Laser processing method and laser processing apparatus

Abstract

To provide a laser processing method and a laser processing apparatus which are capable of accurately dividing a wafer along a division line while reducing splash damage in laser processing for forming a modified layer inside the wafer by emitting a laser along the division line.SOLUTION: A laser processing method comprises a first laser processing step of forming a modified layer along a first division line, and a second laser processing step which is performed after the first laser processing step and forms a modified layer along a second division line that intersects the first division line. In the second laser processing step, a first modified layer 15A and a second modified layer 15B are formed at different positions in a thickness direction of a wafer 10, and at an intersection between the first division line 11 and the second division line, a distance from the first division line 11 is made larger in the second modified layer 15B than in the first modified layer 15A.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a laser processing method and a laser processing apparatus for irradiating a wafer with a laser to form a modified layer inside the wafer. [Background technology]

[0002] Wafers on which various elements such as semiconductor devices and electronic components are formed are divided into individual chips by dividing along grid-like dividing lines. In relation to such wafer division, for example, Patent Document 1 discloses a technology for forming a first modified layer and a second modified layer at different positions in the thickness direction of the wafer inside the wafer by laser processing in which a laser is irradiated along the dividing lines. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-63987 Summary of the Invention [Problem to be solved by the invention]

[0004] However, splash damage, which is heat damage caused by laser processing, can occur in wafers that undergo laser processing. Such splash damage is likely to occur at intersections where dividing lines intersect. In Patent Document 1, at the intersections of dividing lines, one of the dividing lines is designated as a non-processing area, but there is still room for improvement in reducing splash damage and accurately dividing the wafer along the dividing lines. [Means for solving the problem]

[0005] A laser processing method that solves the above problem forms a modified layer inside a wafer by irradiating a laser along a dividing line. The laser processing method includes a first laser processing step of forming the modified layer along a first dividing line extending in a first direction, and a second laser processing step, which is performed after the first laser processing step, of forming the modified layer along a second dividing line extending in a second direction intersecting the first dividing line. In the second laser processing step, a first modified layer and a second modified layer are formed at different positions in the thickness direction of the wafer, and the distance between the first dividing line in the second direction at the intersection of the first dividing line and the second dividing line is made different between the first modified layer and the second modified layer.

[0006] A laser processing apparatus that solves the above problem includes a work table that supports a wafer, a laser irradiation unit that irradiates the wafer with a laser, a relative movement mechanism that moves the work table and the laser irradiation unit relative to each other, and a control device that controls the laser irradiation unit and the relative movement mechanism so that a modified layer is formed inside the wafer along a division line, wherein the control device performs a first laser processing process that forms a modified layer along a first division line that extends in a first direction, and after the first laser processing process, a second laser processing process that forms a modified layer along a second division line that extends in a second direction that intersects the first direction and intersects the first division line, and in the second laser processing process, a first modified layer and a second modified layer that are located at different positions in the thickness direction of the wafer are formed, and at the intersection of the first division line and the second division line, the distance between the first division line in the second direction is made different between the first modified layer and the second modified layer. [Effects of the Invention]

[0007] According to the present invention, it is possible to accurately divide a wafer along a dividing line while reducing splash damage to the wafer caused by laser processing. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view schematically showing a wafer on which laser processing is performed using an embodiment of a laser processing method in the first embodiment. [Figure 2] FIG. 2 is a diagram showing a schematic configuration of an embodiment of a laser processing apparatus according to the first embodiment, and a wafer on which a first modified layer and a second modified layer are formed along a first dividing line. [Figure 3] FIG. 3 is a functional block diagram showing the electrical configuration of the laser processing device in the first embodiment. [Figure 4] FIG. 4 is a flowchart showing the procedure of one embodiment of the laser processing method in the first embodiment. [Figure 5] FIG. 5 is a flowchart showing an example of a procedure of the first laser processing process in the first embodiment. [Figure 6] FIG. 6 is a flowchart showing an example of the procedure of the second laser processing process in the first embodiment. [Figure 7] In the first embodiment, Figure 7(a) is a diagram schematically showing the OFF position for the first modified layer in the second laser processing process, and Figure 7(b) is a diagram schematically showing the ON position for the first modified layer in the second laser processing process. [Figure 8] In the first embodiment, Figure 8(a) is a diagram schematically showing the OFF position for the second modified layer in the second laser processing process, and Figure 8(b) is a diagram schematically showing the ON position for the second modified layer in the second laser processing process. [Figure 9] FIG. 9 is a functional block diagram showing the electrical configuration of the laser processing device in the second embodiment. [Figure 10] FIG. 10 is a functional block diagram showing the electrical configuration of the laser processing device in the second embodiment. [Figure 11] FIG. 11 is a diagram schematically showing the processing direction in the second laser processing step in the third embodiment. [Figure 12]In the third embodiment, Figure 12(a) is a diagram schematically showing how a first modified layer is formed while moving the work table in the +X direction, and Figure 12(b) is a diagram schematically showing how a first modified layer is formed while moving the work table in the -X direction. [Figure 13] In the third embodiment, Figure 13(a) is a diagram showing a schematic diagram of how the second modified layer is formed while moving the work table in the +X direction, and Figure 13(b) is a diagram showing a schematic diagram of how the second modified layer is formed while moving the work table in the -X direction. [Figure 14] FIG. 14 is a cross-sectional view showing an example of a wafer on which a third modified layer and a fourth modified layer are formed in a modified example. [Figure 15] FIG. 15 is a cross-sectional view showing an example of a wafer on which a fifth modified layer and a sixth modified layer are formed in a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0009] (First embodiment) A first embodiment of the laser processing method will be described with reference to FIGS. 1, wafer 10 is divided into individual chips by being divided along a grid of dividing lines formed by first dividing lines 11 extending in a first direction D1 and second dividing lines 12 extending in a second direction D2. The surface of wafer 10 on which various elements such as semiconductor devices and electronic components are formed is called device surface 10a, and the surface opposite device surface 10a is called back surface 10b (see FIG. 2). The intersections of first dividing lines 11 and second dividing lines 12 are called intersections 13.

[0010] In the following description, the planar directions in which the device surface 10a and back surface 10b of the wafer 10 extend are referred to as the XY direction, one direction in the XY direction is referred to as the X direction, and the direction perpendicular to the X direction in the XY direction is referred to as the Y direction. The X direction is the direction in which the parting lines to be processed in each process extend. Regarding the X direction, the direction indicated by the arrow in the figure may be referred to as the +X direction, and the direction opposite to the +X direction as the -X direction. The direction perpendicular to the XY direction is referred to as the Z direction. The Z direction is the thickness direction of the wafer 10.

[0011] (Laser processing equipment) 2, the wafer 10 is subjected to laser processing using a laser processing device 20. The laser processing device 20 has a work table 21, a laser irradiation unit 22, a relative movement mechanism 23, an imaging device 24, and a control device 25.

[0012] The work table 21 supports the wafer 10 via the dicing tape 16. The work table 21 is configured to be movable in the X direction and rotatable around the Z direction as a rotation axis by a relative movement mechanism 23. The movement speed of the work table 21 in the X direction is called the laser processing speed.

[0013] The laser irradiation unit 22 irradiates the wafer 10 supported on the work table 21 with a laser beam LB. The laser irradiation unit 22 is configured to be movable in the Y and Z directions by a relative movement mechanism 23. The laser irradiation unit 22 is configured to be able to temporarily interrupt irradiation of the wafer 10 with the laser beam LB by shutter control or the like.

[0014] The laser irradiation unit 22 has a laser emission unit 26 and a condenser lens 27. The laser emission unit 26 and the condenser lens 27 are configured to be relatively movable in the Z direction by a movement mechanism (not shown). The laser emission unit 26 emits a laser beam LB of a predetermined wavelength toward the condenser lens 27. The laser beam LB is a pulsed laser. The condenser lens 27 focuses the laser beam LB emitted by the laser emission unit 26 at a focal point P. The focal point P is the irradiation position of the laser beam LB. Inside the wafer 10 irradiated with the laser beam LB, a modified layer with a destroyed crystalline structure is formed near the focal point P. The modified layer is a region that is more fragile than a portion not subjected to laser processing. It is preferable that the laser irradiation unit 22 use an optical element, such as an acousto-optic modulator, that can quickly turn the laser beam LB on and off.

[0015] The irradiation position of the laser LB in the X and Y directions is adjusted by the relative movement between the work table 21 and the laser irradiation unit 22. Moreover, the irradiation position of the laser LB in the Z direction is adjusted by the movement of the laser irradiation unit 22 in the Z direction or the relative movement between the laser emission unit 26 and the condenser lens 27 in the Z direction.

[0016] The imaging device 24 is attached to the laser irradiation unit 22. The imaging device 24 captures an image of an alignment mark provided on the wafer 10. The imaging device 24 outputs image data indicating the captured image to the control device 25.

[0017] The control device 25 controls the laser irradiation unit 22, the relative movement mechanism 23, and the imaging device 24, thereby controlling the overall operation of the laser processing device 20. The laser processing apparatus 20 performs laser processing on the wafer 10, whose device surface 10a is supported on a work table 21 via a dicing tape 16. In this case, the back surface 10b of the wafer 10 serves as the incident surface of the laser beam LB. The laser processing apparatus 20 performs laser processing on each of the first division lines 11, and then performs laser processing on each of the second division lines 12. The laser processing apparatus 20 forms first modified layers 15A at each of the division lines 11, 12, aligned near the device surface 10a (farther from the incident surface of the laser beam LB), and then forms second modified layers 15B at each of the division lines 11, 12, aligned near the back surface 10b. Note that FIG. 2 illustrates the wafer 10 in a state in which the modified layers 15A, 15B have been formed along the first division lines 11. That is, the X direction is the first direction D1, and the Y direction is the second direction D2.

[0018] (Control device) The controller 25 can be realized, for example, by circuitry, i.e., one or more dedicated hardware circuits such as an ASIC, one or more processing circuits operating according to a computer program (software), or a combination of both. The processing circuitry includes a CPU and memory (such as ROM and RAM) that stores programs executed by the CPU. Memory, i.e., computer-readable media, includes any available media that can be accessed by a general-purpose or special-purpose computer.

[0019] As shown in FIG. 3, the control device 25 is electrically connected to the laser irradiation unit 22, the relative movement mechanism 23, the imaging device 24, and also to an input unit 29. The input unit 29 receives various information input by an operator to the laser processing device 20. The input unit 29 is configured with, for example, a mouse, a keyboard, a touch panel, and the like.

[0020] The operator inputs laser processing conditions through the input unit 29. Specifically, the operator inputs, as the laser processing conditions, the output and repetition frequency of the laser LB, the position of the first modified layer 15A in the Z direction, the position of the second modified layer 15B in the Z direction, and the laser processing speed. The operator also inputs, as the laser processing conditions, the first distance L1 and the second distance L2 to be used in the second laser processing process described below.

[0021] The control device 25 has an alignment detection unit 31 and a laser processing control unit 32 as functional units that function by executing various programs. The alignment detection unit 31 executes an alignment detection process to detect the positions of the first dividing lines 11 and the second dividing lines 12 on the wafer 10.

[0022] For example, in the alignment detection process, the alignment detection unit 31 controls the relative movement mechanism 23 to adjust the position of the imaging device 24 relative to the alignment marks provided on the wafer 10. Next, the alignment detection unit 31 photographs the alignment marks using the imaging device 24 and obtains image data representing the photographed image. Then, the alignment detection unit 31 performs image processing on the image data to detect the positions of each of the first dividing lines 11 and each of the second dividing lines 12.

[0023] The laser processing control unit 32 executes a first laser processing process to form modified layers 15A, 15B along each of the first parting lines 11, and a second laser processing process to form modified layers 15A, 15B along each of the second parting lines 12. The laser processing control unit 32 holds the laser processing conditions and the positions of each of the parting lines 11, 12 based on the alignment detection process. The laser processing control unit 32 executes each laser processing process by controlling the relative movement mechanism 23 and the laser irradiation unit 22 based on the laser processing conditions and the positions of each of the parting lines 11, 12.

[0024] (Laser processing method) As shown in FIG. 4, the laser processing method includes an alignment detection step (step S101), a first laser processing step (step S102), and a second laser processing step (step S103).

[0025] In the alignment detection step, the alignment detection unit 31 of the control device 25 executes the above-mentioned alignment detection process, thereby detecting the positions of the first dividing lines 11 and the second dividing lines 12 on the wafer 10.

[0026] In the first laser processing step, the laser processing control unit 32 of the control device 25 executes a first laser processing process. By the first laser processing process, a first modified layer 15A and a second modified layer 15B are formed on the wafer 10 along each of the first dividing lines 11.

[0027] In the second laser processing step, the laser processing control unit 32 of the control device 25 executes the second laser processing. By the second laser processing, a first modified layer 15A and a second modified layer 15B are formed on the wafer 10 along each of the second dividing lines 12.

[0028] (First laser processing process) 5, in the first laser processing, the laser processing control unit 32 first aligns the first division line 11 to be processed with the laser irradiation unit 22 (step S201). Specifically, the laser processing control unit 32 rotates the work table 21 about the Z direction as the rotation axis so that the first division line 11 to be processed extends in the X direction. The laser processing control unit 32 also moves the work table 21 in the X and Y directions so that the laser irradiation unit 22 is positioned above the end of the first division line 11 in the +X direction.

[0029] Next, the laser processing control unit 32 forms a first modified layer 15A on the first parting line 11 of the processing target (step S202). Specifically, the laser processing control unit 32 adjusts the irradiation position of the laser LB so that the first modified layer 15A is formed. Thereafter, the laser processing control unit 32 starts irradiating the laser LB and moving the work table 21 along the -X direction. Then, when the work table 21 moves to a position where the laser irradiation unit 22 is located above the end of the first parting line 11 in the -X direction, the laser processing control unit 32 ends the irradiation of the laser LB and the movement of the work table 21. As a result, first modified layers 15A aligned in the X direction are continuously formed on the first parting line 11 of the processing target (see FIG. 2).

[0030] Next, the laser processing control unit 32 forms a second modified layer 15B on the first parting line 11 of the processing target. Specifically, the laser processing control unit 32 adjusts the irradiation position of the laser LB so that the second modified layer 15B is formed. Thereafter, the laser processing control unit 32 starts irradiating the laser LB and moving the work table 21 in the +X direction. Then, when the work table 21 moves to a position where the laser irradiation unit 22 is located above the end of the first parting line 11 in the +X direction, the laser processing control unit 32 ends the irradiation of the laser LB and the movement of the work table 21. As a result, second modified layers 15B lined up in the X direction are continuously formed on the back surface 10b side of the first modified layer 15A on the first parting line 11 of the processing target (see FIG. 2).

[0031] Next, the laser processing control unit 32 determines whether or not the formation of the modified layers 15A, 15B has been completed on all of the first division lines 11 (step S204). If the formation of the modified layers 15A, 15B has not been completed on all of the first division lines 11 (step S204: NO), the laser processing control unit 32 repeats steps S201 to S203 until the modified layers 15A, 15B have been formed on all of the first division lines 11. On the other hand, if the formation of the modified layers 15A, 15B has been completed on all of the first division lines 11 (step S204: YES), the laser processing control unit 32 ends the first laser processing process.

[0032] (Second laser processing process) 6, in the second laser processing, the laser processing control unit 32 first aligns the second dividing line 12 to be processed with the laser irradiation unit 22 (step S301). Specifically, the laser processing control unit 32 rotates the work table 21 about the Z direction as the rotation axis so that the second dividing line 12 to be processed extends in the X direction. The laser processing control unit 32 also moves the work table 21 in the X and Y directions so that the laser irradiation unit 22 is positioned above the end of the second dividing line 12 in the +X direction.

[0033] Next, the laser processing control unit 32 starts forming the first modified layer 15A on the second parting line 12 of the processing target (step S302). Specifically, the laser processing control unit 32 adjusts the irradiation position of the laser LB so as to form the first modified layer 15A. Thereafter, the laser processing control unit 32 starts irradiating the laser LB and moving the work table 21 in the -X direction.

[0034] Next, the laser processing control unit 32 determines whether or not the moving work table 21 has reached the OFF position (step S303). As shown in Fig. 7(a), the OFF position is a position where the first modified layer 15A is formed at a position a first distance L1 away from the first dividing line 11 in the +X direction. In Fig. 7(a), the arrows overlapping the first modified layer 15A indicate the order in which the first modified layer 15A is formed. The first distance L1 is equal to or greater than the interval at which the modified layer is formed based on the laser processing conditions.

[0035] When the work table 21 reaches the OFF position (step S303: YES), the laser processing control unit 32 stops the irradiation of the laser LB (step S304). Next, the laser processing control unit 32 determines whether or not the moving work table 21 has reached the ON position (step S305).

[0036] As shown in Fig. 7(b), the ON position is a position where the first modified layer 15A is formed at a position away from the first dividing line 11 by a first distance L1 in the -X direction. In Fig. 7(b), the arrows overlapping the first modified layers 15A indicate the order in which the first modified layers 15A are formed. When the work table 21 reaches the ON position (step S305: YES), the laser processing control unit 32 resumes irradiating the laser LB (step S306).

[0037] Next, the laser processing control unit 32 determines whether or not the formation of the first modified layer 15A on the second parting line 12 of the processing target has been completed (step S307). For example, the laser processing control unit 32 determines that the formation of the first modified layer 15A has been completed when the work table 21 has moved to a position where the laser irradiation unit 22 is located above the other end of the second parting line 12 in the +X direction. If the formation of the first modified layer 15A has not been completed (step S307: NO), the laser processing control unit 32 repeats steps S303 to S307.

[0038] If the formation of the first modified layer 15A is complete (step S307: YES), the laser processing control unit 32 ends the irradiation of the laser LB and the movement of the work table 21, and then starts forming the second modified layer 15B on the second parting line 12 to be processed (step S308). Specifically, the laser processing control unit 32 adjusts the irradiation position of the laser LB so that the second modified layer 15B is formed, and then starts the irradiation of the laser LB and the movement of the work table 21 in the -X direction.

[0039] Next, the laser processing control unit 32 determines whether or not the work table 21 has reached the OFF position (step S309). 8(a), the OFF position in this case is the position of the work table 21 where the second modified layer 15B is formed at a position a second distance L2 away from the first parting line 11 in the -X direction. In FIG. 8(a), the arrows overlapping the second modified layer 15B indicate the order in which the first modified layer 15A is formed. When the work table 21 reaches the OFF position (step S309: YES), the laser processing control unit 32 interrupts the irradiation of the laser beam LB (step S310).

[0040] Next, the laser processing control unit 32 determines whether or not the work table 21 has reached the ON position (step S311). As shown in Fig. 8(b), the ON position is a position where the second modified layer 15B is formed at a position away from the first parting line 11 by a second distance L2 in the +X direction. In Fig. 8(b), the arrows overlapping the second modified layer 15B indicate the order in which the second modified layer 15B is formed. When the work table 21 reaches the ON position (step S311: YES), the laser processing control unit 32 resumes irradiating the laser LB (step S312).

[0041] Next, the laser processing control unit 32 determines whether or not the formation of the second modified layer 15B has been completed along the second parting line 12 to be processed (step S313). For example, the laser processing control unit 32 determines that the formation of the second modified layer 15B has been completed when the work table 21 moves to a position where the laser irradiation unit 22 is positioned above the end of the second parting line 12 in the +X direction. If the formation of the second modified layer 15B has not been completed (step S313: NO), the laser processing control unit 32 repeats steps S309 to S313.

[0042] On the other hand, if the formation of the second modified layer 15B has been completed (step S313: YES), the laser processing control unit 32 determines whether the formation of the modified layers 15A, 15B has been completed at all second division lines 12 after finishing the irradiation of the laser LB and the movement of the work table 21 (step S314).

[0043] If the formation of the modified layers 15A, 15B has not been completed on all of the second division lines 12 (step S314: NO), the laser processing control unit 32 repeats steps S301 to S314 until the formation of the modified layers 15A, 15B on all of the second division lines 12. On the other hand, if the formation of the modified layers 15A, 15B on all of the second division lines 12 has been completed (step S314: YES), the laser processing control unit 32 ends the second laser processing process.

[0044] The wafer 10 on which the modified layers 15A and 15B have been formed by the above-described laser processing method is divided into individual chips along the division lines 11 and 12 by a division process such as expanding or breaking.

[0045] The operation and effects of the first embodiment will be described. (1-1) The energy of the laser LB irradiated onto the wafer 10 can be broadly divided into modification energy that modifies the area around the irradiation position, dissipated energy that dissipates as it moves toward the back surface of the laser incident side without reaching the back surface of the laser incident side, and excess energy that is diffused around the irradiation position and reaches the back surface of the laser incident side, causing splash damage. Because the energy dissipated when passing through the modified area is small, the proportion of the modification energy increases as the proportion of the area surrounding the irradiation position that is occupied by the pre-modified portion increases. On the other hand, the proportion of the excess energy increases as the proportion of the area surrounding the irradiation position that is occupied by the modified portion increases.

[0046] Furthermore, when forming a modified layer along the second dividing line 12, the proportion of the modified portion near the intersection 13 is greater when forming the second modified layer 15B than when forming the first modified layer 15A.

[0047] Based on this, in the second laser processing step (step S103) of the above-described laser processing method, the distance from the first dividing line 11 is set larger in the second modified layer 15B than in the first modified layer 15A. This reduces excess energy generated near the intersection 13 when forming the second modified layer 15B. As a result, splash damage to the wafer 10 can be reduced. Furthermore, since the reduced excess energy makes it easier to obtain the desired brittleness near the intersection 13, the wafer 10 can be divided along the dividing lines 11, 12 with high precision.

[0048] (1-2) The first modified layer 15A is formed at a position closer to the device surface 10a of the wafer 10 in the Z direction than the second modified layer 15B. A first distance L1 between the first modified layer 15A and the first dividing line 11 is smaller than a second distance L2 between the first modified layer 15A and the second modified layer 15B.

[0049] This configuration increases the brittleness of the device surface 10a of the wafer 10. This allows the wafer 10 to be divided along the first division lines 11 and the second division lines 12 with high precision on the device surface 10a. As a result, the quality of the device surface 10a of the divided chips can be ensured.

[0050] (Second embodiment) A second embodiment of the laser processing method will be described with reference to Figures 9 and 10. The laser processing method of the second embodiment has the same main configuration as the first embodiment. Therefore, in the second embodiment, only the parts that are different from the first embodiment will be described in detail, and the same parts as the first embodiment will be denoted by the same reference numerals and will not be described in detail again.

[0051] It is known that the wafer 10 expands due to laser processing. In the laser processing method of the second embodiment, the OFF position and ON position in the second laser processing step are adjusted based on the degree of expansion of the wafer 10 after the first laser processing.

[0052] 9, the control device 25 has a position correction unit 33 as a functional unit that functions by executing various programs. The position correction unit 33 corrects the position of the second parting line 12 held by the laser processing control unit 32 based on the degree of expansion of the wafer 10 after the first laser processing.

[0053] Specifically, as shown in FIG. 10 , the position corrector 33 acquires the size W of the wafer 10 in the second direction D2 near the center in the first direction D1 before and after the first laser processing. For example, the position corrector 33 acquires the size W of the wafer 10 by performing image processing on image data obtained by capturing an image of a reference mark provided on the wafer 10. The size of the wafer 10 before the first laser processing is referred to as the reference size W1, and the size of the wafer 10 after the first laser processing is referred to as the post-processing size W2. The reference mark may be an alignment mark. The position corrector 33 acquires an average expansion size Wa (=(W1-W2) / n) as the degree of expansion, obtained by subtracting the post-processing size W2 from the reference size W1 and dividing the result by the number n of the second division lines 12. The position corrector 33 then corrects the position of each second division line 12 stored in the laser processing control unit 32 based on the average expansion size Wa.

[0054] In the second laser processing step, the laser processing control unit 32 determines whether the moving work table 21 has reached the OFF position or the ON position based on the position of the second dividing line 12 after correction.

[0055] The operation and effects of the second embodiment will be described. (2-1) In the second laser processing step, the degree of expansion of the wafer 10 in the second direction D2 is acquired, and the irradiation position of the laser LB in the second direction D2 is adjusted according to the acquired degree of expansion. This improves the accuracy of the OFF and ON positions of the laser LB according to the degree of expansion of the wafer 10 due to the first laser processing step. As a result, the effect described in (1-1) can be more reliably achieved.

[0056] (Third embodiment) A third embodiment of the laser processing method will be described with reference to Figures 11 to 13. The laser processing method of the third embodiment has the same main configuration as the first embodiment. Therefore, in the third embodiment, only the parts that are different from the first embodiment will be described in detail, and the parts that are the same as those in the first embodiment will be denoted by the same reference numerals and will not be described in detail again.

[0057] In the second laser processing step of the laser processing method of the third embodiment, the laser processing control unit 32 performs laser processing in a processing direction in which a modified layer is formed on both sides of the intersection 13 in the second direction D2 so as to approach the intersection 13.

[0058] Specifically, as shown by arrows 41 and 42 in Figure 11, the laser processing control unit 32 performs laser processing by setting the central area between the intersections 13 as the ON position and positions away from the intersections 13 toward the ON position by distances L1 and L2.

[0059] More specifically, as shown in Fig. 12(a), when forming the first modified layer 15A, the laser processing control unit 32 moves the work table 21 in the +X direction to form the first modified layer 15A corresponding to the arrow 41. Then, as shown in Fig. 12(b), the laser processing control unit 32 moves the work table 21 in the -X direction to form the first modified layer 15A corresponding to the arrow 42. The ON position corresponding to the arrow 41 and the ON position corresponding to the arrow 42 are different positions in the X direction. The ON position corresponding to the arrow 42 is adjacent to the ON position corresponding to the arrow 41 on the side of the modified layer unformed region in the X direction (the +X direction side in this embodiment).

[0060] 13(a), when forming the second modified layer 15B, the laser processing control unit 32 moves the work table 21 in the +X direction to form the second modified layer 15B corresponding to the arrow 41. Thereafter, as shown in FIG. 13(b), the laser processing control unit 32 moves the work table 21 in the -X direction to form the second modified layer 15B corresponding to the arrow 42.

[0061] The operation and effects of the third embodiment will be described. (3-1) According to the above-described laser processing method, the energy of the laser LB irradiated onto the wafer 10 can be stabilized compared to when the ON position is provided near the intersection 13. This improves the accuracy of the formation position of the modified layers 15A, 15B near the intersection 13 and also makes it easier to obtain the desired brittleness near the intersection 13. As a result, the effect described in (1-1) can be more reliably obtained, and the wafer 10 can be divided along the second dividing line 12 with higher accuracy.

[0062] (3-2) The ON position corresponding to the arrow 41 and the ON position corresponding to the arrow 42 are different from each other, so that splash damage near the ON position corresponding to the arrow 42 can be reduced more reliably.

[0063] The first to third embodiments can be modified as follows: The first to third embodiments and the following modifications can be combined with each other within the scope of technical compatibility.

[0064] The laser processing device 20 may be configured so that the work table 21 and the laser irradiation unit 22 can be relatively moved in the X and Y directions by the relative movement mechanism 23. Therefore, the laser processing device 20 may move the laser irradiation unit 22 during laser processing.

[0065] The laser LB is not limited to a pulsed laser, but may be a CW (Continuous wave) laser. The back surface 10 b of the wafer 10 may be supported on the work table 21 via a dicing tape 16 .

[0066] The first distance L1 of the first modified layer 15A may be greater than the second distance L2 of the second modified layer 15B. For example, as shown in FIG. 14 , in addition to the first modified layer 15A and the second modified layer 15B, the wafer 10 may have a third modified layer 15C and a fourth modified layer 15D formed on the back surface 10b side of the wafer 10 relative to the second modified layer 15B as modified layers at different positions in the thickness direction. The third modified layer 15C is formed on the opposite side of the second modified layer 15B from the first modified layer 15A. The fourth modified layer 15D is formed on the opposite side of the third modified layer 15C from the second modified layer 15B. In this case, the laser processing device 20 preferably performs laser processing on the third modified layer 15C with an OFF position set to a position spaced a third distance L3 (≧L2) from the first parting line 11. The laser processing device 20 preferably performs laser processing on the fourth modified layer 15D with an OFF position set to a position spaced a fourth distance L4 (≧L3) from the first parting line 11. That is, in addition to the first modified layer 15A and the second modified layer 15B, the wafer 10 may be formed with a third modified layer, ..., an nth modified layer (n is an integer equal to or greater than 3). In this case, it is preferable that the laser processing device 20 performs laser processing on the nth modified layer 15n, with a position that is an nth distance Ln (≧L2) away from the first dividing line 11 as the OFF position. This configuration can reduce splash damage to the device surface 10a while increasing the proportion of the modified layer in the thickness direction. As a result, the wafer 10 can be divided along the second dividing line 12 with greater accuracy.

[0067] 15, in addition to the third modified layer 15C and fourth modified layer 15D described above, a fifth modified layer 15E and a sixth modified layer 15F may be formed on the back surface 10b side of the fourth modified layer 15D as modified layers at different positions in the thickness direction. The fifth modified layer 15E is formed on the back surface 10b side of the fourth modified layer 15D. The sixth modified layer 15F is formed on the back surface 10b side of the fifth modified layer 15E. The fifth modified layer 15E and the sixth modified layer 15F are back surface-side modified layers. The back surface-side modified layer is a modified layer that is sufficiently separated from the device surface 10a and does not affect the device surface 10a due to splash damage caused by the formation of the back surface-side modified layer. When forming the fifth modified layer 15E and the sixth modified layer 15F, the laser processing apparatus 20 may continuously irradiate the fifth modified layer 15E and the sixth modified layer 15F along the second dividing lines 12 without turning the laser on and off. That is, the laser processing apparatus 20 may form the fifth modified layer 15E and the sixth modified layer 15F by irradiating the laser LB along the second dividing lines 12 so that the modified layers are formed at predetermined intervals based on the laser processing conditions. This configuration makes it possible to more accurately divide the wafer 10 along the second dividing lines 12 while reducing splash damage to the device surface 10a.

[0068] The technical ideas that can be understood from the above-described embodiment and modified examples will be described. [Appendix 1] A laser processing method for forming a modified layer inside a wafer by irradiating a laser along a division line, the method comprising: a first laser processing step for forming a modified layer along a first division line extending in a first direction; and a second laser processing step performed after the first laser processing step for forming a modified layer along a second division line extending in a second direction intersecting the first direction and intersecting the first division line, wherein in the second laser processing step, a first modified layer and a second modified layer are formed at different positions in the thickness direction of the wafer, and the distance between the first division line in the second direction at the intersection of the first division line and the second division line is made different between the first modified layer and the second modified layer.

[0069] [Appendix 2] The laser processing method described in [Appendix 1], wherein the first modified layer is a modified layer formed at a position closer to the device surface of the wafer in the thickness direction than the second modified layer, and the distance between the first dividing line in the second direction is made smaller for the first modified layer than for the second modified layer.

[0070] [Appendix 3] When n is an integer greater than or equal to 3, in the second laser processing step, an nth modified layer is further formed on the back surface side opposite the device surface to the (n-1)th modified layer as a modified layer positioned at a different position in the thickness direction of the wafer, and at the intersection, when the distance between the second modified layer and the first division line in the second direction is distance L2 and the distance between the nth modified layer and the first division line in the second direction is distance Ln, distance Ln ≧ distance L(n-1).

[0071] [Appendix 4] In the second laser processing step, a back-side modified layer is formed on the back side of the nth modified layer as a modified layer at a different position in the thickness direction of the wafer, and the back-side modified layer is formed by continuously irradiating the laser along the second dividing line. [Appendix 3] The laser processing method described in

[0072] [Appendix 5] A laser processing method described in any one of [Appendix 1] to [Appendix 4], wherein in the second laser processing step, the laser irradiation position in the second direction is adjusted depending on the degree of expansion of the wafer due to the first laser processing step.

[0073] [Appendix 6] A laser processing method described in any one of [Appendix 1] to [Appendix 5], wherein in the second laser processing step, laser processing is performed on both sides of the intersection in the second direction, with the processing direction being the direction in which a modified layer is formed so as to approach the first dividing line. [Explanation of symbols]

[0074] 10...wafer, 10a...device surface, 10b...back surface, 11...first division line, 12...second division line, 13...intersection, 15A...first modified layer, 15B...second modified layer, 15C...third modified layer, 15D...fourth modified layer, 15E...fifth modified layer, 15F...sixth modified layer, 16...dicing tape, 20...laser processing device, 21...work table, 22...laser irradiation unit, 23...relative movement mechanism, 24...imaging device, 25...control device, 26...laser emission unit, 27...condensing lens, 29...input unit, 31...alignment detection unit, 32...laser processing control unit, 33...position correction unit.

Claims

1. A laser processing method for forming a modified layer inside a wafer by irradiating a laser along a dividing line, comprising: a first laser processing step of forming a modified layer along a first dividing line extending in a first direction; a second laser processing step that is performed after the first laser processing step and that forms a modified layer along a second division line that extends in a second direction intersecting the first direction and intersects with the first division line, In the second laser processing step, a first modified layer and a second modified layer are formed at different positions in the thickness direction of the wafer, and a distance between the first dividing line and the second dividing line in the second direction at an intersection between the first dividing line and the second dividing line is made different between the first modified layer and the second modified layer. Laser processing method.

2. the first modified layer is a modified layer formed at a position closer to a device surface of the wafer than the second modified layer in the thickness direction, The distance between the first dividing line and the first modified layer in the second direction is made smaller in the first modified layer than in the second modified layer. The laser processing method according to claim 1 .

3. When n is an integer of 3 or more, In the second laser processing step, an n-th modified layer is further formed on a back surface side opposite to the device surface with respect to the (n−1)-th modified layer, as a modified layer having a different position in the thickness direction of the wafer, At the intersection, the distance between the second modified layer and the first dividing line in the second direction is defined as a distance L2, and the distance between the nth modified layer and the first dividing line in the second direction is defined as a distance Ln, where Ln is a distance L(n-1). The laser processing method according to claim 2 .

4. In the second laser processing step, a rear surface modified layer is formed on the rear surface side of the nth modified layer as a modified layer having a different position in the thickness direction of the wafer, The rear surface modified layer is formed by continuously irradiating the laser along the second parting line. The laser processing method according to claim 3.

5. In the second laser processing step, the irradiation position of the laser in the second direction is adjusted according to the degree of expansion of the wafer due to the first laser processing step. The laser processing method according to claim 1 .

6. In the second laser processing step, laser processing is performed on both sides of the intersection in the second direction, with the direction in which a modified layer is formed so as to approach the first division line as a processing direction. The laser processing method according to claim 1 .

7. a work table for supporting the wafer; a laser irradiation unit that irradiates the wafer with a laser; a relative movement mechanism that moves the work table and the laser irradiation unit relative to each other; a control device that controls the laser irradiation unit and the relative movement mechanism so that a modified layer is formed inside the wafer along a dividing line, The control device a first laser processing step for forming a modified layer along a first dividing line extending in a first direction; After the first laser processing, a second laser processing is performed to form a modified layer along a second division line that extends in a second direction intersecting the first direction and intersects with the first division line; In the second laser processing, a first modified layer and a second modified layer are formed at different positions in the thickness direction of the wafer, and a distance between the first dividing line and the second dividing line in the second direction at an intersection of the first dividing line and the second dividing line is made different between the first modified layer and the second modified layer. Laser processing equipment.

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