Correction method for optical axis of laser processing device and laser processing device

Abstract

To provide a correction method for optical axis of laser processing device that corrects a deviation amount of an optical axis of a laser processing part with respect to a planned crack formation line.SOLUTION: A method for correcting deviation between a planned crack formation line of a work-piece and an optical axis of a laser processing part includes the steps of: eccentrically irradiating a work-piece, that is provided with a first area to which a planned crack formation line is set and a second area which exists on both sides of the planned crack formation line and has a reflection rate different from a reflection rate of the first area with first detection light and second detection light, which are decentered from an optical axis of a condenser lens of a crack measurement part while moving a focal spot in a thickness direction of the work-piece, and detecting each reflectance reflected from the work-piece; acquiring positional information concerning a boundary between the first area and the second area from the detected detection value; obtaining an amount of deviation between the planned crack formation line and the optical axis of the laser processing part from the positional information; and performing correction for the optical axis of the laser processing part from the mount of deviation.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an optical axis correcting method for a laser processing device and a laser processing device. [Background technology]

[0002] Conventionally, there is known a laser processing device (also called a laser dicing device) that irradiates a workpiece such as a semiconductor wafer with a focal point aligned with the interior of the workpiece along a planned crack formation line, thereby forming cracks that serve as starting points for cutting within the workpiece along the planned crack formation line. The workpiece with the cracks formed therein is then cleaved along the planned crack formation line by a cleaving process such as expanding or breaking, and divided into individual chips (see, for example, Patent Document 1).

[0003] A known laser processing device for performing such laser processing is equipped with a laser unit (hereinafter referred to as the laser processing unit) that forms cracks by irradiating one side of the wafer with laser light, and a crack measurement unit that measures the depth of the crack created in the wafer by irradiating the laser light (see Patent Document 2).

[0004] In conventional laser processing devices, the position of the planned crack formation line is determined in advance before irradiating the wafer with laser light, and then a crack is formed inside the wafer by irradiating the wafer along the planned crack formation line, and the depth of the formed crack is then measured using a crack measurement unit. In measuring the crack using the crack measurement unit, the crack measurement unit is positioned on the planned crack formation line based on position information of the planned crack formation line obtained in advance before irradiating the laser light, and the crack measurement is performed. This type of crack measurement is based on the assumption that the crack will be formed along the planned crack formation line and that the optical axis of the laser processing unit and the optical axis of the crack measurement unit are aligned.

[0005] However, when laser light is irradiated onto the wafer from the laser processing unit to form cracks, the wafer expands due to heat and other factors, which can cause the position of the planned crack formation line to gradually shift (displace).As a result, the position of the optical axis of the laser light irradiated from the laser processing unit can deviate from the planned crack formation line.

[0006] If the position of the optical axis of the laser light deviates from the planned crack formation line, there is a risk of damaging the devices formed on the wafer, so it is necessary to correct the position of the optical axis of the laser processing unit.

[0007] For example, in a laser processing device having two optical axes, a technique is known in which a modified region formed on a wafer is photographed using an infrared imaging optical system, and the modified region is aligned with the optical axis of the infrared imaging optical system to correct the optical axis misalignment (see Patent Document 3). However, in a laser processing device equipped with a laser processing unit and a crack measurement unit, a means for correcting the optical axis of the laser processing unit using the crack measurement unit was not known. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-133997 [Patent Document 2] Japanese Patent Publication No. 2022-117054 [Patent Document 3] Japanese Patent Publication No. 2020-088365 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide an optical axis correction method for a laser processing device and a laser processing device that can detect and correct the amount of deviation of the optical axis of the laser processing section from the planned crack formation line when the planned crack formation line is displaced by laser irradiation of the workpiece. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention employs the following configuration. [1] A method for correcting a misalignment between a planned crack formation line on a workpiece and an optical axis of a laser processing section, a step of eccentrically irradiating a first detection light and a second detection light, which are mutually eccentric from the optical axis of a focusing lens of a crack measurement unit, onto the workpiece, which has a first region in which the planned crack formation line is set and second regions on both sides of the planned crack formation line and which have a reflectance different from the reflectance of the first region, while moving the focusing point in the thickness direction of the workpiece, and detecting each reflected light reflected from the workpiece; acquiring position information of the boundary between the first region and the second region from the detected value; A step of obtaining a deviation amount between the planned crack formation line and the optical axis of the laser processing portion from the position information; a step of correcting the optical axis of the laser processing portion based on the amount of deviation; A method for correcting the optical axis of a laser processing device, comprising: [2] acquiring position information of the boundary from a change in the detection value of the reflected light; [1] A method for correcting the optical axis of the laser processing device described above. [3] A method for correcting a misalignment between a planned crack formation line on a workpiece and the optical axis of a laser processing portion, Before laser processing, a step of eccentrically irradiating detection light eccentric from the optical axis of the condenser lens of the crack measurement unit while moving the condenser point in the thickness direction of the workpiece, and detecting reflected light reflected from the workpiece; After the laser processing, a step of eccentrically irradiating detection light eccentric from the optical axis of the condenser lens of the crack measurement unit while moving the condenser point in the thickness direction of the workpiece, and detecting the reflected light reflected from the workpiece; A step of acquiring a deviation amount between the planned crack formation line and the optical axis of the laser processing portion from the detection values ​​of reflected light before and after laser processing; a step of correcting the optical axis of the laser processing portion based on the amount of deviation; A method for correcting the optical axis of a laser processing device, comprising: [4] A step of measuring the depth of the crack from the detected value. A method for correcting the optical axis of a laser processing device according to [1] or [3]. [5] A laser processing device that performs the method for correcting the optical axis of a laser processing device described in any one of [1] to [3]. [6] A laser processing device that performs the method for correcting the optical axis of the laser processing device described in [4].

[0011] The present invention may also have the following configuration. [A] A laser processing unit that forms a crack along a planned crack formation line in a workpiece; a control unit having position information of the planned crack formation line; a crack measurement unit that measures the depth of the crack in a state where the optical axis of a condenser lens is positioned at an optical axis position that is set based on the position information, A method for correcting the position of an optical axis of the laser processing unit when the relative position of the planned crack formation line of the workpiece with respect to the laser processing device is displaced to a position different from the optical axis position based on the position information, the workpiece has a device formation surface, and the device formation surface is provided with a first region in which the planned crack formation line is set, and second regions that are located on both sides of the planned crack formation line in a longitudinal direction and have an optical reflectance different from the optical reflectance of the first region; a first step of arranging the condenser lens of the crack measurement unit above the workpiece after the relative position of the planned crack formation line with respect to the laser processing device has been displaced, the first step being to arrange the optical axis of the condenser lens at the optical axis position set based on the position information; a second step of acquiring positional information of the boundary of the second region by irradiating the device formation surface of the workpiece with detection light decentered from the optical axis of the condenser lens while moving the condenser lens of the crack measurement unit in a vertical direction relative to the workpiece, and detecting reflected light of the detection light reflected at the boundary of the second region on the device formation surface; a third step of obtaining a relative positional deviation amount between the position of the planned crack formation line of the workpiece after displacement and the optical axis position based on positional information of the boundary of the second region obtained in the second step; a fourth step of correcting the position of the optical axis of the laser processing unit when the amount of relative positional deviation obtained in the third step exceeds a threshold value; A method for correcting an optical axis of a laser processing device, comprising: [B] The second step is a step of irradiating the device formation surface of the workpiece with first detection light and second detection light decentered from the optical axis of the condenser lens while moving the condenser lens of the crack measurement unit vertically with respect to the workpiece after the relative position of the planned crack formation line has been displaced, and detecting the reflected light of the first detection light and the reflected light of the second detection light reflected at the boundaries of one and the other of the second regions on both sides of the planned crack formation line, thereby obtaining a measurement value Ha of position information of the boundary of one of the second regions using the reflected light of the first detection light and a measurement value Hb of position information of the boundary of the other of the second regions using the reflected light of the second detection light, The third step is a step of obtaining the relative positional deviation amount d between the position of the planned crack formation line of the workpiece after displacement and the optical axis position using the following equation (1): d=(Ha-Hb) / (1 / tanα+1 / tanβ) …(1) In the above equation (1), d is the amount of relative positional deviation, Ha is the measured value of the position information of the boundary of one of the second regions using the reflected light of the first detection light, Hb is the measured value of the position information of the boundary of the other of the second regions using the reflected light of the second detection light, α is the incident angle (°) of the first detection light with respect to the vertical thickness of the workpiece, and β is the incident angle (°) of the second detection light with respect to the vertical thickness of the workpiece. [C] A laser processing unit that forms a crack along a planned crack formation line in the workpiece; a control unit having position information of the planned crack formation line; a crack measurement unit that measures the depth of the crack in a state where the optical axis of a condenser lens is positioned at an optical axis position that is set based on the position information, A method for correcting the position of an optical axis of the laser processing unit when the relative position of the planned crack formation line of the workpiece with respect to the laser processing device is displaced to a position different from the optical axis position based on the position information, the workpiece has a device formation surface, and the device formation surface is provided with a first region in which the planned crack formation line is set, and second regions that are located on both sides of the planned crack formation line in a longitudinal direction and have an optical reflectance different from the optical reflectance of the first region; a first step of arranging the condenser lens of the crack measurement unit above the workpiece before the relative position of the planned crack formation line with respect to the laser processing device is displaced, and arranging the optical axis of the condenser lens at the optical axis position set based on the position information; a second step of irradiating the device formation surface of the workpiece with detection light decentered from the optical axis of the condenser lens while moving the condenser lens of the crack measurement unit in a vertical direction relative to the workpiece, and detecting reflected light of the detection light reflected at the boundary of the second region on the device formation surface, thereby acquiring first position information of the boundary of the second region; a third step of arranging the condenser lens above the workpiece after the relative position of the planned crack formation line with respect to the laser processing device has been displaced, and arranging the optical axis of the condenser lens at the optical axis position set based on the position information; a fourth step of irradiating the device forming surface of the workpiece with detection light decentered from the optical axis of the condenser lens while moving the condenser lens of the crack measurement unit in a vertical direction relative to the workpiece, and detecting reflected light of the detection light reflected at the boundary of the second region on the device forming surface, thereby acquiring second position information of the boundary of the second region; a fifth step of obtaining a relative positional deviation amount between the position of the planned crack formation line of the workpiece after displacement and the optical axis position based on first position information of the boundary of the second region obtained in the second step and second position information of the boundary of the second region obtained in the fourth step; a sixth step of correcting the position of the optical axis of the laser processing unit when the amount of relative positional deviation obtained in the fifth step exceeds a threshold value; A method for correcting an optical axis of a laser processing device, comprising: [D] The second step is a step of irradiating the device formation surface of the workpiece with one detection light decentered from the optical axis of the condenser lens while vertically moving the condenser lens of the crack measurement unit with respect to the workpiece before the relative position of the planned crack formation line is displaced, and detecting the reflected light of the detection light reflected at the boundary of one of the second regions on both sides of the planned crack formation line, thereby obtaining a measurement value Ha0 of position information of the boundary of one of the second regions, The fourth step is a step of irradiating the device formation surface of the workpiece with one detection light decentered from the optical axis of the condenser lens while moving the condenser lens of the crack measurement unit in a vertical direction with respect to the workpiece after the relative position of the planned crack formation line has been displaced, and detecting the reflected light of the detection light reflected at the boundary of one of the second regions on both sides of the planned crack formation line, thereby obtaining a measurement value Ha of position information of the boundary of one of the second regions; The fifth step is a step of obtaining the relative positional deviation d between the position of the planned crack formation line on the workpiece after displacement and the optical axis position using the following equation (2): d = (Ha - Ha0) tan α … (2) In the above equation (1), d is the amount of relative positional deviation, Ha0 is the measured value of the positional information of the boundary of one of the second regions by the reflected light of the detection light with respect to the workpiece before the relative position of the planned crack formation line is displaced, Ha is the measured value of the positional information of the boundary of one of the second regions by the reflected light of the detection light with respect to the workpiece after the relative position of the planned crack formation line is displaced, and α is the incident angle (°) of the detection light with respect to the vertical thickness of the workpiece. [E] The method for correcting the optical axis of a laser processing device according to any one of [A] to [D], further comprising measuring the depth of the crack. [F] A laser processing unit that forms a crack along a planned crack formation line in the workpiece; a control unit having position information of the planned crack formation line; a crack measurement unit that measures the depth of the crack in a state where the optical axis of a condenser lens is positioned at an optical axis position that is set based on the position information, The control unit is equipped with a correction function unit that corrects the position of the optical axis of the laser processing unit when the relative position of the planned crack formation line of the workpiece with respect to the laser processing device is displaced to a position different from the optical axis position based on the position information. [G] The workpiece has a device formation surface, and the device formation surface is provided with a first region in which the planned crack formation line is set, and second regions on both sides of the planned crack formation line in the longitudinal direction, the second regions having an optical reflectivity different from the optical reflectivity of the first region. [F] A laser processing apparatus as described in [F]. [H] The correction function unit a first functional unit that positions the optical axis of the condenser lens of the crack measurement unit at the optical axis position that is set based on the position information when the condenser lens is positioned above the workpiece after the relative position of the planned crack formation line with respect to the laser processing device has been displaced; a second functional unit that irradiates the device formation surface of the workpiece with detection light decentered from the optical axis of the condenser lens while moving the condenser lens of the crack measurement unit in a vertical direction with respect to the workpiece after the relative position of the planned crack formation line has been displaced, and detects the reflected light of the detection light reflected at the boundary of the second region on the device formation surface, thereby acquiring position information of the boundary of the second region; a third functional unit that obtains a relative positional deviation amount between the position of the planned crack formation line of the workpiece after displacement and the optical axis position based on positional information of the boundary of the second region obtained by the second functional unit; a fourth functional unit that corrects the position of the optical axis of the laser processing unit when the amount of relative positional deviation obtained by the third functional unit exceeds a threshold value; The laser processing apparatus according to [G], comprising: [I] The second functional unit irradiates the device formation surface of the workpiece with first detection light and second detection light decentered from the optical axis of the condenser lens while moving the condenser lens of the crack measurement unit vertically with respect to the workpiece after the relative position of the planned crack formation line has been displaced, and detects the reflected light of the first detection light and the reflected light of the second detection light reflected at the boundaries of one and the other of the second regions on both sides of the planned crack formation line, thereby obtaining a measurement value Ha of position information of the boundary of one of the second regions using the reflected light of the first detection light and a measurement value Hb of position information of the boundary of the other of the second regions using the reflected light of the second detection light, The laser processing device described in [H], wherein the third functional unit obtains the relative positional deviation amount d between the position of the planned crack formation line of the workpiece after displacement and the optical axis position using the following equation (1): d=(Ha-Hb) / (1 / tanα+1 / tanβ) …(1) In the above equation (1), d is the amount of relative positional deviation, Ha is the measured value of the position information of the boundary of one of the second regions using the reflected light of the first detection light, Hb is the measured value of the position information of the boundary of the other of the second regions using the reflected light of the second detection light, α is the incident angle (°) of the first detection light with respect to the vertical thickness of the workpiece, and β is the incident angle (°) of the second detection light with respect to the vertical thickness of the workpiece. [J] The correction function unit a first functional unit that positions the optical axis of the condenser lens at the optical axis position that is set based on the position information when the condenser lens of the crack measurement unit is positioned above the workpiece before the relative position of the planned crack formation line with respect to the laser processing device is displaced; a second functional unit that irradiates the device formation surface of the workpiece with detection light decentered from the optical axis of the condenser lens while vertically moving the condenser lens of the crack measurement unit with respect to the workpiece before the relative position of the planned crack formation line is displaced, and detects the reflected light of the detection light reflected at the boundary of the second region on the device formation surface, thereby acquiring first position information of the boundary of the second region; a third functional unit that positions the optical axis of the condenser lens at the optical axis position that is set based on the position information when the condenser lens of the crack measurement unit is positioned above the workpiece after the relative position of the planned crack formation line with respect to the laser processing device has been displaced; a fourth functional unit that irradiates the device formation surface of the workpiece with detection light decentered from the optical axis of the condenser lens while moving the condenser lens of the crack measurement unit in a vertical direction with respect to the workpiece after the relative position of the planned crack formation line has been displaced, and detects the reflected light of the detection light reflected at the boundary of the second region on the device formation surface, thereby acquiring second position information of the boundary of the second region; a fifth functional unit that obtains a relative positional deviation amount between the position of the planned crack formation line of the workpiece after displacement and the optical axis position based on first position information of the boundary of the second region obtained by the second functional unit and second position information of the boundary of the second region obtained by the fourth functional unit; a sixth functional unit that corrects the position of the optical axis of the laser processing unit when the amount of relative positional deviation obtained by the fifth functional unit exceeds a threshold value; The laser processing apparatus according to [G], comprising: [K] The second functional unit irradiates one detection light decentered from the optical axis of the condenser lens onto the device formation surface of the workpiece while vertically moving the condenser lens of the crack measurement unit with respect to the workpiece before the relative position of the planned crack formation line is displaced, and acquires a measurement value Ha0 of positional information of the boundary of one of the second regions by detecting the reflected light of the detection light reflected at the boundary of one of the second regions on both sides of the planned crack formation line, the fourth functional unit irradiates one detection light decentered from the optical axis of the condenser lens onto the device formation surface of the workpiece while moving the condenser lens of the crack measurement unit in a vertical direction with respect to the workpiece after the relative position of the planned crack formation line has been displaced, and detects the reflected light of the detection light reflected at the boundary of one of the second regions on both sides of the planned crack formation line, thereby obtaining a measurement value Ha of positional information of the boundary of one of the second regions; The fifth functional unit obtains the relative positional deviation d between the position of the planned crack formation line on the workpiece after displacement and the optical axis position using the following equation (2): d = (Ha - Ha0) tan α …(2) In the above equation (2), d is the amount of relative positional deviation, Ha0 is the measured value of the positional information of the boundary of one of the second regions by the reflected light of the detection light with respect to the workpiece before the relative position of the planned crack formation line is displaced, Ha is the measured value of the positional information of the boundary of one of the second regions by the reflected light of the detection light with respect to the workpiece after the relative position of the planned crack formation line is displaced, and α is the incident angle (°) of the detection light with respect to the vertical thickness of the workpiece. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an optical axis correction method for a laser processing device and a laser processing device that, when a line where a crack is to be formed is displaced due to laser irradiation of a workpiece, can detect and correct the amount of deviation of the optical axis of the laser processing section from the line where a crack is to be formed. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram showing a laser processing apparatus according to a first embodiment of the present invention; [Figure 2] 1 is a schematic diagram showing a crack measurement unit provided in a laser processing device according to a first embodiment of the present invention; [Figure 3] FIG. 2 is a schematic diagram illustrating a method for detecting the depth position of a crack in the first embodiment of the present invention. [Figure 4] FIG. 2 is a schematic diagram illustrating a method for detecting the depth position of a crack in the first embodiment of the present invention. [Figure 5] FIG. 2 is a schematic diagram illustrating a method for detecting the depth position of a crack in the first embodiment of the present invention. [Figure 6] 4 is a schematic diagram (corresponding to FIG. 3) showing how reflected light is received by a photodetector in the first embodiment of the present invention. FIG. [Figure 7] 5 is a schematic diagram (corresponding to FIG. 4) showing how reflected light is received by a photodetector in the first embodiment of the present invention. FIG. [Figure 8] 5 is a schematic diagram (corresponding to FIG. 5) showing how reflected light is received by a photodetector in the first embodiment of the present invention. [Figure 9] FIG. 2 is a schematic diagram illustrating the path of light reflected from a workpiece and reaching the pupil of an objective lens in the first embodiment of the present invention. [Figure 10] FIG. 1 is a diagram for explaining the optical axis correction method for the laser processing apparatus according to the first embodiment of the present invention, and is a schematic plan view of the front surface of a wafer in a state before the planned crack formation line is displaced, viewed from the back surface side. [Figure 11] 11 is a cross-sectional view illustrating the optical axis correction method for the laser processing device according to the first embodiment of the present invention, taken along line AA' in FIG. 10. FIG. [Figure 12] FIG. 1 is a diagram for explaining the optical axis correction method for the laser processing apparatus according to the first embodiment of the present invention, and is a schematic plan view of the front surface of a wafer in a state where the planned crack formation line has been displaced, viewed from the back surface side. [Figure 13] 13 is a cross-sectional view illustrating the optical axis correction method for the laser processing device according to the first embodiment of the present invention, taken along line BB' in FIG. 12. FIG. [Figure 14] FIG. 2 is a diagram for explaining the optical axis correction method for the laser processing device according to the first embodiment of the present invention, showing the relationship between the movement amount of the condenser lens and the change in reflected light. [Figure 15] FIG. 10 is a diagram for explaining the optical axis correction method for a laser processing apparatus according to the second embodiment of the present invention, and is a schematic plan view of the front surface of a wafer in a state before the planned crack formation line is displaced, viewed from the back surface side. [Figure 16] FIG. 10 is a diagram for explaining the optical axis correction method for a laser processing apparatus according to the second embodiment of the present invention, and is a schematic plan view of the front surface of a wafer in a state after the planned crack formation line has been displaced, viewed from the back surface side. [Figure 17] 16 is a cross-sectional view illustrating a method for correcting an optical axis of a laser processing apparatus according to a second embodiment of the present invention, taken along line CC' in FIG. 15. FIG. [Figure 18] 17 is a cross-sectional view illustrating the optical axis correcting method for a laser processing device according to a second embodiment of the present invention, taken along line DD' in FIG. 16. FIG. [Figure 19] FIG. 10 is a diagram for explaining the optical axis correction method for a laser processing device according to a second embodiment of the present invention, showing the relationship between the movement amount of a condenser lens and the change in reflected light. [Figure 20] FIG. 10 is a cross-sectional view illustrating a method for correcting an optical axis of a laser processing apparatus according to a third embodiment of the present invention. [Figure 21] FIG. 10 is a diagram for explaining a method for correcting an optical axis of a laser processing apparatus according to a third embodiment of the present invention, showing the relationship between the amount of movement of a condenser lens and a change in reflected light. [Figure 22] 3 is a schematic diagram showing an example of a light-shielding mask provided in a crack measurement unit of the laser processing apparatus of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for correcting an optical axis of a laser processing device and a laser processing device according to the present invention will be described.

[0015] First, the background of the present invention will be explained. Wafers with multiple devices formed on their surface are divided into individual chips for each device by applying external stress. To facilitate this division, cracks are sometimes formed inside the wafer by irradiating it with laser light. The cracks are formed along planned crack formation lines set on the wafer. By forming the cracks, the wafer is more easily divided along the crack formation lines.

[0016] A conventional laser processing device includes a laser processing unit that forms cracks along the crack formation line, a crack measurement unit that measures the depth of the formed crack inside the wafer, and a control unit. When forming cracks using a laser processing device, a wafer is placed on the sample stage of the laser processing device and a processing laser beam is irradiated from the laser processing unit to form the cracks.

[0017] The depth of the formed crack within the wafer is measured by a crack measurement unit. The crack measurement unit measures the depth of the upper and lower ends of the crack by irradiating the wafer with a measurement laser light and detecting the light reflected inside the wafer. The position of the optical axis of the crack measurement unit when irradiating the measurement laser light is controlled and positioned based on position information of the planned crack formation line stored in advance in the control unit.

[0018] However, when a processing laser beam is irradiated onto a wafer to form cracks, the wafer may expand as a result. This may gradually displace the position of the planned crack formation line. This may cause the position of the optical axis of the processing laser beam to deviate from the planned crack formation line. If the position of the optical axis of the laser beam deviates from the planned crack formation line, there is a risk of damaging devices formed on the wafer.

[0019] The present invention has been made to solve the above problems. Hereinafter, embodiments of the present invention will be described.

[0020] First Embodiment [Laser processing equipment 1] As shown in FIG. 1, the laser processing apparatus 1 of the first embodiment includes a laser processing unit 2, a crack measurement unit 10, and a control unit 500.

[0021] [Laser Processing Section 2] The laser processing unit 2 is provided to irradiate a processing laser beam L onto a wafer W, which is a workpiece, and form a laser processing region, specifically a crack, inside the wafer W. The laser processing unit 2 includes a laser light source (not shown) and a laser optical system (not shown). The laser optical system includes a condenser lens that emits the processing laser beam toward the wafer W. The laser optical system is configured to guide the processing laser beam emitted from the laser light source to the condenser lens. The condenser lens irradiates the laser beam while scanning in the X direction of FIG. 1, and the laser beam condensed by the condenser lens is irradiated toward the wafer W. The position of the optical axis A1 of the condenser lens in the Y direction is aligned with the position of the optical axis A2 of the condenser lens 504 of the crack measurement unit 10 (described later) in the Y direction.

[0022] [Control unit 500] The control unit 500 is realized by, for example, a personal computer or a workstation. The control unit 500 includes a CPU (Central Processing Unit) that controls the operation of each part of the crack measurement unit 10, a ROM (Read Only Memory), a storage device (e.g., an HDD (Hard Disk Drive) or an SSD (Solid State Drive)) that stores a control program, and an SDRAM (Synchronous Dynamic Random Access Memory) that can be used as a working area for the CPU.

[0023] 2, the control unit 500 of this embodiment may be equipped with an operation unit 506 and a display unit 508. The operation unit 506 is a means for accepting operation input from an operator, and includes, for example, a keyboard, a mouse, or a touch panel. The display unit 508 is a device for displaying an operation GUI (Graphical User Interface) for operating the crack measurement unit 10 and images (for example, crack detection results, etc.). For example, a liquid crystal display can be used as the display unit 508.

[0024] The control unit 500 receives an operation input from an operator via the operation unit 506, and transmits a control signal according to the operation input to each part of the crack measurement unit 10 to control the operation of each part.

[0025] Furthermore, the control unit 500 of this embodiment stores position information (hereinafter, sometimes referred to as position information) of a line along which a crack is to be formed on the wafer W, which is the workpiece.

[0026] Furthermore, in order to correct the misalignment between the planned crack formation line on the wafer W, which is the workpiece, and the optical axis of the laser processing unit 2, the control unit 500 has the function of eccentrically irradiating a wafer W having a first area where the planned crack formation line is set and second areas on both sides of the planned crack formation line and having a reflectance different from that of the first area with first detection light and second detection light that are mutually eccentric from the optical axis A2 of the focusing lens 504 of the crack measurement unit 10 while moving the focusing point in the thickness direction of the wafer W, detecting each reflected light reflected from the wafer W, obtaining position information of the boundary between the first area and the second area from the detected detection value, obtaining the amount of misalignment between the planned crack formation line and the optical axis A1 of the laser processing unit 2 from the position information, and correcting the optical axis of the laser processing unit from the amount of misalignment.

[0027] That is, the control unit 500 is equipped with a correction function unit that corrects the position of the optical axis A1 of the focusing lens of the laser processing unit 2 when the relative position of the planned crack formation line on the wafer W with respect to the laser processing device 1 is displaced to a position different from the optical axis position based on the position information.

[0028] The correction function unit has a first function unit, a second function unit, a third function unit, and a fourth function unit. These are realized as functions of the CPU that constitutes the control unit 500. The configuration of each function unit is as follows. The operation of each function unit will be described in detail later.

[0029] (First functional part) When placing the focusing lens 504 above the wafer W after the relative position of the planned crack formation line relative to the laser processing device 1 has been displaced, the first functional unit positions the optical axis A2 of the focusing lens 504 of the crack measurement unit 10 at the optical axis position set based on the position information.

[0030] (Second functional part) The second functional unit moves the focusing lens 504 vertically relative to the wafer W after the relative position of the planned crack formation line has been displaced, and irradiates the device formation surface of the wafer W with detection light that is decentered from the optical axis A2 of the focusing lens 504 of the crack measurement unit 10, and obtains position information of the boundary of the second region by detecting the reflected light of the detection light reflected at the boundary of the second region on the device formation surface.

[0031] (Third Functional Section) The third functional unit obtains the amount of relative positional deviation between the position of the planned crack formation line on the displaced wafer W and the optical axis position based on the positional information of the boundary of the second region obtained by the second functional unit.

[0032] (Fourth Functional Section) The fourth functional unit corrects the position of the optical axis A1 of the laser processing unit 2 when the amount of relative positional deviation obtained by the third functional unit exceeds a threshold value.

[0033] In addition, the second functional unit may be configured to move the focusing lens 504 of the crack measurement unit 10 vertically relative to the wafer W after the relative position of the planned crack formation line has been displaced, irradiate the first detection light and the second detection light that are eccentric from the optical axis A2 of the focusing lens 504 onto the device formation surface of the wafer W, and detect the reflected light of the first detection light and the reflected light of the second detection light that are respectively reflected at the boundaries of one and the other second regions on both sides of the planned crack formation line, thereby obtaining a measurement value Ha of the position information of the boundary of one second region using the reflected light of the first detection light, and a measurement value Hb of the position information of the boundary of the other second region using the reflected light of the second detection light.

[0034] The third functional unit may obtain the relative positional deviation d between the position of the planned crack formation line on the displaced wafer W and the optical axis position using the following equation (1).

[0035] d=(Ha-Hb) / (1 / tanα+1 / tanβ) …(1)

[0036] In the above equation (1), d is the amount of relative positional deviation, Ha is the measured value of the position information of the boundary of one of the second regions using the reflected light of the first detection light, Hb is the measured value of the position information of the boundary of the other second region using the reflected light of the second detection light, α is the incident angle (°) of the first detection light with respect to the vertical thickness of the wafer W, and β is the incident angle (°) of the second detection light with respect to the vertical thickness of the wafer W.

[0037] [Crack measurement section 10] FIG. 2 is a block diagram showing the crack measurement unit 10. The crack measurement unit 10 is an apparatus used in combination with a laser processing unit 2 that forms a laser processing area (crack) inside the workpiece, a wafer W, and is arranged to be movable integrally with the laser processing unit 2, as shown in Figure 1.

[0038] The crack measurement unit 10 detects the crack depth of a crack K formed inside the wafer W by irradiating a wafer W such as a silicon wafer with detection light L1 and detecting reflected light L2 from the wafer W. In the following description, a three-dimensional Cartesian coordinate system is used in which the stage 510 on which the wafer W is placed is defined as a plane parallel to the XY plane, and the Z direction is the thickness direction of the wafer W.

[0039] As shown in FIG. 2, the crack measurement unit 10 includes a light source unit 100, an illumination optical system 200, an interface detection optical system 300, a crack detection optical system 400, a focal point position moving mechanism 502, and a focusing lens 504.

[0040] [Light source section 100] The light source unit 100 emits detection light L1. The detection light L1 is used to detect the interface position of the wafer W and to detect cracks K formed inside the wafer W. The detection light in this embodiment is also used to measure the relative positional deviation d. Here, when the wafer W is a silicon wafer, light that is transparent to the wafer W, for example, infrared light with a wavelength of 1,000 nm or more, is used as the detection light L1.

[0041] The light source unit 100 includes light sources 102A, 102B, and 102C and a half mirror 104. The light sources 102A, 102B, and 102C and the half mirror 104 are arranged along an optical axis AX that is coaxial with the optical axis A2 of the condenser lens 504.

[0042] The light sources 102A, 102B, and 102C emit detection light L1 along an optical axis AX. As the light sources 102A, 102B, and 102C, for example, a laser light source (infrared laser light source, laser diode) or an LED (Light Emitting Diode) light source can be used.

[0043] Light source 102A has a laser aperture capable of illuminating substantially the entire surface of condenser lens pupil 504a of condenser lens 504. Light source 102A is used for interface detection, which will be described later.

[0044] The light sources 102B and 102C each have a laser aperture capable of illuminating only a portion of the condenser lens pupil 504a of the condenser lens 504 that is decentered from the optical axis A2 of the condenser lens. The light sources 102B and 102C are used for crack detection and measurement of the relative positional deviation d, which will be described later.

[0045] Although not shown in the drawings, the detection light L1 emitted from the light sources 102A, 102B, and 102C will be referred to as detection light L1(A), first detection light L1a, and second detection light L1b, respectively. In this embodiment, these may be collectively referred to as detection light L1.

[0046] The half mirror 104 reflects the detection light L1 (L1(A)) emitted from the light source 102A for interface detection and transmits the detection light L1 (L1a, L1b) emitted from the light sources 102B and 102C for crack detection.

[0047] The light sources 102A, 102B, and 102C are each connected to a control unit 500, and the control unit 500 controls the emission of the light sources 102A, 102B, and 102C.

[0048] [Illumination optical system 200] The illumination optical system 200 guides the detection light L1 emitted from the light source unit 100 to the condenser lens 504. The illumination optical system 200 includes relay lenses 202 and 206 and a mirror 204 (for example, a total reflection mirror).

[0049] The detection light L1 emitted from the light source unit 100 passes through the relay lens 202 and is reflected by the mirror 204, thereby bending the optical path. The detection light L1 reflected by the mirror 204 passes through the relay lens 206, and is then reflected by the half mirror 304 and the half mirror 302 in this order, and is emitted toward the condenser lens 504.

[0050] The return light (observation light) reflected by the wafer W and transmitted through the half mirror 302 can be observed using an observation optical system 600 (for example, a photodetector).

[0051] [Condenser lens 504] The condenser lens 504 condenses (focuses) the detection light L1 emitted from the illumination optical system 200 onto the wafer W. The condenser lens 504 is disposed at a position facing the wafer W. The optical axis A2 of the condenser lens 504 is coaxial with the main optical axis AX. As described above with reference to FIG. 1, the Y-direction position of the optical axis A2 of the condenser lens 504 is aligned with the Y-direction position of the optical axis A1 of the laser processing unit 2. The optical axis A2 of the condenser lens 504 corresponds to the optical axis of the crack measurement unit 10 of this embodiment.

[0052] The condenser lens 504 can be moved in the X direction or the Y direction by a driving means such as an actuator. The condenser lens 504 can condense the detection light L1 emitted from the illumination optical system 200 at any position on the wafer W in the X direction or the Y direction.

[0053] In this embodiment, the condenser lens 504 is moved in the X and Y directions, but the stage 510 on which the wafer W is placed may be moved in the X or Y direction, or both the condenser lens 504 and the stage 510 may be movable.

[0054] [Focusing point position movement mechanism 502] The focal point position moving mechanism 502 changes the position of the focal point of the detection light L1 in the vertical direction (Z direction (direction of the optical axis A2 of the focusing lens 504)). The focal point position moving mechanism 502 includes an actuator (e.g., a piezoelectric actuator, not shown) that moves the focusing lens 504 in the Z direction. The focal point position moving mechanism 502 moves the focusing lens 504 in the Z direction by driving the piezoelectric actuator under the control of the control unit 500. This changes the relative distance in the Z direction between the focusing lens 504 and the wafer W, thereby adjusting the position of the focal point of the detection light L1 in the Z direction.

[0055] Furthermore, the focal point position moving mechanism 502 may include a Z drive mechanism that moves the crack measurement unit 10 in the Z direction relative to the stage 510. The Z drive mechanism moves the crack measurement unit 10 in the Z direction, thereby aligning the focusing lens 504 with the wafer W in the Z direction with a larger adjustment range than the piezoelectric actuator.

[0056] As described above, when the position adjustment (coarse adjustment) of the focal point by the Z drive mechanism and the position adjustment (fine adjustment) of the focal point by the piezoelectric actuator are combined, the degree of freedom (adjustment range) in adjusting the position of the focal point of the detection light L1 in the Z direction is increased compared to when only the piezoelectric actuator is used, which makes it possible to detect cracks in wafers W of various thicknesses.

[0057] The reflected light L2 collected by the collecting lens 504 and reflected by the wafer W is guided to the interface detection optical system 300 and the crack detection optical system 400, and is used to detect the interface and cracks, respectively, of the wafer W. The reflected light L2 is also used to measure the relative positional deviation d.

[0058] [Interface detection optical system 300] The interface detection optical system 300 is an optical system for detecting the interface (front surface Wa or back surface Wb) of the wafer W, and includes a half mirror 302, a half mirror 304, a relay lens 306, a half mirror 308, and a photodetector 310.

[0059] The light source 102A emits detection light L1(A). When detecting the front surface Wa of the wafer W as the interface of the wafer W, the control unit 500 instructs the light source 102A to irradiate the wafer W with the detection light L1(A).

[0060] The relay lens 206 converts the detection light L1(A) emitted from the light source 102A into laser light having an aperture of approximately the same size as the condenser lens pupil 504a of the condenser lens 504. The detection light L1(A) is then reflected sequentially by the half mirror 304 and the half mirror 302 and guided to the condenser lens 504. The detection light L1(A) is irradiated onto approximately the entire surface of the condenser lens pupil 504a of the condenser lens 504.

[0061] Here, the reflected light L2(A) obtained by reflecting the detection light L1(A) from the wafer W is referred to as L2(A). The reflected light L2(A) is reflected by the half mirror 302, passes through the half mirror 304, and is then guided to the relay lens 306. The reflected light L2(A) that passes through the relay lens 306 is reflected by the half mirror 308 and is then guided to the photodetector 310.

[0062] The photodetector 310 is a device for receiving reflected light L2(A) from the wafer W and detecting the interface of the wafer W, and includes a detector body 310A and a pinhole panel 310B.

[0063] The detector main body 310A can be a photodetector (for example, a photodiode) that converts received light into an electrical signal and outputs it to the control unit 500, an infrared camera, or the like.

[0064] A pinhole is formed in the pinhole panel 310B to transmit a portion of the incident light. The pinhole panel 310B is disposed upstream of the light receiving surface of the detector body 310A, and is disposed so that the pinhole in the pinhole panel 310B is positioned on the optical axis of the reflected light L2(A). The position of the pinhole in the pinhole panel 310B is optically conjugate with the focal point (front focal position) of the condenser lens 504 (confocal pinhole). The size of the pinhole in the pinhole panel 310B is adjusted to approximately the diffraction limit of the condenser lens 504.

[0065] (Method for detecting the interface of a wafer W using an interface detection optical system) A method for detecting the interface of the wafer W using an interface detection optical system will be described below. In this embodiment, the interface of the surface Wa of the wafer W (the surface in contact with the stage 510, which is the device formation surface on which devices are formed) is detected, and then, as will be described later, the depth of a crack is detected based on the interface position of the surface Wa of the wafer W. The measured interface position of the surface Wa is also used to measure the relative positional deviation d.

[0066] In this embodiment, the crack depth is detected and the relative positional deviation amount d is measured using the front surface Wa of the wafer W as a reference, but the present invention is not limited to this. For example, the crack depth may be detected and the relative positional deviation amount d may be measured using the back surface Wb of the wafer W as a reference. It is also possible to calculate the average value of the crack depths and the average value of the relative positional deviation amount d detected using the interface positions of both the front surface Wa and the back surface Wb of the wafer W as references, respectively.

[0067] The reflected light L2(A) reflected by the wafer W is focused at the position of a pinhole in the pinhole panel 310B, which is optically conjugate with the focusing point of the focusing lens 504. When the focusing point of the focusing lens 504 coincides with the surface Wa of the wafer W, which serves as the reflective surface, the light beam of the detection light L1(A) is reflected by the surface Wa of the wafer W, becomes a parallel light beam, and returns after passing through the focusing lens 504. Therefore, the signal D (see FIG. 14, etc.) output from the detector main body 310A has a sharp peak when the focusing point of the focusing lens 504 coincides with the position of the surface Wa of the wafer W, which serves as the reflective surface.

[0068] The control unit 500 changes the relative distance between the condenser lens 504 and the wafer W using the condenser position moving mechanism 502 while irradiating the wafer W with the detection light L1(A) from the light source 102A, thereby moving the position of the condenser of the detection light L1(A) (i.e., the front focal position of the condenser lens 504) in the Z direction. This causes the condenser of the detection light L1(A) to be scanned in the Z direction. The control unit 500 detects the reflected light L2(A) from the wafer W when the condenser of the detection light L1(A) is scanned in the Z direction using the photodetector 310, and detects the interface position Z(0) of the surface Wa of the wafer W by detecting the peak of the signal from this photodetector 310.

[0069] [Crack detection optical system 400] The crack detection optical system 400 includes a relay lens 402 and photodetectors 404 and 406. In Fig. 2, the crack detection optical system 400 also includes a half mirror 308, which mainly functions as an optical element of the interface detection optical system.

[0070] The relay lens 306 and the relay lens 402 guide the reflected light L2a and L2b reflected by the wafer W to the photodetectors 404 and 406. Note that the reflected light L2a and L2b are the first detection light L1a and the second detection light L1b emitted from the light sources 102B and 102C, respectively, reflected by the wafer W when detecting a crack K formed inside the wafer W and when measuring the relative positional deviation amount d, as will be described later.

[0071] The photodetectors 404 and 406 are devices that receive reflected light L2a and L2b from the wafer W to detect cracks K inside the wafer W and measure the relative positional deviation d. As the photodetectors 404 and 406, a photodetector (e.g., a photodiode) that converts the received light into an electrical signal and outputs it to the control unit 500, an infrared camera, or the like can be used.

[0072] The photodetectors 404 and 406 are arranged at positions conjugate with the condenser lens pupil 504a, and are further arranged at positions offset from the optical axis of the condenser lens 504 so as to receive the detection light beams L1a and L1b.

[0073] (Method for detecting cracks K using crack detection optical system 400) Hereinafter, a method for detecting a crack K formed inside the wafer W using the crack detection optical system 400 will be described with reference to FIGS.

[0074] When detecting a crack K formed inside the wafer W, the control unit 500 causes the light sources 102B and 102C to emit light and irradiate the wafer W with a first detection light L1a and a second detection light L1b. The light sources 102B and 102C each have a laser aperture at a position offset from the main optical axis AX. As a result, the first detection light L1a and the second detection light L1b, which are eccentric with respect to the optical axis A2 of the condenser lens 504, are irradiated onto the wafer W. Note that the second detection light L1b is not shown in FIGS. 3 to 8.

[0075] The first detection light L1a and the second detection light L1b are reflected by the wafer W, resulting in reflected light L2a and reflected light L2b, which are then reflected by the half mirror 302 and then transmitted through the half mirror 304, the relay lens 306, and the half mirror 308, before entering the relay lens 402. The reflected light L2a and L2b transmitted through the relay lens 402 are received by the photodetectors 404 and 406, respectively. Note that the reflected light L2b is not shown in FIGS. 3 to 8.

[0076] The photodetectors 404 and 406 receive the reflected light L2a and L2b from the wafer W to detect cracks K inside the wafer W.

[0077] 3 to 5 are explanatory diagrams showing the state when the first detection light L1a is obliquely illuminated onto the wafer W. Fig. 3 shows a case where a crack K is present at the focal point of the condenser lens 504, Fig. 4 shows a case where the crack K is not present at the focal point of the condenser lens 504, and Fig. 5 shows a case where the focal point of the condenser lens 504 coincides with the crack depth (the crack upper end position) of the crack K.

[0078] 6 to 8 are diagrams showing the state of the reflected light L2a received by the photodetectors 404 and 406, and correspond to the cases shown in FIGS. 3 to 5, respectively.

[0079] 9 is a diagram for explaining the path of reflected light L2 from the wafer W reaching the condenser lens pupil 504a. Here, a case will be described in which the first detection light L1 passes through a first region G1 on one side (the right side in FIG. 9) of the condenser lens pupil 504a and obliquely illuminates the wafer W.

[0080] 3, if a crack K is present at the focal point of the condenser lens 504, the first detection light L1a is totally reflected by the crack K, and the reflected light L2a thereof follows a path on the same side as the optical path of the first detection light L1a with respect to the optical axis A2, and becomes a component that reaches an area of ​​the condenser lens pupil 504a on the same side as the first detection light L1a. That is, as shown in FIG. 9, when the path of the first detection light L1 when the first detection light L1a from the light source unit 100 is irradiated onto the wafer W via the condenser lens 504 is defined as R1, the reflected light L2 that is totally reflected by the crack K inside the wafer W follows a path R2 on the same side (right side in FIG. 9) with respect to the optical axis A2 as the path R1 of the first detection light L1a, and passes through a first area G1 of the condenser lens pupil 504a.

[0081] 4, when no crack K is present at the focal point of the condenser lens 504, the first detection light L1a is reflected by the surface Wa of the wafer W, and the reflected light L2 is a component that reaches a region of the condenser lens pupil 504a on the opposite side to the detection light L1a. That is, as shown in Fig. 9, the reflected light L2 reflected by the surface Wa of the wafer W follows a path R3 on the opposite side of the optical axis A2 (the left side in Fig. 9) from the path R1 of the first detection light L1a, and passes through a second region G2 of the condenser lens pupil 504a.

[0082] 5, when the focal point of the condenser lens 504 coincides with the lower end position of the crack K, the detection light L1a is split into a reflected light component L2a and a non-reflected light component L2b. The reflected light component L2a is totally reflected by the crack K, then reflected by the surface Wa to reach an area of ​​the condenser lens pupil 504a on the same side as the detection light L1, while the non-reflected light component L2b is not totally reflected by the crack K, but is reflected by the surface Wa of the wafer W to reach an area of ​​the condenser lens pupil 504a on the opposite side to the detection light L2. That is, as shown in Figure 9, of the reflected light L2, the reflected light component L2a that is totally reflected by the crack K inside the wafer W follows a path R2 on the same side of the main optical axis AX (the right side in Figure 9) as the path R1 of the detection light L1 and passes through a first region G1 of the focusing lens pupil 504a, while the non-reflected light component L2b that is not totally reflected by the crack K and is reflected by the surface Wa of the wafer W follows a path R3 on the opposite side of the main optical axis AX (the left side in Figure 9) from the path R1 of the detection light L1 and passes through a second region G2 of the focusing lens pupil 504a.

[0083] The photodetectors 404 and 406 are arranged at positions optically conjugate with the first region G1 and the second region G2 of the condenser lens pupil 504a, respectively, so that the photodetectors 404 and 406 can selectively receive light that has passed through the first region G1 and the second region G2 of the condenser lens pupil 504a, respectively.

[0084] 3 (where crack K exists at the focal point of condenser lens 504), reflected light L2 is incident on light receiving surface 404C of photodetector 404, out of photodetectors 404 and 406. Therefore, as shown in FIG. 6, the level of the detection signal output from light receiving surface 404C of photodetector 404 becomes higher than the level of the detection signal output from light receiving surface 406C of photodetector 406.

[0085] 4 (where crack K is not present at the focusing point of focusing lens 504), the reflected light is incident on light receiving surface 406C of photodetector 406, of photodetectors 404 and 406. Therefore, as shown in FIG. 7, the level of the detection signal output from light receiving surface 406C of photodetector 406 is higher than the level of the detection signal output from light receiving surface 404C of photodetector 404.

[0086] 5 (where the focal point of the condenser lens 504 coincides with the lower end position of the crack K), the components L2a and L2b of the reflected light L2 are incident on the light receiving surfaces 404C and 406C of the photodetectors 404 and 406, respectively. Therefore, as shown in FIG. 8, the levels of the detection signals output from the light receiving surfaces 404C and 406C of the photodetectors 404 and 406 become approximately equal.

[0087] In this way, the amount of light received by the light receiving surfaces 404C and 406C of the photodetectors 404 and 406 changes depending on whether or not a crack K is present at the focal point of the condenser lens 504. In this embodiment, this property is utilized to detect the crack depth (the crack upper end position or the crack lower end position) of the crack K formed inside the wafer W.

[0088] The control unit 500 (see Figure 2) controls the focal point position moving mechanism 502 to move the focal point of the detection light L1 in the Z direction, sequentially changing it from the interface position of the surface Wa of the wafer W to the thickness direction of the wafer W (Z direction), while sequentially acquiring detection signals output from the light receiving surfaces 404C and 406C of the photodetectors 404 and 406, and can detect the crack depth of the crack K (the lower end position or the upper end position of the crack) based on these detection signals.

[0089] (Method for correcting the optical axis A1 of the laser processing portion 2 using the crack detection optical system 400 of this embodiment) Next, a method for correcting the optical axis A1 of the laser processing device 1 of this embodiment will be described with reference to FIGS.

[0090] In this embodiment, the method for correcting the optical axis A1 of the laser processing unit 2 involves correcting the misalignment between the planned crack formation line on the wafer W and the optical axis A1 of the laser processing unit 2. The wafer W has a first region where the planned crack formation line is set and second regions on both sides of the planned crack formation line that have a reflectance different from that of the first region. The method includes the steps of: irradiating the wafer W with first and second detection lights that are mutually eccentric from the optical axis A2 of the condenser lens 504 of the crack measurement unit 10 while moving the focusing point in the thickness direction of the wafer W; detecting the respective reflected lights from the wafer W; acquiring positional information of the boundary between the first and second regions from the detected detection values; obtaining the amount of misalignment between the planned crack formation line and the optical axis A1 of the laser processing unit 2 from the positional information; and correcting the optical axis A1 of the laser processing unit 2 based on the amount of misalignment. This will be explained in detail below.

[0091] FIG. 10 is a schematic plan view of the front surface Wa of the wafer W as viewed from the back surface Wb side. 10, a plurality of device regions D are formed on the front surface Wa (device formation surface) of the wafer W. A plurality of strip-shaped first regions S1 arranged in a grid pattern are disposed between each of the device regions D. In each of the first regions S1, for example, a crack formation line CL is set in the center of the width direction thereof, extending along the longitudinal direction of the first region S1.

[0092] In addition, the position of the planned crack formation line CL when the wafer W is placed on the stage 510 is stored in advance as position information in the control unit 500 as a relative position with respect to the laser processing device 1 before irradiation with the processing (crack formation) laser light.

[0093] Second regions S21 and S22 are provided between the first region S1 and the device region D. The second regions S21 and S22 are arranged on both sides in the longitudinal direction of the planned crack formation line CL, i.e., on both sides in the width direction of the first region S1.

[0094] The first region S1 and the second regions S21 and S22 each have the property of reflecting the detection light L1 when the detection light L1 is obliquely illuminated onto the wafer W. That is, the first region S1 and the second regions S21 and S22 each have a constant reflectance within each region, but the reflectances are different. For example, the reflectances of the second regions S21 and S22 are relatively low compared to the reflectance of the first region S1.

[0095] Furthermore, the device region D also has the property of reflecting the detection light L1 when the detection light L1 is obliquely illuminated onto the wafer W. The reflectance of the device region D is different from the reflectance of the first region S1 and the second regions S21 and S22.

[0096] As will be described later, the optical axis correction method of this embodiment utilizes the property that the reflectances of the regions D, S1, S21, and S22 are different.

[0097] 10 is placed on the stage 510 of the laser processing apparatus 1. At this stage, the wafer W is in a state before the relative position with respect to the laser processing apparatus 1 is displaced. The state before the relative position is displaced means that there is no deformation of the wafer W induced by the irradiation of the processing laser light onto the wafer W, and the position of the planned crack formation line CL set on the wafer W matches the position information of the planned crack formation line held in the control unit 500 of the laser processing apparatus 1.

[0098] FIG. 11 shows a schematic cross-sectional view taken along line AA' in FIG. 11, as described above, the wafer W is in a state before displacement relative to the laser processing apparatus 1. When performing crack measurement on the wafer W, the optical axis A2 of the condenser lens 504 of the crack measurement unit 10 is moved to the optical axis position set in the control unit 500 based on the position information of the planned crack formation line, and in FIG. 11, the set optical axis position is located directly above the planned crack formation line CL on the wafer W.

[0099] In this case, as shown in Figure 11, the relative positional deviation between the position of the planned crack formation line CL on the wafer W and the optical axis position of the optical axis A2 of the focusing lens 504 of the crack measurement unit 10 is 0 (zero). Here, the position of the optical axis A2 of the focusing lens 504 of the crack measurement unit 10 and the position of the optical axis A1 of the focusing lens of the laser processing unit 2 coincide in the Y direction. Therefore, the relative positional deviation between the position of the planned crack formation line CL and the optical axis position of the optical axis A1 of the focusing lens of the laser processing unit 2 is 0 (zero). Therefore, in the case of Figure 11, there is no need to correct the optical axis A1 of the focusing lens of the laser processing unit 2.

[0100] Next, Fig. 12 shows a schematic plan view of the front surface Wa of the wafer W as seen from the back surface Wb side, similar to Fig. 10. The wafer W in Fig. 12 is placed on the stage 510 of the laser processing apparatus 1, similar to Fig. 10, but the wafer W in Fig. 12 is in a state where the relative position of the planned crack formation line CL with respect to the laser processing apparatus 1 has been displaced. The state where the relative position of the planned crack formation line CL has been displaced means that, as a result of deformation of the wafer W induced by irradiation of the wafer W with a processing laser beam, etc., the position of the planned crack formation line CL set on the wafer W does not match the position information of the planned crack formation line held in the control unit 500 of the laser processing apparatus 1.

[0101] FIG. 13 is a schematic cross-sectional view taken along line BB' in FIG. As described above, the wafer W in Fig. 13 is in a state after the relative position of the planned crack formation line CL with respect to the laser processing device 1 has been displaced. When performing crack measurement on the wafer W, the optical axis A2 of the condenser lens 504 of the crack measurement unit 10 is moved to the optical axis position set in the control unit 500 based on the position information of the planned crack formation line, but in Fig. 13, the set optical axis position is not directly above the planned crack formation line CL on the wafer W, but is located away from the planned crack formation line CL in the Y direction.

[0102] That is, the amount of relative positional deviation between the position of the planned crack formation line CL on the wafer W and the optical axis position of the optical axis A2 of the condenser lens 504 of the crack measurement unit 10 is d. In other words, the amount of relative positional deviation between the position of the planned crack formation line CL and the optical axis position of the optical axis A1 of the condenser lens of the laser processing unit 2 is d. If this d exceeds a threshold value, it is necessary to correct the position of the optical axis A1 of the condenser lens of the laser processing unit 2. Therefore, the amount of relative positional deviation d is measured as follows.

[0103] (First stage) As already described, in the first step, the optical axis A2 of the focusing lens 504 of the crack measurement unit 10 is moved to the optical axis position set in the control unit 500 based on the position information of the planned crack formation line, as shown in Fig. 13. The optical axis position of the optical axis A2 of the focusing lens 504 is spaced apart from the position of the planned crack formation line CL on the wafer W by a relative positional deviation amount d in the Y direction.

[0104] (Phase 2) In the second stage, the focusing lens 504 of the crack measurement unit 10 is moved in the vertical direction (Z direction) relative to the wafer W, and the wafer W is obliquely illuminated with the first detection light L1a and the second detection light L1b that are eccentric from the optical axis A2 of the focusing lens 504, and the reflected light of the detection light L1a and L1b reflected at the boundary between the second regions S21 and S22 on the surface Wa (device formation surface) is detected to obtain positional information of the boundary between the second regions S21 and S22.

[0105] Specifically, the first detection light L1a passes through one region (first region G1 in FIG. 9) of the condenser lens 504, is incident on the wafer W, is condensed on the optical axis A2 of the condenser lens 504, and is further reflected by the surface Wa of the wafer to become reflected light L2a. The angle of incidence of the first detection light L1a on the wafer W is set to α° with respect to the thickness direction (Z direction) of the wafer W.

[0106] The second detection light L1a passes through one region (second region G2 in FIG. 9) of the condenser lens 504, is incident on the wafer W, is condensed on the optical axis A2 of the condenser lens 504, and is further reflected by the surface Wa of the wafer to become reflected light L2b. The incident angle of the second detection light L1b on the wafer W is β° with respect to the thickness direction (Z direction) of the wafer W.

[0107] When the condenser lens 504 is moved along the Z direction toward the wafer W, the intersection Pa between the optical path of the first detection light L1a and the optical axis A2 of the condenser lens 504 moves in the direction of arrow z1 toward the surface Wa of the wafer W. The reflection position of the first detection light L1a on the surface Wa of the wafer moves in the direction of arrow y1. At this time, the reflection position of the first detection light L1a on the surface Wa passes through the boundary between the first region S1 and one of the second regions S21 of the wafer W. Because the first region S1 and the second region S21 have different reflectivities, the amount of reflected light L2a of the first detection light L1a changes during this passage. The position of the intersection Pa at the point when this amount of light changes is detected. Specifically, the height of the intersection Pa relative to the surface Wa of the wafer W is detected as a measurement value Ha. Because the position of the intersection Pa corresponds to the position of the condenser lens 504, the measurement value Ha can be obtained based on the output of the focus position mechanism 502 that controls the condenser lens 504. The measurement value Ha is output to the control unit 500 as position information of the boundary of one of the second regions S21.

[0108] Similarly, when the condenser lens 504 is moved toward the wafer W, an intersection Pb between the optical path of the second detection light L1b and the optical axis A2 of the condenser lens 504 moves in the direction of arrow z2 toward the surface Wa of the wafer W. The reflection position of the second detection light L1b on the surface Wa of the wafer moves in the direction of arrow y2. At this time, the reflection position of the second detection light L1b on the surface Wa passes through the boundary between the first region S1 and the other second region S22 of the wafer W. Because the first region S1 and the second region S22 have different reflectivities, the amount of reflected light L2b of the second detection light L1b changes during this passage. The position of the intersection Pb at the point when this amount of light changes is detected. Specifically, the height of the intersection Pb relative to the surface Wa of the wafer W is detected as a measurement value Hb. Because the position of the intersection Pb corresponds to the position of the condenser lens 504, the measurement value Hb can be calculated based on the output of the focal position mechanism 502 that controls the condenser lens 504. The measurement value Hb is output to the control unit 500 as position information of the boundary of the other second region S22.

[0109] In this embodiment, the positions of the intersection points Pa and Pb are detected by utilizing the change in reflectance at the boundary between the second regions S21 and S22 on the first region S1 side. However, the present invention is not limited to this, and the change in reflectance at the boundary between the second regions S21 and S22 on the device region D side may also be utilized.

[0110] However, when detecting the positions of intersections Pa and Pb, it is necessary to use the change in reflectance at the boundary at a symmetrical position. That is, if the change in reflectance at the boundary of the second region S21 on the first region S1 side is used when detecting the position of intersection Pa, it is also necessary to use the change in reflectance at the boundary of the second region S21 on the first region S1 side when detecting the position of intersection Pb.

[0111] (Third Stage) Next, in the third stage, based on the measurement values ​​Ha and Hb obtained in the second stage, the relative positional deviation d between the position of the planned crack formation line CL on the wafer W after displacement and the optical axis position of the focusing lens 504 of the crack measurement unit 10 is obtained using the following equation (1).

[0112] d=(Ha-Hb) / (1 / tanα+1 / tanβ) …(1)

[0113] In the above equation (1), d is the amount of relative positional deviation, Ha is the measured value of the positional information of the boundary of one of the second regions S21 by the reflected light L2a of the first detection light L1a, Hb is the measured value of the positional information of the boundary of the other second region S22 by the reflected light L2b of the second detection light L1b, α is the incident angle (°) of the first detection light L1a with respect to the thickness of the wafer in the vertical direction, and β is the incident angle (°) of the second detection light L1b with respect to the thickness of the wafer W in the vertical direction.

[0114] (Fourth Stage) If the relative positional deviation amount d obtained in the third stage exceeds the threshold value, the optical axis position of the laser processing unit 2 is corrected. Specifically, the position information of the planned crack formation line CL held in the control unit 500 is corrected based on the relative positional deviation amount d.

[0115] FIG. 14 shows the relationship between the movement amount of the condenser lens 504 and the intensities (sensor values) of the reflected light L2a and the reflected light L2b.

[0116] As shown in the upper part of Figure 14, when the optical axis position of the focusing lens 504 of the crack measurement unit 10 is directly above the planned crack formation line CL (as in Figures 10 and 11), as shown in the measurement graph, the changes in the intensity of the reflected light L2a and the reflected light L2b behave similarly depending on the amount of movement of the focusing lens 504. Furthermore, the intensity curves of the reflected light L2a and the reflected light L2b almost overlap, and the heights Ha and Hb are almost the same.

[0117] On the other hand, as shown in the middle of Figure 14, when the optical axis position of the focusing lens 504 deviates from the intended crack formation line CL (as in Figures 12 and 13), as shown in the measurement graph, the intensities of the reflected light L2a and the reflected light L2b behave in a similar manner depending on the amount of movement of the focusing lens 504, but the intensity curves of the reflected light L2a and the reflected light L2b do not overlap, and the heights of Ha and Hb are different.

[0118] Furthermore, as shown in the lower part of Figure 14, when the optical axis position of the focusing lens 504 of the crack measurement unit 10 deviates significantly from the planned crack formation line CL, as shown in the measurement graph, the intensities of the reflected light L2a and the reflected light L2b behave in a similar manner depending on the amount of movement of the focusing lens 504, but the intensity curves of the reflected light L2a and the reflected light L2b deviate significantly, and the difference in height between Ha and Hb becomes larger.

[0119] 14 is the interface detection peak of the wafer W detected by the interface detection optical system of the crack measurement unit 10, and is a peak corresponding to the surface Wa of the wafer W. In the second stage, the heights Ha and Hb are obtained from the position of this peak.

[0120] As described above, according to this embodiment, if the planned crack formation line CL is displaced before or after laser processing of the wafer W, the amount of deviation of the optical axis A1 of the laser processing unit 2 from the planned crack formation line can be detected, and the optical axis A2 of the laser processing unit 2 can be corrected.

[0121] <Second embodiment> Next, a second embodiment of the present invention will be described. The difference between this embodiment and the first embodiment lies in the wafer W, which is the workpiece. That is, in the first embodiment, the first region S1 in the wafer W has a constant reflectance within that region, and a planned crack formation line CL is set in the center of the first region in the width direction. On the other hand, in this embodiment, the first region S1 in the wafer W has a different reflectance within that region, and a planned crack formation line CL is set in the center of the first region S1 in the width direction, which is different from the wafer W in the first embodiment. In this embodiment, such a wafer is used as the measurement target.

[0122] [Laser processing equipment] The laser processing apparatus of this embodiment differs from the laser processing apparatus 1 of the first embodiment in the configuration of the control unit. That is, in order to correct the deviation between the planned crack formation line on the wafer W and the optical axis A1 of the laser processing unit 2, the control unit of this embodiment has the functions of, before laser processing, eccentrically irradiating the detection light that is eccentric from the optical axis A2 of the condenser lens 504 of the crack measurement unit 10 while moving the focal point in the thickness direction of the wafer W, detecting the reflected light from the wafer W, and, after laser processing, eccentrically irradiating the detection light that is eccentric from the optical axis A2 of the condenser lens 504 of the crack measurement unit 10 while moving the focal point in the thickness direction of the wafer W, detecting the reflected light from the wafer W, obtaining the amount of deviation between the planned crack formation line and the optical axis A1 of the laser processing unit 2 from the detected values ​​of the reflected light before and after laser processing, and correcting the optical axis A1 of the laser processing unit 2 from the deviation amount.

[0123] More specifically, the optical axis correcting section of the control section in this embodiment includes the following first, second, third, fourth, fifth and sixth functional sections.

[0124] (First functional part) When the focusing lens 504 of the crack measurement unit 10 is placed above the wafer W before the relative position of the planned crack formation line relative to the laser processing device is displaced, the optical axis A2 of the focusing lens 504 is placed at the optical axis position set based on the position information of the planned crack formation line CL.

[0125] (Second functional part) While moving the focusing lens 504 vertically relative to the wafer W before displacement, detection light decentered from the optical axis A2 of the focusing lens 504 is irradiated onto the device formation surface of the wafer W, and the reflected light of the detection light reflected at the boundary of the second region on the device formation surface is detected to obtain first position information of the boundary of the second region.

[0126] (Third Functional Section) When placing the focusing lens 504 of the crack measurement unit 10 above the wafer W after the relative position of the planned crack formation line with respect to the laser processing device has shifted, the optical axis A2 of the focusing lens 504 is placed at the optical axis position set based on the position information.

[0127] (Fourth Functional Section) While moving the focusing lens 504 of the crack measurement unit 10 vertically relative to the wafer W after the relative position of the planned crack formation line has been displaced, detection light decentered from the optical axis A2 of the focusing lens 504 is irradiated onto the device formation surface of the wafer W, and the reflected light of the detection light reflected at the boundary of the second region on the device formation surface is detected to obtain second position information of the boundary of the second region.

[0128] (5th Functional Section) Based on the first position information of the boundary of the second region obtained by the second functional unit and the second position information of the boundary of the second region obtained by the fourth functional unit, the relative positional deviation amount between the position of the planned crack formation line CL on the wafer W after the displacement and the optical axis position is obtained.

[0129] (6th Functional Department) When the relative positional deviation amount d obtained in the fifth functional unit exceeds a threshold value, the position of the optical axis A1 of the laser processing unit 2 is corrected.

[0130] In addition, the second functional unit may be configured to move the focusing lens 504 of the crack measurement unit 10 vertically relative to the wafer W before the relative position of the planned crack formation line is displaced, irradiate one detection light decentered from the optical axis A2 of the focusing lens 504 onto the device formation surface of the wafer W, and detect the reflected light of the detection light reflected at the boundary of one of the second areas on both sides of the planned crack formation line CL, thereby obtaining a measurement value Ha0 of the position information of the boundary of one of the second areas.

[0131] In addition, the fourth functional unit may move the focusing lens 504 of the crack measurement unit 10 vertically relative to the wafer W after the relative position of the planned crack formation line has been displaced, irradiate one detection light that is decentered from the optical axis A2 of the focusing lens 504 onto the device formation surface of the wafer W, and obtain a measurement value Ha of the position information of the boundary of one of the second areas by detecting the reflected light of the detection light reflected at the boundary of one of the second areas on both sides of the planned crack formation line CL.

[0132] Furthermore, the fifth functional unit may obtain the relative positional deviation amount d between the position of the crack formation line CL on the wafer W after displacement and the position of the optical axis by the following equation (2).

[0133] d = (Ha - Ha0) tan α … (2)

[0134] In the above equation (2), d is the amount of relative positional deviation, Ha0 is the measured value of the positional information of the boundary of one of the second regions by the reflected light of the detection light relative to the wafer W before the displacement of the line where the crack is to be formed, Ha is the measured value of the positional information of the boundary of one of the second regions by the reflected light of the detection light relative to the wafer W after the displacement of the line where the crack is to be formed, and α is the angle of incidence (°) of the detection light relative to the vertical thickness of the wafer W.

[0135] (Optical axis correction method of this embodiment) Next, a method for correcting the optical axis of the laser processing device of this embodiment will be described with reference to FIGS.

[0136] The optical axis correction method of the laser processing device of this embodiment corrects the misalignment between the planned crack formation line on the wafer W and the optical axis A1 of the laser processing unit 2, and includes the steps of: before laser processing, eccentrically irradiating the wafer W with detection light that is eccentric from the optical axis A2 of the condenser lens 504 of the crack measurement unit 10 while moving the focal point in the thickness direction of the wafer W and detecting the reflected light; after laser processing, eccentrically irradiating the wafer W with detection light that is eccentric from the optical axis A2 of the condenser lens 504 of the crack measurement unit 10 while moving the focal point in the thickness direction of the wafer W and detecting the reflected light; obtaining the amount of misalignment between the planned crack formation line and the optical axis A1 of the laser processing unit 2 from the detected values ​​of the reflected light before and after laser processing; and correcting the optical axis A1 of the laser processing unit 2 based on the amount of misalignment. This will be described in detail below.

[0137] FIG. 15 is a schematic plan view of the front surface Wa of the wafer W as viewed from the back surface Wb side. 15 shows a wafer W having a front surface Wa (device formation surface) on which a plurality of device regions D are formed. A plurality of strip-shaped first regions S1 arranged in a grid pattern are disposed between the device regions D. In each first region S1, a crack formation line CL is set, for example, at the center in the width direction thereof, extending along the longitudinal direction of the first region S1.

[0138] In addition, the position of the planned crack formation line CL when the wafer W is placed on the stage 510 is stored in advance as position information in the control unit 500 as a relative position with respect to the laser processing device 1 before irradiation with the processing (crack formation) laser light.

[0139] Second regions S21 and S22 are provided between the first region S1 and the device region D. The second regions S21 and S22 are arranged on both sides in the longitudinal direction of the planned crack formation line CL, i.e., on both sides in the width direction of the first region S1.

[0140] The first region S1 and the second regions S21 and S22 each have the property of reflecting the detection light L1 when the detection light L1 is obliquely illuminated onto the wafer W. The reflectance of the device region D is different from the reflectance of the first region S1 and the second regions S21 and S22.

[0141] The first region S1 has different reflectances within the region. That is, the first region S1 includes a first portion S11 and a second portion S12 adjacent to the first portion S11 and having a different reflectance from the first portion S11. The first portion S11 and the second portion S12 each extend along the longitudinal direction of the first region S1. In the example of FIG. 15, the first portion S11 and the second portion S12 have the same width. Therefore, the planned crack formation line CL located at the center of the first region S1 in the width direction is located at the boundary between the first portion S11 and the second portion S12.

[0142] Moreover, each of the second regions S21 and S22 has a constant reflectance within the region.

[0143] The first region S1 and the second regions S21 and S22 have different reflectances. For example, the reflectances of the second regions S21 and S22 are relatively low compared to the reflectances of the first portion S11 and the second portion S12 of the first region S1.

[0144] Furthermore, the device region D also has the property of reflecting the detection light L1a when the detection light L1a is obliquely illuminated onto the wafer W. The reflectance of the device region D is different from the reflectance of the first region S1 and the second regions S21 and S22.

[0145] As will be described later, the optical axis correction method of this embodiment utilizes the property that the reflectances of the regions D, S1, S21, and S22 are different.

[0146] 15, the wafer W is placed on the stage 510 of the laser processing apparatus 1. At this stage, the wafer W is in a state before the relative position with respect to the laser processing apparatus 1 is displaced. The state before the relative position is displaced means that there is no deformation of the wafer W induced by irradiation of the processing laser light onto the wafer W, and the position of the planned crack formation line CL set on the wafer W matches the position information of the planned crack formation line held in the control unit 500 of the laser processing apparatus 1.

[0147] 16 is in a state where the relative position of the wafer W with respect to the laser processing apparatus 1 has been displaced. The state where the relative position has been displaced means that, as a result of deformation of the wafer W induced by irradiation of the processing laser light onto the wafer W, the position of the planned crack formation line CL set on the wafer W does not match the position information of the planned crack formation line held in the control unit 500 of the laser processing apparatus 1.

[0148] When performing crack measurement on a wafer W, the optical axis A2 of the focusing lens 504 of the crack measurement unit 10 is moved to the optical axis position set in the control unit 500 based on the position information of the planned crack formation line CL.However, in Figure 16, the set optical axis position is not directly above the planned crack formation line CL on the wafer W, but is located away from the planned crack formation line CL in the Y direction.

[0149] That is, the amount of relative positional deviation between the position of the planned crack formation line CL on the wafer W and the optical axis position of the optical axis A2 of the condenser lens 504 of the crack measurement unit 10 is d. In other words, the amount of relative positional deviation between the position of the planned crack formation line CL and the optical axis position of the optical axis A1 of the condenser lens of the laser processing unit 2 is d. If this d exceeds a threshold value, it is necessary to correct the position of the optical axis A1 of the condenser lens of the laser processing unit 2. Therefore, the amount of relative positional deviation d is measured as follows.

[0150] In this embodiment, the first and second stages are performed in advance on the wafer W before displacement as shown in Fig. 15, and then the third and fourth stages are performed on the wafer W after its relative position with respect to the laser processing device has been displaced by irradiation with the processing laser light as shown in Fig. 16. Each stage will be described below.

[0151] (First Stage) Fig. 17 is a schematic cross-sectional view taken along the line CC' in Fig. 14. As described above, in Fig. 15, the wafer W is in a state where the relative position of the crack formation line CL with respect to the laser processing device 1 is before displacement. In the first stage, the optical axis A2 of the condenser lens 504 of the crack measurement unit 10 is moved to the optical axis position set by the control unit 500 based on the position information of the planned crack formation line CL relative to the wafer W before the relative position of the planned crack formation line CL is displaced. The optical axis position of the optical axis A2 of the condenser lens 504 is positioned directly above the position of the planned crack formation line CL on the wafer W.

[0152] (Phase 2) In the second stage, the focusing lens 504 of the crack measurement unit 10 is moved vertically (Z direction) with respect to the wafer W before the relative position of the planned crack formation line CL is displaced, and the wafer W is obliquely illuminated with the first detection light L1a that is eccentric from the optical axis A2 of the focusing lens 504, and the reflected light L2a of the first detection light L1a reflected at the boundary of the second region S21 on the surface Wa (device formation surface) is detected to obtain position information of the boundary of the second region S21.

[0153] Specifically, the first detection light L1a passes through one region (first region G1 in FIG. 9) of the condenser lens 504, is incident on the wafer W, is condensed on the optical axis A2 of the condenser lens 504, and is further reflected by the surface Wa of the wafer to become reflected light L2a. The angle of incidence of the first detection light L1a on the wafer W is set to α° with respect to the thickness direction (Z direction) of the wafer W.

[0154] When the condenser lens is moved toward the wafer W, an intersection Pa0 between the optical path of the first detection light L1a and the optical axis A2 of the condenser lens 504 moves in the direction of arrow z1 toward the surface Wa of the wafer W. The reflection position of the first detection light L1a on the surface Wa of the wafer moves in the direction of arrow y1. At this time, the reflection position of the first detection light L1a on the surface Wa passes through the boundary between the second portion S12 of the first region S1 of the wafer W and the second region S21. Because the second portion S12 and the second region S2 of the first region S1 have different reflectivities, the reflected light L2a of the first detection light L1a changes in light intensity during this passage. The position of the intersection Pa0 at the point in time when this light intensity changes is detected. Specifically, the height of the intersection Pa0 relative to the surface Wa of the wafer W is detected as a measurement value Ha0. Since the position of the intersection point Pa0 corresponds to the position of the condenser lens 504, the measurement value Ha0 can be obtained based on the output of the focal position mechanism 502 that controls the condenser lens 504. The measurement value Ha0 is output to the control unit 500 as position information of the boundary of the second region S21.

[0155] (Third Stage) Next, the third stage is performed on the wafer W after the relative position of the planned crack formation line CL with respect to the laser processing device 1 has been displaced, as shown in Fig. 16. Fig. 18 shows a schematic cross-sectional view taken along line DD' in Fig. 16.

[0156] When performing crack measurement on the wafer W, the optical axis A2 of the condenser lens 504 of the crack measurement unit 10 is moved to the optical axis position set in the control unit 500 based on the position information of the planned crack formation line, but in Figure 16, the set optical axis position is not directly above the planned crack formation line CL on the wafer W, but is located away from the planned crack formation line CL in the Y direction. The amount of relative positional deviation in this case is designated as d.

[0157] 18, the optical axis A2 of the focusing lens 504 of the crack measurement unit 10 is moved to the optical axis position set in the control unit 500 based on the position information of the planned crack formation line. The optical axis position of the optical axis A2 of the focusing lens 504 is spaced apart from the position of the planned crack formation line CL on the wafer W by a relative positional deviation amount d in the Y direction.

[0158] (Fourth Stage) In the fourth stage, as in the second stage, after the relative position of the planned crack formation line CL of the wafer W has been displaced, the focusing lens 504 of the crack measurement unit 10 is moved closer to the wafer W in the vertical direction (Z direction), and the wafer W is obliquely illuminated with the first detection light L1a that is eccentric from the optical axis A2 of the focusing lens 504, and the reflected light L2a of the first detection light L1a reflected at the boundary of the second region S21 on the surface Wa is detected to obtain positional information of the boundary of the second region S21.

[0159] In this fourth stage, the condenser lens 504 is moved toward the wafer W. An intersection Pa between the optical path of the first detection light L1a and the optical axis A2 of the condenser lens 504 moves in the direction of arrow z1 toward the surface Wa of the wafer W. The reflection position of the first detection light L1a on the surface Wa of the wafer moves in the direction of arrow y1. At this time, the reflection position of the first detection light L1a passes through the boundary between the second portion S12 of the first region S1 of the wafer W and the second region S21. Because the second portion S2 of the first region S1 and the second region S2 have different reflectivities, the amount of reflected light L2a of the first detection light L1a changes during this boundary. The position of the intersection Pa at the point when this amount of light changes is detected. Specifically, the height of the intersection Pa relative to the surface Wa of the wafer W is detected as a measurement value Ha. Because the position of the intersection Pa corresponds to the position of the condenser lens 504, the measurement value Ha can be obtained based on the output of the focus position mechanism 502 that controls the condenser lens 504. The measurement value Ha is output to the control unit 500 as position information of the boundary of the second region S21.

[0160] In this embodiment, the positions of the intersections Pa0 and Pa are detected by utilizing the change in reflectance at the boundary of the second region S21 on the second portion S12 side of the first region S1, but the present invention is not limited to this, and the change in reflectance at the boundary of the second region S21 on the device region D side may also be utilized.

[0161] However, it is necessary to use the change in reflectance at the same position when detecting the positions of intersection Pa0 and intersection Pa. That is, if the change in reflectance at the boundary of second region S21 on the second portion S12 side of first region S1 is used when detecting the position of intersection Pa0, it is also necessary to use the change in reflectance at the boundary of second region S21 on the second portion S12 side when detecting the position of intersection Pa.

[0162] Furthermore, in this embodiment, the first detection light L1a is used to detect the positions of the intersections Pa0 and Pa, but the present invention is not limited to this, and the second detection light L1b may also be used.

[0163] (Stage 5) Next, in the fifth stage, based on the measurement value Ha0 obtained in the second stage and the measurement value Ha obtained in the fourth stage, the relative positional deviation d between the position of the planned crack formation line CL on the wafer W after displacement and the optical axis position of the focusing lens 504 of the crack measurement unit 10 is obtained using the following equation (2).

[0164] d = (Ha - Hb) tan α …(2)

[0165] In the above equation (2), d is the amount of relative positional deviation, Ha0 is the measured value of the positional information of the boundary of one of the second regions S21 by the reflected light L2a of the first detection light L1a relative to the wafer W before the relative position of the planned crack formation line CL is displaced, Ha is the measured value of the positional information of the boundary of one of the second regions S21 by the reflected light L2a of the detection light L1a relative to the wafer W after the relative position of the planned crack formation line CL is displaced, and α is the incident angle (°) of the first detection light L1a relative to the vertical thickness of the wafer W.

[0166] (Stage 6) If the relative positional deviation amount d obtained in the fifth stage exceeds the threshold value, the position of the optical axis A1 of the laser processing unit 2 is corrected. Specifically, the position information of the planned crack formation line CL held in the control unit 500 is corrected based on the relative positional deviation amount d.

[0167] FIG. 19 shows the relationship between the amount of movement of the condenser lens 504 and the intensity (sensor value) of the reflected light L2a.

[0168] As shown in FIG. 19, the change in intensity of the reflected light L2a according to the amount of movement of the condenser lens 504 before and after the displacement exhibits similar behavior.

[0169] 19 is the interface detection peak of the wafer W detected by the interface detection optical system of the crack measurement unit 10, and is a peak corresponding to the surface Wa of the wafer W. In the second and fourth stages, the heights Ha0 and Ha are obtained from the position of this peak.

[0170] As shown in FIG. 19 , the shape of the curve showing the change in light intensity is more complex than that of the first embodiment. In FIG. 14 of the first embodiment, the shape of the curve showing the change in light intensity is convex downward and is substantially symmetrical with respect to the direction of the vertical axis of FIG. 14 . However, in FIG. 19 , the shape of the curve showing the change in light intensity is asymmetric with respect to the direction of the vertical axis of FIG. 19 . Therefore, in this embodiment, it is difficult to calculate the relative positional deviation amount d using the first detected light and the second detected light and the boundary of the second region as a guide, as in the first embodiment. Therefore, when the change in the light intensity of the reflected light forms an asymmetric pattern, as in this embodiment, the relative positional deviation amount d is calculated by comparing information on the device formation surface of the wafer W before and after the displacement, i.e., before and after laser processing.

[0171] As described above, according to this embodiment, if the planned crack formation line CL is displaced before or after laser processing of the wafer W, the amount of deviation of the optical axis A2 of the crack measurement unit 10 from the planned crack formation line can be detected, and the optical axis A1 of the laser processing unit 2 can be corrected.

[0172] <Third embodiment> In the present invention, it is possible to detect the relative positional deviation amount d and measure the depth of the crack. Fig. 20 is a schematic diagram illustrating an example of this. Fig. 20 shows a state in which the first detection light L1a and the second detection light L1b are eccentrically irradiated onto the wafer W after the relative position of the planned crack formation line CL with respect to the laser processing device 1 has been displaced. The wafer W in Fig. 20 is in a state after the relative position of the planned crack formation line CL with respect to the laser processing device 1 has been displaced, similar to the case of Fig. 13.

[0173] As in the first stage of the first embodiment, the optical axis A2 of the focusing lens 504 of the crack measurement unit 10 is moved to the optical axis position set in the control unit 500 based on the position information of the planned crack formation line, as shown in Fig. 20. The optical axis position of the optical axis A2 of the focusing lens 504 is spaced apart from the position of the planned crack formation line CL on the wafer W by a relative positional deviation amount d in the Y direction.

[0174] Next, as in the second step of the first embodiment, the condenser lens 504 of the crack measurement unit 10 is moved closer to the wafer W in the vertical direction (Z direction) while the wafer W is obliquely illuminated with the first detection light L1a and the second detection light L1b that are decentered from the optical axis A2 of the condenser lens 504, and the positional information of the boundary of the second region is acquired by detecting the reflected light of the detection light L1a and L1b that is reflected at the boundary of the second region on the surface Wa (device formation surface). In addition, the depth of the crack K is measured by detecting the non-reflected light of the detection light L1a and L1b that is irradiated to the upper end KT and the lower end KD of the crack K.

[0175] Specifically, the first detection light L1a passes through one region (first region G1 in FIG. 9) of the condenser lens 504, is incident on the wafer W, is condensed on the optical axis A2 of the condenser lens 504, and is further reflected by the surface Wa of the wafer to become reflected light L2a. The angle of incidence of the first detection light L1a on the wafer W is set to α° with respect to the thickness direction (Z direction) of the wafer W.

[0176] The second detection light L1b passes through one region (second region G2 in FIG. 9) of the condenser lens 504, is incident on the wafer W, is condensed on the optical axis A2 of the condenser lens 504, and is further reflected by the surface Wa of the wafer to become reflected light L2b. The incident angle of the second detection light L1b on the wafer W is β° with respect to the thickness direction (Z direction) of the wafer W.

[0177] When the condenser lens is moved toward the wafer W, the intersection Pa of the optical path of the first detection light L1a and the optical axis A2 of the condenser lens 504 moves in the direction of arrow z1 toward the surface Wa of the wafer W. In addition, the reflection position of the first detection light L1a on the surface Wa of the wafer moves in the direction of arrow y1.

[0178] Here, the changes in the optical path of the first detection light L1a when the intersection Pa moves sequentially in the z1 direction are indicated by the symbols L1a-1, L1a-2, and L1a-3.

[0179] 20, when the first detection light L1a-1 passes through the boundary of the second region S21 on the device region D side, the light intensity of the reflected light L2a-1 changes due to the difference in reflectivity between the regions S1 and S21. The position of the intersection Pa at the time when this light intensity changes is detected. Specifically, the height of the intersection Pa relative to the surface Wa of the wafer W when passing through the boundary is detected as a measurement value Ha. The measurement value Ha is output to the control unit 500 as position information of the boundary of the second region S21.

[0180] Furthermore, the first detection lights L1a-2 and L1a-3 passing through the upper end KT and lower end KD of the crack K, respectively, are reflected by the surface Wa of the wafer W to become reflected lights L2a-2 and L2a-3, but the amount of light changes as they pass through the upper end KT and lower end KD. The position of the intersection point Pa at the time when this amount of light changes is detected. Specifically, the heights of the intersection point Pa at the time when the upper end KT and lower end KD pass relative to the surface Wa of the wafer W are detected as measurement values ​​HTa and HDa. The measurement values ​​HTa and HDa are output to the control unit 500 as depth position information of the crack K.

[0181] Similarly, when the condenser lens 504 is moved toward the wafer W, an intersection Pb between the optical path of the second detection light L1b and the optical axis A2 of the condenser lens 504 moves sequentially in the z1 direction. The optical paths of the second detection light L1b in this case are indicated by the symbols L1b-1, L1b-2, and L1b-3.

[0182] 20, the position of the intersection Pb when the second detection light L1b-1 passes through the boundary of the second region S22 on the device region D side is detected as a measurement value Hb. The measurement value Hb is output to the control unit 500 as position information of the boundary of the second region S22.

[0183] Furthermore, the positions of the intersection Pb when the second detection lights L1b-2 and L1b-3 pass through the upper end KT and lower end KD of the crack K are detected as measurement values ​​HTb and HDb. The measurement values ​​HTa and HDa are output to the control unit 500 as crack depth position information.

[0184] The relative positional deviation amount d is calculated by the formula (1) in the same manner as in the first embodiment.

[0185] d=(Ha-Hb) / (1 / tanα+1 / tanβ) …(1)

[0186] The position of the upper end KT of the crack K is determined as the average value of the measured values ​​HTa and HTb, and the position of the lower end KD of the crack K is determined as the average value of the measured values ​​HDa and HDb.

[0187] FIG. 21 shows the relationship between the amount of movement of the condenser lens 504 and the intensity of the reflected light L2a and L2b.

[0188] 21, the changes in the intensities of the reflected light L2a and L2b before and after the displacement behave in a similar manner depending on the amount of movement of the condenser lens 504. In the case of this embodiment, if the length of the crack K in the z direction increases, the range over which the optical paths of the detection light L1a and L1b are blocked increases, which may hinder the measurement of the relative positional deviation amount d. Therefore, when applying this embodiment, it is preferable that the length of the crack K in the z axis direction is as short as possible.

[0189] As described above, according to this embodiment, if the planned crack formation line CL is displaced before or after laser processing of the wafer W, the amount of deviation of the optical axis A2 of the crack measurement unit 10 from the planned crack formation line can be detected, and the optical axis A1 of the laser processing unit 2 can be corrected. Furthermore, according to this embodiment, the depth of the crack K can be measured simultaneously with the correction of the optical axis A1 of the laser processing unit 2.

[0190] The present invention may further include the following configurations.

[0191] In each embodiment of the present invention, the condenser lens 504 is moved in the Z direction while the detection light L1 is eccentrically irradiated, thereby moving the reflection position of the detection light L1 on the surface Wa of the wafer W in the Y direction and detecting changes in the reflectance on the surface Wa of the wafer W. Here, the larger the incidence angles α and β of the detection light L1, the wider the movement range of the reflection position on the surface Wa in the Y direction, making it easier to detect boundaries between areas with different reflectances and arbitrary change points in reflectance.

[0192] Therefore, in order to increase the incident angles α and β of the first detection light L1a and the second detection light L1b, a light-shielding mask may be disposed between the light sources 102B and 102C and the mirror 104, instead of the laser apertures. FIG. 22 shows an example of a light-shielding mask 414. The light-shielding mask 414 is provided with multiple laser apertures H1 to H4 that allow the incident angles α and β to be varied. The light-shielding mask 414 also has a bearing C into which a rotation shaft of an actuator can be inserted. The attitude of the light-shielding mask 414 relative to the light sources 102B and 102C is changed by an actuator or the like, thereby selecting one of the multiple laser apertures H1 to H4 provided in the light-shielding mask 414 to emit the first detection light L1a and the second detection light L1b. By using H3 and H4 among the laser apertures H1 to H4, the incident angles α and β can be increased compared to when H1 and H2 are used.

[0193] With the above configuration, the angles of incidence α and β of the first detection light L1a and the second detection light L1b can be varied, and the range of movement of the reflection position on the surface Wa in the Y direction can be increased.

[0194] The present invention may further include the following configurations.

[0195] In the present invention, it has been described that the correction method of either the first embodiment or the second embodiment is applied depending on the difference in reflection characteristics between the first region S1 and the second regions S21, S22 on the device formation surface (front surface Wa) of the wafer W, that is, depending on whether the wafer W is the one shown in Figures 10 and 12 or the one shown in Figures 15 and 16. Here, in the second embodiment, measurement is required before the position of the planned crack formation line CL is displaced, but in the first embodiment, measurement is not required before the position of the planned crack formation line CL is displaced.

[0196] Therefore, in the present invention, the periphery of the planned crack formation line CL on the device formation surface (front surface Wa) of the wafer W is observed in advance with an optical microscope or the like to determine whether the wafer W is the wafer W shown in Figures 10 and 12 or the wafer W shown in Figures 15 and 16, and then it is determined whether to apply the correction method of either the first embodiment or the second embodiment. In other words, based on the results of observation of the periphery of the planned crack formation line CL on the device formation surface (front surface Wa) of the wafer W with an optical microscope or the like, it may be determined whether to perform measurement at a time point before the position of the planned crack formation line CL is displaced. [Explanation of symbols]

[0197] 1...laser processing device, 2...laser processing unit, 10...crack measurement unit, 504...condensing lens, A1...optical axis of laser processing unit, A2...optical axis of condensing lens, K...crack, KT...upper end position of crack in depth direction, L1a...first detection light, L1b...second detection light, W...wafer (workpiece), X...direction perpendicular to Y direction and Z direction, Y...direction perpendicular to Z direction, Z...vertical direction.

Claims

1. A method for correcting a misalignment between a planned crack formation line of a workpiece and an optical axis of a laser processing portion, comprising: a step of eccentrically irradiating a first detection light and a second detection light, which are mutually eccentric from the optical axis of a focusing lens of a crack measurement unit, onto the workpiece, which has a first region in which the planned crack formation line is set and second regions on both sides of the planned crack formation line and which have a reflectance different from the reflectance of the first region, while moving the focusing point in the thickness direction of the workpiece, and detecting each reflected light reflected from the workpiece; acquiring position information of the boundary between the first region and the second region from the detected value; A step of obtaining a deviation amount between the planned crack formation line and the optical axis of the laser processing portion from the position information; a step of correcting the optical axis of the laser processing portion based on the amount of deviation; A method for correcting the optical axis of a laser processing device, comprising:

2. acquiring position information of the boundary from a change in the detected value of the reflected light; 2. The method for correcting the optical axis of a laser processing device according to claim 1.

3. A method for correcting a misalignment between a planned crack formation line of a workpiece and an optical axis of a laser processing portion, comprising: Before laser processing, a step of eccentrically irradiating detection light eccentric from the optical axis of the condenser lens of the crack measurement unit while moving the condenser point in the thickness direction of the workpiece, and detecting reflected light reflected from the workpiece; After the laser processing, a step of eccentrically irradiating detection light eccentric from the optical axis of the condenser lens of the crack measurement unit while moving the condenser point in the thickness direction of the workpiece, and detecting the reflected light reflected from the workpiece; A step of acquiring a deviation amount between the planned crack formation line and the optical axis of the laser processing portion from the detection values ​​of reflected light before and after laser processing; a step of correcting the optical axis of the laser processing portion based on the amount of deviation; A method for correcting the optical axis of a laser processing device, comprising:

4. measuring the depth of the crack from the detected value; 4. A method for correcting an optical axis of a laser processing device according to claim 1.

5. A laser processing apparatus that performs the method for correcting the optical axis of a laser processing apparatus according to any one of claims 1 to 3.

6. A laser processing apparatus that performs the method for correcting the optical axis of a laser processing apparatus according to claim 4.