Wafer processing method

Abstract

The invention provides a wafer processing method, which can expose a linear crack which does not move in a bending manner relative to a division preset line on the division preset line, and can properly divide a wafer with high precision. The wafer processing method includes: a first processing step in which a focal point of a first laser beam of a first output having a wavelength permeable to the wafer is positioned near a front surface of a division line and the first laser beam is irradiated to the wafer to form a first modified layer in which a crack does not reach the front surface of the division line; a second processing step in which a focal point of a second laser beam having a second output having a wavelength that is stronger than the first output and is permeable to the wafer is positioned on the inner side of the back surface of the wafer corresponding to the division line, the second laser beam is irradiated to the wafer, and a second modified layer is formed along the division line; and a dividing step of applying an external force to the wafer to divide the wafer into individual device chips.

Description

Technical Field

[0001] The present invention relates to a wafer processing method for dividing a wafer having a plurality of devices formed on a front surface thereof by being divided by a plurality of intersecting planned dividing lines into individual device chips. Background Art

[0002] A wafer having a plurality of devices such as ICs and LSIs formed on the front side thereof divided by a plurality of intersecting predetermined dividing lines is divided into individual device chips using a laser processing apparatus, and the divided device chips are used in electronic devices such as mobile phones and personal computers.

[0003] The laser processing device is constructed to include: a chuck worktable that holds a chip; a laser beam irradiation unit that positions the focal point of a laser beam of a wavelength that is transmissive to the chip held by the chuck worktable to the inside of the chip corresponding to the predetermined splitting line and irradiates the laser beam; and a feeding mechanism that performs processing and feeding of the chuck worktable and the laser beam irradiation unit relative to each other. By appropriately setting the laser processing conditions, the laser processing device can form a shield tunnel consisting of a pore and a modified layer surrounding the pore inside the chip corresponding to the predetermined splitting line with high precision, which serves as the starting point of splitting (for example, refer to patent document 1).

[0004] Wafers on which LEDs, power devices, etc. are formed use hard SiC, GaN, diamond, sapphire, etc. as substrates, and therefore, in order to form a modified layer that serves as a starting point for division, it is necessary to irradiate with a relatively strong output laser beam.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-221483

[0006] However, when a strong-output laser beam is irradiated to form a modified layer inside a hard wafer in order to form a starting point for division, there is a problem in which cracks generated from the modified layer bend when reaching the front side of the wafer and deviate from the predetermined division line. When the wafer is divided into individual device chips in this state, there is a problem in which the quality of the device chips after division is reduced. Summary of the invention

[0007] Therefore, an object of the present invention is to provide a wafer processing method capable of exposing a linear crack that does not bend with respect to a planned dividing line on the planned dividing line, thereby enabling the wafer to be divided appropriately with high accuracy.

[0008] According to one aspect of the present invention, a wafer processing method is provided, which divides a wafer divided by a plurality of intersecting predetermined dividing lines and having a plurality of devices formed on the front side into individual device chips, wherein the wafer processing method comprises the following steps: a first processing step, in which a focal point of a first laser beam of a first output having a wavelength that is transparent to the wafer is positioned near the front side of the predetermined dividing line and the first laser beam is irradiated to the wafer to form a first modified layer in which cracks do not reach the front side of the predetermined dividing line; a second processing step, in which a second laser beam of a second output having a wavelength that is transparent to the wafer is irradiated to the wafer to form a first modified layer in which cracks do not reach the front side of the predetermined dividing line; The focal point of the light beam is positioned at the inner side of the back side of the chip corresponding to the predetermined splitting line and the second laser beam is irradiated to the chip to form a second modified layer along the predetermined splitting line; a third processing step is to position the focal point of the second laser beam between the first modified layer and the second modified layer and the second laser beam is irradiated to the chip to form a third modified layer reaching the first modified layer from the second modified layer, and a linear crack along the predetermined splitting line is exposed on the front side of the chip where the predetermined splitting line is formed; and a splitting step is to apply external force to the chip to split the chip into individual device chips.

[0009] Preferably, the first modified layer, the second modified layer, and the third modified layer are respectively composed of shield tunnels, and the shield tunnels are composed of pores and amorphous materials surrounding the pores. Preferably, in the first processing step, the second processing step, and the third processing step, the first laser beam and the second laser beam are irradiated from the front side of the wafer. Preferably, the wafer is selected from the group consisting of SiC wafers, GaN wafers, diamond wafers, and sapphire wafers.

[0010] According to the chip processing method of the present invention, before the splitting process is implemented, a relatively large straight crack is formed along the predetermined splitting line of the chip without bending, thereby reducing the splitting load when implementing the splitting process, and can accurately and appropriately split the chip into individual device chips without causing edge collapse. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is an overall perspective view of the laser processing device.

[0012] Figure 2 is a stereogram of a frame unit, which includes a Figure 1 A wafer processed by the laser processing apparatus shown.

[0013] Figure 3 It is a perspective view showing the manner of carrying out the first processing step.

[0014] Figure 4(a) is a partially enlarged cross-sectional view of a wafer having a shield tunnel formed thereon by performing the first processing step. Figure 4 (b) is in Figure 4 A conceptual diagram of a shield tunnel formed in the first processing step shown in (a).

[0015] Figure 5 (a) is a perspective view showing a method of implementing the second processing step, Figure 5 (b) is the implementation Figure 5 A partially enlarged cross-sectional view of a wafer having a second reformed layer (shield tunnel) formed thereon by the second processing step shown in (a).

[0016] Figure 6 (a) is a perspective view showing a method of implementing the third processing step, Figure 6 (b) is the implementation Figure 6 A partially enlarged cross-sectional view of a wafer having a third modified layer (shield tunnel) formed by the third processing step shown in (a), Figure 6 (c) is formed with Figure 6 (b) is a partially enlarged cross-sectional view of the second third modified layer (shield tunnel) of the wafer with cracks formed.

[0017] Figure 7 It is a perspective view of a frame unit including a wafer in which a linear crack is formed on a planned dividing line by a third processing step.

[0018] Figure 8 It is a cross-sectional view showing an embodiment of the dividing step.

[0019] Description of symbols

[0020] 1: Laser processing device; 2: Base; 2A: Guide rail; 3: Holding unit; 31: X-axis movable plate; 32: Y-axis movable plate; 33: Pillar; 34: Cover plate; 35: Chuck table; 36: Adsorption chuck; 37: Fixture; 4: Moving mechanism; 4a: X-axis moving mechanism; 42a: Motor; 42b: Ball screw; 4b: Y-axis moving mechanism; 44a: Motor; 44b: Ball screw; 5: Frame; 5a: vertical wall; 5b: horizontal wall; 6: alignment unit; 7: laser beam irradiation unit; 71: condenser; 10: wafer; 12: device; 12': device chip; 14: predetermined dividing line; 20a~20d: shield tunnel; 50: controller; 60: dividing device; 62: expansion unit; 62a: expansion drum; 62b: cylinder; 62c: holding component; 62d: clamp; 112: crack. DETAILED DESCRIPTION

[0021] Hereinafter, a wafer processing method according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0022] exist Figure 1 FIG. 1 shows a laser processing device 1 suitable for implementing the wafer processing method of the present embodiment. The laser processing device 1 comprises at least: a holding unit 3, which is arranged on a base 2 and holds a wafer 10 as a workpiece; and a laser beam irradiation unit 7, which irradiates a laser beam to the wafer 10 held by the holding unit 3. In addition, the wafer 10 divided by the wafer processing method of the present embodiment is, for example, Figure 2 Shown is a SiC wafer divided by a plurality of intersecting predetermined dividing lines 14 to form a plurality of devices 12 on the front side 10a, with a thickness of about 500 μm. Adhesive tape T is adhered to the annular frame F and the back side 10b of the wafer 10 to form a whole as a frame unit 15, and the wafer is supported on the annular frame F by means of the adhesive tape T.

[0023] The laser processing device 1 includes: an alignment unit 6, which performs alignment by photographing the chip 10 held by the holding unit 3; a moving mechanism 4, which moves the holding unit 3; a frame 5, which is composed of a vertical wall portion 5a erected on the side of the moving mechanism 4 on the base 2 and a horizontal wall portion 5b extending in a horizontal direction from the upper end of the vertical wall portion 5a; a controller 50; and a display unit not shown in the figure.

[0024] like Figure 1 As shown in the figure, the holding unit 3 includes: a rectangular X-axis movable plate 31, which is mounted on the base 2 so as to be movable in the X-axis direction; a rectangular Y-axis movable plate 32, which is mounted on the X-axis movable plate 31 so as to be movable in the Y-axis direction; a cylindrical support 33, which is fixed to the upper surface of the Y-axis movable plate 32; and a rectangular cover plate 34, which is fixed to the upper end of the support 33. A chuck table 35 extending upward through a long hole formed in the cover plate 34 is arranged on the cover plate 34. A circular adsorption chuck 36 is arranged on the upper surface of the chuck table 35, and the adsorption chuck 36 is formed of a porous material with air permeability, and uses the XY plane determined by the X coordinate and the Y coordinate as a holding surface. The suction chuck 36 is connected to a suction unit (not shown) via a flow path passing through the support 33, and four clamps 37 for holding the annular frame F and used when holding the wafer 10 on the chuck table 35 are arranged at equal intervals around the suction chuck 36. By operating the suction unit, the wafer 10 can be held by suction using the suction chuck 36.

[0025] The moving mechanism 4 includes an X-axis moving mechanism 4a that moves the chuck table 35 in the X-axis direction, a Y-axis moving mechanism 4b that moves the chuck table 35 in the Y-axis direction, and a rotation drive mechanism (not shown) housed in the support column 33 that rotates the chuck table 35. The X-axis moving mechanism 4a converts the rotational motion of the motor 42a into linear motion via a ball screw 42b and transmits it to the X-axis movable plate 31, so that the X-axis movable plate 31 moves in the X-axis direction along a pair of guide rails 2A, 2A arranged in the X-axis direction on the base 2. In addition, the Y-axis moving mechanism 4b converts the rotational motion of the motor 44a into linear motion via a ball screw 44b and transmits it to the Y-axis movable plate 32, so that the Y-axis movable plate 32 moves in the Y-axis direction along a pair of guide rails 31a, 31a arranged in the Y-axis direction on the X-axis movable plate 31.

[0026] The optical system and the alignment unit 6 constituting the above-mentioned laser beam irradiation unit 7 are housed inside the horizontal wall portion 5b of the frame 5. A condenser 71 is arranged on the lower surface side of the front end portion of the horizontal wall portion 5b. The condenser 71 constitutes a part of the laser beam irradiation unit 7 and includes a condenser lens (not shown) for converging the laser beam and irradiating the wafer 10. The repetition frequency, average output, etc. of the laser beam irradiated from the laser beam irradiation unit 7 are appropriately adjusted by the controller 50.

[0027] The alignment unit 6 is a photographing unit that photographs the chip 10 held by the holding unit 3 and detects the position where the laser light should be irradiated. It can detect the height of the front side 10a of the chip 10, that is, the thickness of the chip 10, with the adsorption chuck 36 constituting the holding surface of the chuck worktable 35 as a reference. The alignment unit 6 is arranged at a position adjacent to the above-mentioned condenser 71 in the X-axis direction indicated by the arrow X in the figure.

[0028] The laser processing device 1 used in the wafer processing method of this embodiment is configured to irradiate a first laser beam LB1 having a wavelength that is transparent to the wafer 10 and outputs a relatively weak output, and to irradiate a second laser beam LB2 having a wavelength that is transparent to the wafer 10 and outputs a relatively strong output.

[0029] The controller 50 is composed of a computer and has a central processing unit (CPU) for performing calculations according to a control program, a read-only memory (ROM) for storing the control program, etc., a readable and writable random access memory (RAM) for temporarily storing detected values ​​and calculation results, etc., an input interface, and an output interface (detailed illustration omitted). The controller 50 is connected to the alignment unit 6, the laser beam irradiation unit 7, the X-axis moving mechanism 4a, the Y-axis moving mechanism 4b, and a display unit (not shown) and the like. In addition, the image data captured by the alignment unit 6 is stored in an appropriate memory, and the detected image data, laser processing conditions, etc. are displayed on the display unit.

[0030] The laser processing apparatus 1 of the present embodiment has a substantially structure as described above, and a processing method for dividing a wafer 10 into individual device chips using the laser processing apparatus 1 will be described below.

[0031] (First processing step)

[0032] In the first processing step, the focal point of the first laser beam LB1 having a wavelength that is transparent to the wafer 10 and having a relatively weak output is positioned near the front surface 10a of the wafer 10 corresponding to the predetermined dividing line 14 and irradiated, thereby forming a first modified layer in which the crack does not reach the front surface 10a of the predetermined dividing line 14. Figure 3 , Figure 4 The following will be described in more detail.

[0033] When the first processing step is performed, the wafer 10 is unloaded from a cassette (not shown) storing a plurality of wafers 10 , mounted on the suction chuck 36 of the chuck table 35 and held by suction, and the annular frame F is gripped and fixed by the clamp 37 .

[0034] Next, the moving mechanism 4 is operated to move the wafer 10 to the position directly below the alignment unit 6 for imaging, and the predetermined dividing line 14 formed in the first direction on the front surface 10a of the wafer 10 is aligned with the X-axis direction. In addition, the position of the predetermined dividing line 14 to be processed on the front surface 10a of the wafer 10 is determined by the X-coordinate and the Y-coordinate, and the height of the front surface 10a of the predetermined dividing line 14 is detected and stored in an appropriate memory of the controller 50.

[0035] Next, by operating the X-axis moving mechanism 4a and the Y-axis moving mechanism 4b, Figure 3 As shown in FIG. 1 , the predetermined dividing line 14 of the wafer 10 is moved to the position directly below the condenser 71 of the laser beam irradiation unit 7. Here, the controller 50 causes the light focusing point position adjustment unit (not shown) to operate, such as Figure 4As shown in (a), the focusing point of the first laser beam LB1 having a wavelength that is transparent to the wafer 10 is positioned near the front surface 10a on which the first laser beam LB1 is incident.

[0036] After the focal point of the first laser beam LB1 is positioned as described above, Figure 3 As shown, the laser beam irradiation unit 7 is operated to irradiate the first laser beam LB1 from the condenser 71, and the X-axis moving mechanism 4a is operated, as shown in FIG. Figure 4 As shown in (a), a first modified layer 20a consisting of shield tunnels is formed inside the wafer 10 along the predetermined dividing line 14 of the wafer 10, and the shield tunnels are composed of pores and amorphous materials surrounding the pores. Figure 4 As shown in (b), the shield tunnel of the first modified layer 20a constituting the first layer is composed of a fine hole 22 with a diameter of about 1 μm formed in the center and an amorphous material 24 with a diameter of 10 μm surrounding the fine hole 22. A gap of approximately 50 μm is formed between the upper end of the first modified layer 20a formed at this time and the front surface 10a of the wafer 10, and the first modified layer 20a is not exposed on the front surface 10a side of the wafer 10, and cracks starting from the first modified layer 20a are not exposed on the front surface 10a.

[0037] In addition, the first processing step of the present invention is not limited to forming a shield tunnel that becomes the first modified layer 20a along the predetermined dividing line 14 as described above, and it is also possible to form only a modified layer that does not have a pore 22 in the center. However, in order to generate appropriate cracks by implementing the wafer processing method of this embodiment, it is preferred to form a shield tunnel including a pore 22 and an amorphous material 24 surrounding the pore 22 as described above as the first modified layer 20a. In order to form such a first modified layer 20a, as described in the above-mentioned patent document 1, it is important to set the numerical aperture (NA) of the condenser lens (not shown) provided in the condenser 71 divided by the refractive index (N) of the substrate (SiC in this embodiment) constituting the wafer 10 so that the value (NA / N) falls within the range of 0.05 to 0.2.

[0038] If the first modified layer 20a is formed along the predetermined dividing lines 14 in the first direction, the Y-axis moving mechanism 4b is operated to index the wafer 10 in the Y-axis direction according to the intervals of the dividing lines 14, and the unprocessed dividing lines 14 adjacent in the Y-axis direction are positioned directly below the condenser 71. Then, the focal point of the first laser beam LB1 is positioned inside the vicinity of the front surface 10a of the dividing lines 14 of the wafer 10 and irradiated, and the wafer 10 is processed and fed in the X-axis direction to form the first modified layer 20a. Similarly, the wafer 10 is processed and fed in the X-axis direction and the first modified layer 20a is formed inside all the dividing lines 14 along the first direction.

[0039] Next, the above-mentioned rotation drive mechanism is operated to rotate the wafer 10 by 90 degrees, so that the unprocessed predetermined dividing lines 14 in the second direction perpendicular to the predetermined dividing lines 14 in the first direction on which the first modified layer 20a has been formed are aligned with the X-axis direction. Then, the focal point of the first laser beam LB1 is positioned inside each of the remaining predetermined dividing lines 14 and irradiated by the same steps as above, and the X-axis moving mechanism 4a and the Y-axis moving mechanism 4b are operated to form the first modified layer 20a inside the wafer 10 along all the predetermined dividing lines 14 formed on the front surface 10a of the wafer 10.

[0040] Here, in the first processing step of the present embodiment, laser processing conditions (hereinafter referred to as "first processing conditions") when forming the first reformed layer 20a near the front surface 10a are set, for example, as follows.

[0041] Wavelength: 1064nm

[0042] Repetition frequency: 1kHz

[0043] Average output: 0.25W

[0044] Processing feed speed: 25mm / sec

[0045] When the first modified layer 20a is formed by irradiating the first laser beam LB1 near the front surface 10a of the wafer 10 based on the above-mentioned first processing condition, the height of the shield tunnel constituting the first modified layer 20a in the thickness direction is about 100μm. In addition, according to the above-mentioned repetition frequency and processing feed speed, the distance between the centers of adjacent shield tunnels in the X-axis direction is 25μm, so a gap of about 15μm is formed between adjacent shield tunnels. In addition, in the first processing step, the average output is set to be relatively weak (for example, 0.25W), so that cracks (cracks) will not be exposed on the front surface 10a of the wafer 10 along the predetermined dividing line 14. The first processing step is thus completed.

[0046] (Second processing step)

[0047] After the first processing step is performed, the second processing step is performed as follows: the second laser beam LB2 having a wavelength that is transparent to the wafer 10 and having a relatively strong output (more specifically, having an output stronger than the first laser beam LB1) is positioned at the inner side of the back surface 10b at a position corresponding to the predetermined dividing line 14 and irradiated to form a second modified layer. The second processing step is described in more detail below.

[0048] When implementing the second processing step, Figure 5 As shown in (a), the predetermined dividing line 14 where the first modified layer 20a is formed is positioned directly below the condenser 71 of the above-mentioned laser beam irradiation unit 7. Here, the laser beam irradiation unit 7 is set by the controller 50 to irradiate the second laser beam LB2 having a wavelength that is transparent to the wafer 10 and having a relatively strong output (more specifically, an average output that is stronger than the first laser beam LB1).

[0049] In the second processing step, if Figure 5 As shown in (b), the focal point of the second laser beam LB2 is positioned inside the wafer 10 near the back side 10b of the wafer 10 and irradiated, and the X-axis moving mechanism 4a is operated to form a second modified layer 20b near the back side 10b of the wafer 10 along the predetermined dividing line 14 in the first direction of the wafer 10. The second modified layer 20b is also preferably formed of pores and amorphous materials that shield the pores, similarly to the first modified layer 20a. In addition, a gap of about 50 μm is formed between the lower end of the second modified layer 20b and the back side 10b of the wafer 10.

[0050] While irradiating the second laser beam LB2 along the predetermined dividing line 14, the moving mechanism 4 is operated in the same manner as when forming the first modified layer 20a, and the second modified layer 20b is formed at the above-mentioned position in the thickness direction along all the predetermined dividing lines 14 of the wafer 10, thereby completing the second processing step. In addition, the focusing lens when forming the second modified layer 20b is selected to satisfy the same conditions as the focusing lens when forming the first modified layer 20a of the first layer.

[0051] The laser processing conditions when performing the above-mentioned second processing step (hereinafter referred to as "second processing conditions") are set to increase the output compared with the first processing conditions, for example, as follows.

[0052] Wavelength: 1064nm

[0053] Repetition frequency: 1kHz

[0054] Average output: 0.5W

[0055] Processing feed speed: 25mm / sec

[0056] The repetition frequency and processing feed rate under the second processing condition are set according to the same conditions as the first processing condition, so that the intervals between the shield tunnels constituting the second modified layer 20b are equal to the intervals between the shield tunnels constituting the first modified layer 20a. Even in the case where the second modified layer 20b is formed, since the intervals between adjacent shield tunnels 20a are separated, although not only the first modified layer 20a but also the second modified layer 20b are formed, cracks will not be exposed on the front side 10a and the back side 10b of the wafer 10.

[0057] (Third processing step)

[0058] After the first and second processing steps are performed, the following third processing step is performed: the focal point of the second laser beam LB2 irradiated based on the second processing condition is positioned between the first modified layer 20a and the second modified layer 20b, and the second laser beam LB2 is irradiated to the wafer 10, so as to form a third modified layer from the second modified layer 20b to the first modified layer 20a, and to expose a linear crack along the predetermined splitting line 14 on the front surface 10a where the predetermined splitting line 14 is formed. The third modified layer formed by the third processing step is not limited to being composed of one modified layer, but also includes a case where it is formed by a plurality of modified layers, see Figure 6 (a)~ Figure 7 The following will be described in more detail.

[0059] When implementing the third processing step, if Figure 6 As shown in (a), the predetermined dividing line 14 in the first direction where the first modified layer 20a and the second modified layer 20b are formed is positioned directly below the condenser 71 of the above-mentioned laser light irradiation unit 7. Here, the laser light irradiation unit 7 is set by the controller 5 to irradiate the second laser light LB2 having a wavelength set based on the above-mentioned second processing condition and having transmittance to the wafer 10 and outputting a stronger wavelength than the first processing condition for implementing the first processing step.

[0060] In the third processing step, if Figure 6 As shown in (b), the focal point of the second laser beam LB2 is located between the first modified layer 20a and the second modified layer 20b and on the second modified layer 20b side for irradiation, and the X-axis moving mechanism 4a is operated to form a first third modified layer 20c in a manner of contacting the upper side of the second modified layer 20b along the predetermined dividing line 14 in the first direction of the wafer 10. The first third modified layer 20c is also preferably formed of pores and amorphous material that shields the pores, similarly to the first modified layer 20a and the second modified layer 20b.

[0061] Next, the above-mentioned second laser light LB2 is irradiated, and the X-axis moving mechanism 4a, the Y-axis moving mechanism 4b and the rotation drive mechanism are operated in the same way as the moving mechanism 4 when forming the first modified layer 20a and the second modified layer 20b, so as to form the first third modified layer 20c at a position in the thickness direction of the above-mentioned chip 10 along all the predetermined dividing lines 14 of the chip 10.

[0062] Here, as shown in the figure, in the case where the first third modified layer 20c does not reach the size of the first modified layer 20a, Figure 6 As shown in (c), the focal point of the second laser beam LB2 is positioned between the first modified layer 20a and the first third modified layer 20c and irradiated, and the X-axis moving mechanism 4a is operated to form a second third modified layer 20d that contacts the top of the first third modified layer 20c and reaches the first modified layer 20a along the predetermined dividing line 14 in the first direction of the wafer 10. The second third modified layer 20d is also preferably formed of pores and amorphous materials that shield the pores, similarly to the first third modified layer 20c. In addition, the focusing lens when forming the above two third modified layers 20c and 20d is also selected to satisfy the same condition as the numerical aperture of the focusing lens when forming the first modified layer 20a of the first layer.

[0063] As described above, the focal point of the second laser beam LB2 is positioned between the first modified layer 20a and the second modified layer 20b, and the second laser beam LB2 is irradiated to the wafer 10 to form the third modified layers 20c and 20d. The third modified layers 20c and 20d reach the first modified layer 20a, thereby Figure 6 As shown in (c), cracks 112 are induced to form in the first modified layer 20a. Figure 7 As shown, the straight crack 112 that does not bend is exposed along the planned dividing line 14, and the third processing step is completed. In addition, the number of third modified layers formed in the third processing step is not limited to being composed of two modified layers (third modified layers 20c, 20d) as in the above-mentioned embodiment, and can be appropriately determined according to the thickness of the wafer 10 and the heights of the first to third modified layers. That is, in the case of forming the modified layers from the second modified layer 20b to the first modified layer 30a by forming the first third modified layer 20c, the third modified layer can be one. In addition, the third modified layer can also be composed of three or more.

[0064] (Separation process)

[0065] After the crack 112 that becomes the starting point of division is formed through the above-mentioned first to third processing steps, a division step of dividing the wafer 10 into individual device chips is performed by applying an external force to the wafer 10. The method of applying the external force to the wafer 10 is not particularly limited, and for example, Figure 8 The dividing device 60 shown is implemented.

[0066] exist Figure 8 The splitting device 60 shown in the figure has an expansion unit 62. The expansion unit 62 includes: a cylindrical expansion drum 62a; a plurality of cylinders 62b adjacent to the expansion drum 62a and extending upward at intervals in the circumferential direction; an annular holding member 62c connected to the upper end of each cylinder 62b; and a plurality of clamps 62d arranged at intervals in the circumferential direction on the outer peripheral edge of the holding member 62c. The inner diameter of the expansion drum 62a is larger than the diameter of the wafer 10, and the outer diameter of the expansion drum 62a is smaller than the inner diameter of the annular frame F. In addition, the holding member 62c corresponds to the diameter size of the annular frame F, and the annular frame F is placed on the flat upper surface of the holding member 62c.

[0067] like Figure 8 As shown, the plurality of air cylinders 62b raise and lower the holding member 62c between a reference position where the upper surface of the holding member 62c is at substantially the same height as the upper end of the expansion drum 62a and an expansion position where the upper surface of the holding member 62c is located below the upper end of the expansion drum 62a. Figure 8 In the figure, for the sake of convenience, the wafer 10 held on the adhesive tape T is shown as being raised and lowered together with the expansion drum 62a (shown by solid lines and two-dot chain lines), but in fact, it is the holding member 62c that is raised and lowered.

[0068] When the adhesive tape T supporting the wafer 10 is expanded to apply an external force to the wafer 10, first, the front surface 10a of the wafer 10 on which the device 12 is formed is placed upward, and the annular frame F is placed on the upper surface of the holding member 62c positioned at the reference position, and the annular frame F is fixed by a plurality of clamps 62d. Then, by lowering the holding member 62c to the expanded position, as shown in FIG. Figure 8 As shown by the double-dashed line in the middle, the wafer 10 is expanded together with the adhesive tape T and an external force is applied radially to the wafer 10, so that the wafer 10 attached to the adhesive tape T is divided into individual device chips 12'. Thus, the device chips 12' divided from the wafer 10 can be picked up by an appropriate pickup unit (not shown), and the picked up device chips 12' can be transported to the next process or stored in an appropriate storage box.

[0069] As described above, before the splitting process is performed, a relatively large straight crack 112 is formed along the predetermined splitting line 14 of the wafer 10 without bending, thereby reducing the splitting load during the splitting process and enabling the wafer 10 to be properly split into individual device chips 12' with high precision without causing edge chipping.

[0070] The method of applying external force to the wafer 10 to separate it into individual device chips is not limited to the method using the above-mentioned separation device 60. For example, the wafer 10 can also be placed on a pad having an elastic force, and an external force can be applied while a hard roller is pressed along the predetermined separation line 14 from above the wafer 10 to rotate the roller, or an external force can be applied by pressing a wedge-shaped pressing component along the predetermined separation line 14 of the wafer 10 placed on the pad, thereby separating the wafer 10 into individual device chips 12'.

[0071] In the above embodiment, an example in which the wafer 10 is composed of a SiC substrate is described, but the present invention is not limited thereto. For example, even a GaN substrate, a diamond substrate, or a sapphire substrate can also be applied to the above embodiment to achieve the same function and effect. At this time, the laser processing conditions when performing the first processing step and the second processing step are appropriately adjusted according to the raw material and thickness of the material to be processed.

Claims

1. A method for processing a wafer, wherein a wafer having a plurality of devices formed on a front surface thereof is divided by a plurality of intersecting predetermined dividing lines into individual device chips, wherein: The wafer processing method has the following steps: In a first processing step, a focal point of a first laser beam of a first output having a wavelength that is transparent to the wafer is positioned near the front surface of the predetermined dividing line and the first laser beam is irradiated to the wafer to form a first modified layer in which cracks do not reach the front surface of the predetermined dividing line; A second processing step of positioning a focal point of a second laser beam of a second output stronger than the first output and having a wavelength that is transmissive to the wafer on the inner side of the back surface of the wafer corresponding to the predetermined dividing line and irradiating the wafer with the second laser beam to form a second modified layer along the predetermined dividing line; a third processing step of positioning the focal point of the second laser beam between the first modified layer and the second modified layer and irradiating the wafer with the second laser beam to form a third modified layer extending from the second modified layer to the first modified layer, and exposing a linear crack along the predetermined splitting line on the front side of the wafer on which the predetermined splitting line is formed; as well as In the dividing step, external force is applied to the wafer to divide the wafer into individual device chips.

2. The wafer processing method according to claim 1, wherein: The first modified layer, the second modified layer, and the third modified layer are respectively composed of shield tunnels, and the shield tunnels are composed of pores and amorphous materials surrounding the pores.

3. The wafer processing method according to claim 1, wherein: In the first processing step, the second processing step, and the third processing step, the first laser beam and the second laser beam are irradiated from the front surface of the wafer.

4. The wafer processing method according to claim 1, wherein: The wafer is selected from the group consisting of a SiC wafer, a GaN wafer, a diamond wafer, and a sapphire wafer.

Images