JP4471627B2 - Wafer division method - Google Patents

Description

  The present invention relates to a wafer processing method in which a wafer having a dividing line formed on a surface thereof is divided along a scheduled dividing line.

  In the semiconductor device manufacturing process, a large number of rectangular areas are defined by lines to be cut called streets arranged in a lattice pattern on the surface of a semiconductor wafer such as silicon having a substantially disk shape, and each rectangular area has an IC, A circuit such as an LSI is formed. Individual semiconductor chips are formed by separating the semiconductor wafer on which a large number of circuits are formed in this manner along a line to be cut. This semiconductor chip is widely used in electric devices such as mobile phones and personal computers. The division along the planned cutting line is usually performed by a cutting device called a dicer. This cutting apparatus moves a chuck table that holds a plate-like object such as a semiconductor wafer, a cutting means for cutting a workpiece held on the chuck table, and the chuck table and the cutting means relative to each other. Moving means. The cutting means includes a rotating spindle that is rotated at a high speed and a cutting blade attached to the spindle. The cutting blade is composed of a disk-shaped base and an annular cutting edge mounted on the outer periphery of the side surface of the base. The cutting edge is fixed to the base by electroforming, for example, diamond abrasive grains having a particle size of about 3 μm. It is formed to a thickness of about 20 μm.

On the other hand, in recent years, as a method for dividing a plate-like workpiece such as a semiconductor wafer, a pulse laser beam that uses a pulsed laser beam that is transparent to the workpiece and aligns the condensing point inside the region to be divided is used. A laser processing method for irradiating the film has also been attempted. In the dividing method using this laser processing method, a pulse laser beam in an infrared light region having a light-transmitting property with respect to the work piece is irradiated from the one surface side of the work piece to the inside, and irradiated. A workpiece is formed by continuously forming a modified layer along the planned dividing line inside the workpiece, and applying an external force along the planned dividing line whose strength is reduced by forming the modified layer. Is divided. (For example, refer to Patent Document 1.)
Japanese Patent Laid-Open No. 2002-192367

According to the technique disclosed in the above Japanese Patent Application Laid-Open No. 2002-192667, the pulse width of the pulse laser beam is set to 1 μs or less, and the peak power density of the processed part is set to 1 × 10 ⁸ (W / cm ₂ ) or more. It is shown that a quality layer is formed. The above publication shows that a modified layer can be formed under processing conditions of a laser beam wavelength of 1.06 μm, a pulse width of 30 μs, a pulse repetition frequency of 100 kHz, and a processing feed rate of 100 mm / second.

  Thus, in the dividing method described above, simply forming the modified layer along the street inside the wafer is not divided along the planned dividing line, but after forming the modified layer along the planned dividing line. There is a problem in that productivity is poor because it is necessary to apply external force to each of the division lines.

  The present invention has been made in view of the above-mentioned facts, and its main technical problem is that a deteriorated layer is formed by irradiating a laser beam along a predetermined division line inside the wafer, and the efficiency is improved along the deteriorated layer. It is an object of the present invention to provide a wafer dividing method that can be divided well.

In order to solve the above main technical problem, according to the present invention, a wafer processing method for dividing a wafer along a predetermined division line,
The pulse laser beam chromatic and frequency is set to more than 200kHz permeable to the wafer is irradiated along the dividing line, from one surface of the wafer along the interior of said wafer to said dividing lines An altered layer forming step of forming an altered layer over the other surface ;
Before or after performing the deteriorated layer forming step, the dicing tape is formed in an annular shape so that the outer peripheral portion is attached so as to cover the inner opening of the dicing frame and contracts by heat at a predetermined temperature or higher. A dicing tape adhering step for adhering one surface of the wafer to the surface;
After carrying out the deteriorated layer forming step, the shrinking region between the dicing frame and the pasting region where the wafer is pasted in the dicing tape is heated to shrink the shrinking region, and the pasting region is formed. Dividing the wafer along the deteriorated layer by expanding,
A method of dividing a wafer is provided.

In the deteriorated layer forming step, the repetition frequency of the pulse laser beam is Y (Hz), the focused spot diameter of the pulse laser beam is D (mm), and the processing feed rate (the relative movement speed of the wafer and the pulse laser beam) is V (mm / Second), it is desirable to set the processing conditions to satisfy 1.0 ≦ V / (Y × D) ≦ 2.5. Further, the modified electrolyte layer formed in the above deteriorated layer forming step has to desired to be molten resolidified layer.

In the present invention, one surface of the perforated frequency permeability along the dividing line to the inside of the wafer by irradiating along the dividing line with a pulsed laser beam which is set above 200kHz wafer against the wafer A denatured layer is formed over the other surface, and one surface of the wafer on which the denatured layer is formed is adhered, and the dicing tape that is shrunk by heat at a predetermined temperature or higher is heated to shrink the shrinkage region and is adhered. Since the wafer is divided along the deteriorated layer by expanding the region, the wafer can be divided efficiently.

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

  FIG. 1 shows a perspective view of a semiconductor wafer as a wafer to be divided according to the present invention. The semiconductor wafer 2 shown in FIG. 1 is made of, for example, a silicon wafer having a thickness of 300 μm. A plurality of division lines 21 are formed in a lattice shape on the surface 2 a and are partitioned by the plurality of division lines 21. Circuits 22 are formed in a plurality of regions. Hereinafter, a dividing method for dividing the semiconductor wafer 2 into individual semiconductor chips will be described.

  In order to divide the semiconductor wafer 2 into individual semiconductor chips, a pulsed laser beam having transparency to the wafer is irradiated along the planned division line, and an altered layer is formed along the planned division line inside the wafer. An altered layer forming step is performed. This deteriorated layer forming step is performed using a laser processing apparatus shown in FIGS. A laser processing apparatus 3 shown in FIGS. 2 to 4 includes a chuck table 31 that holds a workpiece, a laser beam irradiation unit 32 that irradiates a workpiece held on the chuck table 31 with a laser beam, and a chuck table 31. An image pickup means 33 for picking up an image of the work piece held on is provided. The chuck table 31 is configured to suck and hold a workpiece, and can be moved in a machining feed direction indicated by an arrow X and an index feed direction indicated by an arrow Y in FIG. Yes.

  The laser beam irradiation means 32 includes a cylindrical casing 321 arranged substantially horizontally. In the casing 321, a pulse laser beam oscillation means 322 and a transmission optical system 323 are disposed as shown in FIG. The pulse laser beam oscillating means 322 includes a pulse laser beam oscillator 322a composed of a YAG laser oscillator or a YVO4 laser oscillator, and a repetition frequency setting means 322b attached thereto. The transmission optical system 323 includes an appropriate optical element such as a beam splitter. A condenser 324 containing a condenser lens (not shown) composed of a combination lens that may be in a known form is attached to the tip of the casing 321. The laser beam oscillated from the pulse laser beam oscillating means 322 reaches the condenser 324 via the transmission optical system 323, and a predetermined focal spot diameter is applied to the workpiece held on the chuck table 31 from the condenser 324. Irradiated with D. As shown in FIG. 4, the focused spot diameter D is D (μm) = 4 × λ × f / (π when a pulse laser beam having a Gaussian distribution is irradiated through the objective condenser lens 324 a of the condenser 324. × W), where λ is the wavelength (μm) of the pulse laser beam, W is the diameter (mm) of the pulse laser beam incident on the objective condenser lens 324a, and f is the focal length (mm) of the objective condenser lens 324a. It is prescribed.

  In the illustrated embodiment, the imaging means 33 mounted on the tip of the casing 321 constituting the laser beam irradiation means 32 is configured to emit infrared rays to the workpiece in addition to a normal imaging element (CCD) that captures 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 the control means described later.

The deteriorated layer forming step performed using the laser processing apparatus 3 described above will be described with reference to FIGS. 2, 5, and 6.
In this deteriorated layer forming step, first, the semiconductor wafer 2 is placed on the chuck table 31 of the laser processing apparatus 3 shown in FIG. 2 with the back surface 2b facing up, and the semiconductor wafer 2 is sucked and held on the chuck table 31. To do. The chuck table 31 that sucks and holds the semiconductor wafer 2 is positioned directly below the imaging means 33 by a moving mechanism (not shown).

  When the chuck table 31 is positioned immediately below the image pickup means 33, an alignment operation for detecting a processing region to be laser processed of the semiconductor wafer 2 is executed by the image pickup means 33 and a control means (not shown). That is, the imaging means 33 and the control means (not shown) include the division line 21 formed in a predetermined direction of the semiconductor wafer 2, and the condenser 324 of the laser beam irradiation means 32 that irradiates the laser beam along the 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. In addition, alignment of the laser beam irradiation position is similarly performed on the division line 21 formed on the semiconductor wafer 2 and extending at right angles 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 means 33 corresponds to the infrared illumination means, the optical system for capturing infrared rays and the infrared rays 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.

  If the division line 21 formed on the semiconductor wafer 2 held on the chuck table 31 is detected and the laser beam irradiation position is aligned as shown above, it is shown in FIG. In this way, the chuck table 31 is moved to the laser beam irradiation region where the condenser 324 of the laser beam irradiation means 32 for irradiating the laser beam is located, and one end (the left end in FIG. 5A) of the predetermined division line 21 is irradiated with the laser beam. Positioned just below the light collector 324 of the means 32. The chuck table 31, that is, the semiconductor wafer 2 is moved at a predetermined feed speed in the direction indicated by the arrow X 1 in FIG. 5A while irradiating a transmissive pulse laser beam from the condenser 324. Then, as shown in FIG. 5B, when the irradiation position of the condenser 324 of the laser beam irradiation means 32 reaches the position of the other end of the planned dividing line 21, the irradiation of the pulsed laser beam is stopped and the chuck table 31, that is, The movement of the semiconductor wafer 2 is stopped. In this deteriorated layer forming step, the condensing point P of the pulse laser beam is matched with the vicinity of the surface 2a (lower surface) of the semiconductor wafer 2, so that the deteriorated layer 210 is exposed to the surface 2a (lower surface) and from the surface 2a toward the inside. Is formed. This altered layer 210 is formed as a melt-resolidified layer.

Note that the processing conditions in the deteriorated layer forming step are set as follows, for example.
Light source: LD excitation Q switch Nd: YVO4 laser wavelength: 1064 nm pulse laser Pulse output: 10 μJ
Condensing spot diameter: φ1μm
Pulse width: 100 ns
Peak power density at the focal point; 1.3 × 10 ¹⁰ W / cm ²
Repetition frequency: 10 to 400 kHz
Processing feed rate: 10 to 400 mm / sec

  When the thickness of the semiconductor wafer 2 is thick, the plurality of deteriorated layers 210 are formed by changing the condensing point P stepwise as shown in FIG. Form. Note that, since the thickness of the deteriorated layer formed at one time is about 50 μm under the above-described processing conditions, in the illustrated embodiment, six deteriorated layers are formed on the wafer 2 having a thickness of 300 μm. . As a result, the altered layer 210 formed inside the semiconductor wafer 2 is formed from the front surface 2a to the back surface 2b along the planned dividing line 21.

  Under the above processing conditions, the coefficient k defined by the repetition frequency Y (Hz) of the pulse laser beam, the focused spot diameter D (mm) of the pulse laser beam, and the processing feed rate V (mm / second), k = V / ( It is desirable to set Y × D) to 1.0 to 2.5. In other words, it is desirable to set the relationship of the repetition frequency Y, the focused spot diameter D, and the processing feed speed V to 1.0 ≦ V / (Y × D) ≦ 2.5.

  More specifically, when the semiconductor wafer 2 is irradiated with a pulsed laser beam having a repetition frequency Y from the condenser 324 of the laser beam application means 32 with a focused spot diameter D and the chuck table 31, that is, the semiconductor wafer 2 is processed and fed, the above coefficient When k is 1, as shown in FIG. 7, the pitch p of the spot of the pulsed laser beam is the same as the focused spot diameter D. Therefore, the focused spot of the pulsed laser beam is in contact with each other (that is, without overlapping each other). In addition, irradiation is continuously performed along the planned dividing line 21 in a state where no gap is generated between adjacent spots. Further, when the coefficient k is less than 1, the spots of the pulse laser beam overlap each other and are continuously irradiated along the scheduled division line 21 as shown in FIG. On the other hand, when the coefficient k is greater than 1, the spot of the pulse laser beam is continuously irradiated along the planned division line 21 with a gap between adjacent spots as shown in FIG. When k becomes 2, the distance s between adjacent spots becomes the same length as the focused spot diameter D.

Experimental Example A semiconductor wafer having a diameter of 6 inches and a thickness of 300 μm is formed by changing the coefficient k from 0.1 to 4.0 under the above-described processing conditions to form the deteriorated layer, and to be divided in each case. The stress required to break the semiconductor wafer along the line was measured. When measuring stress, the back side of the semiconductor wafer is supported along the planned dividing line at a location 2.0 mm away from the planned dividing line on both sides, and a load is applied to the surface of the semiconductor wafer along the planned dividing line. The stress measured in the bending test is the stress in the cross section based on the load when the semiconductor wafer is broken. The measurement results are as shown in FIG. 10, and it can be seen that the stress required to break the semiconductor wafer is small when the coefficient k is 1.0 to 2.5.
FIG. 11 shows the test results obtained by measuring the bending stress necessary for breaking the above-mentioned deteriorated layer by the three-point bending test method, where the horizontal axis represents the repetition frequency (kHz) of the pulse laser beam that formed the deteriorated layer, and the vertical axis represents It is a bending stress (MPa) necessary for breaking the deteriorated layer. As can be seen from FIG. 11, when the repetition frequency of the pulsed laser beam for forming the deteriorated layer is 150 kHz or less, the bending stress necessary for breaking the deteriorated layer increases, but the repetition frequency of the pulsed laser beam for forming the deteriorated layer is 200 kHz. As described above, the bending stress necessary for breaking the deteriorated layer is 2 MPa or less. Therefore, it is desirable to set the repetition frequency of the pulse laser beam irradiated in the deteriorated layer forming step to 200 kHz or more.

  If the deteriorated layer 210 is formed along the division line 21 inside the semiconductor wafer 2 by the above-described deteriorated layer forming step, the outer peripheral portion is mounted so as to cover the inner opening of the support frame and is formed at a predetermined temperature. The dicing tape sticking process of sticking one surface of the wafer to the surface of the dicing tape that shrinks by the above heat is performed. That is, as shown in FIG. 12, the back surface 2b of the semiconductor wafer 2 is adhered to the surface of the dicing tape 42 that is mounted on the outer periphery so as to cover the inner opening of the annular dicing frame 41 and contracts by heat of a predetermined temperature or higher. . As the dicing tape 42, a synthetic resin sheet such as styrene, polyethylene terephthalate, vinyl chloride, polypropylene, polyolefin, polyethylene, or the like that has a property of being stretchable at normal temperature and contracting by heat at a predetermined temperature or higher can be used. In addition, you may implement a dicing tape sticking process before implementing the deteriorated layer formation process mentioned above. That is, the deteriorated layer forming step is performed in a state where the front surface 2a is adhered to the dicing tape 42 with the back surface 2b of the semiconductor wafer 2 facing upward and is supported by the dicing frame 41.

  If the deteriorated layer forming step and the dicing tape attaching step described above are performed, the shrinking region between the attaching region where the wafer is attached to the dicing tape and the support frame is heated to shrink the shrinking region and paste. A dividing step of dividing the wafer along the deteriorated layer is performed by extending the landing area. This dividing step is performed by the dividing device 5 shown in FIG. Here, the dividing device 5 will be described. The dividing device 5 shown in FIG. 13 includes a cylindrical base 51 having a mounting surface 511 on which the dicing frame 41 is mounted on the upper surface, and a concentric arrangement within the base 51 and the dicing tape 42. A support cylinder 52 that supports an adhesion region where the semiconductor wafer 2 is adhered, and an infrared heater 53 as a heating means disposed between the cylindrical base 51 and the support cylinder 52 are provided. A plurality of clamps 512 (four in the illustrated embodiment) for fixing the dicing frame 41 mounted on the mounting surface 511 are attached to the upper outer peripheral surface of the cylindrical base 51. . As shown in FIGS. 14 and 15, the infrared heater 53 includes a metal case 531 in which a metal tube having a rectangular cross section made of stainless steel or the like is formed in an annular shape, a nichrome wire disposed in the metal case 531, or the like. Connected to the heating element 532, an insulator 533 such as magnesium oxide filled in the metal case 531, an oxide layer 534 such as black aluminum oxide mounted on the surface of the metal case 53, and the heating element 532. Terminal 535. The annular infrared heater 53 configured as described above is placed on a heater support 513 provided on the upper inner peripheral surface of a cylindrical base 51 as shown in FIG. 13, and a terminal 535 is a power supply circuit (not shown). Connected to.

A dividing process performed using the dividing apparatus 5 will be described with reference to FIG.
As described above, the dicing frame 41 on which the dicing tape 42 to which the back surface 2b of the semiconductor wafer 2 is bonded is mounted on the mounting surface 511 of the cylindrical base 51 as shown in FIG. , And is fixed to the base 51 by a clamp 512. In the state where the dicing frame 41 is fixed to the cylindrical base 51 as described above, the pasting area 42a to which the semiconductor wafer 2 is pasted in the dicing tape 42 is supported by the support cylinder 52, and the pasting area 42a and the dicing are performed. A contraction region 42 b between the frame 41 and the frame 41 is positioned at a position facing the infrared heater 53.

  Next, the infrared heater 53 is turned on as shown in FIG. As a result, the contraction region 42 b in the dicing tape 42 is heated by infrared rays irradiated by the infrared heater 53. The temperature for heating the shrinkage region 42b is suitably 70 to 100 ° C. And this heating time may be 5 to 10 seconds. As described above, when the contraction region 42b of the dicing tape 42 attached to the dicing frame 41 is heated, the contraction region 42b contracts and the non-heated bonding region 42a extends. As a result, a tensile force acts radially on the semiconductor wafer 2 attached to the attachment region 42 a of the dicing tape 42. When a tensile force acts radially on the semiconductor wafer 2 attached to the attachment region 42a in this manner, the strength of the altered layer 210 formed along the planned division line is reduced, so that the semiconductor wafer 2 is reduced. Is broken along the altered layer 210 and divided into individual semiconductor chips 20. A gap is formed between the individual semiconductor chips 20.

  In the dividing step described above, the semiconductor wafer 2 can be divided along the scheduled dividing line 21 on which the altered layer 210 is formed only by heating the dicing tape 42, so that the productivity is extremely high. In addition, since a gap is formed between the individually divided semiconductor chips 20, contact between adjacent chips during transportation is prevented.

Next, another embodiment of the dicing tape mounted on the dicing frame 41 will be described with reference to FIGS. 17 and 18.
The dicing tape 43 shown in FIG. 17 and FIG. 18 includes a first tape 431 having elasticity and a second tape 432 that is formed in an annular shape and contracts by heat at a predetermined temperature or higher. The back surface of the second tape 432 is attached to the surface of the first tape 431 with an adhesive, and the outer peripheral portion of the surface is attached to the lower surface of the dicing frame 41. The dicing tape 43 shown in FIG. 17 and FIG. 18 is attached to the dicing frame 41 of the second tape 432, with the central portion of the first tape 431 forming an attachment region 43 a to which the semiconductor wafer 2 is attached. The non-existing region forms the contraction region 43b. If the dicing tape 43 configured in this way is used, only the contraction region 43b may be heated in the dividing step, but the entire dicing tape 43 may be heated.

Next, still another embodiment of the dicing tape attached to the dicing frame 41 will be described with reference to FIGS. 19 and 20.
A dicing tape 44 shown in FIGS. 19 and 20 includes a first tape 441 having elasticity and a second tape 442 that is formed in an annular shape and contracts by heat at a predetermined temperature or higher. The second tape 442 has its inner peripheral surface bonded to the outer peripheral surface of the first tape 441 by an adhesive or welding, and the outer peripheral surface is attached to the lower surface of the dicing frame 41. In the dicing tape 44 shown in FIG. 19 and FIG. 20, the first tape 441 forms an attachment region 44 a to which the semiconductor wafer 2 is attached, and the region not attached to the dicing frame 41 in the second tape 442 is an area. A contraction region 44b is formed. If the dicing tape 44 configured in this way is used, only the shrinkage region 44b may be heated in the dividing step as in the dicing tape 43 shown in FIGS. 17 and 18, but the entire dicing tape 44 is heated. May be.

The perspective view of the semiconductor wafer divided | segmented by the division | segmentation method of the wafer by this invention. The principal part perspective view of the laser processing apparatus which implements the deteriorated layer formation process of the division | segmentation method of the wafer by this invention. The block diagram which shows simply the structure of the laser beam irradiation means with which the laser processing apparatus shown in FIG. 2 is equipped. The simplification figure for demonstrating the condensing spot diameter of a pulse laser beam. Explanatory drawing of the altered layer formation process in the division | segmentation method of the wafer by this invention. Explanatory drawing which shows the state formed by laminating | stacking a deteriorated layer inside a wafer in the deteriorated layer formation process shown in FIG. The schematic diagram which shows the spot arrangement | sequence of the pulse laser beam irradiated to a wafer in case the coefficient k is 1 in the deteriorated layer formation process shown in FIG. The schematic diagram which shows the spot arrangement | sequence of the pulse laser beam irradiated to a wafer in case the coefficient k is less than 1 in the process of forming a deteriorated layer shown in FIG. The schematic diagram which shows the spot arrangement | sequence of the pulse laser beam irradiated to a wafer in case the coefficient k exceeds 1 in the process of forming a deteriorated layer shown in FIG. The graph which shows the change of the external force required for the fracture | rupture of a wafer by the fluctuation | variation of the coefficient k. The graph which shows the relationship between the repetition frequency of the pulsed laser beam irradiated in the process of forming a deteriorated layer in the method for dividing a wafer according to the present invention, and the bending stress required to break the deteriorated layer. Explanatory drawing of the dicing tape sticking process in the division | segmentation method of the wafer by this invention. Sectional drawing of the division | segmentation apparatus which implements the division | segmentation process in the division | segmentation method of the wafer by this invention. The perspective view of the infrared heater used for the chip | tip space | interval expansion apparatus shown in FIG. AA line sectional view in FIG. Explanatory drawing of the division | segmentation process in the division | segmentation method of the wafer by this invention. The top view which shows other embodiment of the dicing tape used for the dicing tape sticking process in the division | segmentation method of the wafer by this invention. BB sectional drawing in FIG. The top view which shows other embodiment of the dicing tape used for the dicing tape sticking process in the division | segmentation method of the wafer by this invention. CC sectional view taken on the line in FIG.

Explanation of symbols

2: Semiconductor wafer 20: Semiconductor chip 21: Divided line 22: Circuit 210: Altered layer 3: Laser processing device 31: Chuck table of laser processing device 31: Laser beam irradiation means 33: Imaging means 41: Dicing frames 42, 43, 44: Dicing tape 5: Dividing device 51: Cylindrical base 52: Support cylinder 53: Infrared heater

Claims (3)

A wafer processing method for dividing a wafer along a predetermined division line,
The pulse laser beam chromatic and frequency is set to more than 200kHz permeable to the wafer is irradiated along the dividing line, from one surface of the wafer along the interior of said wafer to said dividing lines An altered layer forming step of forming an altered layer over the other surface ;
Before or after performing the deteriorated layer forming step, the dicing tape is formed in an annular shape so that the outer peripheral portion is attached so as to cover the inner opening of the dicing frame and contracts by heat at a predetermined temperature or higher. A dicing tape adhering step for adhering one surface of the wafer to the surface;
After carrying out the deteriorated layer forming step, the shrinking region between the dicing frame and the pasting region where the wafer is pasted in the dicing tape is heated to shrink the shrinking region, and the pasting region is formed. Dividing the wafer along the deteriorated layer by expanding,
A wafer dividing method characterized by the above.   In the altered layer forming step, the repetition frequency of the pulsed laser beam is Y (Hz), the focused spot diameter of the pulsed laser beam is D (mm), and the processing feed rate (relative moving speed between the wafer and the pulsed laser beam) is V (mm / 2), the wafer dividing method according to claim 1, wherein processing conditions satisfying 1.0 ≦ V / (Y × D) ≦ 2.5 are set. The method for dividing a wafer according to claim 1 , wherein the deteriorated layer formed in the deteriorated layer forming step is a melt-resolidified layer.

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