JP6640005B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a wafer dividing method for dividing a wafer into individual chips.

  In the process of forming a modified layer inside the wafer and then grinding it into a device chip at the same time, the devices singulated during grinding move and the devices come into contact with each other, causing chipping at the corners of the device. there were. Such a problem is caused by the fact that the device moves when it is singulated. Therefore, in order to adjust the degree of crack growth from the modified layer to the surface and adjust the timing of singulation, a processing method of irradiating the inside of the wafer with a laser beam for forming the modified layer in a broken line shape. (For example, see Patent Document 1 below).

JP 2014-33163 A

  However, in recent years, silicon wafers having a crystal orientation at an angle of 45 ° with respect to a line to be divided have been often used to improve electrical characteristics. If the material layer is formed as a broken line, the kerf will meander near the corner of the device. This is considered to be because the cracks from the modified layer to the surface could not grow smoothly along the planned dividing line because the modified layer was formed in a broken line shape.

  The present invention has been made in view of the above circumstances, and in processing in which a modified layer is formed and then ground and divided into individual devices, chipping occurs in device corners, or a kerf near the corners meanders. The purpose is to prevent you from doing so.

According to the present invention, a plurality of first divided lines extending in a predetermined direction on a surface and a plurality of second divided lines formed to intersect the plurality of first divided lines are defined. Is a method of processing a wafer having a device formed in the region (1) along the first planned dividing line and the second planned dividing line, wherein a protective member is attached to the front surface side of the wafer. After the protective member attaching step and the protective member attaching step, the protective member side is held, and a laser beam having a wavelength that is transmissive to the wafer is positioned from the back side of the wafer to a focusing point inside the wafer. A first modified layer forming step of irradiating along the first scheduled dividing line to form a first modified layer inside the wafer along the first scheduled dividing line; Of a wavelength that is transparent A laser beam is irradiated from the back side of the wafer at a condensing point positioned inside the wafer along the second scheduled line, and a second reforming is performed inside the wafer along the second scheduled line. After performing the second modified layer forming step of forming a layer, the first modified layer forming step, and the second modified layer forming step, the protection member side is held and the wafer is held from the back surface. Grinding by a grinding means to reduce the thickness to a finished thickness, and a grinding operation to grow cracks reaching the surface of the wafer from the modified layer as starting points along the planned dividing line, thereby dividing the wafer into individual devices. And in the first modified layer forming step or in the second modified layer forming step, or both the first modified layer forming step and the second modified layer forming step In the modified layer, one divided At least one induction-modified layer for inducing the growth of cracks from the modified layer to the surface of the wafer, and at least one for adjusting the growth of cracks from the modified layer to the surface of the wafer. And one or more adjustment / modification layers, are formed in a composite manner , and the adjustment / reformation layer is provided at a predetermined interval to stop irradiation of the laser beam at least once to one side of each device, The wafer has a non-modified layer region at a predetermined interval inside the wafer, and the induction-modified layer has a predetermined interval shorter than the modified layer region, and is at least one side of each device. By stopping the irradiation of the laser beam once, the wafer has a non-modified layer region smaller than the non-modified layer region at a predetermined interval inside the wafer, and the adjusted and modified layer is formed from the back surface to the front surface of the wafer. And a non-modified layer of the induction-modified layer The area is gradually reduced.

  In the method for processing a wafer according to the present invention, a protective member attaching step of attaching a protective member to the front surface side of the wafer, and a first modified layer is formed inside the wafer along a first dividing line. A first modified layer forming step, a second modified layer forming step of forming a second modified layer inside the wafer along a second scheduled division line, and starting the modified layer by a grinding operation. Dividing the wafer into individual devices by growing cracks reaching the surface of the wafer along the planned dividing line, and in the first modified layer forming step or in the second modified layer forming step Alternatively, in both the first modified layer forming step and the second modified layer forming step, the modified layer formed inside the wafer is transferred from the modified layer to the surface of the wafer for each division line. Induces crack growth Since at least one induction-modified layer and at least one adjustment-modified layer for adjusting the growth of cracks from the modified layer to the surface of the wafer are formed in a complex manner, the induction modification is performed. The cracks generated from the modified layer by the modified layer are guided to the surface side of the wafer, and the growth state of the cracks reaching the surface is adjusted by the modified layer, so that when the wafer is divided into individual devices, Chips can be prevented from being chipped at corners and meandering from a kerf near the corners.

  The adjustment-modified layer has a non-modified layer region at a predetermined interval inside the wafer by stopping irradiation of the laser beam at least once to one side of each device at a predetermined interval. Therefore, when the wafer is divided, cracks do not occur from the non-modified layer region, and the timing of device singulation is adjusted so that adjacent devices do not come into contact with each other. The meandering of a nearby calf can be effectively prevented.

  The induction-modified layer is provided with a predetermined interval shorter than the non-modified layer region, and the laser beam irradiation is stopped at least once on one side of each device, so that a predetermined interval is formed inside the wafer. Has a non-modified layer region smaller than the non-modified layer region, cracks are not induced from such a small non-modified layer region, restricting the movement of the device at the time of dividing the wafer, to the corners of the device. The occurrence of chipping and the meandering of the calf near the corner can be more effectively prevented.

It is a perspective view which shows a protection member sticking process. It is a partially expanded sectional view which shows a modified layer formation process. FIG. 4 is a partially enlarged cross-sectional view showing a state in which one or more induction-modified layers and one or more adjusted modified layers have been formed inside a wafer by a modified-layer forming step. It is a partially expanded sectional view which shows a division process. (A) is sectional drawing which shows the state before implementation of an expanding process. (B) is a cross-sectional view showing a state in which the intervals between the devices have been expanded by the expanding step. It is a partially expanded sectional view which shows the 1st modification of a modified layer formation process. It is a partially expanded sectional view which shows the 2nd modification of a modified layer formation process.

  The wafer W shown in FIG. 1 is an example of a workpiece having a circular plate-shaped substrate. On the surface Wa of the wafer W, for example, a plurality of first division lines S1 extending in a first direction as a predetermined direction and a plurality of second extensions extending in a second direction intersecting the plurality of first division lines S1. The devices D are formed in a plurality of regions partitioned by the scheduled division line S2. On the other hand, the surface of the wafer W opposite to the front surface Wa is the back surface Wb to be ground. The wafer W is, for example, a silicon wafer whose crystal orientation is formed at an angle of 45 ° with respect to the extending direction of the first planned division line S1 and the second planned division line S2, and Has a notch N oriented at 45 ° to the crystal orientation. Hereinafter, a method of processing a wafer that divides the wafer W into individual devices D will be described.

(1) Protective Member Adhering Step As shown in FIG. 1, the protective member 1 is adhered to the front surface Wa of the wafer W. The protection member 1 is formed to have at least substantially the same diameter as the wafer W. When the entire surface Wa of the wafer W is covered with the protection member 1, each device D is protected. The material of the protection member 1 is not particularly limited as long as it has at least adhesiveness.

(2) Tape Adhering Step As shown in FIG. 2, an expandable tape T is attached to a lower portion of the annular frame F, and the tape T is attached to the entire surface of the protective member 1 attached to the wafer W. . Thus, the wafer W is formed integrally with the frame F in a state where the back surface Wb side is exposed upward.

(3) Modified layer forming step The modified layer forming step is performed by being divided into a first modified layer forming step and a second modified layer forming step. In the present embodiment, a case where the second modified layer forming step is performed after the first modified layer forming step is performed will be described. The first modified layer forming step may be performed after the second modified layer forming step is performed.

(3-1) First Modified Layer Forming Step After performing the protective member attaching step and the tape attaching step, the protective member 1 side is held by the rotatable holding table 10, and the upper side of the holding table 10 is The modified layer M (first modified layer m1) is formed inside the wafer W along the first scheduled division line S1 by using the arranged laser beam irradiation means 20. The upper surface of the holding table 10 serves as a holding surface 11 for sucking and holding the wafer W under a suction action from a suction source. Although not shown, the holding table 10 has moving means for relatively moving the holding table 10 and the laser beam irradiation means 20 in a horizontal direction (X-axis direction and Y-axis direction) perpendicular to the vertical direction (Z-axis direction). It is connected.

  The laser beam irradiation means 20 includes an oscillator 21 that oscillates a laser beam LB having a wavelength that is transparent to the wafer W, a condenser 22 for condensing the laser beam LB, and an output adjustment for adjusting the output of the laser beam. At least. The laser beam irradiating means 20 is movable in the Z-axis direction, and can adjust the focusing position of the laser beam LB by moving the condenser 22 in the Z-axis direction.

  When forming the first modified layer m1 inside the wafer W, the wafer T is placed on the holding surface 11 of the holding table 10 with the tape T facing downward, and the back surface Wb of the wafer W is oriented upward, The protection member 1 is suction-held on the holding surface 11 of the holding table 10 by the suction force of the suction source. The laser beam irradiation means 20 lowers the condenser 22 in the Z-axis direction approaching the wafer W, and adjusts the focal point P of the laser beam LB to a desired position. Subsequently, by moving the holding table 10 in the X-axis direction by, for example, a moving unit, the laser beam irradiation unit 20 and the holding table 10 are relatively moved in a direction (X-axis direction) parallel to the back surface Wb of the wafer W. While being moved, the laser beam LB having a wavelength that is transparent to the wafer W from the oscillator 21 is radiated from the back surface Wb side of the wafer W in a broken line along the first scheduled division line S1, and the inside of the wafer W The first modified layer m1 is formed. When the first modified layer m1 is formed by irradiating the laser beam LB along all the first scheduled division lines S1, the first modified layer forming step is completed.

(3-2) Second Modified Layer Forming Step Next, the modified layer M (second modified layer m2) is placed inside the wafer W along the second scheduled division line S2 using the laser beam irradiation means 20. To form Specifically, by rotating the holding table 10 and rotating the wafer W shown in FIG. 1 by 90 °, the second scheduled division line S2 oriented in the second direction is oriented, for example, in the X-axis direction. The laser beam irradiation means 20 lowers the condenser 22 in the Z-axis direction approaching the wafer W, and adjusts the focal point P of the laser beam LB to a desired position. Subsequently, for example, by moving the holding table 10 in the X-axis direction, the laser beam irradiation means 20 and the holding table 10 are relatively moved to the back surface W of the wafer W.
The laser beam irradiating means 20 transmits a laser beam LB having a wavelength that is transmissive to the wafer W from the back surface Wb side of the wafer W to the second dividing line S2 while moving the laser beam LB in a direction (X-axis direction) parallel to b. Is irradiated in a broken line along the line to form a second modified layer m2 inside the wafer W. When the second modified layer m2 is formed by irradiating the laser beam LB along all the second scheduled division lines S2, the second modified layer forming step is completed.

  The modified layer M (the first modified layer m1 and the second modified layer m2) is a region in which the intensity and physical characteristics inside the wafer W have changed by the irradiation of the laser beam LB. As shown in the partially enlarged view of FIG. 2, the modified layer M is formed above the light converging point P, and the width t between the upper end and the lower end of the modified layer M is, for example, about 20 to 30 μm. Has become.

  Here, when the first modified layer forming step, the second modified layer forming step, or both the first modified layer forming step and the second modified layer forming step are performed, the wafer W As shown in FIG. 3, the modified layer M (the first modified layer m1 and the second modified layer m2) formed inside the wafer W is divided from the modified layer M to the wafer W for each division line. At least one induction-modified layer Mi for inducing the growth of a crack reaching the surface Wa of the wafer W, and at least one or more adjustment modification for adjusting the growth of the crack from the modified layer M to the surface Wa of the wafer W. And the composite layer Ma. In the illustrated example, the modified layer M is composed of one induction-modified layer Mi formed at a position closest to the surface Wa of the wafer W, and two layers formed on the induction-modified layer Mi. And the material layer Ma.

  When forming the induction-modified layer Mi inside the wafer W, the laser beam irradiating means 20 shifts the position of the condenser 22 so that the laser beam LB is positioned in a state where the focal point P of the laser beam LB is positioned closer to the surface Wa. Irradiate to form the induction-modified layer Mi. The number and thickness of the induction reforming layer Mi are not particularly limited. Therefore, it is preferable to set the number and thickness of the induction-modified layer Mi according to the thickness of the wafer W and the like. In the example of FIG. 3, the induction-modified layer Mi is formed at a position closest to the surface Wa of the wafer W, but is not limited to this position. However, as shown in the present embodiment, the modified layer M may be formed at the height position 6 where it is ground and removed in a later dividing step.

  In addition, when forming the adjustment modified layer Ma inside the wafer W, the laser beam irradiation means 20 shifts the position of the light collector 22 further upward so as to form an even interval from the front surface Wa side to the rear surface Wb side. The laser beam LB is radiated stepwise to form a two-layer modified and modified layer Ma. At this time, the laser beam irradiation means 20 is controlled so as to stop the irradiation of the laser beam LB at least once to one side of each device D shown in FIG. 1 with a predetermined interval H1. Specifically, the laser beam irradiation unit 20 sets the predetermined interval H1 in the first planned division line S1 or the second planned division line S2, or in both the first planned division line S1 and the second planned division line S2. The laser beam LB is applied to a region other than the predetermined interval H1 without irradiating the provided portion with the laser beam LB. The adjusted modified layer Ma thus formed has a non-modified layer region 2 separated by a predetermined interval H1 inside the wafer W, and the intensity of the portion irradiated with the laser beam LB is reduced. The non-modified layer region 2 is a region where the strength inside the wafer W is not reduced and cracks do not occur at the time of subsequent division. There is no particular limitation on the number or thickness of the adjustment reforming layer Ma.

(4) Dividing Step After performing the first modified layer forming step and the second modified layer forming step, as shown in FIG. 4, the protection member 1 side is held by a rotatable chuck table 40, The back surface Wb of the wafer W is ground by the grinding means 30 to be thinned to a finished thickness of 100, and a crack extending from the modified layer M to the front surface Wa of the wafer W by a grinding operation is grown along the dividing line, The wafer W is divided into individual devices D. The chuck table 40 includes a holding portion 41 formed of, for example, a porous member, and the upper surface thereof is a holding surface 42 for sucking and holding the wafer W. A suction source (not shown) is connected to the holding surface 42. The grinding means 30 includes a spindle 31 having a vertical axis, a grinding wheel 32 mounted below the spindle 31, and a grinding wheel 33 fixed in a ring shape below the grinding wheel 32. The whole can be moved up and down while rotating 32.

  As shown in FIG. 4, the tape T side is held by the chuck table 40, the back surface Wb of the wafer W is turned upward, and the chuck table 40 is rotated. The grinding means 30 lowers the grinding wheel 32 at a predetermined grinding feed speed while rotating the grinding wheel 32, for example, in the direction of arrow A, and grinds to a predetermined finishing thickness 100 while pressing the back surface Wb of the wafer W with the grinding wheel 33. To make the wafer W thinner. By this grinding operation, a crack starting from the modified layer M and reaching the surface Wa of the wafer W is grown along the first planned division line S1 and the second planned division line S2. That is, when a crack occurs from the position where the modified layer M is formed, the crack is induced toward the surface Wa by the induced modified layer Mi shown in FIG. Further, cracks do not occur from the non-modified layer region 2 of the adjusted modified layer Ma, the growth of cracks from the modified layer M to the surface Wa is adjusted, and the timing at which the device D is singulated is adjusted. You. Therefore, when the wafer W is divided into the individual devices D due to the thinning, the adjacent devices D are prevented from contacting and being damaged.

(5) Expanding Step After the dividing step is performed, as shown in FIG. 5, the space between the divided individual devices D is expanded by the tape expanding means 50. As shown in FIG. 5A, the tape expanding means 50 includes a support table 51 for supporting the wafer W, a frame mounting table 52 disposed on the outer peripheral side of the support table 51 and mounting the frame F, The apparatus includes a clamp unit 53 for clamping the frame F placed on the mounting table 52, and lifting means 54 connected to a lower portion of the frame mounting table 52 to move the frame mounting table 52 up and down. The elevating means 54 includes a cylinder 54a and a piston 54b driven up and down by the cylinder 54a, and the piston 54b moves up and down, so that the frame mounting table 52 can be moved up and down.

  When expanding the wafer W, the protection member 1 is placed on the support table 51 and the frame F is placed on the frame mounting table 52. Thereafter, the clamp portion 53 presses the upper portion of the frame F and fixes it so as not to move. Next, as shown in FIG. 5B, the piston 54 b moves downward to lower the frame mounting table 52, and lowers the frame mounting table 52 relative to the support table 51. As a result, the tape T and the protection member 1 are radially expanded, an external force is applied to the wafer W in the radial direction, the intervals between the devices D are widened, and the gaps 5 are formed between the devices D. Then, each device D is picked up by a transport unit or the like and transported to a desired transport destination.

  As described above, in the wafer processing method according to the present invention, in the first modified layer forming step, in the second modified layer forming step, or in the first modified layer forming step and the second modified layer forming step. In both steps of the quality layer forming step, the modified layer M formed inside the wafer W has at least one crack that induces the growth of cracks from the modified layer M to the surface Wa of the wafer W per one dividing line. Since at least one induced modified layer Mi and at least one or more adjusted modified layers Ma for adjusting the growth of cracks from the modified layer M to the surface Wa of the wafer W are formed in a composite manner. In addition, the crack generated from the modified layer M by the induction modified layer Mi is guided to the surface Wa side of the wafer W, and the growth degree of the crack reaching the surface Wa is adjusted by the adjusted modified layer Ma. The It is possible to prevent meandering kerf near the corner or caused lack of the device chip corner of that or generated upon the division into devices D. In addition, since the adjusted and modified layer Ma has the non-modified layer region 2 separated by the predetermined interval H1, when the dividing step is performed, the device D adjacent to the non-modified layer region 2 is formed by the non-modified layer region 2. Since the timing at which the device D is singulated is adjusted so as not to come into contact with the device D, it is possible to effectively prevent the chip of the device D from being chipped or the kerf near the corner from meandering.

  The modified layer M1 (first modified layer m1 and second modified layer m2) shown in FIG. 6 is formed inside the wafer W1 by the first modified example of the modified layer forming step. . In the same manner as described above, the modified layer M1 performs the first modified layer forming step and the second modified layer forming step, thereby deriving the one layer formed at the position closest to the front surface Wa side of the wafer W1. It is composed of a modified layer Mi2 and two adjusted modified layers Ma formed on the induction modified layer Mi2.

  When forming the induction-modified layer Mi2 inside the wafer W1, the laser beam irradiating means 20 adjusts the position of the condenser 22 so that the focal point P of the laser beam LB is positioned closer to the front surface Wa. A predetermined interval H2 shorter than the non-modified layer region 2 of the modified layer Ma is provided, and control is performed such that the irradiation of the laser beam LB to one side of each device D is stopped at least once. Specifically, the laser beam irradiating means 20 is used for the first planned dividing line S1 or the second planned dividing line S2 shown in FIG. 1 or both the first planned dividing line S1 and the second planned dividing line S2. The laser beam LB is applied to a region other than the predetermined interval H2 without irradiating the portion provided with the predetermined interval H2 with the laser beam LB. The induction-modified layer Mi2 thus formed has a non-modified layer region 3 smaller than the non-modified layer region 2 at a predetermined interval H2 inside the wafer W1, and a portion of the wafer W1 irradiated with the laser beam LB. The strength has decreased. The non-modified layer region 3 is a region in which no crack occurs at the time of division, like the non-modified layer region 2.

  After the first modified example of the modified layer forming step is performed, the process proceeds to the same dividing step as described above, and a crack reaching the surface Wa of the wafer W1 from the modified layer M1 as a starting point by a grinding operation is formed into a first dividing line S1. And growing along the second scheduled division line S2. That is, when a crack occurs from the position where the modified layer M1 is formed, the crack is induced toward the surface Wa by the induced modified layer Mi2. Further, cracks do not occur from the non-modified layer region 2 of the adjusted modified layer Ma and the non-modified layer region 3 of the induction modified layer Mi2, and the devices D are separated into individual pieces so that adjacent devices D do not come into contact with each other. The timing is adjusted so that the wafer W1 can be divided into individual devices D. As described above, in the modified layer M1, since the induction-modified layer Mi2 has the non-modified layer region 3 smaller than the non-modified layer region 2 of the adjusted modified layer Ma, a small non-modified layer region 3 is formed when the wafer W1 is divided. Since cracks are not guided to the surface Wa of the wafer W1 from the modified layer region 3 as well, the movement of the device D to be singulated can be restricted, and chipping occurs at the corners of the device D or the kerf near the corners. Can be more effectively prevented from meandering.

  The modified layer M2 (first modified layer m1 and second modified layer m2) shown in FIG. 7 is formed inside the wafer W2 by the second modified example of the modified layer forming step. . In the same manner as described above, the modified layer M2 performs the first modified layer forming step and the second modified layer forming step, thereby deriving the one layer formed at the position closest to the front surface Wa side of the wafer W2. It is composed of a modified layer Mi2 and two adjusted modified layers Ma, Ma2 formed on the induction modified layer Mi2 and having different predetermined intervals. The configuration of the induction reforming layer Mi2 and the adjustment reforming layer Ma is the same as that of the first modification.

  When forming the modified modified layer Ma2 inside the wafer W2, the laser beam irradiation means 20 provides a predetermined interval H3 longer than the non-modified layer region 3 and shorter than the non-modified layer region 2, Control is performed so that irradiation of the laser beam LB to one side of the device D is stopped at least once. Specifically, the laser beam irradiating means 20 is used for the first planned dividing line S1 or the second planned dividing line S2 shown in FIG. 1 or both the first planned dividing line S1 and the second planned dividing line S2. The laser beam LB is applied to a region other than the predetermined interval H2 without irradiating the laser beam LB to the portion provided with the predetermined interval H3. The adjusted and modified layer Ma2 has a non-modified layer region 4 that is larger than the non-modified layer region 3 and smaller than the non-modified layer region 2 at a predetermined interval H3 inside the wafer W2. The intensity of the part irradiated with LB is reduced.

  After the second modified example of the modified layer forming step is performed, the process proceeds to the same dividing step as described above, and a crack reaching the surface Wa of the wafer W2 from the modified layer M2 as a starting point by a grinding operation is converted into a first dividing line S1. And growing along the second scheduled division line S2. That is, when a crack occurs from the position where the modified layer M2 is formed, the crack is induced toward the surface Wa by the induced modified layer Mi2. Further, since cracks do not occur from the non-modified layer regions 2, 3, and 4, and the timing at which the devices D are singulated is adjusted, the wafer W2 can be divided into individual devices D. As described above, since the modified layer M2 is configured such that the region not irradiated with the laser beam LB from the rear surface Wb to the front surface Wa of the wafer W2 is gradually reduced in the order of the non-modified layer regions 2, 4, and 3, the modified layer M2 is singulated. The movement of the device D can be restricted, and the occurrence of chipping at the corner of the device D and the meandering of the chipped portion can be prevented.

  The laser irradiation conditions used in the modified layer forming step shown in the present embodiment include, for example, a light source, a wavelength, an output, a feed speed of the holding table 10, and a width of predetermined intervals H1 to H3 at which the laser beam LB is not irradiated. The predetermined intervals H1 to H3 set for each of the dividing lines do not have to be constant. Since the central portion of the wafer W is harder to move than the outer peripheral portion and undivided regions are more likely to occur, for example, the width of the predetermined intervals H1 to H3 may be set narrower in the central portion. The grinding conditions used in the dividing step include, for example, the type of the grinding wheel 33, the grinding feed speed, the rotation speed of the chuck table 40, and the like. Note that the laser irradiation conditions and the grinding conditions may be appropriately adjusted and combined according to the thickness, material, and the like of the wafer W.

1: Protection member 2, 3, 4: Non-modified layer region 5: Gap 6: Height position 10: Holding table 11: Holding surface 20: Laser beam irradiation means 21: Oscillator 22: Condenser 30: Grinding means 31: Spindle 32: Grinding wheel 33: Grinding wheel 40: Chuck table 41: Holding part 42: Holding surface 50: Tape expanding means 51: Support table 52: Frame mounting table 53: Clamp part 54: Elevating means 54a: Cylinder 54b: Piston W , W1, W2: Wafer Wa: Front surface Wb: Back surface D: Device S1: First planned dividing line S2: Second planned dividing line M, M1, M2: Modified layer m1: First modified layer m2: Second modified layers Mi, Mi2: induction modified layers Ma, Ma2: adjusted modified layers H1, H2, H3: predetermined intervals

Claims (1)

A device is formed in a plurality of regions defined by a plurality of first division lines extending in a predetermined direction on the surface and a plurality of second division lines formed to intersect the plurality of first division lines. A wafer processing method for dividing the wafer on which is formed along the first planned dividing line and the second planned dividing line,
A protective member attaching step of attaching a protective member to the surface side of the wafer,
After the protection member adhering step, the first division is to be performed by holding the protection member side, and positioning a laser beam having a wavelength that is transparent to the wafer from the back surface side of the wafer to a focusing point inside the wafer. A first modified layer forming step of irradiating along a line and forming a first modified layer inside the wafer along the first scheduled dividing line;
A laser beam having a wavelength that is transmissive to the wafer is irradiated from the back side of the wafer along the second dividing line with the condensing point positioned inside the wafer and the second dividing line inside the wafer. A second modified layer forming step of forming a second modified layer along the line;
After performing the first modified layer forming step and the second modified layer forming step, while holding the protective member side, the wafer is ground from the back surface of the wafer by grinding means to reduce the thickness to a finished thickness. A cracking step of growing a crack reaching the surface of the wafer starting from the modified layer by the grinding operation along the planned dividing line, and dividing the wafer into individual devices;
In the first modified layer forming step, in the second modified layer forming step, or in both the first modified layer forming step and the second modified layer forming step,
The modified layer has at least one or more induced modified layers that induce the growth of cracks from the modified layer to the surface of the wafer per one scheduled division line, and extends from the modified layer to the surface of the wafer. And at least one or more adjustment-modification layers for adjusting the growth of cracks ;
The adjusted and modified layer has a non-modified layer region at a predetermined interval inside the wafer by stopping irradiation of the laser beam at least once to one side of each device at a predetermined interval. And
The induction-modified layer is provided with a predetermined interval shorter than the modified layer region, and stops irradiation of the laser beam at least once to one side of each device, so that a predetermined interval is formed inside the wafer. Having a non-modified layer region smaller than the non-modified layer region,
A method for processing a wafer, wherein the non-modified layer region of the adjustment-modified layer and the induction-modified layer is gradually reduced from the back surface to the front surface of the wafer.

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