Laser processing device

Abstract

To provide a laser processing device capable of reducing wafer warpage caused by laser processing.SOLUTION: A laser processing device (10-1) includes a laser processing unit (16) that forms a laser processing area inside a substrate of a wafer, a control unit (12) that forms, inside the substrate of the wafer, a laser processing area and a stress adjusting processing area that generates internal stress counteracting internal stress generated inside the wafer by the laser processing area, and a condition setting unit (12) that sets second laser processing conditions for forming the stress adjusting processing area that generates internal stress counteracting internal stress generated inside the wafer by the laser processing area, on the basis of first laser processing conditions when forming the laser processing area.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a laser processing method and apparatus, and more particularly to a laser processing method and apparatus for dividing a wafer starting from a laser processing region formed inside the wafer.

Background Art

[0002] Conventionally, a laser processing apparatus (also referred to as a laser dicing apparatus) is known which focuses a laser beam on a point inside a wafer such as silicon and irradiates it along a planned division line to form a laser processing region serving as a starting point for cutting inside the wafer along the planned division line. The wafer in which the laser processing region is formed is transported to a grinding apparatus (grinder), and the back side of the wafer is ground by the grinding apparatus. Then, the wafer is divided into individual chips by expanding a back grind tape adhered to the surface of the wafer (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described wafer processing, the laser processing region is formed in the vicinity of the target value of the thickness of the wafer after grinding (hereinafter referred to as the target thickness) in order to reliably divide the wafer into chips.

[0005] FIG. 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, FIG. 7 shows an example in which 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 surfaces of the chips.

[0006] In both cases of FIGS. 6 and 7, the laser processing regions R1 and R2 are formed so as to be unevenly distributed on the side closer to the surface Wa (the side 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, warpage occurs in the wafer W due to internal cracks or the like that progress from the laser processing regions R1 and R2. The amount of warpage at the peripheral portion of the wafer W may be about several millimeters.

[0007] When warpage occurs in the wafer W, when the wafer W is transferred from the laser processing apparatus to the grinding apparatus, the wafer W cannot be stably adsorbed to the arm of the transfer means, and transfer failures such as the wafer W falling during transfer may occur. Further, after the wafer W is transferred to the grinding apparatus, the wafer W cannot be stably adsorbed and held on the chuck table, and an adsorption error may occur during the grinding process, resulting in the grinding process stopping.

[0008] The present invention has been made in view of such circumstances, and an object thereof is to provide a laser processing method and apparatus capable of reducing warpage of a wafer caused by laser processing.

Means for Solving the Problems

[0009] In order to solve the above problems, a laser processing method according to a first aspect of the present invention includes a laser processing region forming step of forming a laser processing region along a division planned line of a wafer by condensing laser light inside a substrate of the wafer on which a device layer is laminated on the surface of the substrate, and a stress adjustment processing region forming step of forming a stress adjustment processing region that generates an internal stress that counteracts the internal stress generated inside the wafer by the laser processing region by condensing laser light inside the wafer.

[0010] A laser processing method according to a second aspect of the present invention includes, in the first aspect, a condition setting step of setting second laser processing conditions for forming a stress adjustment processing region that generates an internal stress that counteracts the internal stress generated inside the wafer by the laser processing region based on first laser processing conditions when forming the laser processing region, and in the laser processing region forming step, forming the laser processing region based on the first laser processing conditions, and in the stress adjustment processing region forming step, forming the stress adjustment processing region based on the second laser processing conditions.

[0011] A laser processing method according to a third aspect of the present invention includes, in the second aspect, the second laser processing conditions including at least one of the number of layers, the number of lines, and the processing height of the stress adjustment processing region, and the interval in the scanning direction of the condensing point and the power of the laser light when forming the stress adjustment processing region.

[0012] A laser processing apparatus according to a fourth aspect of the present invention includes a laser processing unit that forms a laser processing region along a division planned line of a wafer inside a substrate of the wafer on which a device layer is 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 region and a stress adjustment processing region that generates an internal stress that counteracts the internal stress generated inside the wafer by the laser processing region.

[0013] The laser processing apparatus according to the fifth aspect of the present invention, in the fourth aspect, is provided with a condition setting unit that sets second laser processing conditions for forming a stress adjustment processing region that generates an internal stress that counteracts the internal stress generated inside the wafer by the laser processing region based on the first laser processing conditions when forming the laser processing region.

Effects of the Invention

[0014] According to the present invention, it is possible to reduce the warpage of the wafer generated due to laser processing.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0016] Hereinafter, embodiments of a laser processing method and apparatus according to the present invention will be described with reference to the accompanying drawings.

[0017] [Wafer Processing System] The wafer processing system 10 according to this embodiment includes a laser processing apparatus 10-1 (see FIG. 1) and a grinding apparatus 10-2 (see FIG. 2). The laser processing apparatus 10-1 forms a laser processing region inside the wafer W along the division planned line of the wafer W (laser processing step). The grinding apparatus 10-2 performs grinding on the back surface Wb of the wafer W to make the thickness of the wafer W the target thickness (grinding step). Then, the wafer W is divided into individual chips C by expanding the back grind tape BG attached to the front surface Wa of the wafer W (division step).

[0018] (Laser processing) FIG. 1 is a block diagram showing the configuration of a laser processing apparatus among wafer processing systems according to an embodiment of the present invention.

[0019] As shown in FIG. 1, the laser processing apparatus 10-1 includes a control unit 12, a wafer moving unit 14, and a laser processing unit 16.

[0020] The control unit 12 has a CPU (Central Processing Unit), a memory (for example, ROM (Read Only Memory), RAM (Random Access Memory), etc.), a storage (for example, HDD (Hard Disk Drive), SSD (Solid State Drive), etc.), and an input / output circuit unit, etc., and controls the operations of each part of the laser processing apparatus 10-1. The control unit 12 is realized by, for example, a personal computer or a workstation.

[0021] The wafer moving unit 14 includes a suction stage T1 that sucks and holds the wafer W, and an XYZθ table provided on the main body base (not shown) of the laser processing apparatus 10-1 that moves the suction stage T1 in the XYZθ directions.

[0022] 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 a lattice-shaped region by a plurality of planned division lines extending in the XY direction, and devices (device layers) such as electronic circuits are formed (stacked) in each of these lattice-shaped regions.

[0023] When dividing the wafer W into individual chips C, first, a back grind tape (protective tape) BG is attached to the surface Wa of the wafer W, and the wafer W is placed on the holding surface of the table T of the laser processing apparatus 10-1 with the surface Wa facing downward. Then, the wafer W is sucked and held by the suction stage T1. Note that the wafer W may be sucked and held without attaching the back grind tape BG.

[0024] The laser processing unit 16 includes a laser light source, optical elements such as a condenser lens, and driving means for finely moving the laser light L in the Z direction with respect to the wafer W. As the laser light source, for example, a semiconductor laser-excited Nd:YAG (Yttrium Aluminum Garnet) laser is used. The laser light L emitted from the laser light source is condensed inside the wafer W by the condenser lens. Thereby, laser processing regions R1 and R2 and a stress adjustment processing region RL are formed inside the wafer W.

[0025] Here, the laser processing regions R1 and R2 and the stress adjustment processing region RL refer to regions where physical properties such as density, refractive index, and mechanical strength inside the wafer W become different from the surroundings due to the irradiation of the laser light L, and the strength is lower than that of the surroundings. The laser processing regions R1 and R2 and the stress adjustment processing region RL are, for example, regions including crack regions.

[0026] The laser processing unit 16 adjusts the position of the focus point FP of the laser beam L to sequentially form laser processing regions R1 and R2 on the 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. Since this internal stress acts to expand the surface Wa side of the wafer W, the peripheral portion of the wafer W warps upward toward the back surface Wb side.

[0027] Therefore, the laser processing unit 16 adjusts the position of the focus point FP of the laser beam 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 that expands the back surface Wb side of the wafer W on 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 a stress adjustment processing region RL that can generate an 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 magnitudes of the internal stresses are substantially equal. More preferably, the laser processing conditions are set so that the internal stress generated by the stress adjustment processing region RL balances (cancels out) the internal stress generated by the laser processing regions R1 and R2. Here, the laser processing conditions for the stress adjustment processing region RL are, for example, the number of layers of the stress adjustment processing region RL, the power of the laser beam L (e.g., intensity or irradiation time, etc.), and the position of the focus point FP (interval in the scan direction (XY direction) (hereinafter referred to as index) and position in the thickness direction (Z direction) (distance from the back surface Wb)). The stress adjustment processing region RL will be described later.

[0028] When forming the laser processing regions R1 and R2 and the stress adjustment processing region RL on the wafer W, the laser beam 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 beam L is accurately set to a predetermined position inside the wafer W by adjusting the Z-direction position of the wafer W by the XYZθ table and controlling the position of the condenser lens.

[0029] In this state, the XYZθ table is processed and fed in the X direction, which is the dicing direction. Thereby, the laser processing regions R1 and R2 and the stress adjustment processing region RL are formed in one line along the planned division line of the wafer W. Then, when the laser processing regions R1 and R2 and the stress adjustment processing region RL are formed in one line along the planned division line, the XYZθ table is indexed and fed by one pitch in the Y direction, and the laser processing regions R1 and R2 and the stress adjustment processing region RL are also formed on the next planned division line. Next, when the laser processing regions R1 and R2 and the stress adjustment processing region RL are formed along all the planned division lines in the X direction, the XYZθ table is rotated 90° around the Z axis, and the laser processing regions R1 and R2 and the stress adjustment processing region RL are similarly formed on the planned division line in the X direction after rotation.

[0030] Incidentally, 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 laser processing region R1 on the entire surface of the wafer W, the second-layer (on the back surface Wb side of the wafer W) laser processing region R2 may be formed, and then the stress adjustment processing region RL may be formed. Here, the laser processing conditions for forming the laser processing regions R1 and R2 and the stress adjustment processing region RL may be different from each other or the same. Alternatively, a branching portion (e.g., a beam splitter, etc.) for branching the laser beam L is provided, and the laser beam L is focused on two condensing points having different positions (depths) in the Z direction inside the wafer W, so that the two-layer laser processing regions R1 and R2 and the one-layer or multiple-layer stress adjustment processing region RL can be formed in one scan. That is, the laser processing region forming step and the stress adjustment processing region forming step may be carried out simultaneously in parallel or separately.

[0031] 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 apparatus 10-1 to the grinding apparatus 10-2, the back surface of the wafer W is ground, a part of the back surface side laser processing region R2 is removed, and it is divided into individual chips (see FIG. 2).

[0032] In this embodiment, the laser processing region is two layers of R1 and R2, but the present invention is not limited to this. The laser processing region may be formed of only one layer or a plurality of three or more layers.

[0033] (Grinding) FIG. 2 is a block diagram showing the configuration of a grinding apparatus in a wafer processing system according to an embodiment of the present invention. FIG. 2 shows a state in which the back surface Wb of the wafer W is ground to Wb1.

[0034] As shown in FIG. 2, the grinding apparatus 10-2 according to this embodiment includes a grinding control unit 18, a thickness measurement unit 20, a wafer moving unit 22, and a grinder 50. The grinder 50 includes a rotary grinding disk 52 and a grinding wheel 54 attached to the rotary grinding disk 52.

[0035] The grinding control unit 18 includes a motor for rotating the rotary grinding machine 52 around the shaft. The grinding control unit 18 supplies slurry from a slurry supply port (not shown) to the back surface Wb of the wafer W according to a command from the control unit 12, adjusts the Z-direction position of the rotary grinding machine 52, and brings the grinding wheel 54 into contact with and rotates it on the back surface Wb of the wafer W.

[0036] The wafer transfer unit 22 includes a chuck table T2 that adsorbs and holds the wafer W, and an XY table (not shown) that moves the chuck table T2 in the XY directions within the grinding device 10-2.

[0037] 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 transferred to the grinding device 10-2. Then, the wafer W is placed on the holding surface of the chuck table T2 with the front surface Wa facing downward and is adsorbed and held by the chuck table T2. Next, while the chuck table T2 is moved in the XY directions by the wafer transfer unit 22, the grinding wheel 54 is brought into contact with and rotated on the back surface Wb of the wafer W by the grinding control unit 18, so that the entire back surface Wb of the wafer W is ground.

[0038] The thickness measurement unit 20 is a means for measuring the thickness of the wafer W. The thickness measurement unit 20 can measure the thickness of the wafer W in-situ during the grinding of the back surface Wb of the wafer W. As the thickness measurement unit 20, a contact-type means for measuring by bringing a contact-type height gauge into contact with the back surface Wb of the wafer W may be used. Also, as the thickness measurement unit 20, a non-contact type means (for example, ToF (Time-of-Flight) method) for measuring the distance to the back surface Wb of the wafer W by irradiating laser light from a laser light source (for example, a semiconductor laser) onto the back surface Wb of the wafer W may be used.

[0039] Based on the output from the thickness measurement unit 20, the grinding control unit 18 calculates the thickness of the wafer W while grinding the back surface Wb of the wafer W. As a result, the thickness of the wafer W can be set to the target thickness.

[0040] In the example shown in FIG. 2, the grinding apparatus 10-2 is controlled by the same control unit 12 as the laser processing apparatus 10-1. However, it may be controlled by a control unit separate from the laser processing apparatus 10-1 (for example, a personal computer or a workstation, etc.). That is, the laser processing apparatus 10-1 and the grinding apparatus 10-2 may be separate and independent apparatuses. In this case, the control unit of the grinding apparatus 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 thickness of the wafer W from the control unit 12 of the laser processing apparatus 10-1 via a communication line or a storage device, etc.

[0041] [Example of the processing region for stress adjustment] Next, an example of the processing region RL for stress adjustment will be described.

[0042] (Relationship between laser processing conditions and internal stress) Table 1 and Table 2 summarize the relationships between the laser processing conditions (the first laser processing condition and the second laser processing condition) when forming the laser processing region and the processing region RL for stress adjustment, respectively, and the internal stress generated inside the wafer W. Note that the same reference signs are assigned to the corresponding conditions in both Table 1 and Table 2.

[0043]

Table 1

[0044] As shown in Table 1, (A) the greater the number of layers in the laser processing region, or (B) the greater the number of lines in the laser processing region (the number in the XY direction. The number of division lines), the greater the influence of the internal stress generated on the surface Wa side of the wafer W. Also, (C) the shorter the interval (index) in the scanning direction (XY direction) of the focus point FP during laser processing, the greater the influence of the internal stress generated on the surface Wa side of the wafer W.

[0045] And, (D) the closer the laser processing region is to the surface Wa of the wafer W, or (E) the greater the power of the laser beam L during laser processing (for example, intensity or irradiation time, etc.), the greater the influence of the internal stress generated on the surface Wa side of the wafer W.

[0046] By adjusting either of the conditions (D) and (E) among the laser processing conditions, it is possible to adjust the half-cut (HC) conditions and the stealth (ST) conditions. Here, the HC condition means that the crack K extending from the laser processing region R reaches the surface Wa of the wafer W, which refers to the case where at least one of the conditions of (D) the distance (processing height) between the focus point FP of the laser beam L and the surface Wa of the wafer W, and (E) the power of the laser beam L during laser processing is adjusted. Also, the ST condition means that the crack K extending from the laser processing region R does not reach the surface Wa of the wafer W, which refers to the case where at least one of the conditions of (D) the distance (processing height) between the focus point FP of the laser beam L and the surface Wa of the wafer W, and (E) the power of the laser beam L during laser processing is adjusted. In the case of the HC condition, the crack K extending from the laser processing region R reaches the surface Wa of the wafer W, so the influence of the internal stress generated on the surface Wa side of the wafer W is greater compared to the case of the ST condition.

[0047]

Table 2

[0048] The relationship between the laser processing conditions of the processing region RL for stress adjustment and the internal stress generated on the back surface Wb side of the wafer W is the same as described above. That is, as shown in Table 2, (A) the greater the number of layers in the processing region RL for stress adjustment, or (B) the greater the number of lines (the number in the XY direction) in the processing region RL for stress adjustment, the greater the influence 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 direction) of the focus point FP during laser processing, the greater the influence of the internal stress generated on the back surface Wb side of the wafer W.

[0049] And, (D) the closer the processing region RL for stress adjustment is to the back surface Wb of the wafer W, or (E) the greater the power (for example, intensity or irradiation time, etc.) of the laser light L during laser processing, the greater the influence of the internal stress generated on the back surface Wb side of the wafer W. That is, in the case of the HC condition (crack K in FIG. 4 B ), since the crack extending from the processing region RL for stress adjustment reaches the back surface Wb of the wafer W, compared with the case of the ST condition (crack K in FIG. 5 C ), the influence of the internal stress generated on the back surface Wb side of the wafer W becomes greater.

[0050] The laser processing conditions of the laser processing region are determined according to the manufacturing conditions (chip size, thickness, etc.) of the chips (for example, semiconductor devices, etc.) to be produced. For this reason, in the present embodiment, the laser processing conditions of the processing region RL for stress adjustment are adjusted according to the laser processing conditions of the laser processing region. Thereby, the warpage of the wafer W generated due to laser processing can be reduced.

[0051] Note that the processing region RL for stress adjustment is preferably formed uniformly over the entire surface of the wafer W in order to reduce the warpage and deflection of the wafer W.

[0052] The following describes a method for setting the laser processing conditions of the stress adjustment processing area RL. First, the control unit 12 evaluates the factors listed in Table 1 for the laser processing conditions of the laser processing area, and evaluates the influence of the internal stress generated on the surface Wa side of the wafer W. Then, the laser processing conditions (Table 2) of the stress adjustment processing area RL for generating an internal stress that balances the internal stress generated on the surface Wa side of the wafer W are set on the back surface Wb side.

[0053] Here, the laser processing conditions of the stress adjustment processing area RL may be set manually using the control unit 12, or may be set automatically when the control unit 12 receives the input of the laser processing conditions of the laser processing area.

[0054] Note that since the stress adjustment processing area RL disappears in the grinding step, depending on the magnitude of the influence of the internal stress caused by the laser processing area, the balance of the internal stress of the wafer W may be broken during the grinding step and a grinding error may occur. For this reason, it is conceivable to form the stress adjustment processing area RL more inward (on the surface Wa side).

[0055] For example, when the evaluation value of the magnitude of the influence of the internal stress caused by the laser processing area is equal to or greater than the threshold value, a constraint condition (lower limit value) is set for the distance (processing height) from the back surface Wb of the (D) wafer W of the stress adjustment processing area RL. Then, under this constraint condition, the conditions of (A) to (C) and (E) are set. Thereby, the position of the stress adjustment processing area RL can be restricted to the inside (surface Wa side), and a grinding error can be prevented.

[0056] Also, when setting the laser processing conditions for the stress adjustment processing area RL, the throughput of the laser processing process may be considered. For example, it may be possible to set whether to prioritize throughput together with the laser processing conditions for the laser processing area. When a setting that prioritizes throughput is made, the following constraints are set: (A) reducing the number of layers (for example, 1 layer), (B) making the number of lines the same as or less than that of the laser processing area, and (C) making the index the same as or less than that of the laser processing area. Then, under these constraints, the control unit 12 adjusts at least one of the conditions of (D) the distance (processing height) from the back surface Wb of the wafer W and (E) the power of the laser beam L.

[0057] (Example 1) FIG. 3 is a cross-sectional view showing Example 1 of the stress adjustment processing area.

[0058] In the example shown in FIG. 3, two layers of laser processing areas R1 and R2 are formed on the surface Wa side of the wafer W. And the stress adjustment processing area RL A is formed symmetrically with respect to the center line Lc in the thickness direction of the wafer W before grinding, with the laser processing areas R1 and R2.

[0059] That is, in FIG. 3, the number of layers and the number of lines of the laser processing areas R1 and R2 and the stress adjustment processing area RL A are equal respectively (conditions (A) and (B)).

[0060] Also, the distance H between the surface Wa of the wafer W and the laser processing area R1 R1 is equal to the distance H between the back surface Wb of the wafer W and the stress adjustment processing area RL A1 and the distance H A1 is equal to the distance H between the surface Wa of the wafer W and the laser processing area R2 R2 is equal to the distance H between the back surface Wb of the wafer W and the stress adjustment processing area RL A2 and the distance H A2 is equal (condition (D)).

[0061] Also, the intervals (indexes) in the scanning direction (XY direction) of the condensing points FP when forming the laser processing regions R1 and R2 and the stress adjustment processing region RL A are equal (condition (C)), and the power of the laser beam L is equal (condition (E)).

[0062] According to Example 1, the same laser processing conditions for the laser processing regions R1 and R2 and the stress adjustment processing region RL A are used to perform equivalent laser processing. As a result, since the stress adjustment processing region RL A is formed symmetrically with respect to the center line Lc with the laser processing regions R1 and R2, the internal stress of the wafer W can be equalized.

[0063] (Example 2) FIG. 4 is a cross-sectional view showing Example 1 of the stress adjustment processing region. FIG. 4(a) is a cross-sectional view of the wafer W, and FIG. 4(b) is a partially enlarged cross-sectional view of FIG. 4(a).

[0064] In the example shown in FIG. 4(a), two layers of the laser processing regions R1 and R2 are formed, and one layer of the stress adjustment processing region RL A is formed (see condition (A) in Table 3).

[0065] In Example 2, conditions (B) and (C) when forming the laser processing regions R1 and R2 and the stress adjustment processing region RL B are the same respectively.

[0066] In Example 2, the condition for forming the laser processing regions R1 and R2 is the ST condition, while the condition for forming the stress adjustment processing region RL B is the HC condition. That is, as shown in FIG. 4(b), cracks K R extending from the laser processing regions R1 and R2 do not reach the surface Wa of the wafer W, and (D) the distance H R1 between the condensing point FP of the laser beam L and the surface Wa of the wafer W R2(Processing height), and at least one of the conditions of the power of the laser beam L during (E) laser processing is adjusted. Further, a processing region RL for stress adjustment B A crack K extending from B reaches the back surface Wb of the wafer W, and the distance H between the focus point FP of the laser beam L and the back surface Wb of the wafer W B (Processing height), and at least one of the conditions of the power of the laser beam L during (E) laser processing is adjusted.

[0067] In Example 2, by causing the crack KB to reach the back surface Wb side of the wafer W, the internal stress on the back surface Wb side of the wafer W is increased. Thereby, even if the number of layers of the processing region RL for stress adjustment B is one layer, it becomes possible to balance the internal stresses on the front surface Wa and the back surface Wb sides of the wafer W. And since the number of layers of the processing region RL for stress adjustment B can be one layer, the throughput in laser processing can be increased.

[0068]

Table 3

[0069] (Example 3) FIG. 5 is a cross-sectional view showing Example 1 of a processing region for stress adjustment. FIG. 5(a) is a cross-sectional view of the wafer W, and FIG. 5(b) is a partially enlarged cross-sectional view of FIG. 5(a).

[0070] In the example shown in FIG. 5(a), two layers of laser processing regions R1 and R2 are formed, and a processing region RL for stress adjustment A is formed as one layer (see condition (A) in Table 4).

[0071] In Example 3, the conditions (B) for forming the laser processing regions R1 and R2 and the processing region RL for stress adjustment B are the same.

[0072] Also, both conditions (D) and (E) are ST conditions. That is, the processing region RL for stress adjustmentC Crack K extending therefrom C The distance H between the focusing point FP of the laser beam L and the back surface Wb of the wafer W is adjusted so that the crack K does not reach the back surface Wb of the wafer W C (Processing height), and at least one of the conditions of the power of the laser beam L during laser processing (E) is adjusted

[0073] In Example 3, the index D when forming the stress adjustment processing region RL C is set to half of the index D when forming the laser processing regions R1 and R2. That is, D C = D R / 2, and in one example D C = 1.0 mm, D R = 0.5 mm R C

[0074] In Example 3, by shortening the index D when forming the stress adjustment processing region RL C the internal stress on the back surface Wb side of the wafer W is increased. Thereby, even if the number of layers of the stress adjustment processing region RL C is one layer, it becomes possible to balance the internal stresses on the front surface Wa and the back surface Wb sides of the wafer W C

[0075]

Table 4

[0076] According to the present embodiment, by adjusting the laser processing conditions of the stress adjustment processing region RL according to the laser processing conditions of the laser processing region, warping and deflection of the wafer W can be reduced

[0077] ​​​When the interval (index) in the scanning direction (XY direction) of the condensing point FP is reduced during the formation of the laser processing regions R1 and R2, the warp of the wafer W tends to increase. For this reason, in the conventional GAL (Grind After Laser) process, it has been difficult to reduce the index. On the other hand, in the present embodiment, since the stress adjustment processing region RL can reduce the warp even when the index in the laser processing region is reduced, it becomes possible to realize the laser processing of the GAL process with a small index.

[0078] When the power of the laser beam L during laser processing is high, damage (hereinafter referred to as splash damage) may occur to the devices formed on the surface Wa side due to the light leaking to the surface Wa side of the wafer W. For this reason, for devices that have hitherto selected the LAG (Laser After Grind) process with a small index, the low splash processing, which is an advantage of the GAL process (since the thickness dimension of the wafer W during laser irradiation is large and the laser processing region can be formed away from the surface Wa, low splash processing is easier to perform compared to the LAG process), can be applied.

[0079] In addition, the accuracy problem due to the wafer deflection (minute chip movement during processing) during laser processing, which is a problem specific to the LAG process, can be reduced.

[0080] In Examples 1 to 3, the stress adjustment processing regions RL (RL A , RL B and RL C ) are formed so as to overlap the laser processing regions R1 and R2 (so that the positions in the scanning direction (XY direction) of the condensing point FP coincide) (see FIGS. 4(b) and 5(b)), but the present invention is not limited to this. The lateral positions of the stress adjustment processing region RL and the condensing point FP during the formation of the laser processing regions R1 and R2 may be different from each other.

[0081] Also, in FIGS. 3 to 5, although the illustration of the position of the target thickness is omitted, the laser processing regions R1 and R2 may be formed either outside or inside with respect to the position of the target thickness, or may be formed so as to overlap the position of the target thickness.

Description of Reference Numerals

[0082] 10… Wafer processing system, 10-1… Laser processing apparatus, 10-2… Grinding apparatus, 12… Control unit, 14… Wafer transfer unit, 16… Laser processing unit, 18… Grinding control unit, 20… Thickness measurement unit, 22… Wafer transfer unit, 50… Grinding machine, 52… Rotating grinding wheel, 54… Grinding wheel, T1… Adsorption stage, T2… Chuck table

Claims

1. 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 control unit that forms, within a substrate of the wafer, the laser processing area and a stress adjustment processing area that generates an internal stress counter to the internal stress generated within 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:

2. 2. The laser processing apparatus according to claim 1, 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.

Images