Laser processing apparatus and laser processing method

Abstract

This laser processing apparatus is provided with: a support unit that supports a wafer; a light source; a spatial light modulator; a light collecting part; a moving unit that moves the light-collecting unit relative to the surface in an optical axis direction that is a direction perpendicular to the surface; a visible imaging unit that acquires a captured image by detecting the light propagating through the wafer via the light collecting unit; and a control unit configured to execute: a first process for controlling the moving unit; a second process for controlling the light source (3) and continuously emitting laser light; a third process of controlling the visible imaging unit, detecting light reflected by the back surface of the wafer, and continuously acquiring a plurality of captured images; and a fourth process for obtaining an optical axis profile, which is a profile image of the laser light along the optical axis direction, by combining the plurality of captured images.

Description

Technical Field

[0001] One aspect of the present invention relates to a laser processing apparatus and a laser processing method. Background Art

[0002] Conventionally, there is known a laser processing device that forms a modified region in an object by irradiating the object with laser light (see, for example, Patent Document 1). Such a laser processing device includes, for example, a support portion that supports the object; a light source that emits laser light; a spatial light modulator that modulates the laser light emitted from the light source; and a focusing portion that focuses the laser light modulated by the spatial light modulator. Prior art literature Patent Literature

[0003] Patent Document 1: Japanese Patent Application Publication No. 2011-051011 Summary of the invention The problem the invention is intended to solve

[0004] The modulation pattern set in the spatial light modulator is set based on simulation, etc., and then the processing is actually performed to optimize it. Here, even if the modulation pattern is optimized by the above method, there are cases where the desired laser processing cannot be performed using the modulation pattern due to various reasons.

[0005] One aspect of the present invention has been developed in view of the above circumstances, and an object of the present invention is to provide a laser processing apparatus and a laser processing method capable of performing desired laser processing. Technical means of solving problems

[0006] [E1] A laser processing device according to one aspect of the present invention comprises: A support portion that supports a wafer having a first surface and a second surface; a light source that emits laser light; A spatial light modulator that modulates the laser light emitted from the light source; a light focusing unit that focuses the laser light modulated by the spatial light modulator onto the wafer from the first surface side of the wafer; a moving portion that moves the light-collecting portion relative to the first surface in an optical axis direction that is a direction perpendicular to the first surface; an imaging unit that acquires an image by detecting light propagating on the wafer via the focusing unit; and A control unit is configured to execute: a first process of controlling a moving unit to move a focusing unit relative to a first surface in an optical axis direction; a second process of controlling a light source to continuously emit laser light while the first process is being executed; a third process of controlling an imaging unit to detect light reflected from a second surface of a wafer and continuously obtain a plurality of imaging images while the second process is being executed; and a fourth process of obtaining an optical axis contour as a contour image of the laser light along the optical axis direction by synthesizing a plurality of imaging images continuously obtained in the third process.

[0007] A laser processing device according to one aspect of the present invention irradiates laser light while moving a focusing portion along the optical axis direction, detects light reflected on the second surface of a wafer, and continuously obtains a plurality of camera images. In addition, in the laser processing device, by synthesizing a plurality of camera images, an optical axis profile is obtained as a profile image of the laser light along the optical axis direction. In this way, while moving the laser light focusing point along the optical axis direction (the depth direction of the wafer), the reflected light from the back side of the wafer, i.e., the second surface, is detected to obtain the above-mentioned optical axis profile, thereby being able to grasp the irradiation condition of the laser light along the optical axis direction (e.g., the focusing point, position, intensity, etc.), that is, grasp the focusing state of the laser internal processing. Thus, for example, it is possible to judge whether a certain abnormality has occurred in the laser processing device, whether it is necessary to adjust the modulation pattern set in the spatial light modulator, etc., and the desired laser processing can be performed more accurately. Furthermore, in the laser processing device according to one aspect of the present invention, the focusing state of the laser internal processing can be grasped without actually performing laser processing on the wafer (before laser processing), and the modulation pattern can be optimized.

[0008] [E2] In the laser processing device of [E1], the control unit may further perform a fifth process of adjusting the modulation pattern of the spatial light modulator based on the optical axis profile obtained in the fourth process. According to such a structure, the modulation pattern can be optimized in consideration of the optical axis profile, and the desired laser processing can be performed more accurately. That is, the information on the focusing state of the laser internal processing that has been obtained can be fed back to the modulation pattern generation, and the desired laser processing can be performed.

[0009] [E3] The laser processing device of the above-mentioned [E2] may be configured so that the wafer includes a birefringent material. In the fifth processing, the control unit determines the focal point according to the ordinary ray and the focal point according to the extraordinary ray based on the optical axis profile, and adjusts the modulation pattern so that the light intensity of one of the two focal points becomes larger and the light intensity of the other focal point becomes smaller. In the case of focusing the laser on a wafer containing a birefringent material, the refractive indexes of the P polarized light component and the S polarized light component in the incident light are different from each other. In addition, these incident lights are divided into ordinary rays and extraordinary rays, and the extraordinary rays propagate at a refraction angle different from that of the ordinary rays and do not follow Snell's law. According to these circumstances, the P polarized light component and the S polarized light component are focused at different positions in the depth direction of the wafer. In this way, the focal point is branched in the depth direction, so that multiple focal points are unintentionally formed on the wafer, resulting in incorrect cracks. Therefore, there is a risk of reduced processing quality such as slippage. In this regard, the modulation pattern is adjusted based on the optical axis profile so that the intensity of one of the focal points becomes larger and the intensity of the other focal point becomes smaller, thereby suppressing the reduction in processing quality caused by forming the above-mentioned multiple focal points.

[0010] [E4] In the laser processing device of [E3] described above, the control unit may adjust the modulation pattern in the fifth process so that the intensity of the light of the light-converging point on the side close to the second surface of the two light-converging points increases, and the intensity of the light of the light-converging point on the side away from the second surface decreases. By adjusting the modulation pattern, the intensity ratio of the two light-converging points can be changed, but neither of the light-converging points can be completely eliminated. For example, when the light-converging point on the side away from the second surface is mainly used and the intensity of the light of the light-converging point on the side close to the second surface is minimized, since the light-converging point on the side away from the second surface is set to the processing target height, the light-converging point on the side close to the second surface exists, although it is weak. Since the device is provided on the second surface, it is possible that the device is damaged by the influence of the light-converging point on the side close to the second surface. In this regard, when the light-converging point on the side close to the second surface is mainly used, since the light-converging point on the side close to the second surface is set as the processing target height, there is no light-converging point on the side closer to the second surface, so the damage to the device on the second surface can be reduced. Furthermore, for a wafer without a device on the second surface, the laser processing device can also be equipped with the above-mentioned structure, so that the damage to the second surface can be reduced.

[0011] [E5] In any of the laser processing devices described in [E2] to [E4], the control unit may adjust the modulation pattern by using a slit pattern that blocks a part of the polarized light component of the laser light in the fifth process. With such a configuration, the intensity of light at any one of the focusing points can be easily reduced.

[0012] [E6] In any of the laser processing devices [E2] to [E5] above, the control unit may change the spherical aberration condition determined by the modulation pattern while performing the first process, the second process, the third process and the fourth process under the respective conditions. In the fifth process, the maximum values ​​of the brightness values ​​of the laser light represented by the optical axis profiles obtained under various conditions are compared with each other, and the modulation pattern is adjusted to achieve the spherical aberration condition according to the optical axis profile with the maximum brightness value. According to such a structure, even for a wafer with an unknown refractive index, accurate spherical aberration correction can be implemented.

[0013] [E7] In any of the laser processing devices described in [E1] to [E6] above, the control unit may further perform a sixth process, which compares the optical axis profile obtained in the fourth process with the comparison data of the profile image used for comparison, and when the difference between the compared data is within a specified range, determines that the optical axis profile is normal, and when the difference is outside the specified range, determines that the optical axis profile is abnormal, and outputs the determination result. According to such a structure, by setting the profile image of the laser processing device in a normal state as comparison data in advance, it is possible to easily determine whether a certain abnormality has occurred in the laser processing device based on the comparison of the optical axis profile and the comparison data. In addition, by outputting the determination result, the laser processing device can be adjusted in consideration of the determination result. As described above, according to the above structure, the desired laser processing can be more accurately performed.

[0014] [E8] In any of the laser processing devices described in [E1] to [E7] above, the control unit may control the light source to emit laser light with a lower output than the output during wafer processing in the second process. Thus, the optical axis profile can be obtained without actually performing laser processing.

[0015] [E9] In any of the laser processing devices described in [E1] to [E8] above, the optical axis profile may be three-dimensional data obtained by synthesizing a plurality of two-dimensional camera images. By obtaining the optical axis profile as three-dimensional data, the irradiation conditions of the laser along the optical axis direction (e.g., the position and intensity of the focal point) can be understood in more detail.

[0016] [E10] A laser processing method according to one embodiment of the present invention comprises: A first step of moving a laser beam modulated by a spatial light modulator from a first surface side of a wafer having a first surface and a second surface to a focusing portion of the wafer in an optical axis direction which is a direction perpendicular to the first surface; A second step of continuously emitting laser light while executing the first step; A third step of continuously acquiring a plurality of camera images by detecting light reflected on the second surface while executing the second step; and The fourth step is to obtain an optical axis profile that is a profile image of the laser light along the optical axis direction by synthesizing the plurality of captured images continuously obtained in the third step.

[0017] [E11] The laser processing method of the above-mentioned [E10] may further include: a fifth step of adjusting a modulation pattern of the spatial light modulator based on the optical axis profile obtained in the fourth step.

[0018] [E12] In the laser processing method of [E11] above, the wafer may include a birefringent material. In step 5, based on the optical axis profile, the focal point according to the ordinary ray and the focal point according to the extraordinary ray are determined, and the modulation pattern is adjusted so that the light intensity of one of the two focal points becomes larger and the light intensity of the other focal point becomes smaller.

[0019] [E13] As in the laser processing method [E12] described above, the modulation pattern may be adjusted in step 5 so that the intensity of light at the focal point close to the second surface of the two focal points increases, while the intensity of light at the focal point away from the second surface decreases.

[0020] [E14] In any of the laser processing methods described in [E11] to [E13] above, in the fifth step, the modulation pattern may be adjusted by using a slit pattern that blocks a part of the polarization component of the laser light.

[0021] [E15] In any of the laser processing methods [E11] to [E14] above, the first step, the second step, the third step and the fourth step may be performed under the respective conditions while changing the conditions of the spherical aberration determined by the modulation pattern. In the fifth step, the maximum values ​​of the brightness values ​​of the laser light indicated by the optical axis profiles obtained under the respective conditions are compared with each other, and the modulation pattern is adjusted so as to achieve the condition of the spherical aberration according to the optical axis profile having the maximum brightness value.

[0022] [E16] In any of the laser processing methods [E10] to [E15] above, it may also include: step 6, which compares the optical axis contour obtained in step 4 with the comparison data of the contour image used for comparison, and when the difference between the compared data is within a specified range, it is determined that the optical axis contour is normal; when the difference is outside the specified range, it is determined that the optical axis contour is abnormal, and the determination result is output.

[0023] [E17] In any of the laser processing methods described in [E10] to [E16] above, in the second step, a laser beam having an output lower than an output during wafer processing may be emitted.

[0024] [E18] In any of the laser processing methods described in [E10] to [E17] above, the optical axis profile may be three-dimensional data obtained by synthesizing a plurality of two-dimensional camera images. Effects of the Invention

[0025] According to the laser processing apparatus and the laser processing method according to one aspect of the present invention, desired laser processing can be performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a diagram showing the structure of a laser processing device according to one embodiment. Figure 2 yes Figure 1 A cross-sectional view of a portion of a spatial light modulator is shown. Figure 3 (a) is a diagram illustrating continuous imaging along the Z direction. Figure 3 (b) is a diagram showing an optical axis profile obtained by synthesizing captured images. Figure 4 (a) is a cross-sectional view showing the optical axis profile represented by two-dimensional data, Figure 4 (b) is a diagram showing the optical axis profile represented by three-dimensional data. Figure 5 : is a flowchart showing the optical axis profile acquisition process. Figure 6 (a) is a diagram showing the optical axis profile of a wafer including a birefringent material, Figure 6 (b) is a diagram illustrating damage to the device caused by lack of light. Figure 7 (a) and (b) are diagrams for explaining the focusing points of birefringent materials. Figure 8 (a) is a diagram showing the optical axis profile of a wafer including a birefringent material, Figure 8 (b) shows that considering Figure 8Graph of the optical axis profile in the case where the modulation pattern is adjusted in contrast to the optical axis profile shown in (a). Fig. 9 (a) is the image of the focal point when no countermeasures are taken. Fig. 9 (b) is the image of the focal point when the intensity of the focal point on the surface side is increased. Fig. 9 (c) is the image of the focal point when the intensity of the focal point on the back side is increased. Fig.10 (a) is a diagram showing the intensity ratio in the case of no slit pattern, Fig.10 (b) is a diagram showing the intensity ratio when the slit A is provided. Fig.11 (a) is a diagram showing the intensity ratio when the slit B is provided. Fig.11 (b) is a diagram showing the intensity ratio when the slit C is provided. Fig.12 is a flowchart of the modulation pattern adjustment process. Fig.13 This is a flowchart of error state determination processing of a laser processing device. Fig.14 (a) is a diagram showing an optical axis profile when a wafer with an unknown refractive index is processed with an incorrect modulation pattern. Fig.14 (b) shows that considering Fig.14 Graph of the optical axis profile in the case where the modulation pattern is adjusted in contrast to the optical axis profile shown in (a). Fig.15 This is a diagram for explaining the adjustment of spherical aberration. Fig.16 : is a flowchart showing the spherical aberration adjustment process. DETAILED DESCRIPTION

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In each of the drawings, the same or corresponding parts are denoted by the same reference numerals and overlapping descriptions may be omitted. [Structure of laser processing device]

[0028] like Figure 1 As shown, the laser processing device 1 includes: a support part 2, a light source 3, an optical axis adjustment part 4, a spatial light modulator 5, a focusing part 6, a moving part 7, a visual camera part 8 (camera part), and a control part 10. Furthermore, the camera part can also be an infrared camera. The laser processing device 1 is a device for forming a modified area 12 on the wafer 11 by irradiating the laser L to the wafer 11. In the following description, the three directions orthogonal to each other are respectively referred to as the X direction, the Y direction and the Z direction. In this embodiment, the X direction is the first horizontal direction, the Y direction is the second horizontal direction perpendicular to the first horizontal direction, and the Z direction is the vertical direction.

[0029] The support part 2 supports the wafer 11 having a surface 11a (first surface) and a back surface 11b (second surface). As an example, the support part 2 supports the wafer 11 in a manner that the surface 11a of the wafer 11 is orthogonal to the Z direction by adsorbing a thin film (not shown) attached to the wafer 11. The support part 2 can move in each direction of the X direction and the Y direction, and can rotate with an axis parallel to the Z direction as a center line.

[0030] The light source 3 emits laser light L. As an example, the light source 3 emits the laser light L by a pulse oscillation method. The laser light L is transmissive to the wafer 11 .

[0031] The optical axis adjusting unit 4 adjusts the optical axis of the laser light L emitted from the light source 3. In the present embodiment, the optical axis adjusting unit 4 changes the traveling direction of the laser light L emitted from the light source 3 to be along the Z direction while adjusting the optical axis of the laser light L. The optical axis adjusting unit 4 is composed of, for example, a plurality of reflective mirrors capable of adjusting positions and angles.

[0032] The spatial light modulator 5 is disposed in the housing H. The spatial light modulator 5 modulates the laser light L emitted from the light source 3. In the present embodiment, the laser light L traveling downward along the Z direction from the optical axis adjustment unit 4 is incident on the housing H, and the laser light L incident on the housing H is horizontally reflected by the reflector M1 in a manner that forms an angle with respect to the Y direction, and the laser light L reflected by the reflector M1 is incident on the spatial light modulator 5 again. The spatial light modulator 5 modulates the incident laser light L while reflecting it horizontally along the Y direction in this manner.

[0033] The spatial light modulator 5 of this embodiment is, for example, a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM: Spatial Light Modulator). Figure 2 As shown, the spatial light modulator 5 is constructed by sequentially stacking a drive circuit layer 52 , a pixel electrode layer 53 , a reflective film 54 , an alignment film 55 , a liquid crystal layer 56 , an alignment film 57 , a transparent conductive film 58 and a transparent substrate 59 on a semiconductor substrate 51 .

[0034] The semiconductor substrate 51 is, for example, a silicon substrate. The driving circuit layer 52 forms an active matrix circuit on the semiconductor substrate 51. The pixel electrode layer 53 includes a plurality of pixel electrodes 53a arranged in a matrix along the surface of the semiconductor substrate 51. Each pixel electrode 53a is formed of a metal material such as aluminum. A voltage is applied to each pixel electrode 53a through the driving circuit layer 52.

[0035] The reflective film 54 is, for example, a dielectric multilayer film. The orientation film 55 is provided on the surface of the liquid crystal layer 56 on one side of the reflective film 54, and the orientation film 57 is provided on the surface of the liquid crystal layer 56 on the opposite side to the reflective film 54. Each of the orientation films 55 and 57 is made of a polymer material such as polyimide, and a rubbing treatment is applied to the contact surface of each of the orientation films 55 and 57 that contacts the liquid crystal layer 56. The orientation films 55 and 57 align the liquid crystal molecules 56a contained in the liquid crystal layer 56 in a certain direction.

[0036] The transparent conductive film 58 is provided on the surface of the transparent substrate 59 on one side of the orientation film 57, and faces the pixel electrode layer 53 via the liquid crystal layer 56. The transparent substrate 59 is, for example, a glass substrate. The transparent conductive film 58 is formed of a light-transmitting and conductive material such as ITO. The transparent substrate 59 and the transparent conductive film 58 allow the laser light L to pass through.

[0037] In the spatial light modulator 5 constructed as described above, if a signal indicating a modulation pattern is input from the control unit 10 to the drive circuit layer 52, a voltage according to the signal is applied to each pixel electrode 53a, and an electric field is formed between each pixel electrode 53a and the transparent conductive film 58. When the electric field is formed, the arrangement direction of the liquid crystal molecules 216a changes in each region corresponding to each pixel electrode 53a in the liquid crystal layer 56, and the refractive index changes in each region corresponding to each pixel electrode 53a. This state is a state in which the modulation pattern is expressed in the liquid crystal layer 56.

[0038] In a state where the modulation pattern is displayed on the liquid crystal layer 56, if the laser light L is incident on the liquid crystal layer 56 from the outside via the transparent substrate 59 and the transparent conductive film 58, and then is reflected by the reflective film 54, and is emitted from the liquid crystal layer 56 via the transparent conductive film 58 and the transparent substrate 59 to the outside, the laser light L is modulated according to the modulation pattern displayed on the liquid crystal layer 56. In this way, if the modulation pattern displayed on the liquid crystal layer 56 is appropriately set by the spatial light modulator 5, the laser light L can be modulated (for example, the intensity, amplitude, phase, polarization, etc. of the laser light L can be modulated).

[0039] like Figure 1As shown, the focusing section 6 is mounted on the bottom wall of the frame H. The focusing section 6 focuses the laser light L modulated by the spatial light modulator 5 on the wafer 11 supported by the support section 2. In the present embodiment, the laser light L horizontally reflected along the Y direction by the spatial light modulator 5 is reflected downward along the Z direction by the beam splitter M2, and the laser light L reflected by the beam splitter M2 is incident on the focusing section 6. The focusing section 6 focuses the laser light L thus incident on the wafer 11 from the surface 11a (first surface) side along the Z direction. In the present embodiment, the focusing section 6 is formed by mounting a focusing mirror unit 61 on the bottom wall of the frame H via a driving mechanism 62. The focusing mirror unit 61 has a function of focusing parallel light on a point on the optical axis. The driving mechanism 62 moves the focusing mirror unit 61 along the Z direction by, for example, the driving force of a piezoelectric component.

[0040] Furthermore, an imaging optical system (not shown) is arranged between the spatial light modulator 5 and the focusing section 6 in the housing H. The imaging optical system is a bilateral telecentric optical system in which the reflection surface of the spatial light modulator 5 and the entrance pupil surface of the focusing section 6 are in an imaging relationship. Thus, the image of the laser light L on the reflection surface of the spatial light modulator 5 (the image of the laser light L modulated by the spatial light modulator 5) is similarly transferred (imaged) on the entrance pupil surface of the focusing section 6.

[0041] A pair of distance measuring sensors S1 and S2 are arranged on the bottom wall of the frame H so as to be located on both sides of the condenser unit 61 in the X direction. Each distance measuring sensor S1 and S2 emits distance measuring light (such as laser) to the surface 11a of the wafer 11, and detects the distance measuring light reflected by the surface 11a, thereby obtaining displacement data of the surface 11a.

[0042] The moving part 7 moves the focusing part 6 relative to the surface 11a of the wafer 11 in a direction perpendicular to the surface 11a of the wafer 11, that is, in the direction of the optical axis (that is, in the Z direction). The moving part 7 is a moving mechanism (including a driving source such as an actuator and a motor) that moves the focusing part 6 relative to the surface 11a of the wafer 11 by moving at least one of the frame H and the support part 2. In this embodiment, the moving part 7 moves the support part 2 in the respective directions of the X direction and the Y direction, and rotates the support part 2 with the axis parallel to the Z direction as the center line, so that the frame H moves in the Z direction.

[0043] The visible camera unit 8 is disposed in the housing H. The visible camera unit 8 emits visible light V, and acquires an image of the wafer 11 passing through the visible light V as an image. In the present embodiment, the visible light V emitted from the visible camera unit 8 is irradiated to the wafer 11 via the spectroscope M2 and the focusing unit 6, and the visible light V reflected by the wafer 11 is detected by the visible camera unit 8 via the focusing unit 6 and the spectroscope M2. That is, the visible camera unit 8 acquires a camera image by detecting the light propagated on the wafer 11 via the focusing unit 6.

[0044] The control unit 10 controls the operation of each part of the laser processing device 1. The control unit 10 has a processing unit 101, a memory unit 102 and an interface unit 103. The processing unit 101 is configured as a computer device including a processor, a memory, a storage, a communication device, etc. In the processing unit 101, the processor executes software (program) loaded in the memory, etc., controls the reading and writing of data in the memory and the storage, and the communication through the communication device. The memory unit 102 is, for example, a hard disk, which stores various data. The interface unit 103 is an interface unit that displays various data to the operator or receives input of various data from the operator. In this embodiment, the interface unit 103 constitutes a GUI (Graphical User Interface).

[0045] In the laser processing device 1 constructed as described above, if the laser L is focused inside the wafer 11, the laser L is absorbed in the portion corresponding to the focal point C of the laser L, and a modified region 12 is formed inside the wafer 11. The modified region 12 is a region in which the density, refractive index, mechanical strength, other physical properties, etc. are formed to be different from the surrounding non-modified regions. The modified region 12 includes, for example, a melt processing region, a crack region, an insulation breakdown region, a refractive index change region, etc. The modified region 12 has a characteristic that cracks easily extend from the modified region 12 along the incident side of the laser L and the opposite side thereof. Such characteristics of the modified region 12 are used, for example, for cutting the wafer 11.

[0046] As an example, the operation of the laser processing apparatus 1 will be described regarding a case where the modified region 12 is formed inside the wafer 11 along the line 15 for cutting the wafer 11 .

[0047] First, the laser processing apparatus 1 rotates the support unit 2 with the axis parallel to the Z direction as the center line so that the line 15 set on the wafer 11 is parallel to the X direction. Next, the laser processing apparatus 1 moves the support unit 2 in the X direction and the Y direction so that the focal point C of the laser light L is located on the line 15 when viewed from the Z direction.

[0048] Next, the laser processing apparatus 1 moves the frame H (i.e., the focusing unit 6) along the Z direction so that the focusing point C of the laser light L is located on the surface 11a based on the image (e.g., the image of the surface 11a of the wafer 11) acquired by the visual imaging unit 8. Next, the laser processing apparatus 1 moves the frame H (i.e., the focusing unit 6) along the Z direction so that the focusing point C of the laser light L is located at a predetermined depth from the surface 11a, using this position as a reference.

[0049] Next, the laser processing device 1 emits the laser light L from the light source 3, and moves the support unit 2 along the X direction in such a manner that the focal point C of the laser light L moves relatively along the line 15. At this time, the laser processing device 1 operates the driving mechanism 62 of the focusing unit 6 so that the focal point C of the laser light L is located at a predetermined depth from the surface 11a based on the displacement data of the surface 11a obtained by the distance measuring sensor located on the front side (the front side in the relative movement direction of the laser light L with respect to the wafer 11) of the pair of distance measuring sensors S1 and S2.

[0050] According to the above method, a row of modified regions 12 is formed along the line 15 and at a certain depth from the surface 11a of the wafer 11. If the laser L is emitted from the light source 3 by pulse oscillation, a plurality of modified points 12s are formed in a row along the X direction. One modified point 12s is formed by irradiation with one pulse of laser L. A row of modified regions 12 is a collection of a plurality of modified points 12s arranged in a row. Adjacent modified points 12s may be connected or separated depending on the pulse spacing of the laser L (the relative moving speed of the focal point C to the wafer 11 divided by the repetition frequency of the laser L). [Obtaining the optical axis profile]

[0051] The following describes the acquisition process of the optical axis profile performed in the laser processing device 1. The so-called optical axis profile is data obtained by synthesizing a plurality of camera images continuously acquired by synthesizing the light reflected on the back side 11b of the wafer 11 detected by the visible camera unit 8 while the focusing unit 6 moves relative to the surface 11a in the Z direction and emits laser light. Specifically, the optical axis profile is a contour image of the laser along the Z direction acquired by synthesizing the above-mentioned plurality of camera images. Based on the optical axis profile, the irradiation condition of the laser along the optical axis direction (for example, the position and intensity of the focusing point of the wafer 11, etc.) is determined. Thus, for example, it is possible to determine whether some abnormality has occurred in the laser processing device 1, whether it is necessary to adjust the modulation pattern set in the spatial light modulator 5, etc. (as described in detail later).

[0052] Figure 3 (a) is a diagram for explaining continuous imaging along the Z direction. Figure 3 (a) shows, from the left, the image of the cross section A, the image of the cross section B, the image of the cross section C, and the image of the cross section D. Figure 3 In the example shown in (a), the focusing unit 6 moves relatively along the Z direction in a manner gradually approaching the wafer 11 from left to right in the figure. Figure 3As shown in (a), if the position of the focusing unit 6 moves by ΔZ, the path of the laser reflected by the back surface 11b of the wafer 11 and photographed by the visual camera unit 8 changes by ΔZ×2 in total in the forward path and the return path. The focusing unit 6 moves together with the visual camera unit 8 through, for example, the moving unit 7. That is, both the focusing point of the laser and the observation surface (camera imaging surface) of the visual camera unit 8 move. Furthermore, the focusing mirror unit 61 of the focusing unit 6 can also be moved by the driving mechanism 62.

[0053] In this case, the control unit 10 performs: a first process of controlling the moving unit 7 so that the focusing unit 6 moves relative to the surface 11a of the wafer 11 in the Z direction; and a second process of controlling the light source 3 so that the laser is continuously emitted while the first process is being executed. The control unit 10 controls the light source 3 so that in the second process, a laser with an output lower than the output when the wafer 11 is processed is emitted. Further, the control unit 10 performs a third process of controlling the visible camera unit 8 so that the light reflected on the back side 11b of the wafer 11 is detected while the second process is being executed and a plurality of camera images are continuously acquired. Further, the control unit 10 performs a fourth process so as to acquire a contour image of the laser along the Z direction, i.e., an optical axis contour, by synthesizing a plurality of camera images continuously acquired in the third process.

[0054] Figure 3 (b) is a diagram showing the optical axis profile obtained by synthesizing the captured images. Figure 3 The lower layer of (a) shows the camera images of each of the sections A, B, C, and D. By synthesizing the camera images obtained continuously, as shown in FIG. Figure 3 As shown in (b), an optical axis profile is obtained that can determine the irradiation conditions of the laser (for example, the position and intensity of the focal point C).

[0055] Figure 4 (a) is a cross-sectional view showing the optical axis profile represented by two-dimensional data, Figure 4 (b) is a diagram showing the optical axis profile represented by three-dimensional data. The optical axis profile can also be obtained by, for example, synthesizing a plurality of two-dimensional camera images to obtain three-dimensional data (see Figure 4 (b)). Alternatively, Figure 4 As shown in (b), in the three-dimensional data, the color is differentiated according to the intensity of the laser. Alternatively, the optical axis profile can also be generated from the two-dimensional data obtained from the three-dimensional data (see Figure 4 (a)). Figure 4 As shown in the right figure of (a), a graph showing the intensity of the laser light in each area may be displayed in parallel with the two-dimensional data.

[0056] Figure 51 is a flowchart showing the optical axis profile acquisition process performed by the laser processing apparatus 1. In the optical axis profile acquisition process, first, the thin film attached to the wafer 11 is sucked by the support unit 2 (step S1).

[0057] Next, by controlling the control unit 10, the moving unit 7 moves the focusing unit 6, thereby moving the wafer 11 to the position directly below the objective lens of the focusing unit 6 (step S2). In this state, the moving unit 7 moves under the control of the control unit 10 in such a manner that the height in the Z direction is set at the focus position of the reticle (step S3). Further, the moving unit 7 moves under the control of the control unit 10 in such a manner that the height in the Z direction is reduced by an amount equivalent to the thickness of the wafer 11 (step S4).

[0058] Next, a signal indicating a modulation pattern is inputted from the control unit 10 to the spatial light modulator 5. Specifically, a modulation pattern indicating, for example, a strain correction pattern and a spherical aberration twice the wafer thickness is inputted to the spatial light modulator 5 (step S5).

[0059] Next, all light sources except the light source 3 of the laser processing device 1 are turned off, and the control unit 10 controls the light source 3 to emit laser light (step S6). In order to reliably check the laser light, the control unit 10 performs various settings such as the output of the laser light.

[0060] Next, it is determined whether ablation occurs on the surface of the wafer 11 (step S8). If ablation occurs, the laser output is adjusted or the attenuator output is adjusted to a state where ablation does not occur (step S9). In addition, the light sources other than the light source 3 of the laser processing device 1 are turned on (step S10), and it is confirmed that there is a position where ablation does not occur and the objective lens of the focusing unit 6 is above the wafer 11 (step S11), and the process of step S3 is implemented again.

[0061] On the other hand, if it is determined in step S8 that ablation has not occurred, fine adjustment in the Z direction is performed at the position where the laser light is most focused (step S12), and the setting values ​​of the laser visible imaging unit 8 and the like are confirmed to be in an optimal state (step S13).

[0062] Then, under the control of the control unit 10, the driving mechanism 62 as the actuator for the objective lens of the focusing unit 6 or the moving unit 7 related to the movement in the Z-axis direction is moved while the visual camera unit 8 continuously performs imaging (step S14). Finally, the control unit 10 synthesizes a plurality of captured images to obtain the optical axis profile near the focal point (step S15).

[0063] The above is an example of the optical axis profile acquisition process. Hereinafter, as processes performed using the optical axis profile acquired in the fourth process, the focusing point adjustment of the birefringent material, the error state determination of the laser processing device 1, and the spherical aberration adjustment processes are sequentially described. [Adjustment of the focal point of birefringent materials]

[0064] Figure 6 (a) is a diagram showing the optical axis profile of a wafer 11 composed of a birefringent material. When laser light is irradiated into a birefringent material, two focal points, a focal point C1 according to ordinary light and a focal point C2 according to extraordinary light, are generated according to the difference in the refractive index of polarized light, unlike silicon, glass, etc. For example, in the case of dicing by laser irradiation, even if the focal point branches upward or downward in the cutting direction (Z direction), it will not cause a big problem. On the other hand, in the case of sliding in the slicing direction, there is a risk of deterioration in processing accuracy due to the influence of the branching of the focal point. In addition, if Figure 6 As shown in (b), as the wafer 11 becomes thinner, countermeasures against device damage due to lack of light become necessary. Figure 6 As shown in the left figure of (b), if the focal point on the lower side (here, the focal point C2 based on the extraordinary ray) is sufficiently separated from the device on the back side 11b (e.g., the electrode 200), damage to the electrode 200 due to lack of light will not be a problem. On the other hand, for example Figure 6 As shown in the right figure of (b), when the focal point on the lower side (here, the focal point C2 based on the extraordinary ray) is close to the device (e.g., electrode 200) on the back side 11b, damage to the electrode 200 due to lack of light becomes a problem. As described above, when laser light is injected into a birefringent material, certain measures need to be taken to suppress deterioration of processing accuracy and damage to the device.

[0065] Furthermore, if Figure 7 (a) and Figure 7 As shown in (b), when the laser is incident on the birefringent material, the focal point C1 according to the ordinary ray branches upwards compared to the focal point C2 according to the extraordinary ray (refer to Figure 7 (a)), or conversely, branching downward from the focal point C2 according to the extraordinary ray (refer to Figure 7 (b)) is based on the type of birefringent material. Specifically, for positive birefringent materials such as GaN or crystal, Figure 7 As shown in (a), the focal point C1 of the ordinary ray branches upwards compared to the focal point C2 of the extraordinary ray. On the other hand, for negative birefringent materials such as calcite or sapphire, Figure 7 As shown in (b), the focal point C1 based on the ordinary ray branches downward than the focal point C2 based on the extraordinary ray.

[0066] The control unit 10 further performs a fifth process of adjusting the modulation pattern of the spatial light modulator 5 based on the optical axis profile obtained in the fourth process. In the fifth process, the control unit 10 determines the light-converging point C1 based on the ordinary ray and the light-converging point C2 based on the extraordinary ray based on the optical axis profile, and adjusts the modulation pattern so that the intensity of light at one of the two determined light-converging points increases and the intensity of light at the other light-converging point decreases.

[0067] Figure 8 (a) is a diagram showing the optical axis profile of a wafer 11 including a birefringent material, Figure 8 (b) shows that considering Figure 8 The optical axis profile of the case where the modulation pattern is adjusted is shown in (a). Figure 8 In the example shown in (a), the control unit 10 determines the focal point C1 based on the ordinary ray and the focal point C2 based on the extraordinary ray that branch upward and downward from the optical axis profile. In addition, the control unit 10 confirms the optical axis profile, such as Figure 8 As shown in (b), the modulation pattern is adjusted so that the intensity of the light at the focal point C2 based on the extraordinary ray increases, and the intensity of the light at the focal point C1 based on the ordinary ray decreases. In this way, the influence of the focal point C1 where the light intensity decreases can be minimized, and the disadvantages caused by the upward and downward branching of the focal point can be suppressed.

[0068] Here, in order to increase the intensity of either the light-converging point C1 of the ordinary ray or the light-converging point C2 of the extraordinary ray (using either light-converging point), the wafer 11 may be made of a positive birefringent material (see Figure 7 (a)) or made of negative birefringent material (refer to Figure 7 (b)) composition is different.

[0069] For example, for positive birefringent materials (see Figure 7 The situation of (a)) is explained below. Fig. 9 (a) is the image of the focal point when no countermeasures are taken (the intensity ratio of the two focal points is not changed). Fig. 9 (b) is the image of the focal point when the intensity of the focal point on the surface side is increased. Fig. 9 (c) is the image of the focal point when the intensity of the focal point on the back side is increased. Now, since a positive birefringent material is used, the focal point on the front side refers to the focal point C1 based on the ordinary ray. In addition, the focal point on the back side refers to the focal point C2 based on the extraordinary ray.

[0070] like Fig. 9As shown in (a), when the intensity ratio of the two focal points C1 and C2 is not changed, it is considered that the device (electrode 200) provided on the back surface 11b is damaged due to the lack of light from the focal point C2 based on the extraordinary ray closer to the back surface 11b. Fig. 9 As shown in (b), when the intensity of the focal point C1 based on the ordinary ray is increased and the intensity of the focal point C2 based on the extraordinary ray is reduced, the intensity of the focal point C2 based on the extraordinary ray closer to the back surface 11b becomes smaller. Therefore, although it is smaller than Fig. 9 In the example shown in (a), the device (e.g., electrode 200) is not easily damaged, but the influence of the focal point C2 remains, so the damage to the device (e.g., electrode 200) cannot be fully reduced. So far, the focal point C1 based on the ordinary ray is set as the processing target height (refer to Fig. 9 (a) and Fig. 9 (b)).

[0071] On the other hand, Fig. 9 As shown in (c), when the focal point C2 based on the extraordinary ray is set as the processing target height, and the intensity of the focal point C2 based on the extraordinary ray is increased, and the intensity of the focal point C1 based on the ordinary ray is reduced, compared with Fig. 9 In the example shown in (b), the distance from the back side 11b to the focal point C2 becomes longer. In this case, since the extended lack of light is irradiated on the device (e.g., electrode 200), the damage to the device (e.g., electrode 200) can be sufficiently reduced. Furthermore, since the focal point C2 according to the extraordinary ray is set as the processing target height, laser processing can be appropriately implemented by the laser according to the focal point C2 of the extraordinary ray. As described above, in the case of using a positive birefringent material, the control unit 10 can also adjust the modulation pattern in the above-mentioned fifth processing in such a way that the intensity of light at the focal point (the focal point C2 according to the extraordinary ray) on the side close to the back side 11b of the two focal points becomes larger, and the intensity of light at the focal point (the focal point C1 according to the ordinary ray) on the side away from the back side 11b becomes smaller.

[0072] In the fifth process, the control unit 10 may adjust the modulation pattern by using a slit pattern that blocks a part of the polarized light component of the laser light. Such a slit pattern is set as a part of the modulation pattern displayed on the liquid crystal layer 56 of the spatial light modulator 5. In the spatial light modulator 5, by appropriately setting the modulation pattern displayed on the liquid crystal layer 56, the laser light L can be modulated (for example, the intensity, amplitude, phase, polarized light, etc. of the laser light L can be modulated). The modulation pattern refers to a holographic pattern to which modulation is applied, including a slit pattern.

[0073] Fig.10(a) is a diagram showing the intensity ratio when there is no slit pattern, Fig.10 (b) is a diagram showing the intensity ratio when the slit A is set, Fig.11 (a) is a diagram showing the intensity ratio when the slit B is provided, Fig.11 (b) is a diagram showing the intensity ratio when the slit C is provided. Fig.10 (a)~ Fig.11 (b) shows the modulation pattern (including the slit pattern) displayed in the liquid crystal layer 56 of the spatial light modulator 5 on the upper layer, and shows the two-dimensional data of the optical axis profile on the lower layer.

[0074] Fig.10 (b) Fig.11 (a), and Fig.11 The slit pattern shown in (b) is provided with fan-shaped slits. In the following, the idea of ​​bringing the light-converging point closer to one point and the reason for using fan-shaped slits are described with respect to birefringent materials.

[0075] Generally, when laser light is focused on a wafer made of birefringent material, the refractive indexes of the P polarized light component and the S polarized light component in the laser light are different from each other. The laser light is divided into ordinary light and extraordinary light, and the extraordinary light propagates at a different refraction angle from the ordinary light and does not follow Snell's law. Therefore, in the depth direction of the wafer, the P polarized light component and the S polarized light component are focused at different positions (the focusing points become two points).

[0076] Radially polarized light (radially polarized light) enters the wafer as P polarized light. In addition, azimuthally polarized light (azimuthally polarized light) enters the wafer as S polarized light. Therefore, by converting linear polarized light into either radially polarized light or azimuthally polarized light, the polarized light components of the laser can be unified into either P polarized light or S polarized light, and the focal point can be appropriately close to one point.

[0077] Furthermore, it is not possible to extract only one of the radial polarization light or the azimuthal polarization light from the linear polarization light. However, by applying the above-mentioned slit, the intensity ratio of either side can be increased. Fig.10 (b) Fig.11 (a) and Fig.11 As described in (b), by using a fan-shaped slit with the center of the optical axis as the boundary, the polarized light of one of the radial polarized light and the azimuth polarized light can be effectively utilized. For example, consider the case where you want to process only the radial polarized light component from the linear polarized light. In the case of using a linear slit, the azimuth polarized light component will remain if the slit is not narrowed, but the effective pattern area can be narrowed by narrowing the slit. In this regard, in the fan-shaped slit, the processing of the part with a strong radial component can be performed while ensuring the effective pattern area.

[0078] Comparison includes Fig.10 The modulation pattern MP2 of the slit pattern SP2 of the fan-shaped slit A shown in (b) includes Fig.11 The modulation pattern MP3 of the slit pattern SP3 of the fan-shaped slit B shown in (a), and the modulation pattern MP3 including Fig.11 The modulation pattern MP4 of the slit pattern SP4 of the fan-shaped slit C shown in (b) is as follows: the area of ​​the slit pattern SP3 is larger than the area of ​​the slit pattern SP2, and the area of ​​the slit pattern SP4 is larger than the area of ​​the slit pattern SP3. In this case, according to the intensity difference between the focal point C2 of the extraordinary ray and the focal point C1 of the ordinary ray, there is no slit pattern ( Fig.10 (a)) becomes the smallest, and the modulation pattern MP2 including the slit pattern SP2 ( Fig.10 (b)) becomes the second smallest, and the modulation pattern MP3 including the slit pattern SP3 ( Fig.11 (a)) becomes the next smallest, and the modulation pattern MP4 ( Fig.11 (b)) becomes the largest.

[0079] As mentioned above, the larger the slit pattern area is, the greater the intensity difference between the two focal points becomes. However, since the effective pattern area is narrowed, it is necessary to increase the laser output. In addition, the influence of combining with other patterns such as branches becomes more obvious. For example, in Fig.11 The modulation pattern MP4 shown in (b) has a negative impact on the light focusing property due to the excessive cutting of the laser light by the slit pattern SP4, which causes astigmatism.

[0080] Fig.12 1 is a flowchart of the modulation pattern adjustment process. In the modulation pattern adjustment process, first, the optical axis profile near the focal point is acquired (step S101).

[0081] Next, the distance from the light-converging point C1 based on the ordinary ray to the light-converging point C2 based on the extraordinary ray is measured (step S102). This distance is information required when setting the light-converging point C2 based on the extraordinary ray as the processing target height when the extraordinary ray is used in laser processing, assuming that the processing conditions are made with the refractive index of the ordinary ray.

[0082] Next, it is determined whether the extraordinary ray is used in the laser processing (step S103). If it is determined in step S103 that the extraordinary ray is used, the modulation pattern is adjusted so that the intensity of the focal point C2 based on the extraordinary ray becomes larger (step S104).

[0083] In addition, after adjusting the modulation pattern, the optical axis profile near the focal point is obtained again (step S105). Then, the intensities of the focal point C2 based on the extraordinary ray and the focal point C1 based on the ordinary ray are compared (step S106), and it is determined whether they are within the normal range (step S107). If they are not within the normal range, the processing of step S104 is performed again. If they are within the normal range, the distance obtained in step S102 is reflected in the processing recipe, and the focal point C2 based on the extraordinary ray is set as the processing target height (step S108).

[0084] On the other hand, when it is determined in step S103 that the extraordinary ray is not used (the ordinary ray is used), the modulation pattern is adjusted so that the intensity of the focal point C1 based on the ordinary ray becomes larger (step S109).

[0085] Furthermore, after adjusting the modulation pattern, the optical axis profile near the focal point is obtained again (step S110). Then, the intensities of the focal point C1 based on the ordinary ray and the focal point C2 based on the extraordinary ray are compared (step S111), and it is determined whether they are within the normal range (step S112). If they are within the normal range, the process of step S109 is performed again, and if they are within the normal range, the process is terminated. [Determination of error status of laser processing equipment]

[0086] The control unit 10 compares the optical axis profile obtained in the fourth process with the comparison data of the profile image for comparison, and determines that the optical axis profile is normal when the difference between the compared data is within a predetermined range, and determines that the optical axis profile is abnormal when the difference is outside the predetermined range, and may further perform a sixth process of outputting the determination result. The optical axis profile abnormality referred to herein means that the laser processing device 1 is in a certain error state.

[0087] The control unit 10 may use, for example, an optical axis profile acquired in the past as a comparative profile image. Alternatively, the control unit 10 may use, for example, data created based on a simulation as a comparative profile image.

[0088] When the optical axis profile fails to confirm the focal point, the control unit 10 determines that it is a serious error and outputs the determination result. A serious error refers to, for example, an abnormality of the laser processing device, a measurement error (wafer error), etc. In addition, when the focusing state is different from the ideal state, the control unit 10 determines that it is an abnormality of the spatial light modulator 5 (for example, spherical aberration, strain correction error, etc.) when the laser adjustment is correct, and performs laser readjustment when the laser adjustment is incorrect.

[0089] Fig.13This is a flowchart of the error state identification process of the laser processing device 1. In the error state identification process, first, the optical axis profile near the focal point is acquired (step S201).

[0090] Next, the obtained optical axis profile is compared with the comparison data of the comparison profile image (for example, the optical axis profile obtained in the past) (step S202), and it is determined whether the difference between the compared data is within a predetermined normal range (step S203). The difference between the data refers to, for example, the difference in the position or intensity of the focal point. If it is determined to be normal in step S203, it is indicated as normal by the control unit 10 (step S204).

[0091] If it is determined that step S203 is abnormal, the control unit 10 indicates an error (step S205). In addition, the control unit 10 confirms the content of the error and determines whether there is a focal point (step S206). If it is determined that there is no focal point in step S206, it is determined to be a serious error (step S207). A serious error refers to, for example, an abnormality of the laser processing device, a measurement error (wafer error), etc.

[0092] If it is determined in step S206 that there is a focal point, the control unit 10 determines whether the adjustment of the laser is correct (step S208). If the adjustment of the laser is correct, it is determined that there is an abnormality in the spatial light modulator 5 (for example, spherical aberration, error in strain correction, etc.) (step S209). If the adjustment of the laser is incorrect, the laser is readjusted (step S210). [Spherical aberration adjustment]

[0093] The control unit 10 may also change the spherical aberration condition determined by the modulation pattern while implementing the above-mentioned first, second, third and fourth processes under respective conditions. In the fifth process, the maximum values ​​of the brightness values ​​of the laser represented by the optical axis profiles obtained under respective conditions are compared with each other, and the modulation pattern is adjusted to achieve the spherical aberration condition of the optical axis profile having the maximum brightness value.

[0094] For example, for a wafer 11 whose refractive index is unknown, there are cases where processing is performed with an incorrect modulation pattern. Fig.14 As shown in (a), by obtaining the optical axis profile, the position deviation of the focal point can be determined and it can be found that an incorrect modulation pattern is set for the wafer 11 with an unknown refractive index. Then, the control unit 10 confirms that Fig.14 The optical axis profile shown in (a) is obtained while spherical aberration correction is performed to obtain Fig.14 The optical axis profile shown in (b) makes it possible to set a correct modulation pattern for laser processing of a wafer 11 whose refractive index is unknown.

[0095] The control unit 10 corrects the spherical aberration as a reference while changing the correction value, selects the brightness value of the focal point as the maximum correction value, and adjusts the modulation pattern to become the condition of the spherical aberration after correction according to the correction value. The spherical aberration as a reference can be, for example, a spherical aberration of twice the thickness of the wafer 11.

[0096] exist Fig.15 In the example shown, the maximum brightness values ​​are shown for the case where the spherical aberration used as the reference is corrected by the correction value A, the case where the correction is corrected by the correction value B, the case where the correction is corrected by the correction value C, and the case where the correction is corrected by the correction value D. Then, in consideration of these results, the modulation pattern is adjusted so as to achieve the condition of the spherical aberration with the maximum brightness of 248 by correction with the optimal correction value.

[0097] Fig.16 3 is a flow chart showing the spherical aberration adjustment process. In the spherical aberration adjustment process, first, the spherical aberration of twice the wafer thickness, which is considered to be the best, is determined as a reference (step S301). In addition, the control unit 10 sets the modulation pattern in a manner that becomes the condition of the spherical aberration used as the reference (step S302), and obtains the optical axis profile near the focal point (step S303).

[0098] Furthermore, the control unit 10 sets the modulation pattern so as to obtain the condition of the spherical aberration having an arbitrary value smaller than the spherical aberration serving as the reference (step S304), and obtains the optical axis profile near the light-converging point (step S305). Furthermore, the control unit 10 sets the modulation pattern so as to obtain the condition of the spherical aberration having an arbitrary value larger than the spherical aberration serving as the reference (step S306), and obtains the optical axis profile near the light-converging point (step S307).

[0099] Next, the control unit 10 determines whether the maximum brightness value of the spherical aberration smaller than the spherical aberration used as the reference is larger based on the obtained optical axis profile (step S308). When it is determined in step S308 that the maximum brightness value of the spherical aberration set to the smaller value is larger, the control unit 10 sets the spherical aberration smaller than the reference as a new reference (step S309), and the processing after step S302 is performed again.

[0100] On the other hand, if it is determined in step S308 that the maximum brightness value of the spherical aberration set to an arbitrary small value is not large (that is, the maximum brightness value set as the reference is large), the control unit 10 determines whether the maximum brightness value of the spherical aberration used as the reference is the maximum (step S310). In step S310, if it is determined that the maximum brightness value of the spherical aberration used as the reference is the maximum, the control unit 10 reflects a value of 1 / 2 of the spherical aberration used as the reference in the processing recipe (step S311).

[0101] On the other hand, when it is determined in step S310 that the maximum brightness value of the spherical aberration serving as the reference is not the maximum (i.e., the maximum brightness value of the spherical aberration of an arbitrary value is the maximum), the spherical aberration of an arbitrary value is set as a new reference by the control unit 10 (step S312), and the processing after step S302 is implemented again. [Effects]

[0102] The laser processing device 1 comprises: a support unit 2 for supporting a wafer 11 having a surface 11a and a back surface 11b; a light source 3 for emitting laser light; a spatial light modulator 5 for modulating the laser light emitted from the light source 3; a focusing unit 6 for focusing the laser light modulated by the spatial light modulator 5 on the wafer 11 from the surface 11a side of the wafer 11; a moving unit 7 for moving the focusing unit 6 relative to the surface 11a in a direction perpendicular to the surface 11a, i.e., in the direction of the optical axis; a visual camera unit 8 for acquiring a camera image by detecting light propagating on the wafer 11 via the focusing unit 6; and a control unit 10, which is configured to execute: a first process of controlling the moving part 7 to move the focusing part 6 relative to the surface 11a in the optical axis direction; a second process of controlling the light source 3 to continuously emit laser light while executing the first process; a third process of controlling the visible camera part 8 to detect the light reflected from the back side 11b of the wafer 11 and continuously obtain a plurality of camera images while executing the second process; and a fourth process of obtaining a contour image of the laser along the optical axis direction, i.e., the optical axis contour, by synthesizing the plurality of camera images continuously obtained in the third process.

[0103] In the laser processing device 1 of the present embodiment, the laser is irradiated while the focusing section 6 is moved along the optical axis direction, and the light reflected on the back side 11b of the wafer 11 is detected, and a plurality of camera images are continuously acquired. In addition, in the laser processing device 1, a contour image of the laser along the optical axis direction, i.e., the optical axis contour, is acquired by synthesizing a plurality of camera images. In this way, while the laser light focal point is moved along the optical axis direction (the depth direction of the wafer 11), the reflected light from the back side 11b of the wafer 11 is detected, and the above-mentioned optical axis contour is acquired, thereby the irradiation condition of the laser along the optical axis direction (e.g., the position and intensity of the light focal point) can be grasped. Thus, for example, it is possible to determine whether a certain abnormality has occurred in the laser processing device 1, whether it is necessary to adjust the modulation pattern set in the spatial light modulator 5, etc., and the desired laser processing can be implemented more accurately.

[0104] The control unit 10 may further execute a fifth process of adjusting the modulation pattern of the spatial light modulator 5 based on the optical axis profile obtained in the fourth process. With such a configuration, the modulation pattern can be optimized in consideration of the optical axis profile, and desired laser processing can be performed more accurately.

[0105] The wafer 11 is formed by containing a birefringent material. In the fifth process, the control unit 10 determines the focal point according to the ordinary ray and the focal point according to the extraordinary ray based on the optical axis profile, and adjusts the modulation pattern so that the light intensity of one of the two focal points becomes larger and the light intensity of the other focal point becomes smaller. In the case of focusing the laser on the wafer 11 containing a birefringent material, the refractive indexes of the P polarized light component and the S polarized light component in the incident light are different from each other. In addition, these incident lights are divided into ordinary rays and extraordinary rays, and the extraordinary rays propagate at a refraction angle different from that of the ordinary rays and do not follow Snell's law. According to these circumstances, in the depth direction of the wafer 11, the P polarized light component and the S polarized light component are focused at different positions from each other. In this way, the focal point is branched in the depth direction, so that multiple focal points are unintentionally formed on the wafer 11, resulting in incorrect cracks. Therefore, there is a risk of reduced processing quality such as slippage. In this regard, the modulation pattern is adjusted based on the optical axis profile so that the intensity of one of the focal points becomes larger and the intensity of the other focal point becomes smaller, thereby suppressing the reduction in processing quality caused by forming the above-mentioned multiple focal points.

[0106] The control unit 10 may also adjust the modulation pattern in the fifth process so that the intensity of the light of the light-converging point on the side close to the back 11b of the two light-converging points increases, and the intensity of the light of the light-converging point on the side far from the back 11b decreases. By adjusting the modulation pattern, the intensity ratio of the two light-converging points can be changed, but any of the light-converging points cannot be completely eliminated. For example, when the light-converging point on the side far from the back 11b is mainly used and the intensity of the light of the light-converging point on the side close to the back 11b is reduced as much as possible, since the light-converging point on the side far from the back 11b is set to the processing target height, the light-converging point on the side close to the back 11b exists although it is weak. Since a device is provided on the back 11b, it is possible that the device is damaged by the influence of the light-converging point on the side close to the back 11b. In this regard, when the focusing point on the side close to the back side 11b is mainly used, since the focusing point on the side close to the back side 11b is set to the processing target height, there is no focusing point on the side closer to the back side 11b, so the damage to the device on the back side 11b can be reduced.

[0107] The control unit may adjust the modulation pattern by using a slit pattern that blocks a part of the polarized light component of the laser light in the fifth process. According to such a configuration, the intensity of light at any one of the light-converging points can be easily weakened.

[0108] The control unit 10 can also change the spherical aberration condition determined by the modulation pattern while performing the first process, the second process, the third process, and the fourth process under the respective conditions. In the fifth process, the maximum values ​​of the brightness values ​​of the laser light represented by the optical axis profile obtained under the respective conditions are compared with each other, and the modulation pattern is adjusted to achieve the spherical aberration condition of the optical axis profile with the maximum brightness value. According to such a structure, even for the wafer 11 with an unknown refractive index, for example, accurate spherical aberration correction can be performed.

[0109] The control unit 10 compares the optical axis profile obtained in the fourth process with the comparison data of the profile image for comparison, and determines that the optical axis profile is normal when the difference between the compared data is within a prescribed range, and determines that the optical axis profile is abnormal when the difference is outside the prescribed range, and outputs the sixth process of the determination result. According to such a structure, by setting the profile image when the laser processing device is normal in advance as comparison data, it is possible to easily determine whether a certain abnormality has occurred in the laser processing device 1 based on the comparison of the optical axis profile and the comparison data. In addition, by outputting the determination result, the laser processing device 1 can be adjusted in consideration of the determination result. As described above, according to the above structure, the desired laser processing can be more accurately performed.

[0110] The control unit 10 may control the light source 3 so that, in the second process, a laser beam having an output lower than that in processing the wafer 11 is emitted. In this way, the optical axis profile can be obtained without actually performing laser processing.

[0111] The optical axis profile is three-dimensional data obtained by combining multiple two-dimensional camera images. By obtaining the optical axis profile as three-dimensional data, the irradiation status of the laser along the optical axis direction (such as the position and intensity of the focal point) can be understood in more detail. Explanation of symbols

[0112] 1...laser processing device, 2...supporting part, 3...light source, 5...spatial light modulator, 6...focusing part, 7...moving part, 8...visual imaging part (imaging part), 10...control part, 11...wafer, 11a...surface (first surface), 11b...back side (second surface).

Claims

1. A laser processing device, wherein: have: A support portion that supports a wafer having a first surface and a second surface; a light source that emits laser light; a spatial light modulator for modulating the laser light emitted from the light source; a focusing unit that focuses the laser light modulated by the spatial light modulator onto the wafer from the first surface side of the wafer; a moving portion that moves the light-collecting portion relative to the first surface along an optical axis direction that is a direction perpendicular to the first surface; an imaging unit configured to acquire an image by detecting the light propagating through the wafer via the light focusing unit; and a control unit for executing: a first process of controlling the moving unit in such a manner that the focusing unit moves relative to the first surface in the direction of the optical axis; a second process of controlling the light source in such a manner that the laser light is continuously emitted while the first process is executed; and a third process of controlling the imaging unit in such a manner that the light reflected on the second surface of the wafer is detected and a plurality of the imaging images are continuously acquired while the second process is executed; and a fourth process of synthesizing the plurality of captured images continuously acquired in the third process to acquire an optical axis profile as a profile image of the laser light along the optical axis direction.

2. The laser processing device according to claim 1, wherein: The control unit further executes a fifth process of adjusting a modulation pattern of the spatial light modulator based on the optical axis profile acquired in the fourth process.

3. The laser processing device according to claim 2, wherein: The wafer comprises a birefringent material, In the fifth processing, the control unit determines the focal point according to the ordinary ray and the focal point according to the extraordinary ray based on the optical axis profile, and adjusts the modulation pattern in such a way that the light intensity of one of the two focal points becomes larger and the light intensity of the other focal point becomes smaller.

4. The laser processing device according to claim 3, wherein: In the fifth process, the control unit adjusts the modulation pattern in such a manner that the light intensity of the light focal point on the side close to the second surface of the two light focal points becomes larger and the light intensity of the light focal point on the side far from the second surface becomes smaller.

5. The laser processing device according to claim 2, wherein: In the fifth process, the control unit adjusts the modulation pattern using a slit pattern that blocks a part of the polarization component of the laser light.

6. The laser processing device according to claim 2, wherein: The control unit: while changing the condition of spherical aberration determined by the modulation pattern, performing the first process, the second process, the third process, and the fourth process under the respective conditions, In the fifth process, the maximum values ​​of the brightness values ​​of the laser light indicated by the optical axis profiles obtained under the respective conditions are compared with each other, and the modulation pattern is adjusted so as to meet the condition of the spherical aberration according to the optical axis profile having the maximum brightness value.

7. The laser processing device according to any one of claims 1 to 6, wherein: The control unit also executes: comparing the optical axis contour obtained in the fourth process with comparison data of the contour image used for comparison, and when the difference between the compared data is within a specified range, judging that the optical axis contour is normal; when the difference is outside the specified range, judging that the optical axis contour is abnormal, and outputting the judgment result of the sixth process.

8. The laser processing device according to any one of claims 1 to 6, wherein: The control unit controls the light source so as to emit the laser light having an output lower than an output during wafer processing in the second process.

9. The laser processing device according to any one of claims 1 to 6, wherein: The optical axis profile is three-dimensional data obtained by synthesizing a plurality of two-dimensional captured images.

10. A laser processing method, wherein: Include: A first step of focusing laser light modulated by a spatial light modulator from a wafer having a first surface and a second surface on a first surface side of the wafer to a focusing portion of the wafer, and moving the laser light in an optical axis direction which is a direction perpendicular to the first surface; A second step of continuously emitting laser light while executing the first step; A third step of continuously acquiring a plurality of camera images by detecting light reflected on the second surface while executing the second step; and The fourth step is to obtain an optical axis profile that is a profile image of the laser light along the optical axis direction by synthesizing the plurality of captured images continuously obtained in the third step.

11. The laser processing method according to claim 10, wherein: The method further includes: a fifth step of adjusting a modulation pattern of the spatial light modulator based on the optical axis profile obtained in the fourth step.

12. The laser processing method according to claim 11, wherein: The wafer comprises a birefringent material, In the fifth step, based on the optical axis profile, the focal point according to the ordinary ray and the focal point according to the extraordinary ray are determined, and the modulation pattern is adjusted in such a way that the light intensity of one of the two focal points becomes larger and the light intensity of the other focal point becomes smaller.

13. The laser processing method according to claim 12, wherein: In the fifth step, the modulation pattern is adjusted so that the light intensity of the light-converging point on the side close to the second surface of the two light-converging points becomes larger and the light intensity of the light-converging point on the side far from the second surface becomes smaller.

14. The laser processing method according to claim 11, wherein: In the fifth step, the modulation pattern is adjusted by using a slit pattern that blocks a part of the polarization component of the laser light.

15. The laser processing method according to claim 11, wherein: while changing the condition of spherical aberration determined by the modulation pattern, performing the first step, the second step, the third step and the fourth step under the respective conditions, In the fifth step, the maximum values ​​of the brightness values ​​of the laser light indicated by the optical axis profiles obtained under the respective conditions are compared with each other, and the modulation pattern is adjusted so as to meet the condition of the spherical aberration according to the optical axis profile having the maximum brightness value.

16. The laser processing method according to any one of claims 10 to 15, wherein: It also includes: Step 6, which compares the optical axis contour obtained in the step 4 with the comparison data of the contour image used for comparison. When the difference between the compared data is within the specified range, it is determined that the optical axis contour is normal; when the difference is outside the specified range, it is determined that the optical axis contour is abnormal, and the determination result is output.

17. The laser processing method according to any one of claims 10 to 15, wherein: In the second step, the laser light is emitted at an output lower than an output during wafer processing.

18. The laser processing method according to any one of claims 10 to 15, wherein: The optical axis profile is three-dimensional data obtained by synthesizing a plurality of two-dimensional captured images.

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