JP2019009273A - Processing method of wafer - Google Patents

Abstract

To reduce wafer warpage.SOLUTION: A processing method of a wafer includes a first laser processing step of forming a first modified region in the wafer, by irradiating some of multiple scheduled division lines with a first laser beam of a wavelength having permeability for the wafer and then focusing, and a second laser processing step of forming a second modified region in the wafer, by irradiating the remaining multiple scheduled division lines with a second laser beam of a wavelength having permeability for the wafer and then focusing. The first modified region includes multiple modified layers having height positions different from each other, and a crack elongating from the modified layer closest to the surface to the wafer surface and exposed to the surface side. The second modified region includes multiple modified layers having height positions different from each other, and the number of the modified layers included in the second modified region is smaller than the number of the modified layers included in the first modified region.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wafer processing method.

  Electronic devices incorporate a large number of chips on which devices such as ICs and LEDs are mounted. In a processing method for forming a chip by processing a semiconductor wafer, a plurality of division lines that intersect the surface of the wafer are set, devices are formed in each region partitioned by the division lines, The wafer is divided along the division line. In recent years, since the demand for thinning a chip is increasing, for example, before the wafer is divided, the back surface of the wafer is ground to thin the wafer. Then, a thinned chip can be manufactured.

  In order to divide the wafer along the planned dividing line, for example, the wafer is irradiated with a transparent laser beam from the back side of the wafer along the planned dividing line. Then, the laser beam is condensed inside the wafer to cause multiphoton absorption, thereby forming a modified layer serving as a starting point of division inside the wafer. Next, an external force is applied to the wafer to extend cracks from the modified layer in the thickness direction of the wafer, and then the wafer is ground from the back side to divide the wafer into individual chips (Patent Document 1). reference).

  In contrast to the wafer processing method as described above, for example, a processing method in which grinding of the back surface side of the wafer and elongation of cracks are simultaneously performed has been studied. That is, a modified layer is formed inside the wafer, and then the back side of the wafer is ground to thin the wafer, and a crack is extended from the modified layer to the surface by the force generated by grinding. Divide the wafer. In this way, the wafer processing method can be simplified by performing the division and grinding simultaneously.

  Furthermore, when forming the modified layer by irradiating the laser beam from the back surface of the wafer, the laser irradiation conditions of the laser processing apparatus are adjusted to form the modified layer and reach the surface of the wafer from the modified layer. A method for processing a wafer for forming a crack has been studied. In the processing method, the wafer can be more reliably divided by forming a crack reaching the surface of the wafer together with the modified layer. And in order to divide | segment a wafer reliably, the technique which determines the formation condition of the crack in this processing method is examined (refer patent document 2).

  After the modified layer is formed inside the wafer, the wafer is transferred from the laser processing device to a grinding device or the like to grind the back side of the wafer, and the wafer is ground with the wafer surface facing downward. Place on the chuck table of the device. In the grinding apparatus, the wafer is sucked and held on the chuck table, and the grinding wheel and the wafer are brought into contact with each other while the grinding wheel and the chuck table are rotated, respectively.

JP 2005-86161 A Japanese Patent Laid-Open No. 2015-12015

  When the crack is formed from the modified layer to the surface of the wafer when the modified layer is formed, the crack is exposed on the surface of the wafer along the division line. Both wall surfaces of the crack are joined before the crack is formed, and when the crack is formed, the both wall surfaces move by the amount of space occupied by the crack.

  Therefore, when the crack is formed in all of the plurality of division lines, a force (stress) toward the outer periphery is applied to the surface of the wafer. On the other hand, such a force is not applied to the back surface of the wafer. Then, the wafer warps so that the back surface is the inside.

  If the wafer is warped so that the back surface is inward, the transfer mechanism of the laser processing apparatus cannot properly hold the wafer, and the wafer may not be transferred. Further, even when the wafer can be transferred to the grinding apparatus, when the wafer is placed on the chuck table with the surface facing downward, the surface of the wafer is partially lifted off the chuck table. Then, even if it is attempted to suck and hold the wafer by applying a negative pressure from the chuck table, the negative pressure leaks from the floating portion, making it difficult to properly hold the wafer.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a wafer processing method that reduces wafer warpage, facilitates wafer conveyance, and enables suction and holding of the wafer. Is to provide.

  According to one aspect of the present invention, there is provided a method for processing a wafer having a surface on which a device is formed in each region partitioned by a plurality of division lines arranged in a lattice pattern, and is permeable to the wafer. A first laser beam having a wavelength of λ is irradiated and condensed from the back side of the wafer along the partial division lines of the plurality of division lines to the inside of the wafer. A first laser processing step for forming a first modified region, and a second laser beam having a wavelength transparent to the wafer along the remaining split lines of the plurality of split lines. A second laser processing step of forming a second modified region in the wafer by irradiating and condensing the wafer from the back side thereof, wherein the first modified region comprises: , Mutual A plurality of modified layers having different height positions, and cracks extending from the modified layer closest to the surface of the plurality of modified layers to the surface of the wafer and exposed to the surface side, The second modified region includes a plurality of modified layers having different height positions, and the number of modified layers included in the second modified region is included in the first modified region. There is provided a wafer processing method characterized in that the number is less than the number of modified layers.

  In the aspect of the invention, the plurality of division lines may extend in a first direction and a second direction intersecting the first direction, and the one of the plurality of division lines may be And the remaining division lines of the plurality of division lines are alternately arranged in each of the first direction and the second direction, and in the first direction. After performing the first laser processing step along the partial division lines arranged side by side, implementing the second laser processing step along the remaining division lines arranged in the first direction. Also good.

  According to the method of processing a wafer according to one aspect of the present invention, a crack reaching the surface from all of the modified layers formed along a plurality of division lines on the surface of the wafer is not generated, but a part of the modified layer is formed. The crack is formed only on the division line. That is, no cracks are formed in the remaining lines to be divided, so that the warpage of the wafer is reduced accordingly.

  When the warpage of the wafer is reduced, the wafer is easily transported by the transport mechanism, and is easily sucked and held by the chuck table of the grinding apparatus. If there are no cracks reaching the surface of the wafer, the wafer will not warp, but it will be difficult to divide the wafer into individual chips. When cracks reaching the surface are formed appropriately, it becomes easy to divide the wafer into chips, and problems due to warpage of the wafer can be suppressed.

  Also, if cracks from all the modified layers to the surface occur before grinding the backside of the wafer, when the wafer is thinned by grinding the backside of the wafer, the wafer It is divided at the earlier timing. The grinding process is continued even after the wafer is divided into individual chips. Then, force is applied by further grinding, and individual chips move in a plane parallel to the surface, and the chips collide with each other. In particular, when the corners of the chip collide with each other, damage such as chipping or unnecessary cracks is likely to occur in the chip.

  On the other hand, cracks reaching the surface from all the modified layers should not be generated, cracks reaching only the surface from some of the modified layers should be generated, and cracks reaching the surface should be generated from the remaining modified layers During grinding, the wafer division proceeds in stages.

  When the grinding progresses step by step, the bonding is maintained at a portion where there is no crack from the modified layer to the surface in the initial stage of the division, and a combined body of a plurality of chips is formed. Since the combined body is larger than the individual chips, it is difficult to move even when a grinding force is applied, and collision between the combined bodies is suppressed until the combined body is further divided into individual chips. Therefore, according to one embodiment of the present invention, damage to a formed chip can be reduced.

  Therefore, according to one embodiment of the present invention, there is provided a wafer processing method that reduces wafer warpage, facilitates wafer conveyance, and enables suction and holding of the wafer.

FIG. 1A is a top view of a wafer schematically showing an example of a plurality of division lines, and FIG. 1B is an upper surface of a wafer schematically showing another example of a plurality of division lines. FIG. FIG. 2A is a schematic cross-sectional view for explaining the first laser processing step, and FIG. 2B is a schematic cross-sectional view for explaining the second laser processing step. It is a cross-sectional schematic diagram explaining a grinding step.

  Embodiments according to the present invention will be described. FIG. 1A shows a top view of a wafer 1 which is a workpiece according to this embodiment. The wafer 1 that is a workpiece is, for example, a disk-shaped substrate made of a material such as silicon, SiC (silicon carbide), or another semiconductor, or a material such as sapphire, glass, or quartz.

  As shown in FIG. 1A, the surface 1a of the wafer 1 includes a plurality of division lines 3a parallel to the first direction 1c and a second direction 1d (for example, intersecting the first direction 1c). And a plurality of division lines 3b parallel to the first direction 1c). Devices 5 such as ICs (Integrated Circuits) and LEDs (Light Emitting Diodes) are formed in the partitioned areas. The wafer 1 is finally divided along the division lines 3 to form individual chips.

  In order to protect the device 5 during the wafer processing method according to the present embodiment, the surface 1a of the wafer 1 is surface protected as shown in FIGS. The tape 13 may be attached.

  In the wafer processing method according to the present embodiment, the plurality of division lines 3a parallel to the first direction 1c and the plurality of division lines 3b parallel to the second direction 1d are each divided into two groups. It is done. Then, a first laser processing step described later is performed along one division planned line of the two groups, and a second laser processing step described later is performed along the remaining planned division lines of the two groups. .

  For example, a part of the plurality of scheduled division lines 3a parallel to the first direction 1c is defined as the first division planned line 3c, and the remaining divisional lines 3a parallel to the first direction 1c are left. The division planned line is set as a second division planned line 3d. Further, a part of the plurality of scheduled division lines 3b parallel to the second direction 1d is defined as a third scheduled division line 3e, and the remainder of the plurality of scheduled division lines 3b parallel to the second direction 1d is set. The division planned line is a fourth division planned line 3f.

  In FIG. 1A and FIG. 1B described later, the first division planned line 3c and the third division planned line 3e are indicated by a two-dot chain line, and the second division planned line 3d and the fourth division scheduled. Line 3f is indicated by a one-dot chain line. As shown in FIG. 1A, for example, the first scheduled division line 3c and the second scheduled division line 3d are set so as to be alternately arranged, and the third scheduled division line 3e and the fourth divided line are arranged. The scheduled lines 3f are set so as to be alternately arranged.

  The setting of the first to fourth division planned lines is not limited to the arrangement shown in FIG. 1A, and may be set to the arrangement shown in FIG. 1B, for example. That is, for example, the first scheduled division line 3c and the third scheduled division line 3e are arranged so as to cross the vicinity of the center of the wafer 1, and the second scheduled division line 3d and the fourth scheduled division line 3f are arranged on the wafer 1. You may arrange | position so that the center vicinity of may not be crossed.

  In the above, the wafer 1 and the example of setting the 1st thru | or 4th division | segmentation scheduled line were demonstrated using FIG. 1 (A) and FIG. 1 (B). In the wafer processing method according to the present embodiment, the first to fourth division lines may be set to an arrangement other than the setting example described.

  Next, a method for processing the wafer 1 according to this embodiment will be described. In the processing method, the first laser processing step is performed. In this step, the first modified region is formed by irradiating a part of the plurality of division lines with a first laser beam having a wavelength that is transmissive to the wafer 1. . A part of the plurality of scheduled division lines is, for example, the first scheduled division line 3c.

  FIG. 2A is a schematic cross-sectional view illustrating a first laser processing step for forming a first modified region. In the drawing, for convenience of explanation, some components are not hatched.

  In the first laser processing step, the height of the condensing point is changed along the first planned dividing line 3c from the back surface 1b side of the wafer 1 to the inside of the wafer 1, and the first laser beam is applied a plurality of times. Irradiation forms a first modified region within the wafer 1. The first modified region includes a plurality of first modified layers having different height positions. The plurality of first modified layers are formed, for example, as three layers as shown in FIG.

  The laser processing apparatus 2 used in the first laser processing step includes a chuck table 4 that sucks and holds the wafer 1 and a processing head 8 that oscillates a laser beam. The chuck 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 a holding surface 6 on the chuck table 4. The holding surface 6 is composed of a porous member. When the negative pressure generated by the suction source is applied to the wafer 1 placed on the holding surface 6 through the porous member, the chuck table 4 holds the wafer 1 by suction.

The processing head 8 has a function of condensing the oscillated first laser beam inside the wafer 1 and forms a modified layer by causing multiphoton absorption at a predetermined depth inside the wafer 1. . As the first laser beam, for example, a laser beam having a wavelength that oscillates using Nd: YVO ₄ or Nd: YAG as a medium and is transmissive to the wafer 1 is used. The laser processing apparatus 2 can focus the first laser beam at an arbitrary height inside the wafer 1.

  The chuck table 4 is fed in the machining feed direction (for example, the direction of the arrow in FIG. 2A) of the laser machining apparatus 2 by a machining feed means (not shown) powered by a pulse motor or the like. The wafer 1 is processed and fed by the chuck table 4 being fed in the machining feed direction.

  In the first laser processing step, first, the wafer 1 is placed on the holding surface 6 of the chuck table 4 of the laser processing apparatus 2 with the surface 1a of the wafer 1 facing downward. Then, a negative pressure is applied from the chuck table 4 to suck and hold the wafer 1.

  Next, the first laser beam is irradiated from the processing head 8 of the laser processing apparatus 2 to the back surface 1b of the wafer 1 along one of the first scheduled division lines 3c. The first laser beam is focused to a predetermined depth of the wafer 1 and the wafer 1 is processed and sent, and the first modified layer closest to the surface 1a of the wafer 1 among the plurality of first modified layers. 9a is formed.

  Next, the condensing point of the first laser beam is positioned at a height position on the back surface 1b side with respect to the first modified layer 9a, and the wafer 1 is processed and fed along the same first division planned line 3c. Then, the first modified layer 9b is formed at a height position closer to the back surface 1b than the first modified layer 9a is irradiated with the first laser beam. When the first modified layer 9b is formed, the wafer 1 is processed and fed in the opposite direction to that when the first modified layer 9a is formed.

  Further, the condensing point of the first laser beam is positioned at a height position on the back surface 1b side with respect to the first modified layer 9b, and the wafer 1 is processed and fed along the same first division planned line 3c. Irradiation of the first laser beam forms a first modified layer 9c closest to the back surface 1b among the plurality of first modified layers. When the first modified layer 9c is formed, the wafer 1 is processed and fed in the opposite direction to that when the first modified layer 9b is formed.

  By the irradiation of the first laser beam when forming the first modified layer 9c, a crack 7 extending from the first modified layer 9a closest to the surface 1a to the surface 1a is formed. As described above, a first modified region including the plurality of first modified layers and the cracks 7 is formed along one of the first planned division lines 3c. After the first modified region is formed along one first scheduled division line 3c, the wafer 1 is indexed and fed. Then, first modified regions are formed one after another along the remaining first division line 3c.

  For example, when a silicon wafer is used as the wafer 1, the first laser beam irradiated when forming the plurality of first modified layers is, for example, a pulse laser having a wavelength of 1342 nm that is transmissive to silicon. Use a beam. The output is 0.9 W to 1.1 W, the repetition frequency is 90 kHz, and the feed speed of the wafer 1 is set to 700 mm / s.

  The first modified layer 9a closest to the surface 1a is formed at a height position that is 65 μm to 75 μm away from the surface 1a. The height position of the first modified layer 9a is set to a height at which the crack does not reach the adjacent device 5 when the crack extends from the first modified layer 9a. The first modified layer 9b to be formed next is formed at a height of 60 μm to 70 μm away from the first modified layer 9a on the back surface 1b side. Furthermore, the first modified layer 9c closest to the back surface 1b side is formed at a height position 60 μm to 70 μm away from the first modified layer 9b on the back surface 1b side.

  In the wafer processing method according to the present embodiment, the second laser processing step is performed next. The second laser processing step will be described with reference to FIG. In this step, the second modified region is formed by irradiating a second laser beam having a wavelength that is transmissive to the wafer 1 along the remaining division lines of the plurality of division lines. The remaining divided lines of the plurality of divided lines are, for example, the second divided line 3d.

  FIG. 2B is a schematic cross-sectional view illustrating the second laser processing step for forming the second modified region. In the drawing, for convenience of explanation, hatching attached to some components is omitted.

  In the second laser processing step, the inside of the wafer 1 is irradiated with the second laser beam a plurality of times while changing the height of the condensing point from the back surface 1b side of the wafer 1 to the inside of the wafer 1. A second modified region is formed. The second modified region includes a plurality of modified layers having different height positions, and the number of modified layers included in the second modified region is included in the first modified region. Less than the number of modified layers. The plurality of second modified layers are formed, for example, in two layers as shown in FIG.

  In this step, a laser processing apparatus 2a similar to the laser processing apparatus 2 used in the first laser processing step is used. The laser processing apparatus 2a includes a chuck table 4a whose upper surface is a holding surface 6a, and a processing head 8a.

  Note that the laser processing apparatus 2 used in the first laser processing step may be used in the second laser processing step. In that case, the first laser processing step and the second laser processing step can be continuously performed while the wafer 1 is sucked and held on the chuck table 4.

  In the second laser processing step, first, similarly to the first laser processing step, the wafer 1 is placed on the holding surface 6a and is sucked and held by the chuck table 4a. When the second laser processing step is performed continuously after the first laser processing step using the laser processing apparatus 2, suction holding by the chuck table 4 is performed after the first laser processing step is completed. continue.

  In the second laser processing step, the back surface 1b of the wafer 1 is irradiated with the second laser beam along one of the second scheduled division lines 3d from the processing head 8a of the laser processing apparatus 2a. The second laser beam is focused to a predetermined depth of the wafer 1 and the wafer 1 is processed and sent, and the second modified layer closest to the surface 1a of the wafer 1 among the plurality of second modified layers. 11a is formed.

  Next, the condensing point of the second laser beam is positioned at a height position on the back surface 1b side with respect to the second modified layer 11a, and the wafer 1 is processed and fed along the same scheduled dividing line. The second modified layer 11b is formed at a height position closer to the back surface 1b than the second modified layer 11a by irradiation with a laser beam. When the second modified layer 11b is formed, the wafer 1 is processed and fed in the direction opposite to that when the second modified layer 11a is formed. Thus, a second modified region including a plurality of second modified layers is formed along one of the second scheduled division lines 3d.

  After the second modified region is formed along one second scheduled division line 3d, the wafer 1 is indexed and fed. Then, second modified regions are formed one after another along the remaining second division line 3d.

  For example, when a silicon wafer is used as the wafer 1, the second laser beam irradiated when forming the plurality of second modified layers is, for example, a pulse laser having a wavelength of 1342 nm that is transmissive to silicon. Use a beam. The output is 1.1 W to 1.3 W, the repetition frequency is 90 kHz, and the feeding speed of the wafer 1 is set to 700 mm / s.

  The second modified layer 11a closest to the surface 1a is formed at a height position separated from the surface 1a by 80 μm to 90 μm. The height position of the second modified layer 11a is set to a height at which the crack does not reach the adjacent device 5 when the crack extends from the second modified layer 11a. The next second modified layer 11b is formed at a height of 60 μm to 70 μm away from the second modified layer 11a on the back surface 1b side.

  When an external force acts on the modified layer formed inside the wafer 1, a crack extending from the modified layer is generated. When the laser beam is irradiated so as to form a further modified layer that overlaps the modified layer already formed inside the wafer 1, an external force can be applied to the existing modified layer. When the external force applied to the modified layer formed in the region close to the surface 1a of the wafer 1 exceeds a predetermined level, a crack extending from the modified layer reaches the surface 1a of the wafer 1, and the crack is formed on the surface 1a. Exposed to.

  Therefore, in the wafer processing method according to the present embodiment, the number of modified layers included in the second modified region formed in the second laser processing step is formed in the first laser processing step. Less than the number of modified layers included in the first modified region. For example, the number of first modified layers included in the first modified region is 3, and the number of second modified layers included in the second modified region is 2.

  Then, in the first modified region, the external force applied to the first modified layer 9a closest to the surface 1a of the wafer 1 exceeds a predetermined level, and cracks extending from the first modified layer 9a occur. It reaches the surface 1a. On the other hand, in the second modified region, the external force applied to the second modified layer 11a closest to the surface 1a of the wafer 1 is unlikely to exceed a predetermined level.

  In the wafer processing method according to the present embodiment, cracks from the modified layer to the surface 1a are not formed along all the division lines, while the modified layer is formed along some of the division lines. To the surface 1a. Therefore, the warpage of the wafer 1 can be suppressed as compared with the case where cracks extending from the modified layer to the surface 1a are formed along all the division lines.

  Further, the first modified layer 9a closest to the surface 1a of the plurality of first modified layers and the second modified layer 11a closest to the surface 1a of the plurality of second modified layers are separated from the surface 1a. Is formed to be deeper than the finished thickness of each individual chip to be manufactured.

  When the modified layer is formed at a depth shallower than the finished thickness, when the wafer 1 is thinned and divided into individual chips, the modified layer remains on the side surfaces of the individual chips, When subjected to impact or the like, damage such as chipping or cracking may occur from the modified layer. Therefore, the depth of the modified layer is set in this way so that the modified layer is removed by grinding in the process of thinning the wafer 1 in the grinding step described later.

  Note that the first laser processing step and the second laser processing step may be performed in this order, or the order of both may be switched. When the second laser processing step is performed later, the crack 7 reaching the surface 1a of the wafer 1 is formed, and the modified layer 9b is formed in a state in which a force (stress) directed toward the outer periphery is applied to the surface 1a of the wafer 1. Can be easily divided.

  When the first laser processing step and the second laser processing step are performed, the modified layer is formed along all of the plurality of division lines 3a parallel to the first direction 1c. Then, the chuck table 4 is rotated to switch the direction in which the wafer 1 is processed and fed to irradiate the laser beam, and a modified layer is formed along all the planned division lines.

  That is, for the plurality of scheduled division lines 3b parallel to the second direction 1d, the first laser processing step is performed along some of the scheduled division lines, while the remaining division planned lines are processed along the remaining division lines. 2 laser processing steps are performed. Here, for example, some of the planned division lines are the third division planned lines 3e, and the remaining division planned lines are the fourth division planned lines 3f.

  The order of performing the laser processing steps is not limited to this. For example, the first laser processing step is continuously performed on the first scheduled division line 3c and the third scheduled division line 3e. Next, the second laser processing step is continuously performed on the second scheduled division line 3d and the fourth scheduled division line 3f. In this case, since the number of times of changing the laser beam irradiation conditions can be reduced, each laser processing step can be performed more stably.

  When a crack is formed from the modified layer to the surface 1a of the wafer 1, a force is applied to move both wall surfaces of the crack. When the crack is formed in all the division lines 3 of the wafer 1, a force (stress) directed toward the outer periphery of the wafer 1 is applied to the front surface 1 a of the wafer 1 as a sum of the forces, and the wafer 1 has the back surface 1 b inside. And then bend. Therefore, in the wafer processing method according to the present embodiment, the cracks are prevented from being formed in all the division planned lines 3.

  In the wafer processing method according to the present embodiment, the first scheduled division line 3c and the second scheduled division line 3d constituting the plurality of scheduled division lines 3a parallel to the first direction 1c are shown in FIG. As shown, for example, they may be arranged alternately. In this case, the number of modified layers in which cracks reaching the surface 1a occur is about half of all the modified layers, and the force applied to the surface 1a side of the wafer 1 can be uniformly reduced over the entire surface 1a.

  Next, the grinding step will be described with reference to FIG. FIG. 3 is a partial cross-sectional view for schematically explaining a cross section of the wafer 1 in the grinding step. In the figure, for convenience of explanation, some components are not hatched. The grinding step is performed after the first laser processing step and the second laser processing step are performed. 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 chips.

  In this step, the grinding apparatus 10 is used. The grinding apparatus 10 includes a spindle 12 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 12 and includes a grinding wheel 16 on the lower side. A rotation drive source (not shown) such as a motor is connected to the other end side of the spindle 12, and when the motor rotates the spindle 12, the grinding wheel 14 mounted on the spindle 12 also rotates.

  The grinding device 10 also has a chuck table 18 that faces the grinding wheel 14 and holds the object to be ground. On the upper surface of the chuck table 18, a porous member connected to a suction source (not shown) is disposed. The chuck table 18 is rotatable around an axis substantially perpendicular to the holding surface 20.

  In the grinding step, first, the wafer 1 is placed on the holding surface 20 of the chuck table 18 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 hold the wafer 1 on the chuck table 18.

  At this time, if the crack 7 reaching the surface of the wafer 1 along all the division lines 3 set for the wafer 1 is generated, the warpage of the wafer 1 is likely to increase. Then, when the wafer 1 is placed on the holding surface 20 of the chuck table 18 with the surface 1 a of the wafer 1 facing downward, a large gap is generated between the surface 1 a of the wafer 1 and the holding surface 20. Therefore, even if a negative pressure is applied from the chuck table 18 to suck and hold the wafer 1 on the chuck table 18, the negative pressure leaks from the gap and is difficult to hold.

  In contrast, in the wafer processing method according to the present embodiment, cracks 7 extending from a part of the modified layer formed on the wafer 1 to the surface 1a of the wafer 1 occur. The crack does not occur from the layer. Therefore, warpage of the wafer 1 is reduced. Then, when the wafer 1 is placed on the chuck table 18, the gap between the surface 1 a of the wafer 1 and the holding surface 20 becomes small, and a negative pressure is easily applied to the wafer 1 from the chuck table 18. Therefore, suction holding becomes easy.

  After the wafer 1 is sucked and held on the chuck table 18, the chuck table 18 is rotated, and the spindle 12 is further rotated to rotate the grinding wheel 14. When the grinding wheel 14 is lowered and the grinding wheel 16 comes into contact with the back surface 1b of the wafer 1, grinding of the back surface 1b is started. The grinding wheel 14 is further lowered to thin the wafer 1 to a predetermined thickness. When a crack extends from the modified layer in the thickness direction of the wafer 1 during the grinding process, and the crack penetrates the wafer 1 in the thickness direction, the wafer 1 is divided by the crack.

  For example, when the cracks 7 from all the modified layers to the surface 1a are formed in advance, in the grinding step, the wafer 1 is divided into individual chips by the cracks 7 at an early timing. Grinding is continued thereafter, and force is applied to each chip so that the chip moves in a plane parallel to the surface 1a, and the chips collide with each other. In particular, when the corners of the chip collide with each other, a large impact occurs and damage such as chipping occurs on the chip.

  On the other hand, in the present embodiment, since the crack 7 extending from a part of the modified layer to the surface 1a is generated, the division of the wafer 1 proceeds in stages in the grinding step. That is, as the grinding progresses, the wafer 1 is first divided at a location where the crack 7 reaching the surface 1a exists. Next, the wafer 1 is divided at a location where the modified layer 9 where the crack 7 is not present exists.

  When the division proceeds stepwise, when the wafer 1 is divided at the location where the crack 7 reaching the surface 1a exists, the bonding is maintained at the location where the crack 7 does not exist, and a combined body of a plurality of chips is formed. . Since the combined body is larger than each chip, even if a grinding force is applied, the combined body is harder to move than the chip, and until the combined body is further divided into individual chips, the collision between the combined bodies does not occur. It is suppressed. Therefore, according to one embodiment of the present invention, damage to a formed chip can be reduced.

  Then, cracks extend from all the modified layers, the cracks penetrate the wafer 1 up and down, and when the wafer 1 is ground to the finished thickness of the chips, individual chips are formed.

  By the wafer processing method described above, the warpage of the wafer 1 can be reduced and the wafer 1 can be sucked and held, and individual chips can be formed by grinding the wafer 1 appropriately.

  In addition, this invention is not limited to description of the said embodiment, A various change can be implemented. For example, in the above-described embodiment, the first laser processing step is performed for all of the first scheduled division lines 3c, and the second laser processing step is performed for all of the second scheduled division lines 3d before and after that. Although described, the present invention is not limited to this.

  For example, the first scheduled division line 3c and the second scheduled division line 3d may be set to be alternately arranged, and the modified layer may be formed in this order by irradiating the laser beam in the arrangement order. . At this time, the laser beam under the irradiation condition in the first laser processing step and the laser beam under the irradiation condition in the second laser processing step are alternately irradiated onto the respective scheduled division lines. When the laser beam is irradiated in this manner, the total distance for indexing and feeding the wafer 1 can be minimized, so that the time required for laser processing can be minimized.

  In the first laser processing step and the second laser processing step, the case where the laser beam is irradiated from the back surface side of the wafer along each division line has been described. However, for example, in the first laser processing step and the second laser processing step, the laser beam may be irradiated from the surface side of the wafer. In that case, the plurality of modified layers included in the first modified region and the second modified region are formed in order from the back surface 1 b side of the wafer 1.

  Furthermore, in the said embodiment, the case where a laser beam was irradiated in multiple times by changing the height of a condensing point along each division planned line in the 1st laser processing step and the 2nd laser processing step was demonstrated. . However, in the first laser processing step and the second laser processing step, it is not necessary to irradiate the laser beam a plurality of times along each division planned line.

  For example, the laser beam may be irradiated using a multifocal optical system capable of condensing the laser beam at a plurality of different height positions with a single laser beam irradiation. When the multifocal optical system is used, a plurality of modified layers having different heights can be simultaneously formed along a predetermined division line only by processing and feeding the wafer 1 once while irradiating the inside of the wafer with a laser beam. .

  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 1st direction 1d 2nd direction 3 Planned division line 3a Planned division line parallel to 1st direction 3b Planned division line parallel to 2nd direction 3c 1st planned division line 3d 2nd planned split line 3e 3rd planned split line 3f 4th planned split line 5 device 7 crack 9a, 9b, 9c first modified layer 11a, 11b second modified layer 13 surface protective tape 2, 2a Laser processing device 4, 4a Chuck table 6, 6a Holding surface 8, 8a Processing head 10 Grinding device 12 Spindle 14 Grinding wheel 16 Grinding wheel 18 Chuck table 20 Holding surface

Claims (2)

A method of processing a wafer having a surface on which devices are respectively formed in each region partitioned by a plurality of division lines arranged in a grid pattern,
By irradiating and condensing a first laser beam having a wavelength that is transparent to the wafer along the partial division lines of the plurality of division lines, and condensing the inside of the wafer. A first laser processing step for forming a first modified region;
A second laser beam having a wavelength that is transmissive to the wafer is irradiated and condensed along the remaining division lines of the plurality of division lines to be focused inside the wafer. A second laser processing step for forming two modified regions,
The first modified region includes a plurality of modified layers having different height positions from each other, and a modified layer closest to the surface of the plurality of modified layers extending to the surface of the wafer and extending toward the surface side. An exposed crack,
The second modified region includes a plurality of modified layers having different height positions from each other,
The wafer processing method, wherein the number of modified layers included in the second modified region is smaller than the number of modified layers included in the first modified region. The plurality of division lines extend in a first direction and a second direction intersecting the first direction,
The partial division lines of the plurality of division lines and the remaining division lines of the plurality of division lines are alternately in each of the first direction and the second direction. Lined up in
After performing the first laser processing step along the part of the planned division lines arranged in the first direction, the second laser is produced along the remaining divisional lines arranged in the first direction. The wafer processing method according to claim 1, wherein a processing step is performed.