JP6235396B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a wafer processing method in which a wafer having a plurality of devices formed on a surface is divided along a plurality of scheduled division lines that divide the device.

  As is well known to those skilled in the art, in a semiconductor device manufacturing process, a semiconductor wafer in which a plurality of devices such as ICs and LSIs are formed in a matrix on the surface of a semiconductor substrate (Si, GaN, etc.) is formed. In the semiconductor wafer formed in this way, the above-described devices are partitioned by division planned lines, and individual devices are manufactured by dividing along the planned division lines.

  As a method for dividing a wafer such as the semiconductor wafer described above, there is also a laser processing method in which a pulse laser beam having a wavelength that is transparent to the wafer is used, and a focused laser beam is positioned inside the region to be divided and irradiated with the pulse laser beam. Has been tried. The division method using this laser processing method is to divide the inside of the work piece by irradiating a pulse laser beam having a wavelength that is transparent to the wafer by aligning the condensing point from one side of the wafer. This is a technique for dividing a wafer by continuously forming a modified layer along a line and applying an external force along a street whose strength is reduced by forming the modified layer. (For example, refer to Patent Document 1.)

  In addition, as a method of dividing a wafer such as a semiconductor wafer along the planned division line, a laser processing groove is formed by performing ablation processing by irradiating the wafer along the planned division line with a pulsed laser beam having a wavelength that absorbs the wafer. And a technique of cleaving by applying an external force along a planned dividing line in which a laser-processed groove serving as a starting point of breakage is formed. (For example, see Patent Document 2.)

Japanese Patent No. 3408805 JP-A-10-305420

Therefore, when ablation processing is performed by irradiating a pulse laser beam having a wavelength that absorbs the wafer along the division line, and the wafer is divided into individual devices, many cracks are formed on the side from which the laser beam is extracted. There is a problem that it occurs and lowers the bending strength of the device.
In addition, by applying a pulsed laser beam having a wavelength that is transmissive to the wafer to the inside of the wafer and irradiating the wafer along the planned division line, a modified layer is continuously formed, and the wafer is applied to each device. When divided, there is a problem that the device is broken by an impact force such as dropping due to internal strain remaining in the modified layer.

  The present invention has been made in view of the above-mentioned facts, and the main technical problem thereof is that the wafer is divided into lines so that the device is not broken by an impact force without lowering the bending strength of the device. It is to provide a method of processing a wafer that can be divided along a line.

In order to solve the above main technical problem, according to the present invention, a wafer processing method for dividing a wafer having a plurality of devices formed on a surface along a plurality of division lines to divide the device,
A condensing point of a laser beam having a wavelength that is transparent to the wafer is positioned from the back side of the wafer to the inside and irradiated along the planned dividing line, and the modified layer that propagates cracks toward the wafer surface is scheduled to be divided A modified layer forming step of forming along the line;
It is formed along the planned dividing line by performing ablation processing by irradiating the wafer subjected to the modified layer forming step with a laser beam having a wavelength that absorbs the wafer along the planned dividing line from the back side of the wafer. An ablation process to remove the modified layer,
A wafer dividing step of dividing the wafer on which the ablation processing step has been performed into individual devices by cracks formed along a line to be divided.
A method for processing a wafer is provided.

In the ablation processing step, the crack formed by the modified layer forming step is propagated to the surface of the wafer.
Further, before performing the modified layer forming step, a back surface grinding step is performed in which the back surface of the wafer is ground to form the wafer to a predetermined thickness.

In the wafer processing method according to the present invention, a condensing point of a laser beam having a wavelength that is transmissive to the wafer is positioned from the back side of the wafer to the inside, and is irradiated along the planned dividing line, and cracks are directed toward the surface of the wafer. A modified layer forming process that forms a modified layer that propagates along the line to be divided, and ablation processing by irradiating a laser beam having a wavelength that absorbs the wafer from the back side of the wafer along the line to be divided Ablation processing step for removing the modified layer formed along the planned dividing line and a wafer dividing step for dividing the wafer into individual devices by cracks formed along the planned dividing line. Therefore, internal strain is removed by ablation along with the modified layer formed in the modified layer forming process. It is therefore able to withstand the impact force such as dropping, to solve a problem that is destroyed by the impact force due to internal strain remaining in the modified layer.
In addition, the laser beam irradiated from the back surface b side of the wafer in the ablation processing step is not absorbed by the modified layer and grows to the surface by growing a crack extending from the modified layer to the surface side. In addition, many cracks are not generated toward the device side, and the problem that the bending strength of the device is reduced due to the generation of many cracks toward the device side is also solved.

The perspective view of the semiconductor wafer as a wafer processed by the processing method of the wafer by this invention. FIG. 2 is a perspective view illustrating a state in which the semiconductor wafer illustrated in FIG. 1 is attached to a dicing tape mounted on an annular frame. The principal part perspective view of the grinding device for implementing the back surface grinding process in the processing method of the wafer by the present invention. Explanatory drawing of the back surface grinding process in the processing method of the wafer by this invention. The principal part perspective view of the laser processing apparatus for implementing the modified layer formation process in the processing method of the wafer by this invention. Explanatory drawing of the modified layer formation process in the processing method of the wafer by this invention. The perspective view of the principal part of the laser processing apparatus for implementing the ablation processing process in the processing method of the wafer by this invention. Explanatory drawing of the ablation processing process in the processing method of the wafer by this invention. The perspective view of the tape expansion apparatus for implementing the wafer division | segmentation process in the processing method of the wafer by this invention. Explanatory drawing of the wafer division | segmentation process in the processing method of the wafer by this invention.

  Preferred embodiments of the wafer processing method according to the present invention will be described below in more detail with reference to the accompanying drawings.

  FIG. 1 is a perspective view of a semiconductor wafer as a wafer processed by the wafer processing method according to the present invention. The semiconductor wafer 2 shown in FIG. 1 is made of, for example, a silicon wafer having a diameter of 200 mm and a thickness of 600 μm. A plurality of division lines 21 are formed in a lattice shape on the surface 2a, and the plurality of division lines are formed. Devices 22 such as ICs and LSIs are formed in a plurality of regions partitioned by 21.

  In order to divide the above-described semiconductor wafer 2 along the scheduled division line 21, a wafer support process is performed in which the semiconductor wafer 2 is adhered to the surface of a dicing tape attached to an annular frame. That is, as shown in FIG. 2, the surface 2 a of the semiconductor wafer 2 is attached to the surface of the dicing tape 30 with the outer peripheral portion mounted so as to cover the inner opening of the annular frame 3. Accordingly, the back surface 2b of the semiconductor wafer 2 attached to the front surface of the dicing tape 30 is on the upper side.

  If the wafer support process described above is performed, a back surface grinding process is performed in which the back surface 2b of the semiconductor wafer 2 is ground to form the semiconductor wafer 2 with a predetermined finished thickness of the device. This back grinding process is performed using the grinding apparatus 4 shown in FIG. The grinding apparatus 4 shown in FIG. 3 includes a chuck table 41 that holds a workpiece, and a grinding means 42 that grinds the workpiece held on the chuck table 41. The chuck table 41 is configured to suck and hold a workpiece on the upper surface, which is a holding surface, and is rotated in a direction indicated by an arrow 41a in FIG. 3 by a rotation driving mechanism (not shown). The grinding means 42 includes a spindle housing 421, a rotating spindle 422 that is rotatably supported by the spindle housing 421 and rotated by a rotation driving mechanism (not shown), a mounter 423 attached to the lower end of the rotating spindle 422, and the mounter And a grinding wheel 424 attached to the lower surface of 423. The grinding wheel 424 includes an annular base 425 and a grinding wheel 426 that is annularly attached to the lower surface of the base 425, and the base 425 is attached to the lower surface of the mounter 423 by fastening bolts 427. ing.

  In order to carry out the back surface grinding process using the grinding device 4 described above, the dicing tape 30 side on which the semiconductor wafer 2 is adhered is placed on the upper surface (holding surface) of the chuck table 41 as shown in FIG. To do. Then, the semiconductor wafer 2 is sucked and held on the chuck table 41 via the dicing tape 30 by operating a suction means (not shown) (wafer holding step). Accordingly, the back surface 2b of the semiconductor wafer 2 held on the chuck table 41 is on the upper side. In FIG. 3, the annular frame 3 to which the dicing tape 30 is attached is omitted, but the annular frame 3 is fixed by appropriate frame fixing means provided on the chuck table 41. When the semiconductor wafer 2 is sucked and held on the chuck table 41 via the dicing tape 30 in this way, the grinding wheel of the grinding means 42 is rotated while the chuck table 41 is rotated in the direction indicated by the arrow 41a in FIG. 3 is rotated in the direction indicated by the arrow 424a in FIG. 3 at, for example, 6000 rpm, and the grinding wheel 426 constituting the grinding wheel 424 is brought into contact with the back surface 2b of the semiconductor wafer 2 which is the processing surface as shown in FIG. The wheel 424 is ground and fed by a predetermined amount downward (in a direction perpendicular to the holding surface of the chuck table 41) at a grinding feed rate of 1 μm / second, for example, as indicated by an arrow 424b in FIGS. As a result, the back surface 2b of the semiconductor wafer 2 is ground to form the semiconductor wafer 2 with a predetermined thickness (for example, 200 to 300 μm). Note that before the semiconductor wafer 2 is attached to the dicing tape 30, a back surface grinding step of grinding the back surface of the semiconductor wafer 2 may be performed.

  If the back surface grinding step is performed as described above, the condensing point of the laser beam having a wavelength that is transmissive to the semiconductor wafer 2 is positioned from the back surface side of the semiconductor wafer 2 and irradiated along the planned division line 21. Then, a modified layer forming step is performed in which a modified layer that propagates cracks toward the surface of the semiconductor wafer 2 is formed along the division line. This modified layer forming step is performed using a laser processing apparatus shown in FIG. A laser processing apparatus 5 shown in FIG. 5 has a chuck table 51 that holds a workpiece, a laser beam irradiation means 52 that irradiates a workpiece held on the chuck table 51 with a laser beam, and a chuck table 51 that holds the workpiece. An image pickup means 53 for picking up an image of the processed workpiece is provided. The chuck table 51 is configured to suck and hold a workpiece. The chuck table 51 is moved in a processing feed direction indicated by an arrow X in FIG. 5 by a processing feed means (not shown) and is also shown in FIG. 5 by an index feed means (not shown). It can be moved in the index feed direction indicated by the arrow Y.

  The laser beam irradiation means 52 includes a cylindrical casing 521 disposed substantially horizontally. In the casing 521, a pulse laser beam oscillation means having a pulse laser beam oscillator and a repetition frequency setting means (not shown) are arranged. A condenser 522 for condensing the pulse laser beam oscillated from the pulse laser beam oscillating means is attached to the tip of the casing 521. The laser beam irradiation unit 52 includes a condensing point position adjusting unit (not shown) for adjusting the condensing point position of the pulse laser beam collected by the condenser 522.

  In the illustrated embodiment, the image pickup means 53 mounted on the tip of the casing 521 constituting the laser beam irradiation means 52 emits infrared rays to the workpiece in addition to a normal image pickup device (CCD) that picks up an image with visible light. Infrared illumination means for irradiating, an optical system for capturing infrared light emitted by the infrared illumination means, an image pickup device (infrared CCD) for outputting an electrical signal corresponding to the infrared light captured by the optical system, and the like Then, the captured image signal is sent to a control means (not shown).

  By using the laser processing apparatus 5 described above, the semiconductor wafer 2 on which the above-described wafer support process and back surface grinding process have been carried out is provided with a condensing point of a pulse laser beam having a wavelength transmissive to the semiconductor wafer 2. A modified layer forming step is performed in which a modified layer that is positioned inward from the back surface side of the wafer and is irradiated along the planned division line 21 to propagate a crack toward the surface of the semiconductor wafer 2 is formed along the planned division line. First, the dicing tape 30 side on which the semiconductor wafer 2 is adhered is placed on the chuck table 51. Then, by operating a suction means (not shown), the semiconductor wafer 2 is held on the chuck table 51 via the dicing tape 30 (wafer holding step). Therefore, the back surface 2b of the semiconductor wafer 2 held on the chuck table 51 is on the upper side. In FIG. 5, the annular frame 3 to which the dicing tape 30 is mounted is omitted, but the annular frame 3 is fixed to an appropriate frame fixing means provided on the chuck table 51. In this manner, the chuck table 51 that sucks and holds the semiconductor wafer 2 is positioned directly below the imaging unit 53 by a processing feed unit (not shown).

  When the chuck table 51 is positioned immediately below the image pickup means 53, an alignment operation for detecting a processing region to be laser processed of the semiconductor wafer 2 is executed by the image pickup means 53 and a control means (not shown). That is, the image pickup unit 53 and a control unit (not shown) include the planned division line 21 formed in a predetermined direction of the semiconductor wafer 2, and the condenser 522 of the laser beam irradiation unit 52 that irradiates the laser beam along the planned division line 21. Image processing such as pattern matching is performed to align the laser beam, and alignment of the laser beam irradiation position is performed (alignment process). In addition, alignment of the laser beam irradiation position is similarly performed on the division lines 21 formed on the semiconductor wafer 2 in a direction orthogonal to the predetermined direction. At this time, the surface 2a on which the division line 21 of the semiconductor wafer 2 is formed is located on the lower side, but the imaging unit 53 corresponds to the infrared illumination unit, the optical system for capturing infrared rays and the infrared ray as described above. Since the image pickup device is provided with an image pickup device (infrared CCD) or the like that outputs an electric signal, the division planned line 21 can be picked up through the back surface 2b.

  When the alignment step described above is performed, the chuck table 51 is moved to the laser beam irradiation region where the condenser 522 of the laser beam irradiation means 52 for irradiating the laser beam is positioned as shown in FIG. The planned line 21 is positioned directly below the light collector 522. At this time, as shown in FIG. 6A, the semiconductor wafer 2 is positioned so that one end of the planned dividing line 21 (the left end in FIG. 6A) is located directly below the condenser 522. And the condensing point P of the pulsed laser beam LB condensed by the condenser 522 is positioned at a position of, for example, the 40 μm rear surface 2b side (upper surface side) from the front surface 2a (lower surface) of the semiconductor wafer 2. The chuck table 51 is radiated with a pulse laser beam having a wavelength that is transmissive to the semiconductor wafer 2 made of silicon wafer from the condenser 522, and the chuck table 51 is fed at a predetermined feed speed in the direction indicated by the arrow X1 in FIG. Move with. Then, as shown in FIG. 6B, when the irradiation position of the condenser 522 of the laser beam irradiation means 52 reaches the position of the other end of the planned dividing line 21, the irradiation of the pulse laser beam is stopped and the chuck table 51 Stop moving. As a result, inside the semiconductor wafer 2, there is a modified layer 23 having a thickness of about 40 μm, for example, as a starting point for breaking along the planned dividing line 21 as shown in FIGS. 6B and 6C. It is formed. When the modified layer 23 is formed in this way, a crack 24 propagates from the modified layer 23 toward the surface 2a (lower surface) inside the semiconductor wafer 2 as shown in FIG. 6C. . The crack 24 may not reach the surface 2a as shown in FIG. 6D due to processing conditions such as the output of the pulse laser beam to be irradiated.

The processing conditions in the modified layer forming step are set as follows, for example.
Wavelength: 1064 nm pulse laser Repetition frequency: 50 kHz
Average output: 1W
Condensing spot diameter: φ2μm
Processing feed rate: 200 mm / sec

  As described above, when the modified layer forming step is performed along the predetermined division line 21, the chuck table 51 is indexed and moved in the direction indicated by the arrow Y by the interval of the division line 21 formed on the semiconductor wafer 2. (Indexing step), the modified layer forming step is performed. When the modified layer forming step is performed along all the division lines 21 formed in the predetermined direction in this way, the chuck table 51 is rotated 90 degrees. And a modified layer formation process is implemented along all the division | segmentation scheduled lines 21 formed in the direction orthogonal to the said predetermined direction.

  If the above-described modified layer forming step is performed, ablation processing is performed by irradiating the semiconductor wafer 2 with a laser beam having a wavelength that is absorptive to the semiconductor wafer 2 from the back surface side of the semiconductor wafer 2 along the division line 21. An ablation process for removing the modified layer 23 formed along the division line 21 is performed. This ablation process is performed using a laser processing apparatus 50 shown in FIG. In addition, since the laser processing apparatus 50 is substantially the same as the structural member of the laser processing apparatus 5 shown in the said FIG. 5, the same code | symbol is attached | subjected to the same member and description is abbreviate | omitted.

  In order to perform the ablation processing step on the semiconductor wafer 2 on which the above-described modified layer forming step has been performed using the laser processing apparatus 50 described above, a dicing tape in which the semiconductor wafer 2 is adhered on the chuck table 51. Place the 30 side. Then, by operating a suction means (not shown), the semiconductor wafer 2 is held on the chuck table 51 via the dicing tape 30 (wafer holding step). And the alignment process mentioned above is implemented similarly.

  Next, as shown in FIG. 8 (a), the chuck table 51 is moved to a laser beam irradiation area where the condenser 522 of the laser beam application means 52 for irradiating the laser beam, and the predetermined division line 21 is moved to the collector. Positioned directly below 522. At this time, as shown in FIG. 8A, the semiconductor wafer 2 is positioned so that one end of the semiconductor wafer 2 (the left end in FIG. 8A) is located directly below the condenser 522. Then, the condensing point P of the pulse laser beam LB irradiated from the condenser 522 is positioned near the back surface 2 b (upper surface) of the semiconductor wafer 2. Next, the chuck table 51 is indicated by an arrow X1 in FIG. 8 (a) while irradiating the semiconductor wafer 2 made of silicon wafer from the condenser 522 of the laser beam irradiation means 52 with a pulse laser beam having an absorptive wavelength. Move in the direction at a predetermined machining feed rate. Then, as shown in FIG. 8B, when the other end of the planned dividing line 21 (the right end in FIG. 8B) reaches a position directly below the condenser 522, the irradiation of the pulse laser beam is stopped and the chuck is stopped. The movement of the table 51 is stopped. As a result, the semiconductor wafer 2 is subjected to ablation processing from the back surface 2b (upper surface) along the planned division line 21, and a laser processing groove 25 is formed as shown in FIG. In the forming process, the internal strain is removed together with the modified layer 23 formed along the division line 21 inside the semiconductor wafer 2. Thus, when the laser processing groove 25 is formed, if the crack 24 propagated from the modified layer 23 toward the surface 2a (lower surface) in the modified layer forming step does not reach the surface 2a, the crack 24 is formed. Is propagated to the surface 2a (lower surface). In the ablation process, the pulse laser beam irradiated from the back surface 2b side of the semiconductor wafer 2 is absorbed by the modified layer 23 and grows a crack 24 extending from the modified layer 23 to the surface 2a side to reach the surface 2a. Even if it exists, since it does not come out to the surface 2a side, many cracks are not generated toward the device 22 side.

The ablation process is performed under the following processing conditions, for example.
Laser beam wavelength: 355 nm
Repetition frequency: 50 kHz
Output: 7W
Condensing spot diameter: φ10μm
Processing feed rate: 100 mm / sec

  When the ablation process is performed along the predetermined division line 21 as described above, the chuck table 51 is indexed and moved in the direction indicated by the arrow Y by the interval of the division line 21 formed on the semiconductor wafer 2 (indexing). Step), the ablation step is performed. When the ablation process is performed along all the planned division lines 21 formed in the predetermined direction in this way, the chuck table 51 is rotated 90 degrees. And an ablation process is implemented along all the division | segmentation scheduled lines 21 formed in the direction orthogonal to the said predetermined direction.

  When the ablation process is performed as described above, a wafer division process is performed in which the semiconductor wafer 2 is divided into individual devices by the cracks 24 formed along the planned division line 21. This wafer dividing step is performed using a tape expansion device 6 shown in FIG. The tape expansion device 6 shown in FIG. 9 includes a frame holding means 61 for holding the annular frame 3 and a tape extending means for expanding the dicing tape 30 attached to the annular frame 3 held by the frame holding means 61. 62 and a pickup collet 63. The frame holding means 61 includes an annular frame holding member 611 and a plurality of clamps 612 as fixing means provided on the outer periphery of the frame holding member 611. An upper surface of the frame holding member 611 forms a mounting surface 611a on which the annular frame 3 is placed, and the annular frame 3 is placed on the mounting surface 611a. The annular frame 3 placed on the placement surface 611 a is fixed to the frame holding member 611 by the clamp 612. The frame holding means 61 configured in this manner is supported by the tape expanding means 62 so as to be able to advance and retract in the vertical direction.

  The tape expansion means 62 includes an expansion drum 621 disposed inside the annular frame holding member 611. The expansion drum 621 has an inner diameter and an outer diameter smaller than the inner diameter of the annular frame 3 and larger than the outer diameter of the semiconductor wafer 2 attached to the dicing tape 30 attached to the annular frame 3. Further, the expansion drum 621 includes a support flange 622 at the lower end. The tape expansion means 62 in the illustrated embodiment includes support means 623 that can advance and retract the annular frame holding member 611 in the vertical direction. The support means 623 includes a plurality of air cylinders 623 a disposed on the support flange 622, and the piston rod 623 b is connected to the lower surface of the annular frame holding member 611. As described above, the supporting means 623 including the plurality of air cylinders 623a is configured such that the annular frame holding member 611 is placed at the reference position where the mounting surface 611a is substantially at the same height as the upper end of the expansion drum 621 as shown in FIG. Then, as shown in FIG. 10 (b), it is moved in the vertical direction between the extended positions below the upper end of the expansion drum 621 by a predetermined amount.

  A wafer dividing process performed using the tape expansion device 6 configured as described above will be described with reference to FIG. That is, the annular frame 3 on which the dicing tape 30 to which the semiconductor wafer 2 subjected to the ablation process has been attached is attached to the frame constituting the frame holding means 61 as shown in FIG. It mounts on the mounting surface 611a of the holding member 611, and is fixed to the frame holding member 611 by the clamp 612 (frame holding process). At this time, the frame holding member 611 is positioned at the reference position shown in FIG. Next, the plurality of air cylinders 623a as the supporting means 623 constituting the tape extending means 62 are operated to lower the annular frame holding member 611 to the extended position shown in FIG. Accordingly, since the annular frame 3 fixed on the mounting surface 611a of the frame holding member 611 is also lowered, the dicing tape 30 attached to the annular frame 3 is an expansion drum as shown in FIG. Expansion is performed in contact with the upper edge of 621 (tape expansion process). As a result, since a tensile force acts radially on the semiconductor wafer 2 adhered to the dicing tape 30, the crack 24 formed along the planned dividing line 21 in the semiconductor wafer 2 is the starting point of the division. It is divided into individual devices 22 and a space S is formed between the devices.

  Next, as shown in FIG. 10C, the pick-up collet 63 is operated to adsorb the device 22, peeled off from the dicing tape 30, picked up, and conveyed to a tray or die bonding process (not shown). In the pickup process, as described above, the gap S between the individual devices 22 attached to the dicing tape 30 is widened, so that the pickup can be easily performed without contacting the adjacent devices 22. it can.

  The device 22 divided as described above can withstand impact force such as dropping because the internal strain is removed by the ablation process together with the modified layer 23 formed in the modified layer forming step. The problem of destruction due to impact force due to internal strain remaining in the modified layer is solved. Further, as described above, the pulse laser beam irradiated from the back surface 2b side of the semiconductor wafer 2 in the ablation processing step grows a crack 24 that is absorbed by the modified layer 23 and extends from the modified layer 23 to the surface 2a side. Even if it reaches the surface 2a, it does not come out to the surface 2a side, so that many cracks are not generated toward the device 22 side, and many cracks are generated toward the device side. The problem of lowering is also eliminated.

2: Semiconductor wafer 21: Planned division line 22: Device 23: Modified layer 24: Crack 3: Ring frame 30: Dicing tape 4: Grinding device 41: Chuck table 42 of grinding device: Grinding means 424: Grinding wheel 5: Laser processing apparatus 50: Laser processing apparatus 51: Laser processing apparatus chuck table 52: Laser beam irradiation means 522: Condenser 6: Tape expansion apparatus 61: Frame holding means 62: Tape expansion means 63: Pickup collet

Claims (3)

A wafer processing method for dividing a wafer having a plurality of devices formed on a surface along a plurality of division lines that divide the device,
A condensing point of a laser beam having a wavelength that is transparent to the wafer is positioned from the back side of the wafer to the inside and irradiated along the planned dividing line, and the modified layer that propagates cracks toward the wafer surface is scheduled to be divided A modified layer forming step of forming along the line;
It is formed along the planned dividing line by performing ablation processing by irradiating the wafer subjected to the modified layer forming step with a laser beam having a wavelength that absorbs the wafer along the planned dividing line from the back side of the wafer. An ablation process to remove the modified layer,
A wafer dividing step of dividing the wafer on which the ablation processing step has been performed into individual devices by cracks formed along a line to be divided.
A method for processing a wafer.   The wafer processing method according to claim 1, wherein in the ablation processing step, the crack formed by the modified layer forming step is propagated to the surface of the wafer.   3. The wafer processing method according to claim 1 or 2, wherein a back surface grinding step of grinding the back surface of the wafer to form the wafer to a predetermined thickness is performed before the modified layer forming step.

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