JP2024152435A - Wafer processing method - Google Patents

Abstract

[Problem] To provide a wafer processing method capable of suppressing misalignment of a modified layer formed to suppress device damage during grinding. [Solution] The wafer processing method processes a wafer with a chamfered outer periphery, and includes an annular modified layer forming step 3 in which a focal point of a laser beam having a wavelength that is transparent to the wafer is positioned a predetermined distance inward from the outer periphery of the wafer, and the laser beam is irradiated from the back side of the wafer along the outer periphery to form an annular modified layer inside the wafer, and a thinning step 4 in which, after performing the annular modified layer forming step 3, the back side of the wafer is ground to thin it down to a predetermined thickness, and further includes a planarization step 2 in which, before performing the annular modified layer forming step 3, at least an irradiation region on the back side of the wafer irradiated with the laser beam in the annular modified layer forming step 3 is planarized. [Selected Figure] Figure 3

Description

The present invention relates to a wafer processing method.

In recent years, the development of 3D stacked semiconductor wafers has progressed in line with the trend toward lower profile and higher integration of device chips. For example, TSV (Through-Silicon Via) wafers enable the connection of the electrodes of two chips by bonding them together using through electrodes.

These wafers are ground and thinned while bonded to a supporting wafer (silicon, glass, ceramics, etc.) that serves as the base. Normally, the outer edge of the wafer is chamfered, so when the wafer is ground to an extremely thin thickness, the outer edge becomes a knife edge, and chipping of the edge occurs easily during grinding. This can cause the chip to extend to the device, potentially resulting in damage to the device.

As a countermeasure against the knife edge, an edge trimming method has been devised in which after bonding the wafers together, a laser beam is irradiated along the outer periphery of the device to form an annular modified layer, thereby preventing chipping of the wafer edge that occurs during grinding from extending into the device (see Patent Document 1).

JP 2020-057709 A

In the method of Patent Document 1, since an annular modified layer is formed near the outer periphery of the wafer, the area to which the laser beam is irradiated may be set to a chamfered portion formed on the outer periphery of the wafer. In this case, the position to which the laser beam is irradiated is an inclined surface, which causes problems such as the processing position of the modified layer being shifted.

The present invention was made in consideration of these problems, and its purpose is to provide a wafer processing method that can suppress misalignment of the processing position of the modified layer formed to suppress device damage during grinding.

In order to solve the above problems and achieve the object, the wafer processing method of the present invention is a wafer processing method for processing a wafer with a chamfered outer periphery, and includes an annular modified layer forming step in which a focal point of a laser beam having a wavelength that is transparent to the wafer is positioned a predetermined distance inward from the outer periphery of the wafer, and the laser beam is irradiated from the back side of the wafer along the outer periphery to form an annular modified layer inside the wafer, and after the annular modified layer forming step is performed, a thinning step in which the back side of the wafer is ground to thin it to a predetermined thickness, and further includes a planarization step in which at least the irradiation area of the back side of the wafer that is irradiated with the laser beam in the annular modified layer forming step is planarized before the annular modified layer forming step is performed.

In addition, in the wafer processing method of the present invention, the planarization step may be a grinding step in which the entire back surface of the wafer is flat-ground so that the thickness of the wafer is not reduced to less than half.

The wafer processing method of the present invention may further include a bonding step of bonding the front side of the wafer to a support wafer different from the wafer before carrying out the thinning step.

The present invention can reduce misalignment of the modified layer formed to prevent damage to the device during grinding.

FIG. 1 is a perspective view showing an example of a wafer to be processed by a wafer processing method according to an embodiment. FIG. 2 is a cross-sectional view taken along the line II-II shown in FIG. FIG. 3 is a flowchart showing a flow of the wafer processing method according to the embodiment. FIG. 4 is a perspective view showing one state of the bonding step shown in FIG. FIG. 5 is an enlarged cross-sectional view of a portion of the wafer after the bonding step of FIG. FIG. 6 is a side view, partly in section, showing one state of the planarizing step shown in FIG. FIG. 7 is an enlarged cross-sectional view of a portion of the wafer after the planarization step of FIG. FIG. 8 is a side view, partly in section, showing one state of the annular modified layer forming step shown in FIG. FIG. 9 is a side view, partly in section, showing one state of the thinning step shown in FIG. FIG. 10 is an enlarged cross-sectional view of a portion of the wafer after the thinning step of FIG. FIG. 11 is a side view, partially in section, showing one state of the flattening step in the modified example. FIG. 12 is an enlarged cross-sectional view of a portion of the wafer after the planarization step of FIG. FIG. 13 is a side view, partly in section, showing one state of the annular modified layer forming step in the modified example.

The following describes in detail the form (embodiment) for carrying out the present invention with reference to the drawings. The present invention is not limited to the contents described in the following embodiment. The components described below include those that a person skilled in the art can easily imagine and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. Various omissions, substitutions, or modifications of the configuration can be made without departing from the spirit of the present invention.

[Embodiment]
A method for processing a wafer 10 according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a perspective view showing an example of a wafer 10 to be processed by the method for processing a wafer 10 according to the embodiment. Fig. 2 is a cross-sectional view taken along line II-II shown in Fig. 1.

1 and 2 is a disk-shaped semiconductor wafer, an optical device wafer, or the like, having a substrate 11 made of silicon (Si), sapphire (Al ₂ O ₃ ), gallium arsenide (GaAs), silicon carbide (SiC), or the like, and in this embodiment is a silicon wafer. As shown in FIG. 2, the outer peripheral edge 12 of the wafer 10 is chamfered (beveled).

After the front surface 13 of the wafer 10, which is the device surface, is bonded to, for example, a support wafer 30 (see FIG. 4, etc.) to form a bonded wafer, the back surface 14 is ground to thin it. In the wafer 10 of the embodiment, the bevel portion on the back surface 14 side is wider and gentler than the bevel portion on the front surface 13 side. The back surface 14 of the wafer 10 includes an inclined surface 15 of the bevel portion and a flat surface 16.

As shown in FIG. 1, the wafer 10 includes a device region 17 on the surface 13 side of the substrate 11, and an outer peripheral region 18 surrounding the device region 17. The device region 17 has a plurality of planned division lines 19 set in a grid pattern on the surface 13 of the substrate 11, and devices 20 formed in each region partitioned by the planned division lines 19. The outer peripheral region 18 is a region that surrounds the device region 17 all around, and in which no devices 20 are formed.

In the embodiment, the device 20 constitutes a 3D NAND flash memory and includes an electrode pad and a through electrode connected to the electrode pad. The through electrode penetrates the back surface 14 side of the substrate 11 when the substrate 11 is thinned and the devices 20 are individually separated from the wafer 10. That is, the wafer 10 of the embodiment is a so-called TSV wafer in which the individually separated devices 20 have through electrodes. Note that the wafer 10 of the present invention is not limited to a TSV wafer having through electrodes as in the embodiment, and may be a device wafer without through electrodes.

Figure 3 is a flow chart showing the flow of the processing method of the wafer 10 according to the embodiment. As shown in Figure 3, the processing method of the wafer 10 according to the embodiment includes a bonding step 1, a planarization step 2, an annular modified layer formation step 3, and a thinning step 4. The processing method of the wafer 10 is a processing method in which an annular modified layer 25 is formed along the boundary between the device region 17 and the outer peripheral region 18 inside the wafer 10 with the chamfered outer peripheral edge 12, and then the back surface 14 side is ground to thin the wafer to a predetermined thickness 27 and the outer peripheral region 18 is removed.

(Lamination step 1)
Fig. 4 is a perspective view showing one state of the bonding step 1 shown in Fig. 3. Fig. 5 is an enlarged cross-sectional view showing a part of the wafer 10 after the bonding step 1 of Fig. 4. The bonding step 1 is a step of bonding the front surface 13 side of the wafer 10 to a support wafer 30 different from the wafer 10.

The support wafer 30 shown in FIG. 4 is a disk-shaped substrate wafer having a substrate 31 made of silicon, glass, ceramics, or the like and the same diameter as the wafer 10, but in the present invention, it may be a TSV wafer similar to the wafer 10. The support wafer 30 has a chamfered (beveled) outer periphery 32, similar to the wafer 10. In addition, in the embodiment of the support wafer 30, the bevel portion on the other surface 34 is wider and gentler than the bevel portion on one surface 33, which is the surface to be bonded to the wafer 10.

In the bonding step 1, first, as shown in FIG. 4, the front surface 13 of the wafer 10 and one surface 33 of the support wafer 30 are opposed to each other with a gap therebetween. Next, the front surface 13 of the wafer 10 and one surface 33 of the support wafer 30 are bonded together. This forms a bonded wafer.

In this case, if a bonding layer is provided between the wafer 10 and the support wafer 30, the bonding layer is laminated on one of the front surface 13 of the wafer 10 and one surface 33 of the support wafer 30, and then the front surface 13 of the wafer 10 and one surface 33 of the support wafer 30 are bonded together via the bonding layer. The bonding layer may be a double-sided tape with an adhesive layer laminated on the front and back surfaces of a base layer, an oxide film, or one formed by applying an adhesive containing a resin or the like. The wafer 10 and the support wafer 30 may also be directly bonded together without using a bonding layer.

As shown in the flowchart in FIG. 3, in the embodiment, the bonding step 1 is performed before the planarization step 2, but it may be performed after the planarization step 2 and before the annular modified layer formation step 3. Also, the bonding step 1 may be performed after the annular modified layer formation step 3 and before the thinning step 4.

In the embodiment of the method for processing the wafer 10, each processing of the wafer 10 is performed in a state in which the support wafer 30 is bonded to the front surface 13 side of the wafer 10. However, the wafer 10 processed in the present invention is not necessarily limited to the wafer 10 constituting a bonded wafer, and a single wafer 10 may be processed. In other words, the bonding step 1 does not have to be performed.

(Planarization Step 2)
Fig. 6 is a side view partially in cross section showing one state of the planarization step 2 shown in Fig. 3. Fig. 7 is a cross-sectional view showing an enlarged portion of the wafer 10 after the planarization step 2 in Fig. 6. In Fig. 7, the outline of the wafer 10 before processing is depicted by a dotted line. The planarization step 2 is performed before the annular modified layer formation step 3 described below is performed. The planarization step 2 is a step of planarizing a predetermined region on the back surface 14 side of the wafer 10.

The predetermined area includes at least the irradiation area 21 to which the laser beam 53 is irradiated in the annular modified layer formation step 3 described below. In the embodiment, the predetermined area to be planarized is the entire surface of the back surface 14 side of the wafer 10. The planarization step 2 in the embodiment is a grinding step in which the entire surface of the back surface 14 side of the wafer 10 is planar-ground so that the thickness 23 of the wafer 10 is not reduced to less than half.

In the planarization step 2 of the embodiment, the entire surface of the back surface 14 of the wafer 10 is plane-ground by a grinding device 40 shown in FIG. 6. The grinding device 40 includes a holding table 41, a grinding unit 42, and a moving unit (not shown) that moves the holding table 41 and the grinding unit 42 relative to one another.

The holding table 41 holds the wafer 10 by suction on the holding surface (upper surface) via the support wafer 30, and rotates around a vertical axis. The grinding unit 42 includes a spindle 43 which is a rotating shaft member, a grinding wheel 44 attached to the lower end of the spindle 43, a grinding stone 45 attached to the lower surface of the grinding wheel 44, and a grinding water supply unit (not shown). The spindle 43 and the grinding wheel 44 rotate on a rotation axis parallel to the axis of the holding table 41. The diameter of the grinding wheel 44 is at least greater than the radius of the wafer 10.

In the planarization step 2, first, the other surface 34 of the support wafer 30 is suction-held on the holding surface (upper surface) of the holding table 41. Next, the wafer 10 held on the holding table 41 is aligned with the grinding wheel 44 via the support wafer 30. Specifically, the holding table 41 is moved to the processing area below the grinding wheel 44 by a moving unit (not shown), and the grinding wheel 45 is brought into opposition to the back surface 14 of the wafer 10.

Next, while the holding table 41 is rotated about its axis, the grinding wheel 44 is rotated about its axis. Grinding water is supplied to the processing point by a grinding water supply unit (not shown), and the grinding wheel 45 of the grinding wheel 44 is brought closer to the holding table 41 at a predetermined feed speed, so that the grinding wheel 45 grinds the entire surface of the back surface 14 of the wafer 10. As a result, the entire surface of the back surface 14 of the wafer 10 is flattened, as shown in FIG. 7.

Here, the entire surface of the back surface 14 side may include the irradiation area 21 to which the laser beam 53 is irradiated in the annular modified layer formation step 3 described later, and may not necessarily include a part of the inclined surface 15 on the outer periphery 12 side from the irradiation area 21. The irradiation area 21 is set at the boundary between the device area 17 and the outer periphery area 18, which is a predetermined distance inside from the outer periphery 12. That is, the outer diameter of the flat surface 22 flattened by grinding may be smaller than the outer diameter of the wafer 10. In the embodiment, since the irradiation area 21 is located on the inclined surface 15, grinding is performed in the flattening step 2 until at least the irradiation area 21 of the inclined surface 15 is flattened. At this time, the thickness 24 of the flattened wafer 10 is greater than half the original thickness 23.

(Annular modified layer formation step 3)
8 is a side view partially in cross section showing one state of the annular modified layer forming step 3 shown in FIG. The annular modified layer forming step 3 is performed after the flattening step 2. The annular modified layer forming step 3 is a step in which a focal point 54 of a laser beam 53 having a wavelength that is transparent to the wafer 10 is positioned a predetermined distance inward from the outer circumferential edge 12 of the wafer 10, and the laser beam 53 is irradiated from the back surface 14 (flat surface 22) of the wafer 10 along the outer circumferential edge 12 to form an annular modified layer 25 inside the wafer 10.

In the annular modified layer formation step 3 of the embodiment, an annular modified layer 25 is formed inside the wafer 10 by stealth dicing using a laser processing device 50. The laser processing device 50 includes a holding table 51, a laser beam irradiation unit 52, a moving unit (not shown) that moves the holding table 51 and the laser beam irradiation unit 52 relative to each other, and an imaging unit (not shown) that images the wafer 10 held on the holding table 51.

The holding table 51 holds the wafer 10 on its holding surface (upper surface) and can rotate around a vertical axis. The laser beam irradiation unit 52 irradiates the wafer 10 held on the holding table 51 with a laser beam 53. The laser beam irradiation unit 52 has, for example, a laser oscillator, a collector that focuses and irradiates the laser beam 53 emitted from the laser oscillator onto the wafer 10 held on the holding table 51, and various optical components that propagate the laser beam 53 from the laser oscillator to the collector.

In the annular modified layer formation step 3, a laser beam 53 is irradiated along the irradiation area 21, which is a predetermined distance inside the outer periphery 12, specifically, along the boundary between the device area 17 and the outer periphery area 18 of the wafer 10, to form an annular modified layer 25. The laser beam 53 is a laser beam with a wavelength that is transparent to the wafer 10, such as infrared rays (IR).

Here, the modified layer 25 refers to a region in which the density, refractive index, mechanical strength, or other physical properties are different from those of the surrounding area as a result of irradiation with the laser beam 53. The modified layer 25 is, for example, a melting process region, a crack region, an insulation breakdown region, a refractive index change region, or a region in which these regions are mixed. The modified layer 25 has a lower mechanical strength, etc. than other parts of the wafer 10.

In the annular modified layer formation step 3, first, the other surface 34 of the support wafer 30 is sucked and held on the holding surface (upper surface) of the holding table 51. Next, the wafer 10 is aligned with the condenser of the laser beam irradiation unit 52. Specifically, the holding table 51 is moved to the processing area below the laser beam irradiation unit 52 by a moving unit (not shown). Next, the wafer 10 is photographed and aligned by an imaging unit (not shown) to vertically face the irradiation area 21 at a predetermined distance inside from the outer periphery 12 of the wafer 10, and then the focal point 54 of the laser beam 53 is set inside the wafer 10.

In the annular modified layer formation step 3, the holding table 51 is then rotated around a vertical axis while the laser beam 53 is irradiated from the laser beam irradiation unit 52 onto the back surface 14 (flat surface 22) of the wafer 10. In this manner, the laser beam 53 is irradiated along the irradiation area 21 a predetermined distance inward from the outer peripheral edge 12 of the wafer 10, forming an annular modified layer 25 inside the wafer 10.

The crack 26 extends from the modified layer 25 formed by the irradiation of the laser beam 53, forming a cylindrical splitting starting point having a side perpendicular to the surface 13 of the wafer 10. In the annular modified layer formation step 3, it is preferable to irradiate the laser beam 53 so that the crack 26 extending from the modified layer 25 appears on the surface 13. Note that "perpendicular to the surface 13 of the wafer 10" means that the inclination of the approximation plane, which approximates the entire extended crack 26 to a plane, with respect to the vertical plane is within ±5 degrees, preferably within ±2 degrees.

In the annular modified layer forming step 3, the height of the focal point 54 of the laser beam 53 is changed in the thickness direction of the wafer 10 and the laser beam 53 is irradiated multiple times, that is, the laser beam 53 having one focal point 54 is irradiated once along an area a predetermined distance inside from the outer circumferential edge 12 of the wafer 10, and then the height of the focal point 54 is changed in the thickness direction of the wafer 10 and the laser beam 53 is irradiated multiple times in the same manner to form multiple modified layers 25 in an annular shape and in a direction perpendicular to the surface 13 of the wafer 10. Alternatively, multiple modified layers 25 may be formed in a direction perpendicular to the surface 13 of the wafer 10 by irradiating a laser beam 53 having multiple focal points 54 spaced apart in the thickness direction of the wafer 10.

(Thinning Step 4)
Fig. 9 is a side view, partially in cross section, showing one state of the thinning step 4 shown in Fig. 3. Fig. 10 is an enlarged cross-sectional view showing a part of the wafer 10 after the thinning step 4 of Fig. 9. The thinning step 4 is performed after the annular modified layer forming step 3. The thinning step 4 is a step of grinding the back surface 14 (flat surface 22) of the wafer 10 to thin it down to a predetermined thickness 27.

In the embodiment, in the thinning step 4, the back surface 14 (flat surface 22) of the wafer 10 is ground by a grinding device 40 to thin the wafer 10 to a predetermined thickness 27. The grinding device 40 used in the thinning step 4 may be the same device as the grinding device 40 used in the flattening step 2, or may be a separate device.

In the thinning step 4, first, the other surface 34 of the support wafer 30 is suction-held on the holding surface (upper surface) of the holding table 41. Next, the wafer 10 held on the holding table 41 is aligned with the grinding wheel 44 via the support wafer 30. Specifically, the holding table 41 is moved to the processing area below the grinding wheel 44 by a moving unit (not shown), and the grinding wheel 45 is brought into opposition to the flat surface 22 of the wafer 10.

Next, while the holding table 41 is rotated about its axis, the grinding wheel 44 is rotated about its axis. Grinding water is supplied to the processing point by a grinding water supply unit (not shown), and the grinding wheel 45 of the grinding wheel 44 is brought closer to the holding table 41 at a predetermined feed speed, so that the grinding wheel 45 grinds the flat surface 22 side of the wafer 10, thinning the wafer 10 to the predetermined thickness 27 shown in FIG. 10. At this time, the outer peripheral region 18 of the wafer 10 is removed by the grinding load.

[Modifications]
Next, a modified example of the method for processing the wafer 10 will be described with reference to the drawings.

(Planarization Step 2)
Fig. 11 is a side view showing one state of the planarization step 2 in the modified example, partially in cross section. Fig. 12 is a cross-sectional view showing an enlarged part of the wafer 10 after the planarization step 2 in Fig. 11. The planarization step 2 in the modified example is different from the planarization step 2 in the embodiment in that the planarization step 2 flattens only the vicinity of the outer circumferential edge 12 on the back surface 14 side of the wafer 10, whereas the planarization step 2 in the embodiment flattens the entire surface on the back surface 14 side of the wafer 10. That is, in the modified example, the predetermined area to be flattened is an annular area including the irradiation area 28 on the back surface 14 side of the wafer 10 to which the laser beam 53 is irradiated in the annular modified layer formation step 3.

In the planarization step 2 of the embodiment, the vicinity of the outer peripheral edge 12 on the back surface 14 side of the wafer 10 is surface-ground by a grinding device 60 shown in FIG. 11. The basic configuration of the grinding device 60 is similar to that of the grinding device 40 shown in FIG. 6, and includes a holding table 61, a grinding unit 62, and a moving unit (not shown) that moves the holding table 61 and the grinding unit 62 relative to one another.

The holding table 61 holds the wafer 10 by suction on the holding surface (upper surface) via the support wafer 30, and rotates around a vertical axis. The grinding unit 62 includes a spindle 63 which is a rotating shaft member, a grinding wheel 64 attached to the lower end of the spindle 63, a grinding stone 65 attached to the lower surface of the grinding wheel 64, and a grinding water supply unit (not shown). The spindle 63 and the grinding wheel 64 rotate on a rotation axis parallel to the axis of the holding table 61. The diameter of the grinding wheel 64 is smaller than the diameter of the grinding wheel 44 of the grinding device 40 shown in FIG. 6.

In the planarization step 2 of the modified example, first, the other surface 34 of the support wafer 30 is suction-held on the holding surface (upper surface) of the holding table 61. Next, the wafer 10 held on the holding table 61 via the support wafer 30 is aligned with the grinding wheel 64. Specifically, the holding table 61 is moved to the processing area below the grinding wheel 64 by a moving unit (not shown), and the grinding wheel 65 is opposed to the outer periphery of the device area 17 on the back surface 14 side of the wafer 10 and the inclined surface 15 which is the outer periphery area 18.

Next, while the holding table 61 is rotated about its axis, the grinding wheel 64 is rotated about its axis. Grinding water is supplied to the processing point by a grinding water supply unit (not shown), and the grinding wheel 65 of the grinding wheel 64 is brought closer to the holding table 61 at a predetermined feed speed, so that the grinding wheel 45 grinds the inclined surface 15 on the back surface 14 side of the wafer 10. As a result, as shown in FIG. 12, the inclined surface 15 on the back surface 14 side of the wafer 10 is flattened.

Here, the inclined surface 15 to be flattened may include the irradiation area 28 to which the laser beam 53 is irradiated in the annular modified layer formation step 3 described later, and may not necessarily include a portion of the inclined surface 15 on the outer periphery 12 side from the irradiation area 28. The irradiation area 28 is set at the boundary between the device area 17 and the outer periphery area 18, which is a predetermined distance inside from the outer periphery 12. That is, the outer diameter of the annular flat surface 29 flattened by grinding may be smaller than the outer diameter of the wafer 10. In the embodiment, since the irradiation area 28 is located on the inclined surface 15, grinding is performed in the flattening step 2 until at least the irradiation area 28 of the inclined surface 15 is flattened. At this time, the thickness 24 of the flat surface 29 portion of the flattened wafer 10 is greater than half the original thickness 23.

(Annular modified layer formation step 3)
13 is a side view partially in cross section showing one state of annular modified layer forming step 3 in the modified example. The annular modified layer forming step 3 in the modified example is performed after the flattening step 2 in the modified example. The procedure of the annular modified layer forming step 3 in the modified example is the same as that in the embodiment, except that the "irradiated region 21" and the "flat surface 22" are replaced with "irradiated region 28" and "flat surface 29", and therefore a description thereof will be omitted.

As described above, in the processing method of the wafer 10 of the embodiment and the modified example, in the annular modified layer forming step 3, an annular modified layer 25 is formed inside the wafer 10, which serves as a splitting starting point for removing the outer peripheral region 18. Here, the irradiation regions 21, 28 onto which the laser beam 53 for forming the modified layer 25 is irradiated are near the outer peripheral edge 12, and therefore may be set on the chamfered portion of the outer peripheral edge 12, i.e., the inclined surface 15.

When the inclined surface 15 is irradiated with the laser beam 53, the thickness of the wafer 10 in the irradiated regions 21 and 28 is not constant, so the height position of the modified layer 25 that is formed may shift unintentionally. In addition, when the laser beam 53 is incident on the inclined surface 15, that is, when the laser beam 53 is incident from an oblique direction relative to the incident surface, the radial position of the modified layer 25 that is formed may shift unintentionally. In contrast, in the embodiment and modified example, at least the irradiated regions 21 and 28 are flattened before the annular modified layer formation step 3, so that the laser processing can be performed stably.

The present invention is not limited to the above-mentioned embodiment and modified examples. In other words, various modifications can be made without departing from the gist of the present invention. For example, the planarization step 2 is not limited to grinding, and planarization may be achieved by laser processing using irradiation of a laser beam or cutting processing using a cutting blade.

In addition, in the embodiment, in the annular modified layer formation step 3, a cylindrical split starting point having a side perpendicular to the surface 13 of the wafer 10 is formed, but in the present invention, the modified layer 25 and the crack 26 may be formed along a direction having a predetermined inclination from the direction perpendicular to the surface 13 of the wafer 10, to form a split starting point having a truncated cone shape.

In addition, to facilitate removal of the peripheral region 18 in the thinning step 4, laser processing to divide the peripheral region 18 into multiple regions in advance may be performed prior to the thinning step 4. In this case, for example, the peripheral region 18 may be divided radially by forming a radial modified layer in the peripheral region 18 by stealth dicing.

Alternatively, the outer peripheral region 18 may be removed by applying an external force. The external force may be, for example, a mechanical external force such as a shearing force caused by pressing the outer peripheral region 18 from above or lifting the outer peripheral region 18, or crushing by a roller, or may be an ultrasonic vibration, a collision force between a liquid and/or a solid when the liquid and/or a solid are sprayed onto the outer peripheral region 18, or a radial external force caused by expanding an expandable tape attached to the grinding finish surface of the wafer 10.

REFERENCE SIGNS LIST 10 wafer 11 substrate 12 outer periphery 13 front surface 14 back surface 15 inclined surface 16 flat surface 17 device region 18 outer periphery region 19 planned division line 20 device 21, 28 irradiation region 22, 29 flat surface 23, 24, 27 thickness 25 modified layer 26 crack 30 supporting wafer 53 laser beam 54 focal point

Claims (3)

A wafer processing method for processing a wafer having a chamfered outer periphery, comprising the steps of:
an annular modified layer forming step of positioning a focal point of a laser beam having a wavelength that is transparent to the wafer at a predetermined distance inside from the outer periphery of the wafer, and irradiating the laser beam from the back side of the wafer along the outer periphery to form an annular modified layer inside the wafer;
After the annular modified layer forming step is performed, a thinning step of grinding the back surface of the wafer to a predetermined thickness,
A wafer processing method, characterized in that it further comprises a planarization step of planarizing at least an irradiation area on the back side of the wafer that is irradiated with the laser beam in the annular modified layer formation step before performing the annular modified layer formation step. 2. The wafer processing method according to claim 1, wherein the planarization step is a grinding step of surface-grinding the entire back surface of the wafer so that the thickness of the wafer is not reduced to less than half. Prior to carrying out the thinning step,
3. The wafer processing method according to claim 1, further comprising a bonding step of bonding the front surface side of the wafer to a support wafer different from the wafer.

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