Processing methods

Abstract

To provide a processing method for obtaining desired processing results without advancing a crack on a required region side when an arbitrary required region is obtained by performing processing for removing an unnecessary region from a workpiece relative to the workpiece.SOLUTION: A processing method of a workpiece having a necessary region and an unnecessary region includes a protection wall forming step and an unnecessary region removing step. In the protection wall forming step, a laser beam of a wavelength having transparency relative to the workpiece is irradiated to a region that defines a necessary region and an unnecessary region to form a plurality of shield tunnels composed of a hole and a modified tube surrounding the hole and form a protective wall. In the unnecessary region removing step, the unnecessary region is removed.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for processing a workpiece that includes a required area and an unnecessary area. [Background technology]

[0002] Wafers with multiple devices such as ICs and LSIs formed on their surfaces, which are divided by planned division lines, are then divided into individual device chips using a dicing machine or laser processing machine, and these are used in electrical devices such as mobile phones and personal computers.

[0003] The laser processing device is generally composed of a chuck table that holds the wafer, an imaging means that images the wafer held on the chuck table and detects the area to be processed, a laser beam application means that applies a laser beam to the wafer held on the chuck table, and a processing feed means that feeds the chuck table and the laser beam application means relative to each other, and is capable of processing wafers with high precision (see, for example, Patent Document 1).

[0004] Laser beam application means include a type that applies a laser beam of a wavelength that is absorbed by the wafer to perform ablation processing (see, for example, Patent Document 2), a type that applies a laser beam of a wavelength that is transparent to the wafer to perform internal processing to form a modified layer inside (see, for example, Patent Document 3), and a type that applies a laser beam of a wavelength that is transparent to the wafer and in which the numerical aperture (NA) of the concentrator divided by the refractive index (N) of the wafer is in the range of 0.05 to 0.2 to form a shield tunnel consisting of a pore inside and a modified cylinder surrounding the pore (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-085347 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-188475 [Patent Document 3] Patent No. 3408805 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-221483 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the workpiece is, for example, a wafer having a plurality of devices formed on its surface partitioned by dividing lines, and a metal layer called a TEG (Test Elementary Group) for evaluating and managing the devices is formed on the dividing lines, when a laser beam is irradiated onto the dividing lines for processing, it is necessary to irradiate the laser beam with a strong power. As a result, there is a problem that cracks caused by the irradiation of the laser beam may progress into the necessary areas where devices are formed that extend beyond the dividing lines, damaging the devices.

[0007] The above-mentioned problem is not necessarily limited to cases where the TEG is disposed on the dividing line. Even if a TEG is not formed on the dividing line, when a laser beam is irradiated onto the dividing line, cracks may easily propagate in the area extending beyond the dividing line due to the crystalline structure of the material constituting the wafer. Furthermore, the above-mentioned crack problem can also occur when dividing into individual device chips by cutting along the dividing line with a rotatably held cutting blade. Furthermore, this problem is not limited to cases where laser processing is performed along the dividing line of a wafer on a surface on which multiple devices are formed, partitioned by the dividing line. Even when removing unnecessary areas from a plate-like workpiece to divide required areas of any shape, cracks may propagate from the unnecessary areas toward the required areas, resulting in a problem of not being able to obtain the desired processing results.

[0008] The present invention has been made in consideration of the above facts, and its main technical object is to provide a processing method that, when processing a workpiece to remove unnecessary areas from the workpiece to obtain any necessary area, can obtain the desired processing results without causing cracks to propagate toward the necessary area. [Means for solving the problem]

[0009] According to the present invention, a method for processing a workpiece including a necessary region and an unnecessary region includes a protective wall forming step of irradiating a region that defines the necessary region and the unnecessary region with a laser beam having a wavelength that is transparent to the workpiece to form a plurality of shield tunnels each consisting of a hole and a modified tube surrounding the hole, thereby forming a protective wall, and an unnecessary region removing step of removing the unnecessary region. The protective wall forming step includes a first protective wall forming step of forming successive shield tunnels on the planned division line at intervals of at least one shield tunnel, and a second protective wall forming step of forming successive shield tunnels in the region of the planned division line with the intervals. A processing method is provided.

[0010] Applicable The shield tunnel formed in the first protective wall forming step and the shield tunnel formed in the second protective wall forming step may be formed with alternating steps in the thickness direction of the workpiece, and the shield tunnels may be stacked in the thickness direction in the protective wall forming process.

[0011] The protective wall forming step may include, when stacking shield tunnels in the thickness direction, a third protective wall forming step of forming a shield tunnel above the shield tunnel formed in the first protective wall forming step, and a fourth protective wall forming step of forming a shield tunnel above the shield tunnel formed in the second protective wall forming step. When stacking shield tunnels in the thickness direction in the protective wall forming step, an upper shield tunnel may be stacked adjacent to a lower shield tunnel so as not to come into contact with the lower shield tunnel.

[0012] The workpiece may be a wafer having a plurality of devices formed on its surface partitioned by a plurality of planned dividing lines, the necessary region being a region where the devices are formed, and the unnecessary region being a region where the planned dividing lines are formed, and in the protective wall forming step, the protective walls are formed on both sides defining the width of the planned dividing lines, and in the unnecessary region removing step, a planned dividing line removing process is carried out to remove the planned dividing lines, which are unnecessary regions sandwiched between the protective walls. Also, it is preferable that the planned dividing line removing process is either laser processing using irradiation of a laser beam or cutting processing carried out with a cutting blade. Furthermore, in the protective wall forming step, Process The wavelength of the laser beam irradiated in this case is 532 nm, and the energy per pulse is 2.0 to 4.0·10 -5 J, and the spot interval is preferably 10 to 15 μm.

[0013] Na In this invention, the necessary area is an area that is used as is in another process after being separated from the workpiece by laser processing, cutting processing, etc., and the unnecessary area is an area that is not used as is after the processing has been performed, such as an area that is discarded or an area that is recycled. [Effects of the Invention]

[0014] The processing method of the present invention is a method for processing a workpiece that includes a necessary region and an unnecessary region, and includes a protective wall forming step in which a laser beam of a wavelength that is transparent to the workpiece is irradiated onto the region that defines the necessary region and the unnecessary region to form a plurality of shield tunnels consisting of holes and modified cylinders surrounding the holes, thereby forming a protective wall, and an unnecessary region removing step in which the unnecessary region is removed. The protective wall forming step includes a first protective wall forming step in which shield tunnels are formed continuously on the planned division line at intervals of at least one shield tunnel, and a second protective wall forming step in which shield tunnels are formed continuously in the region of the planned division line with the intervals. Therefore, even if the unnecessary region is removed by irradiating it with a high-power laser beam or by destroying it with a cutting blade, the protective wall prevents cracks from progressing into the region where the necessary region is formed, and the problem of damage to the necessary region to be divided is solved. 。 [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an overall perspective view of a laser processing apparatus suitable for the processing method of the present invention. [Figure 2] FIG. 1 is a perspective view of a wafer, which is a workpiece of the present embodiment. [Figure 3] (a) is a perspective view showing an embodiment of the protective wall forming step, (b) is an enlarged plan view of a portion of the wafer shown in (a), and (c) is an enlarged cross-sectional view of a portion of the wafer shown in (b). [Figure 4] FIG. 10 is a perspective view showing an embodiment in which the unnecessary region removing step is performed by laser processing. [Figure 5] FIG. 10 is a perspective view showing an aspect in which the unnecessary region removing step is performed by cutting. [Figure 6] FIG. 10 is a partially enlarged cross-sectional view showing another embodiment of the protective wall forming step. [Figure 7] FIG. 10 is a plan view illustrating another embodiment of a workpiece. DETAILED DESCRIPTION OF THE INVENTION

[0016] A laser processing apparatus suitable for carrying out a processing method configured based on the present invention will be described below with reference to the accompanying drawings, and then the processing method of this embodiment will be described.

[0017] Fig. 1 shows an overall perspective view of a laser processing apparatus 1. The laser processing apparatus 1 is disposed on a base 2 and includes a holding means 3 for holding a wafer 10 (see Fig. 2), which will be described later, a moving means 4 for moving the holding means 3 in the X-axis and Y-axis directions, an imaging means 6 for imaging the wafer 10 held by the holding means 3, and a laser beam application means 7 for applying a laser beam to the wafer 10 held by the holding means 3 to perform the desired processing. The apparatus also includes a frame 5 made up of a vertical wall 5a erected on the side of the moving means 4 and a horizontal wall 5b extending horizontally from the upper end of the vertical wall 5a. The imaging means 6 and the laser beam application means 7 are housed and held inside the horizontal wall 5b.

[0018] 1, the holding means 3 includes a rectangular X-axis direction movable plate 31 mounted on the base 2 so as to be movable in the X-axis direction, a rectangular Y-axis direction movable plate 32 mounted on the X-axis direction movable plate 31 so as to be movable in the Y-axis direction, a cylindrical support 33 fixed to the upper surface of the Y-axis direction movable plate 32, and a rectangular cover plate 34 fixed to the upper end of the support 33. A chuck table 35 extending upward through an elongated hole formed in the cover plate 34 is disposed on the cover plate 34. The chuck table 35 is a means for holding the wafer 10 using an XY plane specified by the X and Y coordinates as a holding surface, and is configured to be rotatable by a rotation drive means (not shown) housed in the support 33. A suction chuck 36 formed of a porous material with air permeability as the holding surface is disposed on the upper surface of the chuck table 35. The suction chuck 36 is connected to a suction means (not shown) by a flow path that passes through the support 33, and four clamps 37, which are used to hold the wafer 10 (described later) on the chuck table 35, are arranged at equal intervals around the suction chuck 36. By operating the suction means, the wafer 10 can be suction-held by the suction chuck 36.

[0019] The moving means 4 includes an X-axis moving means 4a that moves the chuck table 35 in the X-axis direction, and a Y-axis moving means 4b that moves the chuck table 35 in the Y-axis direction. The X-axis moving means 4a converts the rotational motion of the motor 42a into linear motion via a ball screw 42b and transmits the linear motion to the X-axis movable plate 31, moving the X-axis movable plate 31 in the X-axis direction along a pair of guide rails 2A, 2A that are arranged on the base 2 along the X-axis direction. The Y-axis moving means 4b converts the rotational motion of the motor 44a into linear motion via a ball screw 44b and transmits the linear motion to the Y-axis movable plate 32, moving the Y-axis movable plate 32 in the Y-axis direction along a pair of guide rails 31a, 31a that are arranged on the X-axis movable plate 31 along the Y-axis direction.

[0020] The above-described laser processing apparatus 1 is controlled by a control means (not shown). The control means is configured by a computer and includes a central processing unit (CPU) that performs calculations according to a control program, a read-only memory (ROM) that stores the control program, etc., a readable / writable random access memory (RAM) that temporarily stores detected values, calculation results, etc., an input interface, and an output interface (details not shown). The image capturing means 6, the laser beam application means 7, the X-axis moving means 4a, the Y-axis moving means 4b, etc. that constitute the moving means 4 are connected to and controlled by the control means.

[0021] An example of a workpiece to be processed by a processing method configured according to the present invention is a wafer 10 shown in Fig. 2. The wafer 10 is a SiC wafer having a thickness of, for example, about 100 µm, and having a plurality of devices 12 formed on a surface 10a defined by planned division lines 14. When the wafer 10 is processed by the laser processing apparatus 1, the wafer 10 is supported via adhesive tape T by an annular frame F having an opening Fa capable of accommodating the wafer 10.

[0022] FIG. 2 shows an enlarged perspective view of a portion of the wafer 10. As can be seen from the enlarged perspective view, a TEG 16, which is a metal layer for evaluating and managing the device 12, is disposed on the planned dividing line 14 formed on the surface 10a of the wafer 10 in this embodiment.

[0023] In the processing method of this embodiment, the wafer 10 is processed as described below, so that the division lines 14, which are unnecessary areas of the wafer 10, are removed, and the necessary areas where the devices 12 are formed are divided into individual chips.

[0024] In the processing method of this embodiment, first, a protective wall forming step is carried out in which a laser beam having a wavelength that is transparent to the wafer 10 is irradiated onto an area that defines a necessary area where the devices 12 are formed and an unnecessary area along the planned dividing lines 14, thereby forming a plurality of shield tunnels each consisting of a pore and a modified cylinder surrounding the pore, thereby forming a protective wall. The procedure for carrying out the protective wall forming step of this embodiment will be described in more detail below.

[0025] When the protective wall forming process is performed, once the wafer 10 described above is prepared, the wafer 10 is placed on the chuck table 35 of the laser processing apparatus 1 shown in Fig. 1 and held by suction, and the frame F is clamped and fixed by the clamps 37. Next, the moving means 4 described above is operated to position the wafer 10 directly below the imaging means 6, and an image is taken of the wafer 10, and positional information of the devices 12 and the planned dividing lines 14 on the wafer 10 is detected. Furthermore, based on the positional information, the moving means 4 and the like are operated to align the predetermined planned dividing lines 14 on the wafer 10 in the X-axis direction.

[0026] 3(a), the wafer 10 is positioned directly below the condenser 71 of the laser beam application means 7, and while the X-axis moving means 4a is operated to process and feed the wafer 10 in the X-axis direction based on the position information detected by the imaging means 6, a laser beam LB1 is applied to the area defining the devices 12 and the planned dividing lines 14, and two protective walls 100 are formed, as can be seen from FIG. 3(b), which shows an enlarged view of a portion of the planned dividing lines 14. In this embodiment, the area defining the devices 12 and the planned dividing lines 14 is the area on both sides that defines the width of the planned dividing lines 14, which are unnecessary areas, as can be seen from FIG. 3(b).

[0027] When irradiating the laser beam LB1, the numerical aperture (NA) of the condenser lens constituting the condenser 71 of the laser beam application means 7 of this embodiment is set so that the value divided by the refractive index (N) of the wafer 10 is in the range of 0.05 to 0.2, for example, and the wavelength of the laser beam LB1 is set to 532 nm which is transparent to the wafer 10, the average output is set to 0.2 to 0.4 W, the repetition frequency is set to 10 kHz, and the energy per pulse is set to 2.0 to 4.0·10 -5 The distance between the spots is set to J, and the spot spacing is set to 10 to 15 μm. By positioning the focal point inside the wafer 10 and irradiating the laser beam LB1 under these laser processing conditions, shield tunnels 102, 104 are formed as shown in FIG. 3(c). As shown in the enlarged perspective view at the bottom of FIG. 3(c), the shield tunnels 102, 104 consist of a narrow hole 130 and a transformation tube 140 surrounding the narrow hole 130. For example, the diameter of the narrow hole 130 is approximately 1 μm, and the diameter of the transformation tube 140 is approximately 10 μm. The shield tunnels 102, 104 are formed adjacent to each other and continuously to form the protective wall 100 along the planned division line 14. The energy per pulse of the laser beam LB1 irradiated when forming the protective wall 100 is set to a value that does not serve as a division starting point when dividing the wafer 10 along the planned division line 14.

[0028] When forming the protective wall 100 shown in FIG. 3 , for example, a first protective wall forming step is performed in which shield tunnels 102 are continuously formed along the region that defines the above-described devices 12 and the planned division lines 14, with at least one shield tunnel spaced apart (approximately 10 to 13 μm). Next, a second protective wall forming step is performed in which shield tunnels 104 are continuously formed in the spaced apart region. That is, the protective wall 100 is formed by alternately forming the shield tunnels 102 and 104 along the X-axis direction. In this way, by performing the first protective wall forming step and the second protective wall forming step when forming the protective wall 100, the influence of heat accumulation that occurs when the laser beam LB1 is irradiated adjacent to the shield tunnels is avoided, and the propagation of cracks into the necessary region (the region where the devices 12 are formed), which occurs when the shield tunnels 102, 104 are formed, can be avoided.

[0029] As described above, after two protective walls 100 consisting of shield tunnels 102, 104 are formed along predetermined dividing lines 14, the wafer 10 is indexed and fed in the Y-axis direction to position adjacent unprocessed dividing lines 14 in the Y-axis direction directly below the collector 71. Then, in the same manner as described above, the focal point of the laser beam LB1 is positioned within the region defining the width of the dividing lines 14 on the wafer 10 and irradiated, thereby sequentially executing the first protective wall forming step and the second protective wall forming step. This forms the shield tunnels 102, 104 and two protective walls 100. In the same manner, the wafer 10 is processed and fed in the X-axis direction and the Y-axis direction to form two protective walls 100 along all dividing lines 14 along the X-axis direction. Next, the wafer 10 is rotated 90 degrees in the direction indicated by arrow R1, and the unprocessed dividing lines 14 that are perpendicular to the dividing lines 14 on which the protective walls 100 have already been formed are aligned in the X-axis direction. Then, the focal point of the laser beam LB1 is positioned and irradiated in the same manner as described above into the interior of the region that defines the remaining devices 12 and the dividing lines 14, and protective walls 100 are formed corresponding to all of the dividing lines 14 formed on the front surface 10a of the wafer 10, as shown in the lower part of Figure 3(a), thereby completing the protective wall forming process of this embodiment.

[0030] After the protective wall forming step described above has been performed, an unnecessary region removing step is performed to remove the intended dividing lines 14, which are unnecessary regions. More specifically, the wafer 10 on which the protective walls 100 have been formed corresponding to all of the intended dividing lines 14 is transported to a laser processing apparatus 20 (only a portion of which is shown) shown in Fig. 4. The laser processing apparatus 20 includes a holding means (not shown), a laser beam application means 21 that applies a laser beam LB2 to the wafer 10 held by the holding means, an X-axis feed means that feeds the holding means and the laser beam application means 21 relatively in the X-axis direction, a Y-axis feed means that feeds the holding means and the laser beam application means 21 relatively in the Y-axis direction perpendicular to the X-axis direction, and a rotary drive means that rotates the holding means (all of which are not shown).

[0031] The wafer 10, which has been transported to the laser processing device 20 and held by the holding means, undergoes an alignment step using alignment means (not shown) disposed in the laser processing device 20, which detects the positions of the dividing lines 14 formed on the surface 10a, and rotates the wafer 10 by the rotation drive means to align the dividing lines 14 in a predetermined direction with the X-axis direction. Information on the detected positions of the dividing lines 14 is stored in control means (not shown).

[0032] Based on the position information of the dividing lines 14 detected by the alignment step described above, the condenser 22 of the laser beam application means 21 is positioned at a processing start position of the dividing lines 14 in a predetermined direction, and the focal point of the laser beam LB2 is positioned on the surface 10a of the wafer 10 and irradiated, while the wafer 10 is processed and fed in the X-axis direction together with the holding means to perform ablation processing along the predetermined dividing lines 14 of the wafer 10. In this way, a removal groove 200 is formed that divides the wafer 10 along the dividing lines 14. As shown in an enlarged partial view of the wafer 10 on the right side of FIG. 4, the removal groove 200 is formed so as to remove an unnecessary region sandwiched between protective walls 100 formed on both sides to define the width of the dividing lines 14, and the laser beam LB2 oscillated and applied by the laser beam application means 21 is a laser beam of a wavelength (e.g., 355 nm) that is absorbent by, for example, SiC constituting the wafer 10.

[0033] After forming the removal grooves 200 along predetermined dividing lines 14 as described above, the wafer 10 is indexed and fed in the Y-axis direction by the distance between the dividing lines 14, so that adjacent, unprocessed dividing lines 14 in the Y-axis direction are positioned directly below the collector 22. Then, in the same manner as described above, the focal point of the laser beam LB2 is positioned on the surface of the dividing lines 14 of the wafer 10 and irradiated, and the wafer 10 is fed in the X-axis direction to form the removal grooves 200. Similarly, the wafer 10 is fed in the X-axis and Y-axis directions to form the removal grooves 200 along all dividing lines 14 along the X-axis. Next, the wafer 10 is rotated 90 degrees in the direction indicated by arrow R2, so that dividing lines 14 that do not have removal grooves 200 formed thereon are aligned in the X-axis direction in a direction perpendicular to the dividing lines 14 along which the removal grooves 200 have already been formed. Then, for each of the remaining dividing lines 14, the focusing point of the laser beam LB2 is positioned and irradiated in the same manner as described above, and dividing line removal processing is performed to form removal grooves 200 along all of the dividing lines 14 formed on the wafer 10, as shown in the lower part of Fig. 4. In this manner, the devices 12 are divided from the wafer 10, and the unnecessary region removal process is completed.

[0034] The unnecessary region removing step performed in the present invention is not limited to the laser processing using the above-described laser beam LB2. For example, the wafer 10 on which the protective walls 100 are formed on all of the planned dividing lines 14 may be transported to a cutting device 50 (only a part of which is shown) shown in FIG. 5 and may be performed by the cutting device 50.

[0035] The cutting device 50 includes a chuck table (not shown) that holds the wafer 10 by suction, and cutting means 52 that cuts the wafer 10 held by suction on the chuck table. The chuck table is rotatable and includes a moving means (not shown) that feeds the chuck table for processing in the direction indicated by the arrow X in the figure. The cutting means 52 includes a spindle 54 rotatably held in a spindle housing 53 disposed in the Y-axis direction indicated by the arrow Y in the figure, and an annular cutting blade 56 held at the tip of the spindle 54, and includes a Y-axis moving means (not shown) that indexes and feeds the cutting blade 56 in the Y-axis direction. The spindle 54 is driven to rotate by a spindle motor (not shown).

[0036] To perform the unnecessary region removal process, first, the wafer 10 is placed on the chuck table of the cutting device 50 with the front surface 10a facing upward and held by suction. The predetermined dividing runs 14 of the wafer 10 are aligned in the X-axis direction and aligned with the cutting blade 56. Next, the cutting blade 56, rotated at high speed, is positioned in the unnecessary region between the protective walls 100 formed on both sides of the dividing lines 14 aligned in the X-axis direction and cuts into the unnecessary region from the front surface 10a side, while the chuck table is moved in the X-axis direction to form a removal groove 220 that divides the wafer 10. Next, the cutting blade 56 of the cutting means 52 is indexed and moved to a dividing line 14 adjacent in the Y-axis direction to the dividing line 14 where the removal groove 220 has been formed but where no removal groove 220 has been formed. By repeating these steps, removal grooves 220 are formed along all dividing lines 14 along the X-axis direction. Next, the chuck table is rotated 90 degrees in the direction indicated by arrow R3, the direction perpendicular to the direction in which the removal grooves 220 were previously formed is aligned with the X-axis direction, and the above-mentioned cutting process is performed on all of the dividing lines 14 newly aligned with the X-axis direction, thereby forming the removal grooves 220 along all of the dividing lines 14 formed on the wafer 10. In this manner, the cutting process is performed to perform dividing line removal processing, which divides the wafer 10 along the dividing runs 14 into device chips each containing a device 12, and the unnecessary region removing process is completed, and the devices 12, which are the necessary regions, are divided, similar to the wafer 10 shown in the lower part of FIG.

[0037] As described above, in this embodiment, when the unnecessary area removal process for removing the planned dividing lines 14, which are unnecessary areas, is carried out, a laser beam of a wavelength that is transparent to the wafer 10 is irradiated onto the area that defines the necessary area where the devices 12 are formed and the unnecessary area where the planned dividing lines 14 are formed, to form shield tunnels 102, 104 consisting of holes and modified cylinders surrounding the holes, thereby forming protective walls 100.Therefore, even if the planned dividing lines 14 are removed by irradiating them with a high-power laser beam or by destroying them with a cutting blade, the protective walls 100 prevent cracks from progressing into the necessary area where the devices 12 are formed, thereby eliminating the problem of damaging the devices 12 to be individually divided.

[0038] The present invention is not limited to the above-described embodiment. When forming the shield tunnels in the protective wall forming step, the shield tunnels may be stacked by vertically shifting the position of the focal point when irradiating the laser beam LB1 in the thickness direction of the wafer 10. For example, in the protective wall forming step performed on a wafer 10 having a thickness of 500 μm, as can be seen from the cross-sectional view of the wafer 10 shown in FIG. 6 , the following steps may be performed: a first protective wall forming step in which consecutive shield tunnels 111 are formed along the dividing line 14 aligned in the X-axis direction of the wafer 10 with a spacing of at least one shield tunnel; a second protective wall forming step in which consecutive shield tunnels 112 are formed along the dividing line 14 with the spacing; a third protective wall forming step in which shield tunnel 113 is formed above the formed shield tunnel 111; and a fourth protective wall forming step in which shield tunnel 114 is formed above the shield tunnel 112 formed in the second protective wall forming step. 6, in addition to the first to fourth protective wall forming steps described above, fifth and sixth protective wall forming steps are carried out to form shield tunnels 115 and 116 so as to be further stacked on shield tunnels 113 and 114, thereby forming protective wall 110. The positions of the focal points when irradiating laser beam LB1 to form shield tunnels 111 to 116 are positioned so as to be shifted in the vertical direction, and by stacking shield tunnels in the thickness direction, it is possible to effectively form protective wall 110 that prevents crack propagation even in a thick workpiece.

[0039] In the embodiment shown in FIG. 6 , when the second protective wall forming step is performed after the first protective wall forming step, the shield tunnels 111 formed in the first protective wall forming step and the shield tunnels 112 formed in the second protective wall forming step are formed with alternating steps in the thickness direction of the wafer 10. This more effectively avoids the effects of heat accumulation when performing processing to remove unnecessary regions on a thick workpiece, and the protective wall 110 prevents cracks from progressing into necessary regions. In this embodiment, when the shield tunnels 113 to 116 are formed in the third to sixth protective wall forming steps, they are also formed with alternating steps in the thickness direction. Note that, when the shield tunnels are stacked in the thickness direction in the first to sixth protective wall forming steps, the upper shield tunnels are stacked so as not to contact the lower shield tunnels. This makes it possible to suppress the occurrence of cracks when the upper shield tunnels are formed to contact the lower shield tunnels. Furthermore, if the shield tunnels formed in the protective wall formation process are formed so that the altered tubes of adjacent shield tunnels come into contact with each other, it is possible to effectively prevent cracks from progressing from the unnecessary areas to the necessary areas when the unnecessary area removal process is carried out.

[0040] In the above-described embodiment, the workpiece is a wafer 10 having a plurality of devices 12 formed on its surface 10a, which is defined by division lines 14. However, the present invention is not limited to this. For example, the workpiece may be a circular SiC plate-like member 60 formed by a required region 62 defined by a generally rectangular shape in the center and an unnecessary region 64 on the outer periphery surrounding the required region 62, as shown on the left side of FIG. 7 . When processing the plate-like member 60 using the processing method of the present invention, the plate-like member 60 is held by an annular frame (not shown) using adhesive tape and transported to the laser processing apparatus 1. Next, a laser beam having a wavelength, for example, 532 nm, that is transparent to the plate-like member 60 is focused and irradiated into the region defining the boundary between the required region 62 and the unnecessary region 64, forming a shield tunnel consisting of a hole and a modified cylinder surrounding the hole. A protective wall forming process is then performed to form a protective wall 120 along the outer periphery of the required region 62. The protective wall forming step is carried out under the same conditions as those for the protective walls 100 and 110 in the protective wall forming step described above, and therefore a detailed description thereof will be omitted.

[0041] After the protective wall 120 is formed as described above, an unnecessary region removal process is performed to remove the unnecessary region 64 surrounding the required region 62 along the protective wall 120. The unnecessary region removal process is performed, for example, by laser processing using the laser processing device 20. As shown in a partially enlarged view on the right side of FIG. 7 , the laser beam LB2 having a wavelength absorbed by the plate-shaped member 60 is irradiated along the outside of the protective wall 120 to form first removal grooves 130 that divide the plate-shaped member 60, and multiple second removal grooves 132 extending radially from the first removal grooves 130 to the outer periphery of the plate-shaped member 60. By forming the first removal grooves 130 and the second removal grooves 132 in this manner, the unnecessary region 64 of the plate-shaped member 60 is removed, leaving only the required region 62. This prevents cracks from propagating from the unnecessary region 64 to the required region, damaging the required region 62. [Explanation of symbols]

[0042] 1: Laser processing equipment 2: Base 2A: Guide rail 3: Holding means 31:X-axis movable plate 32: Y-axis direction movable plate 33: Post 34: Cover plate 35: Chuck table 36: Vacuum chuck 37: Clamp 4. Transportation 4a:X-axis movement means 4b: Y-axis movement means 5:Frame body 5a: Vertical wall 5b:Horizontal wall part 6: Imaging means 7: Laser beam irradiation means 71: Concentrator 10: Wafer 10a: surface 12: Device 14: Planned division line 16:TEG 20: Laser processing equipment 21: Laser beam irradiation means 22: Concentrator 50: Cutting equipment 52:Cutting means 56: Cutting blade 100: Protective wall 102, 104: Shield tunnel 110: Protective wall 111~116: Shield Tunnel 200, 220: Removal groove LB1: Laser beam LB2: Laser beam

Claims

1. A method for processing a workpiece including a required area and an unnecessary area, a protective wall forming process in which a laser beam having a wavelength that is transparent to the workpiece is irradiated onto an area that defines a necessary area and an unnecessary area to form a plurality of shield tunnels each consisting of a hole and a modified tube surrounding the hole, thereby forming a protective wall; an unnecessary region removing step of removing an unnecessary region, In the protective wall forming step, a first protective wall forming step of forming shield tunnels continuously along the planned division line at intervals of at least one shield tunnel; a second protective wall forming step of continuously forming shield tunnels in the region of the spaced planned dividing lines.

2. 2. The processing method according to claim 1, wherein the shield tunnel formed in the first protective wall forming step and the shield tunnel formed in the second protective wall forming step are formed with alternating steps in the thickness direction of the workpiece.

3. 3. The processing method according to claim 1, wherein the shield tunnels are stacked in the thickness direction in the protective wall forming step.

4. 4. The processing method according to claim 3, wherein, in the protective wall forming step, when stacking shield tunnels in the thickness direction, the protective wall forming step includes a third protective wall forming step of forming a shield tunnel above the shield tunnel formed in the first protective wall forming step, and a fourth protective wall forming step of forming a shield tunnel above the shield tunnel formed in the second protective wall forming step.

5. 5. The processing method according to claim 3, wherein in the protective wall forming step, when the shield tunnels are stacked in the thickness direction, an upper shield tunnel is stacked adjacent to a lower shield tunnel so as not to come into contact with the lower shield tunnel.

6. the workpiece is a wafer having a plurality of devices formed on a surface thereof partitioned by a plurality of planned dividing lines; the necessary region is a region in which a device is formed, and the unnecessary region is a region in which a planned dividing line is formed, In the protective wall forming step, the protective walls are formed on both sides that define the width of the planned division line, 6. The processing method according to claim 1, wherein the unnecessary region removing step includes a dividing line removing process for removing the dividing line, which is the unnecessary region sandwiched between the protective walls.

7. 7. The processing method according to claim 6, wherein the division line removal processing is laser processing using irradiation of a laser beam or cutting processing performed with a cutting blade.

8. 8. The wafer processing method according to claim 1, wherein the wavelength of the laser beam irradiated in the protective wall formation step is 532 nm, the energy per pulse is 2.0 to 4.0 10 J, and the spot interval is 10 to 15 μm.

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