Processing method

Abstract

To provide a processing method capable of suppressing reduction in wafer diameter even when the outer periphery is removed before grinding.SOLUTION: A processing method is a processing method for a wafer having a front surface and a back surface of the back surface of the front surface and having a chamfered portion formed on the outer periphery, and includes a modified region forming step 101 of irradiating the outer periphery of the wafer with a laser beam to form a ring-shaped modified region inside the wafer, and a removal step 102 of forming a removed portion by removing a portion of the outer periphery of the wafer from the wafer starting from the modified region after performing the modified region forming step 101, and the modified region is formed at a position where the maximum diameter of the wafer after the portion is removed in the removal step 102 is the same as the maximum diameter of the wafer before performing the removal step 102.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for processing a wafer having a first surface and a second surface and a chamfered portion formed on the outer periphery. [Background technology]

[0002] When the back surface of the wafer is ground to thin it, the chamfered portion on the outer periphery of the wafer forms a so-called sharp edge that acts like an overhang, and to prevent the wafer from being damaged from the sharp edge, the chamfered portion is removed before grinding.

[0003] Therefore, a method has been proposed in which a laser beam is applied to the wafer to divide the wafer into an inner peripheral portion and an outer peripheral portion, and the outer peripheral portion is removed before grinding the wafer (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

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

[0005] However, the diameter of the wafer from which the outer periphery has been removed is reduced.

[0006] A typical chuck table for suction-holding a wafer has a suction-holding surface with the same diameter as the diameter of the wafer, in order to hold a wafer with a diameter of, for example, 6 inches, 8 inches, or 300 mm.

[0007] If the diameter of the wafer changes to a smaller size, for example, even if an attempt is made to hold the wafer by suction on a chuck table in a subsequent process, the negative pressure will leak and the wafer will not be able to be held by suction.

[0008] Another problem occurs when bonding a wafer to another wafer after removing the outer periphery to form a bonded wafer. In a typical bonding machine, the bonding position is adjusted based on the outer periphery of the wafer, so if the wafer diameter is reduced, the bonding position will shift.

[0009] An object of the present invention is to provide a processing method that can prevent the diameter of the wafer from being reduced even if the outer periphery is removed before grinding. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems and achieve the object, the processing method of the present invention is a method for processing a wafer having a first surface and a second surface behind the first surface, with a chamfered portion formed on the outer periphery, and includes a modified area formation step in which a laser beam is irradiated onto the outer periphery of the wafer to form a ring-shaped modified area inside the wafer, and a removal step in which, after performing the modified area formation step, a portion of the outer periphery of the wafer is removed from the wafer starting from the modified area to form a removed portion, wherein the modified area is formed at a position where the maximum diameter of the wafer after the portion is removed in the removal step is the same as the maximum diameter of the wafer before performing the removal step.

[0011] In the processing method, the modified region forming step may include forming an annular floor inside the wafer consisting of an annular modified region of a predetermined width extending from the outer edge of the wafer toward the center, and forming an annular wall inside the wafer consisting of an annular modified region of a predetermined depth extending from the first surface side toward the second surface side.

[0012] In the processing method, the modified region forming step may include irradiating the wafer with a laser beam from the first surface side to form the annular floor, and then forming the annular wall.

[0013] In the processing method, the modified region forming step may include irradiating the wafer with a laser beam from the second surface side to form the annular wall and then forming the annular floor.

[0014] In the above processing method, the modified region forming step may form a plurality of the annular beds in order from the outer periphery of the wafer toward the center.

[0015] The processing method may further include a stacked wafer formation step in which, after the removal step, the first surface of the wafer is faced to a second wafer to form a stacked wafer by stacking the wafer on the second wafer.

[0016] The processing method may further include, after the laminated wafer forming step, a grinding step of grinding the second surface of the laminated wafer to a thickness that reaches the removed portion. [Effects of the Invention]

[0017] The present invention has the effect of preventing the diameter of the wafer from being reduced even if the outer periphery is removed before grinding. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a perspective view schematically showing a wafer to be processed by the processing method according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a flowchart showing the flow of the processing method according to the first embodiment. [Figure 4] FIG. 4 is a perspective view schematically showing an example of the configuration of a laser processing device that performs the modified region forming step of the processing method shown in FIG. [Figure 5] FIG. 5 is a side view, partially in cross section, schematically illustrating the annular bed forming step of the modified region forming step of the processing method shown in FIG. [Figure 6] FIG. 6 is an enlarged cross-sectional view of a portion VI in FIG. [Figure 7] FIG. 7 is a side view, partially in cross section, schematically showing the annular wall forming step of the modified region forming step of the processing method shown in FIG. [Figure 8] FIG. 8 is an enlarged cross-sectional view of part VIII in FIG. [Figure 9] FIG. 9 is a cross-sectional view of a main portion of the wafer after the removal step of the processing method shown in FIG. [Figure 10] FIG. 10 is a cross-sectional view of a main part of the laminated wafer formed in the laminated wafer forming step of the processing method shown in FIG. [Figure 11] FIG. 11 is a side view, partly in section, schematically showing the grinding step of the processing method shown in FIG. [Figure 12] FIG. 12 is a flowchart showing the flow of the processing method according to the second embodiment. [Figure 13] FIG. 13 is a side view, partially in cross section, schematically showing the annular wall forming step of the modified region forming step of the processing method shown in FIG. [Figure 14] FIG. 14 is an enlarged cross-sectional view of the portion XIV in FIG. [Figure 15] FIG. 15 is a side view, partially in cross section, schematically illustrating the annular bed forming step of the modified region forming step of the processing method shown in FIG. [Figure 16] FIG. 16 is an enlarged cross-sectional view of a portion XVI in FIG. [Figure 17] FIG. 17 is a cross-sectional view schematically showing the annular bed forming step of the modified region forming step in the processing method according to the modified example of the first and second embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0019] 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.

[0020] [Embodiment 1] A processing method according to a first embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a perspective view schematically showing a wafer to be processed by the processing method according to the first embodiment. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. Fig. 3 is a flowchart showing the flow of the processing method according to the first embodiment.

[0021] (wafer) The processing method according to the first embodiment is a method for processing a wafer 1 shown in Fig. 1. In the first embodiment, the wafer 1 is a disk-shaped semiconductor wafer, optical device wafer, or the like, which uses silicon, sapphire, gallium, or the like as a substrate and has a front surface 2 which is a first surface, and a back surface 3 which is a second surface behind the front surface 2. As shown in Fig. 1, the wafer 1 has a plurality of planned dividing lines 4 set on the front surface 2, which intersect with each other, and devices 5 formed in areas defined by the planned dividing lines 4.

[0022] The device 5 is, for example, an integrated circuit such as an IC (Integrated Circuit) or an LSI (Large Scale Integration), an image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), or a memory (semiconductor storage device).

[0023] 2, the wafer 1 has a chamfered portion 6 formed on the outer periphery. The chamfered portion 6 is formed from the front surface 2 to the back surface 3, and is formed in an arc-shaped cross section so that the center in the thickness direction is located on the outermost side.

[0024] In the present invention, the wafer 1 may be a wafer other than a disk-shaped wafer, and the device 5 may not be formed on the surface 2.

[0025] (Processing method) 3, the processing method includes a modified region forming step 101, a removing step 102, a stacked wafer forming step 103, and a grinding step 104. The modified region forming step 101 is performed by a laser processing apparatus 20 shown in FIG.

[0026] (Laser processing equipment) Next, a description will be given of the laser processing apparatus 20. Fig. 4 is a perspective view that schematically shows an example of the configuration of a laser processing apparatus that performs the modified region forming step of the processing method shown in Fig. 3.

[0027] As shown in FIG. 4, the laser processing device 20 includes a holding table 30, a moving unit 40, a laser beam irradiation unit 50, an imaging unit 60, and a control unit .

[0028] The holding table 30 is disk-shaped, and has a flat holding surface 31 formed of porous ceramic or the like along the horizontal direction for holding the wafer 1. The holding table 30 is also provided so as to be movable by a moving unit 40 between a processing area below the laser beam irradiation unit 50 and a carry-in / out area spaced from below the laser beam irradiation unit 50 where the wafer 1 is carried in and out.

[0029] The holding table 30 has a holding surface 31 connected to a vacuum suction source (not shown), and is sucked by the vacuum suction source to suck and hold the wafer 1 placed on the holding surface 31.

[0030] The moving unit 40 moves the holding table 30 and the laser beam irradiation unit 50 relatively. The moving unit 40 includes a Y-axis moving unit 41 which is an indexing feed unit that moves the holding table 30 in the Y-axis direction parallel to the horizontal direction, an X-axis moving unit 42 which is a processing feed unit that moves the holding table 30 in the X-axis direction parallel to the horizontal direction and perpendicular to the Y-axis direction, a rotational moving unit 43 that rotates the holding table 30 around an axis parallel to the Z-axis direction parallel to the vertical direction, and a Z-axis moving unit 44 that moves the laser beam irradiation unit 50 in the Z-axis direction.

[0031] The Y-axis moving unit 41 is installed on the device main body 21, and moves the moving plate 22 on which the X-axis moving unit 42 is installed in the Y-axis direction, thereby moving the holding table 30 in the Y-axis direction. The X-axis moving unit 42 is installed on the moving plate 22, and moves the second moving plate 23 on which the rotational moving unit 43 is installed in the X-axis direction, thereby moving the holding table 30 in the X-axis direction.

[0032] The rotational movement unit 43 is installed on the second moving plate 23 and supports the holding table 30, thereby rotating the holding table 30 around its axis. The Z-axis movement unit 44 is installed on the standing wall 24 that stands from the end of the device body 21 in the Y-axis direction, and moves the support column 25, which has the laser beam irradiation unit 50 and the imaging unit 60 at its tip, along the Z axis, thereby moving the laser beam irradiation unit 50 and the imaging unit 60 in the Z axis direction.

[0033] The Y-axis moving unit 41 moves each moving plate 22, the X-axis moving unit 42, the second moving plate 23, the rotational moving unit 43, and the holding table 30 in the Y-axis direction. The X-axis moving unit 42 moves each second moving plate 23, the rotational moving unit 43, and the holding table 30 in the X-axis direction.

[0034] The Y-axis moving unit 41, the X-axis moving unit 42, and the Z-axis moving unit 44 each include a well-known ball screw rotatably mounted about its axis, a well-known motor for rotating the ball screw about its axis, and a well-known guide rail for supporting the moving plates 22, 23 or the support column 25 movably in the X-axis, Y-axis, or Z-axis direction. The rotational moving unit 43 includes a well-known motor for rotating the holding table 30 about its axis.

[0035] The laser beam irradiation unit 50 is partially provided at the tip of the support column 25. The laser beam irradiation unit 50 irradiates the wafer 1 held on the holding table 30 with a laser beam 51 having a wavelength that is transparent to the wafer 1.

[0036] In addition, in the first embodiment, the laser beam irradiation unit 50 is capable of freely switching between a state in which the laser beam 51 is split into multiple beams (five beams in the first embodiment) in the Y-axis direction and irradiated onto the wafer 1 held on the holding table 30, and a state in which the laser beam 51 is not split but a single laser beam 51 is irradiated onto the wafer 1 held on the holding table 30. When splitting the laser beam 51, the laser beam irradiation unit 50 may split the laser beam 51 into two or more beams, and preferably splits the laser beam 51 into five or more beams.

[0037] In addition, in the present invention, the laser processing device 20 may be equipped with a laser beam irradiation unit that branches a separate laser beam 51 into multiple beams in the Y-axis direction and irradiates the wafer 1 held on the holding table 30, and a laser beam irradiation unit that irradiates the wafer 1 held on the holding table 30 with a single laser beam 51 without branching the laser beam 51.

[0038] The imaging unit 60 is provided at the tip of the support column 25, and is arranged in a position aligned with the laser beam irradiation unit 50 in the X-axis direction. The imaging unit 60 has an imaging element that images an area to be divided of the wafer 1 held on the holding table 30 before laser processing. The imaging element is, for example, a CCD (Charge-Coupled Device) imaging element or a CMOS (Complementary MOS) imaging element. The imaging unit images the wafer 1 held on the holding table 30, obtains an image for performing alignment between the wafer 1 and the laser beam irradiation unit 50, and outputs the obtained image to the control unit 70.

[0039] The control unit 70 controls each component of the laser processing apparatus 20 to cause the laser processing apparatus 20 to perform processing operations on the wafer 1. The control unit 70 is a computer having an arithmetic processing device with a microprocessor such as a CPU (central processing unit), a storage device with memory such as a ROM (read only memory) or RAM (random access memory), and an input / output interface device. The arithmetic processing device of the control unit 70 performs arithmetic processing in accordance with a computer program stored in the storage device, and outputs control signals for controlling the laser processing apparatus 20 to each component of the laser processing apparatus 20 via the input / output interface device.

[0040] The control unit 70 is connected to a display unit (not shown) that is configured with a liquid crystal display device or the like that displays the status of the machining operation, images, etc., and an input unit (not shown) that the operator uses to register machining content information, etc. The input unit is configured with at least one of a touch panel provided on the display unit and an external input device such as a keyboard.

[0041] (Modified region forming step) Fig. 5 is a side view, partially in cross section, schematically showing the annular bed forming step of the modified region forming step of the processing method shown in Fig. 3. Fig. 6 is a cross-sectional view, partially in cross section, showing an enlarged view of part VI in Fig. 5. Fig. 7 is a side view, partially in cross section, schematically showing the annular wall forming step of the modified region forming step of the processing method shown in Fig. 3. Fig. 8 is a cross-sectional view, partially in cross section, showing an enlarged view of part VIII in Fig. 7.

[0042] The modified area forming step 101 is a step of irradiating the chamfered portion 6 of the wafer 1 with a laser beam 51 to form an annular modified area, that is, an annular bed 10 and an annular wall 15 (shown in FIG. 8), inside the wafer 1. As shown in FIG. 3, the modified area forming step 101 includes an annular bed forming step 101-1 and an annular wall forming step 101-2, and after the annular bed forming step 101-1 is performed, the annular wall forming step 101-2 is performed.

[0043] In embodiment 1, in annular bed formation step 101-1, the back surface 3 of the wafer 1 is placed on the holding surface 31 of the holding table 30 positioned in the loading / unloading area of ​​the laser processing device 20, and the back surface 3 of the wafer 1 is suction-held on the holding surface 31 of the holding table 30. In embodiment 1, in annular bed formation step 101-1, the laser processing device 20 moves the holding table 30 to the processing area using the moving unit 40, and images the wafer 1 with the imaging unit 60 to perform alignment.

[0044] In embodiment 1, in the annular bed formation step 101-1, as shown in Figure 5, the laser processing device 20 positions the focal point 52 at a position where the distance from the surface 2 is equal to or greater than the finishing thickness to which the wafer 1 will be thinned in the grinding step 104 and is closer to the surface 2 than the center of the wafer 1 in the thickness direction, and irradiates the laser beam 51 from the surface 2 side of the wafer 1 to the outer periphery 7 while rotating the holding table 30 around its axis.

[0045] The outer peripheral portion 7 is the region between the chamfered portion 6 of the wafer 1 and the region where the device 5 is formed on the front surface 2. In the first embodiment, in the annular bed formation step 101-1, the laser beam irradiation unit 50 of the laser processing device 20 branches the laser beam 51 into multiple beams in the Y-axis direction, and sets the focal point 52 of each of the branched laser beams 51 at a position inside the substrate described above, and irradiates the laser beam 51.

[0046] 6, a plurality of modified regions 11 with a disordered crystal structure are formed in a line in the radial direction of the wafer 1, centered around a focal point 52 inside the substrate of the wafer 1, and cracks 12 extend from the modified regions 11 in the radial direction of the wafer 1 along a predetermined crystal plane of the wafer 1. In embodiment 1, in the annular bed formation step 101-1, the cracks 12 connect the modified regions 11 to each other, and the cracks 12 extend from the innermost modified region 11 in the inner circumferential direction of the wafer 1, and the cracks 12 extending from the outermost modified region 11 in the outer circumferential direction of the wafer 1 appear in the chamfered portion 6.

[0047] As a result, in embodiment 1, in annular bed formation step 101-1, an annular bed 10 is formed inside the substrate of wafer 1 around the entire circumference of wafer 1, which is an annular region including multiple modified regions 11 and cracks 12 propagating radially from each of the multiple modified regions 11 to the wafer 1. Thus, in embodiment 1, in annular bed formation step 101-1 of modified region formation step 101, an annular bed 10 is formed inside the substrate of wafer 1, which is an annular modified region of a predetermined width extending from the outer peripheral edge of wafer 1 toward the center.

[0048] 7, in the annular wall forming step 101-2, the laser processing device 20 positions the focal point 52 between the inner edge of the annular bed 10 and the surface 2 of the wafer 1, and irradiates the laser beam 51 from the surface 2 side of the wafer 1 to the outer periphery 7 while rotating the holding table 30 about its axis. Also, in the embodiment 1, in the annular wall forming step 101-2, the laser beam irradiation unit 50 of the laser processing device 20 does not branch the laser beam 51 into multiple beams in the Y-axis direction, but sets the focal point 52 of the single laser beam 51 to a position inside the substrate described above, and irradiates the laser beam 51.

[0049] 8, a modified portion 13 having a disordered crystal structure is formed around a focal point 52 inside the substrate of the wafer 1, and a crack 14 extends from the modified portion 13 in the thickness direction of the wafer 1 along a predetermined crystal plane of the wafer 1. In the annular wall formation step 101-2 of the first embodiment, the crack 14 extending toward the rear surface 3 of the wafer 1 connects with the inner edge of the crack 12 in the annular floor 10, and the crack 14 extending toward the front surface 2 of the wafer 1 is exposed on the front surface 2 of the wafer 1.

[0050] As a result, in embodiment 1, in annular wall formation step 101-2, annular wall 15, which is an annular region including modified region 13 and crack 14 propagating from modified region 13 in the thickness direction of wafer 1, is formed around the entire circumference of wafer 1 inside the substrate of wafer 1. In embodiment 1, in annular wall formation step 101-2 of modified region formation step 101, annular wall 15, which is an annular modified region of a predetermined depth extending from front surface 2 side toward back surface 3 side, is formed inside the substrate of wafer 1.

[0051] Thus, in the modified region forming step 101 of the first embodiment, the laser beam 51 is irradiated from the front surface 2 side of the wafer 1 to form the annular floor 10, and then the annular wall 15 is formed. Also, in the modified region forming step 101 of the first embodiment, the focal point 52 is set at the position described above, so that the modified region, that is, the annular floor 10 and the annular wall 15, are formed at a position where the maximum diameter of the wafer 1 after a portion is removed in the removing step 102 is the same as the maximum diameter of the wafer 1 before the removing step 102 is performed (i.e., a position where they are equal).

[0052] (Removal step) Fig. 9 is a cross-sectional view of a main portion of a wafer after the removal step of the processing method shown in Fig. 3. The removal step 102 is a step that follows the modified region formation step 101, in which a portion of the outer periphery 7 and the chamfered portion 6 of the wafer 1 are removed from the wafer 1 starting from the annular floor 10 and the annular wall 15 to form a removed portion 9.

[0053] In the first embodiment, in the removing step 102, ultrasonic vibrations are applied to the chamfered portion 6 of the wafer 1 via a liquid such as pure water, for example, to break the substrate of the wafer 1 starting from the annular floor 10 and the annular wall 15, and as shown in Fig. 9, a part of the outer periphery 7 and the chamfered portion 6 between the annular floor 10 and the front surface 2 and on the outer periphery side of the annular wall 15 are removed, thereby forming a removed portion 9 on the wafer 1. Note that the removed portion 9 is formed in a stepped shape on the outer edge of the wafer 1 by removing a part closer to the front surface 2 than the center in the thickness direction of the periphery of the wafer 1 than the region where the device 5 is formed, and includes an annular wall 8 along a direction perpendicular to the front surface 2 and the back surface 3.

[0054] In addition, in the present invention, in the removal step 102, a portion of the outer peripheral portion 7 and the chamfered portion 6 between the annular floor 10 and the surface 2 of the wafer 1 and on the outer peripheral side of the annular wall 15 may be removed from the wafer 1 starting from the annular floor 10 and the annular wall 15 by air blowing or spraying high-pressure fluid, etc.

[0055] (Stacked wafer formation step) Fig. 10 is a cross-sectional view of a main part of the laminated wafer formed in the laminated wafer forming step of the processing method shown in Fig. 3. The laminated wafer forming step 103 is a step in which, after the removal step 102 is performed, the front surface 2 side of the wafer 1 faces the second wafer 16 and the wafer 1 is laminated on the second wafer 16 to form a laminated wafer 17.

[0056] In the first embodiment, in the stacked wafer forming step 103, a second wafer 16 having the same configuration as the wafer 1 is prepared. Note that the same parts of the second wafer 16 as those of the wafer 1 are denoted by the same reference numerals and will be described. In the first embodiment, in the stacked wafer forming step 103, the surfaces 2 of the wafers 1 and 16 are placed face to face, and the wafers 1 and 16 are positioned so that their outer edges overlap with each other based on the outer edges of the wafers 1 and 16.

[0057] In the first embodiment, in the stacked wafer formation step 103, the surfaces 2 of the wafers 1 and 16 are bonded together to form a stacked wafer 17 in which the wafers 1 and 16 are stacked, as shown in Fig. 10. The wafers 1 and 16 can be bonded together by fusion bonding, direct bonding, or bonding using a temporary adhesive, and the bonding method is not limited. In the first embodiment, the second wafer 16 has the same configuration as the wafer 1, but the second wafer 16 may have a different configuration as long as its outer diameter is the same as that of the wafer 1.

[0058] (Grinding step) Fig. 11 is a side view, partially in cross section, schematically showing the grinding step of the processing method shown in Fig. 3. Grinding step 104 is a step in which, after stacked wafer formation step 103 is performed, back surfaces 3 of wafers 1 of stacked wafers 17 are ground to a finishing thickness that reaches removed portion 9.

[0059] 11 suction-holds the back surface 3 of the second wafer 16 of the stacked wafers 17 on a holding surface 82 of a holding table 81. In the grinding step 104 of the first embodiment, as shown in FIG. 11 , the grinding device 80 rotates a grinding wheel 84 about its axis with a spindle 83 and rotates the holding table 81 about its axis while supplying grinding water, and grinds the back surface 3 of the wafer 1 of the stacked wafers 17 with the grinding stone 85 by bringing the grinding stone 85 into contact with the back surface 3 of the wafer 1 of the stacked wafers 17 and moving the grinding stone 85 toward the holding table 81 at a predetermined feed rate.

[0060] In the first embodiment, in the grinding step 104, the grinding device 80 grinds the backsides 3 of the wafers 1 of the stacked wafers 17 until the wafers 1 of the stacked wafers 17 reach a predetermined finished thickness.

[0061] In the processing method of the first embodiment described above, in the modified area formation step 101, the annular floor 10 and annular wall 15, which are modified areas, are formed at a position where the maximum diameter of the wafer 1 does not change before and after the removal step 102, and then in the removal step 102, the outer periphery 7 and part of the chamfered portion 6 of the wafer 1 are removed from the wafer 1 starting from the annular floor 10 and the annular wall 15.

[0062] As a result, the processing method according to the first embodiment has the effect of being able to prevent the diameter of the wafer 1 from being reduced even if the outer periphery is removed before the grinding step 104.

[0063] Furthermore, in the processing method according to embodiment 1, if the annular bed 10 is slanted, a sharp edge will be formed when the wafer is ground and thinned. However, by forming the annular wall 15, an annular wall 8 can be formed on the outer periphery 7 of the wafer 1 after the removal step 102, and no sharp edge will be formed when the wafer is ground and thinned.

[0064] Furthermore, in the processing method of embodiment 1, if the annular wall 15 extends further toward the back surface 3 than the annular floor 10, it will lead to cracks during grinding. However, by first forming the annular floor 10 by irradiating the laser beam 51 from the front surface 2 side, it is possible to prevent the cracks 14 generated when forming the annular wall 15 from extending further toward the back surface 3 of the wafer 1 than the lower end of the annular floor 10.

[0065] Furthermore, in the processing method according to the first embodiment, since the laminated wafer 17 is formed after the removing step 102, it is possible to prevent the second wafer 16 from being damaged.

[0066] [Embodiment 2] A processing method according to a second embodiment will be described with reference to the drawings. FIG. 12 is a flowchart showing the flow of the processing method according to the second embodiment. FIG. 13 is a side view, partially in cross section, schematically showing the annular wall forming step of the modified region forming step of the processing method shown in FIG. 12. FIG. 14 is a cross-sectional view, partially in cross section, schematically showing the annular bed forming step of the modified region forming step of the processing method shown in FIG. 12. FIG. 16 is a cross-sectional view, partially in cross section, schematically showing the annular bed forming step of the modified region forming step of the processing method shown in FIG. 15. Note that in FIGS. 12, 13, 14, 15, and 16, the same parts as those in the first embodiment are designated by the same reference numerals, and their description will be omitted.

[0067] In embodiment 2, the modified region forming step 101 includes an annular wall forming step 101-2 and an annular bed forming step 101-1, as shown in FIG. 12, and is the same as embodiment 1 except that the annular wall forming step 101-2 is performed first and then the annular bed forming step 101-1 is performed.

[0068] In the second embodiment, in the annular wall forming step 101-2, the laser processing device 20 places the front surface 2 of the wafer 1 on the holding surface 31 of the holding table 30 positioned in the carry-in / out area, and suction-holds the front surface 2 of the wafer 1 on the holding surface 31 of the holding table 30. In the second embodiment, in the annular wall forming step 101-2, the laser processing device 20 moves the holding table 30 to the processing area using the moving unit 40, and performs alignment by capturing an image of the wafer 1 with the imaging unit 60, which is an infrared camera.

[0069] 13, in the annular wall forming step 101-2, the laser processing device 20 positions the focal point 52 closer to the front surface 2 than the center in the thickness direction of the wafer 1, and irradiates the laser beam 51 from the back surface 3 side of the wafer 1 to the outer periphery 7 while rotating the holding table 30 about its axis. Also, in the annular wall forming step 101-2 in the embodiment 2, the laser beam irradiation unit 50 of the laser processing device 20 does not branch the laser beam 51 into multiple beams in the Y-axis direction, but sets the focal point 52 of the single laser beam 51 to a position inside the substrate described above, and irradiates the laser beam 51.

[0070] 14, a modified portion 13 having a disordered crystal structure is formed around a focal point 52 inside the substrate of the wafer 1, and a crack 14 extends from the modified portion 13 in the thickness direction of the wafer 1 along a predetermined crystal plane of the wafer 1. In the second embodiment, in the annular wall forming step 101-2, the crack 14 extends toward the rear surface 3 of the wafer 1, and the crack 14 extending toward the front surface 2 of the wafer 1 is exposed on the front surface 2 of the wafer 1.

[0071] As a result, in embodiment 2, in annular wall formation step 101-2, annular wall 15 including modified region 13 and crack 14 propagating from modified region 13 in the thickness direction of wafer 1 is formed around the entire circumference of wafer 1 inside the substrate of wafer 1. Thus, in embodiment 2, in annular wall formation step 101-2 of modified region formation step 101, annular wall 15, which is an annular modified region of a predetermined depth extending from front surface 2 side toward back surface 3 side, is formed inside the substrate of wafer 1.

[0072] 15, in annular bed formation step 101-1, laser processing device 20 positions focal point 52 at a distance from front surface 2 equal to or greater than the finishing thickness to which wafer 1 is thinned in grinding step 104, on the outer periphery side of annular wall 15, and closer to front surface 2 than the center in the thickness direction of wafer 1, and irradiates laser beam 51 from back surface 3 side to outer periphery 7 of wafer 1 while rotating holding table 30 around its axis. Also in embodiment 2, in annular bed formation step 101-1, laser beam irradiation unit 50 of laser processing device 20 branches laser beam 51 into multiple beams in the Y-axis direction, and sets focal point 52 of each branched laser beam 51 at a position inside the substrate described above, and irradiates laser beam 51.

[0073] 16, a plurality of modified regions 11 with a disordered crystal structure are formed in a line in the radial direction of the wafer 1, centered around a focal point 52 inside the substrate of the wafer 1, and cracks 12 extend from the modified regions 11 in the radial direction of the wafer 1 along a predetermined crystal plane of the wafer 1. In the second embodiment, in the annular bed formation step 101-1, the cracks 12 connect the modified regions 11 to each other, and the crack 12 extending from the innermost modified region 11 in the inner circumferential direction of the wafer 1 connects to the crack 14 extending to the rear surface 3 of the annular wall 15, and the crack 12 extending from the outermost modified region 11 in the outer circumferential direction of the wafer 1 appears on the surface of the chamfered portion 6.

[0074] As a result, in embodiment 2, in annular bed formation step 101-1, an annular bed 10 including a plurality of modified regions 11 and cracks 12 propagating radially from each of the plurality of modified regions 11 around the entire circumference of wafer 1 is formed inside the substrate of wafer 1. Thus, in embodiment 2, in annular bed formation step 101-1 of modified region formation step 101, an annular bed 10, which is an annular modified region of a predetermined width extending from the outer peripheral edge of wafer 1 toward the center, is formed inside the substrate of wafer 1.

[0075] Thus, in the modified region forming step 101 of the second embodiment, the laser beam 51 is irradiated from the back surface 3 side of the wafer 1 to form the annular wall 15, and then the annular floor 10 is formed. Also, in the modified region forming step 101 of the second embodiment, the focal point 52 is set to the position described above, so that the annular floor 10 and the annular wall 15 are formed at a position where the maximum diameter of the wafer 1 after a portion is removed in the removing step 102 is the same as the maximum diameter of the wafer 1 before the removing step 102 is performed (i.e., the positions are equal).

[0076] In the processing method of embodiment 2, in the modified area formation step 101, a modified area consisting of an annular floor 10 and annular wall 15 is formed at a position where the maximum diameter of the wafer 1 does not change before and after the removal step 102, and then in the removal step 102, the outer periphery 7 and part of the chamfered portion 6 of the wafer 1 are removed from the wafer 1 starting from the annular floor 10 and the annular wall 15.Therefore, as in embodiment 1, the effect is achieved that even if the outer periphery is removed before the grinding step 104, the diameter of the wafer 1 can be prevented from shrinking.

[0077] Furthermore, in the processing method according to the second embodiment, although cracks 14 are usually difficult to extend on the front surface 2 on which devices 5 are formed, since the laser beam 51 is irradiated from the back surface 3, cracks 14 tend to extend to the front surface 2, and if the wafer 1 is a device wafer on which devices 5 are formed, the device layer constituting the devices 5 is easily removed by the cracks 14.

[0078] Furthermore, when the laser beam 51 is irradiated onto the back surface 3 side of the wafer 1, it is difficult to form the annular wall 15 after forming the annular floor 10. However, in the processing method of embodiment 2, the annular floor formation step 101-1 is performed after the annular wall formation step 101-2, so that the annular floor 10 and the annular wall 15, which are the modified areas, can be formed inside the wafer 1.

[0079] [Modification] The processing methods according to the modifications of the first and second embodiments will be described with reference to the drawings. Fig. 17 is a cross-sectional view schematically illustrating the annular bed forming step of the modified region forming step of the processing methods according to the modifications of the first and second embodiments. In Fig. 17, the same parts as those in the first embodiment are designated by the same reference numerals, and their description will be omitted.

[0080] In the processing method according to the modified example, the annular bed forming step 101-1 of the modified region forming step 101 is the same as in the first embodiment, except that the laser processing apparatus 20 forms a plurality of annular beds 10 sequentially from the outer periphery of the wafer 1 toward the center, as shown in FIG. 17. Note that while FIG. 17 illustrates an example in which the laser beam 51 is irradiated from the front surface 2 side of the wafer 1, in the present invention, the laser beam 51 may also be irradiated from the back surface 3 side of the wafer 1. Note that in the present invention, when the laser beam 51 is irradiated from the back surface 3 side of the wafer 1, it is desirable to form the annular wall 15 first and then form a plurality of annular beds 10 sequentially from the outer periphery toward the center.

[0081] In the processing method of the modified example, in the modified area formation step 101, a modified area consisting of an annular floor 10 and annular wall 15 is formed at a position where the maximum diameter of the wafer 1 does not change before and after the removal step 102, and then in the removal step 102, the outer periphery 7 and part of the chamfered portion 6 of the wafer 1 are removed from the wafer 1 starting from the annular floor 10 and the annular wall 15.Therefore, as in embodiment 1, the effect is achieved that even if the outer periphery is removed before the grinding step 104, the diameter of the wafer 1 can be prevented from shrinking.

[0082] In addition, the processing method according to the modified example forms an annular bed 10 from the outer peripheral edge toward the center, so that the annular bed 10 formed on the outer peripheral edge of the wafer 1 opens, and therefore the crack 12 caused by the laser beam 51 irradiated later tends to extend to the outer periphery of the wafer 1.

[0083] The present invention is not limited to the above-described embodiment, and can be implemented in various modifications without departing from the gist of the present invention. [Explanation of symbols]

[0084] 1 wafer 2 Surface (first side) 3 Back side (2nd side) 6 Chamfered part 7 Outer periphery 9 Removal part 10 Annular bed (reforming zone) 15 Annular wall (modified area) 16 Second wafer 17 Stacked wafers 51 Laser Beam 101 Modified region formation step 102 Removal Steps 103 Stacked wafer formation step 104 Grinding Step

Claims

1. A method for processing a wafer having a first surface and a second surface behind the first surface and having a chamfered portion formed on an outer periphery, comprising: a modified region forming step of irradiating a laser beam onto the outer periphery of the wafer to form an annular modified region inside the wafer; a removing step of forming a removed portion by removing a part of the outer periphery of the wafer from the wafer starting from the modified region after the modified region forming step is performed, The modified region is formed at a position where the maximum diameter of the wafer after the portion is removed in the removing step does not change from the maximum diameter of the wafer before the removing step is performed.

2. The processing method described in claim 1, wherein the modified area forming step forms an annular floor inside the wafer consisting of an annular modified area of ​​a predetermined width extending from the outer peripheral edge of the wafer toward the center, and forms an annular wall inside the wafer consisting of an annular modified area of ​​a predetermined depth extending from the first surface side toward the second surface side.

3. 3. The processing method according to claim 2, wherein in the modified region forming step, a laser beam is irradiated from the first surface side of the wafer to form the annular floor, and then the annular wall is formed.

4. 3. The processing method according to claim 2, wherein in the modified region forming step, a laser beam is irradiated from the second surface side of the wafer to form the annular wall and then the annular floor.

5. 3. The processing method according to claim 2, wherein the modified region forming step forms a plurality of the annular beds in order from the outer periphery of the wafer toward the center.

6. 3. The processing method according to claim 1, further comprising a stacked wafer forming step of, after performing the removing step, forming a stacked wafer by stacking the wafer on a second wafer with the first surface side of the wafer facing the second wafer.

7. 7. The processing method according to claim 6, further comprising a grinding step of grinding the second surface of the laminated wafers to a thickness that reaches the removed portion after the laminated wafer forming step is performed.

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