Processing method of workpiece

Abstract

To provide a processing method that forms a horny layer by irradiating a processing schedule region with a laser beam, and controls so that a region is accurately peeled by forming the horny layer.SOLUTION: A method comprises: a setting step of setting a processing schedule region; a boundary processing step of processing a boundary for segmenting the processing schedule region into a plurality of regions or the processing schedule region and the other region; a correlation relationship threshold value generation step of generating a correlation relationship threshold value from a correlation relationship between an energy of a first laser beam LB1 for forming the horny layer and a pulse interval; an energy and a pulse interval setting step of setting the pulse interval of the first laser beam to the correlation relationship threshold value or less; a horny layer formation step of forming a horny layer 180 by irradiating the processing schedule region with the first laser beam after an execution of the setting step, the boundary processing step, and the energy and pulse interval setting step; and a peeling step of peeling the horny layer from the workpiece.SELECTED DRAWING: Figure 15

Description

[Technical field]

[0001] The present invention relates to a method for machining a workpiece. [Background technology]

[0002] A wafer having a number of devices such as ICs and LSIs formed on its front surface and partitioned along planned dividing lines has its back surface ground by a grinding machine to form it to the desired thickness. The wafer is then divided into individual device chips by a laser processing machine and used in electrical devices such as mobile phones and personal computers.

[0003] It is also known that when dividing the wafer into individual device chips using a laser processing device, the planned dividing line of the wafer is set as the planned processing area, and a laser beam of a wavelength that is absorbent for the wafer is irradiated along the planned processing area to form dividing grooves and divide the wafer into individual device chips (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-019252 A Summary of the Invention [Problem to be solved by the invention]

[0005] According to the technology described in the above-mentioned Patent Document 1, a laser groove serving as a starting point for division is formed on the surface of a wafer by irradiation with a laser beam, and the wafer can be divided into individual device chips. However, when a laser groove is formed by performing ablation processing by irradiating a laser beam having an absorbent wavelength on the wafer, a large amount of debris is generated by the ablation processing and adheres to the wafer, resulting in contamination of the device chips and a decrease in the quality of the device chips.

[0006] The present applicant has proposed a laser processing method including the following steps for generating a correlation threshold for forming a stratum corneum on the upper surface of a plate-shaped workpiece from the correlation between the energy per pulse and the pulse interval on the surface of a wafer: a laser processing condition setting step for setting laser processing conditions such that the pulse energy of the pulsed laser beam irradiated from the laser beam application means is equal to or greater than the correlation threshold and the pulse interval is equal to or less than the correlation threshold; and a stratum corneum formation step for irradiating the workpiece with a pulsed laser beam based on the laser processing conditions to form a stratum corneum on the upper surface of the workpiece (Patent Application No. 2022-055878, hereinafter referred to as "prior art").

[0007] According to the above-mentioned prior art, it is possible to easily remove the region where the stratum corneum is formed in the plate-shaped workpiece, and it is known that the productivity during grinding can be improved. And, according to the above-mentioned prior art, since the surface of the workpiece can be easily peeled off and removed, it is possible to form the above-mentioned stratum corneum along the planned dividing line of the wafer, for example, and form a groove that serves as the starting point of division by removing the stratum corneum.

[0008] However, if a stratum corneum is formed on the upper surface of the workpiece by irradiating a laser beam on the planned processing area set on the planned dividing line to be removed based on the laser processing conditions of the prior art, and then removed, it is difficult to strictly control the area where the stratum corneum is peeled off and removed, and there is a risk that the peeled area may expand to areas other than the area where the stratum corneum is formed when removing the stratum corneum. More specifically, for example, when the stratum corneum is formed and removed along the planned dividing line of the wafer, the area to be peeled off and removed may extend beyond the planned processing area set in advance on the planned dividing line, which may cause a problem in that the quality of the device chips to be individually divided may be impaired.

[0009] The above-mentioned problems are not limited to cases where a stratum corneum is formed along a planned dividing line of a wafer and then peeled off and removed, but can also occur when removing a portion of the surface of a wafer; more specifically, when performing so-called edge trimming, in which, for example, a ring-shaped planned processing area is set along a chamfer formed on the outer peripheral edge of the wafer, the above-mentioned stratum corneum is formed to a desired depth in the ring-shaped planned processing area, and the ring-shaped formed stratum corneum is removed; or when markings such as letters or symbols are formed on a wafer by forming and removing the stratum corneum.

[0010] Furthermore, for example, in the case where the entire surface of the wafer is set as the area to be processed, and a stratum corneum is formed and then removed over the entire surface, there is a risk that peeling will occur in unintended areas in the area where the stratum corneum is formed during formation of the stratum corneum, which will inhibit the formation of the stratum corneum by applying a laser beam; therefore, even when performing such processing, it is desirable to precisely control the area where the stratum corneum is peeled off to the intended area.

[0011] The present invention has been made in consideration of the above-mentioned facts, and its main technical object is to provide a method for processing a workpiece, which, when irradiating a laser beam onto an area to be processed to form a stratum corneum and peeling and removing the stratum corneum from the workpiece, can control the area to be peeled off by forming the stratum corneum so that it is peeled off precisely in the intended area. [Means for solving the problem]

[0012] In order to solve the above-mentioned main technical problem, according to the present invention, there is provided a method for processing a workpiece, comprising: a setting step for setting a to-be-processed area; a boundary processing step for processing a boundary that divides the to-be-processed area into a plurality of areas or a boundary that divides the to-be-processed area from other areas; a correlation threshold generating step for generating a correlation threshold from the correlation between the energy per pulse and the pulse interval of a first laser beam that forms a stratum corneum in the to-be-processed area; an energy and pulse interval setting step for setting the energy per pulse of the first laser beam to be equal to or greater than the correlation threshold and setting the pulse interval of the first laser beam to be equal to or less than the correlation threshold; a stratum corneum forming step for irradiating the to-be-processed area with the first laser beam to form a stratum corneum after performing the setting step, the boundary processing step, and the energy and pulse interval setting step; and a peeling step for peeling the stratum corneum from the workpiece.

[0013] The boundary processing step is preferably performed by irradiating the workpiece with a second laser beam having a wavelength that is absorbent for the workpiece, and forming a groove at the boundary of the workpiece. The boundary processing step is preferably performed by irradiating the workpiece with a third laser beam having a wavelength that is permeable for the workpiece, and forming a modified layer and a crack extending from the modified layer inside the workpiece corresponding to the boundary. Furthermore, the boundary processing step is preferably performed by positioning the focal point of a fourth laser beam having a wavelength that is permeable for the workpiece at a position corresponding to the boundary of the workpiece and at a depth corresponding to the thickness of the stratum corneum from the one surface, and irradiating the workpiece with the fourth laser beam to form the crack extending along the surface direction of the workpiece.

[0014] In addition, it is preferable that the stratum corneum is produced by a chain reaction of compressive plastic strain that occurs when large thermal stress that tries to rapidly expand the local area of ​​the workpiece irradiated with the laser beam is generated, and this large thermal stress is restrained by the low-temperature surrounding area and exceeds the yield stress of the workpiece.

[0015] The correlation threshold is determined by an approximation formula, which is expressed as follows, where the horizontal axis is the pulse interval (μs) and the vertical axis is the energy per pulse (μJ): Energy per pulse = a{b-(pulse interval / μs-c) 2} It is preferable that the coefficients a, b, and c are set according to the type of the workpiece.

[0016] Also, if the workpiece is silicon (Si), a=4, b=1, c=0.9 and the approximation is set to Energy per pulse = 4{1-(pulse interval / μs-0.9) 2} The pulse interval can be set within the range of 0.02 μs to 0.8 μs.

[0017] The irradiation pitch of the laser beam used in the stratum corneum formation step is preferably set to 10 to 200 nm, and the pulse width of the laser beam is preferably set in the range of 0.3 to 100 ps. Effect of the Invention

[0018] The method for processing a workpiece of the present invention includes a setting step of setting a region to be processed, a boundary processing step of processing a boundary that divides the region to be processed into a plurality of regions or a boundary that divides the region to be processed from another region, a correlation threshold generating step of generating a correlation threshold from the correlation between the energy per pulse and the pulse interval of a first laser beam that forms a stratum corneum in the region to be processed, an energy and pulse interval setting step of setting the energy per pulse of the first laser beam to be equal to or higher than the correlation threshold and setting the pulse interval of the first laser beam to be equal to or lower than the correlation threshold, a stratum corneum forming step of irradiating the region to be processed with the first laser beam to form a stratum corneum after performing the setting step, the boundary processing step, and the energy and pulse interval setting step, and a peeling step of peeling the stratum corneum from the workpiece. Therefore, when the region to be processed is irradiated with a laser beam to form a stratum corneum and the stratum corneum is peeled off and removed from the workpiece, the region to be peeled off by forming the stratum corneum can be controlled so that it is peeled off precisely in the intended region. [Brief description of the drawings]

[0019] [Figure 1] FIG. 2A is an overall perspective view of a laser processing apparatus according to the present embodiment, and FIG. 2B is a schematic block diagram showing an optical system of a laser beam application means disposed in the laser processing apparatus shown in FIG. [Diagram 2] FIG. 2A is a perspective view of a wafer processed in the first embodiment of the present invention, and FIG. 2B is an enlarged perspective view of a portion A in FIG. [Diagram 3] FIG. 2A is a perspective view showing an embodiment of the boundary processing step in Example 1, and FIG. 2B is an enlarged perspective view showing a part of the embodiment shown in FIG. [Figure 4] (a) A partially enlarged cross-sectional view showing a processed groove obtained by the boundary processing step shown in Figure 3, (b) a partially enlarged cross-sectional view showing a modified layer and cracks processed by another embodiment of the boundary processing step, and (c) a partially enlarged cross-sectional view showing a cut groove processed by yet another embodiment of the boundary processing step. [Diagram 5]FIG. 13 is a perspective view of a dummy wafer processed by the correlation threshold generation step. [Figure 6] FIG. 2A is a perspective view showing a mode of processing a dummy wafer in a correlation threshold generating step, and FIG. 2B is a partially enlarged cross-sectional view showing a stratum corneum formed by the processing shown in FIG. [Figure 7] 7(a) is an oblique view of a dummy wafer on which a stratum corneum has been formed over the entire surface area by the correlation threshold generation step shown in FIG. 6, (b) is an enlarged partial cross-sectional view of the dummy wafer shown in (a) and a cross-sectional photograph capturing the actual enlarged partial cross-sectional view. [Figure 8] FIG. 11 is a correlation diagram created by a correlation threshold generation step. [Figure 9] (a) is an oblique view showing an embodiment of the stratum corneum formation step, (b) is an oblique view showing an enlarged portion of the embodiment shown in (a), and (c) is an enlarged cross-sectional view showing a portion of the stratum corneum formed by the embodiment shown in (b). [Figure 10] FIG. 1A is a plan view of a wafer to be processed in Example 2 of the present invention, and FIG. 1B is an enlarged plan view showing a region of the wafer shown in FIG. [Figure 11] FIG. 11 is a perspective view of a wafer processed in Example 3 of the present invention; (b) is a perspective view showing a manner in which a boundary processing step is performed on the wafer shown in (a). [Figure 12] 12 is a perspective view showing an embodiment in which a stratum corneum forming step is performed on the wafer shown in FIG. 11. FIG. [Figure 13] 13 is a side view showing an embodiment in which the surface is peeled off by carrying out the stratum corneum formation step shown in FIG. 12. FIG. [Figure 14] FIG. 4 is a perspective view of a laminated wafer processed in Example 4-1 and Example 4-2 of the present invention. [Figure 15] 15(a) to 15(d) are side views showing, in partial cross section, embodiments of a boundary processing step and a stratum corneum forming step performed on the laminated wafers shown in FIG. 14. [Figure 16]15(a) to 15(e) are side views showing, in partial cross section, another embodiment of the boundary processing step and the stratum corneum forming step performed on the laminated wafers shown in FIG. [Figure 17] FIG. 2 is a block diagram showing another embodiment of the optical system of the laser irradiation means shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for processing a workpiece configured based on the present invention will be described in detail with reference to the accompanying drawings.

[0021] 1(a) shows a laser processing apparatus 1 suitable for carrying out the method for processing a workpiece of this embodiment. The laser processing apparatus 1 is an apparatus that performs laser processing on a wafer W1 held on an annular frame F via a protective tape T as shown in the figure. The laser processing apparatus 1 is disposed on a base 2 and includes at least a laser beam application means 7 that applies a laser beam to the wafer W1.

[0022] In addition to the laser beam application means 7 described above, the laser processing apparatus 1 is equipped with: holding means 3 for holding the wafer W1; alignment means 6 for imaging the wafer W1 held by the holding means 3 and performing alignment; movement means 4 including X-axis movement means 4a for moving the holding means 3 in the X-axis direction and Y-axis movement means 4b for moving the holding means 3 in the Y-axis direction; a frame 5 consisting of a vertical wall portion 5a erected on the side of the X-axis movement means 4a and the Y-axis movement means 4b on the base 2 and a horizontal wall portion 5b extending horizontally from the upper end of the vertical wall portion 5a; and control means 9 to which a display means 8 is connected and which controls each operating section.

[0023] The holding means 3 is a means for holding the wafer W1 with the XY plane specified by the X coordinate and the Y coordinate as a holding surface, and includes, as shown in FIG. 1, 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 is disposed on the cover plate 34 and extends upward through an elongated hole formed on the cover plate 34. The chuck table 35 is configured to be rotatable by a rotation drive means (not shown) housed in the support 33. A circular suction chuck 36 made of a porous material having air permeability and having the XY plane specified by the X coordinate and the Y coordinate as a 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 passing through the support 33, and four clamps 37 are arranged at equal intervals around the suction chuck 36 to grip the frame F when holding the wafer W1 on the chuck table 35.

[0024] The X-axis moving means 4a constituting the moving means 4 converts the rotational motion of the motor 42a into linear motion via a ball screw 42b, transmits it to the X-axis movable plate 31, and moves the X-axis movable plate 31 in the X-axis direction along a pair of guide rails 2A, 2A arranged along the X-axis direction on the base 2. The Y-axis moving means 4b converts the rotational motion of the motor 44a into linear motion via a ball screw 44b, transmits it to the Y-axis movable plate 32, and moves the Y-axis movable plate 32 in the Y-axis direction along a pair of guide rails 31a, 31a arranged along the Y-axis direction on the X-axis movable plate 31.

[0025] The horizontal wall 5b of the frame 5 accommodates an optical system constituting the laser beam application means 7 and the alignment means 6. A condenser 71 that constitutes part of the laser beam application means 7 and irradiates the wafer W1 with a laser beam is disposed on the lower surface side of the tip of the horizontal wall 5b. The alignment means 6 is an imaging means that captures an image of the wafer W1 held by the holding means 3 to detect the position and orientation of the wafer W1, the laser processing position to be irradiated with the laser beam, etc., and is disposed in a position adjacent to the condenser 71 in the X-axis direction.

[0026] FIG. 1(b) shows a block diagram showing an outline of the optical system of the laser beam application means 7. The laser beam application means 7 includes at least an oscillator 72 that oscillates a pulsed laser beam LB, a reflecting mirror 73 that changes the optical path of the laser beam LB oscillated by the oscillator 72 toward the condenser 71, and a condenser lens 74 disposed on the condenser 71 that condenses the laser beam LB on the wafer W1, which is the workpiece. A control means 9 is connected to the oscillator 72 of the laser beam application means 7, and the laser processing conditions (wavelength, repetition frequency, output, pulse interval, etc.) when the laser beam LB is oscillated from the oscillator 72 are adjusted by the control means 9. Although omitted in FIG. 1(b), the laser beam application means 7 of this embodiment is configured to be able to switch the condenser lens 74 depending on the laser processing conditions.

[0027] The control means 9 is configured by a computer and includes a central processing unit (CPU) that performs calculation processing according to a control program, a read-only memory (ROM) that stores the control program, etc., a readable / writable random access memory (RAM) for temporarily storing the detected values, calculation results, etc., an input interface, and an output interface (details are not shown in the drawings). In addition to the above-mentioned laser beam application means 7, the movement means 4, alignment means 6, display means 8, etc. are connected to the control means 9.

[0028] The laser processing apparatus 1 of this embodiment has a configuration generally as described above, and an embodiment of a method for processing a workpiece based on the present invention, which is carried out using the above-described laser processing apparatus 1, will be described below.

[0029] The method for processing a workpiece of the present invention includes a setting step for setting a region to be processed, a boundary processing step for processing a boundary that divides the region to be processed into a plurality of regions or a boundary that divides the region to be processed from other regions, a correlation threshold generating step for generating a correlation threshold from the correlation between the energy per pulse and the pulse interval of a first laser beam that forms a stratum corneum in the region to be processed, an energy and pulse interval setting step for setting the energy per pulse of the first laser beam to be equal to or greater than the correlation threshold and setting the pulse interval of the first laser beam to be equal to or less than the correlation threshold, a stratum corneum forming step for irradiating the region to be processed with the first laser beam to form a stratum corneum after performing at least the boundary processing step, the energy setting step, and the pulse interval setting step, and a peeling step for peeling the stratum corneum from the workpiece.

[0030] The method of processing a workpiece according to the present invention is not limited to being performed by the above-described laser processing apparatus 1, and may be of a different form from the above-described laser processing apparatus 1 as long as the processing apparatus is capable of performing the processing method described below.

[0031] Example 1 2(a) shows a perspective view of a wafer W1 to be processed by a method for processing a workpiece configured according to the present invention. The wafer W1 is a silicon (Si) wafer with a plurality of devices D formed on its surface W1a, partitioned by planned division lines L, and is, for example, a wafer with a diameter of 200 mm and a thickness of 500 μm. The surface W1a of the wafer W1 faces upward and is positioned in the center of an opening Fa of an annular frame F. A protective tape T is attached to the back surface (opposite side of the surface W1a) of the wafer W1 and the frame F, so that the wafer W1 is supported by the frame F via the protective tape T.

[0032] (Setup Step) When carrying out the method for processing a workpiece according to this embodiment, a setting step is first carried out to set a processing target area. The processing target area according to this embodiment is an area indicated by the number 100 in FIG. 2(b) which is an enlarged view of part A in FIG. 2(a), and is an area in which a stratum corneum is formed by a stratum corneum formation step described later, which is formed along a division line L of the wafer W1, and is an area surrounded by boundaries 102, 102 which separate the processing target area 100 from other areas (areas in which devices are formed). Once the position of the processing target area 100 on the wafer W1 is set, position information on the processing target area 100 is stored in the control means 9 of the laser processing device 1. Note that in FIG. 2(b), for convenience of explanation, the above-mentioned boundaries are indicated by dashed lines, but are not actually written on the wafer W1.

[0033] (Boundary processing step) Based on the boundary 102 that defines the processing target area 100 set in the setting step described above, a boundary processing step is carried out to process the boundary 102 that separates the processing target area 100 from other areas.

[0034] When performing the boundary processing step, first, the wafer W1 is placed on the chuck table 35 of the laser processing device 1, and a suction means (not shown) is activated to generate negative pressure in the suction chuck to suck in the wafer W1, while the frame F supporting the wafer W1 is grasped and held by the clamp 37.

[0035] Next, the wafer W1 is moved directly below the alignment means 6 to image the surface of the wafer W1, and the direction of the predetermined division line L (region to be processed 100) is aligned with the X-axis direction in the drawing, and the coordinate positions of the region to be processed 100 and the boundaries 102, 102 on the laser processing device 1 are detected. In this way, when the coordinate positions of the region to be processed 100 and the boundaries 102, 102 are detected, the position information is stored in the control means 9 of the laser processing device 1.

[0036] Based on the coordinate position information of the boundaries 102, 102 detected by the alignment means 6, the moving means 4 is operated to position the condenser 71 of the laser beam application means 7 above the boundary 102 in the predetermined direction, as shown in FIG. 3(a). In FIG. 3(a), other components including the clamp 37 are omitted for convenience of explanation. Next, a laser beam (hereinafter referred to as "second laser beam LB2") having a wavelength absorbed by the wafer W1 is irradiated by positioning a focusing point on the boundary 102 dividing the processing target area 100 of the wafer W1, and the X-axis moving means 4a is operated to process and feed the wafer W1 held on the chuck table 35 in the X-axis direction. As a result, as shown in FIG. 3(b), laser processing is performed along the predetermined boundary 102 of the wafer W1 to form a laser processed groove 104.

[0037] After the laser groove 104 is formed along the predetermined boundary 102, the Y-axis moving means 4b is operated to index and feed the wafer W1 in the Y-axis direction by the width of the region to be processed 100 or the width to the adjacent boundary 102 across the device D, and the adjacent unprocessed boundary 102 in the Y-axis direction is positioned directly under the condenser 71. Then, in the same manner as described above, the focal point of the second laser beam LB2 is positioned at the boundary 102 of the wafer W1 and irradiated, and the wafer W1 is processed and fed in the X-axis direction to form the laser groove 104. The depth of the laser groove 104 is set corresponding to the depth of the stratum corneum formed in the stratum corneum formation step described later (the depth indicated by the broken line 105 in FIG. 4(a) showing the EE cross section of FIG. 3(b)), and the laser groove 104 of the desired depth can be obtained by repeating the scanning of the second laser beam LB2 along the boundary 102 multiple times. As a result, as can be seen from FIG. 4(a), laser processing is performed on the boundaries 102, 102 that separate the region to be processed 100 from the other regions, and laser processed grooves 104, 104 of a desired depth are formed.

[0038] As described above, when the wafer W1 is processed and fed in the X-axis direction and the laser grooves 104 are formed along all the boundaries 102 along the X-axis direction, the wafer W1 is rotated 90 degrees to align the unprocessed boundaries 102 perpendicular to the boundaries 102 where the laser grooves 104 have already been formed, with the X-axis direction. Then, for each of the remaining boundaries 102, the focal point of the second laser beam LB2 is positioned and irradiated in the same manner as described above to form the laser grooves 104 along the boundaries 102 that divide all the regions to be processed 100 formed on the front surface W1a of the wafer W1, completing the boundary processing step.

[0039] As described above, the laser processing conditions (laser processing conditions 1) when performing the boundary processing step of irradiating the second laser beam LB2 are set, for example, as follows. Wavelength: 265nm, 532nm, 355nm Average power output: 40W Repetition frequency: 10MHz Pulse energy: average power / repetition rate Pulse interval: 1 second / repetition frequency

[0040] The processing performed on the boundary 102 by the boundary processing step of the present invention is not limited to the above-mentioned ablation processing by irradiating the second laser beam LB2 having a wavelength absorbent for the wafer W1 to form the laser processing groove 104. For example, as shown in FIG. 4(b) corresponding to the cross section shown in FIG. 4(a), instead of the above-mentioned laser beam LB2, a third laser beam LB3 having a wavelength transmittable for the wafer W1 is irradiated with a focal point positioned inside corresponding to the boundary 102, and the moving means 4 is operated to form a modified layer 110 along the boundary 102. As a result, a crack 112 is formed in the depth direction as shown in the figure along the boundary 102 of the processing target area 100 set on the planned dividing line L of the wafer W1. In addition, when the crack 112 is precisely formed in the depth direction, the focal point of the third laser beam LB3 may be positioned at a plurality of, for example, three or more depth positions at the position corresponding to the boundary 102, and the modified layer 110 may be formed.

[0041] As described above, the laser processing conditions (laser processing conditions 2) when performing the boundary processing step of irradiating the third laser beam LB3 are set, for example, as follows. Wavelength: 1064nm Average power output: 1W Repetition frequency: 100kHz Pulse energy: average power / repetition rate Pulse interval: 1 second / repetition frequency

[0042] Furthermore, in the processing by the boundary processing step of the present invention, in addition to forming the above-mentioned laser processing groove 104 in the depth direction or forming the crack 112 extending in the depth direction as described above, for example, as shown in Fig. 4 (c), the focal point of the fourth laser beam LB4 having a wavelength that is transparent to the wafer W1 is positioned at a position corresponding to the boundary on the opposite side of the upper surface (surface W1a side) of the wafer W1, and at a position (position indicated by dashed line 105) according to the thickness of the region where the stratum corneum is to be formed from the surface W1a side, and the fourth laser beam LB4 is irradiated to the wafer W1 to form a plurality of modified layers 113 in the surface direction (horizontal direction) of the wafer W1, thereby forming cracks 114 extending along the surface direction (horizontal direction) connected by the plurality of modified layers 113. Such cracks 114 may be formed over the entire area of ​​the above-mentioned processing target region 100.

[0043] The laser processing conditions of the fourth laser beam LB can be, for example, as follows (laser processing conditions 3). Pulsed laser beam wavelength: 1064nm Average power output: 7~16W Repetition frequency: 30kHz Machining feed speed: 165mm / s

[0044] Furthermore, the processing by the boundary processing step of the present invention is not limited to the above-mentioned ablation processing by irradiating the wafer W1 with a laser beam having an absorbent wavelength to form a laser groove, or the above-mentioned irradiating the wafer W1 with a laser beam having a transparent wavelength to form a modified layer to form a crack, but may also be a processing step of forming a cutting groove corresponding to the above-mentioned laser groove 104 along the boundary 102 using a cutting means that rotatably supports an annular cutting blade (not shown).

[0045] (Correlation threshold generation step) Before the stratum corneum formation step described later, more preferably before the setting step and boundary processing step described above, a correlation threshold generation step is performed to generate a correlation threshold for appropriately forming a stratum corneum on the upper surface of the workpiece (wafer W1 in this embodiment 1) from the correlation between the energy per pulse (hereinafter referred to as "pulse energy") Pe of the first laser beam LB1 (different from the second to fourth laser beams LB2 to LB4 described above) irradiated to form a stratum corneum in the processing target region 100 of the wafer W1 and the pulse interval Pw. This correlation threshold generation step can be performed by a laser processing experiment in the laser processing device 1 described above, but may also be performed by another laser processing device for setting a correlation threshold. In the following description, it is assumed that the step is performed in the laser processing device 1.

[0046] When the correlation threshold generating step is performed, a dummy wafer Wd of silicon (Si) formed of the same material as the workpiece as shown in Fig. 5 is prepared. Next, a protective tape T is attached to the front surface Wda of the dummy wafer Wd to form an integral body, and the dummy wafer Wd is inverted to place the back surface Wdb of the dummy wafer Wd facing upward and the protective tape T side facing downward on the chuck table 35 of the laser processing device 1 and suction-hold it (for convenience of explanation, configurations other than those shown, including the clamp 37, are omitted). Note that the correlation threshold generating step generates a correlation threshold that distinguishes between a region of laser processing conditions in which a stratum corneum is formed on the upper surface of the workpiece and a region of laser processing conditions in which a stratum corneum is not formed, based on a laser processing experiment, and therefore uses a dummy wafer Wd on which no device D is formed.

[0047] After the dummy wafer Wd is held on the chuck table 35, the dummy wafer Wd is positioned directly under the alignment means 6, and an image of the dummy wafer Wd is picked up and appropriately displayed on the display means 8, while the outer shape and the like of the dummy wafer Wd are detected. Next, based on the information of the dummy wafer Wd detected by the alignment means 6, the condenser 71 of the laser beam application means 7 is positioned at an appropriate processing start position. Next, based on the laser processing conditions described later, as shown in Figures 6(a) and 6(b), the condensing point of the first laser beam LB1 is positioned on the back surface Wdb of the dummy wafer Wd and irradiated, and the dummy wafer Wd is fed together with the chuck table 35 in the X-axis direction indicated by the arrow X in the figure, to perform laser processing on the back surface Wdb of the dummy wafer Wd. After the laser processing has been performed in this manner, the dummy wafer Wd is indexed and fed in the Y-axis direction by a predetermined interval (for example, 15 μm) to position the adjacent unprocessed area in the Y-axis direction directly under the condenser 71. Then, in the same manner as described above, the focusing point of the first laser beam LB1 is positioned on the back surface Wdb of the dummy wafer Wd and irradiated, and the dummy wafer Wd is fed for processing in the X-axis direction. By repeating such processing, the above-mentioned laser processing is performed on the entire back surface Wdb of the dummy wafer Wd, as shown in FIG. 7(a).

[0048] Here, in the laser processing experiment performed in the correlation threshold generation step, the laser processing conditions when performing the laser processing are appropriately changed, and whether or not a good stratum corneum 120 is generated on the back surface Wdb of the dummy wafer Wd is verified according to the correlation between the pulse energy Pe [μJ] and the pulse interval Pw [μs], as shown in the conceptual diagram of FIG. 7(b), and a threshold for whether or not a good stratum corneum 120 is generated is found. When finding the threshold, the dummy wafer Wd may be subjected to boundary processing under the same processing conditions as those in the boundary processing step, and then the laser beam LB1 may be irradiated to determine whether or not a good stratum corneum is generated. This makes it possible to obtain a more accurate correlation threshold. In addition, it is not necessarily necessary to process the entire surface of the dummy wafer Wd, and it may be possible to determine whether or not a good stratum corneum is generated by processing only a part of the dummy wafer Wd. This makes it possible to reduce the consumption of the dummy wafer Wd.

[0049] The stratum corneum 120 is a layer generated by a chain reaction of compressive plastic strains that occurs when the back surface Wdb of the dummy wafer Wd is irradiated with the first laser beam LB1, causing a large thermal stress that rapidly expands the local area of ​​the dummy wafer Wd, and the large thermal stress exceeds the yield stress of silicon (Si) that constitutes the dummy wafer Wd by being restrained by the low-temperature surroundings. As is clear from the actual image of a part of the internal configuration of the dummy wafer Wd shown in FIG. 7(b), an interface 122 along the XY plane is generated inside the dummy wafer Wd by the chain reaction of compressive plastic strains, and the layer that is peeled off to the upper surface side with the interface 122 as a boundary becomes the stratum corneum 120 of this embodiment. The laser processing experiment in this embodiment is carried out by changing each parameter within the range of laser processing conditions shown below, for example. Target wafer: Silicon (Si) wafer Wavelength: 266nm, 355nm, 532nm, 1064nm Average power output: 1~50W Repetition frequency: 0.1 to 50 MHz Pulse width: 0.3~1000ps *Pulse energy Pe: average power / repetition frequency [μJ] *Pulse interval Pw: 1 [s] / repetition frequency [μs]

[0050] Among the above-mentioned laser processing conditions, the wavelengths of 266 nm, 355 nm, and 532 nm are absorbent for silicon (Si), and the wavelength of 1064 nm is transparent for silicon (Si). As described above, the pulse interval Pw is a value that is uniquely determined by determining the repetition frequency, and the pulse energy Pe of the first laser beam LB1 is determined by determining the repetition frequency and the average output. The procedure of the above-mentioned laser processing experiment will be described in more detail below.

[0051] <Laser processing experiment procedure> a) The wavelength (532 nm in this embodiment) to be irradiated from the oscillator 72 of the laser beam application means 7 is determined. a) The average output is appropriately changed within the range of 1 to 50 W. c) The repetition frequency is appropriately changed within the range of 0.1 to 50 MHz. d) The pulse width is appropriately changed within the range of 0.3 to 1000 ps. E) Laser processing is performed by irradiating a pulsed laser beam LB.

[0052] According to the above-mentioned procedure, laser processing was performed while changing each value (average output, repetition frequency, pulse width), and it was confirmed by an appropriate electron microscope whether the above-mentioned stratum corneum 120 was well formed or not, and it was verified whether the stratum corneum 120 could be easily peeled off and removed from the back surface Wdb side of the dummy wafer Wd.

[0053] According to the procedure of the laser processing experiment described above, laser processing was performed by changing the processing conditions within the range of the laser processing conditions described above, and each time, it was confirmed whether the stratum corneum 120 was formed well or not. As a result, the following thresholds 1 to 10 were confirmed as correlation thresholds.

[0054] 1) Threshold 1 Pulse interval Pw: 0.02 μs (repetition frequency: 50 MHz) Pulse energy Pe: 0.25μJ (average output: 12.5W) 2) Threshold 2 Pulse interval Pw: 0.04 μs (repetition frequency: 25 MHz) Pulse energy Pe: 0.5μJ (average output: 12.5W) 3) Threshold 3 Pulse interval Pw: 0.1 μs (repetition frequency: 10 MHz) Pulse energy Pe: 1μJ (average output: 10W) 4) Threshold 4 Pulse interval Pw: 0.2 μs (repetition frequency: 5 MHz) Pulse energy Pe: 1.8μJ (average output: 9W) 5) Threshold 5 Pulse interval Pw: 0.25μs (repetition frequency: 4MHz) Pulse energy Pe: 2.2μJ (average output: 8.8W) 6) Threshold 6 Pulse interval Pw: 0.4 μs (repetition frequency: 2.5 MHz) Pulse energy Pe: 3μJ (average output: 7.5W) 7) Threshold 7 Pulse interval Pw: 0.5 μs (repetition frequency: 2 MHz) Pulse energy Pe: 3.3μJ (average output: 6.6W) 8) Threshold 8 Pulse interval Pw: 0.6 μs (repetition frequency: 1.66 MHz) Pulse energy Pe: 3.5μJ (average output: 5.8W) 9) Threshold 9 Pulse interval Pw: 0.7 μs (repetition frequency: 1.42 MHz) Pulse energy Pe: 3.6μJ (average output: 5.1W) 10) Threshold 10 Pulse interval Pw: 0.8 μs (repetition frequency: 1.25 MHz) Pulse energy Pe: 3.8μJ (average output: 4.75W)

[0055] In addition, in the above-mentioned laser processing experiment, the inventors also performed laser processing under the following laser processing conditions that exceed the threshold value of 10, but the stratum corneum 120 was not formed well, so it was confirmed that the following laser processing conditions are the limit values ​​at which the stratum corneum 120 is not formed well. Pulse interval Pw: 0.9 μs (repetition frequency: 1.11 MHz) Pulse energy Pe: 3.8μJ (average output: 4.22W)

[0056] The threshold values ​​1 to 10 are plotted as actual measured values ​​in a correlation diagram with the horizontal axis being the pulse interval Pw [μs] and the vertical axis being the pulse energy Pe [μJ] as shown in FIG. 8, and are connected by straight lines (the limit values ​​are indicated by × for reference). The threshold values ​​1 to 10 are actual measured values ​​found as correlation threshold values ​​that separate the region (A) where the stratum corneum 120 is well formed from the region (B) where the stratum corneum 120 is not well formed by the above-mentioned laser processing experiment. That is, it was confirmed by the above-mentioned laser processing experiment that when the laser processing conditions are set in the region (A) where the pulse energy Pe is equal to or greater than the correlation threshold and the pulse interval Pw is equal to or less than the correlation threshold, a good stratum corneum 120 is formed, and when the laser processing conditions are set in the region (B) where the pulse energy Pe is less than the correlation threshold and the pulse interval Pw is greater than the correlation threshold, a good stratum corneum 120 is not formed. This correlation threshold is stored in the control means 9.

[0057] In addition, similar correlation thresholds were obtained when other wavelengths of 266 nm and 355 nm, which are absorbent for silicon wafers, were selected as the wavelength of the first laser beam LB1 to be irradiated in the above-mentioned laser processing experiment, whereas when the above-mentioned laser processing experiment was performed by selecting a wavelength of 1064 nm, which is transparent to silicon wafers, as the wavelength of the first laser beam LB1 to be irradiated, no good stratum corneum was formed in any region.

[0058] In this manner, a correlation threshold capable of forming a good stratum corneum on the upper surface of the workpiece is generated from the correlation between the pulse energy Pe, which is the energy per pulse, and the pulse interval Pw, and the correlation threshold is stored in the control means 9, thereby completing the correlation threshold generation step.

[0059] In addition, the correlation threshold generating step in the present invention may generate an approximation formula based on the correlation threshold and use the approximation formula as the correlation threshold, instead of generating the correlation threshold based on the actual measurement value as described above. The inventors have found that, within the scope of the laser processing experiment that showed good results in the laser processing experiment when generating the correlation threshold described above, the correlation threshold based on the actual measurement value can be approximated by the following approximation formula (1).

[0060] Approximation formula (1) is specified as follows when the horizontal axis represents the pulse interval Pw [μs] and the vertical axis represents the pulse energy Pe [μJ]. Pe=a{b-(Pw / μs-c) 2} ···(1) *The pulse interval Pw is made dimensionless by dividing it by the unit [μs]. *The coefficients a, b, and c are set appropriately depending on the type of workpiece (e.g., Si, SiC, GaN, sapphire, etc.).

[0061] The above-mentioned laser processing experiment was conducted on a silicon (Si) dummy wafer Wd, and it was found that when the above-mentioned approximate formula (1) is applied to the silicon (Si) dummy wafer Wd, the coefficients a, b, and c can be set to a=4, b=1, and c=0.9 at least within the range of the pulse interval Pw of 0.02 μs or more and 0.8 μs or less, and can be used as a correlation threshold for generating a good stratum corneum 120. That is, the approximate formula (1) is expressed by the following approximate formula (2), and by using the following approximate formula (2), it is possible to easily set the laser processing conditions for generating a good stratum corneum 120. Pe=4{1-(Pw / μs-0.9) 2} ···(2) In this embodiment, the correlation threshold value is obtained while changing both the pulse energy and the pulse interval in the correlation threshold value generating step. However, the correlation threshold value may be obtained by processing the dummy wafer Wd while changing only the pulse energy with the pulse interval fixed to a predetermined value. The correlation threshold value may also be obtained by processing the dummy wafer Wd while changing only the pulse interval with the pulse energy fixed to a predetermined value.

[0062] (Energy and pulse interval setting steps) Using the correlation threshold obtained by the correlation threshold generation step described above, an energy and pulse interval setting step is carried out in which the pulse energy Pe, which is the energy per pulse of the first laser beam LB1, is set to be equal to or greater than the correlation threshold, and the pulse interval Pw of the first laser beam LB1 is set to be equal to or less than the correlation threshold.

[0063] Specifically, the control means 9 sets the laser processing conditions for the wafer W1, which is the workpiece, so that the pulse energy Pe of the first laser beam LB1 irradiated from the laser beam application means 7 is equal to or greater than the correlation threshold value and the pulse interval Pw is equal to or less than the correlation threshold value. That is, the laser processing conditions are set and stored such that the pulse energy Pe and pulse interval Pw of the first laser beam LB1 can be irradiated in the laser processing device 1 within the region (A) in the correlation diagram shown in Fig. 8. Note that by increasing the repetition frequency and decreasing the pulse interval Pw, it is possible to reliably form the stratum corneum 120 with a smaller pulse energy Pe, and by increasing the pulse energy Pe, it is possible to adjust the thickness of the stratum corneum 120 to a larger value. Therefore, the pulse energy Pe and pulse interval Pw of the first laser beam LB1 are set in consideration of the energy efficiency, the thickness of the stratum corneum 120 to be formed, and the like. Furthermore, if the value of the pulse energy Pe of the first laser beam LB1 is too large, leakage light may reach the outside of the processing area 100 to be irradiated with the first laser beam LB1, for example the area where the device D is to be formed, and cause damage, so the pulse energy Pe is set within a range where no effects are caused by the leakage light.

[0064] (Stratum corneum formation step) At least after the setting step, the boundary processing step, and the energy and pulse interval setting step are performed, the first laser beam LB1 is irradiated onto the processing target region 100 to form the stratum corneum, and a stratum corneum formation step is performed. Note that the correlation threshold generation step in this embodiment 1 is performed in advance before the boundary processing step, and the stratum corneum formation step described below is performed by the laser processing device 1 after the boundary processing step. In addition, in a laser processing experiment in the correlation threshold generation step, it was confirmed that the thickness of the stratum corneum 120 and the thickness of the interface 122 are stably formed by setting the pulse width of the first laser beam LB1 to 0.3 to 100 ps, ​​so in the energy and pulse interval setting step, the pulse width is set within the above range. In the above laser processing experiment, it was also confirmed that a good stratum corneum 120 was formed when the irradiation pitch of the first laser beam LB1 irradiated to the dummy wafer Wd was 10 to 200 nm (see FIG. 6(b)), and the processing feed speed in the X-axis direction was appropriately adjusted according to the repetition frequency of the first laser beam LB1 to be adjusted to fall within the above-mentioned irradiation pitch range. The stratum corneum formation step is performed by setting the laser processing conditions (laser processing conditions 4) based on the pulse energy Pe and pulse interval Pw thus adjusted and set based on the energy and pulse interval setting step described above.

[0065] When performing the stratum corneum formation step, it is preferable to appropriately replace the condenser lens 74 of the condenser 71 used in the boundary processing step. When forming the laser processing groove 104 in the above-mentioned boundary processing step, the second laser beam LB2 is irradiated to the boundary 102 that defines the processing target area 100 where the stratum corneum is to be formed. At this time, a condenser lens with a larger NA is used to reduce (thin) the beam diameter compared to the laser processing for forming the stratum corneum. This makes it possible to precisely form the laser processing groove 104, and the fluence of the second laser beam LB2 increases, making it a laser beam more suitable for ablation processing. On the other hand, when irradiating the first laser beam LB1 in the stratum corneum formation step, the condenser lens is replaced with one with a smaller NA. As a result, the beam diameter of the first laser beam LB1 is expanded and the fluence is reduced, making it a laser beam more suitable for stratum corneum formation.

[0066] In carrying out the stratum corneum formation step, based on the position information of the processing target area 100 obtained by the alignment means 6, as shown in Fig. 9(a), the focal point of the first laser beam LB1, whose processing conditions are set based on the above-mentioned laser processing conditions 4, is positioned and irradiated to the desired processing target area 100, which is positioned along the X-axis direction on the surface W1a of the wafer W1 and is sandwiched between the laser processing grooves 104, 104 formed along the boundary 102 by processing in the boundary processing step, and the X-axis moving means 4a is operated to process and feed the wafer W1. Then, the Y-axis moving means 4b is operated to move the chuck table 35 in the Y-axis direction, and the focal point of the first laser beam LB1 is indexed and fed in the Y-axis direction within the processing target area 100 at intervals of, for example, 15 μm, as shown in Fig. 9(b), and the first laser beam LB1 is scanned to form the stratum corneum 120 on the surface within the processing target area 100. Then, by irradiating the first laser beam LB1 and operating the X-axis moving means 4a and the Y-axis moving means 4b, the stratum corneum 120 is formed in the processing target area 100 sandwiched between the laser processing grooves 104, as shown in Fig. 9(c). The thickness (depth) of the stratum corneum 120 is, for example, 200 µm. As can be seen from Fig. 9(c), in the wafer W1 of this Example 1, the fourth laser beam LB4 is irradiated at a depth of the thickness (200 µm) where the stratum corneum 120 is to be formed in the processing target area 100, thereby forming a plurality of modified layers 113, and thus cracks 114 extending in the surface direction (horizontal direction) of the wafer W1 are formed.

[0067] When carrying out the above-mentioned stratum corneum forming step, an antireflection film formed of a solution in which at least a water-soluble resin, an organic solvent, and an absorbent that absorbs laser beams are mixed may be formed in advance on the surface W1a of the wafer W1. The water-soluble resin is selected from, for example, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, polyethylene oxide, methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, polyacrylic acid, poly-N-vinylacetamide, and polyglycerin. The organic solvent is an organic compound for dissolving substances such as ultraviolet absorbents. The organic solvent is, for example, selected from any of alkylene glycol monoalkyl ethers, alkylene glycols, or alkylene glycol monoalkyl ether acetates. An example of an alkylene glycol monoalkyl ether is propylene glycol monomethyl ether. Furthermore, the absorbent is, for example, selected from any of cinnamic acid derivatives. An example of a cinnamic acid derivative is ferulic acid (i.e., 4-hydroxy-3-methoxycinnamic acid), but the cinnamic acid derivative may be isoferulic acid, caffeic acid, sinapinic acid, or chlorogenic acid.By forming the above-mentioned antireflection film on the surface W1a, it is possible to suppress reflection loss when irradiating the first laser beam LB1, and it is possible to efficiently form the stratum corneum 120. This antireflection film may be formed before the boundary processing step is performed. Since this antireflection film contains a water-soluble resin, it can be easily removed by spraying pure water.

[0068] (peeling step) After the above-mentioned stratum corneum forming step is performed, a peeling step is performed to peel off the stratum corneum 120 from the wafer W1. The stratum corneum 120 formed by the above-mentioned stratum corneum forming step is formed in a state that is easy to peel off, and a peeling step is performed to peel off and remove the stratum corneum 120 by an appropriate method. For example, the tip of an air nozzle (not shown) is positioned at the division line L on which the stratum corneum 120 of the wafer W1 is formed, and high-pressure air is sprayed from the air nozzle toward the stratum corneum 120 to peel off and remove the stratum corneum 120 formed in the processing area 100. The method of peeling off the stratum corneum 120 is not limited to this, and for example, the stratum corneum 120 can be removed by spraying high-pressure water toward the stratum corneum 120 to peel off the stratum corneum 120, or by attaching an adhesive tape to the surface W1a and peeling it off. Furthermore, by carrying out the above-mentioned stratum corneum formation step, the stratum corneum 120 is in a state where it can be easily peeled off, so that peeling of the stratum corneum 120 may progress at the same time as carrying out the stratum corneum formation step. That is, the peeling step of the present invention also includes a case where the stratum corneum 120 is peeled off and removed at the same time as carrying out the stratum corneum formation step. If only the end of the stratum corneum 120 remains connected to the substrate despite the progress of peeling, the end may be irradiated with a laser beam having a wavelength absorbed by the wafer W1 to perform ablation processing and remove the stratum corneum 120, thereby completely peeling off the stratum corneum 120. Completion of the peeling step completes the processing method of the present invention for processing a workpiece.

[0069] As described above, the processing method described based on the present embodiment 1 includes a boundary processing step for processing the boundary 102 that separates the processing target area 100 from other areas (areas where devices are formed), and includes a correlation threshold generating step, an energy and pulse interval setting step, a stratum corneum forming step, and a peeling step, so that it is possible to form an easily peeled stratum corneum 120 in the predetermined processing target area 100 while suppressing the generation of debris. Furthermore, since the stratum corneum 120 peeled off in the peeling step is restricted by the laser processed grooves 104 (or may be cracks 112, 114) formed in the boundary processing step, the peeling of the stratum corneum 120 does not extend outside the processing target area 100, and it is possible to precisely control the peeled area, thereby solving the problem of peeling extending to the area where devices are formed.

[0070] In the correlation threshold generating step and the energy and pulse interval setting step, the beam area (spot diameter) of the first laser beam LB1 is constant. However, even if the pulse energy Pe is the same, if the beam area (spot diameter) changes, the formation of the stratum corneum 120 is affected. Therefore, it is also possible to set the correlation threshold using the pulse energy per beam area (spot diameter) (Pe [J] / beam area [cm]), that is, the so-called fluence. However, as described above, since the fluence and the pulse energy Pe are in a proportional relationship, setting the correlation threshold based on the fluence instead of the pulse energy Pe is equivalent to setting the correlation threshold based on the pulse energy Pe.

[0071] Example 2 The present invention is not limited to the above-described embodiment 1 in which grooves serving as starting points for dividing the wafer W1 are formed by the stratum corneum along the dividing line L. With reference to Fig. 10, embodiment 2 in which the present invention is applied to form recesses as local markings on a workpiece will be described.

[0072] FIG. 10(a) shows a wafer W2 to be processed in this embodiment 2. The wafer W2 is a silicon (Si) wafer equivalent to the wafer W1 in the embodiment 1 described above, and is processed to form concave markings W2m indicating the serial code of the wafer W2 and the processing conditions when processing the wafer W2 in the surplus area on the outer periphery side where the device D is not formed. Although not shown in the figure, the wafer W2 is also processed in a state supported by an annular frame F via an adhesive tape T, similar to the wafer W1 described above. In addition, the markings W2m in the embodiment 2 shown in FIG. 10 are all shown as square shapes for convenience of explanation, but in reality, letters, numbers, symbols, etc. are formed in a concave shape.

[0073] The processing of the marking W2m will be described with reference to Fig. 10(b), which is an enlarged view of the area where the marking W2m is formed in Fig. 10(a). The illustrated marking W2m is composed of three symbols m1 to m3 (shown by dashed lines). The processing method of this embodiment 2 is also composed of a setting step, a boundary processing step, a correlation threshold generating step, an energy and pulse interval setting step, a stratum corneum forming step, and a peeling step, similar to the above-mentioned embodiment 1.

[0074] (Setup Step) When carrying out the processing method of this embodiment, a setting step is first carried out to set a processing area. The processing area of ​​this embodiment is a processing area 130 constituting symbols m1 to m3 as shown by a dashed line in Fig. 10(b), and is set as an area surrounded by boundaries 132, 132 that divide the processing area 130. Once the position of the processing area 130 on the wafer W2 is set, position information regarding the processing area 130 is stored in the control means 9 of the laser processing device 1.

[0075] (Boundary processing step) Based on the position information of the region to be processed 130 set in the setting step described above, a boundary processing step is carried out to process the boundary 132 that separates the region to be processed 130 from other regions.

[0076] When performing the boundary processing step, first, the wafer W2 is placed on the chuck table 35 of the laser processing device 1, and a suction means (not shown) is activated to generate negative pressure in the suction chuck to suck in the wafer W2, while a frame (not shown) supporting the wafer W2 is grasped and held by a clamp 37.

[0077] Next, the wafer W2 is moved directly under the alignment means 6 to capture an image of the surface of the wafer W2, and the coordinate positions of the to-be-processed region 130 and the boundaries 132, 132 of the symbols m1 to m3 constituting the marking W2m on the laser processing device 1 are detected. When the coordinate positions of the to-be-processed region 130 and the boundaries 132, 132 are detected, the position information is stored in the control means 9 of the laser processing device 1.

[0078] Based on the coordinate position information of the boundaries 132, 132 detected by the alignment means 6, the moving means 4 is operated to position the condenser 71 of the laser beam application means 7 above the boundary 132 in a predetermined direction. Next, the focus point of the second laser beam LB2 is positioned on the wafer W2 and irradiated to the boundary 132 dividing the processing target area 130 of the wafer W2 according to the laser processing condition 1 described above, and the X-axis moving means 4a, the Y-axis moving means 4b, and the rotary drive means for rotating the chuck table 35 are operated to feed the wafer W2 held on the chuck table 35 in the X-axis and Y-axis directions for processing. As a result, laser processing is performed along the boundary 132 surrounding the processing target area 130 to form the laser processed groove 104 described based on the first embodiment (the processing method for forming the laser processed groove 104 is the same as the processing method for the groove formed in the first embodiment described above, so details are omitted).

[0079] In addition, the processing of the boundary 132 described above is not limited to forming a laser groove 104, as in Example 1, but may also be performed in accordance with the processing conditions of the laser processing condition 2 described above, by positioning the focal point of a third laser beam LB3 having a wavelength that is transparent to the wafer W2 inside the boundary 132 and irradiating it, and operating the moving means 4 to form a modified layer inside along the boundary 132, and forming a crack in the depth direction along the boundary 132 surrounding the processing area 130 set in the symbols m1 to m3 of the marking W2m. Furthermore, in the processing method of this Example 2, in accordance with the above-mentioned laser processing condition 3, the focal point of a fourth laser beam LB4 having a wavelength that is transparent to the wafer W2 is positioned at a position corresponding to the boundary on the opposite side of the upper surface (surface W2a side) of the wafer W2, and at a position according to the depth of the processing area 130 in which the stratum corneum is to be formed from the surface W2a side, and the fourth laser beam LB4 is irradiated to the wafer W2 to form cracks extending in the surface direction (horizontal direction) of the wafer W2 throughout the entire processing area 130 described above (details are omitted as they are the same as the procedure explained based on Example 1).

[0080] (Correlation threshold generation step, energy and pulse interval setting step) In this embodiment 2, the correlation threshold generating step and the energy and pulse interval setting step are performed in the same manner as in the embodiment 1. Note that the procedures of the correlation threshold generating step and the energy and pulse interval setting step performed here are the same as those in the embodiment 1, and therefore detailed explanations will be omitted.

[0081] (stratum corneum formation step, peeling step) As described above, after the setting step, boundary processing step, correlation threshold generating step, and energy and pulse interval setting step are performed, the first laser beam LB1 is irradiated from the surface W2a of the wafer W2 to the processing target area 130, and the moving means 4 is operated to perform the stratum corneum forming step of forming the stratum corneum and the peeling step (not shown). Note that the correlation threshold generating step in this embodiment 2 is performed in advance before the above-mentioned boundary processing step, and the stratum corneum forming step is performed following the above-mentioned boundary processing step. Also, as in the embodiment 1, in the laser processing experiment in the correlation threshold generating step, it was confirmed that the thickness of the stratum corneum and the depth of the interface were stably formed by setting the pulse width of the first laser beam LB1 to 0.3 to 100 ps, ​​so in the laser processing in the stratum corneum forming step, the pulse width is set in the above range. Furthermore, it has been confirmed that a good stratum corneum is formed when the irradiation pitch of the first laser beam LB1 is 10 to 200 nm (see FIG. 6(b)), and the processing feed speed in the X-axis direction is appropriately adjusted according to the repetition frequency of the first laser beam LB1 to be adjusted to fall within the above-mentioned irradiation pitch range. In this manner, the laser processing conditions (laser processing conditions 4) based on the pulse energy Pe and pulse interval Pw set based on the energy and pulse interval setting step are set, and a stratum corneum is formed in the processing target region 130 surrounded by the boundary 132, and a peeling step is also performed. The stratum corneum formation step and peeling step performed here are also performed in the same procedure as in the above-mentioned Example 1, and therefore detailed explanations are omitted.

[0082] According to the processing method described based on the above-mentioned second embodiment, the boundary processing step for processing the boundary 132 that separates the processing target area 130 from other areas is included, and a correlation threshold generating step, an energy and pulse interval setting step, a stratum corneum forming step, and a peeling step are performed, so that it is possible to form a stratum corneum that is easy to peel off in the predetermined processing target area 130 while suppressing the generation of debris from the marking W2m area. Furthermore, the area of ​​the stratum corneum to be peeled off in the peeling step is precisely controlled so that it does not protrude from the area defined by the boundary 132 formed in the boundary processing step, and even if the markings m1 to m3 are symbols, numbers, or letters, they can be precisely formed. Furthermore, by forming a crack in the boundary that is the bottom surface of the processing target area 130 by the fourth laser beam LB4, it is possible to prevent the wafer W2 from being peeled off to a depth greater than the desired depth in the stratum corneum forming step and the peeling step.

[0083] Example 3 The present invention is not limited to the above-mentioned first and second embodiments in which the boundary processing step processes the boundary that divides the region to be processed from other regions, but also includes a case in which the boundary processing step processes the region to be processed into a plurality of regions. A third embodiment in which the boundary processing step processes the region to be processed into a plurality of regions will be described in detail with reference to Figs. 11 to 13.

[0084] FIG. 11(a) shows a perspective view of a wafer W3 to be processed by a method for processing a workpiece configured based on the present invention, and a chuck table 35 of a laser processing device 1 that holds the wafer W3 (for convenience of explanation, configurations other than those shown in the figure are omitted). The wafer W3 is a silicon (Si) wafer, for example, a wafer having a diameter of 200 mm and a thickness of 700 μm. This embodiment 3 is an embodiment in which a wafer W3 that is difficult or time-consuming to grind can be processed so that it can be relatively easily thinned by removing the front surface W3a. In the processing method described below, processing is performed on the front surface W3a of the silicon wafer W3 shown in FIG. 11(a), and the back surface (opposite side of the front surface W3a) of the wafer W3 is held by the chuck table 35 with a protective tape T attached thereto, and processing is performed by the processing method of this embodiment described below.

[0085] (Setup Step) When carrying out the method for processing a workpiece according to the present embodiment 3, a setting step is first carried out to set a processing target area. The processing target area in the present embodiment 3 is the entire surface W3a of the wafer W3 shown in Fig. 11(a) and is indicated by the number 140. Once the processing target area 140 on the wafer W3 has been set in this manner, information about the processing target area 140 (information about the outline surrounding the entire surface W3a of the wafer W3) is stored in the control means 9 of the laser processing device 1.

[0086] (Boundary processing step) The boundary processing step of this embodiment 3 processes boundaries that divide the processing target area 140 set on the wafer W3 into a plurality of areas. The method of setting the boundaries is not particularly limited, but for example, it is preferable to set a linear boundary 142 in a direction (i.e., the X-axis direction indicated by the arrow X in FIG. 11(b)) perpendicular to the direction in which the processing area expands when forming the stratum corneum in the stratum corneum formation step described later (the Y-axis direction indicated by the arrow Y in FIG. 11(b), see also FIG. 12). In this embodiment 3, the direction in which the processing area for forming the stratum corneum expands in the stratum corneum formation step is a direction perpendicular to the direction from the notch W3n indicating the crystal orientation toward the center of the wafer W3, as shown in FIG. 12. Therefore, in this embodiment 3, as shown in FIG. 11(b), the boundaries 142 are set by a plurality of boundaries 142 set along the direction from the notch W3n toward the center of the wafer W3, and a plurality of boundaries 142 set along a direction perpendicular to the direction from the notch W3n toward the center of the wafer W3, and a lattice shape is formed by the plurality of boundaries 142.

[0087] Similarly to the first embodiment, the boundary 142 is irradiated with the second laser beam LB2 according to the laser processing condition 1, and the X-axis moving means 4a, the Y-axis moving means 4b, and the chuck table 35 are rotated to form a laser processed groove 144 similar to the laser processed groove 104. As in the first and second embodiments, the processing of the boundary 142 is not limited to irradiating the second laser beam LB2 to form a laser processed groove 144 similar to the laser processed groove 104, but may be performed by positioning the focal point of a third laser beam LB3 having a wavelength that is transparent to the wafer W3 in accordance with the laser processing condition 2 inside the boundary 142 to form a modified layer and cracks, or by forming a cut groove by a cutting means including a rotatably held cutting blade. Furthermore, the focal point of a fourth laser beam LB4 having a wavelength that is transparent to the wafer W3 may be positioned at a depth from the surface W3a (one side) of the wafer W3 that corresponds to the thickness at which the stratum corneum is to be formed, and the fourth laser beam LB4 may be irradiated onto the wafer W3 to form the crack extending in the surface direction of the wafer W3.

[0088] (Correlation threshold generation step, energy and pulse interval setting step) In this embodiment 3, the correlation threshold generating step and the energy and pulse interval setting step are performed similarly to the above-mentioned embodiments 1 and 2. Note that the procedures of the correlation threshold generating step and the energy and pulse interval setting step performed here are similar to those in embodiment 1, and therefore detailed explanations will be omitted.

[0089] (stratum corneum formation step, peeling step) After the above-mentioned setting step, boundary processing step, and energy and pulse interval setting step are performed, a stratum corneum forming step is performed in which the first laser beam LB1 is irradiated to the entire surface W3a of the wafer W3 (region to be processed 140) according to the above-mentioned laser processing condition 4 set based on the energy and pulse interval setting step, as shown in FIG. 12, to form the stratum corneum 150. At this time, the first laser beam LB1 is irradiated from the processing start point where the notch W3n is formed, and the first laser beam LB1 is scanned in a direction perpendicular to the direction from the notch W3n toward the center of the wafer W3 (X-axis direction) to form the stratum corneum 150, and the wafer W3 held on the chuck table 35 is indexed and fed at a predetermined interval (e.g., 15 μm) in the Y-axis direction. Finally, the stratum corneum 150 is formed over the entire surface W3a of the wafer W3. The thickness of the stratum corneum 150 formed at this time is, for example, 200 μm. The laser processing condition 4 performed in this stratum corneum formation step is the same as the processing described in the above Examples 1 and 2, and detailed description will be omitted. The order of the locations where the first laser beam LB1 is irradiated to form the stratum corneum 150 is not limited to this. For example, the order may be such that the stratum corneum 150 is formed over the entire surface of one area separated by a processed groove formed in the boundary processing step, and then the stratum corneum 150 is formed over the entire surface of an area separated by a processed groove formed in the boundary processing step adjacent in the X direction.

[0090] After the above-mentioned stratum corneum forming step, or simultaneously with the stratum corneum forming step, a peeling step is performed. This peeling step includes a method of peeling and removing the surface W3a on which the stratum corneum 150 is formed by grinding the surface W3a with a known grinding device (not shown), a method of removing the surface W3a of the wafer W3 by polishing it with a polishing device, a method of peeling and removing the stratum corneum 150 by spraying high-pressure air or high-pressure water onto the surface W3a of the wafer W3, and the like. Furthermore, it also includes a case where the stratum corneum 150 is peeled off and removed from the surface W3a of the wafer W3 by performing the stratum corneum forming step of forming the stratum corneum 150.

[0091] According to the processing method shown in the above-mentioned Example 3, it is possible to form an easily peelable stratum corneum in the to-be-processed region 140 while suppressing the generation of debris. Furthermore, since the stratum corneum 150 to be peeled off in the peeling step is defined by the processing grooves or cracks formed in the boundary processing step, the peeling of the stratum corneum 150 is controlled, and the region to be peeled off can be precisely controlled, and the problem that peeling extends to undesired regions during the formation of the stratum corneum 150 and inhibits the formation of the stratum corneum 150 is eliminated.

[0092] In particular, in the above-mentioned boundary processing step in this Example 3, a plurality of boundaries 142 are set in a direction perpendicular to the direction in which the processing region in which the stratum corneum 150 is formed expands (Y-axis direction in FIG. 12), i.e., in a direction perpendicular to the direction from the notch W3n toward the center of the wafer W3 (X-axis direction in FIG. 12), and processing is performed in the boundary processing step. As a result, as shown in FIG. 13, even when the stratum corneum 150 is formed in the above-mentioned stratum corneum formation step and the peeling step progresses to peel the stratum corneum 150, the peeling of the stratum corneum 150 is restricted by the laser processed grooves 144 formed in the above-mentioned boundaries 142, and the problem that the peeling extends to an unintended region, i.e., the region in which the stratum corneum 150 is to be formed, and a satisfactory stratum corneum 150 is not formed is avoided. Furthermore, the problem of the peeled stratum corneum 150 turning up and covering the area where a stratum corneum is to be formed blocking the first laser beam LB1 and preventing a good stratum corneum from being formed is avoided.

[0093] (Example 4-1) The present invention is not limited to the processing method shown in the above-mentioned Examples 1 to 3, and may be, for example, the processing method of Example 4-1 described below. FIG. 14 shows a perspective view of a wafer W4 processed by this Example 4-1, and the wafer W4 is held on a chuck table 35 of a laser processing device 1 that holds the wafer W4 (for convenience of explanation, configurations other than those shown, including a clamp 37, are omitted). The wafer W4 is a stacked wafer in which a first wafer W4A and a second wafer W4B, both of which are silicon wafers, are stacked and bonded via an oxide film. This Example 4-1 is a process for peeling and removing the outer periphery of the first wafer W4A of the wafer W4 shown in FIG. 14 (so-called edge trim), and is carried out by the following procedure.

[0094] (Setup Step) When carrying out the processing method of this embodiment, a setting step is first carried out to set a processing target area. The processing target area of ​​this embodiment is an annular processing target area W4Ab surrounding a central area W4Aa in which a stratum corneum is not formed by a stratum corneum formation step described later in a first wafer W4A forming the upper surface of the wafer W4 shown in FIG. 14. The central area W4Aa and the processing target area W4Ab are divided by an annular boundary 161d. After the area of ​​the processing target area W4Ab on the wafer W4 is set in this manner, position information regarding the processing target area W4Ab is stored in the control means 9 of the laser processing device 1.

[0095] (Boundary processing step) Based on the position information of the processing-predetermined region W4Ab set by the setting step described above, a boundary for dividing the processing-predetermined region W4A into a plurality of regions and a boundary for dividing the processing-predetermined region W4Ab from other regions (the central region W4Aa described above) are set, and a boundary processing step for processing the boundaries is performed. In this embodiment 4-1, for example, as shown in FIG. 14, in the annular processing-predetermined region W4Ab, a plurality of concentric boundaries 161a, 161b, 161c, and 161d having different diameters are set at equal intervals from the outer circumferential end side, and further, a plurality of radial boundaries 162 for dividing the processing-predetermined region W4Ab into a plurality of regions are set in the processing-predetermined region W4Ab. Note that the illustrated boundaries 162 are set at equal intervals of 30° on the outer periphery of the first wafer W4A, but the present invention is not limited thereto, and may be set at intervals of 60° or 90°, for example, or a single annular boundary 161d may be set.

[0096] The annular boundaries 161a, 161b, 161c and the multiple radial boundaries 162 are boundaries that divide the processing area W4Ab into multiple areas, and the annular boundary 161d is a boundary that divides the processing area W4Ab from the central area W4Aa where the stratum corneum is not formed. In FIG. 14, the above-mentioned boundaries are shown by dashed lines for the convenience of explanation, but they are not actually written on the wafer W4A. Position information on these boundaries is stored in the control means 9 of the laser processing device 1. In the first wafer W4A, the width of the processing area W4Ab is set to about 0.5 to 20 mm, and in FIG. 14, the width of the processing area W4Ab is exaggerated for the convenience of explanation.

[0097] After each boundary is set as described above, the alignment means 6 of the laser processing device 1 shown in FIG. 1 captures an image of the wafer W4, and the coordinate positions of each boundary to be processed in the laser processing device 1 are detected and stored in the control means 9. Next, the moving means 4 is operated to position the condenser 71 of the laser beam application means 7 above the wafer W4 in accordance with the laser processing condition 2 described above, and the focal point of the third laser beam LB3 having a wavelength that is transparent to the first wafer W4A is positioned on the deepest side of the interior corresponding to the boundary 161a (the second wafer W4B side) and irradiated, and the chuck table 35 is rotated by operating the rotation drive means (not shown). As a result, as shown in FIG. 15(a), a ring-shaped modified layer 171 is formed inside the first wafer W4A along the position corresponding to the boundary 161a. In this embodiment 4-1, in order to form the modified layers 171 at a plurality of different depth positions inside the boundary 161a, the focal point of the third laser beam LB3 is gradually raised and moved toward the center of the wafer W4 (in the direction indicated by the arrow R1 in the figure) to form a plurality of modified layers 171 (three in the illustrated embodiment 4-1). As a result, as can be seen from FIG. 15(a), the cracks 172 connecting the modified layers 171 are inclined toward the inside of the first wafer W4A (in the direction indicated by the arrow R1). In the illustrated embodiment, the modified layer 171 is formed on the deep side, and the cracks 172 are formed in a state where they reach the lower surface side of the first wafer W4A but do not reach the surface side.

[0098] As described above, after the modified layer 171 and the crack 172 are formed inside the portion corresponding to the annular boundary 161a, a plurality of modified layers 173 and cracks 174 are formed inside the portion corresponding to the boundary 161b, a plurality of modified layers 175 and cracks 176 are formed inside the portion corresponding to the boundary 161c, and a plurality of modified layers 177 and cracks 178 are formed inside the portion corresponding to the boundary 161d. Each of the cracks 174, 176, and 178 is formed in a shape inclined toward the inside of the first wafer W4A, similar to the crack 172 described above.

[0099] Next, although not shown in the figure, the third laser beam LB3 is irradiated to the inside corresponding to the radial boundary 162 according to the above-mentioned laser processing condition 2, and the moving means 4 and the rotary driving means of the chuck table 35 are operated to form a plurality of modified layers and cracks along the boundary 162. When forming the modified layers and cracks in the inside corresponding to the radial boundary 162, the position where the light condensing point is positioned is moved vertically upward to form the modified layers radially, so that the cracks formed by the modified layers are formed vertically. With the above, the boundary processing step in this embodiment 4-1 is completed. The processing of the boundary processing step for the radial boundary 162 may be performed before the processing of the boundary processing step for the annular boundaries 161a to 161d is performed.

[0100] (Correlation threshold generation step, energy and pulse interval setting step) In this embodiment 4-1, the correlation threshold generating step and the energy and pulse interval setting step are performed in the same manner as in the above-mentioned embodiments 1 to 3. The procedure of the correlation threshold generating step and the energy and pulse interval setting step performed here is the same as in the above-mentioned embodiment 1, so detailed explanations are omitted, but it is preferable to perform them before performing the processing by the above-mentioned boundary processing step.

[0101] (stratum corneum formation step, peeling step) After the above-mentioned setting step, boundary processing step, and energy and pulse interval setting step are performed, the first laser beam LB1 is irradiated to the processing target region W4Ab of the first wafer W4A according to the processing conditions (laser processing conditions 4) set based on the energy and pulse interval setting step, and a stratum corneum 180 is formed on the surface of the first wafer W4A as shown in FIG. 15(b). At this time, the irradiation of the first laser beam LB1 is started from the outer peripheral end side of the first wafer W4A, and the focusing point of the first laser beam LB1 is gradually moved as shown by the arrow R2 in the figure by operating the above-mentioned moving means 4 and the rotary driving means of the chuck table 35, and the entire annular region from the outer peripheral end of the first wafer W4A to the above-mentioned boundary 161d is scanned to form the stratum corneum 180. The thickness of the stratum corneum 180 formed at this time is, for example, 200 μm.

[0102] By carrying out the above-mentioned stratum corneum formation step, the stratum corneum 180 is formed over the entire area of ​​the planned processing area W4Ab. In the area where the stratum corneum 180 is formed, stress acts on the adhesive surface between the first wafer W4A and the second wafer W4B, and as shown by arrow R3 in Figure 15(c), a peeling step progresses in which the first wafer W4A is peeled off from the second wafer W4B. The planned processing area W4Ab where the stratum corneum 180 has been formed is peeled off from the second wafer W4B with fractures 179 formed starting from each crack (including each crack formed corresponding to the boundary 162 described above). If the region to be processed W4Ab on which the stratum corneum 180 is formed is not completely removed from the state shown in Fig. 15(c), it can be completely removed by spraying a fluid such as high-pressure air or high-pressure water against the upper surface of the outer periphery region of the first wafer W4A or the bonding surface with the second wafer W4B, or by carrying out a well-known grinding or polishing process. By carrying out the above-mentioned stratum corneum forming step and peeling step, the outer periphery of the first wafer W4A is removed (edge ​​trimmed) as shown in Fig. 15(d), and the desired shape can be obtained.

[0103] In the above-mentioned Example 4-1, in the processing of the boundaries 161a to 161d and 162 by the boundary processing step, the modified layer and cracks are formed using the third laser beam LB3, but the present invention is not limited thereto. For example, the above-mentioned boundaries 161a to 161d and 162 can be irradiated with the second laser beam LB2 according to the laser processing condition 1 to form a laser processing groove, or the third laser beam LB3 can be irradiated to form a modified layer and cracks along a direction perpendicular to the substrate surface, or a cutting means having a rotatable cutting blade can be used to form a cutting groove. Furthermore, the boundaries 161a to 161d and the boundary 162 can be processed by combining the second laser beam LB2, the third laser beam LB3, and a cutting means including a rotatable cutting blade. For example, in the boundary processing step for the annular boundaries 161a to 161d, a modified layer and cracks are formed by the third laser beam LB3, and in the boundary processing step for the radial boundary 162, a laser processed groove is formed using the above-mentioned second laser beam LB2, or a cutting groove is formed by cutting means equipped with a rotatable cutting blade.

[0104] According to the processing method shown in the above-mentioned Example 4-1, it is possible to form the stratum corneum 180 that makes it easy to peel off the processing target area W4Ab while suppressing the generation of debris. Furthermore, since the stratum corneum 180 peeled off in the peeling step is restricted by the cracks (or grooves) formed by the boundary processing step, it is possible to precisely control the area where the stratum corneum 180 is peeled off, and the problem of peeling extending to an undesired area, for example, the central area W4Aa, is eliminated. In particular, in this Example 4-1, a plurality of annular modified layers 171, 173, 175, 177 are formed by the third laser beam LB3 on the deep side of the first wafer W4A, and inclined cracks 172, 174, 176, 178 are formed, so that the peeling of the processing target area W4Ab set on the outer periphery side of the first wafer W4A is well and precisely controlled, and the outer periphery of the first wafer W4A is easily removed (edge ​​trimmed).

[0105] (Example 4-2) The processing method for peeling off and removing the outer periphery of the wafer W4 (a laminated wafer in which a first wafer W4A and a second wafer W4B are stacked and bonded via an oxide film) shown in FIG. 14 (so-called edge trimming) according to the present invention is not limited to the form of the processing method described based on Example 4-1 above, and may be carried out by the processing method of Example 4-2 described below.

[0106] (Setup Step) The setting steps in this embodiment 4-2 are performed in the same procedure as the setting steps in the above-described embodiment 4-1 (detailed description will be omitted).

[0107] (Correlation threshold generation step, energy and pulse interval setting step) In this embodiment 4-2, the correlation threshold generating step and the energy and pulse interval setting step are performed in the same manner as in the above-mentioned embodiments 1 to 3 and 4-1. Note that the procedure of the correlation threshold generating step and the energy and pulse interval setting step performed here is the same as that in the above-mentioned embodiment 1, so detailed explanations are omitted.

[0108] (Boundary processing step, stratum corneum formation step, peeling step) As in the above-mentioned Example 4-1, a boundary for dividing the processing area W4Ab into a plurality of areas and a boundary for dividing the processing area W4Ab from other areas (the above-mentioned central area W4Aa) are set based on the position information of the processing area W4Ab set by the setting step. As described based on Fig. 14, the boundaries in this Example 4-2 are set in the annular processing area W4Ab surrounding the central area W4Aa where the stratum corneum is not formed, with concentric boundaries 161a, 161b, 161c, 161d having different diameters being set at equal intervals from the outer peripheral end side, and further, in the annular processing area W4Ab, a plurality of radial boundaries 162 for dividing the processing area W4Ab into a plurality of areas are set at equal intervals of 30°.

[0109] The annular boundaries 161a, 161b, 161c and the multiple radial boundaries 162 are boundaries that divide the region to be processed W4Ab into multiple regions, and the boundary 161d is a boundary that divides the region to be processed W4Ab from a central region W4Aa, which is the other region where the stratum corneum is not formed. Position information regarding each of these boundaries is stored in the control means 9 of the laser processing device 1.

[0110] In this embodiment 4-2, processing of a plurality of radial boundaries 162 that divide the processing target area W4Ab into a plurality of regions is performed before processing of the annular boundaries 161a to 161d. Processing of the boundary 162 is performed by the same procedure as processing of the boundary 162 described in the above embodiment 4-1, and a focus point of the third laser beam LB3 having transparency to the first wafer W4A is positioned inside the boundary 162 and irradiated, and a plurality of modified layers and cracks are formed along the boundary 162 by operating the moving means 4 and the rotation driving means of the chuck table 35 (not shown). When forming modified layers and cracks inside the radial boundaries 162, a position for positioning the focus point is moved vertically upward to form a plurality of modified layers radially, and the cracks formed to connect the modified layers are formed vertically.

[0111] This Example 4-2 is different from Example 4-1 in that processing of the annular boundaries 161a to 161d in a boundary processing step, processing in a stratum corneum forming step, and a peeling step are performed alternately. This will be described in more detail below.

[0112] As described above, when the modified layer and cracks are formed inside the radial boundary 162, as shown in Fig. 16(a), the focal point of the third laser beam LB3 is positioned inside the position corresponding to the outermost boundary 161a set on the first wafer W4A and irradiated, and the rotation drive means of the chuck table 35 is operated to gradually raise the focal point of the third laser beam LB3 and move it toward the center of the wafer W4 (in the direction indicated by the arrow R4) to form the modified layers 171 at a plurality of different depth positions, thereby forming a plurality of modified layers 171 (for example, three) in an inclined shape. As a result, as can be seen from Fig. 16(a), cracks 172 connecting the modified layers 171 are formed, and the cracks 172 are inclined toward the inside of the first wafer W4A. The process for forming the modified layer 171 and the cracks 172 is the same as the process for forming the modified layer 171 and the cracks 172 in the above-mentioned Example 4-1.

[0113] When the modified layer 171 and the cracks 172 are formed inside the position corresponding to the outermost boundary 161a, the stratum corneum forming step and the peeling step are performed as described below. When performing this stratum corneum forming step, the condensation point of the first laser beam LB1 is positioned on the outer periphery side of the annular boundary 161a (the region where the modified layer 171 and the cracks 172 are formed) in the processing target region W4Ab based on the processing conditions (for example, the above-mentioned laser processing condition 4) set based on the above-mentioned energy and pulse interval setting step, and irradiation is started, and the rotation drive means of the chuck table 35 is operated to rotate the wafer W4, and the condensation point is gradually moved toward the center of the wafer W4 (in the direction indicated by the arrow R5 in the figure) to the position corresponding to the boundary 161a, as shown in FIG. 16(b). As a result, the stratum corneum forming step is partially performed, and the stratum corneum 180 is formed in an annular shape from the outermost periphery of the first wafer W4A to the region reaching the boundary 161a. The thickness of the stratum corneum 180 thus formed is, for example, 200 μm.

[0114] As a result of the formation of the stratum corneum 180 as described above, stress acts on the adhesive surface between the first wafer W4A and the second wafer W4B in the area where the stratum corneum 180 is formed outside the boundary 161a, forming a fracture 179, and a peeling step progresses in which the area where the stratum corneum 180 is formed is partially peeled off from the second wafer W4B, as shown by arrow R6 in Figure 16(b).

[0115] As described above, after the stratum corneum formation step and the peeling step are performed in the region corresponding to the boundary 161a and peeled off, as shown in FIG. 16(c), the focal point of the third laser beam LB3 is positioned and irradiated inside the position corresponding to the boundary 161b set on the first wafer W4A again, and the rotation drive means of the chuck table 35 is operated to rotate the wafer W4. Then, in order to form the modified layers 173 at a plurality of different depth positions, the focal point of the third laser beam LB3 is gradually raised and moved toward the center of the wafer W4 (in the direction indicated by the arrow R7 in the figure), and a boundary processing step is performed to form a plurality of modified layers 173 (for example, three) in an inclined shape. As a result, as can be seen from FIG. 16(c), cracks 174 connecting the modified layers 173 are formed, and the cracks 174 are inclined toward the inside of the first wafer W4A. The process for forming the modified layer 173 and the cracks 174 is the same as the process for forming the modified layer 173 and the cracks 174 in the above-mentioned Example 4-1.

[0116] Next, based on the processing conditions (e.g., laser processing condition 4) set based on the energy and pulse interval setting step described above, as shown in Fig. 16(d), the focal point of the first laser beam LB1 is positioned at a position adjacent to the area where the stratum corneum 180 was previously formed, which is an area on the outer periphery side of the area where the modified layer 173 and cracks 174 were formed in the to-be-processed area W4Ab, and irradiation is started, and the rotation drive means of the chuck table 35 is operated to rotate the wafer W4, and the focal point is moved in the direction indicated by the arrow R8 to the position where the modified layer 173 was formed. As a result, a stratum corneum formation step is performed in which the stratum corneum 180 is formed annularly between the boundary 161a and the boundary 161b, as shown in Fig. 16(d). Furthermore, as the stratum corneum 180 is formed, stress acts on the adhesive surface between the first wafer W4A and the second wafer W4B, even in the area where the new stratum corneum 180 has been formed, forming a fracture 179 along the crack 174, and the first wafer W4A is peeled off from the second wafer W4B as shown by the arrow R3 in Figure 16(d) (peeling step).

[0117] Although not shown in the figures, following the above-mentioned processing, a stratum corneum forming step is carried out in which a processing similar to the above-mentioned boundary processing step is carried out inside a position corresponding to boundary 161c to form a modified layer and cracks, and a stratum corneum 180 is formed in the region between boundaries 161b and 161c, and then a stratum corneum forming step is carried out in which a processing similar to the above-mentioned boundary processing step is carried out inside a position corresponding to boundary 161d to form a modified layer and cracks, and a stratum corneum 180 is formed in the region between boundaries 161c and 161d. As a result, as shown in Fig. 16(e), fractures 179 are formed in the regions corresponding to the cracks, and the entire region corresponding to the region to be processed W4Ab of the first wafer W4A is peeled off from the second wafer W4B by the boundary processing step as shown by arrow R3 (the state becomes the same as that of the wafer W4 shown in Fig. 15(c)).

[0118] As shown in Fig. 16(e), after the entire area of ​​the area corresponding to the processing area W4Ab of the first wafer W4 is peeled off from the second wafer W4B, if the area where the stratum corneum 180 is formed (processing area W4Ab) is not completely removed from the first wafer W4A, it can be completely removed by spraying a fluid such as high-pressure air or high-pressure water onto the first wafer W4A or by carrying out a well-known grinding or polishing process, as in the above-mentioned Example 4-1. As a result, as explained based on Fig. 15(d), the outer periphery of the first wafer W4A is removed (edge ​​trimmed) to give a desired shape.

[0119] The laser beam application means 7 used in the present invention is not limited to the form described based on Fig. 1(b). For example, instead of the laser beam application means 7 arranged in the laser processing apparatus 1 shown in Fig. 1, a laser beam application means 80 of another form shown in Fig. 17 may be provided. The illustrated laser beam application means 80 includes an oscillator 82 that oscillates a pulsed laser beam LB, an X-axis galvano scanner 83 that oscillates the laser beam LB oscillated by the oscillator 82 in the X-axis direction, a Y-axis galvano scanner 84 that oscillates the laser beam LB in the Y-axis direction, and a condenser 81 including an fθ lens 85 that irradiates the laser beam LB oscillated in the X-axis direction and the Y-axis direction at a desired position of the wafer W4 held on the chuck table 35.

[0120] The X-axis galvanometer scanner 83 and the Y-axis galvanometer scanner 84 are configured in a known manner including a mirror (not shown) and an angle adjustment actuator for adjusting the reflection angle of the mirror. The fθ lens 85 irradiates the wafer W4 perpendicularly with the laser beam LB oscillated in the X-axis direction and the Y-axis direction by the action of the X-axis galvanometer scanner 83 and the Y-axis galvanometer scanner 84. The X-axis galvanometer scanner 83 and the Y-axis galvanometer scanner 84 in this embodiment function as a substitute for the moving means 4 of the laser processing apparatus 1 described above.

[0121] The oscillator 82, the X-axis galvano scanner 83, and the Y-axis galvano scanner 84 are controlled by the control means 9 of the laser processing apparatus 1. The laser beam LB oscillated by the oscillator 82 of the laser beam application means 80 is oscillated in the X-axis and Y-axis directions by the X-axis galvano scanner 83 and the Y-axis galvano scanner 84 and guided to the fθ lens 85, and then irradiated via the fθ lens 85 onto a desired position of the wafer W4 held on the chuck table 35. The laser beam application means is not limited to the galvano scanner described above, and may be configured using, for example, a polygon mirror, an acousto-optical element, an electro-optical element, or the like.

[0122] The above-mentioned laser beam application means 80 can be used to carry out the processing method for the above-mentioned Examples 1 to 3, 4-1, and 4-2. In particular, the laser beam application means 80 can apply the laser beam LB to any position, and is suitable for carrying out laser processing on the annular processing target area W4Ab set on the wafer W4, which is the laminated wafer described above. In addition, when the size of the area where optical scanning is possible with the laser beam application means 80 is narrower than the size of the processing target area, processing may be performed on the wafer W4 while moving the X-axis moving means 4a and the Y-axis moving means 4b in addition to the optical scanning by the laser beam application means 80.

[0123] In each of the above-mentioned embodiments, the case where the workpiece wafer is a silicon (Si) wafer has been described, but the present invention is not limited to this, and the present invention can be implemented in the same manner as in the above-mentioned embodiments 1 to 3, 4-1, and 4-2 for plate-shaped workpieces made of other materials, such as SiC substrates, GaN substrates, sapphire substrates, etc., by appropriately performing the correlation threshold generation step and energy and pulse interval setting steps of the present invention. When a laser beam is irradiated to the area to be processed to form a stratum corneum, and the stratum corneum is peeled off and removed from the workpiece, the area to be peeled off can be controlled by forming the stratum corneum so that it is peeled off in the intended area.

[0124] The anti-reflection film described in the above-mentioned Example 1 is not limited to being used in the form of Example 1, but can be used in any of the forms of Examples 2, 3, 4-1, and 4-2 described above, and can obtain the same effect as that of Example 1. [Explanation of symbols]

[0125] 1: Laser irradiation device 2: Base 3: Holding means 31:X-axis movable plate 32: Y-axis direction movable plate 33: Strut 34: Cover plate 35: Chuck table 36: Suction 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: Alignment method 7: Laser beam irradiation means 71: Concentrator 72: Oscillator 73: Reflective mirror 74: Condenser lens 8:Display means 9: Control means 80: Laser beam irradiation means 81: Concentrator 82: Oscillator 83: X-axis galvanometer scanner 84: Y-axis galvanometer scanner 85: fθ lens 100: Area to be processed 102: Boundary 104: Laser processed groove 110: Modified layer 112: Crack 113: Modified layer 114: Crack 120: stratum corneum 122: Interface 130: Area to be processed 132: Boundary 140: Area to be processed 142: Boundary 144: Laser processed groove 150: stratum corneum 161a-161d: Boundary (circular) 162: Boundary (radial) 171, 173, 175, 177: Modified layer 172, 174, 176, 178: Crack 179: Fracture 180: stratum corneum LB1: First laser beam LB2: Second laser beam LB3: The third laser beam LB4: The fourth laser beam W1, W2, W3: Wafer W2m: Marking W4: Wafer (stacked wafer) W4A: First wafer W4Aa: Central area W4Ab: Area to be processed W4B: Second wafer Wd: dummy wafer

Claims

1. A method for processing a workpiece, comprising the steps of: A setting step for setting a processing area; a boundary processing step of processing a boundary that divides the processing target area into a plurality of areas or a boundary that divides the processing target area from other areas; a correlation threshold generating step of generating a correlation threshold based on a correlation between an energy per pulse of a first laser beam that forms a stratum corneum in the processing target area and a pulse interval; an energy and pulse interval setting step of setting the energy per pulse of the first laser beam to be equal to or higher than the correlation threshold value and setting the pulse interval of the first laser beam to be equal to or lower than the correlation threshold value; a stratum corneum forming step of irradiating the first laser beam to the processing target area to form a stratum corneum after the setting step, the boundary processing step, and the energy and pulse interval setting step are performed; A peeling step of peeling the stratum corneum from the workpiece; A method for processing a workpiece comprising the steps of:

2. 2. The method for processing a workpiece according to claim 1, wherein said boundary processing step comprises irradiating said workpiece with a second laser beam having a wavelength which is absorbed by said workpiece, thereby forming a groove at said boundary of said workpiece.

3. 3. The method for processing a workpiece as described in claim 1 or 2, wherein the boundary processing step comprises irradiating the workpiece with a third laser beam having a wavelength that is transparent to the workpiece, thereby forming a modified layer and a crack extending from the modified layer within the workpiece corresponding to the boundary.

4. 3. The method for processing a workpiece as described in claim 1 or 2, wherein the boundary processing step includes positioning a focal point of a fourth laser beam having a wavelength that is transparent to the workpiece at a position corresponding to the boundary of the workpiece and at a depth from the one surface corresponding to the thickness at which the stratum corneum is to be formed, and irradiating the fourth laser beam onto the workpiece to form the crack extending along the surface direction of the workpiece.

5. 4. The method for processing a workpiece as described in claim 3, wherein the boundary processing step includes positioning a focal point of a fourth laser beam having a wavelength that is transparent to the workpiece at a position corresponding to the boundary of the workpiece and at a depth from the one surface equivalent to the thickness at which the stratum corneum is to be formed, and irradiating the fourth laser beam onto the workpiece to form the crack extending in the surface direction of the workpiece.

6. The method for processing a workpiece as described in claim 1, wherein the stratum corneum is produced by a chain reaction of compressive plastic strain caused by large thermal stress that rapidly expands the local area of ​​the workpiece irradiated with the laser beam, and the large thermal stress is restrained by the low-temperature surrounding area and exceeds the yield stress of the workpiece.

7. The correlation threshold is determined by an approximation, where the horizontal axis represents the pulse interval (μs) and the vertical axis represents the energy per pulse (μJ), and the approximation is expressed as follows: Energy per pulse = a {b - (pulse interval / μs-c) ２ } 2. The method for machining a workpiece according to claim 1, wherein the coefficients a, b, and c are set depending on the type of the workpiece.

8. When the workpiece is silicon (Si), a=4, b=1, c=0.9 and the approximation is set to Energy per pulse = 4 {1 - (pulse interval / μs - 0.9) ２ } 8. The method for machining a workpiece according to claim 7, wherein the pulse interval is set in the range of 0.02 μs to 0.8 μs.

9. 2. The method for processing a workpiece according to claim 1, wherein the irradiation pitch of the laser beam used in the stratum corneum forming step is set to 10 to 200 nm.

10. 2. The method for processing a workpiece according to claim 1, wherein the pulse width of the laser beam is set in the range of 0.3 to 100 ps.

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