Wafer processing method

Abstract

To provide a processing method for a wafer capable of solving a problem caused by processed waste adhering to a side face of a device chip.SOLUTION: A processing method for a wafer includes: a division start point forming step of forming a start point of division on a division schedule line; a protection member arranging step of arranging a protection member which protects a front face 2a of a wafer 2; a rear face grinding step of grinding a rear face 2b of the wafer 2 into a desired thickness, forming a dividing groove 48 on the division schedule line, and dividing the wafer 2 into device chips 50; a sheet arranging step of arranging an extensible / contractable sheet 54 on the rear face 2b of the wafer 2 and removing the protection member from the front face 2a of the wafer 2; an adhesive liquid coating step of coating the front face 2a of the wafer 2 with an adhesive liquid 56 having flowability; a sheet extending / contracting step of extending / contracting the sheet 54 in such a manner that the adhesive liquid 56 enters the dividing groove 48 and the adhesive liquid 56 is discharged from the dividing groove 48; and a washing step of removing the adhesive liquid 56 from the front face 2a of the wafer 2 and washing a side face of the dividing groove 48.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a wafer processing method for dividing a wafer having a plurality of devices formed on its surface by dividing lines into individual device chips. [Background technology]

[0002] A wafer has a plurality of devices such as ICs and LSIs formed on its surface, separated by planned dividing lines. The back surface is ground to the desired thickness, and then the wafer is divided into individual device chips using a dicing machine and a laser processing machine. Each of the divided device chips is used in electrical equipment such as mobile phones and personal computers.

[0003] The present applicant has also proposed a technology in which the focal point of a laser beam having a wavelength that is transparent to the wafer is positioned inside the intended dividing line, the laser beam is irradiated onto the wafer, and a modified layer that serves as the starting point for dividing is formed, and then the back surface of the wafer is ground to the desired thickness and the wafer is divided into individual device chips (see, for example, Patent Document 1).

[0004] The technology described in Patent Document 1 has the advantage that the focal point of the laser beam is positioned inside the wafer before grinding (i.e., a relatively thick wafer), and therefore a modified layer can be formed appropriately inside the dividing lines. However, if the wafer is too thin, it becomes difficult to position the focal point of the laser beam inside the dividing lines, and there may be an area inside the dividing lines where no modified layer is formed.

[0005] Furthermore, the technology described in Patent Document 1 not only allows the wafer to be formed to the desired thickness, but also has the advantage that cracks extending from the modified layer to the surface during grinding cause the wafer to be divided into individual device chips by cleavage, thereby increasing the flexural strength of the device chips even when the wafer is finished to be thin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-78569 Summary of the Invention [Problem to be solved by the invention]

[0007] However, processing debris generated during grinding can get into the division grooves formed along the division lines and adhere to the side surfaces of the device chips. In such cases, the processing debris that falls and scatters from the side surfaces of the device chips can interfere with bonding during subsequent processes such as wire bonding, die bonding, and stacking of device chips, and can also adhere to the surfaces of the device chips, damaging the stacked device chips.

[0008] Such problems can also occur in a technique known as pre-dicing (see, for example, Japanese Patent Application Laid-Open No. 11-40520), in which grooves having a depth equivalent to the finished thickness of the device chips are formed along the intended dividing line as the starting point for dividing, and the back surface of the wafer is ground until the thickness reaches the finished thickness of the device chips to divide the wafer into individual device chips.

[0009] An object of the present invention is to provide a wafer processing method that can solve the problems caused by processing debris adhering to the side surfaces of device chips. [Means for solving the problem]

[0010] According to the present invention, there is provided the following wafer processing method that solves the above-mentioned problems. "A wafer processing method for dividing a wafer having a plurality of devices formed on its surface by dividing lines into individual device chips, a division starting point forming step of forming a division starting point on the planned division line; a protective member providing step of providing a protective member for protecting the surface of the wafer before or after the dividing start point forming step; a backside grinding step in which the protective member side of the wafer is held on a chuck table and the backside of the wafer is ground to a desired thickness, and division grooves are formed along the intended division lines 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 front surface of the wafer; an adhesive liquid coating step of coating a surface of the wafer with an adhesive liquid having fluidity; a sheet stretching step of stretching the sheet disposed in the sheet disposing step so as to expand the width of the dividing grooves to allow the adhesive liquid to penetrate into the dividing grooves and to contract the width of the dividing grooves to discharge the adhesive liquid from the dividing grooves; and a cleaning step of removing the adhesive liquid from the surface of the wafer and cleaning at least the side surfaces of the division grooves.

[0011] Preferably, in the dividing starting point forming step, the focal point of a laser beam having a wavelength that is transparent to the wafer is positioned inside the intended dividing line, and the laser beam is irradiated onto the wafer to form a modified layer that will serve as the dividing starting point.

[0012] In the dividing starting point forming step, it is desirable to form grooves having a depth corresponding to the finished thickness of the device chips along the dividing lines to serve as dividing starting points.

[0013] The protective member providing step may be performed after the division start point forming step.

[0014] The adhesive used in the adhesive coating step contains any one of polyvinyl alcohol, polyethylene oxide, polyacrylamide, carboxymethyl cellulose, resol-type phenolic resin, methylolated urea resin, and methylolated melamine resin, and it is preferable that the adhesive be removed by supplying washing water in the washing step. [Effects of the Invention]

[0015] The wafer processing method of the present invention includes: a division starting point forming step of forming a division starting point on the planned division line; a protective member providing step of providing a protective member for protecting the surface of the wafer before or after the dividing start point forming step; a backside grinding step in which the protective member side of the wafer is held on a chuck table and the backside of the wafer is ground to a desired thickness, and division grooves are formed along the intended division lines 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 front surface of the wafer; an adhesive liquid coating step of coating a surface of the wafer with an adhesive liquid having fluidity; a sheet stretching step of stretching the sheet disposed in the sheet disposing step so as to expand the width of the dividing grooves to allow the adhesive liquid to penetrate into the dividing grooves and to contract the width of the dividing grooves to discharge the adhesive liquid from the dividing grooves; and a cleaning step of removing the adhesive liquid from the surface of the wafer and cleaning at least the side surfaces of the division grooves. By capturing the processing debris adhering to the side surfaces of the device chips with the fluid adhesive liquid and then cleaning the side surfaces of the division grooves, the processing debris can be removed from the side surfaces of the device chips together with the adhesive liquid, thereby solving problems caused by processing debris adhering to the side surfaces of the device chips. [Brief explanation of the drawings]

[0016] [Figure 1] Schematic diagram showing a protective member disposing step. [Figure 2] (a) Schematic diagram of forming a modified layer in the dividing starting point forming process, (b) Cross-sectional view of a wafer on which a modified layer has been formed along the planned dividing line, (c) Perspective view of a wafer on which a modified layer has been formed along the planned dividing line. [Figure 3] 10 is a schematic diagram illustrating a case where a groove having a depth corresponding to the finished thickness of a device chip is formed by ablation processing in a division starting point forming step. [Figure 4]10 is a schematic diagram illustrating a case where a groove having a depth corresponding to the finished thickness of a device chip is formed by cutting in a dividing starter forming step. FIG. [Figure 5] (a) A schematic diagram showing the state in which a protective member is disposed on the surface of a wafer on which grooves of a depth corresponding to the finished thickness of the device chips are formed along the planned dividing lines, and (b) a cross-sectional view showing the state in which a protective member is disposed on the surface of the wafer shown in (a). [Figure 6] FIG. 2(a) is a schematic diagram showing a back grinding process, and FIG. 2(b) is a perspective view of a wafer on which division grooves are formed. [Figure 7] (a) A schematic diagram showing the state in which an expandable sheet is placed on the back surface of a wafer in the sheet placement process, and (b) a schematic diagram showing the state in which a protective member is removed from the front surface of the wafer in the sheet placement process. [Figure 8] (a) Schematic diagram showing the adhesive liquid coating step, (b) Cross-sectional view of a wafer coated with adhesive liquid. [Figure 9] Schematic diagram showing a sheet stretching process. [Figure 10] Schematic diagram showing a cleaning process. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, preferred embodiments of the wafer processing method of the present invention will be described with reference to the drawings.

[0018] (Wafer 2) 1 shows a disk-shaped wafer 2 to be processed by the wafer processing method of the present invention. The wafer 2 may be made of an appropriate semiconductor material such as silicon. The surface 2a of the wafer 2 is partitioned into a plurality of rectangular regions by grid-like dividing lines 4, and a device 6 such as an IC or LSI is formed in each of the rectangular regions.

[0019] (Protective member installation process) 1, a protective member providing step is first carried out in which a protective member 8 is provided to protect the front surface 2a of the wafer 2. A circular adhesive tape having a diameter substantially the same as that of the wafer 2 can be used as the protective member 8. Then, the protective member 8 is attached to the front surface 2a of the wafer 2.

[0020] (Split starting point formation process) In the illustrated embodiment, after the protective member providing step is performed, a dividing start point forming step is performed in which dividing start points are formed on the planned dividing lines 4.

[0021] The dividing starting point forming step can be performed using, for example, a laser processing apparatus 10 shown in Fig. 2(a) The laser processing apparatus 10 includes a chuck table 12 that suction-holds the wafer 2, an oscillator (not shown) that oscillates a pulsed laser beam LB having a wavelength that is transparent to the wafer 2, a condenser 14 that condenses the pulsed laser beam LB oscillated by the oscillator and irradiates the wafer 2 suction-held on the chuck table 12 with the condensed laser beam, and an imaging means (not shown) that images the wafer 2 suction-held on the chuck table 12.

[0022] The chuck table 12 is configured to be rotatable about an axis extending in the vertical direction, and to be movable in the X-axis direction indicated by the arrow X in Fig. 2(a) and the Y-axis direction (the direction indicated by the arrow Y in Fig. 2(a)) perpendicular to the X-axis direction. The XY plane defined by the X-axis direction and the Y-axis direction is substantially horizontal.

[0023] The imaging means includes a conventional imaging element (CCD) that images the wafer 2 using visible light, an infrared irradiation means that irradiates infrared light that passes through the wafer 2, an optical system that captures the infrared light irradiated by the infrared irradiation means, and an imaging element (infrared CCD) that outputs an electrical signal corresponding to the infrared light captured by the optical system.

[0024] 2(a), in the dividing starting point forming step, first, the wafer 2 is suction-held on the upper surface of the chuck table 12 with the back surface 2b of the wafer 2 facing upward. Next, infrared rays are irradiated from the imaging means, and the front surface 2a side of the wafer 2 is imaged by the infrared rays transmitted through the back surface 2b of the wafer 2. Based on the image of the wafer 2 imaged by the imaging means, the dividing lines 4 are aligned in the X-axis direction. Furthermore, a laser beam LB is aimed at the dividing lines 4 aligned in the X-axis direction, and the focal point of the laser beam LB is positioned inside the dividing lines 4.

[0025] Next, while the chuck table 12 is being processed and fed in the X-axis direction, a laser beam LB having a wavelength that is transparent to the wafer 2 is irradiated onto the wafer 2 from the condenser 14, and a modified layer 16 that serves as the starting point for division is formed inside the wafer 2 along the planned division lines 4, as shown in Figures 2(a) and 2(b). From the viewpoint of preventing a decrease in the bending strength of the device chips, it is preferable to form the modified layer 16 to a depth that can be removed when the back surface 2b of the wafer 2 is ground in the back surface grinding step described below.

[0026] Next, the chuck table 12 is indexed and fed in the Y-axis direction relative to the condenser 14 by an amount corresponding to the spacing in the Y-axis direction of the planned dividing lines 4. Then, by alternately repeating the irradiation of the laser beam LB and the indexing and feeding, modified layers 16 are formed inside the wafer 2 along all of the planned dividing lines 4 aligned in the X-axis direction.

[0027] Then, the chuck table 12 is rotated 90 degrees, and irradiation of the laser beam LB and indexing are alternately repeated to form modified layers 16 inside the wafer 2 along all of the planned dividing lines 4 that are perpendicular to the dividing lines 4 on which the modified layers 16 were previously formed. In this manner, the dividing start point forming step is carried out, and lattice-shaped modified layers 16 are formed inside the wafer 2 along the lattice-shaped planned dividing lines 4, as shown in Figure 2(c).

[0028] Such a division starting point forming step can be carried out, for example, under the following processing conditions. Pulse laser beam wavelength: 1342nm Average power: 1.0W Repetition frequency: 90kHz Feed speed: 700mm / s

[0029] In the above description, the modified layer 16 is formed by irradiating the laser beam LB from the back surface 2b side of the wafer 2, but the modified layer 16 may also be formed by irradiating the laser beam LB from the front surface 2a side of the wafer 2, in which case the protective member arrangement process is carried out after the splitting starting point formation process.

[0030] In the illustrated embodiment, an example has been described in which the modified layer 16 is formed as the starting point for division, but it is also possible to form grooves having a depth corresponding to the finished thickness of the device chips on the front surface 2a of the wafer 2 along the planned division lines 4 to serve as starting points for division. Such grooves can be formed by ablation processing using irradiation with a laser beam or by cutting processing using a dicing device.

[0031] (Ablation processing) Explaining with reference to Figure 3, in the case of ablation processing, before a protective member 8 is placed on the front surface 2a of the wafer 2, the wafer 2 is suction-held by the chuck table 12 with the front surface 2a facing upward. Next, the planned dividing line 4 is aligned in the X-axis direction, and a laser beam LB' having a wavelength that is absorbent for the wafer 2 is aimed at the planned dividing line 4. In addition, the focal point of the laser beam LB' is positioned on the front surface 2a.

[0032] Then, by irradiating the wafer 2 with the laser beam LB' while feeding the chuck table 12 in the X-axis direction, laser-processed grooves 18 having a depth corresponding to the finished thickness of the device chips can be formed in the surface 2a along the planned dividing lines 4. As in the case of forming the modified layer 16, irradiation of the laser beam LB' and indexing feed are alternately repeated to form lattice-shaped laser-processed grooves 18 in the surface 2a along the lattice-shaped planned dividing lines 4.

[0033] When the starting point of the division is the laser processed groove 18, the division starting point forming step can be carried out under the following processing conditions, for example. Laser beam wavelength: 355nm Average power: 2.0W Repetition frequency: 80kHz Feed speed: 300mm / s

[0034] (cutting) When forming grooves by cutting, for example, a dicing device 20 shown in Fig. 4 can be used. The dicing device 20 includes a chuck table 22 that holds the wafer 2 by suction, and cutting means 24 that cuts the wafer 2 held by suction on the chuck table 22. The cutting means 24 includes a spindle 26 that is configured to be rotatable about the Y-axis direction, and an annular cutting blade 28 fixed to the tip of the spindle 26.

[0035] In the case of cutting, before the protective member 8 is placed on the front surface 2a of the wafer 2, the wafer 2 is suction-held on the upper surface of the chuck table 22 with the front surface 2a facing upward. Next, the cutting edge of the cutting blade 28, which is rotated at high speed, is cut into the planned division lines 4 aligned in the X-axis direction, from the front surface 2a to a depth corresponding to the finished thickness of the device chips, and the chuck table 22 is moved in the X-axis direction while cutting water is supplied to the part where the cutting edge of the cutting blade 28 is to be cut.

[0036] This allows cutting grooves 30 having a depth corresponding to the finished thickness of the device chip to be formed along the planned dividing lines 4. When performing cutting processing, the formation of cutting grooves 30 and indexing feed are repeated alternately to form grid-like cutting grooves 30 on the surface 2a along the grid-like planned dividing lines 4.

[0037] When the cutting groove 30 is used as the starting point of the division, the division starting point forming step can be carried out under the following processing conditions, for example. Cutting blade diameter: φ50mm Cutting blade rotation speed: 30,000 rpm Cutting water supply: 2 liters / min Feed speed: 50mm / s

[0038] The grooves 18, 30 serving as starting points for division are formed on the front surface 2a side of the wafer 2. Therefore, when forming the grooves 18, 30 as starting points for division, the protective member disposing step is carried out after the dividing starting point forming step, as shown in Figures 5(a) and 5(b).

[0039] (Back grinding process) After the protective member placement process and the division starting point formation process are performed, the protective member 8 side is held on a chuck table, and the back surface 2b of the wafer 2 is ground to the desired thickness, and a back surface grinding process is performed in which division grooves are formed along the planned division lines 4 to divide the wafer 2 into individual device chips.

[0040] The back surface grinding step can be performed using, for example, a grinding device 32 shown in Fig. 6(a) . The grinding device 32 includes a chuck table 34 that holds the wafer 2 by suction, and a grinding means 36 that grinds the wafer 2 held by suction on the chuck table 34.

[0041] The grinding means 36 includes a spindle 38 extending in the vertical direction and a disk-shaped wheel mount 40 fixed to the lower end of the spindle 38. An annular grinding wheel 44 is fastened to the underside of the wheel mount 40 by bolts 42. A plurality of grinding stones 46 are fixed to the outer periphery of the underside of the grinding wheel 44, and are arranged in an annular shape at intervals in the circumferential direction.

[0042] In the backside grinding process, first, the wafer 2 is suction-held on the upper surface of the chuck table 34 with the backside 2b of the wafer 2 facing upward. Next, the spindle 38 is rotated at a predetermined rotational speed (e.g., 6000 rpm) in the direction indicated by the arrow R1 in Figure 6(a). Also, the chuck table 34 is rotated at a predetermined rotational speed (e.g., 300 rpm) in the direction indicated by the arrow R2.

[0043] Next, the spindle 38 is lowered to bring the grinding wheel 46 into contact with the back surface 2b of the wafer 2, and grinding water is supplied to the portion of the back surface 2b where the grinding wheel 46 is in contact. Thereafter, the spindle 38 is lowered at a predetermined grinding feed rate (for example, 1.0 μm / s), thereby grinding the back surface 2b of the wafer 2 and thinning the wafer 2 to the finished thickness of the device chips.

[0044] When the modified layer 16 is formed as a starting point for division, cracks extend from the modified layer 16 in the thickness direction of the wafer 2 due to the pressing force acting when the wafer 2 is ground, and the wafer 2 is divided into individual device chips 50, as shown in Fig. 6(b). In addition, the cracks extending from the modified layer 16 form division grooves 48 (grooves extending from the front surface 2a to the back surface 2b), and the side surfaces of the device chips 50 become cleavage planes.

[0045] On the other hand, when laser processed grooves 18 or machined grooves 30 are formed as starting points for division, the depth of these grooves 18, 30 corresponds to the finished thickness of the device chips 50, and so by grinding the back surface 2b of the wafer 2 until the above thickness is reached, the grooves 18, 30 appear on the back surface 2b of the wafer 2 and form division grooves 48. In this way, the wafer 2 is divided into individual device chips 50.

[0046] (Sheet placement process) After the back surface grinding step is performed, a sheet providing step is performed in which a stretchable sheet is provided on the back surface 2b of the wafer 2 and the protective member 8 is removed from the front surface 2a of the wafer 2.

[0047] In the sheet disposing step, as shown in FIG. 7(a), the wafer 2 is disposed on a circular sheet 54 fixed to a frame 52 having an annular periphery. A stretchable adhesive tape (for example, a vinyl chloride adhesive tape) can be used as the sheet 54. In this case, the back surface 2b of the wafer 2 is adhered to the adhesive surface of the sheet 54. After the sheet 54 is disposed on the back surface 2b, the protective member 8 is removed from the front surface 2a as shown in FIG. 7(b).

[0048] (Adhesive liquid coating process) After the sheet disposing step is performed, an adhesive liquid coating step is performed in which the surface 2a of the wafer 2 is coated with an adhesive liquid having fluidity.

[0049] 8(a), in the adhesive liquid coating step, the front surface 2a of the wafer 2 is faced upward, and a fluid adhesive liquid 56 is dripped onto the center of the front surface 2a. In the cleaning step described below, it is preferable to use a water-soluble resin as the adhesive liquid 56 so that the adhesive liquid 56 can be easily removed from the wafer 2. Examples of water-soluble resins that can be used as the adhesive liquid 56 include polyvinyl alcohol, polyethylene oxide, polyacrylamide, carboxymethyl cellulose, resol-type phenolic resin, methylolated urea resin, and methylolated melamine resin.

[0050] After the adhesive liquid 56 is dropped onto the center of the front surface 2a of the wafer 2, the wafer 2 is rotated in the direction indicated by the arrow R3, and centrifugal force causes the adhesive liquid 56 to flow. This allows the adhesive liquid 56 to coat the front surface 2a with a substantially uniform thickness, as shown in Figure 8(b).

[0051] (Sheet stretching process) After the adhesive liquid coating process is performed, a sheet stretching process is performed in which the width of the dividing groove 48 is expanded to allow the adhesive liquid 56 to penetrate into the dividing groove 48, and the width of the dividing groove 48 is reduced to expel the adhesive liquid 56 from the dividing groove 48, thereby stretching the sheet 54 arranged in the sheet arrangement process.

[0052] The sheet stretching process can be carried out using, for example, a stretching device 58 shown in Fig. 9. The stretching device 58 includes a cylindrical drum 60, an annular holding member 62 arranged on the outer periphery of the drum 60, and a plurality of air cylinders 64 that raise and lower the holding member 62. A plurality of clamps 66 are arranged at intervals in the circumferential direction on the outer periphery of the holding member 62.

[0053] In the sheet stretching process, first, the frame 52 is placed on the upper surface of the holding member 62 with the wafer 2, on which the dividing grooves 48 have been formed, facing upward. Next, the frame 52 is fixed with multiple clamps 66. Next, the holding member 62 is lowered by multiple air cylinders 64, applying radial tension to the sheet 54. This causes the width of the dividing grooves 48 to expand, as shown by the two-dot chain lines in Figure 9, and the adhesive liquid 56 penetrates into the dividing grooves 48.

[0054] Next, the holding member 62 is raised by the multiple air cylinders 64, the radial tension applied to the sheet 54 is released, the width of the dividing grooves 48 is reduced, and the adhesive liquid 56 is discharged from the dividing grooves 48. In this way, the width of the dividing grooves 48 is expanded and reduced multiple times, and the adhesive liquid 56 is repeatedly introduced into the dividing grooves 48 and discharged from the dividing grooves 48, so that the processing debris adhering to the side surfaces of the device chips 50 can be captured by the adhesive liquid 56.

[0055] (Cleaning process) After the sheet stretching step is performed, the adhesive liquid 56 is removed from the front surface 2a of the wafer 2, and a cleaning step is performed to clean at least the side surfaces of the dividing grooves 48.

[0056] 10, in the cleaning process, cleaning water 68 is supplied from above toward the wafer 2 (device chips 50) while the width of the dividing grooves 48 is expanded by the expansion device 58. This makes it possible to remove processing debris together with the adhesive liquid 56 from the surfaces and sides of the device chips 50.

[0057] As described above, in the wafer processing method of the illustrated embodiment, the processing debris adhering to the side of the device chip 50 is captured by the fluid adhesive liquid 56, and then the side of the division groove 48 is washed, thereby removing the processing debris together with the adhesive liquid 56 from the side of the device chip 50.

[0058] Therefore, in wire bonding, die bonding, stacking of device chips 50, etc., which are performed in later processes, the problem of processing debris falling or scattering from the side of the device chip 50 interfering with bonding and adhering to the surface of the device chip 50 and damaging the stacked device chips 50 can be eliminated. [Explanation of symbols]

[0059] 2: Wafer 2a: Surface of wafer 2b: Backside of wafer 4: Planned division line 6: Device 8: Protective material 16: Modified layer (starting point of division) 18: Laser processed groove (starting point of division) 30: Cutting groove (starting point of division) 48: Dividing groove 50: Device chip 54: Sheet 56:Adhesive liquid 68: Cleaning water

Claims

1. A wafer processing method for dividing a wafer having a plurality of devices formed on a surface thereof by division lines into individual device chips, comprising: a division starting point forming step of forming a division starting point on the planned division line; a protective member providing step of providing a protective member for protecting the surface of the wafer before or after the dividing start point forming step; a backside grinding step in which the protective member side of the wafer is held on a chuck table and the backside of the wafer is ground to a desired thickness, and division grooves are formed along the intended division lines 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 front surface of the wafer; an adhesive liquid coating step of coating a surface of the wafer with an adhesive liquid having fluidity; a sheet stretching step of stretching the sheet disposed in the sheet disposing step so as to expand the width of the dividing grooves to allow the adhesive liquid to penetrate into the dividing grooves and to contract the width of the dividing grooves to discharge the adhesive liquid from the dividing grooves; a cleaning step of removing the adhesive liquid from the surface of the wafer and cleaning at least the side surfaces of the division grooves.

2. In the division starting point forming step, 2. A wafer processing method according to claim 1, wherein the focal point of a laser beam having a wavelength that is transparent to the wafer is positioned within the intended dividing line, and the laser beam is irradiated onto the wafer to form a modified layer that serves as the starting point for dividing.

3. In the division starting point forming step, 2. The wafer processing method according to claim 1, wherein grooves having a depth corresponding to the finished thickness of the device chips are formed along the intended dividing lines to serve as starting points for dividing.

4. 4. The wafer processing method according to claim 3, wherein the protective member providing step is carried out after the dividing start point forming step.

5. the adhesive used in the adhesive coating step contains any one of polyvinyl alcohol, polyethylene oxide, polyacrylamide, carboxymethyl cellulose, resol-type phenolic resin, methylolated urea resin, and methylolated melamine resin; 2. The wafer processing method according to claim 1, wherein in said cleaning step, cleaning water is supplied to remove the adhesive liquid.

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