Laser processing device

Abstract

Laser processing device (10) for forming a parting groove in a wafer (100) by irradiating an upper surface of the wafer (100) held by a clamping table (43) with a laser beam, wherein the laser processing device (10) comprises: a laser oscillator (61) configured to emit the laser beam (200); a slit (72) which is configured to narrow the width of the laser beam (200) emitted by the laser oscillator (61) to a width corresponding to the separation groove in order to form the separation groove with a predetermined width; a gap movement mechanism (71) configured to move the gap in a direction corresponding to a width direction of the parting groove; a mirror (65) configured to reflect the laser beam (210) emitted by the laser oscillator (61) and to irradiate the wafer (100) held on the clamping table (43) with the laser beam (200); and a camera (67) arranged on the back side of the mirror (65) and configured to image a transmitted laser beam (210) when the laser beam (200) emitted by the laser oscillator (61) passes through the mirror (65); and an adjustment unit (51) which is configured to align a center point of the slit (72) and a cross-sectional center point (201) of the laser beam entering the slit (72) in a direction in which the slit movement mechanism (71) moves the slit (72), wherein the adjustment unit (51) comprises: a center point identification section (53) configured to identify a cross-sectional center point (211) of the transmitted laser beam (210) in accordance with a shape of a bright area (91), wherein the bright area (91) is an area of ​​pixels of a recorded image that is brighter than a preset brightness, and a first control section (54) which is configured to control the slit movement mechanism (71) on the basis of the cross-sectional center point of the transmitted laser beam (210), wherein the cross-sectional center point is identified by the center point identification section (53) such that the cross-sectional center point of the laser beam (200) and the center point of the slit (72) coincide in a direction of movement of the slit (72).

Description

BACKGROUND OF THE INVENTION AREA OF THE INVENTION

[0001] The present invention relates to a laser processing device. DESCRIPTION OF THE RELATED STATE OF THE ART

[0002] As disclosed in patent applications JP 2010 - 158 710 A and JP 2020 - 182 960 A, a laser processing device performs an ablation process that forms separation grooves extending in the X-axis direction in the surface of a wafer by irradiating the wafer with a laser beam. Subsequently, chips are formed as small pieces by a separation process that divides the wafer along the formed separation grooves.

[0003] The width of each of the separation grooves is made narrower to produce a large number of chips. Therefore, a narrow slit is used, corresponding to the width of each separation groove to be formed. Each narrow-width separation groove is created by irradiating the wafer with a laser beam, the width of which is reduced by the narrow slit.

[0004] For the use of such a gap, as disclosed in patent application JP 2010-158710 A, a plate is used which has the gap formed within it (mask plate). As disclosed in patent application JP 2020-182960 A, the gap is formed by a space between two plates.

[0005] Furthermore, patent application JP 2021-87975A discloses a laser processing machine in which a control section adjusts the position of a mask plate in an axial direction to maximize the energy of a laser beam L. For this purpose, the center point of a slot and the center point of an optical axis of the laser beam L are aligned, and an end section of the laser beam is symmetrically shielded by the slot. Consequently, the energy distribution of the laser beam L becomes symmetrical in the axial direction. The laser beam processing device of patent application JP 2005-186100A also deals with the cross-sectional shape of a laser beam to efficiently process a workpiece. Further patent applications dealing with the shape, size or position of laser beams are in DE 10 2020 210 788 A1, DE 10 2018 128 801 A1, DE 10 2020 215 369 A1, DE 2017 215 973 A1 and US 2006 / 0 202 115 A1. SUMMARY OF THE INVENTION

[0006] However, the centerline of the laser beam (optical axis of an optical system) can be offset in the lateral direction of the slit due to secular degradation in a laser oscillator. This means that the center of the slit and the cross-sectional center of the laser beam may not coincide. In this case, the separation grooves may not have a predetermined depth because the laser beam power required to form the separation grooves is insufficient, or for similar reasons.

[0007] It is therefore an object of the present invention to provide a laser processing device which can align the center of the slit and the cross-sectional center of the laser beam.

[0008] In accordance with one aspect of the present invention, a laser processing device for forming a parting groove in a wafer by irradiating an upper surface of the wafer, which is held by a clamping table, is provided with a laser beam, wherein the laser processing device comprises a laser oscillator configured to emit the laser beam, a slit configured to narrow the width of the laser beam emitted by the laser oscillator to a width corresponding to the parting groove in order to form the parting groove with a predetermined width, a slit movement mechanism configured to move the slit in a direction corresponding to a width direction of the parting groove, and an adjustment unit configured to align a center point of the slit and a cross-sectional center point of the laser beam entering the slit in a directionto align the gap movement mechanism with each other.

[0009] Furthermore, the laser processing device includes a camera mounted on the back side of a mirror and configured to image a transmitted laser beam as a laser beam emitted by the laser oscillator and passing through the slit and the mirror. Additionally, a center-of-cross-section identification section is provided to identify the cross-sectional center point of the transmitted laser beam in accordance with the shape of a bright area, wherein the bright area is a region of pixels in a captured image that is brighter than a preset brightness.

[0010] Preferably, the laser processing device further includes a power meter configured to measure the power of the laser beam passing through the slit, wherein the setting unit has a second control section configured to measure the power of the laser beam through the power meter while the slit is moved by the slit movement mechanism in the direction corresponding to the width direction of the cutting groove, and to stop the movement of the slit at a position where the measured power is at its maximum.

[0011] Furthermore, the laser processing device preferably includes a mirror configured to reflect the laser beam emitted by the laser oscillator and irradiate the wafer held on the clamping table with the laser beam, and a camera arranged on the back side of the mirror and configured to image a transmitted laser beam as the laser beam emitted by the laser oscillator and passing through the mirror, wherein the adjustment unit has a center point identification section configured to identify a cross-sectional center point of the transmitted laser beam based on the brightness of pixels of an image captured by the camera, and a first control section configured to control the slit movement mechanism based on the cross-sectional center point of the transmitted laser beam.wherein the cross-sectional center point is identified by the center point identification section, such that the cross-sectional center point of the laser beam and the center point of the slit coincide in one direction of movement of the slit.

[0012] In the laser processing device of the present invention, the adjustment unit aligns the cross-sectional center of the laser beam and the center of the slit. For example, the second control section of the control unit controls the position of the slit to maximize a specific amount of laser beam power, or the first control section of the control unit adjusts the position of the slit based on the cross-sectional center of the transmitted laser beam. The cross-sectional center of the laser beam and the center of the slit are thus aligned. This makes it possible to prevent insufficient laser beam power, allowing a parting groove of a predetermined depth to be formed in the wafer.

[0013] The above and other objects, features and advantages of the present invention and the manner of its implementation will best become clearer by studying the following description and the attached claims with reference to the attached drawings, which show a preferred embodiment of the invention, and the invention itself will best be understood by this. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a perspective view illustrating the setup of a laser processing device; Fig. Figure 2 is an explanatory diagram illustrating the structure of a laser processing mechanism; Fig. Figure 3 is an explanatory diagram illustrating a state in which the center of a slit and the center of a laser beam are offset from each other; Fig. Figure 4 is a graph showing the energy distribution of the laser beam in the area shown. Fig. 3 illustrates the state; Fig. Figure 5 is an explanatory diagram illustrating a state in which the center of the slit and the center of the laser beam coincide; Fig. Figure 6 is a graph showing the energy distribution of the laser beam in the area shown. Fig. 5 illustrates the state; Fig. Figure 7 is an explanatory diagram illustrating an example of an image taken by the camera; Fig. Figure 8 is an explanatory diagram illustrating an example of the image captured by the camera; Fig. Figure 9 is a graph illustrating the energy distribution of a symmetrical laser beam; and Fig. Figure 10 is a graph illustrating the energy distribution of an asymmetric laser beam. DETAILED EXPLANATION OF THE PREFERRED FORM OF EXECUTION

[0014] One embodiment of the present invention is described below with reference to the accompanying drawings. Fig. 1 The illustrated laser processing device 10 is a device for forming a parting groove in a wafer 100 by irradiating the upper surface of the wafer 100 held by a clamping table 43 with a laser beam.

[0015] The laser processing device 10 comprises a rectangular, cuboid base 11, a standing wall section 13 erected at one end of the base 11, and a control unit 51 that controls various elements of the laser processing device 10. The control unit 51 is, for example, a computer that includes a processing device and a storage device. The control unit 51 controls the operation of the various parts of the laser processing device 10, or similar components, so that the wafer 100 is processed correctly. The processing device is typically a central processing unit (CPU). The processing device performs various operations necessary to control the different parts.The storage device includes, for example, a main storage device, such as a Dynamic Random Access Memory (DRAM), and an auxiliary storage device, such as a hard disk drive or flash memory. The functions of the setting unit 51 are implemented, for example, by the operation of the processing device in accordance with software, such as a program stored in the storage device.

[0016] A clamping table movement mechanism 14 is provided on the upper surface of the base 11, which moves the clamping table 43. The clamping table movement mechanism 14 moves the clamping table 43 in an X-axis direction for machining and positions the clamping table 43 in a Y-axis direction perpendicular to the X-axis direction.

[0017] The clamping table motion mechanism 14 includes a clamping table unit 40, which comprises the clamping table 43, a Y-axis motion mechanism 20 that moves the clamping table 43 in the Y-axis direction as the approach direction, and an X-axis motion mechanism 30 that moves the clamping table 43 in the X-axis direction as the machining feed direction. The clamping table 43 has a holding surface 44 for holding the wafer 100.

[0018] The Y-axis movement mechanism 20 moves the clamping table 43 in relation to a laser processing mechanism 12 in the Y-axis direction parallel to the holding surface 44 and perpendicular to the X-axis direction.

[0019] The Y-axis motion mechanism 20 includes a pair of guide rails 23 extending in the Y-axis direction, a Y-axis table 24 attached to the guide rails 23, a ball screw 25 extending parallel to the guide rails 23, and a drive motor 26 that rotates the ball screw 25.

[0020] The pair of guide rails 23 is arranged on the upper surface of the base 11 such that it is parallel to the Y-axis direction. The Y-axis table 24 is installed on the pair of guide rails 23 such that it is slidable along these guide rails 23. The X-axis motion mechanism 30 and the clamping table unit 40 are attached to the Y-axis table 24.

[0021] The ball screw 25 is screwed into a nut section (not illustrated) provided to the Y-axis table 24. The drive motor 26 is coupled to an end section of the ball screw 25. The drive motor 26 rotates the ball screw 25. When the ball screw 25 is rotated, the Y-axis table 24, the X-axis motion mechanism 30, and the clamping table unit 40 move in the Y-axis direction along the guide rails 23.

[0022] The X-axis movement mechanism 30 moves the clamping table 43 in relation to the laser processing mechanism 12 in the X-axis direction parallel to the holding surface 44.

[0023] The X-axis motion mechanism 30 includes a pair of guide rails 31 extending in the X-axis direction, an X-axis table 32 attached to the guide rails 31, a ball screw 33 extending parallel to the guide rails 31, and a drive motor 35 that rotates the ball screw 33.

[0024] The pair of guide rails 31 is arranged on the upper surface of the Y-axis table 24 such that it is parallel to the X-axis direction. The X-axis table 32 is attached to the pair of guide rails 31 such that it is slidable along these guide rails 31. The clamping table unit 40 and a power meter 80 are attached to the X-axis table 32.

[0025] The ball screw 33 is screwed into a nut section (not illustrated) provided to the X-axis table 32. The drive motor 35 is coupled to an end section of the ball screw 33. The drive motor 35 rotates the ball screw 33. When the ball screw 33 is rotated, the X-axis table 32 and the clamping table unit 40 move along the guide rails 31 in the machining feed direction (X-axis direction).

[0026] The clamping table unit 40 is used to hold the wafer 100 as an example of a workpiece. As in Fig. As illustrated in Figure 1, the wafer 100 is held by the clamping table unit 40 as a workpiece set 110, which includes a ring frame 111, an adhesive strip 113 and the wafer 100.

[0027] The clamping table unit 40 includes the clamping table 43, which holds the wafer 100, clamping units 45 provided on the circumference of the clamping table 43, and a θ-table 47, which supports the clamping table 43. The θ-table 47 is provided on the upper surface of the X-axis table 32 such that it is rotatable in an XY plane.

[0028] The clamping table 43 is an element for holding the wafer 100. The clamping table 43 is disc-shaped and is provided on the θ-table 47.

[0029] The holding surface 44, formed from a porous material, is designed as the upper surface of the clamping table 43. This holding surface 44 is manufactured in such a way that it is in contact with a suction source (not illustrated) and can thereby draw in and hold the wafer 100 in the workpiece set 110.

[0030] Four clamping units 45 are provided on the circumference of the clamping table 43. The four clamping units 45 are driven by a pneumatic drive (not illustrated) and thereby hold and fix the ring frame 111 to the circumference of the wafer 100 held on the clamping table 43 from four directions.

[0031] The stationary wall section 13 of the laser processing device 10 is positioned behind the clamping table movement mechanism 14. The laser processing mechanism 12 is located on the front surface of the stationary wall section 13.

[0032] The laser processing mechanism 12 performs ablation processing on the wafer 100 held on the clamping table 43 by applying a laser beam. In particular, the laser processing mechanism 12 forms a parting groove in the wafer 100 along a planned parting line by irradiating the upper surface of the wafer 100 with the laser beam.

[0033] The laser processing mechanism 12 includes a processing head 18 that irradiates the wafer 100 with the laser beam, and an arm section 17 that supports the processing head 18.

[0034] The arm section 17 projects from the stationary wall section 13 in the direction of the clamping table movement mechanism 14. The machining head 18 is supported by a distal end of the arm section 17 in such a way that it faces the clamping table 43 of the clamping table unit 40 or the power meter 80 in the clamping table movement mechanism 14.

[0035] An optical system of the laser processing mechanism 12 is provided in the arm section 17 and the processing head 18.

[0036] As in Fig. 1 and Fig. As illustrated in Figure 2, the laser processing mechanism 12 in the arm section 17 includes a laser oscillator 61 that generates and emits a laser beam 200, a beam expander 62 for adjusting the laser beam emitted by the laser oscillator 61 to collimated light, and an energy distribution corrector 63 that corrects an energy distribution of the laser beam 200.

[0037] As in Fig. As illustrated in Figure 2, the laser processing mechanism 12 in the processing head 18 also includes a mirror 65 that reflects the laser beam 200, and a condenser (condenser lens) 66 that focuses and emits the laser beam 200.

[0038] The mirror 65 serves, for example, to reflect the laser beam 200 emitted by the laser oscillator 61 and to focus it onto the mounting surface 44 (see Fig. 1) to irradiate the wafer 100 held by the clamping table 43 with the laser beam 200. In addition, the mirror 65 is arranged so that it transmits part of the incident laser beam 200.

[0039] Furthermore, the laser processing mechanism 12 includes a camera 67 on the side surface of the processing head 18 and on the back of the mirror 65.

[0040] The laser oscillator 61, for example, is a solid-state laser light source. The laser oscillator 61 emits the laser beam 200 in a -Y direction in the arm section 17. The energy distribution of the laser beam 200 can be approximated by a Gaussian distribution. Therefore, the energy of the laser beam 200 has a distribution that is indicated by an arrow 300 in a section in the W-axis direction.

[0041] The W-axis direction is a direction perpendicular to a central axis (optical axis of the optical system) along the direction of movement of the laser beam 200 and perpendicular to the X-axis direction as the processing feed direction (direction perpendicular to a paper plane of the Fig. 2) The W-axis direction thus coincides with a Z-axis direction in the arm section 17 and coincides with the Y-axis direction in the processing head 18 (at a position on the -Z-direction side of the mirror 65). This W-axis direction is, incidentally, a direction that corresponds to the width direction of a parting groove to be formed in the wafer 100.

[0042] The energy distribution corrector 63 is arranged between the laser oscillator 61 and the mirror 65. The energy distribution corrector 63 corrects the energy distribution in the W-axis direction of the laser beam 200 by blocking a portion of the laser beam 200.

[0043] The laser beam 200, passing through the energy distribution corrector 63, is reflected by the mirror 65 in the processing head 18 in a -Z direction and directed to the condenser 66. The condenser 66 concentrates the laser beam 200 and focuses it in the -Z direction on the outside of the processing head 18.

[0044] At the time of processing the in Fig. In the illustrated wafer 100, the laser beam 200, bundled by the condenser 66, is applied to the wafer 100 on the clamping table 43.

[0045] On the other hand, at the time of correction of the energy distribution of the laser beam 200, as in Fig. Figure 2 illustrates the laser beam 200 applied to the power meter 80.

[0046] The setup of the energy distribution corrector 63 is described here. As indicated by arrow 301, the energy distribution corrector 63 corrects the energy distribution in the W-axis direction of the laser beam 200 to an energy distribution obtained by vertically cutting a foot part of the Gaussian distribution. The width (length in the W-axis direction) of the laser beam 200 is thereby adjusted.

[0047] As in Fig. As illustrated in Figure 2, the energy distribution corrector 63 includes a slit plate 70 with a slit 72 arranged on the center line of the laser beam 200, and a slit movement mechanism 71 which moves the slit plate 70 in the W-axis direction.

[0048] As in Fig. 2 and Fig. As illustrated in Figure 3, the slit plate 70 is arranged in the arm section 17 such that it is parallel to a ZX plane which in the arm section 17 is a plane perpendicular to the center line of the laser beam 200.

[0049] The slit 72 formed in the slit plate 70 is used to reduce the width of the laser beam 200 emitted by the laser oscillator 61 to a width corresponding to a parting groove, in order to form the parting groove of a predetermined width in the wafer 100. As shown in Fig. As illustrated in Figure 3, the gap 72 has a rectangular shape and is defined by a first width HX in the X-axis direction and a second width HW in the W-axis direction, which corresponds to the separating groove.

[0050] The slit movement mechanism 71 moves the slit plate 70, which has the slit 72, in the W-axis direction (Z-axis direction in the arm section 17) in a direction corresponding to the width direction of the parting groove to be formed in the wafer 100. The slit movement mechanism 71 can thereby align a center point 73 of the slit 72 in the direction of movement of the slit 72 with a cross-sectional center point 201 of the laser beam 200 passing through the slit 72. This cross-sectional center point 201 is the center point of a section in the ZX plane of the laser beam 200 entering the slit 72 and corresponds to the apex of the Gaussian distribution of the laser beam 200 (the center line of the laser beam 200 and the optical axis of the optical system).

[0051] The in Fig. 1 and Fig. The power meter 80, as illustrated in Figure 2, is connected downstream of the condenser 66 in the direction of travel of the laser beam 200. The power meter 80 is irradiated with the laser beam 200 focused by the condenser 66. The power meter 80 thus measures the power (amount of energy) of the laser beam 200 that has passed through the slit 72.

[0052] The setting unit 51 performs an ablation process on the wafer 100 by controlling various elements of the laser processing device 10.

[0053] Furthermore, the adjustment unit 51 performs a correction of the energy distribution on the laser beam 200 by adjusting the Fig. 2 illustrated gap movement mechanism 71 controls to adjust the shape of the separation groove to be formed in the wafer 100 by the ablation processing.

[0054] This means that the adjusting unit 51 brings the center point of the slit 72 and the cross-sectional center point 201 of the laser beam 200 entering the slit 72 into alignment or coincidence in the direction of movement of the slit 72 by controlling the slit movement mechanism 71 and thereby moving the slit plate 70 with the slit 72 in the W-axis direction (Z-axis direction).

[0055] If the center of the slit 72 coincides with the cross-sectional center 201 of the laser beam 200, the energy distribution of the laser beam 200 passing through the slit 72 has only the power required to form a parting line, with the base part of the Gaussian distribution being vertically cut. The shape of the parting line formed in the wafer 100 can thus be made to have a proper shape with a predetermined depth.

[0056] The following is a description of the work of the energy distribution correction on the laser beam 200 by the adjustment unit 51.

[0057] As in Fig. As illustrated in Figure 2, the control unit 51 includes a second control section 52.

[0058] The second control section 52 measures the power of the laser beam 200 with the power meter 80 while it moves the slit 72 in the W-axis direction by the slit movement mechanism 71. The second control section 52 stops the movement of the slit 72 when the measured power is at its maximum, that is, when it is determined that the center point 73 of the slit 72 and the cross-sectional center point 201 of the laser beam 200 coincide in the W-axis direction.

[0059] In particular, the second control section 52 measures the power of the laser beam 200 in the W-axis direction by the power meter 80, for example, by controlling the slit movement mechanism 71, while continuously and slightly moving the slit 72 of the slit plate 70 in a -W direction and a +W direction. Then, when the power of the laser beam 200 measured by the power meter 80 is at its maximum, the second control section 52 stops the position of the slit 72 in the W-axis direction. That is, the second control section 52 adjusts the position of the slit 72 in the W-axis direction so that the power of the laser beam 200 is maximized.

[0060] For example, as in Fig. Figure 3 illustrates that the center point 73 of the slit 72 and the cross-sectional center point 201 of the laser beam 200 are slightly offset from each other in the W-axis direction (Z-axis direction).

[0061] In this case, the end sections of the laser beam 200 are blocked asymmetrically (irregularly) by the slit 72. As a result, as in Fig. Figure 4 illustrates that the energy distribution (density) of the laser beam 200 is asymmetrical in the W-axis direction. If a parting line is formed in the wafer 100 under these conditions, the parting line may not have a predetermined depth or similar characteristics due to insufficient power of the laser beam 200 required to form the parting line. Furthermore, a processing defect (form defect) may occur, such as a difference in depth in the W-axis direction (Y-axis direction) within the parting line and the resulting unevenness of the lower surface of the line.

[0062] Furthermore, in a case where a low-k film is formed on planned separation lines and the low-k film is cut by laser processing, a processing error can occur by failing to cut the low-k film or by turning one side of the cut low-k film upwards.

[0063] Accordingly, in the present embodiment, the second control section 52 adjusts the position of the slit 72, as described above, in the W-axis direction such that the energy of the laser beam 200 is maximized. In a Fig. 3 and Fig. In the illustrated example 5, this setting lowers the gap plate 70, which has the gap 72, as indicated by an arrow 250 in Fig. 5 is displayed, in the -W direction.

[0064] Consequently, in the W-axis direction, the center point 73 of the slit 72 and the cross-sectional center point 201 of the laser beam 200 coincide, and end sections of the laser beam 200 are symmetrically blocked by the slit 72. As in Fig. As illustrated in Figure 6, this makes the energy distribution (density) of the laser beam 200 symmetrical in the W-axis direction, so that insufficient power of the laser beam 200 can be resolved. This makes it possible to form a separation groove with a predetermined depth and a suitable shape in the wafer 100.

[0065] Furthermore, in the present embodiment, the W-axis direction, which is the direction in which the slit movement mechanism 71 moves the slit plate 70, is the Z-axis direction perpendicular to the X-axis direction. It is therefore possible to prevent any offset between the center point 73 of the slit and the cross-sectional center 201 of the laser beam 200 in the X-axis direction by moving the slit plate 70.

[0066] As in Fig. As illustrated in Figure 2, a portion of the laser beam 200, which has passed through the energy distribution corrector 63, passes through the mirror 65 and enters the camera 67, which is located on the back side of the mirror 65. The camera 67 images the incident laser beam 200. That is, the camera 67 images a transmitted laser beam 210 as a laser beam that was emitted by the laser oscillator 61 and passed through the mirror 65.

[0067] In the present embodiment, the adjustment unit 51 can correct the energy distribution of the laser beam 200 based on an image captured by the camera 67. A description of a process for correcting the energy distribution in this case is given below.

[0068] As in Fig. As illustrated in Figure 2, the setting unit 51 includes a center point identification section 53 and a first control section 54. The center point identification section 53 identifies the cross-sectional center point of the transmitted laser beam 210 based on the brightness of the pixels of the image captured by the camera 67.

[0069] The first control section 54 controls the slit movement mechanism 71 on the basis of the cross-sectional center point of the transmitted laser beam 210, which is identified by the center point identification section 53, so that the cross-sectional center point 201 of the laser beam 200 and the center point 73 of the slit 72 coincide in the W-axis direction as the direction of movement of the slit 72.

[0070] Fig. 7 and Fig. Figure 8 illustrates examples of the image captured by camera 67. Furthermore, these figures illustrate the center point 73 of the slit 72 and the cross-sectional center 211 of the transmitted laser beam 210.

[0071] In these figures, a bright area 91 in the captured image, that is, an area of ​​pixels brighter than a preset brightness, corresponds to the transmitted laser beam 210. The center point identification section 53 identifies the cross-sectional center point 211 of the transmitted laser beam 210, for example, in accordance with the shape of the bright area 91. That is, the bright area 91 is an image of a portion of a circle as the cross-section of the transmitted laser beam 210. Accordingly, the center point identification section 53 determines the position of the center point of the circle containing the bright area 91 in the captured image and identifies this position as the position of the cross-sectional center point 211 of the transmitted laser beam 210.

[0072] Furthermore, the center point identification section 53 identifies the position of the center point 73 of the slit 72 in the W-axis direction as the position of the center point of a width in the W-axis direction in the bright area 91.

[0073] In the Fig. In the illustrated example 7, the cross-sectional center 211 of the transmitted laser beam 210 and the center point 73 of the slit 72 are slightly offset from each other in the W-axis direction (Z-axis direction). In this case, as in Fig. Figure 3 illustrates that the cross-sectional center 201 of the laser beam 200 is also offset in the W-axis direction relative to the center 73 of the slit 72, and end sections of the laser beam 200 are blocked asymmetrically by the slit 72. As a result, the energy distribution (density) of the laser beam 200, as shown in Fig. Figure 4 illustrates the asymmetrical shape in the W-axis direction. Therefore, the parting groove, as described above, may not have the specified depth, resulting in a machining error.

[0074] Accordingly, the first control section 54 sets the position of the slit plate 70 including the slit 72 in the W-axis direction by controlling the slit movement mechanism 71 on the basis of the cross-sectional center 211 of the transmitted laser beam 210 such that the cross-sectional center 201 of the laser beam 200 and the center 73 of the slit 72 coincide in the W-axis direction.

[0075] In particular, the first control section 54 detects in the recorded image a positional relationship between the cross-sectional center 211 of the transmitted laser beam 210 and the center point 73 of the slit 72, wherein the cross-sectional center 211 and the center point 73 are identified by the center point identification section 53, and the first control section 54 moves the slit 72 of the slit plate 70 in the W-axis direction by controlling the slit movement mechanism 71 such that the cross-sectional center 211 and the center point 73 coincide in the W-axis direction.

[0076] As a result of this setting, the captured image, as shown in Fig. Figure 8 illustrates that the center point 73 of the slit 72 and the cross-sectional center 211 of the transmitted laser beam 210 coincide in the W-axis direction. As shown in Fig. As illustrated in Figure 5, the cross-sectional center 201 of the laser beam 200 thus coincides in the W-axis direction with the center 73 of the slit 72, and end sections of the laser beam 200 are symmetrically blocked by the slit 72. As shown in Fig. As illustrated in Figure 6, the energy distribution of the laser beam 200 consequently becomes symmetrical in the W-axis direction, so that insufficient power of the laser beam 200 can be resolved. This makes it possible to form a separation groove with a predetermined depth and a suitable shape in the wafer 100.

[0077] Incidentally, the transmitted laser beam 210 is refracted when passing through the mirror 65 (the degree of refraction depends on the specific mirror). Therefore, a deviation can occur between the cross-sectional center 201 of the laser beam 200 and the cross-sectional center 211 of the transmitted laser beam 210. In a case where such a deviation occurs, the first control section 54 can pre-store the position of the cross-sectional center 211 of the transmitted laser beam 210 in the recorded image if the cross-sectional center 201 of the laser beam 200 and the center point 73 of the slit 72 coincide. When the first control section 54 sets the position of the slit 72, the first control section 54 can move the slit 72 so that the stored position of the cross-sectional center 211 of the transmitted laser beam 210 in the recorded image coincides with the center 73 of the slit 72 in the W-axis direction.

[0078] Furthermore, the correction of the energy distribution of the laser beam 200 (alignment of the slit 72) by the second control section 52 using the power meter 80, and the correction of the energy distribution of the laser beam 200 by the center point identification section 53 and the first control section 54 using the image captured by the camera 67, as described above, can be performed regularly. This makes it easy to form a parting groove with a predetermined depth and a suitable shape in the wafer 100.

[0079] As described above, the energy distribution of the laser beam can also be 200, as in Fig. Figure 9 illustrates how the Gaussian distribution can be approximated. In this case, the diameter of the beam can be described as a beam diameter of 601 at 1 / e 2a maximum energy value is defined in the energy distribution. Furthermore, in this case, the position of the cross-sectional center 201 of the laser beam 200, which is obtained in the present embodiment, is a position that corresponds to a peak of the Gaussian distribution in the laser beam 200.

[0080] On the other hand, as in Fig. Figure 10 illustrates that the energy distribution of the laser beam 200 may be disturbed, resulting in an asymmetrical shape. In this case, the beam diameter can be defined as an aperture diameter 602. For the aperture diameter 602, a circle is calculated that contains a specific percentage (typically 86.5%) of the energy relative to a maximum energy value in the total energy of the laser beam 200. The aperture diameter 602 is derived from the diameter of this circle. Furthermore, in this case, the position of the cross-sectional center 201 of the laser beam 200, obtained in the present embodiment, is a position that corresponds to the center of the aperture diameter 602.

[0081] Furthermore, in a case where the cross-sectional center 201 of the laser beam 200 is obtained by using the camera 67, the setting unit 51 can determine, based on the brightness of the pixels of the image captured by the camera 67, whether the shape of the laser beam 200 is as shown in Fig. Figure 10 illustrates an asymmetrical shape. In this regard, the setting unit 51 can be configured to determine whether the shape of the laser beam 200 is asymmetrical or not, and to communicate the result of the determination to a worker using a notification device not illustrated.

Claims

[1] Laser processing device (10) for forming a parting groove in a wafer (100) by irradiating an upper surface of the wafer (100) held by a clamping table (43) with a laser beam, wherein the laser processing device (10) comprises: a laser oscillator (61) configured to emit the laser beam (200); a slit (72) which is configured to narrow the width of the laser beam (200) emitted by the laser oscillator (61) to a width corresponding to the separation groove in order to form the separation groove with a predetermined width; a gap movement mechanism (71) configured to move the gap in a direction corresponding to a width direction of the parting groove; a mirror (65) configured to reflect the laser beam (210) emitted by the laser oscillator (61) and to irradiate the wafer (100) held on the clamping table (43) with the laser beam (200); and a camera (67) arranged on the back side of the mirror (65) and configured to image a transmitted laser beam (210) when the laser beam (200) emitted by the laser oscillator (61) passes through the mirror (65); and an adjustment unit (51) which is configured to align a center point of the slit (72) and a cross-sectional center point (201) of the laser beam entering the slit (72) in a direction in which the slit movement mechanism (71) moves the slit (72), wherein the adjustment unit (51) comprises: a center point identification section (53) configured to identify a cross-sectional center point (211) of the transmitted laser beam (210) in accordance with a shape of a bright area (91), wherein the bright area (91) is an area of ​​pixels of a recorded image that is brighter than a preset brightness, and a first control section (54) which is configured to control the slit movement mechanism (71) on the basis of the cross-sectional center point of the transmitted laser beam (210), wherein the cross-sectional center point is identified by the center point identification section (53) such that the cross-sectional center point of the laser beam (200) and the center point of the slit (72) coincide in a direction of movement of the slit (72). [2] Laser processing device (10) according to claim 1, further comprising: a power meter (80) configured to measure the power of the laser beam (200) passing through the slit (72), the setting unit (51) comprising: a second control section (52) which is set up to measure the power of the laser beam (200) by the power meter (80) while the slit (72) is moved by the slit movement mechanism (71) in the direction corresponding to the width direction of the separation groove, and to stop the movement of the slit (72) at a position where the measured power is at its maximum.

Images