Wafer Processing Method

Abstract

To suppress a crack from reaching a device when forming a laser processing groove by performing ablation processing on a wafer using green laser beams.SOLUTION: The present invention relates to a processing method for a wafer for processing with pulsed green laser beams the wafer comprising a device region where a plurality of devices is formed and an outer peripheral excessive region enclosing the device region on a front face side and having absorbability with respect to the green laser beams. The processing method for the wafer includes: a first laser processing step of forming an annular first laser processing groove or a first laser processing hole in the outer peripheral excessive region; and a second laser processing step of forming a plurality of second laser processing grooves by irradiating the wafer with the green laser beams of lower output than output of the green laser beams in the first laser processing step so as to pass the first laser processing groove or the first laser processing hole along each predetermined dividing line.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a wafer processing method for processing a wafer having absorptivity for a green laser beam with a pulsed green laser beam. [Background technology]

[0002] A method has been proposed in which a laser beam is irradiated onto an oxide single crystal wafer having a plurality of planned dividing lines set in a lattice pattern on the surface, and devices such as SAW (Surface Acoustic Wave) filters formed in each area partitioned by the plurality of planned dividing lines, to perform ablation processing and form laser-processed grooves along each planned dividing line (see, for example, Patent Document 1).

[0003] The above-mentioned document describes a method of performing ablation processing on a single crystal wafer of lithium niobate (LiNbO3, hereafter abbreviated as LN) by irradiating the single crystal wafer with a pulsed laser beam having a wavelength (266 nm) that is absorbed by the single crystal wafer.

[0004] Also described is a method of performing ablation processing on a single crystal wafer of lithium tantalate (LiTaO3, hereafter abbreviated as LT) by irradiating the single crystal wafer with a pulsed laser beam having a wavelength (193 nm) that is absorbed by the single crystal wafer.

[0005] In this way, a pulsed laser beam having a wavelength in the ultraviolet (UV) range is usually used for ablation processing of single crystal wafers such as LN and LT. The third harmonic of an Nd:YAG laser (wavelength 355 nm) may also be used as a pulsed laser beam having a wavelength in the ultraviolet range.

[0006] Incidentally, when performing ablation processing on a wafer, a wafer unit may be created in which the wafer is supported on a metal annular frame via a resin protective tape, and the ablation processing may be performed on the wafer while the wafer is held by suction on a chuck table via the protective tape.

[0007] However, when attempting to divide a wafer by ablation processing using a pulsed ultraviolet laser beam as described above, there is a problem that the laser beam reaches the protective tape and burns off the protective tape.

[0008] Therefore, in order to suppress damage to the protective tape, it is conceivable to use a green laser beam that corresponds to the second harmonic of an Nd:YAG laser (having a wavelength of 532 nm, which is in the visible light band).

[0009] However, since the absorption rate of green laser beams is lower in single crystal wafers such as LN and LT than in UV laser beams, it is difficult to form laser grooves by ablation. Although it is possible to form laser grooves by increasing the output of the green laser beam, there is a problem that cracks extend from the laser grooves and reach the device. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 10-305420 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in consideration of these problems, and aims to prevent cracks from reaching devices when a green laser beam is used to perform ablation processing on a wafer to form laser processing grooves. [Means for solving the problem]

[0012] According to one aspect of the present invention, there is provided a wafer processing method for processing a wafer having a surface side on which a device region in which devices are formed in each region partitioned by a plurality of planned division lines set on the surface, and a peripheral excess region surrounding the device region, the wafer being absorbent to the green laser beam, with a pulsed green laser beam, the method comprising: a first laser processing step in which the green laser beam is irradiated onto the wafer along the outer periphery of the wafer to form a ring-shaped first laser-machined groove or first laser-machined hole in the peripheral excess region; and a second laser processing step in which, after the first laser processing step, the green laser beam is irradiated onto the wafer at an output lower than the output of the green laser beam in the first laser processing step so as to pass through the first laser-machined groove or first laser-machined hole along each planned division line, to form a plurality of second laser-machined grooves.

[0013] Preferably, the wafer processing method further includes, after the second laser processing step, a dividing step of dividing the wafer along the plurality of second laser processing grooves with a cutting blade having a blade thickness smaller than the width of each second laser processing groove.

[0014] Also, preferably, the wafer has a single crystal substrate of lithium tantalate, and in the first laser processing step, the first laser processing groove or the first laser processing hole is formed in the single crystal substrate, and in the second laser processing step, the plurality of second laser processing grooves are formed in the single crystal substrate. Effect of the Invention

[0015] In the first laser processing step according to one aspect of the present invention, a green laser beam having a predetermined output is irradiated onto the peripheral excess area to form a first laser processed groove or a first laser processed hole. At this time, an altered area having an improved absorption rate of the green laser beam compared to before processing is formed near the first laser processed groove or the first laser processed hole.

[0016] In the second laser processing step after the first laser processing step, the ablation processing proceeds from the altered area near the first laser processing groove or the first laser processing hole as the starting point. Therefore, if the green laser beam is irradiated so as to pass through the first laser processing groove, the ablation processing can be performed in the device area even if the output of the green laser beam is reduced compared to the first laser processing step.

[0017] Therefore, in the second laser processing step in which ablation processing is performed along the planned division line, it is possible to prevent cracks from reaching the device. For example, compared to the case in which the second laser processing step is performed with the same output as the first laser processing step, the device is not damaged, and a second laser processing groove with fewer and shorter cracks (i.e., good processing quality) can be formed in the device region. [Brief description of the drawings]

[0018] [Figure 1] FIG. [Diagram 2] FIG. 1 is a flow diagram of a wafer processing method. [Diagram 3] FIG. 2 is a diagram showing a first laser processing step. [Figure 4] FIG. 4 is a cross-sectional view of a first laser-processed groove. [Diagram 5] FIG. 4 illustrates a second laser processing step. [Figure 6] Figure 6(A) is a cross-sectional view of a wafer in which two laser-processed grooves are formed for each planned division line, Figure 6(B) is a cross-sectional view of the wafer in which the remaining area between the two laser-processed grooves has been removed, and Figure 6(C) is a cross-sectional view of the wafer after the second laser processing step. [Figure 7] FIG. [Figure 8] FIG. 4 is a cross-sectional view showing a division step. [Figure 9] FIG. 11 is a diagram showing a first laser processing step according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] An embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. First, a wafer 11 to be processed will be described. Fig. 1 is a perspective view of the wafer 11. The wafer 11 of this embodiment has a disk-shaped single crystal substrate 13 made of TL (lithium tantalate).

[0020] The diameter of single crystal substrate 13 is, for example, about 150 mm (6 inches), and the thickness of single crystal substrate 13 from front surface 13a to back surface 13b is, for example, about 200 μm. However, the diameter and thickness of single crystal substrate 13 are not limited to this example.

[0021] Note that front surface 13a of single crystal substrate 13 corresponds to front surface 11a of wafer 11, and back surface 13b of single crystal substrate 13 corresponds to back surface 11b of wafer 11. A plurality of planned division lines (streets) 15 are set in a lattice pattern on front surface 11a.

[0022] A plurality of devices 17 functioning as SAW filters are formed in each of the rectangular regions defined by the plurality of planned division lines 15. Surrounding the device region 17a is a substantially flat peripheral excess region 17b in which no devices 17 are formed, surrounding the device region 17a.

[0023] In this manner, a device region 17a having a plurality of devices 17 and a peripheral surplus region 17b exist on the front surface 11a side of the wafer 11. For convenience, the boundary between the device region 17a and the peripheral surplus region 17b is shown by a dashed line in FIG.

[0024] Before processing the wafer 11, the center of a circular resin dicing tape 19 (see FIG. 6(A) etc.) is attached to the back surface 11b side of the wafer 11. In addition, one surface of a metal annular frame (not shown) having an opening with a larger diameter than the wafer 11 is attached to the outer periphery of the dicing tape 19.

[0025] In this manner, a wafer unit is formed in which the wafer 11 is supported by the annular frame via the dicing tape 19. Then, the front surface 11a side is irradiated with a green laser beam L (see FIG. 3) to perform an ablation process on the wafer 11.

[0026] Fig. 2 is a flow diagram of a method for processing a wafer 11. A laser processing device 2 (see Fig. 3) is used in a first laser processing step S10. As shown in Fig. 3, the laser processing device 2 has a chuck table 4 in the shape of a disk.

[0027] The chuck table 4 has a disk-shaped metal frame. A disk-shaped recess is formed in the frame, and a disk-shaped porous plate (not shown) made of porous ceramics is fixed in the recess.

[0028] A negative pressure from a suction source (not shown) such as an ejector acts on the porous plate through a flow path (not shown) formed in the frame. The upper surface of the porous plate and the upper surface of the frame are substantially flush with each other, and form a holding surface 4a (see FIG. 6(A)) that holds the wafer 11 by suction.

[0029] A rotary drive source (not shown) is provided below the chuck table 4, and this rotary drive source enables the chuck table 4 to rotate about a predetermined rotation axis that is approximately parallel to the height direction A3 (for example, the vertical direction).

[0030] A ball screw type first moving mechanism (e.g., an X-axis direction moving mechanism) is provided below the rotary drive source, and a ball screw type second moving mechanism (e.g., a Y-axis direction moving mechanism) is provided between the first moving mechanism and the rotary drive source.

[0031] The second moving mechanism moves the chuck table 4, the rotary drive source, etc., together in the indexing feed direction A2, and the first moving mechanism moves the chuck table 4, the rotary drive source, the second moving mechanism, etc., together in the processing feed direction A1. The processing feed direction A1, the indexing feed direction A2, and the height direction A3 are perpendicular to each other.

[0032] A laser beam irradiation unit 6 is provided above the chuck table 4. The laser beam irradiation unit 6 has a laser oscillator (not shown). The laser oscillator includes Nd:YAG as a laser medium.

[0033] The pulsed laser beam emitted from the laser oscillator is converted to a second harmonic by a nonlinear crystal such as KTP (KTiOPO4) crystal or LBO (LiB3O5), and becomes a pulsed green laser beam L having a central wavelength of 532 nm.

[0034] In this embodiment, the green laser beam L has a central wavelength of 532 nm, but is not limited to this, and a green laser beam L having a predetermined central wavelength of 501 nm or more and 561 nm or less may be used.

[0035] The laser beam irradiation unit 6 has a head portion 8 that houses a mirror, a condenser lens, etc. (not shown). The green laser beam L is irradiated toward the holding surface 4a through the head portion 8. In addition, a microscope camera unit 10 including a condenser lens, an image sensor, etc. is provided near the head portion 8.

[0036] Although the wafer 11 has some absorbency for the green laser beam L, the absorptivity of the green laser beam L is lower than that of a UV laser beam. Therefore, it is generally difficult to perform ablation processing using the green laser beam L.

[0037] Therefore, in order to form a laser groove by ablation, it is conceivable to increase the output of the green laser beam L. However, if the output of the green laser beam L is increased to the extent that a laser groove can be formed, there is a problem that cracks will extend from the formed laser groove.

[0038] If the cracks reach the device 17, the device 17 will be damaged. Faced with such a problem, the applicant has explored a processing method for reducing the number and length of cracks formed in the device region 17a while still forming laser processed grooves in the device region 17a.

[0039] The applicant noticed that when ablation processing is performed at a relatively high output to form a laser groove, cracks extend from the laser groove, but in the vicinity of this laser groove, an altered area is formed in which the absorption rate of the green laser beam L is improved compared to before the ablation processing.

[0040] We have come to the conclusion that by forming an altered area in the outer peripheral excess area 17b with a relatively high output, and then irradiating the intended division line 15 with a relatively low output green laser beam L starting from the altered area, it is possible to form a laser-processed groove in the device area 17a while reducing the number and length of cracks.

[0041] The processing method of this embodiment that embodies this idea will be described below. First, a protective film (not shown) containing a water-soluble resin is uniformly formed on the front surface 11a of the wafer 11 using a protective film forming unit (not shown), and then the back surface 11b of the wafer 11 is held by the holding surface 4a.

[0042] Next, with the focal point of the green laser beam L positioned approximately in the height direction A3 at a location in the peripheral surplus region 17b that is a predetermined distance B (see Figure 3) from the peripheral edge of the wafer 11, the chuck table 4 is rotated in a predetermined direction (first laser processing step S10).

[0043] For example, the annular first laser processing groove 21 is formed by rotating the chuck table 4 once. Fig. 3 is a diagram showing the first laser processing step S10. Note that the dicing tape 19, the annular frame, etc. are omitted in Fig. 3. The processing conditions in the first laser processing step S10 are set, for example, as follows.

[0044] Center wavelength: 532nm Repetition frequency: 50kHz Pulse width: 110ns Average power output: 2.5W Circumferential speed at focal point: 100mm / s Defocus amount: 0.1 mm (amount of deviation of the light-focusing point toward the upper side of the surface 11a)

[0045] 4 is a cross-sectional view showing an example of a first laser processed groove 21 formed along the outer periphery of the wafer 11. The first laser processed groove 21 has, for example, a depth 21a of about 9 μm and a width 21b of about 20 μm.

[0046] Affected areas 21c (dotted in FIG. 4) that are affected by heat during ablation are formed on the bottom and sides of the first laser-processed groove 21. Cracks 21d extending up to about 60 μm are formed near the first laser-processed groove 21, starting from the bottom and sides.

[0047] However, the predetermined distance B (FIG. 3) from the inner peripheral side surface of the first laser processed groove 21 to the end of the device 17 closest to the outer peripheral edge is, for example, 1 mm or more, so that the crack 21d will not reach the device 17.

[0048] After the first laser processing step S10, first, alignment is performed using the microscope camera unit 10, and the intended division line 15 in one direction is positioned approximately parallel to the processing feed direction A1.

[0049] Thereafter, with the focal point of the green laser beam L positioned at a predetermined height in the height direction A3, the chuck table 4 is moved in the processing feed direction A1 so that the focal point passes through the first laser processing groove 21 and moves along each planned division line 15.

[0050] As a result, second laser processed grooves 23 (see FIG. 5) are formed along each of the division lines 15 in the one direction. After the green laser beam L is irradiated along each of the division lines 15 parallel to the one direction, the chuck table 4 is rotated 90 degrees.

[0051] As a result, the division lines 15 in the other direction perpendicular to the one direction are made substantially parallel to the processing feed direction A1. Then, the green laser beam L is irradiated onto the division lines 15 along the other direction.

[0052] In this manner, the second laser processing grooves 23 are formed along each of the planned division lines 15 (second laser processing step S20). Fig. 5 is a diagram showing the second laser processing step S20. The processing conditions in the second laser processing step S20 are set, for example, as follows.

[0053] Center wavelength: 532nm Repetition frequency: 50kHz Pulse width: 110ns Average output: 1.25W Circumferential speed of the focal point: 100mm / s Defocus amount: None (just in focus)

[0054] In this way, the output of the green laser beam L in the second laser processing step S20 is set lower than the output of the green laser beam L in the first laser processing step S10. The average output in the second laser processing step S20 is set to a predetermined value that is 25% to 50% of the average output in the first laser processing step S10.

[0055] If it is less than 25%, the ablation process can hardly be performed. If it exceeds 50%, the ablation process can be performed, but there is a risk that cracks will extend from the second laser processed groove 23 formed and reach the device 17. Therefore, it is preferable to set the predetermined value to 25% to 50% of the average output in the first laser processing step S10.

[0056] In the second laser processing step S20, in order to suppress the formation of cracks on the surface 11a, the wafer 11 is not completely cut in the thickness direction of the wafer 11. The cutting of the wafer 11 is performed using a cutting blade 22 (see FIG. 7) after the second laser processing step S20.

[0057] In the second laser processing step S20, a second laser processing groove 23 having a width wider than the blade thickness 22a of the cutting blade 22 (see Figure 8) is formed by moving the focal point of the green laser beam L multiple times along one planned division line 15.

[0058] The second laser processing step S20 will be described in more detail. In the second laser processing step S20 of this embodiment, the second laser processing grooves 23 are formed in each of the intended division lines 15 by a technique called π-cut. The π-cut in the second laser processing step S20 will be described with reference to Figs. 6(A) to 6(C).

[0059] In the π-cut, first, two laser processed grooves 25 are formed for each of the division lines 15. Fig. 6(A) is a cross-sectional view of the wafer 11 in which two laser processed grooves 25 are formed for each of the division lines 15.

[0060] Each laser processed groove 25 has a depth 25a of, for example, about 5 μm and a width 25b of several μm to about 5 μm. A remaining region 25c between two laser processed grooves 25 is also similarly removed by ablation processing.

[0061] When removing the remaining region 25c, the cracks will not reach the device 17, so the output of the green laser beam L may be increased compared to when one laser processed groove 25 is formed.

[0062] Fig. 6(B) is a cross-sectional view of the wafer 11 from which the remaining region 25c between the two laser processed grooves 25 has been removed, and Fig. 6(C) is a cross-sectional view of the wafer 11 including the second laser processed groove 23 after the second laser processing step S20. The second laser processed groove 23 has, for example, a depth 23a of about 5 µm and a width 23b of about 20 µm.

[0063] In the second laser processing step S20 of this embodiment, the ablation processing starts from the altered region 21c of the first laser processed groove 21. Therefore, if the green laser beam L is irradiated so as to pass through the first laser processed groove 21, the ablation processing can be performed in the device region 17a even if the output is reduced compared to the first laser processing step S10.

[0064] Therefore, in the second laser processing step S20, it is possible to prevent the cracks from reaching the device 17. For example, compared to the case where the second laser processing step S20 is performed with the same output as the first laser processing step S10, the device 17 is not damaged, and the number of cracks is small and the length of the cracks is short (i.e., the processing quality is good), and second laser processed grooves 23 can be formed in the device region 17a.

[0065] After the second laser processing step S20, the cutting device 12 (see FIG. 7) is used to cut the cutting blade 22 into the second laser processed grooves 23 to divide the wafer 11 (dividing step S30). First, the cutting device 12 used in the dividing step S30 will be described.

[0066] The cutting device 12 has a disk-shaped chuck table 14. The chuck table 14 is substantially the same as the above-mentioned chuck table 4, so a detailed description will be omitted. A rotation drive source (not shown), such as a motor, is provided below the chuck table 14.

[0067] A ball screw type third movement mechanism (for example, an X-axis direction movement mechanism not shown) is provided below the rotary drive source. The chuck table 14 and the rotary drive source are configured to be movable together along the processing feed direction A1 by the third movement mechanism.

[0068] A cutting unit 16 is disposed above the holding surface 14a (see FIG. 8) of the chuck table 14. As shown in FIG. 8, the cutting unit 16 has a cylindrical spindle housing 18 whose longitudinal portion is disposed along the indexing feed direction A2.

[0069] A part of a cylindrical spindle 20 is rotatably housed in the spindle housing 18. A rotation drive source such as a motor is provided at the base end of the spindle 20. The tip of the spindle 20 protrudes from the spindle housing 18, and a cutting blade 22 having an annular cutting edge is attached to the tip of the spindle 20.

[0070] The cutting edge of the cutting blade 22 has a blade thickness 22a (for example, 15 μm) smaller than the width 23b (for example, 20 μm) of each second laser processed groove 23. The cutting blade 22 is, for example, a hubless type (washer type) constituted only by a cutting edge.

[0071] A blade cover 24 is connected to the spindle housing 18 so as to cover the upper part of the cutting blade 22. The blade cover 24 is provided with a plurality of nozzles 26 for supplying cutting water such as pure water to the cutting blade 22 during cutting.

[0072] A ball screw type fourth movement mechanism (for example, a Z-axis direction movement mechanism, not shown) is provided in the spindle housing 18. The fourth movement mechanism allows the spindle housing 18 to move along the height direction A3.

[0073] The fourth moving mechanism is provided with a ball screw type fifth moving mechanism (for example, a Y-axis direction moving mechanism, not shown). The fifth moving mechanism allows the spindle housing 18 to move along the indexing feed direction A2.

[0074] In the dividing step S30, first, a microscope camera unit (not shown) fixed to the spindle housing 18 is used to position the second laser processed groove 23 in one direction substantially parallel to the processing feed direction A1.

[0075] Thereafter, the lower end of the rotating cutting blade 22 is positioned at a height between the dicing tape 19 and the holding surface 14a, and further, the cutting edge of the cutting blade 22 is positioned approximately at the center of the width of the second laser-machined groove 23 in the indexing feed direction A2.

[0076] Next, the chuck table 14 is moved along the processing feed direction A1 to form cut grooves 27 along the second laser processed grooves 23 in one direction, and the wafer 11 is cut.

[0077] Fig. 7 is a perspective view showing the dividing step S30, and Fig. 8 is a cross-sectional view showing the dividing step S30. The processing conditions in the dividing step S30 are set, for example, as follows.

[0078] Spindle speed: 32,000 rpm Machining feed speed: 20mm / s Cutting water flow rate: 1L / min

[0079] After cutting the wafer 11 along each of the second laser processed grooves 23 parallel to one direction, the chuck table 14 is rotated 90 degrees to cut the wafer 11 along each of the second laser processed grooves 23 in another direction perpendicular to the one direction. In this manner, the wafer 11 is divided into device chips (not shown), each having a device 17.

[0080] Since the second laser processed grooves 23 have already been formed on the front surface 11a side, cracks formed in the dividing step S30 do not reach the devices 17. After the dividing step S30, the protective film is washed and removed using a spinner washing device (not shown), and each device chip is washed.

[0081] In this embodiment, compared to the case where the second laser processing step S20 is performed with the same output as the first laser processing step S10, the device 17 is not damaged, and the second laser processing grooves 23 with fewer and shorter cracks can be formed in the device region 17a, thereby improving the yield rate of device chips.

[0082] Next, a second embodiment will be described with reference to Fig. 9. In the first laser processing step S10 of the second embodiment, a plurality of dot-shaped first laser processing holes 31 are formed in an annular shape in the outer peripheral excess area 17b. More specifically, the first laser processing holes 31 are formed at both ends of one planned division line 15 (shown by a dashed line in Fig. 9).

[0083] 9 is a diagram showing a first laser processing step S10 according to the second embodiment. Each of the first laser-processed holes 31 is a cylindrical hole having a depth of about 9 μm and a diameter of about 20 μm, and an altered region (not shown) that has been altered by heat during ablation processing is formed at the bottom and side of each of the first laser-processed holes 31.

[0084] In the subsequent second laser processing step S20, a second laser processing groove 23 (see Figure 5) is formed along one of the planned division lines 15 from a first laser processing hole 31 formed at one end of the one of the planned division lines 15 to a first laser processing hole 31 formed at the other end of the one of the planned division lines 15, passing through the first laser processing hole 31.

[0085] At the start of the second laser processing step S20, the focal point of the green laser beam L may be positioned outside the first laser processing hole 31 formed at one end of one of the planned dividing lines 15 on the wafer 11.

[0086] Furthermore, at the end of the second laser processing step S20, the focal point of the green laser beam L may be positioned outside the wafer 11 relative to the first laser processing hole 31 formed at the other end of one of the planned dividing lines 15.

[0087] In any case, in the second laser processing step S20, the second laser processed groove 23 can be formed by scanning with the focusing point between the two first laser processed holes 31 formed at both ends of one planned division line 15. Also in the second embodiment, the second laser processed groove 23 with good processing quality can be formed in the device region 17a.

[0088] In addition, the structures, methods, etc. according to the above-mentioned embodiments can be appropriately modified and implemented without departing from the scope of the present invention. For example, in the second laser processing step S20, the second laser processed groove 23 can be formed by a method other than the above-mentioned π cut.

[0089] Furthermore, the wafer 11 is not limited to the LT single crystal substrate 13, but may be a single crystal substrate made of silicon carbide (SiC), gallium arsenide (GaAs), or indium phosphide (InP), and may be processed according to the above-mentioned processing method. [Explanation of symbols]

[0090] 2: laser processing device, 4: chuck table, 4a: holding surface 6: laser beam irradiation unit, 8: head unit, 10: microscope camera unit 11: wafer, 11a: front surface, 11b: back surface, 13: single crystal substrate, 13a: front surface, 13b: back surface, 15: planned division line 12: cutting device, 14: chuck table, 14a: holding surface 16: cutting unit, 18: spindle housing, 20: spindle 17: device, 17a: device area, 17b: peripheral surplus area 19: Dicing tape 21: First laser processed groove 21a: depth, 21b: width, 21c: affected area, 21d: crack 22: cutting blade, 22a: blade thickness, 24: blade cover, 26: nozzle 23: second laser processed groove, 23a: depth, 23b: width 25: laser processed groove, 25a: depth, 25b: width, 25c: residual area 27: Cutting groove, 31: First laser processing hole A1: Machining feed direction, A2: Indexing feed direction, A3: Height direction, B: Predetermined distance L: Green laser beam

Claims

1. A wafer processing method comprising the steps of: processing a wafer having a surface side including a device region, in which devices are formed in each region defined by a plurality of planned division lines set on the surface, and a peripheral surplus region surrounding the device region, the wafer being absorbent to a green laser beam, with a pulsed green laser beam, the method comprising the steps of: a first laser processing step of irradiating the wafer with the green laser beam along the outer periphery of the wafer to form a first annular laser processed groove or a first laser processed hole in the outer periphery excess region; After the first laser processing step, a second laser processing step is performed in which the green laser beam is irradiated onto the wafer at an output lower than that of the green laser beam in the first laser processing step so as to pass through the first laser processing grooves or first laser processing holes along each of the planned division lines, thereby forming a plurality of second laser processing grooves; A wafer processing method comprising:

2. 2. The wafer processing method according to claim 1, further comprising a dividing step of dividing the wafer along the second laser processing grooves with a cutting blade having a blade thickness smaller than the width of each of the second laser processing grooves after the second laser processing step.

3. the wafer having a single crystal substrate of lithium tantalate; In the first laser processing step, the first laser processing groove or the first laser processing hole is formed in the single crystal substrate, 3. The wafer processing method according to claim 1, wherein in the second laser processing step, the plurality of second laser processed grooves are formed in the single crystal substrate.

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