Crack detection device

Abstract

To provide a crack detection device that enables miniaturization of the device. [Solution] The illumination optical system 104 (afocal optical system) of the crack detection device includes a first relay lens 130 located on the light source unit 102 side and a second relay lens 132 located on the objective lens 112 side. The first relay lens 130 is positioned so that the distance between it and the light source unit 102 is shorter than the focal length of the first relay lens 130, and the second relay lens 132 is positioned so that the distance between it and the pupil 112A of the objective lens 112 is longer than the focal length of the second relay lens 132.

Description

Technical Field

[0001] The present invention relates to a technique for forming a laser processing region inside a workpiece by irradiating the workpiece with laser light while aligning the condensing point inside the workpiece.

Background Art

[0002] Conventionally, there has been known a technique for forming a laser processing region serving as a starting point for cutting inside a workpiece along a planned cutting line of the workpiece by irradiating the workpiece with laser light while aligning the condensing point inside the workpiece (see, for example, Patent Document 1).

[0003] In the technique described in Patent Document 1, the laser light is modulated by a spatial light modulator so that the aberration of the laser light generated at the position where the condensing point of the laser light inside the workpiece is aligned is below a predetermined aberration. Specifically, in this technique, an adjustment optical system having a first lens and a second lens is provided on the optical path of the laser light between the spatial light modulator and the condensing optical system. Then, the distance between the spatial light modulator and the first lens is the focal length f1 of the first lens, the distance between the condensing optical system and the second lens is the focal length f2 of the second lens, the distance between the first lens and the second lens is f1 + f2, and the first lens and the second lens are arranged so as to form a bilateral telecentric optical system.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the arrangement described in Patent Document 1, the spatial light modulator and the principal point of the focusing optical system are optically conjugate, so it is not always possible to obtain the desired light distribution at the focal plane (processing point) of the focusing optical system, making it difficult to correct aberrations with a predetermined accuracy. As a result, the effects of aberrations cannot be sufficiently suppressed, and there is a problem in that the laser processing region that serves as the starting point for cutting cannot be formed with high precision and efficiency.

[0006] The present invention has been made in view of these circumstances, and aims to provide an afocal optical system that can suppress the effects of aberrations and form a laser processing region that serves as the starting point for cutting with high precision and efficiency, as well as a laser processing apparatus equipped with the afocal optical system and a crack detection apparatus. [Means for solving the problem]

[0007] To achieve the above objective, the following invention is provided.

[0008] A laser processing apparatus according to a first aspect of the present invention is a laser processing apparatus that forms a laser processing region inside a workpiece by irradiating it with laser light while focusing the light point inside the workpiece, and comprises a spatial light modulator for modulating laser light, a processing lens for focusing the laser light modulated by the spatial light modulator into the workpiece, and a double-sided telecentric relay optical system having a first lens and a second lens and arranged on the optical path between the spatial light modulator and the processing lens, wherein the spatial light modulator and the lens pupil of the processing lens are in an optically conjugate relationship.

[0009] In the laser processing apparatus according to the second aspect of the present invention, in the first aspect, the distance between the second lens and the lens pupil is longer than the focal length of the second lens.

[0010] In the laser processing apparatus according to the third aspect of the present invention, in the first or second aspect, the optical modulation surface of the spatial light modulator and the lens pupil are in an optically conjugate relationship.

[0011] A laser processing apparatus according to a fourth aspect of the present invention includes a spatial light modulator control unit that controls a spatial light modulator so that the aberration of the laser light generated at the position where the focal point of the laser light inside the workpiece is aligned is less than or equal to a predetermined aberration, in any one aspect of the first to third aspects.

[0012] A fifth aspect of the present invention is a laser processing method for forming a laser processing region inside a workpiece by irradiating it with laser light while focusing the light point inside the workpiece. The method comprises a spatial light modulator for modulating laser light and a processing lens for focusing the laser light modulated by the spatial light modulator into the workpiece. A double-sided telecentric relay optical system having a first lens and a second lens is arranged on the optical path between the spatial light modulator and the processing lens. The spatial light modulator and the lens pupil of the processing lens are arranged to be optically conjugate. The spatial light modulator is controlled so that the aberration of the laser light generated at the position where the focus point of the laser light inside the workpiece is aligned is less than or equal to a predetermined aberration.

[0013] An afocal optical system according to another aspect of the present invention is an afocal optical system that relays light between an objective lens used for processing or measuring a workpiece and an optical element positioned conjugate to the pupil of the objective lens, comprising a first lens positioned on the optical element side and a second lens positioned on the objective lens side, wherein the distance between the second lens and the pupil of the objective lens is longer than the focal length of the second lens.

[0014] In the afocal optical system described above, the first lens is positioned such that the distance between it and the optical element is shorter than the focal length of the first lens.

[0015] Another aspect of the present invention relates to a laser processing apparatus comprising an objective lens, an optical element, and the above-mentioned afocal optical system, wherein the optical element is a spatial light modulator that modulates laser light to be focused into the inside of a workpiece and irradiated to form a laser processing area inside the workpiece, and the afocal optical system relays the laser light modulated by the spatial light modulator to the objective lens.

[0016] A crack detection device according to another aspect of the present invention comprises an objective lens, an optical element, and the above-mentioned afocal optical system, wherein the optical element is a laser light source that outputs laser light for detecting cracks extending from a laser-processed area formed inside a workpiece, the afocal optical system relays the laser light output from the laser light source to the objective lens, and the objective lens further comprises a detector that irradiates the inside of the workpiece with the laser light and detects the laser light reflected by cracks inside the workpiece or by the back surface.

[0017] A crack detection device according to another aspect of the present invention comprises an objective lens, an optical element, and the above-mentioned afocal optical system, wherein the optical element is a detector that detects laser light reflected by the crack inside the workpiece or the back surface when irradiated onto a crack extending from a laser processing area formed inside the workpiece, the objective lens receives the laser light reflected from the inside or back surface of the workpiece, and the afocal optical system relays the laser light incident on the objective lens to the detector. [Effects of the Invention]

[0018] According to the present invention, the laser processing region that serves as the starting point for cutting can be formed with high precision and efficiency while suppressing the effects of aberrations. [Brief explanation of the drawing]

[0019] [Figure 1] This is a schematic diagram showing a laser processing apparatus according to one embodiment of the present invention. [Figure 2] This is a block diagram showing the configuration of the control device in a laser processing machine. [Figure 3] This is a conceptual diagram illustrating the laser processing region formed near the focal point inside the wafer. [Figure 4] This is a conceptual diagram illustrating the laser processing region formed near the focal point inside the wafer. [Figure 5] This is a conceptual diagram illustrating a state in which laser-processed areas are formed in a multi-layered structure within a wafer. [Figure 6]This is a diagram showing an example of an optical system layout configuration in a laser processing apparatus. [Figure 7] This diagram shows another example of an optical system arrangement configuration in a laser processing apparatus. [Figure 8] This is a flowchart illustrating the aberration adjustment method for the laser processing apparatus of this embodiment. [Figure 9] This diagram illustrates the aberration adjustment method for the laser processing apparatus of this embodiment. [Figure 10] This diagram illustrates the aberration adjustment method for the laser processing apparatus of this embodiment. [Figure 11] This diagram illustrates the aberration adjustment method for the laser processing apparatus of this embodiment. [Figure 12] This is a schematic diagram showing an example of a laser processing apparatus equipped with an aberration change detection device. [Figure 13] This is a schematic diagram showing another example of a laser processing apparatus equipped with an aberration change detection device. [Figure 14] This figure shows a crack detection device according to one embodiment of the present invention. [Figure 15] This diagram shows the optical arrangement of the main components of the crack detection device, including the illumination optical system. [Figure 16] This diagram shows the optical arrangement of the main components of the crack detection device, including the detection optical system. [Figure 17] This is an explanatory diagram showing what happens when a workpiece is illuminated by the biased beam of detection light. [Figure 18] This diagram illustrates the path that reflected light from a workpiece takes to reach the lens pupil. [Modes for carrying out the invention]

[0020] Embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0021] (Configuration of laser processing equipment) Figure 1 is a schematic diagram showing a laser processing apparatus according to one embodiment of the present invention. As shown in Figure 1, the laser processing apparatus 10 of this embodiment comprises a stage 12, a processing apparatus body (optical system unit) 20, a processing lens 26, and a control device 50. In this embodiment, the processing apparatus body 20 and the control device 50 are configured separately, but the configuration is not limited to this, and the processing apparatus body 20 may include part or all of the control device 50.

[0022] Stage 12 is used to hold the workpiece by suction. Stage 12 is configured to be movable in the X and θ directions by a stage drive mechanism 28 (see Figure 2). The stage drive mechanism 28 can be composed of various mechanisms, such as a ball screw mechanism or a linear motor mechanism. The operation of the stage drive mechanism 28 is controlled by a control device 50 (movement control unit 54). In Figure 1, the three directions X, Y, and Z are orthogonal to each other, of which the X and Y directions are horizontal, and the Z direction is vertical. The θ direction is a rotational direction with the vertical axis (Z axis) as the axis of rotation.

[0023] In this embodiment, a semiconductor wafer (hereinafter referred to as "wafer") W, such as a silicon wafer, is used as the workpiece. The wafer W is divided into multiple regions by cutting lines arranged in a grid pattern, and various devices constituting a semiconductor chip are formed in each of these divided regions. In this embodiment, the case in which wafer W is used as the workpiece is described, but the present invention is not limited to this, and for example, glass substrates, piezoelectric ceramic substrates, glass substrates, etc. can also be used.

[0024] A wafer W has a backgrind tape (hereinafter referred to as BG tape) with adhesive material attached to the surface (device surface) on which the device is formed, and is placed on the stage 12 with the back surface facing upwards. There are no particular restrictions on the thickness of the wafer W, but it is typically 700 μm or more, and more typically 700 to 800 μm.

[0025] Alternatively, the wafer W may be placed on the stage 12 with a dicing tape having an adhesive material attached to one side, and the wafer W integrated with the frame via this dicing tape.

[0026] The processing apparatus body 20 comprises a housing 21, a laser light source 22, a spatial light modulator 24, a relay optical system 30, a beam expander 32, and a λ / 2 wave plate 34.

[0027] Inside the housing 21 are a laser light source 22, a spatial light modulator 24, a relay optical system 30, a beam expander 32, and a λ / 2 wave plate 34. The laser light source 22 may also be located outside the housing 21 (for example, on the top or side of the housing 21). A processing lens 26 is detachably attached to the bottom of the housing 21.

[0028] The processing apparatus body 20 is configured to be movable in the Y and Z directions by a body drive mechanism 29 (see Figure 2). The body drive mechanism 29 can be composed of various mechanisms, such as a ball screw mechanism or a linear motor mechanism. The operation of the body drive mechanism 29 is controlled by a control device 50 (movement control unit 54). This allows the processing apparatus body 20 to be moved in the Y direction and also moved in the Z direction according to the processing position on the wafer W (the position where the laser processing area is formed). Therefore, the position of the focal point of the laser beam L focused by the processing lens 26 can be changed to form the laser processing area at a desired position on the wafer W.

[0029] The laser light source (IR laser light source) 22 emits laser light L for processing to form a laser processing area inside the wafer W. The emission operation of the laser light L by the laser light source 22 is controlled by the control device 50 (laser control unit 56). The conditions for the laser light L are, for example, a semiconductor laser-pumped Nd:YAG laser as the light source, a wavelength of 1.1 μm, and a laser light spot cross-section of 3.14 × 10⁻¹⁴. -8 cm 2The oscillation mode is Q-switched pulse, the repetition frequency is 80-200 kHz, the pulse width is 180-370 ns, and the output power is 8 W.

[0030] The spatial light modulator 24 is a phase-modulation type spatial light modulator that has a light modulation surface consisting of multiple pixels (micro-modulation elements) arranged in two dimensions, and modulates the phase of light incident on the light modulation surface pixel by pixel. The spatial light modulator 24 is positioned at a position optically conjugate to the lens pupil (exit pupil) 26a of the processed lens 26 (see Figures 6 and 7). Based on a predetermined modulation pattern set by the spatial light modulator control unit 58, which will be described later, the spatial light modulator 24 modulates the phase of light incident on the light modulation surface pixel by pixel and emits the modulated light in a predetermined direction. For example, a reflective liquid crystal on silicon (LCOS) spatial light modulator (SLM) is used as the spatial light modulator 24. The operation of the spatial light modulator 24 and the modulation pattern presented by the spatial light modulator 24 are controlled by the control device 50 (spatial light modulator control unit 58). The modulation pattern may be a pattern (two-dimensional information) in which control values ​​(phase change amounts) corresponding to each of the multiple pixels constituting the optical modulation surface of the spatial light modulator 24 are distributed in two dimensions, or it may be something like coefficient information when the modulation within the modulation region (optical modulation surface) is expressed as a function. Since the specific configuration of the spatial light modulator 24 is already publicly known, a detailed explanation is omitted here.

[0031] The processing lens 26 is an objective lens (focusing optical system) that focuses the laser beam L into the wafer W. The numerical aperture (NA) of this processing lens 26 is, for example, 0.65.

[0032] The relay optical system 30 is provided in the optical path of the laser beam L between the spatial light modulator 24 and the processing lens 26. The relay optical system 30 has at least two lenses 30a and 30b (hereinafter referred to as "first lens 30a" and "second lens 30b"). The relay optical system 30 constitutes an afocal optical system (a bilaterally telecentric optical system) and projects the laser beam L modulated by the spatial light modulator 24 onto the processing lens 26. This relay optical system 30 is a bilaterally telecentric reduction optical system, and its projection magnification (hereinafter simply referred to as "magnification") is less than 1 (for example, 0.66).

[0033] The beam expander 32 expands the laser light L emitted from the laser light source 22 to a beam diameter suitable for the spatial light modulator 24. The λ / 2 wave plate 34 adjusts the polarization plane of the laser light incident on the spatial light modulator 24.

[0034] Although not shown in the diagram, the processing apparatus body 20 is also equipped with an alignment optical system for aligning with the wafer W, and an autofocus unit for maintaining a constant distance (working distance) between the wafer W and the processing lens 26.

[0035] The control device 50 is implemented by a general-purpose computer, such as a personal computer or a microcomputer.

[0036] The control unit 50 includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and an input / output interface. In the control unit 50, various programs, such as control programs stored in ROM, are loaded into RAM, and the CPU executes the programs loaded into RAM. This realizes the functions of each part of the control unit 50 shown in Figure 2, and various arithmetic and control processes are executed via the input / output interface.

[0037] Figure 2 is a block diagram showing the configuration of the control device 50. As shown in Figure 2, the control device 50 functions as a main control unit 52, a motion control unit 54, a laser control unit 56, a spatial light modulator control unit 58, and a memory unit 60.

[0038] The main control unit 52 comprehensively controls each component of the control device 50 (including the movement control unit 54, laser control unit 56, spatial light modulator control unit 58, and memory unit 60).

[0039] The movement control unit 54 controls the relative movement between the stage 12 and the processing device body 20. The movement control unit 54 outputs control signals to the stage drive mechanism 28 to control the movement of the stage 12 in the X and θ directions, and outputs control signals to the main body drive mechanism 29 to control the movement of the processing device body 20 in the Y and Z directions.

[0040] The laser control unit 56 controls the emission of laser light L. The laser control unit 56 outputs control signals to the laser light source 22 that control the wavelength, pulse width, intensity, emission timing, and repetition frequency of the laser light L.

[0041] The spatial light modulator control unit 58 outputs a control signal to the spatial light modulator 24 to control its operation. In other words, the spatial light modulator control unit 58 controls the spatial light modulator 24 to present a predetermined modulation pattern. Specifically, the spatial light modulator control unit 58 sets a modulation pattern for the spatial light modulator 24 to modulate the laser light L so that the aberration of the laser light L generated at the position where the focal point of the laser light L is aligned inside the wafer W is less than or equal to a predetermined aberration.

[0042] The memory unit 60 is composed of an external memory (e.g., a hard disk or flexible disk) or internal memory (e.g., RAM or ROM made of semiconductor memory) provided in the control device 50. In addition to the various programs such as the control program described above, the memory unit 60 stores aberration correction information S. The aberration correction information S is the information that the spatial light modulator control unit 58 uses to determine the modulation pattern to be presented to the spatial light modulator 24. The aberration correction information S includes the first aberration correction information S1, the second aberration correction information S2, and the third aberration correction information S3, which will be described later.

[0043] Figures 3 and 4 are conceptual diagrams illustrating the laser processing region formed near the focal point inside the wafer. Figure 3 shows the state in which a laser beam L incident inside the wafer W forms a laser processing region P at the focal point. Figure 4 shows the state in which the wafer W is moved horizontally under pulsed laser beam L, and discontinuous laser processing regions P, P, ... are formed in a row. In this state, the wafer W either breaks naturally starting from the laser processing region P, or it can be broken starting from the laser processing region P by applying a slight external force. In this case, the wafer W is easily divided into chips without chipping occurring on the front or back surface.

[0044] Figure 5 is a conceptual diagram illustrating a state in which laser processing regions are formed in multiple layers inside a wafer. When the wafer W is thick and a single layer of laser processing region P is insufficient to cleave it, as shown in Figure 5, the laser processing region P can be formed in multiple layers by changing the focal point of the laser beam L in the thickness direction of the wafer W and scanning the wafer W with the laser beam L multiple times. Using the laser processing region P thus formed in multiple layers as a starting point, the wafer W will either cleave naturally or cleave with a small external force.

[0045] Although Figures 3 to 5 show discontinuous laser processing regions P, P, ... formed by pulsed laser light L, a continuous laser processing region P may also be formed under a continuous wave of laser light L.

[0046] (Operation of the laser processing machine) Next, the operation (laser processing method) of the laser processing apparatus 10 of this embodiment will be described.

[0047] First, the wafer W to be processed is placed on the stage 12 with its back surface (opposite to the device surface) facing upwards (i.e., with the device surface of the wafer W facing the stage 12). Then, the wafer W is aligned using an alignment optical system (not shown). After that, the height position (Z-direction position) of the processing apparatus body 20 relative to the wafer W is adjusted so that the focal point of the laser beam L focused by the processing lens 26 is at a predetermined depth (processing depth) from the laser beam incident surface of the wafer W. This sets the distance between the processing lens 26 and the wafer W (working distance) to an appropriate distance corresponding to the processing depth.

[0048] Next, the wafer W is irradiated with laser light L and moved relative to it along the planned cutting line. The relative movement of the laser light L is performed by feeding the stage 12, which holds the wafer W by adsorption, in the X direction.

[0049] At this time, the laser light L emitted from the laser light source 22 is reflected by the mirror 36 and incident on the beam expander 32. The laser light L incident on the beam expander 32 has its beam diameter expanded by the beam expander 32 and is emitted from the beam expander 32. The laser light L emitted from the beam expander 32 is reflected by the mirror 38 and incident on the λ / 2 wave plate 34. The laser light L incident on the λ / 2 wave plate 34 has its polarization direction changed by the λ / 2 wave plate 34 and is emitted from the λ / 2 wave plate 34. The laser light L emitted from the λ / 2 wave plate 34 is incident on the spatial light modulator 24.

[0050] The laser light L incident on the spatial light modulator 24 is modulated according to a predetermined modulation pattern presented to the spatial light modulator 24 and emitted from the spatial light modulator 24. At this time, the spatial light modulator control unit 58 sets a modulation pattern for modulating the laser light L in the spatial light modulator 24 so that the aberration of the laser light L generated at the position where the focal point of the laser light L is aligned inside the wafer W is less than or equal to a predetermined aberration. The spatial light modulator 24 presents the modulation pattern set by the spatial light modulator control unit 58. As a result, the aberration of the laser light L generated at the position where the focal point of the laser light L is aligned inside the wafer W is less than or equal to a predetermined aberration.

[0051] The laser beam L emitted from the spatial light modulator 24 is sequentially reflected by mirrors 40 and 42, then passes through the first lens 30a, is sequentially reflected again by mirrors 44 and 46, passes through the second lens 30b, and enters the processing lens 26. Thus, the laser beam L emitted from the spatial light modulator 24 is projected onto the processing lens 26 by the relay optical system 30 having the first lens 30a and the second lens 30b. The laser beam L that enters the processing lens 26 is then focused by the processing lens 26 into the wafer W placed on the stage 12. As a result, a laser processing region is formed inside the wafer W near the focal point of the laser beam L. Therefore, one scan along the planned cutting line can form a single layer of laser processing inside the wafer W.

[0052] In this way, once a single scan along the planned cutting line forms one layer of laser-processed material inside the wafer W, the processing device body 20 is indexed and fed one pitch in the Y direction, and the next planned cutting line is similarly processed to form a laser-processed material.

[0053] Once laser processing areas are formed along all planned cutting lines parallel to the X direction, stage 12 is rotated 90°, and laser processing areas are formed in the same way along lines perpendicular to the previous lines. As a result, laser processing areas are formed along all planned cutting lines.

[0054] After the laser processing area is formed along the planned cutting line as described above, a backside grinding process is performed using a grinding device (not shown) to grind the backside of the wafer W and thin the wafer W.

[0055] After the back grinding process, an expandable tape (dicing tape) is attached to the back surface of the wafer W. After the BG tape attached to the front surface of the wafer W is peeled off, an expandable process is performed in which tension is applied to the expandable tape attached to the back surface of the wafer W to stretch it. As a result, the wafer W is cut along the planned cutting line, starting from the laser-modified region formed inside the wafer W, and divided into multiple chips.

[0056] (Optical system configuration of laser processing equipment) Next, the optical system configuration in the laser processing apparatus 10 will be described in detail. Figure 6 is a diagram showing an example of the optical system configuration in the laser processing apparatus 10. In Figure 6, parts unrelated to the explanation have been omitted in order to make the optical arrangement relationship of the spatial light modulator 24, processing lens 26, and relay optical system 30 easier to understand. Also, in Figure 6, f1 is the focal length of the first lens 30a, f2 is the focal length of the second lens 30b, and fobj is the focal length of the processing lens 26. The same applies to Figure 7, which will be described later.

[0057] As shown in Figure 6, in this embodiment, the spatial light modulator 24 and the lens pupil 26a of the processed lens 26 are optically conjugate.

[0058] Specifically, a relay optical system 30 is positioned between the spatial light modulator 24 and the processing lens 26. The relay optical system 30 has a first lens 30a and a second lens 30b that constitute a bilaterally telecentric reduction optical system. That is, the distance between the first lens 30a and the second lens 30b is the sum of the focal length f1 of the first lens 30a and the focal length f2 of the second lens 30b (f1+f2). Also, the distance between the spatial light modulator 24 and the first lens 30a is the focal length f1 of the first lens 30a, and the distance between the lens pupil 26a of the processing lens 26 and the second lens 30b is the focal length f2 of the second lens 30b.

[0059] As shown in the optical system configuration in Figure 6, the components (optical system) are arranged such that the spatial light modulator 24 and the lens pupil 26a of the processing lens 26 are optically conjugate. Therefore, the wavefront shape formed by the spatial light modulator 24 is projected onto the lens pupil 26a of the processing lens 26, and the desired light distribution can be obtained at the focal plane (processing point) of the processing lens 26. This suppresses the effects of aberrations and allows for the formation of the laser processing region, which serves as the starting point for cutting, with high precision and efficiency.

[0060] Furthermore, the optical system arrangement shown in Figure 6 makes it easier to align (position) each optical system when assembling it, and also makes it easier to control the spatial light modulator 24 to suppress aberrations of the laser beam L that occur at the position where the focal point of the laser beam L is aligned inside the wafer W, compared to the case where the spatial light modulator 24 and the principal point of the processed lens 26 are arranged to be optically conjugate.

[0061] In this embodiment, more precisely, it is desirable that the optical modulation surface (reflecting surface) of the spatial light modulator 24 and the lens pupil 26a of the processed lens 26 be optically conjugate. However, if the effect of the change in wavefront shape when projecting the wavefront shape formed by the spatial light modulator 24 onto the lens pupil 26a of the processed lens 26 is small, the lens pupil 26a of the processed lens 26 may be optically conjugate to a position shifted from the optical modulation surface of the spatial light modulator 24 (for example, the surface of the spatial light modulator 24 or near its surface). In this case, adjustment of the optical system becomes easier.

[0062] Furthermore, in this embodiment, as an example of a preferred configuration, a configuration is shown in which the distance between the lens pupil 26a of the processed lens 26 and the second lens 30b is the focal length f2 of the second lens 30b. However, the optical system arrangement is not limited to the configuration shown in Figure 6, as long as the spatial light modulator 24 and the lens pupil 26a of the processed lens 26 are optically conjugate.

[0063] Figure 7 is a diagram showing another example of the optical system arrangement configuration in the laser processing apparatus 10. As shown in Figure 7, in this other example of the optical system arrangement configuration, the distance between the pupil 26a of the processing lens 26 and the second lens 30b is longer than the focal length f2 of the second lens 30b. In this case, the distance between the spatial light modulator 24 and the first lens 30a is shorter than the focal length f1 of the first lens 30a.

[0064] Specifically, as shown in Figure 7, if we let g2 be the distance between the pupil 26a of the processed lens 26 and the second lens 30b, and Δx2 be the absolute value of the difference between that distance g2 and the focal length f2 of the second lens 30b (|g2-f2|), and let g1 be the distance between the spatial light modulator 24 and the first lens 30a, and Δx1 be the absolute value of the difference between that distance g1 and the focal length f1 of the first lens 30a (|g1-f1|), then the following equation is satisfied.

[0065] Δx² = (f² / f¹) 2 ×Δx1···(1) Furthermore, if the magnification (f2 / f1) of the relay optical system 30 (a double-sided telecentric reduction optical system) is m, then equation (1) can be expressed as equation (2) below.

[0066] Δx² = m 2 ×Δx1···(2) According to the optical system configuration shown in Figure 7, each component (optical system) is arranged such that the spatial light modulator 24 and the lens pupil 26a of the processed lens 26 are optically conjugate, thus achieving the same effect as the optical system configuration shown in Figure 6.

[0067] Furthermore, according to the optical system arrangement shown in Figure 7, even if the distance between the second lens 30b and the processing lens 26 cannot be shortened due to mechanical constraints, a lens with a smaller focal length can be used as the second lens 30b, contributing to the miniaturization of the device. In other words, in this optical system arrangement, as a means of making the optical system in the laser processing device 10 compact, a lens with a focal length shorter than the distance between the second lens 30b and the processing lens 26 (the second lens 30b) is used to shorten the overall length of the relay optical system 30, thereby enabling the optical system to be made more compact.

[0068] (Method for adjusting aberrations in laser processing equipment) Next, the aberration adjustment method in the laser processing apparatus 10 of this embodiment will be described.

[0069] Due to individual differences in the laser processing device 10, the effect of aberrations occurring in the laser processing device 10 varies from device to device. Therefore, it is necessary to perform adjustment work for aberrations occurring in the laser processing device 10 during the manufacturing stage.

[0070] For example, if the aberrations (wavefronts) generated in the entire laser processing apparatus, including the processing device body and processing lens, are measured collectively, and adjustments are made to cancel out these aberrations, then it becomes impossible to predict what kind of aberrations will occur in the entire laser processing apparatus if the processing lens is replaced with a different one, and it becomes impossible to compensate for the aberrations generated in the laser processing apparatus. In this case, it becomes impossible to suppress the aberrations generated in the laser processing apparatus, which leads to problems in forming the laser processing area with high precision and efficiency.

[0071] In this embodiment, in order to solve these problems, aberration adjustment work is performed during the manufacturing stage of the laser processing apparatus 10 as follows.

[0072] Figure 8 is a flowchart showing the aberration adjustment method for the laser processing apparatus 10 of this embodiment. Figures 9 to 11 are diagrams illustrating the aberration adjustment method for the laser processing apparatus 10 of this embodiment. The aberration adjustment method for the laser processing apparatus 10 of this embodiment will be described below in accordance with the flowchart shown in Figure 8. In this embodiment, the laser processing apparatus 10 can be used by exchanging multiple processing lenses 26 with different magnifications.

[0073] [First aberration correction information acquisition process] First, first aberration correction information S1 is acquired and stored to correct the aberrations of the processing apparatus body 20 (steps S10 to S16).

[0074] Specifically, as shown in Figure 9, in the laser processing apparatus 10 with the processing lens 26 removed, a wavefront sensor 70 is placed at a position corresponding to the vicinity of the pupil of the processing lens 26 (it does not need to be precisely). The wavefront of the laser light L output from the processing apparatus body 20 is then measured by the wavefront sensor 70 (step S10). The wavefront measured by the wavefront sensor 70 is output to the spatial light modulator control unit 58.

[0075] The spatial light modulator control unit 58 adjusts the modulation pattern of the spatial light modulator 24 based on the wavefront measured by the wavefront sensor 70 (step S12). Specifically, the spatial light modulator control unit 58 changes the modulation pattern set for the spatial light modulator 24 so that the wavefront measured by the wavefront sensor 70 approaches a plane wave.

[0076] Next, the spatial light modulator control unit 58 determines whether the wavefront measured by the wavefront sensor 70 is a plane wave without aberrations (step S14). If it is determined that the wavefront measured by the wavefront sensor 70 is not a plane wave, the process returns to step S10. Then, the process from step S10 to step S14 is repeated until it is determined that the wavefront measured by the wavefront sensor 70 is a plane wave.

[0077] On the other hand, if the wavefront measured by the wavefront sensor 70 is determined to be a plane wave, the spatial light modulator control unit 58 stores the modulation pattern set in the spatial light modulator 24 when it is determined to be a plane wave as first aberration correction information S1 in the memory unit 60 (step S16).

[0078] [Second aberration correction information acquisition process] Next, second aberration correction information S2 for correcting the aberrations of the processed lens 26 is acquired and stored (steps S18 to S28).

[0079] Specifically, as shown in Figure 10, a processing lens 26 is attached to the laser processing apparatus 10, and a planar mirror 72 is placed opposite the processing lens 26. The position where the planar mirror 72 is placed serves as a reference (aberration correction reference) for correcting the aberrations of the processing lens 26, and preferably, the planar mirror 72 is placed at the focal point of the processing lens 26.

[0080] Furthermore, the beam splitter (e.g., a half-mirror) 74 and the wavefront sensor 76 are arranged as shown in Figure 10. That is, the beam splitter 74 is placed on the optical path of the laser beam L, behind the processing lens 26 (on the side into which the laser beam L is incident). Then, the laser beam L from the laser light source 22 is irradiated onto the plane mirror 72 via the processing lens 26, the reflected light from the plane mirror 72 is incident on the wavefront sensor 76 via the processing lens 26, and the wavefront of the reflected light incident on the wavefront sensor 76 is measured by the wavefront sensor 76 (step S18). The wavefront measured by the wavefront sensor 76 is output to the spatial light modulator control unit 58.

[0081] Furthermore, since the optical path of the laser beam L directed towards the plane mirror 72 passing through the processing lens 26 and the optical path of the laser beam L reflected by the plane mirror 72 passing through the processing lens 26 pass through symmetrical positions around the optical axis of the processing lens 26, the wavefront sensor 76 cannot measure asymmetric aberration, but it can measure symmetric aberration of the processing lens 26.

[0082] The spatial light modulator control unit 58 adjusts the modulation pattern of the spatial light modulator 24 based on the wavefront measured by the wavefront sensor 76 (step S20). Specifically, the spatial light modulator control unit 58 changes the modulation pattern set for the spatial light modulator 24 so that the wavefront measured by the wavefront sensor 76 approaches a plane wave.

[0083] Next, the spatial light modulator control unit 58 determines whether the wavefront measured by the wavefront sensor 76 is a plane wave without aberrations (step S22). If it is determined that the wavefront measured by the wavefront sensor 76 is not a plane wave, the process returns to step S18. The spatial light modulator control unit 58 then repeats the process from step S18 to step S22 until it is determined that the wavefront measured by the wavefront sensor 76 is a plane wave.

[0084] On the other hand, if the wavefront measured by the wavefront sensor 76 is determined to be a plane wave, the spatial light modulator control unit 58 stores the modulation pattern set in the spatial light modulator 24 when it is determined to be a plane wave in the memory unit 60 as total aberration correction information T1.

[0085] Here, if we denote the aberration of the processing apparatus body 20 as R1, the aberration of the processing lens 26 as R2, and the aberration included in the wavefront measured by the wavefront sensor 76 (total aberration) as RA, then the following equation (3) holds.

[0086] RA = R1 + 2 × R2 ... (3) By rearranging equation (3), we obtain the following equation (4).

[0087] R2 = (RA - R1) / 2 ... (4) This is because the laser light L emitted from the laser light source 22 passes through the components of the processing apparatus body 20 (including the spatial light modulator 24 and the relay optical system 30) and is irradiated onto the plane mirror 72 via the processing lens 26, and the reflected light from the plane mirror 72 is guided to the wavefront sensor 76 via the processing lens 26, and its wavefront is measured by the wavefront sensor 76. In other words, the aberration RA included in the wavefront measured by the wavefront sensor 76 can be expressed as the sum of the aberration R1 of the processing apparatus body 20 and twice the aberration R2 of the processing lens 26.

[0088] As can be understood from the above, the second aberration correction information S2 corresponds to half the control value (phase change amount) for each pixel in the differential aberration correction information, when the difference between the total aberration correction information T1 and the first aberration correction information S1 is used as differential aberration correction information. In other words, the second aberration correction information S2 can be simply represented by the following equation (5).

[0089] S2 = (T1 - S1) / 2 ... (5) In this way, the spatial light modulator control unit 58 obtains the second aberration correction information S2 based on the first aberration correction information S1 and the total aberration correction information T1 stored in the memory unit 60. Then, the spatial light modulator control unit 58 stores the second aberration correction information S2 in the memory unit 60 in association with the processed lens 26 (step S24).

[0090] Next, it is determined whether or not the second aberration correction information S2 corresponding to all processing lenses 26 has been acquired (step S26). If the second aberration correction information S2 corresponding to all processing lenses 26 has not been acquired, the processing lens 26 is replaced with another processing lens 26 (step S28), and the process from step S18 to step S28 is repeated until it is determined that the second aberration correction information S2 corresponding to all processing lenses 26 has been acquired. As a result, the second aberration correction information S2 is acquired for each processing lens 26 usable by the laser processing device 10, and the second aberration correction information S2 is stored in the memory unit 60 in association with each processing lens 26.

[0091] The second aberration correction information S2 is information for correcting the aberration of the processing lens 26 alone and does not include information for correcting the aberration of the processing device body 20. Therefore, it is not always necessary to measure the aberration of the entire laser processing device 10 with the processing lens 26 attached to the processing device body 20. For example, the aberration of the processing lens 26 alone may be measured using a predetermined measuring device, and the second aberration correction information S2 may be obtained based on the measurement results.

[0092] Furthermore, asymmetric aberrations that cannot be measured in the aberration adjustment method of this embodiment (such as coma aberration) can be identified by standard performance evaluation of the processed lens 26 alone. By taking measures such as selecting processed lenses with low coma aberration, aberration correction that does not pose practical problems becomes possible.

[0093] [Third aberration correction information acquisition process] Next, third aberration correction information S3 is acquired and stored to correct aberrations according to the machining depth (steps S30 to S40).

[0094] Specifically, as shown in Figure 11, a workpiece piece 78 is prepared and placed between the processing lens 26 and the plane mirror 72. Here, the workpiece piece 78 has a thickness corresponding to the processing depth. Specifically, the thickness of the workpiece piece 78 corresponds to the aberration added after the laser beam L is incident on the workpiece (wafer W) via the processing lens 26 until the laser beam L reaches the processing depth where the focal point is formed. In other words, the workpiece piece 78 has a thickness corresponding to the optical path length from the laser beam incident surface (aberration correction reference position) of the workpiece to the processing depth. Then, in the same manner as in step S18 described above, the laser beam L from the laser light source 22 is irradiated onto the plane mirror 72 via the processing lens 26, the reflected light from the plane mirror 72 is incident on the wavefront sensor 76 via the processing lens 26, and the wavefront of the reflected light incident on the wavefront sensor 76 is measured by the wavefront sensor 76 (step S30). The wavefront measured by the wavefront sensor 76 is output to the spatial light modulator control unit 58.

[0095] The spatial light modulator control unit 58 adjusts the modulation pattern of the spatial light modulator 24 based on the wavefront measured by the wavefront sensor 76 (step S32). Specifically, the spatial light modulator control unit 58 changes the modulation pattern set for the spatial light modulator 24 so that the wavefront measured by the wavefront sensor 76 approaches a plane wave.

[0096] Next, the spatial light modulator control unit 58 determines whether the wavefront measured by the wavefront sensor 76 is a plane wave without aberrations (step S34). If it is determined that the wavefront measured by the wavefront sensor 76 is not a plane wave, the process returns to step S30. The spatial light modulator control unit 58 then repeats the process from step S30 to step S34 until it is determined that the wavefront measured by the wavefront sensor 76 is a plane wave.

[0097] On the other hand, if the wavefront measured by the wavefront sensor 76 is determined to be a plane wave, the spatial light modulator control unit 58 stores the modulation pattern set in the spatial light modulator 24 when it is determined to be a plane wave in the memory unit 60 as total aberration correction information T2.

[0098] Here, since the workpiece piece 78 has a thickness corresponding to the processing depth, the spatial light modulator control unit 58 can obtain the third aberration correction information S3 as the difference between the total aberration correction information T2 and the total aberration correction information T1. That is, the third aberration correction information S3 can be simply expressed by the following equation (6).

[0099] S3 = (T2 - T1) / 2 ... (6) In this way, the spatial light modulator control unit 58 obtains third aberration correction information S3 based on the total aberration correction information T1 and total aberration correction information T2 stored in the memory unit 60. Then, the spatial light modulator control unit 58 stores the third aberration correction information S3 in the memory unit 60 in association with the processing depth (step S36).

[0100] Next, it is determined whether or not third aberration correction information S3 corresponding to all processing depths has been acquired (step S38). If third aberration correction information S3 corresponding to all processing depths has not been acquired, the processing depth is changed (step S40), and the workpiece piece 78 corresponding to the changed processing depth is placed between the processing lens 26 and the plane mirror 72. Then, the process from step S30 to step S40 is repeated until it is determined that third aberration correction information S3 has been acquired for all processing depths. As a result, third aberration correction information S3 is acquired for each processing depth that can be set in the laser processing device 10, and the third aberration correction information S3 is stored in the memory unit 60 in association with each processing depth. Note that since the third aberration correction information S3 changes with the change in processing depth, it can also be expressed as a function of processing depth.

[0101] Then, if it is determined that the third aberration correction information S3 has been acquired for all machining depths, the flowchart shown in Figure 8 is terminated.

[0102] After the aberration adjustment work is completed as described above, when the laser processing apparatus 10 is in operation, the spatial light modulator control unit 58 acquires from the memory unit 60 the first aberration correction information S1, the second aberration correction information S2 corresponding to the processing lens 26 used in the laser processing apparatus 10, and the third aberration correction information S3 corresponding to the processing depth. Then, based on the acquired aberration correction information S1, S2, and S3, the spatial light modulator control unit 58 generates a modulation pattern that includes combined aberration correction information U, which is a combination of these aberration correction information S1, S2, and S3, and controls the spatial light modulator 24 to present the generated modulation pattern.

[0103] Here, as a method for storing aberration correction information (including first aberration correction information S1, second aberration correction information S2, and third aberration correction information S3) (in a format stored in the memory unit 60), it can be stored as two-dimensional information indicating the control value (phase change amount) corresponding to each pixel on the optical modulation plane of the spatial light modulator 24.

[0104] Alternatively, another retention method is to acquire aberration correction information (wavefront data) as a Zernike polynomial and retain the coefficients of the Zernike polynomial. When aberration correction information is held as the coefficients of the Zernike polynomial (Zernike coefficients), the combined aberration correction information U can be easily obtained by simply adding up the coefficients of the first aberration correction information S1, the second aberration correction information S2, and the third aberration correction information S3.

[0105] For example, regarding the coefficient of third-order spherical aberration, if we denote the coefficient of the first aberration correction information S1 as Z1, the coefficient of the second aberration correction information S2 as Z2, the coefficient of the third aberration correction information S3 as Z3, and the coefficient of the combined aberration correction information U as Z, then the coefficient Z of the combined aberration correction information U can be determined by the following equation (7).

[0106] Z = Z1 + Z2 + Z3 ... (7) Furthermore, the coefficients are not limited to those of the Zernike polynomial; coefficients of other forms of polynomial expansions are also acceptable.

[0107] Furthermore, in this embodiment, the modulation pattern presented to the spatial light modulator 24 may include other modulation patterns besides the combined aberration correction information U. Examples of other modulation patterns include patterns for modulating the laser beam so that the laser beam L focused by the processing lens 26 is focused at multiple positions (see, for example, Japanese Patent Application Publication No. 2016-111315).

[0108] Furthermore, in this embodiment, the interior of the workpiece may be used as the aberration correction reference position. Since the machining depth is often the interior of the workpiece, there may be situations where it is more convenient to use the position of the focal point of the laser beam L that focuses to a predetermined depth from the laser beam incident surface of the workpiece as the aberration correction reference position. In that case, the same approach as described above can be applied. That is, a second aberration correction information S2 corresponding to the reference machining depth to be used as the aberration correction reference position can be obtained, and a third aberration correction information S3 corresponding to the distance (depth) from the reference machining depth can be obtained.

[0109] Furthermore, in this embodiment, when a high-power laser light source is used as the laser light source 22, it is desirable to avoid being affected by thermal deformation due to heat during the operation of the laser processing apparatus 10. If this effect becomes significant, it may cause a change in the aberration of the laser light L that occurs at the position where the focal point of the laser light L is aligned inside the wafer W.

[0110] Therefore, in this embodiment, the laser processing apparatus 10 is preferably equipped with an aberration change detection device that measures changes in the aberration of the laser beam L in real time during processing operation in order to prevent the effects of thermal deformation and the like. The aberration change detection device will be described below.

[0111] (Aberration change detection device) Figure 12 is a schematic diagram showing an example of a laser processing apparatus equipped with an aberration change detection device. In Figure 12, elements common to Figure 1 are given the same numbers, and their explanations are omitted.

[0112] The laser processing apparatus 10A shown in Figure 12 is equipped with an aberration change detection device 80 for measuring changes in the aberration (wavefront change) of the laser beam L in real time during processing.

[0113] As shown in Figure 12, the aberration change detection device 80 includes a beam splitter (e.g., a half-mirror) 82 positioned on the optical path of the laser beam L on the rear side of the processed lens 26 (the side into which the laser beam L is incident), and a wavefront sensor 84 positioned on the optical path of the laser beam L branched by the beam splitter 82.

[0114] Then, a portion of the laser light L that enters the processing lens 26 via the components of the processing apparatus body 20 (including the spatial light modulator 24 and the relay optical system 30) from the laser light source 22 is split by the beam splitter 82, and the wavefront of the split laser light L is measured by the wavefront sensor 84. The wavefront measured by the wavefront sensor 84 is output to the spatial light modulator control unit 58.

[0115] The spatial light modulator control unit 58 corrects the modulation pattern of the spatial light modulator 24 based on the wavefront measured by the wavefront sensor 84.

[0116] When the wavefront measurement is performed, the spatial light modulator control unit 58 sets the modulation pattern based on the first aberration correction information S1 stored in the memory unit 60 to the spatial light modulator 24 so that a plane wave is incident on the processed lens 26. Since the modulation pattern based on the first aberration correction information S1 should be adjusted so that a plane wave is incident on the processed lens 26, if there is an aberration in this state, it can be determined that it is being affected by thermal deformation or the like. In other words, the discrepancy between the wavefront measured by the wavefront sensor 84 and the plane wave corresponds to the aberration change due to the effects of thermal deformation or the like. Therefore, the spatial light modulator control unit 58 corrects the first aberration correction information S1 stored in the memory unit 60 so that this aberration change is canceled out, and controls the spatial light modulator 24 based on the corrected first aberration correction information S1. In other words, the spatial light modulator control unit 58 obtains combined aberration correction information U from the corrected first aberration correction information S1, second aberration correction information S2, and third aberration correction information S3, and controls the spatial light modulator 24 to present this combined aberration correction information U. This enables stable processing during the processing operation of the laser processing apparatus 10 without being affected by aberration changes caused by the processing apparatus body 20.

[0117] The aberration change detection device 80 may be incorporated as part of the processing device body 20, or it may be configured to be detachable from the processing device body 20 as needed.

[0118] Here, the aberration changes that occur in the laser processing apparatus 10A may include not only aberration changes caused by the processing apparatus body 20, but also aberration changes caused by the processing lens 26.

[0119] The aberration changes caused by the processed lens 26 can be inferred as follows: The processing apparatus body 20 is affected by heat, and at the same time, the processed lens 26 is similarly affected by heat. These two (the processing apparatus body 20 and the processed lens 26) are not completely independent, and there is a certain correlation between the aberration changes of the processing apparatus body 20 and the aberration changes of the processed lens 26. Therefore, if this correlation is determined experimentally or empirically and stored in the memory unit 60, the spatial light modulator control unit 58 can refer to the correlation stored in the memory unit 60 and infer the aberration changes of the processed lens 26 based on the aberration changes of the processing apparatus body 20 detected by the aberration change detection device 80 (wavefront sensor 84).

[0120] The spatial light modulator control unit 58 then corrects the second aberration correction information S2 based on the estimated aberration change of the processed lens 26. Furthermore, the spatial light modulator control unit 58 obtains combined aberration correction information U from the corrected first aberration correction information S1, the corrected second aberration correction information S2, and the third aberration correction information S3, and controls the spatial light modulator 24 to present this combined aberration correction information U. This makes it possible to perform more stable processing without being affected not only by aberration changes caused by the processing apparatus body 20, but also by aberration changes caused by the processed lens 26.

[0121] Figure 13 is a configuration diagram showing another example of a laser processing apparatus equipped with an aberration change detection device. The laser processing apparatus 10B shown in Figure 13 is equipped with an aberration change detection device 90, which has a different configuration from the aberration change detection device 80 shown in Figure 12. This aberration change detection device 90 comprises a beam splitter (e.g., a half mirror) 92, an imaging lens 94, a pinhole forming member 96, and a detector 98.

[0122] The beam splitter 92 is positioned on the optical path of the laser beam L behind the processing lens 26 (the side into which the laser beam L is incident) and splits a portion of the laser beam L that is incident on the processing lens 26. The imaging lens 94 forms an image of the light split by the beam splitter 92.

[0123] The pinhole forming member 96 has a pinhole (hole) 96a through which a portion of the light imaged by the imaging lens 94 can pass.

[0124] The detector 98, for example, consists of a photodiode and detects the amount of light corresponding to the light that has passed through the pinhole 96a. The detector 98 then outputs an electrical signal corresponding to the detected amount of light to the spatial light modulator control unit 58.

[0125] Here, the output of the detector 98 is maximized when a plane wave without aberrations is incident on the imaging lens 94. The spatial light modulator control unit 58 acquires the output of the detector 98 and adjusts the spatial light modulator 24 to maximize the output of the detector 98. For example, the modulation pattern of the spatial light modulator 24 is generated in the form of a Zernike polynomial, and an optimization method is used with the coefficients of the polynomial as variables to maximize the output of the detector 98. As an optimization method, for example, the DLS method (damped least squares method) can be used. The DLS method is well known, so its explanation is omitted here.

[0126] In the laser processing apparatus 10B shown in Figure 13, as with the laser processing apparatus 10A shown in Figure 12, stable processing is possible without being affected by aberration changes caused by the processing apparatus body 20 during the processing operation of the laser processing apparatus 10B. Alternatively, the aberration changes of the processing lens 26 may be estimated based on the aberration changes of the processing apparatus body 20 detected by the aberration change detection device 90. In this case, even more stable processing is possible without being affected not only by aberration changes caused by the processing apparatus body 20 but also by aberration changes caused by the processing lens 26.

[0127] (Effects of this embodiment) According to this embodiment, since the spatial light modulator 24 and the lens pupil 26a of the processing lens 26 are optically conjugate, the wavefront shape formed by the spatial light modulator 24 is projected onto the lens pupil 26a of the processing lens 26, and a desired light distribution can be obtained at the focal plane (processing point) of the processing lens 26. As a result, the effects of aberrations can be suppressed, and the laser processing region that serves as the starting point for cutting can be formed with high precision and efficiency.

[0128] Furthermore, according to this embodiment, in the adjustment work performed during the manufacturing stage of the laser processing apparatus 10, first aberration correction information S1 for correcting aberrations of the processing apparatus body 20, second aberration correction information S2 for correcting aberrations of the processing lens 26, and third aberration correction information S3 for correcting aberrations caused by the processing depth of the laser processing area are obtained, and these aberration correction information S1, S2, and S3 are stored in the memory unit 60. Note that the aberration adjustment work in this embodiment is not limited to the manufacturing stage of the laser processing apparatus 10, but may also be performed after the manufacturing (after shipment) of the laser processing apparatus 10.

[0129] During processing by the laser processing apparatus 10, the spatial light modulator control unit 58 acquires first aberration correction information S1, second aberration correction information S2, and third aberration correction information S3 from the memory unit 60. Based on the acquired aberration correction information S1, S2, and S3, it generates a modulation pattern including combined aberration correction information U, and controls the spatial light modulator 24 to present the generated modulation pattern. By performing this control, even if the processing lens 26 is replaced or the processing depth is changed, the aberration of the laser beam L that occurs at the position where the focal point of the laser beam L is aligned inside the wafer W can be suppressed without being affected by these changes.

[0130] In this embodiment, the system is configured to acquire first aberration correction information S1, second aberration correction information S2, and third aberration correction information S3, and to control the spatial light modulator 24 based on these aberration correction information S1, S2, and S3. However, the present invention is not limited to this configuration, and it is sufficient to acquire at least first aberration correction information S1 and second aberration correction information S2, and to control the spatial light modulator 24 based on these aberration correction information S1 and S2. In this case, it is possible to suppress the aberration of the laser L without being affected by the replacement of the processing lens 26.

[0131] Furthermore, the laser processing apparatus 10 of this embodiment is preferably equipped with aberration change detection devices 80 and 90 that measure changes in the aberration of the laser beam L in real time during processing (see Figures 12 and 13). This enables stable processing during the processing operation of the laser processing apparatus 10 without being affected by aberration changes caused by the processing apparatus body 20.

[0132] In this embodiment, a reflective spatial light modulator (LCOS-SLM) is used as the spatial light modulator 24, but it is not limited to this, and a MEMS-SLM or DMD (Deformable Mirror Device) may also be used. Furthermore, the spatial light modulator 24 is not limited to the reflective type, but may also be a transmissive type. In addition, examples of spatial light modulators 24 include liquid crystal cell type or LCD type.

[0133] Furthermore, in this embodiment, the stage 12 is configured to be movable in the X and θ directions, and the processing device body 20 is configured to be movable in the Y and Z directions. However, other configurations are also possible as long as the stage 12 and the processing device body 20 can be moved relative to each other in the X, Y, Z, and θ directions. For example, the stage 12 may be configured to be movable in the X, Y, and θ directions, and the processing device body 20 may be configured to be movable in the Z direction.

[0134] (Examples of application) Although the above embodiment described a laser processing apparatus, the optical system arrangement according to the above embodiment can also be used to detect cracks extending from the laser processing area.

[0135] Next, an example of applying the optical system arrangement according to the above embodiment to a crack detection device will be described with reference to Figures 14 to 18. Figure 14 is a diagram showing a crack detection device according to one embodiment of the present invention.

[0136] As shown in Figure 14, the crack detection device 100 according to this embodiment is a device that measures the crack depth of a crack K formed inside a workpiece W by irradiating the workpiece W with detection light L1 and detecting the reflected light L2 from the workpiece W. The crack detection device 100 can also be configured in combination with the laser processing device 10 according to the above embodiment. Furthermore, in this embodiment, the crack depth of the crack K is described as the distance from the back surface of the workpiece W to the lower or upper end of the crack K, but of course, it is not limited to this, and may be the distance from the surface of the workpiece W (the detection light irradiation surface).

[0137] As shown in Figure 14, the crack detection device 100 comprises a light source unit 102, an illumination optical system 104, a dichroic mirror 106, a half mirror 108, a dichroic mirror 110, an objective lens 112, a detection optical system 114, a photodetector 116, an alignment mechanism 118, and a control unit 150. The workpiece W is placed on a stage (not shown).

[0138] The light source unit 102 emits detection light L1 for detecting the crack depth of a crack K formed inside the workpiece W. The light source unit 102 is positioned conjugate to the lens pupil 112A of the objective lens 112. Here, if the workpiece W is a silicon wafer, it is desirable to use infrared light with a wavelength of 1100 nm or longer for the detection light L1. The light source unit 102 has a light source optical axis Q that is parallel to the principal optical axis P, which is coaxial with the lens optical axis of the objective lens 112, and is eccentric from the principal optical axis P. A and Q BThe system includes light sources 102A and 102B, each having the same characteristics. Specifically, light source 102 emits detection light L1 along the principal optical axis P from a position eccentric to the principal optical axis P. Light source 102 is connected to a control unit 150, and the control unit 150 controls the emission of light from light source 102.

[0139] In this embodiment, two light sources 102A and 102B are used to perform biased illumination. However, the present invention is not limited to this. For example, biased illumination can also be performed using one light source and means for shielding a part of the aperture of the light source.

[0140] The illumination optical system 104 includes a pair of relay lenses 130 and 132. The pair of relay lenses 130 and 132 constitute a non-telecentric afocal optical system.

[0141] The dichroic mirror 106 bends the principal optical axis P by 90 degrees. That is, the dichroic mirror 106 reflects the detected light L1 from the light source 102 at a right angle and guides it to the objective lens 112 via the half mirror 108 and the dichroic mirror 110. Alternatively, a total internal reflection mirror may be used instead of the dichroic mirror 106.

[0142] The half mirror 108 is positioned between the illumination optical system 104 and the dichroic mirror 110, transmitting a portion of the incident light and reflecting a portion of it. Specifically, the half mirror 108 reflects a portion of the detection light L1 incident from the light source 102 via the illumination optical system 104, and guides the detection light L1 to the focusing lens 102 via the dichroic mirror 110. On the other hand, the half mirror 108 transmits a portion of the reflected light L2 of the detection light L1 from the workpiece W, and guides the transmitted reflected light L2 to the detection optical system 114.

[0143] The dichroic mirror 110 reflects the incident detection light L1, which passes through the half mirror 108, at a right angle and guides it to the objective lens 112. On the other hand, the dichroic mirror 110 also reflects the reflected light L2 from the workpiece W at a right angle and guides it to the half mirror 108. A total reflection mirror may be used instead of the dichroic mirror 110.

[0144] The objective lens 112 is positioned opposite the workpiece W and focuses the detection light L1 incident from the light source 102 through the illumination optical system 104, dichroic mirror 106, half mirror 108, and dichroic mirror 110 into the workpiece W. The optical axis of the objective lens 112 is coaxial with the principal optical axis P. Once the detection light L1 is focused into the workpiece W by the objective lens 112, the reflected light L2 from the workpiece W passes through the objective lens 112 and dichroic mirror 110, then through the half mirror 108, and is guided to the detection optical system 114.

[0145] The detection optical system 114 is for guiding the reflected light L2 reflected by the half-mirror 108 to the photodetector 116, and includes a pair of relay lenses 134 and 136. The pair of relay lenses 134 and 136 constitute a bilaterally telecentric afocal optical system.

[0146] The photodetector 116 detects reflected light L2, which changes depending on the presence or absence of a crack K formed inside the workpiece W. The photodetector 116 is positioned conjugate to the pupil 112A of the objective lens 112. The photodetector 116 includes two photodetectors 116A and 116B. Each photodetector 116A and 116B outputs a detection signal to the control unit 150 corresponding to the amount of light they receive. Note that instead of two photodetectors, a segmented photodetector with multiple light-receiving surfaces (e.g., a two-segment photodetector, a four-segment photodetector, etc.) may be used as the photodetector 116. Alternatively, instead of the photodetector 116, an infrared camera may be used to capture images and perform image processing.

[0147] The control unit 150 can adjust the focal point of the objective lens 112 in the thickness direction (Z direction) of the workpiece W by moving the focus lens group using a focus adjustment mechanism (not shown). In this specification, the focal point of the objective lens 112 refers to the position of the focal point of the detection light L1 focused by the objective lens 112. The depth position (Z direction position) of the focal point of the objective lens 112 is indicated by the distance from the back surface of the workpiece W.

[0148] The alignment mechanism 118 is an example of an alignment means, and performs relative positioning (alignment) of the objective lens 112 and the workpiece W in the horizontal direction (XY direction). The alignment mechanism 118 has a lens drive unit (not shown) that moves the objective lens 112 in a small amount of horizontal movement perpendicular to the lens optical axis. The lens drive unit is connected to the control unit 150, and by controlling the lens drive unit with the control unit 150, relative positioning of the objective lens 112 and the workpiece W in the horizontal direction is performed. Alternatively, instead of the alignment mechanism 118, a stage (not shown) on which the workpiece W is placed may be moved relative to the objective lens 112.

[0149] The control unit 150 consists of a CPU (Central Processing Unit), memory, input / output circuit section, etc., and controls the operation of each part of the crack detection device 100. Specifically, the control unit 150 changes the focal point of the objective lens 112 in the thickness direction (Z direction) of the workpiece W using the focus adjustment mechanism 28, sequentially acquires detection signals output from the photodetector 116, and performs a crack detection process (crack detection process) to detect the crack depth (crack upper end position or crack lower end position) of the crack K formed inside the workpiece W based on the acquired detection signals. The control unit 150 is an example of a crack detection means.

[0150] Here, the principle of the crack detection process in this embodiment will be explained. For this explanation, we will describe the case where the lower end position of the crack is detected as the crack depth of the crack K.

[0151] FIG. 15 and FIG. 16 are diagrams showing the optical arrangement of the main components including the illumination optical system 104 and the detection optical system 114 of the crack detection device 100. In FIGS. 15 and 16, for the sake of simplicity of the drawings, the illustration of the dichroic mirrors 106, 110 and the half mirror 108 is omitted.

[0152] As shown in FIG. 15, the detection light L1 from the light source 102 is emitted along the principal axis P from a position eccentric with respect to the principal axis P. Therefore, the detection light L1 enters a region on one side of the lens pupil 112A of the objective lens 112 (that is, a position deviated from the lens optical axis coaxial with the principal axis P). Accordingly, the irradiation direction of the detection light L1 that has passed through the objective lens 112 becomes an oblique direction with respect to the image plane (condensing plane) of the objective lens 112. That is, deflected illumination is performed in which the detection light L1 is irradiated on the workpiece W in an oblique direction. Note that the image plane of the objective lens 112 is arranged to be parallel to the surface of the workpiece W (detection light irradiation surface).

[0153] As shown in FIG. 16, the detection light L1 is reflected by the crack K inside the workpiece W or the back surface. Then, the reflected light L2 from the workpiece W reaches the photodetector via the objective lens 112 and the detection optical system 114.

[0154] As shown in FIG. 15, the illumination optical system 104 includes a first relay lens 130 and a second relay lens 132, and constitutes an afocal optical system. F11 in FIG. 15 A and F11 B are the focal positions of the first relay lens 130, and F12 A and F12 B are the focal positions of the second relay lens 132. Here, the relay lenses 130 and 132 respectively correspond to the first lens and the second lens of the present invention.

[0155] As shown in FIG. 15, the distance g 12 between the lens pupil 112A of the objective lens 112 and the second relay lens 132 12It is longer than that. The laser emission apertures 102a and 102b of the light source unit 102 (light sources 102A and 102B) are positioned in a conjugate relationship with the lens pupil 112A of the objective lens 112. In this case, the distance g between the laser emission apertures 102a and 102b of the light source unit 102 (light sources 102A and 102B) and the first relay lens 130 is 11 The focal length of the first relay lens 130 is f 11 It will be shorter than that.

[0156] distance g 12 and the focal length f of the second relay lens 132 12 The difference between this and Δx 12 (=|g 12 -f 12 |), distance g 11 and the focal length f of the first relay lens 130 11 The difference between this and Δx 11 (=|g 11 -f 11 If we let |), then Δx 11 and Δx 12 The relationship is shown by equation (8) below.

[0157] Δx 11 =( f 11 / f 12 ) 2 ×Δx 12 ...(8) The magnification of the illumination optical system 104 is m1(=f 12 / f 11 If we assume that, then equation (8) can be expressed as equation (9).

[0158] Δx 12 =m1 2 ×Δx 11 ...(9) In the optical system configuration shown in Figure 15, each component (optical system) is arranged such that the laser emission apertures 102a and 102b and the lens pupil 112A of the objective lens 112 are optically conjugate. Therefore, the plane wave output from the laser emission aperture 102a or 102b reaches the lens pupil 112A as a plane wave, and the illumination optical system 104 has the properties of a 4F optical system.

[0159] According to the optical system configuration shown in Figure 15, the distance g between the pupil 112A of the objective lens 112 and the second relay lens 132 is defined as the second relay lens 132. 12 This allows the use of lenses with shorter focal lengths, contributing to the miniaturization of the device.

[0160] Note that in the optical system configurations shown in Figures 14 and 15, relay lenses 130 and 132 are not essential. For example, in Figure 14, if the distance between the light source 102 and the half mirror 108 can be set short, the light sources 102A and 102B can be positioned eccentrically with respect to the optical axis (as long as the laser does not spread) and the relay lenses 130 and 132 can be omitted.

[0161] As shown in Figure 16, the detection optical system 114 includes a first relay lens 136 and a second relay lens 134, and constitutes an afocal optical system. F21 in Figure 16 A and F21 B This is the focal position of the first relay lens 136, F22 A and F22 B is the focal position of the second relay lens 134. Here, the first relay lens 136 and the second relay lens 134 correspond to the first lens and the second lens of the present invention, respectively.

[0162] As shown in Figure 16, the distance g between the pupil 112A of the objective lens 112 and the second relay lens 134 is as follows: 22 The second relay lens 134 has a focal length f 22 It is longer than that. The light-receiving surfaces 116a and 116b of the photodetectors (photodetectors 116A and 116B) are positioned in a conjugate relationship with the lens pupil 112A of the objective lens 112. In this case, the distance g between the light-receiving surfaces 116a and 116b of the photodetectors (photodetectors 116A and 116B) and the first relay lens 136 is longer than that. 21 The focal length of the first relay lens 130 is f 21 It will be shorter than that.

[0163] distance g 22 and the focal length f of the second relay lens 134 22 The difference between this and Δx 22 (=|g 22 -f 22 |), distance g 22 and the focal length f of the first relay lens 136 21 The difference between this and Δx 21 (=|g 21 -f 21 If we let |), then Δx 21 and Δx 22 The relationship is shown by equation (10) below.

[0164] Δx 21 =( f 21 / f 22 ) 2 ×Δx 22 ...(10) The magnification of the detection optical system 114 is m² (=f 21 / f 22 If we assume that , then equation (10) can be expressed as equation (11).

[0165] Δx 21 =m2 2 ×Δx 22 ...(11) In the optical system configuration shown in Figure 16, each component (optical system) is arranged such that the light-receiving surfaces 116a and 116b and the pupil 112A of the objective lens 112 are optically conjugate. Therefore, the plane wave at the pupil 112A of the objective lens 112 reaches the light-receiving surfaces 116a and 116b as a plane wave, and the detection optical system 114 has the properties of a 4F optical system.

[0166] The total length L of the detection optical system 114 (the distance between the lens pupil 112A of the objective lens 112 and the light-receiving surfaces 116a and 116b of the photodetectors 116A and 116B) is expressed by the following equation (12).

[0167] L=2f 22 (1-m2)-Δx 21 (1-m2 2 ) ···(12) For example, the distance g between the pupil 112A of the objective lens 112 and the second relay lens 134. 22 =100mm, focal length f of the second relay lens 134 22 If we set L = 60mm and magnification m2 = -1, then L = 240mm. Note that the magnification m2 takes a negative value because the image is inverted before and after the detection optical system 114.

[0168] As a comparative example, the position of the pupil 112A of the objective lens 112 is set to the focal position F222 on the objective lens 112 side of the second relay lens 134. A When this is matched, the photodetector will be at the focal position F21 on the photodetector side of the first relay lens 136. B It will be placed at a distance g. 22 =f 22 =f 21 Assuming = 100 mm, the total length of the detection optical system in the comparative example is 400 mm.

[0169] Therefore, according to the optical system configuration shown in Figure 16, the distance g between the pupil 112A of the objective lens 112 and the second relay lens 132 is defined as the second relay lens 132. 22 This allows the use of lenses with shorter focal lengths, contributing to the miniaturization of the device.

[0170] Furthermore, by changing the arrangement of the dichroic mirror 106 and the half mirror 108, it is possible to share the second relay lens 134 with the illumination optical system 104 and omit the second relay lens 132, or to share the detection optical system 114 with the illumination optical system 104.

[0171] Figures 17A to 17C are explanatory diagrams showing the situation when the workpiece W is illuminated by the detected light L1. Figure 17A shows the case when a crack K exists at the focal point of the objective lens 112, Figure 17B shows the case when there is no crack K at the focal point of the objective lens 112, and Figure 17C shows the case when the focal point of the objective lens 112 coincides with the crack depth (lower end position of the crack) of the crack K. Figure 18 is a diagram to explain the path of the reflected light L2 from the workpiece W to the lens pupil 112A. Here, we will explain the case in which the detected light L1 passes through the first region G1 on one side of the lens pupil 112A (right side in Figure 4) and illuminates the workpiece W by the detected light L1.

[0172] As shown in Figure 17A, if a crack K exists at the focal point of the objective lens 112, the detected light L1 undergoes total internal reflection at the crack K, and the reflected light L2 follows the same path as the optical path of the detected light L1 with respect to the principal optical axis P, becoming a component that reaches the same region of the lens pupil 112A as the detected light L1. That is, as shown in Figure 18, when the detected light L1 from the light source 102 is irradiated onto the workpiece W via the objective lens 112, the path of the detected light L1 is R1. The reflected light L2 that undergoes total internal reflection at the crack K inside the workpiece W follows a path R2 that is on the same side (right side in Figure 18) as the path R1 of the detected light L1 with respect to the principal optical axis P, and passes through the first region G1 of the lens pupil 112A. In this case, as shown in Figure 4A, the reflected light L2 is received on one of the light-receiving surfaces 116a and 116b of the photodetector 116, on the light-receiving surface 116a, and the level of the detection signal output from the light-receiving surface 116a increases.

[0173] As shown in Figure 17B, if there is no crack K at the focal point of the objective lens 112, the detected light L1 is reflected from the back surface of the workpiece W, and the reflected light L2 becomes a component that reaches the region of the lens pupil 112A opposite to the detected light L1. That is, as shown in Figure 18, the reflected light L2 reflected from the back surface of the workpiece W follows a path R3 that is opposite to the path R1 of the detected light L1 with respect to the principal optical axis P (left side in Figure 18) and passes through the second region G2 of the lens pupil 112A. In this case, as shown in Figure 4B, the reflected light is received on the other light-receiving surface 116b of the photodetector 116, and the level of the detection signal output from the light-receiving surface 116b becomes higher.

[0174] As shown in Figure 17C, when the focal point of the objective lens 112 coincides with the lower end position of the crack K, the detected light L1 is divided into a reflected light component L2a that undergoes total internal reflection at the crack K and reaches the same region of the lens pupil 112A as the detected light L1, and a non-reflected light component L2b that is not totally reflected at the crack K but is reflected from the back surface of the workpiece W and reaches the region of the lens pupil 112A opposite to the detected light L1. In other words, as shown in Figure 18, of the reflected light L2, the reflected light component L2a that is totally reflected by the crack K inside the workpiece W follows path R2, which is on the same side as the detection light L1 with respect to the principal optical axis P (right side in Figure 18), and passes through the first region G1 of the lens pupil 112A. The unreflected light component L2b that is not totally reflected by the crack K and is reflected from the back surface of the workpiece W follows path R3, which is on the opposite side of the detection light L1 with respect to the principal optical axis P (left side in Figure 18), and passes through the second region G2 of the lens pupil 112A. In this case, as shown in Figure 4C, the respective components L2a and L2b of the reflected light L2 are received by the light-receiving surfaces 116a and 116b of the photodetector 116, and the levels of the detection signals output from the light-receiving surfaces 116a and 116b are approximately equal.

[0175] Thus, the amount of light received by the light-receiving surfaces 116a and 116b of the photodetector 116 changes depending on whether or not a crack K exists at the focal point of the objective lens 112. In this embodiment, this property can be used to detect the crack depth (lower end position of the crack or upper end position of the crack) of a crack K formed inside the workpiece W.

[0176] Specifically, when the outputs of the detection signals from the light-receiving surfaces 116a and 116b of the photodetector 116 are denoted as D1 and D2, respectively, the evaluation value S, which shows the relationship between the focal point of the objective lens 112 and the crack depth of the crack K, can be expressed by the following equation.

[0177] S = (D1 - D2) / (D1 + D2) ... (13) In equation (1), when the condition S=0 is met, that is, when the amount of light received by the light-receiving surfaces 116a and 116b of the photodetector 116 is the same, it indicates that the focal point of the objective lens 112 coincides with the lower end position of the crack (or the upper end position of the crack).

[0178] Therefore, the control unit 150 controls the focus adjustment mechanism 28 to change the focal point of the objective lens 112 in the thickness direction (Z direction) of the workpiece W, while sequentially acquiring detection signals output from each light-receiving surface 116a, 116b of the photodetector 116. Based on the acquired detection signals, it calculates an evaluation value S shown in equation (1), and by evaluating this evaluation value S, it can detect the crack depth (lower end position of the crack or upper end position of the crack) of the crack K.

[0179] It is also possible to detect the lower end (or upper end) of the crack using only the detection light that is not reflected by crack K, or only the detection light that is reflected by crack K. In that case, for example, the lower end (or upper end) of the crack is defined as the position where the amount of detected light is halved compared to the detection light when crack K is absent.

[0180] Although embodiments of the present invention have been described above, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the spirit of the present invention. [Explanation of Symbols]

[0181] 10...Laser processing device, 12...Stage, 20...Processing device body, 21...Housing, 22...Laser light source, 24...Spatial light modulator, 26...Processing lens, 30...Relay optical system, 30a...First lens, 30b...Second lens, 32...Beam expander, 34...λ / 2 wave plate, 50...Control device, 52...Main control unit, 54...Movement control unit, 56...Laser control unit, 58...Spatial light modulator control unit, 60...Memory unit, 70...Wave Surface sensor, 72…Reflection mirror, 74…Beam splitter, 76…Wavefront sensor, 78…Workpiece piece, 80…Aberration change detection device, 82…Beam splitter, 84…Wavefront sensor, 90…Aberration change detection device, 92…Beam splitter, 94…Imaging lens, 96…Pinhole forming member, 98…Detector, S1…First aberration correction information, S2…Second aberration correction information, S3…Third aberration correction information, U…Composite aberration correction information

Claims

1. A crack detection device comprising an objective lens used for measuring a workpiece, an optical element positioned conjugate to the pupil of the objective lens, and an afocal optical system that relays light between the objective lens and the optical element, The afocal optical system comprises a first lens disposed on the optical element side, positioned such that the distance between the first lens and the optical element is shorter than the focal length of the first lens, and a second lens disposed on the objective lens side, positioned such that the distance between the second lens and the pupil of the objective lens is longer than the focal length of the second lens. The optical element is a laser light source that outputs laser light for detecting cracks extending from a laser-processed area formed inside the workpiece. The afocal optical system relays the laser light output from the laser light source to the objective lens. The objective lens irradiates the laser beam into the workpiece, A crack detection device further comprising a detector for detecting the laser light reflected by a crack inside or on the back surface of the workpiece.

2. A crack detection device comprising an objective lens used for measuring a workpiece, an optical element positioned conjugate to the pupil of the objective lens, and an afocal optical system that relays light between the objective lens and the optical element, The afocal optical system comprises a first lens disposed on the optical element side, positioned such that the distance between the first lens and the optical element is shorter than the focal length of the first lens, and a second lens disposed on the objective lens side, positioned such that the distance between the second lens and the pupil of the objective lens is longer than the focal length of the second lens. The optical element is a detector that detects laser light reflected by the crack or back surface of the workpiece when irradiated onto a crack extending from a laser processing region formed inside the workpiece. The objective lens receives the laser light reflected from the inside or back surface of the workpiece. The afocal optical system is a crack detection device that relays the laser light incident on the objective lens to the detector.

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