Method of processing a wafer

Abstract

Provided is a wafer processing method that does not leave a modified layer or debris on the outer periphery of a wafer and enables a device region to be set close to a region in which a ring-shaped reinforcing portion is formed. The method includes: a modified layer forming step of forming a modified layer that does not reach a finished thickness of the wafer in a ring shape by irradiating a laser beam on the wafer from the back surface of the wafer in such a manner that a condensing point of the laser beam, which has a wavelength that is transmissive to the wafer, is positioned inside the wafer corresponding to a region remaining from the outer periphery; a protective member fitting step of fitting a protective member on the front surface of the wafer; a reinforcing portion forming step of holding the protective member side with a chuck table, grinding the back surface of the wafer, causing a cleavage surface to reach the front surface from the modified layer formed in a ring shape and removing the modified layer, and thinning a region of the wafer corresponding to the device region to the finished thickness, thereby forming a ring-shaped reinforcing portion in a region of the wafer corresponding to a region remaining from the outer periphery; and a back surface processing step of performing a prescribed processing on the back surface of the wafer.

Description

TECHNICAL FIELD

[0001] The present application relates to a wafer processing method, which is formed with a device region and a peripheral remaining region surrounding the device region on a front surface. BACKGROUND

[0002] A wafer formed with a device region in which a plurality of devices such as ICs, LSIs, and the like are divided by a plurality of division lines, and a peripheral remaining region surrounding the device region on a front surface is formed to a prescribed thickness by grinding the back surface with a grinding device, and is divided into individual device chips by a cutting device, a laser processing device, and the like, and is used for electronic equipment such as mobile phones, personal computers, and the like.

[0003] In addition, the present applicant has proposed a technology in which, after a ring-shaped reinforcing portion is formed on the back surface of a wafer corresponding to a peripheral remaining region by grinding the back surface of the wafer corresponding to a device region, the wafer is processed, and the ring-shaped reinforcing portion of the peripheral remaining region is removed to divide the wafer into individual device chips (for example, see Patent Document 1).

[0004] Patent Document 1: Japanese Patent Application Laid-Open (JP A) No. 2007-019461

[0005] According to the technology of the above-described Patent Document 1, a ring-shaped reinforcing portion is formed on the back surface corresponding to a peripheral remaining region, whereby a wafer whose back surface side corresponding to a device region is thinned by grinding can be stably supported, and the operability at the time of processing is optimized. However, in order to divide the wafer formed with the reinforcing portion into individual device chips, it is necessary to remove the reinforcing portion with a cutting tool. When the reinforcing portion is removed with the cutting tool, there is a concern that a device located in the vicinity of the reinforcing portion will be damaged, and therefore it is necessary to set the outer edge of the device region in such a manner as to be sufficiently separated inward from the region in which the reinforcing portion is formed, and therefore there is a problem in that the region in which the device region is set is limited, and the productivity is poor.

[0006] In addition, in the case where the ring-shaped reinforcing portion formed on the periphery of the wafer is removed by laser processing, the following problem occurs: a modified layer or a chip is left on the periphery of the wafer, and the wafer is damaged from the portion at which the modified layer or the chip is left. SUMMARY

[0007] Thus, an object of the present application is to provide a wafer processing method in which a modified layer or a chip is not left on the periphery of a wafer, and a device region close to a region in which a ring-shaped reinforcing portion is formed can be set.

[0008] According to one embodiment of the present application, there is provided a wafer processing method for a wafer on which a plurality of device regions divided by a plurality of division lines and a peripheral remaining region surrounding the device regions are formed on a front surface, the wafer processing method comprising: a modification layer forming step of forming a modification layer that does not reach a finished thickness of the wafer in a ring shape by irradiating a laser beam having a wavelength that is transparent to the wafer from a back surface of the wafer so that a focal point of the laser beam is positioned inside the wafer corresponding to the peripheral remaining region; a protective member providing step of providing a protective member on the front surface of the wafer before or after the modification layer forming step; a reinforcement portion forming step of holding the protective member side by a chuck table, grinding the back surface of the wafer so that a cleavage plane reaches the front surface from the modification layer formed in the ring shape and the modification layer is removed, and thinning a region of the wafer corresponding to the device regions to the finished thickness to form a ring-shaped reinforcement portion in a region of the wafer corresponding to the peripheral remaining region; and a back surface processing step of performing a predetermined processing on the back surface of the wafer.

[0009] Preferably, the wafer processing method further comprises: a transfer step of removing the ring-shaped reinforcement portion along the cleavage plane formed in the reinforcement portion forming step after the back surface processing step, removing the protective member from the front surface of the wafer, sticking the back surface of the wafer on a dicing tape, and supporting an outer periphery of the dicing tape by a frame having an opening portion in which the wafer is accommodated; and a division step of dividing the wafer into individual device chips by performing a processing on the division lines of the wafer.

[0010] In the wafer processing method according to one aspect of the present application, since the wafer is divided along the cleavage plane and the modification layer is removed, the modification layer and the chippings are not left on the wafer. Thus, the problem that the wafer is broken from the portion where the modification layer or the chippings are left is eliminated. In addition, since the wafer is divided along the cleavage plane, the device regions can be set to the margin of the region where the ring-shaped reinforcement portion is formed. Therefore, the productivity is improved. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a perspective view showing a manner of implementing the protective member providing step of the present embodiment.

[0012] Figure 2 is a perspective view showing a manner of holding the wafer on a chuck table of a laser processing apparatus.

[0013] Figure 3 (a) of is a perspective view showing an embodiment of the modification layer forming step, Figure 3 (b) of is a partial enlarged cross-sectional view corresponding to a portion of (a) of Figure 3

[0014] is a perspective view showing a manner of implementing the protective member providing step of the present embodiment.Figure 4 (a) is a perspective view showing an embodiment of the reinforcing portion forming step, Figure 4 (b) is a partial enlarged cross-sectional view corresponding to a part of (a). Figure 4 (a) of the present embodiment.

[0015] Figure 5 is a perspective view showing a manner in which the wafer is supported to the frame by means of a dicing tape.

[0016] Figure 6 is a perspective view showing a manner in which the reinforcing portion and the protective member are removed in the transfer step.

[0017] Figure 7 is a perspective view showing an embodiment of the dividing step.

[0018] Figure 8 is a cross-sectional view showing an embodiment of the pickup step.

[0019] Explanation of Reference Numerals

[0020] 10: wafer; 10a: front surface; 10b: back surface; 10c: reinforcing portion; 10d: cleaving surface; 12: device; 14: division intended line; 16a: device region; 16b: peripheral remaining region; 17: boundary; 20: protective member (adhesive tape); 30: laser processing apparatus; 32: chuck table; 34: laser beam irradiation unit; 36: condenser; 40: grinding apparatus; 41: chuck table; 42: grinding unit; 43: spindle housing; 44: spindle; 46: grinding wheel; 48: grinding tool; 50: cutting apparatus; 52: cutting unit; 54: spindle; 56: cutting tool; 60: pickup apparatus; 62: pickup chuck; 64: extension unit; 100: modified layer; 110: division groove; F: frame; T: dicing tape; LB: laser beam. DETAILED DESCRIPTION

[0021] Hereinafter, an embodiment of the present application will be described in detail with reference to the drawings.

[0022] In Figure 1 , a wafer 10 processed by a processing method of the wafer of the present embodiment is shown. The wafer 10 is a circular plate-shaped member formed in a thickness of 700 μm, has a front surface 10a and a back surface 10b, and is formed of, for example, silicon. On the front surface 10a of the wafer 10, a device region 16a in which a plurality of devices 12 are divided by a plurality of division intended lines 14 and a peripheral remaining region 16b surrounding the device region 16a are formed. In addition, on the back surface 10b of the wafer 10, a modified layer 100 is formed in a region corresponding to the device region 16a. Figure 1 In Figure 1 , a wafer 10 processed by a processing method of the wafer of the present embodiment is shown. The wafer 10 is a circular plate-shaped member formed in a thickness of 700 μm, has a front surface 10a and a back surface 10b, and is formed of, for example, silicon. On the front surface 10a of the wafer 10, a device region 16a in which a plurality of devices 12 are divided by a plurality of division intended lines 14 and a peripheral remaining region 16b surrounding the device region 16a are formed. In addition, on the back surface 10b of the wafer 10, a modified layer 100 is formed in a region corresponding to the device region 16a. Figure 1 , a boundary 17 that distinguishes the device region 16a from the peripheral remaining region 16b is shown by a double-dot chain line, but the boundary 17 is an imaginary line described for convenience of explanation and is not formed on the front surface 10a of the actual wafer 10.

[0023] In implementing the wafer processing method of the present embodiment, a protective member 20 as shown in FIG. 2 is prepared. The protective member 20 is, for example, a circular adhesive tape having the same diameter as the wafer 10. After such a protective member 20 is prepared, the protective member 20 is attached to the front surface 10a of the wafer 10 (protective member attaching step). Figure 1

[0024] Next, as shown in FIG. 3, the wafer 10 is carried to a laser processing device 30 (only a part is shown), the back surface 10b side of the wafer 10 is made to face upward, the protective member 20 side is made to face downward, and the wafer 10 is placed on a holding surface 32a of a chuck table 32 with the center of the wafer 10 positioned at the center of the chuck table 32. The chuck table 32 has a not-shown rotation drive mechanism and is capable of rotating the chuck table 32. The holding surface 32a is a flat surface formed of a material having air permeability and is connected to a not-shown suction source via the inside of the chuck table 32. The suction source is made to operate to suction-retain the wafer 10 placed on the holding surface 32a. Figure 2

[0025] Next, the chuck table 32 is positioned directly below a not-shown alignment unit, an alignment step is implemented, the wafer 10 is detected and the laser processing position of the wafer 10 is detected, and the position information is stored in a not-shown control unit of the laser processing device 30. Next, based on the position information, as shown in (a) of FIG. 4, the wafer 10 is positioned directly below a condenser 36 of a laser beam irradiation unit 34. The laser beam irradiation unit 34 is a unit that irradiates a laser beam LB, and the position at which the laser beam LB is irradiated is a position corresponding to the outer peripheral remaining region 16b and is a position that is outside the boundary 17 between the device region 16a and the outer peripheral remaining region 16b. Figure 3

[0026] The depth position of the condensing point of the laser beam LB is positioned inside the position corresponding to the outer peripheral remaining region 16b described above and is a position at which the modified layer 100 that does not reach the finished thickness of the wafer 10 from the back surface 10b side is formed in a ring shape (see (b) of FIG. 4). In addition, since the finished thickness of the wafer 10 in the present embodiment is set to about 30 μm, the modified layer 100 is formed above the front surface 10a on which the device 12 is formed by 30 μm or more. In this way, the position corresponding to the outer peripheral remaining region 16b of the wafer 10 is positioned directly below the condenser 36 of the laser beam irradiation unit 34, the laser beam irradiation unit 34 is made to operate to irradiate the laser beam LB, and the chuck table 32 is made to rotate in the direction indicated by an arrow Rl, whereby the modified layer 100 is formed in a ring shape inside the entire circumference of the position corresponding to the outer peripheral remaining region 16b. Figure 3 Figure 3 ​​​​The modified layer 100 is shown in (b). The modified layer formation process is completed through the above steps.

[0027] Furthermore, the laser processing conditions implemented in the above-mentioned modified layer formation process are set as shown below.

[0028] Wavelength: 1342nm

[0029] Repetition frequency: 60kHz

[0030] Average output: 1.6W

[0031] Chuck table speed: 0.5 rpm

[0032] After performing the modified layer formation process as described above, the following reinforcement formation process is performed: the wafer 10 is transferred to... Figure 4 The grinding apparatus 40 shown in (a) (only a portion is shown) grinds the back side 10b of the wafer 10, causing the cleavage surface formed starting from the annular modified layer 100 to reach the front side 10a of the wafer 10. The modified layer 100 is removed, and the region of the wafer 10 corresponding to the device region 16a is thinned to the finished thickness. An annular reinforcement is formed in the region corresponding to the remaining peripheral region 16b. Furthermore, in the above embodiment, a protective component placement process is performed before the modified layer formation process; however, the present invention is not limited to this, and the protective component placement process may be performed after the modified layer formation process and before the reinforcement formation process described below. Hereinafter, refer to... Figure 4 (a) and Figure 4 (b) provides a more detailed explanation of the process for forming the reinforcing section.

[0033] like Figure 4 As shown in (a), the grinding apparatus 40 includes: a chuck stage 41 that attracts and holds the wafer 10; and a grinding unit 42 that grinds the wafer 10 held by the chuck stage 41. The chuck stage 41 has a rotary drive mechanism (not shown) that rotates the chuck stage 41 at a predetermined speed in the direction indicated by arrow R2. In addition, the chuck stage 41 has a holding surface (not shown) formed of a breathable raw material, which is connected to an attraction source (not shown).

[0034] The grinding unit 42 has a spindle housing 43, a spindle 44 rotatably held to the spindle housing 43, a spindle motor (not shown) that rotates the spindle 44 at a predetermined rotational speed, a circular plate-shaped grinding wheel 46 fixed to a lower end of the spindle 44, and a plurality of grinding stones 48 arranged in a ring shape at equal intervals on an outer peripheral edge portion of a lower surface of the grinding wheel 46. By operating the spindle motor, the spindle 44 is rotated in the direction indicated by an arrow R3 to rotate the grinding wheel 46. In addition, the diameter of the grinding wheel 46 is set to be substantially identical to the radius of the wafer 10.

[0035] When the reinforcing portion forming process is implemented, the wafer 10 is placed and suction-held on the chuck table 41 with the protective member 20 side of the wafer 10 facing downward and with the center of the wafer 10 positioned at the center of the chuck table 41. Next, the position of the wafer 10 with respect to the grinding stones 48 is set so that the grinding stones 48 arranged in a ring pass through the center of the wafer 10 and the end portions on the outer side of the grinding stones 48 are positioned radially inward of the outer periphery of the wafer 10. At this time, the end portions on the outer side of the grinding stones 48 are positioned at positions corresponding to the outer peripheral remaining region 16b and slightly outward of the positions at which the modified layer 100 is formed.

[0036] Next, the chuck table 41 is rotated in the direction indicated by the arrow R2 at a predetermined rotational speed (for example, 300 rpm), and the spindle 44 of the grinding unit 42 is rotated in the direction indicated by the arrow R3 at a predetermined rotational speed (for example, 6000 rpm). Next, the lifting mechanism of the grinding unit 42 (not shown) is operated to lower the grinding wheel 46, and the grinding stones 48 are brought into contact with the back surface 10b of the wafer 10. Then, the grinding wheel 46 is fed at a predetermined grinding feed rate (for example, 1 μm / sec).

[0037] As described above, the end portions on the outer side of the grinding stones 48 are positioned outward of the positions at which the modified layer 100 is formed, and by performing the grinding process described above, the modified layer 100 is ground, and in addition, the cleavage surface 10d extends from the positions at which the modified layer 100 is formed toward the front surface 10a on which the device 12 is formed. When the back surface 10b of the wafer 10 is thus ground until the finished thickness (30 μm) is reached, as shown in FIG. 6B, the modified layer 100 is ground, and in addition, the cleavage surface 10d extends from the positions at which the modified layer 100 is formed toward the front surface 10a on which the device 12 is formed. Figure 4As shown in (b), the modification layer 100 is completely removed, and the cleavage plane 10d extending from the position where the modification layer 100 was formed reaches the front surface 10a side, and a ring-shaped division line is formed by the continuous cleavage plane 10d. Also, the portion including the region corresponding to the device region 16a is thinned from the back surface 10b, and a reinforcing portion 10c is formed in the region corresponding to the outer peripheral remaining region 16b, the reinforcing portion 10c being in a ring-shaped convex shape. In addition, the width of the reinforcing portion 10c is set to a width (for example, about 2 mm to 3 mm) at which the wafer 10 thinned to the finished thickness can be stably handled. The reinforcing portion forming process is completed by the above process.

[0038] Next, a back surface processing process is performed in which the wafer 10 on which the reinforcing portion 10c is formed is carried to a back surface processing device (omitted from the drawing), and the back surface 10b of the thinned region of the wafer 10 is subjected to a prescribed processing. The back surface processing device is, for example, a device that covers the back surface 10b of the region of the wafer 10 thinned by the processing performed by the reinforcing portion forming process with a metal film 11 (refer to Figure 5 ) on which an electrode or the like is formed. At the time of carrying the wafer 10 to the back surface processing device, although the region corresponding to the device region 16a is thinned to 30 μm, since the ring-shaped reinforcing portion 10c is formed, the wafer 10 can be stably handled without being deflected, and the back surface processing process can be easily performed on the wafer 10. Also, as a result of performing the wafer processing method including the modification layer forming process, the protection member disposing process, the reinforcing portion forming process, and the back surface processing process, the device region 16a and the outer peripheral remaining region 16b of the wafer 10 are divided in a ring shape by the cleavage plane 10d, and it is possible to set the device region 16a to the margin of the region in which the ring-shaped cleavage plane 10d is formed. That is, it is possible to set more devices 12 in the device region 16a, and thus the productivity is improved.

[0039] After the wafer processing method described above is performed, that is, after the back surface processing process is performed, a division process can also be performed as needed in which the ring-shaped reinforcing portion 10c is removed along the cleavage plane 10d formed in the reinforcing portion forming process to divide the wafer 10 into individual device chips. Hereinafter, the division process will be described on the basis of Figure 5 Figures 6 to 8 .

[0040] When the division process is performed, first, as shown in Figure 5 , a ring-shaped frame F having an opening portion Fa capable of receiving the wafer 10 and a dicing tape T are prepared. The dicing tape T is circular, and the diameter thereof is larger than the opening portion Fa, and the outer periphery of the dicing tape T is adhered to the back surface of the frame F. As shown in Figure 5 ​As shown, the wafer 10 is flipped over so that the back surface 10b side on which the metal film 11 is formed is directed downward, and the wafer 10 is positioned in the center of the opening portion Fa of the frame F and attached to the dicing tape T, and the wafer 10 is supported by the dicing tape T to the frame F.

[0041] According to Figure 5 As shown, the wafer 10 is flipped over so that the back surface 10b side on which the metal film 11 is formed is directed downward, and the wafer 10 is positioned in the center of the opening portion Fa of the frame F and attached to the dicing tape T, and the wafer 10 is supported by the dicing tape T to the frame F. Figure 6 As shown, the wafer 10 is flipped over so that the back surface 10b side on which the metal film 11 is formed is directed downward, and the wafer 10 is positioned in the center of the opening portion Fa of the frame F and attached to the dicing tape T, and the wafer 10 is supported by the dicing tape T to the frame F.

[0042] Next, in order to perform the dicing process on the wafer 10 transferred to the dicing tape T and held by the frame F, the wafer 10 held by the frame F is conveyed to Figure 7 the cutting apparatus 50 shown. The cutting apparatus 50 has a chuck table (omitted from the drawing) that suction-holds the wafer 10, and a cutting unit 52 that cuts the wafer 10 suction-held to the chuck table. The chuck table is configured to be rotatable, and has a moving mechanism (omitted from the drawing) that feeds the chuck table in the direction indicated by the arrow X in the drawing. Also, the cutting unit 52 has a spindle 54 disposed in the Y-axis direction indicated by the arrow Y in the drawing and held, a ring-shaped cutting tool 56 held to the tip of the spindle 54, and a Y-axis moving mechanism (omitted from the drawing) that index-feeds the cutting tool 56 in the Y-axis direction. The spindle 54 is rotationally driven by a spindle motor (omitted from the drawing).

[0043] During the dicing process, firstly, the wafer 10 is placed on the chuck table of the cutting device 50 with its front side 10a facing upwards and held in place by suction, aligning the predetermined dicing line 14 of the wafer 10 with the X-axis direction, and aligning it with the cutting tool 56. Next, the high-speed rotating cutting tool 56 is positioned on the predetermined dicing line 14 aligned with the X-axis direction, cutting in from the front side 10a, and the chuck table is fed along the X-axis direction to form a dicing groove 110. Then, the cutting tool 56 of the cutting unit 52 is indexed and fed to a predetermined dicing line 14 adjacent to the dicing line 14 with the dicing groove 110 in the Y-axis direction but without the dicing groove 110, and the cutting process to form the dicing groove 110 is performed in the same manner as described above. By repeating these steps, dicing grooves 110 are formed along all the predetermined dicing lines 14 along the X-axis direction. Next, the chuck stage is rotated 90 degrees so that the direction perpendicular to the previously formed dividing groove 110 is aligned with the X-axis direction. The aforementioned cutting process is then performed on all the pre-defined dividing lines 14 newly aligned with the X-axis direction, forming dividing grooves 110 along all the pre-defined dividing lines 14 formed on the wafer 10. By performing the dividing process in this way, the wafer 10 is divided into device chips for each device 12 along the pre-defined dividing lines 14 (dividing process).

[0044] After performing the segmentation process as described above, it can also be done as needed, such as Figure 8 The pick-up process of picking up device chip 12' from dicing tape T is performed as shown. The pick-up process can, for example, use... Figure 8 The pickup device 60 shown is used to implement this. The pickup device 60 has: a pickup chuck 62 that picks up and transports the device chip 12'; and an extension unit 64 that extends the dicing strip T and extends the spacing between adjacent device chips 12'.

[0045] like Figure 8 As shown, the expansion unit 64 includes: a cylindrical expansion drum 64a; a plurality of cylinders 64b adjacent to the expansion drum 64a and extending upwardly at intervals in the circumferential direction; an annular holding member 64c connected to the upper end of each of the cylinders 64b; and a plurality of clamps 64d disposed at intervals in the circumferential direction on the outer periphery of the holding member 64c. The inner diameter of the expansion drum 64a is larger than the diameter of the wafer 10, and the outer diameter of the expansion drum 64a is smaller than the inner diameter Fa of the frame F. Furthermore, the holding member 64c corresponds to the frame F, and the frame F is mounted on the flat upper surface of the holding member 64c.

[0046] like Figure 8As shown, the plurality of cylinders 64b relatively raise and lower the holding member 64c with respect to the expansion drum 64a between a reference position (indicated by a solid line) in which the upper surface of the holding member 64c is at substantially the same height as the upper end of the expansion drum 64a and an expanded position (indicated by a double-dotted line) in which the upper surface of the holding member 64c is positioned lower than the upper end of the expansion drum 64a.

[0047] Figure 8 The pickup chuck 64 shown is configured to be movable in the horizontal direction and the vertical direction. In addition, a suction source (not shown) is connected to the pickup chuck 64, and the device chip 12' is sucked by the lower surface of the tip of the pickup chuck 64.

[0048] Referring to Figure 8 Continuing the explanation, in the pickup process, first, the wafer 10 divided into individual device chips 12' is oriented upward, and the frame F is placed on the upper surface of the holding member 64c positioned at the reference position. Next, the annular frame 16 is fixed by the plurality of jigs 74d. Next, the holding member 74c is lowered to the expanded position, and a radial tension is applied to the dicing tape T. As a result, as shown by the double-dotted line in the middle, the spacing of the device chips 12' adhered to the dicing tape T is expanded. Figure 8 Figure 8 Continuing the explanation, in the pickup process, first, the wafer 10 divided into individual device chips 12' is oriented upward, and the frame F is placed on the upper surface of the holding member 64c positioned at the reference position. Next, the annular frame 16 is fixed by the plurality of jigs 74d. Next, the holding member 74c is lowered to the expanded position, and a radial tension is applied to the dicing tape T. As a result, as shown by the double-dotted line in the middle, the spacing of the device chips 12' adhered to the dicing tape T is expanded.

[0049] Next, the pickup chuck 64 is positioned above the device chip 12' that is the object of pickup and is lowered, and the upper surface of the device chip 12' is sucked by the lower surface of the tip of the pickup chuck 72. Next, the pickup chuck 72 is raised, and the device chip 12' is peeled from the dicing tape T and picked up. Next, the picked-up device chip 12' is transported to a tray or the like, not shown, or to a prescribed transport position of the next process. Then, this pickup operation is sequentially performed on all of the device chips 12', and the pickup process is completed.

[0050] According to the above-described embodiment, since the wafer 10 is divided along the cleavage plane 10d and the modified layer is removed, the modified layer or the chippings do not remain on the wafer 10. Thus, the problem of breakage of the wafer 10 from the portion where the modified layer or the chippings remain is eliminated. In addition, since the wafer 10 is divided along the cleavage plane 10d, the device region 16a can be set to the margin of the region where the annular reinforcing portion 10c is formed. Thus, the productivity is improved.

Claims

1. A wafer processing method of a wafer on which a plurality of device regions divided by a plurality of division lines and a peripheral remaining region surrounding the device regions are formed on a front surface, wherein the wafer processing method comprises the steps of: a modification layer forming step of forming a modification layer which does not reach a finished thickness of the wafer in a ring shape by irradiating a laser beam having a wavelength which is transparent to the wafer from a back surface of the wafer in a manner that a condensing point of the laser beam is positioned inside the wafer corresponding to the peripheral remaining region; a protection member providing step of providing a protection member on the front surface of the wafer before or after the modification layer forming step; a reinforcement portion forming step of holding the protection member side with a chuck table, grinding the back surface of the wafer so that a cleavage plane reaches the front surface from the modification layer formed in the ring shape and the modification layer is removed, and removing the reinforcement portion in the ring shape along the cleavage plane extending from the modification layer to the front surface in a state where the modification layer is removed, and thinning a region of the wafer corresponding to the device regions to the finished thickness and forming a reinforcement portion in a ring shape in a region of the wafer corresponding to the peripheral remaining region; and a back surface processing step of performing a prescribed processing on the back surface of the wafer.

2. The wafer processing method according to claim 1, wherein the wafer processing method further comprises the steps of: a transfer step of removing the reinforcement portion in the ring shape along the cleavage plane formed in the reinforcement portion forming step after the back surface processing step, removing the protection member from the front surface of the wafer, sticking the back surface of the wafer on a dicing tape and supporting an outer periphery of the dicing tape with a frame having an opening portion in which the wafer is accommodated; and a division step of dividing the wafer into individual device chips by performing a processing on the division lines of the wafer. ​ ​ ​ ​ ​ ​ ​ ​ ​

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