Method for processing a workpiece, processing apparatus, and method for manufacturing a chip

Abstract

Precisely machine workpieces with varying thicknesses in different areas. [Solution] A workpiece (10) having a first region (15) and a second region (16) that is thinner than the first region is held by a holding member (22), and a laser beam (L) is irradiated onto the workpiece while adjusting the position of the focal point according to the thickness of the workpiece to form a modified layer (S) inside, and when forming the modified layer, the laser beam is not irradiated onto boundary regions (M, N) that include at least a part of the boundary between the first region and the second region.

Description

Technical Field

[0001] The present invention relates to a processing method for processing a workpiece, a processing apparatus, and a manufacturing method for manufacturing chips.

Background Art

[0002] In a processing method for processing a workpiece or a manufacturing method for manufacturing a plurality of chips by processing a workpiece, a technique of condensing a laser beam inside the workpiece to form a modified layer is known (for example, Patent Document 1). The workpiece is divided starting from the modified layer to manufacture a plurality of chips.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the case of a workpiece having a partially different thickness, in a boundary region where the thickness of the workpiece changes, the laser beam is condensed on the outer surface of the workpiece or a position in the immediate vicinity of the outer surface, and the outer surface is ablated, which may deteriorate the processing quality.

[0005] An object of the present invention is to provide a processing method, a processing apparatus, and a manufacturing method for manufacturing chips that can accurately process even a workpiece having a partially different thickness.

Means for Solving the Problems

[0006] One aspect of the present invention is a method for processing a workpiece, comprising: a holding step of holding a workpiece having a first region and a second region thinner than the first region with a holding member; and a modified layer forming step of irradiating the workpiece with a laser beam while adjusting the position of the focusing point according to the thickness of the workpiece to form a modified layer inside, wherein in the modified layer forming step, at least a boundary region including the boundary between the first region and the second region is not irradiated with the laser beam.

[0007] In one embodiment of the modified layer formation step, multiple modified layers are formed at different depths in the thickness direction of the workpiece, and the laser beam is prevented from irradiating the boundary region of the modified layer formed at the depth closest to the irradiation surface of the laser beam.

[0008] In one embodiment of the modified layer formation step, multiple modified layers are formed at different depths in the thickness direction of the workpiece, and the laser beam is prevented from irradiating the second region of the modified layer formed at the depth closest to the irradiation surface.

[0009] For example, the first region is formed in the center of the workpiece, and the second region is formed on the outer periphery of the workpiece, surrounding the first region.

[0010] Preferably, the boundary region in the workpiece that is not irradiated by the laser beam includes the boundary line between the first region and the second region, and a predetermined range from the boundary line of the second region.

[0011] One aspect of the present invention is a processing apparatus comprising: a holding member for holding a workpiece having a first region and a second region thinner than the first region; a laser irradiation unit for irradiating the workpiece with a laser beam to form a modified layer inside, while adjusting the position of the focusing point according to the thickness of the workpiece held by the holding member; and a control unit, wherein the control unit controls the laser irradiation unit so as not to irradiate the laser beam into a boundary region including at least a portion of the boundary between the first region and the second region.

[0012] One aspect of the present invention is a method for manufacturing chips using the above-described processing method, wherein the modified layer formation step comprises forming the modified layer along a division line that divides the workpiece into chips, and after the modified layer formation step, an external force is applied to the workpiece to widen the spacing between the plurality of chips formed by dividing the workpiece starting from the modified layer, wherein in at least one of the modified layer formation step and the chip spacing widening step, the workpiece is divided starting from the modified layer and a plurality of chips are manufactured. [Effects of the Invention]

[0013] According to each of the above embodiments, it is possible to process workpieces with partially different thicknesses with high precision. [Brief explanation of the drawing]

[0014] [Figure 1] This is a perspective view of a laser processing machine. [Figure 2] This figure shows the steps for forming a modified layer using a laser processing device. [Figure 3] This is a plan view of the workpiece unit. [Figure 4] This is a cross-sectional view showing a processing example in which a modified layer is formed on a workpiece of the first form in the modified layer formation step. [Figure 5] This is a cross-sectional view showing a processing example in which a modified layer is formed on a workpiece of the first form in the modified layer formation step. [Figure 6] This is a cross-sectional view showing a processing example in which a modified layer is formed on a workpiece of the first form in the modified layer formation step. [Figure 7] This is a cross-sectional view showing a processing example in which a modified layer was formed on a workpiece of the second form in the modified layer formation step. [Figure 8] This is a cross-sectional view showing a processing example in which a modified layer was formed on a workpiece of the second form in the modified layer formation step. [Figure 9] This is a cross-sectional view showing a processing example in which a modified layer was formed on a workpiece of the second form in the modified layer formation step. [Figure 10]It is a plan view of a workpiece unit of a modified example in which the formation position of a modified layer in an excess region on the outer periphery of a workpiece is different. [Figure 11] It is a cross-sectional view showing a workpiece of a comparative example in which a modified layer is formed. [Figure 12] It is a diagram showing a chip interval expansion step by an expand device. [Figure 13] It is a diagram showing a chip interval expansion step by an expand device.

Embodiments for Carrying out the Invention

[0015] Hereinafter, with reference to the accompanying drawings, a method for processing a workpiece, a processing apparatus, and a method for manufacturing a chip according to the present disclosure will be described. The X-axis direction, Y-axis direction, and Z-axis direction shown in each drawing are perpendicular to each other. In the processing according to the present disclosure, in order to manufacture a plurality of chips 11 (see FIG. 3) from the workpiece 10, the workpiece 10 is processed along a division planned line 12 (see FIG. 3). The workpiece 10 has a plurality of device compartments partitioned in a lattice shape by a plurality of division planned lines 12, and chips 11 are formed in each device compartment. As an example, the workpiece 10 is a disk-shaped semiconductor wafer, and the chip 11 is a semiconductor device, but the shape of the workpiece 10 and the type of the chip 11 are not limited.

[0016] As shown in FIG. 3, the workpiece 10 is attached inside a ring-shaped frame 3 via a flexible tape 2 to constitute a workpiece unit 1. In a laser processing apparatus 20 and an expand device 70 described later, processing of the workpiece 10 and manufacturing of the chip 11 (division of the workpiece 10) are performed in the state of the workpiece unit 1. In the workpiece 10, the surface on the side attached to the tape 2 is referred to as a held surface 13, and the surface opposite to the held surface 13 is referred to as an irradiation surface 14 (see FIGS. 2, 4 to 9, and 12). The held surface 13 and the irradiation surface 14 are one surface and the other surface in the thickness direction of the workpiece 10. Note that the processing method and manufacturing method of the present disclosure can also be applied to the case where the workpiece 10 is not attached to the tape 2 and the frame 3.

[0017] Figures 4 to 9 show cross-sectional views of the workpiece 10 at positions along one of the multiple planned division lines 12 shown in Figure 3. The workpiece 10 has partially different thicknesses, comprising a first region 15 with a relatively large thickness in the Z-axis direction and a second region 16 with a relatively small (thin) thickness in the Z-axis direction. The height position of the irradiation surface 14 in the first region 15 and the height position of the irradiation surface 14 in the second region 16 are different from each other.

[0018] The first form of the workpiece 10, shown in Figures 4 to 6, has a first region 15 in the radial center and a second region 16 in the outer annular portion surrounding the outside of the first region 15. The second form of the workpiece 10, shown in Figures 7 to 9, has a second region 16 in the radial center and a first region 15 in the outer annular portion surrounding the outside of the second region 16. In both of these forms of the workpiece 10, a cylindrical stepped surface 17 is formed at the boundary between the first region 15 and the second region 16, centered on the central axis C of the workpiece 10 extending in the Z-axis direction. The stepped surface 17 constitutes the boundary line between the first region 15 and the second region 16 when the workpiece 10 is viewed from above, as shown in Figure 3. In the first form of the workpiece 10, the stepped surface 17 faces the outer circumference, while in the second form of the workpiece 10, the stepped surface 17 faces the inner circumference. Figure 3 is a diagram that corresponds to both the first form of the workpiece 10 and the second form of the workpiece 10. When applied to the first form of the workpiece 10, the center is the first region 15 and the outer periphery is the second region 16. When applied to the second form of the workpiece 10, the center is the second region 16 and the outer periphery is the first region 15.

[0019] Figures 1 and 2 show a laser processing device 20, which is used to process a workpiece 10. In processing using the laser processing device 20, a laser beam L is irradiated onto the workpiece 10 from the irradiation surface 14 along the planned division line 12, focusing the beam into the interior of the workpiece 10, and forming a modified layer S (see Figures 4 to 9) at the focal point of the laser beam L. Modification means that the density, refractive index, mechanical strength, and other physical properties inside the workpiece 10 become different from the surrounding area due to the energy of the irradiated laser beam L, etc. As a result of modification, the modified layer S becomes a region with reduced strength compared to the surrounding area. In addition, depending on the state of modification, cracks are formed from the modified layer S in the thickness direction of the workpiece 10. Therefore, by forming a modified layer S inside the workpiece 10, the workpiece 10 is divided or becomes easier to divide along the planned division line 12, starting from the modified layer S. In other words, the laser processing by the laser processing device 20 creates a dividing starting point along the planned dividing line 12 inside the workpiece 10. Although Figure 2 shows the processing of a first type of workpiece 10 (see Figures 4 to 6) in which the thickness is large in the center and small on the outer edge, the laser processing device 20 can also process a second type of workpiece 10 (see Figures 7 to 9) in which the thickness is small in the center and large on the outer edge.

[0020] The expander 70 shown in Figures 12 and 13 applies an external force to the workpiece 10 on which the modified layer S has been formed by the laser processing device 20, thereby widening the spacing between the multiple chips 11. In one case, the workpiece 10 is divided into multiple chips 11 at the stage when the modified layer S is formed by the laser processing device 20, and in another case, the workpiece 10 is divided into multiple chips 11 by applying an external force using the expander 70 or the like after the modified layer S has been formed on it. In addition, in another case, a part of the workpiece 10 is divided at the stage when the modified layer S is formed by the laser processing device 20, and the remaining part of the workpiece 10 is divided by applying an external force using the expander 70 or the like. In other words, in at least one of the modified layer formation step performed in the laser processing device 20 and the chip spacing expansion step performed in the expander 70, the workpiece 10 is divided starting from the modified layer S to produce multiple chips 11. Regardless of whether the division into multiple chips 11 occurs during the modified layer formation step or the chip spacing expansion step, the expansion device 70 widens the spacing between the multiple chips 11, making it easier to pick up the manufactured multiple chips 11 from the tape 2. Figures 12 and 13 show the application of external force to a workpiece 10 of the first form, which has a large thickness in the center and a small thickness on the outer periphery (see Figures 4 to 6). However, the expansion device 70 can also apply external force to a workpiece 10 of the second form, which has a small thickness in the center and a large thickness on the outer periphery (see Figures 7 to 9). The details of the processing of the workpiece 10 using the laser processing device 20 and the details of applying external force to the workpiece 10 (expansion of chip spacing) using the expansion device 70 will be explained in order below.

[0021] As shown in Figures 1 and 2, the laser processing apparatus 20 holds the workpiece unit 1 on a holding table 22, which is a holding member provided on a base 21, and processes the workpiece 10 on the holding table 22 by irradiating it with a laser beam L from a laser irradiation unit 23 positioned above the holding table 22.

[0022] As shown in Figure 2, the holding table 22 has a recess 25 on the upper side of a disc-shaped frame 24, and a porous plate 26 made of porous material is installed in the recess 25. A flow path 27 is formed inside the frame 24, leading to the bottom of the recess 25, and the flow path 27 is connected to a suction source 29 via an on-off valve 28. By opening the on-off valve 28 and operating the suction source 29, air is drawn in from the porous plate 26 via the flow path 27, applying a suction force to the holding surface, which is the upper surface of the porous plate 26, and the holding surface 13 of the workpiece 10 can be held via the tape 2. Four clamp parts 30 are provided on the outside of the frame 24 at equal intervals in the circumferential direction. Each clamp part 30 has a support part 31 and a pressing part 32 that can be opened and closed relative to the support part 31, and the frame 3 can be clamped and fixed in the Z-axis direction by the support part 31 and the pressing part 32. In this way, the workpiece unit 1 is held on the holding table 22.

[0023] As shown in Figure 1, the holding table 22 is moved in the X-axis direction by the X-axis movement mechanism 34 and in the Y-axis direction by the Y-axis movement mechanism 35. By moving the holding table 22 in the X-axis direction and the Y-axis direction using the X-axis movement mechanism 34 and the Y-axis movement mechanism 35, the workpiece unit 1 held on the holding table 22 and the laser irradiation unit 23 are moved relative to each other in the horizontal direction, and the irradiation position of the laser beam L from the laser irradiation unit 23 to the workpiece 10 can be changed in the horizontal direction.

[0024] The X-axis movement mechanism 34 includes a pair of X-axis guide rails 36 extending in the X-axis direction, an X-axis table 37 supported by the X-axis guide rails 36 so as to be movable in the X-axis direction, an X-axis ball screw 38 extending in the X-axis direction and screwed into a nut portion of the X-axis table 37, and a motor 39 for rotating the X-axis ball screw 38. When the motor 39 rotates the X-axis ball screw 38, the X-axis table 37 moves in the X-axis direction along the X-axis guide rails 36.

[0025] The Y-axis movement mechanism 35 includes a pair of Y-axis guide rails 40 extending in the Y-axis direction, a Y-axis table 41 supported by the Y-axis guide rails 40 so as to be movable in the Y-axis direction, a Y-axis ball screw 42 extending in the Y-axis direction and screwed into a nut portion of the Y-axis table 41, and a motor 43 for rotating the Y-axis ball screw 42. When the motor 43 rotates the Y-axis ball screw 42, the Y-axis table 41 moves in the Y-axis direction along the Y-axis guide rails 40. The Y-axis guide rails 40, the Y-axis ball screw 42, and the motor 43 are supported on the upper surface of the base 21, and the X-axis guide rail 36, the X-axis ball screw 38, and the motor 39 are supported on the upper surface of the Y-axis table 41.

[0026] The holding table 22 is supported on the X-axis table 37 via a table rotation mechanism 44. The table rotation mechanism 44 can rotate the holding table 22 about its Z-axis axis using a motor (not shown).

[0027] The laser processing apparatus 20 includes a vertical wall 45 that protrudes upward from one end of the base 21 in the Y-axis direction, and a projection 46 that protrudes horizontally (in the Y-axis direction) from the vertical wall 45. The laser irradiation unit 23 is provided on the projection 46.

[0028] As shown in Figure 2, the optical system of the laser irradiation unit 23 includes a laser oscillator 47 that emits a laser beam L, which is a pulsed laser with a wavelength absorbed by the workpiece 10; an output adjustment unit 48 that adjusts the laser beam L emitted by the laser oscillator 47 to a predetermined output; a mirror 50 that reflects the laser beam L whose output has been adjusted by the output adjustment unit 48 and guides it to the processing head 49; and a focusing lens 51 provided on the processing head 49 that focuses the laser beam L. The processing head 49 is located at the Y-axis end of the protruding portion 46 (see Figure 1).

[0029] The machining head 49 can be moved in the Z-axis direction using the Z-axis movement mechanism 52 shown in Figure 2. The Z-axis movement mechanism 52 includes a Z-axis guide rail 53 extending in the Z-axis direction, a slider 54 supported by the Z-axis guide rail 53 so as to be movable in the Z-axis direction, a feed screw 55 extending in the Z-axis direction and screwed into a nut on the slider 54, and a motor 56 that rotates the feed screw 55. When the motor 56 rotates the feed screw 55, the slider 54 moves in the Z-axis direction along the Z-axis guide rail 53. The slider 54 is connected to the machining head 49, and as the machining head 49 moves in the Z-axis direction along with the slider 54, the position of the focal point of the laser beam L focused by the focusing lens 51 changes in the Z-axis direction. In other words, the operation of the Z-axis movement mechanism 52 makes it possible to change the focal point of the laser beam L emitted from the laser irradiation unit 23 in the thickness direction of the workpiece 10.

[0030] By using the X-axis movement mechanism 34, Y-axis movement mechanism 35, and Z-axis movement mechanism 52 configured as described above, the holding table 22 and the laser irradiation unit 23 can be moved relative to each other in the X-axis, Y-axis, and Z-axis directions, thereby focusing the laser beam L at any position inside the workpiece 10 to form a modified layer S.

[0031] The configuration for moving the holding table 22 and the laser irradiation unit 23 relative to each other is not limited to that of this embodiment. For example, in the structure supporting the holding table 22, only one of the X-axis movement mechanism 34 and the Y-axis movement mechanism 35 may be provided, and the laser irradiation unit 23 may be configured to move in the direction in which the holding table 22 does not move, either in the X-axis direction or the Y-axis direction. Alternatively, the holding table 22 may not move in either the X-axis direction or the Y-axis direction, and instead the laser irradiation unit 23 may be configured to move in both the X-axis direction and the Y-axis direction. Furthermore, instead of moving the processing head 49 of the laser irradiation unit 23 in the Z-axis direction, the holding table 22 may be configured to move in the Z-axis direction.

[0032] At the Y-axis end of the protruding portion 46, height detection sensors 57 and 58 are provided on both sides in the X-axis direction, flanking the machining head 49. The height detection sensors 57 and 58 are non-contact sensors capable of measuring the height position (distance to the irradiation surface 14) of the workpiece 10. For example, ultrasonic sensors that measure the height position of the irradiation surface 14 based on the time it takes for ultrasonic waves to reflect off the irradiation surface 14 and return, and optical sensors that measure the height position of the irradiation surface 14 based on the time it takes for light to reflect off the irradiation surface 14 and return, can be applied.

[0033] In the processing method using sensors such as height detection sensor 57 and height detection sensor 58, the technology described in Japanese Patent Application Publication No. 2023-026125 measures the height of the irradiation surface of the workpiece with a sensor and controls the focusing position of the laser beam based on the measurement data, thereby enabling the laser beam to be focused at a uniform depth from the irradiation surface on the workpiece.

[0034] In the processing method of this embodiment, the height detection sensors 57 and 58 are used to detect changes in the height of the irradiation surface 14 facing the processing head 49 prior to the irradiation of the laser beam L when processing the workpiece 10, and to adjust the position of the focusing point of the laser beam L according to the thickness of the workpiece 10. Furthermore, the height detection sensors 57 and 58 are also used as means for detecting the timing of switching the irradiation of the laser beam L on and off when performing the control described later, in which the laser beam L is not irradiated into the boundary region including the boundary between the first region 15 and the second region 16 of the workpiece 10. Note that it is not essential to provide the height detection sensors 57 and 58 on both sides of the processing head 49. When the horizontal processing feed direction is always the same when processing the workpiece 10, or when data measured when processing in the first direction is used when processing while processing in the second direction opposite to the first direction, only one height detection sensor corresponding to the processing feed direction may be provided.

[0035] Each part of the laser processing apparatus 20 is controlled by the control unit 60. The control unit 60 includes a processor for calculation processing, a memory that stores control programs, and a communication interface for sending and receiving signals to and from each part of the laser processing apparatus 20. Based on the program stored in the memory, the processor performs various calculations and sends control signals to each part of the laser processing apparatus 20. Figure 2 shows only the connection relationships of the control unit 60 to some of the components of the laser irradiation unit 23, but the control unit 60 also controls the operation of the X-axis movement mechanism 34, the Y-axis movement mechanism 35, the table rotation mechanism 44, and the suction mechanism of the holding table 22 (on-off valve 28, suction source 29). The operation of the laser processing apparatus 20 described below is primarily controlled by the control unit 60.

[0036] [Holding step] When processing a workpiece 10 with the laser processing device 20, a holding step is performed in which the workpiece 10 is held by a holding table 22, which is a holding member. As shown in Figure 2, in the holding step, the workpiece unit 1 is brought into the laser processing device 20, the held surface 13 of the workpiece 10 is placed on the holding surface of the holding table 22 (the upper surface of the porous plate 26) via tape 2, and the frame 3 is placed on the support parts 31 of each of the multiple clamp parts 30. The on / off valve 28 is opened and the suction source 29 is operated to suction and hold the workpiece 10 on the holding surface of the holding table 22, and the frame 3 is pressed by the pressing parts 32 of each clamp part 30, so that the workpiece unit 1 is held in a fixed state relative to the holding table 22. When the workpiece 10 is held by the holding table 22, the irradiation surface 14 faces upward.

[0037] [Modified layer formation step] In the processing of the workpiece 10 by the laser processing device 20, a modified layer formation step is performed following the holding step. In the modified layer formation step, the laser beam L is irradiated onto the workpiece 10 while adjusting the position of the focal point of the laser beam L according to the thickness of the workpiece 10, thereby forming a modified layer S inside the workpiece 10.

[0038] The control unit 60 controls the X-axis movement mechanism 34 and the Y-axis movement mechanism 35 to position the irradiation position of the laser beam L on the workpiece 10 at one end (start end) of one of the multiple division lines 12 extending in the X-axis direction. Then, the X-axis movement mechanism 34 is operated to move the holding table 22 and the laser irradiation unit 23 relatively in the X-axis direction (machining feed) so that the irradiation position of the laser beam L changes along the division line 12, while the laser beam L is irradiated onto the workpiece 10 from the machining head 49 of the laser irradiation unit 23. The laser beam L irradiated from the machining head 49 enters the workpiece 10 from the irradiation surface 14 and is focused at a focal point set inside the workpiece 10, modifying the workpiece 10. As a result, a modified layer S (see Figures 4 to 9) is formed inside the workpiece 10 along the division line 12. When the irradiation position of the laser beam L reaches the other end (end) of the division line 12, the irradiation of the laser beam L from the laser irradiation unit 23 is stopped. Next, the X-axis movement mechanism 34 and the Y-axis movement mechanism 35 are operated to position the irradiation position of the laser beam L at one end (start) of the next division line 12. Then, while performing the machining feed operation in the X-axis direction as described above, the laser beam L is irradiated onto the workpiece 10, thereby forming a modified layer S inside the workpiece 10 along the next division line 12. Once the formation of the modified layer S is completed for all division lines 12 aligned in the X-axis direction, the table rotation mechanism 44 is operated to rotate the holding table 22 by 90 degrees. This leaves the unprocessed division lines 12, where the modified layer S has not yet been formed, extending in the X-axis direction. Then, using the same procedure as described above, the laser beam L is irradiated along these unprocessed division lines 12 to sequentially form the modified layer S. In this way, a modified layer S is formed along multiple planned division lines 12 on the workpiece 10.

[0039] In the processing method of this embodiment, as shown in Figures 4 to 9, multiple modified layers S are formed at different positions in the thickness direction of the workpiece 10 for each planned division line 12. That is, multiple target focusing positions are set in the thickness direction of the workpiece 10. Then, by performing a processing operation in the direction in which the processing feed operation extends along each planned division line 12 while focusing the laser beam L at each target focusing position, multiple modified layers S are formed.

[0040] The workpiece 10 has varying thicknesses, comprising a first region 15 with a relatively larger thickness and a second region 16 that is thinner than the first region 15. With the workpiece 10 held on the holding table 22 on the side to be held 13, the height position of the irradiation surface 14 onto which the laser beam L is irradiated differs between the first region 15 and the second region 16. When forming each modified layer S, the control unit 60 sets the target focusing position so that it is a predetermined depth from the irradiation surface 14 in both the first region 15 and the second region 16, based on the height position of the irradiation surface 14 detected by the height detection sensors 57 and 58. The control unit 60 then controls the position of the processing head 49 in the Z-axis direction using the Z-axis movement mechanism 52 to adjust the position of the focusing point of the laser beam L, thereby forming each modified layer S. In other words, the depth of the target focusing position when forming the modified layer S inside the workpiece 10 is managed with respect to the irradiation surface 14. In this case, when feeding the workpiece along the planned division line 12, the Z-axis movement mechanism 52 moves the workpiece 49 in the Z-axis direction according to the difference in height of the irradiation surface 14 in the first region 15 and the second region 16, at the timing when the area irradiated with the laser beam L switches from the first region 15 to the second region 16, or from the second region 16 to the first region 15. This allows the laser beam L to be focused to a target focusing position corresponding to the respective thicknesses of the first region 15 and the second region 16. If the timing of the switching of the area irradiated with the laser beam L from the first region 15 to the second region 16 is stored in coordinate data such as the X-axis direction, the Y-axis direction perpendicular to the X-axis direction, or polar coordinates with the rotation axis of the holding table 22 as the pole, the timing of the switching from the first region 15 to the second region 16 may be detected based on the stored coordinate data and the current workpiece position, and a height detection sensor may not be required.

[0041] Each modified layer S formed in this manner includes a central modified portion Sa, which serves as the dividing point in the central device region where the chip 11 is formed, and an outer peripheral modified portion Sb, which serves as the dividing point in the excess region on the outer periphery where the chip 11 is not formed, as shown in Figures 4 to 9. The central modified portion Sa and the outer peripheral modified portion Sb are at different height positions in the Z-axis direction. In the first form of workpiece 10 shown in Figures 4 to 6, of the central modified portion Sa and outer peripheral modified portion Sb belonging to the same modified layer S, the central modified portion Sa is located above the outer peripheral modified portion Sb in the Z-axis direction. In the second form of workpiece 10 shown in Figures 7 to 9, of the central modified portion Sa and outer peripheral modified portion Sb belonging to the same modified layer S, the central modified portion Sa is located below the outer peripheral modified portion Sb in the Z-axis direction.

[0042] In the case of the first form of workpiece 10 shown in Figures 4 to 6, when forming the modified layer S from one end to the other of the planned division line 12, the target of the laser beam L is switched in the order of the outer peripheral second region 16, the central first region 15, and the outer peripheral second region 16. For example, when forming the modified layer S by moving the holding table 22 in the direction indicated by the arrow Fa in Figure 2 using the X-axis movement mechanism 34 (processing feed), the height detection sensor 57 passes above the boundary (step surface 17) between the first region 15 and the second region 16 before the processing head 49 of the laser irradiation unit 23 passes above the boundary. The distance between the height detection sensor 57 and the processing head 49 in the X-axis direction is stored in the memory of the control unit 60 in advance as a specification of the laser processing device 20. Then, from the moment the height detection sensor 57, which measures the height position of the irradiation surface 14, detects that it has passed the boundary between the first region 15 and the second region 16, the control unit 60 operates the Z-axis movement mechanism 52 to change the position of the focal point of the laser beam L in the thickness direction of the workpiece 10 when the holding table 22 has been moved by arrow Fa by the distance between the height detection sensor 57 and the machining head 49 in the X-axis direction. Alternatively, the control unit 60 may refer to the amount of machining feed movement per unit time of the holding table 22 moved by the X-axis movement mechanism 34, and operate the Z-axis movement mechanism 52 to change the position of the focal point of the laser beam L in the thickness direction of the workpiece 10 after the time required to move the holding table 22 by the distance between the height detection sensor 57 and the machining head 49 in the X-axis direction from the moment the height detection sensor 57 detects that it has passed the boundary between the first region 15 and the second region 16. By changing the position of the focal point of the laser beam L through this control, a modified layer S can be formed that includes a central modified portion Sa corresponding to the central device region (first region 15) and an outer peripheral modified portion Sb corresponding to the excess region on the outer periphery (second region 16).When the X-axis movement mechanism 34 moves the holding table 22 in the direction indicated by the arrow Fb in Figure 2 (processing feed) to form the modified layer S, the height detection sensor 58 on the opposite side of the height detection sensor 57 is used to detect the timing of passing the boundary between the first region 15 and the second region 16. With the same control as described above, the modified layer S can be formed, which includes a central modified portion Sa corresponding to the central device region (first region 15) and an outer peripheral modified portion Sb corresponding to the outer peripheral excess region (second region 16).

[0043] In the case of the second form of workpiece 10 shown in Figures 7 to 9, when forming the modified layer S from one end to the other of the planned division line 12, the target of the laser beam L is switched in the order of the outer peripheral first region 15, the central second region 16, and the outer peripheral first region 15. In the second form of workpiece 10 as well, when forming the modified layer S by moving the holding table 22 (processing feed) with the X-axis movement mechanism 34, after a predetermined distance has been moved or a predetermined time has elapsed from the timing when the height detection sensor 57 or height detection sensor 58 has passed the boundary between the first region 15 and the second region 16, the Z-axis movement mechanism 52 is operated to change the position of the focal point of the laser beam L in the thickness direction of the workpiece 10, thereby forming a modified layer S that includes a central modified portion Sa corresponding to the central device region (second region 16) and an outer peripheral modified portion Sb corresponding to the outer peripheral excess region (first region 15).

[0044] In the case of the first form of workpiece 10 shown in Figures 4 to 6, the central device region where the chip 11 is formed is the first region 15, which has a greater thickness, and the thin second region 16 surrounding the outside of the first region 15 is a surplus region where the chip 11 is not formed. In the case of the second form of workpiece 10 shown in Figures 7 to 9, the central device region where the chip 11 is formed is the thin second region 16, and the thick first region 15 surrounding the outside of the second region 16 is a surplus region where the chip 11 is not formed. In both forms of workpiece 10, when dividing into multiple chips 11, if the surplus region on the outer periphery of the workpiece 10 is not divided and maintains an annular shape, there is a risk that the chip 11 will not be divided properly in the device region inside it. Therefore, in the modified layer formation step, a modified layer S is formed in the surplus region on the outer periphery where the chip 11 is not formed to provide a starting point for division, thereby ensuring that the workpiece 10 is divided reliably.

[0045] When the Z-axis movement mechanism 52 operates to change the focal point of the laser beam L in the Z-axis direction, a predetermined amount of time is required. During the formation of the modified layer S, if the holding table 22 is moved horizontally (in the X-axis direction) while the focal point shift operation is performed to change the position of the focal point of the laser beam L between the central modified section Sa and the outer peripheral modified section Sb, the position of the focal point of the laser beam L inside the workpiece 10 in the portion between the central modified section Sa and the outer peripheral modified section Sb will change in an oblique direction that includes both a horizontal (X-axis direction) component and a Z-axis direction component. Therefore, as shown in Figures 4 to 9, a transitional modified section Sc extending obliquely between the central modified section Sa and the outer peripheral modified section Sb is formed in each modified layer S. The control unit 60 takes into account the shape (trajectory) of the transition modification section Sc and controls the start and end timing of the Z-axis movement mechanism 52's operation so that the transition modification section Sc does not excessively bias towards either the first region 15 side or the second region 16 side in the machining feed direction.

[0046] Figure 11 shows a comparative example of a workpiece 100 in which a modified layer S was formed without applying the processing method of this disclosure. The upper part of Figure 11 shows a type of workpiece 100 having a first region 15 with a large thickness in the center, and the lower part of Figure 11 shows a type of workpiece 100 having a second region 16 with a small thickness in the center. In either of these types of workpieces 100, when the modified layer S is formed close to the irradiation surface 14, the transitional modified portion Sc intersects with the irradiation surface 14 or is located very close to the irradiation surface 14 near the boundary between the first region 15 and the second region 16 (near the stepped surface 17), and there is a risk that the irradiation surface 14 will be ablated by the energy of the laser beam L. If the irradiation surface 14, which is the outer surface of the workpiece 100 and not the interior in the thickness direction of the workpiece 10, is ablated, it will generate processing debris, which will cause a decrease in the quality of the workpiece 100 and the chip. In particular, when multiple modified layers S are formed at different positions in the thickness direction of the workpiece 100, this problem is more likely to occur in the modified layer S formed at the depth closest to the irradiation surface 14. Furthermore, in the first region 15 of the workpiece 100, which has a larger thickness, the transitional modified layer Sc extends away from the irradiation surface 14, starting from the point where it connects to the central modified layer Sa, whereas in the second region 16, which is thinner, the transitional modified layer Sc extends towards the irradiation surface 14, starting from the point where it connects to the outer peripheral modified layer Sb. Therefore, ablation is more likely to occur in the second region 16 in particular, as the transitional modified layer Sc approaches the irradiation surface 14. In the workpiece 100 of the comparative example in Figure 11, the transitional modified layer Sc also intersects with the stepped surface 17, which is the boundary between the first region 15 and the second region 16, and there is a risk of ablation occurring on the stepped surface 17 as well.

[0047] To resolve these issues, in the processing performed by the laser processing apparatus 20 of this embodiment, based on the control of the control unit 60, in the modified layer formation step, at least a portion of the thickness direction of the workpiece 10, including the boundary region between the first region 15 and the second region 16, is prevented from being irradiated by the laser beam L. Figures 4 to 6 show processing examples applied to a first type of workpiece 10 in which the thickness is large in the center and small on the outer periphery, and Figures 7 to 9 show processing examples applied to a second type of workpiece 10 in which the thickness is small in the center and large on the outer periphery.

[0048] In the first example of workpiece processing shown in Figure 4, for the modified layer S formed at the depth closest to the irradiation surface 14, a central modified portion Sa is formed in the first region 15 and an outer peripheral modified portion Sb is formed in the second region 16. At the same time, the laser beam L is controlled so as not to irradiate the boundary region M, which includes the boundary between the first region 15 and the second region 16, so that the modified layer S does not include a transitional modified portion Sc. In other words, while the holding table 22 is moved in the X-axis direction as the processing feed and the processing head 49 is moving above the boundary region M, the control unit 60 stops the irradiation of the laser beam L from the laser irradiation unit 23 to the workpiece 10. During this time, the control unit 60 operates the Z-axis movement mechanism 52 to switch the focal point position between the position corresponding to the central modified portion Sa and the position corresponding to the outer peripheral modified portion Sb. The boundary region M includes a predetermined width on the first region 15 side and a predetermined width on the second region 16 side, straddling the stepped surface 17 which is the boundary line between the first region 15 and the second region 16 in the radial direction of the workpiece 10. In the modified layer S formed at the depth closest to the irradiation surface 14, by not forming a transitional modified portion Sc extending diagonally in the boundary region M, it is possible to avoid a situation in which the focal point of the laser beam L comes too close to the irradiation surface 14, particularly on the second region 16 side of the boundary region M, thereby preventing the laser beam L from ablating the irradiation surface 14. Furthermore, since the boundary region M includes the stepped surface 17, by temporarily stopping the irradiation of the laser beam L in the boundary region M so that the transitional modified portion Sc does not intersect the stepped surface 17, it is also possible to prevent the laser beam L from ablating the stepped surface 17.

[0049] The method for stopping the irradiation of the laser beam L to the boundary region M is not limited. For example, the control unit 60 controls the system to stop the oscillation of the laser beam L by the laser oscillator 47. Alternatively, a movable shielding member capable of blocking the laser beam L midway through its path may be provided, and while the oscillation of the laser beam L by the laser oscillator 47 continues, the control unit 60 operates the shielding member to switch whether or not the laser beam L reaches the workpiece 10.

[0050] In the example of processing the workpiece 10 of the first form shown in Figure 5, the laser beam L is not irradiated in the boundary region M, which includes the boundary between the first region 15 and the second region 16, with respect to the modified layer S formed at the depth closest to the irradiation surface 14. In addition, the laser beam L is controlled not to be irradiated to the entire second region 16, which is on the outer periphery of the boundary region M. In other words, the modified layer S formed at the depth closest to the irradiation surface 14 is prevented from forming an outer peripheral modified portion Sb and a transitional modified portion Sc. This prevents the focal point of the laser beam L from getting too close to the irradiation surface 14 throughout the entire second region 16, thereby preventing the laser beam L from ablating the irradiation surface 14. Since the second region 16, which is the surplus region on the outer periphery, is thinner than the first region 15, the processing example in Figure 5 can be applied if, even if the modified layer S does not include an outer peripheral modified portion Sb in a part of the thickness direction, other modified layers S include an outer peripheral modified portion Sb, and a sufficient effect can be obtained as the starting point for dividing the second region 16.

[0051] In the first example of workpiece processing shown in Figure 6, the modified layer S formed at the depth closest to the irradiation surface 14 includes a central modified portion Sa and an outer peripheral modified portion Sb, and furthermore, a transitional modified portion Sc is formed within the range of the first region 15. The formation range of the transitional modified portion Sc is set so as not to extend beyond the stepped surface 17, which is the boundary between the first region 15 and the second region 16, towards the second region 16. In other words, the range from the stepped surface 17 to a predetermined width on the second region 16 side is set as a boundary region N where the laser beam L is not irradiated. In the first region 15, the transitional modified portion Sc extends away from the irradiation surface 14, starting from the point where it connects to the central modified portion Sa, so even if the transitional modified portion Sc is formed, there is no risk of the irradiation surface 14 of the first region 15 being ablated by the laser beam L. In contrast, in the second region 16, the transitional modification section Sc extends towards the irradiation surface 14, starting from the point where it connects to the outer peripheral modification section Sb. Therefore, if the transitional modification section Sc is formed in the boundary region N, the irradiation surface 14 of the second region 16 becomes more susceptible to ablation by the laser beam L. Accordingly, by not irradiating the boundary region N on the second region 16 side with the laser beam L and not forming the transitional modification section Sc, it is possible to avoid a situation where the focal point of the laser beam L gets too close to the irradiation surface 14, thereby preventing the laser beam L from ablating the irradiation surface 14. Furthermore, to prevent ablation at the stepped surface 17, the control unit 60 controls the irradiation range of the laser beam L so that the transitional modification section Sc does not intersect with the stepped surface 17. In other words, the stepped surface 17 is included in the boundary region N where the laser beam L is not irradiated when forming the modified layer S which is formed at the depth closest to the irradiation surface 14, thus preventing the laser beam L from ablating the stepped surface 17.

[0052] Depending on conditions such as the diameter of the workpiece 10, it is preferable to ensure a boundary region N width of 150 μm or more on one side of the workpiece 10 in the radial direction. Experimental results showed that by satisfying this condition, ablation of the irradiated surface 14, which tends to occur in the second region 16 near the stepped surface 17, could be reliably prevented. Taking into account errors during processing, the width of the boundary region N on one side of the workpiece 10 in the radial direction may be set to a maximum of approximately 300 μm.

[0053] In the example of processing shown in Figure 4, it is preferable to set the width on one side in the radial direction of the portion of the boundary region M from the stepped surface 17 to the second region 16 to 150 μm or more (in the range of 150 μm to 300 μm).

[0054] In the second embodiment of the workpiece 10 shown in Figure 7, similar to the example shown in Figure 4, the modified layer S formed at the depth closest to the irradiation surface 14 includes a central modified portion Sa and an outer peripheral modified portion Sb. However, in the boundary region M, which includes the boundary between the first region 15 and the second region 16, the control unit 60 controls the process so that the laser beam L is not irradiated, thereby ensuring that the modified layer S does not include a transitional modified portion Sc. By not forming a transitional modified portion Sc in the boundary region M in the modified layer S formed at the depth closest to the irradiation surface 14, it is possible to prevent the focal point of the laser beam L from getting too close to the irradiation surface 14, particularly in the second region 16 of the boundary region M, thereby preventing ablation of the irradiation surface 14. Furthermore, since the boundary region M includes a stepped surface 17, it is also possible to prevent the laser beam L from ablating the stepped surface 17.

[0055] In the processing example of the workpiece 10 of the second form shown in Figure 8, the laser beam L is not irradiated in the boundary region M, which includes the boundary between the first region 15 and the second region 16, with respect to the modified layer S formed at the depth closest to the irradiation surface 14. In addition, the laser beam L is controlled so that it is not irradiated throughout the entire second region 16. In other words, the central modified portion Sa and the transitional modified portion Sc are not formed in the modified layer S formed at the depth closest to the irradiation surface 14. Therefore, similar to the processing example shown in Figure 7, it is possible to prevent the focal point of the laser beam L in the second region 16 of the boundary region M from getting too close to the irradiation surface 14, thereby preventing ablation of the irradiation surface 14. Furthermore, by not forming the central modified portion Sa at a depth close to the irradiation surface 14 in the second region 16, the control of the irradiation of the laser beam L to the second region 16 can be simplified. Since the second region 16, which is the device region having the chip 11, is thinner than the first region 15, which is the excess region on the outer periphery, if the division of the device region is not hindered even if a portion of the central modified portion Sa is not formed in a part of the thickness direction, the processing example in Figure 8 can be applied.

[0056] In the second example of workpiece processing shown in Figure 9, similar to the example shown in Figure 6, the modified layer S formed at the depth closest to the irradiation surface 14 includes a central modified portion Sa and an outer peripheral modified portion Sb. Furthermore, the transitional modified portion Sc is formed only within the range of the first region 15 so that it does not extend beyond the stepped surface 17, which is the boundary between the first region 15 and the second region 16, towards the second region 16. In other words, the range from the stepped surface 17 to a predetermined width on the second region 16 side is set as a boundary region N where the laser beam L is not irradiated. Similar to the example of processing shown in Figure 6 described earlier, the control unit 60 controls the irradiation range of the laser beam L so that the transitional modified portion Sc does not intersect with the stepped surface 17, and the stepped surface 17 is included in the boundary region N where the laser beam L is not irradiated. This prevents the focal point of the laser beam L from getting too close to the irradiation surface 14 in the boundary region N on the second region 16 side, thereby preventing the laser beam L from ablating the irradiation surface 14. It also prevents the laser beam L from ablating the stepped surface 17.

[0057] For the portion of boundary region M on the second region 16 side in the machining example in Figure 7, and for boundary region N in the machining example in Figure 9, it is preferable to set the width on one side in the radial direction to 150 μm or more (in the range of 150 μm to 300 μm), similar to the machining examples in Figure 4 and Figure 7.

[0058] Information such as the radial dimensions of the first region 15 and the second region 16 of the workpiece 10, the radial width of the boundary region M and boundary region N, and the distance between the height detection sensors 57 and 58 and the machining head 49 in the X-axis direction is stored in the memory of the control unit 60.

[0059] In each processing example from Figure 4 to Figure 9, the timing of switching the laser beam L on and off can be controlled by referring to the detection results of the height detection sensor 57 and the height detection sensor 58. When the holding table 22 moves in the processing feed direction (X-axis direction), the height detection sensor 57 and the height detection sensor 58 detect the switching between the state in which the irradiation surface 14 of the workpiece 10 is below and the state in which it is not, allowing the control unit 60 to determine the timing when the processing head 49 reaches above the outer edge of the workpiece 10. When the holding table 22 moves in the processing feed direction (X-axis direction), the height detection sensor 57 and the height detection sensor 58 detect the switching between the irradiation surface 14 of the first region 15 and the irradiation surface 14 of the second region 16, allowing the control unit 60 to determine the timing when the processing head 49 reaches the boundary (step surface 17) between the first region 15 and the second region 16. The control unit 60 refers to information stored in memory, such as the radial dimensions of the first region 15 and the second region 16, the radial width of the boundary region M and boundary region N, and the distance between the height detection sensors 57 and 58 and the processing head 49, and calculates the timing for turning the laser beam L on and off based on the arrival timing described above.

[0060] As can be seen from the above processing examples, the boundary region of the workpiece 10 that the control unit 60 manages so that the laser beam L is not irradiated in the modified layer formation step only needs to include at least the boundary line (step surface 17) between the first region 15 and the second region 16 to a predetermined range of the second region 16, as shown in boundary region N in the processing examples of Figures 6 and 9. When switching the focal point of the laser beam L between the position of the central modified portion Sa and the position of the outer peripheral modified portion Sb, the focal point tends to approach the irradiation surface 14, especially in boundary region N. Therefore, by not irradiating the boundary region N with the laser beam L, the best effect in preventing ablation of the irradiation surface 14 can be obtained.

[0061] For the first region 15, even if a transitional modification portion Sc is formed in the modified layer S formed at the depth closest to the irradiation surface 14, it is unlikely to cause ablation of the irradiation surface 14. Therefore, as shown in the processing examples in Figures 6 and 9, the laser beam L may be irradiated up to near the step surface 17, which is the boundary with the second region 16. However, if the timing of switching the irradiation of the laser beam L on and off is off, the laser beam L may be focused on the step surface 17 or the irradiation surface 14 in the area on the second region 16 side of the step surface 17 (boundary region N). Therefore, highly precise operation and control are required so that there is no error between the timing of switching the irradiation of the laser beam L on and off and the timing of the processing head 49 passing over the boundary region N. In the machining examples shown in Figures 4 and 7, by setting the boundary region M to include an area where the laser beam L is not irradiated not only on the second region 16 side but also on the first region 15 side, a slight error is allowed between the timing of switching the laser beam L on and off and the timing when the machining head 49 passes over the boundary region M, making it easier for the control unit 60 to perform control.

[0062] In the processing examples shown in Figures 4 to 9, when multiple modified layers S are formed at different depths in the thickness direction of the workpiece 10, the laser beam L is not irradiated to the boundary regions M and N, but the method is not limited to this configuration. For modified layers S that are second to third closest to the irradiation surface 14, if there is a risk of ablation occurring on the irradiation surface 14 when a modified layer S (transitional modified portion Sc) is formed near the boundary between the first region 15 and the second region 16, it is preferable to prevent the laser beam L from irradiating the boundary regions.

[0063] Although it depends on conditions such as the energy density per irradiation of the laser beam L and the material of the workpiece 10, experimental results showed that when the distance from the outer surface of the workpiece 10 to the focal point of the laser beam L is 40 μm or less in the thickness direction of the workpiece 10, ablation is likely to occur on the outer surface of the workpiece 10. Therefore, it is desirable not to form the modified layer S in the range where the depth from the irradiation surface 14, which is one of the outer surfaces in the thickness direction of the workpiece 10, is 40 μm or less. For example, in the processing examples in Figures 4, 5, 6, 7, and 9, it is desirable to form the modified layer S, which is formed at the depth closest to the irradiation surface 14 of the workpiece 10, by setting the depth from the irradiation surface 14 to the central modified part Sa to 40 μm or more. Furthermore, by turning off the irradiation of the laser beam L in boundary regions M and N, which include the boundary between the first region 15 and the second region 16, it is possible to prevent the formation of the modified layer S (especially the transitional modified portion Sc) in boundary regions M and N as well, in the range where the depth from the irradiation surface 14 is 40 μm or less. In addition, in the processing examples in Figures 4, 6, 7, 8, and 9, it is desirable to form the outer peripheral modified portion Sb such that the modified layer S formed at the depth closest to the irradiation surface 14 is 40 μm or more from the irradiation surface 14.

[0064] Furthermore, from the standpoint of preventing damage to the outer surface of the workpiece 10, it is desirable to control the formation of the modified layer S on the holding surface 13 opposite to the irradiation surface 14, so as not to form below a predetermined depth (e.g., 40 μm) from the holding surface 13. When the tape 2 is attached to the holding surface 13, as in the workpiece unit 1 of this embodiment, preventing leakage of the laser beam L to the holding surface 13 can prevent damage to the workpiece 10 on the holding surface 13 side and damage to the tape 2 that is in close contact with it. If the workpiece 10 on the holding surface 13 side is damaged by leakage light, the strength of the chip 11 may decrease. Also, if the tape 2 is damaged by leakage light, it may not be possible to properly apply external force to the workpiece 10 via the tape 2 in the chip spacing expansion step described later. Therefore, in order to protect the workpiece 10 and the tape 2 on the holding surface 13 side from damage, it is preferable not to generate leakage light on the holding surface 13 in the modified layer formation step. Furthermore, when processing the workpiece 10 in a standalone state without attaching the tape 2 or frame 3, preventing light leakage to the held surface 13 prevents damage to the holding surface of the holding table 22 that holds the held surface 13. In addition, by preventing processing due to light leakage on the held surface 13, damage to the held surface 13 and the adhesion of debris to the held surface 13 can be prevented, thereby improving processing quality.

[0065] As a processing control measure to prevent processing due to stray light from the held surface 13, for example, in the first form of workpiece 10 shown in Figures 4 to 6, it is desirable to form the modified layer S, which is formed at the depth closest to the held surface 13, with a depth of 40 μm or more from the held surface 13 to the central modified portion Sa, and not form the outer peripheral modified portion Sb or the transitional modified portion Sc in areas where the depth from the held surface 13 is 40 μm or less (i.e., do not irradiate with laser beam L during processing feed). In the second form of workpiece 10 shown in Figures 7 to 9, if the modified layer S, which is formed at the depth closest to the held surface 13 of the workpiece 10, is formed with a depth of 40 μm or more from the held surface 13 to the central modified portion Sa, the outer peripheral modified portion Sb and the transitional modified portion Sc can be formed at positions where the depth from the held surface 13 is greater than that of the central modified portion Sa. Alternatively, the modified layer S formed at the depth closest to the surface to be held 13 may be formed such that the depth from the surface to be held 13 is constant throughout the entire planned dividing line 12, without forming a transitional modified section Sc in between.

[0066] In each processing example from Figures 4 to 9, as shown in Figure 3, a linear division line 12 is set that continuously crosses the workpiece 10 from the central device region where the chip 11 is formed to the outer periphery excess region. In the modified layer formation step, a modified layer S including a central modified portion Sa and an outer periphery modified portion Sb is formed on each of the division line 12. By making the processing conditions, such as the number and position of the modified layers S, the same in the central device region where the chip 11 is formed and the outer periphery excess region, except for areas (boundary regions M and N) where the irradiation of the laser beam L is partially turned off to prevent ablation of the outer surface of the workpiece 10, efficient processing can be performed in the modified layer formation step, and the excess region as well as the device region can be easily divided. In particular, in the second form of workpiece 10 shown in Figures 7 to 9, the effect of being able to effectively divide the first region 15 on the outer periphery, which has a large thickness, can be obtained.

[0067] However, it is also possible to differentiate the processing conditions in the modified layer formation step between the central device region where chips 11 are formed and the surplus region on the outer periphery where chips 11 are not formed. As an example, in the modified workpiece 10 shown in Figure 10, in the modified layer formation step, a modified layer Sd is formed along a grid-like division line 12 that demarcates multiple chips 11 in the central device region, and an annular modified layer Se is formed along the boundary line (step surface 17) between the first region 15 and the second region 16. Furthermore, in the surplus region on the outer periphery, a radial modified layer Sf extending in the radial direction of the workpiece 10 is formed. The radial modified layers Sf are arranged at eight approximately equal intervals in the circumferential direction of the workpiece 10. In other words, in the surplus region on the outer periphery, fewer modified layers Sf are formed than the modified layers Sd in the central device region in a plan view, and some of the modified layers Sf are formed in a different direction from the modified layers Sd in the device region. Furthermore, multiple modified layers Sd, multiple modified layers Se, and multiple modified layers Sf may be formed at different depths in the thickness direction of the workpiece 10.

[0068] In the workpiece 10 shown in Figure 10, when the central device region is divided along the grid-like division lines 12 (modified layer Sd) that demarcate multiple chips 11, the modified layers Se and Sf act as dividing points, dividing the excess region on the outer periphery, thus not hindering the division of the chips 11 in the device region. Since the number of modified layers Sf in the excess region is small compared to the number of modified layers Sd in the device region, this is particularly suitable for workpieces 10 of the type in which the excess region on the outer periphery is a thin second region 16 (a type with a small division load on the excess region), such as the first form of workpiece 10 shown in Figures 4 to 6. Note that if the ease of dividing the excess region on the outer periphery can be ensured by forming radial modified layers Sf, the setting of not forming annular modified layers Se may be selected.

[0069] Conversely, in the case of the second type of workpiece 10 shown in Figures 7 to 9, where the excess region on the outer periphery is a thick first region 15, it is possible to form the modified layer Sf in the excess region at a narrower interval than the interval of the modified layer Sd in the device region, thereby improving the ease of dividing the excess region.

[0070] Thus, the excess region on the outer circumference of the workpiece 10 only needs to be divided to the extent that it does not hinder the divisibility of the device region, and it is not a necessary condition that the modified layer in the excess region be formed in the same number and arrangement as the planned division lines of the device region during the modified layer formation step.

[0071] The processing conditions in the modified layer formation step include not only the number of modified layers in a plan view of the workpiece 10 (number of laser beams L irradiations), the number of modified layers in the thickness direction of the workpiece 10, and the position of the modified layers (irradiation position of the laser beams L), but also the depth of the modified layers (irradiation depth of the laser beams L) and the energy density per irradiation of the laser beams L. The energy density per irradiation of the laser beams L can be adjusted by changing at least one of the following: the output adjustment unit 48 of the laser irradiation unit 23, the repetition frequency of the pulsed laser beam, and the processing feed speed that moves the laser irradiation unit 23 and the holding table 22 that holds the workpiece 10 relative to each other in the processing feed direction, thereby adjusting the overlap rate of the laser irradiation marks of the laser beams L.

[0072] For example, in the workpiece 10 shown in Figure 10, when forming a modified layer Sf in the excess region on the outer periphery, the energy density per irradiation of the laser beam L may be increased to accelerate the degree of modification of the modified layer Sf, thereby enabling efficient division of the excess region with a smaller number of modified layers Sf.

[0073] In the first form of the workpiece 10 shown in Figures 4 to 6, the thinner outer peripheral second region 16 is more easily divided than the thicker central first region 15. Therefore, the energy density per irradiation of the laser beam L when forming the central modified region Sa in the first region 15 may be set to a larger value than the energy density per irradiation of the laser beam L when forming the outer peripheral modified region Sb in the second region 16, so that the difference between the external force that divides the first region 15 and the external force that divides the second region 16 becomes smaller.

[0074] In the second form of the workpiece 10 shown in Figures 7 to 9, the energy density per irradiation of the laser beam L when forming the outer peripheral modified portion Sb in the thicker outer peripheral first region 15 may be set to a larger value than the energy density per irradiation of the laser beam L when forming the central modified portion Sa in the thin central second region 16, so that the difference between the external force that divides the first region 15 and the external force that divides the second region 16 becomes smaller.

[0075] Furthermore, in the first form of workpiece 10 shown in Figures 4 to 6, an additional modified layer similar to the central modified portion Sa of other modified layers S may be formed in the central first region 15 at a position close to the held surface 13, thereby increasing the number of division starting points in the first region 15, which has a greater thickness, in the thickness direction. In the second form of workpiece 10 shown in Figures 7 to 9, an additional modified layer similar to the outer peripheral modified portion Sb of other modified layers S may be formed in the outer peripheral first region 15 at a position close to the held surface 13, thereby increasing the number of division starting points in the first region 15, which has a greater thickness, in the thickness direction.

[0076] As described above, the modified layer formation step is performed by the laser processing apparatus 20. Once the modified layer formation step is complete, the workpiece unit 1 is removed from the laser processing apparatus 20 and transported to the expander 70 shown in Figures 12 and 13. The expander 70 is equipped with an annular holding base 71 capable of holding the frame 3 of the workpiece unit 1, and the frame 3 can be fixed onto the holding base 71 via a plurality of clamping parts 72 that can be opened and closed relative to the holding base 71. The holding base 71 can be moved in the Z-axis direction by a lifting mechanism 73 composed of an air cylinder or the like. A central opening 74 that penetrates in the Z-axis direction is formed in the center of the holding base 71, and a cylindrical push-up member 75 is arranged inside the central opening 74.

[0077] [Chip spacing expansion step] The workpiece unit 1, transported to the expander 70, is held as shown in Figure 12. The upper surface of the holding base 71 and the upper end of the push-up member 75 are set to approximately the same height, and the frame 3 is placed on the upper surface of the holding base 71 and fixed to the frame 3 with the clamp portion 72. At this stage, the tape 2 is supported in a flat shape from the upper surface of the holding base 71 to the upper end of the push-up member 75, and the workpiece 10 is positioned above the hollow internal space of the push-up member 75.

[0078] As shown in Figure 12, once the workpiece unit 1 is held, the lifting mechanism 73 is operated to move the holding base 71 downward. Then, as shown in Figure 13, the central part of the tape 2 to which the workpiece 10 is attached is restricted from moving downward by the upper end of the push-up member 75, while the outer circumference of the tape 2 is pulled downward by the holding base 71 together with the frame 3. As a result, the tape 2 is pulled and expanded, and an external force acts on the workpiece 10 supported by the tape 2 in a direction that expands its diameter. The application of this external force by the expander 70 performs a chip spacing expansion step that widens the spacing between the multiple chips 11. In at least one of the modified layer formation step performed by the laser processing device 20 and the chip spacing expansion step performed by the expander 70, the workpiece 10 is divided into multiple chips 11 starting from the modified layer S (Sd, Se, Sf), and multiple individual chips 11 can be manufactured from the workpiece 10. For example, if the workpiece 10 has already been divided into multiple chips 11 and the chips 11 have been manufactured in the modified layer formation step, the chip spacing expansion step widens the spacing between the divided chips 11. If the workpiece 10 is not divided at the stage of the modified layer formation step, the expander 70 applies an external force to the workpiece 10, dividing the workpiece 10 into multiple chips 11 starting from the modified layer S, and then widening the spacing between the chips 11. Widening the spacing between the multiple chips 11 makes it easier to remove each manufactured chip 11 from the tape 2.

[0079] The application of external force to the workpiece 10 in the chip spacing expansion step may be performed using a device with a different configuration than the expanded device 70 shown in the figure. For example, instead of the push-up member 75, a pressing roller may be provided above the workpiece 10. The roller is supported so as to be rotatable about an axis extending in the Y-axis direction. With the workpiece unit 1 held as shown in Figure 12, the roller can be pressed against the workpiece 10 by raising the holding base 71 by the lifting mechanism 73 or by lowering the roller, and the roller can be moved in the X-axis direction, thereby applying external force to the workpiece 10 to divide it into multiple chips 11 or widening the spacing between the multiple chips 11.

[0080] Alternatively, instead of the push-up member 75, the device may be provided with a holding portion that clamps the workpiece 10 from above and below, and a pressing portion that presses the workpiece 10 in the Z-axis direction near the holding portion. By repeatedly performing the operation of holding the workpiece 10 with the holding portion and pressing it with the pressing portion for each of the multiple planned division lines 12, an external force can be applied to the workpiece 10 to divide it into multiple chips 11 or to widen the spacing between the multiple chips 11.

[0081] As described above, a modified layer is formed on the workpiece 10 using a processing method that includes a holding step and a modified layer formation step, and multiple chips 11 are manufactured by dividing the workpiece 10 starting from the modified layer. In the modified layer formation step, boundary regions M and N, including the boundary (step surface 17) between the first region 15 and the second region 16, are controlled so that the laser beam L does not irradiate at least a portion of the thickness direction of the workpiece 10. This prevents the outer surface of the workpiece 10 (especially the irradiation surface 14 irradiated with the laser beam L) from being ablated by the energy of the laser beam L, and allows the workpiece 10 to be processed with high precision.

[0082] Furthermore, in the modified layer formation step, multiple modified layers S are formed at different depths in the thickness direction of the workpiece 10, and at least the modified layer S formed at the depth closest to the irradiation surface 14 to which the laser beam L is irradiated is targeted so that the laser beam L is not irradiated in the boundary regions M and N. This ensures that situations that increase the risk of ablation occurring on the irradiation surface 14 can be reliably avoided.

[0083] Furthermore, as shown in the processing examples in Figures 5 and 8, in the modified layer formation step, multiple modified layers S may be formed at different depths in the thickness direction of the workpiece 10, and at least the modified layer S formed at the depth closest to the irradiation surface 14 to which the laser beam L is irradiated may be set so that the laser beam L is not irradiated in the second region 16. This prevents ablation of the irradiation surface 14 in the second region 16 and simplifies the irradiation control of the laser beam L, enabling efficient processing. In addition, when forming the modified layer S at the depth closest to the irradiation surface 14, the processing examples in Figures 5 and 8 may be applied to the second region 16 to prevent irradiation with the laser beam L, and the processing examples in Figures 6 and 9 may be applied to the first region 15 to form the modified layer S (transition modified portion Sc) up to the immediate vicinity of the boundary (step surface 17) with the second region 16.

[0084] As shown in the processing examples above, the processing method of this disclosure can be applied to both a first type of workpiece 10 (Figures 4 to 6) in which a thin second region 16 surrounds the outer periphery of a thick central first region 15, and a second type of workpiece 10 (Figures 7 to 9) in which a thick first region 15 surrounds the outer periphery of a thin central second region 16.

[0085] As shown in the processing examples in Figures 6 and 9, it is desirable that the boundary region N not irradiated by the laser beam L includes at least the boundary line (step surface 17) between the first region 15 and the second region 16, and a predetermined range within the second region 16 from the said boundary line (step surface 17). This effectively prevents ablation at the location where ablation of the irradiated surface 14 is most likely to occur.

[0086] As shown in the processing examples in Figures 4 and 7, the boundary region M that is not irradiated by the laser beam L may further include a predetermined range from the boundary line (step surface 17) of the first region 15. This allows for some error between the timing of switching the laser beam L on and off at the boundary region M and the timing of the processing head 49 passing the position corresponding to the boundary region M, making it easier for the control unit 60 to perform control.

[0087] In the processing examples shown in Figures 4 to 9, three modified layers S are formed at different positions in the thickness direction of the workpiece 10. However, the number of modified layers in the thickness direction of the workpiece 10 is not limited. The number of modified layers provided in the thickness direction of the workpiece 10 may be one, two, or four or more.

[0088] The laser processing apparatus 20 described above detects the height position of the irradiation surface 14 of the workpiece 10 using height detection sensors 57 and 58, and controls the on / off of the laser beam L irradiation in the laser irradiation unit 23 based on the processing feed amount and the elapsed processing feed time from the time a change in the height position of the irradiation surface 14 is detected. However, the on / off of the laser beam L irradiation may be controlled in a different way. For example, the apparatus may be equipped with an imaging unit capable of capturing alignment indicators or key patterns formed on the workpiece 10, and based on the indicators or key patterns captured by the imaging unit, relative position information of the processing head 49 of the laser irradiation unit 23 with respect to the workpiece 10 can be acquired, and based on this position information, the apparatus can be controlled to switch the on / off of the laser beam L irradiation when the processing head 49 reaches a desired position on the workpiece 10.

[0089] In the laser processing apparatus 20 of the above embodiment, the control unit 60 manages the position of the focal point of the laser beam L in the thickness direction of the workpiece 10 as the depth from the irradiation surface 14 of the workpiece 10 detected by the height detection sensor 57 and the height detection sensor 58. In contrast to this embodiment, the position of the focal point of the laser beam L may also be managed based on the depth from the holding surface 13 of the workpiece 10 or the holding surface of the holding table 22.

[0090] In the above embodiment, the laser processing apparatus 20 irradiates the laser beam L from the irradiation surface 14 side, where the height positions of the first region 15 and the second region 16 are different. However, the processing method of this disclosure can also be applied when the laser beam is irradiated from the held surface 13 side, which is opposite to the irradiation surface 14. For example, the holding member that holds the workpiece 10 may be made of a material that can transmit the laser beam (such as glass) instead of the holding table 22, and the laser beam may be irradiated through the holding member toward the held surface 13 and focused into the inside of the workpiece 10. In this case as well, if the modified layer is formed at a position close to the irradiation surface 14 (the surface opposite to the held surface 13, which is the actual irradiation surface), while adjusting the position of the laser beam's focusing point according to the thickness of the workpiece 10, there is a risk that the laser beam will ablate the irradiation surface 14. Therefore, the processing method of this disclosure described above is effective as a means of avoiding such problems.

[0091] In the above embodiment, the workpiece 10 has an irradiation surface 14 on one side in the thickness direction, which is positioned differently from the first region 15 and the second region 16 in the thickness direction, and a holding surface 13 that is flat from the first region 15 to the second region 16. However, the surface corresponding to the holding surface 13 may have a shape that includes irregularities, like the irradiation surface 14. For example, this method can also be applied when processing a workpiece that has a convex shape (a shape in which the center protrudes relative to the outer periphery) on one side in the thickness direction, similar to the irradiation surface 14 shown in Figures 4 to 6, and a concave shape (a shape in which the center is recessed relative to the outer periphery) on the other side in the thickness direction, similar to the irradiation surface 14 shown in Figures 7 to 9. In this case, when a laser beam is irradiated onto the workpiece while adjusting the position of the focal point according to the thickness of the workpiece to form a modified layer inside, the focal points of the laser beam become locally close on each of the two sides in the thickness direction, making ablation more likely to occur. Therefore, the processing method described above in this disclosure is effective.

[0092] Furthermore, the processing method of this disclosure may also be applied to workpieces in which both surfaces in the thickness direction have a convex shape similar to the irradiation surface 14 shown in Figures 4 to 6, or to workpieces in which both surfaces in the thickness direction have a concave shape similar to the irradiation surface 14 shown in Figures 7 to 9.

[0093] Furthermore, in the case of a workpiece in which one surface in the thickness direction is convex and the other surface in the thickness direction is concave, if the amount of protrusion of one surface and the amount of recess of the other surface are equal, the thickness of the central region (device region) and the outer peripheral region (excess region) of the workpiece will be approximately the same. The processing method of this disclosure can also be applied to workpieces of such modified forms. That is, in the above embodiment, the first region 15 and the second region 16 of the workpiece 10 are treated as two regions with different thicknesses (the second region 16 is thinner than the first region 15), but as a concept that encompasses the above embodiment and the modified form, the first region and the second region of the workpiece can also be defined as two regions in which at least one of the surfaces on both sides in the thickness direction is positioned differently from each other in the thickness direction, regardless of whether the thicknesses are different or the same. Then, in the modified layer formation step, a focus point is set at different positions in the thickness direction in the first region and the second region, and a laser beam is irradiated onto the workpiece to form a modified layer inside.

[0094] In the above embodiment, a modified layer S is formed inside a workpiece 10 having a plurality of chips 11 in the central device region as a starting point for dividing it into individual chips 11. However, the processing method of this disclosure may also be applied to applications other than dividing into a plurality of chips (applications other than manufacturing chips), for example, when forming a modified layer that becomes a peeling layer that spreads in the planar direction of the workpiece.

[0095] Furthermore, the embodiments of the present invention are not limited to the embodiments and modifications described above, and may be modified, substituted, or altered in various ways without departing from the spirit of the technical idea of ​​the present invention. Moreover, if the technical idea of ​​the present invention can be realized in a different way by advances in the art or by other derived arts, it may be implemented by that method. Accordingly, the claims cover all embodiments that may fall within the scope of the technical idea of ​​the present invention. [Industrial applicability]

[0096] According to the present invention, it is possible to process workpieces with partially different thicknesses with high precision, thereby improving the processing quality and manufacturing efficiency of workpieces and chips manufactured by dividing workpieces. [Explanation of Symbols]

[0097] 1: Workpiece Unit 10: Workpiece 11: Tip 12: Planned division line 13: Surface to be held 14: Irradiation surface 15:First area 16:Second area 17: Step surface (boundary, boundary line) 20: Laser processing equipment (processing equipment) 22: Holding table (holding member) 23: Laser irradiation unit 34:X-axis movement mechanism 35:Y-axis movement mechanism 44: Table rotation mechanism 47: Laser oscillator 48: Output adjustment section 49: Machining head 51: Focusing lens 52:Z-axis movement mechanism 57: Height detection sensor 58: Height detection sensor 60: Control Unit 70: Expanding device 71: Holding stand 73: Lifting mechanism 75: Push-up member L: Laser beam M: Boundary area N: Boundary area S: Modified layer Sa: Central Modification Department Sb: Outer periphery modified section Sc: Transition Modification Unit Sd: Modified layer Se: Modified layer Sf: Modified layer

Claims

1. A method for processing a workpiece, A holding step in which a workpiece having a first region and a second region thinner than the first region is held by a holding member, The process includes a modified layer formation step in which a laser beam is irradiated onto the workpiece while adjusting the position of the focusing point according to the thickness of the workpiece to form a modified layer inside, A method for processing a workpiece, characterized in that, in the modified layer formation step, a boundary region including at least a portion of the first region and the second region is not irradiated with the laser beam.

2. The modified layer formation step is, A method for processing a workpiece according to claim 1, characterized in that a plurality of modified layers are formed at different depths in the thickness direction of the workpiece, and the laser beam is not irradiated in the boundary region of the modified layer formed at the depth closest to the irradiation surface of the laser beam.

3. The modified layer formation step is, The method for processing a workpiece according to claim 1, characterized in that a plurality of modified layers are formed at different depths in the thickness direction of the workpiece, and the laser beam is not irradiated in the second region of the modified layer formed at the depth closest to the irradiation surface.

4. The method for processing a workpiece according to claim 1, characterized in that the first region is formed in the center of the workpiece, and the second region is formed on the outer periphery of the workpiece surrounding the first region.

5. The method for processing a workpiece according to claim 1, characterized in that the boundary region not irradiated by the laser beam includes the boundary line between the first region and the second region, and a predetermined range from the boundary line of the second region.

6. A processing device, A holding member for holding a workpiece having a first region and a second region that is thinner than the first region, A laser irradiation unit that irradiates a workpiece with a laser beam to form a modified layer inside, while adjusting the position of the focusing point according to the thickness of the workpiece held by the holding member, It includes a control unit, The processing apparatus is characterized in that the control unit controls the laser irradiation unit so as not to irradiate the laser beam into a boundary region including at least a portion of the first region and the second region.

7. A method for manufacturing a chip using the processing method described in claim 1, The modified layer formation step involves forming the modified layer along the planned division lines that demarcate the workpiece into chips, The process further includes a chip spacing expansion step in which an external force is applied to the workpiece after the modified layer formation step to widen the spacing between the multiple chips formed by dividing the workpiece starting from the modified layer. A method for manufacturing chips, wherein in at least one of the steps of forming the modified layer and expanding the chip spacing, the workpiece is divided starting from the modified layer to produce a plurality of chips.

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