Laser processing method

Abstract

A laser processing method is provided, which can prevent the generation of a notch at the corner of a device chip. The laser processing method includes the following steps: a first modified layer forming step, forming a modified layer (16) inside a plurality of first predetermined splitting lines (4a) extending along a first direction (D1); and a second modified layer forming step, forming a modified layer (22) inside a plurality of second predetermined splitting lines (4b) extending along a second direction (D2) intersecting the first direction (D1). In the second modified layer forming step, a laser beam (LB) is irradiated from a central area (18) of the second predetermined splitting lines (4b) limited by an intersection (C1) of the second predetermined splitting lines (4b) and the first predetermined splitting lines (4a) on which the modified layer (16) has been formed, and an adjacent intersection (C2) to form a modified layer (22).

Description

Technical Field

[0001] The present invention relates to a laser processing method, in which the laser beam is irradiated to the chip by positioning the focal point of the laser beam of a wavelength that is transparent to the chip inside the predetermined splitting line, thereby forming a modified layer inside the predetermined splitting line as a starting point for splitting the chip into chips. Background Art

[0002] A wafer having a plurality of devices such as IC and LSI formed on the front side thereof is divided by a plurality of first predetermined dividing lines extending along a first direction and a plurality of second predetermined dividing lines extending along a second direction intersecting the first direction, and is divided into individual device chips by a cutting device and a laser processing device. The device chips obtained by division are used in electronic devices such as mobile phones and personal computers.

[0003] The laser processing device is constructed to include: a holding member that holds a chip; a laser beam irradiation member that positions the focal point of a laser beam of a wavelength that is transmissive to the chip held by the holding member inside the first and second predetermined splitting lines and irradiates the chip with the laser beam, thereby forming a modified layer inside the first and second predetermined splitting lines as a starting point for splitting the chip into device chips; a feeding member that feeds the holding member and the laser beam irradiation member relative to each other; a photographing member that photographs through the chip; and a control member. The laser processing device is capable of splitting the chip with high precision (for example, refer to patent document 1).

[0004] Patent Document 1: Japanese Patent No. 3408805

[0005] However, after the modified layer is formed inside the first predetermined splitting line, when the modified layer is formed inside the second predetermined splitting line, there is a problem of notches being generated at the corners of the device chip. Specifically, among the corners of the device chip, notches are often generated at the corners of the chip located on the upstream side of the moving direction of the focal point of the laser light along the second predetermined splitting line.

[0006] In particular, the above-mentioned problem is likely to occur when a protective member is disposed on the front surface of the wafer, the back surface of the wafer is ground with a grinding wheel to thin the wafer, and the wafer is divided into individual device chips along the reformed layer. Summary of the invention

[0007] The present invention has been made in view of the above circumstances and aims to provide a laser processing method capable of preventing chipping from occurring at the corner of a device chip.

[0008] The present invention provides the following laser processing method to solve the above-mentioned problems. That is, the present invention provides a laser processing method, which positions the focal point of a laser beam of a wavelength that is transparent to a wafer inside a predetermined splitting line and irradiates the wafer with the laser beam, so as to form a modified layer inside the predetermined splitting line as a starting point for splitting the wafer into chips, wherein the laser processing method includes the following steps: a first modified layer forming step, forming a modified layer inside a plurality of first predetermined splitting lines extending along a first direction; and a second modified layer forming step, forming a modified layer inside a plurality of second predetermined splitting lines extending along a second direction intersecting the first direction, in which the laser beam is irradiated from the central area of ​​the second predetermined splitting line limited by the intersection of the second predetermined splitting line and the first predetermined splitting line on which the modified layer has been formed and the adjacent intersection to form the modified layer.

[0009] The laser processing method of the present invention includes the following steps: a first modified layer forming step, forming a modified layer inside a plurality of first predetermined splitting lines extending along a first direction; and a second modified layer forming step, forming a modified layer inside a plurality of second predetermined splitting lines extending along a second direction intersecting the first direction. In the second modified layer forming step, laser light is irradiated from a central area of ​​the second predetermined splitting lines limited by the intersection points of the second predetermined splitting lines and the first predetermined splitting lines on which the modified layer has been formed and adjacent intersection points to the vicinity of each intersection point to form a modified layer. Therefore, when the modified layer is formed inside the second predetermined splitting lines, the laser light will not irradiate the modified layer formed inside the first predetermined splitting lines, thereby preventing the formation of notches at the corners of the device chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 (a) is a three-dimensional image of a chip with adhesive tape attached to the back side. Figure 1 (b) is a three-dimensional image of a chip with an adhesive tape attached to the front side.

[0011] Figure 2 (a) is a perspective view showing a state where the first modified layer forming step is performed with the front side of the wafer facing upward, Figure 2 (b) is a cross-sectional view showing a state in which the first reforming layer forming step is performed with the front side of the wafer facing upward.

[0012] Figure 3 This is a perspective view showing a state in which the first reforming layer forming step is performed with the back surface of the wafer facing upward.

[0013] Figure 4 It is a partial top view of the wafer showing the trajectory of the focal point of the laser beam in the second reforming layer forming step.

[0014] Figure 5(a) is a partial top view of the wafer showing the trajectory of the focal point of the laser light moving from the central area of ​​the second predetermined dividing line limited between adjacent intersections toward one side of the second direction in the second modified layer forming step, Figure 5 (b) is a partial top view of the chip showing the trajectory of the focal point of the laser light moving from the central area of ​​the second predetermined dividing line limited between adjacent intersections toward the other side in the second direction in the second modified layer forming step.

[0015] Figure 6 It is a perspective view showing a state where a dividing step is performed.

[0016] Figure 7 This is a perspective view showing a state where a wafer is divided into individual device chips along the reformed layer.

[0017] Description of symbols

[0018] 2: chip; 2a: front side of chip; 2b: back side of chip; 4: predetermined dividing line; 4a: first predetermined dividing line; 4b: second predetermined dividing line; 16: modified layer formed inside the first predetermined dividing line; 18: central area; 22: modified layer formed inside the second predetermined dividing line; 22a: modified layer extending from the starting position to the vicinity of intersection C1; 22b: modified layer extending from the starting position to the vicinity of intersection C2; D1: first direction; D2: second direction; LB: pulsed laser light; FP: focal point; C1, C2: intersections. DETAILED DESCRIPTION

[0019] Hereinafter, preferred embodiments of the laser processing method of the present invention will be described with reference to the accompanying drawings.

[0020] exist Figure 1 2 shows a disk-shaped wafer 2 processed by the laser processing method of the present invention. The wafer 2 can be formed of silicon or the like. The front side 2a of the wafer 2 is divided into a plurality of rectangular areas by a grid-shaped predetermined splitting line 4, and a plurality of devices 6 such as ICs and LSIs are formed in the plurality of rectangular areas. The grid-shaped predetermined splitting line 4 has a plurality of first predetermined splitting lines 4a extending along a first direction D1 and a plurality of second predetermined splitting lines 4b extending along a second direction D2 intersecting the first direction D1. In addition, the first predetermined splitting lines 4a of the illustrated embodiment are perpendicular to the second predetermined splitting lines 4b.

[0021] The wafer 2 is attached to the adhesive tape 10 whose periphery is fixed to the ring frame 8, and is supported by the ring frame 8 via the adhesive tape 10. Figure 1 As shown in (a), the back side 2b of the wafer 2 may be attached to the adhesive tape 10, or as Figure 1 As shown in (b), the front side 2a of the wafer 2 can be attached to the adhesive tape 10.

[0022] In the laser processing method of the illustrated embodiment, first, a first modified layer forming step is performed to form a modified layer inside a plurality of first planned dividing lines 4a extending along the first direction D1. The first modified layer forming step can be performed, for example, in Figure 2 The laser processing device 12 partially shown in FIG.

[0023] like Figure 2 As shown, the laser processing device 12 includes: a chuck worktable (not shown), which attracts and holds the chip 2; a condenser 14, which irradiates a pulsed laser beam LB with a wavelength that is transparent to the chip 2 attracted and held by the chuck worktable; and a shooting component (not shown), which shoots the chip 2 attracted and held by the chuck worktable.

[0024] The chuck table for sucking and holding the wafer 2 on the upper surface is configured to be rotatable around an axis extending in the vertical direction, and is configured to be Figure 2 The X-axis direction indicated by the arrow X in (a) and the Y-axis direction perpendicular to the X-axis direction ( Figure 2 The condenser 14 includes a condenser lens (not shown) for condensing the pulsed laser beam LB oscillated by the pulsed laser beam oscillator (not shown) of the laser processing device 12 and irradiating it to the wafer 2. The imaging component includes: a conventional imaging element (CCD) that uses visible light to image the wafer 2; an infrared irradiation component that irradiates infrared light to the wafer 2; an optical system that captures the infrared light irradiated by the infrared irradiation component; and an imaging element (infrared CCD) that outputs an electrical signal corresponding to the infrared light captured by the optical system. In addition, the XY plane defined by the X-axis direction and the Y-axis direction is substantially horizontal.

[0025] Reference Figure 2 Continuing with (a), in the first modified layer forming step, first, the wafer 2 is placed on the upper side and the adhesive tape 10 is placed on the lower side, and the wafer 2 is sucked and held by the upper surface of the chuck table. Next, the wafer 2 is photographed from above by a photographing member, and based on the image of the wafer 2 photographed by the photographing member, the first predetermined splitting line 4a is aligned with the X-axis direction, and the first predetermined splitting line 4a aligned with the X-axis direction is positioned below the condenser 14.

[0026] Next, the condenser 14 is raised and lowered by a light-converging point position adjustment member (not shown) of the laser processing device 12, and the light-converging point FP is positioned inside the first predetermined dividing line 4a. Next, while the chuck table is relatively processed and fed along the X-axis direction at a predetermined feed speed relative to the condenser 14, a pulsed laser beam LB having a wavelength that is transparent to the wafer 2 is irradiated from the condenser 14, thereby forming a modified layer 16 having a smaller intensity than the surrounding area inside the wafer 2 along the first predetermined dividing line 4a.

[0027] Next, the chuck table is indexed and fed relative to the condenser 14 in the Y-axis direction by an amount corresponding to the interval in the Y-axis direction of the first predetermined dividing line 4a. Then, by alternately repeating the irradiation of the pulsed laser beam LB and the indexing and feeding, a modified layer 16 is formed inside the wafer 2 along all the first predetermined dividing lines 4a that coincide with the X-axis direction.

[0028] exist Figure 2 In the example shown, in the first modified layer forming step, the pulsed laser beam LB is irradiated to the wafer 2 from the front surface 2a side of the wafer 2. Figure 3 As shown, the pulsed laser beam LB may also be irradiated to the wafer 2 from the back side 2b of the wafer 2. As described above, the imaging component of the laser processing device 12 includes an infrared irradiation component, an optical system for capturing infrared rays, and an imaging element (infrared CCD) that outputs an electrical signal corresponding to the infrared rays. Therefore, even when the back side 2b of the wafer 2 faces upward, the predetermined dividing line 4 on the front side 2a of the wafer 2 can be photographed from above the back side 2b of the wafer 2.

[0029] After the first reforming layer forming step is performed, a second reforming layer forming step is performed to form a reforming layer inside the plurality of second planned dividing lines 4b extending in the second direction D2 intersecting the first direction D1. The second reforming layer forming step can also be performed using the laser processing device 12 described above.

[0030] In the second modified layer forming step, first, the chuck table that attracts and holds the wafer 2 is rotated 90 degrees. Next, based on the image of the wafer 2 captured in the first modified layer forming step, the second predetermined splitting line 4b is aligned with the X-axis direction, and the second predetermined splitting line 4b aligned with the X-axis direction is positioned below the condenser 14.

[0031] Next, the focusing point FP is positioned inside the second planned splitting line 4b and in the central area of ​​the second planned splitting line 4b limited by the intersection of the second planned splitting line 4b and the first planned splitting line 4a on which the reformed layer 16 has been formed and the adjacent intersection.

[0032] Reference Figure 4For illustration, the intersection of the second predetermined dividing line 4b and the first predetermined dividing line 4a on which the modified layer 16 has been formed is, for example, the intersection indicated by the reference numeral C1, and the intersection adjacent to the intersection C1 is the intersection adjacent in the second direction D2, for example, the intersection indicated by the reference numeral C2. Figure 4 As shown in the middle mark 18, the central area of ​​the second predetermined dividing line 4b limited by the intersection C1 and the intersection C2 refers to an area equivalent to the length of one side of the device 6. In the illustrated embodiment, the focal point FP is positioned at an arbitrary starting position 20 in the central area 18. In addition, the starting position 20 may not be the middle position of the central area 18, and may also be biased towards any intersection.

[0033] Next, from the starting position 20 to the vicinity of the intersection C1, while the chuck table is relatively processed and fed in the X-axis direction at a predetermined feed speed relative to the condenser 14, a pulsed laser beam LB having a wavelength that is transparent to the wafer 2 is irradiated from the condenser 14, thereby forming a modified layer 22a inside the wafer 2 along the second predetermined splitting line 4b. The front end of the modified layer 22a (the end on the opposite side of the starting position 20) is not connected to the modified layer 16 of the first predetermined splitting line 4a, and there is a region where the modified layer is not formed between the front end of the modified layer 22a and the modified layer 16. That is, when the modified layer 22a is formed, the pulsed laser beam LB will not irradiate the modified layer 16.

[0034] Next, the chuck table is moved to position the focal point FP at the starting position 20 again. Then, from the starting position 20 to the vicinity of the intersection C2, while the chuck table is relatively processed and fed in the X-axis direction at a predetermined feed speed relative to the condenser 14, a pulsed laser beam LB having a wavelength that is transparent to the wafer 2 is irradiated from the condenser 14, thereby forming a modified layer 22b inside the wafer 2 along the second planned dividing line 4b. The front end of the modified layer 22b is not connected to the modified layer 16, and there is a region where the modified layer is not formed between the front end of the modified layer 22b and the modified layer 16. When forming the modified layer 22b, the pulsed laser beam LB will not irradiate the modified layer 16, just like when forming the modified layer 22a.

[0035] In this way, the pulsed laser beam LB is irradiated from the central area 18 of the second predetermined dividing line 4b limited by the intersection C1 and the intersection C2 to the vicinity of each intersection C1 and C2, forming a modified layer 22 having a modified layer 22a extending from the starting position 20 to the vicinity of the intersection C1 and a modified layer 22b extending from the starting position 20 to the vicinity of the intersection C2. In addition, the properties of the modified layer 22 are substantially the same as those of the modified layer 16, and the strength of the modified layer 22 is smaller than the strength of the surrounding.

[0036] Next, in the second predetermined division line 4b where the focal point FP is initially positioned, the modified layer 22 is sequentially formed in each area limited by the adjacent intersections and the intersections. Then, indexing is performed, and the modified layer 22 is formed inside the wafer 2 along all the second predetermined division lines 4b that coincide with the X-axis direction. Thus, the modified layers 16, 22 that serve as the starting point for dividing the wafer 2 into chips of each device 6 can be formed inside the wafer 2 along the predetermined division lines 4.

[0037] In the second modified layer forming step, the modified layer 22 may be sequentially formed in each region of the second predetermined dividing line 4b limited by adjacent intersections and intersections as described above, but the pulsed laser beam LB may be intermittently irradiated while the focal point FP is relatively moved from one end to the other end of the second predetermined dividing line 4b. Alternatively, Figure 5 As shown in (a), by alternately setting the irradiation interval and the non-irradiation interval of the pulse laser light LB on the second predetermined dividing line 4b, a region extending from the starting position 20 to the predetermined dividing line 4b is formed in each region of the second predetermined dividing line 4b limited by adjacent intersections and intersections. Figure 5 The modified layer 22a extending to the right side of Figure 5 As shown in (b), a flow from the starting position 20 to Figure 5 The modified layer 22b extends to the left side.

[0038] The above-mentioned first / second reformed layer forming step can be performed, for example, under the following processing conditions.

[0039] Wavelength of pulsed laser light: 1342nm

[0040] Repetition frequency: 90kHz

[0041] Average output: 1.2W

[0042] Feed speed: 700mm / s

[0043] After the second modified layer forming step is performed, the adhesive tape 10 may be expanded to divide the wafer 2 into device chips. However, in the present embodiment, the following dividing step is performed: a protective member is provided on the front surface 2a of the wafer 2, the back surface 2b of the wafer 2 is ground with a grinding wheel to thin the wafer 2, and the wafer 2 is divided into chips of each device 6 along the modified layers 16 and 22. The dividing step can be performed, for example, Figure 6 The grinding device 24 is implemented by using a grinding device 24 partially shown in FIG. The grinding device 24 includes a chuck table 26 for holding the wafer 2 by suction, and a grinding member 28 for grinding the wafer 2 held by the chuck table 26 by suction.

[0044] The chuck table 26 for sucking and holding the wafer 2 on the upper surface is configured to be rotatable around an axis extending in the vertical direction. The grinding member 28 includes a spindle 30 extending in the vertical direction and a disc-shaped wheel mounting seat 32 fixed to the lower end of the spindle 30. An annular grinding wheel 36 is fixed to the lower surface of the wheel mounting seat 32 by bolts 34. A plurality of grinding tools 38 arranged in an annular shape at intervals in the circumferential direction are fixed to the outer peripheral edge of the lower surface of the grinding wheel 36.

[0045] In the separation process, first, the protection member 40 for protecting the device 6 is arranged on the front side 2a of the wafer 2. Figure 6 As shown, the back side 2b of the wafer 2 is facing upward, and the wafer 2 is held by suction by the upper surface of the chuck table 26. Next, the chuck table 26 is rotated counterclockwise at a predetermined rotation speed (e.g., 300 rpm) when viewed from above. In addition, the spindle 30 is rotated counterclockwise at a predetermined rotation speed (e.g., 6000 rpm) when viewed from above. Next, the spindle 30 is lowered by the lifting member (not shown) of the grinding device 24, and after the grinding tool 38 is brought into contact with the back side 2b of the wafer 2, the spindle 30 is lowered at a predetermined grinding feed speed (e.g., 1.0 μm / s). In this way, the back side 2b of the wafer 2 can be ground and the wafer 2 can be thinned to a desired thickness.

[0046] When the wafer 2 is ground, a predetermined pressing force generated by the grinding feed acts on the wafer 2, so that cracks (not shown) are generated in the modified layers 16 and 22 formed inside the wafer 2 along the thickness direction of the wafer 2. Figure 7 As shown, the wafer 2 is divided into chips of individual devices 6 along the modified layers 16 , 22 .

[0047] As described above, in the laser processing method of the illustrated embodiment, when the modified layer 22 is formed inside the second predetermined splitting line 4b, the pulsed laser light LB does not irradiate the modified layer 16 formed inside the first predetermined splitting line 4a, thereby preventing the formation of a chip at the corner of the device chip.

Claims

1. A laser processing method, wherein the laser beam is irradiated to the wafer by positioning the focal point of a laser beam of a wavelength that is transparent to the wafer inside a predetermined dividing line, thereby forming a modified layer inside the predetermined dividing line as a starting point for dividing the wafer into chips, wherein: The laser processing method includes the following steps: a first modified layer forming step of forming a modified layer inside a plurality of first planned dividing lines extending along a first direction; and a second modified layer forming step of forming a modified layer inside a plurality of second planned dividing lines extending in a second direction intersecting the first direction, In the second modified layer forming step, in a central area of ​​the second predetermined dividing line limited by the intersection of the second predetermined dividing line and the first predetermined dividing line on which the modified layer has been formed and the adjacent intersection, the focal point is positioned at an arbitrary starting position in the central area, and from the starting position, a laser beam is irradiated toward one intersection along a second direction extending from the second predetermined dividing line until near the intersection on one side to form a modified layer, then, the focal point is positioned again at the starting position in the central area, and from the starting position, a laser beam is irradiated toward another intersection along the second direction extending from the same second predetermined dividing line until near the intersection on the other side to form a modified layer, The central region is a region corresponding to the length of one side of the device in the second direction.

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