Laser processing device and laser processing method

Abstract

To improve the precision of detecting a crack forming position by shortening a time for detecting a crack formed in a workpiece.SOLUTION: A laser processing device related to one embodiment of the present invention is a laser processing device which comprises: a light source for emitting processing laser light for forming a modification region in a workpiece to the workpiece, a condenser lens for condensing the processing laser light on the workpiece; and lens drive means for moving over the condenser lens for displacing a focal point of the processing laser light in a thickness direction of the workpiece. The laser processing device comprises: top face height position detecting means for detecting a top face height position of the workpiece; and crack detecting means for detecting a crack depth of a crack formed in the workpiece, wherein the top face height position detecting means detects the top face height position when processing the workpiece with the processing laser light, and the crack detecting means detects a bottom face height position of the workpiece on the basis of a substantial refractive index and the top face height position of the workpiece.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laser processing apparatus and a laser processing method. [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 laser beam along a planned dividing line by focusing the laser beam on the inside of the workpiece, thereby forming a laser processing area that serves as a starting point for cutting within the workpiece along the planned dividing line. The workpiece with the laser processing area formed therein is then divided along the planned dividing line by a dividing process such as expanding or breaking, and separated into individual chips (see, for example, Patent Document 1).

[0003] When a laser processing area is formed on a workpiece using a laser processing device, a crack propagates from the laser processing area in the thickness direction of the workpiece. Since the crack formed inside the workpiece becomes the starting point when the workpiece is divided, the distance from the interface of the workpiece to the crack, i.e., the degree of crack propagation, affects the quality of the chips after the workpiece is divided. Therefore, it is necessary to detect the location and propagation of the crack.

[0004] Patent Document 2 discloses a crack detection device that can detect the position and propagation degree of a crack. Specifically, the crack detection device acquires the position of the interface of a workpiece using an interface detection mechanism, and then detects or calculates the position and propagation degree (crack depth) of a crack formed inside the workpiece using the crack detection mechanism.

[0005] Therefore, after forming the laser processing area using a laser processing device, by detecting the position and depth of the crack formed inside the workpiece before the cutting process, it is possible to predict whether the workpiece will be successfully divided into chips during the cutting process. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-139726 [Patent Document 2] Japanese Patent Publication No. 2022-117056 Summary of the Invention [Problem to be solved by the invention]

[0007] In conventional crack detection methods or crack detection devices, the top surface of the workpiece is detected over the entire area where a crack is to be formed before a crack is formed inside the workpiece. Then, a crack is formed inside the workpiece and the crack is detected. Therefore, it takes time from the detection of the top surface of the workpiece to the detection of the crack. Furthermore, the height of the workpiece may change due to changes over time or temperature between the time the top surface of the workpiece is detected and the time the crack is detected. This may result in a discrepancy between the data of the top surface of the workpiece detected before the crack formed and the actual top surface of the workpiece at the time of crack detection. This may result in a decrease in the accuracy of detecting the crack position.

[0008] The present invention has been made in view of the above circumstances, and aims to reduce the time required to detect a crack formed inside a workpiece and to improve the detection accuracy of detecting the position where the crack is formed. [Means for solving the problem]

[0009] The present invention has been made to solve the above problems, and proposes the following means. A laser processing apparatus according to one aspect of the present invention is a laser processing apparatus comprising: a light source that emits processing laser light onto a workpiece to form a modified region inside the workpiece; a focusing lens that focuses the processing laser light on the workpiece; and a lens driving means that moves the focusing lens to displace the focusing point of the processing laser light in the thickness direction of the workpiece. The laser processing apparatus also comprises: an upper surface height position detection means that detects the upper surface height position of the workpiece; and a crack detection means that detects the crack depth of a crack formed inside the workpiece, wherein the upper surface height position detection means detects the upper surface height position when the workpiece is processed with the processing laser light, and the crack detection means detects the lower surface height position of the workpiece based on the effective refractive index and the upper surface height position of the workpiece.

[0010] A laser processing method according to one aspect of the present invention is a laser processing method applied to a laser processing device that includes a light source that emits processing laser light onto a workpiece to form a modified region inside the workpiece, a focusing lens that focuses the processing laser light on the workpiece, a lens driving means that moves the focusing lens to displace the focusing point of the processing laser light in the thickness direction of the workpiece, an upper surface height position detection means that detects the upper surface height position of the workpiece, and a crack detection means that detects the crack depth of a crack formed inside the workpiece, wherein the upper surface height position is detected when the workpiece is processed with the processing laser light, and the lower surface height position of the workpiece is detected based on the effective refractive index of the workpiece and the upper surface height position. [Effects of the Invention]

[0011] According to the laser processing apparatus and laser processing method of the above aspects of the present invention, it is possible to shorten the measurement time for cracks formed inside the workpiece and improve the detection accuracy of the position where the crack is formed. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing an example of the configuration of a laser processing device according to a first embodiment. [Figure 2] FIG. 1 is a schematic diagram for explaining the function of detecting the upper surface of a wafer by an AF (autofocus) device. [Figure 3] 10 is a graph showing the output characteristics of an AF signal E. [Figure 4] 10 is an explanatory diagram showing a state in which a wafer is subjected to oblique illumination with detection light; FIG. [Figure 5] 10 is an explanatory diagram showing a state in which a wafer is subjected to oblique illumination with detection light; FIG. [Figure 6] 10 is an explanatory diagram showing a state in which a wafer is subjected to oblique illumination with detection light; FIG. [Figure 7] 10 is a diagram showing the upper surface height position detected by a conventional crack detection device and the upper surface height position detected by an AF device. FIG. [Figure 8] FIG. 10 is a diagram showing an example of the upper surface height position of an arbitrary point detected by a conventional crack detection device, the upper surface height position of an arbitrary point detected by an AF device, and changes over time. [Figure 9] 1 is a diagram showing an example of the position of the upper end of a crack at an arbitrary point detected by the crack detection device of this embodiment and the position of the upper end of a crack at an arbitrary point detected by a conventional crack detection device. [Figure 10] 3 is a flowchart showing an example of a laser processing method according to the first embodiment. [Figure 11] 3 is a flowchart showing an example of a crack detection method according to the first embodiment. [Figure 12] 10 is a schematic diagram showing various parameters required to calculate the height position of the lower surface of the planned processing point from the position of the condenser lens. FIG. [Figure 13] FIG. 10 is a schematic diagram showing an example of the configuration of a laser processing device and a crack detection device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] (First embodiment) Hereinafter, a laser processing apparatus 10 according to a first embodiment of the present invention will be described with reference to the drawings. Note that the XYZθ directions indicate a positive direction and a negative direction opposite to the positive direction. The θ direction is the direction of rotation around the Z axis.

[0014] FIG. 1 is a schematic diagram showing an example of the configuration of a laser processing apparatus 10 according to the first embodiment. 1, the laser processing apparatus 10 includes a stage 12, a laser head 20, an AF (autofocus) device 200, a crack detection device 300, etc. For example, the AF device 200 is an example of an upper surface height position detection means, and the crack detection device 300 is an example of a crack detection means. Note that the AF device 200 and / or the crack detection device 300 are provided integrally with the laser processing apparatus 10, but may also be provided separately.

[0015] The laser processing apparatus 10 may include a control unit (not shown) that controls each part of the laser processing apparatus 10, such as the stage 12, the laser head 20, the AF device 200, and the crack detection device 300. This control unit is realized by, for example, a personal computer, a workstation, or a PLC (Programmable Logic Controller). The control unit includes a CPU (Central Processing Unit) that controls the operation of each part of the laser processing apparatus 10, a ROM (Read Only Memory), a storage device (for example, 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.

[0016] The stage 12 is, for example, a table that is movable in the X, Y, and Z directions and rotatable in the θ direction. The stage 12 holds a workpiece, for example, a wafer W. When processing the wafer W, the stage 12 moves in the X, Y, and Z directions with the wafer W placed on it and rotates in the θ direction.

[0017] The laser head 20 irradiates the wafer W with processing laser light L1. By irradiating the wafer W with the laser light L1, the laser head 20 forms a modified region R inside the wafer W, which can serve as a starting point for cleaving the wafer W.

[0018] The laser head 20 is composed of a processing laser light source 100, a collimating lens 102, a dichroic mirror 104, a condensing lens 106, and a first actuator 108. The collimating lens 102, the dichroic mirror 104, and the condensing lens 106 are arranged in this order from the processing laser light source 100 side on a first optical path OP1 which is the optical path of the processing laser light L1.

[0019] The processing laser light source 100 emits processing laser light L1 for forming a modified region inside the wafer W. The processing laser light L1 emitted from the processing laser light source 100 is collimated by a collimating lens 102, passes through a dichroic mirror 104, and is then focused inside the wafer W by a focusing lens 106.

[0020] The dichroic mirror 104 transmits the processing laser light L1 and reflects, toward the condenser lens 106, AF detection light L2 emitted from an AF (autofocus) device 200, which will be described later.

[0021] The first actuator 108 (corresponding to a lens driving means) adjusts the Z-direction position (position in the wafer thickness direction) of the focal point of the processing laser beam L1 by slightly moving the condenser lens 106 in the Z-direction (the optical axis direction of the processing laser beam L1). Note that the first actuator 108 does not have to be provided in the laser head 20, and may be provided in another device or part of the laser processing apparatus 10 as long as it can adjust the condenser lens 106.

[0022] The AF device 200 is a linear motion mechanism and device that enables processing to be performed while maintaining a constant processing position. More specifically, the AF device 200 irradiates detection light (detection light for autofocus, detection light for AF) onto the upper surface Wb of the wafer W. Furthermore, the AF device 200 detects position information (height position, Z direction position, height position information, Z direction position information) of the upper surface Wb of the wafer W based on the reflected light.

[0023] FIG. 2 is a schematic diagram illustrating the function of the AF device 200 in detecting the top surface Wb of the wafer W. As shown in FIG. 2, the wafer W has a top surface Wb and a bottom surface Wa opposite the top surface Wb. As shown in FIG. 2, the AF device 200 irradiates the wafer W with AF detection light (detection light) L2, receives the AF detection light L2 reflected by the top surface Wb of the wafer W, and detects the height position (position in the Z direction) of the top surface Wb of the wafer W based on the received reflected light. Specifically, the AF device 200 detects the top surface Wb of the wafer W while moving relative to the wafer W in the processing direction. Based on the height position of the top surface Wb detected as the AF device 200 moves relative to the wafer W, the AF device 200 causes the first actuator 108 to slightly move the condenser lens 106 in the Z direction.

[0024] The AF device 200 includes an AF light source (detection light source) 202, a collimator lens 204, a knife edge 205, a focus optical system 206, a second actuator 216, a half mirror 220, an imaging lens 236, a detector 238, and a processing device control unit 260. The AF device 200 has the same optical axis as the processing laser light L1.

[0025] The AF light source 202 is composed of a laser light source such as an LD (Laser Diode) light source or an SLD (Super Luminescent Diode) light source. The AF light source 202 emits AF detection light L2 having a wavelength that is different from the wavelength of the processing laser light L1 and that can be reflected by the upper surface Wb of the wafer W.

[0026] 1, the AF detection light L2 emitted from the AF light source 202 is collimated by the collimating lens 204, and a portion of the light is blocked by the knife edge 205. The light that travels without being blocked by the knife edge 205 is reflected successively by the half mirror 220 and the dichroic mirror 104, and is collected by the collecting lens 106 to be irradiated onto the wafer W.

[0027] The focus optical system 206 is disposed on the second optical path OP2 of the AF detection light L2, at a position independent of the optical path shared with the first optical path OP1 of the processing laser light L1. The second optical path OP2 is the optical path of the AF detection light L2. The second optical path OP2 is bent by the dichroic mirror 104, and partially shares an optical path with the first optical path OP1 of the processing laser light L1.

[0028] Here, in the second optical path OP2, a condenser lens 106 is disposed on the shared optical path that partially shares the optical path with the first optical path OP1. Therefore, the optical axis of the AF detection light L2 and the optical axis of the processing laser light L1 can partially share the same axis.

[0029] The focusing optical system 206 is disposed between the dichroic mirror 104 and the imaging lens 236 in the AF light reflection path 214. The AF light reflection path 214 is a path for guiding the reflected light of the AF detection light L2 reflected by the upper surface Wb of the wafer W to the detector 238.

[0030] The path along which the AF detection light L2 emitted from the AF light source 202 is guided to the condenser lens 106 is referred to as an AF light irradiation path 212.

[0031] The focus optical system 206 is composed of a plurality of lenses including a movable lens configured to be movable at least along the second optical path OP2, and in this embodiment, is composed of, in order from the subject side (wafer W side), a fixed lens (positive lens) 208 provided immovably along the second optical path OP2, and a movable lens (negative lens) 210 provided movably along the second optical path. The focus optical system 206 is an example of a focal point adjustment optical system.

[0032] The focus optical system 206 adjusts the focal point of the AF detection light L2 in the Z direction (thickness direction of the wafer) independently of the focal point of the processing laser light L1.

[0033] The second actuator 216 moves the movable lens 210 along the second optical path OP2. When the movable lens 210 moves along the second optical path OP2, the Z-direction position of the focal point of the processing laser beam L1 remains fixed, and the Z-direction position of the focal point of the AF detection beam L2 changes in accordance with the direction and amount of movement of the movable lens 210. In other words, the relative distance between the focal point of the processing laser beam L1 and the focal point of the AF detection beam L2 changes.

[0034] The reflected light of the AF detection light L2 reflected by the upper surface Wb of the wafer W is refracted by the condenser lens 106, reflected by the dichroic mirror 104, passes through the focus optical system 206, and passes through the half mirror 220. Furthermore, this reflected light is condensed by the imaging lens 236 and irradiated onto the detector 238, forming a condensed image on the light-receiving surface of the detector 238.

[0035] The detector 238 is made of a two-part photodiode having two split light receiving elements (photoelectric conversion elements). The detector 238 splits and receives the collected image of the reflected light of the AF detection light L2, and outputs output signals (electrical signals) according to the respective light intensities to the AF signal processing unit 262, which will be described later.

[0036] The processing device control unit 260 controls each unit in the laser processing device 10 and the AF device 200, such as the stage 12, the laser head 20, and each unit of the AF device 200. The processing device control unit 260 can send and receive various data, information, and signals to and from the crack detection device 300. The processing device control unit 260 may also be capable of controlling the crack detection device 300. The processing device control unit 260 may also be configured with a control unit that controls the laser processing device 10, such as the stage 12 and the laser head 20, and a control unit that controls each unit of the AF device 200, separately. In this case, the control unit that controls the laser processing device 10 and the control unit that controls each unit of the AF device 200 may each be provided in a device or part other than the AF device 200. The control performed by the processing device control unit 260 may be performed by a control unit that controls the laser processing device 10, such as the laser head 20, instead of the processing device control unit 260.

[0037] The processing device control unit 260 controls the AF device 200 to detect position information of the upper surface Wb of the wafer W, and controls the laser head 20 based on the position information of the upper surface Wb of the wafer W to process the wafer W. For example, the processing device control unit 260 detects position information of the upper surface Wb of the wafer W immediately before or approximately simultaneously (or in real time) with processing the wafer W, and processes the wafer based on the position information of the upper surface Wb. The processing device control unit 260 includes a light source control unit 261, an AF signal processing unit 262, a processing laser control unit 263, a first lens driving means control unit 264, a stage control unit 265, and the like.

[0038] The light source control unit 261 controls the AF light source 202. For example, the light source control unit 261 can set parameters such as the output intensity of the AF light source 202.

[0039] The AF signal processing unit 262 generates an AF signal (autofocus signal), AF data, or AF information as a displacement signal (detection signal) indicating a displacement (defocus distance) of the upper surface Wb of the wafer W from a reference position in the Z direction based on the output signals output from each light-receiving element of the detector 238. For example, the AF signal corresponds to the height position of the upper surface Wb of the wafer at a predetermined position of the wafer W. In other words, the AF signal processing unit 262 detects the height position of the upper surface Wb of the wafer W based on the output signals output from each light-receiving element of the detector 238. The AF signal processing unit 262 is an example of a displacement signal generating means.

[0040] The above-mentioned AF signal is generated by the AF signal processing unit 262 as wafer displacement information indicating the displacement of the upper surface Wb of the wafer W in the Z direction from the reference position, and is output to the first lens driving means control unit 264.

[0041] FIG. 3 is a graph showing the output characteristics of the AF signal E. 3, the horizontal axis indicates the displacement (defocus distance) in the Z direction (thickness direction of the wafer) from the reference position on the top surface Wb of the wafer W, and the vertical axis indicates the output value of the AF signal E. It is assumed that the focus point of the AF detection light L2 is adjusted in advance to coincide with the reference position (origin) on the top surface Wb of the wafer W.

[0042] As shown in FIG. 3, the output characteristic of the AF signal E is an S-shaped curve with the reference position (origin) of the top surface Wb of the wafer W as the zero-cross point. Furthermore, when the position of the top surface Wb of the wafer W is within the range indicated by the arrow in FIG. 3, i.e., within the measurement range (pull-in range) in which the displacement of the top surface Wb of the wafer W can be detected, the relationship between the displacement of the top surface Wb of the wafer W and the output of the AF signal E is a monotonically increasing (or monotonically decreasing) curve passing through the origin, and shows an approximately linear change over most of the curve. In other words, if the output of the AF signal E is zero, it can be determined that the top surface Wb of the wafer W is at a focal position that coincides with the focal point of the AF detection light L2. On the other hand, if the output of the AF signal E is not zero, the direction and amount of displacement of the top surface Wb of the wafer W can be determined.

[0043] The AF signal processing unit 262 determines whether the AF signal E (the height position of the upper surface Wb of the wafer W) is located within a predetermined range. Note that the AF signal processing unit 262 does not have to determine whether the height position of the upper surface Wb of the wafer W is located within a predetermined range. For example, the AF signal processing unit 262 determines whether the position (hereinafter sometimes referred to as the actuator height position) obtained by converting the height position of the upper surface Wb of the wafer W acquired based on the AF signal E into the position of the first actuator 108, that is, the position (actuator height position) of the first actuator 108 corresponding to the position of the condenser lens 106 disposed so that the focal point of the AF detection light L2 is located on the upper surface Wb of the wafer W, is located within the predetermined range.

[0044] Here, the predetermined range is, for example, the distance over which the first actuator 108 can move, or the range (full stroke) minus the distance or range over which the first actuator 108 moves necessary to measure the entire thickness of the wafer W (hereinafter, sometimes referred to as the thickness detectable range). For example, if the thickness of the wafer W is 400 μm, the effective refractive index is 4, and the full stroke of the first actuator 108 is 120 μm (and the downward or upward direction in the Z direction is positive), the first actuator 108 needs to move 100 μm in the Z direction (=wafer thickness / effective refractive index=400 μm / 4) to measure the entire thickness of the wafer W. Therefore, if the actuator height position is located within a range of 20 μm from 0 μm (e.g., the initial position or reference position of the first actuator 108 in the Z direction), the thickness of the wafer W can be measured over the entire wafer W by controlling the first actuator 108 to move the condenser lens 106. This determination makes it possible to improve the accuracy of detecting the height position of the upper surface Wb, and also improve the accuracy of crack detection, which will be described later.

[0045] The AF signal processing unit 262 outputs the generated AF signal E to the first lens driving means control unit 264 and the crack detection control unit 340 of the crack detection device 300, for example, the bottom surface detection unit 342. For example, when the AF signal processing unit 262 determines that the height position of the top surface Wb of the wafer W is located within a predetermined range, it may output the generated AF signal E to the first lens driving means control unit 264 and the crack detection control unit 340 of the crack detection device 300. Note that the AF signal processing unit 262 may output the generated AF signal E to the first lens driving means control unit 264 and the crack detection control unit 340 of the crack detection device 300 regardless of whether the height position of the top surface Wb of the wafer W is located within the predetermined range or not.

[0046] The processing laser control unit 263 controls the processing laser light source 100. The processing laser control unit 263 can set parameters of the processing laser light source 100, such as the output intensity and pulse width.

[0047] The first lens driving means control unit 264 controls the driving of the first actuator 108 and the second actuator 216 so that the distance between the condenser lens 106 and the upper surface Wb of the wafer W is constant or approximately constant. The first lens driving means control unit 264 controls the driving of the first actuator 108 based on the AF signal output from the AF signal processing unit 262 so that the distance between the condenser lens 106 and the top surface Wb of the wafer W is constant or approximately constant. In addition, the first lens driving means control unit 264 slightly moves the condenser lens 106 in the Z direction (thickness direction of the wafer) so as to follow the displacement of the top surface Wb of the wafer W, thereby positioning the focal point of the processing laser beam L1 at a constant or approximately constant distance (depth) from the top surface Wb of the wafer W. By controlling the driving of the first actuator 108 with the first lens driving means control unit 264, the laser processing apparatus 10 can form a modified region R at a desired distance (depth) inside the wafer W.

[0048] Incidentally, in a configuration in which the condenser lens 106 is disposed on a shared optical path between the first optical path OP1 of the processing laser light L1 and the second optical path OP2 of the AF detection light L2, as in this embodiment, when the relative distance between the condenser lens 106 and the wafer W changes to change the crack depth of the crack K in the modified region R, the Z-direction position of the focal point of the processing laser light L1 and the focal point of the AF detection light L2 relative to the wafer W changes. Therefore, the first lens driving means control unit 264 controls the driving of the second actuator 216 to move the movable lens 210 of the focus optical system 206 along the second optical path OP2 so that the focal point of the AF detection light L2 coincides with the upper surface Wb of the wafer W (specifically, so that the output of the AF signal becomes zero).

[0049] In this way, even if the relative distance between the focusing lens 106 and the wafer W changes, the first lens driving means control unit 264 can move the movable lens 210 to align the focusing point of the AF detection light L2 with the top surface Wb of the wafer W while keeping the Z-direction position of the focusing point of the processing laser light L1 fixed.

[0050] When processing the wafer W, the stage control unit 265 moves the stage 12 with the wafer W placed thereon in the X, Y, Z, and θ directions.

[0051] 1, the configuration of the crack detection device 300 will be described. The crack detection device 300 detects the crack depth of a crack K formed inside the wafer W. The crack detection device 300 includes a light source unit 301, an illumination optical system 310, a half mirror 322, a half mirror 324, a crack detection optical system 330, a crack detection control unit 340, and the like.

[0052] The light source unit 301 includes light sources 302 A and 302 B. The light sources 302 A and 302 B are arranged so as to share a part of their optical axes with the main optical axis AX, which is the optical axis of the condenser lens 106.

[0053] The light sources 302A and 302B emit detection light L3 that partially shares the main optical axis AX and is used for crack detection, which will be described later. The light sources 302A and 302B may be, for example, laser light sources (infrared laser light sources, laser diodes) or LED (Light Emitting Diode) light sources. The detection light L3 emitted from the light sources 302A and 302B is referred to as L3(A) and L3(B), respectively.

[0054] Light sources 302A and 302B each have a laser aperture capable of illuminating only a portion of condenser lens pupil 106a of condenser lens 106 that is decentered from main optical axis AX (lens optical axis).

[0055] The illumination optical system 310 guides the detection light L3 emitted from the light source unit 301 to the condenser lens 106. The illumination optical system 310 includes a relay lens 312, a relay lens 316, and a mirror 314 (for example, a total reflection mirror).

[0056] The detection light L3 emitted from the light source unit 301 passes through the relay lens 312 and is reflected by the mirror 314, causing the optical path to bend. The detection light L3 reflected by the mirror 314 passes through the relay lens 316, is then reflected by the half mirror 324 and the half mirror 322 in this order, and is emitted toward the condenser lens 106.

[0057] The crack detection optical system 330 includes a relay lens 326 , a relay lens 332 , a photodetector 334 , and a photodetector 336 .

[0058] The photodetector 334 and the photodetector 336 are devices for detecting cracks K inside the wafer W. More specifically, the photodetector 334 and the photodetector 336 detect the cracks K by receiving reflected light L4(A) corresponding to the detection light L3(A) and reflected light L4(B) corresponding to the detection light L3(B). As the photodetector 334 and the photodetector 336, a photodetector (e.g., a photodiode) or an infrared camera that converts the received light into an electrical signal and outputs it to a crack detection unit 343 (described later) may be used.

[0059] The photodetector 334 and the photodetector 336 are disposed at positions conjugate with the condenser lens pupil 106a. Furthermore, the photodetector 334 and the photodetector 336 are disposed on an optical path different from the second optical path OP2 of the AF device 200 in order to receive the reflected light L4(A) and the reflected light L4(B).

[0060] The crack detection control unit 340 controls each unit of the crack detection device 300. The crack detection control unit 340 can send and receive various data, various information, and various signals to the processing device control unit 260. The crack detection control unit 340 may also be able to control each unit in the laser processing device 10 and the AF device 200.

[0061] The crack detection control unit 340 detects position information (height position, Z-direction position, height position information, Z-direction position information) of the lower surface Wa based on the actual refractive index (effective refractive index) n of the workpiece, for example, the wafer W, which has been acquired in advance, and the position information of the upper surface Wb detected by the AF device 200, and detects the presence or absence of a crack and the crack depth based on the position information of the lower surface Wa. The crack detection control unit 340 includes a light source control unit 341, a bottom surface detection unit 342, a crack detection unit 343, a second lens driving means control unit 344, and the like.

[0062] The light source control unit 341 controls the emission of the detection light L3 emitted from the light source 302A and the light source 302B.

[0063] The bottom surface detection unit (corresponding to bottom surface detection means) 342 detects the height position of the bottom surface Wa using the previously acquired effective refractive index n of the wafer W and the height position of the top surface Wb detected by the AF device 200. For example, the bottom surface detection unit 342 detects (or calculates) the height position of the bottom surface Wa (or position information of the bottom surface Wa) based on the effective refractive index n and the AF signal output from the AF signal processing unit 262. The bottom surface detection unit 342 outputs the detected (or calculated) position information of the bottom surface Wa to the crack detection unit 343.

[0064] The method for obtaining the effective refractive index n of the wafer W is not particularly limited. For example, it may be obtained by performing a simulation calculation. The "effective refractive index" refers to the effective refractive index of a condensed light beam having a certain width when a specific numerical aperture (NA) of the condenser lens into which the condensed light beam is incident is set. Furthermore, the numerical aperture is determined by the characteristics of the condenser lens and the light beam incident on the condenser lens. Therefore, if the characteristics of the condenser lens to be used and the light beam incident on the condenser lens are known, the effective refractive index can be obtained in advance by a simulation calculation or the like based on the characteristics.

[0065] Here, a method for detecting the lower surface height position will be described in detail. The position B of the focusing point of the focusing lens 106 when the focusing point is aligned with the lower surface Wa of the planned processing point P' can be expressed by the following equation using the position T of the focusing point of the focusing lens 106 when the focusing point is aligned with the upper surface Wb of the planned processing point P', the thickness D of the wafer W (known), and the effective refractive index n of the wafer W (known). B=T+D / n (1)

[0066] By using the above formula (1), it is possible to calculate the position B of the focal point of the condenser lens 106 when the focal point is aligned with the lower surface of the target processing point P'.

[0067] Here, the position B of the light condensing point is the relative position of the light condensing point with respect to the lower surface Wa when the light condensing point of the condensing lens 106 is aligned with the lower surface Wa of the intended processing point P'. The height position of the lower surface Wa of the planned processing point P' can be obtained by calculating the following equation (2) by multiplying both sides of equation (1) by the effective refractive index n. nB=nT+D (2) For example, the lower surface detection unit 342 detects (or calculates) the height position of the lower surface Wa by the above-mentioned formula (2) based on the effective refractive index n and the AF signal output from the AF signal processing unit 262 (the position T of the light-focusing point when the planned processing point P' is aligned with the upper surface Wb.

[0068] The crack detection unit 343 (corresponding to a crack detection means) detects the crack depth of a crack K formed inside the wafer W. More specifically, the crack detection unit 343 detects the presence or absence and the crack depth of the crack K based on the detection signals output from the photodetector 334 and the photodetector 336, using the position of the lower surface Wa of the wafer W detected by the lower surface detection unit 342 as a reference.

[0069] The second lens driving means control section 344 controls the first actuator 108 to move the focal point of the crack detection light L3 in the Z direction.

[0070] The crack detection method will be described below. After the wafer W is processed, the crack detection control unit 340 performs crack detection at a predetermined position on the wafer W. The crack detection control unit 340 calculates the height position of the lower surface Wa (the front surface of the wafer W; the surface in contact with the stage 12) at the predetermined position on the wafer W based on the effective refractive index n of the wafer W acquired in advance and the height position of the upper surface Wb (the back surface of the wafer W) detected by the AF device 200. Then, the crack detection control unit 340 detects the presence or absence of a crack K and the depth of the crack at the predetermined position on the wafer W using the calculated height position of the lower surface Wa of the wafer W as a reference using the crack detection optical system 330.

[0071] 4 to 6 are explanatory diagrams showing the state when the detection light L3 is obliquely illuminated onto the wafer W. Fig. 4 shows a case where a crack K is present at the focal point of the condenser lens 106, Fig. 5 shows a case where the crack K is not present at the focal point of the condenser lens 106, and Fig. 6 shows a case where the focal point of the condenser lens 106 coincides with the crack depth (position of the bottom end of the crack) of the crack K. For ease of explanation, the region on the same side as the detection light L3 with respect to the main optical axis AX will be referred to as a first region G1, and the region on the opposite side of the main optical axis AX from the detection light L3 will be referred to as a second region G2.

[0072] As shown in Figure 4, if a crack K is present at the focal point of the focusing lens 106, the detection light L3 is totally reflected by the crack K, and the reflected light L4 travels along a path on the same side of the main optical axis AX as the optical path of the detection light L3, and becomes a component that reaches an area of ​​the focusing lens pupil 106a on the same side as the detection light L3.

[0073] As shown in Figure 5, if there is no crack K at the focal point of the focusing lens 106, the detection light L3 is reflected by the underside Wa of the wafer W, and the reflected light L4 becomes a component that reaches an area on the opposite side of the focusing lens pupil 106a from the detection light L3.

[0074] 6, when the focal point of the condenser lens 106 coincides with the lower end position of the crack K, the detection light L3 is split into a reflected light component L4a and a non-reflected light component L4b. The reflected light component L4a is totally reflected by the crack K, then reflected by the lower surface Wa, and reaches an area of ​​the condenser lens pupil 106a on the same side as the detection light L3, while the non-reflected light component L4b is not totally reflected by the crack K, but is reflected by the lower surface Wa of the wafer W, and reaches an area of ​​the condenser lens pupil 106a on the opposite side to the detection light L3.

[0075] The photodetector 334 and the photodetector 336 are disposed so as to be optically conjugate with the first region G1 and the second region G2 of the condenser lens pupil 106a, respectively. This allows the photodetector 334 and the photodetector 336 to selectively receive light that has passed through the first region G1 and the second region G2 of the condenser lens pupil 106a, respectively. Therefore, the photodetector 334 outputs a first-region-side detection signal as a detection signal obtained on the first region G1 side, and the photodetector 336 outputs a second-region-side detection signal as a detection signal obtained on the second region G2 side.

[0076] 4 (where crack K exists at the focal point of collecting lens 106), reflected light L4 is incident on the light receiving surface of photodetector 334, out of photodetectors 334 and 336. Therefore, the intensity of the detection signal output from the light receiving surface of photodetector 334 becomes higher than the intensity of the detection signal output from the light receiving surface of photodetector 336.

[0077] 5 (where no crack K is present at the focal point of the condenser lens 106), the reflected light is incident on the light-receiving surface of the photodetector 336, of the photodetectors 334 and 336. Therefore, the intensity of the detection signal output from the light-receiving surface of the photodetector 336 becomes higher than the intensity of the detection signal output from the light-receiving surface of the photodetector 334.

[0078] 6 (where the focal point of the condenser lens 106 coincides with the lower end position of the crack K), components L4a and L4b of the reflected light L4 are incident on the light receiving surfaces 334C and 336C of the photodetectors 334 and 336, respectively. As a result, the intensities of the detection signals output from the light receiving surfaces 334C and 336C of the photodetectors 334 and 336 become approximately equal.

[0079] In this way, the amount of light received by the light receiving surfaces of the photodetectors 334 and 336 varies depending on whether or not the crack K exists at the light focusing point of the focusing lens 106. By utilizing such a property, the crack detection control unit 340 (crack detection unit 343) detects the crack depth (crack bottom end position or crack top end position) of the crack K formed inside the wafer W.

[0080] The crack detection unit 343 detects the presence of crack K and the crack depth of crack K through the following process. First, when the detection signals output from the light receiving surfaces 334C and 336C of the photodetector 334 and the photodetector 336, i.e., the outputs of the first area side detection signal and the second area side detection signal, are defined as D1 and D2, respectively, the evaluation value S for determining the presence of crack K at the focusing point of the focusing lens 106 can be expressed by the following equation.

[0081] S = (D1 - D2) / (D1 + D2) ... (3) In equation (3), when the condition S=0 is satisfied, that is, when the amount of light received by the light receiving surfaces 334C and 336C of the photodetector 334 and the photodetector 336 is the same, the focal point of the focusing lens 106 and the bottom end position of the crack (or the top end position of the crack) are aligned.

[0082] Furthermore, half of the detection light L3(A) and the detection light L3(B) are blocked by the upper and lower end positions of the crack K. Therefore, the positions where the intensity of the detection signals from the photodetector 334 and the photodetector 336 is half (i.e., the positions where the difference between the maximum value of the signal intensity and the minimum value of the signal intensity is half) correspond to the positions of the upper and lower ends of the crack. The crack detection unit 343 can calculate the depth positions of the upper and lower end positions of the crack from the upper surface Wb and the lower surface Wa of the wafer W using the positions of the upper surface Wb and the lower surface Wa detected by the AF device 200.

[0083] In this way, the crack detection unit 343 calculates the evaluation value S and evaluates the evaluation value S, the position of the condenser lens 106, and the detection signals of the photodetector 334 and the photodetector 336, thereby determining the presence of the crack K and detecting the crack depth (the crack lower end position or the crack upper end position) of the crack K. Specifically, the crack detection unit 343 calculates the crack depth of the crack K by plotting the peak intensities of the detection signals of the photodetector 334 and the photodetector 336 when the condenser lens 106 is moved in the positive direction of the Z axis from the height position of the lower surface Wa of the processing point P against the movement amount of the condenser lens 106.

[0084] FIG. 7 is a diagram showing the upper surface height position detected by a conventional crack detection device and the upper surface height position detected by the AF device 200. In FIG. 7, the height position of the top surface Wb is detected along an arbitrary diameter portion of the wafer W having a diameter of 300 mm using the AF device 200. In addition, in the example shown in Fig. 7, the position of the center of the top surface Wb of the wafer W is set to 0 mm, and the top surface height position is plotted against the distance in the X-axis direction from the center of the top surface Wb of the wafer W.

[0085] Note that Figure 7 shows the top surface height position detected by a crack detection device having a conventional interface detection mechanism (hereinafter, sometimes referred to as a conventional crack detection device or a conventional configuration, etc.) as a comparative example of the top surface height position of the wafer W detected by the AF device 200.

[0086] 7, the vertical axis indicates the upper surface height position (surface height position), and the horizontal axis indicates the distance in the X-axis direction from the center of the upper surface Wb of the wafer W. Also, in Fig. 7, the detection result of the height position of the upper surface Wb by the AF device 200 is indicated by a solid line, and the detection result of the height position of the upper surface Wb with a conventional configuration is indicated by a dashed line. As can be seen from FIG. 7, there is a slight difference between the height position of the upper surface of the wafer W detected by the AF device 200 and the height position of the upper surface detected by the conventional crack detection device.

[0087] FIG. 8 is a diagram showing an example of the upper surface height position of an arbitrary point detected by a conventional crack detection device, the upper surface height position of an arbitrary point detected by the AF device 200, and changes over time. In the example shown in Fig. 8, the AF device 200 is used to detect the height position of the top surface Wb at an arbitrary point on the wafer W as it changes over time. For example, in Fig. 8, the AF device 200 is used to detect the height position of the top surface Wb at an arbitrary identical point on the wafer W for approximately 60 minutes.

[0088] As a comparative example, Fig. 8 also shows the upper surface height position detected by a conventional crack detection device under the same conditions as the AF device 200. In Fig. 8, the detection result by the AF device 200 is shown by a thick solid line, and the detection result by a crack detection device having a conventional interface detection mechanism is shown by a dashed line.

[0089] 8, the detection results by the AF device 200 showed less variation in the detection results than the detection results by the conventional crack detection device. More specifically, the PV value (maximum-minimum value of the graph) of the detection results by the conventional crack detection device was 1.8 μm, while the PV value of the detection results by the AF device 200 was 0.75 μm. This shows that the AF device 200 can detect the height position of the top surface Wb on the wafer W more stably and accurately than the conventional crack detection device.

[0090] FIG. 9 is a diagram showing an example of the position of the upper end of a crack at an arbitrary point detected by the crack detection device 300 of this embodiment and the position of the upper end of a crack at an arbitrary point detected by a conventional crack detection device. Figure 9 shows the crack upper end position at the processing point P detected by the crack detection device 300 of this embodiment (detection result by this embodiment), and, as a comparison example, the crack upper end position at the processing point P detected by a conventional crack detection device (detection result by a conventional configuration).

[0091] The conventional crack detection device detects the height position of the upper surface Wb corresponding to the peak value of the sensor value of the detection signal detected by the upper surface height position detection means relative to the movement amount of the lens driving means (corresponding to the first actuator 108). The upper end position of the crack K is detected by the same procedure as the crack detection device 300.

[0092] In the detection according to this embodiment, the AF device 200 is used to detect the height position of the upper surface Wb at an arbitrary processing point P on the wafer W, and the crack detection device 300 is used to detect the upper end position of a crack K formed at the processing point P based on the height position of the upper surface Wb. The height position of the upper surface Wb detected by the AF device 200 is detected by calculating an AF signal from the output signal output from the detector 238, as described above. The upper end position of the crack K is determined by calculating the evaluation value S as described above, and by evaluating this evaluation value S and the focal point position information, the presence of the crack K is determined, and the crack upper end position of the crack K is detected.

[0093] In the measurement graph of the detection results using the conventional configuration in Figure 9, the detection signal detected by the conventional crack detection device relative to the amount of movement of the lens driving means corresponding to the first actuator 108 is shown by a solid line, and the signal related to the upper surface height position detected by the interface detection mechanism of the conventional crack detection device relative to the amount of movement of the lens driving means is shown by a dashed line.

[0094] In the measurement graph of the detection results according to this embodiment in Figure 9, the detection signal detected by the crack detection device relative to the amount of movement of the first actuator 108 is shown by a solid line, and the top surface height position detected by the AF device 200 relative to the amount of movement of the first actuator 108 is shown by a dashed line.

[0095] 9 shows the height position of the upper surface Wb detected by a conventional crack detection device and this embodiment, and the upper end position of the crack K formed at the processing point P. As shown in FIG. 9, there is a slight difference between the upper surface height position and the upper end position of the crack corresponding to the detection results by the conventional configuration and the upper surface height position and the upper end position of the crack corresponding to the detection results by this embodiment.

[0096] FIG. 10 is a flowchart showing an example of the laser processing method according to this embodiment. The AF device 200 (or the laser processing device 10) performs alignment by adjusting the relative position between the target processing point P' and the condenser lens 106 to a preset reference position in the Z direction using the first actuator 108 (S1001). More specifically, the AF device 200 (or the laser processing device 10) performs this alignment after placing the unprocessed wafer W on the stage 12. The AF device 200 (or the laser processing device 10) irradiates the planned processing point P' with the AF detection light L2 (S1002). The AF device 200 (or the laser processing device 10) detects the reflected light of the AF detection light L2 reflected at the intended processing point P' (S1003). Then, the AF device 200 (or the laser processing device 10) acquires (or detects) an AF signal E based on the detected reflected light (S1004). That is, the AF device 200 acquires (or detects) the height position of the upper surface Wb of the wafer W. The AF device 200 (or the laser processing device 10) acquires the adjusted position of the condenser lens 106 by controlling the first actuator 108 based on the AF signal E (S1005). For example, the AF device 200 (or the laser processing device 10) acquires the position of the focal point of the condenser lens 106 when the focal point of the condenser lens 106 is aligned with the upper surface Wb of the intended processing point P'. The AF device 200 (or the laser processing device 10) determines whether the height position of the upper surface Wb of the wafer W acquired based on the AF signal E is located within the thickness detectable range (S1006). If it is determined that the acquired height position of the upper surface Wb of the wafer W is located within a predetermined range (YES in S1006), the AF device 200 transmits the position of the focusing lens 106 to the lower surface detection unit 342 of the crack detection device 300 (S1007).

[0097] Immediately after S1007, the AF device 200 (or the laser processing device 10) processes the planned processing point P' on the wafer W. For example, the processing laser light L1 is irradiated to form a modified region R and / or a crack K inside the wafer W. Here, "immediately after" means, for example, that the processing of the wafer W is performed almost simultaneously with the completion of the detection of the upper surface height position (determination (S1006) or transmission of the condenser lens position (S1007)), or that the processing of the wafer W is performed immediately after the detection of the upper surface height position is performed, without the wafer W moving or the state of the wafer W changing.

[0098] If it is determined that the acquired height position of the upper surface Wb of the wafer W is not within a predetermined range (NO in S1006), the AF device 200 adjusts the relative position (relative distance) in the Z direction between the wafer W and the focusing lens 106 (S1008) and executes the process of S1002.

[0099] In processing the wafer W, the AF device 200 (or the laser processing device 10) controls the driving of the first actuator 108, which adjusts the position of the focusing lens 106, thereby adjusting the Z-direction position of the focusing point of the processing laser beam L1. The AF device 200 (or the laser processing device 10) processes the interior of the intended processing point P' with the processing laser beam L1 (to form a modified region R and / or a crack K).

[0100] Since the processing laser light L1 reaches the interior of the planned processing point P' immediately or approximately at the same time as the AF detection light L2 reaches the planned processing point P', the AF device 200 (or the laser processing device 10) forms a crack K and / or a modified region R inside the planned processing point P' immediately or approximately at the same time as detecting the upper surface height position of the planned processing point P' (determination (S1006) or transmission of the focusing lens position (S1007)). Therefore, when processing of the wafer W is performed immediately or approximately at the same time as detecting the upper surface height position, the crack detection device 300 can detect the lower surface height position based on the upper surface height position of the planned processing point P' immediately before the modified region R and / or crack K are formed. Therefore, the lower surface height position, which serves as the reference when calculating the crack depth of the crack K, can be detected more accurately.

[0101] FIG. 11 is a flowchart showing an example of a crack detection method according to this embodiment. The crack detection device 300 detects the lower surface height position of the planned processing point P' on the wafer W based on the real refractive index of the wafer W obtained in advance by simulation or the like and the upper surface height position of the planned processing point P' on the wafer W (S1101). The crack detection device 300 detects the lower surface height position of the planned processing point P' based on, for example, the real refractive index of the wafer W and the upper surface height position of the planned processing point P' detected in S1004 (AF signal E).

[0102] The crack detection device 300 detects the reflected crack detection light L4 (S1102). In detail, the crack detection device 300 controls the first actuator 108 to move the focusing point of the detection light L3 in the Z direction from the lower surface height position of the processing point P, and sequentially detects the reflected crack detection light L4 on the light receiving surfaces of the photodetector 334 and the photodetector 336.

[0103] The crack detection device 300 detects the presence or absence of a crack K based on the detection signals output from the photodetector 334 and the photodetector 336 (S1103). If it is determined that there is no crack K (NO in S1104), the crack detection device 300 ends the crack detection. If it is determined that there is a crack K (YES in S1104), the crack detection device 300 detects (or calculates) the crack depth of the crack K (S1105) and ends the crack detection. For example, the crack detection device 300 calculates the evaluation value S based on the above-mentioned formula (3) from the signals of the photodetector 334 and the photodetector 336, and detects the presence or absence of a crack K or the relative position of the bottom end or top end of the crack K (crack depth) based on the position of the condenser lens 106 corresponding to the height position of the bottom surface Wa. Therefore, the time from detecting the height position of the top surface Wb to forming a crack inside the wafer W can be shortened.

[0104] According to this embodiment, the laser processing apparatus 10 includes a stage 12, a laser head 20, an AF device 200, a crack detection device 300, and the like. The AF device 200 generates (or acquires) an AF signal (height position of the upper surface Wb) during processing of the wafer W and outputs it to the crack detection device 300. During crack detection, the crack detection device 300 detects the height position of the lower surface Wa of the wafer W based on the effective refractive index calculated in advance by simulation or the like and the AF signal (height position of the upper surface Wb) output from the AF device 200. Therefore, the height position of the lower surface Wa, which serves as a reference during crack detection, can be detected based on the height position of the upper surface Wb acquired substantially simultaneously with processing. This suppresses changes over time compared to conventional methods of detecting the height position of the upper surface by interface detection after laser processing. Therefore, according to this embodiment, the detection accuracy of the height position of the upper surface Wb can be improved, and the detection accuracy of the height position of the lower surface Wa can be improved during crack detection. As a result, according to this embodiment, the accuracy of crack detection can be improved.

[0105] Furthermore, the crack detection device 300 (or laser processing device 10) of this embodiment does not have an interface detection mechanism, and there is no need to detect the effective refractive index n and the height position of the upper surface Wb by interface detection, so the crack measurement time can also be shortened. Furthermore, because the crack detection device 300 (or laser processing device 10) of this embodiment does not have an interface detection mechanism, it is possible to reduce costs and make it more compact.

[0106] In the first embodiment, the opening for detecting the upper surface height position (AF light source 202) and the opening for detecting cracks (light sources 302A and 302B) are provided separately, but this is not limiting. For example, one opening may be used for both purposes, and a light blocking means may be used to switch between the opening for detecting the upper surface height position and the opening for detecting cracks.

[0107] Other embodiments and other modifications of the first embodiment will be described below. In the other embodiments and other modifications, the same reference numerals will be used to designate the same components as those in the first embodiment, and detailed descriptions thereof will be omitted.

[0108] (Variation) The modified crack detection device 300 does not detect (or calculate) the height position of the underside Wa of the planned processing point P' by multiplying the position B of the focusing point in equation (2) by the effective refractive index n as shown in the first embodiment, but detects (or calculates) the height position of the underside Wa of the planned processing point P' from the position of the focusing lens 106. FIG. 12 is a schematic diagram showing various parameters required to calculate the height position of the lower surface of the planned processing point from the position of the condenser lens. 12, L indicates the distance between the position of the condenser lens 106 adjusted in S1001 etc. of Fig. 10 and the planned processing point P'. ΔL (not shown) is the distance between the position of the condenser lens 106 readjusted in S1008 etc. of Fig. 10 and the planned processing point P'. In Fig. 12, ΔP indicates the amount of extension of the first actuator 108 when a voltage is applied to the first actuator 108 (the positive direction of the Z axis is taken as positive).

[0109] The distance ΔZ from the position of the condenser lens 106 to the height position of the lower surface Wa can be expressed by the following equation (4). ΔZ=nB+L+(ΔL+ΔP) (4)

[0110] For example, the crack detection device 300 detects (or calculates) the height position of the lower surface Wa of the planned processing point P' using the above-mentioned formula (4) based on the effective refractive index n and the AF signal (position T of the light-focusing point when aligned with the upper surface Wb of the planned processing point P') output from the AF signal processor 262. According to this modification, the same effects as those of the first embodiment can be obtained.

[0111] (Second embodiment) The laser processing apparatus 10A and crack detection apparatus 300A of the second embodiment are different in configuration from the laser processing apparatus and crack detection apparatus of the first embodiment. Specifically, the laser processing apparatus 10A differs from the laser processing apparatus 10 of the first embodiment in that it includes a control unit 50. The crack detection apparatus 300A also differs from the crack detection apparatus 300 of the first embodiment in that the crack detection control unit 340 includes a light source control unit 261 and an AF signal processing unit 262.

[0112] FIG. 13 is a schematic diagram showing an example of the configuration of a laser processing apparatus 10A and a crack detection apparatus 300A according to the second embodiment. In the second embodiment, the laser processing apparatus 10A includes a stage 12, a laser head 20, a control unit 50, and the like.

[0113] The control unit 50 controls each part of the laser processing apparatus 10A and the laser head 20. The control unit 50 has, for example, a processing laser control unit 263, a first lens driving means control unit 264, and a stage control unit 265. The control unit 50 is connected to, for example, a crack detection control unit 340 of the crack detection device 300A. Note that the control unit 50 may be capable of controlling the crack detection device 300A.

[0114] The crack detection device 300A includes an AF device 200, a light source unit 301, an illumination optical system 310, a half mirror 322, a half mirror 324, a crack detection optical system 330, a crack detection control unit 340, and the like.

[0115] The AF device 200 includes a focus optical system 206 , a second actuator 216 , a half mirror 220 , an imaging lens 236 , and a detector 238 .

[0116] The crack detection control unit 340 is connected to and controls the first actuator 108 and each part of the crack detection device 300A, such as the AF device 200, the light source unit 301, the illumination optical system 310, the half mirror 322, the half mirror 324, the crack detection optical system 330, and the crack detection control unit 340. The crack detection control unit 340 can send and receive various data, information, and signals to the control unit 50. The crack detection control unit 340 may also be capable of controlling each part within the laser processing apparatus 10A. The crack detection control unit 340 includes a light source control unit 261, an AF signal processing unit 262, a light source control unit 341, a bottom surface detection unit 342, a crack detection unit 343, a second lens driving means control unit 344, and the like. According to the second embodiment, the same effects as those of the first embodiment and the modified example can be obtained.

[0117] The technical scope of the present invention is not limited to the above-described embodiments and modifications, and various modifications can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0118] 10, 10A laser processing equipment 100 Laser light source for processing 108 First actuator (lens driving means) 200 AF device 202 AF light source 216 Second Actuator 238 detector 264 First lens driving means control section 300, 300A Crack Detector 340 Crack detection control unit 342 Bottom detection unit 343 Crack detection unit 344 Second lens driving means control section W wafer Wa bottom Wb top surface L1 Laser beam for processing L2 AF detection light

Claims

1. A laser processing device comprising: a light source that emits processing laser light onto a workpiece to form a modified region inside the workpiece; a condenser lens that condenses the processing laser light onto the workpiece; and lens driving means that moves the condenser lens to displace the focal point of the processing laser light in the thickness direction of the workpiece, an upper surface height position detecting means for detecting the upper surface height position of the workpiece; a crack detection means for detecting the depth of a crack formed inside the workpiece; Equipped with the upper surface height position detecting means detects the upper surface height position when the workpiece is processed by the processing laser light, The crack detection means detects the height position of the lower surface of the workpiece based on the effective refractive index and the height position of the upper surface of the workpiece.

2. 2. The laser processing device according to claim 1, wherein the effective refractive index is calculated by simulation calculation based on the characteristics of the condenser lens and the light incident on the condenser lens.

3. 2. The laser processing device according to claim 1, wherein the crack detection means does not include a mechanism for detecting the height of the upper surface of the workpiece.

4. A laser processing method applied to a laser processing device including: a light source that emits processing laser light onto a workpiece to form a modified region inside the workpiece; a condenser lens that condenses the processing laser light onto the workpiece; lens driving means that moves the condenser lens to displace the condensing point of the processing laser light in the thickness direction of the workpiece; upper surface height position detection means that detects the height position of an upper surface of the workpiece; and crack detection means that detects the crack depth of a crack formed inside the workpiece, detecting the height position of the upper surface when processing the workpiece with the processing laser light; a laser processing method for detecting a lower surface height position of the workpiece based on the effective refractive index of the workpiece and the upper surface height position.

Images