Laser processing apparatus and laser processing method

Abstract

A laser processing apparatus includes a light source that emits a processing laser for forming a modified region inside a workpiece; a condenser lens that condenses the processing laser onto the workpiece; and a lens drive unit that moves the condenser lens in order to displace a condensing point of the processing laser in a thickness direction of the workpiece. The laser processing apparatus includes an upper surface height position detection unit that detects an upper surface height position of the workpiece; and a crack detection unit that detects a crack depth of a crack formed inside the workpiece. The upper surface height position detection unit detects the upper surface height position when the processing laser processes the workpiece. The crack detection unit detects a lower surface height position of the workpiece based on an actual refractive index of the workpiece and the upper surface height position.

Description

Technical Field

[0001] This invention relates to a laser processing apparatus and a laser processing method. This application claims priority based on Japanese Patent Application No. 2024-045181, filed on March 21, 2024, the contents of which are incorporated herein by reference. Background Technology

[0002] A laser processing apparatus (also known as a laser scribing apparatus) is known in the past, which forms a laser processing region inside the workpiece, such as a semiconductor wafer, by aligning a focal point with a laser beam and irradiating it along a predetermined dicing line. This forms a cutting start point along the predetermined dicing line. The workpiece with the laser processing region formed is then cut along the predetermined dicing line by a cutting process such as wafer expansion or wafer splitting to split it into individual chips (see, for example, Patent Document 1).

[0003] When a laser processing area is formed in a workpiece using a laser processing device, cracks (fissures) propagate from the laser processing area along the thickness direction of the workpiece. Since these cracks, formed within the workpiece, become the starting point for splitting the workpiece, the distance from the workpiece interface to the crack—that is, the extent of crack propagation—affects the quality of the chip after splitting. Therefore, it is necessary to detect the location and extent of the cracks.

[0004] Patent document 2 discloses a crack detection device capable of detecting the location and extent of cracks. Specifically, after obtaining the location of the interface of the workpiece through an interface detection mechanism, the crack detection device detects or calculates the location and extent of cracks (crack depth) formed inside the workpiece through the crack detection mechanism.

[0005] Therefore, after the laser processing area is formed by the laser processing device, by detecting the location and depth of the cracks formed inside the workpiece before the cutting process, it is possible to predict whether the chip splitting process will be successful.

[0006] Patent Document 1: Japanese Patent Publication No. 2016-139726

[0007] Patent Document 2: Japanese Patent Publication No. 2022-117056

[0008] In existing crack detection methods or devices, the entire area to which crack formation is expected is inspected on the upper surface of the workpiece before cracks form inside it. Then, cracks form inside the workpiece, and these cracks are detected. Therefore, time is consumed from the time the upper surface of the workpiece is inspected until the crack is detected.

[0009] Furthermore, between the detection of the workpiece's surface and the detection of the crack, the height of the workpiece may change due to variations in time or temperature. Therefore, there may be a discrepancy between the data of the workpiece's surface detected before crack formation and the actual surface at the time of crack detection. Consequently, the accuracy of crack location detection may be reduced. Summary of the Invention

[0010] The present invention was made in view of the above circumstances, and its object is to shorten the detection time for cracks formed inside the workpiece and improve the detection accuracy of the location of the cracks.

[0011] This invention was made to solve the above-mentioned problems and proposes the following solutions.

[0012] A laser processing apparatus according to one aspect of the present invention includes: a light source that emits a processing laser for forming a modified region inside a workpiece; a focusing lens that focuses the processing laser onto the workpiece; and a lens driving unit that moves the focusing lens to displace the focusing point of the processing laser in the thickness direction of the workpiece. The laser processing apparatus further includes: an upper surface height position detection unit that detects the upper surface height position of the workpiece; and a crack detection unit that detects the crack depth of cracks formed inside the workpiece. The upper surface height position detection unit detects the upper surface height position when the processing laser processes the workpiece, and the crack detection unit detects the lower surface height position of the workpiece based on the actual refractive index of the workpiece and the upper surface height position.

[0013] The laser processing method according to one aspect of the present invention is applied to a laser processing apparatus, which includes: a light source that emits a processing laser for forming a modified region inside the workpiece; a focusing lens that focuses the processing laser onto the workpiece; a lens driving unit that moves the focusing lens to displace the focusing point of the processing laser in the thickness direction of the workpiece; an upper surface height position detection unit that detects the upper surface height position of the workpiece; and a crack detection unit that detects the crack depth of cracks formed inside the workpiece, wherein the upper surface height position is detected when the processing laser processes the workpiece, and the lower surface height position of the workpiece is detected based on the actual refractive index of the workpiece and the upper surface height position.

[0014] According to the laser processing apparatus and laser processing method described above, the measurement time for cracks formed inside the workpiece can be shortened, and the detection accuracy of the location of the crack can be improved. Attached Figure Description

[0015] Figure 1 This is a schematic diagram showing a structural example of the laser processing apparatus according to the first embodiment.

[0016] Figure 2 This is a schematic diagram illustrating the detection function of the AF (autofocus) device on the upper surface of the wafer.

[0017] Figure 3 This is a graph showing the output characteristics of the AF signal E.

[0018] Figure 4 This is an explanatory diagram showing the oblique illumination of the wafer when testing it with light.

[0019] Figure 5 This is an explanatory diagram showing the oblique illumination of the wafer when testing it with light.

[0020] Figure 6 This is an explanatory diagram showing the oblique illumination of the wafer when testing it with light.

[0021] Figure 7 This is a diagram showing the upper surface height position detected by an existing crack detection device and the upper surface height position detected by an AF device.

[0022] Figure 8 This is a diagram illustrating an example of the time-varying change in the upper surface height position of an arbitrary point detected by an existing crack detection device versus the upper surface height position of an arbitrary point detected by an AF device.

[0023] Figure 9 This is a diagram showing an example of the upper position of a crack at any point detected by the crack detection device of this embodiment and the upper position of a crack at any point detected by a conventional crack detection device.

[0024] Figure 10 This is a flowchart illustrating an example of the laser processing method according to the first embodiment.

[0025] Figure 11 This is a flowchart illustrating an example of the crack detection method according to the first embodiment.

[0026] Figure 12 This is a schematic diagram showing the various parameters required to calculate the lower surface height position of a predetermined machining point based on the position of the condenser lens.

[0027] Figure 13 This is a schematic diagram showing a structural example of the laser processing apparatus and crack detection apparatus according to the second embodiment. Detailed Implementation

[0028] (First Implementation)

[0029] The laser processing apparatus 10 according to the first embodiment of the present invention will be described below with reference to the accompanying drawings. The positive direction (+) and the negative direction (-), which is opposite to the positive direction (+), are shown in the XYZθ directions. The θ direction is the direction of rotation about the Z-axis.

[0030] Figure 1 This is a schematic diagram showing a structural example of the laser processing apparatus 10 according to the first embodiment.

[0031] like Figure 1 As shown, the laser processing apparatus 10 includes a stage 12, a laser head 20, an AF (autofocus) device 200, and a crack detection device 300. For example, the AF device 200 is an example of an upper surface height position detection unit, and the crack detection device 300 is an example of a crack detection unit. Furthermore, the AF device 200 and / or the crack detection device 300 are integrated with the laser processing apparatus 10, but they can also be installed separately.

[0032] The laser processing apparatus 10 may also include a control unit (not shown) that controls various parts of the laser processing apparatus 10, such as the stage 12, laser head 20, AF device 200, and crack detection device 300. This control unit may be implemented, for example, via a personal computer, workstation, or programmable logic controller (PLC). The control unit includes a central processing unit (CPU) that controls the operation of various parts of the laser processing apparatus 10, read-only memory (ROM), a storage device for storing control programs (e.g., a hard disk drive (HDD) or solid-state drive (SSD), etc.), and synchronous dynamic random access memory (SDRAM) that can be used as the CPU's working area.

[0033] The stage 12 is, for example, a worktable capable of moving in the XYZ directions and rotating in the θ direction. The stage 12 holds the workpiece, such as a wafer W. When processing the wafer W, the stage 12 moves in the XYZ directions and rotates in the θ direction while the wafer W is mounted.

[0034] Laser head 20 irradiates processing laser L1 onto wafer W. By irradiating wafer W with laser L1, laser head 20 forms a modified region R inside wafer W, which can serve as the starting point for cutting wafer W.

[0035] The laser head 20 consists of a processing laser source 100, a collimating lens 102, a dichroic mirror 104, a condenser lens 106, and a first actuator 108. On the optical path of the processing laser L1, i.e., the first optical path OP1, starting from the processing laser source 100 side, the collimating lens 102, the dichroic mirror 104, and the condenser lens 106 are arranged sequentially.

[0036] A processing laser L1 is emitted from a processing laser source 100 to form a modified region inside the wafer W. The processing laser L1 emitted from the processing laser source 100 is collimated by a collimating lens 102 and transmitted through a dichroic mirror 104, and then focused into the wafer W by a focusing lens 106.

[0037] Dichroic mirror 104 transmits the processing laser L1 and reflects the AF detection light L2 emitted from the AF (autofocus) device 200 toward the condenser lens 106.

[0038] The first actuator 108 (equivalent to a lens drive unit) adjusts the Z-direction position (wafer thickness direction position) of the focusing point of the processing laser L1 by slightly moving the condenser lens 106 in the Z-direction (optical axis direction of the processing laser L1). Alternatively, the first actuator 108 may not be provided in the laser head 20, and can be provided in other devices or other parts outside the laser processing apparatus 10, as long as the condenser lens 106 can be adjusted.

[0039] The AF device 200 is a linear motion mechanism and apparatus for performing machining while maintaining a certain machining position. More specifically, the AF device 200 illuminates a detection light (autofocus detection light, AF detection light) onto the upper surface Wb of the wafer W. Furthermore, the AF device 200 detects the 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.

[0040] Figure 2 This is a schematic diagram illustrating the detection function of the AF device 200 on the upper surface Wb of wafer W. For example... Figure 2 As shown, wafer W has an upper surface Wb and a lower surface Wa opposite to the upper surface Wb. As Figure 2As shown, the AF device 200 illuminates the wafer W with an AF detection light (detection light) L2, receives the reflected light from the upper surface Wb of the wafer W, and detects the height position (Z-direction position) of the upper surface Wb of the wafer W based on the received reflected light. Specifically, the AF device 200 detects the upper surface Wb of the wafer W while moving relative to the wafer W along the processing direction. Based on the height position of the upper surface Wb detected by the relative movement of the AF device 200 relative to the wafer W, the AF device 200 slightly moves the focusing lens 106 in the Z-direction via the first actuator 108.

[0041] The AF device 200 includes an AF light source (detection light source) 202, a collimating lens 204, a cutting edge 205, a focusing optical system 206, a second actuator 216, a semi-transparent mirror 220, an imaging lens 236, a detector 238, and a processing device control unit 260. The AF device 200 and the processing laser L1 have the same optical axis.

[0042] The AF light source 202 is composed of laser sources such as laser diode (LD) light sources and super luminescent diode (SLD) light sources. The AF light source 202 emits AF detection light L2, which has a wavelength that is different from the processing laser L1 and can be reflected by the upper surface Wb of the wafer W.

[0043] like Figure 1 As shown, the AF detection light L2 emitted from the AF light source 202 is collimated by the collimating lens 204, and a portion of it is blocked by the knife edge 205. Furthermore, the light that is not blocked by the knife edge 205 is reflected in sequence by the semi-transparent mirror 220 and the dichroic mirror 104, and then focused by the condenser lens 106 to illuminate the wafer W.

[0044] The focusing optical system 206 is positioned independently of the shared optical path of the second optical path OP2 of the AF detection light L2 and the first optical path OP1 of the processing laser L1. The second optical path OP2 is the optical path of the AF detection light L2. The second optical path OP2 is deflected by the dichroic mirror 104 and shares a portion of the optical path with the first optical path OP1 of the processing laser L1.

[0045] In the second optical path OP2, a focusing lens 106 is arranged on the shared optical path that shares a portion with the first optical path OP1. Therefore, the optical axis of the AF detection light L2 and the optical axis of the processing laser L1 can be the same in that part.

[0046] The focusing optical system 206 is disposed on the AF light reflection path 214 between the dichroic mirror 104 and the imaging lens 236. The AF light reflection path 214 is a path used to guide the reflected light of the AF detection light L2, which is reflected by the upper surface Wb of the wafer W, to the detector 238.

[0047] In addition, the path used to guide the AF detection light L2 emitted from the AF light source 202 to the condenser lens 106 is set as the AF light illumination path 212.

[0048] The focusing optical system 206 comprises at least a plurality of lenses, including a movable lens configured to move along the second optical path OP2. In this embodiment, starting from the subject side (wafer W side), it consists sequentially of a fixed lens (positive lens) 208 configured not to move along the second optical path OP2 and a movable lens (negative lens) 210 configured to move along the second optical path. The focusing optical system 206 is an example of a focusing point adjustment optical system.

[0049] The focusing optical system 206 independently adjusts the focusing point of the detection light L2 for AF in the Z direction (wafer thickness direction) in relation to the focusing point of the processing laser L1.

[0050] 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, with the Z-direction position of the focusing point of the processing laser L1 fixed, the Z-direction position of the focusing point of the AF detection light L2 changes according to the moving direction and amount of the movable lens 210. That is, the relative distance between the focusing point of the processing laser L1 and the focusing point of the AF detection light L2 changes.

[0051] The reflected light from the upper surface Wb of wafer W, and the detection light L2 of AF, is refracted by the condenser lens 106, reflected by the dichroic mirror 104, and transmitted through the focusing optical system 206 and the semi-transparent mirror 220. Then, the reflected light is focused by the imaging lens 236 and illuminates the detector 238, forming a focused image on the light-receiving surface of the detector 238.

[0052] The detector 238 consists of a light-emitting diode divided into two parts, each having a light-receiving element (photoelectric conversion element) divided into two parts. The detector 238 divides and receives a focused image of the reflected light from the detection light L2 used for AF, and outputs an output signal (electrical signal) corresponding to the light amount of each part to the AF signal processing unit 262 described later.

[0053] The processing apparatus control unit 260 controls various components within the laser processing apparatus 10 and the AF apparatus 200, such as the stage 12, the laser head 20, and other parts of the AF apparatus 200. The processing apparatus control unit 260 can transmit and receive various data, information, and signals with the crack detection device 300. Furthermore, the processing apparatus control unit 260 can also control the crack detection device 300. In addition, the control unit within the processing apparatus control unit 260 that controls the laser processing apparatus 10, such as the stage 12 and the laser head 20, and the control unit that controls the various parts of the AF apparatus 200 can be separately configured. In this case, the control unit controlling the laser processing apparatus 10 and the control unit controlling the various parts of the AF apparatus 200 can be respectively located in devices or parts outside the AF apparatus 200. Furthermore, the control performed by the processing apparatus control unit 260 can also be performed by the control unit that controls the laser processing apparatus 10, such as the laser head 20, instead of the processing apparatus control unit 260.

[0054] The processing apparatus control unit 260 controls the AF device 200 to detect the position information of the upper surface Wb of the wafer W, and controls the laser head 20 to process the wafer W based on the position information of the upper surface Wb of the wafer W. For example, the processing apparatus control unit 260 detects the position information of the upper surface Wb of the wafer W before or approximately simultaneously (or in real time) before processing the wafer W, and processes the wafer based on the position information of the upper surface Wb.

[0055] 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 drive unit control unit 264, and a stage control unit 265.

[0056] The light source control unit 261 controls the aforementioned 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.

[0057] The AF signal processing unit 262 generates an AF signal (autofocus signal), AF data, or AF information as a displacement signal (detection signal) based on the output signals from each light-receiving element of the detector 238. This displacement signal represents the displacement (defocus distance) of the upper surface Wb of the wafer W relative to a reference position in the Z direction. For example, the AF signal corresponds to the height position of the upper surface Wb of the wafer W at a predetermined position. 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 from each light-receiving element of the detector 238. Furthermore, the AF signal processing unit 262 is an example of a displacement signal generation unit.

[0058] The aforementioned AF signal is generated by the AF signal processing unit 262 as wafer displacement information representing the displacement of the upper surface Wb of wafer W relative to the reference position in the Z direction, and is output to the first lens driving unit control unit 264.

[0059] Figure 3 This is a graph showing the output characteristics of the AF signal E.

[0060] exist Figure 3 In the diagram, the horizontal axis represents the displacement (defocus distance) of the upper surface Wb of wafer W relative to the reference position in the Z direction (wafer thickness direction), and the vertical axis represents the output value of the AF signal E. It is assumed that the focusing point of the AF detection light L2 has been pre-adjusted to coincide with the reference position (origin) of the upper surface Wb of wafer W.

[0061] like Figure 3 As shown, the output characteristic of the AF signal E is an S-shaped curve with the reference position (origin) of the upper surface Wb of wafer W as the zero-crossing point. Furthermore, when the position of the upper surface Wb of wafer W is located at... Figure 3 When the range indicated by the middle arrow is within the measurement range (capture range) that can detect the displacement of the upper surface Wb of wafer W, the relationship between the displacement of the upper surface Wb of wafer W and the output of the AF signal E is a monotonically increasing curve (or monotonically decreasing curve) passing through the origin. This curve largely shows a roughly linear change. That is, if the output of the AF signal E is 0, it can be known that the upper surface Wb of wafer W is located at the focal point corresponding to the focusing point of the detection light L2 used in the AF. On the other hand, if the output of the AF signal E is not 0, the displacement direction and amount of the upper surface Wb of wafer W can be determined.

[0062] 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 within a predetermined range. Alternatively, the AF signal processing unit 262 may not determine whether the height position of the upper surface Wb of the wafer W is within a predetermined range. For example, the AF signal processing unit 262 determines whether the position of the first actuator 108 (the position obtained by converting the height position of the upper surface Wb of the wafer W obtained based on the AF signal E into the position of the first actuator 108 (hereinafter sometimes referred to as the actuator height position), which corresponds to the position of the focusing lens 106 when the focusing point of the AF detection light L2 is located on the upper surface Wb of the wafer W, is within a predetermined range.

[0063] Here, the defined range is, for example, the distance obtained by subtracting the distance the first actuator 108 needs to move to determine the overall thickness of wafer W from the distance or range (full stroke) that the first actuator 108 can move, or the range obtained by subtracting the range of movement of the first actuator 108 (hereinafter sometimes referred to as the thickness detectable range). For example, when the thickness of wafer W is 400 μm, the actual refractive index is 4, and the full stroke of the first actuator 108 is 120 μm (with the downward or upward direction of the Z direction as positive), in order to determine the overall thickness of wafer W, the first actuator 108 needs to move 100 μm in the Z direction (= wafer thickness / actual refractive index = 400 μm / 4). Therefore, if the actuator height position is in the range of 0 μm (e.g., the initial position or reference position of the first actuator 108 in the Z direction) to 20 μm, the thickness of wafer W can be measured throughout the entire wafer by controlling the first actuator 108 to move the condenser lens 106. This determination can improve the detection accuracy of the height position of the upper surface Wb, and also improve the accuracy of crack detection described later.

[0064] The AF signal processing unit 262 outputs the generated AF signal E to the first lens driving unit control unit 264 and the crack detection control unit 340 of the crack detection device 300, such as the lower surface detection unit 342. For example, the AF signal processing unit 262 may output the generated AF signal E to the first lens driving unit control unit 264 and the crack detection control unit 340 of the crack detection device 300 when it is determined that the height position of the upper surface Wb of the wafer W is within a predetermined range. Alternatively, the AF signal processing unit 262 may output the generated AF signal E to the first lens driving unit control unit 264 and the crack detection control unit 340 of the crack detection device 300 regardless of whether the height position of the upper surface Wb of the wafer W is within the predetermined range.

[0065] The processing laser control unit 263 controls the processing laser source 100. For example, the processing laser control unit 263 can set parameters such as the output intensity and pulse width of the processing laser source 100.

[0066] The first lens driving unit 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.

[0067] The first lens driving unit 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 upper surface Wb of the wafer W is constant or approximately constant. Furthermore, the first lens driving unit control unit 264 slightly moves the condenser lens 106 in the Z direction (wafer thickness direction) to follow the displacement of the upper surface Wb of the wafer W, thereby positioning the focusing point of the processing laser L1 at a constant or approximately constant distance (depth) from the upper surface Wb of the wafer W. By controlling the driving of the first actuator 108 using the first lens driving unit control unit 264, the laser processing apparatus 10 is able to form a modified region R at a desired distance (depth) inside the wafer W.

[0068] In the structure described in this embodiment, where a focusing lens 106 is arranged on the shared optical path of the first optical path OP1 of the processing laser L1 and the second optical path OP2 of the AF detection light L2, when the relative distance between the focusing lens 106 and the wafer W changes in order to change the crack depth of the crack K in the modified region R, the Z-direction position of the focusing point of the AF detection light L2 relative to the wafer W also changes, along with the focusing point of the processing laser L1. Therefore, the first lens driving unit control unit 264 controls the driving of the second actuator 216, causing the moving lens 210 of the focusing optical system 206 to move along the second optical path Op2, thereby aligning the focusing point of the AF detection light L2 with the upper surface Wb of the wafer W (specifically, making the AF signal output zero).

[0069] In this way, even when the relative distance between the condenser lens 106 and the wafer W changes, the first lens drive unit control unit 264 can move the movable lens 210 so that the condenser point of the processing laser L1 in the Z direction is fixed, and the AF detection light L2 aligns with the upper surface Wb of the wafer W.

[0070] When processing wafer W, the stage control unit 265 moves the stage 12, which is in the state of holding wafer W, in the XYZθ direction.

[0071] Back Figure 1 The structure of the crack detection device 300 will be described. The crack detection device 300 detects the crack depth of cracks K formed inside the wafer W. The crack detection device 300 includes a light source unit 301, an illumination optical system 310, a semi-transparent mirror 322, a semi-transparent mirror 324, a crack detection optical system 330, and a crack detection control unit 340.

[0072] The light source unit 301 includes light sources 302A and 302B. Light sources 302A and 302B are configured to share a portion of the optical axis with the optical axis of the condenser lens 106, namely the principal optical axis AX.

[0073] Light sources 302A and 302B emit detection light L3 by sharing a portion of the optical axis with the principal optical axis AX, for use in crack detection as described later. Light sources 302A and 302B can be, for example, laser sources (infrared laser sources, laser diodes) or light-emitting diodes (LEDs). Furthermore, the detection beams emitted from light sources 302A and 302B in detection light L3 are designated as L3(A) and L3(B), respectively.

[0074] Light sources 302A and 302B each have a laser opening that can only illuminate a portion of the condenser lens pupil 106a of the condenser lens 106 that is off-center from the principal optical axis AX (lens optical axis).

[0075] The illumination optical system 310 guides the detection light L3 emitted from the light source 301 to the condenser lens 106. The illumination optical system 310 includes relay lenses 312 and 316 and a reflector 314 (e.g., a total reflection mirror).

[0076] The detection light L3 emitted from the light source 301 is transmitted through the relay lens 312 and reflected by the reflector 314, thus reversing its optical path. After being reflected by the reflector 314, the detection light L3 is transmitted through the relay lens 316 and then reflected sequentially by the semi-transparent lens 324 and semi-transparent lens 322 before being emitted toward the condenser lens 106.

[0077] The optical system 330 for crack detection includes relay lenses 326 and 332, photodetector 334 and photodetector 336.

[0078] Photodetectors 334 and 336 are devices for detecting cracks K inside wafer W. More specifically, photodetectors 334 and 336 detect the crack 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). Photodetectors 334 and 336 can be photodetectors such as photodiodes (e.g., photodiodes) that convert the received light into electrical signals and output them to the crack detection unit 343 described later.

[0079] Photodetectors 334 and 336 are configured in a position conjugate to the pupil 106a of the condenser lens. Furthermore, photodetectors 334 and 336 are configured on an optical path different from the second optical path OP2 of the AF device 200 in order to receive reflected light L4(A) and reflected light L4(B).

[0080] The crack detection control unit 340 controls various parts of the crack detection device 300. The crack detection control unit 340 can send and receive various data, information, and signals with the processing device control unit 260. Furthermore, the crack detection control unit 340 can also control various parts within the laser processing device 10 and the AF device 200.

[0081] The crack detection control unit 340 detects the position information (height position, Z-direction position, height position information, Z-direction position information) of the lower surface Wa based on the pre-acquired actual refractive index (actual refractive index) n of the workpiece, such as wafer W, and the position information of the upper surface Wb detected by the AF device 200, and detects the presence and depth of cracks based on the position information of the lower surface Wa.

[0082] The crack detection control unit 340 includes a light source control unit 341, a lower surface detection unit 342, a crack detection unit 343, and a second lens drive unit control unit 344, etc.

[0083] 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.

[0084] The lower surface detection unit (equivalent to the lower surface detection unit) 342 uses the pre-acquired actual refractive index n of the wafer W and the height position of the upper surface Wb detected by the AF device 200 to detect the height position of the lower surface Wa. For example, the lower surface detection unit 342 detects (or calculates) the height position (or position information of the lower surface Wa) based on the actual refractive index n and the AF signal output from the AF signal processing unit 262. The lower surface detection unit 342 outputs the detected (or calculated) position information of the lower surface Wa to the crack detection unit 343.

[0085] Furthermore, the method for obtaining the actual refractive index n of wafer W is not particularly limited. For example, it can be obtained through simulation calculations. The "actual refractive index" refers to the actual refractive index related to a condenser lens when a condenser beam of a certain width is incident on it at a specific numerical aperture (NA). This numerical aperture is determined by the characteristics of the condenser lens and the beam incident on it. Therefore, if the characteristics of the condenser lens used and the beam incident on it are known, the actual refractive index can be obtained in advance through simulation calculations or similar methods based on these characteristics.

[0086] Here, the method for detecting the height position of the lower surface is described in detail.

[0087] When the focusing point of the condenser lens 106 is aligned with the lower surface Wa of the predetermined processing point P', the position B of the focusing point can be expressed by the following formula using the position T of the focusing point when the focusing point of the condenser lens 106 is aligned with the upper surface Wb of the predetermined processing point P', the thickness D of the wafer W (known), and the actual refractive index n of the wafer W (known).

[0088] B = T + D / n … (1)

[0089] By using the above formula (1), the position B of the focusing point of the focusing lens 106 when it is aligned with the lower surface of the predetermined processing point P' can be calculated.

[0090] Wherein, the position B of the focusing point is the relative position of the focusing point with reference to the lower surface Wa when the focusing point of the focusing lens 106 is aligned with the lower surface Wa of the predetermined processing point P'.

[0091] The height position of the lower surface Wa of the predetermined processing point P' can be obtained by calculating the following equation (2) obtained by multiplying both sides of equation (1) by the actual refractive index n.

[0092] nB=nT+D…(2)

[0093] For example, the lower surface detection unit 342 detects (or calculates) the height position of the lower surface Wa based on the actual refractive index n and the AF signal output from the AF signal processing unit 262 (the position T of the focusing point when aligned with the upper surface Wb of the predetermined processing point P') using the aforementioned formula (2).

[0094] The crack detection unit 343 (equivalent to a crack detection unit) detects the crack depth of the crack K formed inside the wafer W. More specifically, the crack detection unit 343 uses the position of the lower surface Wa of the wafer W detected by the lower surface detection unit 342 as a reference, and detects the presence and depth of the crack K based on the detection signals output from the photodetector 334 and the photodetector 336.

[0095] The second lens drive unit control unit 344 controls the first actuator 108 to move the focusing point of the crack detection light L3 in the Z direction.

[0096] The following explains the method for detecting cracks.

[0097] After wafer W is processed, the crack detection control unit 340 performs crack detection at a predetermined location on wafer W. At the predetermined location on wafer W, the crack detection control unit 340 calculates the height of the lower surface Wa (the front surface of wafer W; the surface in contact with the stage 12) based on the pre-acquired actual refractive index n of wafer W and the height of the upper surface Wb (the back side of wafer W) detected by the AF device 200. Then, the crack detection control unit 340 uses the crack detection optical system 330, with the calculated height of the lower surface Wa of wafer W as a reference, to detect the presence and depth of crack K at the predetermined location on wafer W.

[0098] Figures 4 to 6 This is an explanatory diagram showing the oblique illumination of the detection light L3 on wafer W. Specifically, Figure 4 This illustrates the presence of a crack K at the focusing point of the condenser lens 106. Figure 5 This shows the case where there is no crack K at the focusing point of the condenser lens 106. Figure 6 This illustrates the case where the focusing point of the condenser lens 106 coincides with the crack depth (lower end position of the crack) of the crack K. For ease of explanation, the region on the same side as the principal optical axis AX and the detection light L3 will be referred to as the first region G1, and the region on the opposite side of the principal optical axis AX and the detection light L3 will be referred to as the second region G2.

[0099] like Figure 4 As shown, when there is a crack K at the focal point of the condenser lens 106, the detection light L3 undergoes total internal reflection at the crack K, and its reflected light L4 becomes the component of the condenser lens pupil 106a that is on the same side as the detection light L3 along the same path as the principal optical axis AX.

[0100] like Figure 5 As shown, when there is no crack K at the focusing point of the condenser lens 106, the detection light L3 is reflected on the lower surface Wa of the wafer W, and the reflected light L4 becomes the component that reaches the region opposite to the detection light L3 in the pupil of the condenser lens 106a.

[0101] like Figure 6 As shown, when the focusing point of the condenser lens 106 coincides with the lower end 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 undergoes total internal reflection at the crack K and is reflected at the lower surface Wa, reaching the same side region of the condenser lens pupil 106a as the detection light L3; the non-reflected light component L4b does not undergo total internal reflection at the crack K, but is reflected at the lower surface Wa of the wafer W, reaching the opposite side region of the condenser lens pupil 106a as the detection light L3.

[0102] Photodetectors 334 and 336 are configured to be optically conjugate with the first region G1 and the second region G2 of the condenser lens pupil 106a, respectively. Therefore, photodetectors 334 and 336 can selectively receive light passing through the first region G1 and the second region G2 of the condenser lens pupil 106a, respectively. Consequently, photodetector 334 outputs a first region-side detection signal as the detection signal obtained on the first region G1 side, and photodetector 336 outputs a second region-side detection signal as the detection signal obtained on the second region G2 side.

[0103] Among them, Figure 4 In the example shown (where a crack K exists at the focal point of the condenser lens 106), the reflected light L4 is incident on the light-receiving surface of the photodetector 334, which is one of the photodetectors 334 and 336. Therefore, the intensity of the detection signal output from the light-receiving surface of the photodetector 334 is higher than the intensity of the detection signal output from the light-receiving surface of the photodetector 336.

[0104] On the other hand, Figure 5 In the example shown (where there is no crack K at the focal point of the condenser lens 106), the reflected light is incident on the light-receiving surface of the photodetector 336, which is one of the photodetectors 334 and 336. Therefore, the intensity of the detection signal output from the light-receiving surface of the photodetector 336 is higher than the intensity of the detection signal output from the light-receiving surface of the photodetector 334.

[0105] exist Figure 6 In the example shown (where the focusing point of the condenser lens 106 coincides with the lower end of the crack K), the components L4a and L4b of the reflected light L4 are incident on the light-receiving surfaces of the photodetector 334 and the photodetector 336, respectively. Therefore, the intensity of the detection signals output from the light-receiving surface 334C of the photodetector 334 and the light-receiving surface 336C of the photodetector 336 are approximately equal.

[0106] Thus, the amount of light received by the light-receiving surfaces of photodetector 334 and photodetector 336 varies depending on whether there is a crack K at the focusing point of the condenser lens 106.

[0107] Utilizing this property, the crack detection control unit 340 (crack detection unit 343) detects the crack depth (lower end position or upper end position) of the crack K formed inside the wafer W.

[0108] The crack detection unit 343 detects the presence and depth of crack K by the following process. First, when the outputs of the detection signals from the light-receiving surface 334C of the photodetector 334 and the light-receiving surface 336C of the photodetector 336, namely the first region side detection signal and the second region side detection signal, are set to D1 and D2 respectively, the evaluation value S used to determine the presence of crack K at the focusing point of the condenser lens 106 can be expressed by the following formula.

[0109] S=(D1-D2) / (D1+D2)…(3)

[0110] In equation (3), when the condition S=0 is met, that is, when the amount of light received by the light-receiving surface 334C of the photodetector 334 and the light-receiving surface 336C of the photodetector 336 is the same, it indicates that the focusing point of the condenser lens 106 is consistent with the position of the lower end of the crack (or the position of the upper end of the crack).

[0111] Furthermore, detection lights L3(A) and L3(B) are partially blocked by the upper and lower ends of the crack K. Therefore, the positions where the intensity of the detection signals of photodetectors 334 and 336 is half (that is, the positions where the difference between the maximum and minimum signal intensity is half) correspond to the upper and lower ends of the crack. The crack detection unit 343 can calculate the depth from the upper surface Wb and lower surface Wa of the wafer W to the upper and lower ends of the crack by using the positions of the upper surface Wb and lower surface Wa detected by the AF device 200.

[0112] 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 photodetectors 334 and 336, thereby determining the existence of crack K and detecting the crack depth (lower or upper end of the crack). Specifically, the crack detection unit 343 calculates the crack depth of crack K by plotting the peak intensity of the detection signals of the photodetectors 334 and 336 relative to the amount of movement of the condenser lens 106 as the condenser lens 106 is moved from the height position of the lower surface Wa of the processing point P along the positive Z-axis.

[0113] Figure 7 This is a diagram showing the upper surface height position detected by an existing crack detection device and the upper surface height position detected by an AF device 200.

[0114] exist Figure 7 In the example shown, the AF device 200 is used to detect the height position of the upper surface Wb along an arbitrary diameter portion of a wafer W with a diameter of 300 mm. Furthermore, in Figure 7In the example shown, the center position of the upper surface Wb of wafer W is set to 0mm, and the height position of the upper surface is plotted as a curve relative to the distance in the X-axis direction from the center of the upper surface Wb of wafer W.

[0115] In addition, Figure 7 In the example shown, as a comparative example of the upper surface height position of wafer W detected by AF device 200, the upper surface height position detected by a crack detection device with an existing interface detection mechanism (hereinafter sometimes referred to as an existing crack detection device or existing structure, etc.) is shown.

[0116] exist Figure 7 In the diagram, the vertical axis represents the height position of the upper surface (surface height position), and the horizontal axis represents the distance along the X-axis from the center of the upper surface Wb of wafer W. Furthermore, in... Figure 7 In the diagram, the height position detection results of the AF device 200 on the upper surface Wb are shown in solid lines, while the height position detection results of the upper surface Wb of the existing structure are shown in dashed lines.

[0117] from Figure 7 It can be seen that the height position of the upper surface of wafer W detected by AF device 200 is slightly different from the height position of the upper surface detected by existing crack detection device.

[0118] Figure 8 This is a diagram illustrating an example of the time-dependent change in the upper surface height position of an arbitrary point detected by an existing crack detection device versus the upper surface height position of an arbitrary point detected by the AF device 200.

[0119] exist Figure 8 In the example shown, the AF device 200 was used to detect the height position of the upper surface Wb at any point on the wafer W that was changing over time. For example, in Figure 8 In the process, the height position of the upper surface Wb at any point on the same location on the wafer W was detected for approximately 60 minutes using an AF device 200.

[0120] In addition, Figure 8 In the example shown, as a comparison, the upper surface height position detected by a conventional crack detection device under the same conditions as AF device 200 is illustrated. Figure 8 In the diagram, the detection results of the AF device 200 are shown in thick solid lines, while the detection results of the crack detection device with an existing interface detection mechanism are shown in dashed lines.

[0121] like Figure 8As shown, the detection results of the AF device 200 show a smaller deviation compared to those of existing crack detection devices. More specifically, the PV value (maximum-minimum value of the curve) of the existing crack detection device is 1.8 μm, while the PV value of the AF device 200 is 0.75 μm. Therefore, compared to existing crack detection devices, the AF device 200 can more stably and accurately detect the height position of the upper surface Wb on the wafer W.

[0122] Figure 9 This is a diagram showing an example of the upper position of a crack at any point detected by the crack detection device 300 of this embodiment and the upper position of a crack at any point detected by a conventional crack detection device.

[0123] exist Figure 9 The diagram shows the upper position of the crack at the processing point P detected by the crack detection device 300 of this embodiment (the detection result of this embodiment), and, as a comparative example, the upper position of the crack at the processing point P detected by a conventional crack detection device (the detection result of the conventional structure).

[0124] The existing 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 unit relative to the amount of movement of the lens drive unit (equivalent to the first actuator 108). The upper position of the crack K is detected by the same steps as in the crack detection device 300.

[0125] In this embodiment, the AF device 200 is used to detect the height position of the upper surface Wb of any processing point P on the wafer W. Based on the height position of the upper surface Wb, the crack detection device 300 is used to detect the upper end position of the crack K formed at the processing point P. The height position of the upper surface Wb of the AF device 200 is detected by calculating the AF signal based on the output signal output from the detector 238, as described above. Regarding the upper end position of the crack K, the presence of the crack K is determined by calculating an evaluation value S as described above and evaluating the evaluation value S and the focal point position information, thereby detecting the upper end position of the crack K.

[0126] exist Figure 9 In the measurement curve of the detection results of the existing structure, the solid line shows the detection signal detected by the existing crack detection device relative to the amount of movement of the lens drive unit corresponding to the first actuator 108, and the dashed line shows the signal associated with the upper surface height position detected by the interface detection mechanism of the existing crack detection device relative to the amount of movement of the lens drive unit.

[0127] exist Figure 9In the measurement curve of the detection results of this embodiment, the solid line shows the detection signal detected by the crack detection device relative to the amount of movement of the first actuator 108, and the dashed line shows the upper surface height position detected by the AF device 200 relative to the amount of movement of the first actuator 108.

[0128] also, Figure 9 The diagram shows the height position of the upper surface Wb and the upper end position of the crack K formed at the processing point P, as detected by existing crack detection devices and this embodiment. Figure 9 As shown, the upper surface height position and the upper end position of the crack corresponding to the test results of the existing structure are slightly different from those corresponding to the test results of this embodiment.

[0129] Figure 10 This is a flowchart illustrating an example of the laser processing method according to this embodiment.

[0130] The AF device 200 (or laser processing device 10) is positioned by the first actuator 108, adjusting the relative position of the predetermined processing point P' and the condenser lens 106 to a pre-set reference position in the Z direction (S1001). More specifically, the AF device 200 (or laser processing device 10) performs this positioning after placing the unprocessed wafer W on the stage 12.

[0131] The AF device 200 (or laser processing device 10) irradiates the predetermined processing point P' with the AF detection light L2 (S1002).

[0132] The AF device 200 (or laser processing device 10) detects the reflected light of the AF detection light L2 reflected at the predetermined processing point P' (S1003).

[0133] Then, the AF device 200 (or laser processing device 10) acquires (or detects) the AF signal E (S1004) based on the detected reflected light. That is, the AF device 200 acquires (or detects) the height position of the upper surface Wb of the wafer W.

[0134] The AF device 200 (or laser processing device 10) acquires the position of the condenser lens 106 adjusted by controlling the first actuator 108 based on the AF signal E (S1005). For example, the AF device 200 (or laser processing device 10) acquires the position of the condenser lens 106 when the condenser lens 106's focusing point is aligned with the upper surface Wb of the predetermined processing point P'.

[0135] The AF device 200 (or laser processing device 10) determines whether the height position of the upper surface Wb of the wafer W obtained based on the AF signal E is within the thickness detection range (S1006).

[0136] When it is determined that the height position of the upper surface Wb of the obtained wafer W is within the specified range ("Yes" in S1006), the AF device 200 sends the position of the condenser lens 106 to the lower surface detection unit 342 of the crack detection device 300 (S1007).

[0137] Immediately following S1007, the AF device 200 (or laser processing device 10) processes the predetermined processing point P' of the wafer W. For example, the processing laser L1 is irradiated to form a modified region R and / or a crack K inside the wafer W. Here, "immediately following" means, for example, that the processing of the wafer W is performed almost simultaneously with the completion of the upper surface height position detection (determination (S1006) or the sending of the condenser lens position (S1007)), or immediately after the upper surface height position detection is performed without any movement or change in the state of the wafer W.

[0138] When it is determined that the height position of the upper surface Wb of the acquired wafer W is not within the specified range ("No" in S1006), the AF device 200 adjusts the relative position (relative distance) of the wafer W and the condenser lens 106 in the Z direction (S1008) and performs the processing of S1002.

[0139] During the processing of wafer W, the AF device 200 (or laser processing device 10) controls the drive of the first actuator 108. By adjusting the position of the condenser lens 106 through the first actuator 108, the Z-direction position of the focusing point of the processing laser L1 is adjusted. The AF device 200 (or laser processing device 10) processes the interior of the predetermined processing point P' (forming a modified region R and / or a crack K) using the processing laser L1.

[0140] Since the processing laser L1 arrives at the interior of the predetermined processing point P' immediately or approximately simultaneously with the arrival of the detection light L2 in the AF process, the AF device 200 (or the laser processing device 10) forms a crack K and / or a modified region R inside the predetermined processing point P' immediately or approximately simultaneously with the detection (determination (S1006) or transmission of the condenser lens position (S1007)) of the upper surface height position of the predetermined processing point P'. Therefore, when the processing of the wafer W is performed immediately or approximately simultaneously with the detection of the upper surface height position, the crack detection device 300 can perform a lower surface height position detection based on the upper surface height position of the predetermined processing point P' before the formation of the modified region R and / or crack K. Thus, the lower surface height position, which serves as the reference for calculating the crack depth of crack K, can be detected more accurately.

[0141] Figure 11 This is a flowchart illustrating an example of the crack detection method according to this embodiment.

[0142] The crack detection device 300 detects the lower surface height position of the predetermined processing point P' of the wafer W based on the actual refractive index of the wafer W obtained in advance through simulation or the like (S1101). The crack detection device 300 also detects the lower surface height position of the predetermined processing point P' based, for example, on the actual refractive index of the wafer W and the upper surface height position of the predetermined processing point P' detected in S1004 (AF signal E).

[0143] The crack detection device 300 detects the reflected light L4 for crack detection (S1102). In detail, the crack detection device 300 controls the first actuator 108 to move the focusing point of the detection light L3 for crack detection from the lower surface height position of the processing point P along the Z direction, and sequentially detects the reflected light L4 for crack detection on the light-receiving surface of the photodetector 334 and the light-receiving surface of the photodetector 336.

[0144] The crack detection device 300 detects the presence or absence of cracks K based on the detection signals output from the photodetector 334 and the photodetector 336 (S1103).

[0145] When it is determined that there is no crack K ("No" in S1104), the crack detection device 300 ends the crack detection. When it is determined that there is a crack K ("Yes" in S1104), the crack detection device 300 detects (or calculates) the crack depth of crack K (S1105) and ends the crack detection.

[0146] For example, the crack detection device 300 calculates the evaluation value S based on the signals from the photodetectors 334 and 336, using the position of the condenser lens 106 corresponding to the height position of the lower surface Wa as a reference, and detects the presence or absence of crack K, or the lower or upper position of crack K (crack depth). Therefore, the time from detecting the height position of the upper surface Wb to the formation of a crack inside the wafer W can be shortened.

[0147] According to this embodiment, the laser processing apparatus 10 includes a stage 12, a laser head 20, an AF device 200, and a crack detection device 300. When processing wafer W, the AF device 200 generates (or acquires) an AF signal (the height position of the upper surface Wb) and outputs it to the crack detection device 300. When detecting cracks, the crack detection device 300 detects the height position of the lower surface Wa of wafer W based on the actual refractive index calculated in advance through simulation or the AF signal (the height position of the upper surface Wb) output from the AF device 200. Therefore, based on the height position of the upper surface Wb acquired approximately simultaneously with processing, the height position of the lower surface Wa, which serves as a reference during crack detection, can be detected. Compared to the existing method of detecting the upper surface height position through interface detection after laser processing, changes over time can be suppressed. 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 in crack detection. As a result, according to this embodiment, the accuracy of crack detection can be improved.

[0148] Furthermore, since the crack detection device 300 (or laser processing device 10) of this embodiment does not have an interface detection mechanism, it is not necessary to detect the actual refractive index and the height position of the upper surface Wb through interface detection, thus shortening the crack measurement time. Furthermore, since the crack detection device 300 (or laser processing device 10) of this embodiment does not have an interface detection mechanism, it can also reduce costs and achieve compactness.

[0149] Furthermore, in the first embodiment, an opening for detecting the height position of the upper surface (AF light source 202) and an opening for detecting cracks (light sources 302A and 302B) are respectively provided, but this is not a limitation. For example, a single opening may be used, and a light-shielding unit may be used to switch between the opening for detecting the height position of the upper surface and the opening for detecting cracks.

[0150] The following describes other embodiments and variations besides the first embodiment. In other embodiments and variations, the same reference numerals are used to mark the same structures as in the first embodiment, and detailed descriptions are omitted.

[0151] (Modified example)

[0152] The modified crack detection device 300 does not detect (or calculate) the height position of the lower surface Wa of the predetermined processing point P' by multiplying the position B of the focusing point in equation (2) by the actual refractive index n as shown in the first embodiment. Instead, it detects (or calculates) the height position of the lower surface Wa of the predetermined processing point P' based on the position of the focusing lens 106.

[0153] Figure 12This is a schematic diagram showing the various parameters required to calculate the lower surface height position of a predetermined machining point based on the position of the condenser lens.

[0154] exist Figure 12 In the text, L represents... Figure 10 The distance between the adjusted position of the condenser lens 106 (S1001, etc.) and the predetermined processing point P'. ΔL (not shown) is, for example, the distance between the position of the condenser lens 106 and the predetermined processing point P'. Figure 10 The distance between the position of the condenser lens 106, after readjustment by S1008, and the predetermined processing point P'. Figure 12 In this context, ΔP represents the expansion of the first actuator 108 when a voltage is applied to it (with the positive Z-axis direction as positive).

[0155] The distance ΔZ from the position of the condenser lens 106 to the height position of the lower surface Wa can be represented by the following formula (4).

[0156] ΔZ=nB+L+(ΔL+ΔP)…(4)

[0157] For example, the crack detection device 300 detects (or calculates) the height position of the lower surface Wa of the predetermined processing point P' based on the actual refractive index n and the AF signal output from the AF signal processing unit 262 (the position T of the focusing point when aligned with the upper surface Wb of the predetermined processing point P'). According to this modified example, the same effect as the first embodiment can be obtained.

[0158] (Second Implementation)

[0159] The laser processing apparatus 10A and crack detection apparatus 300A of the second embodiment differ in structure from those of 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. Furthermore, the crack detection apparatus 300A differs from the crack detection apparatus 300 of the first embodiment in that its crack detection control unit 340 includes a light source control unit 261 and an AF signal processing unit 262.

[0160] Figure 13 This is a schematic diagram showing a structural example of the laser processing apparatus 10A and the crack detection apparatus 300A according to the second embodiment.

[0161] In the second embodiment, the laser processing apparatus 10A includes a stage 12, a laser head 20, and a control unit 50, etc.

[0162] The control unit 50 controls various parts of the laser processing apparatus 10A and the laser head 20. The control unit 50 includes, for example, a processing laser control unit 263, a first lens drive unit control unit 264, and a stage control unit 265. The control unit 50 is connected, for example, to the crack detection control unit 340 of the crack detection apparatus 300A. Furthermore, the control unit 50 can also control the crack detection apparatus 300A.

[0163] The crack detection device 300A includes an AF device 200, a light source unit 301, an illumination optical system 310, a semi-transparent mirror 322, a semi-transparent mirror 324, a crack detection optical system 330, and a crack detection control unit 340.

[0164] The AF device 200 includes a focusing optical system 206, a second actuator 216, a semi-transparent mirror 220, an imaging lens 236, and a detector 238.

[0165] The crack detection control unit 340 is connected to and controls various parts of the first actuator 108 and the crack detection device 300A, such as the AF device 200, the light source unit 301, the illumination optical system 310, the semi-transparent mirror 322, the semi-transparent mirror 324, the crack detection optical system 330, and the crack detection control unit 340 itself. The crack detection control unit 340 can transmit and receive various data, information, and signals with the control unit 50. Furthermore, the crack detection control unit 340 can also control various parts within the laser processing apparatus 10A.

[0166] The crack detection and control unit 340 includes a light source control unit 261, an AF signal processing unit 262, a lower surface detection unit 342, a crack detection unit 343, and a second lens drive unit control unit 344.

[0167] According to the second embodiment, the same effects as the first embodiment and its variations can be obtained.

[0168] Furthermore, the technical scope of the present invention is not limited to the aforementioned embodiments and variations. Various modifications can be made without departing from the spirit of the present invention.

[0169] Symbol Explanation

[0170] 10, 10A Laser Processing Equipment

[0171] 100 Laser source for processing

[0172] 108 First actuator (lens drive unit)

[0173] 200 AF device

[0174] 202 AF Light Source

[0175] 216 Second Actuator

[0176] 238 detectors

[0177] 264 First Lens Drive Unit Control Section

[0178] 300, 300A Crack Detection Device

[0179] 340 Crack Detection and Control Department

[0180] 342 Lower Surface Inspection Unit

[0181] 343 Crack Detection Department

[0182] 344 Second Lens Drive Unit Control Section

[0183] W wafer

[0184] Wa lower surface

[0185] Wb upper surface

[0186] L1 laser for processing

[0187] L2 AF detection light

Claims

1. A laser processing apparatus comprising: a light source for emitting a processing laser onto a workpiece to form a modified region within the workpiece; a focusing lens for focusing the processing laser onto the workpiece; and a lens driving unit for moving the focusing lens to displace the focusing point of the processing laser in the thickness direction of the workpiece, wherein... The laser processing apparatus includes: The upper surface height position detection unit detects the upper surface height position of the workpiece; and The crack detection unit detects the depth of cracks formed inside the workpiece. The upper surface height position detection unit detects the upper surface height position when the processing laser processes the workpiece. The crack detection unit detects the lower surface height position of the workpiece based on its actual refractive index and the upper surface height position.

2. The laser processing apparatus according to claim 1, wherein, The actual refractive index is calculated through simulation based on the characteristics of the condenser lens and the light incident on the condenser lens.

3. The laser processing apparatus according to claim 1, wherein, The crack detection unit does not have a mechanism for detecting the height of the upper surface of the workpiece.

4. A laser processing method applied to a laser processing apparatus, the laser processing apparatus comprising: a light source for emitting a processing laser towards a workpiece to form a modified region within the workpiece; a focusing lens for focusing the processing laser onto the workpiece; a lens driving unit for moving the focusing lens to displace the focusing point of the processing laser in the thickness direction of the workpiece; an upper surface height position detection unit for detecting the height position of the upper surface of the workpiece; and a crack detection unit for detecting the crack depth of cracks formed within the workpiece, wherein... The height position of the upper surface is detected when the workpiece is processed by the processing laser. Based on the actual refractive index of the workpiece and the height position of the upper surface, the height position of the lower surface of the workpiece is detected.

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