Wafer processing method

Abstract

To provide a wafer processing method which can suppress the harmful effect in detachment of a portion of an outer periphery excessive region surrounding a device region of a bonded wafer.SOLUTION: A wafer processing method comprises: Step (1) of forming a bonded wafer by bonding one surface having a device region and an outer periphery excessive region of a first wafer whose outer peripheral edge is chamfered, to one surface of a second wafer; Step (2) of forming an annular modified region by emitting a laser beam along the outer peripheral edge of the first wafer, and dividing the first wafer into a first outer periphery annular portion and a center region; Step (3) of bonding an expand tape to the other surface of the first wafer; Step (4) of dividing the first wafer into the outer periphery annular portion and the center region with the modified region as a starting point by expanding the expand tape, and detaching the outer periphery annular portion from the bonded wafer; and Step (5) of thinning the first wafer to a finish thickness by grinding it from the other surface side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In the manufacturing process of semiconductor devices, processes that bond two wafers together are used, such as the process of 3D stacked chips like TSV (Through-Silicon Via) and the process of BSI (Back Side Illumination) type CMOS (Complementary Metal Oxide Semiconductor) image sensors, in which two wafers on which pixel integrated circuits are formed are bonded together.

[0003] Such bonded wafers are generally ground to thin them to accommodate the back-to-bottom design of device chips. However, because the outer peripheral edge is chamfered and formed into an R-shape, grinding creates an acute angle (a so-called knife edge), making the edge prone to chipping. Since the extension of this edge chipping can lead to damage to the device, a technology has been proposed for removing a portion of the outer peripheral portion (edge trimming) before grinding the wafer (see Patent Document 1). Another technology has been proposed for irradiating a laser beam along the outer peripheral edge of the device region to form a modified layer, preventing edge chipping that occurs during grinding from extending into the device (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-173961 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-108532 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the method described in Patent Document 1 has the problem that the device is contaminated by cutting debris generated during cutting, and cleaning may not be able to remove all of the contamination. Also, the method described in Patent Document 2 has a different problem in that the peripheral excess area portion breaks off in a ring or arc shape during grinding, damaging the grinding wheel and adversely affecting the processing results, and accumulating inside the grinding device, requiring frequent cleaning.

[0006] The present invention has been made in consideration of such problems, and its purpose is to provide a wafer processing method that can suppress adverse effects that occur when removing a portion of the peripheral excess region that surrounds the device region of a bonded wafer. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, the wafer processing method of the present invention includes a bonded wafer forming step of bonding one surface of a first wafer, the first wafer having a device region where devices are formed and a peripheral excess region surrounding the device region and having a chamfered peripheral edge, to one surface of a second wafer to form a bonded wafer; a dividing step of irradiating the first wafer with a laser beam having a wavelength that is transparent to the first wafer along a position a predetermined distance inside from the peripheral edge of the first wafer to form an annular modified region, and dividing the first wafer into an outer peripheral annular portion corresponding to the peripheral excess region and a central region corresponding to the device region; and an expanding tape applying step of applying an expandable expanding tape to the other surface of the first wafer before or after the execution of the bonding wafer forming step, the dividing step, and the expanding tape applying step; an outer annular portion separating step of expanding the expanding tape to divide the first wafer into the outer annular portion and the central region starting from the annular modified region and separating the outer annular portion from the bonded wafer; and a grinding step of grinding the first wafer of the bonded wafer from the other surface side to thin it to a finishing thickness after the outer annular portion separating step.After the outer annular portion removing step is performed and before the grinding step is performed, ultraviolet light is irradiated to a limited irradiation area so that the ultraviolet light is not irradiated to the outer annular portion, and only the other surface corresponding to the central region of the first wafer is peeled off from the expanding tape. It is characterized by:

[0008] Furthermore, in the wafer processing method of the present invention, the dividing step may include a preliminary dividing step in which, after dividing the outer annular portion and the central region, the laser beam is irradiated onto the outer annular portion to form a modified region in the radial direction, and the outer annular portion is divided into a plurality of arc-shaped portions.

[0009] In the wafer processing method of the present invention, the outer peripheral annular portion detaching step may include a cooling and expanding step of expanding the expanding tape while cooling it.

[0010] Furthermore, in the wafer processing method of the present invention, the outer peripheral annular portion removing step may further include a heating and shrinking step of heating and shrinking a slack portion of the expanding tape formed by expanding the expanding tape after the cooling and expanding step is performed. [Effects of the Invention]

[0011] The present invention can suppress adverse effects that occur when the peripheral excess region surrounding the device region of the bonded wafer is separated. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a flowchart showing the flow of a wafer processing method according to an embodiment. [Figure 2] FIG. 2 is a perspective view showing one state of the bonded wafer forming step shown in FIG. [Figure 3] FIG. 3 is a perspective view showing a state after FIG. 2 in the bonded wafer forming step shown in FIG. [Figure 4] FIG. 4 is a cross-sectional view schematically showing one state of the dividing step shown in FIG. [Figure 5] FIG. 5 is a plan view schematically showing the wafer after the dividing step shown in FIG. [Figure 6]FIG. 6 is a cross-sectional view schematically showing one state of the preliminary cutting step in the cutting step shown in FIG. [Figure 7] FIG. 7 is a plan view schematically showing the wafer after the preliminary dividing step. [Figure 8] FIG. 8 is a cross-sectional view schematically showing one state of the expanding tape applying step shown in FIG. [Figure 9] FIG. 9 is a cross-sectional view schematically showing one state of the outer circumferential annular portion removing step shown in FIG. [Figure 10] FIG. 10 is a cross-sectional view schematically showing one state of the cooling and expanding step during the outer circumferential annular portion removing step shown in FIG. [Figure 11] FIG. 11 is a cross-sectional view schematically showing one state of the heat shrinking step in the outer circumferential annular portion removing step shown in FIG. [Figure 12] FIG. 12 is a cross-sectional view schematically showing one state of the grinding step shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] Modes (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiments. Furthermore, the components described below include those that can be easily imagined by a person skilled in the art and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the configuration can be made within the scope of the gist of the present invention.

[0014] [Embodiment] A method for processing a wafer 10 (see FIG. 2, etc.) according to an embodiment of the present invention will be described with reference to the drawings. The method for processing a wafer 10 according to the embodiment is a method for bonding one surface side of a pair of wafers 10 together and thinning one wafer 10 (first wafer 10-1) to a predetermined finishing thickness.

[0015] In the following description, when distinguishing between the wafers 10 of a pair of wafers 10, one wafer 10 will be referred to as a first wafer 10-1 and the other wafer 10 will be referred to as a second wafer 10-2, and when no distinction is required, they will simply be referred to as wafers 10. In the embodiment, the other, second wafer 10-2, which is not thinned, will be described as a TSV wafer similar to the first wafer 10-1, but in the present invention, it may be a simple substrate wafer without a pattern.

[0016] 1 is a flowchart showing the flow of a method for processing a wafer 10 according to an embodiment. As shown in FIG. 1, the method for processing a wafer 10 according to the embodiment includes a bonded wafer forming step 1, a dividing step 2, an expandable tape applying step 3, an outer peripheral annular portion removing step 4, and a grinding step 5.

[0017] (Bonded wafer formation step 1) Fig. 2 is a perspective view showing one state of the bonded wafer formation step 1 shown in Fig. 1. Fig. 3 is a perspective view showing one state of the bonded wafer formation step 1 shown in Fig. 1 after Fig. 2. The bonded wafer formation step 1 is a step of bonding one surface of a first wafer 10-1 to one surface of a second wafer 10-2 to form a bonded wafer.

[0018] First, the configuration of the wafer 10 to be processed (first wafer 10-1 and second wafer 10-2) will be described. The wafer 10 is a disk-shaped semiconductor wafer, optical device wafer, or other wafer with a substrate 11 made of silicon (Si), sapphire (Al2O3), gallium arsenide (GaAs), silicon carbide (SiC), or the like. The wafer 10 has a chamfered outer periphery 12. In this embodiment, the outer periphery 12 of the wafer 10 is formed into an arc-shaped cross section extending from the front surface 13 to the back surface 14 of the substrate 11, with the center in the thickness direction protruding furthest toward the outer periphery. In this embodiment, the wafer 10 has a diameter of 300 mm and a thickness of 700 μm.

[0019] The wafer 10 has a device region 15 on the surface 13 side of the substrate 11, and a peripheral excess region 16 surrounding the device region 15. The device region 15 has a plurality of planned division lines 17 set in a grid pattern on the surface 13 of the substrate 11, and devices 18 formed in each region defined by the planned division lines 17. The peripheral excess region 16 is a region that surrounds the device region 15 all around and in which no devices 18 are formed.

[0020] In the embodiment, the device 18 constitutes a 3D NAND flash memory and includes an electrode pad and a through-electrode connected to the electrode pad. The through-electrode penetrates the back surface 14 of the substrate 11 when the substrate 11 is thinned and the devices 18 are individually separated from the wafer 10. That is, the wafer 10 of the embodiment is a so-called TSV wafer in which the individually separated devices 18 have through-electrodes. Note that the wafer 10 of the present invention is not limited to a TSV wafer having through-electrodes as in the embodiment, and may be a device wafer without through-electrodes.

[0021] In the bonded wafer formation step 1, one surface of the first wafer 10-1, which has the device region 15 and the peripheral excess region 16, is bonded to one surface of the second wafer 10-2. That is, in the bonded wafer formation step 1 of the embodiment, the front surface 13 of the first wafer 10-1 is bonded to the front surface 13 of the second wafer 10-2.

[0022] In the bonded wafer formation step 1, an adhesive layer 20 is laminated on one of the front surface 13 of the first wafer 10-1 and the front surface 13 of the second wafer 10-2. In the embodiment, the adhesive layer 20 is laminated on the front surface 13 of the second wafer 10-2. Note that, in the embodiment, the adhesive layer 20 is a double-sided tape in which adhesive layers are laminated on the front and back surfaces of a base layer, but the present invention is not limited to double-sided tape and may be, for example, an oxide film or one formed by applying an adhesive containing a resin or the like.

[0023] In the bonded wafer formation step 1, first, the surface 13 of the first wafer 10-1 and the surface 13 of the second wafer 10-2 are placed opposite each other with a gap therebetween, as shown in Fig. 2. Next, the surface 13 of the first wafer 10-1 and the surface 13 of the second wafer 10-2 are bonded together via an adhesive layer 20, as shown in Fig. 3. This forms a bonded wafer.

[0024] (Dividing step 2) Fig. 4 is a cross-sectional view schematically showing one state of the dividing step 2 shown in Fig. 1. Fig. 5 is a plan view schematically showing the wafer 10 after the dividing step 2 shown in Fig. 1. The dividing step 2 is a step of dividing the first wafer 10-1 into a central region 22 corresponding to the device region 15 and an outer circumferential annular portion 23 corresponding to the outer circumferential excess region 16.

[0025] In the dividing step 2, a laser beam 30 is irradiated onto a position a predetermined distance inward from the outer peripheral edge 12 of the first wafer 10-1 to form a modified region 21 that will serve as a starting point for division. The position a predetermined distance inward from the outer peripheral edge 12 of the first wafer 10-1 refers to the position where the central region 22 and the outer peripheral annular portion 23 of the first wafer 10-1 are to be divided, i.e., the outer peripheral edge of the device region 15. The laser beam 30 is a laser beam with a wavelength that is transparent to the first wafer 10-1, such as infrared rays (IR).

[0026] The modified region 21 refers to a region in which the density, refractive index, mechanical strength, or other physical properties are different from those of the surrounding area. The modified region 21 is, for example, a melt-processed region, a crack region, a dielectric breakdown region, a refractive index change region, or a region in which these regions are mixed. The modified region 21 has lower mechanical strength, etc. than other parts of the first wafer 10-1.

[0027] In the dividing step 2, modified regions 21 are formed in the first wafer 10-1 by stealth dicing using a laser processing device 35. The laser processing device 35 includes a chuck table 36, a laser beam irradiation unit 37 that irradiates a laser beam 30 toward the wafer 10 held on the holding surface of the chuck table 36, and a movement unit that moves the chuck table 36 and the laser beam irradiation unit 37 relative to each other.

[0028] In the dividing step 2, first, the back surface 14 side of the second wafer 10-2 is suction-held on the holding surface of the chuck table 36, and then the moving unit moves the chuck table 36 to the processing position. Next, a laser beam irradiation unit 37 is moved vertically from the back surface 14 side of the first wafer 10-1 toward the outer periphery of the device region 15, and then a focal point 31 of the laser beam 30 is set inside the first wafer 10-1.

[0029] In the dividing step 2, the chuck table 36 is then rotated about an axis parallel to the vertical direction while the laser beam 30 is irradiated onto the first wafer 10-1 from the laser beam irradiation unit 37. That is, the laser beam 30 is irradiated along the outer periphery of the device region 15 of the first wafer 10-1 to form a continuous, annular modified region 21 along the outer periphery.

[0030] In this case, in the dividing step 2, the height of the focal point 31 of the laser beam 30 is changed and the laser beam 30 is irradiated multiple times, or a laser beam having multiple focal points spaced apart in the thickness direction of the first wafer 10-1 is irradiated, thereby forming multiple modified regions 21 in the thickness direction of the first wafer 10-1. Cracks extend from the modified regions 21, and the connection between the modified regions 21 and the cracks divides the first wafer 10-1 into a central region 22 corresponding to the device region 15 and an outer peripheral annular portion 23 corresponding to the outer peripheral excess region 16.

[0031] In the embodiment, the processing conditions by the laser processing device 35 in the dividing step 2 are set so that the wavelength of the laser beam 30 is IR, the frequency is 90 kHz, the number of passes in the thickness direction is 6 passes, and the average output is 6 W.

[0032] (Preliminary cutting step) In the dividing step 2 of the embodiment, a preliminary dividing step as shown below is further performed. Fig. 6 is a cross-sectional view schematically showing one state of the preliminary dividing step in the dividing step 2 shown in Fig. 1. Fig. 7 is a plan view schematically showing the wafer 10 after the preliminary dividing step. The preliminary dividing step is a step in which, after dividing the central region 22 and the outer peripheral annular portion 23, the outer peripheral annular portion 23 is divided into a plurality of arc-shaped portions 25.

[0033] In the preliminary cutting step, a laser beam 30 is irradiated between the inner and outer edges of the outer annular portion 23 at a predetermined circumferential position on the outer annular portion 23 of the first wafer 10-1 to form a modified region 24 in the radial direction, which serves as the starting point for separation.

[0034] In the preliminary cutting step, first, the laser beam irradiation unit 37 is vertically positioned facing a predetermined position on the outer edge of the device region 15 from the back surface 14 side of the first wafer 10-1, and then the focal point 31 of the laser beam 30 is set inside the first wafer 10-1.

[0035] In the preliminary cutting step, the chuck table 36 and the laser beam application unit 37 are then moved relative to each other by the moving unit, while the laser beam application unit 37 irradiates the first wafer 10-1 with the laser beam 30. At this time, the chuck table 36 is moved so that the focal point 31 of the laser beam 30 moves radially outward of the first wafer 10-1. That is, by irradiating the outer circumferential annular portion 23 corresponding to the outer circumferential excess region 16 with the laser beam 30 in the radial direction, a modified region 24 that is continuous in the radial direction is formed.

[0036] In this case, in the preliminary dividing step, the height of the focal point 31 of the laser beam 30 is changed and the laser beam 30 is irradiated multiple times, or a laser beam having multiple focal points spaced apart in the thickness direction of the first wafer 10-1 is irradiated, thereby forming multiple modified regions 24 in the thickness direction of the first wafer 10-1. Cracks extend from the modified regions 24, and by connecting the modified regions 24 and the cracks, the outer peripheral annular portion 23 corresponding to the outer peripheral excess region 16 of the first wafer 10-1 is divided into multiple arc-shaped portions 25.

[0037] 7 , the outer peripheral annular portion 23 is divided into eight arc-shaped portions 25. However, in the present invention, the number of divisions may be further doubled, for example, to 16. Alternatively, the number of divisions may be appropriately set depending on the diameter of the first wafer 10-1 and the width of the outer peripheral annular portion 23. In the embodiment, the laser beam 30 is applied while the chuck table 36 is moved so that the focal point 31 moves from the radially inner side to the radially outer side of the first wafer 10-1. However, in the present invention, the laser beam 30 may be applied while the chuck table 36 is moved so that the focal point 31 moves from the radially outer side to the radially inner side of the first wafer 10-1. In this case, the application of the laser beam 30 is stopped when the focal point 31 reaches the annular modified region 21. In the embodiment, the processing conditions used by the laser processing device 35 in the preliminary dividing step are set to the same conditions as those used to form the modified region 21.

[0038] (Expanding tape application step 3) Fig. 8 is a cross-sectional view schematically showing one state of the expanding tape applying step 3 shown in Fig. 1. The expanding tape applying step 3 is a step of applying an expandable expanding tape 40 to the other surface of the first wafer 10-1 opposite to the surface to which the second wafer 10-2 is applied.

[0039] That is, in the expanding tape application step 3 of the embodiment, an expanding tape 40 is applied to the back surface 14 of the first wafer 10-1. The expanding tape application step 3 is performed before or after the cutting step 2. If the expanding tape application step 3 is performed before the cutting step 2, then in the cutting step 2, the first wafer 10-1 is irradiated with a laser beam 30 through the expanding tape 40.

[0040] The expanding tape 40 has, for example, a base layer made of synthetic resin and an adhesive layer laminated on the base layer. In the expanding tape application step 3, the expanding tape 40 is applied to the back surface 14 of the first wafer 10-1 by, for example, a mounter 45. The mounter 45 includes a holder 46 and a roller 47 that rolls in a direction parallel to the holding surface of the holder 46.

[0041] In the expanding tape application step 3, first, one surface of an annular frame 41, the inner diameter of which is larger than the outer diameter of the second wafer 10-2, and the back surface 14 of the second wafer 10-2 are held on the holding surface of the holder 46. At this time, the mounter 45 holds the second wafer 10-2 inside the opening of the frame 41 in a position where it is coaxial with the frame 41.

[0042] In the expanding tape application step 3, the expanding tape 40 is then applied to the frame 41 and the back surface 14 of the first wafer 10-1, and the expanding tape 40 is pressed against the frame 41 and the back surface 14 of the first wafer 10-1 by a roller 47 that moves along the back surface 14 of the first wafer 10-1, thereby adhering them in close contact.

[0043] (Outer annular part removal step 4) Fig. 9 is a cross-sectional view schematically showing one state of outer annular portion separating step 4 shown in Fig. 1. In outer annular portion separating step 4, the first wafer 10-1 is divided into an outer annular portion 23 and a central region 22 starting from the annular modified region 21, and the outer annular portion 23 is separated from the bonded wafer.

[0044] The outer peripheral annular portion separation step 4 is performed after the bonded wafer formation step 1, the division step 2, and the expanding tape application step 3. In the outer peripheral annular portion separation step 4, the expansion device 50 applies an external force in the radial direction to the expanding tape 40, expanding the expanding tape 40 in the planar direction, thereby dividing the first wafer 10-1 into the outer peripheral annular portion 23 and the central region 22. The expansion device 50 includes a chuck table 51, clamp members 52, a lifting unit 53, push-up members 54, roller members 55, and a heating unit 56. The expansion device 50 is also provided in a chamber 57 that can be sealed and whose interior can be cooled.

[0045] In outer peripheral annular portion detachment step 4, first, the back surface 14 of the first wafer 10-1 is placed on the holding surface of the chuck table 51 via the expanding tape 40, and the outer periphery of the frame 41 is fixed with the clamp members 52. At this time, the roller members 55 abut against the expanding tape 40 between the inner peripheral edge of the frame 41 and the outer peripheral edge 12 of the first wafer 10-1. In outer peripheral annular portion detachment step 4, a cooling expansion step and a heating contraction step are carried out in this order.

[0046] (Cooling and expanding step) Fig. 10 is a cross-sectional view schematically showing one state of the cooling and expanding step in the outer circumferential annular portion removing step 4 shown in Fig. 1. The cooling and expanding step is a step in which the expanding tape 40 is expanded while being cooled.

[0047] In the cooling and expanding step, the expanding tape 40 is cooled and hardened. In the cooling and expanding step of the embodiment, the entire chamber 57 that houses the expansion device 50 is constantly cooled. The expanding tape 40 is carried into the cooled chamber 57 together with the bonded wafers (first wafer 10-1, second wafer 10-2) held by the frame 41, and is sufficiently cooled before expansion begins. The cooling temperature in the chamber 57 is, for example, about 0°C. Note that in the cooling and expanding step of the present invention, the expanding tape 40 may be cooled by cooling the chuck table 51.

[0048] In the cooling and expanding step, the chuck table 51 and push-up members 54 are raised together by the lifting unit 53 while the expanding tape 40 is cooled in the cooled chamber 57. Because the outer periphery of the expanding tape 40 is fixed by the clamp members 52 via the frame 41, the portion between the inner periphery of the frame 41 and the outer periphery of the central region 22 of the first wafer 10-1 is expanded in the planar direction. At this time, roller members 55 provided at the upper end of the push-up members 54 reduce friction with the expanding tape 40, so the entire expanding tape 40 is expanded in the planar direction.

[0049] In the cooling-expanding step, as a result of the expansion of the expanding tape 40, a radial tensile force acts on the expanding tape 40. When the radial tensile force acts on the expanding tape 40, the central region 22 of the first wafer 10-1 is separated into each of the arc-shaped portions 25 of the outer peripheral annular portion 23, starting from the modified region 21 formed between the central region 22 and the outer peripheral annular portion 23 and the modified region 24 formed radially on the outer peripheral annular portion 23, as shown in Fig. 10. At this time, because the expanding tape 40 has hardened due to cooling, the external force required to separate the central region 22 from each of the arc-shaped portions 25 of the outer peripheral annular portion 23 is efficiently transmitted.

[0050] (heat shrinkage step) Fig. 11 is a cross-sectional view schematically showing one state of the heat shrinking step in the outer annular portion removing step 4 shown in Fig. 1. The heat shrinking step is performed after the cooling expanding step. The heat shrinking step is a step in which the slack portion of the expanding tape 40 formed by expanding the expanding tape 40 is heated and contracted.

[0051] After the cooling and expanding step, in a state in which the expanding tape 40 has expanded in the planar direction, the cross section of the expanding tape 40 in the portion between the inner peripheral edge of the frame 41 and the outer peripheral edge of the central region 22 of the first wafer 10-1 is linear from the lower surface of the frame 41 to the upper surface of the roller member 55. In this state, in the heat and shrinking step, first, the chuck table 51 sucks the back surface 14 of the first wafer 10-1 via the expanding tape 40. This maintains the expanded width between the central region 22 and each of the arc-shaped portions 25 of the outer peripheral annular portion 23.

[0052] Next, in the heat shrinking step, the chuck table 51 and the push-up members 54 are lowered together. At this time, the outer periphery of the expanding tape 40 is fixed to the clamp members 52 via the frame 41, and the center is sucked to the chuck table 51. Therefore, the inner periphery of the frame 41 and the outer periphery of the central region 22 of the first wafer 10-1 are brought into close proximity, which reduces the radial tensile force acting on the expanding tape 40 and causes sagging in the expanding tape 40 in the portion between the inner periphery of the frame 41 and the outer periphery of the central region 22 of the first wafer 10-1.

[0053] Therefore, in the heat shrinking step of the embodiment, the chuck table 51 and the push-up members 54 are lowered together, and the slack portion of the expanding tape 40 is heated and shrunk by the heating unit 56. The heating temperature by the heating unit 56 is, for example, about 600°C.

[0054] The heat source of the heating unit 56 heats the expanding tape 40, for example, while moving along the circumferential direction of the portion between the inner peripheral edge of the frame 41 and the outer peripheral edge 12 of the first wafer 10-1. This causes the portion of the expanding tape 40 between the inner peripheral edge of the frame 41 and the outer peripheral edge 12 of the first wafer 10-1 to shrink. Note that, although the embodiment has been described as the case where the heating unit 56 is provided inside the chamber 57, after the cooling and expanding step, the expanding tape 40 may be transported to a separate processing unit having a heating unit and subjected to the heating and shrinking step.

[0055] When peeling the bonded wafer from the expanding tape 40 using an ultraviolet irradiation device after the cooling and expanding step and the heating and shrinking step have been performed, it is preferable to use a jig or the like that limits the irradiation area so that ultraviolet (UV) is not irradiated onto the outer peripheral annular portion 23. In this way, only the back surface 14 corresponding to the central region 22 of the first wafer 10-1 is peeled from the expanding tape 40, and the outer peripheral annular portion 23 remains on the expanding tape 40.

[0056] (Grinding step 5) 12 is a cross-sectional view schematically illustrating one state of the grinding step 5 shown in FIG. The grinding step 5 is a step in which the first wafer 10-1 is ground from the other side to thin it down to a predetermined finished thickness. The grinding step 5 is performed after the outer circumferential annular portion removing step 4 is performed. In the grinding step 5 of this embodiment, the first wafer 10-1 is ground from the back surface 14.

[0057] In the grinding step 5, a grinding device 60 grinds the back surface 14 of the first wafer 10-1 held on the holding surface of a chuck table 61. The grinding device 60 includes a chuck table 61, a spindle 62 which is a rotating shaft member, a grinding wheel 63 attached to the lower end of the spindle 62, and a grinding stone 64 attached to the lower surface of the grinding wheel 63. The grinding wheel 63 rotates on an axis of rotation parallel to the axis of the chuck table 61.

[0058] In grinding step 5, first, the back surface 14 of the second wafer 10-2 is suction-held on the holding surface of the chuck table 61. Next, while the chuck table 61 is rotated about its axis, the grinding wheel 63 is rotated about its axis. Grinding water is supplied to the processing point, and the grinding stone 64 of the grinding wheel 63 is brought closer to the chuck table 61 at a predetermined feed rate, thereby grinding the back surface 14 of the first wafer 10-1 with the grinding stone 64, thinning it down to a predetermined finishing thickness.

[0059] As described above, in the processing method for the wafer 10 according to each embodiment, after forming the bonded wafer, and before thinning by grinding, modified regions 21, 24 serving as the starting points for separation are formed along the outer edge of the device region 15 using a laser beam 30, and the outer annular portion 23 corresponding to the outer periphery excess region 16 is removed by expanding an expand tape 40 attached to the wafer 10 (first wafer 10-1) on which the modified regions 21, 24 have been formed.

[0060] Therefore, the outer peripheral annular portion 23 does not come off during grinding, eliminating the risk that the detached outer peripheral annular portion 23 will damage the grinding wheel 64 and adversely affect the processing results. Also, because the outer peripheral excess region 16 does not come off and accumulate in the processing chamber during grinding, it is possible to significantly reduce the frequency of cleaning. Because each arc-shaped portion 25 of the outer peripheral annular portion 23 comes off from the central region 22 while still attached to the expanding tape 40, it will not come off unintentionally, and adverse effects caused by the detachment of the outer peripheral annular portion 23 can be suppressed.

[0061] The present invention is not limited to the above-described embodiment. In other words, various modifications can be made without departing from the gist of the present invention. For example, in the cooling and expanding step, although the chuck table 51 is raised to expand the expanding tape 40 in the embodiment, the clamp members 52 may be lowered. In other words, the chuck table 51 may be raised relative to the clamp members 52, and the clamp members 52 may be lowered relative to the chuck table 51. Furthermore, the expanding tape 40 may be expanded by lowering the chuck table 51 relative to the clamp members 52 and raising the clamp members 52 relative to the chuck table 51 while the push-up members 54 are in contact with the upper surface of the expanding tape 40. [Explanation of symbols]

[0062] 10 wafers 10-1 First wafer 10-2 Second wafer 11 Circuit Board 12 outer edge 13 Surface 14 Back side 15 Device Area 16 Surplus outer area 17 Planned division line 18 devices 20 Adhesive layer 21, 24 Modified area 22 Central area 23 Outer ring 25 Arc-shaped section 30 Laser Beam 40 Expanding Tape

Claims

1. a bonded wafer forming step of bonding one surface of a first wafer, the first wafer having a device region in which devices are formed and a peripheral excess region surrounding the device region and having a chamfered peripheral edge, to one surface of a second wafer to form a bonded wafer; a dividing step of irradiating the first wafer with a laser beam having a wavelength that is transparent to the first wafer along a position a predetermined distance inside from an outer circumferential edge of the first wafer to form an annular modified region, and dividing the first wafer into an outer circumferential annular portion corresponding to the outer circumferential excess region and a central region corresponding to the device region; an expanding tape applying step of applying an expanding tape having expandability to the other surface of the first wafer before or after the dividing step; an outer annular portion separating step of, after the bonded wafer forming step, the dividing step, and the expanding tape applying step, expanding the expanding tape to divide the first wafer into the outer annular portion and the central region starting from the annular modified region, and separating the outer annular portion from the bonded wafer; a grinding step of grinding the first wafer of the bonded wafer from the other surface side thereof to thin it to a finish thickness after the outer peripheral annular portion removing step is performed; and a wafer processing method in which, after the outer annular portion removing step is performed and before the grinding step is performed, ultraviolet light is irradiated while limiting the irradiation area so that the ultraviolet light is not irradiated onto the outer annular portion, and only the other surface corresponding to the central region of the first wafer is peeled off from the expanding tape.

2. the dividing step includes a preliminary dividing step of, after dividing the outer annular portion and the central region, irradiating the outer annular portion with the laser beam to form a modified region in a radial direction and dividing the outer annular portion into a plurality of arc-shaped portions; The wafer processing method according to claim 1 .

3. The outer peripheral annular portion removing step includes a cooling and expanding step of expanding the expanding tape while cooling it.

3. The wafer processing method according to claim 1 or 2.

4. The outer peripheral annular portion removing step further includes a heating and shrinking step of heating and shrinking a slack portion of the expanding tape formed by expanding the expanding tape after the cooling and expanding step is performed. The wafer processing method according to claim 3 .

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