Method for machining a workpiece

Abstract

Method for machining a distorted workpiece (W) exhibiting internal stresses with several intersecting parting lines (S) provided thereon, wherein the method comprises: a placement step involving placing the distorted workpiece (W) with an upward convex orientation on a holding surface (13a) of a holding table (13) which is capable of holding the workpiece (W) under suction;After the placement step, a distortion elimination step is carried out by holding the workpiece (W) under suction on the holding surface (13a) of the holding table (13) and by applying a laser beam (40a), the wavelength of which is transmissible through the workpiece (W), to the workpiece while positioning a focal point of the laser beam (40a) in the workpiece (W) at a predetermined first position in the thickness direction of the workpiece (W) in order to form modified layers (K1) in the workpiece (W) and cracks (Ka) extending from the modified layers (K1) to a lower surface (Wa) of the workpiece (W) along all projected parting lines (S), the cracks releasing the internal stresses near the lower surface (Wa), which allows the lower surface (Wa) of the workpiece (W) to expand, thereby eliminating the deformation of the workpiece (W);and after the distortion removal step, a formation step of a modified layer (K2, K3) by applying the laser beam (40a) to the workpiece (W) while positioning the focal point of the laser beam (40a) in the workpiece (W) at a position above the first position, away from the lower surface (Wa) of the workpiece (W), in order to form modified layers (K2, K3) in the workpiece (W) along the projected parting lines (S), wherein the distortion removal step each time includes the steps of sensing the vertical position of an upper surface (Wb) of the workpiece (W) when the laser beam (40a) is applied to the workpiece (W) along each of the projected parting lines (S), and of positioning the focal point of the laser beam (40a) in the workpiece (W) based on the sensed vertical position of the upper surface (Wb) of the workpiece (W).

Description

BACKGROUND OF THE INVENTION AREA OF THE INVENTION

[0001] The present invention relates to a method for machining a distorted workpiece with several intersecting projected dividing lines arranged on it. DESCRIPTION OF THE RELATED STATE OF THE ART

[0002] Previously, it was known in the technical field, as disclosed for example in JP 2020-136 457 A, to form several modified layers in a wafer at positions that differ in the thickness direction across the wafer, along each of the projected separation lines formed thereon.

[0003] One problem with forming modified layers in a wafer at positions that differ in thickness direction across the wafer is as follows. A laser beam with a wavelength that can be transmitted through a wafer is emitted from a beam condenser and applied to the wafer. When the laser beam is focused at a position closer to the beam condenser, modified layers form in the wafer at that closer position. If the laser beam is focused at a position further away from the beam condenser, the previously formed modified layers tend to oppose the focusing of the laser beam at the more distant position, making it difficult to form modified layers at that more distant location.

[0004] As disclosed in JP 2020-136 457 A, a general approach was to sequentially form modified layers in a wafer at positions differing in the thickness direction, proceeding from the most distant to the nearest positions. After several modified layers had been formed in the wafer at positions differing in the thickness direction along a projected parting line, several modified layers were similarly formed in the wafer at positions differing in the thickness direction along an adjacent projected parting line. The process was repeated until several modified layers had been formed in the wafer along all projected parting lines on it. SUMMARY OF THE INVENTION

[0005] In a case where a wafer is warped, internal stresses exist within the wafer due to the deformation. As multiple modified layers form at different positions along a projected dividing line within the wafer, these internal stresses can be relieved, potentially leading to the development of a crack. If the crack reaches components on the wafer, these components are likely to be damaged.

[0006] Furthermore, when internal stresses are relieved, projected parting lines on the wafer may be curved or bent. Device chips manufactured by dividing the wafer along curved or bent projected parting lines tend to have chip sizes that deviate from a design size and consequently become defective if their chip sizes fall outside an acceptable range.

[0007] It is therefore an object of the present invention to provide a method for machining a workpiece in such a way that deformation of the workpiece is eliminated and several modified layers are formed in the workpiece at different positions in the thickness direction.

[0008] In accordance with one aspect of the present invention, a method for processing a distorted workpiece with several intersecting projected parting lines is provided, comprising a placement step in which the workpiece is placed in an upwardly directed convex orientation on a holding surface of a holding table capable of holding the workpiece under suction, followed by a distortion removal step in which the workpiece is held under suction on the holding surface of the holding table and a laser beam, the wavelength of which is transmissible through the workpiece, is applied to the workpiece while positioning a focal point of the laser beam in the workpiece at a predetermined first position in the thickness direction across the workpiece in order to form modified layers in the workpiece and cracks.which extend from the modified layers to a lower surface of the workpiece along all projected parting lines in order to eliminate the deformation of the workpiece, and after the distortion elimination step includes a formation step of a modified layer with an application of the laser beam to the workpiece while positioning the focal point of the laser beam in the workpiece at a position above the first position away from the lower surface of the workpiece in order to form modified layers along the projected parting lines in the workpiece, wherein the distortion elimination step includes the steps of capturing the vertical position of an upper surface of the workpiece each time,when the laser beam is applied to the workpiece along each of the projected dividing lines and involves positioning the focal point of the laser beam in the workpiece based on the detected vertical position of the upper surface of the workpiece.

[0009] Preferably, the method for processing a distorted workpiece further includes a separation step after the formation step of a modified layer with a separation of the workpiece along the projected separation lines by applying external forces to the workpiece.

[0010] Preferably, the formation step of a modified layer includes the steps of applying the laser beam to the workpiece along each of the projected parting lines while positioning the focal point of the laser beam in the workpiece at a second position above the first position in order to form a second modified layer in the workpiece, and then applying the laser beam to the workpiece along the projected parting line while positioning the focal point of the processing laser beam in the workpiece at a third position above the second position in order to form a third modified layer in the workpiece.

[0011] Preferably, the workpiece is distorted such that its upper surface has a convex shape; the placement step includes the step of placing the workpiece on the holding table while the lower surface of the workpiece is facing downwards towards the holding surface of the holding table; a holding step includes the step of holding the lower surface of the workpiece on the holding table; and the distortion removal step and the formation step of a modified layer each include the step of applying the laser beam to the workpiece from its upper surface.

[0012] In accordance with the present invention, the focal point of the laser beam can be positioned at a predetermined location in the thickness direction across the workpiece, causing the cracks to reliably reach the lower surface of the workpiece to eliminate the workpiece's deformation. The vertical position of the upper surface of the workpiece can vary due to the removal of the workpiece's deformation caused by the modified layers formed in the workpiece. However, since the vertical position of the upper surface of the workpiece is determined immediately before the workpiece is processed, the focal point of the laser beam can be positioned at a predetermined location in the thickness direction across the workpiece.

[0013] The modified layer formation step described above prevents the development of unexpected cracks in the workpiece and prevents projected parting lines on the wafer from being curved or bent during the modified layer formation step, provided that the deformation has been corrected during the distortion removal step. Accordingly, it prevents damage to components on the workpiece and prevents defects in chips produced from the workpiece.

[0014] The above and other items, features and advantages of the present invention and its implementation will best become clearer by studying the following description and 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. List of characters Fig. 1A is a perspective view that illustrates a workpiece as an example; Fig. 1B is a side view illustrating the way in which the workpiece is warped; Fig. 2 is a perspective view illustrating a frame unit; Fig. Figure 3 is a perspective view illustrating an exemplary laser processing device; Fig. Figure 4 is a sectional view illustrating the layout of a laser processing head and a measuring head; Fig. 5A is an enlarged partial sectional view illustrating the way in which a laser beam is applied to the workpiece when the workpiece is moved in a first direction; Fig. 5B is an enlarged partial section view illustrating the way in which a laser beam is applied to the workpiece when the workpiece is moved in a second direction; Fig. 6A is a sectional view illustrating an example where a single measuring head is provided; Fig. Figure 6B is an enlarged partial sectional view of an arrangement comprising a laser beam application head capable of selectively applying a measuring laser beam and a processing laser beam, and illustrates the manner in which the measuring laser beam is applied to the workpiece; Fig. Figure 6C is an enlarged sectional view of the arrangement which includes the laser beam application head which is capable of selectively applying the measuring laser beam and the processing laser beam, and illustrates the way in which the processing laser beam is applied to the workpiece; Fig. Figure 7 is a flowchart of a sequence of steps of a method for machining a workpiece in accordance with an embodiment of the present invention; Fig. Figure 8 is a sectional view illustrating an example placement step; Fig. Figure 9 is a sectional view illustrating an example of a holding step; Fig. Figure 10A is a sectional view illustrating an exemplary distortion removal step; Fig. 10B is a sectional view illustrating an exemplary training step of a modified layer; Fig. Figure 11A is a sectional view illustrating an example separation step; and Fig. Figure 11B is a sectional view illustrating the workpiece that has been separated into component chips. DETAILED DESCRIPTION OF THE PREFERRED EXECUTION FORM

[0015] A preferred embodiment of the present invention is described in detail below with reference to the drawings. Fig. Figure 1 illustrates, as an example, a warped workpiece W in perspective. As in Fig. As illustrated in Figure 1, the workpiece W, which has a circular shape, has a wafer made of a material such as silicon (Si), silicon carbide (SiC), gallium nitride (GaN), gallium arsenide (GaAs), or another semiconductor. Alternatively, the workpiece W has a wafer made of a complex oxide such as lithium tantalate (LT) or lithium niobate (LN). Furthermore, the workpiece W can alternatively have a substrate made of a material such as sapphire, glass, or quartz. The glass can be alkali glass, non-alkali glass, soda-lime glass, lead glass, borosilicate glass, fused silica, or similar.

[0016] The workpiece W has an end face Wa on which building elements D are formed in a regular pattern, separated from each other by intersecting projected dividing lines or roads S which extend between the building elements D.

[0017] As in Fig. As illustrated in Figure 1B, the workpiece W is warped such that the end face Wa has shrunk into a concave shape and a back face Wb opposite the end face Wa has expanded into a convex shape. Alternatively, the workpiece W can be warped such that the end face Wa has expanded into a convex shape.

[0018] As in Fig. As illustrated in Figure 2, the workpiece W has its back side Wb attached to a circular, expandable band T and is secured by the expandable band T to an annular frame F. The workpiece W, the expandable band T, and the annular frame F are handled as a frame unit U. The end face Wa of the workpiece W in the frame unit U is exposed upwards. The expandable band T has an adhesive surface, i.e., Fig. 2. A lower surface to which the workpiece W and the ring-shaped frame F are attached. The expandable band T can be expanded radially outwards.

[0019] A protective band (not illustrated) can be attached to the exposed end face Wa of the workpiece W. If the workpiece W is warped such that the back face Wb has shrunk to a concave shape and the end face Wa has expanded to a convex shape, the end face Wa is attached to the expandable band T. In addition to being combined with the ring-shaped frame F and handled as a frame unit U, the workpiece W can be handled independently. The expandable band T does not need to have an adhesive surface.

[0020] Fig. Figure 3 illustrates, by way of an example, a laser processing device for processing the workpiece W in perspective. The laser processing device, designated by 10, includes a laser beam application mechanism 12 for applying a laser beam to the workpiece W and a holding table 13 with an upper surface for holding the workpiece W. The laser processing device 10 processes the workpiece W during a relative movement of the laser beam application mechanism 12 and the holding table 13.

[0021] The laser processing device 10 has a base 11 in the form of a rectangular cuboid. The upper surface of the base 11 supports a movement mechanism 14 for advancing the holding table 13 in the X-axis directions and for positioning the holding table 13 in the Y-axis directions perpendicular to the X-axis directions. An upright wall 16 extends from the base 11 behind the movement mechanism 14. The laser beam application mechanism 12 is supported on a front surface of the upright wall 16, projecting beyond the holding table 13.

[0022] The movement mechanism 14 includes an adjustment mechanism 20 for movement of the holding table 13 relative to the laser beam application mechanism 12 in adjustment directions, i.e. the Y-axis directions, and a processing feed mechanism 21 for movement of the holding table 13 relative to the laser beam application mechanism 12 in processing feed directions, i.e. the X-axis directions.

[0023] After the workpiece W has been processed on the holding table 13 by means of a laser beam applied to it along one of the projected parting lines S by means of the laser beam application mechanism 12, the positioning mechanism 20 moves the holding table 13 in one of the positioning directions or positions it in order to process the workpiece W along a next parallel, projected parting line S with the laser beam.

[0024] After one of the projected parting lines S on the workpiece W, which was captured by an image acquisition camera (not illustrated), has been aligned on a processing head 40 of the laser beam application mechanism 12, the processing feed mechanism 21 moves the holding table 13 in one of the processing feed directions or guides it in this direction for processing in order to process the workpiece W along the projected parting line S with the laser beam.

[0025] The holding table 13 is rotatable about a vertical axis (rotation in the figure-eight direction) along Z-axis directions perpendicular to the X-axis directions and the Y-axis directions. Four clamps 39 are provided at angularly equal-spaced positions around the holding table 13 to clamp the ring-shaped frame F of the frame unit U to the holding table 13 at its position.

[0026] As in Fig. As illustrated in Figure 4, a holding plate 13b, made of a porous ceramic material, is attached to an upper side of the holding table 13 and has a horizontal holding surface 13a as its upper surface for holding the workpiece W. The holding plate 13b is connected to a suction source 28 via a valve 29. When the suction source 28 is actuated, it creates a vacuum and applies it to the holding surface 13a, which holds the workpiece W against the holding surface 13a by suction.

[0027] As in Fig. As illustrated in Figure 3, the laser beam application mechanism 12 comprises a laser oscillator for generating a processing laser beam, a condenser lens for focusing the laser beam emitted by the laser oscillator onto the workpiece W held on the holding table 13, and a mirror for guiding the emitted laser beam from the laser oscillator to the condenser lens. Fig. As illustrated in Figure 4, the processing head 40 of the laser beam application mechanism 12 applies the processing laser beam, which is marked by 40a, to the workpiece W on the holding table 13.

[0028] The processing laser beam 40a has its focal point successively set at predetermined positions in the thickness direction across the workpiece W, which are properly corrected as will be described in detail later.

[0029] As in Fig. As illustrated in Figure 3, the laser beam application mechanism 12 also includes a laser oscillator for generating laser beams to measure the vertical position of the upper surface, i.e., the back side Wb of the workpiece W, a condenser lens for focusing the laser beams emitted by the laser oscillator onto the workpiece W held on the holding table 13, and a mirror for guiding the laser beams emitted by the laser oscillator to the condenser lens. As shown in the Fig. 4, Fig. 5A and Fig. As illustrated in Figure 5B, the laser beam application mechanism 12 includes two measuring heads 51 and 52, each of which applies measuring laser beams 51a and 52a to the workpiece W.

[0030] As in Fig. As illustrated in Figure 4, the measuring head 51 continuously projects the measuring laser beam 51a onto the workpiece W. The vertical position of the upper surface of the workpiece W, as measured by the measuring laser beam 51a, is fed back to a control unit of the laser processing device 10 (not illustrated) at intervals of 0.5 meters along the longitudinal direction of the projected parting line S. Based on the vertical position of the upper surface of the workpiece thus reported, the control unit corrects the focal point of the processing laser beam 40a to precisely position the focal point of the processing laser beam 40a at a predetermined distance from the upper surface, i.e., the rear side Wb of the workpiece W, or at a predetermined distance from the lower surface, i.e., the end face Wa, of the workpiece W, as shown in Figure 4. Fig. 5A illustrates how to position.

[0031] As in Fig. As illustrated in Figure 4, the measuring heads 51 and 52 are arranged on both sides of the machining head 40 in the machining feed directions, i.e., the X-axis directions. When the holding table 13 moves along one of the X-axis directions, i.e., along a first direction X1, during a forward stroke, the vertical position of the upper surface, i.e., the back side Wb, of the workpiece W, which lies directly in front of the machining head 40 in the first direction X1, is as shown in Figure 4. Fig. 5A illustrates the measurement laser beam 51a, which is emitted by the measuring head 51. When the holding table 13, as in Fig. Figure 5B illustrates that, furthermore, during a reverse stroke along the other of the X-axis directions, i.e. along a second direction X2, the vertical position of the upper surface, i.e. the back side Wb of the workpiece W, which lies in the second direction X2 immediately in front of the machining head 40, is detected by the measuring laser beam 52a emitted by the measuring head 52.

[0032] With the measuring heads 51 and 52 thus arranged relative to each other on both sides of the machining head 40, it is possible to machine the workpiece W along a certain projected parting line S in both the forward stroke and the reverse stroke of the movement of the holding table 13.

[0033] As in Fig. As illustrated in Figure 6A, alternatively only one measuring head 53 can be arranged next to the machining head 60, so that the workpiece W can be machined while the holding table 13 moves in a forward stroke along the first direction X1, the vertical position of the upper surface, i.e. the back Wb, of the workpiece W.

[0034] As in the Fig. 6B and Fig. As illustrated in Figure 6C, the laser beam application mechanism can alternatively include a laser beam application head 45, which is capable of selectively applying either a measuring laser beam 45a or a processing laser beam 45b. After the laser beam application head 45 has applied the measuring laser beam 45a to the workpiece W along a specific projected parting line S, while the holding table 13 moves along the first direction X1 in a forward stroke, the holding table 13 moves, as shown in Fig. Figure 6b illustrates that, in a reverse stroke along the second direction X2, the laser beam application head 45 returns to its starting position, and then the processing laser beam 45b, as shown in Fig. Figure 6C illustrates the movement onto the workpiece W, while the holding table 13 moves again along the first direction X1 in a forward stroke.

[0035] A method for processing a workpiece on the laser processing device 10 is described in detail below. Fig. Figure 7 is a flowchart of a sequence of steps in the method for machining a workpiece in accordance with an embodiment of the present invention. The steps of the method include a strip application step, a placement step, a holding step, a distortion removal step, a formation step of a modified layer, and a separation step. <bandanbringschritt>

[0036] The tape application step is, as in Fig. Figure 2 illustrates a step involving attaching the back side Wb of the workpiece W to the expandable belt T. The workpiece W, with its back side Wb attached to the expandable belt T, is integrally combined with the annular frame F by the expandable belt T, thus forming the frame unit U. Alternatively, the end face Wa of the workpiece W can be attached to the expandable belt T. In a case where the workpiece W is placed directly on the holding table 13, the belt attachment step is omitted. <platzierschritt>

[0037] As in Fig. As illustrated in Figure 8, the placement step is a step involving placing the workpiece W in a convex orientation upwards on the holding surface 13a of the holding table 13.

[0038] In the Fig. In the illustrated example 8, the workpiece W is distorted such that its back side Wb has an upwardly directed convex shape and its end side Wa has a downwardly directed concave shape facing the holding surface 13a of the holding table 13. As described in detail later, a laser beam is applied to the wafer W from its back side Wb. As in Fig. As illustrated in Figure 8, a gap 15 exists between the end face Wa of the workpiece W and the holding surface 13a, and the annular frame F is positioned on the clamps 39. In a case where the workpiece W is warped such that its end face Wa is convex upwards, the back face Wb of the workpiece W is placed on the holding surface 13a. <halteschritt>

[0039] As in Fig. As illustrated in Figure 9, the holding step following the placement step involves holding the workpiece W under suction on the holding table 13. Specifically, the valve 29 is opened to fluidically connect the holding table 13 to the suction source 28, and the suction source 28 is actuated to create a vacuum on the holding surface 13a. This attracts the end face Wa of the workpiece W to the holding surface 13a and holds the workpiece W against the holding surface 13a under suction. Additionally, the clamps 39 grip the annular frame F. <verzugsbeseitigungsschritt>

[0040] As in Fig. As illustrated in Figure 10A, the distortion elimination step after the holding step is a step involving the application of the processing laser beam 40a, whose wavelength is transmissible through the workpiece W, to the workpiece W while positioning the focal point of the processing laser beam 40a in the workpiece W at a predetermined first position in the thickness direction of the workpiece W, in order to form modified layers K1 in the workpiece W and cracks Ka, which extend from the modified layers K1 to the lower surface, i.e. the end face Wa, of the workpiece W along all projected parting lines S, thereby eliminating the deformation of the workpiece W.

[0041] In the Fig. In the illustrated example 10A, the predetermined first position in the thickness direction is set over the workpiece W to a position that is spaced from the lower surface, i.e., the end face Wa, of the workpiece W, or to a position that is spaced by a distance H2 from the upper surface, i.e., the back face Wb, of the workpiece W. A distance H0, which represents the sum of the distance H1 and the distance H2, corresponds to the thickness of the workpiece W.

[0042] Since the cracks Ka reach the lower surface, i.e., the end face Wa, of the workpiece W, the internal stresses present in the workpiece W near its lower surface are released, allowing the lower surface of the workpiece W to expand and thereby eliminate the deformation of the workpiece W. The cracks Ka develop in the workpiece W along all projected parting lines S.

[0043] In the distortion removal step, immediately before the processing laser beam 45b is applied to the workpiece W along each of the projected separation lines S, the vertical position of the upper surface, i.e. the back Wb, of the workpiece W is detected, and the focal point of the processing laser beam 45b is positioned on the basis of the detected vertical position of the upper surface, i.e. the back Wb, of the workpiece W.

[0044] In particular, before the formation of the modified layers K1, the measuring heads 51 and 52 bring the respective measuring laser beams 51a and 52a, as in the Fig. 5A and Fig. Figure 5B illustrates the process of measuring the vertical position of the upper surface, i.e., the back side Wb, of the workpiece W, which is immediately in front of the processing head 40. The measured vertical position of the upper surface, i.e., the back side Wb of the workpiece W, is fed back to the control unit, whereupon the control unit corrects the focal point of the processing laser beam 45b.

[0045] Even if the workpiece W is distorted to a large extent, the focal point of the processing laser beam can therefore be positioned in the thickness direction over the workpiece W at a predetermined position, which causes the cracks Ka to reliably reach the lower surface, i.e. the end face Wa, of the workpiece W to eliminate the deformation of the workpiece W.

[0046] The vertical position of the upper surface, i.e., the back surface Wb, of the workpiece W can vary due to the removal of deformation caused by the modified layers K1 formed in the workpiece W. While the vertical position of the upper surface, i.e., the back surface Wb, of the workpiece W is determined immediately before processing the workpiece W, the focal point of the processing laser beam can be positioned at a predetermined location in the thickness direction of the workpiece W.

[0047] The modified layers K1 are formed in the workpiece W along all projected parting lines S as follows. As in Fig. As illustrated in Figure 5A, the workpiece W is fed in the first direction X1 for processing, and the processing laser beam 40a is applied to the workpiece W to form a modified layer K1 in the workpiece W along a specific projected parting line S. Afterwards, the workpiece W is tilted along one of the Y-axis directions by a predetermined distance. Then, the workpiece W is, as shown in Fig. Figure 5B illustrates that the workpiece is fed in the second direction X2 for processing, and the processing laser beam 40a is applied to the workpiece W to form a modified layer K1 in the workpiece W along the next projected parting line S. After the modified layers K1 have been formed in the workpiece W along all projected parting lines S extending in the X-axis directions, the workpiece W is rotated 90° about its central axis, and then the modified layers K1 are formed in the same manner as described above along all projected parting lines S extending perpendicular to the projected parting lines S along which the modified layers K1 have already been formed in the workpiece W. <Ausbildungsschritt einer modifizierten Schicht>

[0048] As in Fig. As illustrated in Figure 10B, the formation step of a modified layer after the distortion removal step is a step involving the application of the processing laser beam 40a to the workpiece W along a projected parting line while positioning the focal point of the processing laser beam 40a in the workpiece W at positions above the first position away from the lower surface, i.e. the end face Wa, of the workpiece W, which forms modified layers K2 and K3 along the projected parting line in the workpiece W.

[0049] In the Fig. In the example illustrated in Figure 10B, the processing laser beam 40a is applied to the workpiece W along each of the projected parting lines, while the focal point of the processing laser beam 40a is positioned at a second position above the first position in the workpiece W, thereby forming a second modified layer K2 in the workpiece W. Subsequently, the processing laser beam 40a is applied to the workpiece W along the projected parting line, while the focal point of the processing laser beam 40a is positioned at a third position above the second position in the workpiece W, thereby forming a third modified layer K3 in the workpiece W. Cracks Ka, Kb, and Kc are formed from the modified layers K1, K2, and K3, respectively, so that they extend from the end face Wa to the back face Wb of the workpiece W. As shown in Figure 10B, the processing laser beam 40a is applied to the workpiece W along the projected parting line, while the focal point of the processing laser beam 40a is positioned at a third position above the second position in the workpiece W, thereby forming a third modified layer K3 in the workpiece W. Cracks Ka, Kb, and Kc are formed from the modified layers K1, K2, and K3, respectively, so that they extend from the end face Wa to the back face Wb of the workpiece W. Fig. As illustrated in Figure 10B, the modified layers K1, K2, and K3 are formed in the workpiece W such that the cracks Ka, Kb, and Kc developed from the modified layers K1, K2, and K3 have their heads connected to each other or positioned close enough to each other to be connected. Alternatively, the modified layers K1, K2, and K3 can be formed in the workpiece W such that the cracks Ka, Kb, and Kc developed from the modified layers K1, K2, and K3 have their heads spaced apart from each other, with gaps between them.

[0050] The two additional modified layers K2 and K3 can be formed sequentially along each projected parting line S in the workpiece W. Alternatively, the modified layers K3 can be formed along all projected parting lines S in the workpiece W after modified layers K2 have been formed along all projected parting lines S in the workpiece W. The structure of the laser processing device 10, which is described in the Fig. 4, Fig. 5A and Fig. As illustrated in Figure 5B, it allows a modified layer K2 to be formed in the workpiece W while the holding table 13 moves in a forward stroke along the first direction X1, and also allows a modified layer K3 to be formed in the workpiece W while the holding table 13 moves in a backward stroke along the second direction X2.

[0051] Furthermore, the processing laser beam can alternatively be split into multiple laser beams, and the focal points of the laser beams can be positioned at respective locations in the workpiece W, spaced apart along the laser beams, to form multiple modified layers in the workpiece W along a projected parting line when the workpiece W is fed for processing in one stroke. Moreover, there is no limit to the number of modified layers to be formed in the workpiece W along a projected parting line S.

[0052] Provided that the deformation of workpiece W has been eliminated during the distortion removal step, the modified layer formation step described above prevents the development of unexpected cracks in workpiece W and prevents projected parting lines S on the wafer from being bent or curved during the modified layer formation step. Accordingly, it prevents damage to components on workpiece W and ensures that the component chips produced from workpiece W are not defective in size. [Separation step]

[0053] As in the Fig. 11A and Fig. As illustrated in Figure 11B, after the formation step of a modified layer, a separation step is a step involving the separation of the workpiece W along the projected separation lines S, in which external forces are applied to the workpiece W.

[0054] The Fig. 11A and Fig. Figure 11B illustrates a separating device 80 for separating the workpiece W in its cross-section. As shown in the Fig. 11A and Fig. As illustrated in Figure 11B, the separating device 80 includes a frame holding mechanism 81 for gripping the ring-shaped frame F of the frame unit U, an actuating mechanism 84 for raising and lowering the frame holding mechanism 81, and a tubular extension drum 83 for bearing against the extendable belt T of the frame unit U from below.

[0055] When the actuating mechanism 84 lowers the frame holding mechanism 81, while the frame holding mechanism 81 grips the annular frame F, the expandable band T, as shown in Fig. 11A illustrates that it is held from below on the extension drum 83 and is extended radially outwards while being pulled through the frame holding mechanism 81.

[0056] When the expandable tape T is expanded radially outwards, it exerts radially outward external forces on the workpiece W attached to the expandable tape T. This separates the workpiece W from the modified layers at the separation trigger point along the projected separation lines S in the component chips C. After the workpiece W has been separated, the expandable tape T is shrunk by heat, thus keeping the component chips C spaced apart from each other.

[0057] In addition to extending the expandable band T radially outwards to divide the workpiece W, the back side Wb of the workpiece W with the modified layers formed therein can be ground to divide the workpiece W.

[0058] Alternatively, the number of modified layers formed in the workpiece W can be increased to develop multiple cracks in the workpiece W and thereby divide the workpiece W, after which the expandable band T can be expanded radially outwards to increase the spaces between the component chips, followed by shrinkage of the expandable band T by heat, so that the component chips are kept spaced apart from each other.

[0059] The present invention is not limited to the details of the preferred embodiment described above. The scope of protection of the invention is defined by the appended claims, and all modifications and variations that fall within the equivalent scope of protection of the claims are therefore included in the invention. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2020136457 A [0002, 0004]< / verzugsbeseitigungsschritt> < / halteschritt> < / platzierschritt> < / bandanbringschritt>

Claims

[1] A method for machining a warped workpiece having a plurality of intersecting parting lines arranged thereon, the method comprising: a placing step of placing the workpiece with an upwardly convex orientation on a holding surface of a holding table capable of holding the workpiece thereon under suction; after the placing step, a distortion removal step comprising holding the workpiece under suction on the holding surface of the holding table and applying a laser beam, the wavelength of which is transmissible through the workpiece, to the workpiece while positioning a focal point of the laser beam in the workpiece at a predetermined first position in the thickness direction of the workpiece, to thereby form modified layers in the workpiece and cracks extending from the modified layers to a lower surface of the workpiece along all projected parting lines, thereby removing the deformation of the workpiece; and after the distortion removal step, a modified layer forming step comprising applying the laser beam to the workpiece while positioning the focal point of the laser beam in the workpiece at a position above the first position, away from the lower surface of the workpiece, to thereby form modified layers in the workpiece along the projected parting lines, wherein the warp removing step includes the steps of detecting the vertical position of an upper surface of the workpiece each time the laser beam is applied to the workpiece along each of the projected parting lines, and positioning the focal point of the laser beam in the workpiece based on the detected vertical position of the upper surface of the workpiece. [2] A method of machining a warped workpiece according to claim 1, further comprising: after the formation step of a modified layer, a separation step with a separation of the workpiece along the projected separation lines by applying external forces to the workpiece. [3] A method for machining a warped workpiece according to claim 1 or 2, wherein the modified layer forming step includes the steps of applying the laser beam to the workpiece along each of the projected parting lines while positioning the focal point of the laser beam in the workpiece at a second position above the first position to thereby form a second modified layer in the workpiece, and thereafter applying the laser beam to the workpiece along the projected parting line while positioning the focal point of the machining laser beam in the workpiece at a third position above the second position to thereby form a third modified layer in the workpiece. [4] A method for machining a warped workpiece according to any one of the preceding claims, in which the workpiece is distorted so that its upper surface has a convex shape, the placing step includes the step of placing the workpiece on the holding table while the lower surface of the workpiece is facing downwards towards the holding surface of the holding table, a holding step includes the step of holding the lower surface of the workpiece on the holding table, and both the distortion removal step and the modified layer formation step include the step of applying the laser beam to the workpiece from its upper surface.

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