Laser processing method and laser processing apparatus

Abstract

The present application provides a kind of laser processing method and laser processing device, in the laser processing of the modification layer being formed in the inside of wafer by laser along the division line, can reduce splash damage, and the precision is good along the division line and carries out the division of wafer.Laser processing method has: first laser processing step, forms modification layer along first division line;And second laser processing step, after first laser processing step, forms modification layer along second division line crossing with first division line.In second laser processing step, first modification layer (15A) and second modification layer (15B) different in the thickness direction of wafer (10) are formed, and in the intersection part formed by first division line (11) and second division line, the distance between second modification layer (15B) and first division line (11) is greater than the distance between first modification layer (15A) and first division line (11).

Description

Technical Field

[0001] This invention relates to a laser processing method and a laser processing apparatus for forming a modified layer inside a wafer by irradiating it with a laser. Background Technology

[0002] Wafers that form various components such as semiconductor devices or electronic parts are divided into individual wafers by slicing along lattice-like dividing lines. For example, Patent Document 1 discloses a technique for such wafer slicing, in which a first modifier layer and a second modifier layer located at different positions in the thickness direction of the wafer are formed inside the wafer by laser processing that irradiates a laser along the dividing lines. Existing technical documents Patent documents

[0003] Patent Document 1: Japanese Patent Application Publication No. 2018-63987 Summary of the Invention The problem that the invention aims to solve

[0004] However, when laser processing is performed on wafers, thermal damage, also known as splash damage, can sometimes occur due to the laser processing itself. This splash damage tends to occur at the intersections of the dicing lines. Patent Document 1 has designated one side of the dicing line as a non-processing area at the intersections of the dicing lines, but there is still room for improvement in reducing splash damage and in accurately dicing the wafer along the dicing lines. Methods for solving problems

[0005] A laser processing method for solving the above-mentioned problems forms a modified layer inside a wafer by irradiating a laser along a dicing line. The laser processing method includes: a first laser processing step, forming a modified layer along a first dicing line extending in a first direction; and a second laser processing step, performed after the first laser processing step, forming a modified layer along a second dicing line extending in a second direction, wherein the second direction intersects the first direction, and the second dicing line intersects the first dicing line. In the second laser processing step, the first and second modified layers are formed at different positions in the thickness direction of the wafer, and at the intersection formed by the first and second dicing lines, the distance between the first modified layer in the second direction and the first dicing line in the second direction is different from the distance between the second modified layer in the second direction and the first dicing line in the second direction.

[0006] A laser processing apparatus for solving the above-mentioned problems includes: a worktable supporting a wafer; a laser irradiation unit irradiating the wafer with a laser; a relative movement mechanism for moving the worktable relative to the laser irradiation unit; and a control device controlling the laser irradiation unit and the relative movement mechanism to form a modified layer along a cleaving line inside the wafer. The control device performs a first laser processing process and a second laser processing process. In the first laser processing process, a modified layer is formed along a first cleaving line extending in a first direction. The second laser processing process is performed after the first laser processing process, and a modified layer is formed along a second cleaving line extending in a second direction. The second direction intersects the first direction, and the second cleaving line intersects the first cleaving line. In the second laser processing process, a first modified layer and a second modified layer are formed at different positions in the thickness direction of the wafer. Furthermore, at the intersection formed by the first cleaving line and the second cleaving line, the distance between the first modified layer in the second direction and the first cleaving line in the second direction is different from the distance between the second modified layer in the second direction and the first cleaving line in the second direction. Invention Effects

[0007] According to the present invention, wafer sputtering damage caused by laser processing can be reduced, and wafer dicing can be performed with good accuracy along the dicing line. Attached Figure Description

[0008] Figure 1 This is a schematic top view of a wafer laser-processed according to an embodiment of the first embodiment using a laser processing method. Figure 2 This is a schematic diagram illustrating a general configuration of one embodiment of the laser processing apparatus in the first embodiment, and showing a wafer with a first modified layer and a second modified layer formed along a first dividing line. Figure 3 This is a functional block diagram representing the electronic configuration of the laser processing apparatus in the first embodiment. Figure 4 This is a flowchart illustrating the sequence of one embodiment of the laser processing method in the first embodiment. Figure 5 This is a flowchart illustrating an example of the sequence of the first laser processing step in the first embodiment. Figure 6 This is a flowchart illustrating an example of the sequence of the second laser processing in the first embodiment. Figure 7 (a) is a schematic diagram showing the OFF position of the second laser processing in the first embodiment with respect to the first modified layer. Figure 7(b) is a diagram schematically showing the ON position of the second laser processing in the first embodiment with respect to the first modified layer. Figure 8 (a) is a schematic diagram showing the OFF position of the second laser processing with respect to the second modified layer in the first embodiment. Figure 8 (b) is a diagram schematically showing the ON position of the second laser processing with respect to the second modified layer in the first embodiment. Figure 9 This is a functional block diagram representing the electronic configuration of the laser processing apparatus in the second embodiment. Figure 10 This is a block diagram schematically illustrating the electrical structure of the laser processing apparatus in the second embodiment. Figure 11 This is a diagram schematically showing the processing direction of the second laser processing step in the third embodiment. Figure 12 (a) is a schematic diagram showing the state in the third embodiment where the worktable is moved in the +X direction while the first modified layer is formed. Figure 12 (b) is a diagram schematically showing the state in the third embodiment where the worktable is moved in the -X direction while the first modified layer is formed. Figure 13 (a) is a schematic diagram showing the state in the third embodiment where the worktable is moved in the +X direction while the second modified layer is formed. Figure 13 (b) is a diagram schematically showing the state in the third embodiment where the worktable is moved in the -X direction while the second modified layer is formed. Figure 14 This is a cross-sectional view of a wafer in a modified example having a third and a fourth modified layer. Figure 15 A cross-sectional view showing an example of a wafer in which a fifth and sixth modified layers are formed. Detailed Implementation

[0009] (First Implementation) Reference Figures 1 to 8 The first embodiment of the laser processing method will be described. like Figure 1 As shown, wafer 10 is divided into wafers by a lattice-like dividing line formed by a first dividing line 11 extending in the first direction D1 and a second dividing line 12 extending in the second direction D2. In wafer 10, the surface on which various components such as semiconductor devices or electronic parts are formed is called the device surface 10a, and the surface opposite to the device surface 10a is called the back surface 10b (see reference). Figure 2Furthermore, the portion where the first dividing line 11 intersects with the second dividing line 12 is called the intersection 13.

[0010] Furthermore, the directions extending from the device surface 10a and the back surface 10b of wafer 10 are referred to as the XY directions. One of the XY directions is called the X direction, and the direction perpendicular to the X direction is called the Y direction. The X direction is the direction in which the dividing line of the processed object extends in each step. In the X direction, the direction indicated by the arrow in the figure is called the +X direction, and the opposite direction of the +X direction is called the -X direction, depending on the situation. In addition, the direction perpendicular to the XY direction is called the Z direction. The Z direction is the thickness direction of wafer 10.

[0011] (Laser processing equipment) like Figure 2 As shown, a laser processing apparatus 20 is used to perform laser processing on a wafer 10. The laser processing apparatus 20 includes a worktable 21, a laser irradiation unit 22, a relative movement mechanism 23, a camera 24, and a control device 25.

[0012] The worktable 21 supports the wafer 10 via the cutting tape 16. The worktable 21 is configured to move in the X direction via the relative movement mechanism 23 and to rotate about the Z direction as the rotation axis. The movement speed of the worktable 21 in the X direction is called the laser processing speed.

[0013] The laser irradiation unit 22 irradiates the wafer 10 supported on the worktable 21 with laser LB. The laser irradiation unit 22 is configured to move in the Y and Z directions with the relative movement mechanism 23. The laser irradiation unit 22 is configured to temporarily interrupt the irradiation of the wafer 10 by laser LB through shutter control or the like.

[0014] The laser irradiation unit 22 includes a laser emitting unit 26 and a focusing lens 27. The laser emitting unit 26 and the focusing lens 27 are configured to move relative to each other in the Z direction via a moving mechanism (not shown). The laser emitting unit 26 emits a laser beam LB of a predetermined wavelength toward the focusing lens 27. The laser beam LB is a pulsed laser. The focusing lens 27 focuses the laser beam LB emitted by the laser emitting unit 26 onto a focusing point P. The focusing point P is the irradiation position of the laser beam LB. In the interior of the wafer 10 irradiated by the laser beam LB, a modified layer with disrupted crystal structure forms near the focusing point P. This modified layer is a more fragile area than the area not subjected to laser processing. Furthermore, the laser irradiation unit 22 preferably uses an optical element capable of high-speed processing of the ON / OFF state of the laser beam LB, such as an acousto-optic modulator.

[0015] The irradiation position of the laser LB in the XY direction is adjusted by the relative movement between the worktable 21 and the laser irradiation unit 22. In addition, 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 by the relative movement between the laser emission unit 26 and the focusing lens 27 in the Z direction.

[0016] Camera 24 is mounted on laser illumination unit 22. Camera 24 captures images of alignment marks set on wafer 10. Camera 24 outputs image data representing the captured image to control device 25.

[0017] The control device 25 controls the operation of the laser processing device 20 in a comprehensive manner by controlling the laser irradiation unit 22, the relative movement mechanism 23, and the camera 24. The laser processing apparatus 20 performs laser processing on the wafer 10, wherein the device surface 10a is supported on the worktable 21 by a cutting tape 16. At this time, the back surface 10b of the wafer 10 serves as the incident surface of the laser LB. The laser processing apparatus 20 performs laser processing on each first dicing line 11, and then on each second dicing line 12. The laser processing apparatus 20 forms a first modified layer 15A on each dicing line 11, 12 near the device surface 10a (away from the incident surface of the laser LB), and then forms a second modified layer 15B near the back surface 10b. Furthermore, Figure 2 This refers to a wafer 10 in which modified layers 15A and 15B are formed along the first dividing line 11. That is, the X direction is the first direction D1, and the Y direction is the second direction D2.

[0018] (Control device) The control device 25 can be implemented, for example, through a circuit, namely one or more dedicated hardware circuits such as an application-specific integrated circuit (ASIC), one or more processing circuits that operate according to a computer program (software), or a combination of both. The processing circuit has a CPU and memory (ROM and RAM, etc.) that stores the program executed by the CPU. Memory is also known as computer-readable medium, which contains all available media that can be accessed by a general-purpose or special-purpose computer.

[0019] like Figure 3 As shown, the control device 25 is electrically connected to the laser irradiation unit 22, the relative movement mechanism 23, and the camera 24, as well as to the input unit 29. The input unit 29 receives various information input by the operator into the laser processing device 20. The input unit 29 may also be composed of, for example, a mouse, keyboard, or touch panel.

[0020] The operator inputs laser processing conditions through input unit 29. Specifically, the operator inputs the output or repetition frequency of 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 as laser processing conditions. In addition, the operator inputs the first distance L1 and the second distance L2 used in the second laser processing described later as laser processing conditions.

[0021] The control device 25 has an alignment detection unit 31 and a laser processing control unit 32 as functional units, which perform functions by executing various programs. The alignment detection unit 31 performs alignment detection processing to detect the position of each first dividing line 11 and each second dividing line 12 in the wafer 10.

[0022] For example, in the alignment detection process, the alignment detection unit 31 adjusts the position of the camera 24 relative to the alignment marks provided on the wafer 10 by controlling the relative movement mechanism 23. Then, the alignment detection unit 31 uses the camera 24 to capture images of the alignment marks, obtaining image data displaying the captured images. Furthermore, the alignment detection unit 31 performs image processing on the image data to detect the position of each first dividing line 11 and each second dividing line 12.

[0023] The laser processing control unit 32 executes a first laser processing process and a second laser processing process. In the first laser processing process, modified layers 15A and 15B are formed along each first dividing line 11, and in the second laser processing process, modified layers 15A and 15B are formed along each second dividing line 12. The laser processing control unit 32 maintains the laser processing conditions and the positions of each dividing line 11 and 12 according to the alignment detection process. The laser processing control unit 32 controls the relative movement mechanism 23 and the laser irradiation unit 22 according to the laser processing conditions and the positions of each dividing line 11 and 12, thereby executing each laser processing process.

[0024] (Laser processing method) like Figure 4 As shown, 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] During the alignment detection step, the alignment detection unit 31 of the control device 25 performs the above-described alignment detection process. In this way, the control device 25 detects the position of each first dividing line 11 and each second dividing line 12 in the wafer 10.

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

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

[0028] (First laser processing step) like Figure 5 As shown, in the first laser processing step, the laser processing control unit 32 first aligns the first dividing line 11 of the workpiece with the laser irradiation unit 22 (step S201). Specifically, the laser processing control unit 32 rotates the worktable 21 about the Z-axis, causing the first dividing line 11 of the workpiece to extend in the X-axis. Furthermore, the laser processing control unit 32 moves the worktable 21 in the XY-axis, positioning the laser irradiation unit 22 above the end of the first dividing line 11 in the +X-axis direction.

[0029] Next, the laser processing control unit 32 forms a first modified layer 15A on the first dividing line 11 of the workpiece (step S202). Specifically, in order to form the first modified layer 15A, the laser processing control unit 32 adjusts the irradiation position of the laser LB. Then, the laser processing control unit 32 starts irradiating the laser LB and moves the worktable 21 along the -X direction. Then, when the worktable 21 moves to a position above the end of the first dividing line 11 in the -X direction where the laser irradiation unit 22 is positioned, the laser processing control unit 32 ends the irradiation of the laser LB and the movement of the worktable 21. In this way, the first modified layer 15A is continuously formed on the first dividing line 11 of the workpiece in the X direction (see reference). Figure 2 ).

[0030] Next, the laser processing control unit 32 forms a second modified layer 15B on the first dividing line 11 of the workpiece. Specifically, in order to form the second modified layer 15B, the laser processing control unit 32 adjusts the irradiation position of the laser LB. Then, the laser processing control unit 32 starts irradiating the laser LB and moves the worktable 21 in the +X direction. Then, when the worktable 21 moves to a position above the end of the first dividing line 11 in the +X direction where the laser irradiation unit 22 is positioned, the laser processing control unit 32 ends the irradiation of the laser LB and the movement of the worktable 21. In this way, the second modified layer 15B is continuously formed on the first dividing line 11 of the workpiece in the X direction relative to the back surface 10b side of the first modified layer 15A (see reference). Figure 2).

[0031] Next, the laser processing control unit 32 determines whether the formation of the modified layers 15A and 15B on all the first dividing lines 11 has been completed (step S204). If the formation of the modified layers 15A and 15B on all the first dividing lines 11 has not been completed (step S204: No), the laser processing control unit 32 repeats steps S201 to S203 until the modified layers 15A and 15B are formed on all the first dividing lines 11. On the other hand, when the formation of the modified layers 15A and 15B on all the first dividing lines 11 is completed (step S204: Yes), the laser processing control unit 32 ends the first laser processing.

[0032] (Second laser processing step) like Figure 6 As shown, in the second laser processing step, the laser processing control unit 32 first aligns the second dividing line 12 of the workpiece with the laser irradiation unit 22 (step S301). Specifically, the laser processing control unit 32 rotates the worktable 21 about the Z-axis, causing the second dividing line 12 of the workpiece to extend in the X-direction. Furthermore, the laser processing control unit 32 moves the worktable 21 in the XY-direction, positioning the laser irradiation unit 22 above the end of the second dividing line 12 in the +X direction.

[0033] Next, the laser processing control unit 32 begins to form a first modified layer 15A on the second dividing line 12 of the workpiece (step S302). Specifically, in order to form the first modified layer 15A, the laser processing control unit 32 adjusts the irradiation position of the laser LB. Then, the laser processing control unit 32 begins irradiation of the laser LB and moves the worktable 21 along the -X direction.

[0034] Next, the laser processing control unit 32 will determine whether the moving worktable 21 has reached the OFF position (step S303). like Figure 7 As shown in (a), when in the OFF position, a first modified layer 15A is formed at a position at a first distance L1 in the +X direction from the first dividing line 11. Figure 7 In (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 the distance above the formation interval of the modified layer according to the laser processing conditions.

[0035] When the worktable 21 reaches the OFF position (step S303: Yes), the laser processing control unit 32 will interrupt the irradiation of the laser LB (step S304). Next, the laser processing control unit 32 will determine whether the moving worktable 21 has reached the ON position (step S305).

[0036] like Figure 7 As shown in (b), when in the ON position, a first modified layer 15A is formed at a position at a first distance L1 in the -X direction from the first dividing line 11. Figure 7 In (b), the arrows overlapping the first modified layer 15A indicate the order in which the first modified layer 15A is formed. When the worktable 21 reaches the ON position (step S305: Yes), the laser processing control unit 32 will restart the irradiation of the laser LB (step S306).

[0037] Next, the laser processing control unit 32 determines whether the formation of the first modified layer 15A on the second dividing line 12 of the workpiece has been completed (step S307). For example, when the worktable 21 moves to a position above the other end of the second dividing line 12 in the +X direction where the laser irradiation unit 22 is positioned, the laser processing control unit 32 determines that the formation of the first modified layer 15A has been completed. When 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] When the formation of the first modified layer 15A is completed (step S307: Yes), the laser processing control unit 32 will begin forming the second modified layer 15B on the second dividing line 12 of the workpiece after the irradiation of the laser LB and the movement of the worktable 21 are completed (step S308). Specifically, in order to form the second modified layer 15B, the laser processing control unit 32 will start the irradiation of the laser LB and move the worktable 21 along the -X direction after adjusting the irradiation position of the laser LB.

[0039] Next, the laser processing control unit 32 will determine whether the worktable 21 has reached the OFF position (step S309). like Figure 8 As shown in (a), when the worktable 21 is in the OFF position at this time, a second modified layer 15B is formed at a position at a second distance L2 in the -X direction from the first dividing line 11. Figure 8 In (a), the arrows overlapping the second modified layer 15B indicate the order in which the first modified layer 15A is formed. When the worktable 21 reaches the OFF position (step S309: Yes), the laser processing control unit 32 will interrupt the irradiation of the laser LB (step S310).

[0040] Next, the laser processing control unit 32 will determine whether the worktable 21 has reached the ON position (step S311). like Figure 8As shown in (b), when in the ON position, a second modified layer 15B is formed at a position at a second distance L2 in the +X direction from the first dividing line 11. Figure 8 In (b), the arrows overlapping the second modified layer 15B indicate the order in which the second modified layer 15B is formed. When the worktable 21 reaches the ON position (step S311: Yes), the laser processing control unit 32 will restart the irradiation of the laser LB (step S312).

[0041] Next, the laser processing control unit 32 determines whether the formation of the second modified layer 15B on the second dividing line 12 of the workpiece has been completed (step S313). For example, when the worktable 21 moves to a position above the end of the second dividing line 12 in the +X direction where the laser irradiation unit 22 is positioned, the laser processing control unit 32 determines that the formation of the second modified layer 15B has been completed. 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, when the formation of the second modified layer 15B is completed (step S313: Yes), the laser processing control unit 32 will determine whether the formation of the modified layers 15A and 15B on all the second dividing lines 12 has been completed after the laser LB irradiation and the movement of the worktable 21 ends (step S314).

[0043] When the formation of the modified layers 15A and 15B on all the second dividing lines 12 is not yet complete (step S314: No), the laser processing control unit 32 will repeat steps S301 to S314 until the modified layers 15A and 15B are formed on all the second dividing lines 12. On the other hand, when the formation of the modified layers 15A and 15B on all the second dividing lines 12 is complete (step S314: Yes), the laser processing control unit 32 will end the second laser processing.

[0044] The wafer 10 with modified layers 15A and 15B formed by the above laser processing method can be divided into wafers along the dividing lines 11 and 12 by performing dividing processes such as expansion or breaking.

[0045] The function and effects of the first embodiment will be explained. (1-1) The energy of the laser LB irradiating wafer 10 can be roughly divided into: the modification energy that modifies the area near the irradiation location; the energy that disappears before reaching the back surface of the laser incident as it moves towards the back surface; and the remaining energy that diffuses to the periphery of the irradiation location and reaches the back surface, becoming the cause of sputtering damage. Since the energy that disappears when passing through the modification area is smaller, the larger the proportion of the area around the irradiation location before modification, the larger the proportion of modification energy. On the other hand, the larger the proportion of the area around the irradiation location after modification, the larger the proportion of remaining energy.

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

[0047] Based on the above facts, in the second laser processing step (step S103) of the aforementioned laser processing method, the distance between the second modified layer 15B and the first dividing line 11 is set to be greater than the distance between the first modified layer 15A and the first dividing line 11. In this way, the residual energy generated near the intersection 13 during the formation of the second modified layer 15B can be reduced. As a result, sputtering damage to the wafer 10 can be reduced. Furthermore, since the residual energy is reduced, the required brittleness can be easily obtained near the intersection 13, thus enabling precise dicing of the wafer 10 along the dividing lines 11 and 12.

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

[0049] With this configuration, the brittleness of the wafer 10 on the device surface 10a side is increased. In this way, the wafer 10 can be diced with good precision along each of the first dicing line 11 and the second dicing line 12 on the device surface 10a side. As a result, the quality of the diced wafers on the device surface 10a can be ensured.

[0050] (Second Implementation) Reference Figure 9 and Figure 10 A second embodiment of the laser processing method will be described. Furthermore, the laser processing method of the second embodiment has the same main components as the first embodiment. Therefore, in the second embodiment, the parts that differ from the first embodiment will be described in detail, while the parts that are the same as the first embodiment will be given the same reference numerals and their detailed descriptions will be omitted.

[0051] It is known that wafer 10 will expand under laser processing. The laser processing method of the second embodiment adjusts the OFF and ON positions in the second laser processing step according to the degree of expansion of wafer 10 after the first laser processing.

[0052] like Figure 9 As shown, the control device 25 has a position correction unit 33 as a functional unit, which performs its function by executing various programs. The position correction unit 33 corrects the position of the second dividing line 12 held by the laser processing control unit 32 according to the degree of expansion of the wafer 10 after the first laser processing.

[0053] Specifically, such as Figure 10 As shown, the position correction unit 33 obtains the size W of the wafer 10 in the second direction D2 near the center of the first direction D1 before and after the first laser processing. For example, the position correction unit 33 obtains the size W of the wafer 10 by performing image processing on image data of a reference mark set on the wafer 10. The size of the wafer 10 before the first laser processing is called the reference size W1, and the size of the wafer 10 after the first laser processing is called the processed size W2. The reference mark can also be an alignment mark. The position correction unit 33 uses the average expansion size Wa (=(W1-W2) / n) obtained by subtracting the processed size W2 from the reference size W1 and dividing it by the number of lines n of the second dividing line 12 as the degree of expansion. Then, the position correction unit 33 corrects the position of each second dividing line 12 held by the laser processing control unit 32 according to the average expansion size Wa.

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

[0055] The function and effects of the second embodiment will be explained. (2-1) The second laser processing step obtains the degree of expansion of the wafer 10 in the second direction D2, and adjusts the irradiation position of the laser LB in the second direction D2 according to the obtained degree of expansion. In this way, the accuracy of the OFF and ON positions of the laser LB can be improved according to the degree of expansion of the wafer 10 caused by the first laser processing step. As a result, the effect described in (1-1) can be ensured.

[0056] (Third Implementation) Reference Figures 11-13A third embodiment of the laser processing method will be described. Furthermore, the main components of the laser processing method in the third embodiment are the same as those in the first embodiment. Therefore, in the third embodiment, the parts that differ from the first embodiment will be described in detail, while the parts that are the same as those in the first embodiment will be given the same reference numerals and their detailed descriptions will be omitted.

[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 the following processing direction: forming a modified layer by moving from both sides of the intersection 13 on the second direction D2 toward the intersection 13.

[0058] Specifically, such as Figure 11 As shown by arrows 41 and 42, the laser processing control unit 32 sets the central area between the intersections 13 to the ON position and sets the positions at intervals L1 and L2 from the intersections 13 toward the ON position to the OFF position for laser processing.

[0059] More specifically, such as Figure 12 As shown in (a), when forming the first modified layer 15A, the laser processing control unit 32 moves the worktable 21 in the +X direction while forming the first modified layer 15A corresponding to arrow 41. Then, as... Figure 12 As shown in (b), the laser processing control unit 32 moves the worktable 21 in the -X direction while forming the first modified layer 15A corresponding to arrow 42. The ON position corresponding to arrow 41 and the ON position corresponding to arrow 42 are different in the X direction. The ON position corresponding to arrow 42 is located on the X-direction side where the modified layer has not been formed (in this embodiment, the +X direction side) adjacent to the ON position corresponding to arrow 41.

[0060] In addition, such as Figure 13 As shown in (a), when forming the second modified layer 15B, the laser processing control unit 32 moves the worktable 21 in the +X direction while forming the second modified layer 15B corresponding to arrow 41. Then, as... Figure 13 As shown in (b), the laser processing control unit 32 moves the worktable 21 in the -X direction while forming the second modified layer 15B corresponding to arrow 42.

[0061] The function and effects of the third embodiment will be explained. (3-1) According to the laser processing method described above, compared with the case where the ON position is set near the intersection 13, the energy of the laser LB irradiating the wafer 10 can be made more stable. In this way, the accuracy of the formation position of the modified layers 15A and 15B near the intersection 13 can be improved, and the desired brittleness can be easily obtained near the intersection 13. As a result, the effect described in (1-1) can be obtained more reliably, and the wafer 10 can be diced along the second dividing line 12 with higher accuracy.

[0062] (3-2) By making the ON position of the corresponding arrow 41 different from the ON position of the corresponding arrow 42, splash damage near the ON position of the corresponding arrow 42 can be reduced more reliably.

[0063] The first to third embodiments can also be modified as follows. The first to third embodiments and the following modifications can be combined and implemented to a extent that they are not technically contradictory.

[0064] The laser processing apparatus 20 only needs to be configured such that the worktable 21 and the laser irradiation unit 22 can move relative to each other in the XY direction via the relative movement mechanism 23. Therefore, the laser processing apparatus 20 can also move the laser irradiation unit 22 during laser processing.

[0065] Laser LB is not limited to pulsed lasers; it can also be a continuous wave laser. The wafer 10 can also be supported on the worktable 21 by cutting the tape 16.

[0066] The first distance L1 of the first modified layer 15A can also be greater than the second distance L2 of the second modified layer 15B. For example Figure 14As shown, in addition to forming the first modified layer 15A and the second modified layer 15B, the wafer 10 may also form a third modified layer 15C and a fourth modified layer 15D on the back side 10b of the second modified layer 15B, as modified layers with different positions in the thickness direction. The third modified layer 15C is formed on the side opposite to the first modified layer 15A relative to the second modified layer 15B. The fourth modified layer 15D is formed on the side opposite to the second modified layer 15B relative to the third modified layer 15C. In this case, the laser processing apparatus 20 preferably performs laser processing on the third modified layer 15C by setting a position at a third distance L3 (≥L2) from the first dividing line 11 to the OFF position. Furthermore, the laser processing apparatus 20 preferably performs laser processing on the fourth modified layer 15D by setting a position at a fourth distance L4 (≥L3) from the first dividing line 11 to the OFF position. In detail, in addition to forming the first modified layer 15A and the second modified layer 15B, the wafer 10 can also form a third modified layer, ..., an nth modified layer (n is an integer of 3 or more). In this case, the laser processing apparatus 20 preferably sets the position at an nth distance Ln (≥L2) from the first dividing line 11 to the OFF position to perform laser processing on the nth modified layer 15n. With this configuration, sputtering damage to the device surface 10a can be reduced, and the proportion of the modified layer in the thickness direction can be increased. As a result, the wafer 10 can be diced along the second dividing line 12 with greater accuracy.

[0067] In addition, such as Figure 15 As shown, in addition to forming the third modified layer 15C and the fourth modified layer 15D, a fifth modified layer 15E and a sixth modified layer 15F can also be formed on the back side 10b of the fourth modified layer 15D, as modified layers with different positions in the thickness direction. The fifth modified layer 15E is formed on the back side 10b of the fourth modified layer 15D. The sixth modified layer 15F is formed on the back side 10b of the fifth modified layer 15E. The fifth modified layer 15E and the sixth modified layer 15F are back-side modified layers. The back-side modified layer is a modified layer that is quite far from the device surface 10a, and the spatter damage associated with the formation of the back-side modified layer will not affect the device surface 10a. When forming such a fifth modified layer 15E and a sixth modified layer 15F, the laser processing apparatus 20 can continuously irradiate each of the fifth modified layer 15E and the sixth modified layer 15F with laser along the second dividing line 12 without setting ON / OFF. In detail, the laser processing apparatus 20 can also form a fifth modified layer 15E and a sixth modified layer 15F by irradiating the second dividing line 12 with laser LB at predetermined intervals according to the laser processing conditions. With this configuration, sputtering damage to the device surface 10a can be reduced, and the wafer 10 can be divided along the second dividing line 12 with greater accuracy.

[0068] The following describes the technical ideas that can be grasped from the above embodiments and modifications. [Appendix 1] A laser processing method for forming a modified layer inside a wafer by irradiating a laser along a slit line includes: a first laser processing step of forming the modified layer along a first slit line extending in a first direction; and a second laser processing step performed after the first laser processing step of forming the modified layer along a second slit line extending in a second direction, wherein the second direction intersects the first direction and the second slit line intersects the first slit line. In the second laser processing step, the first modified layer and the second modified layer are formed at different positions in the thickness direction of the wafer, and in the intersection formed by the first slit line and the second slit line, the distance between the first modified layer in the second direction and the first slit line in the second direction is different from the distance between the second modified layer in the second direction and the first slit line in the second direction.

[0069] [Appendix 2] The laser processing method as described in [Appendix 1], wherein the first modified layer is 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 modified layer and the first dividing line in the second direction is less than the distance between the second modified layer and the first dividing line in the second direction.

[0070] [Appendix 3] The laser processing method as described in [Appendix 2], wherein when n is set to an integer greater than or equal to 3, in the second laser processing step, an nth modified layer is formed on the back side opposite to the device surface of the (n-1)th modified layer. As modified layers with different positions in the thickness direction of the wafer, in the intersection, when the distance between the second modified layer in the second direction and the first dividing line is set to distance L2, and the distance between the nth modified layer in the second direction and the first dividing line is set to distance Ln, distance Ln ≥ distance L(n-1).

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

[0072] [Appendix 5] The laser processing method as described in any one of [Appendix 1] to [Appendix 4], wherein, 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 caused by the first laser processing step.

[0073] [Appendix 6] The laser processing method as described in any one of [Appendix 1] to [Appendix 5], wherein in the second laser processing step, the laser processing is performed in the following processing direction: the modified layer is formed by moving from both sides of the intersection in the second direction toward the first dividing line. Explanation of reference numerals in the attached figures

[0074] 10…Wafer, 10a…Device side, 10b…Back side, 11…First dividing line, 12…Second dividing 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…Cutting tape, 20…Laser processing apparatus, 21…Worktable, 22…Laser irradiation unit, 23…Relative movement mechanism, 24…Camera, 25…Control device, 26…Laser emission unit, 27…Condensing lens, 29…Input unit, 31…Alignment and detection unit, 32…Laser processing control unit, 33…Position correction unit

Claims

1. A laser processing method, wherein a modified layer is formed inside a wafer by irradiating a laser along a cleaving line, comprising: The first laser processing step involves forming a modified layer along a first dividing line extending in a first direction; and The second laser processing step, performed after the first laser processing step, involves forming a modified layer along a second dividing line extending in a second direction, wherein the second direction intersects the first direction, and the second dividing line intersects the first dividing line. In the second laser processing step described above, a first modified layer and a second modified layer are formed at different positions in the thickness direction of the wafer, and in the intersection formed by the first dividing line and the second dividing line, the distance between the first modified layer in the second direction and the first dividing line in the second direction is different from the distance between the second modified layer in the second direction and the first dividing line in the second direction.

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

3. The laser processing method according to claim 2, wherein, When n is set to an integer greater than or equal to 3 In the second laser processing step described above, an nth modification layer is further formed on the back side opposite to the device surface of the (n-1)th modification layer, thus creating modification layers positioned differently in the thickness direction of the wafer. In the aforementioned intersection, when the distance between the second modified layer in the second direction and the first dividing line is set as distance L2, and the distance between the nth modified layer in the second direction and the first dividing line is set as distance Ln, then distance Ln ≥ distance L(n-1).

4. The laser processing method according to claim 3, wherein, In the second laser processing step described above, a back-side modified layer is formed on the back side of the nth modified layer, serving as modified layers positioned differently in the thickness direction of the wafer. The aforementioned modified back side layer is formed by continuously irradiating the aforementioned laser along the aforementioned second dividing line.

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

6. The laser processing method according to claim 1, wherein, In the second laser processing step described above, the laser processing is performed in the following direction: the modified layer is formed by moving from both sides of the intersection in the second direction toward the first dividing line.

7. A laser processing apparatus, comprising: The worktable supports the wafer; The laser irradiation section irradiates the aforementioned wafer with a laser. The relative movement mechanism causes the worktable to move relative to the laser irradiation unit; and The control device controls the laser irradiation unit and the relative movement mechanism to form a modified layer along the cleaving line inside the wafer. The aforementioned control device performs the first laser processing and the second laser processing. In the aforementioned first laser processing, a modified layer is formed along a first dividing line extending in a first direction. The second laser processing is performed after the first laser processing, forming a modified layer along a second dividing line extending in a second direction. The second direction intersects the first direction, and the second dividing line intersects the first dividing line. In the second laser processing described above, a first modified layer and a second modified layer are formed at different positions in the thickness direction of the wafer, and in the intersection formed by the first dividing line and the second dividing line, the distance between the first modified layer in the second direction and the first dividing line in the second direction is different from the distance between the second modified layer in the second direction and the first dividing line in the second direction.

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