Wafer processing method

Abstract

To provide a method of processing a wafer in which a circumference excessive region of a bonded wafer can be removed in a grinding process while suppressing break of a device.SOLUTION: A method processing a wafer comprising a first modified-layer formation step 1 that a laser beam is irradiated along an annular shape shifted by a predetermined distance inward from the outer peripheral edge of a first wafer so as to form an annular first modified layer inside and a first crack which extends from the first modified layer and is exposed to the front face, causing generation of a bend in an outer peripheral region on the outer peripheral edge side more than the first modified layer and the first crack, the first wafer having a plurality of device on its front face and a chamfered outer peripheral edge, the laser beam having a wavelength transmitting the first wafer; a wafer formation step 2 that the front face of the first wafer is bonded to a second wafer to form a bonded wafer; and a grinding step 6 that the first wafer of the bonded wafer is ground form its rear side and made thin to a finished thickness.SELECTED DRAWING: Figure 3

Description

Technical Field

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[0001] The present invention relates to a method for processing a wafer.

Background Art

[0002] <000​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ However, the method described in Patent Document 1 had problems such as the possibility of causing chipping that could reach the device and damage it when the outer edge of the wafer surface was cut in an annular shape, and the device being easily contaminated due to the large amount of cutting debris produced. Furthermore, in the method described in Patent Document 2, since the bonding layer that adheres the wafer extends beyond the annularly formed modified layer to the outer edge, the region on the outer edge may remain stuck, and the scrap material in the outer region may not peel off and remain. If the outer region remains, there is a possibility that the region outside and inside the annular modified layer will collide with each other and be damaged, or that the polishing pad may be damaged in the subsequent polishing process.

[0007] This invention has been made in view of the above problems, and its objective is to provide a wafer processing method that can remove excess peripheral region while suppressing device damage during grinding of bonded wafers. [Means for solving the problem]

[0008] To solve the above-mentioned problems and achieve the objective, the wafer processing method of the present invention comprises: a first modified layer formation step in which a laser beam of a wavelength that penetrates the first wafer is irradiated in an annular manner along a position a predetermined distance inward from the outer edge of the first wafer, on a first wafer on which a plurality of devices are formed on the surface side and whose outer edge is chamfered, thereby forming an annular first modified layer and a first crack extending from the first modified layer and appearing on the surface side of the first wafer, thereby causing warping in the outer peripheral region on the outer edge side of the first modified layer and the first crack; a bonded wafer formation step in which, after performing the first modified layer formation step, the surface side of the first wafer is bonded to a second wafer to form a bonded wafer; and a grinding step in which, after performing the bonded wafer formation step, the first wafer of the bonded wafer is ground from the back side to thin it to the finish thickness. In the first modified layer formation step, the focusing point of the laser beam is positioned on the surface side of the position that bisects the thickness of the first wafer, and the first modified layer is formed on the surface side of the position that bisects the thickness of the first wafer. It is characterized by the following.

[0009] Furthermore, the wafer processing method of the present invention may further include a second modified layer formation step, in which, after performing the bonded wafer formation step and before performing the grinding step, a laser beam of a wavelength that penetrates the first wafer is irradiated in an annular manner from the back side of the first wafer along a position a predetermined distance inward from the outer edge of the first wafer, thereby forming an annular second modified layer and a second crack extending from the second modified layer and connecting to the first modified layer inside the first wafer; and a removal step, in which an external force is applied to the outer peripheral region to remove the outer peripheral region.

[0010] Furthermore, the wafer processing method of the present invention may further include a third modified layer formation step, which involves irradiating the outer peripheral region with a laser beam of a wavelength that penetrates the first wafer, after performing the first modified layer formation step and before performing the grinding step, to form a radial third modified layer that divides the outer peripheral region into at least two or more sections.

[0011] Furthermore, the wafer processing method of the present invention may further include a fourth modified layer formation step, in which, before performing the bonded wafer formation step, a laser beam with a wavelength that penetrates the first wafer is irradiated in an annular manner along a predetermined distance toward the outer edge from the position where the first modified layer is formed in the first modified layer formation step, thereby forming a plurality of annular fourth modified layers and fourth cracks extending from the fourth modified layer and appearing on the surface side of the first wafer inside the first wafer.

[0012] Furthermore, the wafer processing method of the present invention may further include a fifth modified layer formation step, in which, before performing the bonded wafer formation step, a laser beam of a wavelength that penetrates the first wafer is irradiated onto the outer peripheral region to form a fifth modified layer and a fifth crack extending from the fifth modified layer in a direction parallel to the surface of the first wafer inside the first wafer. [Effects of the Invention]

[0013] The invention of the present application can remove the outer peripheral surplus region while suppressing damage to the device in the grinding of bonded wafers.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1 is a perspective view showing an example of a wafer to be processed in a wafer processing method according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II shown in FIG. 1. [Figure 3] FIG. 3 is a flowchart showing the flow of a wafer processing method according to an embodiment. [Figure 4] FIG. 4 is a side view showing a partial cross-section of the first modified layer formation step shown in FIG. 3. [Figure 5] FIG. 5 is a perspective view showing a state of the bonding step shown in FIG. 3. [Figure 6] FIG. 6 is a cross-sectional view showing the bonded wafer after the bonding step shown in FIG. 3. [Figure 7] FIG. 7 is a side view showing a partial cross-section of the second modified layer formation step shown in FIG. 3. [Figure 8] FIG. 8 is a plan view showing an example of the bonded wafer after the third modified layer formation step shown in FIG. 3. [Figure 9] FIG. 9 is a side view showing a partial cross-section of the removal step shown in FIG. 3. [Figure 10] FIG. 10 is a side view showing a partial cross-section of the grinding step shown in FIG. 3. [Figure 11] FIG. 11 is a side view showing a state after FIG. 10 of the grinding step shown in FIG. 3 in a partial cross-section. [Figure 12] FIG. 12 is a cross-sectional view showing the first wafer during the fourth modified layer formation step according to the first modification example. [Figure 13] FIG. 13 is a plan view showing an example of the first wafer after the fourth modified layer formation step according to the first modification example. [Figure 14]FIG. 14 is a cross-sectional view showing the first wafer during the fifth modified layer formation step according to the second modification example. [Figure 15] FIG. 15 is a plan view showing an example of the first wafer after the fifth modified layer formation step according to the second modification example. MODE FOR CARRYING OUT THE INVENTION

[0015] A mode (embodiment) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the content described in the following embodiments. Further, the constituent elements described below include those that can be easily assumed by those skilled in the art and substantially identical ones. Furthermore, the configurations described below can be combined as appropriate. Also, various omissions, substitutions, or changes in the configuration can be made without departing from the gist of the present invention.

[0016] Embodiment A method for processing a wafer 10 according to an embodiment of the present invention will be described based on the drawings. FIG. 1 is a perspective view showing an example of a wafer 10 to be processed in the method for processing a wafer 10 according to the embodiment. FIG. 2 is a cross-sectional view taken along line II-II shown in FIG. 1.

[0017] The wafer 10 shown in FIGS. 1 and 2 is a disk-shaped semiconductor wafer having a substrate 11 made of silicon (Si), sapphire (Al2O3), gallium arsenide (GaAs), silicon carbide (SiC), or the like, or a wafer such as an optical device wafer, and is a silicon wafer in the embodiment. As shown in FIG. 2, the wafer 10 has its outer peripheral edge 12 chamfered so that the center in the thickness direction protrudes most to the outer peripheral side and has a cross-sectional arc shape extending from the front surface 13 to the back surface 14 of the substrate 11. The wafer 10 of the embodiment has a diameter of 300 mm and a thickness of 775 μm.

[0018] As shown in Figure 1, the wafer 10 includes a device region 15 on the surface 13 side of the substrate 11 and an outer peripheral region 16 surrounding the device region 15. The device region 15 has a plurality of division lines 17 set in a grid pattern on the surface 13 of the substrate 11, and devices 18 formed in each region partitioned by the division lines 17. The outer peripheral region 16 surrounds the device region 15 all around and is a region where no devices 18 are formed.

[0019] In this embodiment, device 18 constitutes a 3D NAND flash memory and includes electrode pads and through electrodes connected to the electrode pads. The through electrodes penetrate to the back surface 14 of the substrate 11 when the substrate 11 is thinned and the device 18 is individually separated from the wafer 10. That is, the wafer 10 in this embodiment is a so-called TSV wafer in which the individually separated devices 18 have through electrodes. However, the wafer 10 of this invention is not limited to a TSV wafer having through electrodes as in this embodiment, and may be a device wafer without through electrodes.

[0020] Figure 3 is a flowchart showing the flow of the wafer 10 processing method according to the embodiment. As shown in Figure 3, the wafer 10 processing method of the embodiment comprises a first modified layer formation step 1, a bonded wafer formation step 2, a second modified layer formation step 3, a third modified layer formation step 4, a removal step 5, and a grinding step 6. The wafer 10 processing method of the embodiment involves bonding the surface 13 sides of a pair of wafers 10 together and thinning one of the wafers 10 (first wafer 10-1) to a predetermined finish thickness 26.

[0021] In the following description, when distinguishing between the pair of wafers 10, one wafer 10 will be referred to as the first wafer 10-1, and the other wafer 10 as the second wafer 10-2 (see Figure 5). If they are not distinguished, they will simply be referred to as wafer 10. The second wafer 10-2, which is not thinned, will be described as a TSV wafer similar to the first wafer 10-1 in this embodiment, but in the present invention, it may be a simple substrate wafer without a pattern. When the second wafer 10-2 is a substrate wafer, the surface to be bonded to the first wafer 10-1 is not limited to the surface 13 side.

[0022] (First modified layer formation step 1) Figure 4 is a side view showing a partial cross-section of the first modified layer formation step 1 shown in Figure 3. The first modified layer formation step 1 is a step in which an annular first modified layer 21 and a first crack 22 extending from the first modified layer 21 and appearing on the surface 13 side are formed inside the first wafer 10-1 at a predetermined distance inward from the outer peripheral edge 12. In the first modified layer formation step 1, the first modified layer 21 and the first crack 22 are formed inside the first wafer 10-1 by stealth dicing using a laser processing apparatus 40.

[0023] The laser processing apparatus 40 comprises a holding table 41 and a laser beam irradiation unit 42. The holding table 41 holds the wafer 10 on its holding surface and is rotatable around a vertical axis. The laser beam irradiation unit 42 irradiates the wafer 10 held on the holding table 41 with a laser beam 43. The laser processing apparatus 40 further comprises a moving unit (not shown) for moving the holding table 41 and the laser beam irradiation unit 42 relative to each other, and an imaging unit (not shown) for imaging the wafer 10 held on the holding table 41.

[0024] In the first modified layer formation step 1, a laser beam 43 is irradiated along a position a predetermined distance inward from the outer edge 12 of the first wafer 10-1 to form an annular modified layer (first modified layer 21). The position a predetermined distance inward from the outer edge 12 of the first wafer 10-1 is the boundary between the device region 15 and the outer region 16, and exhibits an annular shape in plan view. In this embodiment, the predetermined distance is 2 mm. The laser beam 43 is a laser beam with a wavelength that is penetrating to the first wafer 10-1, for example, infrared rays (IR).

[0025] A modified layer refers to a region whose density, refractive index, mechanical strength, or other physical properties differ from those of the surrounding area. Examples of modified layers include melted regions, cracked regions, dielectric breakdown regions, refractive index change regions, and regions containing a mixture of these areas. The modified layer has lower mechanical strength, etc., than other parts of the first wafer 10-1.

[0026] In the first modified layer formation step 1, the surface 13 side of the first wafer 10-1 is first held by suction to the holding surface (upper surface) of the holding table 41. Next, the first wafer 10-1 is aligned with the focuser of the laser beam irradiation unit 42. Specifically, the holding table 41 is moved to the irradiation area below the laser beam irradiation unit 42 by a moving unit (not shown).

[0027] Next, the first wafer 10-1 is photographed and aligned using an imaging unit (not shown) to position the irradiation part of the laser beam irradiation unit 42 vertically opposite to the outer edge 12 at a predetermined distance inward. Then, the focal point 44 of the laser beam 43 is set inside the first wafer 10-1. At this time, the focal point 44 is set to a position on the surface 13 side of the center in the thickness direction of the first wafer 10-1.

[0028] In the first modified layer formation step 1, the holding table 41 is rotated around a vertical axis while a laser beam 43 is irradiated from the laser beam irradiation unit 42 from the back surface 14 side of the first wafer 10-1. That is, the laser beam 43 is irradiated along a position a predetermined distance inward from the outer peripheral edge 12 of the first wafer 10-1 to form a continuous annular modified layer (first modified layer 21).

[0029] In this case, a crack (first crack 22) extends from the first modified layer 21 and is exposed on the surface 13 side. As described above, when forming the first modified layer 21, it is preferable to position the focal point 44 on the surface 13 side of the position that bisects the thickness of the first wafer 10-1, and to form the first modified layer 21 on the surface 13 side of the position that bisects the thickness of the first wafer 10-1. Furthermore, it is preferable that the first modified layer 21 is formed at a position where the first crack 22 extending from the first modified layer 21 is exposed on the surface 13.

[0030] As the first modified layer 21 and the first crack 22 bulge, the first wafer 10-1 bulges outwards on the surface 13 side than on the back surface 14 side in the outer peripheral region 16 on the outer peripheral edge 12 side of the first modified layer 21 and the first crack 22. As a result, the first wafer 10-1 develops a warp in the outer peripheral region 16, with the surface 13 side being convex. Once the first modified layer 21 and the first crack 22 are formed in an annular shape along the entire circumference of the first wafer 10-1, the first modified layer formation step 1 is completed, and the process moves on to the bonded wafer formation step 2.

[0031] In the first modified layer formation step 1, the laser beam 43 may be irradiated multiple times by changing the height of the focal point 44 of the laser beam 43, or by irradiating the first wafer 10-1 with a laser beam 43 having multiple focal points 44 that are separated in the thickness direction of the first wafer 10-1, thereby forming multiple first modified layers 21 in the thickness direction of the first wafer 10-1. In this case, the first modified layers 21 present in the thickness direction are formed as a whole at a position closer to the surface 13 than the center in the thickness direction of the first wafer 10-1.

[0032] (Laminated wafer formation step 2) Figure 5 is a perspective view showing one state of the bonded wafer formation step 2 shown in Figure 3. Figure 6 is a cross-sectional view showing the bonded wafer 20 after the bonded wafer formation step 2 shown in Figure 3. The bonded wafer formation step 2 is performed after the first modified layer formation step 1 is carried out. The bonded wafer formation step 2 is a step in which the surface 13 side of the first wafer 10-1 is bonded to the second wafer 10-2 to form the bonded wafer 20.

[0033] In the laminated wafer formation step 2 of the embodiment, the surface 13 side of the second wafer 10-2 is described as being bonded to the surface 13 side of the first wafer 10-1. However, if the second wafer 10-2 is a substrate wafer, the surface to be bonded to the first wafer 10-1 is not limited to the surface 13 side. In the laminated wafer formation step 2, first, as shown in Figure 5, a bonding layer 19 is laminated to one of the surfaces 13 of the first wafer 10-1 and the second wafer 10-2. In the embodiment, the bonding layer 19 is laminated to the surface 13 of the second wafer 10-2. In the embodiment, the bonding layer 19 is a double-sided tape in which adhesive layers are laminated on the front and back surfaces of a substrate layer. However, the present invention is not limited to a double-sided tape, and may be, for example, an oxide film, or formed by applying an adhesive containing resin, etc. Alternatively, the first wafer 10-1 and the second wafer 10-2 may be directly bonded without using the bonding layer 19.

[0034] In the bonded wafer formation step 2, as shown in Figure 5, the surface 13 of the first wafer 10-1 and the bonding layer 19 laminated on the surface 13 side of the second wafer 10-2 are then placed opposite each other with a gap between them. Next, the surface 13 of the first wafer 10-1 and the surface 13 of the second wafer 10-2 are bonded together via the bonding layer 19. This forms a bonded wafer 20.

[0035] As shown in Figure 6, in the bonded wafer 20, due to the warping of the outer peripheral region 16 that occurred in the first modified layer formation step 1, the surface 13 of the outer peripheral region 16 of the first wafer 10-1 is not parallel to the bonding layer 19, and therefore the surface 13 of the first wafer 10-1 does not adhere closely to the bonding layer 19. As a result, the bonding in the outer peripheral region 16 is incomplete.

[0036] (Second modified layer formation step 3) Figure 7 is a side view showing a partial cross-section of the second modified layer formation step 3 shown in Figure 3. The second modified layer formation step 3 is performed after the bonded wafer formation step 2 and before the grinding step 6. The second modified layer formation step 3 is a step in which an annular second modified layer 23 and a second crack 24 extending from the second modified layer 23 and connecting to the first modified layer 21 are formed inside the first wafer 10-1 at a predetermined distance inward from the outer peripheral edge 12. In the second modified layer formation step 3, the second modified layer 23 and the second crack 24 are formed inside the first wafer 10-1 by stealth dicing using a laser processing device 40.

[0037] In the second modified layer formation step 3, a laser beam 43 is irradiated along a position a predetermined distance inward from the outer edge 12 of the first wafer 10-1 to form an annular modified layer (second modified layer 23). In a plan view, the position where the laser beam 43 is irradiated is the same position as where the first modified layer 21 was formed. The second modified layer 23 is formed on the back surface 14 side from the position where the first modified layer 21 was formed. The laser beam 43 is a laser beam with a wavelength that is transparent to the first wafer 10-1, and may be the same processing conditions as the laser beam 43 irradiated in the first modified layer formation step 1.

[0038] In the second modified layer formation step 3, first, the back surface 14 side of the second wafer 10-2 is held by suction to the holding surface (upper surface) of the holding table 41. Next, the first wafer 10-1 is aligned with the focuser of the laser beam irradiation unit 42. Specifically, the holding table 41 is moved to the irradiation area below the laser beam irradiation unit 42 by a moving unit (not shown).

[0039] Next, the first wafer 10-1 is photographed and aligned using an imaging unit (not shown) to position the irradiation part of the laser beam irradiation unit 42 vertically opposite to a position a predetermined distance inward from the outer edge 12. Then, the focal point 44 of the laser beam 43 is set inside the first wafer 10-1. At this time, the focal point 44 is set in the thickness direction of the first wafer 10-1 to a position on the back surface 14 side of the position where the first modified layer 21 is formed.

[0040] In the second modified layer formation step 3, the holding table 41 is rotated around a vertical axis while a laser beam 43 is irradiated from the laser beam irradiation unit 42 from the back surface 14 side of the first wafer 10-1. That is, the laser beam 43 is irradiated along a position a predetermined distance inward from the outer peripheral edge 12 of the first wafer 10-1 to form a continuous annular modified layer (second modified layer 23).

[0041] In this case, a crack (second crack 24) extends from the second modified layer 23 and connects with the first modified layer 21. The second crack 24 may extend and be exposed on the back surface 14 side of the first wafer 10-1. In this way, within the first wafer 10-1, a splitting point consisting of the first modified layer 21, the first crack 22, the second modified layer 23, and the second crack 24 is formed at the boundary between the device region 15 and the outer peripheral region 16.

[0042] (Third modified layer formation step 4) Figure 8 is a plan view showing an example of a bonded wafer 20 after the third modified layer formation step 4 shown in Figure 3. The third modified layer formation step 4 is performed after the first modified layer formation step 1 and before the grinding step 6. The third modified layer formation step 4 is a step in which a radial third modified layer 25 is formed that divides the outer peripheral region 16 into at least two or more parts. In the third modified layer formation step 4, the third modified layer 25 is formed inside the first wafer 10-1 by stealth dicing using a laser processing device 40.

[0043] In the third modified layer formation step 4, as shown in Figure 8, a third radial modified layer 25 is formed by irradiating a laser beam 43 along the radial direction in the outer peripheral region 16 of the first wafer 10-1, on the outer peripheral edge 12 side from the position where the first modified layer 21 and the second modified layer 23 are formed. That is, at a predetermined position in the circumferential direction in the outer peripheral region 16 of the first wafer 10-1, a third modified layer 25, which serves as the splitting starting point, is formed radially between the inner peripheral edge and the outer peripheral edge 12 of the outer peripheral region 16. The laser beam 43 is a laser beam with a wavelength that is transparent to the first wafer 10-1, and may have the same processing conditions as the laser beam 43 irradiated in the first modified layer formation step 1 and the second modified layer formation step 3.

[0044] In the third modified layer formation step 4, first, the first wafer 10-1 and the laser beam irradiation unit 42 are aligned so that the irradiation part of the laser beam irradiation unit 42 faces a predetermined position in the circumferential direction of the outer peripheral region 16, and then the focal point 44 of the laser beam 43 is set inside the first wafer 10-1.

[0045] Next, a moving unit (not shown) moves the holding table 41 and the laser beam irradiation unit 42 relative to each other, and the laser beam 43 is irradiated from the laser beam irradiation unit 42 onto the back surface 14 of the first wafer 10-1. At this time, the holding table 41 is moved so that the focal point 44 of the laser beam 43 moves radially outward from the first wafer 10-1. That is, by irradiating the outer peripheral region 16 with the laser beam 43 in the radial direction, a third modified layer 25 that is continuous in the radial direction is formed.

[0046] In the third modified layer formation step 4 shown in Figure 8, the outer peripheral region 16 is divided into 8 parts in the circumferential direction. However, in the present invention, for example, it may be divided into 16 parts, or the number of divisions may be set appropriately according to the diameter of the first wafer 10-1 and the width of the outer peripheral region 16. Also, in the above description, the laser beam 43 is irradiated while moving the holding table 41 so that the focal point 44 moves from the radially inside to the radially outside of the first wafer 10-1. However, in the present invention, the laser beam 43 may be irradiated while moving the holding table 41 so that the focal point 44 moves from the radially outside to the radially inside of the first wafer 10-1. In this case, the irradiation of the laser beam 43 is stopped when the focal point 44 reaches the third modified layer 25. Furthermore, in the wafer processing method, the third modified layer 25 is not necessarily formed, and the third modified layer formation step 4 may be omitted.

[0047] (Removal step 5) Figure 9 is a side view showing a partial cross-section of removal step 5 shown in Figure 3. Removal step 5 is a step in which an external force is applied to the outer peripheral region 16 of the first wafer 10-1 to remove the outer peripheral region 16. In the embodiment, removal step 5 involves holding the second wafer 10-2 with the removal device 50 shown in Figure 9, lifting the outer peripheral region 16 of the first wafer 10-1, and applying a shear force in the thickness direction to remove the outer peripheral region 16.

[0048] The removal device 50 comprises a holding table 51 and a removal unit 52. The holding table 51 holds the wafer 10 (second wafer 10-2) on its holding surface and is rotatable about a vertical axis. The removal unit 52 is movable vertically relative to the holding table 51. The removal unit 52 is provided with one or more gripping members 53 on its lower surface. The gripping members 53 protrude downward from the lower surface of the removal unit 52 and have a wedge shape with their tips facing inward. In a plan view, the pair of gripping members 53 are movable radially. The removal device 50 further comprises a moving unit (not shown) for moving the holding table 51 and the removal unit 52 relative to each other.

[0049] In removal step 5, first, the back surface 14 side of the second wafer 10-2 is held by suction against the holding surface (upper surface) of the holding table 51. Next, the first wafer 10-1 and the gripping member 53 of the removal unit 52 are aligned. Specifically, a moving unit (not shown) moves the holding table 51 to below the removal unit 52, and the tip of the gripping member 53 is opened radially outward from the outer peripheral edge 12 of the first wafer 10-1.

[0050] In removal step 5, the removal unit 52 is then lowered downward, and the height of the gripping member 53 is adjusted so that the tip of the gripping member 53 is directed toward the boundary between the first wafer 10-1 and the second wafer 10-2. Next, the gripping member 53 is moved radially inward, and the tip of the gripping member 53 is driven between the first wafer 10-1 and the second wafer 10-2. Next, the removal unit 52 is raised upward, and the upper surface of the tip of the gripping member 53 lifts the outer peripheral region 16 of the first wafer 10-1 from the surface 13 side. As an upward external force is applied to the outer peripheral region 16, the device region 15 and the outer peripheral region 16 are separated, starting from the first modified layer 21, the second modified layer 23, and the third modified layer 25, and the outer peripheral region 16 of the first wafer 10-1 is removed.

[0051] (Grinding step 6) Figure 10 is a side view showing a partial cross-section of grinding step 6 shown in Figure 3. Figure 11 is a side view showing a partial cross-section of grinding step 6 after Figure 10. Grinding step 6 is performed after the bonded wafer formation step 2 is carried out. Grinding step 6 is a step in which the first wafer 10-1 of the bonded wafer 20 is ground from the back surface 14 side to thin it to the finished thickness 26.

[0052] In the wafer processing method, when the second modified layer formation step 3 (and the third modified layer formation step 4) and removal step 5 are performed, the grinding step 6 is performed after these steps. Figure 10 shows the case where the second modified layer formation step 3 is performed, the removal step 5 is not performed, and the grinding step 6 is performed with the outer peripheral region 16 of the first wafer 10-1 remaining.

[0053] In grinding step 6, the back surface 14 of the first wafer 10-1 is ground by the grinding device 60 to thin it to a predetermined finished thickness 26. The grinding device 60 comprises a holding table 61, a spindle 62 which is a rotating shaft member, a grinding wheel 63 attached to the lower end of the spindle 62, a grinding wheel 64 mounted on the lower surface of the grinding wheel 63, and a grinding water supply unit 65. The grinding wheel 63 rotates on a rotation axis parallel to the axis of the holding table 61.

[0054] In grinding step 6, first, the back surface 14 of the second wafer 10-2 is held by suction to the holding surface of the holding table 61. Next, with the holding table 61 rotating around its axis, the grinding wheel 63 is rotated around its axis. Grinding water is supplied to the processing point by the grinding water supply unit 65, and the grinding wheel 64 of the grinding wheel 63 is brought closer to the holding table 61 at a predetermined feed rate, thereby grinding the back surface 14 of the first wafer 10-1 with the grinding wheel 64 and thinning it to a predetermined finished thickness 26. At this time, the outer peripheral region 16 of the first wafer 10-1 is removed by the grinding load.

[0055] As described above, the wafer 10 processing method according to the embodiment involves forming an annular first modified layer 21 at a predetermined distance inward from the outer peripheral edge 12 before bonding the first wafer 10-1 to the second wafer 10-2, and generating a first crack 22 extending from the first modified layer 21 to the surface 13. This causes warping in the outer peripheral region 16, leading to poor bonding or reduced bonding strength of the bonded wafer 20 in the warped outer peripheral region 16. This has the effect of making it easier to remove the scrap material of the outer peripheral region 16 starting from the first modified layer 21. Therefore, by suppressing the extension of edge chipping of the first wafer 10-1 that occurs during grinding to the device 18, it is possible to remove the outer peripheral region 16 while suppressing damage to the device 18.

[0056] It should be noted that the present invention is not limited to the embodiments described above. That is, it can be implemented with various modifications without departing from the core principles of the present invention.

[0057] For example, the method of applying an external force in removal step 5 is not limited to the method of lifting the outer peripheral region 16 of the embodiment and applying an external force in the shear direction, but may also be, for example, by pressing the outer peripheral region 16 from above, or by crushing with a roller. Furthermore, it is not limited to a mechanical external force, but may also be an external force in the radial direction by ultrasonic vibration or by expanding the expanded tape attached to the back surface 14 of the first wafer 10-1.

[0058] Furthermore, as shown in the first and second modified examples below, another modified layer (fourth modified layer 27, fifth modified layer 29) may be formed on the outer peripheral edge 12 side of the first modified layer 21.

[0059] [First variation] Figure 12 is a cross-sectional view showing the first wafer 10-1 during the fourth modified layer formation step according to the first modified example. Figure 13 is a plan view showing an example of the first wafer 10-1 after the fourth modified layer formation step according to the first modified example. The fourth modified layer formation step is performed before the bonded wafer formation step 2 is carried out. The fourth modified layer formation step is a step in which an annular fourth modified layer 27 and a plurality of fourth cracks 28 extending from the fourth modified layer 27 and appearing on the surface 13 are formed inside along a predetermined distance on the outer peripheral edge 12 side from the position where the first modified layer 21 is formed.

[0060] In other words, in the fourth modified layer formation step, multiple fourth modified layers 27, which are concentric with the annular first modified layer 21, are formed on the outer edge 12 side of the first modified layer 21. When multiple such annular fourth modified layers 27 are formed, the fourth modified layer formation step can be carried out in almost the same procedure as the first modified layer formation step 1.

[0061] In the fourth modification layer formation step, a fourth modification layer 27 and a fourth crack 28 are formed inside the first wafer 10-1 by stealth dicing using a laser processing apparatus 40. First, the first wafer 10-1 and the laser beam irradiation unit 42 are aligned so that the irradiation part of the laser beam irradiation unit 42 faces a predetermined position on the outer edge 12 side of the first modification layer 21. Then, the focal point 44 of the laser beam 43 is set inside the first wafer 10-1. At this time, the focal point 44 is set in the thickness direction of the first wafer 10-1, at a position closer to the surface 13 than the center.

[0062] Next, similar to the first modified layer formation step 1, the holding table 41 is rotated around a vertical axis while a laser beam 43 is irradiated from the laser beam irradiation unit 42 from the back surface 14 side of the first wafer 10-1. As a result, a fourth modified layer 27 is formed on the outer peripheral edge 12 side of the first modified layer 21, in a concentric, annular shape and continuous with the first modified layer 21.

[0063] At this time, a crack (the fourth crack 28) extends from the fourth modified layer 27 and is exposed on the surface 13 side. Due to the bulging of the fourth modified layer 27 and the fourth crack 28, the first wafer 10-1 warps in the outer peripheral region 16 on the outer peripheral edge 12 side of the first modified layer 21 and the first crack 22, causing the surface 13 side to become convex.

[0064] The warpage in this case is greater when multiple fourth modified layers 27 are formed compared to when only the first modified layer 21 is formed. Specifically, for example, when the first modified layer 21 is formed 2 mm inward from the outer edge 12 of a first wafer 10-1 with a diameter of 300 mm, a warpage occurs where the surface 13 moves about 1 to 2 μm towards the back surface 14 at the position of the outer edge 12. In contrast, when multiple fourth modified layers 27 are formed, the warpage is about 10 to 20 μm.

[0065] In the fourth modified layer formation step, similar to the first modified layer formation step 1, the laser beam 43 may be irradiated multiple times by changing the height of the focal point 44 of the laser beam 43, or by irradiating with a laser beam 43 having multiple focal points 44 that are separated in the thickness direction of the first wafer 10-1, thereby forming multiple fourth modified layers 27 in the thickness direction of the first wafer 10-1. In this case, the fourth modified layers 27 present in the thickness direction are formed as a whole at a position closer to the surface 13 than the center in the thickness direction of the first wafer 10-1.

[0066] [Second variation] Figure 14 is a cross-sectional view showing the first wafer 10-1 during the fifth modified layer formation step according to the second modified example. Figure 15 is a plan view showing an example of the first wafer 10-1 after the fifth modified layer formation step according to the second modified example. The fifth modified layer formation step is performed before the bonded wafer formation step 2 is carried out. The fifth modified layer formation step is a step of forming a fifth modified layer 29 and a fifth crack 30 extending from the fifth modified layer 29 along a direction parallel to the surface 13 of the first wafer 10-1 inside the outer peripheral region 16 of the first wafer 10-1. Note that the parallel direction means that the inclination of the approximate plane, which approximates the entire extended fifth crack 30 as a plane, with respect to the horizontal plane is within ±5 degrees, preferably within ±2 degrees.

[0067] In the fifth modification layer formation step, a fifth modification layer 29 and a fifth crack 30 are formed inside the first wafer 10-1 by stealth dicing using a laser processing device 40. First, the first wafer 10-1 and the laser beam irradiation unit 42 are aligned so that the irradiation part of the laser beam irradiation unit 42 is facing a position on the outer edge 12 side from the position where the first modification layer 21 is formed. Then, the focal point 44 of the laser beam 43 is set inside the first wafer 10-1. At this time, multiple focal points 44 are formed radially in the outer region 16 of the first wafer 10-1.

[0068] Next, similar to the third modified layer formation step 4, the holding table 41 is rotated around a vertical axis while a laser beam 43 is irradiated from the back surface 14 side of the first wafer 10-1 from the laser beam irradiation unit 42. That is, the laser beam 43 is irradiated so that multiple focal points 44 of the radially branched laser beam 43 move along the outer edge 12. After processing the outer peripheral region 16 all the way around, the positions of the multiple focal points 44 are moved radially, and the processing is carried out in a concentric manner in the same way until the entire annular outer peripheral region 16 in a plan view is processed. As a result, an annular fifth modified layer 29 is formed over the entire outer peripheral region 16.

[0069] At this time, a crack (the fifth crack 30) extends from the fifth modified layer 29 along a direction parallel to the surface 13 of the first wafer 10-1, and extends across the entire outer peripheral region 16 in a plan view. As a result, a layer is formed in the outer peripheral region 16 of the first wafer 10-1 that separates the surface 13 side from the back surface 14 side. Due to the bulging of the fifth modified layer 29 and the fifth crack 30, the first wafer 10-1 develops a warp in the outer peripheral region 16 on the outer edge 12 side of the first modified layer 21 and the first crack 22, with the surface 13 side becoming convex.

[0070] The warpage in this case is greater when a fifth modified layer 29 is formed in addition to the first modified layer 21 compared to when only the first modified layer 21 is formed. Specifically, for example, when the first modified layer 21 is formed 2 mm inward from the outer edge 12 of a first wafer 10-1 with a diameter of 300 mm, a warpage occurs where the surface 13 moves about 1 to 2 μm towards the back surface 14 at the position of the outer edge 12. In contrast, when a fifth modified layer 29 is formed, the warpage is about 2 to 5 μm. [Explanation of symbols]

[0071] 10 wafers 10-1 First Wafer 10-2 Second wafer 11 circuit boards 12 Outer edge 13 Surface 14 Back side 15 Device Area 16 Outer area 17 planned division lines 18 devices 19 Bonding layer 20 Laminated wafers 21 First Modified Layer 22 First Crack 23 Second Modified Layer 24 The second crack 25. Third Modification Layer 26 Finishing thickness 27. Fourth Modification Layer 28. The Fourth Crack 29. Fifth Modification Layer 30 The Fifth Crack 43 Laser beam 44 Focusing points

Claims

1. A method for processing wafers, A first modified layer formation step involves irradiating a first wafer, which has multiple devices formed on its surface and whose outer edge is chamfered, with a laser beam of a wavelength that penetrates the first wafer in an annular manner along a position a predetermined distance inward from the outer edge of the first wafer, thereby forming an annular first modified layer and a first crack extending from the first modified layer and appearing on the surface side of the first wafer, thereby causing warping in the outer peripheral region on the outer edge side of the first modified layer and the first crack; After performing the first modified layer formation step, the surface side of the first wafer is bonded to the second wafer to form a bonded wafer in a bonded wafer formation step, After performing the bonded wafer formation step, a grinding step is performed in which the first wafer of the bonded wafer is ground from the back side to thin it to the finished thickness, Equipped with, The first modified layer formation step is characterized in that the focusing point of the laser beam is positioned on the surface side of the position that bisects the thickness of the first wafer, and the first modified layer is formed on the surface side of the position that bisects the thickness of the first wafer. Wafer processing method.

2. After performing the bonded wafer forming step, and before performing the grinding step, A second modification layer formation step involves irradiating the first wafer with a laser beam of a wavelength that penetrates the first wafer in an annular manner from the back side of the first wafer along a position a predetermined distance inward from the outer edge of the first wafer, thereby forming an annular second modification layer and a second crack extending from the second modification layer and connecting to the first modification layer inside the first wafer. A removal step of applying an external force to the outer peripheral region to remove the outer peripheral region, A further feature comprising: The wafer processing method according to claim 1.

3. After the first modified layer formation step is carried out, and before the grinding step is carried out, The method further comprises a third modification layer formation step, in which a laser beam of a wavelength that penetrates the first wafer is irradiated radially onto the outer peripheral region to form a radial third modification layer that divides the outer peripheral region into at least two or more sections. A method for processing a wafer according to claim 1 or 2.

4. Before performing the bonded wafer formation step, The method further comprises a fourth modification layer formation step, in which a laser beam of a wavelength that penetrates the first wafer is irradiated in an annular manner along a predetermined distance toward the outer edge from the position where the first modification layer is formed in the first modification layer formation step, thereby forming a plurality of annular fourth modification layers and fourth cracks extending from the fourth modification layer and appearing on the surface side of the first wafer inside the first wafer. A method for processing a wafer according to claim 1 or 2.

5. Before performing the bonded wafer formation step, The present invention further comprises a fifth modification layer formation step, in which a laser beam of a wavelength that penetrates the first wafer is irradiated onto the outer peripheral region to form a fifth modification layer and a fifth crack extending from the fifth modification layer in a direction parallel to the surface of the first wafer within the first wafer. A method for processing a wafer according to claim 1 or 2.

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