Wafer processing method

Abstract

To provide a wafer processing method capable of solving a problem caused by processing debris adhering to the sides and surfaces of device chips.SOLUTION: A wafer processing method includes a division start point forming step of forming a division start point on a planned division line, a sheet disposing step of disposing a wafer 2 on an elastic sheet 10 before or after the division start point forming step, and a separation step of expanding the sheet 10 and applying an external force to the wafer 2 to separate the wafer 2 into individual device chips 6. The separation step includes an adhesive liquid coating step of coating the exposed surface of the wafer 2 with a fluid adhesive liquid before or after expanding the sheet 10, and allowing the adhesive liquid to penetrate into separation grooves 54 formed by separation. After the separation step, the method includes a solidified film forming step of solidifying the adhesive liquid in a state in which the sheet 10 is expanded to form a solidified film 52', and a processing debris removing step of peeling off the solidified film 52' to remove processing debris 56 attached to the side surface of the device chip 6.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to a method for processing a wafer that divides a wafer, on which a plurality of devices are formed on a surface partitioned by a division planned line, into individual device chips.

Background Art

[0002] A wafer, on which a plurality of devices such as ICs and LSIs are formed on a surface partitioned by a division planned line, is ground on the back surface to a desired thickness and then divided into individual device chips by a dicing device or a laser processing device. Each divided device chip is used in an electric device such as a mobile phone or a personal computer.

[0003] In addition, a technique has been proposed in which a laser beam having a wavelength that is transmissive to the wafer is irradiated onto the wafer with the focus point of the laser beam positioned inside the division planned line to form a modified layer serving as a starting point for division, and then an external force is applied to the wafer to divide the wafer into individual device chips (see, for example, Patent Document 1).

[0004] Furthermore, the applicant has proposed a technique in which a laser beam having a wavelength that is transmissive to the wafer is irradiated onto the wafer with the focus point of the laser beam positioned inside the division planned line to form a modified layer serving as a starting point for division, and then the back surface of the wafer is ground to a desired thickness and the wafer is divided into individual device chips (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when an external force is applied to a wafer in which a modified layer is formed inside the planned division line to divide it into individual device chips, there is a problem that dust scatters due to the destruction of the modified layer and adheres to the surface of the device chip, deteriorating the quality of the device chip.

[0007] In addition, residues of the destroyed modified layer adhere to the side surfaces of the device chips, and in post-processes such as the pickup process, wire bonding, die bonding, and stacking of device chips, the residues of the modified layer that have fallen or scattered from the side surfaces of the device chips interfere with bonding and adhere to the surfaces of the device chips, deteriorating the quality of the stacked device chips.

[0008] Furthermore, there is a problem that grinding debris generated during grinding enters the division grooves formed in the planned division line and adheres to the side surfaces of the device chips, deteriorating the quality of the device chips in the same way as in the post-processes.

[0009] Such a problem can also occur in a technique called pre-dicing in which a groove having a depth corresponding to the finished thickness of the device chip is formed in the planned division line as a starting point for division, and the back surface of the wafer is ground until the finished thickness of the device chip is reached to divide the wafer into individual device chips (see, for example, Japanese Patent Application Laid-Open No. 11-40520).

[0010] An object of the present invention is to provide a method for processing a wafer that can solve problems caused by processing debris adhering to the side and surface of a device chip.

Means for Solving the Problems

[0011] According to the present invention, there is provided the following method for processing a wafer that solves the above problems. That is, "A method for processing a wafer that divides a wafer in which a plurality of devices are partitioned by a planned division line and formed on the surface into individual device chips, A dividing starting point forming step of forming a dividing starting point on the dividing planned line, A sheet disposing step of disposing a wafer on a stretchable sheet before or after the dividing starting point forming step, A separating step of expanding the sheet to apply an external force to the wafer to separate the wafer into individual device chips, including: In the separating step, a sticky liquid coating step of coating a sticky liquid having fluidity on the exposed surface of the wafer before or after expanding the sheet and allowing the sticky liquid to penetrate into the separation grooves formed by the separation is provided. After the separating step, A solidified film forming step of solidifying the sticky liquid in a state where the sheet is expanded to form a solidified film, A processing chip removing step of peeling off the solidified film to remove processing chips attached to the side surfaces of the device chips is provided. A method for processing a wafer is provided.

[0012] Further, according to the present invention, a method for processing a wafer for solving the above problems is provided. That is, "A method for processing a wafer that divides a wafer on which a plurality of devices are partitioned by a dividing planned line and formed on the surface into individual device chips, A dividing starting point forming step of forming a dividing starting point on the dividing planned line, A protective member disposing step of disposing a protective member for protecting the surface of the wafer before or after the dividing starting point forming step, After the dividing starting point forming step, the side of the protective member is held by a chuck table, the back surface of the wafer is ground to finish to a desired thickness, and a dividing groove is formed on the dividing planned line to divide the wafer into individual device chips. A back surface grinding step, A sheet disposing step of disposing a stretchable sheet on the back surface of the wafer and removing the protective member from the surface of the wafer, An expanding step of expanding the sheet to expand the intervals between the individual device chips, including: In the expanding step, a sticky liquid coating step of coating a sticky liquid having fluidity on the exposed surface of the wafer before or after expanding the sheet and allowing the sticky liquid to penetrate into the dividing groove is provided. After the expanding step, A solidified film forming step of solidifying the adhesive liquid in a state where the sheet is expanded to form a solidified film; A method for processing a wafer is provided, which includes a step of removing processed chips adhering to the side surface of the device chip by peeling the solidified film.

[0013] Preferably, in the splitting start point forming step, the condensing point of a laser beam having a wavelength that is permeable to the wafer is positioned inside the splitting planned line, and the wafer is irradiated with the laser beam to form a modified layer serving as a starting point for splitting.

[0014] After the processed chip removing step, it is desirable to include a cleaning step of cleaning the wafer.

[0015] The adhesive liquid is preferably a water-soluble resin or a silicone-based adhesive resin containing any one of polyvinyl alcohol, polyethylene oxide, polyacrylamide, carboxymethyl cellulose, resol type phenol resin, methylolated urea resin, methylolated melamine resin, vinyl acetate resin-based emulsion fixing material, and (PVA + borax).

Advantages of the Invention

[0016] In the method for processing a wafer of the present invention, the adhesive liquid having fluidity entraps the processed chips adhering to the side surface of the device chip. Therefore, by peeling the solidified film formed by solidifying the adhesive liquid, the processed chips can be removed from the side surface of the device chip. As a result, in subsequent processes such as wire bonding, die bonding, and stacking of device chips, the processed chips do not fall or scatter from the side surface of the device chip. Further, even if the processed chips adhere to the surface of the device chip, the processed chips can be removed from the surface of the device chip by peeling the solidified film. Therefore, according to the present invention, problems caused by the processed chips adhering to the side surface and the surface of the device chip can be solved.

Brief Description of the Drawings

[0017]

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Figure 17

Embodiments for Carrying Out the Invention

[0018] First, a first embodiment of a wafer processing method according to the present invention will be described with reference to FIGS. 1 to 10.

[0019] (Wafer 2) FIG. 1 shows a disk-shaped wafer 2 to be processed by the wafer processing method of the present invention. The wafer 2 can be formed from an appropriate semiconductor material such as silicon. The surface 2a of the wafer 2 is partitioned into a plurality of rectangular regions by grid-shaped planned division lines 4. Devices 6 such as ICs and LSIs are formed in each of the plurality of rectangular regions.

[0020] (Sheet Disposition Process) In this embodiment, first, a sheet arranging step of arranging the wafer 2 on a stretchable sheet is performed. However, the sheet arranging step may be performed after the following dividing start point forming step. In the sheet arranging step, as shown in FIG. 1(a), the wafer 2 can be arranged on a circular sheet 10 whose periphery is fixed to a frame 8 having an annular shape. As the sheet 10, an adhesive tape having an adhesive layer on one side (for example, an adhesive tape made of vinyl chloride) may be used. In this case, the back surface 2b of the wafer 2 is attached to the adhesive surface of the sheet 10 (see FIG. 1(b)). Further, the sheet 10 used in the sheet arranging step may be a thermocompression bonding sheet having no adhesive layer. The thermocompression bonding sheet is a sheet made of a thermoplastic synthetic resin (for example, a polyolefin resin), and when heated to a temperature near the melting point, it softens or melts and exhibits an adhesive force.

[0021] (Dividing start point forming step) In this embodiment, after performing the sheet arranging step, a dividing start point forming step of forming a dividing start point on the dividing planned line 4 is performed.

[0022] The dividing start point forming step can be performed, for example, using a laser processing apparatus 12 shown in FIG. 2(a). The laser processing apparatus 12 includes a chuck table (not shown) that sucks and holds the wafer 2, an oscillator (not shown) that oscillates a pulsed laser beam LB having a wavelength that is transmissive to the wafer 2, a condenser 14 that condenses the pulsed laser beam LB oscillated by the oscillator and irradiates the wafer 2 sucked and held by the chuck table, and an imaging means (not shown) that images the wafer 2 sucked and held by the chuck table.

[0023] The chuck table is rotatable about the vertical axis and movable in the X-axis direction indicated by an arrow X in FIG. 2(a) and in the Y-axis direction (the direction indicated by an arrow Y in FIG. 2(a)) orthogonal to the X-axis direction. Note that the XY plane defined by the X-axis direction and the Y-axis direction is substantially horizontal.

[0024] In the process of forming the starting points for division, first, with the surface 2a of the wafer 2 facing upward, the wafer 2 is sucked and held on the upper surface of the chuck table. Next, the wafer 2 is imaged from above by the imaging means, and based on the image of the wafer 2 captured by the imaging means, the planned division line 4 is aligned in the X-axis direction. Also, the aiming of the laser beam LB is aligned with the planned division line 4 aligned in the X-axis direction, and the focus point of the laser beam LB is positioned inside the planned division line 4.

[0025] Next, while the chuck table is being processed and fed in the X-axis direction, a laser beam LB having a wavelength that is transmissive to the wafer 2 is irradiated from the condenser 14 onto the wafer 2. Thereby, a modified layer 16 serving as the starting point for division can be formed inside the wafer 2 along the planned division line 4 (see Fig. 3(b)). Next, the chuck table is indexed and fed in the Y-axis direction with respect to the condenser 14 by the interval in the Y-axis direction of the planned division line 4. Then, by alternately repeating the irradiation of the laser beam LB and the indexing feed, the modified layer 16 is formed inside the wafer 2 along all of the planned division lines 4 aligned in the X-axis direction.

[0026] Also, after rotating the chuck table by 90 degrees, the irradiation of the laser beam LB and the indexing feed are alternately repeated. Thereby, the modified layer 16 is formed inside the wafer 2 along all of the planned division lines 4 orthogonal to the planned division line 4 where the modified layer 16 was previously formed. In this way, the process of forming the starting points for division is carried out, and as shown in Fig. 3(a), the modified layer 16 is formed in a lattice pattern inside the wafer 2 along the lattice-shaped planned division lines 4.

[0027] Such a process of forming the starting points for division can be carried out, for example, under the following processing conditions. Wavelength of the pulsed laser beam: 1342 nm Average output: 1.0 W Repetition frequency: 90 kHz Feed rate: 700 mm / s

[0028] Here, an example in which the modified layer 16 is formed by irradiating the laser beam LB from the surface 2a side of the wafer 2 has been described. However, in the dividing start point forming step, as shown in FIG. 2(b), the modified layer 16 may be formed by irradiating the laser beam LB from the back surface 2b side of the wafer 2. In this case, since the surface 2a of the wafer 2 comes into contact with the holding surface of the chuck table, it is preferable to dispose a protective member on the surface 2a of the wafer 2.

[0029] Further, when irradiating the laser beam LB from the back surface 2b side of the wafer 2, the imaging means of the laser processing apparatus 12 includes a normal imaging element (CCD) that images the wafer 2 through the sheet 10 with visible light, an infrared irradiation means that irradiates infrared rays that pass through the wafer 2, an optical system that captures the infrared rays irradiated by the infrared irradiation means, and an imaging element (infrared CCD) that outputs an electrical signal corresponding to the infrared rays captured by the optical system. Then, after sucking and holding the wafer 2 on the upper surface of the chuck table with the back surface 2b of the wafer 2 facing upward, infrared rays are irradiated from the imaging means, and the surface 2a side of the wafer 2 is imaged by the infrared rays transmitted through the back surface 2b of the wafer 2. Thereby, based on the image of the wafer 2 imaged by the imaging means, the dividing planned line 4 can be aligned in the X-axis direction. Thereafter, the laser beam LB is irradiated onto the wafer 2 in the same manner as described above, and a lattice-shaped modified layer 16 is formed inside the wafer 2 along the lattice-shaped dividing planned line 4.

[0030] (Separation step · Adhesive liquid coating step) After performing the dividing start point forming step, a separation step is performed in which the sheet 10 is expanded to apply an external force to the wafer 2 to separate the wafer 2 into individual device chips 6. The separation step includes an adhesive liquid coating step of coating the exposed surface (surface 2a) of the wafer 2 with a fluid adhesive liquid before or after expanding the sheet 10 to allow the adhesive liquid to penetrate into the separation grooves formed by the separation. The separation step · Adhesive liquid coating step can be performed using, for example, the expansion device 18 and the adhesive liquid coating device 20 shown in FIG. 4.

[0031] (Expansion device 18) Referring to FIGS. 4 and 5 for description, the expansion device 18 includes a frame support portion 22 that supports the frame 8, a wafer support portion 24 that supports the wafer 2 via the sheet 10, an expansion means 26 that relatively separates the frame support portion 22 and the wafer support portion 24 to expand the sheet 10, and a shrink means 28 (see FIG. 5) that heats and shrinks the slack sheet 10.

[0032] (Frame support portion 22) The frame support portion 22 includes an annular member 30 and a plurality of clamps 32 attached to the outer periphery of the annular member 30 at circumferential intervals. The outer diameter and inner diameter of the annular member 30 correspond to the outer diameter and inner diameter of the frame 8, and the frame 8 is placed on the upper surface of the annular member 30. The frame support portion 22 fixes and supports the frame 8 placed on the annular member 30 with the clamps 32.

[0033] (Wafer support portion 24) A circular suction chuck 34 is arranged at the upper end portion of the wafer support portion 24. The suction chuck 34 is formed of a porous member such as porous ceramics. The suction chuck 34 is also connected to a suction means (not shown). In the wafer support portion 24, a suction force is generated on the upper surface of the suction chuck 34 by the suction means, and the wafer 2 placed on the upper surface of the suction chuck 34 is suction-held.

[0034] The wafer support portion 24 is cylindrical and is arranged radially inside the frame support portion 22. A gap is provided between the outer periphery of the wafer support portion 24 and the inner periphery of the annular member 30 of the frame support portion 22. Also, as shown in FIG. 4, the wafer support portion 24 of the present embodiment is fixed to the upper surface of a rotating plate 36. The rotating plate 36 is rotatably mounted on a substrate 38 of the expansion device 18. A motor 42 for rotating the rotating plate 36 is attached to the substrate 38 via a belt 40.

[0035] (Expansion means 26) The expanding means 26 is composed of a plurality of air cylinders that raise and lower the frame support portion 22. The upper ends of the pistons of the plurality of air cylinders are connected to the annular member 30 of the frame support portion 22. Also, the lower ends of the plurality of air cylinders are fixed to the upper surface of the circular rotating plate 36. In the expanding means 26, by lowering the pistons of the plurality of air cylinders of the annular member 30 of the frame support portion 22, the frame support portion 22 and the wafer support portion 24 are relatively separated. As a result, tension is applied to the sheet 10 fixed to the frame 8 supported by the frame support portion 22, and the wafer 2 with a formed splitting starting point is separated into individual device chips 6. Note that the expanding means 26 may raise and lower the wafer support portion 24 with respect to the frame support portion 22.

[0036] (Shrinking means 28) As shown in FIG. 5, the shrinking means 28 is annular and is disposed between the frame support portion 22 and the wafer support portion 24. Then, the shrinking means 28 heats and shrinks the slack sheet 10 between the wafer 2 and the frame 8 by sending hot air upward or irradiating infrared rays upward. Note that the shrinking means 28 is connected to the frame support portion 22 via an appropriate bracket (not shown) and is configured to move up and down together with the frame support portion 22.

[0037] (Adhesive liquid coating device 20) Referring to FIG. 4, the adhesive liquid coating device 20 will be described. The adhesive liquid coating device 20 includes an adhesive liquid supply source 44, a nozzle 46 that drops the adhesive liquid supplied from the adhesive liquid supply source 44 onto the exposed surface of the wafer 2 supported by the wafer support portion 24 of the expanding device 18, a pipe line 48 that connects the adhesive liquid supply source 44 and the nozzle 46, and an on-off valve 50 installed in the pipe line 48.

[0038] In the separation step, first, the frame 8 is supported by the frame support portion 22, and the wafer 2 is supported by the wafer support portion 24. Specifically, as shown in FIG. 5, the frame 8 is placed on the annular member 30 of the frame support portion 22, and the frame 8 is fixed to the annular member 30 by the clamp 32. Regarding the wafer 2, with the surface 2a facing upward, the wafer 2 is placed on the suction chuck 34 of the wafer support portion 24 via the sheet 10. At this time, the height of the upper surface of the frame support portion 22 and the height of the upper surface of the wafer support portion 24 are made substantially the same. Also, at this point, the suction means of the wafer support portion 24 is not operated, and the wafer 2 is not sucked and held by the suction chuck 34.

[0039] In the separation step, after the frame 8 is supported by the frame support portion 22 and the wafer 2 is supported by the wafer support portion 24, an adhesive liquid coating step is performed in which an adhesive liquid having fluidity is coated on the exposed surface (surface 2a) of the wafer 2 and the adhesive liquid is allowed to penetrate into the separation groove formed by separation. The adhesive liquid may be coated on the surface 2a of the wafer 2 before or after the sheet 10 is expanded. However, in this embodiment, an example in which the adhesive liquid is coated on the surface 2a of the wafer 2 before the sheet 10 is expanded will be described.

[0040] In the adhesive liquid coating step, first, the nozzle 46 of the adhesive liquid coating device 20 is positioned above the center of the wafer 2. Next, the on-off valve 50 of the adhesive liquid coating device 20 is opened, and the adhesive liquid having fluidity is supplied from the adhesive liquid supply source 44 to the nozzle 46. Then, as shown in FIG. 5, the adhesive liquid 52 is dropped from the nozzle 46 onto the center of the surface 2a of the wafer 2. After the adhesive liquid 52 is dropped onto the wafer 2, the rotary plate 36 is rotated by the motor 42 to rotate the wafer 2. Then, due to the centrifugal force, the adhesive liquid 52 flows toward the outer periphery of the wafer 2, so that the adhesive liquid 52 can be coated on the surface 2a of the wafer 2 with a substantially uniform thickness.

[0041] The adhesive liquid 52 having fluidity may be a water-soluble resin containing, for example, polyvinyl alcohol, polyethylene oxide, polyacrylamide, carboxymethyl cellulose (CMC), resol type phenol resin, methylolated urea resin, methylolated melamine resin, vinyl acetate resin-based emulsion fixing material, or (PVA + borax). Alternatively, a silicone-based adhesive resin can also be used as the adhesive liquid 52.

[0042] After coating the surface 2a of the wafer 2 with the adhesive liquid 52, the sheet 10 is expanded to apply an external force to the wafer 2, and the wafer 2 is separated into individual device chips 6. Specifically, as shown in FIG. 6, by lowering the frame support portion 22 by the expansion means 26, the upper surface of the frame support portion 22 is lowered below the upper surface of the wafer support portion 24. Thereby, a radial tension is applied to the sheet 10 to expand the sheet 10. Then, a radial tension (external force) is applied to the wafer 2. As described above, since the modified layer 16 as a starting point of division is formed on the division planned line 4 of the wafer 2, when a radial tension (external force) is applied to the wafer 2, the wafer 2 is separated into individual device chips 6 along the division planned line 4.

[0043] The adhesive liquid 52 penetrates into the separation groove 54 (see FIG. 9(b)) formed by the separation into the device chip 6. In the present embodiment, since the surface 2a of the wafer 2 is coated with the adhesive liquid 52 before expanding the sheet 10, when the separation groove 54 is formed, the separation groove 54 is in a vacuum state. Therefore, the adhesive liquid 52 penetrates into the separation groove 54 by capillary action due to the atmospheric pressure. Therefore, it is preferable to coat the surface 2a of the wafer 2 with the adhesive liquid 52 before expanding the sheet 10.

[0044] Further, when the wafer 2 is separated into individual device chips 6, processing debris (dust) is generated due to the destruction of the modified layer 16. An example of the processing debris is indicated by reference numeral 56 in FIG. 9(b). In the present embodiment, since the adhesive liquid 52 is coated on the surface 2a of the wafer 2 before expanding the sheet 10, scattering of the processing debris 56 can be suppressed, and adhesion of the processing debris 56 to the surface (upper surface) of the device chip 6 can be prevented. Further, the processing debris 56 remaining on the side surface of the device chip 6 is caught by the adhesive liquid 52 that has entered the separation groove 54.

[0045] After performing the adhesive liquid coating step, the wafer 2 divided into individual device chips 6 is sucked and held on the upper surface of the suction chuck 34. That is, in a state where the sheet 10 is expanded, the suction means of the wafer support portion 24 is operated. As a result, since a suction force is generated on the upper surface of the suction chuck 34, the wafer 2 separated into individual device chips 6 is sucked and held on the upper surface of the suction chuck 34. As a result, even if the frame support portion 22 is raised to the original position, the interval between the device chips 6 can be maintained.

[0046] After sucking and holding the individual device chips 6 with the suction chuck 34, the frame support portion 22 is raised to the original position (the position before expanding the sheet 10). Then, while the interval between the device chips 6 is maintained at the interval when the sheet 10 is expanded, since no tension acts on the sheet 10, as shown in FIG. 7, the sheet 10 between the wafer 2 and the frame 8 becomes slack.

[0047] Therefore, after raising the frame support portion 22 to the original position, the shrinkage means 28 is operated to heat and shrink the slack sheet 10 between the wafer 2 and the frame 8. Specifically, hot air is sent upward from the upper end of the shrinkage means 28, or infrared rays are irradiated. As a result, as shown in FIG. 8, the sheet 10 can be shrunk, and the slack of the sheet 10 can be removed. As a result, even if the suction holding by the suction chuck 34 is released, the interval between the device chips 6 is maintained at the interval when the sheet 10 is expanded.

[0048] (Curing Film Formation Step) After performing the separation step, a curing film formation step is carried out in which the adhesive liquid 52 is cured in an extended state of the sheet 10 to form a cured film 52' (see FIG. 9). In the curing film formation step, the wafer 2 coated with the adhesive liquid 52 can be left for a certain period of time to cure the adhesive liquid 52 by natural drying to form the cured film 52'. Alternatively, the adhesive liquid 52 may be forcibly cured by irradiating the adhesive liquid 52 with infrared rays or the like to form the cured film 52'. Forcibly curing the adhesive liquid 52 takes less time than natural drying, so it is preferable in terms of productivity.

[0049] (Processing Scrap Removal Step) After performing the curing film formation step, as shown in FIG. 10, a processing scrap removal step is carried out in which the cured film 52' is peeled off to remove the processing scraps 56 attached to the side surface of the device chip 6. As described above, when the adhesive liquid 52 enters the separation groove 54, the adhesive liquid 52 entangles the processing scraps 56. Therefore, by peeling off the cured film 52' in which the adhesive liquid 52 has solidified from the device chip 6, the processing scraps 56 can be removed from the side surface of the device chip 6. Further, even if the processing scraps 56 are attached to the surface of the device chip 6, the processing scraps 56 can be removed from the surface of the device chip 6 by peeling off the cured film 52'. Therefore, according to the present embodiment, problems caused by the processing scraps 56 attached to the side surface and the surface of the device chip 6 can be solved.

[0050] (Washing Step) Furthermore, after performing the processing scrap removal step, it is preferable to perform a washing step of washing the wafer 2. Although not shown, in the washing step, washing water is supplied to the wafer 2 (individual device chips 6) supported by the sheet 10 to wash the wafer 2. Then, dry air is blown onto the wafer 2 to remove the washing water and dry the wafer 2.

[0051] Next, a second embodiment of the wafer processing method according to the present invention will be described with reference to FIGS. 11 to 17.

[0052] (Protective Member Disposal Step) In the second embodiment, first, as shown in FIG. 11, a protective member disposing step of disposing a protective member 58 for protecting the surface 2a of the wafer 2 is performed. However, the protective member disposing step may be performed after the following dividing start point forming step. As the protective member 58, a circular adhesive tape or a thermocompression bonding sheet having a diameter substantially the same as the diameter of the wafer 2 can be used.

[0053] (Dividing start point forming step) In the present embodiment, after performing the protective member disposing step, a dividing start point forming step of forming a dividing start point on the dividing planned line 4 is performed. The dividing start point forming step can be performed, for example, using the laser processing apparatus 12 described above. In FIG. 2, for the sake of convenience, the chuck table of the laser processing apparatus 12 is not shown, but in FIG. 12, the chuck table of the laser processing apparatus 12 is indicated by reference numeral 13.

[0054] As shown in FIG. 12(a), in the dividing start point forming step, first, the back surface 2b of the wafer 2 is turned upward, and the wafer 2 is sucked and held on the upper surface of the chuck table 13. Next, infrared rays are irradiated from the imaging means, and the surface 2a side of the wafer 2 is imaged by the infrared rays transmitted through the back surface 2b of the wafer 2. Next, based on the image of the wafer 2 captured by the imaging means, the dividing planned line 4 is aligned in the X-axis direction. In addition, the aiming of the laser beam LB is aligned with the dividing planned line 4 aligned in the X-axis direction, and the focusing point of the laser beam LB is positioned inside the dividing planned line 4.

[0055] Next, while the chuck table 13 is processed and fed in the X-axis direction, a laser beam LB having a wavelength that is transmissive to the wafer 2 is irradiated from the condenser 14 to the wafer 2. Thereby, a modified layer 16 serving as a dividing start point can be formed inside the wafer 2 along the dividing planned line 4 (see FIG. 12(b)). From the viewpoint of preventing a decrease in the flexural strength of the device chip 6, it is preferable to form the modified layer 16 in a portion to be removed by grinding on the back surface 2b of the wafer 2 in the back surface grinding step described later.

[0056] Next, the chuck table 13 is indexed and fed in the Y-axis direction with respect to the condenser 14 by the interval in the Y-axis direction of the planned division line 4. Then, by alternately repeating the irradiation of the laser beam LB and the indexing feed, a modified layer 16 is formed inside the wafer 2 along all of the planned division lines 4 aligned in the X-axis direction.

[0057] Also, after rotating the chuck table 13 by 90 degrees, the irradiation of the laser beam LB and the indexing feed are alternately repeated. As a result, a modified layer 16 is formed inside the wafer 2 along all of the planned division lines 4 orthogonal to the planned division lines 4 where the modified layer 16 was previously formed. In this way, the division start point forming step is carried out, and as shown in FIG. 12(c), a lattice-shaped modified layer 16 is formed inside the wafer 2 along the lattice-shaped planned division lines 4.

[0058] Such a division start point forming step can be carried out, for example, under the following processing conditions. Wavelength of pulsed laser beam: 1342 nm Average output: 1.0 W Repetition frequency: 90 kHz Feed rate: 700 mm / s

[0059] Here, an example in which the modified layer 16 is formed by irradiating the laser beam LB from the back surface 2b side of the wafer 2 has been described. However, in the division start point forming step, the modified layer 16 may be formed by irradiating the laser beam LB from the front surface 2a side of the wafer 2 through the protective member 58. Alternatively, a protective member disposing step may be carried out after the division start point forming step.

[0060] Also, in the above description, the starting point of division was the modified layer 16, but the starting point of division may be a groove having a depth corresponding to the finished thickness of the device chip 6. The groove as the starting point of division is formed on the front surface 2a side of the wafer 2 along the planned division line 4. Further, the groove as the starting point of division can be formed by ablation processing by irradiation of a laser beam or cutting processing using a dicing device.

[0061] (Ablation processing) First, with reference to FIG. 13, the case of forming a groove as a starting point of division by ablation processing will be described. In this case, before disposing the protection member 58 on the surface 2a of the wafer 2, the wafer 2 is sucked and held by the chuck table 13 with the surface 2a facing upward. Next, the division planned line 4 is aligned in the X-axis direction, and the aiming of the laser beam LB' having an absorbable wavelength with respect to the wafer 2 is adjusted to the division planned line 4. Also, the focus point of the laser beam LB' is positioned on the surface 2a. Note that it is preferable to coat the surface with a protective film so that debris does not adhere to the surface 2a of the wafer 2.

[0062] Then, while the chuck table 13 is fed in the X-axis direction for processing, the wafer 2 is irradiated with the laser beam LB' having an absorbable wavelength with respect to the wafer 2. As a result, a laser processing groove 60 having a depth corresponding to the finished thickness of the device chip 6 is formed on the surface 2a along the division planned line 4. Also, similar to the case of forming the modified layer 16, the irradiation of the laser beam LB' and the indexing feed are alternately repeated, and the laser processing grooves 60 are formed in a lattice pattern on the surface 2a of the wafer 2 along the lattice-shaped division planned line 4.

[0063] When forming the laser processing groove 60 as a starting point of division, for example, the starting point forming step can be carried out under the following processing conditions. Wavelength of laser beam: 355 nm Average output: 2.0 W Repetition frequency: 80 kHz Feed rate: 300 mm / s

[0064] (Cutting processing) Next, with reference to FIG. 14, a case where a groove as a starting point of division is formed by cutting will be described. When forming a groove by cutting, for example, a dicing apparatus 62 shown in FIG. 14 can be used. The dicing apparatus 62 includes a chuck table 64 that sucks and holds the wafer 2, and a cutting means 66 that cuts the wafer 2 sucked and held by the chuck table 64. The cutting means 66 includes a spindle 68 that is rotatably configured about the Y-axis direction, and an annular cutting blade 70 fixed to the tip of the spindle 68.

[0065] Also when forming a groove as a starting point of division by cutting, similar to the ablation process, before disposing the protective member 58 on the surface 2a of the wafer 2, the wafer 2 is sucked and held on the upper surface of the chuck table 64 with the surface 2a facing upward. Next, the cutting edge of the high-speed rotating cutting blade 70 is cut into the division planned line 4 aligned in the X-axis direction to a depth corresponding to the finished thickness of the device chip 6 from the surface 2a, and while supplying cutting water to the portion where the cutting edge of the cutting blade 70 is cut, the chuck table 64 is fed in the X-axis direction for processing. Thereby, a cutting groove 72 having a depth corresponding to the finished thickness of the device chip 6 is formed along the division planned line 4. Also when performing cutting, the formation of the cutting groove 72 and the indexing feed are alternately repeated, and the cutting grooves 72 are formed in a lattice pattern on the surface 2a of the wafer 2 along the lattice-shaped division planned line 4.

[0066] When forming the cutting groove 72 as a starting point of division, for example, the starting point formation step can be carried out under the following processing conditions. Diameter of cutting blade: φ50 mm Rotational speed of cutting blade: 30,000 rpm Supply amount of cutting water: 2 liters / minute Feed speed: 50 mm / s

[0067] Since the grooves 60 and 72 as the starting points of division are formed on the surface 2a side of the wafer 2, when forming the grooves 60 and 72 as the starting points of division, as shown in FIGS. 15(a) and 15(b), the protective member disposing step is carried out after the starting point of division forming step.

[0068] (Back grinding step) After carrying out the protective member disposing step and the starting point of division forming step, the back surface 2b of the wafer 2 is ground to a desired thickness while holding the protective member 58 side by the chuck table, and a dividing groove is formed in the dividing planned line 4 to divide the wafer 2 into individual device chips 6, and the back grinding step is carried out.

[0069] The back grinding step can be carried out, for example, using the grinding device 74 shown in FIG. 16(a). The grinding device 74 includes a chuck table 76 that sucks and holds the wafer 2, and grinding means 78 that grinds the wafer 2 sucked and held by the chuck table 76. The grinding means 78 includes a spindle 80 extending in the vertical direction and a disk-shaped wheel mount 82 fixed to the lower end of the spindle 80. An annular grinding wheel 86 is fastened to the lower surface of the wheel mount 82 by bolts 84. A plurality of grinding wheels 88 are fixed to the outer peripheral edge portion of the lower surface of the grinding wheel 86 in an annular manner at intervals in the circumferential direction.

[0070] In the back grinding step, first, with the back surface 2b of the wafer 2 facing upward, the wafer 2 is sucked and held on the upper surface of the chuck table 76. Next, the spindle 80 is rotated at a predetermined rotational speed (for example, 6000 rpm) in the direction indicated by the arrow R1 in FIG. 16(a). Also, the chuck table 76 is rotated at a predetermined rotational speed (for example, 300 rpm) in the direction indicated by the arrow R2. Next, the spindle 80 is lowered to bring the grinding wheel 88 into contact with the back surface 2b of the wafer 2, and grinding water is supplied to the portion where the grinding wheel 88 contacts the back surface 2b. Thereafter, the spindle 80 is lowered at a predetermined grinding feed rate (for example, 1.0 μm / s). Thereby, the back surface 2b of the wafer 2 is ground to thin the wafer 2 to the finished thickness of the device chip 6.

[0071] When the modified layer 16 is formed as the starting point of the division, due to the pressing force acting when the wafer 2 is being ground, cracks extend from the modified layer 16 in the thickness direction of the wafer 2, and as shown in Fig. 16(b), the wafer 2 is divided into individual device chips 6. Further, since the cracks extending from the modified layer 16 form division grooves 90 (grooves reaching from the front surface 2a to the back surface 2b), the side surfaces of the device chips 6 become cleavage surfaces.

[0072] On the other hand, regarding the case where the laser processing groove 60 or the cutting groove 72 is formed as the starting point of the division, since the depths of these grooves 60 and 72 correspond to the finished thickness of the device chip 6, by grinding the back surface 2b of the wafer 2 until the above thickness is reached, the grooves 60 and 72 appear on the back surface 2b of the wafer 2 to form the division groove 90. Thereby, the wafer 2 is divided into individual device chips 6. After grinding the back surface 2b of the wafer 2, cleaning water is supplied to the back surface 2b of the wafer 2 to clean the wafer 2, and at the same time, the wafer 2 is dried by blowing dry air onto the back surface 2b of the wafer 2.

[0073] (Sheet Arrangement Step) After performing the back surface grinding step and cleaning the wafer 2, a sheet arrangement step is performed in which a sheet 10 having elasticity is arranged on the back surface 2b of the wafer 2 and the protective member 58 is removed from the front surface 2a of the wafer 2. As shown in Fig. 17(a), in the sheet arrangement step, first, a circular sheet 10 whose periphery is fixed to a frame 8 having an annular shape is arranged on the back surface 2b of the wafer 2. The sheet 10 may be an adhesive tape or a thermocompression bonding sheet having elasticity. After arranging the sheet 10 on the back surface 2b of the wafer 2, as shown in Fig. 17(b), the protective member 58 is removed from the front surface 2a of the wafer 2.

[0074] (Expansion Step · Adhesive Liquid Coating Step) After performing the sheet placement step, an expansion step is performed to expand the sheet 10 and widen the intervals between the individual device chips 6. The expansion step includes an adhesive liquid coating step of coating the exposed surface (surface 2a) of the wafer 2 with an adhesive liquid 52 having fluidity before or after expanding the sheet 10, and causing the adhesive liquid 52 to penetrate into the dividing grooves 90. Similar to the separation step and the adhesive liquid coating step in the first embodiment, the expansion step and the adhesive liquid coating step can be performed using the expansion device 18 and the adhesive liquid coating device 20.

[0075] In the expansion step, first, the frame 8 is placed on the annular member 30 of the frame support portion 22, and the frame 8 is fixed to the annular member 30 with the clamp 32 (see FIG. 5). Regarding the wafer 2, with the surface 2a facing upward, the wafer 2 is placed on the suction chuck 34 of the wafer support portion 24 via the sheet 10. At this time, the height of the upper surface of the frame support portion 22 and the height of the upper surface of the wafer support portion 24 are made substantially the same. Also, at this point, the suction means of the wafer support portion 24 is not operated, and the wafer 2 is not sucked and held by the suction chuck 34.

[0076] Next, in the expansion step, after supporting the frame 8 by the frame support portion 22 and supporting the wafer 2 by the wafer support portion 24, the adhesive liquid coating step is performed. In the adhesive liquid coating step, after dropping the adhesive liquid 52 from the nozzle 46 onto the center of the wafer 2, the wafer 2 is rotated. As a result, the adhesive liquid 52 flows toward the outer periphery of the wafer 2 by centrifugal force, so that the adhesive liquid 52 can be coated on the surface 2a of the wafer 2 with a substantially uniform thickness. Note that, as the adhesive liquid 52, the examples of the adhesive liquid (for example, polyvinyl alcohol) can be used.

[0077] After coating the surface 2a of the wafer 2 with the adhesive liquid 52, the sheet 10 is expanded to widen the intervals between the individual device chips 6. Specifically, by lowering the frame support portion 22 by the expansion means 26, the upper surface of the frame support portion 22 is lowered below the upper surface of the wafer support portion 24. Then, since a radial tension is applied to the sheet 10, the sheet 10 expands and the intervals between the device chips 6 expand (see FIG. 6).

[0078] When the interval between the device chips 6 expands and the width of the dividing groove 90 between the device chips 6 increases, the adhesive liquid 52 penetrates into the dividing groove 90. In the second embodiment, since the dividing groove 90 has already been formed before the interval between the device chips 6 is expanded, when the surface 2a of the wafer 2 is coated with the adhesive liquid 52 (before expansion), the adhesive liquid 52 can penetrate into the dividing groove 90. However, by expanding the interval between the device chips 6, more adhesive liquid 52 penetrates into the dividing groove 90 than before the expansion. Then, the adhesive liquid 52 that has penetrated into the dividing groove 90 entangles the processing chips 56 remaining on the side surfaces of the device chips 6. Note that the processing chips 56 in the second embodiment include not only dust resulting from the destruction of the modified layer 16, but also cutting chips generated when forming the cutting grooves 72 and grinding chips generated in the back grinding process and pushed into the dividing groove 90 by the grinding wheel 88.

[0079] After performing the adhesive liquid coating step, the wafer 2 divided into individual device chips 6 is sucked and held on the upper surface of the suction chuck 34. That is, in a state where the sheet 10 is expanded, the suction means of the wafer support portion 24 is operated. As a result, since a suction force is generated on the upper surface of the suction chuck 34, the wafer 2 divided into individual device chips 6 is sucked and held on the upper surface of the suction chuck 34. As a result, even if the frame support portion 22 is raised to its original position, the interval between the device chips 6 can be maintained.

[0080] After individually sucking and holding the device chips 6 with the suction chuck 34, the frame support portion 22 is raised to its original position (the position before expanding the sheet 10). Then, while the interval between the device chips 6 is maintained at the interval when the sheet 10 is expanded, since no tension acts on the sheet 10, slack occurs in the sheet 10 between the wafer 2 and the frame 8 (see FIG. 7).

[0081] Therefore, also in the second embodiment, when the frame support portion 22 is raised to its original position, the shrinking means 28 is operated to heat and shrink the slack sheet 10 between the wafer 2 and the frame 8. Specifically, hot air is sent upward from the upper end of the shrinking means 28, or infrared rays are irradiated. As a result, the sheet 10 can be shrunk, and the slack of the sheet 10 can be removed (see FIG. 8). As a result, even when the suction holding by the suction chuck 34 is released, the interval between the device chips 6 is maintained at the interval when the sheet 10 is expanded.

[0082] (Solidified film forming step) After the expansion step is performed, in the same manner as in the first embodiment, a solidified film forming step is performed in which the adhesive liquid 52 is solidified in the expanded state of the sheet 10 to form a solidified film 52' (see FIG. 9).

[0083] (Processing waste removal step) After the solidified film forming step is performed, in the same manner as in the first embodiment, a processing waste removal step is performed in which the solidified film 52' is peeled off to remove the processing waste 56 attached to the side surface of the device chip 6 (see FIG. 10). When the adhesive liquid 52 enters the dividing groove 90, the adhesive liquid 52 entangles the processing waste 56. Therefore, by peeling the solidified film 52' in which the adhesive liquid 52 has solidified from the device chip 6, the processing waste 56 can be removed from the side surface of the device chip 6. Further, even if the processing waste 56 adheres to the surface of the device chip 6, the processing waste 56 can be removed from the surface of the device chip 6 by peeling the solidified film 52'. Therefore, also in the second embodiment, the problems caused by the processing waste 56 attached to the side surface and the surface of the device chip 6 can be solved.

[0084] (Washing step) Furthermore, also in the second embodiment, after the processing waste removal step is performed, it is preferable to perform a washing step of washing the wafer 2.

[0085] As described above, in both the first and second embodiments, the adhesive liquid 52 having fluidity entraps the machining chips 56 adhering to the side surface of the device chip 6. Therefore, by peeling off the solidified film 52' in which the adhesive liquid 52 has solidified, the machining chips 56 can be removed from the side surface of the device chip 6. As a result, in wire bonding, die bonding, and lamination of the device chip 6, which are performed in subsequent processes, the machining chips 56 do not fall or scatter from the side surface of the device chip 6. Further, even if the machining chips 56 adhere to the surface of the device chip 6, the machining chips 56 can be removed from the surface of the device chip 6 by peeling off the solidified film 52'. Therefore, in both the first and second embodiments, the problems caused by the machining chips 56 adhering to the side surface and the surface of the device chip 6 can be solved.

Explanation of Signs

[0086] 2: Wafer 2a: Surface of the wafer 2b: Back surface of the wafer 4: Division planned line 6: Device, device chip 10: Sheet 16: Modified layer (starting point of division) 52: Adhesive liquid 52’: Solidified film 54: Separation groove 56: Machining chips 58: Protection member 60: Laser processing groove (starting point of division) 72: Cutting groove (starting point of division) 90: Division groove

Claims

1. A method for processing a wafer that divides a wafer formed on a surface partitioned by a division planned line into individual device chips by a plurality of devices, comprising: a division start point forming step of forming a division start point on the division planned line; a sheet disposing step of disposing the wafer on a stretchable sheet before or after the division start point forming step; a separation step of expanding the sheet to apply an external force to the wafer to separate the wafer into individual device chips, wherein in the separation step, a pressure-sensitive adhesive liquid applying step is provided in which a pressure-sensitive adhesive liquid having fluidity is coated on the exposed surface of the wafer before or after expanding the sheet, and the pressure-sensitive adhesive liquid is allowed to penetrate into the separation groove formed by the separation; after the separation step, a solidified film forming step of solidifying the pressure-sensitive adhesive liquid in a state where the sheet is expanded to form a solidified film; A method for processing a wafer, comprising a processing waste removing step of peeling off the solidified film to remove processing waste adhering to the side surface of the device chip.

2. A method for processing a wafer that divides a wafer formed on a surface partitioned by a division planned line into individual device chips by a plurality of devices, comprising: a division start point forming step of forming a division start point on the division planned line; a protective member disposing step of disposing a protective member for protecting the surface of the wafer before or after the division start point forming step; a back grinding step of holding the protective member side on a chuck table after the division start point forming step, grinding the back surface of the wafer to finish it to a desired thickness, and forming a division groove on the division planned line to divide the wafer into individual device chips; a sheet disposing step of disposing a stretchable sheet on the back surface of the wafer and removing the protective member from the surface of the wafer; an expansion step of expanding the sheet to expand the interval between individual device chips, wherein in the expansion step, a pressure-sensitive adhesive liquid applying step is provided in which a pressure-sensitive adhesive liquid having fluidity is coated on the exposed surface of the wafer before or after expanding the sheet, and the pressure-sensitive adhesive liquid is allowed to penetrate into the division groove; after the expansion step, a solidified film forming step of solidifying the pressure-sensitive adhesive liquid in a state where the sheet is expanded to form a solidified film; A method for processing a wafer, comprising a processing waste removing step of peeling off the solidified film to remove processing waste adhering to the side surface of the device chip.

3. In the division start point forming step, The method for processing a wafer according to claim 1 or 2, wherein a laser beam having a wavelength that is transmissive to the wafer is irradiated onto the wafer with the focus point of the laser beam positioned inside the planned division line to form a modified layer that serves as a starting point for division.

4. The method for processing a wafer according to claim 1 or 2, further comprising a cleaning step of cleaning the wafer after the processing waste removal step.

5. The adhesive liquid is a water-soluble resin or a silicone-based adhesive resin containing any one of polyvinyl alcohol, polyethylene oxide, polyacrylamide, carboxymethyl cellulose, resol-type phenol resin, methylolated urea resin, methylolated melamine resin, vinyl acetate resin-based emulsion fixing material, and (PVA + borax). The method for processing a wafer according to claim 1 or 2.

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