit 51 forms a reformed layer along the reference position B on the verification wafer 1 .

[0064] That is, the control unit 51 controls the index feed unit 20 to move the holding table 43 holding the confirmation wafer 1 , and sets the irradiation position of the laser beam L from the processing head 18 on the confirmation wafer 1 to the reference position B.

[0065] In this state, if Figure 8 As shown, the control unit 51 controls the optical system of the processing head 18 to position the focal point P of the processing head 18 inside the substrate 2 in the confirmation wafer 1. Furthermore, the control unit 51 irradiates the laser beam L from the processing head 18 toward the confirmation wafer 1 from the back surface 4 side, and controls the processing feed unit 30 to move the holding table 43 in the processing feed direction as indicated by arrow A, thereby moving the processing head 18 relative to the confirmation wafer 1 in the processing feed direction.

[0066] Then, the control unit 51 changes the height of the focal point P of the processing head 18 inside the substrate 2 , and similarly performs irradiation with the laser beam L and processing feeding of the holding stage 43 .

[0067] Thus, along Figure 7 The reference position B shown is Figure 9 As shown, a reformed layer T is formed in the substrate 2. In the reformed layer forming step, the wavelength of the laser beam L is, for example, 1064 nm, the output of the laser beam L is, for example, 1.5 W, and the moving speed of the processing feed unit 30 is, for example, 700 mm / sec.

[0068] (3) Confirmation steps

[0069] In this step, the user checks the influence of the laser beam L irradiated in the reforming layer forming step on the front surface of the metal foil 5 based on the positions of the linear processing marks M1 and M2.

[0070] That is, in the modification layer forming step, the laser beam L is irradiated from the back surface 4 side of the substrate 2 in a manner that the condensing point P is positioned inside the substrate 2. At this time, a part of the laser beam L that does not contribute to the formation of the modification layer sometimes reaches the front surface 3 side of the substrate 2 directly, or reaches the front surface 3 side of the substrate 2 by reflection, scattering, refraction through the modification layer or the cracks generated at the periphery of the modification layer. The laser beam thus reaching the front surface side of the substrate 2 can possibly cause adverse effects on the device on the front surface for the workpiece actually used for manufacturing products. Also, in the confirmation wafer 1, the laser beam thus reaching the front surface side of the substrate 2 leaves a front surface damage (laser damage) LD on the front surface of the metal foil 5 as shown in FIG. 6. In this step, the user observes such a front surface damage LD. In this confirmation step, the confirmation wafer 1 is taken out from the holding stage 43, and the front surface damage LD is confirmed from the front surface side of the metal foil 5 laminated on the front surface of the substrate 2. Figure 9

[0071] As described above, in the present confirmation method, in the linear processing mark forming step, the laser beam L is irradiated at two positions that are apart from the reference position B by a prescribed offset distance, thereby forming two linear processing marks Ml and M2 on the front surface of the metal foil 5 of the confirmation wafer 1. Also, by irradiating the laser beam L along the reference position B, the modification layer T is formed in the middle of the two linear processing marks Ml and M2.

[0072] Here, although the modification layer T formed inside the substrate 2 is not easily visible, the linear processing marks Ml and M2 on both sides thereof are formed as molten traces of the metal foil 5 on the front surface of the metal foil 5 clearly, so the user can easily see them.

[0073] Therefore, the user can easily grasp the position of the modification layer T, that is, the irradiation position of the laser beam L at the time of forming the modification layer T, from the appearance of the confirmation wafer 1 based on the linear processing marks Ml and M2. Therefore, the user can acquire the positional relationship (distance, etc.) of the irradiation position of the laser beam L at the time of forming the modification layer T and the front surface damage LD formed on the front surface of the metal foil 5 due to the laser beam reaching the front surface of the substrate 2, so can properly confirm the generation condition of the front surface damage LD, that is, the influence of the light leakage on the front surface 3 of the substrate 2. As a result, the user can easily confirm the influence of the irradiation of the laser beam L on the front surface of the workpiece.

[0074] ​Therefore, the user can, for example, select appropriate processing conditions in the laser processing apparatus 10 and detect abnormalities in the laser processing apparatus 10. If laser damage LD is confirmed to have formed outside the pair of linear processing marks M1 and M2 on the front surface of the metal foil 5 during the reformed layer formation step, the processing conditions can be appropriately modified, for example, by reducing the output of the laser beam L during reformed layer formation, or by changing the position of the focal point, repetition frequency, processing feed speed, pulse width, and so on. On the other hand, if multiple laser damage LDs are displaced from the center of the pair of linear processing marks M1 and M2, i.e., the position of the reformed layer, toward one of the linear processing marks, it is determined that there may be optical axis displacement, and the optical system of the laser processing apparatus 10 can be inspected.

[0075] Furthermore, in this embodiment, the linear processing mark forming step is performed before the modified layer forming step. In this regard, due to the relationship between the formation position of the modified layer T (reference position B) and the formation positions of the linear processing marks M1 and M2, if the modified layer T is formed first, there is a possibility that the irradiation of the laser beam L used to form the linear processing marks M1 and M2 will be blocked by the modified layer T. However, by performing the linear processing mark forming step first as in this embodiment, this situation can be prevented.

[0076] Furthermore, in this embodiment, a reference position setting step is performed before the linear machining mark forming step. Thus, the planned formation position of the modified layer T is set as the reference position B, and the linear machining marks M1 and M2 and the modified layer T can be formed based on the reference position B. This facilitates the formation of the modified layer T between the linear machining marks M1 and M2.

[0077] In this embodiment, two linear machining marks M1 and M2 are formed at positions offset by a distance d in the +Y and -Y axis directions from the reference position B. Alternatively, the machining feed unit 30 may be fed from the +X side to the -X side to form the first linear machining mark M1, and then the holding table 43 may be moved in the -Y axis direction to feed the machining feed unit 30 from the -X side to the +X side to form the second linear machining mark M2.

[0078] Alternatively, when the machining head 18 is configured to be able to irradiate two laser beams L simultaneously, two linear machining marks M1 and M2 can be formed simultaneously.

[0079] In addition, if Figure 10 As shown, a single linear processing mark M can be formed only on one side in the index feed direction of the reference position B. Even with this configuration, the irradiation position of the laser beam L during the formation of the modified layer T can be understood from the appearance of the confirmation wafer 1 based on the visible linear processing mark M and the positional relationship (offset distance d) between the linear processing mark M and the reference position B.

[0080] In the modification layer forming step, the control unit 51 does not need to irradiate the laser beam L from one end to the other end of the outer periphery of the confirmation wafer 1. However, it is preferable to form the modification layer T in a length equal to or less than the two linear processing marks Ml and M2 formed in the linear processing mark forming step.

[0081] In the present embodiment, the linear processing mark forming step is implemented before the modification layer forming step, but the linear processing mark forming step can be implemented after the modification layer forming step.

[0082] In addition, the reference position setting step implemented in the present embodiment can not necessarily be implemented. For example, the linear processing mark forming step can be implemented to form two linear processing marks Ml and M2 at any two positions in the confirmation wafer 1, and the modification layer forming step can be implemented to form the modification layer T at a position that is intermediate of them.

[0083] In the present embodiment, in the modification layer forming step, the irradiation of the laser beam L and the processing feed of the holding stage 43 are implemented twice by changing the height of the focal point P inside the substrate 2. Instead, in the modification layer forming step, the irradiation of the laser beam L and the processing feed of the holding stage 43 can be implemented only once, or three or more times.

Claims

1. A method for confirming the occurrence of front surface damage formed on a front surface of a workpiece by irradiating a laser beam of a wavelength that is transparent to the workpiece with a laser processing device from the back side of the workpiece to form a modified layer inside the workpiece, wherein: The confirmation method has the following steps: a confirmation wafer preparation step of preparing a confirmation wafer having a metal foil laminated on the front surface of a substrate; a reference position setting step of setting a position on the confirmation wafer where the modified layer is to be formed as a reference position after the confirmation wafer preparation step is performed; a modified layer forming step of irradiating the substrate with a laser beam having a wavelength that is transparent to the substrate from the back side thereof while positioning a focal point within the substrate of the confirmation wafer, and moving the focal point and the confirmation wafer relative to each other in a processing feed direction, thereby forming a modified layer within the substrate along a reference position; a linear processing mark forming step of positioning a focal point at an interface between the substrate and the metal foil of the confirmation wafer in an indexing feed direction perpendicular to the processing feed direction and at a position a predetermined distance from the irradiation position of the laser beam in the modified layer forming step, irradiating the substrate with a laser beam of a wavelength that is transparent to the substrate from the back side of the substrate in this state, and relatively moving the focal point and the confirmation wafer in the processing feed direction, thereby forming linear processing marks on both sides of the front side of the metal foil at a predetermined distance from the reference position in the indexing feed direction; as well as A confirmation step, after implementing the modified layer forming step and the linear processing mark forming step, grasps the irradiation position of the laser beam in the confirmation chip in the modified layer forming step based on the position of the linear processing mark, and obtains the positional relationship between the irradiation position and the front damage formed on the front surface of the metal foil due to the laser beam irradiated in the modified layer forming step, thereby confirming the generation condition of the front damage formed on the front surface of the workpiece.

2. The confirmation method according to claim 1, wherein: The reforming layer forming step is performed after the linear processing mark forming step is performed.

3. The confirmation method according to claim 1 or 2, wherein: In the reforming layer forming step, the reference position is irradiated with a laser beam. In the linear processing mark forming step, the laser beam is irradiated to a position that is the predetermined distance away from the reference position in the index feeding direction.

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