JP2015037172A - Wafer processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer processing method capable of reducing the warpage of a wafer.SOLUTION: A wafer processing method comprises a holding step, a modified layer forming step, a warpage reducing division step and a grinding step. The holding step holds a wafer W on a chuck table 11. The modified layer forming step forms a division starting point modified layer Ks along a predetermined dividing line on the surface Wa side inside the wafer W after the holding step. The warpage reducing division step divides the wafer W before or during the modified layer forming step and reduces the warpage occurred to the wafer W from forming the division starting point modified layer Ks. The grinding step forms a plurality of chips with a finishing thickness by grinding the wafer W from a starting point of at least the division starting point modified layer Ks to attain the finishing thickness with which the wafer W can be divided and removing the starting point modified layer Ks after the modified layer forming step and the warpage reducing division step.

Description

  The present invention relates to a method for processing a wafer that is divided by irradiation with a laser beam.

  A so-called first dicing method is known, in which a chip is half-cut with a cutting blade along a planned dividing line of a wafer having a device formed on the surface, and then the back surface of the wafer is ground to produce individual chips having a predetermined thickness. Instead of half-cutting with a cutting blade, a modified layer is formed inside the wafer using a laser beam that is expected to reduce the cutting margin and improve the die bending strength, and then grind the backside of the wafer A processing method for manufacturing individual chips having a thickness of 10 mm has been developed (see, for example, Patent Document 1).

Japanese Patent Application No. 2012-32751

  In such a wafer processing method, the modified layer formed inside the wafer expands and the modified layer concentrates on the surface side of the wafer, so that the wafer is easily warped. If the laser beam is irradiated while the wafer is warped, the relative position in the thickness direction of the wafer with respect to the condensing point of the laser beam changes. Therefore, the modified layer cannot be formed at a predetermined position, and the modified layer is not formed on the wafer. May be biased to the surface. If the modified layer is biased toward the front surface of the wafer, even if the back surface is ground until the wafer has a predetermined thickness, the modified layer may remain on the side surface of the chip and the strength of the chip may be lowered. Further, when the warped wafer is placed on the chuck table of the grinding apparatus, there is a possibility that it cannot be sucked and held.

  The present invention has been made in view of the above, and an object of the present invention is to provide a wafer processing method capable of reducing wafer warpage.

  In order to solve the above-described problems and achieve the object, the wafer processing method of the present invention includes a plurality of first division lines extending in the first direction and a direction intersecting the first division lines. A wafer processing method for thinning a wafer having a plurality of second scheduled dividing lines extending on the surface and dividing the wafer along the scheduled dividing lines to form a plurality of chips having a predetermined finish thickness, A holding step for attaching a protective member to the front surface and holding the wafer on the holding surface of the chuck table via the protective member, and a condensing point of a laser beam having a wavelength transmissive to the wafer after the holding step Is positioned in an area that does not reach the finished thickness of the chip inside the wafer, and a laser beam is irradiated from the back side of the wafer along the planned dividing line, and the surface side inside the wafer. A modified layer forming step for forming a split starting point modified layer along the planned split line, and one or more split lines in the first direction and the second direction before or during the modified layer forming step In the state where the condensing point of the laser beam is positioned inside the wafer, the wafer is divided in the thickness direction of the wafer, and the warpage is reduced by reducing the warpage generated in the wafer due to the formation of the division starting point modified layer. After the dividing step, the modified layer forming step, and the warp reducing dividing step, the back surface of the wafer is ground and thinned to a finish thickness at which the wafer can be divided at least from the dividing starting modified layer. And a grinding step for forming a plurality of chips having a finished thickness.

  According to the wafer processing method of the present invention, before or during the modified layer forming step, one or more of each of the first scheduled division line and the second scheduled division line in the thickness direction of the wafer. Since the dividing process for dividing the wafer is performed, the wafer is divided along at least one scheduled division line in each of the first scheduled division line and the second scheduled division line. For this reason, according to the wafer processing method, the relative area of the wafer after the division with respect to the wafer before the division is reduced, and the accumulation of expansion inside the wafer by the division starting point modification layer is also reduced. Wafer warpage caused by the formation of the modified layer can be reduced.

FIG. 1 is an explanatory diagram of a holding step of a wafer processing method according to an embodiment. FIG. 2 is a schematic configuration diagram of the wafer held on the chuck table by the holding step. FIG. 3 is an explanatory diagram of a modified layer forming step of the wafer processing method according to the embodiment. FIG. 4 is an explanatory diagram of a warp reduction division step of the wafer processing method according to the embodiment. FIG. 5 is an explanatory diagram of the split starting point modified layer and the split modified layer formed inside the wafer. FIG. 6 is an explanatory diagram of a grinding step of the wafer processing method according to the embodiment.

  DESCRIPTION OF EMBODIMENTS Embodiments (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the structures described below can be combined as appropriate. In addition, various omissions, substitutions, or changes in the configuration can be made without departing from the scope of the present invention.

Embodiment
FIG. 1 is an explanatory diagram of a holding step of a wafer processing method according to an embodiment. FIG. 2 is a schematic configuration diagram of the wafer held on the chuck table by the holding step. FIG. 3 is an explanatory diagram of a modified layer forming step of the wafer processing method according to the embodiment. FIG. 4 is an explanatory diagram of a warp reduction division step of the wafer processing method according to the embodiment. FIG. 5 is an explanatory diagram of the split starting point modified layer and the split modified layer formed inside the wafer. FIG. 6 is an explanatory diagram of a grinding step of the wafer processing method according to the embodiment.

  This embodiment relates to a wafer processing method. In the wafer processing method according to the present embodiment, as shown in FIG. 1, a plurality of first scheduled division lines S1 and second scheduled division lines S2 that intersect each other are set on the surface Wa, and the first division is performed. This is a processing method of the wafer W in which the device WD is formed on the surface Wa of the region partitioned by the planned line S1 and the second planned divided line S2. The wafer processing method according to the present embodiment includes a holding step, a modified layer forming step, a warp reduction division step, and a grinding step.

Here, the wafer W to be processed is not particularly limited. For example, a plate-like semiconductor wafer, optical device wafer, ceramic, glass, sapphire (Al ₂ O) using silicon, gallium arsenide (GaAs), or the like as a base material. ₃ ) Various plate-like processed materials such as a plate-like inorganic material substrate and a plate-like ductile material such as metal or resin. As shown in FIG. 1, the wafer W is, for example, an IC (Integrated Circuit) or an LSI (Large Scale Integration) in an area partitioned by the first scheduled division line S1 and the second scheduled division line S2. A device WD is formed. The wafer W is supported by the annular frame F via the adhesive tape T. The adhesive tape T is also called a dicing tape, and is a protective member that is attached to the surface Wa of the wafer W.

  The first scheduled division line S1 and the second scheduled division line S2 are set in advance on the surface Wa of the wafer W based on a plurality of devices WD formed on the surface Wa of the wafer W. The first division line S1 extends in the first direction X. The second scheduled division line S2 extends in a direction intersecting with the first scheduled division line S1, and extends in the second direction Y in the present embodiment. The first scheduled division line S1 and the second scheduled division line S2 are orthogonal to each other in this embodiment. The area defined by the first scheduled division line S1 and the second scheduled division line S2 is a square in this embodiment.

(Holding step)
As shown in FIG. 2, the holding step is a step for sucking and holding the wafer W on the chuck table 11. The holding step is performed by the laser processing apparatus 10 shown in FIG.

  Here, as shown in FIG. 4, the laser processing apparatus 10 includes a chuck table 11, a laser beam irradiation unit 12, an imaging unit 13, and a moving unit (not shown).

  The chuck table 11 has a clamp (not shown) that fixes the outer peripheral edge of the annular frame F while holding the wafer W by suction. As shown in FIG. 2, the chuck table 11 is formed in a disk shape and has an upper surface formed in parallel with the horizontal direction. As shown in FIG. 3, the chuck table 11 has a holding surface 11a formed flush with the upper surface. The holding surface 11a is made of porous ceramic and is connected to a vacuum suction source (not shown).

  As shown in FIG. 4, the laser beam irradiating means 12 includes a laser head 12a that irradiates the wafer W with the laser beam L, and a casing 12b that houses a laser beam oscillating means (not shown). The laser head 12 a irradiates a laser beam L having a wavelength with transparency to the wafer W sucked and held by the chuck table 11. The laser head 12 a can change the condensing point P of the laser beam L in the thickness direction inside the wafer W. As shown in FIG. 3, the laser head 12 a irradiates a laser beam L with a condensing point P positioned in a predetermined region on the division lines S <b> 1 and S <b> 2 inside the wafer W, so that the surface Wa inside the wafer W is irradiated. A split starting point modified layer Ks is formed on the side. Further, as shown in FIG. 4, the laser head 12a is positioned so that the condensing points P are stacked in the thickness direction of the wafer from the front surface Wa side to the back surface Wb side inside the wafer, and irradiates the laser beam L a plurality of times. As a result, a plurality of divided reforming layers Kd are formed. In the present embodiment, the predetermined region is the back surface Wb side from the thickness at which the wafer W is divided into individual chips as the wafer W is thinned, that is, the back surface Wb side from the finished thickness d of the chip. This is a region that does not reach the finished thickness d of the chip.

  In the present embodiment, as shown in FIG. 3, the division starting point modified layer Ks is irradiated with the laser beam L at the same depth on the surface Wa side in the region not reaching the finished thickness d of the chip inside the wafer W. Is formed. Further, in the present embodiment, as shown in FIG. 5, the modification layer for division Kd is stacked in the thickness direction of the wafer W from the front surface Wa side to the back surface Wb side rather than the finished thickness d of the chip inside the wafer W. Thus, the laser beam L is irradiated and formed. Each of the modified layers Ks and Kd is a region where the density, refractive index, mechanical strength, and other physical characteristics are different from those of the surroundings. Each of the modified layers Ks and Kd is, for example, a melt processing region, a crack region, a dielectric breakdown region, a refractive index change region, and a region in which these regions are mixed.

  The imaging means 13 is, for example, a camera using a CCD (Charge Coupled Device) image sensor that captures visible light, infrared light, and the like. The imaging means 13 includes an irradiating means for irradiating the wafer W with infrared rays having transparency in addition to visible light. The imaging means 13 can detect the first scheduled division line S1 and the second scheduled division line S2 set on the front surface Wa side of the wafer W by irradiating infrared rays from the rear surface Wb side of the wafer W. The imaging unit 13 captures an image from the back surface Wb side of the wafer W and generates alignment adjustment image data.

  The moving means moves the chuck table 11 in the X-axis direction and moves the laser beam irradiation means 12 in the Y-axis direction and the Z-axis direction. The moving means can also rotate the chuck table 11 around its central axis. The moving means moves the chuck table 11 in the X-axis direction to irradiate the laser beam L emitted from the laser head 12a along the first scheduled division line S1. In the present embodiment, the X-axis direction is a direction orthogonal to the vertical direction. The Y-axis direction is a direction orthogonal to the X-axis direction and the vertical direction. The Z-axis direction is a direction perpendicular to the X-axis direction and the Y-axis direction, and is a vertical direction.

  In the laser processing apparatus 10 configured as described above, the wafer W is unloaded from the frame cassette, and the wafer W is placed on the holding surface 11a of the chuck table 11 via the adhesive tape T of the annular frame F as shown in FIG. The front surface Wa side is placed. Next, in the laser processing apparatus 10, the surface Wa side of the wafer W is sucked and held on the holding surface 11 a of the chuck table 11 by a vacuum suction source (not shown).

  As shown in FIG. 2, when the surface Wa of the wafer W is sucked and held on the holding surface 11 a of the chuck table 11 by the laser processing apparatus 10 via the adhesive tape T of the annular frame F, the holding step ends.

(Modified layer formation step and warp reduction division step)
As shown in FIG. 3, the modified layer forming step is a step of forming the division starting point modified layer Ks along the first division planned line S1 and the second division planned line S2 after the holding step. . The warp reduction division step is a step of reducing the warpage generated in the wafer W by dividing the wafer W along the division planned lines S1 and S2 passing through the center of the wafer W in the middle of the modified layer forming step. The modified layer forming step and the warp reduction dividing step are performed by the laser processing apparatus 10.

  In the laser processing apparatus 10, after the holding step, the wafer W sucked and held on the chuck table 11 is irradiated with infrared rays from the back surface Wb side by the imaging means 13, and an image for alignment adjustment is taken and alignment adjustment is performed. Image data is generated. Next, in the laser processing apparatus 10, the alignment between the chuck table 11 and the laser beam irradiation means 12 is adjusted based on the alignment adjustment image data. Next, in the laser processing apparatus 10, the condensing point P of the laser beam L is positioned in an area that does not reach the finished thickness d inside the wafer W in the first scheduled division line S <b> 1 set on the surface of the wafer W. Further, the chuck table 11 and the laser beam irradiation means 12 are moved by the moving means.

  Next, in the laser processing apparatus 10, the chuck table 11 and the laser beam irradiation unit 12 are moved by the moving unit in a state where the condensing point P of the laser beam L is positioned in the region not reaching the finishing thickness d inside the wafer W. Are moved relative to each other, and a laser beam L having a wavelength that is transmissive to the wafer W from the first scheduled division line S1 on one end side to the first scheduled division line S1 passing through the center of the wafer W. Irradiation is sequentially performed from the back surface Wb side of W. At this time, the split starting point modified layer Ks is formed in the region that is on the surface Wa side inside the wafer W and does not reach the finished thickness d of the chip along the first split line S1.

  Next, in the laser processing apparatus 10, as shown in FIGS. 4 and 5, the surface Wa is more than the finish thickness d of the chip inside the wafer W along the first division line S <b> 1 passing through the center of the wafer W. The laser beam L is repeatedly irradiated a plurality of times so as to be stacked in the thickness direction of the wafer W from the side to the back surface Wb side. At this time, the wafer W is divided in the thickness direction of the wafer W along the first division line S1 passing through the center of the wafer W.

  Next, in the laser processing apparatus 10, the chuck table 11 and the laser beam irradiation unit 12 are relatively moved by the moving unit, and the laser beam L is sequentially irradiated to the first scheduled division line S1 on the other end side. At this time, the split starting point modified layer Ks is formed in the region that is on the surface Wa side inside the wafer W and does not reach the finished thickness d of the chip along the first split line S1.

  Next, in the laser processing apparatus 10, after the chuck table 11 is rotated by 90 degrees, the condensing point P of the laser beam L does not reach the finished thickness d inside the wafer W on the second scheduled division line S2. In the same manner as the first scheduled division line S1, the laser beam L sequentially lasers from the second scheduled division line S2 on one end side to the second scheduled division line S2 passing through the center of the wafer. A light beam L is irradiated. At this time, the split starting point modified layer Ks is formed in the region on the surface Wa side inside the wafer W and not reaching the finished thickness d of the chip along the second planned split line S2.

  Next, in the laser processing apparatus 10, as shown in FIGS. 4 and 5, the surface Wa is more than the finish thickness d of the chip inside the wafer W along the second scheduled division line S <b> 2 passing through the center of the wafer W. The laser beam L is repeatedly irradiated a plurality of times so as to be stacked in the thickness direction of the wafer W from the side to the back surface Wb side. At this time, the wafer W is divided in the thickness direction of the wafer W along the second scheduled division line S2 passing through the center of the wafer W.

  Next, in the laser processing apparatus 10, the chuck table 11 and the laser beam irradiation unit 12 are relatively moved by the moving unit, and the laser beam L is sequentially irradiated to the second scheduled division line S2 on the other end side. At this time, the split starting point modified layer Ks is formed in the region on the surface Wa side inside the wafer W and not reaching the finished thickness d of the chip along the second planned split line S2. The split starting point modified layer Ks formed along the planned split lines S1 and S2 is closer to the back surface Wb than the device WD formed on the front surface Wa of the wafer W, and closer to the back surface Wb than the finished thickness d. To position. Further, since the wafer W is divided into four at equal intervals in the circumferential direction, the relative area of the wafer W after the division is smaller than the wafer W before the division, and the wafer W formed by the division starting point modified layer Ks. The accumulation of internal expansion is also reduced, and the warpage of the wafer W caused by the formation of the split starting point modified layer Ks is reduced.

  Next, in the laser processing apparatus 10, the suction by the vacuum suction source is stopped, and the suction and holding of the wafer W by the chuck table 11 is released. Then, the wafer W after the laser processing is removed from the chuck table 11 by the frame transport unit. Housed in a frame cassette.

  When the split starting point modified layer Ks is formed along all of the planned split lines S1 and S2, the modified layer forming step ends. Further, when the wafer W is divided along each of the division lines S1 and S2 passing through the center of the wafer W, the warp reduction division step ends.

(Grinding step)
The grinding step is a step of grinding the back surface of the wafer W after the modified layer forming step and the warp reduction dividing step, removing the division starting point modified layer Ks, and forming a plurality of chips having a finished thickness d. . The grinding step is performed by a known grinding apparatus 20 as shown in FIG.

  Here, the grinding device 20 includes a chuck table 21 and a grinding means 22 as shown in FIG.

  Similar to the chuck table 11 of the laser processing apparatus 10, the chuck table 21 is formed in a disk shape and has a holding surface 21a. The holding surface 21a is made of porous ceramic and is connected to a vacuum suction source (not shown).

  The grinding means 22 includes a spindle 22a, a mounter 22b, a base portion 22c, and a grinding wheel 22d. The spindle 22a is rotatably supported by a rotation drive mechanism (not shown). The mounter 22b attaches the base portion 22c to the spindle 22a in a detachable manner. A grinding wheel 22d is disposed on the lower surface of the base portion 22c. The grinding means 22 contacts the grinding wheel 22d on the back surface Wb side of the wafer W while rotating the grinding wheel 22d and the chuck table 21 in the same direction while supplying grinding water from a grinding water supply nozzle (not shown). Grind W.

  In the grinding apparatus 20 configured in this manner, after the modified layer forming step and the warp reduction dividing step, the wafer W after laser processing is unloaded from the frame cassette by a frame transfer means (not shown), and the annular frame The surface Wa side of the wafer W is placed on the holding surface 21 a of the chuck table 21 via the F adhesive tape T. Next, in the grinding device 20, the surface Wa side of the wafer W is sucked and held on the holding surface 21 a of the chuck table 21 by a vacuum suction source (not shown).

  Next, in the grinding apparatus 20, grinding water is supplied from a grinding water supply nozzle (not shown), and the spindle 22a of the grinding means 22 and the chuck table 21 are rotated in the same direction as shown in FIG. The grinding wheel 22d is brought into contact with the back surface Wb, and the back surface Wb of the wafer W is ground. Next, in the grinding apparatus 20, the thickness of the wafer W is measured by a known contact-type thickness measurement gauge (not shown), and the measured thickness of the wafer W is determined from at least the split starting point modified layer Ks. When the thickness is reduced to a finish thickness d that can be divided, grinding by the grinding means 22 is stopped. At this time, since a grinding load is applied from the grinding wheel 22d to the division starting point modified layer Ks, cracks starting from the division starting point modified layer Ks are generated inside the wafer W, and along the division planned lines S1 and S2. The wafer W is divided. As a result, the division starting point modified layer Ks is removed, and a plurality of chips having a finished thickness d are formed. The formed plurality of chips are supported by the adhesive tape T. For this reason, the annular frame F supports a plurality of chips in which the form of the wafer W is maintained via the adhesive tape T.

  Next, in the grinding apparatus 20, after the suction by the vacuum suction source is stopped and the suction holding of the plurality of chips by the chuck table 21 is released, the plurality of chips are put on the cleaning / drying unit (not shown) by the frame transport unit. Be transported. Next, in the grinding apparatus 20, a plurality of cleaned and dried chips are stored in the frame cassette from the cleaning / drying unit by the frame transport unit.

  When the wafer W is thinned to the finished thickness d and a plurality of chips having the finished thickness d are formed, the grinding step ends.

  As described above, according to the wafer processing method according to the present embodiment, the reforming for splitting is performed along at least one of the plurality of first scheduled split lines S1 during the reformed layer forming step. The layer Kd is formed, and the dividing reforming layer Kd is formed along at least one of the plurality of second scheduled division lines S2. Further, according to the wafer processing method according to the present embodiment, at least one of the scheduled division lines S1 and S2 passes through the center of the wafer W. That is, according to the wafer processing method according to the present embodiment, the wafer W is divided at least once along the first scheduled division line S1 that passes through the center of the wafer W, and the second division that passes through the center of the wafer W. The wafer W is divided at least once along the planned line S2. Therefore, according to the wafer processing method according to the present embodiment, it is possible to reduce the cumulative expansion of the division starting point modified layer Ks and to reduce the warpage of the wafer as compared with the case where the wafer W is not divided. .

  Further, according to the wafer processing method according to the present embodiment, since the warpage of the wafer can be reduced, the dividing starting point for all of the planned dividing lines before forming the correction modification portion on the back surface Wb side of the wafer W. The warpage of the wafer W can be reduced as compared with the conventional processing method for forming the modified layer. Further, in the prior art, a large number of correction modification portions are provided for the dividing starting point modification layer, whereas in the processing method of the wafer W according to the present embodiment, there is one, and the processing efficiency is good.

  Further, according to the wafer processing method of the present embodiment, since the wafer warpage can be reduced, the change in the relative position in the thickness direction of the wafer W with respect to the focal point P of the laser beam L is suppressed. The division starting point modified layer Ks can be positioned in a region that does not reach the finished thickness d of the chip. For this reason, according to the wafer processing method, when the wafer W is thinned to a finish thickness d that can divide the wafer W from at least the division starting point modified layer Ks, the division starting point modified layer Ks can be removed. .

  In addition, according to the wafer processing method according to the present embodiment, the split starting point modified layer Ks is removed by performing the grinding step, and therefore the bending strength due to the split starting point modified layer Ks remaining on the side surface of the chip. Can be suppressed.

  Further, according to the wafer processing method according to the present embodiment, since the warpage of the wafer can be reduced, the wafer can be placed on the chuck table 21 of the grinding apparatus 20 and held by suction.

  In the above embodiment, the warp reduction division step is a step of reducing the warp caused by the division starting point modified layer Ks being formed inside the wafer W, and therefore before the modified layer forming step. You may implement. In this case, since the division starting point modified layer Ks is formed on the wafer W that has been divided in advance, the warp is more warped than when the divided starting point modified layer Ks is formed on the wafer W that is not divided. Can be reduced.

  Further, the division modification layer Kd formed on the wafer W in the warp reduction division step is not limited to one that passes through the center of the wafer W in each of the division planned lines S1 and S2. The number which can reduce the curvature of the wafer W should just be formed. That is, it suffices if one or more of the dividing modification layers Kd is formed in each of the division lines S1 and S2. It should be noted that the dividing reforming layer Kd is formed in one or two in each of the planned dividing lines S1 and S2 in order not to increase the processing time for forming the dividing reforming layer Kd in the warp reduction dividing step. It is preferable that

  In the warp reduction division step, the division modification layer Kd is formed from the front surface Wa side with respect to the finished thickness d of the chip, but within a predetermined region, that is, the rear surface Wb side from the finished thickness d of the chip. You may make it form from the surface Wa side of the area | region used. Accordingly, when the back surface Wb of the wafer W is ground until the predetermined thickness is obtained by the grinding step, the dividing modified layer Kd is removed, and the dividing modified layer Kd does not remain on the side surfaces of the divided chips. Therefore, it is possible to suppress a decrease in bending strength due to the split modification layer Kd remaining on the side surface of the chip.

  In the warp reduction division step, the wafer W is divided by forming the division modification layer Kd. However, the wafer W may be divided by performing ablation with the laser beam L a plurality of times. Also in this case, it is preferable to divide the wafer W along one or more of the division lines S1 and S2 as in the case of the division modification layer Kd.

  Further, the wafer W is not limited to a circular shape, and may be, for example, a square shape or a polygonal shape.

  In the above embodiment, the holding step is performed by the mounter device and the laser processing device 10, the modified layer forming step and the warp reduction dividing step are performed by the laser processing device 10, and the grinding step is performed by the grinding device 20. The steps may be performed on one device. In this case, the processing efficiency for the wafer W can be improved.

11 Chuck table 11a Holding surface d Finishing thickness L Laser beam T Adhesive tape (protective member)
W Workpiece Wa Front surface Wb Back surface Ks Division start modification layer Kd Division modification layer S1 First segmentation line S2 Second segmentation line P Condensing point

Claims (1)

While thinning a wafer having a plurality of first division lines extending in the first direction and a plurality of second division lines extending in a direction intersecting the first division line set on the surface A wafer processing method of dividing a plurality of chips having a predetermined finish thickness divided along the division line,
Attaching a protective member to the front side of the wafer, and holding the wafer on a holding surface of a chuck table via the protective member;
After the holding step, the laser beam is focused from the back side of the wafer in a state where a condensing point of a laser beam having a wavelength transmissive to the wafer is located in a region not reaching the finished thickness of the chip inside the wafer. A modified layer forming step of irradiating a light beam along the planned dividing line and forming a split starting point modified layer along the planned dividing line on the surface side inside the wafer;
Before or during the modified layer forming step, the condensing point of the laser beam is positioned inside the wafer at one or more of the division lines in the first direction and the second direction, respectively. In this state, the laser beam is irradiated a plurality of times along the planned dividing line from the back side of the wafer, and the dividing process is performed to divide the wafer in the thickness direction of the wafer, thereby forming the dividing starting point modified layer A warp reduction dividing step for reducing warpage generated in the wafer by:
After the modified layer forming step and the warp reduction dividing step, the back surface of the wafer is ground and thinned to the finished thickness at which the wafer can be divided at least from the dividing starting point modified layer, and the dividing starting point is obtained. And a grinding step of forming a plurality of chips having the finished thickness by removing the modified layer.

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