Laser processing device and laser processing method

Abstract

To provide a laser processing device and a laser processing method which can make improvement in processing speed and suppression of deterioration in processing quality compatible.SOLUTION: A laser processing device 1 comprises: a stage 2 for supporting an object 11; a laser irradiating part 3 that irradiates the object 11 supported on the stage 2 with laser light L while forming a first light-condensing point C1 of the laser light L and a second light-condensing point C2 of the laser light L positioned closer to an incidence plane side of the laser light L in the object 11 than the first light-condensing point C1; driving parts 4 and 5 that move at least either of the stage 2 and the laser irradiating part 3 so that the first light-condensing point C1 and the second light-condensing point C2 move relatively to the object 11; and a control part 6 that controls the laser irradiating part 3 and the driving parts 4 and 5.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a laser processing apparatus and a laser processing method. [Background technology]

[0002] Patent Document 1 describes a laser processing device. This laser processing device includes a focusing lens, and forms a processed layer on a single-crystal material using laser light emitted from the focusing lens. The focusing lens includes a sub-focusing system onto which the laser light is incident, and a main focusing system onto which the laser light emitted from the sub-focusing system is incident and which irradiates the laser light toward the single-crystal material. The sub-focusing system includes a cylindrical lens array formed by an integral arrangement of multiple cylindrical lenses, and a cylindrical convex lens that transmits light from the cylindrical lens array.

[0003] In this laser processing device, the laser light incident on the cylindrical lens is split into multiple beams, which then form focal points before entering the cylindrical convex lens, forming a thin, parallel beam with an elongated shape on the irradiation surface and entering the main focusing system. The laser light emitted from the main focusing system is split into multiple beams that enter the irradiated surface of the single crystal member, forming multiple focal points inside the single crystal member. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-19120 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-described laser processing device, the processing layer is formed while forming multiple focal points of the laser light, thereby improving the speed at which the processing layer is formed. That is, in the above-described technical field, there is a demand for an improvement in the processing speed. Meanwhile, in the above-described technical field, there is a demand for processing to cut out a central region (effective region) of the object by removing an annular region (removal region) including the outer edge of the object from the object. The effective region is, for example, a region where a device is formed. Therefore, in the above-described technical field, there is also a demand for suppressing deterioration in the quality of the effective region (i.e., processing quality).

[0006] Therefore, an object of the present invention is to provide a laser processing apparatus and a laser processing method that can achieve both an improvement in processing speed and suppression of deterioration in processing quality. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems and have come to the following findings. Specifically, when cutting out an effective area from an object, the following two types of processing can be considered. The first processing is a processing in which a modified area is formed at the boundary between the effective area and the removal area by irradiating the boundary between the effective area and the removal area with laser light. The second processing is a processing in which a modified area is formed in the removal area from the outer edge of the object to the boundary between the effective area and the removal area by irradiating the boundary between the effective area and the removal area with laser light from the outer edge of the object to divide the annular removal area into multiple parts to make them easier to remove.

[0008] Here, from the viewpoint of improving the speed of forming the modified region, it is conceivable to form multiple rows of modified regions in the thickness direction of the object by forming multiple focal points in the thickness direction of the object. In this case, it is possible to increase the amount of crack propagation from the modified region by offsetting the focal points in the direction of movement of the focal points (the direction of processing). If the amount of crack propagation increases, it is possible to reduce the number of rows of modified regions in the thickness direction of the object required to cut the object. Therefore, in the first processing described above, when forming modified regions at the boundary between the effective area and the removal area, it is possible to improve the processing speed by offsetting the focal points.

[0009] In contrast, during the second processing described above, if the focal points are offset in the processing direction, for example, when one focal point reaches the boundary between the effective area and the removal area, another focal point offset forward in the processing direction from the first focal point will advance into the effective area by a distance corresponding to the offset amount. In this case, a modified area is formed within the effective area. Therefore, in this case, by reducing the offset amount between the focal points, the modified area formed within the effective area can be reduced, and degradation of the quality of the effective area can be suppressed.

[0010] On the other hand, if the laser beam irradiation is turned off when the boundary between the effective area and the removal area is reached so that the other focal point does not advance into the effective area, the one focal point will not reach the effective area by a distance corresponding to the offset amount. In this case, the modified area will not be formed so as to reach the effective area, which may result in a deterioration in the quality of the cut surface when the object is cut along the boundary between the effective area and the removal area. Therefore, in this case, the deterioration in the quality of the cut surface can be suppressed by reducing the offset amount between the focal points.

[0011] As described above, by relatively increasing the offset amount between the focal points in the first processing and relatively decreasing the offset amount between the focal points in the second processing, it is possible to improve the processing speed while suppressing degradation of processing quality. The present invention was made based on this finding.

[0012] That is, the laser processing apparatus according to the present invention is a laser processing apparatus for irradiating an object with laser light to form a modified region, and includes a support part for supporting the object, a laser irradiation part for irradiating the object supported by the support part with laser light while forming a first focal point of the laser light and a second focal point of the laser light located closer to the incident surface of the object than the first focal point, a movement mechanism for moving at least one of the support part and the laser irradiation part so that the first focal point and the second focal point move relative to the object, and a control part for controlling the laser irradiation part and the movement mechanism, wherein the object includes a first part located inside the object when viewed from a direction intersecting the incident surface, and a second part located outside the first part and including the outer edge of the object, and the object includes a first part located inside the object when viewed from a direction intersecting the incident surface, and a second part located outside the first part and including the outer edge of the object. In this case, a first line extending in a ring shape on the boundary between the first portion and the second portion, and a second line extending in the second portion from the outer edge of the object toward the inside of the object and reaching the boundary are set, and the control unit executes a first process of controlling the laser irradiation unit and the movement mechanism so that, in a state where the distance between the first focal point and the second focal point in a direction along the first line is set to a first distance, the first focal point and the second focal point are moved relatively along the first line, and the control unit executes a second process of controlling the laser irradiation unit and the movement mechanism so that, in a state where the distance between the first focal point and the second focal point in a direction along the second line is set to a second distance smaller than the first distance, the first focal point and the second focal point are moved relatively along the second line, and the control unit executes

[0013] Furthermore, a laser processing method according to the present invention is a laser processing method for irradiating an object with laser light to form a modified region, and includes a laser irradiation step of irradiating the object with laser light while forming a first focal point of the laser light and a second focal point of the laser light located closer to the laser light incident surface side of the object than the first focal point, wherein the object includes a first portion located inside the object when viewed from a direction intersecting the incident surface, and a second portion located outside the first portion and including an outer edge of the object, and the object includes a first line extending in a ring shape on the boundary between the first portion and the second portion when viewed from the direction intersecting the incident surface, and and a second line extending from the outer edge of the object toward the inside of the object and reaching the boundary, and the laser irradiation process includes a first irradiation process in which, in a state in which the distance between the first focal point and the second focal point in a direction along the first line is set to a first distance, the object is irradiated with laser light while the first focal point and the second focal point are moved relatively along the first line, and a second irradiation process in which, in a state in which the distance between the first focal point and the second focal point in a direction along the second line is set to a second distance smaller than the first distance, the object is irradiated with laser light while the first focal point and the second focal point are moved relatively along the second line.

[0014] In these devices and methods, a first line extending annularly on the boundary between a first portion located inside and a second portion located outside the first portion is set on the object, and a second line extending from the outer edge of the object toward the inside of the object and reaching the boundary in the second portion. Then, in each of the processing along the first line and the processing along the second line, laser light is irradiated onto the object while forming two focal points of the laser light on the object. In this case, when processing along the first line, the distance between the focal points along the first line is relatively large. Therefore, as shown in the above findings, it is possible to improve the processing speed. On the other hand, when processing along the second line, the distance between the focal points along the second line is relatively small. Therefore, as shown in the above findings, it is possible to reduce the processing quality.

[0015] In the laser processing apparatus according to the present invention, the control unit may perform the second process multiple times for one second line while varying the positions of the first and second focal points in the direction intersecting the incident plane. In this way, it is effective to perform the second process multiple times for one second line in which the distance between the focal points is relatively small.

[0016] In the laser processing device according to the present invention, the control unit may, after performing the second process an nth time (n is an integer greater than or equal to 1), perform the second process an mth time (m is an integer greater than n) in a state in which at least one of the first and second focus points is positioned between the first and second focus points in a direction intersecting the plane of incidence during the nth second process. In this case, the modified regions are formed more densely in the direction intersecting the plane of incidence, improving processing quality.

[0017] In the laser processing apparatus according to the present invention, after performing the second process n times (n is an integer equal to or greater than 1), the control unit may perform the second process n+1 times in a state in which the first focusing point is positioned closer to the incident surface than the position of the first focusing point in the direction intersecting the incident surface during the nth second process. In this way, by performing the second process by aligning the focusing points in order from the side farthest from the incident surface, the modified region can be more suitably formed.

[0018] The laser processing apparatus according to the present invention may further include an input unit for receiving input and a display unit for displaying information, wherein the input unit receives an input of a first distance before the first process, and the control unit, before the first process, may cause the display unit to display information prompting the user to confirm the first input value if the first input value, which is the input value of the first distance received by the input unit, is smaller than a first threshold, and may execute the first process if the first input value is equal to or greater than the first threshold. In this case, in the first process, it is ensured that the first and second focusing points are equal to or greater than the threshold, thereby reliably increasing the amount of crack growth and improving the processing speed.

[0019] In the laser processing device according to the present invention, the input unit may accept an input of the second distance before the second process, and the control unit may, before the second process, cause the display unit to display information prompting the user to confirm the second input value if the second input value, which is the input value of the second distance accepted by the input unit, is greater than a second threshold, and may execute the second process if the second input value is equal to or less than the second threshold. In this case, in the second process, it is ensured that the distance between the first and second focal points is equal to or less than the threshold, thereby reliably improving processing quality. [Effects of the Invention]

[0020] According to the present invention, a laser processing apparatus and a laser processing method are provided that can improve the processing speed while suppressing a decrease in processing quality. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a laser processing device according to one embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of the laser irradiation unit shown in FIG. [Figure 3] FIG. 3 is a schematic diagram showing the configuration of the laser irradiation unit shown in FIG. [Figure 4] FIG. 4 is a cross-sectional photograph showing the processing result when the distance Dx is set to 0. [Figure 5] FIG. 5 is a cross-sectional photograph showing another processing result when the distance Dx is set to 0. [Figure 6] FIG. 6 is a flowchart showing an example of the laser processing method according to this embodiment. [Figure 7] FIG. 7 is a plan view showing one step of the laser processing method shown in FIG. [Figure 8] FIG. 6 is a diagram illustrating the object shown in FIG. [Figure 9] FIG. 9 is a diagram showing one step of the laser processing method shown in FIG. [Figure 10] FIG. 10 is a diagram showing one step of the laser processing method shown in FIG. [Figure 11] FIG. 11 is a diagram showing an example of a setting screen displayed on the input receiving unit. [Figure 12] FIG. 12 is a diagram showing one step of the laser processing method shown in FIG. [Figure 13] FIG. 13 is a diagram showing one step of the laser processing method shown in FIG. [Figure 14] FIG. 14 is a photograph showing the cross section after the modified region was formed. [Figure 15] FIG. 15 is a diagram showing one step of the peeling process. [Figure 16] FIG. 16 is a diagram showing one step of the peeling process. DETAILED DESCRIPTION OF THE INVENTION

[0022] An embodiment will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and redundant explanations may be omitted. Each drawing may also show a Cartesian coordinate system defined by the X-axis, Y-axis, and Z-axis.

[0023] Fig. 1 is a schematic diagram showing the configuration of a laser processing apparatus according to one embodiment. As shown in Fig. 1, the laser processing apparatus 1 includes a stage (support unit) 2, a laser irradiation unit 3, drive units (movement units) 4 and 5, and a control unit 6. The laser processing apparatus 1 is an apparatus for forming a modified region 12 in an object 11 by irradiating the object 11 with laser light L.

[0024] The stage 2 supports the object 11, for example, by holding a film attached to the object 11. The stage 2 is rotatable about an axis parallel to the Z direction. The stage 2 may be movable along both the X and Y directions. The X and Y directions are first and second horizontal directions that intersect (are perpendicular to) each other, and the Z direction is the vertical direction.

[0025] The laser irradiation unit 3 focuses laser light L, which is transparent to the object 11, and irradiates the object 11 with the focused laser light. When the laser light L is focused inside the object 11 supported by the stage 2, the laser light L is particularly absorbed in a portion corresponding to the focusing point C of the laser light L, and a modified region 12 is formed inside the object 11.

[0026] The modified region 12 is a region whose density, refractive index, mechanical strength, and other physical properties differ from those of the surrounding unmodified region. Examples of the modified region 12 include a melt-treated region, a crack region, a dielectric breakdown region, and a refractive index change region. The modified region 12 can be formed so that a crack extends from the modified region 12 to the incident side of the laser light L and to the opposite side. Such modified region 12 and cracks are used, for example, to cut the object 11.

[0027] As an example, when the stage 2 is moved along the X direction and the focal point C is moved along the X direction relative to the object 11, multiple modified spots 12s are formed in a row along the X direction. One modified spot 12s is formed by irradiating one pulse of laser light L. A row of modified regions 12 is a collection of multiple modified spots 12s lined up in a row. Adjacent modified spots 12s may be connected to each other or separated from each other depending on the relative moving speed of the focal point C with respect to the object 11 and the repetition frequency of the laser light L.

[0028] The driving unit 4 rotates the stage 2 about an axis parallel to the Z direction as a rotation axis. The driving unit 4 may move the stage 2 along both the X direction and the Y direction. The driving unit 5 supports the laser irradiation unit 3. The driving unit 5 moves the laser irradiation unit 3 along the X direction, the Y direction, and the Z direction.

[0029] The control unit 6 controls the operations of the stage 2, the laser irradiation unit 3, and the drive units 4 and 5. The control unit 6 has a processing unit 61, a storage unit 62, and an input reception unit (display unit, input unit) 63. The processing unit 61 is configured as a computer device including a processor, memory, storage, communication devices, etc. In the processing unit 61, the processor executes software (programs) loaded into the memory, etc., and controls reading and writing of data from the memory and storage, as well as communication via the communication devices. The storage unit 62 is, for example, a hard disk, and stores various data. The input reception unit 63 is an interface unit that displays various information and receives input of various information from the user. In this embodiment, the input reception unit 63 constitutes a GUI (Graphical User Interface).

[0030] 2 and 3 are schematic diagrams showing the configuration of the laser irradiation unit shown in Fig. 1. As shown in Figs. 2 and 3, the laser irradiation unit 3 has a light source 31, a spatial light modulator 32, and a condenser lens 33. The light source 31 outputs laser light L, for example, by a pulse oscillation method. Note that the laser irradiation unit 3 may be configured not to have the light source 31, but to introduce the laser light L from outside the laser irradiation unit 3.

[0031] The spatial light modulator 32 modulates the laser light L output from the light source 31. The spatial light modulator 32 is a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM). The condenser lens 33 condenses the laser light L modulated by the spatial light modulator 32. The spatial light modulator 32 includes a liquid crystal layer (not shown) and modulates the laser light L according to a modulation pattern displayed on the liquid crystal layer. Here, the spatial light modulator 32 displays at least a branching pattern for branching the laser light L into multiple beams (here, two beams). As a result, the laser light L incident on the spatial light modulator 32 is branched into two laser beams L1 and L2 by the spatial light modulator 32 and condensed by the condenser lens 33 to form a first condensing point C1 and a second condensing point C2.

[0032] This point will be explained in more detail. The spatial light modulator 32 branches the laser light L so that the first focal point C1 and the second focal point C2 are formed at different positions in at least the Z direction intersecting the back surface 11b, which is the incident surface of the laser light L in the object 11. Therefore, by moving the first focal point C1 and the second focal point C2 relative to the object 11, two rows of modified regions 121 and modified regions 122 are formed as the modified region 12 at different positions in the Z direction.

[0033] The modified region 121 corresponds to the laser beam L1 and its first focal point C1, and the modified region 122 corresponds to the laser beam L2 and its second focal point C2. The first focal point C1 and the modified region 121 are located on the opposite side of the back surface 11b (on the front surface 11a side of the object 11) with respect to the second focal point C2 and the modified region 122. The spatial light modulator 32 is capable of varying the distance Dz (vertical branching amount) between the first focal point C1 and the second focal point C2 in the Z direction.

[0034] Furthermore, when branching the laser beam L into laser beams L1 and L2, the spatial light modulator 32 is capable of changing the distance Dx (amount of horizontal branching) in the horizontal direction (X direction in the illustrated example) between the first focal point C1 and the second focal point C2. In the example of Fig. 2, the spatial light modulator 32 sets the distance Dx to be greater than 0 so that the first focal point C1 is positioned forward of the second focal point C2 in the X direction (machining progress direction). In the example of Fig. 3, the spatial light modulator 32 sets the distance Dx between the first focal point C1 and the second focal point C2 to 0.

[0035] FIG. 4 is a cross-sectional photograph showing the processing result when the distance Dx is set to 0. The processing result in FIG. 4 is obtained when the output of the laser light L is 2 W (the pulse energy of each of the laser lights L1 and L2 is 10 μJ), the output ratio of the laser light L1 to the laser light L2 is 50:50, and the distance Dz (vertical branching amount) is changed from 15 μm to 70 μm. As shown in FIG. 4, when the distance Dx is set to 0, when the distance Dz is 15 μm and 20 μm, a region 12N where the modified region 12 (modified region 121) is not formed on the surface 11a side is generated. However, when the distance Dz is set to 25 μm or more, the modified region 121 is formed throughout. Note that the specific irradiation conditions of the laser lights L1 and L2 in the example of FIG. 4 are a frequency of 80 kHz, a processing speed of 430 mm / s, a pulse pitch of 5.375 μm, and a pulse width of 700 ns.

[0036] On the other hand, Figure 5 is a cross-sectional photograph showing another processing result when the distance Dx is set to 0. The processing result in Figure 5 is a processing result when the output of the laser light L is 4 W (the pulse energy of each of the laser lights L1 and L2 is 20 μJ), the output ratio of the laser light L1 to the laser light L2 is 50:50, and the distance Dz is changed from 15 μm to 70 μm. As shown in Figure 5, compared to the example in Figure 4, by increasing the output of the laser light L, the area 12N on the surface 11a where the modified region 12 is not formed is reduced, and the modified region 12 is formed over almost the entire surface for all distances Dz from 15 μm to 70 μm. Note that the specific irradiation conditions of the laser lights L1 and L2 in the example in Figure 5 are a frequency of 80 kHz, a processing speed of 430 mm / s, a pulse pitch of 5.375 μm, and a pulse width of 700 ns.

[0037] According to the inventor's findings, the closer the distance Dx is to 0, the more difficult it is to form the modified region 12 (modified region 121) on the front surface 11a due to the influence of the second focusing point C2 and the modified region 12 (modified region 122) on the back surface 11b. Therefore, as described above, the modified region 121 is sufficiently formed when the distance Dx is set to 0, and therefore, when the distance Dx is greater than 0 (example of FIG. 2), the modified region 121 can be more reliably formed. In particular, by setting the distance Dx to 8 μm or more, the influence of the second focusing point C2 and the modified region 122 is reduced, and the modified region 121 can be reliably formed.

[0038] As described above, the laser irradiation unit 3 can irradiate the object 11 supported on the stage 2 with the laser beams L1 and L2 while forming a first focal point C1 of the laser beam L1 and a second focal point C2 of the laser beam L2 located closer to the incident surface (back surface 11b) of the object 11 than the first focal point C1. In particular, the laser irradiation unit 3 can split the laser beam L into the laser beams L1 and L2, and the distances between the first focal point C1 and the second focal point C2 in each direction are variable.

[0039] Next, the laser processing apparatus 1 will be described in detail while citing an example of a laser processing method executed by the laser processing apparatus 1. FIG. 6 is a flowchart showing an example of a laser processing method according to this embodiment. Here, the laser processing apparatus 1 performs trimming processing and radiation cutting processing on the object 11. The trimming processing is processing for forming a modified region in order to remove unnecessary portions in the object 11. The radiation cutting processing is processing for forming a modified region in order to separate the unnecessary portions to be removed by the trimming processing. Here, first, the object 11 is supported on the stage 2 as shown in FIG. 7.

[0040] FIG. 8 is a diagram showing the object shown in FIG. 8(a) is a plan view, and FIG. 8(b) is a side view. As shown in FIGS. 7 and 8, the object 11 here includes, for example, a semiconductor wafer formed in a disk shape. However, the object 11 is not particularly limited and can be formed in various shapes using various materials. As an example, a functional element (not shown) is formed on the surface 11a of the object 11. The functional element is, for example, a light-receiving element such as a photodiode, a light-emitting element such as a laser diode, a circuit element such as a memory, etc. The object 11 is supported by the stage 2 so that the back surface 11b, which is opposite the surface 11a, faces the laser irradiation unit 3.

[0041] The target object 11 has an effective area R (first portion) and a removal area E (second portion). The effective area R is a device area in which a functional element is formed. The effective area R is, for example, a disk-shaped portion including a central portion when viewed in the thickness direction of the target object 11 (the direction from the front surface 11a toward the back surface 11b, the Z direction). In other words, the effective area R is a portion located more inward in the target object 11 than the removal area E.

[0042] The removal area E is a portion located outside the effective area R of the object 11 and includes the outer edge of the object 11. Here, the removal area E is a portion of the object 11 other than the effective area R, and is a ring-shaped portion that surrounds the effective area R when viewed from the Z direction. The removal area E includes the peripheral portion (bevel portion of the outer edge) of the object 11 when viewed from the Z direction. The removal area E is a radiation cut area that is the target of radiation cut processing.

[0043] A line (first line) M1 and a line (second line) M2 are set on the object 11. The line M1 is a line intended to form a modified region in trimming processing. When viewed from the Z direction, the line M1 extends in an annular (ring-like) shape on the boundary between the effective region R and the removal region E. When viewed from the Z direction, the line M1 coincides with the outer edge of the effective region R (the inner edge of the removal region E). In other words, the line M1 indicates the boundary between the effective region R and the removal region E. The line M2 is a line intended to form a modified region in radial cutting processing. When viewed from the Z direction, the line M2 extends linearly (radially) along the radial direction of the object 11.

[0044] When viewed from the Z direction, line M2 extends from the outer edge of object 11 in removal area E toward the inside of object 11, reaching the boundary between effective area R and removal area E. Line M2 does not reach within effective area R, but is stopped at the intersection with line M1. Of line M2, lines M2a and M2b are arranged on a straight line. Of line M2, lines M2c and M2d are arranged on a straight line in a direction intersecting (orthogonal to) lines M2a and M2b. Lines M1 and M2 can be set by control unit 6. Lines M1 and M2 are, for example, virtual lines or lines specified by coordinates.

[0045] First, trimming is performed on the target object 11 as described above. To do this, first, the control unit 6 accepts input of processing conditions for the trimming (step S1). More specifically, in step S1, the control unit 6 causes the input accepting unit 63 to display information prompting the input of processing conditions. The input accepting unit 63 accepts input of the processing conditions. At this time, the input accepting unit 63 accepts input of at least a distance Dx (first distance) in the trimming. An example of the input value of the distance Dx is 110 μm.

[0046] The input receiving unit 63 can also receive input of other conditions, similar to the values ​​shown in FIG. 11 (described later). For example, the input receiving unit 63 receives input of the number of focal points, the number of passes, the processing speed, the pulse width, and the frequency as basic processing conditions. The number of focal points is the number of branches of the laser light L by the spatial light modulator 32, and is mainly 2 in this example. The number of passes is the number of trimming processes performed on the line M1, i.e., the number of first processes (described later) performed on the line M1, and is the number of scans of the laser lights L1 and L2, and is 4, for example. Therefore, in the trimming process, modified regions 12 are formed in rows whose number corresponds to the number of focal points multiplied by the number of passes in the Z direction.

[0047] Furthermore, the input receiving unit 63 can receive input of detailed processing conditions for each scan. In this case, since 4 is input as the number of passes, the input receiving unit 63 can receive input of processing conditions for each of the four scans. An example of input values ​​for each scan is as follows:

[0048] [First scan] ZH (lower point): 176 ZH(top point):160 Processing output (lower point): 2.6W Processing output (upper point): 2.6W Frequency: 120kHz Speed: 800mm / s. Pulse width: 700nsec Vertical branch distance (VD): 16 [Second scan] ZH (lower point): 140 ZH(top point):115 Processing output (lower point): 2.6W Processing output (upper point): 2.6W Frequency: 120kHz Speed: 800mm / s Pulse width: 700nsec Vertical branch distance (VD): 25 [Third scan] ZH (lower point): 78 ZH(top point):40 Processing output (lower point): 2.6W Processing output (upper point): 2.6W Frequency: 120kHz Speed: 800mm / s Pulse width: 700nsec Vertical branch distance (VD): 38 [4th scan] (1 focus in this case) ZH (lower point): 22 ZH(upper point):- Processing output (lower point): 2.6W Processing output (upper point):- Frequency: 120kHz Speed: 800mm / s Pulse width: 700nsec Vertical branch distance (VD):-

[0049] ZH (lower point) corresponds to the position of the first focal point C1 in the Z direction. ZH (upper point) corresponds to the position of the second focal point C2 in the Z direction. ZH (lower point) and ZH (upper point) are based on the rear surface 11b, which is the incident surface of the laser beams L1 and L2, so the larger the numerical value, the farther from the rear surface 11b. The vertical branching distance (VD) is the distance Dz, which corresponds to the difference between ZH (lower point) and ZH (upper point). The processing output (lower point) is the output of the laser beam L1, and the processing output (upper point) is the output of the laser beam L2. Here, the same value is input for the processing output (lower point) and the processing output (upper point). Therefore, the output ratio of the laser beams L1 and L2 is 50:50.

[0050] In the next step, the control unit 6 determines whether the first input value, which is the input value of the distance Dx received by the input receiving unit 63, is equal to or greater than a first threshold value (step S2). The first threshold value is, for example, 50 μm. If the determination result in step S2 shows that the first input value of the distance Dx is equal to or greater than the first threshold value (step S2: YES), the control unit 6 sets (generates) a branch pattern according to the first input value of the distance Dx (step S3). Note that if the determination result in step S2 shows that the first input value of the distance Dx is not equal to or greater than the first threshold value (step S2: NO), the control unit 6 displays information on the input receiving unit 63 prompting the user to confirm the first input value (step S9), and the process returns to step S1 to prompt the user to re-input the distance Dx.

[0051] In the next step, the control unit 6 actually performs processing (step S4: laser irradiation step, first irradiation step). More specifically, as shown in FIGS. 9 and 10(a), the control unit 6 controls the drive unit 5 (and / or drive unit 4) to move the laser irradiation unit 3 so that the first focal point C1 and the second focal point C2 are located on the line M1 when viewed from the Z direction. At the same time, the control unit 6 controls the spatial light modulator 32 to display a branching pattern on the spatial light modulator 32 so that the first focal point C1 is located forward of the second focal point C2 by a distance Dx in the X direction and the second focal point C2 is located on the back surface 11b side by a distance Dz from the first focal point C1. Note that FIG. 9(a) is a plan view, and FIG. 9(b) is a cross-sectional view taken along the line B1-B1 in FIG. 9(a). 10(a) and (c) are side views, and FIG. 10(b) is a plan view.

[0052] Next, in step S4, the control unit 6 controls the drive unit 4 to rotate the stage 2 about the rotation axis A, and also controls the laser irradiation unit 3 to irradiate the object 11 with laser beams L1 and L2. The rotation axis A is the center of the object 11 and the line M1. As a result, the first and second focus points C1 and C2 are moved relative to the object 11 in a direction along the line M1 that is opposite to the rotation direction AR of the stage 2 (here, the X direction). That is, here, the distance Dx is the distance between the first and second focus points C1 and C2 in the direction along the line M1 (the tangential direction of the line M1).

[0053] Here, the control unit 6 controls the start and stop of irradiation of the laser beams L1 and L2 based on the rotation angle of the stage 2 while rotating the stage 2 at a constant rotation speed. The control unit 6 irradiates the object 11 with the laser beams L1 and L2 along the entire circumference of the line M1. As a result, a modified region 12 (modified region 121) corresponding to the laser beam L1 and the first focal point C1, and a modified region 12 (modified region 122) corresponding to the laser beam L2 and the second focal point C2 are formed on the line M1 at least inside the object 11.

[0054] That is, in the laser processing apparatus 1, the drivers 4 and 5 are movement mechanisms that move the stage 2 so that the first and second focal points C1 and C2 move relative to the object 11. Furthermore, the controller 6 controls the laser irradiation unit 3 and the drivers 4 and 5. Then, in a state in which the distance Dx between the first and second focal points C1 and C2 in the direction along the line M1 is set to a first input value (first distance), the controller 6 executes a first process that controls the laser irradiation unit 3 and the drivers 4 and 5 so that the object 11 is irradiated with laser light L while relatively moving the first and second focal points C1 and C2 along the line M1.

[0055] The control unit 6 controls the drive unit 5 to move the laser irradiation unit 3 in the Z direction, thereby varying the Z-direction positions of the first focal point C1 and the second focal point C2, thereby executing the first process multiple times (the number of passes described above). As a result, as shown in (b) and (c) of FIG. 10, the modified region 12 and cracks extending from the modified region 12 can be formed from the front surface 11a to the back surface 11b of the object 11. However, the modified region 12 and the cracks may reach at least one of the front surface 11a and the back surface 11b, or may not reach at least one of the front surface 11a and the back surface 11b. This completes the trimming process. Subsequently, the radiation cutting process is performed.

[0056] In the next step, the control unit 6 accepts input of processing conditions for the radial cut processing (step S5). More specifically, in this step S5, the control unit 6 causes the input accepting unit 63 to display information prompting the input of processing conditions. The input accepting unit 63 accepts input of processing conditions. At this time, the input accepting unit 63 accepts input of at least the distance Dx (second distance) in the radial cut processing. The input accepting unit 63 also accepts input of various other processing conditions. This point will be described in detail.

[0057] 11 is a diagram showing an example of a setting screen displayed on the input receiving unit. As shown in FIG. 11, input of wafer thickness, LBA-X offset, LBA-Y offset, and horizontal branching distance (distance Dx) is received as selection content Q. The LBA-X offset is the offset amount in the X direction (direction along line M1) between the center of a spherical aberration correction pattern, among various patterns displayed on the spatial light modulator 32, and the center of the entrance pupil plane of the condenser lens 33. Similarly, the LBA-Y offset is the offset amount in the Y direction (direction intersecting line M1) between the center of the spherical aberration correction pattern and the center of the entrance pupil plane of the condenser lens 33. Here, 0 is input as the horizontal branching distance (distance Dx).

[0058] The input receiving unit 63 also receives input of the number of focal points, number of passes, processing speed, pulse width, and frequency as basic processing conditions H0. The number of focal points is the number of branches of the laser light L by the spatial light modulator 32, which is 2 in this example. The number of passes is the number of times the radiation cut processing is performed on one line M2, i.e., the number of times the second process is performed on one line M2, and is the number of scans of the laser lights L1 and L2. Therefore, in the radiation cut processing, modified regions 12 are formed in the Z direction in a number of rows corresponding to the number of focal points multiplied by the number of passes. The processing speed is the speed of relative movement of the first focal point C1 and the second focal point C2 with respect to the target object 11.

[0059] Furthermore, the input receiving unit 63 receives input of detailed processing conditions for each scan. Here, since 6 is input as the number of passes, the input receiving unit 63 receives input of processing conditions H1 to H6 for each of the six scans. In the processing conditions H1 to H6, ZH (lower point) corresponds to the position of the first focusing point C1 in the Z direction. ZH (upper point) corresponds to the position of the second focusing point C2 in the Z direction. ZH (lower point) and ZH (upper point) are based on the back surface 11b, which is the incident surface of the laser beams L1 and L2, so the larger the numerical value, the farther from the back surface 11b.

[0060] The vertical branch distance (VD) is the distance Dz, which corresponds to the difference between ZH (lower point) and ZH (upper point). The processing output (lower point) is the output of laser light L1, and the processing output (upper point) is the output of laser light L2. Here, the same value is input for the processing output (lower point) and the processing output (upper point). Therefore, the output ratio of laser light L1 to laser light L2 is 50:50.

[0061] In the next step, the control unit 6 determines whether the second input value, which is the input value of the distance Dx (for cutting radiation) received by the input receiving unit 63, is equal to or less than a second threshold value (step S6). The second threshold value is a value smaller than the first threshold value used in the trimming process (first process), e.g., 15 μm. If the determination result in step S6 is that the second input value of the distance Dx is equal to or less than the second threshold value, the control unit 6 sets (generates) a branch pattern according to the second input value of the distance Dx (step S7). Note that if the determination result in step S6 is that the second input value of the distance Dx is not equal to or less than the second threshold value (step S6: NO), the control unit 6 displays information on the input receiving unit 63 prompting the user to confirm the second input value (step S10) and proceeds to step S5 to prompt the user to re-input the distance Dx.

[0062] In the subsequent steps, actual processing is performed (step S8: laser irradiation step, second irradiation step). More specifically, as shown in FIGS. 12 and 13(a), the control unit 6 controls the drive unit 5 (and / or drive unit 4) to move the laser irradiation unit 3 so that, when viewed from the Z direction, the first focal point C1 and the second focal point C2 enter the object 11 from outside the object 11 and move along the line M2. At the same time, the control unit 6 controls the spatial light modulator 32 to display a branching pattern on the spatial light modulator 32 so that the second focal point C2 is located a distance Dz away from the first focal point C1 on the rear surface 11b side. Here, as described above, 0 is input as the second input value of the distance Dx. Therefore, the positions of the first focal point C1 and the second focal point C2 along the line M2 are aligned. Note that Fig. 12(a) is a plan view, and Fig. 12(b) is a cross-sectional view taken along line B2-B2 in Fig. 12(a). Fig. 13(a) is a side view, and Fig. 13(b) is a plan view.

[0063] Here, the control unit 6 irradiates the object 11 with laser beams L1 and L2 while relatively moving the first and second focusing points C1 and C2 for one line M2a of the lines M2 from the outer edge of the object 11 toward the inside of the object 11. The object 11 is positioned so that the line M2a is along the X direction. As a result, the first and second focusing points C1 and C2 are relatively moved in the X direction. That is, here, the distance Dx is the distance between the first and second focusing points C1 and C2 in the X direction along the line M2a (here, it is 0).

[0064] In this way, the control unit 6 sets the distance Dx between the first focal point C1 and the second focal point C2 in the direction along the line M2 (line M2a) to a second input value (second distance) smaller than the distance Dx (first distance) during trimming processing, and then executes a second process to control the laser irradiation unit 3 and the drive unit 5 (and / or drive unit 4) to irradiate the target object 11 with laser light L1, L2 while moving the first focal point C1 and the second focal point C2 relatively along the line M2.

[0065] The control unit 6 continues the relative movement of the first and second focusing points C1 and C2, and turns off the irradiation of the laser beams L1 and L2 when the first and second focusing points C1 and C2 reach an intersection of the line M2a and the line M1. Thereafter, the control unit 6 turns on the irradiation of the laser beams L1 and L2 when the position (position in the X direction) where the first and second focusing points C1 and C2 are formed reaches an intersection of the line M1 and another line M2b of the line M2 that is collinear with the line M2a. As with the line M2a, the control unit 6 irradiates the target 11 with the laser beams L1 and L2 while moving the first and second focusing points C1 and C2 relatively in the X direction on the line M2b. Furthermore, the control unit 6 similarly performs the second process on further lines M2c and M2d of the line M2.

[0066] As described above, the number of scans (number of passes) of the laser beams L1 and L2 per line M2 is input as 6. Therefore, the control unit 6 controls the drive unit 5 to move the laser irradiation unit 3 in the Z direction for one line M2, thereby executing the second process multiple times (six times in this case) while varying the positions of the first and second focusing points C1 and C2 in the Z direction.

[0067] In particular, when the control unit 6 performs the second process multiple times on one line M2, after performing the second process for the nth time (n is an integer greater than 1), it can perform the second process for the mth time (m is an integer greater than n) in a state in which at least one of the first focusing point C1 and the second focusing point C2 is positioned between the first focusing point C1 and the second focusing point C2 in the Z direction during the nth second processing.

[0068] 11, a value between the ZH (lower point) and ZH (upper point) values ​​in the first scan is input as the ZH (lower point) value in the second scan. Also, a value smaller than the ZH (upper point) value in the first scan is input as the ZH (upper point) value in the second scan. The same applies to the relationship between the fourth and third scans, and the relationship between the sixth and fifth scans.

[0069] In other words, in the example of Figure 11, after the control unit 6 performs the second process for the first, third, and fifth times, it performs the second process for the second, fourth, and sixth times while positioning only the first focusing point C1 at a position between the first focusing point C1 and the second focusing point C2 in the Z direction during the first, third, and fifth times of the second process.

[0070] In other words, in the example of Figure 11, after performing the second process for the 2n-1th time (n is an integer greater than or equal to 1), the control unit 6 positions the first focusing point C1 between the positions of the first focusing point C1 and the second focusing point C2 in the Z direction during the 2n-1th second process, and performs the 2nth second process in a state in which the second focusing point C2 is positioned closer to the back surface 11b than the position of the second focusing point C2 in the Z direction during the 2n-1th second process.

[0071] 11, with respect to each of the first and second focusing points C1 and C2, the positions in the Z direction are sequentially moved toward the rear surface 11b from the first to sixth times. That is, in the example of FIG. 11, after performing the second process for an nth time (n is an integer greater than or equal to 1), the control unit 6 performs the second process for an (n+1) time in a state in which the first focusing point C1 is positioned closer to the rear surface 11b in the Z direction than the position of the first focusing point C1 in the nth time in the second process. Furthermore, after performing the second process for an nth time (n is an integer greater than or equal to 1), the control unit 6 performs the second process for an (n+1) time in a state in which the second focusing point C2 is positioned closer to the rear surface 11b in the Z direction than the position of the second focusing point C2 in the nth time in the second process.

[0072] As a result, modified regions 12 are formed for all lines M2, as shown in (b) of Figure 13. In particular, as shown in (a) of Figure 14, a modified region 12 (modified region 121) on the surface 11a side of the second scan P2 is formed between a pair of modified regions 12 (modified regions 121, 122) formed in the first scan P1, a modified region 12 on the surface 11a side of the fourth scan P4 is formed between a pair of modified regions 12 formed in the third scan P3, and a modified region 12 on the surface 11a side of the sixth scan P2 is formed between a pair of modified regions 12 formed in the fifth scan P5.

[0073] This forms a modified region 12 and a crack extending from the modified region 12 from the front surface 11a to the back surface 11b of the object 11. However, the modified region 12 and the crack may reach at least one of the front surface 11a and the back surface 11b, or may not reach at least one of the front surface 11a and the back surface 11b. Figure 14 is a photograph showing a cross section after the modified region has been formed.

[0074] 15, the removal area E is separated and removed (removed) using, for example, a jig or air, with the modified area 12 on the line M1 as the boundary, thereby forming an object 11A from the object 11 (the effective area R is cut out). After that, the laser processing device 1 can perform peeling. Next, the peeling process will be described. Note that (a) in FIG. 15 is a plan view, (b) is a side view, and (c) is a side view.

[0075] As shown in FIG. 15, a virtual surface M3 is set on the object 11A as a surface to be peeled. The virtual surface M3 is a surface on which a modified region is to be formed by peeling. The virtual surface M3 is a surface opposite to the back surface 11b, which is the laser light incident surface of the object 11A. The virtual surface M3 is a surface parallel to the back surface 11b and has, for example, a circular shape. The virtual surface M3 is a virtual region and is not limited to a flat surface, but may also be a curved surface or a three-dimensional surface. The setting of the virtual surface M3 can be performed by the control unit 6. The virtual surface M3 may be specified by coordinates.

[0076] In peeling, the control unit 6 controls the drive unit 4 to rotate the stage 2 at a constant rotational speed while irradiating the laser beam L3 from the laser irradiation unit 3. At the same time, the control unit 6 controls the drive unit 5 to move the laser irradiation unit 3 so that the focal point C3 of the laser beam L3 moves from the outer edge of the imaginary plane M3 to the inside. As a result, as shown in FIG. 16(a), a modified region 12 is formed inside the target object 11A along the imaginary plane M3, extending in a spiral shape (involute curve) centered on the position of the rotation axis A (see FIG. 9). The formed modified region 12 includes multiple modified spots. Note that FIG. 16(a) is a plan view, and the others are side views.

[0077] Next, as shown in (b) and (c) of FIG. 16, a portion of the object 11A is peeled off, for example, using a suction tool, with the modified region 12 extending across the virtual plane M3 as the boundary. The object 11A may be peeled off on the stage 2 or moved to a dedicated peeling area. The object 11A may be peeled off using air blow or tape. If the object 11A cannot be peeled off by external stress alone, the modified region 12 may be selectively etched with an etching solution (e.g., KOH or TMAH) that reacts with the object 11A. This makes it possible to easily peel off the object 11A. As shown in (b) of FIG. 16, the peeled surface 11h of the object 11A is subjected to finish grinding or polishing with an abrasive material KM such as a grindstone. If the object 11A is peeled off by etching, the polishing process can be simplified. As a result, the semiconductor device 11B is obtained.

[0078] As described above, in the laser processing apparatus 1 and the laser processing method thereof, a line M1 extending annularly on the boundary between the effective area R located inside the effective area R and the removal area E located outside the effective area R, and a line M2 extending from the outer edge of the object 11 toward the inside of the object 11 in the removal area E to reach the boundary are set on the object 11. Then, in each of processing along the line M1 (trimming processing) and processing along the line M2 (radiation cutting processing), the laser light L is irradiated onto the object 11 while forming a first focal point C1 and a second focal point C2 of the laser light L on the object 11. At this time, when processing along the line M1, the distance Dx along the line M1 between the first focal point C1 and the second focal point C2 is relatively large. This allows for an improvement in processing speed. On the other hand, when processing along the line M2, the distance Dx along the line M2 between the first focal point C1 and the second focal point C2 is relatively small. This allows for a reduction in processing quality.

[0079] 14(b) is a photograph showing a cross section of the boundary portion between the effective area R and the removal area E. As shown in FIG. 14(b), when processing along the line M2, the distance Dx between the first focus point C1 and the second focus point C2 is set relatively small (for example, 0), so that the end of the modified area 12 corresponding to the first focus point C1 and the end of the modified area 12 corresponding to the second focus point C2 are aligned. That is, in this case, it is possible to prevent one of the first focus point C1 and the second focus point C2 from entering the effective area R and forming a modified area 12 within the effective area R, or to prevent the other of the first focus point C1 and the second focus point C2 from reaching the effective area R and creating an unmodified area in the removal area E.

[0080] Furthermore, in the laser processing apparatus 1, the control unit 6 can perform the second process multiple times for one line M2 while varying the positions of the first and second focus points C1 and C2 in the Z direction intersecting with the back surface 11b. In this way, it is effective to perform the second process multiple times for one line M2, at least for the second process in which the distance Dx between the first and second focus points C1 and C2 is relatively small.

[0081] Furthermore, in the laser processing apparatus 1, after performing the second process for the nth time (n is an integer greater than or equal to 1), the control unit 6 can perform the second process for the mth time (m is an integer greater than n) in a state in which at least one of the first focus point C1 and the second focus point C2 is positioned between the first focus point C1 and the second focus point C2 in the Z direction during the nth time of the second process. In this case, the modified regions 12 are formed more densely in the Z direction, improving the processing quality.

[0082] Furthermore, in the laser processing apparatus 1, after performing the second process for the nth time (n is an integer greater than or equal to 1), the control unit 6 can perform the second process for the (n+1)th time in a state in which the first focal point C1 is positioned closer to the back surface 11b in the Z direction than the first focal point C1 was in in the nth time of the second process. In this way, by performing the second process by aligning the focal points in order from the side farthest from the back surface 11b, the modified region 12 can be formed more suitably.

[0083] The laser processing apparatus 1 further includes an input receiving unit 63 for receiving input and displaying information. The input receiving unit 63 receives an input of a distance Dx in the first process before the first process. Before the first process, if a first input value, which is the input value of the distance Dx received by the input receiving unit 63, is smaller than a first threshold, the control unit 6 causes the input receiving unit 63 to display information prompting the user to confirm the first input value, and if the first input value is equal to or greater than the first threshold, the control unit 6 executes the first process. Therefore, in the first process, the distance Dx is ensured to be equal to or greater than the threshold, which reliably increases the amount of crack growth and improves the processing speed.

[0084] Furthermore, in the laser processing apparatus 1, the input accepting unit 63 accepts an input of the distance Dx in the second process before the second process. Before the second process, if the second input value, which is the input value of the distance Dx accepted by the input accepting unit 63, is greater than a second threshold, the control unit 6 causes the input accepting unit 63 to display information prompting the user to confirm the second input value, and if the second input value is equal to or less than the second threshold, the control unit 6 executes the second process. Therefore, in the second process, it is ensured that the distance Dx between the first focus point C1 and the second focus point C2 is equal to or less than the threshold, thereby reliably improving the processing quality.

[0085] The above embodiment is an explanation of one mode of the present invention, therefore, the present invention is not limited to the above-described mode and can be arbitrarily modified.

[0086] 6, in both the first process and the second process, the input of at least the distance Dx is received, and a branching pattern corresponding to the received distance Dx is set and displayed on the spatial light modulator 32. However, the branching pattern may be set automatically. That is, in the laser processing apparatus 1, the branching pattern can be set automatically in each of the first process and the second process so that the distance Dx in the first process is relatively larger than the distance Dx in the second process (in other words, so that the distance Dx in the second process is relatively smaller than the distance Dx in the first process), and the first process and the second process can be executed.

[0087] In the above embodiment, the laser beam L is split into two laser beams L1 and L2 to form the first focal point C1 and the second focal point C2. However, the laser processing apparatus 1 may split the laser beam L into three or more laser beams to form respective focal points. In that case, it is sufficient that the relationship of distance Dx in the first process > distance Dx in the second process is satisfied for two of the three or more focal points.

[0088] Furthermore, in the above embodiment, the line M1 extends on the boundary between the effective region R, which is the device region where the functional elements are formed, and the removal region E outside of it. However, the line M1 may be set on the boundary between an area wider than the device region as described above (an area obtained by expanding the above-mentioned effective region R toward the removal region E) and an area even further outside of that area. Alternatively, the line M1 may be set on the boundary between any first and second portions of the object 11, regardless of the effective region R and the removal region E. [Explanation of symbols]

[0089] 1...laser processing device, 2...stage (support part), 3...laser irradiation part, 4, 5...drive part (movement mechanism), 6...control part, 11...target object, 63...input receiving part (input part, display part), C1...first focusing point, C2...second focusing point, Dx...distance, L, L1, L2...laser light, M1...line (first line), M2...line (second line).

Claims

1. A laser processing device for irradiating a target with laser light to form a modified region, a support portion for supporting the object; a laser irradiation unit for irradiating the object supported by the support unit with the laser light while forming a first focusing point of the laser light and a second focusing point of the laser light that is positioned closer to the incident surface of the object than the first focusing point; a movement mechanism that moves at least one of the support unit and the laser irradiation unit so that the first focal point and the second focal point move relative to the object; a control unit that controls the laser irradiation unit and the movement mechanism; Equipped with the object includes a first portion located inside the object when viewed from a direction intersecting the incident plane, and a second portion located outside the first portion and including an outer edge of the object, a first line extending in a ring shape on a boundary between the first portion and the second portion, and a second line extending from an outer edge of the object toward an inside of the object and reaching the boundary in the second portion, when viewed from a direction intersecting the incident surface; The control unit a first process of controlling the laser irradiation unit and the moving mechanism so as to irradiate the laser light onto the object while relatively moving the first and second focusing points along the first line, in a state in which a distance between the first focusing point and the second focusing point in a direction along the first line is set to a first distance; a second process of controlling the laser irradiation unit and the movement mechanism so that the laser light is irradiated onto the object while relatively moving the first and second focusing points along the second line, in a state in which a distance between the first focusing point and the second focusing point in a direction along the second line is set to a second distance smaller than the first distance; In the laser irradiation unit, a vertical branching amount, which is a distance between the first focusing point and the second focusing point in a direction intersecting the incident surface, is variable. Laser processing equipment.

2. the laser irradiation unit irradiates the laser beam while forming three or more focal points of the laser beam including the first focal point and the second focal point. The laser processing device according to claim 1 .

3. A laser processing method for forming a modified region by irradiating a target with laser light, comprising: a laser irradiation step of irradiating the object with the laser light while forming a first focal point of the laser light and a second focal point of the laser light that is positioned closer to an incident surface of the object than the first focal point, the object includes a first portion located inside the object when viewed from a direction intersecting the incident plane, and a second portion located outside the first portion and including an outer edge of the object, a first line extending in a ring shape on a boundary between the first portion and the second portion, and a second line extending from an outer edge of the object toward an inside of the object and reaching the boundary in the second portion, when viewed from a direction intersecting the incident surface; The laser irradiation step includes: a first irradiation step of irradiating the object with the laser light while relatively moving the first and second focusing points along the first line in a state where a distance between the first and second focusing points in a direction along the first line is set to a first distance; a second irradiation step of irradiating the object with the laser light while relatively moving the first and second focusing points along the second line in a state where a distance between the first and second focusing points in a direction along the second line is set to a second distance smaller than the first distance, In the laser irradiation step, a vertical branching amount, which is a distance between the first focusing point and the second focusing point in a direction intersecting the incident surface, is variable. Laser processing method.

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