Laser processing method

Abstract

The objective is to provide a laser processing method that can reduce wafer warping caused by laser processing. [Solution] The laser processing method involves focusing laser light into the interior of a wafer substrate, on which a device layer is laminated on the surface of the substrate, to form laser processing regions (R1, R2) along the planned division lines of the wafer; focusing laser light into the interior of the wafer to form a stress adjustment processing region (RL) that generates internal stress to counteract the internal stress generated inside the wafer by the laser processing region; and setting second laser processing conditions for forming the stress adjustment processing region based on first laser processing conditions for forming the laser processing region. If the evaluation value of the magnitude of the influence of internal stress caused by the laser processing region is greater than or equal to a threshold, a constraint condition is set on the processing height of the stress adjustment processing region, and under the constraint condition, second laser processing conditions other than the processing height are set.

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 technology]

[0002] Conventionally, laser processing equipment (also called laser dicing equipment) is known that focuses a laser beam onto the inside of a wafer such as silicon, irradiating it along the planned division line, thereby forming 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 then transported to a grinding device (grinder), where the back side of the wafer is ground. Then, by expanding a backgrind tape attached to the surface of the wafer, the wafer is divided into individual chips (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2005-086111 [Overview of the project] [Problems that the invention aims to solve]

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

[0005] Figure 6 shows an example in which laser processing areas R1 and R2 are formed on the outside of the wafer W at the target thickness Ht1. In this case, the laser processing areas R1 and R2 are removed by grinding. On the other hand, Figure 7 shows an example in which laser processing areas R1 and R2 are formed on the inside of the wafer W at the target thickness Ht2. In this case, after the wafer W is divided, the laser processing areas R1 and R2 remain on the side surface of the chip.

[0006] In both Figure 6 and Figure 7, the laser processing regions R1 and R2 are formed so as to be biased toward the side closer to the 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, the wafer W warps due to internal cracks propagating from the laser processing regions R1 and R2. The amount of warping at the periphery of the wafer W may be several millimeters.

[0007] If the wafer W warps, when transporting the wafer W from the laser processing machine to the grinding machine, the transport arm may not be able to stably hold the wafer W, which may cause transport problems such as the wafer W falling during transport. Furthermore, after transporting the wafer W to the grinding machine, the chuck table may not be able to stably hold the wafer W, which may cause a suction error during grinding and stop the grinding process.

[0008] This invention has been made in view of these circumstances, and aims to provide a laser processing method and apparatus that can reduce wafer warping caused by laser processing. [Means for solving the problem]

[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. In the laser processing region forming step, the laser processing region is formed based on the first laser processing conditions, and in the stress adjustment processing region forming step, the stress adjustment processing region is formed 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, that the second laser processing conditions include 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] A laser processing apparatus according to a fifth aspect of the present invention, in the fourth aspect, includes a condition setting unit that sets a second laser processing condition for forming a stress adjustment processing area that generates internal stress to counteract the internal stress generated inside the wafer by the laser processing area, based on a first laser processing condition for forming a laser processing area. [Effects of the Invention]

[0014] According to the present invention, it is possible to reduce wafer warping caused by laser processing. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a block diagram showing the configuration of a laser processing apparatus in a wafer processing system according to one embodiment of the present invention. [Figure 2] Figure 2 is a block diagram showing the configuration of a grinding apparatus in a wafer processing system according to one embodiment of the present invention. [Figure 3] Figure 3 is a cross-sectional view showing Example 1 of the stress adjustment machining region. [Figure 4] Figure 4 is a cross-sectional view showing Example 2 of the stress adjustment machining region. [Figure 5] Figure 5 is a cross-sectional view showing Example 3 of the stress adjustment machining region. [Figure 6] Figure 6 is a cross-sectional view showing an example in which a laser processing area is formed outside the target thickness position of the wafer. [Figure 7] Figure 7 is a cross-sectional view showing an example in which a laser processing area is formed inward relative to the target thickness of the wafer. [Modes for carrying out the invention]

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

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

[0018] (Laser processing) Figure 1 is a block diagram showing the configuration of a laser processing apparatus in a wafer processing system according to one embodiment of the present invention.

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

[0020] The control unit 12 includes 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.), and input / output circuitry, and controls the operation of each part of the laser processing apparatus 10-1. The control unit 12 is implemented, for example, by a personal computer or workstation.

[0021] The wafer moving unit 14 includes an adsorption stage T1 for adsorbing and holding the wafer W, and an XYZθ table provided on the main body base (not shown) of the laser processing apparatus 10-1 for moving the adsorption stage T1 in the XYZθ direction.

[0022] Wafer W is, for example, a disc-shaped semiconductor wafer made of silicon. The surface Wa of the substrate of wafer W is divided into grid-like regions by multiple division lines extending in the X and Y directions, and devices (device layers) such as electronic circuits are formed (stacked) in each of these grid-like regions.

[0023] When dividing a wafer W into individual chips C, first, a backgrind 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 downwards. Then, the wafer W is held by adsorption stage T1. Alternatively, the wafer W may be held by adsorption without attaching the backgrind tape BG.

[0024] The laser processing unit 16 includes a laser light source, optical elements such as a condenser lens, and a driving means for moving the laser beam L in a minute direction relative to the wafer W. For example, a semiconductor laser-pumped Nd:YAG (Yttrium Aluminum Garnet) laser is used as the laser light source. The laser beam L emitted from the laser light source is focused into the wafer W by the condenser lens. As a result, 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 the physical properties of the wafer W, such as density, refractive index, and mechanical strength, become different from the surrounding areas due to irradiation with laser light L, resulting in a decrease in strength compared to the surrounding areas. The laser processing regions R1 and R2, and the stress adjustment processing region RL, for example, include regions containing crack areas.

[0026] The laser processing unit 16 adjusts the position of the focal point FP of the laser beam L to sequentially form laser processing regions R1 and R2 on the inner surface Wa side of the wafer W. As shown in Figure 1, when laser processing regions R1 and R2 are formed, internal stress (tensile stress) is generated inside the wafer W that expands the wafer W in the direction (±Y direction) in which the laser processing regions R1 and R2 were formed. This internal stress acts to expand the surface Wa side of the wafer W, causing the peripheral edge of the wafer W to warp upward towards the back surface Wb side.

[0027] Therefore, the laser processing unit 16 adjusts the position of the focal point FP of the laser beam L to form a stress adjustment processing region RL on the back surface Wb side of the wafer W. The stress adjustment processing region RL generates 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 a 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 stresses 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 out) the internal stress generated by the laser processing regions R1 and R2. Here, the laser processing conditions for the stress adjustment processing area RL include, for example, the number of layers in the stress adjustment processing area RL, the power of the laser beam L (e.g., intensity or irradiation time), and the position of the focusing point FP (the interval in the scan direction (XY direction) (hereinafter referred to as the index) and the position in the thickness direction (Z direction) (distance from the back surface Wb)). The stress adjustment processing area RL will be described later.

[0028] When forming laser processing areas R1 and R2 and a stress adjustment processing area RL on a wafer W, 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 precisely set to a predetermined position inside the wafer W by adjusting the Z-direction position of the wafer W using an XYZθ table and controlling the position of the condenser lens.

[0029] In this state, the XYZθ table is fed in the X direction, which is the dicing direction. This forms one line of laser processing areas R1 and R2 and a stress adjustment processing area RL along the planned division line of the wafer W. Once one line of laser processing areas R1 and R2 and a stress adjustment processing area RL is formed along the planned division line, the XYZθ table is indexed and fed one pitch in the Y direction, and laser processing areas R1 and R2 and a stress adjustment processing area RL are formed on the next planned division line. Next, once laser processing areas R1 and R2 and a stress adjustment processing area RL are formed along all planned division lines in the X direction, the XYZθ table is rotated 90° around the Z axis, and laser processing areas R1 and R2 and a stress adjustment processing area RL are similarly formed on the planned division lines in the X direction after the rotation.

[0030] The procedure for forming the laser processing areas R1 and R2 and the stress adjustment processing area RL is not particularly limited. For example, as shown in Figure 1, the first layer laser processing area R1 may be formed over the entire surface of the wafer W, then the second layer laser processing area R2 (on the back surface Wb side of the wafer W) may be formed, and then the stress adjustment processing area RL may be formed. Here, the laser processing conditions for forming the laser processing areas R1 and R2 and the stress adjustment processing area RL may be different from or the same. Alternatively, a branching section (e.g., a beam splitter) may be provided to split the laser beam L, and the beam may be focused to two focal points at different positions (depths) in the Z direction inside the wafer W, thereby forming two layers of laser processing areas R1 and R2 and one or more layers of stress adjustment processing areas RL in a single scan. In other words, the laser processing area formation step and the stress adjustment processing area formation step may be performed simultaneously or separately.

[0031] The wafer W, on which laser processing areas R1 and R2 and stress adjustment processing area RL are formed, is transported from the laser processing device 10-1 to the grinding device 10-2, where the back surface of the wafer W is ground, removing a portion of the laser processing area R2 on the back side and dividing it into individual chips (see Figure 2).

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

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

[0034] As shown in Figure 2, the grinding apparatus 10-2 according to this embodiment comprises a grinding control unit 18, a thickness measuring unit 20, a wafer moving unit 22, and a grinding machine (grinder) 50. The grinding machine 50 comprises a rotary grinding machine 52 and a grinding wheel 54 attached to the rotary grinding machine 52.

[0035] 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 from a slurry supply port (not shown) to the back surface Wb of the wafer W, thereby bringing the grinding wheel 54 into contact with the back surface Wb of the wafer W and rotating it.

[0036] The wafer moving unit 22 includes a chuck table T2 for adsorbing and holding the wafer W, and an XY table (not shown) for moving the chuck table T2 in the XY direction within the grinding apparatus 10-2.

[0037] After the laser processing areas R1 and R2 and the stress adjustment processing area RL are formed in the laser processing apparatus 10-1, the wafer W is transported to the grinding apparatus 10-2. The wafer W is then placed on the holding surface of the chuck table T2 with its surface Wa facing downwards and is held in place by the chuck table T2. Next, while the chuck table T2 is moved in the XY direction by the wafer moving unit 22, the grinding control unit 18 brings the grinding wheel 54 into contact with the back surface Wb of the wafer W and rotates it, thereby grinding the entire back surface Wb of the wafer W.

[0038] 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 grinding the back surface Wb of the wafer W. The thickness measuring unit 20 may use a contact-type means in which a contact-type height gauge is brought into contact with the back surface Wb of the wafer W for measurement. Alternatively, the thickness measuring unit 20 may use a non-contact means (for example, a Time-of-Flight (ToF) method) in which laser light from a laser light source (for example, a semiconductor laser) is irradiated onto the back surface Wb of the wafer W to measure the distance to the back surface Wb of the wafer W.

[0039] The grinding control unit 18 calculates the thickness of the wafer W based on the output from the thickness measuring unit 20 and grinds the back surface Wb of the wafer W. This allows the thickness of the wafer W to be brought to the target thickness.

[0040] In the example shown in Figure 2, the grinding device 10-2 is controlled by the same control unit 12 as the laser processing device 10-1. However, it may be controlled by a different control unit (for example, a personal computer or workstation). 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 position and size of the laser processing areas R1 and R2, and information regarding the target thickness of the wafer W, with the control unit 12 of the laser processing device 10-1 via a communication line or storage device.

[0041] [Example of a machining area for stress adjustment] Next, we will describe an example of a stress adjustment machining region RL.

[0042] (Relationship between laser processing conditions and internal stress) Tables 1 and 2 summarize the relationship between the laser processing conditions (first laser processing conditions and second laser processing conditions) and the internal stress generated inside the wafer W when forming the laser processing area and the stress adjustment processing area RL, respectively. In both Tables 1 and 2, corresponding conditions are denoted by the same reference numerals.

[0043] [Table 1]

[0044] 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 of lines in the XY direction; number of lines to be divided), the greater the influence of internal stress generated on the surface Wa side of the wafer W. Also, (C) the shorter the interval (index) of the scanning direction (XY direction) of the focusing point FP during laser processing, the greater the influence of internal stress generated on the surface Wa side of the wafer W.

[0045] Furthermore, (D) the closer the laser processing area is to the surface Wa of the wafer W, or (E) the greater the power of the laser beam L during laser processing (e.g., intensity or irradiation time), the greater the influence of internal stress generated on the surface Wa side of the wafer W.

[0046] By adjusting either condition (D) or (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 the crack K extending from the laser processing area. R This refers to the case where at least one of the following conditions is adjusted so that (D) the distance between the focal point FP of the laser beam L and the surface Wa of the wafer W (processing height), and (E) the power of the laser beam L during laser processing, so that the laser beam L reaches the surface Wa of the wafer W. ST condition refers to the crack K extending from the laser processing area. R This refers to a case where at least one of the following conditions is adjusted so that the laser beam does not reach the surface Wa of the wafer W: (D) the distance between the focal point FP of the laser beam L and the surface Wa of the wafer W (processing height), and (E) the power of the laser beam L during laser processing. In the case of HC conditions, cracks K extending from the laser processing area R Because the stress reaches the surface Wa of the wafer W, the influence of internal stress generated on the surface Wa side of the wafer W becomes greater compared to the ST condition.

[0047] [Table 2]

[0048] The relationship between the laser processing conditions of the stress adjustment processing area RL 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 more layers there are in the stress adjustment processing area RL, or (B) the more lines there are in the stress adjustment processing area RL (number of lines in the XY direction), 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) of the focusing point FP in the scanning direction (XY direction) during laser processing, the greater the influence of the internal stress generated on the back surface Wb side of the wafer W.

[0049] Furthermore, the closer the stress adjustment processing area RL is to the back surface Wb of the wafer W, or the greater the power of the laser beam L during laser processing (e.g., intensity or irradiation time), the greater the influence of internal stress generated on the back surface Wb of the wafer W. That is, in the case of HC conditions (crack K in Figure 4), B In this case, a crack extending from the stress adjustment processing region RL reaches the back surface Wb of the wafer W, therefore, under ST conditions (crack K in Figure 5) C Compared to the case shown, the influence of internal stress occurring on the back surface Wb side of the wafer W becomes greater.

[0050] The laser processing conditions in the laser processing area are determined according to the manufacturing conditions (chip size, thickness, etc.) of the chip to be produced (e.g., semiconductor device). Therefore, in this embodiment, the laser processing conditions of the stress adjustment processing area RL are adjusted according to the laser processing conditions in the laser processing area. This makes it possible to reduce the warping of the wafer W caused by laser processing.

[0051] Furthermore, it is preferable to form the stress adjustment processing area RL evenly across the entire surface of the wafer W in order to reduce warping and deflection of the wafer W.

[0052] The following describes how to set the laser processing conditions for 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, it sets the laser processing conditions (Table 2) for the stress adjustment processing area RL to generate an internal stress on the back surface Wb side that balances the internal stress generated on the surface Wa side of the wafer W.

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

[0054] Furthermore, since the stress adjustment processing area RL disappears during the grinding step, depending on the magnitude of the influence of internal stress caused by the laser processing area, the balance of internal stress in the wafer W may be disrupted during the grinding step, potentially leading to a grinding error. For this reason, it is conceivable to form the stress adjustment processing area RL further inward (towards the surface Wa).

[0055] For example, if the evaluation value of the magnitude of the influence of internal stress caused by the laser processing area exceeds a threshold, a constraint condition (lower limit) is set for the distance (processing height) of the stress adjustment processing area RL from the back surface Wb of the wafer W (D). Then, under this constraint condition, conditions (A) to (C) and (E) are set. This restricts the position of the stress adjustment processing area RL to the inside (surface Wa side), thereby preventing grinding errors.

[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, (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 are set as constraint conditions. Then, 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 under these constraint conditions.

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

[0061] Furthermore, there are laser processing areas R1 and R2 and a stress adjustment processing area RL. A When forming the focal point FP, the spacing (index) of the focal points FP in the scanning direction (XY direction) is equal (condition (C)), and the power of the laser beam L is equal (condition (E)).

[0062] According to Example 1, the laser processing areas R1 and R2 and the stress adjustment processing area RL A Perform equivalent laser processing using the same laser processing conditions. This will create a stress adjustment processing area RL. A Since the laser-processed regions R1 and R2 are formed symmetrically with respect to the center line Lc, the internal stress of the wafer W can be equalized.

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

[0064] In the example shown in Figure 4(a), two layers are formed in the laser processing areas R1 and R2, and the stress adjustment processing area RL A A single layer is formed (see condition (A) in Table 3).

[0065] In Example 2, the laser processing areas R1 and R2 and the stress adjustment processing area RL are used. B The conditions (B) and (C) when forming are the same.

[0066] In Example 2, the conditions for forming laser processing regions R1 and R2 are ST conditions, whereas the stress adjustment processing region RL B The conditions for forming the cracks are HC conditions. That is, as shown in Figure 4(b), cracks K extending from the laser processing regions R1 and R2 R (D) The distance H between the focal point FP of the laser beam L and the surface Wa of the wafer W is such that the beam does not reach the surface Wa of the wafer W. R1 and H R2(E) At least one of the following conditions is adjusted: (processing height) and (E) power of the laser beam L during laser processing. Furthermore, the stress adjustment processing area RL B Crack K extending from B (D) The distance H between the focal point FP of the laser beam L and the back surface Wb of the wafer W, such that the beam reaches the back surface Wb of the wafer W. B (E) At least one of the following conditions is adjusted: (processing height) and (E) power of the laser beam L during laser processing.

[0067] In Example 2, the internal stress on the back surface Wb side of the wafer W is increased by allowing the crack KB to reach the back surface Wb side of the wafer W. This creates a stress adjustment processing area RL. B Even with only one layer, it becomes possible to balance the internal stresses on the front surface Wa and back surface Wb of the wafer W. Furthermore, the stress adjustment processing area RL B Since the number of layers can be reduced to one, the throughput in laser processing can be increased.

[0068] [Table 3]

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

[0070] In the example shown in Figure 5(a), two layers are formed in the laser processing areas R1 and R2, and the stress adjustment processing area RL A A single layer is formed (see condition (A) in Table 4).

[0071] In Example 3, the laser processing areas R1 and R2 and the stress adjustment processing area RL are used. B The conditions (B) when forming are the same.

[0072] Furthermore, conditions (D) and (E) shall both be ST conditions. That is, the stress adjustment machining area RLC Crack K extending from C (D) The distance H between the focal point FP of the laser beam L and the back surface Wb of the wafer W, so that the beam does not reach the back surface Wb of the wafer W. C (E) At least one of the following conditions is adjusted: (processing height) and (E) power of the laser beam L during laser processing.

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

[0074] In Example 3, the stress adjustment machining area RL C Index D when forming C By shortening the length, the internal stress on the back surface Wb side of the wafer W is increased. This results in a stress adjustment processing area RL. C Even with only one layer, it becomes possible to balance the internal stresses on the front surface Wa and back surface Wb of the wafer W.

[0075] [Table 4]

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

[0077] When the spacing (index) of the focusing points FP in the scanning direction (XY direction) during the formation of laser processing regions R1 and R2 is reduced, the warping of the wafer W tends to increase. For this reason, it has been difficult to reduce the index in conventional GAL (Grind After Laser) processes. In contrast, in this embodiment, warping can be reduced even when the index in the laser processing region is reduced by the stress adjustment processing region RL, making it possible to realize laser processing of a small-index GAL process.

[0078] If the laser beam L power is high during laser processing, light passing through to the surface Wa side of the wafer W can damage the device formed on the surface Wa side (hereinafter referred to as splash damage). For this reason, for devices where the LAG (Laser After Grind) process has been selected for small index devices until now, the advantages of the GAL process, namely low splash processing (the wafer W thickness dimension is large during laser irradiation, and the laser processing area can be formed at a distance from the surface Wa, making low splash processing easier compared to the LAG process), can be applied.

[0079] Furthermore, it can reduce accuracy problems caused by wafer deflection (minute chip movement during processing), which is a challenge specific to the LAG process.

[0080] In Examples 1 to 3, the stress adjustment machining area RL (RL A , RL B and RL C The stress adjustment processing area RL is formed so as to overlap with the laser processing areas R1 and R2 (so that the positions of the focusing points FP in the scanning direction (XY direction) coincide) (see Figures 4(b) and 5(b)), but the present invention is not limited thereto. The lateral positions of the focusing points FP when the stress adjustment processing area RL and the laser processing areas R1 and R2 are formed may be different from each other.

[0081] Furthermore, although the position of the target thickness is not shown in Figures 3 to 5, the laser processing areas R1 and R2 may be formed either outside or inside the position of the target thickness, or they may be formed to overlap with the position of the target thickness. [Explanation of Symbols]

[0082] 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

1. A laser processing region formation step involves focusing laser light into the interior of a wafer substrate, in which a device layer is laminated on the surface of the substrate, thereby forming a laser processing region along the planned division line of the wafer. A stress adjustment processing region formation step, in which a stress adjustment processing region is formed by focusing laser light into the wafer, thereby generating an internal stress that counteracts the internal stress generated in the wafer by the laser processing region, A condition setting step for setting a second laser processing condition for forming the stress adjustment processing area based on a first laser processing condition for forming the laser processing area, wherein if the evaluation value of the magnitude of the influence of internal stress caused by the laser processing area is greater than or equal to a threshold, a constraint condition is set on the processing height of the stress adjustment processing area, and under the constraint condition, the second laser processing condition other than the processing height is set. A laser processing method comprising the following features.

2. In the laser processing region formation step, the laser processing region is formed based on the first laser processing conditions. The laser processing method according to claim 1, wherein in the step of forming the stress-adjusting processing region, the stress-adjusting processing region is formed based on the second laser processing conditions.

3. The laser processing method according to claim 1 or 2, 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 adjustment processing region, and the spacing of the scanning direction of the focal points when forming the stress adjustment processing region and the power of the laser beam.

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