Substrate manufacturing method and laser processing method

Abstract

The release layer helps to suppress damage to the substrate when separating a portion of the workpiece that will become the substrate from the rest of the workpiece. [Solution] A method for manufacturing a substrate having a thickness less than the thickness of a workpiece, comprising: irradiating the workpiece with a laser beam of a wavelength that penetrates the material of the workpiece so that the focal point is located inside the workpiece, while relatively moving the focal point and the workpiece, thereby forming a delamination layer inside the workpiece that includes a modified portion and cracks extending from the modified portion; and peeling off a portion of the workpiece that will become a substrate from the rest, starting from the delamination layer, wherein the irradiation conditions of the laser beam are set to form a delamination layer in which the modified portion ratio, which is the ratio of the area of ​​the modified portion to the area of ​​the delamination layer when the workpiece is viewed from above, is greater than 0% and less than or equal to 24%.

Description

Technical Field

[0004] , , , , , , , , ,

[0005] , , , , , ,

[0001] The present invention relates to a method for manufacturing a substrate for manufacturing a substrate having a thickness less than the thickness of a workpiece from the workpiece, and a laser processing method for forming a release layer including a modified portion and cracks extending from the modified portion inside the workpiece.

Background Art

[0002] A die of a semiconductor device is generally manufactured using a substrate made of a single crystal such as silicon (Si) or silicon carbide (SiC). This substrate is manufactured, for example, by forming a release layer including a modified portion and cracks extending from the modified portion inside a workpiece such as an ingot, and then separating the workpiece starting from the release layer. That is, in this case, a part of the workpiece is peeled off from the remaining part starting from the release layer to become the substrate.

[0003] Such a release layer is formed using a laser beam having a wavelength that penetrates the material of the workpiece (see, for example, Patent Document 1). Specifically, such a release layer is formed by relatively moving the condensing point and the workpiece while irradiating the workpiece with a laser beam so that the condensing point is positioned inside the workpiece.

Prior Art Documents

Patent Documents

[0004] <0​​​​​​​​​​​​​When separating a workpiece using the delamination layer as a starting point, that is, when peeling a portion of it from the rest, an external force is applied to the workpiece in such a way that it further extends the cracks formed in the delamination layer. However, if a strong external force is required for this delamination, the cracks may extend in an unexpected direction as a result of this force. In this case, the manufactured substrate may be damaged to such an extent that it cannot be used for the manufacture of semiconductor devices.

[0006] In view of this, the present invention aims to provide a method for manufacturing a substrate and a laser processing method that can suppress damage to the substrate when peeling off a portion of a workpiece that will become a substrate from the rest of the workpiece, starting from the peeling layer. [Means for solving the problem]

[0007] The inventors of the present invention have discovered that when a peel layer is formed on a workpiece in which the modified area ratio, which is the ratio of the area of ​​the modified area to the area of ​​the peel layer when the workpiece is viewed in plan, is greater than 0% and less than or equal to 24%, it is possible to suppress damage to the substrate when peeling off a part of the workpiece from the rest of the workpiece starting from the peel layer, and have completed the present invention.

[0008] Specifically, according to one aspect of the present invention, a method for manufacturing a substrate having a thickness less than the thickness of a workpiece is provided, comprising: irradiating the workpiece with a laser beam having a wavelength that penetrates the material of the workpiece so that the focal point is located inside the workpiece, while relatively moving the focal point and the workpiece, thereby forming a delamination layer inside the workpiece that includes a modified portion and cracks extending from the modified portion; and peeling off a portion of the workpiece that will become the substrate from the rest, starting from the delamination layer, wherein the irradiation conditions of the laser beam are set to form a delamination layer in which the modified portion ratio, which is the ratio of the area of ​​the modified portion to the area of ​​the delamination layer when the workpiece is viewed from above, is greater than 0% and less than or equal to 24%.

[0009] Furthermore, it is preferable that the irradiation conditions be set to form a peel layer in which the modified portion ratio is 16% or less. In addition, it is preferable that the peeling of the part of the workpiece from the rest is carried out after the peel layer ratio, which is the ratio of the area of ​​the peel layer to the area of ​​the workpiece when the workpiece is viewed from above, reaches 98% or more. Moreover, it is preferable that the material is a single crystal made of silicon.

[0010] Furthermore, according to another aspect of the present invention, a laser processing method is provided for forming a peel layer inside a workpiece, which includes a modified portion and cracks extending from the modified portion, by using a laser beam with a wavelength that penetrates the material of the workpiece, and moving the workpiece relatively while irradiating the workpiece with the laser beam so that the focal point is located inside the workpiece, thereby forming a peel layer in which the modified portion ratio, which is the ratio of the area of ​​the modified portion to the area of ​​the peel layer when the workpiece is viewed from above, is greater than 0% and less than or equal to 24%. [Effects of the Invention]

[0011] In this invention, a release layer is formed on the workpiece such that, when the workpiece is viewed from above, the modified area ratio, which is the ratio of the area of ​​the modified area to the area of ​​the release layer, is greater than 0% and less than or equal to 24%. This makes it possible to suppress damage to the substrate when a part of the workpiece is peeled off from the rest of the workpiece, starting from the release layer. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic perspective view showing an ingot used in the manufacture of a circuit board. [Figure 2] Figure 2 is a schematic top view of the ingot shown in Figure 1. [Figure 3] Figure 3 is a schematic flowchart illustrating an example of a procedure for manufacturing a substrate, using the ingot shown in Figure 1 as the workpiece to produce a substrate with a thickness less than the thickness of the ingot. [Figure 4]Figure 4 is a schematic top view showing an example of multiple regions in which the delamination layer is formed sequentially in the delamination layer formation step shown in Figure 3. [Figure 5] Figure 5 is a schematic diagram showing an example of a laser processing apparatus used in the peel layer formation step shown in Figure 3. [Figure 6] Figure 6 is a schematic top view showing an ingot held and oriented by the holding table of the laser processing apparatus shown in Figure 5. [Figure 7] Figure 7 is a flowchart illustrating an example of the procedure for sequentially forming delamination layers in the multiple regions shown in Figure 4. [Figure 8] Figure 8(A) is a schematic top view showing the laser beam irradiation step shown in Figure 7, and Figure 8(B) is a schematic partial cross-sectional side view showing the laser beam irradiation step shown in Figure 7. [Figure 9] Figure 9 is a schematic cross-sectional view showing the delamination layer formed inside the ingot during the laser beam irradiation step shown in Figure 7. [Figure 10] Figures 10(A) and 10(B) are schematic partial cross-sectional side views illustrating an example of the peeling step shown in Figure 3. [Figure 11] Figures 11(A) and 11(B) are schematic partial cross-sectional side views illustrating another example of the peeling step shown in Figure 3. [Figure 12] Figures 12(A) and 12(B) are schematic partial cross-sectional side views illustrating yet another example of the peeling step shown in Figure 3. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view schematically showing an example of an ingot (ingot 11) used in the production of a substrate, and FIG. 2 is a top view schematically showing the ingot 11. In FIG. 1, those exposed on the plane included in the ingot 11 among the crystal planes of the material are also shown. In FIG. 2, the crystal orientation of the material of the ingot 11 is also shown.

[0014] The ingot 11 is made of a single crystal of silicon as a material. In the ingot 11, a specific crystal plane included in the crystal plane {100} (here, for convenience, the crystal plane (100)) is exposed on each of the front surface 11a and the back surface 11b. That is, in this ingot 11, the perpendiculars (crystal axes) of the front surface 11a and the back surface 11b respectively are along the crystal orientation

[0100] .

[0015] Although the ingot 11 is manufactured such that the crystal plane (100) is exposed on each of the front surface 11a and the back surface 11b, due to processing errors during manufacturing, etc., a plane slightly inclined from the crystal plane (100) may be exposed on each of the front surface 11a and the back surface 11b. Specifically, on each of the front surface 11a and the back surface 11b of the ingot 11, a plane having an angle of 1° or less with respect to the crystal plane (100) may be exposed. That is, the crystal axis of the ingot 11 may be along a direction having an angle of 1° or less with respect to the crystal orientation

[0100] .

[0016] An orientation flat 13 is formed on the side surface 11c of the ingot 11, and the center C of the ingot 11 is located in a specific crystal orientation included in the crystal orientation <110> (here, for convenience, the crystal orientation

[0011] ) as viewed from this orientation flat 13. That is, in this orientation flat 13, the crystal plane (011) is exposed.

[0017] FIG. 3 is a flowchart schematically showing an example of the procedure of a method for manufacturing a substrate having a thickness less than the thickness of the ingot 11 with the ingot 11 as a workpiece. In this method, first, a release layer including a modified portion and cracks extending from the modified portion is formed inside the ingot 11 (release layer forming step S1).

[0018] In this release layer forming step S1, the release layer is formed in order for a plurality of regions included in the ingot 11 and each extending linearly. FIG. 4 is a top view schematically showing an example of a plurality of regions in which the release layer is formed in order in the release layer forming step S1. In FIG. 4, the crystal orientation of the material of the ingot 11 is also shown.

[0019] As shown in FIG. 4, each of the plurality of regions 11d (for example, n regions 11d_1, 11d_2, 11d_3, 11d_4~11d_n-1, 11d_n) extends along the crystal orientation

[0010] , and the widths thereof (lengths along the crystal orientation

[0001] ) are equal to each other. Also, the center-to-center interval I in the crystal orientation

[0001] of the plurality of regions 11d is equal to the width of each region 11d, and is, for example, 50 μm or more and 500 μm or less.

[0020] Note that the center-to-center interval I is the interval between a straight line L1 passing through the center of one of a pair of adjacent regions 11d (for example, region 11d_2) and extending along the crystal orientation

[0010] , and a straight line L2 passing through the center of the other (for example, region 11d_3) and extending along the crystal orientation

[0010] . Also, each of the width of each region 11d and the center-to-center interval I is set to be approximately equal to the width of the release layer formed in the release layer forming step S1 (length in a direction orthogonal to the traveling direction of the processing point in plan view).

[0021] Then, in the release layer forming step S1, a release layer is formed in each of the plurality of regions 11d using a laser processing apparatus. FIG. 5 is a diagram schematically showing an example of a laser processing apparatus (laser processing apparatus 2) used in the release layer forming step S1.

[0022] In Figure 5, the directions indicated by arrow X (X direction) and arrow Y (Y direction) are mutually orthogonal directions on the horizontal plane, and the direction indicated by arrow Z is a direction perpendicular to both the X and Y directions (vertical direction). Also, in Figure 5, some of the components of the laser processing apparatus 2 are shown as blocks.

[0023] The laser processing apparatus 2 includes a holding table 4 for holding the ingot 11, and a laser beam irradiation unit 6 for irradiating the ingot 11 held by the holding table 4 with a laser beam LB.

[0024] The holding table 4 has a circular upper surface (holding surface) parallel to the X and Y directions. The holding table 4 also has a disc-shaped porous plate (not shown) whose upper surface is exposed on this holding surface. Furthermore, this porous plate can communicate with a suction source (not shown), such as an ejector, via a flow path or the like formed inside the holding table 4.

[0025] When the suction source communicating with this porous plate is activated, a suction force acts on the space near the holding surface of the holding table 4. Therefore, by placing the ingot 11 on the holding surface of the holding table 4 and then activating the suction source communicating with the porous plate, it is possible to hold the ingot 11 on the holding surface of the holding table 4.

[0026] Furthermore, the holding table 4 is connected to a rotating mechanism (not shown). This rotating mechanism includes, for example, a driven pulley connected to the holding table 4, a belt wrapped around the driven pulley, a drive pulley connected to the driven pulley via the belt, and a motor for rotating the drive pulley.

[0027] When this rotation mechanism (specifically, its motor) is activated, the holding table 4 rotates around a straight line along the Z-direction passing through the center of the holding table 4 as the axis of rotation. Therefore, by activating the rotation mechanism while the ingot 11 is held on the holding surface of the holding table 4, it is possible to adjust the orientation of the ingot 11 (specifically, the angle between the specific crystal orientation of the material of the ingot 11 and the X or Y direction).

[0028] The laser beam irradiation unit 6 has a laser oscillator 8. This laser oscillator 8 has, for example, Nd:YAG as the laser medium. The laser oscillator 8 emits a pulsed laser beam LB with a wavelength (for example, 1064 nm or 1342 nm) that penetrates the material of the ingot 11 (a single crystal made of silicon) (for example, a frequency of 10 kHz or more and 200 kHz or less).

[0029] The laser beam LB is adjusted in the attenuator 10 so that its output (power) is, for example, between 3W and 10W, and then supplied to the branching unit 12. This branching unit 12 includes, for example, a spatial light modulator and / or a diffractive optical element (DOE) that includes a liquid crystal phase control element called LCoS (Liquid Crystal on Silicon).

[0030] The branching unit 12 then branches the laser beam LB emitted from the head 16 (described later) into a number of focal points equal to the number of focal points (for example, 3 to 16, or 4 in Figure 5 for convenience) aligned along the Y direction. The branched laser beam LB is then guided to the head 16 via an optical system including a mirror 14 housed in a housing (not shown).

[0031] The head 16 is positioned higher than the holding table 4. The head 16 also houses a lens (not shown) for focusing the branched laser beam LB. The laser beam LB, focused by this lens, is then emitted directly downwards from the head 16.

[0032] Furthermore, the head 16 is located at the tip of a housing (not shown) that houses an optical system for guiding the laser beam LB to the head 16, and an X-direction movement mechanism (not shown), a Y-direction movement mechanism (not shown), and a Z-direction movement mechanism (not shown) are connected to the base end of this housing. Each movement mechanism includes, for example, a ball screw whose nut is connected to the housing, and a motor for rotating the screw shaft of the ball screw.

[0033] When at least one of these moving mechanisms (specifically, their motors) is operated, the head 16 and housing move along the X, Y, and / or Z directions. Therefore, by operating these moving mechanisms, it is possible to adjust the position (coordinates) in the X, Y, and / or Z directions of the focal point where the laser beam LB emitted from the head 16 towards the holding surface of the holding table 4 is focused.

[0034] When performing the delamination layer formation step S1 in the laser processing apparatus 2, first, the ingot 11 is brought into the holding table 4 with its surface 11a facing upwards, and then the back surface 11b of the ingot 11 is held on the holding surface of the holding table 4. Next, the orientation of the ingot 11 is adjusted as necessary. Figure 6 is a schematic top view showing the ingot 11 held on the holding surface of the holding table 4 and with its orientation adjusted. In addition, the crystal orientation of the material of the ingot 11 is also shown in Figure 6.

[0035] The orientation of the ingot 11 is adjusted, for example, so that the angle between the direction from the orientation flat 13 toward the center C of the ingot 11 (crystal orientation

[0011] ) and the X and Y directions is 45°. That is, the orientation of the ingot 11 is adjusted so that, for example, the crystal orientation

[0010] is parallel to the X direction and the crystal orientation

[0001] is parallel to the Y direction.

[0036] Once the orientation of the ingot 11 held on the holding surface of the holding table 4 is adjusted in this way, peel layers are sequentially formed in multiple regions 11d. Figure 7 is a schematic flowchart showing an example of the procedure for sequentially forming peel layers in multiple regions 11d. In this procedure, first, the laser beam LB is irradiated onto the ingot 11 so that the focal point is positioned inside the ingot 11, while the focal point and the ingot 11 are moved relative to each other along the crystal orientation

[0010] (laser beam irradiation step S11).

[0037] Figure 8(A) is a schematic top view showing the laser beam irradiation step S11, and Figure 8(B) is a schematic partial cross-sectional side view showing the laser beam irradiation step S11. Figure 9 is a schematic cross-sectional view showing the delamination layer formed inside the ingot 11 during the laser beam irradiation step S11. In this laser beam irradiation step S11, for example, the delamination layer is first formed in region 11d_1 located at one end of a plurality of regions 11d in the Y direction (crystal orientation

[0001] ).

[0038] Specifically, first, in a plan view, the head 16 of the laser beam irradiation unit 6 is positioned such that region 11d_1 (more specifically, the center of region 11d_1 in the Y direction (crystal orientation

[0001] ) as viewed from the center of the head 16 in a plan view) is positioned in the X direction. Next, the head 16 is raised and lowered so that the multiple focal points formed by focusing the branched laser beam LB are positioned at a depth of, for example, 100 μm to 1500 μm from the surface 11a of the ingot 11.

[0039] Next, while emitting the laser beam LB from the head 16 toward the holding table 4, the head 16 is moved at a speed of, for example, 100 mm / s to 1500 mm / s or less so that it passes from one end to the other in the X direction (crystal orientation

[0010] ) of the ingot 11 (see Figures 8(A) and 8(B)). When the head 16 is moved while emitting the laser beam LB from the head 16 in this way, the multiple focal points are positioned inside the ingot 11, and the multiple focal points and the ingot 11 move relative to each other along the X direction (crystal orientation

[0010] ), that is, the laser beam LB is irradiated onto the ingot 11 with the X direction (crystal orientation

[0010] ) as the scanning direction of the laser beam LB.

[0040] At this time, the pulse energy of each branched laser beam LB, that is, the energy obtained by dividing the output of the laser beam LB adjusted in the attenuator 10 by the frequency and the number of branches, is set to be, for example, 0.001 mJ or more and 0.1 mJ or less, typically 0.01 mJ. Also, the irradiation pitch of each branched laser beam LB, that is, the distance obtained by dividing the moving speed (processing feed rate) of the head 16 that emits the laser beam LB by the frequency of the laser beam LB, is set to be, for example, 1 μm or more and 10 μm or less, typically 6.75 μm.

[0041] As a result, in region 11d_1, a modified portion 15a is formed where the crystal structure of the silicon single crystal is disordered and becomes amorphous silicon, centered around each of the multiple focal points. Furthermore, when the modified portion 15a is formed in region 11d_1, the volume of region 11d_1 expands, generating internal stress. The cracks 15b are then formed by the internal stress acting in a way that cleaves the portion near the modified portion 15a. Consequently, a delamination layer 15 is formed in region 11d_1, containing multiple modified portions 15a and cracks 15b extending from each of the multiple modified portions 15a.

[0042] Here, the irradiation conditions of the laser beam LB in the laser beam irradiation step S11 are set so that when the ingot 11 is viewed from above, the modified portion ratio, which is the ratio of the area of ​​the modified portion 15a to the area of ​​the peeling layer 15, is greater than 0% and less than or equal to 24%, preferably less than or equal to 16%, to form a peeling layer 15. This makes it possible to suppress damage to the portion when peeling off a part of the ingot 11 from the rest, starting from the peeling layer 15.

[0043] The percentage of the modified portion is calculated by, for example, referring to an image formed by photographing the ingot 11 from directly above while irradiating the ingot 11 with light of a wavelength that penetrates the material of the ingot 11 (for example, infrared (IR)) from diagonally above. Specifically, the light is not reflected in the region of the ingot 11 where the peeling layer 15 is not formed, while it is reflected in the region where the peeling layer 15 is formed.

[0044] Furthermore, within the delamination layer 15, there is a space where the internal pressure is below atmospheric pressure in the region where cracks 15b are formed, and the light is more easily reflected at the boundary of this space. As a result, in the delamination layer 15, the light is more easily reflected in the region where cracks 15b are formed than in the region where modified portion 15a is formed. Therefore, the ingot 11 shown in this image contains three regions with different brightness levels.

[0045] Specifically, in the ingot 11 shown in this image, the areas where the delamination layer 15 is formed are brighter than the areas where it is not formed, and in the delamination layer 15, the areas where cracks 15b are formed are brighter than the other areas (i.e., the areas where modified parts 15a are formed).

[0046] Furthermore, this image may be subjected to trinarization if necessary to clearly delineate the three regions. Alternatively, the peeled layer 15 shown in this image may be subjected to binarization if necessary to clearly delineate the region where cracks 15b are formed from the region where modified portions 15a are formed.

[0047] The percentage of the modified portion is calculated by dividing the area of ​​the region in the peeling layer 15 shown in the image in which the modified portion 15a is formed by the area of ​​the peeling layer 15 (i.e., the sum of the area in the region in which the modified portion 15a is formed and the area in the region in which the crack 15b is formed).

[0048] Furthermore, these irradiation conditions are set such that, for example, the width of the delamination layer 15 in a plan view (here, the distance between one end and the other end of the delamination layer 15 in the Y direction (crystal orientation

[0001] )) is approximately equal to the width of each region 11d. These irradiation conditions include the output, frequency, and number of branches of the laser beam LB, as well as the movement speed of the head 16 that emits the laser beam LB.

[0049] Then, if the irradiation of all of the multiple regions 11d with the laser beam LB has not been completed (step S12:NO), the position where the focal point is formed and the ingot 11 are moved relative to each other along the Y direction (crystal orientation

[0001] ) (indexing feed step S13).

[0050] In this indexing feed step S13, the head 16 is moved along the Y direction (crystal orientation

[0001] ) by a distance (index amount) corresponding to the center spacing I mentioned above. As a result, the head 16 (more specifically, the center of the head 16 in a plan view from the line L1 mentioned above) is positioned in the X direction (crystal orientation

[0010] ) when viewed from region 11d_2.

[0051] Next, the laser beam irradiation step S11 is performed again. This laser beam irradiation step S11 is performed as described above, except that the scanning direction of the laser beam LB is in the opposite direction to the X direction (crystal orientation [0-10]). Therefore, a detailed explanation is omitted.

[0052] Furthermore, the indexing and feeding step S13 and the laser beam irradiation step S11 are repeatedly performed alternately until a delamination layer 15 is formed in all of the multiple regions 11d contained in the ingot 11. Once a delamination layer 15 is formed in all of the multiple regions 11d (in short, the entire area of ​​the ingot 11) (step S12: YES), the delamination layer formation step S1 is completed.

[0053] In step S1, the peeling layer 15 does not need to be formed over the entire surface of the ingot 11. However, from the viewpoint of suppressing damage to a portion of the ingot 11 when peeling it off from the rest of the ingot 11 starting from the peeling layer 15, it is preferable in step S1 to set the peeling layer ratio, which is the ratio of the area of ​​the peeling layer 15 to the area of ​​the ingot 11 when viewed from above, to 98% or more.

[0054] The delamination layer ratio is calculated by referring to, for example, the image used when calculating the modified portion ratio described above, or an image obtained by applying a binarization process to this image to clearly delineate the areas where the delamination layer 15 is formed from the areas where it is not formed. Specifically, the delamination layer ratio is calculated by dividing the area of ​​the area where the delamination layer 15 is formed shown in the image by the area of ​​the ingot 11.

[0055] Furthermore, in the exfoliation layer formation step S1, the laser beam LB may be irradiated onto the ingot 11 in only one direction (for example, the X direction (crystal orientation

[0010] )). That is, in the exfoliation layer formation step S1, the laser beam LB may be irradiated onto the ingot 11 with the scanning direction in the same direction as the ingot 11, without making the opposite direction of the ingot 11 (for example, the opposite direction of the X direction (crystal orientation [0-10])) the scanning direction of the laser beam LB.

[0056] Furthermore, in the exfoliation layer formation step S1, the irradiation of the ingot 11 with the laser beam LB may be performed along a direction nonparallel to the crystal orientation

[0010] . That is, in the exfoliation layer formation step S1, instead of the laser beam irradiation step S11 and the indexing feed step S13, the irradiation of the ingot 11 with the laser beam LB, with a scanning direction nonparallel to the crystal orientation

[0010] , and the relative movement of the ingot 11 between the position where a focal point is formed along a direction perpendicular to the scanning direction in a plan view and the ingot 11 may be repeated alternately.

[0057] However, from the viewpoint of suppressing the thickening of the peeling layer 15 formed in the peeling layer formation step S1 and improving the productivity of substrates manufactured from the ingot 11, it is preferable that this scanning direction is parallel to the crystal orientation

[0010] . This point will be explained below.

[0058] A single crystal made of silicon is most easily cleaved at a specific crystal plane within the crystal plane {111}. For example, in an ingot 11 where the crystal plane (100), which is a specific crystal plane within the crystal plane {100}, is exposed on both the front surface 11a and the back surface 11b, the crystal orientation is such that <110> When a laser beam LB is irradiated along a specific crystal orientation

[0011] contained within the ingot 11 to form a modified portion 15a, many cracks 15b are generated that extend along a specific crystal plane within the crystal plane {111} that is parallel to the crystal orientation

[0011] (specifically, the crystal plane shown in (1) below).

number

[0059] Here, the angle that crystal plane (100) makes with a specific crystal plane included in crystal plane {111} is approximately 54.7°. Therefore, when the laser beam LB is irradiated onto the ingot 11 in this manner, many cracks 15b are generated in which the component along the thickness direction is larger than the component along the direction parallel to the surface 11a and back surface 11b of the ingot 11.

[0060] On the other hand, crystal orientation

[0010] is crystal orientation <110> This is a direction with a large angle (for example, 45°) with respect to a specific crystal orientation (for example, crystal orientation

[0011] ) contained within the crystal plane. Therefore, in the method shown in Figure 3, cracks are less likely to occur that extend from the modified portion 15a formed inside the ingot 11 by irradiation with the laser beam LB, along a specific crystal plane (for example, the crystal plane shown in (1) above) contained within the crystal plane {111}.

[0061] Furthermore, in the laser beam irradiation step S11, many cracks are generated from the modified portion 15a formed inside the ingot 11 by irradiation with the laser beam LB, extending along specific crystal planes within the crystal plane {110} that are parallel to the crystal orientation

[0010] (specifically, the crystal planes shown in (2) below).

number

[0062] Furthermore, the angle between a specific crystal plane included in crystal plane {111} and crystal plane (100) is approximately 54.7°, while the angle between a specific crystal plane included in crystal plane {110} that is parallel to the crystal orientation

[0010] (for example, crystal plane (101)) and crystal plane (100) is 45°.

[0063] Therefore, in the laser beam irradiation step S11, the occurrence of cracks 15b in which the component along the thickness direction is larger than the component along the direction parallel to the surface 11a and back surface 11b of the ingot 11 is suppressed. In other words, in the laser beam irradiation step S11, the thickening of the delamination layer 15 formed inside the ingot 11 is suppressed.

[0064] Furthermore, in the delamination layer formation step S1, the irradiation of the ingot 11 with the laser beam LB may be performed in a spiral trajectory. That is, in the delamination layer formation step S1, for example, the laser beam LB may be irradiated onto the ingot 11 in such a way that the focal point of the laser beam LB and the center of the ingot 11 are gradually brought closer together or further apart in a plan view while rotating the holding table 4 that holds the ingot 11.

[0065] Following the release layer formation step S1, a portion of the ingot 11 that will become the substrate is peeled off from the rest, starting from the release layer 15 (peeling step S2). Figures 10(A) and 10(B) are schematic cross-sectional side views showing an example of peeling step S2. This peeling step S2 is carried out, for example, in the peeling apparatus 18 shown in Figures 10(A) and 10(B).

[0066] The peeling device 18 has a holding table 20 for holding an ingot 11 on which a peeling layer 15 has been formed. The holding table 20 has a circular upper surface (holding surface) perpendicular to the vertical direction, and a porous plate (not shown) is exposed on this holding surface. Furthermore, this porous plate can communicate with a suction source (not shown), such as an ejector, via a flow path or the like formed inside the holding table 20.

[0067] When the suction source communicating with this porous plate is activated, a suction force acts on the space near the holding surface of the holding table 20. Therefore, by placing the ingot 11 on the holding surface of the holding table 20 and then activating the suction source communicating with the porous plate, it is possible to hold the ingot 11 on the holding surface of the holding table 20.

[0068] Furthermore, the holding table 20 is connected to a rotating mechanism (not shown). This rotating mechanism includes, for example, a driven pulley connected to the holding table 20, a belt wrapped around the driven pulley, a drive pulley connected to the driven pulley via the belt, and a motor for rotating the drive pulley.

[0069] When this rotation mechanism (specifically, its motor) is activated, the holding table 20 rotates around a straight line along the vertical direction passing through the center of the holding table 20 as the axis of rotation. Therefore, by operating the rotation mechanism while the ingot 11 is held on the holding surface of the holding table 20, it is possible to adjust the orientation of the ingot 11.

[0070] A holding unit 22 is provided above the holding table 20. This holding unit 22 has a cylindrical support member 24. The lower end of the support member 24 is fixed to the center of the upper part of a disc-shaped holding plate 26. This holding plate 26 has a circular lower surface (holding surface) perpendicular to the vertical direction, and multiple suction ports are formed on this holding surface.

[0071] Furthermore, the support member 24 is connected to a lifting mechanism (not shown). This lifting mechanism includes a ball screw whose nut is connected to the support member 24, and a motor for rotating the screw shaft of the ball screw. When this lifting mechanism (specifically, its motor) is operated, the support member 24 moves up and down.

[0072] Therefore, by operating the lifting mechanism to raise the holding plate 26 prior to loading or unloading the ingot 11 onto or from the holding table 20, it is possible to keep the holding plate 26 sufficiently away from the holding table 20 so as not to interfere with the loading or unloading of the ingot 11. Furthermore, by operating the lifting mechanism to lower the holding plate 26 after the ingot 11 has been held on the holding surface of the holding table 20, it is possible to bring the holding surface of the holding plate 26 into contact with the ingot 11 (specifically, its upper surface).

[0073] Furthermore, each of the multiple suction ports formed on the holding surface of the holding plate 26 can communicate with a suction source (not shown), such as an ejector, via a flow path or the like formed inside the holding plate 26. When a suction source communicating with the multiple suction ports is activated, a suction force acts on the space near the holding surface of the holding plate 26.

[0074] Therefore, by bringing the holding surface of the holding plate 26 into contact with the ingot 11 (specifically, its upper surface) held on the holding surface of the holding table 20, and then operating the suction source which communicates with multiple suction ports, it is possible to clamp the ingot 11 between the holding table 20 and the holding plate 26.

[0075] In addition, the support member 24 is connected to a rotating mechanism (not shown). This rotating mechanism includes, for example, a driven pulley connected to the support member 24, a belt wrapped around the driven pulley, a drive pulley connected to the driven pulley via the belt, and a motor for rotating the drive pulley.

[0076] When this rotation mechanism (specifically, its motor) is activated, the support member 24 and the holding plate 26 rotate around a straight line in the vertical direction passing through the center of the holding plate 26 as the axis of rotation. Therefore, by clamping the ingot 11 between the holding table 20 and the holding plate 26 and then activating the rotation mechanism, it is possible to adjust the orientation of the ingot 11.

[0077] A nozzle 28 is provided diagonally above the holding table 20. This nozzle 28 is connected to a lifting mechanism (not shown). The lifting mechanism includes a ball screw whose nut is connected to the nozzle 28, and a motor for rotating the screw shaft of the ball screw.

[0078] When this lifting mechanism (specifically, its motor) is operated, the nozzle 28 moves up and down. Therefore, by clamping the ingot 11 between the holding table 20 and the holding plate 26 and then operating the lifting mechanism, it is possible to position the nozzle 28 at a height corresponding to the height of the peeling layer 15 formed on the ingot 11.

[0079] Furthermore, the nozzle 28 can communicate with an air supply source (not shown), such as a compressor. When the air supply source connected to the nozzle 28 is activated, air A is ejected from the nozzle 28 in a direction that is roughly perpendicular to the vertical and directed toward the center of the holding table 20 in a plan view. Therefore, by positioning the nozzle 28 at a height corresponding to the height of the stripping layer 15 formed on the ingot 11 and then activating the air supply source connected to the nozzle 28, it is possible to eject air A toward a specific location on the outer circumference of the stripping layer 15 within the ingot 11.

[0080] When performing the peeling step S2 in the peeling apparatus 18, first, the ingot 11 is loaded onto the holding table 20 with the gap between the holding table 20 and the holding plate 26 being greater than the thickness of the ingot 11, for example, with the surface 11a facing upwards (see Figure 10(A)). Next, the back surface 11b of the ingot 11 is held by the holding surface of the holding table 20. Then, the holding plate 26 is lowered until its holding surface contacts the surface 11a of the ingot 11.

[0081] Next, the surface 11a side of the ingot 11 is held on the holding surface of the holding plate 26, that is, the ingot 11 is clamped between the holding table 20 and the holding plate 26. Then, the nozzle 28 is raised and lowered to a height corresponding to the height of the peeling layer 15 formed on the ingot 11. Next, air A is sprayed from the nozzle 28 while the holding table 20 and the holding plate 26 are rotated in the same direction (i.e., clockwise or counterclockwise in a plan view) at the same peripheral speed (see Figure 10(B)).

[0082] As a result, an external force is applied to the entire outer circumference of the delamination layer 15 of the ingot 11, causing the crack 15b to extend further. Consequently, the surface 11a side of the ingot 11 (i.e., the substrate used in the manufacture of semiconductor device dies) is peeled off from the back surface 11b side, starting from the delamination layer 15, and the delamination step S2 is completed.

[0083] In addition, in the peeling step S2, the surface 11a side of the ingot 11 may be peeled from the back surface 11b side using a peeling device having a different structure from the peeling device 18. Figures 11(A) and 11(B), and 12(A) and 12(B) are schematic partial cross-sectional side views showing examples of peeling step S2 performed in peeling devices (peeling devices 30, 42) different from the peeling device 18.

[0084] The peeling apparatus 30 shown in Figures 11(A) and 11(B) has a holding table 32 for holding an ingot 11 on which a peeling layer 15 has been formed. The holding table 32 has a circular upper surface (holding surface) perpendicular to the vertical direction, and a porous plate (not shown) is exposed on this holding surface. Furthermore, this porous plate can communicate with a suction source (not shown), such as an ejector, via a flow path or the like formed inside the holding table 32.

[0085] When the suction source communicating with this porous plate is activated, a suction force acts on the space near the holding surface of the holding table 32. Therefore, by placing the ingot 11 on the holding surface of the holding table 32 and then activating the suction source communicating with the porous plate, it is possible to hold the ingot 11 on the holding surface of the holding table 32.

[0086] A driving unit 34 is provided above the holding table 32. This driving unit 34 has a cylindrical support member 36. The lower end of the support member 36 is fixed to the center of the upper part of a disc-shaped base 38. On the lower side of the outer peripheral region of the base 38, a number of movable members 40 are provided at roughly equal intervals along the circumferential direction of the base 38.

[0087] Each movable member 40 has a plate-shaped hanging portion 40a that hangs down from the lower surface of the base 38. The inner surface of the lower end of this hanging portion 40a is provided with a plate-shaped wedge portion 40b that extends toward the center of the base 38 and becomes thinner as it approaches the tip.

[0088] Furthermore, the support member 36 is connected to a lifting mechanism (not shown). This lifting mechanism includes a ball screw whose nut is connected to the support member 36, and a motor for rotating the screw shaft of the ball screw. When this lifting mechanism (specifically, its motor) is operated, the support member 36, the base 38, and the multiple movable members 40 move up and down.

[0089] Therefore, by operating the lifting mechanism to raise the multiple movable members 40, etc., prior to loading the ingot 11 into or unloading it from the holding table 32, it is possible to sufficiently separate the multiple movable members 40, etc., from the holding table 32 so as not to interfere with the loading and unloading of the ingot 11. Furthermore, by operating the lifting mechanism to lower the support members 36, etc., after the ingot 11 has been held on the holding surface of the holding table 32, it is possible to position the tip of the wedge portion 40b of each movable member 40 at a height corresponding to the height of the peeling layer 15 formed on the ingot 11.

[0090] Furthermore, the upper end of the hanging portion 40a of each movable member 40 is connected to an actuator such as an air cylinder built into the base 38, and by operating this actuator, the movable member 40 moves along the radial direction of the base 38. Therefore, by positioning the tip of the wedge portion 40b of each movable member 40 at a height corresponding to the height of the peeling layer 15 formed in the ingot 11 and then operating the actuator, it is possible to drive multiple wedge portions 40b into multiple locations near the outer circumference of the peeling layer 15.

[0091] In addition, the support member 36 is connected to a rotating mechanism (not shown). This rotating mechanism includes, for example, a driven pulley connected to the support member 36, a belt wrapped around the driven pulley, a drive pulley connected to the driven pulley via the belt, and a motor for rotating the drive pulley.

[0092] When this rotation mechanism (specifically, its motor) is activated, the support member 36, the base 38, and the multiple movable members 40 rotate around a straight line along the vertical direction passing through the center of the base 38 as the axis of rotation. Therefore, by driving multiple wedge portions 40b into multiple locations near the outer circumference of the peeling layer 15 and then activating the rotation mechanism, it is possible to make each wedge portion 40b driven into the peeling layer 15 rotate so as to trace its outer circumference.

[0093] When performing the peeling step S2 in the peeling apparatus 30, first, the distance between the holding table 32 and the multiple movable members 40 in the vertical direction is made greater than the thickness of the ingot 11, and each of the multiple movable members 40 is positioned radially outward from the base 38, and the ingot 11 is then loaded onto the holding table 32, for example, with the surface 11a facing upward.

[0094] Next, the holding surface of the holding table 32 holds the back side 11b of the ingot 11. Then, the movable members 40 are lowered until the tips of the wedge portions 40b of each movable member 40 are positioned at a height corresponding to the height of the peeling layer 15 formed on the ingot 11. Next, multiple wedge portions 40b are driven into multiple locations near the outer circumference of the peeling layer 15 (see Figure 11(A)).

[0095] Next, the multiple wedge portions 40b are rotated. Then, the multiple wedge portions 40b are raised (see Figure 11(B)). This applies an external force to the entire outer circumference of the delamination layer 15 of the ingot 11, causing the crack 15b to extend further. As a result, the surface 11a side of the ingot 11 (i.e., the substrate 17 used for manufacturing semiconductor device dies) is peeled off from the back surface 11b side, starting from the delamination layer 15, and the delamination step S2 is completed.

[0096] The peeling apparatus 42 shown in Figures 12(A) and 12(B) has a suction table 44 for sucking up the ingot 11 on which the peeling layer 15 has been formed. The suction table 44 has a circular upper surface (suction surface) perpendicular to the vertical direction, and a porous plate (not shown) is exposed on this suction surface. Furthermore, this porous plate can communicate with a suction source (not shown), such as a vacuum pump, via a flow path formed inside the suction table 44.

[0097] When the suction source connected to this porous plate is activated, a suction force acts on the space near the suction surface of the suction table 44. Therefore, by placing the ingot 11 on the suction surface of the suction table 44 and then activating the suction source connected to the porous plate, it is possible to pull the ingot 11 placed on the suction surface of the suction table 44 downwards.

[0098] A suction unit 46 is provided above the suction table 44. This suction unit 46 has a cylindrical support member 48. The lower end of the support member 48 is fixed to the center of the upper part of a disc-shaped suction plate 50. This suction plate 50 has a circular lower surface (suction surface) perpendicular to the vertical direction, and multiple suction ports are formed on this suction surface.

[0099] Furthermore, the support member 48 is connected to a lifting mechanism (not shown). This lifting mechanism includes a ball screw whose nut is connected to the support member 48, and a motor for rotating the screw shaft of the ball screw. When this lifting mechanism (specifically, its motor) is operated, the support member 48 moves up and down.

[0100] Therefore, by operating the lifting mechanism to raise the suction plate 50 prior to loading or unloading the ingot 11 onto or from the suction table 44, it is possible to keep the suction plate 50 sufficiently away from the suction table 44 so as not to interfere with the loading or unloading of the ingot 11. Furthermore, by operating the lifting mechanism to lower the suction plate 50 after applying suction force to the ingot 11 from the suction surface of the suction table 44, it is possible to bring the suction surface of the suction plate 50 into contact with the ingot 11 (specifically, its upper surface).

[0101] Furthermore, each of the multiple suction ports formed on the suction surface of the suction plate 50 can communicate with a suction source (not shown), such as a vacuum pump, via a flow path or the like formed inside the suction plate 50. When the suction source communicating with the multiple suction ports is operated, a suction force acts on the space near the suction surface of the suction plate 50.

[0102] Therefore, by bringing the suction surface of the suction plate 50 into contact with the ingot 11 (specifically, its upper surface) on which suction force is acting from the suction surface of the suction table 44, and then operating the suction source that communicates with multiple suction ports, it is possible to suck the ingot 11 upward.

[0103] When performing the peeling step S2 in the peeling apparatus 42, first, the ingot 11 is loaded onto the suction table 44 with the surface 11a facing upwards, for example, with the distance between the suction table 44 and the suction plate 50 being greater than the thickness of the ingot 11. Next, a suction force is applied from the suction surface of the suction table 44 to the back surface 11b of the ingot 11. Then, the suction plate 50 is lowered until the suction surface contacts the surface 11a of the ingot 11 (see Figure 12(A)).

[0104] Next, a suction force is applied from the suction surface of the suction plate 50 to the surface 11a side of the ingot 11. Then, the suction plate 50 is raised (see Figure 12(B)). This applies an external force to the delamination layer 15 along the thickness direction of the ingot 11, causing the crack 15b to extend further. As a result, the surface 11a side of the ingot 11 (i.e., the substrate 17 used for manufacturing semiconductor device dies) is peeled off from the back surface 11b side, starting from the delamination layer 15, and the delamination step S2 is completed.

[0105] Furthermore, in the peeling step S2, ultrasonic waves may be applied to the surface 11a side of the ingot 11 prior to peeling the surface 11a side of the ingot 11 from the back surface 11b side, starting from the peeling layer 15. In this case, the cracks 15b contained in the peeling layer 15 extend further, making it easier to peel the surface 11a side of the ingot 11 from the back surface 11b side. Alternatively, in the peeling step S2, the surface 11a side of the ingot 11 may be peeled from the back surface 11b side simply by applying ultrasonic waves to the surface 11a side.

[0106] In the above-described embodiment, in the delamination layer formation step S1, a delamination layer 15 is formed on the ingot 11 such that the modified portion ratio, which is the ratio of the area of ​​the modified portion 15a to the area of ​​the delamination layer 15 when the ingot 11 is viewed from above, is greater than 0% and less than or equal to 24%. This makes it possible to suppress damage to the substrate 17 when, in the delamination step S2, a portion of the ingot 11 that will become the substrate 17 is peeled off from the rest of the ingot 11, starting from the delamination layer 15.

[0107] In the embodiments described above, the workpiece used to manufacture the substrate 17 is not limited to the ingot 11 shown in Figures 1 and 2, etc. This workpiece may be, for example, a single crystal made of silicon in which crystal planes not included in the crystal plane {100} are exposed on the front and back surfaces, respectively. Furthermore, this workpiece may be an ingot with notches formed on its side surface, or an ingot in which neither orientation flats nor notches are formed on its side surface.

[0108] Furthermore, the workpiece may be, for example, a bare wafer having a thickness of 2 to 5 times the thickness of the substrate 17 to be manufactured. This bare wafer is manufactured, for example, by separating it from the ingot 11 by a method similar to the one described above. In this case, the substrate 17 can also be described as being manufactured by repeating the above method twice.

[0109] Furthermore, the workpiece may be a device wafer manufactured by forming a semiconductor device on one side of a bare wafer. In this case, it is preferable that the laser beam LB is irradiated onto the device wafer from the other side (the side on which the semiconductor device is not formed) in order to prevent adverse effects on the semiconductor device.

[0110] Furthermore, the material of this workpiece is not limited to a single crystal made of silicon. This material may be, for example, a single crystal made of silicon carbide, gallium nitride, gallium oxide, lithium tantalate (LT), or lithium niobate (LN). [Examples]

[0111] Twelve workpieces, each made from a single crystal of silicon, were irradiated with a laser beam under different irradiation conditions to form a delamination layer. The procedure for forming this delamination layer was the same as that shown in Figure 7. The percentage of modified material in the delamination layer formed on each workpiece was investigated, and the processing quality when a portion of the workpiece was separated from the rest of the workpiece starting from the delamination layer was evaluated.

[0112] Table 1 shows the laser beam irradiation conditions set for 12 workpieces (workpieces W1 to W12). [Table 1]

[0113] The laser beam irradiation conditions for workpieces W1-W6 and W8-W12 are set so that the pulse energy of each branched laser beam is equal to that of the other. Specifically, under these irradiation conditions, the output of each branched laser beam, i.e., the output obtained by dividing the "output (W)" by the "frequency (Hz)" and the "number of branches", is set to 0.01 mJ. Furthermore, the laser beam irradiation conditions for workpiece W7 are set so that the pulse energy of each branched laser beam is 0.0133 mJ.

[0114] Furthermore, the laser beam irradiation conditions for the workpieces W1 to W12 are set so that the irradiation pitch of each branched laser beam is equal to that of the others. Specifically, under these irradiation conditions, the irradiation pitch of each branched laser beam, that is, the distance obtained by dividing the "processing feed rate (mm / s)" by the "frequency (Hz)", is set to 6.75 μm.

[0115] Table 2 shows the percentage of modified areas in the peeling layer formed on each of the workpieces W1 to W12 when irradiated with a laser beam according to the irradiation conditions shown in Table 1, and the processing quality when a portion of the workpieces W1 to W12 is peeled off from the rest, starting from each peeling layer. [Table 2]

[0116] In Table 2, the "×", "△", and "○" shown in the "Processing Quality" column indicate that: damage was found in a portion of the workpiece W1 to W12 that was peeled off from the remaining portion, making it difficult to use for semiconductor device formation; damage was found, although it was possible to use it for semiconductor device formation; and damage was found, although it was possible to use it for semiconductor device formation.

[0117] As shown in Table 2, a correlation was found between the percentage of modified portion in the peeling layer formed on workpieces W1 to W12 and the processing quality when a portion of workpieces W1 to W12 is peeled off from the rest, starting from the peeling layer. Specifically, it was found that when the percentage of modified portion is greater than 0% and 24% or less, damage to the portion when peeling off a portion of workpieces W1 to W12 from the rest, starting from the peeling layer, can be suppressed. Furthermore, it was found that when the percentage of modified portion is greater than 0% and 16% or less, damage to the portion when peeling off a portion of workpieces W1 to W12 from the rest, starting from the peeling layer, can be suppressed even more effectively. [Examples]

[0118] Three workpieces, each made from a single crystal of silicon, were subjected to the formation of delamination layers with different delamination ratios. The proportion of modified areas in the delamination layers formed on each workpiece was investigated, and the processing quality when a portion of the workpiece was separated from the rest, starting from the delamination layer, was evaluated.

[0119] Table 3 shows the proportion of the peeled layer for each of the three workpieces (workpieces W13 to W15), and the processing quality when peeling a portion of workpieces W13 to W15 from the rest, starting from each peeled layer. [Table 3]

[0120] In Table 3, the "×" and "○" in the "Processing Quality" column indicate that damage was found in a portion of the workpiece W1 to W12 that was peeled off from the remaining portion, making it difficult to use for the formation of semiconductor devices, and that the workpiece was suitable for the formation of semiconductor devices and no significant damage was observed, respectively.

[0121] As shown in Table 3, a correlation was found between the proportion of the peeled layer in workpieces W13-W15 and the processing quality when a portion of workpieces W13-W15 is peeled off from the rest of the workpiece, starting from the peeled layer. Specifically, it was found that when the proportion of the peeled layer in workpieces W13-W15 is 98% or more, damage to that portion when peeling it off from the rest of the workpiece, starting from the peeled layer, can be suppressed.

[0122] Furthermore, the structures and methods of the embodiments described above can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0123] 2: Laser processing equipment 4: Holding Table 6: Laser beam irradiation unit 8: Laser Oscillator 10: Attenuator 11: Ingot (11a: Front surface, 11b: Back surface, 11c: Side surface, 11d: Region) 12: Branch Unit 13: Orientation Flat 14: Mirror 15: Detachment layer (15a: Modified area, 15b: Crack) 16: Head 17: Circuit board 18: Peeling device 20: Holding Table 22: Holding unit 24: Support member 26: Holding plate 28: Nozzle 30: Peeling device 32: Holding Table 34: Input Unit 36: Support member 38: Base 40: Movable member (40a: hanging part, 40b: wedge part) 42: Peeling device 44: Suction Table 46: Suction Unit 48: Support member 50: Attraction board

Claims

1. A method for manufacturing a substrate having a thickness less than the thickness of a workpiece, By irradiating the workpiece with a laser beam of a wavelength that penetrates the material of the workpiece, while relatively moving the focal point and the workpiece, a delamination layer including a modified portion and cracks extending from the modified portion is formed inside the workpiece. The process involves peeling off a portion of the workpiece that will become the substrate from the rest of the workpiece, starting from the peeling layer. A method for manufacturing a substrate, wherein the irradiation conditions of the laser beam are set to form a release layer in which the modified portion ratio, which is the ratio of the area of ​​the modified portion to the area of ​​the release layer when the workpiece is viewed from above, is greater than 0% and less than or equal to 24%.

2. The method for manufacturing a substrate according to claim 1, wherein the irradiation conditions are set to form a peel layer in which the proportion of the modified portion is 16% or less.

3. The method for manufacturing a substrate according to claim 1, wherein the peeling of the part of the workpiece from the rest is carried out after the peeling layer ratio, which is the ratio of the area of ​​the peeled layer to the area of ​​the workpiece when the workpiece is viewed in plan, has reached 98% or more.

4. The method for manufacturing a substrate according to any one of claims 1 to 3, wherein the material is a single crystal made of silicon.

5. A laser processing method that uses a laser beam of a wavelength that penetrates the material of a workpiece to form a delamination layer inside the workpiece, which includes a modified portion and cracks extending from the modified portion, A laser processing method comprising irradiating a workpiece with a laser beam so that the focal point is located inside the workpiece, while moving the focal point and the workpiece relative to each other, thereby forming a peel layer in which the modified portion ratio, which is the ratio of the area of ​​the modified portion to the area of ​​the peel layer when the workpiece is viewed from above, is greater than 0% and less than or equal to 24%.

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