JP7656797B2 - Laser processing method and device - Google Patents

Description

The present invention relates to a laser processing method and device, and to a laser processing method and device that divides a wafer starting from a laser processing area formed inside the wafer.

Conventionally, there is known a laser processing device (also called a laser dicing device) that irradiates a laser beam along a planned division line by focusing the beam inside a wafer such as silicon, and forms a laser processing area that serves as the starting point for cutting inside the wafer along the planned division line. The wafer with the laser processing area formed is transported to a grinding device (grinder), which grinds the back side of the wafer. The wafer is then divided into individual chips by expanding a backgrind tape attached to the front side of the wafer (see, for example, Patent Document 1).

JP 2005-086111 A

In the above-described wafer processing, the laser processing area is formed near the desired thickness of the wafer after grinding (hereafter referred to as the target thickness) in order to reliably divide the wafer into chips.

Figure 6 shows an example in which laser processing regions R1 and R2 are formed outside the position of the target thickness Ht1 of the wafer W. In this case, the laser processing regions R1 and R2 are removed by grinding. On the other hand, Figure 7 shows an example in which the laser processing regions R1 and R2 are formed inside the position of the target thickness Ht2 of the wafer W. In this case, after the wafer W is divided, the laser processing regions R1 and R2 remain on the side of the chip.

6 and 7, the laser processing regions R1 and R2 are formed so as to be biased toward the side closer to the front surface Wa (farther from the back surface Wb) with respect to the center line Lc in the thickness direction of the wafer W before grinding (hereinafter referred to as the initial thickness Hi). In this case, when the laser processing regions R1 and R2 are formed, warping occurs in the wafer W due to internal cracks that develop from the laser processing regions R1 and R2. The amount of warping at the peripheral portion of the wafer W can be several mm.

If the wafer W is warped, the wafer W cannot be stably attracted to the arm of the transport means when it is transported from the laser processing device to the grinding device, and transport problems such as the wafer W dropping during transport may occur. In addition, after the wafer W is transported to the grinding device, the wafer W cannot be stably attracted and held on the chuck table, and a suction error may occur during the grinding process, causing the grinding process to stop.

The present invention was made in consideration of these circumstances, and aims to provide a laser processing method and apparatus that can reduce wafer warping caused by laser processing.

In order to solve the above problems, the laser processing method according to the first aspect of the present invention includes a laser processing area forming step in which a laser processing area is formed along a planned dividing line of the wafer by focusing laser light inside the substrate of the wafer having a device layer laminated on the surface of the substrate, and a stress adjustment processing area forming step in which a stress adjustment processing area is formed by focusing laser light inside the wafer to generate internal stress that counteracts the internal stress generated inside the wafer by the laser processing area.

The laser processing method according to the second aspect of the present invention includes a condition setting step for setting second laser processing conditions for forming a stress adjustment processing area that generates an internal stress counteracting the internal stress generated inside the wafer by the laser processing area based on the first laser processing conditions when forming the laser processing area in the first aspect, and in the laser processing area forming step, the laser processing area is formed based on the first laser processing conditions, and in the stress adjustment processing area forming step, the stress adjustment processing area is formed based on the second laser processing conditions.

In the laser processing method according to the third aspect of the present invention, in the second aspect, the second laser processing conditions include at least one of the number of layers in the stress adjustment processing region, the number of lines and the processing height, and the spacing in the scanning direction of the focal points when forming the stress adjustment processing region and the power of the laser light.

The laser processing device according to the fourth aspect of the present invention includes a laser processing unit that forms a laser processing area along the planned dividing line of the wafer inside the substrate of the wafer having a device layer laminated on the surface of the substrate, and a control unit that controls the laser processing unit to form, inside the substrate of the wafer, a laser processing area and a stress adjustment processing area that generates an internal stress counteracting the internal stress generated inside the wafer by the laser processing area.

The laser processing device according to the fifth aspect of the present invention is the fourth aspect, and is provided with a condition setting unit that sets second laser processing conditions for forming a stress adjustment processing area that generates internal stress counteracting the internal stress generated inside the wafer by the laser processing area, based on the first laser processing conditions when forming the laser processing area.

The present invention can reduce wafer warpage caused by laser processing.

FIG. 1 is a block diagram showing the configuration of a laser processing device in a wafer processing system according to an embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of a grinding device in the wafer processing system according to one embodiment of the present invention. FIG. 3 is a cross-sectional view showing a stress adjusting processed region according to a first embodiment. FIG. 4 is a cross-sectional view showing a stress adjusting processed region according to a second embodiment. FIG. 5 is a cross-sectional view showing a stress adjusting processed region according to a third embodiment. FIG. 6 is a cross-sectional view showing an example in which a laser processing region is formed outside the position of the target thickness of the wafer. FIG. 7 is a cross-sectional view showing an example in which a laser processing region is formed inside the position of the target thickness of the wafer.

The following describes an embodiment of the laser processing method and device according to the present invention with reference to the attached drawings.

[Wafer Processing System]
The wafer processing system 10 according to this embodiment includes a laser processing device 10-1 (see FIG. 1) and a grinding device 10-2 (see FIG. 2). The laser processing device 10-1 forms a laser processing area inside the wafer W along a planned dividing line of the wafer W (laser processing step). The grinding device 10-2 performs grinding on the back surface Wb of the wafer W to set the thickness of the wafer W to a target thickness (grinding step). Then, the back grind tape BG attached to the front surface Wa of the wafer W is expanded to divide the wafer W into individual chips C (division step).

(Laser processing)
FIG. 1 is a block diagram showing the configuration of a laser processing device in a wafer processing system according to an embodiment of the present invention.

As shown in FIG. 1, the laser processing device 10-1 includes a control unit 12, a wafer moving unit 14, and a laser processing unit 16.

The control unit 12 has a CPU (Central Processing Unit), memory (e.g., ROM (Read Only Memory), RAM (Random Access Memory), etc.), storage (e.g., HDD (Hard Disk Drive), SSD (Solid State Drive), etc.), input/output circuitry, etc., and controls the operation of each part of the laser processing device 10-1. The control unit 12 is realized, for example, by a personal computer or a workstation.

The wafer moving unit 14 includes a suction stage T1 that suction-holds the wafer W, and an XYZθ table that is provided on the main body base (not shown) of the laser processing device 10-1 and moves the suction stage T1 in the XYZθ directions.

The wafer W is, for example, a disk-shaped semiconductor wafer made of silicon. The surface Wa of the substrate of the wafer W is partitioned into lattice-like regions by a number of planned division lines extending in the XY direction, for example, and devices (device layers) such as electronic circuits are formed (stacked) in each of these lattice-like regions.

When dividing the wafer W into individual chips C, first, a backgrind tape (protective tape) BG is applied to the surface Wa of the wafer W, and the wafer is placed with the surface Wa facing down on the holding surface of the table T of the laser processing device 10-1. The wafer W is then suction-held by the suction stage T1. Note that the wafer W may also be suction-held without the backgrind tape BG being applied.

The laser processing unit 16 includes a laser source, optical elements such as a condensing lens, and a driving means for slightly moving the laser light L in the Z direction relative to the wafer W. As the laser source, for example, a semiconductor laser excited Nd:YAG (Yttrium Aluminum Garnet) laser is used. The laser light L emitted from the laser source is focused inside the wafer W by the condensing lens. As a result, the laser processing regions R1 and R2 and the stress adjustment processing region RL are formed inside the wafer W.

Here, the laser processing regions R1 and R2 and the stress adjustment processing region RL refer to regions where the physical properties such as density, refractive index, and mechanical strength inside the wafer W become different from those of the surrounding area due to irradiation with laser light L, resulting in a lower strength than the surrounding area. The laser processing regions R1 and R2 and the stress adjustment processing region RL are, for example, regions that include crack regions.

The laser processing unit 16 adjusts the position of the focal point FP of the laser light L to sequentially form laser processing regions R1 and R2 on the front surface Wa side inside the wafer W. As shown in FIG. 1, when the laser processing regions R1 and R2 are formed, an internal stress (tensile stress) that expands the wafer W in the direction (±Y direction) in which the laser processing regions R1 and R2 are formed is generated inside the wafer W. This internal stress acts to expand the front surface Wa side of the wafer W, causing the peripheral portion of the wafer W to warp up toward the back surface Wb side.

Therefore, the laser processing unit 16 adjusts the position of the focal point FP of the laser light L to form a stress adjustment processing region RL on the back surface Wb side inside the wafer W. The stress adjustment processing region RL generates an internal stress on the back surface Wb side of the wafer W that expands the back surface Wb side of the wafer W. When forming the stress adjustment processing region RL, the control unit 12 (condition setting unit) is used to set laser processing conditions for forming the stress adjustment processing region RL that can generate internal stress that counteracts the internal stress generated by the laser processing regions R1 and R2 (condition setting step). In other words, the internal stress generated by the stress adjustment processing region RL warps the wafer W in the opposite direction to the internal stress generated by the laser processing regions R1 and R2, and preferably, the laser processing conditions are set so that the magnitude of the internal stress is approximately equal. More preferably, the laser processing conditions are set so that the internal stress generated by the stress adjustment processing region RL balances (cancels) the internal stress generated by the laser processing regions R1 and R2. Here, the laser processing conditions for the stress adjustment processing region RL include, for example, the number of layers in the stress adjustment processing region RL, the power of the laser light L (e.g., intensity or irradiation time, etc.), and the position of the focal point FP (the interval in the scanning direction (XY direction) (hereinafter referred to as the index) and the position in the thickness direction (Z direction) (the distance from the back surface Wb)). The stress adjustment processing region RL will be described later.

When forming the laser processing regions R1 and R2 and the stress adjustment processing region RL on the wafer W, the laser light L is emitted from the laser processing unit 16 and irradiated onto the wafer W via an optical system such as a condenser lens. The Z-direction position of the focal point FP of the irradiated laser light L is accurately set to a predetermined position inside the wafer W by adjusting the Z-direction position of the wafer W using the XYZθ table and controlling the position of the condenser lens.

In this state, the XYZθ table is processed and fed in the X direction, which is the dicing direction. As a result, one line of laser processing regions R1 and R2 and a stress adjustment processing region RL is formed along the planned dividing line of the wafer W. Then, when one line of laser processing regions R1 and R2 and a stress adjustment processing region RL is formed along the planned dividing line, the XYZθ table is indexed and fed one pitch in the Y direction, and laser processing regions R1 and R2 and a stress adjustment processing region RL are formed on the next planned dividing line. Next, when the laser processing regions R1 and R2 and a stress adjustment processing region RL are formed along all the planned dividing lines in the X direction, the XYZθ table is rotated 90° around the Z axis, and laser processing regions R1 and R2 and a stress adjustment processing region RL are similarly formed on the planned dividing line in the X direction after the rotation.

The procedure for forming the laser processing regions R1 and R2 and the stress adjustment processing region RL is not particularly limited. For example, as shown in FIG. 1, after forming the first layer of the laser processing region R1 on the entire surface of the wafer W, the second layer (the back surface Wb side of the wafer W) of the laser processing region R2 may be formed, and then the stress adjustment processing region RL may be formed. Here, the laser processing conditions when forming the laser processing regions R1 and R2 and the stress adjustment processing region RL may be different from each other or may be the same. Alternatively, a branching section (e.g., a beam splitter, etc.) that branches the laser light L may be provided to focus the laser light L on two focusing points with different positions (depths) in the Z direction inside the wafer W, thereby forming two layers of the laser processing regions R1 and R2 and one or more layers of the stress adjustment processing region RL in one scan. That is, the laser processing region forming step and the stress adjustment processing region forming step may be performed simultaneously in parallel or separately.

The wafer W on which the laser processing regions R1 and R2 and the stress adjustment processing region RL are formed is transferred from the laser processing device 10-1 to the grinding device 10-2, where the back surface of the wafer W is ground to remove a portion of the laser processing region R2 on the back surface side, and the wafer W is divided into individual chips (see Figure 2).

In this embodiment, the laser processing area is two layers, R1 and R2, but the present invention is not limited to this. The laser processing area may be formed as a single layer or as multiple layers of three or more layers.

(Grinding)
2 is a block diagram showing the configuration of a grinding device in a wafer processing system according to an embodiment of the present invention, which illustrates a state in which the back surface Wb of the wafer W has been ground down to Wb1.

As shown in FIG. 2, the grinding device 10-2 according to this embodiment includes a grinding control unit 18, a thickness measurement unit 20, a wafer moving unit 22, and a grinding machine (grinder) 50. The grinding machine 50 includes a rotary grinding disk 52 and a grinding wheel 54 attached to the rotary grinding disk 52.

The grinding control unit 18 includes a motor for rotating the rotary grinding machine 52 around a shaft. In response to a command from the control unit 12, the grinding control unit 18 adjusts the Z-direction position of the rotary grinding machine 52 while supplying slurry to the back surface Wb of the wafer W from a slurry supply port (not shown) to rotate the grinding wheel 54 in contact with the back surface Wb of the wafer W.

The wafer moving unit 22 includes a chuck table T2 that holds the wafer W by suction, and an XY table (not shown) that moves the chuck table T2 in the X and Y directions within the grinding device 10-2.

After the laser processing regions R1 and R2 and the stress adjustment processing region RL are formed in the laser processing device 10-1, the wafer W is transported to the grinding device 10-2. The wafer W is then placed with its front surface Wa facing down on the holding surface of the chuck table T2 and is adsorbed and held by the chuck table T2. Next, while the wafer moving unit 22 moves the chuck table T2 in the XY directions, the grinding control unit 18 abuts the grindstone 54 against the back surface Wb of the wafer W and rotates it, thereby grinding the entire back surface Wb of the wafer W.

The thickness measuring unit 20 is a means for measuring the thickness of the wafer W. The thickness measuring unit 20 is capable of measuring the thickness of the wafer W in-situ while the back surface Wb of the wafer W is being ground. The thickness measuring unit 20 may be a contact type means for measuring by contacting a contact height gauge with the back surface Wb of the wafer W. The thickness measuring unit 20 may also be a non-contact type means (e.g., a ToF (Time-of-Flight) method) for measuring the distance to the back surface Wb of the wafer W by irradiating the back surface Wb of the wafer W with laser light from a laser light source (e.g., a semiconductor laser).

The grinding control unit 18 grinds the back surface Wb of the wafer W while calculating the thickness of the wafer W based on the output from the thickness measurement unit 20. This allows the thickness of the wafer W to be set to the target thickness.

In the example shown in FIG. 2, the grinding device 10-2 is controlled by the same control unit 12 as the laser processing device 10-1, but it may be controlled by a control unit (e.g., a personal computer or a workstation) separate from the laser processing device 10-1. In other words, the laser processing device 10-1 and the grinding device 10-2 may be separate and independent devices. In this case, the control unit of the grinding device 10-2 may share information regarding the positions and sizes of the laser processing regions R1 and R2, and information regarding the target thickness of the wafer W, from the control unit 12 of the laser processing device 10-1 via a communication line or a storage device, etc.

[Example of stress adjustment processing area]
Next, an example of the stress adjustment processed region RL will be described.

(Relationship between laser processing conditions and internal stress)
Tables 1 and 2 summarize the relationship between the laser processing conditions (first and second laser processing conditions) when forming the laser processing region and the stress adjustment processing region RL, respectively, and the internal stress generated inside the wafer W. Note that the same symbols are used for corresponding conditions in both Tables 1 and 2.

As shown in Table 1, (A) the greater the number of layers in the laser processing area, or (B) the greater the number of lines in the laser processing area (number in the XY directions; number of planned division lines), the greater the effect of internal stress occurring on the front surface Wa of the wafer W. Also, (C) the shorter the interval (index) in the scanning direction (XY directions) of the focal point FP during laser processing, the greater the effect of internal stress occurring on the front surface Wa of the wafer W.

And, (D) the closer the laser processing area is to the surface Wa of the wafer W, or (E) the greater the power (e.g., intensity or irradiation time) of the laser light L during laser processing, the greater the effect of the internal stress generated on the surface Wa side of the wafer W.

By adjusting either of the conditions (D) and (E) among the laser processing conditions, it is possible to adjust the half cut (HC) condition and the stealth (ST) condition. Here, the HC condition refers to a case where at least one of the conditions (D) the distance (processing height) between the focal point _FP of the laser light L and the surface Wa of the wafer W, and (E) the power of the laser light L during laser processing is adjusted so that the crack _KR extending from the laser processing area reaches the surface Wa of the wafer W. Also, the ST condition refers to a case where at least one of the conditions (D) the distance (processing height) between the focal point FP of the laser light L and the surface Wa of the wafer W, and (E) the power of the laser light L during laser processing is adjusted so that the crack KR extending from the laser processing area does not reach the surface Wa of the wafer W. In the case of the HC condition, the crack _KR extending from the laser processing area reaches the surface Wa of the wafer W, so that the influence of the internal stress generated on the surface Wa side of the wafer W becomes larger compared to the case of the ST condition.

The relationship between the laser processing conditions of the stress adjustment processing region RL and the internal stress generated on the back surface Wb side of the wafer W is similar to that described above. That is, as shown in Table 2, (A) the greater the number of layers in the stress adjustment processing region RL, or (B) the greater the number of lines (number in the XY directions) in the stress adjustment processing region RL, the greater the effect of the internal stress generated on the back surface Wb side of the wafer W. Also, (C) the shorter the interval (index) in the scanning direction (XY directions) of the focal point FP during laser processing, the greater the effect of the internal stress generated on the back surface Wb side of the wafer W.

Furthermore, (D) the closer the stress adjustment processing region RL is to the back surface Wb of the wafer W, or (E) the greater the power (e.g., intensity or irradiation time) of the laser light L during laser processing, the greater the influence of the internal stress occurring on the back surface Wb of the wafer W. That is, in the case of the HC condition (crack K _B in FIG. 4 ), a crack extending from the stress adjustment processing region RL reaches the back surface Wb of the wafer W, so that the influence of the internal stress occurring on the back surface Wb of the wafer W is greater than in the case of the ST condition (crack K _C in FIG. 5 ).

The laser processing conditions of the laser processing area are determined according to the manufacturing conditions (chip size, thickness, etc.) of the chips (e.g., semiconductor devices, etc.) to be produced. For this reason, in this embodiment, the laser processing conditions of the stress adjustment processing area RL are adjusted according to the laser processing conditions of the laser processing area. This makes it possible to reduce warping of the wafer W caused by laser processing.

In addition, it is preferable to form the stress adjustment processing region RL evenly over the entire surface of the wafer W in order to reduce warping and bending of the wafer W.

The method for setting the laser processing conditions for the stress adjustment processing region RL will be described below. First, the control unit 12 evaluates the factors listed in Table 1 for the laser processing conditions for the laser processing region, and evaluates the effect of the internal stress generated on the front surface Wa side of the wafer W. Then, the laser processing conditions (Table 2) for the stress adjustment processing region RL are set to generate an internal stress on the back surface Wb side that balances with the internal stress generated on the front surface Wa side of the wafer W.

Here, the laser processing conditions for the stress adjustment processing region RL may be set manually using the control unit 12, or may be set automatically when the control unit 12 receives input of the laser processing conditions for the laser processing region.

The stress adjustment processing region RL disappears during the grinding step, so depending on the magnitude of the effect of the internal stress caused by the laser processing region, the balance of the internal stress of the wafer W may be broken during the grinding step, resulting in a grinding error. For this reason, it is possible to form the stress adjustment processing region RL further inward (toward the front surface Wa).

For example, if the evaluation value of the magnitude of the effect of internal stress caused by the laser processing area is equal to or greater than a threshold value, a constraint condition (lower limit value) is set for the distance (processing height) of the stress adjustment processing area RL (D) from the back surface Wb of the wafer W. Then, under this constraint condition, conditions (A) to (C) and (E) are set. This makes it possible to limit the position of the stress adjustment processing area RL to the inside (front surface Wa side), thereby preventing grinding errors.

When setting the laser processing conditions for the stress adjustment processing region RL, the throughput of the laser processing process may be taken into consideration. For example, it may be possible to set whether or not to prioritize throughput, along with the laser processing conditions for the laser processing region. When a setting that prioritizes throughput is selected, the constraint conditions are set to (A) reduce the number of layers (e.g., one layer), (B) make the number of lines the same as or smaller than the number of lines in the laser processing region, and (C) make the index the same as or smaller than the number of lines in the laser processing region. Then, under these constraint conditions, the control unit 12 adjusts at least one of the following conditions: (D) the distance from the back surface Wb of the wafer W (processing height) and (E) the power of the laser light L.

Example 1
FIG. 3 is a cross-sectional view showing a stress adjusting processed region according to a first embodiment.

3, two layers of laser processing regions R1 and R2 are formed on the front surface Wa side of the wafer W. The stress adjustment processing region RL _A is formed symmetrically with the laser processing regions R1 and R2 with respect to the center line Lc in the thickness direction of the wafer W before grinding.

That is, in FIG. 3, the number of layers and the number of lines in the laser processed regions R1 and R2 are equal to the number of layers and the number of lines in the stress adjustment processed region RL _A (conditions (A) and (B)).

Further, the distance H _R1 between the front surface Wa of the wafer W and the laser processing region R1 is equal to the distance H A1 between the back surface Wb of the wafer W and the stress adjustment processing region RL _A1 . The distance H _R2 between the front surface Wa of the wafer W and the laser processing region R2 is equal to the distance H _A2 between the back surface Wb of the wafer _W and the stress adjustment processing region RL _A2 (condition (D)).

In addition, the intervals (indexes) in the scanning direction (XY directions) of the focal points FP when forming the laser processed regions R1 and R2 and the stress adjustment processed region RL _A are equal (condition (C)), and the power of the laser light L is equal (condition (E)).

According to the first embodiment, the laser processing conditions of the laser processing regions R1 and R2 and the stress adjustment processing region RL _A are the same, and equivalent laser processing is performed. As a result, the stress adjustment processing region RL _A is formed in line symmetry with the laser processing regions R1 and R2 with respect to the center line Lc, so that the internal stress of the wafer W can be equalized.

Example 2
4A and 4B are cross-sectional views showing a stress adjusting processed region according to a first embodiment of the present invention, in which Fig. 4A is a cross-sectional view of a wafer W, and Fig. 4B is an enlarged cross-sectional view of a portion of Fig. 4A.

In the example shown in FIG. 4(a), two layers of laser processed regions R1 and R2 are formed, and one layer of stress adjustment processed region RL _A is formed (see condition (A) in Table 3).

In the second embodiment, the conditions (B) and (C) for forming the laser processed regions R1 and R2 and the stress adjustment processed region RL- _B are the same, respectively.

In the second embodiment, the conditions for forming the laser processing regions R1 and R2 are ST conditions, whereas the conditions for forming the stress adjustment processing region RL _B are HC conditions. That is, as shown in FIG. 4B, at least one of the conditions of (D) the distances H R1 and H R2 (processing height ₎ between the focal point FP of the laser light L and the front surface Wa of the wafer W, and (E) the power of the laser light L during laser processing is adjusted so that the crack K R extending from the laser processing regions _R1 and _R2 does not reach the front surface _Wa of the wafer W. Furthermore, at least one of the conditions of (D) the distance H _B (processing height) between the focal point FP of the laser light L and the rear surface Wb of the wafer W, and (E) the power of the laser light L during laser processing is adjusted so that the crack K _B extending from the stress adjustment processing region RL B reaches the rear surface Wb of the wafer W.

In Example 2, the crack KB reaches the back surface Wb side of the wafer W, thereby increasing the internal stress on the back surface Wb side of the wafer W. This makes it possible to balance the internal stresses on the front surface Wa and back surface Wb sides of the wafer W even if the number of layers in the stress adjustment processing region RL _B is one. Furthermore, since the number of layers in the stress adjustment processing region RL _B can be one, the throughput in laser processing can be increased.

Example 3
5A and 5B are cross-sectional views showing a stress adjusting processed region according to a first embodiment of the present invention, in which Fig. 5A is a cross-sectional view of a wafer W, and Fig. 5B is an enlarged cross-sectional view of a portion of Fig. 5A.

In the example shown in FIG. 5A, two layers of laser processed regions R1 and R2 are formed, and one layer of stress adjustment processed region RL _A is formed (see condition (A) in Table 4).

In the third embodiment, the conditions (B) for forming the laser processed regions R1 and R2 and the stress adjustment processed region RL _B are the same.

In addition, both of the conditions (D) and (E) are set as ST conditions. That is, at least one of the conditions (D) the distance H _C (processing height ₎ between the focal point FP of the laser light L and the back surface Wb of the wafer W and (E) the power of the laser light L during laser processing is adjusted so that the crack K _C extending from the stress adjustment processing region RL C does not reach the back surface Wb of the wafer W.

In the third embodiment, the index D _C when forming the stress adjusting processing region RL _C is set to half the index D _R when forming the laser processing regions R1 and R2. That is, D _C = D _R /2, and in one example, D _R = 1.0 mm and D _C = 0.5 mm.

In the third embodiment, the index _DC when forming the stress adjustment processing region RL _C is shortened to increase the internal stress on the back surface Wb side of the wafer W. This makes it possible to balance the internal stresses on the front surface Wa and back surface Wb sides of the wafer W even if the number of layers of the stress adjustment processing region RL _C is one.

According to this embodiment, the warping and bending of the wafer W can be reduced by adjusting the laser processing conditions of the stress adjustment processing region RL according to the laser processing conditions of the laser processing region.

When the distance (index) in the scanning direction (XY direction) of the focal points FP during the formation of the laser processing regions R1 and R2 is reduced, the warping of the wafer W tends to increase. For this reason, it was difficult to reduce the index in the conventional GAL (Grind After Laser) process. In contrast, in this embodiment, the stress adjustment processing region RL can be used to reduce warping even if the index in the laser processing region is reduced, making it possible to achieve laser processing using the GAL process with a small index.

If the power of the laser light L during laser processing is high, light may escape to the front surface Wa of the wafer W, causing damage (hereinafter referred to as splash damage) to the device formed on the front surface Wa. For this reason, for devices for which the LAG (Laser After Grind) process has been selected for small indexes up until now, the low-splash processing that is an advantage of the GAL process can be applied (the thickness dimension of the wafer W during laser irradiation is large, and the laser processing area can be formed away from the front surface Wa, making low-splash processing easier to implement compared to the LAG process).

It also reduces accuracy issues caused by wafer bending during laser processing (microscopic chip movement during processing), which is a problem specific to the LAG process.

In Examples 1 to 3, the stress adjustment processing region RL (RL _A , RL _B , and RL _C ) is formed so as to overlap with the laser processing regions R1 and R2 (so that the position of the focal point FP in the scanning direction (XY direction) coincides) (see Figures 4(b) and 5(b)), but the present invention is not limited to this. The lateral positions of the focal point FP when forming the stress adjustment processing region RL and the laser processing regions R1 and R2 may be different from each other.

In addition, although the target thickness position is not shown in Figures 3 to 5, the laser processing regions R1 and R2 may be formed either on the outside or inside of the target thickness position, or may be formed so as to overlap the target thickness position.

10...wafer processing system, 10-1...laser processing device, 10-2...grinding device, 12...control unit, 14...wafer moving unit, 16...laser processing unit, 18...grinding control unit, 20...thickness measuring unit, 22...wafer moving unit, 50...grinding machine, 52...rotary grinding machine, 54...grinding wheel, T1...suction stage, T2...chuck table

Claims (5)

a laser processing region forming step of forming a laser processing region along a planned dividing line of the wafer by focusing a first laser beam branched by a branching unit at a first focusing point inside the substrate of the wafer having a device layer laminated on a surface of the substrate;
a stress adjusting processing region forming step of forming, in parallel with the laser processing region, a stress adjusting processing region that generates an internal stress counter to the internal stress generated in the wafer by the laser processing region by focusing the second laser light branched by the branching portion at a second focusing point inside the substrate of the wafer, the second focusing point being at a different depth from the first focusing point;
A condition setting step of setting second laser processing conditions for forming the stress adjustment processing region based on first laser processing conditions when forming the laser processing region, in which, when an evaluation value of the magnitude of the influence of the internal stress caused by the laser processing region is equal to or greater than a threshold value, a constraint condition is set for the processing height of the stress adjustment processing region, and the second laser processing condition other than the processing height is set under the constraint condition;
A laser processing method comprising: In the laser processing region forming step, the laser processing region is formed based on the first laser processing condition,
2. The laser processing method according to claim 1, wherein in the stress adjustment processing region forming step, the stress adjustment processing region is formed based on the second laser processing condition. 3. The laser processing method according to claim 1, wherein the second laser processing condition includes at least one of the number of layers, the number of lines, and the processing height of the stress adjusting processing region, as well as the interval in the scanning direction of the focusing points when forming the stress adjusting processing region, and the power of the laser light. a laser processing unit that forms a laser processing area along a planned dividing line of a wafer inside a substrate of the wafer, the substrate having a device layer laminated on a surface of the substrate;
A branching unit that branches the laser light;
a control unit that focuses the laser light branched by the branch unit at two focusing points at different depths inside the substrate of the wafer, thereby simultaneously forming the laser processing area and a stress adjustment processing area that generates an internal stress counter to the internal stress generated inside the wafer by the laser processing area;
A condition setting unit that sets second laser processing conditions for forming a stress adjustment processing region that generates internal stress counter to the internal stress generated inside the wafer by the laser processing region based on a first laser processing condition when forming the laser processing region, and when an evaluation value of the magnitude of the effect of the internal stress caused by the laser processing region is equal to or greater than a threshold value, sets a constraint condition on the processing height of the stress adjustment processing region, and sets the second laser processing condition other than the processing height under the constraint condition;
A laser processing apparatus comprising: 5. The laser processing apparatus according to claim 4, wherein the second laser processing condition includes at least one of the number of layers, the number of lines, and a processing height of the stress adjusting processing region, as well as an interval in a scanning direction of a focusing point when forming the stress adjusting processing region, and a power of a laser beam .

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