Wafer processing method

Abstract

A wafer processing method is provided, which can suppress the breakage of a device during grinding. The wafer processing method includes the following steps: a bonding step, in which the front side of a first wafer with a chamfered outer periphery is bonded to the front side of a second wafer; a grinding step, in which after the bonding step, the back side of the second wafer is held by a chuck table, and the back side of the first wafer is ground to thin the first wafer to a finished thickness; and a modified layer forming step, in which before the grinding step, a laser beam having a wavelength that is transparent to the first wafer is irradiated along the boundary between the device region and the peripheral remaining region of the first wafer, so as to form an annular modified layer inside the first wafer near the front side.

Description

Technical Field

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

[0002] The chips obtained by cutting TSV (Through-Silicon Via) wafers can connect the electrodes of two chips bonded to each other through through electrodes. For example, 3D NAND flash memory is manufactured using this technology. In order to reduce the back surface, the TSV wafer is ground to make it thinner, but in this case, it is ground while being bonded to a supporting wafer (silicon, glass, ceramic, etc.) as a base.

[0003] Generally, the outer peripheral side of the wafer is chamfered to form an R shape, so when it is ground to be extremely thin, the outer periphery of the wafer becomes a so-called blade shape, and it is easy to cause edge defects during grinding. When edge defects occur during grinding, there is a concern that the defects will extend to the device and cause damage to the device. As a countermeasure, the so-called edge trimming technology has been developed (for example, refer to Patent Document 1).

[0004] Patent Document 1: Japanese Patent No. 4895594

[0005] However, the edge trimming technology disclosed in Patent Document 1 has the problem that when the outer periphery of the front side of the wafer is cut into a ring shape, chipping may occur to the device, thereby damaging the device, and the device may be easily contaminated by contaminants due to the large amount of cutting chips generated. Summary of the invention

[0006] Therefore, an object of the present invention is to provide a wafer processing method capable of suppressing device breakage during grinding.

[0007] According to one embodiment of the present invention, a method for processing a wafer is provided, characterized in that the method for processing a wafer has the following steps: a bonding step, in which the front side of a first wafer is bonded to the front side of a second wafer, the first wafer having a device area on the front side where a plurality of devices are formed and a peripheral remaining area surrounding the device area, and the peripheral edge of the first wafer is chamfered; a grinding step, in which after the bonding step is performed, the back side of the second wafer is held by a chuck table, and the back side of the first wafer is ground to thin the first wafer to a finished thickness; and a modified layer forming step, in which before the grinding step is performed, a laser beam having a wavelength that is transparent to the first wafer is irradiated along a boundary between the device area and the peripheral remaining area of ​​the first wafer to form an annular modified layer inside the vicinity of the front side of the first wafer, and the defect of the peripheral edge of the first wafer generated in the grinding step is suppressed from extending to the device area.

[0008] Preferably, in the wafer processing method, in the modified layer forming step, the modified layer is formed by irradiating the laser beam from the back side of the first wafer before or after the bonding step.

[0009] Preferably, in the wafer processing method, in the modified layer forming step, before the bonding step, the modified layer is formed using the laser beam irradiated from the front surface side of the first wafer.

[0010] According to another aspect of the present invention, a method for processing a wafer is provided, wherein the method for processing a wafer has the following steps: a bonding step of bonding the front side of a first wafer to the front side of a second wafer, the first wafer having a device area on the front side where a plurality of devices are formed and a peripheral remaining area surrounding the device area, and the peripheral edge of the first wafer is chamfered; a grinding step of, after the bonding step is performed, holding the back side of the second wafer by a chuck table, and grinding the back side of the first wafer to thin the first wafer; and a laser processing groove forming step of, before the bonding step is performed, irradiating a laser beam having a wavelength that is absorptive to the first wafer from the front side of the first wafer along a boundary between the device area and the peripheral remaining area, thereby forming an annular laser processing groove on the front side of the first wafer whose depth exceeds the finished thickness of the first wafer.

[0011] The wafer processing method of the present invention has the effect of being able to suppress damage to devices during grinding. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a perspective view showing an example of a wafer to be processed by the wafer processing method according to the first embodiment.

[0013] Figure 2 It is along Figure 1 Cross-sectional view along line II-II.

[0014] Figure 3 Yes Figure 1 The device of the wafer is shown in a perspective view with the device enlarged.

[0015] Figure 4 This is a flowchart showing the flow of the wafer processing method according to the first embodiment.

[0016] Figure 5 It is shown in Figure 4 The present invention is a perspective view showing a state in which the front surface of a first wafer and the front surface of a second wafer are placed opposite to each other in a bonding step of a wafer processing method shown.

[0017] Figure 6 It is shown in Figure 4A perspective view showing a state where a first wafer and a second wafer are bonded together in a bonding step of a wafer processing method shown.

[0018] Figure 7 It is along Figure 6 Cross-sectional view along line VII-VII.

[0019] Figure 8 It is schematically shown Figure 4 A cross-sectional view of a reforming layer forming step in a wafer processing method is shown.

[0020] Fig. 9 It is schematically shown Figure 4 A cross-sectional view of a grinding step of a wafer processing method is shown.

[0021] Fig.10 It is schematically shown Figure 4 FIG. 1 is a top view of a wafer after the grinding step of the wafer processing method shown.

[0022] Fig.11 This is a flowchart showing the flow of the wafer processing method according to the second embodiment.

[0023] Fig.12 It is schematically shown Fig.11 A cross-sectional view of a reforming layer forming step in a wafer processing method is shown.

[0024] Fig.13 It is schematically shown Fig.11 A cross-sectional view of a modified example of the reforming layer forming step of the wafer processing method shown.

[0025] Fig.14 This is a flowchart showing the flow of a wafer processing method according to the third embodiment.

[0026] Fig.15 It is schematically shown Fig.14 A cross-sectional view showing a state where a water-soluble resin is applied in a laser processing groove forming step of a wafer processing method is shown.

[0027] Fig.16 It is schematically shown Fig.14 A cross-sectional view showing a state where a laser processed groove is formed in a laser processed groove forming step of a wafer processing method is shown.

[0028] Fig.17 It is schematically shown Fig.14 A cross-sectional view showing a state where the water-soluble resin is removed in a laser processing groove forming step of a wafer processing method shown.

[0029] Fig.18 This is a flowchart showing the flow of a wafer processing method according to the fourth embodiment.

[0030] Fig.19 It is schematically shown Fig.18 A cross-sectional view of a pre-grinding step of a wafer processing method is shown.

[0031] Fig. 20 It is schematically shown Fig.18 A cross-sectional view of a reforming layer forming step in a wafer processing method is shown.

[0032] Description of symbols

[0033] 1: wafer; 1-1: first wafer; 1-2: second wafer; 3: device area; 4: peripheral remaining area; 5: front side; 6: device; 8: peripheral edge; 11: back side; 13: modified layer; 14: crack (defect); 15: laser processed groove; 21: laser beam; 32: chuck worktable; 41: laser beam; 100: finished thickness; ST1: bonding step; ST2: modified layer forming step; ST3: grinding step; ST10: laser processed groove forming step; ST20: pre-grinding step. DETAILED DESCRIPTION

[0034] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited by the contents described in the following embodiments. In addition, the constituent elements described below include contents that can be easily thought of by those skilled in the art, and substantially the same contents. In addition, the structures described below can be appropriately combined. In addition, various omissions, substitutions or changes in the structure can be made within the scope of the gist of the present invention.

[0035] [First embodiment]

[0036] A wafer processing method according to a first embodiment of the present invention will be described with reference to the drawings. Figure 1 This is a perspective view showing an example of a wafer to be processed by the wafer processing method according to the first embodiment. Figure 2 It is along Figure 1 Cross-sectional view along line II-II. Figure 3 Yes Figure 1 The device of the wafer is shown in a perspective view with the device enlarged. Figure 4 This is a flowchart showing the flow of the wafer processing method according to the first embodiment.

[0037] The wafer processing method of the first embodiment is Figure 1 In the first embodiment, the wafer 1 is a disk-shaped semiconductor wafer or optical device wafer having a substrate 2 made of silicon, sapphire, gallium arsenide, etc. Figure 1 and Figure 2As shown, the wafer 1 has a device region 3 and a peripheral remaining region 4 surrounding the device region 3 on the front side 5 of the substrate 2, and the peripheral edge 8 is chamfered.

[0038] The device region 3 is formed with a plurality of devices 6, and the devices 6 are respectively formed in respective regions divided by a plurality of intersecting predetermined division lines 7 on the front surface 5 of the substrate 2. That is, the predetermined division lines 7 divide the plurality of devices 6. In the first embodiment, the devices 6 constitute a 3D NAND flash memory, but the present invention is not limited thereto.

[0039] In addition, if Figure 3 As shown, the device 6 has an electrode pad 9 and a through electrode 10 connected to the electrode pad 9. At least one electrode pad 9 is provided on the front surface of the device 6 (plural in the first embodiment). When the substrate 2 is thinned and the devices 6 are separated one by one from the chip 1, the through electrode 10 becomes a through electrode (TSV: Through-Silicon Via) that penetrates the substrate 2 of the device 6. In the first embodiment, the through electrode 10 and the electrode pad 9 are provided in a one-to-one correspondence. One end of the through electrode 10 is connected to the corresponding electrode pad 9, extends from the corresponding electrode pad 9 toward the back side 11 of the substrate 2 of the chip 1, and is buried in the substrate 2. In addition, the length of the through electrode 10 from the front side 5 of the substrate 2 of the chip 1 is equal to the finished thickness 100 of the chip 1, but in the present invention, it can also be longer than the finished thickness 100.

[0040] In addition, in the state before processing of the wafer processing method of the first embodiment, as Figure 2 and Figure 3 As shown, the other end of the through electrode 10 is not exposed on the back surface 11 side but is located inside the substrate 2. In the first embodiment, the device 6 has the through electrode 10, so the wafer 1 is a so-called TSV wafer in which the devices 6 obtained by dividing one by one have the through electrode.

[0041] The peripheral surplus region 4 is a region surrounding the device region 3 along the entire circumference and having no device 6 formed therein. The peripheral edge 8 of the wafer 1 is formed into an arc-shaped cross section from the front surface 5 to the back surface 11 so that the center in the thickness direction protrudes most toward the outer periphery.

[0042] The wafer processing method of the first embodiment is a method of bonding the front surfaces 5 of a pair of wafers 1 to each other and thinning one of the wafers 1 to a finished thickness of 100. In addition, in this specification, when the wafers 1 in the pair of wafers 1 are distinguished from each other, the one wafer 1 is referred to as the first wafer 1-1 and the other wafer 1 is referred to as the second wafer 1-2. When no distinction is made, they are simply referred to as wafers 1. Figure 4As shown, the wafer processing method of the first embodiment includes a bonding step ST1 , a reformed layer forming step ST2 , and a grinding step ST3 .

[0043] (Lamination steps)

[0044] Figure 5 It is shown in Figure 4 The present invention is a perspective view showing a state in which the front surface of a first wafer and the front surface of a second wafer are placed opposite to each other in a bonding step of a wafer processing method shown. Figure 6 It is shown in Figure 4 A perspective view showing a state where a first wafer and a second wafer are bonded together in a bonding step of a wafer processing method shown. Figure 7 It is along Figure 6 Cross-sectional view along line VII-VII.

[0045] The bonding step ST1 is a step of bonding the front surface 5 side of the first wafer 1-1 to the front surface 5 side of the second wafer 1-2. In the bonding step ST1, the adhesive layer 12 is laminated on one of the front surface 5 of the first wafer 1-1 and the front surface 5 of the second wafer 1-2. In the first embodiment, the adhesive layer 12 is laminated on the front surface 5 of the second wafer 1-2. In the bonding step ST1, as shown in FIG. Figure 5 As shown in FIG. 1 , after the front surface 5 of the first wafer 1-1 and the front surface 5 of the second wafer 1-2 are placed opposite to each other with a gap therebetween, as shown in FIG. Figure 6 and Figure 7 As shown, the front surface 5 of the first wafer 1-1 is bonded to the front surface 5 of the second wafer 1-2. In the first embodiment, a double-sided tape having an adhesive material layer laminated on the front and back surfaces of a base layer is used as the adhesive layer 12, but in the present invention, the adhesive layer 12 is not limited to the double-sided tape. When the front surface 5 of the first wafer 1-1 is bonded to the front surface 5 of the second wafer 1-2, the wafer processing method enters the modified layer forming step ST2.

[0046] (Reformed layer forming step)

[0047] Figure 8 It is schematically shown Figure 4 2 is a cross-sectional view of a modified layer forming step of a wafer processing method shown in FIG. The modified layer forming step ST2 is a step of irradiating a laser beam 21 having a wavelength that is transparent to the first wafer 1-1 along a boundary between the device region 3 and the peripheral remaining region 4 of the first wafer 1-1 before the grinding step ST3 and after the bonding step ST1, forming an annular modified layer 13 inside the first wafer 1-1 near the front side 5, and suppressing cracks 14 (which are defects of the outer peripheral edge 8 of the first wafer 1-1) generated in the grinding step ST3. Fig.10 as shown) extends to device region 3.

[0048] In addition, the modified layer 13 refers to a region where the density, refractive index, mechanical strength or other physical properties are in a state different from the surrounding base material, such as a melt-processed region, a crack region, an insulation breakdown region, a refractive index change region, and a region where these regions are mixed, etc. In the first embodiment, the mechanical strength of the modified layer 13 is lower than the mechanical strength of the surrounding.

[0049] In the reforming layer forming step ST2, the laser processing device 20 sucks and holds the back surface 11 side of the second wafer 1-2 on the holding surface 23 of the chuck table 22. In the reforming layer forming step ST2, as shown in FIG. Figure 8 As shown, the laser processing device 20 sets the laser beam 21 focal point 21-1 inside the first wafer 1-1 and close to the front surface 5 after the laser beam irradiation unit 24 irradiating the laser beam 21 is placed in the vertical direction to face the first wafer 1-1 at the outer peripheral side of the device region 3, and irradiates the laser beam 21 from the laser beam irradiation unit 24 to the first wafer 1-1 while rotating the chuck table 22 around the axis parallel to the vertical direction. In the first embodiment, as Figure 8 As shown, the laser processing device 20 makes the laser light irradiation unit 24 that irradiates the laser light 21 be placed along the vertical direction at the boundary or near the boundary between the device area 3 and the peripheral remaining area 4 of the peripheral remaining area 4 of the first chip 1-1, thereby irradiating the laser light 21 to the boundary or near the boundary.

[0050] In the reformed layer forming step ST2, after the laminating step ST1, the laser processing device 20 forms a ring-shaped reformed layer 13 continuous along the entire circumference at a position on the outer peripheral side of the device region 3 inside the first wafer 1-1 using the laser beam 21 irradiated from the back surface 11 side of the first wafer 1-1. In addition, in the first embodiment, in the reformed layer forming step ST2, the laser processing device 20 forms a ring-shaped continuous reformed layer 13 in the range from the front surface 5 of the first wafer 1-1 to the finished thickness 100. In the reformed layer forming step ST2, the laser processing device 20 may irradiate the laser beam 21 under the condition that the cracks generated extend from the reformed layer 13 in the thickness direction. In addition, in the reformed layer forming step ST2, the laser processing device 20 may change the height of the focal point 21-1 of the laser beam 21 and irradiate the laser beam 21 multiple times, thereby forming a multi-layer reformed layer 13. In addition, the total thickness of the modified layer 13 and the crack is formed to be at least 1 / 2 of the finished thickness 100 of the first wafer 1-1, and preferably formed to be greater than the total thickness of the finished thickness 100 of the first wafer 1-1. When the modified layer 13 is formed in a continuous ring shape at a position on the outer peripheral side of the device region 3 of the first wafer 1-1, the wafer processing method enters the grinding step ST3.

[0051] (Grinding steps)

[0052] Fig. 9 It is schematically shown Figure 4 A cross-sectional view of a grinding step of a wafer processing method is shown. Fig.10 It is schematically shown Figure 4 The top view of the wafer after the grinding step of the wafer processing method shown in FIG. The grinding step ST3 is a step of grinding the back side 11 of the first wafer 1-1 by holding the back side 11 of the second wafer 1-2 using the chuck table 32 of the grinding device 30 after the bonding step ST1, thereby thinning the first wafer 1-1 to a finished thickness of 100.

[0053] like Fig. 9 As shown, in the grinding step ST3, the grinding device 30 attracts and holds the back side 11 of the second wafer 1-2 on the holding surface 33 of the chuck table 32, rotates the grinding wheel 35 and the chuck table 32 around the axis through the main shaft 34, supplies grinding water, and makes the grinding tool 31 of the grinding wheel 35 approach the chuck table 32 at a specified feed speed, thereby grinding the back side 11 of the first wafer 1-1 by the grinding tool 31. In the grinding step ST3, the grinding device 30 grinds the first wafer 1-1 and thins it to a finished thickness of 100. In the grinding step ST3, when the grinding device 30 grinds the first wafer 1-1 and thins it to a finished thickness of 100, the other end of the through electrode 10 is exposed or about to be exposed on the back side 11. In addition, Fig. 9 The device 6 and the through-electrode 10 of the second wafer 1-2 are omitted. Fig.10 The other end of the through-electrode 10 is omitted.

[0054] In the grinding step ST3, since the modified layer 13 is continuously formed at the outer peripheral side of the first wafer 1-1 relative to the device region 3, the first wafer 1-1 is broken by the modified layer 13. Therefore, in the grinding step ST3, when the crack 14 generated at the outer peripheral edge 8 of the first wafer 1-1 is Fig.10 When the cracks extend toward the center of the first wafer 1-1 and reach the modified layer 13 as shown, the first wafer 1-1 is blocked by the modified layer 13, so that the cracks can be suppressed from extending to a position closer to the center of the first wafer 1-1 than the modified layer 13. In addition, when the first wafer 1-1 is thinned to a finished thickness of 100, the wafer processing method is terminated.

[0055] The wafer processing method of the first embodiment provides an annular modified layer 13 at a position on the outer peripheral side of the wafer 1 relative to the device region 3, and even if a crack 14 is generated at the outer peripheral edge 8 during grinding, the annular modified layer 13 prevents the crack 14 from extending to the device region 3. Therefore, even if a crack 14 is generated at the outer edge during grinding, the wafer processing method can suppress the crack from extending to the device region 3, thereby achieving ultra-thin grinding of the bonded first wafer 1-1 while suppressing damage to the device 6. As a result, the wafer processing method has the effect of suppressing damage to the device 6 during grinding.

[0056] In addition, the chip processing method irradiates the laser light 21 in the modified layer forming step ST2 to form the modified layer 13, so no processing chips are generated compared to the case of cutting using a cutting tool. This is very effective in processing the chip 1 for forming a device 6 such as an image sensor that avoids dust adhering to the device 6.

[0057] [Second embodiment]

[0058] A wafer processing method according to a second embodiment of the present invention will be described with reference to the drawings. Fig.11 This is a flowchart showing the flow of the wafer processing method according to the second embodiment. Fig.12 It is schematically shown Fig.11 A cross-sectional view of a reforming layer forming step in a wafer processing method is shown. Fig.13 It is schematically shown Fig.11 A cross-sectional view of a modified example of the reforming layer forming step of the wafer processing method shown. Fig.11 , Fig.12 as well as Fig.13 In the present invention, the same parts as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

[0059] like Fig.11 As shown in FIG. 1 , the wafer processing method of the second embodiment is the same as the first embodiment except that the modified layer forming step ST2 is performed before the bonding step ST1. In the modified layer forming step ST2 of the wafer processing method of the second embodiment, the laser processing device 20 sucks and holds the front side 5 of the first wafer 1-1 on which the adhesive layer 12 is laminated on the holding surface 23 of the chuck table 22. In the modified layer forming step ST2, as shown in FIG. Fig.12As shown, the laser processing apparatus 20, similarly to the first embodiment, sets the laser beam 21 irradiation unit 24 for irradiating the laser beam 21 to face the position of the first wafer 1-1 on the outer peripheral side of the device region 3 in the vertical direction, sets the focal point 21-1 of the laser beam 21 to the position inside the first wafer 1-1 and close to the front surface 5, and irradiates the laser beam 21 from the laser beam irradiation unit 24 to the back surface 11 side of the first wafer 1-1 while rotating the chuck table 22 around the axis parallel to the vertical direction. In the reformed layer forming step ST2, before the bonding step ST1, the laser processing apparatus 20 forms the ring-shaped reformed layer 13 continuous along the entire circumference at the position of the inside of the first wafer 1-1 on the outer peripheral side of the device region 3 by using the laser beam 21 irradiated from the back surface 11 side of the first wafer 1-1. The wafer processing method of the second embodiment may also irradiate the laser beam 21 under the condition that the cracks generated extend from the reformed layer 13 in the thickness direction. In addition, the processing method of the wafer of the second embodiment may change the height of the focal point 21-1 of the laser beam 21 and irradiate the laser beam 21 multiple times to form a multi-layer modified layer 13. In addition, the total thickness of the modified layer 13 and the crack is formed to be at least 1 / 2 of the finished thickness 100 of the first wafer 1-1, and preferably formed to be at least the total thickness of the finished thickness 100 of the first wafer 1-1. In addition, in the processing method of the wafer of the second embodiment, in the modified layer forming step ST2, the modified layer 13 is formed in the first wafer 1-1 laminated with the adhesive layer 12, but the present invention may also be affixed to the front side 5 of the first wafer 1-1, and after laser processing is performed while holding the protective tape side with the chuck table 22, the front side 5 of the first wafer 1-1 with the protective tape peeled off is affixed to the second wafer 1-2.

[0060] In addition, in the modified layer forming step ST2 of the wafer processing method of the second embodiment, as Fig.13 As shown, the laser processing device 20 sucks and holds the back side 11 of the first wafer 1-1 in a state where the adhesive layer 12 is not laminated on the holding surface 23 of the chuck table 22 before the bonding step ST1, and irradiates the front side 5 of the first wafer 1-1 with the laser beam 21 from the laser beam irradiation unit 24. In the modified layer forming step ST2 of the wafer processing method of the second embodiment, the laser processing device 20 can form a continuous annular modified layer 13 along the entire circumference at a position on the outer peripheral side of the device region 3 inside the first wafer 1-1 by using the laser beam 21 irradiated from the front side 5 of the first wafer 1-1, similarly to the first embodiment. When the continuous annular modified layer 13 is formed at a position on the outer peripheral side of the device region 3 of the first wafer 1-1, the wafer processing method enters the bonding step ST1.

[0061] The wafer processing method of the second embodiment provides an annular modified layer 13 at a position on the outer peripheral side of the device region 3 of the wafer 1, and even if a crack 14 is generated at the outer peripheral edge 8 during grinding, the annular modified layer 13 prevents the crack from extending to the device region 3. As a result, the wafer processing method has the effect of suppressing the device 6 from being damaged during grinding.

[0062] [Third embodiment]

[0063] A wafer processing method according to a third embodiment of the present invention will be described with reference to the drawings. Fig.14 This is a flowchart showing the flow of a wafer processing method according to the third embodiment. Fig.15 It is schematically shown Fig.14 A cross-sectional view showing a state where a water-soluble resin is applied in a laser processing groove forming step of a wafer processing method is shown. Fig.16 It is schematically shown Fig.14 A cross-sectional view showing a state where a laser processed groove is formed in a laser processed groove forming step of a wafer processing method is shown. Fig.17 It is schematically shown Fig.14 A cross-sectional view showing a state where the water-soluble resin is removed in a laser processing groove forming step of a wafer processing method shown. Fig.14 , Fig.15 , Fig.16 as well as Fig.17 In the present invention, the same reference numerals are used to denote the same parts as those in the first embodiment and the second embodiment, and description thereof will be omitted.

[0064] like Fig.14 As shown, the wafer processing method of the third embodiment is the same as the first and second embodiments except that it includes a laser processing groove forming step ST10 performed before the bonding step ST1 instead of the reforming layer forming step ST2.

[0065] The laser processing groove forming step ST10 is a step of irradiating a laser beam 41 of a wavelength that is absorptive to the first chip 1-1 from the front side 5 of the first chip 1-1 along the outer peripheral edge 8 of the device area 3 before the bonding step ST1 to form an annular laser processing groove 15 on the front side 5 of the first chip 1-1 with a depth exceeding the finished thickness 100 of the first chip 1-1.

[0066] In the laser processing groove forming step ST10, an adhesive tape 101 having a larger diameter than the first wafer 1-1 is adhered to the back surface 11 of the first wafer 1-1, and an annular frame 102 is adhered to the outer periphery of the adhesive tape 101. The resin coating device 50 is as shown in FIG. Fig.15As shown in the figure, the back side 11 of the first wafer 1-1 is sucked and held by the holding surface 52 of the rotating table 51 via the adhesive tape 101, and a liquid water-soluble resin 54 is applied to the front side 5 of the first wafer 1-1 from the coating nozzle 53 in the center of the first wafer 1-1 while the rotating table 51 is rotated around the axis. The water-soluble resin 54 includes a water-soluble liquid resin such as polyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP).

[0067] The water-soluble resin 54 applied to the front surface 5 of the first wafer 1-1 is spread to the outer edge of the first wafer 1-1 by the centrifugal force generated by the rotation of the rotary table 51, and covers the entire front surface 5 of the first wafer 1-1. In the laser processing groove forming step ST10, after applying the water-soluble resin 54 to the front surface 5 of the first wafer 1-1, the resin coating device 50 dries or heats the water-soluble resin 54 to harden it. Fig.16 As shown, the entire front surface 5 of the first wafer 1 - 1 is covered with a water-soluble resin layer 55 .

[0068] In the laser processing groove forming step ST10, the laser processing device 40 sucks and holds the back surface 11 side of the second wafer 1-2 on the holding surface 43 of the chuck table 42 via the adhesive tape 101. In the laser processing groove forming step ST10, as shown in FIG. Fig.16 As shown, the laser processing device 40 sets the focal point of the laser beam 41 to the front surface 5 of the first wafer 1-1 after the laser beam irradiation unit 44 irradiating the laser beam 41 is placed in the vertical direction opposite to the position of the first wafer 1-1 on the outer peripheral side of the device region 3, and irradiates the laser beam 41 from the laser beam irradiation unit 44 to the first wafer 1-1 while rotating the chuck table 42 around the axis parallel to the vertical direction. In addition, in the third embodiment, as Fig.16 As shown, the laser processing device 40 makes the laser light irradiation unit 44 that irradiates the laser light 41 be placed along the vertical direction opposite to the boundary or near the boundary between the device area 3 and the peripheral remaining area 4 of the peripheral remaining area 4 of the first chip 1-1, so as to irradiate the laser light 41 to the boundary or near the boundary.

[0069] In the laser processing groove forming step ST10, the laser processing device 40 performs ablation processing along the entire circumference at a position on the front side 5 of the first wafer 1-1 that is closer to the outer peripheral side than the device region 3, and forms an annular laser processing groove 15 that is continuous along the entire circumference at a position on the front side 5 of the first wafer 1-1 that is closer to the outer peripheral side than the device region 3. In addition, in the third embodiment, in the laser processing groove forming step ST10, the laser processing device 40 forms an annular continuous laser processing groove 15 having a depth exceeding the finished thickness 100 from the front side 5 of the first wafer 1-1.

[0070] In the laser processing groove forming step ST10, after the laser processing groove 15 is formed, Fig.17 As shown, the cleaning device 60 sucks and holds the back side 11 of the first wafer 1-1 on the holding surface 62 of the rotating table 61 through the adhesive tape 101, rotates the rotating table 61 about the axis, and sprays cleaning water 64 from the cleaning water nozzle 63 moving along the holding surface 62 on the first wafer 1-1 toward the front side 5 of the first wafer 1-1. In the laser processing groove forming step ST10, the cleaning water 64 flows smoothly on the front side 5 of the first wafer 1-1 by the centrifugal force generated by the rotation of the rotating table 61, and washes away the debris attached to the resin layer 55 together with the water-soluble resin layer 55, and removes it from the front side 5 of the first wafer 1-1. In the laser processing groove forming step ST10, when the cleaning device 60 supplies the cleaning water 64 to the front side 5 of the first wafer 1-1 while rotating the rotating table 61 for a predetermined time, the cleaning of the first wafer 1-1 is completed, and the first wafer 1-1 is dried.

[0071] In the third embodiment, the resin coating device 50 forms the water-soluble resin layer 55, and the front surface 5 of the first wafer 1-1 is cleaned by the cleaning device 60 different from the resin coating device 50, but the present invention may be that a single device having nozzles 53 and 63 forms the water-soluble resin layer 55 and cleans the front surface 5 of the first wafer 1-1. When the front surface of the first wafer 1-1 is cleaned by the cleaning water 64 and the first wafer 1-1 is dried, the wafer processing method enters the bonding step ST1.

[0072] The wafer processing method of the third embodiment provides an annular laser processing groove 15 at a position on the outer peripheral side of the device region 3 of the wafer 1, and even if a crack 14 is generated at the outer peripheral edge 8 during grinding, the annular laser processing groove 15 prevents the crack 14 from extending to the device region 3. As a result, the wafer processing method has the effect of suppressing the device 6 from being damaged during grinding.

[0073] [Fourth embodiment]

[0074] A wafer processing method according to a fourth embodiment of the present invention will be described with reference to the drawings. Fig.18 This is a flowchart showing the flow of a wafer processing method according to the fourth embodiment. Fig.19 It is schematically shown Fig.18 A cross-sectional view of a pre-grinding step of a wafer processing method is shown. Fig. 20 It is schematically shown Fig.18 A cross-sectional view of a reforming layer forming step in a wafer processing method is shown. Fig.18 , Fig.19 as well as Fig. 20 In the present invention, the same parts as those in the first embodiment, the second embodiment, and the third embodiment are denoted by the same reference numerals, and description thereof is omitted.

[0075] like Fig.18 As shown, the wafer processing method of the fourth embodiment has a pre-grinding step ST20, and is the same as the first embodiment except that the pre-grinding step ST20 is a step of grinding the back surface 11 of the first wafer 1-1 in advance after the bonding step ST1 and before the modified layer forming step ST2.

[0076] In the pre-grinding step ST20, the grinding device 70 sucks and holds the back side 11 of the second wafer 1-2 on the holding surface 73 of the chuck table 72, as shown in FIG. Fig.19 As shown, while the grinding wheel 75 is rotated by the main shaft 74 and the chuck table 72 is rotated about the axis, grinding water is supplied, and the grinding tool 71 of the grinding wheel 75 is brought close to the chuck table 72 at a predetermined feed speed, so that the back side 11 of the first wafer 1-1 is ground by the grinding tool 71.

[0077] In the preliminary grinding step ST20, the first wafer 1-1 is ground to a predetermined thickness thicker than the finished thickness 100. When the first wafer 1-1 is thinned to the predetermined thickness, the wafer processing method proceeds to the reformed layer forming step ST2.

[0078] like Fig. 20 As shown, in the modified layer forming step ST2 of the wafer processing method of the fourth embodiment, the back surface 11 of the first wafer 1-1 ground in the pre-grinding step ST20 is irradiated with the laser beam 21 to form the modified layer 13. Fig.19 and Fig. 20 The device 6 and the through-electrode 10 of the second wafer 1 - 2 are omitted.

[0079] The wafer processing method of the fourth embodiment provides an annular modified layer 13 at a position on the outer peripheral side of the device region 3 of the wafer 1, and even if a crack 14 is generated at the outer peripheral edge 8 during grinding, the annular modified layer 13 prevents the crack 14 from extending to the device region 3. As a result, the wafer processing method has the effect of suppressing the device 6 from being damaged during grinding.

[0080] In addition, in the wafer processing method of the fourth embodiment, the first wafer 1-1 is thinned in the pre-grinding step ST20, so in the modified layer forming step ST2, even if the laser light 21 is irradiated from the back side 11, the modified layer 13 can be formed at a desired position. The wafer processing method of the fourth embodiment has the pre-grinding step ST20, so in the modified layer forming step ST2, the distance between the focusing lens of the laser light irradiation unit 24 and the focusing point 21-1 becomes closer, and the distance through the wafer 1 also becomes shorter, so that the laser light 21 can be fully focused on the focusing point 21-1 without using a focusing lens with a high numerical aperture.

[0081] In the fourth embodiment, the modified layer forming step ST2 is performed after the pre-grinding step ST20, but in the present invention, the modified layer forming step ST2 may be performed before the bonding step ST1. In the fourth embodiment, the modified layer forming step ST2 is performed after the pre-grinding step ST20, but in the present invention, the laser processing groove forming step ST10 may be performed before the bonding step ST1 instead of the modified layer forming step ST2.

[0082] The present invention is not limited to the above-described embodiment, and can be implemented with various modifications within the scope of the present invention.

Claims

1. A method for processing a wafer, characterized in that: The wafer processing method has the following steps: a bonding step of bonding the front side of a first wafer to the front side of a second wafer, wherein the first wafer and the second wafer, which are identical wafers, respectively have a device region on the front side where a plurality of devices are formed and a peripheral remaining region surrounding the device region, and the outer peripheral edges of the first wafer and the second wafer are chamfered; a grinding step, after the laminating step is performed, holding the back side of the second wafer by a chuck table, grinding the back side of the first wafer to thin the first wafer to a finished thickness; and a modified layer forming step, before the grinding step is performed, irradiating a laser beam having a wavelength that is transparent to the first wafer along a boundary between the device region and the peripheral remaining region of the first wafer, so as to form an annular modified layer inside the first wafer near the front side, The annular reformed layer prevents a defect on the outer peripheral edge of the first wafer generated during the grinding step from extending to the device region.

2. The wafer processing method according to claim 1, wherein: In the modified layer forming step, the modified layer is formed by irradiating the first wafer with the laser beam from the back side before or after the bonding step.

3. The wafer processing method according to claim 1, wherein: In the modified layer forming step, the modified layer is formed by irradiating the first wafer with the laser beam from the front surface side before the bonding step.

4. A method for processing a wafer, wherein: The wafer processing method has the following steps: a bonding step of bonding the front side of a first wafer to the front side of a second wafer, wherein the first wafer and the second wafer, which are identical wafers, respectively have a device region on the front side where a plurality of devices are formed and a peripheral remaining region surrounding the device region, and the outer peripheral edges of the first wafer and the second wafer are chamfered; a grinding step of holding the back side of the second wafer by a chuck table and grinding the back side of the first wafer to thin the first wafer after the bonding step; and A laser processing groove forming step is performed before the bonding step. A laser beam having a wavelength that is absorptive to the first wafer is irradiated from the front side of the first wafer along the boundary between the device area and the peripheral remaining area, thereby forming an annular laser processing groove on the front side of the first wafer whose depth exceeds the finished thickness of the first wafer.

Images