JP6053381B2 - Wafer dividing method - Google Patents

Description

  The present invention relates to a wafer dividing method for dividing a wafer into individual chips.

  Conventionally, a cutting device called a dicing saw has been used for cutting a wafer. Recently, however, attention has been focused on a technique of dividing a wafer into devices by laser processing using a laser processing device. One of the laser processing methods using this laser processing equipment is to form a fragile layer (modified layer) inside the wafer using a laser beam with a wavelength that is transmissive to the wafer, resulting in reduced strength. For example, Patent Document 1 discloses a technique for dividing a wafer into chips by applying an external force to the wafer with an expansion device or the like along the modified layer. In this laser processing method, there is no generation of cutting waste that is always generated in the processing of the dicing saw, and there is almost no cutting allowance.

  However, when the thickness of the wafer is reduced to several tens of μm or less, the problem is that it becomes difficult to form an appropriate modified layer at an appropriate position inside the wafer due to the influence of the reflected light from the laser beam transmitted through the wafer. Has occurred. Therefore, a modified layer is formed inside the wafer with a certain thickness of the wafer, and then ground to the finished thickness (Patent Document 2). According to this dividing method, an appropriate modified layer can be formed at an appropriate position, and the internal modified layer can also be removed by grinding. Therefore, in the case of an optical device wafer, brightness can be improved, and usually In the case of this wafer, the bending strength can be improved.

Japanese Patent No. 3408805 JP 2012-49164 A

  However, according to the above dividing method, it is divided along the planned dividing line starting from the internal modified layer at the time of grinding, and the chips are in contact with each other without any cutting allowance. In particular, there is a new problem that cracks and chips are generated due to the friction between the chips at the intersection.

  The present invention has been made in view of the above problems, and its purpose is to prevent cracks and chips at intersections due to rubbing between chips during handling after grinding even when grinding is performed after forming the internal modified layer. It is an object of the present invention to provide a method for suppressing wafer division.

  The wafer dividing method according to the present invention includes a plurality of first division planned lines extending in a predetermined direction on the surface and a plurality of second division planned lines formed intersecting with the plurality of first division planned lines. A wafer dividing method for dividing a wafer having devices formed in a plurality of partitioned areas along the first scheduled dividing line and the second scheduled dividing line, and an expanded tape on the front surface side of the wafer After the expanding tape adhering step and the expanding tape adhering step, the expanding tape side is held, and a laser beam having a wavelength that is transparent to the wafer is focused on the wafer from the back side of the wafer. The first modified layer is formed along the first division line inside the wafer by irradiating along the first division line. The modified layer forming step, and irradiating a laser beam having a wavelength transparent to the wafer from the back surface side of the wafer along the second scheduled division line with the focusing point located inside the wafer. A second modified layer forming step in which a second modified layer is formed along the second line to be divided, the first modified layer forming step, and the second modified layer forming step; Then, the expanded tape side is held and ground from the back surface of the wafer by grinding means to reduce the thickness to the finished thickness, and the cracks reaching the wafer surface starting from the modified layer are ground by the grinding operation. A grinding step for growing along the planned line; and an expanding step for applying an external force after the grinding step to separate the chips along the first planned split line and the second planned split line. , In the second modified layer forming step or in both the first modified layer forming step and the second modified layer forming step, at least 1 is provided for one side of each device with a predetermined interval. By stopping the irradiation of the laser beam twice, a non-continuous modified layer having a non-modified layer region is formed at a predetermined interval inside, and in the grinding step, the region where the modified layer is formed In the expanding step, the non-modified layer region that is not divided in the grinding step is divided along the planned division line.

  In the wafer dividing method according to the present invention, the modified layer is not formed on a part of the dividing line on one or both sides of the intersection. For this reason, the crossing points are not separated into pieces after grinding, and the chip crossing points are prevented from rubbing during handling after grinding, and chip corner chipping and cracking are suppressed.

Drawing 1 is an explanatory view of the expand tape sticking process of the division method of the wafer concerning an embodiment. FIG. 2 is an explanatory diagram of a modified layer forming step of the wafer dividing method according to the embodiment. FIG. 3 is a diagram illustrating a laser beam irradiation target region of the wafer dividing method according to the embodiment. FIG. 4 is an enlarged view showing a laser beam irradiation target area according to the embodiment. FIG. 5 is an explanatory diagram of a grinding process of the wafer dividing method according to the embodiment. FIG. 6 shows the wafer after the grinding process. FIG. 7 is an explanatory diagram of an expanding process of the wafer dividing method according to the embodiment. FIG. 8 is a view showing the wafer after the expanding step. FIG. 9 is an enlarged view showing a laser beam irradiation target area according to a first modification of the embodiment.

  Hereinafter, a wafer dividing method according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by this embodiment. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

[Embodiment]
The embodiment will be described with reference to FIGS. 1 to 8. This embodiment relates to a wafer dividing method. FIG. 1 is an explanatory view of an expanding tape attaching process of a wafer dividing method according to the embodiment, FIG. 2 is an explanatory view of a modified layer forming process of the wafer dividing method according to the embodiment, and FIG. The figure which shows the laser beam irradiation object area | region of the wafer dividing method which concerns on FIG. 4, FIG. 4 is an enlarged view which shows the laser beam irradiation object area | region which concerns on embodiment, FIG. 5 is explanatory drawing of the grinding process of the wafer dividing method which concerns on embodiment 6 is a view showing the wafer after the grinding step, FIG. 7 is an explanatory view of the expanding step of the wafer dividing method according to the embodiment, and FIG. 8 is a view showing the wafer after the expanding step.

  The wafer dividing method according to the present embodiment is a dividing method for dividing a wafer W (see FIG. 1), and the wafer W is irradiated with a laser beam L (see FIG. 2) to modify the inside of the wafer W. This is a dividing method in which the layer K (see FIG. 2) is formed and divided into individual chips DT (see FIG. 7). The wafer W to be divided is, for example, a semiconductor wafer or an optical device wafer whose base material is silicon, sapphire, gallium or the like.

  As shown in FIG. 1, the wafer W has devices D formed in a plurality of regions partitioned by a plurality of first division lines S1 and a plurality of second division lines S2. The device D is formed on the surface WS of the wafer W. The first division line S1 extends in the first direction D1, which is a predetermined direction. The second division line S2 extends in the second direction D2 intersecting the first direction D1. In the present embodiment, the first direction D1 and the second direction D2 are orthogonal to each other. In the present embodiment, the area defined by the scheduled division lines S1 and S2 is a rectangle, for example, a square. The wafer W is divided along the first division line S1 and the second division line S2.

  The wafer dividing method according to the present embodiment divides the wafer W along the first scheduled dividing line S1 and the second scheduled divided line S2, and includes an expanding tape adhering step and a first modification. Including a layer forming step, a second modified layer forming step, a grinding step, and an expanding step.

(Expanding tape sticking process)
In the expand tape attaching step, the expand tape T is attached to the surface WS side of the wafer W. An expandable tape T having ductility is attached to the surface WS of the wafer W. The edge of the expanded tape T is attached to the annular frame F. Thereby, the wafer W is fixed to the annular frame F via the expanded tape T. The expanded tape T is an ultraviolet curing adhesive tape, and the adhesive layer Ta is made of a material that is cured by ultraviolet rays.

(Modified layer formation process)
The first modified layer forming step and the second modified layer forming step are performed after the expanded tape attaching step. In the present embodiment, the second modified layer forming step is executed after the first modified layer forming step. However, the present invention is not limited to this, and after the second modified layer forming step. The first modified layer forming step may be performed.

(First modified layer forming step)
In the first modified layer forming step, the first modified layer K1 (see FIG. 4) is formed inside the wafer W along the first scheduled dividing line S1. As shown in FIG. 2, the first modified layer forming step and the second modified layer forming step are performed by the laser processing unit 1. The laser processing unit 1 includes a chuck table 2, a laser beam irradiation means 3, and a moving means (not shown). The chuck table 2 is a holding unit that holds the wafer W, and for example, sucks and holds the wafer W by a suction force by a negative pressure. The chuck table 2 has a disk shape in which a portion constituting the holding surface 2a is made of porous ceramic or the like, and is connected to a vacuum suction source (not shown) via a vacuum suction path (not shown). The chuck table 2 holds the expanded tape T side of the wafer W. The wafer W is placed on the holding surface 2 a with the surface WS side facing the holding surface 2 a of the chuck table 2. The chuck table 2 sucks and holds the wafer W via the expanded tape T.

  The laser beam irradiation unit 3 irradiates the wafer W held on the chuck table 2 with a laser beam L having a wavelength (for example, 1064 nm) having transparency. In the first modified layer forming step, the laser beam L is applied to the wafer W from the back surface WR side. The laser beam L is irradiated along the first scheduled division line S1 with the focal point positioned inside the wafer W. The condensing point is positioned in a region (depth position) to be ground by a grinding process described later.

  The moving means relatively moves the laser beam irradiation means 3 and the chuck table 2. The moving means can rotate the chuck table 2 around its central axis, and can relatively move the laser beam irradiation means 3 and the chuck table 2 in a direction perpendicular to the optical axis of the laser beam irradiation means 3. When the laser beam L is applied to the wafer W, the modified layer K is formed inside the wafer W.

  The modified layer K means a region where the density, refractive index, mechanical strength and other physical properties are different from those of the surroundings. Examples of the modified layer K include a melt treatment region, a crack region, a dielectric breakdown region, a refractive index change region, and a region in which these regions are mixed.

  Through the first modified layer forming step, the modified layer K (first modified layer K1) is formed in the wafer W along the first scheduled division line S1. The laser processing unit 1 forms the first modified layer K1 by relatively moving the laser beam irradiation means 3 and the chuck table 2 along the first direction D1 while irradiating the laser beam L with the laser beam irradiation means 3. To do. As shown in FIGS. 3 and 4, the wafer W has a first irradiation target region SL1 and a second irradiation target region SL2. The irradiation target areas SL1 and SL2 are areas to be irradiated with the laser beam L. FIG. 4 shows an enlarged view of a part Wa of the wafer W shown in FIG.

  The first irradiation target area SL1 extends along the first scheduled division line S1. The first irradiation target area SL1 is a continuous linear area along the first division planned line S1. The first irradiation target area SL1 is defined as one continuous straight line that divides the wafer W. The first irradiation target region SL1 preferably extends at least across the region where the device D is formed, and both end portions thereof preferably reach the outermost periphery of the wafer W.

  When all of the first scheduled division lines S1 are irradiated with the laser beam L along the first irradiation target region SL1 and the first modified layer K1 is formed, the first modified layer is formed. The process ends.

(Second modified layer forming step)
In the second modified layer forming step, the second modified layer K2 is formed inside the wafer W along the second scheduled dividing line S2. In the second modified layer forming step, the laser processing unit 1 relatively moves the laser beam irradiation means 3 and the chuck table 2 along the second direction D2 while irradiating the laser beam L with the laser beam irradiation means 3. Thereby, the laser beam L is irradiated along the second scheduled division line S2, and the second modified layer K2 is formed. Similarly to the first modified layer forming step, the laser beam irradiation means 3 irradiates the wafer W held on the chuck table 2 with a laser beam L having a wavelength having transparency. The laser beam irradiating means 3 irradiates the wafer W with the laser beam L from the back surface WR side with the focusing point positioned inside the wafer W.

  The second irradiation target area SL2 extends along the second division planned line S2. The second irradiation target region SL2 is determined so that irradiation of the laser beam L is stopped at least once for one side of each device D (one side of each chip DT).

  The second irradiation target region SL2 of the present embodiment is a linear region that is continuously arranged with a predetermined interval along the second direction D2. One linear region along the second scheduled division line S2 is divided at an intersection where the first scheduled division line S1 and the second scheduled division line S2 intersect, and a plurality of second regions are divided. An irradiation target area SL2 is formed. The second irradiation target region SL2 is located between the devices D adjacent to each other.

  A region between the second irradiation target regions SL2 adjacent in the second direction D2 is a region outside the irradiation target of the laser beam L in the second modified layer forming step. The region outside the irradiation target is a region having a predetermined length in the second direction D2 centering on the first irradiation target region SL1. As shown in FIGS. 3 and 4, in the present embodiment, the first irradiation target region SL1 and the second irradiation target region SL2 have no intersection. The length of the region outside the irradiation target (the length in the second direction D2) can be set to a predetermined length on both sides in the second direction D2 from the first irradiation target region SL1.

  By the second modified layer forming step, a modified layer K (second modified layer K2) is formed inside the wafer W along the second scheduled division line S2. The laser processing unit 1 forms the second modified layer K2 by relatively moving the laser beam irradiation means 3 and the chuck table 2 along the second direction D2 while irradiating the laser beam L with the laser beam irradiation means 3. To do. The laser processing unit 1 irradiates the second irradiation target region SL2 with the laser beam L, and does not irradiate the non-irradiation region between the adjacent second irradiation target regions SL2 with the laser beam L. . Therefore, in the second modified layer forming step, the irradiation of the laser beam L is stopped (stopped or interrupted) at least once for one side of each device D. In other words, in the second modified layer forming step, the laser beam L is irradiated at least once in a region between one first scheduled division line S1 and the first divided division line S1 adjacent thereto. Stopped. Irradiation with the laser beam L is stopped with an interval (predetermined interval) between one second irradiation target region SL2 and the second irradiation target region SL2 adjacent thereto.

  As shown in FIG. 4, the second modified layer K2 is formed in the second irradiation target region SL2. The second modified layer K2 is formed at a predetermined interval, and a non-modified layer region NK in which no modified layer is formed is formed between the second modified layers K2 adjacent in the second direction D2. . That is, in the second modified layer forming step, a discontinuous modified layer in which the second modified layer K2 is continuously formed with the non-modified layer region NK interposed therebetween is formed. The non-continuous modified layer includes at least two modified layers K and a non-modified layer region NK interposed between the modified layers K adjacent in the second direction D2. The non-modified layer region NK is located at an intersection where the first division planned line S1 and the second division planned line S2 intersect.

  When all of the second scheduled division lines S2 are irradiated with the laser beam L along the second irradiation target region SL2 and the second modified layer K2 is formed, the second modified layer is formed. The process ends.

(Grinding process)
The grinding process is performed after performing the first modified layer forming process and the second modified layer forming process. In the grinding process, cracks reaching the surface WS of the wafer W from the modified layer K as a starting point by the grinding operation while holding the expanded tape T side and grinding from the back surface WR of the wafer W by grinding means to thin the finished thickness. Is a process of growing along the division lines S1 and S2. In the grinding step, the region where the modified layer K is formed is divided along the division lines S1 and S2. A crack is generated in the region where the modified layer K is formed, and the wafer W is divided at the boundary of the crack. For example, it is preferable that a crack is generated and divided only in a region where the modified layer K is formed, and a region where the modified layer K is not formed does not generate a crack and is not divided.

  The grinding process is executed by the grinding unit 10 shown in FIG. The grinding unit 10 includes a chuck table 11, grinding means 12, and moving means (not shown). The chuck table 11 holds the expanded tape T side of the wafer W. The chuck table 11 sucks and holds the wafer W with a negative pressure, for example, like the chuck table 2 of the laser processing unit 1. As shown in FIG. 5, the wafer W is placed on the holding surface 11 a with the surface WS side facing the holding surface 11 a of the chuck table 11. The chuck table 11 sucks and holds the wafer W via the expanded tape T.

  The grinding means 12 has a grinding wheel 12a and grinds the wafer W while rotating. The moving means has a function of rotating the chuck table 11 around the axis. The grinding unit 10 rotates the chuck table 11 by moving means, and contacts the back surface WR of the wafer W while rotating the grinding wheel 12 a in the same direction as the chuck table 11. The grinding unit 10 grinds and feeds the grinding wheel 12a downward at a predetermined feed speed to grind and thin the wafer W from the back surface WR side. The grinding feed amount of the grinding wheel 12a is determined so as to thin the wafer W to a predetermined finishing thickness t. As shown in FIG. 5, the modified layer K is formed in a region that is ground and removed in the grinding process, in other words, on the side farther from the front surface WS than the position that becomes the back surface WR after the grinding is completed.

  A grinding load from the grinding wheel is applied to each modified layer K by a grinding operation for grinding and feeding the grinding wheel 12a. As a result, cracks extending from the modified layer K to the surface WS are formed along the scheduled division lines S1 and S2 inside the wafer W. As shown in FIG. 6, cracks CK <b> 1 and CK <b> 2 are formed along the scheduled division lines S <b> 1 and S <b> 2 on the wafer W after the grinding process.

  The first crack CK1 is a crack formed along the first planned division line S1. Since the first irradiation target region SL1 is a region continuous from one end to the other end of the first planned division line S1, the first crack CK1 is formed continuously along the first planned division line S1. Is done. Therefore, the wafer W is divided by the first crack CK1.

  The second crack CK2 is a crack formed along the second scheduled division line S2. Since the second irradiation target region SL2 is determined with a predetermined interval, the second crack CK2 is formed with a predetermined interval. As shown in FIG. 6, the second crack CK2 adjacent in the second direction D2 is formed with the first crack CK1 interposed therebetween. It is preferable that the first crack CK1 and the second crack CK2 are not connected, but the first crack CK1 and the second crack CK2 are partially formed in the wafer W depending on the state and variation of the modified layer K and the wafer W. May be connected.

(Expanding process)
The expanding process is performed after the grinding process. The expanding step is a step of applying an external force to separate the chips DT along the first planned division line S1 and the second planned division line S2. In the expanding step, the non-modified layer region NK that is not divided in the grinding step is divided along the second scheduled division line S2. The expanding process is performed by the expansion device 15 shown in FIG.

  The expansion device 15 includes a frame holding unit 25, a pressing member 26, and a moving unit (not shown). The frame holding means 25 holds the annular frame F. The frame holding means 25 sandwiches and holds the annular frame F and the portion of the expanded tape T that is attached to the annular frame F. The pressing member 26 is a member that presses and expands the expanded tape T. The pressing member 26 has a cylindrical shape, and the outer diameter thereof is smaller than the inner diameter of the annular frame F. Further, the inner diameter of the pressing member 26 is larger than the outer diameter of the wafer W.

  The moving means relatively moves the frame holding means 25 and the pressing member 26. The frame holding means 25 and the pressing member 26 are arranged so that their axes coincide with each other, and the moving means relatively moves the frame holding means 25 and the pressing member 26 in the axial direction. The annular frame F is held by the frame holding means 25 with the adhesive layer Ta to which the wafer W is adhered facing upward. The pressing member 26 is pressed against the expanded tape T from below and presses the expanded tape T upward to expand the expanded tape T. The position where the pressing member 26 is pressed is a position on the expanded tape T that is radially outward from the wafer W and radially inward from the annular frame F.

  When the expanded tape T pressed by the pressing member 26 expands, an external force that separates the chips DT from each other acts on the wafer W attached to the expanded tape T. By this external force, the wafer W is divided into individual chips DT along the first division planned line S1 and the second division planned line S2. In the expanding step, the second crack CK2 grows along the second scheduled division line S2. As a result, the second crack CK2 grows into one crack that is connected to each other and divides the wafer W along the second scheduled division line S2. As a result, the chips DT can be separated along the first scheduled division line S1 and the second scheduled division line S2, and the wafer W can be divided into individual chips DT.

  The wafer W after the expanding process is divided into chips DT as shown in FIG. After the expanding process, a pickup process for picking up each chip DT is performed. The pickup process is performed by, for example, the expansion device 15. In this case, the expansion device 15 has a pickup device (not shown). The pickup device removes the chip DT from the expanded tape T by sucking and holding the chip DT. In addition, it is preferable to perform the adhesion layer hardening process of irradiating the expanded tape T with an ultraviolet-ray and hardening the adhesion layer Ta before a pick-up process.

(Experimental results)
An experimental result of division processing by the wafer division method according to the present embodiment will be described. When an experiment was performed with the length of the non-irradiation target area set to 1 mm on each side of the second direction D2 from the first irradiation target area SL1 with respect to 20 mm on one side of the chip DT, good results were obtained. In the experiment, the non-modified layer region NK was not divided in the grinding process, and cracks were formed in the non-modified layer region NK in the expanding step, and the chips were well divided into individual chips DT. Moreover, the quality of the intersection location was also good. Even when the wafer W was handled without using a transfer pad or the like after the grinding step, no chipping or cracking was observed at the corners of the individual chips DT. Therefore, the wafer dividing method according to the present embodiment is effective for improving the quality of the chip DT and improving the yield.

  Note that the length of the non-irradiation region is not limited to this, and may be appropriately determined according to the material and size of the wafer W, the length of one side of the device D, the finishing thickness t, and the like. it can. The length of the non-irradiated region is formed independently of each other without the second crack CK2 (see FIG. 6) being connected in the grinding process, and the wafer W is divided into individual chips DT in the expanding process. In addition, it can be appropriately determined based on experimental results and the like.

  As described above, according to the wafer dividing method according to the present embodiment, the wafer W is not divided into individual chips DT in the grinding process, but is divided into individual chips DT in the expanding process. For this reason, cracks and chippings at intersections due to rubbing between the chips DT during handling after grinding are suppressed.

  In the wafer dividing method according to the present embodiment, the modified layer K is formed on the wafer W having the original thickness before grinding. Therefore, the modified layer K can be satisfactorily formed on the wafer W even when the finished thickness t is small. In addition, the modified layer K can be formed in a portion that is removed in the grinding process, and the remaining of the modified layer K on the ground wafer W can be suppressed. As a result, compared with the case where the modified layer K remains on the wafer W, the bending strength of the divided chip DT can be improved. In the case of an optical device wafer, the luminance can be improved.

[First Modification of Embodiment]
A first modification of the embodiment will be described with reference to FIG. FIG. 9 is an enlarged view showing a laser beam irradiation target area according to a first modification of the embodiment. As shown in FIG. 9, the second irradiation target region SL2 according to the present modification intersects with the first irradiation target region SL1. The non-irradiation region between the adjacent second irradiation target regions SL2 is disposed at the center of one side of the device D. In other words, the second irradiation target region SL2 is a linear region extending from the first irradiation target region SL1 toward both sides in the second direction D2, and the tip thereof is the adjacent first irradiation target. It is on the near side of the intermediate point with the region SL1.

  The size of the gap between the tip of one second irradiation target region SL2 and the tip of the second irradiation target region SL2 adjacent thereto can be determined as appropriate. The size of the gap is such that the second cracks CK2 generated in the second irradiation target region SL2 in the grinding process are not connected to each other, and the wafer W is divided into individual chips DT in the expanding process. It is determined as appropriate based on experimental results.

  Note that the second irradiation target region SL2 is not limited to those exemplified in the above embodiment and this modification. The second irradiation target region SL2 can be variously determined such that the irradiation of the laser beam L is stopped at least once for one side of each device D.

[Second Modification of Embodiment]
Not only in the second modified layer forming step but also in the first modified layer forming step, the irradiation of the laser beam L is stopped at least once for one side of each device D with a predetermined interval. In addition, the first irradiation target area SL1 may be determined. For example, a first irradiation target region SL1 similar to the second irradiation target region SL2 shown in FIGS. 3 and 4 may be defined along the first scheduled division line S1. Alternatively, a first irradiation target region SL1 similar to the second irradiation target region SL2 illustrated in FIG. 9 may be defined along the first planned division line S1.

  When forming a discontinuous modified layer in each of the first modified layer forming step and the second modified layer forming step, the length of one non-modified layer region NK is set to the length of the other non-modified layer. It may be made larger than the length of the region NK.

  The contents disclosed in the above embodiments and modifications can be executed in appropriate combination.

DESCRIPTION OF SYMBOLS 1 Laser processing unit 2,11 Chuck table 3 Laser beam irradiation means 10 Grinding unit 12 Grinding means 15 Expansion device CK1 First crack CK2 Second crack D Device DT Chip F Annular frame K1 First modified layer K2 Second Modified layer L Laser beam NK Non-modified layer region S1 First division planned line S2 Second division planned line SL1 First irradiation target region SL2 Second irradiation target region T Expanding tape W Wafer WR Back surface WS Surface

Claims (1)

A device is provided in a plurality of regions partitioned by a plurality of first division planned lines extending in a predetermined direction on the surface and a plurality of second division planned lines formed intersecting with the plurality of first division planned lines. A wafer dividing method for dividing a formed wafer along the first division line and the second division line,
An expanding tape attaching process for attaching an expanding tape to the front surface side of the wafer;
After the expanding tape sticking step, the first splitting schedule is performed by holding the expanding tape side and positioning a laser beam having a wavelength transmissive to the wafer from the back side of the wafer with the focusing point inside the wafer. A first modified layer forming step of irradiating along the line and forming a first modified layer in the first division planned line inside the wafer;
A laser beam having a wavelength that is transmissive to the wafer is irradiated from the back side of the wafer along the second division line with the focal point positioned inside the wafer, and the second division is scheduled inside the wafer. and second modifying layer forming step of forming a second modified layer in the line,
After carrying out the first modified layer forming step and the second modified layer forming step, the expanded tape side is held and ground from the back surface of the wafer by grinding means to reduce the finished thickness. A grinding step for growing a crack reaching the surface of the wafer from the modified layer as a starting point by the grinding operation along the division line;
After the grinding step, along the first scheduled division line where the first modified layer is formed by applying an external force and the second scheduled division line where the second modified layer is formed And an expanding step for separating the chips,
In modified layer forming step of the second, by stopping the irradiation of the at least one laser beam and at an interval of Jo Tokoro for one side of each device, the non-modified layer at a predetermined interval in the internal Forming a discontinuous modified layer having a region;
In the grinding step, the region where the modified layer is formed is divided along the division planned line,
In the expanding step, the non-modified layer region that is not divided in the grinding step is divided along the division line .
The first modified layer is a continuous straight line and crosses the region where the device is formed;
The method for dividing a wafer , wherein the non-modified layer region is an intersection where the first division line and the second division line intersect .

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