Processing method of wafer

Abstract

To provide a processing method of a wafer, capable of positioning a condensing point of a laser beam to an appropriate position.SOLUTION: A processing method of a wafer includes steps of: bonding a protection tape 12 onto a front surface of a wafer 2; forming a sample modified layer 56 by radiating a laser beam to the wafer 2 from a back surface 2b of the wafer 2; dividing the wafer 2 by applying an external force along the sample modified layer 56 and generating a sample piece 58; generating measurement data by exposing a cross section by folding the sample piece 58 to the protection tape 12 side, imaging it with imaging means 22, and measuring a position of the sample modified layer 56 in a thickness direction of the wafer 2 and a thickness of a device layer 4; setting an appropriate position of a condensing point of the laser beam that is positioned in an internal part of the wafer 2 on the basis of the measurement data; forming a modified layer by radiating the laser beam to the wafer 2 so that the condensing point of the laser beam is positioned at a position set in a condensing point position setting step; and dividing the wafer 2 into individual device chips by applying an external force to a division schedule line.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for processing a wafer having a device layer formed on its surface, the device layer having a plurality of devices partitioned by planned division lines. [Background technology]

[0002] Wafers, on whose surface multiple devices such as ICs and LSIs are formed and partitioned along planned dividing lines, are then divided into individual device chips by a laser processing machine, and each of the divided device chips is used in electrical equipment such as mobile phones and personal computers.

[0003] The laser processing device includes a chuck table that holds the wafer, a laser beam application means that positions the focal point of a laser beam having a wavelength that is transparent to the wafer held on the chuck table inside the area corresponding to the planned division line and irradiates the wafer with the laser beam to form a modified layer that serves as the starting point for division, a feed means that moves the chuck table and the laser beam application means relatively, and an imaging means that images the wafer held on the chuck table to detect the planned division line (see, for example, Patent Document 1). An external force is then applied to the wafer on which the modified layer has been formed by the laser processing device, and the wafer is divided into individual device chips. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-81333 A Summary of the Invention [Problem to be solved by the invention]

[0005] When performing laser processing on a wafer, if the focal point of the laser beam is not positioned properly, the device formed on the surface of the wafer may be damaged. A device is composed of multiple stacked circuits, and even if the manufacturer and type of device are the same, the thickness of the device layer may differ slightly. Furthermore, slight differences in the thickness of the device layer may cause the focal point of the laser beam to be positioned improperly, resulting in damage to the device.

[0006] An object of the present invention is to provide a wafer processing method capable of positioning the focal point of a laser beam at an appropriate position. [Means for solving the problem]

[0007] According to the present invention, there is provided the following wafer processing method that solves the above problems. "A method for processing a wafer having a device layer formed on its surface, the device layer being partitioned by division lines, comprising: a protective tape application step of applying a protective tape to a surface of the wafer; a trial modified layer forming step of forming a trial modified layer by irradiating the wafer with a laser beam having a wavelength that is transparent to the wafer from the back surface of the wafer, the laser beam being focused on the wafer at a focal point inside the wafer; a sample piece generating step of dividing the wafer by applying an external force along the trial modified layer to generate a sample piece; a measurement data generating step of bending the sample piece toward the protective tape side to expose a cross section, imaging the cross section with an imaging means, measuring the position of the trial modified layer in the thickness direction of the wafer and the thickness of the device layer, and generating measurement data; a focal point position setting step of setting an appropriate position of a focal point of the laser beam to be positioned inside the wafer based on the measurement data; a modified layer forming step of returning the sample piece to its original state, positioning the focal point of the laser beam at the position set in the focal point position setting step, and irradiating the wafer with the laser beam to form a modified layer; and a dividing step of dividing the wafer into individual device chips by applying an external force along the intended dividing lines.

[0008] Preferably, in the trial modified layer forming step, the trial modified layer is formed in an outer peripheral excess region of the wafer. In the dividing step, it is preferable that the back surface of the wafer is ground with a grinding wheel to thin the wafer, and the wafer is divided into individual device chips by an external force applied by the grinding. Effect of the Invention

[0009] The wafer processing method of the present invention includes the steps of: A method for processing a wafer having a device layer formed on a surface thereof, the device layer having a plurality of devices partitioned by planned division lines, comprising the steps of: a protective tape application step of applying a protective tape to a surface of the wafer; a trial modified layer forming step of forming a trial modified layer by irradiating the wafer with a laser beam having a wavelength that is transparent to the wafer from the back surface of the wafer, the laser beam being focused on the wafer at a focal point inside the wafer; a sample piece generating step of dividing the wafer by applying an external force along the trial modified layer to generate a sample piece; a measurement data generating step of bending the sample piece toward the protective tape side to expose a cross section, imaging the cross section with an imaging means, measuring the position of the trial modified layer in the thickness direction of the wafer and the thickness of the device layer, and generating measurement data; a focal point position setting step of setting an appropriate position of a focal point of the laser beam to be positioned inside the wafer based on the measurement data; a modified layer forming step of returning the sample piece to its original state, positioning the focal point of the laser beam at the position set in the focal point position setting step, and irradiating the wafer with the laser beam to form a modified layer; Since the method includes a dividing step of dividing the wafer into individual device chips by applying an external force to the dividing lines, the focal point of the laser beam can be positioned at an appropriate position. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2A is a perspective view of a wafer and a protective tape, and FIG. 2B is a perspective view of a wafer with a protective tape attached to its front surface, as viewed from its back surface. [Diagram 2] FIG. [Diagram 3] 1(a) is a perspective view showing the wafer shown in FIG. 1(b) being placed on a chuck table, and FIG. [Figure 4] FIG. 2 is a perspective view of a wafer on which a sample piece is produced. [Diagram 5] FIG. [Figure 6] FIG. [Figure 7] FIG. 2 is a perspective view of a wafer on which a modified layer is formed. [Figure 8] FIG. [Figure 9] FIG. 2 is a perspective view of a wafer divided into device chips. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, preferred embodiments of the wafer processing method according to the present invention will be described with reference to the drawings.

[0012] (Wafer 2) 1 shows a disk-shaped wafer 2 that can be processed by the wafer processing method according to the present invention. The wafer 2 can be made of an appropriate semiconductor material such as silicon. A device layer 4 is formed on the surface of the wafer 2, and a plurality of devices 6 such as ICs and LSIs are partitioned in the device layer 4 by lattice-shaped division lines 8. A notch 10 indicating a crystal orientation is provided on the periphery of the wafer 2. The total thickness of the wafer 2 including the device layer 4 is, for example, about 300 μm.

[0013] (Protective tape application process) In the illustrated embodiment, a protective tape application step is first performed in which a protective tape is applied to the surface of the wafer 2. As shown in FIG. 1, the protective tape 12 may be circular and have a diameter substantially equal to that of the wafer 2. The protective tape 12 may be an adhesive tape having an adhesive layer (glue layer) on one side, or may be a thermocompression sheet having no adhesive layer. The thermocompression sheet is a sheet of thermoplastic synthetic resin (e.g., polyolefin resin), which softens or melts when heated to a temperature near the melting point and exerts adhesive force.

[0014] (Trial modified layer formation process) After carrying out the protective tape application process, a trial modified layer formation process is carried out in which a focal point of a laser beam having a wavelength that is transparent to the wafer 2 is positioned inside the wafer 2 from the back surface 2b of the wafer 2, and the laser beam is irradiated onto the wafer 2 to form a trial modified layer.

[0015] The trial modified layer forming step can be carried out, for example, by using a laser processing device 14 shown in Fig. 2. The laser processing device 14 includes a holding means 16 for holding the wafer 2, a laser beam application means 18 for irradiating the wafer 2 held by the holding means 16 with a laser beam, a feeding means 20 for relatively moving the holding means 16 and the laser beam application means 18, and an imaging means 22 for imaging the wafer 2 held by the holding means 16 to detect the planned division lines 8.

[0016] (Holding means 16) The holding means 16 includes an X-axis movable plate 26 supported on the upper surface of the base 24 so as to be movable in the X-axis direction, a Y-axis movable plate 28 supported on the upper surface of the X-axis movable plate 26 so as to be movable in the Y-axis direction, a support 30 fixed to the upper surface of the Y-axis movable plate 28, and a cover plate 32 fixed to the upper end of the support 30. A long hole 32a extending in the Y-axis direction is formed in the cover plate 32, and a chuck table 34 extending upward through the long hole 32a is rotatably attached to the upper end of the support 30. A porous circular suction chuck 36 connected to a suction means (not shown) is disposed at the upper end of the chuck table 34. In the holding means 16, the suction means generates a suction force on the upper surface of the suction chuck 36, and the wafer 2 placed on the upper surface of the chuck table 34 is suction-held. The chuck table 34 is rotated by a chuck table motor (not shown) built into the support 30.

[0017] The X-axis direction is the direction indicated by the arrow X in Fig. 2, and the Y-axis direction is the direction indicated by the arrow Y in Fig. 2, which is a direction perpendicular to the X-axis direction. The XY plane defined by the X-axis and Y-axis directions is substantially horizontal.

[0018] (Laser beam irradiation means 18) The laser beam application means 18 includes a housing 38 that extends upward from the upper surface of the base 24 and then extends substantially horizontally, an oscillation means (not shown) built into the housing 38, and a condenser 40 arranged on the lower surface at the tip of the housing 38. The oscillation means oscillates a pulsed laser beam LB having a wavelength that is transparent to the wafer 2. The condenser 40 condenses the pulsed laser beam LB oscillated by the oscillator, and irradiates the wafer 2 held by the holding means 16 with the pulsed laser beam LB.

[0019] (Feeding means 20) The feed means 20 includes an X-axis feed means 42 that moves the chuck table 34 in the X-axis direction, and a Y-axis feed means 44 that moves the chuck table 34 in the Y-axis direction.

[0020] The X-axis feed means 42 has a ball screw 46 connected to the X-axis movable plate 26 and extending in the X-axis direction, and a motor 48 that rotates the ball screw 46. The X-axis feed means 42 converts the rotational motion of the motor 48 into linear motion using the ball screw 46 and transmits it to the X-axis movable plate 26, moving the X-axis movable plate 26 in the X-axis direction along the pair of guide rails 24a on the base 24. This causes the chuck table 34 to move in the X-axis direction.

[0021] The Y-axis feed means 44 has a ball screw 50 connected to the Y-axis movable plate 28 and extending in the Y-axis direction, and a motor 52 that rotates the ball screw 50. The Y-axis feed means 44 converts the rotational motion of the motor 52 into linear motion using the ball screw 50 and transmits it to the Y-axis movable plate 28, moving the Y-axis movable plate 28 in the Y-axis direction along the pair of guide rails 26a on the X-axis movable plate 26. This causes the chuck table 34 to move in the Y-axis direction.

[0022] (Imaging means 22) The imaging means 22 is attached to the underside of the tip of the housing 38 at a distance from the light collector 40. Although not shown, the imaging means 22 includes a normal imaging element (CCD) that images the wafer 2 with visible light, infrared irradiating means that irradiates infrared light that penetrates the wafer 2, an optical system that captures the infrared light irradiated by the infrared irradiating means, and an imaging element (infrared CCD) that outputs an electrical signal corresponding to the infrared light captured by the optical system. In addition, a monitor 54 that displays an image captured by the imaging means 22 is provided on the upper surface of the housing 38.

[0023] In the trial modified layer forming process, first, the wafer 2 is suction-held on the chuck table 34. As shown in Fig. 3(a), the wafer 2 is placed on the upper surface of the chuck table 34 with the back surface 2b of the wafer 2 facing up, and then the suction means is operated to generate a suction force on the upper surface of the suction chuck 36. In this manner, the wafer 2 is suction-held on the chuck table 34.

[0024] Once the wafer 2 is held by suction on the chuck table 34, the focal point of the laser beam LB is positioned inside the wafer 2. First, the feed means 20 is operated to position the wafer 2 directly below the imaging means 22, and the imaging means 22 captures an image of the wafer 2. Next, based on the image of the wafer 2, the positional relationship between the collector 40 and the wafer 2 is adjusted to position the focal point of the laser beam LB inside the wafer 2 on the outer periphery side of the wafer 2. The height direction position of the focal point at this time is on the device layer 4 side (the lower surface side of the wafer 2), but is a position that does not reach the device layer 4 (a position above the device layer 4).

[0025] After positioning the focal point, the wafer 2 is irradiated with the laser beam LB to form a trial modified layer on the underside of the wafer 2. Specifically, as shown in Fig. 3(b), the wafer 2 is irradiated with the laser beam LB having a wavelength that is transparent to the wafer 2 from the condenser 40 while the chuck table 34 is moved in the X-axis direction. This allows a trial modified layer 56 that is linear overall to be formed on the underside of the wafer 2.

[0026] After the trial modified layer 56 is formed on the lower surface side of the wafer 2, another trial modified layer 56 is formed above this trial modified layer 56. That is, after appropriately raising the position of the light focusing point, the laser beam LB is irradiated onto the wafer 2 while the chuck table 34 is moved in the X-axis direction, and another trial modified layer 56 is formed above the previously formed trial modified layer 56. In this manner, the formation of the trial modified layer 56 is repeated, and multiple (e.g., three) trial modified layers 56 are formed at intervals in the vertical direction.

[0027] In the trial modified layer forming step, it is preferable to form the trial modified layer 56 in the peripheral excess region of the wafer 2. The peripheral excess region of the wafer 2 is a region on the peripheral side of the wafer 2, in which the device layer 4 exists but a complete device 6 is not formed. By forming the trial modified layer 56 in the peripheral excess region, damage to the device 6 caused by the formation of the trial modified layer 56 is prevented.

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

[0029] (Sample piece production process) After the trial modified layer forming step is performed, a sample piece generating step is performed in which an external force is applied along the trial modified layer 56 to divide the wafer 2 and generate sample pieces.

[0030] In the sample piece generating step, an external force can be applied to the trial modified layer 56 with the wafer 2 placed on the chuck table 34. Alternatively, the suction force of the chuck table 34 may be released, the wafer 2 may be removed from the chuck table 34, and the wafer 2 may be placed on another work table before applying an external force to the trial modified layer 56. For example, an auto punch with a built-in hammer (not shown) can be used to apply the external force.

[0031] 4, by applying an external force along the trial modified layer 56, a dividing groove 57 is formed along the trial modified layer 56, extending from the back surface 2b of the wafer 2 to the device layer 4 (the front surface of the wafer 2). As a result, the wafer 2 can be divided to generate sample pieces 58. At this time, the wafer 2 is divided, but the protective tape 12 is not divided, and therefore the wafer 2 and the sample pieces 58 are connected by the protective tape 12.

[0032] (Measurement data generation process) After the sample piece generation process is performed, the sample piece 58 is bent toward the protective tape 12 to expose the cross section, which is then imaged by the imaging means 22 to measure the position of the trial modified layer 56 in the thickness direction of the wafer 2 and the thickness of the device layer 4, thereby performing a measurement data generation process to generate measurement data.

[0033] In the measurement data generating process, first, the cross section of the sample piece 58 is exposed by an operator. Specifically, the position of the wafer 2 is shifted on the chuck table 34, and the sample piece 58 is positioned outside the chuck table 34. Next, as shown in Fig. 5, the sample piece 58 is bent toward the protective tape 12. In this way, the cross section of the sample piece 58 (the cross section of the division groove 57) is exposed facing upward.

[0034] Once the cross section of the sample piece 58 is exposed, an image of the exposed cross section of the sample piece 58 is taken. Specifically, first, the chuck table 34 is moved to position the sample piece 58 directly below the imaging means 22. Next, as shown in Fig. 5, the cross section of the sample piece 58 exposed upward is imaged by the imaging means 22, and the captured image is displayed on the monitor 54. However, in Fig. 5, the cross section of the sample piece 58 and the wafer 2 displayed on the monitor 54 are exaggerated for convenience.

[0035] After capturing an image of the cross section of the sample piece 58, measurement data is generated based on the captured image of the sample piece 58. When generating the measurement data, appropriate image analysis software can be used. Then, the position of the trial modified layer 56 in the thickness direction of the wafer 2 and the thickness of the device layer 4 are measured to generate the measurement data. Examples of the generated measurement data include the following data. Position of test modified layer: 100μm, 170μm, 250μm from the bottom surface of the wafer Device layer thickness: 10 μm

[0036] (Focusing point position setting process) After the measurement data generating step is performed, a focal point position setting step is performed to set an appropriate position of the focal point of the laser beam LB inside the wafer 2 based on the measurement data. Although the approximate thickness of the device layer 4 is known in advance, the exact thickness of the device layer 4 may vary slightly for each wafer 2 or for each lot of the wafer 2. The appropriate height direction position of the focal point of the laser beam changes depending on the thickness of the device layer 4. Therefore, in this embodiment, the position of the focal point of the laser beam LB is set based on the measurement data.

[0037] The focal point position may be set automatically by a computer or by an operator. When the computer sets the focal point position, the relationship between the thickness of the device layer 4 and the appropriate focal point position is obtained in advance by an experiment or the like, and the measured thickness of the device layer 4 is applied to the relationship to derive the appropriate focal point position. It is preferable to register a plurality of relationships in the computer according to the material and thickness of the wafer 2. On the other hand, when the operator sets the focal point position, the focal point position can be set by deriving the appropriate focal point position by the computer and then appropriately correcting the position derived by the computer in consideration of the cross-sectional image of the sample piece 58.

[0038] In the focusing point position setting step, the number of focusing point positions may be changed from that in the trial modified layer forming step. For example, in the above example, the number of focusing point positions in the trial modified layer forming step is three (1: 100 μm, 2: 170 μm, 3: 250 μm), but in the focusing point position setting step, the number of focusing point positions may be set to four (1: 60 μm, 2: 130 μm, 3: 190 μm, 4: 230 μm). Note that all of the above numerical values ​​are based on the lower surface of the wafer 2.

[0039] (Modified layer forming process) After the focal point position setting step is performed, the sample piece 58 is returned to its original state, the focal point of the laser beam LB is positioned at the position set in the focal point position setting step, and the modified layer forming step is performed in which the laser beam LB is irradiated onto the wafer 2 to form a modified layer. The modified layer forming step can be performed using an apparatus for performing the trial modified layer forming step (for example, the laser processing apparatus 14 shown in FIG. 2).

[0040] In the modified layer forming step, first, the sample piece 58 is returned to its original state (see FIG. 6). Next, the wafer 2 is positioned so as to cover the suction chuck 36 of the chuck table 34, and the wafer 2 is suction-held by the chuck table 34. Next, infrared rays are irradiated from the imaging means 22, and the device layer 4 side (front side of the wafer 2) is imaged by the infrared rays transmitted from the back surface 2b of the wafer 2. Next, based on the image of the wafer 2 imaged by the imaging means 22, the planned division lines 8 are aligned in the X-axis direction. Furthermore, the laser beam LB is aimed at the planned division lines 8 aligned in the X-axis direction, and the focal point of the laser beam LB is positioned at the position set in the focal point position setting step.

[0041] Once the focal point is positioned at the position set in the focal point position setting step, the laser beam LB is irradiated onto the wafer 2 to form a modified layer along the intended dividing line 8. Specifically, as shown in Fig. 6, the laser beam LB having a wavelength that is transparent to the wafer 2 is irradiated onto the wafer 2 from the condenser 40 while the chuck table 34 is moved in the X-axis direction. This allows the modified layer 60 to be formed inside the wafer 2 along the intended dividing line 8.

[0042] Next, the chuck table 34 is indexed in the Y-axis direction by an amount equal to the spacing of the dividing lines 8 in the Y-axis direction. Then, by alternately repeating the irradiation of the laser beam LB and the indexing, a modified layer 60 is formed inside the wafer 2 along all of the dividing lines 8 aligned in the X-axis direction. Then, the chuck table 34 is rotated 90 degrees, and by alternately repeating the irradiation of the laser beam LB and the indexing, a lattice-shaped modified layer 60 is formed inside the wafer 2 along all of the dividing lines 8 that are perpendicular to the dividing lines 8 along which the modified layer 60 was previously formed (see FIG. 7).

[0043] Furthermore, after changing the height of the focal point, the laser beam LB is irradiated onto the wafer 2 in the same manner as described above. Then, by repeating the change of the height of the focal point and the irradiation of the laser beam LB, a lattice-shaped modified layer 60 is formed inside the wafer 2 at all the heights set in the focal point position setting process.

[0044] The modified layer forming step can be carried out under the same processing conditions as those of the trial modified layer forming step, for example, under the following processing conditions. Pulsed laser beam wavelength: 1342nm Average power output: 1.0W Repetition frequency: 90kHz Feed speed: 700mm / s

[0045] (splitting process) After the modified layer forming step is performed, a dividing step is performed in which an external force is applied to the dividing lines 8 to divide the wafer 2 into individual device chips.

[0046] The dividing step can be performed, for example, by using a grinding device 62 shown in Fig. 8. The grinding device 62 includes a chuck table 64 that holds the wafer 2 by suction, and a grinding means 66 that grinds the wafer 2 held by suction on the chuck table 64. The grinding means 66 includes a spindle 68 extending in the vertical direction, and a disk-shaped wheel mount 70 fixed to the lower end of the spindle 68. An annular grinding wheel 74 is fastened to the lower surface of the wheel mount 70 by bolts 72. A plurality of grinding stones 76 are fixed to the outer periphery of the lower surface of the grinding wheel 74, and are arranged in a ring shape at intervals in the circumferential direction.

[0047] In the dividing step, first, the wafer 2 is suction-held on the upper surface of the chuck table 64 with the back surface 2b of the wafer 2 facing upward. Next, the spindle 68 is rotated at a predetermined rotation speed (e.g., 6000 rpm) in the direction indicated by the arrow R1 in Fig. 8. Also, the chuck table 64 is rotated at a predetermined rotation speed (e.g., 300 rpm) in the direction indicated by the arrow R2.

[0048] Next, the spindle 68 is lowered to bring the grinding wheel 76 into contact with the back surface 2b of the wafer 2, and grinding water is supplied to the portion where the grinding wheel 76 is in contact with the back surface 2b. Thereafter, the spindle 68 is lowered at a predetermined grinding feed rate (for example, 1.0 μm / s) to grind the back surface 2b of the wafer 2 with the grinding wheel 76. This allows the wafer 2 to be thinned to a predetermined thickness. Furthermore, cracks extend from the modified layer 60 in the thickness direction of the wafer 2 due to the external force applied by grinding, and the wafer 2 is divided into individual device chips 78 as shown in FIG. 9.

[0049] As described above, in the illustrated embodiment, the position of the trial modified layer 56 in the thickness direction of the wafer 2 and the thickness of the device layer 4 are measured from the cross-sectional image of the sample piece 58 to generate measurement data, and an appropriate position of the focal point of the laser beam LB is set based on the generated measurement data, so that when forming the modified layer 60 for dividing the wafer 2, the focal point of the laser beam LB can be positioned at an appropriate position. Therefore, the device 6 is not damaged when the wafer 2 is irradiated with the laser beam LB. Furthermore, the device 6 is not damaged even by cracks extending from the modified layer 60 when an external force is applied to the wafer 2 in the dividing step. [Explanation of symbols]

[0050] 2: Wafer 2b: Back side of wafer 4: Device layer 6: Device 8: Planned division line 12: Protective tape 56: Trial modification layer 58: Sample piece 60: Modified layer 76: Grinding wheel 78: Device chip

Claims

1. A method for processing a wafer having a device layer formed on a surface thereof, the device layer having a plurality of devices partitioned by planned division lines, comprising the steps of: a protective tape application step of applying a protective tape to a surface of the wafer; a trial modified layer forming step of irradiating the wafer with a laser beam having a wavelength that is transparent to the wafer from the back surface of the wafer by positioning a focal point of the laser beam within the wafer and forming a trial modified layer; a sample piece generating step of dividing the wafer by applying an external force along the trial modified layer to generate a sample piece; a measurement data generating step of bending the sample piece toward the protective tape side to expose a cross section, imaging the cross section with an imaging means, measuring the position of the trial modified layer in the thickness direction of the wafer and the thickness of the device layer, and generating measurement data; a focal point position setting step of setting an appropriate position of a focal point of the laser beam to be positioned inside the wafer based on the measurement data; a modified layer forming step of returning the sample piece to its original state, positioning the focal point of the laser beam at the position set in the focal point position setting step, and irradiating the wafer with the laser beam to form a modified layer; A dividing step of dividing the wafer into individual device chips by applying an external force along the intended dividing lines.

2. 2. The wafer processing method according to claim 1, wherein in the trial modified layer forming step, the trial modified layer is formed in an outer peripheral excess region of the wafer.

3. 2. The wafer processing method according to claim 1, wherein in the dividing step, the back surface of the wafer is ground with a grinding wheel to thin the wafer, and the wafer is divided into individual device chips by an external force applied by the grinding.

Images