Crack Detection Methods

Abstract

The present invention provides a crack detection method, which can easily detect whether cracks are properly formed when a modified layer is formed inside a workpiece by irradiating laser light. The crack detection method includes the following steps: a crack forming step, in which a laser light focal point having a wavelength that is transparent to a plate-shaped workpiece having a first surface and a second surface on the side opposite to the first surface is positioned inside the workpiece from the first surface and irradiated linearly, thereby forming a modified layer inside the workpiece and forming cracks extending from the modified layer to the second surface side; a coating coating step, in which a coating is coated on the second surface; and a crack detection step, in which a portion where the coating is linearly repelled is detected to detect cracks.

Description

Technical Field

[0001] The present invention relates to a crack detection method for detecting cracks formed together with a modified layer by irradiating a workpiece with laser light of a wavelength that is transparent to the workpiece. Background Art

[0002] For a chip that is divided by a plurality of intersecting predetermined dividing lines and has multiple devices such as ICs and LSIs formed on the front side, the focal point of a laser beam with a wavelength that is transparent to the chip is positioned inside the predetermined dividing lines for irradiation to form a modified layer and divide the chip into individual device chips (for example, refer to patent document 1).

[0003] In addition, the following technology has been proposed: after a modified layer is formed inside the predetermined dividing line, the front side provided with a protective tape is held on a chuck table of a grinding device, the back side of the wafer is ground to thin the wafer, and the wafer is divided into individual device chips (for example, refer to patent document 2).

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

[0005] Patent Document 2: Japanese Patent No. 4358762

[0006] In the technology described in Patent Document 2, a modified layer is formed inside along the predetermined dividing line, and cracks are formed from the modified layer to the front surface, thereby being well divided into individual device chips when thinning is performed by a grinding device. However, if cracks do not reach the surface on the side opposite to the side irradiated with laser light from the area where the modified layer is formed, it is difficult to smoothly divide the wafer into individual device chips, so when determining the laser processing conditions when forming the modified layer by the laser processing device, the laser processing conditions are adjusted so that the modified layer is formed inside the predetermined dividing line and cracks are reliably formed from the modified layer to the front surface.

[0007] The above-mentioned adjustment of the laser processing conditions needs to be implemented every time the material and thickness of the chip are changed. However, in order to confirm whether the crack is exposed from the modified layer formed inside the chip to the surface opposite to the side irradiated with the laser light, that is, whether the crack is properly formed, a microscope must be used, which leads to the problem of poor productivity. Summary of the invention

[0008] Therefore, an object of the present invention is to provide a crack detection method capable of easily detecting that a crack is appropriately formed when a modified layer is formed inside a workpiece by irradiating the workpiece with a laser beam having a wavelength that is transparent to the workpiece.

[0009] According to the present invention, a crack detection method is provided, wherein the crack detection method includes the following steps: a crack forming step, wherein a focal point of a laser beam having a wavelength that is transmissive to a plate-shaped workpiece having a first surface and a second surface on the side opposite to the first surface is positioned inside the first surface of the workpiece and linearly irradiated, thereby forming a modified layer inside the workpiece and forming a crack extending from the modified layer to the second surface; a paint coating step, wherein after the crack forming step is implemented, a paint is coated on the second surface; and a crack detection step, wherein a portion where the paint is linearly repelled is detected to detect cracks.

[0010] Preferably, an oil-based marker is used in the paint application step.

[0011] According to the present invention, whether or not a crack is properly formed can be easily confirmed without using a microscope or the like, and laser processing conditions can be quickly adjusted so that a crack is properly formed, thereby solving the problem of poor productivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a perspective view showing a manner in which a plate-shaped workpiece is placed on a chuck table of a laser processing device.

[0013] Figure 2 (a) is a perspective view showing a method of implementing a crack forming step, Figure 2 (b) is the implementation Figure 2 A partially enlarged cross-sectional view of the workpiece during the step shown in (a).

[0014] Figure 3 (a) is a perspective view showing a method of placing a workpiece on an inspection table for performing a crack detection process. Figure 3 (b) is a perspective view showing a state where the coating is applied to the second surface of the workpiece where the crack formation is insufficient. Figure 3 (c) is a perspective view showing a state where the paint is applied to the second surface of the workpiece on which cracks are fully formed.

[0015] Figure 4 This is a perspective view showing a method of attaching a protective tape to a wafer.

[0016] Figure 5 (a) is a perspective view showing an embodiment of a modified layer forming step, Figure 5 (b) is the implementation Figure 5 A partially enlarged cross-sectional view of the chip during the process shown in (a).

[0017] Figure 6 (a) is a perspective view showing a method of placing a wafer on a chuck table of a grinding device, Figure 6(b) is a perspective view showing the manner of implementing the dividing step.

[0018] Figure 7 It is a perspective view showing the method of implementing the tape replacing step.

[0019] Description of symbols

[0020] 10: chip; 10a: front side; 10b: back side; 10A: workpiece (imitation chip); 10Aa: first side; 10Ab: second side; 12: device; 14: predetermined dividing line; 16: protective tape; 20: laser processing device; 22: chuck table; 24: laser beam irradiation unit; 24a: concentrator; 30: grinding device; 32: chuck table; 34: grinding unit; 34b: grinding wheel; 34c: grinding tool; 100, 100A: modified layer; 110, 110A: crack; M: marker pen; LB: laser beam. DETAILED DESCRIPTION

[0021] Hereinafter, the crack detection method of the embodiment of the present invention will be described in detail with reference to the accompanying drawings. In addition, in the following description, a method of confirming whether a crack is formed on a plate-like workpiece by a crack detection method and then performing a process of dividing a wafer formed of the same material and the same size as the workpiece into individual device chips is described in sequence.

[0022] First, when implementing the crack detection method of the present invention, a workpiece 10A (dummy wafer) for crack detection is prepared, which is made of the same material (e.g., silicon (Si)) and the same size (diameter 300 mm, thickness 780 μm) as the plate-shaped wafer to be processed into individual device chips. In addition, nothing is formed on the first surface 10Aa and the second surface 10Ab of the workpiece 10A.

[0023] After the plate-like workpiece 10A is prepared, the workpiece 10A is placed on a surface with the first surface 10Aa facing upward and the second surface 10Ab facing downward. Figure 1 The laser processing apparatus 20 (only a part is shown) is shown in the figure, and a suction unit (not shown) is actuated to suck and hold the laser beam on the chuck table 22 .

[0024] After the workpiece 10A is held on the chuck table 22 as described above, the workpiece 10A is moved together with the chuck table 22, as shown in FIG. Figure 2 As shown in (a), the workpiece 10A is positioned directly below the condenser 24a of the laser beam irradiation unit 24. In addition, at this time, an alignment process may be performed as needed to accurately detect the processing position of the workpiece 10A.

[0025] Then, if Figure 2 As shown in (b), the focal point of the laser beam LB irradiated from the laser beam irradiation unit 24 is positioned at a depth of 700 μm as viewed from the first surface 10Aa constituting the upper surface. After the focal point is positioned at this position, the chuck table 22 is fed in the X-axis direction indicated by the arrow X, and the laser beam irradiation unit 24 is operated to irradiate the workpiece 10A with the laser beam LB in a linear form, forming a modified layer 100A and a crack 110A extending from the modified layer 100A to the second surface 10Ab side inside the workpiece 10A (see Figure 2 (b)). In addition, in this embodiment, if Figure 2 As shown in (a), while changing the irradiation position of the laser beam LB to the Y-axis direction indicated by the arrow Y, the workpiece 10A is subjected to three linear irradiation processes to form three processing lines. Thus, the crack forming process is completed.

[0026] In addition, the laser processing conditions when performing the above-mentioned laser processing are as follows, for example.

[0027] Wavelength: 1342nm

[0028] Repetition frequency: 90kHz

[0029] Average output: 1.1W

[0030] Processing feed speed: 700mm / sec

[0031] exist Figure 2 In (a), for the sake of convenience, the modified layer 100A and the crack 110A formed on the workpiece 10A are indicated by dotted lines. However, in fact, the modified layer 100A and the crack 110A cannot be visually confirmed from either the first surface 10Aa or the second surface 10Ab. Figure 3 The crack detection process described below is carried out.

[0032] The workpiece 10A subjected to the crack forming step as described above is removed from the laser processing device 20 and transported to a Figure 3 The inspection table D for crack detection shown in (a) is placed so that the first surface 10Aa faces downward and the second surface 10Ab faces upward. After the workpiece 10A is placed on the inspection table D, a colored coating is applied to the area P on the second surface 10Ab including the portion where the modified layer 100A and the crack 110A are formed by the crack forming step. The coating application method is not particularly limited, but it has been confirmed that Figure 3As shown in (b), the present inventors use a black or red oily marker M for coating, thereby being able to apply the paint well to the second surface 10Ab of the workpiece 10A. In addition, in this embodiment, there is no particular limitation on the thickness of the oily marker M used when applying the paint, and the marker also includes a pen generally called a signature pen. In addition, the paint actually applied can also use acrylic paint, ink, etc. in addition to oily colored paint, without particular limitation.

[0033] Here, if Figure 3 As shown in (b), when the area P coated with the paint is detected (crack detection process), in the portion where the crack 110A reaches the second surface 10Ab, the paint is linearly repelled, so the linear line indicating the presence of the crack 110A can be easily detected by visual inspection. In the portion where the crack 110A does not reach the second surface 10Ab, the paint is not repelled and the linear line cannot be detected. Figure 3 As shown in (b), when the linear line indicating the crack 110A does not appear continuously, that is, when the paint is discontinuously repelled, it is confirmed that the formation of the crack 110A is insufficient.

[0034] As described above, when the formation of the crack 110A is insufficient, the laser power (average output) in the above laser processing conditions is adjusted. In the present embodiment, for example, in the above laser processing conditions, the average output set to 1.1 W is adjusted to 1.2 W, the above crack forming process is re-implemented, the coating is applied to the second surface 10Ab, and the crack detection process is re-implemented. When the crack 110A reaches the second surface 10Ab well in the entire area irradiated with the laser beam LB, as shown in FIG. Figure 3 As shown in (c), in the area P coated with the paint, the linear line is not cut but formed continuously, confirming that the laser processing conditions are appropriate. According to the laser processing conditions, the plate-shaped workpiece (wafer) is processed as described below.

[0035] After the above crack detection method is implemented and the laser processing conditions are confirmed, a wafer processing method for dividing a wafer divided by a predetermined dividing line and having a plurality of devices formed on the front surface into individual device chips is implemented using a laser processing apparatus as described below.

[0036] The workpiece to be processed by the wafer processing method of this embodiment is, for example, Figure 4 The wafer 10 shown is a wafer made of the same material (silicon (Si)) and the same size (diameter 300 mm, thickness 780 μm) as the plate-shaped workpiece 10A used in the above crack detection method. The wafer 10 is divided by a plurality of intersecting predetermined dividing lines 14 and a plurality of devices 12 are formed on the front surface 10a.

[0037] After the wafer 10 is prepared, Figure 4 As shown in the figure, a protective member (for example, a protective tape 16 made of PVC, PET, etc.) formed with the same outer diameter as the wafer 10 and having an adhesive layer formed on the front surface is attached to the front surface 10a of the wafer 10 to form an integral body. In addition, the protective tape 16 is not limited to the protective member with an adhesive layer formed on the front surface as described above, and a thermocompression sheet without an adhesive layer, for example, made of polyolefin, polyester, etc., may also be used.

[0038] Next, the wafer 10 is transported to Figure 5 The laser processing device 20 (only a part is shown) shown in the figure performs the reforming layer forming step. The laser processing device 20 is the same as the laser processing device 20 that performs the crack detection method described above.

[0039] When implementing the modified layer forming step of this embodiment, Figure 5 As shown in (a), the wafer 10 is placed on a chuck table 22 provided on a laser processing device 20 in such a manner that the back side 10b of the wafer 10 faces upward and the protective tape 16 side faces downward, and a suction unit (not shown) is operated to suction and hold the wafer 10 on the chuck table 22. Next, after a proper alignment process is performed by using infrared rays to detect the predetermined dividing line 14 formed on the front side 10a, the wafer 10 held by the chuck table 22 is positioned directly below the condenser 24a of the laser beam irradiation unit 24. Then, the processing start position of the predetermined predetermined dividing line 14 of the wafer 10 is positioned at the irradiation position of the laser beam LB irradiated from the condenser 24a, as shown in FIG. Figure 5 As shown in (b), the focal point of the laser beam LB is positioned at a depth of 700 μm from the back surface 10b inside the predetermined dividing line 14 of the wafer 10. The position of the focal point is the same as the position of the focal point in the crack forming step implemented in the crack detection method.

[0040] Next, the chuck table 22 is moved along Figure 5 While the laser beam irradiation unit 24 is operated to irradiate the laser beam LB, the modified layer 100 is formed inside the planned dividing line 14 while the laser beam irradiation unit 24 is moved in the X-axis direction shown in FIG.

[0041] In addition, the laser processing conditions when performing the above-mentioned laser processing are as follows.

[0042] Wavelength: 1342nm

[0043] Repetition frequency: 90kHz

[0044] Average output: 1.2W

[0045] Processing feed speed: 700mm / sec

[0046] As described above, the laser processing conditions are conditions under which cracks are well formed by forming a modified layer inside the wafer, as confirmed by the above-mentioned crack detection method. Therefore, by forming a modified layer 100 inside the wafer 10, a crack 110 extending from the modified layer 100 is formed in a manner that reaches the predetermined dividing line 14 on the front side 10a of the wafer 10.

[0047] After the reformed layer 100 and the crack 110 are formed with respect to the predetermined dividing line 14, the chuck table 22 is moved along the Figure 5 The wafer 10 is moved in the Y-axis direction indicated by the arrow Y in (a) (indexing feed), and the irradiation position of the laser beam LB is positioned at the unprocessed predetermined dividing line 14 adjacent to the specified predetermined dividing line 14, and the laser beam LB is irradiated in the same manner as described above to form a modified layer 100 and a crack 110 at a position along the interior of the predetermined dividing line 14. Then, the same laser processing is performed along all the predetermined dividing lines 14 parallel to the specified predetermined dividing line 14 to form a modified layer 100 and a crack 110 inside each predetermined dividing line 14. Furthermore, the wafer 10 is rotated 90 degrees together with the chuck worktable 22, and the same laser processing is also performed on the interior of all the predetermined dividing lines 14 along a direction perpendicular to the above-mentioned specified predetermined dividing line 14 to form a modified layer 100 and a crack 110 (see Figure 6 (a)). Thus, the modified layer forming step is completed. In addition, for the sake of convenience, the modified layer 100 and the crack 110 are indicated by dotted lines in the illustrated wafer 10, but in fact, the modified layer 100 and the crack 110 cannot be visually confirmed from the back side 10b of the wafer 10.

[0048] After the modified layer forming step is performed as described above, the wafer 10 is removed from the chuck table 22 of the laser processing device 20 and transported to the Figure 6 The grinding device 30 (only a portion is shown) shown in (b) is placed and attracted to the holding surface 32a of the chuck table 32 of the grinding device 30 so that the back surface 10b faces upward and the protective tape 16 side faces downward, as shown in FIG. Figure 6 As shown in (b), the chuck table 32 is positioned below the grinding unit 34. The grinding unit 34 includes: a rotating shaft 34a driven by a motor; a grinding wheel 34b disposed at the lower end of the rotating shaft 34a; and a plurality of grinding tools 34c disposed in an annular shape on the lower surface of the grinding wheel 34b.

[0049] After positioning the chuck table 32 below the grinding unit 34, the unillustrated rotation drive unit is activated to rotate the chuck table 32 in the direction indicated by the arrow R1 at a specified rotation speed (e.g., 300 rpm), and the rotation axis 34a of the grinding unit 34 is rotated in the direction indicated by the arrow R2 at a specified rotation speed (e.g., 6000 rpm). Next, the unillustrated lifting unit is activated to lower the grinding unit 34 in the direction indicated by the arrow R3, and while supplying grinding water to the back side 10b of the wafer 10, the grinding tool 34c is brought into contact with the back side 10b of the wafer 10, and the back side 10b of the wafer 10 is ground and thinned at a specified descending speed (e.g., 1.0 μm / sec). Then, as Figure 6 As shown in (b) of FIG. 1 , the wafer 10 is thinned by the grinding process, and the wafer 10 is divided into individual device chips 12 ′ along the planned dividing lines 14 where the reformed layer 100 is formed. Thus, the dividing step is completed.

[0050] In this embodiment, before using the laser processing device 20 and the grinding device 30 to perform the process of dividing the wafer 10 into individual device chips 12', the crack detection method including the crack formation process and the crack detection process is implemented as described above. Therefore, it is possible to easily confirm whether the crack is properly formed without using a microscope, etc., and the laser processing conditions can be quickly adjusted so that the crack is properly formed, thereby eliminating the problem of poor productivity.

[0051] After the separation process is performed as described above, a tape replacement process may be performed as needed to peel off the protective tape 16 attached to the front surface 10a of the wafer 10 and retain the back surface 10b side with the adhesive tape T. When performing the tape replacement process, Figure 7 As shown, a ring-shaped frame F having an opening capable of accommodating the wafer 10 is prepared, and the wafer 10 is positioned in the opening of the frame F with the side to which the protective tape 16 is attached facing upward, and is held on the frame F by means of the adhesive tape T. After the back surface 10b of the wafer 10 is attached to the adhesive tape T and held on the frame F, the protective tape 16 is peeled off from the front surface 10a of the wafer 10. The wafer 10 held by the frame F and from which the protective tape 16 is peeled off is stored in a storage container (e.g., a box) not shown in the figure or is directly sent to the next process (e.g., a pickup process, etc.).

Claims

1. A crack detection method, wherein: The crack detection method has the following steps: A crack forming step of positioning a focal point of a laser beam having a wavelength that is transmissive to a plate-like workpiece having a first surface and a second surface opposite to the first surface from the first surface to the inside of the workpiece and irradiating the workpiece linearly, thereby forming a modified layer inside the workpiece and forming a crack extending from the modified layer to the second surface side; a coating application step of applying a coating on the second surface after the crack forming step is performed; as well as The crack detection process detects cracks by exploring the area where the paint is rejected in a linear manner. The laser processing conditions were confirmed by the fact that the linear lines were not cut off but were continuously formed in the area where the paint was applied.

2. The crack detection method according to claim 1, wherein: In this paint application process, an oil-based marker is used.

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