JP2018098352A - Wafer processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the warp of a wafer.SOLUTION: A wafer processing method comprises: a first laser processing step of condensing, in a wafer, a laser beam of a wavelength having the capability of permeating the wafer on a surface side of the wafer with respect to the center of the wafer in a thickness direction of the wafer, forming a quality-modified layer along each street on the surface side, and causing a crack to extend from the quality-modified layer on the surface side to the wafer surface; a second laser processing step of condensing the laser beam along each scheduled line extending in parallel with the streets between adjacent two streets on the backside with respect to the center of the wafer in the thickness direction in the wafer to form a backside quality-modified layer along the scheduled line in the wafer; and a grinding step of grinding the backside of the wafer to remove the quality-modified layer of the surface side and the backside quality-modified layer and to thin the wafer to a given thickness, and dividing the wafer into individual device chips after execution of the first and second laser processing steps.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a wafer processing method.

  In a wafer processing method of manufacturing a device chip or the like by processing a wafer, for example, the back side of the wafer is ground in order to thin the wafer having a device formed on the surface. Thereafter, the device is divided to form individual device chips. The wafer is divided by, for example, cutting a rotating disk-shaped cutting blade into the wafer along a grid-like street (division planned line).

  For the wafer processing method as described above, for example, as shown in Patent Document 1, a processing method for simultaneously performing grinding on the back side of the wafer and dividing into device chips has been studied. .

  In the processing method, a modified layer is formed in the wafer along the street by a laser processing apparatus, and then the wafer is thinned by grinding the back side of the wafer and the force generated by the grinding is applied to the modified layer. The wafer is divided by forming a crack extending on the surface side by acting on the surface of the wafer. As described above, when the division and the grinding are performed at the same time, the processing method can be simplified.

  Furthermore, depending on the irradiation condition of the laser beam, the modified layer can be formed and a crack extending from the modified layer to the surface side of the wafer can be formed. Then, since the crack which contributes to the division | segmentation of a wafer can be formed before a grinding process, a wafer can be divided | segmented along a street more reliably.

International Publication No. 03/077795

  In the wafer processing method in which a modified layer is formed on the wafer and a crack extending from the modified layer to the surface side is formed, the crack is formed along the street of the wafer before the wafer is transferred to the grinding apparatus. When the crack is formed, an outward force perpendicular to the direction in which the crack (street) extends is applied to both sides of the crack divided by the crack. On the other hand, no cracks are formed on the back side of the wafer, and no such force is generated.

  Therefore, when cracks are formed along the streets on the front surface side of the wafer, stress is applied in the direction of expanding the wafer only on the front surface side of the wafer, so that the wafer is bent so that the back surface is inward. If the wafer is deformed, it may be difficult to transfer the wafer by the transfer device, and the negative pressure cannot be applied properly when the wafer is placed on the chuck table of the grinding device and sucked and held. May occur.

  In recent years, the trend toward miniaturization of the chip size has been remarkable, and the number of device chips formed from the wafer has increased, and as a result, the number of streets set on the wafer has also increased, so it is formed on the surface of the wafer. The number of cracks is also increasing. As the number of cracks formed on the surface of the wafer increases, these problems become more prominent because the wafer curves more greatly.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a wafer processing method capable of suppressing wafer warpage and facilitating conveyance and suction holding of the wafer.

  According to one aspect of the present invention, there is provided a method for processing a wafer having a plurality of streets arranged in a grid and devices formed on each of the regions partitioned by the streets, The wafer is placed on the holding table with the front surface side facing the holding table, the holding step of holding the wafer on the holding table to expose the back surface of the wafer, and the holding step. On the other hand, a laser beam having a wavelength having transparency is condensed on the surface side of the wafer in the thickness direction of the wafer, and the wafer is moved relative to the laser beam along the street. A first laser processing step is formed in which a modified layer on the surface side is formed inside the wafer and cracks extending from the modified layer on the surface side to the surface of the wafer are extended. And after the holding step, a laser beam having a wavelength transparent to the wafer is placed between two adjacent streets on the back side of the wafer in the thickness direction of the wafer. Condensed along a planned irradiation line extending parallel to the street, and moving the wafer relative to the laser beam, the modified layer on the back side inside the wafer along the planned irradiation line After performing the second laser processing step of forming the first laser processing step, the first laser processing step, and the second laser processing step, the rear surface of the wafer is ground, And a grinding step of removing the modified layer on the back surface side to reduce the thickness to a predetermined thickness and dividing the wafer into individual device chips. It is.

  In one aspect of the present invention, after the second laser processing step is performed on all irradiation lines extending in the same direction, the first laser processing is performed along all streets extending in the direction. Steps may be performed. Further, the first laser processing step for the street and the second laser processing step for the irradiation scheduled line adjacent to the street may be alternately performed one after another. Further, in the grinding step, the wafer may be ground from the back surface side to remove the modified layer on the back surface side and the modified layer on the front surface side.

  According to the wafer processing method of one aspect of the present invention, the laser beam is positioned at a depth relatively close to the back surface of the wafer along an irradiation scheduled line set between two adjacent streets by the second laser processing step. Is irradiated to form a modified layer on the back surface side. Therefore, the first laser processing step forms a modified layer on the surface side at a depth position relatively close to the surface of the wafer along each street, and cracks from the modified layer on the surface side to the surface of the wafer occur. Even if formed, the wafer becomes difficult to bend.

  That is, the first laser processing step generates a force in the direction of extending to the outer periphery on the wafer surface, and the second laser processing step generates a force in the direction of extending to the outer periphery on the back surface of the wafer. For this reason, the warping of the wafer is suppressed by canceling out the force of bending so that the wafer is bent with the back surface side inward and the force of bending with the front surface side being inward.

  Here, in the second laser processing step, when a modified layer on the back surface side is formed along the street instead of the planned irradiation line, the modified layer on the front surface side and the modified layer on the back surface side are formed on the street. Both are formed, and the wafer becomes brittle. On the other hand, in the wafer processing method according to one aspect of the present invention, in the second laser processing step, the laser beam is irradiated along the irradiation planned line, and the back surface side is positioned away from the modified layer on the front surface side. Since such a modified layer is formed, such a problem hardly occurs.

  Therefore, according to one embodiment of the present invention, a wafer processing method can be provided in which warpage of the wafer can be suppressed and the wafer can be easily conveyed and sucked and held.

It is a fragmentary sectional view explaining a holding step typically. FIG. 2A is a partial cross-sectional view schematically illustrating the first laser processing step, and FIG. 2B is a partial cross-sectional view schematically illustrating the second laser processing step. FIG. 3A is a partial cross-sectional view for schematically explaining the first laser processing step performed after the second laser processing step, and FIG. 3B is alternated with the first laser processing step. It is a fragmentary sectional view which illustrates typically the 2nd laser processing step implemented to (ii). It is a fragmentary sectional view which illustrates a grinding step typically.

  Embodiments according to the present invention will be described. In the processing method according to the present embodiment, first, a holding step for holding a wafer as a workpiece is performed. Next, a first laser processing step for forming a modified layer on the front surface side in the wafer and a second laser processing step for forming a modified layer on the back surface side in the wafer are performed. Next, a grinding step is performed in which the wafer is ground and thinned from the back side.

  First, a wafer 1 and a laser processing apparatus 2 that are workpieces of the processing method according to the present embodiment will be described with reference to FIG. The wafer 1 is a substrate made of, for example, silicon, SiC (silicon carbide), or another semiconductor material, or a material such as sapphire, glass, or quartz.

  The surface 1a of the wafer 1 is partitioned into a plurality of regions by a plurality of streets (division lines) arranged in a lattice pattern, and a device 3 such as an IC is formed in each region partitioned by the streets. Finally, the wafer 1 is divided along the streets to form individual device chips.

  A surface protective tape 5 for protecting the device 3 and the like is attached to the surface 1 a of the wafer 1. The surface protection tape 5 protects the surface 1a side of the wafer 1 from the impact applied at the time of each step or conveyance and the device 3 is damaged while the wafer processing method according to this embodiment is being performed. It has the function to prevent.

  The surface protection tape 5 has a flexible film-like base material and a glue layer (adhesive layer) formed on one surface of the base material. For example, PO (polyolefin) is used for the base material. PET (polyethylene terephthalate), polyvinyl chloride, polystyrene, or the like having higher rigidity than PO may be used. For the glue layer (adhesive layer), for example, silicone rubber, acrylic material, epoxy material or the like is used. In the processing method according to this embodiment, the surface protective tape 5 does not have to be attached to the surface 1a.

  The laser processing apparatus 2 used in the first laser processing step and the second laser processing step includes a holding table (chuck table) 4 that sucks and holds the wafer 1 and a processing head 6 that oscillates a laser beam. .

  The holding table 4 has a porous member on the upper surface side. The upper surface of the porous member is a holding surface 4 a that holds the wafer 1 of the holding table 4. The holding table 4 has a suction path (not shown) connected to a suction source (not shown) inside, and the other end of the suction path is connected to the porous member. When the wafer 1 is placed on the holding surface 4 a and a negative pressure generated by the suction source is applied to the wafer 1 through the hole of the porous member, the wafer 1 is sucked and held by the holding table 4. The

The processing head 6 has a function of oscillating a laser beam having a wavelength that is transmissive to the wafer 1 and condensing it to a predetermined depth inside the wafer 1, and to the predetermined depth by multiphoton absorption. A first modified layer 9a is formed. For the laser beam, for example, a laser beam oscillated using Nd: YVO ₄ or Nd: YAG as a medium is used.

  The laser processing device 2 uses a processing feed means (processing feed mechanism, not shown) powered by a pulse motor or the like to move the holding table 4 in the processing feed direction of the laser processing device 2 (for example, FIGS. 2A and 2B). ) In the direction of the arrow). At the time of processing the wafer 1, the holding table 4 is sent in the processing feed direction to process and feed the wafer 1. Further, the holding table 4 can be rotated around an axis substantially perpendicular to the holding surface 4a. When the holding table 4 is rotated, the processing feed direction of the wafer 1 can be changed.

  Furthermore, the laser processing apparatus 2 can move the holding table 4 in the indexing and feeding direction (not shown) of the laser processing apparatus 2 by indexing and feeding means (indexing and feeding mechanism, not shown) powered by a pulse motor or the like.

  Hereinafter, each step of the processing method according to the present embodiment will be described. First, the holding step will be described. FIG. 1 is a partial cross-sectional view for schematically explaining the holding step. In the holding step, the wafer 1 is held on the holding table 4 of the laser processing apparatus 2 in preparation for the first laser processing step and the second laser processing step to be performed thereafter.

  In the holding step, first, the front surface 1a of the wafer 1 is directed to the holding table 4 side, the wafer 1 is placed on the holding table 4, and the back surface 1b side of the wafer 1 is exposed. Then, a negative pressure is applied from the holding table 4 to suck and hold the wafer 1 on the holding surface 4 a of the holding table 4. When the surface protective tape 5 is attached to the surface 1 a of the wafer 1, the wafer 1 is held on the holding table 4 through the surface protective tape 5.

  Next, the first laser processing step according to the present embodiment will be described with reference to FIG. After carrying out the holding step, the relative positions of the holding table 4 and the processing head 6 are adjusted so that the modified layer 1d on the surface side can be formed inside the wafer 1 along the street.

  Next, a laser beam is irradiated on the back surface 1b side of the wafer 1 from the processing head 6 of the laser processing apparatus 2, and the laser beam is condensed on the front surface 1a side of the wafer 1 in the thickness direction center 1c. Then, the modified layer 1d on the surface side is formed. The wafer 1 is processed and fed by moving the holding table 4 while irradiating a laser beam so that the modified layer 1d on the surface side is formed along the street.

  At this time, the laser beam irradiation conditions are set so that the modified layer 1d on the surface side is formed and the crack 7 extending from the modified layer 1d on the surface side to the surface 1a of the wafer 1 is formed. If the crack 7 can be formed in the first laser processing step, it is not necessary to separately perform a step for forming the crack 7, and the process can be simplified. Note that when the crack 7 reaching the front surface 1a of the wafer 1 is formed, the crack extends even in the direction of the back surface 1b, but is omitted in each drawing.

  After the surface-side modified layer 1d and the crack 7 are formed along one street, the wafer 1 is indexed and fed, and the surface-side modified layer 1d is successively formed along the adjacent streets. Cracks 7 are formed. After the modified layer 1d on the surface side and the cracks 7 are formed along all the streets along one direction, the holding table 4 for sucking and holding the wafer 1 is rotated by a quarter turn, and the wafer 1 Change the machining feed direction. Then, a modified layer 1 d on the surface side and cracks 7 are formed along all the streets on the surface of the wafer 1.

  Next, the second laser processing step will be described with reference to FIG. In the second laser processing step, the modified layer 1e on the back surface side is formed between two adjacent streets of the wafer 1 along a planned irradiation line extending parallel to the street.

  In the second laser processing step, a laser processing apparatus similar to the laser processing apparatus 2 used in the first laser processing step is used. When the second laser processing step is performed after the first laser processing step, the second laser processing step is performed using the laser processing apparatus 2 as it is.

  In the second laser processing step, as shown in FIG. 2 (B), a laser beam is irradiated from the processing head 6 of the laser processing apparatus 2 to one end of the irradiation scheduled line on the back surface 1b of the wafer 1 to thereby increase the inside of the wafer 1. The rear surface side modified layer 1e is formed by condensing on the back surface 1b side from the center 1c in the thickness direction of the wafer. The holding table 4 is moved while irradiating the laser beam so that the modified layer 1e on the back side is formed along the irradiation line, and the wafer 1 is processed and sent.

  After the modified layer 1 on the back side and the crack 7 are formed along one irradiation planned line, the wafer 1 is indexed and fed, and the modification on the back side is successively performed along the adjacent irradiation planned line. Layer 1d and crack 7 are formed.

  After the modified layer 1d on the back side and the cracks 7 are formed along all the planned irradiation lines along one direction, the holding table 4 for sucking and holding the wafer 1 is rotated by a quarter turn, The processing feed direction of the wafer 1 is changed. Then, the modified layer 1e on the back surface side and the cracks 7 are formed along all the irradiation planned lines on the back surface of the wafer 1.

  When the modified layer 1d on the surface side and the crack 7 are formed in the first laser processing step, an outward force perpendicular to the crack is applied to each side of the crack divided by the crack. Take it. For this reason, when cracks 7 are formed along the streets on the front surface 1a of the wafer 1, only the front surface 1a of the wafer 1 is subjected to stress extending in the outer periphery, so that the wafer 1 warps with the back surface 1b facing inward. To bend.

  Then, the transfer of the wafer 1 by the transfer device may become difficult, and when the wafer 1 is placed on the chuck table of the grinding device for the grinding step described later, the wafer 1 is sucked and held appropriately. There may be a problem that pressure cannot be applied.

  On the other hand, in the processing method according to the present embodiment, the second laser processing step is further performed to form the modified layer 1e on the back surface side and the crack 7 reaching the back surface 1b of the wafer 1 on the wafer 1. . Similarly, a stress in a direction of expanding to the outer periphery is applied to the back surface 1b of the wafer 1, and a force is applied in a bending direction so that the front surface 1a of the wafer 1 is inward.

  Therefore, the force applied in the direction of bending with the back surface 1a of the wafer 1 inward and the force applied in the direction of bending with the back surface 1b of the wafer 1 inward are offset, and warping of the wafer 1 is suppressed.

  In addition, since the irradiation planned line on which the modified layer 1e on the back side is formed mainly overlaps with the device, the wafer 1 is not divided in the irradiation planned line. For this reason, in the second laser processing step, cracks from the modified layer 1e on the back surface side to the surface 1a of the wafer 1 must not be formed. Further, in the second laser processing step, the irradiation planned line mainly overlaps with the device, so that the laser beam irradiated from the back surface 1b side should not affect the device on the front surface 1a side.

  Therefore, the irradiation condition of the laser beam irradiated in the second laser processing step is the same as the irradiation condition of the laser beam irradiated in the first laser processing step or a condition that the degree of processing becomes weaker. preferable.

  In the first laser processing step, for example, a pulse laser beam having a wavelength of 1342 nm, a repetition frequency of 90 kHz, and an output of 1.5 W is irradiated to the surface 1a side of the wafer inside the wafer in the thickness direction 1c. On the other hand, in the second laser processing step, for example, a pulse laser beam having a wavelength of 1342 nm, a repetition frequency of 90 kHz, and an output of 1.2 W to 1.5 W is applied to the back surface 1b side of the wafer inside the wafer thickness direction 1c. Irradiate.

  By the way, if the modified layer remains on the device chip, unnecessary cracks or the like may be generated from the modified layer, and the device chip may be damaged. Therefore, in the first laser processing step, the laser beam is irradiated to a depth position that is closer to the surface 1a than the center 1c in the thickness direction of the wafer and whose depth position from the surface 1a is larger than the finished thickness of the device chip. To do. Then, the modified layer 1d on the surface side is removed in a subsequent grinding step and does not remain on the device chip.

  On the other hand, in the second laser processing step, the modified layer 1e on the back surface side is formed at a depth position closer to the back surface 1b than the modified layer 1d on the front surface side, and the modified layer 1e on the back surface side is formed in the grinding step. Removed. Therefore, there is no restriction on the depth position from the rear surface 1b of the modified layer 1e on the rear surface side.

  Further, in the first laser processing step, in order to reliably form a crack from the surface-side modified layer 1d to the surface of the wafer 1, the surface-side modified layer 1d is formed and then the surface-side modified layer is formed. A modified layer may be further formed at a depth position closer to the back surface 1b than the quality layer 1d.

  That is, a laser beam is irradiated along the modified layer 1d on the surface side, and the laser beam is condensed at the depth position to form a further modified layer. Then, a force is applied to the modified layer 1d on the surface side from this further modified layer, and a crack from the modified layer 1d on the surface side to the surface 1a of the wafer 1 can be formed more reliably.

  In the processing method according to the present embodiment, the first laser processing step is performed to form the surface-side modified layer 1d along all the streets, and then the second laser processing step is performed. This is not limited to the case where the modified layer 1e on the back surface side is formed along the planned irradiation line. For example, as shown in FIG. 3A, the first laser processing step may be performed after the second laser processing step.

  Here, FIG. 3A is a partial cross-sectional view schematically illustrating the first laser processing step performed after the second laser processing step. Note that the cross section shown in FIG. 3A is a cross section orthogonal to the cross sections of the partial cross sectional views shown in FIGS. 2A and 2B.

  When the first laser processing step is performed prior to the second laser processing step, the wafer 1 is bent with the back surface 1b on the inside due to the crack 7 extending from the modified layer 1d on the front surface side and reaching the surface 1a. So force. Then, the outer peripheral edge of the wafer 1 may be lifted from the chuck table 4 and the chuck table 4 may not be able to suck and hold the wafer 1 properly.

  On the other hand, when the second laser processing step is performed before the first laser processing step, a crack 7 is formed from the modified layer 1e on the back side to the back surface 1b, and the front surface 1a is formed on the wafer 1 inside. A force is applied to bend. Then, the center of the wafer 1 is lifted from the chuck table 4, but if the outer peripheral edge of the wafer 1 is not lifted, the negative pressure applied from the chuck table 4 is not released, and the wafer 1 continues to be sucked and held appropriately. For this reason, the second laser processing step may be performed before the first laser processing step.

  In the processing method according to the present embodiment, the first laser processing step for one street and the second laser processing step for one irradiation scheduled line adjacent to the street are alternately performed one after another. Also good. FIG. 3B is a partial cross-sectional view schematically illustrating a second laser processing step performed alternately with the first laser processing step. The cross section shown in FIG. 3B is a cross section orthogonal to the cross sections shown in FIGS. 2A and 2B.

  Then, since the force to bend with the front surface 1a side of the wafer 1 inward and the force to bend with the back surface 1b of the wafer 1 inward are generated in order to cancel each other, the wafer 1 Is suppressed.

  Next, the grinding step will be described with reference to FIG. The grinding step is performed after the first laser processing step and the second laser processing step. In the grinding step, the back surface 1b side of the wafer 1 is ground to thin the wafer 1 to a predetermined thickness, and the wafer 1 is divided into individual device chips.

  FIG. 4 is a partial cross-sectional view schematically illustrating the grinding step. In this step, the grinding device 8 is used. The grinding device 8 includes a spindle 10 that forms a rotation axis perpendicular to the grinding wheel 14, and a disk-shaped grinding wheel 14 that is mounted on one end side of the spindle 10 and includes a grinding wheel 12 on the lower side. A rotation drive source (not shown) such as a motor is connected to the other end side of the spindle 10. When the motor rotates the spindle 10, the grinding wheel 14 attached to the spindle 10 also rotates.

  The grinding device 8 also has a chuck table 16 that faces the grinding wheel 14 and holds a workpiece such as the wafer 1. The holding surface 16a on the chuck table 16 is composed of a porous member connected to a suction source (not shown). The chuck table 16 can be rotated around an axis substantially perpendicular to the holding surface 16a. Further, the grinding device 8 has a lifting mechanism (not shown), and the grinding wheel 14 is processed and fed (lowered) by the lifting mechanism.

  In the grinding step, first, the wafer 1 is placed on the holding surface 16 a of the chuck table 16 with the surface 1 a of the wafer 1 facing downward. Then, a negative pressure by the suction source is applied through the porous member to suck and hold the wafer 1 on the chuck table 16. When the surface protective tape 5 is attached to the surface 1 a of the wafer 1, the wafer 1 is sucked and held on the chuck table 16 through the surface protective tape 5.

  At the time of grinding, the chuck table 16 is rotated and the spindle 10 is rotated to rotate the grinding wheel 14. With the chuck table 16 and the grinding wheel 14 rotating, when the grinding wheel 14 is fed (lowered) and the grinding wheel 12 hits the back surface 1b of the wafer 1, grinding of the back surface 1b is started. Then, the grinding wheel 14 is further processed and fed so that the wafer 1 has a predetermined thickness.

  When the wafer 1 is ground to a predetermined thickness, the modified layer 1d on the front surface side and the modified layer 1e on the back surface side are removed, and the modified layer 1d on the front surface side removes the wafer 1 from the modified layer 1d. The wafer 1 is divided into individual device chips by cracks reaching the surface 1a.

  In addition, this invention is not limited to description of the said embodiment, A various change can be implemented. For example, in the second laser processing step, when forming the modified layer 1e on the back surface side, the crack 7 from the modified layer 1e on the back surface side to the back surface 1b may not be formed. When the modified layer is formed inside the wafer 1, the crystal structure of the wafer 1 is broken and a stress is generated on the wafer 1 from the modified layer toward the periphery thereof. Therefore, the warp of the wafer 1 may be sufficiently suppressed by simply forming the modified layer 1e on the back side.

  In addition, the structure, method, and the like according to the above-described embodiment can be appropriately modified and implemented without departing from the scope of the object of the present invention.

DESCRIPTION OF SYMBOLS 1 Wafer 1a Front surface 1b Back surface 1c Thickness center 1d Surface-side modified layer 1e Back-side modified layer 3 Device 5 Surface protection tape 7 Crack 2 Laser processing device 4 Chuck table 4a Holding surface 6 Processing head 8 Grinding device DESCRIPTION OF SYMBOLS 10 Spindle 12 Grinding wheel 14 Grinding wheel 16 Chuck table 16a Holding surface

Claims (4)

A method of processing a wafer having a plurality of streets arranged in a grid and devices formed on each of the regions partitioned by the streets on the surface,
Holding the wafer on the holding table with the front side of the wafer facing the holding table, holding the wafer on the holding table and exposing the back surface of the wafer; and
After performing the holding step, a laser beam having a wavelength that is transmissive to the wafer is focused on the surface side of the wafer in the thickness direction of the wafer, and the wafer is focused on the laser beam. A first laser processing step of forming a surface-side modified layer in the wafer along the street by relatively moving the surface, and extending a crack from the surface-side modified layer to the surface of the wafer; ,
After performing the holding step, a laser beam having a wavelength that is transmissive to the wafer is placed on the back side of the wafer in the thickness direction between the two streets between the two adjacent streets. Is condensed along an irradiation planned line extending in parallel with the laser beam, and the wafer is moved relative to the laser beam, whereby a modified layer on the back side is formed inside the wafer along the irradiation planned line. A second laser processing step to form;
After performing the first laser processing step and the second laser processing step, the back surface of the wafer is ground, the modified layer on the front surface side, and the modified layer on the back surface side, A grinding step of removing and thinning the wafer to a predetermined thickness and dividing the wafer into individual device chips;
A wafer processing method characterized by comprising: The first laser processing step is performed along all streets extending in the direction after the second laser processing step is performed on all irradiation lines that extend in the same direction. The wafer processing method according to claim 1. The first laser processing step for the street and the second laser processing step for the irradiation scheduled line adjacent to the street are alternately performed one after another. Wafer processing method. The grinding step includes grinding the wafer from the back surface side to remove the modified layer on the back surface side and the modified layer on the front surface side. A method for processing a wafer according to 1.