JP6710464B2 - Wafer processing method - Google Patents

Description

The present invention relates to a wafer processing method.

In the process of processing a wafer on the surface of which a plurality of devices such as ICs and LEDs are formed to produce chips, the back surface of the wafer is ground to thin the wafer, and then the wafer is divided into individual chips. Chips are formed.

On the surface of the wafer before division, devices are arranged in respective regions defined by a plurality of intersecting division lines. The wafer is irradiated with a transparent laser beam from the back surface side of the wafer along the dividing lines, and is condensed to form a modified layer serving as a starting point of division in the wafer by multiphoton absorption. Next, an external force is applied to the wafer to extend cracks from the modified layer in the thickness direction of the wafer to divide the wafer into individual chips.

With respect to the above-described chip manufacturing process, for example, as described in Patent Document 1, a process of simultaneously performing grinding of the back surface side of the wafer and division into chips is being studied. In advance, the modified layer is formed on the wafer, and then the back surface side of the wafer is ground to thin the wafer, and the cracks are extended from the modified layer by the force generated by the grinding to form the wafer. To divide. In this way, the process can be simplified by simultaneously performing the division and the grinding.

Further, when the modified layer is formed by irradiating a laser beam from the back surface of the wafer, the laser irradiation condition of the laser processing apparatus is adjusted to form the modified layer and the modified layer reaches the front surface of the wafer. A process of forming a crack is being studied.

International Publication No. 03/077295

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

When the cracks are formed on all of the plurality of dividing lines, a force (stress) is applied to the surface of the wafer in the outer peripheral direction. On the other hand, no such force is applied to the back surface of the wafer. Therefore, the wafer is warped so that the back surface faces inward.

After forming the modified layer, the wafer is transferred from the laser processing device to the grinding device etc. to grind the back surface side of the wafer, and the wafer is placed on the chuck table of the grinding device with the front surface of the wafer facing downward. Place on. In the grinding apparatus, the wafer is suction-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, to perform grinding.

However, if the wafer is warped so that the back surface faces the inside, the transfer mechanism of the laser processing apparatus may not be able to properly suck and hold the wafer, and the wafer may not be transferred. Further, even if the wafer can be conveyed to the grinding device, when the wafer is placed on the chuck table with its front side facing downward, if the wafer is warped, the surface partially floats from the chuck table. Then, even if a negative pressure is applied from the chuck table to suck and hold the wafer, the negative pressure leaks in the floating portion, and it becomes difficult to appropriately suck and hold the wafer.

The present invention has been made in view of the above problems, and an object thereof is to reduce the warpage of the wafer, facilitate the transportation of the wafer, and provide a wafer processing method that enables suction and holding of the wafer. Is to provide.

According to one aspect of the present invention, each of the plurality of division planned lines parallel to the first direction and the plurality of division planned lines parallel to the second direction intersecting the first direction are partitioned from each other. A method of processing a wafer having a surface on which a device is formed in each region, wherein a transparency to the wafer is provided along a part of a plurality of planned dividing lines parallel to the first direction. Irradiating the inside of the wafer with a first laser beam having a wavelength having the same, forming a first modified layer along the partial dividing line, and cracks from the first modified layer to the surface. And a second laser beam having a wavelength transparent to the wafer along the remaining planned dividing lines of the plurality of planned dividing lines parallel to the first direction. Second laser processing step of irradiating the inside of the wafer with a second modified layer along the remaining division lines, the first laser processing step, and the second laser processing step. And a grinding step of grinding the wafer from the back surface side to thin the wafer to a predetermined thickness and dividing the wafer into individual chips, in the second laser processing step. A method for processing a wafer is provided, which comprises irradiating the second laser beam under an irradiation condition in which a crack reaching the surface of the wafer does not occur.

Note that in one embodiment of the present invention, the part of the planned division lines of the plurality of planned division lines parallel to the first direction is every other line in the plurality of planned division lines parallel to the first direction. It is a line to be divided, and the second laser processing step may be performed after the first laser processing step is performed.

According to the wafer processing method of one embodiment of the present invention, in the laser processing step, cracks from all of the modified layers formed along the plurality of planned dividing lines on the surface of the wafer to the surface may be generated. Instead, the cracks are formed only on some of the planned dividing lines. That is, since no cracks are formed on the remaining planned dividing lines, the warp of the wafer is reduced accordingly.

When the warp of the wafer is reduced, the wafer is easily transferred by the transfer mechanism, and is more easily suction-held on the chuck table of the grinding device. 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 the crack reaching the surface is formed appropriately, the wafer can be easily divided into chips, and the problem due to the warp of the wafer can be suppressed.

In addition, if cracks from all modified layers to the surface are generated before the back surface of the wafer is ground, the wafer is quickly divided by the cracks when the back surface of the wafer is ground to thin the wafer. To be done. Then, the grinding process is continued even after the wafer is divided into individual chips. Then, a force is applied by further grinding, and the individual chips move in a plane parallel to the surface so that the chips collide with each other. In particular, when the corners of the chips collide with each other, the chips are likely to be damaged such as chipping or unnecessary cracks.

On the other hand, without causing cracks reaching the surface from all the modified layers, causing cracks reaching the surface only from some modified layers, unless the cracks reaching the surface from the remaining modified layers , The wafer division does not proceed rapidly during grinding. That is, when grinding is started, the wafer is first divided at the location where the crack exists, and then the crack extends from the modified layer in the thickness direction of the wafer at the location where the remaining modified layer exists. Is divided. That is, the division of the wafer progresses in stages during the grinding process.

When the grinding progresses in stages, in the initial stage of division, the bond is maintained at a portion where there is no crack from the modified layer to the surface, and a bonded body of a plurality of chips is formed. Since the bonded body is larger than the individual chips, it is difficult to move even if a force due to grinding is applied, and the collision between the bonded bodies is suppressed until the bonded body is further divided into the 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, a wafer processing method is provided in which warpage of a wafer is reduced, the wafer can be easily transported, and the wafer can be sucked and held.

FIG. 1A is a plan view of a surface of a wafer illustrating an example of a plurality of planned dividing lines, and FIG. 1B is a plane view of a surface of a wafer illustrating another example of a plurality of planned dividing lines. It is a figure. FIG. 2A is a schematic cross-sectional view for explaining a laser processing step of forming a modified layer and forming a crack reaching the surface of the wafer, and FIG. 2B is a wafer for forming the modified layer. FIG. 6 is a schematic cross-sectional view illustrating a laser processing step that does not form a crack reaching the surface. It is a cross-sectional schematic diagram explaining a grinding step.

An embodiment 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, which is the workpiece, is a 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. 1(A), the front surface 1a of the wafer 1 has a plurality of planned dividing lines 3a parallel to the first direction 1c and a second direction 1d intersecting the first direction 1c (for example, And a plurality of planned dividing lines 3b parallel to the first direction 1c). Devices 5 such as ICs and LEDs are formed in the respective partitioned areas. The wafer 1 is finally divided along the dividing lines 3 to form individual chips.

Further, a part of the plurality of planned dividing lines 3a parallel to the first direction 1c is a first planned dividing line 3c, and the remaining planned dividing lines 3a parallel to the first direction 1c are The planned division line is the second planned division line 3d. FIG. 1A shows an example of setting of the first planned division line 3c and the second planned division line 3d. In addition, in FIG. 1(A) and FIG. 1(B) described later, the first planned dividing line 3c is shown by a two-dot chain line, and the second planned dividing line 3d is shown by a one-dot chain line.

In a first laser processing step described later, a first modified layer (described later) is formed inside the wafer 1 along the first planned dividing line 3c, and the wafer 1 is removed from the first modified layer. A crack reaching the surface 1a is generated. In a second laser processing step described later, a second modified layer (described later) is formed inside the wafer 1 along the second planned dividing line 3d. In the second laser processing step, cracks from the second modified layer to the surface 1a of the wafer 1 are not generated.

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 cracks are formed on all the planned dividing lines 3 of the wafer 1, a force (stress) directed to the outer periphery of the wafer 1 is applied to the front surface 1a of the wafer 1 as a total of the forces, and the back surface 1b of the wafer 1 is inwardly moved. And then it will warp. Therefore, in the wafer processing method according to the present embodiment, the cracks are prevented from being formed on all the planned dividing lines 3.

For example, the first planned dividing line 3c and the second planned dividing line 3d that form the plurality of planned dividing lines 3a parallel to the first direction 1c are arranged alternately as shown in FIG. Will be distributed. That is, the first modified layers and the second modified layers are formed so as to be alternately arranged. Then, the number of modified layers in which cracks reach the surface 1a 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.

The arrangement of the first planned dividing line 3c and the second planned dividing line 3d that form the plurality of planned dividing lines 3a parallel to the first direction 1c is not limited to this. As illustrated in FIG. 1B, the first planned dividing line 3c is arranged so as to cross the vicinity of the center of the wafer 1, and the second planned dividing line 3d is arranged so as not to cross the vicinity of the center of the wafer 1. You may. Then, a crack reaching the surface 1a of the wafer 1 is formed so as to cross the vicinity of the center of the wafer 1.

In the later-described grinding step (see FIG. 3 ), the front surface 1 a of the wafer 1 is held by a rotatable chuck table, and the grinding wheel held by a grinding wheel that rotates on the back surface 1 b side of the wafer 1 while the chuck table is rotated is held. Grinding is carried out by contacting a whetstone. When the grinding is performed in this manner, a relatively large force is applied near the outer periphery of the wafer 1 due to the grinding, and the wafer 1 is likely to be divided, whereas a relatively large force is hardly applied near the center of the wafer 1, The wafer 1 is unlikely to be divided.

Then, the place where the crack is formed from the modified layer to the surface 1a of the wafer 1 is divided by a relatively small force. Therefore, when the first planned dividing line 3c and the second planned dividing line 3d are set as illustrated in FIG. 1B, a crack reaching the surface 1a of the wafer 1 is formed in a portion where a force applied by grinding is small. , It is easy to split.

As described above, with reference to FIGS. 1A and 1B, the first planned dividing line 3c which is a part of the plurality of planned dividing lines 3a parallel to the first direction 1c and the remaining second dividing line 3c. An example of setting the planned division line 3d of and has been described. In the wafer processing method according to the present embodiment, the plurality of planned division lines 3b parallel to the second direction 1d are also part of the first planned division line and the remaining second planned division line. And may be set.

In this case, cracks extending from the modified layer to the surface are also formed along some of the planned dividing lines 3b parallel to the second direction 1d while the remaining planned dividing lines are formed. Since the cracks are not formed along the wafer, the warp of the wafer 1 can be further reduced.

Next, a method of processing the wafer 1 according to this embodiment will be described. In the processing method, a first laser processing step is performed. In this step, the first laser beam is irradiated to the inside of the wafer 1 along the first planned dividing line 3c, and the first modified layer is formed at a predetermined depth along the first planned dividing line 3c. And a crack extending from the first modified layer to the surface 1a of the wafer 1 is generated.

FIG. 2A is a schematic cross-sectional view illustrating a first laser processing step of forming a modified layer and forming a crack reaching the surface 1 a of the wafer 1. In this figure, for convenience of description, hatching attached to some of the components is omitted.

The laser processing apparatus 2 used in the first laser processing step includes a chuck table 4 that holds the wafer 1 by suction and a processing head 8 that oscillates a laser beam. The chuck table 4 has therein a suction path (not shown) connected to a suction source (not shown), 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 made of a porous member, and a negative pressure generated by the suction source is applied to the wafer 1 placed on the holding surface 6 through the porous member so that the chuck table 4 holds the wafer 1 in place. Hold by suction.

The processing head 8 has a function of oscillating a first laser beam to focus the laser beam inside the wafer 1, forms a first modified layer 9a at a predetermined depth, and forms the first modified layer. It is possible to irradiate the first laser beam under the condition that the crack 7 from 9a to the surface 1a of the wafer 1 is generated. As the first laser beam, for example, a laser beam having a wavelength that is oscillated with Nd:YVO ₄ or Nd:YAG as a medium and has a transparency to the wafer 1 is used.

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

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

Next, the back surface 1b of the wafer 1 is irradiated with the first laser beam from the processing head 8 of the laser processing apparatus 2. The first laser beam is focused at a predetermined depth of the wafer 1 to form the crack 7 reaching the surface 1a of the wafer together with the first modified layer 9a. The first modified layer 9a and the crack 7 reaching the surface 1a of the wafer 1 are formed along the first planned dividing line 3c that is a part of the plurality of planned dividing lines 3a parallel to the first direction 1c. The wafer 1 is processed and fed while being irradiated with the first laser beam so as to be formed.

After the first modified layer 9a and the crack 7 reaching the surface of the wafer 1 are formed along one of the first planned dividing lines 3c, the wafer 1 is indexed and fed. Then, the first modified layer 9a and the crack 7 reaching the surface 1a of the wafer 1 are formed one after another along the remaining first planned dividing line 3c.

In this first laser processing step, for example, a pulsed laser beam having a wavelength of 1342 nm is used as the first laser beam having transparency to the wafer 1 made of silicon. The output is set to 1.5 W, the repetition frequency is set to 90 kHz, and the feed rate of the wafer 1 is set to 700 mm/s. When the wafer 1 is irradiated with the laser beam under this irradiation condition, a modified layer and a crack extending from the modified layer to the surface 1a of the wafer 1 can be formed.

Next, the second laser processing step will be described with reference to FIG. In this step, the inside of the wafer 1 is irradiated with the second laser beam along the second planned dividing line 3d, and the second modified layer is formed along the second planned dividing line 3d. FIG. 2B is a schematic cross-sectional view illustrating a second laser processing step in which a crack reaching the surface 1a of the wafer 1 is not formed when forming the modified layer. In this figure, for convenience of description, hatching attached to some of the components is omitted.

In the second laser processing step, the same laser processing apparatus as the laser processing apparatus 2 used in the first laser processing step is used. The laser processing device 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 suction-held on the chuck table 4.

The laser processing apparatus 2a used in the second laser processing step has the same configuration as the laser processing apparatus 2 described above, and thus duplicated description will be omitted. The processing head 8a of the laser processing apparatus 2a used in the second laser processing step can irradiate the laser beam under irradiation conditions for forming the second modified layer 9b at a predetermined depth. However, under the irradiation conditions, the crack 7 extending from the formed second modified layer 9b to the surface 1a of the wafer 1 is not formed.

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 suction-held on the chuck table 4a. In addition, when the second laser processing step is continuously performed after the first laser processing step using the laser processing device 2, after the first laser processing step is completed, suction holding by the chuck table 4 is performed. continue.

Next, the back surface 1b of the wafer 1 is irradiated with the second laser beam from the processing head 8a of the laser processing apparatus 2a. The second laser beam is focused at a predetermined depth within the wafer 1 to form the second modified layer 9b. The wafer 1 is processed and fed while being irradiated with the second laser beam so that the second modified layer 9b is formed along the second planned dividing line 3d.

After the second modified layer 9b is formed along the one second planned dividing line 3d, the wafer 1 is indexed and sent. Then, the second modified layer 9b is sequentially formed along the remaining second planned dividing line 3d. In the second laser processing step, cracks from the second modified layer 9b to the surface of the wafer 1 are not generated.

In the second laser processing step, for example, a pulsed laser beam having a wavelength of 1342 nm is used as the second laser beam that is transparent to the wafer 1 made of silicon. The output is 1.2 W, the repetition frequency is 90 kHz, and the feed rate of the wafer 1 is 700 mm/s. That is, the second laser beam has a lower output than the above-mentioned first laser beam. When the wafer 1 is irradiated with the laser beam under these irradiation conditions, cracks extending from the modified layer to the surface 1a of the wafer 1 are not formed.

The first laser processing step and the second laser processing step may be performed in this order, or may be performed by exchanging the order of both. When the second laser processing step is performed later, the modified layer 9b is formed in a state where the crack 7 reaching the surface of the wafer 1 is formed and the surface 1a of the wafer 1 is applied with a force (stress) directed in the outer peripheral direction. Can be easily divided.

The modified layers 9a and 9b are formed so that the depth from the surface 1a is deeper than the finished thickness of the individual chips to be manufactured. When the reformed layer is formed to a depth shallower than the finished thickness, when the wafer 1 is divided into individual chips, the reformed layer remains on the side surface of each chip and the chips are subject to impact or the like. When received, damage such as chipping or cracks 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.

For example, when the finished thickness of the finally manufactured chip is 50 μm, the modified layers 9a and 9b are formed so that the depth from the surface 1a of the wafer 1 is in the range of 60 μm or more and 90 μm or less. To do.

In order to more reliably form a crack reaching the surface 1a of the wafer 1 in the first laser processing step, a second modified layer is formed in addition to the modified layer 9a so as to overlap with the modified layer 9a. Alternatively, the third and subsequent modified layers may be formed so as to overlap the modified layer 9a. By forming a modified layer that overlaps the modified layer 9a, formation of cracks from the modified layer 9a to the surface 1a of the wafer 1 can be promoted.

When forming a plurality of modified layers overlapping the modified layer 9a, the modified layers of the respective layers are sequentially formed from the side closer to the surface 1a. That is, after forming the modified layer 9a, the second modified layer is formed so as to overlap with the modified layer 9a, and then the third modified layer is formed. This is because when a laser beam is irradiated from the back surface 1b to form the modified layer of each layer, another modified layer is already formed at a position closer to the back surface 1b than the modified layer to be formed. This hinders the irradiation of the laser beam.

When forming the second modified layer overlapping the modified layer 9a, the second modified layer is formed so as to be separated from the modified layer 9a in the thickness direction of the wafer 1 by a range of 60 μm or more and 90 μm or less. To do. Further, when the third modified layer is formed, the third modified layer is formed so as to be separated from the second modified layer in the thickness direction of the wafer 1 to the same extent. That is, the distance between the modified layers of each layer is set to be approximately the same as the distance from the modified layer 9a to the surface 1a.

The irradiation conditions of the laser beam when forming the modified layer overlapping the modified layer 9a are set to be the same as the irradiation conditions of the laser beam when forming the modified layer 9a, except for the focusing depth. Alternatively, the irradiation condition is set such that the output is weaker than the irradiation condition when forming the modified layer 9a.

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

With respect to the plurality of planned dividing lines 3b parallel to the second direction 1d, cracks extending from the modified layer to the surface are formed along some of the planned dividing lines, while the remaining planned dividing lines are The crack may not be formed. In that case, the first laser processing step and the second laser processing step are similarly performed for the plurality of planned dividing lines 3b parallel to the second direction 1d.

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 plurality of planned dividing lines 3a parallel to the first direction 1c and the plurality of planned dividing lines 3b parallel to the second direction 1d. Next, the second laser processing step is continuously performed for both. In this case, since it is possible to reduce the number of times of changing the laser beam irradiation condition, it is possible to more stably perform each laser processing step.

Next, the grinding step will be described with reference to FIG. FIG. 3 is a partial cross-sectional view schematically illustrating the cross section of the wafer 1 in the grinding step. In this figure, for convenience of description, hatching attached to some components is omitted. 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, the wafer 1 is thinned to a predetermined thickness, and the wafer 1 is divided into individual chips.

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

Further, the grinding device 10 has a chuck table 18 that faces the grinding wheel 14 and holds an object to be ground. A porous member connected to a suction source (not shown) is arranged on the upper surface of the chuck table 18. The chuck table 18 is rotatable about 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 front 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 cracks 7 extending from all the modified layers 9 formed on the wafer 1 to the surface of the wafer 1 occur, the wafer 1 warps violently. Then, when the front surface 1a of the wafer 1 faces downward and the wafer 1 is placed on the holding surface 20 of the chuck table 18, a large gap is generated between the front surface 1a of the wafer 1 and the holding surface 20. Therefore, even if an attempt is made to apply a negative pressure from the chuck table 18 to hold the wafer 1 on the chuck table 18 by suction, the negative pressure leaks from the gap, making suction holding difficult.

On the other hand, in the wafer processing method according to the present embodiment, cracks 7 extending from a part of the modified layer 9 formed on the wafer 1 to the surface 1a of the wafer 1 are generated, but other modified layers 9 are formed. No cracks were generated from the above. Therefore, the warp of the wafer 1 is reduced. Then, when the wafer 1 is placed on the chuck table 18, the gap between the surface 1a of the wafer 1 and the holding surface 20 becomes small, and a negative pressure is appropriately applied to the wafer 1 from the chuck table 18. Since it becomes easier, suction and holding become easier.

After sucking and holding the wafer 1 on the chuck table 18, the chuck table 18 is rotated, and further, the spindle 12 is rotated to rotate the grinding wheel 14. Then, when the grinding wheel 14 is lowered and the grinding wheel 16 contacts 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. If 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.

If cracks 7 are formed from all the modified layers 9 to the surface 1a, the wafer 1 is divided into individual chips early by the cracks 7 in the grinding step. Then, the grinding is continued thereafter, and a force is applied to each chip so as to move in a plane parallel to the surface 1a by the grinding, and the chips collide with each other. In particular, when the corners of the chips collide with each other, a large impact is generated, and chips such as chips and unnecessary cracks are damaged.

On the other hand, in the present embodiment, cracks 7 extending from a part of the modified layer 9 to the surface 1a are generated, and cracks 7 reaching the surface 1a from the remaining modified layer 9 are not generated. The division of is progressing in stages. That is, as the grinding progresses, the wafer 1 is first divided at the locations where the cracks 7 reaching the surface 1a exist. Next, the wafer 1 is divided at the location where the modified layer 9 in which the crack 7 is not present is present.

When the division progresses stepwise, when the wafer 1 is divided at the location where the crack 7 reaches the surface 1a, the bond 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 bonded body is larger than the individual chips, it is more difficult to move than the chips even when a force due to grinding is applied, and the collision between the bonded bodies does not occur until the bonded body is further divided into individual chips. 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 warp of the wafer 1 is reduced, the wafer 1 can be held by suction, and the individual chips can be formed by appropriately grinding the wafer 1.

It should be noted that the present invention is not limited to the description of the above embodiment and can be implemented with various modifications. For example, in the above-described embodiment, the case where the first laser processing step is performed for all of the first planned dividing lines 3c and the second laser processing step is performed before and after all of the second planned dividing lines 3d Although described, the present invention is not limited to this.

For example, the first planned dividing lines 3c and the second planned dividing lines 3d may be set to be alternately arranged, and the modified layer may be formed by irradiating the laser beams in the order in which they are arranged. .. 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 to the corresponding planned dividing lines. When the laser beam is irradiated in this way, the total distance for indexing and feeding the wafer 1 can be minimized, and thus the time required for laser processing can be minimized.

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

1 Wafer 1a Front surface 1b Back surface 1c First direction 1d Second direction 3 Planned division line 3a Planned division line parallel to the first direction 3b Planned division line parallel to the second direction 3c First division planned line 3d Second planned dividing line 5 Device 7 Crack reaching wafer surface 9 Modified layer 9a First modified layer 9b Second modified layer 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 surface on which a device is formed in each area partitioned by a plurality of planned dividing lines parallel to the first direction and a plurality of planned dividing lines parallel to the second direction intersecting the first direction A method of processing a wafer having:
The inside of the wafer is irradiated with a first laser beam having a wavelength that is transparent to the wafer along a part of the plurality of planned dividing lines parallel to the first direction, and the part is divided. A first laser processing step of forming a first modified layer along the planned dividing line and generating a crack from the first modified layer to the surface;
The inside of the wafer is irradiated with a second laser beam having a wavelength that is transparent to the wafer along the remaining planned dividing lines of the plurality of planned dividing lines parallel to the first direction, and the remaining A second laser processing step of forming a second modified layer along the dividing line;
After performing the first laser processing step and the second laser processing step, the wafer is ground from the back surface side to be thinned to a predetermined thickness, and the wafer is divided into individual chips. And
In the second laser processing step, the wafer processing method is characterized in that the second laser beam is irradiated under irradiation conditions in which a crack reaching the surface of the wafer does not occur. The partial planned dividing lines of the plurality of planned dividing lines parallel to the first direction are every other planned dividing lines among the plurality of planned dividing lines parallel to the first direction,
The wafer processing method according to claim 1, wherein the second laser processing step is performed after the first laser processing step is performed.