Correction method for optical axis of laser processing device

Abstract

To provide a correction method for optical axis of laser processing device that can detect deviation of relative positions between an optical axis of a laser processing part and an optical axis a crack measurement part.SOLUTION: A correction method for optical axis of laser processing device comprises the steps of: arranging a condenser lens of a crack measurement part so that an optical axis of the condenser lens of the crack measurement part passes a position separated from a crack measurement position by a first prescribed distance, eccentrically irradiating a work-piece with detection light decentered from the optical axis of the condenser lens of the crack measurement part, and detecting reflectance from the work-piece; arranging the condenser lens of the crack measurement part so that the optical axis of the condenser lens of the crack measurement part passes a position separated by a second prescribed distance in a direction opposite to the position separated by the first prescribed distance from the crack measurement position, eccentrically irradiating the work-piece with detection light decentered from the optical axis of the condenser lens of the crack measurement part, and detecting reflectance from the work-piece; and calculating deviation of optical axes between the laser processing part and the crack measurement part from the detected detection value.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Conventionally, there has been known a laser processing device (also called a laser dicing device) that focuses a laser beam on the interior of a workpiece such as a semiconductor wafer, irradiates the workpiece along a planned dividing line, and forms cracks that serve as starting points for cutting within the workpiece along the planned dividing line. The workpiece with the cracks formed therein is then divided into individual chips along the planned dividing line by a dividing process such as expanding or breaking (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 laser light toward one side of the wafer, and a crack measurement unit that is fixed to the laser processing unit and measures the depth of the cracks formed in the wafer (see Patent Document 2).

[0004] In the laser processing device described in Patent Document 2, the optical axis of the laser processing unit and the optical axis of the crack measurement unit may become misaligned. For example, the relative positions of the optical axis of the laser processing unit and the optical axis of the crack measurement unit may become misaligned due to changes over time in the environment, such as the room temperature, of the factory (clean room) in which the laser processing device is installed. Misalignment of the relative positions of the optical axes may make it difficult to detect cracks.

[0005] Here, in order to correct the optical axis misalignment in a laser processing device having two optical axes, a technique is known in which an infrared imaging optical system is used to photograph a modified area formed on a wafer, and the optical axis of the modified area 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 detecting the misalignment of the relative position between the optical axis of the laser processing unit and the optical axis of the crack measurement unit was not known. [Prior art documents] [Patent documents]

[0006] [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]

[0007] An object of the present invention is to provide an optical axis correction method for a laser processing device that makes it possible to detect a deviation in the relative position between the optical axis of the laser processing section and the optical axis of the crack measurement section. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention employs the following configuration. [1] A method for detecting a misalignment of the optical axis between a laser processing unit and a crack measurement unit provided in a laser processing device, a step of positioning the condenser lens of the crack measurement unit so that the optical axis of the condenser lens of the crack measurement unit passes through a position away from the crack measurement position by a first predetermined distance, eccentrically irradiating the workpiece with detection light eccentric from the optical axis of the condenser lens of the crack measurement unit, and detecting reflected light from the workpiece; a step of positioning the condenser lens of the crack measurement unit so that the optical axis of the condenser lens of the crack measurement unit passes through a position that is a second predetermined distance away in the opposite direction from the position that is the first predetermined distance away from the crack measurement position, eccentrically irradiating the workpiece with detection light that is eccentric from the optical axis of the condenser lens of the crack measurement unit, and detecting reflected light from the workpiece; An optical axis correction method for a laser processing device, which calculates the deviation of the optical axis between the laser processing section and the crack measurement section from the detected value. [2] A method for correcting the optical axis of a laser processing device according to claim 1, comprising the step of moving the focal point in the thickness direction of the workpiece and detecting the light reflected from the back surface. [3] The optical axis correction method for a laser processing device described in claim 1, wherein the first predetermined distance and the second predetermined distance are set so that when the focal point is moved by an amount equal to the thickness of the workpiece, the reflected light from the underside of the workpiece passes through the entire thickness of the workpiece at the crack measurement position. [4] The optical axis correction method for a laser processing device described in claim 1, wherein the first predetermined distance and the second predetermined distance are set so that when the focal point is moved by an amount equal to the thickness of the workpiece, the reflected light reflected once on the underside of the workpiece passes through the entire thickness of the workpiece at the crack measurement position. [5] The optical axis correction method for a laser processing device according to claim 1, wherein the calculated optical axis deviation is used to correct the deviation of the optical axis between the laser processing section and the crack measurement section.

[0009] The present invention may also have the following configuration. [A] In a laser processing device equipped with a laser processing unit that forms a crack in a workpiece and a crack measurement unit that measures the depth of the crack, a method for detecting a relative positional deviation between the optical axis of a laser beam from the laser processing unit and the optical axis of a condenser lens of the crack measurement unit, a first positioning step of moving the position of the optical axis of the condenser lens in a direction perpendicular to the longitudinal direction of the row of cracks and the vertical direction to a position away from the measurement position of the cracks by ΔY1 defined by the following formula (1), when placing the condenser lens vertically above the workpiece on which a row of cracks has been formed by a laser processing unit; a first measurement step of obliquely illuminating the workpiece with first detection light decentered from the optical axis of the condenser lens while moving the condenser lens in the vertical direction relative to the workpiece, detecting reflected light from the workpiece, and obtaining a measurement value Ha indicating an upper end position or a lower end position in a depth direction of a crack formed inside the workpiece based on a detection signal corresponding to the reflected light; a second positioning step of moving the position of the optical axis of the focusing lens in a direction perpendicular to the longitudinal direction and the vertical direction of the row of cracks, opposite to the direction of ΔY1, to a position away from the measurement position of the cracks by ΔY2 defined by the following formula (2); a second measurement step of obliquely illuminating the workpiece with second detection light that is eccentric from the optical axis of the condenser lens and that comes from a different direction from the first detection light while moving the condenser lens in a vertical direction relative to the workpiece, detecting reflected light from the workpiece, and obtaining a measurement value Hb that indicates an upper end position or a lower end position in a depth direction of a crack formed inside the workpiece based on a detection signal corresponding to the reflected light; A calculation step of calculating a distance d between a position of a crack formed inside the workpiece and a position of the optical axis of the condenser lens based on the following formula (3); An optical axis correction method for a laser processing device comprising: ΔY1=mwtanα …(1) ΔY2=mwtanβ …(2) d=(Ha-Hb) / (1 / tanα+1 / tanβ) …(3) In the above equations (1) to (3), ΔY1 and ΔY2 are the movement amounts of the focusing lens from the measurement position of the crack, m is an integer greater than or equal to 1, w is the thickness of the workpiece, α is the angle of incidence (°) of the first detection light with respect to the vertical thickness of the workpiece, and β is the angle of incidence (°) of the second detection light with respect to the vertical thickness of the workpiece. [B] An optical axis correction method for a laser processing device described in [A], which includes an adjustment step of adjusting the position of the optical axis of the focusing lens of the crack measurement unit relative to the optical axis position of the laser light of the laser processing unit based on the distance d calculated in the calculation step. [C] The optical axis correction method for a laser processing device described in [A], wherein in the first measurement process and the second measurement process, the detection light and the second detection light are reflected at least once or more on the bottom surface of the workpiece between the time when the first detection light and the second detection light are incident on the workpiece and the time when they are irradiated onto the crack. [D] a laser processing portion that forms a crack in the workpiece; a crack measurement unit for measuring the depth of the crack; a control unit, the control unit has a first placement function unit, a first measurement function unit, a second placement function unit, a second measurement function unit, and a calculation function unit; The first arrangement function unit has an optical axis function of moving the position of the optical axis of the condenser lens in a direction perpendicular to the longitudinal direction of the row of cracks and the vertical direction to a position away from the measurement position of the cracks by ΔY1 defined in the following formula (1), when the condenser lens is arranged vertically above the workpiece on which cracks are formed in a row by the laser processing unit, the first measurement function unit has a function of, after the operation of the first positioning function, obliquely illuminating the workpiece with first detection light decentered from the optical axis of the condenser lens while moving the condenser lens in a vertical direction relative to the workpiece, detecting reflected light from the workpiece, and obtaining a measurement value Ha indicating an upper end position or a lower end position in a depth direction of a crack formed inside the workpiece based on a detection signal corresponding to the reflected light, the second positioning function unit has a function of moving the position of the optical axis of the condenser lens in a direction perpendicular to the longitudinal direction and the vertical direction of the row of cracks and opposite to the direction of ΔY1, to a position away from the measurement position of the cracks by ΔY2 defined by the following formula (2), the second measurement function unit has a function of obliquely illuminating the workpiece with second detection light that is eccentric from the optical axis of the condenser lens and comes from a direction different from the first detection light while moving the condenser lens in a vertical direction relative to the workpiece, detecting reflected light from the workpiece, and obtaining a measurement value Hb that indicates an upper end position or a lower end position in a depth direction of a crack formed inside the workpiece based on a detection signal corresponding to the reflected light, The calculation function unit has a function of calculating a distance d between the position of a crack formed inside the workpiece and the position of the optical axis of the focusing lens based on the following equation (6). ΔY1=mwtanα …(4) ΔY2=mwtanβ …(5) d=(Ha-Hb) / (1 / tanα+1 / tanβ) …(6) In the above equations (4) to (6), ΔY1 and ΔY2 are the movement amounts of the focusing lens from the measurement position of the crack, m is an integer greater than or equal to 1, w is the thickness of the workpiece, α is the angle of incidence (°) of the first detection light with respect to the vertical thickness of the workpiece, and β is the angle of incidence (°) of the second detection light with respect to the vertical thickness of the workpiece. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an optical axis correction method for a laser processing device that makes it possible to detect a deviation in the relative position between the optical axis of a laser processing portion and the optical axis of a crack measurement device. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing a laser processing apparatus according to an embodiment of the present invention; [Figure 2] 1 is a schematic diagram showing a crack measurement unit provided in a laser processing apparatus according to an embodiment of the present invention; [Figure 3] 5A to 5C are schematic diagrams illustrating a method for detecting the depth position of a crack in an embodiment of the present invention. [Figure 4] 5A to 5C are schematic diagrams illustrating a method for detecting the depth position of a crack in an embodiment of the present invention. [Figure 5] 5A to 5C are schematic diagrams illustrating a method for detecting the depth position of a crack in an 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 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 embodiment of the present invention. FIG. [Figure 8] 5A and 5B are schematic diagrams showing how reflected light is received by a photodetector in the embodiment of the present invention; [Figure 9] FIG. 3 is a schematic diagram illustrating the path of light reflected from a workpiece and reaching a condenser lens pupil in an embodiment of the present invention. [Figure 10] 1A and 1B are schematic diagrams illustrating a method for correcting an optical axis of a laser processing apparatus according to an embodiment of the present invention. [Figure 11] 3A to 3C are schematic diagrams illustrating a first arrangement step of the optical axis correcting method for the laser processing machine according to the embodiment of the present invention. [Figure 12] 3A and 3B are schematic diagrams illustrating a first measurement step of the optical axis correction method for the laser processing machine according to the embodiment of the present invention. [Figure 13] 5A to 5C are schematic diagrams illustrating a second arrangement step of the optical axis correcting method for the laser processing machine according to the embodiment of the present invention. [Figure 14] 5A and 5B are schematic diagrams illustrating a second measurement step of the optical axis correcting method for the laser processing machine according to the embodiment of the present invention. [Figure 15] FIG. 2 is a schematic diagram showing an example of a light-shielding mask provided in a crack measurement unit of the laser processing apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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.

[0013] [Laser processing equipment 1] As shown in FIG. 1, the laser processing apparatus 1 of this embodiment includes a laser processing unit 2, a crack measurement unit 10, and a control unit 500.

[0014] [Laser Processing Section 2] The laser processing unit 2 is provided to irradiate a processing laser beam L toward 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 laser beam condensed by the condenser lens is then irradiated toward the back surface of the wafer W. The optical axis A1 of the condenser lens corresponds to the optical axis of the laser processing unit 2 in this embodiment.

[0015] [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. The control unit 500 accepts operation input from an operator via an operation unit 506, and transmits control signals corresponding to the operation input to each part of the crack measurement unit 10 to control the operation of each part.

[0016] The control unit 500 of this embodiment may also 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.

[0017] In addition, the control unit 500 of this embodiment has the function of positioning the focusing lens 504 of the crack measurement unit 10 so that the optical axis A2 of the focusing lens 504 of the crack measurement unit 10 passes through a position a first predetermined distance away from the crack measurement position, eccentrically irradiating the wafer W, which is the workpiece, with detection light eccentric from the optical axis A2 of the focusing lens 504 of the crack measurement unit 10, and detecting reflected light from the wafer W, and then positioning the focusing lens 504 of the crack measurement unit 10 so that the optical axis A2 of the focusing lens 504 of the crack measurement unit 10 passes through a position a second predetermined distance away in the opposite direction from the position a first predetermined distance away from the crack measurement position, eccentrically irradiating the wafer W with detection light eccentric from the optical axis A2 of the focusing lens 504 of the crack measurement unit 10, and detecting reflected light from the wafer W, and calculating the deviation of the optical axes of the laser processing unit 2 and the crack measurement unit 10 from the detected detection value.

[0018] That is, the control unit 500 of this embodiment has a first placement function unit, a first measurement function unit, a second placement function unit, a second measurement function unit, and a calculation 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.

[0019] (1st placement function part) When placing the focusing lens 504 of the crack measurement unit 10 vertically above the wafer W on which a row of cracks K has been formed by the laser processing unit 2, the position of the optical axis A2 of the focusing lens 504 is moved in a direction perpendicular to the longitudinal and vertical directions of the row of cracks K to a position (a position away from the measurement position of the cracks K) that is ΔY1 as defined in the following equation (1) (a position away from the first predetermined distance).

[0020] (First measurement function unit) While moving the focusing lens 504 vertically relative to the wafer W, i.e., while moving the focal point in the thickness direction of the wafer W, the wafer W is obliquely illuminated with a first detection light La that is eccentric from the optical axis A2 of the focusing lens 504, the reflected light from the wafer W is detected, and a measurement value Ha indicating the upper or lower end position in the depth direction of the crack K formed inside the wafer W is obtained based on a detection signal corresponding to the reflected light.

[0021] (Second placement function section) The position of the optical axis A2 of the focusing lens 504 is moved in a direction perpendicular to the longitudinal and vertical directions of the row of cracks K, in the direction opposite to the direction of ΔY1, to a position (a position a second predetermined distance away) from the measurement position of crack K by ΔY2 defined by the following equation (2).

[0022] (Second measurement function unit) While moving the focusing lens 504 vertically relative to the wafer W, i.e., while moving the focal point in the thickness direction of the wafer W, the wafer W is obliquely illuminated with a second detection light Lb that is eccentric from the optical axis A2 of the focusing lens 504 and comes from a direction different from that of the first detection light La, and the reflected light from the wafer W is detected, and a measurement value Hb indicating the upper or lower end position in the depth direction of the crack K formed inside the wafer W is obtained based on the detection signal corresponding to the reflected light.

[0023] (Calculation function section) The distance d between the position of the crack K formed inside the wafer W and the position of the optical axis A2 of the condenser lens 504 is calculated based on the following formula (3).

[0024] ΔY1=mwtanα …(1) ΔY2=mwtanβ …(2) d=(Ha-Hb) / (1 / tanα+1 / tanβ) …(3)

[0025] In the above equations (1) to (3), ΔY1 and ΔY2 are the movement amounts of the focusing lens 504 from the measurement position of the crack, m is an integer greater than or equal to 1, w is the thickness of the wafer W, α is the angle of incidence (°) of the first detection light with respect to the vertical thickness of the wafer W, and β is the angle of incidence (°) of the second detection light with respect to the vertical thickness of the wafer W.

[0026] The first predetermined distance (ΔY1) and the second predetermined distance (ΔY2) are set so that when the focusing point is moved by an amount equivalent to the thickness of the wafer W, the reflected light from the surface Wa of the wafer W passes through the entire thickness of the wafer W at the crack measurement position. Preferably, the first predetermined distance (ΔY1) and the second predetermined distance (ΔY2) are set so that when the focusing point is moved by an amount equivalent to the thickness of the wafer W, the reflected light that has reflected once from the surface Wa of the wafer W passes through the entire thickness of the wafer W at the crack measurement position.

[0027] [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 inside the workpiece, a wafer W, and is arranged to be movable integrally with the laser processing unit 2, as shown in Figure 1.

[0028] 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.

[0029] 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.

[0030] [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. 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] Light sources 102B and 102C each have a laser aperture capable of illuminating only a portion of condenser lens pupil 504a of condenser lens 504 that is decentered from condenser lens optical axis A2. Light sources 102B and 102C are used for crack detection, which will be described later.

[0035] The half mirror 104 reflects the detection light L1 emitted from the light source 102A for interface detection and transmits the detection light L1 emitted from the light sources 102B and 102C for crack detection. Although not shown in the figures, the detection light L1 emitted from the light sources 102A, 102B, and 102C will be referred to as L1(A), L1a, and L1b, respectively. L1a is the first detection light in this embodiment, and L1b is the second detection light in this embodiment.

[0036] 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.

[0037] [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).

[0038] 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.

[0039] 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).

[0040] [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. The optical axis A2 of the condenser lens 504 corresponds to the optical axis of the crack measurement unit 10 of this embodiment.

[0041] 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.

[0042] 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.

[0043] [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.

[0044] 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.

[0045] 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.

[0046] 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 of the wafer W, respectively.

[0047] [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.

[0048] 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).

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] (Method for detecting the interface of a wafer W using an interface detection optical system) The following describes a method for detecting the interface of the wafer W using an interface detection optical system. In this embodiment, the interface of the front surface Wa of the wafer W (the surface that contacts the stage 510 and 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 front surface Wa of the wafer W.

[0055] In this embodiment, the crack depth is detected based on the front surface Wa of the wafer W, but the present invention is not limited to this. For example, the crack depth may be detected based on the back surface Wb of the wafer W, or an average value of crack depths detected based on the interface positions of both the front surface Wa and the back surface Wb of the wafer W may be calculated.

[0056] 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. 10) 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.

[0057] 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.

[0058] [Crack detection optical system 400] The crack detection optical system 400 includes a relay lens 306, 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.

[0059] 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, as will be described later.

[0060] The photodetectors 404 and 406 are devices that receive reflected light L2a and L2b from the wafer W and detect cracks K inside the wafer W. 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.

[0061] 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.

[0062] (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.

[0063] 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 (probe 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 detection lights L1a and L1b, which are decentered with respect to the optical axis A2 of the condenser lens 504, are irradiated onto the wafer W.

[0064] The first detection light (probe light) L1a and the second detection light L1b are reflected by the wafer W, and the reflected lights L2a and L2b are reflected by the half mirror 302, and then transmitted through the half mirror 304, the relay lens 306, and the half mirror 308, and then incident on the relay lens 402. The reflected lights L2a and L2b transmitted through the relay lens 402 are received by the photodetectors 404 and 406.

[0065] The photodetectors 404 and 406 receive the reflected light L2a and L2b from the wafer W to detect cracks K inside the wafer W.

[0066] 3 to 5 are explanatory diagrams showing the state when the detection light L1 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.

[0067] 6 to 8 are diagrams showing the state of reflected light L2 received by photodetectors 404 and 406, and correspond to the cases shown in FIGS. 3 to 5, respectively.

[0068] 9 is a diagram for explaining the path of reflected light L2 from the wafer W reaching the condenser lens pupil 504a. Note that here, a case will be described in which 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 oblique illumination is performed on the wafer W.

[0069] 3, if a crack K is present at the focal point of the condenser lens 504, the detection light L1 is totally reflected by the crack K, and the reflected light L2 travels along a path on the same side of the optical path of the detection light L1 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 detection light L1. That is, as shown in Fig. 9, if the path of the detection light L1 when the detection light L1 from the light source unit 100 is irradiated onto the wafer W via the condenser lens 504 is R1, the reflected light L2 that is totally reflected by the crack K inside the wafer W travels along a path R2 on the same side of the optical axis A2 (the right side in Fig. 9) as the path R1 of the detection light L1, and passes through a first area G1 of the condenser lens pupil 504a.

[0070] 4, when no crack K is present at the focal point of the condenser lens 504, the detection light L1 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 L1. 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 detection light L1, and passes through a second region G2 of the condenser lens pupil 504a.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] (Optical axis correction method of this embodiment) Next, the optical axis correction method of this embodiment will be described with reference to FIGS.

[0079] FIG. 10 shows a schematic cross-sectional view of a wafer W. Inside the wafer, cracks K are arranged in a row in the X direction. The cracks K are formed by irradiation of laser light from the laser processing unit 2. Therefore, the position of the optical axis of the laser processing unit 2 in the Y direction coincides with the position of the cracks K formed in the wafer W in the Y direction.

[0080] 10 also shows a state in which the condenser lens 504 is positioned at the measurement position for the crack K. The condenser lens 504 in the example shown in FIG. 10 is positioned at the same position in the Y direction as the optical axis A1 of the laser processing unit 2, based on the position information of the optical axis A1 of the laser processing unit 2 stored in the control unit 500 of the laser processing apparatus 1. However, the Y direction position of the optical axis A2 of the actually positioned condenser lens 504 may deviate from the Y direction position of the optical axis A1 of the laser processing unit 2. In other words, the Y direction position of the optical axis A2 is not located at the measurement position directly above the crack K, but is shifted by d in the Y direction from the crack K.

[0081] The reason why the position of the optical axis A2 of the condenser lens 504 in the Y direction is shifted from the measurement position of the crack K in this way is because the dimensions of each part of the laser processing apparatus 1 have changed due to the influence of the installation environment of the laser processing apparatus 1, and the position information of the optical axis A1 of the laser processing unit 2 stored in the control unit 500 no longer corresponds to the actual positional relationship. In such a case, it is necessary to measure the amount of optical axis shift d of the optical axis A2 of the condenser lens 504 in the Y direction and correct the relative position information of the optical axis A1 of the laser processing unit 2 and the optical axis A2 of the crack measurement unit 10 stored in the control unit 500.

[0082] Therefore, the optical axis correction method of this embodiment includes the steps of: positioning the condenser lens 504 of the crack measurement unit 10 so that the optical axis A2 of the condenser lens 504 passes through a position a first predetermined distance away from the crack measurement position; eccentrically irradiating the wafer W with detection light eccentric from the optical axis A2 of the condenser lens 504 of the crack measurement unit 10; and detecting reflected light from the wafer W. The method also includes the steps of: positioning the condenser lens of the crack measurement unit 10 so that the optical axis A2 of the condenser lens 504 of the crack measurement unit 10 passes through a position a second predetermined distance away in the opposite direction from the position a first predetermined distance away from the crack measurement position; eccentrically irradiating the wafer W with detection light eccentric from the optical axis A2 of the condenser lens 504 of the crack measurement unit 10; and detecting reflected light from the wafer W. The method also includes the steps of: moving the focal point in the thickness direction of the wafer W;

[0083] That is, in the optical axis correction method of this embodiment, the following first placement process, first measurement process, second placement process, second measurement process and calculation process are carried out in sequence to measure the relative optical axis deviation d between the optical axis A1 of the laser processing unit 2 and the optical axis A2 of the crack measurement unit 10, and based on this deviation d, the relative position information between the optical axis A1 of the laser processing unit 2 and the optical axis A2 of the crack measurement unit 10 is corrected.

[0084] In this embodiment, the optical axis A2 of the condenser lens 504 is positioned away from the measurement position of the crack K (a position away by ΔY1 and ΔY2), thereby increasing the optical path length of the first detection light L1a and the second detection light L1b and enlarging the spot diameter of the first detection light L1a and the second detection light L1b on the crack K. By enlarging the spot diameter, the measurement range of the crack K by the first detection light L1a and the second detection light L1b can be widened. As a result, even if the formation position of the crack K shifts in a meandering manner along the longitudinal direction of the row of cracks K, the crack K can be captured by the first detection light L1a and the second detection light L1b. As a result, the relative position information between the optical axis A1 of the laser processing unit 2 and the optical axis A2 of the crack measurement unit 10 is corrected based on the irradiation results of the first detection light L1a and the second detection light L1b.

[0085] Each step will be described below.

[0086] [First placement process] As shown in FIG. 11 , in the first placement step, the condenser lens 504 is placed vertically (in the Z direction) above the wafer W on which a row of cracks K has been formed by the laser processing unit 2. In the first placement step, when placing the condenser lens 504, the position of the optical axis A2 of the condenser lens 504 is moved in the direction (Y direction) perpendicular to the longitudinal direction (X direction) and the vertical direction (Z direction) of the row of cracks K to a position away from the measurement position of the cracks K by ΔY1 defined by the following equation (1). The measurement position of the cracks K here is the position of the optical axis A2 determined based on the position information of the optical axis A1 of the laser processing unit 2 stored in the control unit 500, which is the position of the optical axis A2 shown in FIG. 10 . This position is shifted in the Y direction from the position of the cracks K by a shift amount d.

[0087] ΔY1=mwtanα …(1)

[0088] In the above equation (1), ΔY1 is the amount of movement of the optical axis A2 of the focusing lens 504 from the measurement position of the crack K, m is an integer greater than or equal to 1, w is the vertical thickness of the wafer W, and α is the incident angle (°) of the first detection light with respect to the vertical thickness of the wafer W.

[0089] By moving the optical axis A2 of the focusing lens 504 to a position away from the wafer W by ΔY1 as defined in equation (1), when the focusing lens 504 is moved vertically in the next first measurement step, it becomes possible to irradiate the first detection light La over the entire vertical thickness direction of the wafer W, thereby making it possible to measure the position of the crack K over the entire vertical thickness direction of the wafer W.

[0090] Since m can be an integer greater than or equal to 1, ΔY1 is not limited to a single point, but can be multiple if multiple reflection regions are included. The larger ΔY1 becomes, the larger the spot diameter of the first detection light L1a at the crack K. Therefore, it is desirable to make m in equation (1) as large as possible. However, since the condenser lens 504 moves in the Y direction by w tan α each time m increases by 1, increasing m will eventually result in the reflected light no longer returning within the effective diameter (pupil diameter) of the condenser lens 504, making it impossible to obtain measurement data. Therefore, it is advisable to determine the maximum value of m taking into account the effective diameter of the condenser lens 504.

[0091] Furthermore, by moving the optical axis A2 of the condenser lens 504 to a position away by ΔY1 defined in equation (1), the first detection light La is reflected at least once by the surface Wa of the wafer W before being irradiated onto the crack K. Since various devices are formed on the surface Wa of the wafer W, the reflecting surface of the first detection light La is an uneven surface. Therefore, the spot diameter of the first detection light La reflected by the surface Wa at the crack K becomes larger.

[0092] The spot diameter ψD of the first detection light La in the crack K can be expressed by the following formula (A): For example, when the thickness w of the wafer W is 500 μm, α=5°, and m=1, the spot diameter ψD of the first detection light La in the crack K is 88 μm.

[0093] ψD=2mwtanα / cosα …(A)

[0094] [First measurement process] Next, as shown in Figure 12, in the first measurement step, the focusing lens 504 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 that is eccentric from the optical axis A2 of the focusing lens 504, and the reflected light from the wafer W is detected by the photodetectors 404c, 406c.A measurement value Ha indicating the upper end position in the depth direction of the crack K formed inside the wafer W is obtained from the amount of movement of the focusing lens 504 at that time.

[0095] Here, the amount of deviation of the optical axis A2 of the condenser lens 504 in the Y direction relative to the crack K is denoted by d, the amount of movement of the optical axis A2 is denoted by ΔY1, and the angle of incidence of the first detection light L1a incident from the right side in the drawing (hereinafter referred to as side a) is denoted by α. Side a corresponds to the first region G1 in Fig. 9. Furthermore, the measured value of the position of the crack upper end position KT by the first detection light L1a (the distance between the intersection Pa of the optical path of the first detection light La and the optical axis A2 of the condenser lens 504 and the surface Wa of the wafer W) is denoted by Ha.

[0096] When the condenser lens 504 is moved in the vertical direction (Z direction), the intersection Pa of the optical path of the first detection light L1a and the optical axis A2 of the condenser lens 504 is moved from the front surface Wa to the back surface Wb of the wafer W. During this time, the reflected light from the wafer W is detected by the photodetectors 404c and 406c. The point in time when the reflected light incident on the photodetectors 404c and 406c reaches the pattern shown in FIG. 8 is then detected. The amount of movement of the condenser lens 504 from the start of movement at this point in time is then obtained. Ha is calculated based on this obtained amount of movement.

[0097] In the first measurement step, since the condenser lens 504 is moved by a large distance of ΔY1, it is difficult to irradiate the crack with the second detection light L1b simultaneously with the first detection light L1a. Therefore, in this embodiment, after the first measurement step, a second placement step and a second measurement step are performed, thereby performing measurement using the second detection light L1b.

[0098] [Second placement process] As shown in Figure 13, in the second placement process, when the focusing lens 504 is placed vertically (Z direction) above the wafer W on which cracks K have been formed in a row by the laser processing unit 2, the position of the optical axis A2 of the focusing lens 504 is moved perpendicular to the longitudinal direction (X direction) and vertical direction (Z direction) of the row of cracks K, and in the direction opposite to the direction of ΔY1, to a position away from the measurement position of the cracks K by ΔY2 defined by the following equation (2).

[0099] ΔY2=mwtanβ …(2)

[0100] In the above equation (2), ΔY2 is the movement amount of the focusing lens 504 from the measurement position of the crack K, m is an integer greater than or equal to 1, w is the vertical thickness of the wafer W, and β is the incident angle (°) of the second detection light L1b with respect to the vertical thickness of the wafer W.

[0101] By moving the optical axis A2 of the focusing lens 504 to a position away from the wafer W by ΔY2 as defined in equation (2), the second detection light L1b can be irradiated over the entire thickness direction of the wafer W in the vertical direction when the focusing lens 504 is moved along the vertical direction in the second measurement step.

[0102] Since m can be an integer greater than or equal to 1, similar to ΔY1, there are multiple ΔY2s if multiple reflection regions are included. As ΔY2 increases, the spot diameter of the second detection light L1b in the crack K increases. Therefore, it is desirable to make m in equation (2) as large as possible. However, for the same reason as ΔY1, the maximum value of m should be determined taking into account the effective diameter of the condenser lens 504.

[0103] Furthermore, by moving the optical axis A2 of the condenser lens 504 to a position away by ΔY2 defined in equation (2), the second detection light L1b is reflected at least once by the surface Wa of the wafer W before being irradiated onto the crack K. Since various devices are formed on the surface Wa of the wafer W, the reflecting surface of the second detection light L1b is an uneven surface. Therefore, the spot diameter of the second detection light L1b reflected by the surface Wa at the crack K becomes larger.

[0104] The spot diameter ψD of the second detection light L1b in the crack K can be expressed by the following formula (B): For example, when the thickness w of the wafer W is 500 μm, β=5°, and m=1, the spot diameter ψD of the second detection light L1b in the crack K is 88 μm.

[0105] ψD=2mwtanβ / cosβ …(B)

[0106] [Second measurement process] Next, as shown in Figure 14, in the second measurement process, the focusing lens 504 is moved in the vertical direction (Z direction) relative to the wafer W, and the wafer W is obliquely illuminated with the second detection light L1b that is eccentric from the optical axis A2 of the focusing lens 504, and the reflected light from the wafer W is detected by the photodetectors 404c and 406c.A measurement value Hb indicating the upper end position in the depth direction of the crack K formed inside the wafer W is obtained from the amount of movement of the focusing lens 504 at that time.

[0107] Here, the amount of deviation of the optical axis A2 of the condenser lens 504 in the Y direction relative to the crack K is denoted by d, the amount of movement of the optical axis A2 is denoted by ΔY2, and the angle of incidence of the second detection light Lb incident from the left side in the drawing (hereinafter referred to as side b) is denoted by β. Side b corresponds to the first region G2 in Fig. 9. Furthermore, the measured value of the position of the crack upper end position KT by the second detection light Lb (the distance between the intersection Pb of the optical path of the second detection light Lb and the optical axis A2 of the condenser lens 504 and the surface Wa of the wafer W) is denoted by Hb.

[0108] When the condenser lens 504 is moved in the vertical direction (Z direction), it is moved until the intersection Pb between the optical path of the second detection light Lb and the optical axis A2 of the condenser lens 504 moves from the front surface Wa to the back surface Wb of the wafer W. During this time, the light reflected from the wafer W is detected by the photodetectors 404c and 406c. The point in time when the reflected light incident on the photodetectors 404c and 406c reaches the pattern shown in FIG. 8 is then detected. The amount of movement of the condenser lens 504 from the start of movement at this point in time is then obtained. Hb is calculated based on this obtained amount of movement.

[0109] [Calculation process] Next, in the calculation process, Ha obtained in the first measurement process and Hb obtained in the second measurement process are introduced into the following equation (3) to determine the deviation d between the position of the crack K formed inside the wafer W and the optical axis A2 of the focusing lens 504.

[0110] d=(Ha-Hb) / (1 / tanα+1 / tanβ) …(3)

[0111] The deviation amount d of the optical axis A2 obtained by equation (3) corresponds to the deviation amount in the Y direction between the optical axis A1 of the laser processing unit 2 and the optical axis A2 of the crack measurement unit 10. Therefore, based on the deviation amount d thus obtained, the position information stored in the control unit 500 is rewritten.

[0112] As described above, according to this embodiment, by positioning the optical axis A2 of the condenser lens 504 at a position away from the measurement position of the crack K (a position away by ΔY1 and ΔY2), the optical path length of the first detection light L1a and the second detection light L1b is increased, thereby enlarging the spot diameter of the first detection light L1a and the second detection light L1b irradiated onto the crack K. By enlarging the spot diameter, the measurement range of the crack K by the first detection light L1a and the second detection light L1b can be expanded. As a result, even if the position of the crack K displaces in a meandering manner along the longitudinal direction of the row of cracks K, the crack K can be captured by the first detection light L1a and the second detection light L1b. This makes it possible to measure the relative positional deviation d between the optical axis A1 of the laser processing unit 2 and the optical axis A2 of the crack measurement unit 10, and to correct the position information stored in the control unit 500.

[0113] The present invention may further include the following configurations.

[0114] In the above embodiment, the optical axis A2 of the condenser lens 504 is moved to a position away from the crack K by ΔY1 defined in formula (1) and ΔY2 defined in formula (2), and then the first detection light L1a and the second detection light L1b are irradiated and the first detection light L1a and the second detection light L1b are reflected at least once by the front surface Wa of the wafer W. At this time, a correction may be made to remove the influence of the device formed on the front surface Wa of the wafer W by performing a preliminary measurement before the crack K is formed. By performing the correction, the upper end position or the lower end position of the crack K can be detected with high accuracy.

[0115] In the preliminary measurement, the condenser lens 504 is moved vertically relative to the wafer W before the crack is formed, and the wafer W is obliquely illuminated with detection light L1 that is eccentric from the optical axis A2 of the condenser lens 504, and the reflected light from the wafer W is detected.

[0116] Then, cracks are formed in the wafer W after the preliminary measurement by the laser processing unit 2, and then the first arrangement step, the first measurement step, the second arrangement step, and the second measurement step are performed.

[0117] Then, the measured values ​​Ha and Hb can be corrected using the following formula (C).

[0118] I=kMV …(C)

[0119] In the above equation (C), I is the corrected measurement values ​​Ha and Hb of the crack K, k is a positive coefficient, M=V / V0, V is the measurement value in the first measurement step and the second measurement step, and V0 is the measurement value in the preliminary measurement.

[0120] The present invention may further include the following configurations.

[0121] In the above embodiment, 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 the first detection light L1a and the second detection light L1b. At this time, the light sources 102B and 102C each have a laser aperture at a position shifted from the main optical axis AX, and thereby irradiate the wafer W with the first detection light L1a and the second detection light L1b that are eccentric with respect to the optical axis A2 of the condenser lens 504.

[0122] Here, larger incident angles α and β of the first detection light L1a and the second detection light L1b are advantageous for increasing the spot diameters of the first detection light L1a and the second detection light L1b irradiated onto the crack K. 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. 15 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. Of the laser apertures H1 to H4, by using H3 and H4, the angles of incidence α and β can be made larger than when H1 and H2 are used.

[0123] With the above configuration, the incident angles α and β of the first detection light L1a and the second detection light L1b can be varied, and the spot diameters of the first detection light L1a and the second detection light L1b irradiated onto the crack K can be increased. [Explanation of symbols]

[0124] 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 detecting a misalignment of the optical axes of a laser processing unit and a crack measurement unit provided in a laser processing device, comprising: a step of positioning the condenser lens of the crack measurement unit so that the optical axis of the condenser lens of the crack measurement unit passes through a position that is a first predetermined distance away from the crack measurement position, eccentrically irradiating the workpiece with detection light that is eccentric from the optical axis of the condenser lens of the crack measurement unit, and detecting reflected light from the workpiece; a step of positioning the condenser lens of the crack measurement unit so that the optical axis of the condenser lens of the crack measurement unit passes through a position that is a second predetermined distance away in the opposite direction from the position that is the first predetermined distance away from the crack measurement position, eccentrically irradiating the workpiece with detection light that is eccentric from the optical axis of the condenser lens of the crack measurement unit, and detecting reflected light from the workpiece; An optical axis correction method for a laser processing device, which calculates the deviation of the optical axis between the laser processing section and the crack measurement section from the detected value.

2. 2. The method for correcting an optical axis of a laser processing machine according to claim 1, further comprising the step of moving the focal point in the thickness direction of the workpiece and detecting the light reflected from the rear surface.

3. 2. The optical axis correction method for a laser processing device according to claim 1, wherein the first predetermined distance and the second predetermined distance are set so that when the focal point is moved by an amount equal to the thickness of the workpiece, the reflected light from the underside of the workpiece passes through the entire thickness of the workpiece at the crack measurement position.

4. 2. The optical axis correction method for a laser processing device according to claim 1, wherein the first predetermined distance and the second predetermined distance are set so that when the focal point is moved by an amount equivalent to the thickness of the workpiece, the reflected light reflected once on the underside of the workpiece passes through the entire thickness of the workpiece at the crack measurement position.

5. 2. The optical axis correcting method for a laser processing device according to claim 1, wherein the calculated optical axis deviation is used to correct the deviation of the optical axes of the laser processing unit and the crack measuring unit.

Images