Wafer processing method and wafer processing apparatus

Abstract

The present invention provides a wafer processing method and a wafer processing apparatus that efficiently divide a wafer into individual chips without detecting the height of the upper surface of a region to be divided. The wafer processing method for dividing a wafer into individual chips includes the following steps: a thermal stress wave generating step of generating a thermal stress wave by irradiating a pulsed laser beam of a wavelength having absorbency for the wafer from the upper surface of the wafer held by a chuck table toward a region to be divided, and making the thermal stress wave propagate inside the region to be divided; and a fracture layer forming step of irradiating a laser beam of a wavelength having permeability for the wafer from the upper surface of the wafer in accordance with the thermal stress wave generated in the thermal stress wave generating step propagating inside at an acoustic velocity corresponding to the material of the wafer to reach a depth position at which a division starting point is to be generated, and generating absorption of the pulsed laser beam of the wavelength having permeability in a region in which the band gap is narrowed by the tensile stress of the thermal stress wave, thereby forming a fracture layer as the division starting point.

Description

Technical Field

[0001] The present invention relates to a wafer processing method for dividing a wafer into individual chips and a wafer processing apparatus for forming the dividing starting points for dividing the wafer into individual chips. Background Technology

[0002] A wafer with multiple devices such as ICs, LSIs, and LEDs formed on its front side by multiple intersecting pre-defined dividing lines is divided into individual device chips by a laser processing device. The divided device chips are used in electronic devices such as mobile phones and personal computers.

[0003] The laser processing apparatus comprises: a chuck stage for holding a workpiece (wafer); a laser beam irradiation unit for irradiating a laser beam of a wavelength that is absorbent to the workpiece held by the chuck stage; an X-axis feed mechanism for feeding the chuck stage and the laser beam irradiation unit relative to each other along the X-axis; and a Y-axis feed mechanism for feeding the chuck stage and the laser beam irradiation unit relative to each other along the Y-axis, perpendicular to the X-axis, thereby positioning a focal point on a predetermined dicing line of the wafer and performing ablation processing to form dicing grooves on the predetermined dicing line to divide the wafer into individual device chips (see, for example, Patent Document 1).

[0004] Furthermore, the laser processing apparatus comprises: a chuck stage for holding the workpiece (wafer); a laser beam irradiation unit for irradiating the workpiece held by the chuck stage with a wavelength that is transparent to the workpiece; an X-axis feed mechanism for feeding the chuck stage and the laser beam irradiation unit relative to each other along the X-axis; and a Y-axis feed mechanism for feeding the chuck stage and the laser beam irradiation unit relative to each other along the Y-axis, perpendicular to the X-axis, thereby positioning the laser beam focus point inside a predetermined dicing line of the wafer and irradiating it, forming a modified layer inside the predetermined dicing line as the starting point for dicing, thereby dicing into individual device chips (see, for example, Patent Document 2).

[0005] Patent Document 1: Japanese Patent Application Publication No. 10-305420

[0006] Patent Document 2: Japanese Patent Application Publication No. 2012-2604

[0007] However, in order to position the laser beam at the appropriate depth in the area to be divided on the wafer, the height of the upper surface of the area to be divided must be detected and stored in advance, which results in poor productivity. Summary of the Invention

[0008] Therefore, the object of the present invention is to provide a wafer processing method and wafer processing apparatus that can efficiently divide a wafer into individual chips without detecting the height of the upper surface of the region to be divided.

[0009] According to one aspect of the present invention, a wafer processing method is provided for dividing a wafer into individual chips, wherein the wafer processing method comprises the following steps: a holding step, in which the wafer is held on a chuck stage; a thermal stress wave generation step, in which pulsed laser light of a wavelength that is absorbent to the wafer is irradiated from the upper surface of the wafer held on the chuck stage toward the area to be divided to generate a thermal stress wave, and the thermal stress wave is allowed to propagate within the area to be divided; a fracture layer formation step, in which pulsed laser light of a wavelength that is transmissible to the wafer is irradiated from the upper surface of the wafer according to the time taken for the thermal stress wave generated in the thermal stress wave generation step to propagate internally at a sound speed corresponding to the material of the wafer and reach a depth position where the division starting point is to be formed, and absorption of the transmissible pulsed laser light is generated in a region where the band gap is narrowed due to the tensile stress of the thermal stress wave, thereby forming a fracture layer as the division starting point; and a division step, in which the wafer is divided into individual chips with the fracture layer as the division starting point.

[0010] According to another aspect of the present invention, a wafer processing apparatus is provided, which forms a slitting starting point for dividing a wafer into individual chips. The wafer processing apparatus includes: a chuck stage for holding the wafer; a thermal stress wave generating unit that generates a thermal stress wave by irradiating a pulsed laser beam of an absorptive wavelength to the wafer from the upper surface of the wafer held by the chuck stage toward the region to be divided, and causes the thermal stress wave to propagate within the region to be divided; and a fracture layer forming unit that irradiates a pulsed laser beam of a transmissive wavelength to the wafer from the upper surface of the wafer, according to the time it takes for the thermal stress wave generated by the thermal stress wave generating unit to propagate within the region to be divided at a speed of sound corresponding to the material of the wafer and reach a depth position at which the slitting starting point is to be formed, thereby generating absorption of the transmissive pulsed laser beam in a region where the bandgap narrows due to the tensile stress of the thermal stress wave, thus forming a fracture layer as the slitting starting point.

[0011] According to the wafer processing method of the present invention, it is not necessary to detect the height of the upper surface of each wafer individually. The position of the broken layer forming the starting point for segmentation can be controlled by the propagation time, which is calculated based on the speed of sound corresponding to the material constituting the wafer, thereby improving productivity.

[0012] The wafer processing apparatus according to the present invention, similar to the wafer processing method, does not require a structure for detecting the height of the upper surface of the wafer one by one. It can control the position of the broken layer forming the starting point of the division by means of the propagation time, which is calculated based on the speed of sound corresponding to the material constituting the wafer, thereby improving productivity. Attached Figure Description

[0013] Figure 1 This is an overall perspective view of the wafer processing apparatus of this embodiment.

[0014] Figure 2 (a) is shown Figure 1 The diagram shows a block diagram of the optical system of the laser beam irradiation unit in the wafer processing apparatus. Figure 2 (b) is an enlarged cross-sectional view showing a portion of the wafer during the thermal stress wave generation process and the fracture layer formation process.

[0015] Figure 3 This is a side view of the dividing device used in the implementation of the dividing process.

[0016] Label Explanation

[0017] 2: Wafer processing apparatus; 3: Base; 4: Holding unit; 21: Movable plate in the X-axis direction; 22: Movable plate in the Y-axis direction; 25: Chuck stage; 25a: Holding surface; 27: Fixture; 6A: First laser beam generating unit; 61: First laser beam generating unit; 611: First laser oscillator; 612: First attenuator; 62: Reflector; 6B: Second laser beam generating unit; 63: Second laser beam generating unit; 631: Second laser oscillator; 632: Second attenuator; 64: Delay unit; 6C: Laser beam guiding unit; 65: Dichroic mirror; 66: Reflector; 67 : Condenser; 671: fθ lens; 7: Imaging unit; 10: Wafer; 10a: Front; 10b: Back; 12: Device; 12': Device chip; 14: Segmentation pre-line; 30: Moving mechanism; 31: X-axis feed unit; 32: Y-axis feed unit; 37: Frame; 37a: Vertical wall; 37b: Horizontal wall; 70: Segmentation device; 71: Frame holding component; 72: Fixture; 73: Expansion drum; PL1: First pulse laser beam; PL2: Second pulse laser beam; S: Fracture layer; H1: Thermal stress wave generation unit; H2: Fracture layer forming unit. Detailed Implementation

[0018] Hereinafter, a wafer processing method according to embodiments of the present invention and a wafer processing apparatus suitable for carrying out the wafer processing method will be described in detail with reference to the accompanying drawings.

[0019] Figure 1A perspective view of the wafer processing apparatus 2 according to this embodiment is shown. The wafer processing apparatus 2 includes: a base 3; a holding unit 4 for holding the workpiece; a laser beam irradiation unit 6 configured to include a thermal stress wave generation unit and a fracture layer formation unit, which will be described in detail later; an imaging unit 7; a moving mechanism 30 for moving the holding unit 4; and a control unit (not shown).

[0020] The holding unit 4 includes: a rectangular movable plate 21 in the X-axis direction, which is movably mounted on the base 3 in the X-axis direction as indicated by arrow X in the figure; a rectangular movable plate 22 in the Y-axis direction, which is movably mounted on the movable plate 21 in the X-axis direction as indicated by arrow Y in the figure; a cylindrical support column 23, which is fixed to the upper surface of the movable plate 22 in the Y-axis direction; and a rectangular cover plate 26, which is fixed to the upper end of the support column 23. A circular chuck worktable 25 extending upward through an elongated hole is disposed on the cover plate 26. The chuck worktable 25 is configured to be rotated by a rotary drive unit (not shown). The holding surface 25a of the upper surface of the chuck worktable 25, defined by the X-axis and Y-axis coordinates, is formed of a porous material and is ventilated. It is connected to the suction unit (not shown) through a flow path inside the support column 23. A clamp 27 is also provided on the chuck table 25. This clamp 27 is used to fix the annular frame F, which supports the workpiece via the protective belt T. Furthermore, the workpiece in this embodiment is, for example,... Figure 1 The wafer 10 shown has a thickness of 1.0 mm. On a silicon substrate, a device 12 is formed on the front side 10a by a predetermined dividing line 14. The wafer 10 is attached to a protective strip T with the front side 10a facing upward and the back side 10b facing downward, and is held by an annular frame F via the protective strip T.

[0021] The moving mechanism 30 is mounted on the base 3 and includes: an X-axis feed unit 31 that feeds the holding unit 4 along the X-axis; and a Y-axis feed unit 32 that indexes the Y-axis movable plate 22 along the Y-axis. The X-axis feed unit 31 converts the rotational motion of the pulse motor 33 into linear motion via the ball screw 34 and transmits it to the X-axis movable plate 21, causing the X-axis movable plate 21 to move forward and backward along the guide rails 3a, 3a on the base 3 in the X-axis direction. The Y-axis feed unit 32 converts the rotational motion of the pulse motor 35 into linear motion via the ball screw 36 and transmits it to the Y-axis movable plate 22, causing the Y-axis movable plate 22 to move forward and backward along the guide rails 21a, 21a on the X-axis movable plate 21 in the Y-axis direction. Furthermore, although not shown in the diagram, position detection units are provided on the X-axis feed unit 31, the Y-axis feed unit 32, and the chuck table 25 to accurately detect the X-axis coordinates, Y-axis coordinates, and circumferential rotational position of the chuck table 25. This position information is sent to a control unit (not shown). Moreover, based on the instruction signal from the control unit according to this position information, the rotation drive units of the X-axis feed unit 31, the Y-axis feed unit 32, and the chuck table 25 (not shown) are driven, thereby enabling the chuck table 25 to be positioned at the desired position on the base 3.

[0022] like Figure 1 As shown, a frame 37 is erected on the side of the moving mechanism 30. The frame 37 has a vertical wall 37a, which is disposed on the base 3; and a horizontal wall 37b, which extends horizontally from the upper end of the vertical wall 37a. The optical system of the laser beam irradiation unit 6 is housed inside the horizontal wall 37b of the frame 37, and a condenser 67, which constitutes part of the optical system, is disposed on the lower surface of the front end of the horizontal wall 37b.

[0023] The imaging unit 7 is disposed on the lower front surface of the horizontal wall portion 37b and spaced apart from the condenser 67 of the laser beam irradiation unit 6 in the X-axis direction. The imaging unit 7 may include, as needed: a conventional imaging element (CCD) that captures images using visible light; an infrared irradiation unit that irradiates infrared light onto the workpiece; an optical system that captures the infrared light irradiated by the infrared irradiation unit; and an imaging element (infrared CCD), which outputs an electrical signal corresponding to the infrared light captured by the optical system. The image captured by the imaging unit 7 is sent to the control unit and appropriately displayed on a display unit (not shown).

[0024] The control unit is composed of a computer and includes: a central processing unit (CPU) that performs calculations according to the control program; a read-only memory (ROM) that stores the control program; and a read-write random access memory (RAM) that stores the calculation results. Furthermore, the control unit is electrically connected to the laser beam irradiation unit 6, the imaging unit 7, and the moving mechanism 30, and controls the operation of each unit.

[0025] Reference Figure 2 (a) The optical system of the laser beam irradiation unit 6 housed in the horizontal wall portion 37b of the wafer processing apparatus 2 will be described.

[0026] Figure 2 The optical system of the laser beam irradiation unit 6 shown in (a) includes: a first laser beam generating unit 6A that generates a first pulsed laser beam PL1 with a wavelength that is absorbed by the wafer 10 being processed; a second laser beam generating unit 6B that generates a second pulsed laser beam PL2 with a wavelength that is transmitted to the wafer 10; and a laser beam guiding unit 6C that guides the first pulsed laser beam PL1 generated by the first laser beam generating unit 6A and the second pulsed laser beam PL2 generated by the second laser beam generating unit 6B to irradiate the upper surface (front side 10a) of the wafer 10 held by the chuck stage 25 of the holding unit 4. Additionally, in Figure 2 In (a), for ease of explanation, the protective strip T and frame F attached to the chip 10 are omitted.

[0027] The first laser beam generating unit 6A of this embodiment includes: a first laser beam generating unit 61; and a reflector 62, which modifies the optical path of a first pulsed laser beam PL1 emitted from the first laser beam generating unit 61. The first laser beam generating unit 61 includes: a first laser oscillator 611, which emits a first pulsed laser beam PL1 with a wavelength of, for example, 355 nm, that is absorptive to the material (Si) constituting the wafer 10; and a first attenuator 612, which adjusts the output of the first pulsed laser beam PL1 emitted from the first laser oscillator 611 to a desired output and emits it toward the reflector 62.

[0028] The second laser beam generating unit 6B includes: a second laser beam generating unit 63; and a delay unit 64, which delays the second pulsed laser beam PL2 emitted from the second laser beam generating unit 63 by a desired time. The second laser beam generating unit 63 includes: a second laser oscillator 631, which emits a second pulsed laser beam PL2 with a wavelength of, for example, 1064 nm, that is transparent to the material (Si) constituting the wafer 10; and a second attenuator 632, which adjusts the output of the second pulsed laser beam PL2 emitted from the second laser oscillator 631. The second laser oscillator 631 is set to operate at the same repetition frequency as the first laser oscillator 611 described above, and emits the second pulsed laser beam PL2 at a timing synchronized with the first pulsed laser beam PL1. The delay unit 64, which delays the second pulsed laser beam PL2 emitted from the second laser oscillator 631, outputs the second pulsed laser beam PL2, for example, via an optical fiber (not shown) with a length corresponding to the delay time.

[0029] The laser beam guide unit 6C includes: a dichroic mirror 65 that reflects the first pulsed laser beam PL1 reflected by the reflector 62 of the first laser beam generator 6A, allowing the second pulsed laser beam PL2 guided from the second laser beam generator 6B to pass through; a reflector 66 that alters the optical path of the light emitted from the dichroic mirror 65; and a concentrator 67 that includes an fθ lens 671 that focuses the light reflected by the reflector 66 onto the position of the predetermined dividing line 14 on the front side 10a of the wafer 10 held by the chuck stage 25 for irradiation. The first pulsed laser beam PL1 and the second pulsed laser beam PL2, guided to the dichroic mirror 65, irradiate the same area on the chuck stage 25.

[0030] The thermal stress wave generating unit H1 of the present invention is formed by the first laser beam generating unit 6A and the laser beam guiding unit 6C described above. The thermal stress wave generating unit H1 is a unit that generates a thermal stress wave by irradiating a pulsed laser beam PL1 of a wavelength that is absorbent to the wafer 10, which is positioned on the front side 10a of the upper surface of the wafer 10 held by the holding unit 4, and causes the thermal stress wave to propagate inside the wafer 10.

[0031] Furthermore, the fractured layer forming unit H2 of the present invention is formed by the aforementioned second laser beam generating unit 6B and laser beam guiding unit 6C. The fractured layer forming unit H2 is a unit that, according to a predetermined time, irradiates a second pulsed laser beam PL2 with a wavelength that is transparent to the wafer 10 from the front surface 10a of the wafer 10, based on the thermal stress wave generated by the thermal stress wave generating unit H1 on the front surface 10a of the wafer 10, which propagates inside the wafer 10 at a sound speed corresponding to the material of the wafer 10 and reaches a depth position (for example, a depth of 0.5 mm from the front surface (10a) of the wafer 10) that is the depth at which the slit should be formed.

[0032] Reference Figure 2 (a) and Figure 2 (b) will be described in more detail an embodiment in which a fracture layer S as a dividing starting point is formed on the wafer 10, which can be implemented using the wafer processing apparatus 2 described above.

[0033] When dividing wafer 10 into individual chips, firstly, holding unit 4 holds wafer 10 (holding process). More specifically, wafer 10, which is prepared to be supported by an annular frame F via protective band T (see reference). Figure 1 The protective belt T is placed on the holding surface 25a of the chuck table 25, causing the suction unit (not shown) to operate and become attracted and held by the chuck table 25.

[0034] Next, the thermal stress wave generation process and the fracture layer formation process are performed. At this time, the moving mechanism 30 is activated to position the wafer 10 below the imaging unit 7, and the front side 10a of the wafer 10 is photographed by the imaging unit 7. As a result, the position of the predetermined dividing line 14, which is the area to be divided, is detected and appropriately stored in the control unit (alignment process).

[0035] After the alignment process is performed, the wafer 10 is moved below the condenser 67. Based on the information detected in the alignment process, the dicing predetermined line 14 is aligned along the X-axis, and the position on the dicing predetermined line 14 where processing should begin is positioned directly below the condenser 67.

[0036] Next, the thermal stress wave generation unit H1 is activated to generate a first pulsed laser beam PL1 with a wavelength of 355nm that is absorbent to the material (Si: silicon) of the wafer 10. The laser beam is then directed from the front side 10a of the wafer 10 to the area to be divided, i.e. the division predetermined line 14, via the laser beam guide section 6C (thermal stress wave generation process).

[0037] The laser irradiation conditions implemented in the above-mentioned thermal stress wave generation process are as follows. In addition, in the thermal stress wave generation process, the average output of the first pulse laser beam PL1, which is adjusted by the first attenuator 612 of the thermal stress wave generation unit H1, is adjusted to a lower output such that the first pulse laser beam PL1 is a laser beam that is absorbent to the wafer 10 and does not produce ablation on the front surface 10a of the wafer 10.

[0038] Wavelength: 355nm

[0039] Repetition frequency: 50kHz

[0040] Average output: 1W

[0041] Pulse width: less than 100ps

[0042] When the first pulsed laser beam PL1 is irradiated onto the front surface 10a of the wafer 10 through the aforementioned thermal stress wave generation process, the front surface 10a of the wafer 10 is thermally excited, as... Figure 2 As shown in (b), the thermal stress wave generated by this thermal excitation propagates inside the wafer 10 as shown by N1→N2 in the figure. The propagation speed of this thermal stress wave N1→N2 is the speed of sound (9620 m / s) corresponding to the material (Si) constituting the wafer 10. Thus, the thermal stress wave propagating in semiconductors such as silicon is a short-pulse tensile stress wave, and the band gap is narrower than usual at the location where tensile stress is applied. That is, the region with the narrower band gap propagates from the front side 10a toward the back side 10b. Moreover, the fracture layer formation process, which is performed together with the above-described thermal stress wave generation process, is performed as follows.

[0043] During the fragmentation layer formation process, the fragmentation layer formation unit H2 is activated, and a second pulsed laser beam PL2 with a wavelength (1064 nm) that is transparent to the material (Si: silicon) constituting the wafer 10 is emitted at the same repetition frequency (50 kHz) as the first laser oscillator 611 via the second laser oscillator 631. Next, the second pulsed laser beam PL2 is adjusted to a predetermined output via the second attenuator 632, and the second pulsed laser beam PL2 is delayed by a predetermined time relative to the first pulsed laser beam PL1 via the delay unit 64 before being output. This predetermined time, delayed by the delay unit 64 of the second laser beam generation unit 6B, refers to the time it takes for the thermal stress wave generated on the front surface 10a of the wafer 10 in the aforementioned thermal stress wave generation process to reach the depth position (0.5 mm) of the wafer 10 where the segmentation starting point should be formed, at the speed of sound (9620 m / s) propagating inside the wafer 10. In this embodiment, this predetermined time is 52 ns. The second pulsed laser beam PL2 is irradiated by the laser beam guide section 6C onto the area on the front side 10a of the wafer 10 that was irradiated by the first pulsed laser beam PL1.

[0044] The laser irradiation conditions implemented in the above-mentioned fracture layer formation process are as follows, for example.

[0045] Wavelength: 1064nm

[0046] Repetition frequency: 50kHz

[0047] Average output: 10W

[0048] Pulse width: 10ns

[0049] During the aforementioned thermal stress wave generation and fracture layer formation processes, the second pulsed laser beam PL2, irradiated by the fracture layer formation unit H2, is delayed by a predetermined time (52 ns) relative to the first pulsed laser beam PL1. Thus, as... Figure 2 As shown in (b), the first pulsed laser beam PL1 irradiates the front surface 10a of the wafer 10, forming a thermal stress wave (N1-N2), which propagates at a sound speed (propagation speed) corresponding to the Si constituting the wafer 10. A region with a narrowed bandgap is formed at a depth P, 0.5 mm from the front surface 10a, which is the region where the segmentation starting point should be formed. At this location P, the second pulsed laser beam PL2 is absorbed. As a result, destructive stress is applied to the interior of the wafer 10 at location P, causing localized fracture within the wafer 10, thereby forming a fracture layer S.

[0050] During the aforementioned thermal stress wave generation and fracture layer formation processes, the moving mechanism 30 also operates simultaneously, feeding the chuck table 25 along the X-axis direction, such as... Figure 2 As shown in (b), a fracture layer S is formed at a predetermined depth (0.5 mm) along the pre-defined dividing line 14 positioned along the X-axis. After the fracture layer S is formed, the Y-axis feed unit of the moving mechanism 30 is activated to index the wafer 10, positioning the adjacent unprocessed pre-defined dividing line 14 directly below the condenser 67. The aforementioned thermal stress wave generation process and fracture layer formation process are performed, and the X-axis feed unit 31 is activated to form the same fracture layer S inside the pre-defined dividing line 14. After the fracture layer S is formed inside all the pre-defined dividing lines 14 along the predetermined direction, a rotary drive unit (not shown) that rotates the chuck stage 25 is controlled to rotate the chuck stage 25 by 90 degrees, forming the fracture layer S inside all the pre-defined dividing lines 14 formed in a direction perpendicular to the pre-defined dividing line 14 where the fracture layer S was first formed. As described above, a fracture layer S is formed along all the pre-defined dividing lines 14 as the starting point for dividing the wafer 10 into individual chips.

[0051] According to the above embodiment, a first pulsed laser beam PL1 with a wavelength that is absorbent to the upper surface 10a of the wafer 10 is irradiated to generate a thermal stress wave and propagate it. A second pulsed laser beam PL2 with a propagation time delay according to the depth position where the thermal stress wave should be generated and the starting point of the segmentation is reached is irradiated. Thus, the position of the fragmented layer S can be controlled without detecting the height of the upper surface (front surface 10a) of the wafer 10.

[0052] As described above, after completing the thermal stress wave generation process and the fracture layer formation process, a dicing process is performed to divide the wafer 10 into individual device chips 12' starting from the fracture layer S. This dicing process can employ known methods, but for example, it can use... Figure 3 The dividing device 70 shown is used to implement this.

[0053] As described above, the wafer 10, in which a fracture layer S is formed inside the predetermined dividing line 14 through the thermal stress wave generation process and the fracture layer formation process, is transported to... Figure 3 The shown is a slitting device 70. The slitting device 70 includes: an annular frame holding member 71 configured to be movable; a clamp 72 which holds the frame F on its upper surface; an expansion drum 73 which is cylindrical in shape with at least an opening at the top, for expanding the spacing between the devices 12 of the wafer 10 mounted on the frame F held by the clamp 72; and a support unit 74 which consists of a plurality of cylinders 74a arranged around the expansion drum 73 and piston rods 74b extending from the cylinders 74a.

[0054] The expansion drum 73 is configured to be smaller than the inner diameter of the frame F and larger than the outer diameter of the chip 10 adhered to the protective strip T mounted on the frame F. Here, as... Figure 3 As shown, the dividing device 70 can raise and lower the frame holding member 71 to a position at approximately the same height as the upper surface of the expansion drum 73 (shown in dashed lines) and to a position where the upper end of the expansion drum 73 is relatively higher than the upper end of the frame holding member 71 (shown in solid lines).

[0055] As described above, when the frame holding member 71 is lowered, causing the upper end of the expansion drum 73 to change from the position shown by the dashed line to a higher position shown by the solid line, the protective strip T mounted on the frame F is expanded by the upper edge of the expansion drum 73. Here, a fracture layer S, which serves as the starting point for slitting, is formed on the wafer 10 along the predetermined slitting line 14. The protective strip T is expanded, and a tensile force (external force) is applied radially to the wafer 10, thereby... Figure 3 As shown, the wafer 10 is divided into device chips 12'. Thus, after the wafer 10 is divided into individual device chips 12', they are picked up by a suitable pickup device (not shown).

[0056] Furthermore, in the above embodiment, by performing a thermal stress wave generation process and a fracture layer formation process, a fracture layer S, serving as a division starting point, is formed inside the wafer 10 along the predetermined division line 14, demonstrating the use of... Figure 3 The example shown illustrates a dicing apparatus 70 used to perform a dicing process to divide the wafer 10 into individual device chips 12'. However, if the wafer 10 is relatively thin, the output of the second pulse laser beam PL2 of the fragmentation layer forming unit H2 can be adjusted, eliminating the need for the dicing apparatus 70. Figure 3 The dicing apparatus 70 shown can divide the wafer 10 into individual device chips 12' simply by performing a thermal stress wave generation process and a fracture layer formation process to form a fracture layer S along the predetermined dicing line 14. That is, in the wafer processing method of the present invention, there is also a case where the thermal stress wave generation process and the fracture layer formation process are combined into a dicing process that divides the wafer 10 into individual device chips 12' with the fracture layer S as the starting point.

[0057] This invention is not limited to the embodiments described above. For example, in the embodiments described above, when the wafer 10 is held in the holding unit 4, the front surface 10a where the device 12 is formed is held as the upper surface, and a first pulsed laser beam PL1 and a second pulsed laser beam PL2 are irradiated from the front surface 10a side, forming a fracture layer S inside along the predetermined dividing line 14. However, the back surface 10b side of the wafer 10 can also be held in the holding unit 4 as the upper surface, and the first pulsed laser beam PL1 and the second pulsed laser beam PL2 are irradiated from the back surface 10b side, forming a fracture layer S inside the wafer 10. In this case, an infrared CCD is provided in the imaging unit 7 to detect the position of the predetermined dividing line 14 formed on the front surface 10a from the back surface 10b side and set the processing position.

[0058] In addition, in the above embodiment, the laser beam guide 6C is shared in the thermal stress wave generating unit H1 and the fractured layer forming unit H2, and the first pulse laser beam PL1 and the second pulse laser beam PL2 are irradiated from the same direction. However, it is not necessary to irradiate from the same direction. Alternatively, the thermal stress wave generating unit H1 and the fractured layer forming unit H2 may be provided with their own laser beam guides, and the first pulse laser beam PL1 and the second pulse laser beam PL2 may be irradiated from different angles.

[0059] Furthermore, in the above embodiment, the fracture layer S, which serves as the starting point for dicing, is formed by absorbing the second pulsed laser beam PL2 at a depth of 0.5 mm from the front surface 10a of the wafer 10. However, by forming the fracture layer S near the front surface 10a, for example at a depth of 0.1 mm from the front surface 10a, it is possible to form dicing grooves on the front surface 10a as if by ablation. Additionally, while the above embodiment shows an example of forming a single fracture layer S inside the wafer 10, multiple fracture layers S can also be formed by overlapping in the vertical direction. In this case, the fracture layers S can be formed sequentially from a deeper position upwards (towards the front surface 10a).

Claims

1. A wafer processing method of dividing a wafer into individual chips, wherein the wafer processing method has the following steps: a holding step of holding the wafer on a chuck table; a thermal stress wave generating step of generating a thermal stress wave by irradiating a pulsed laser light of a wavelength having absorbency for the wafer from an upper surface of the wafer held on the chuck table toward a region to be divided, and propagating the thermal stress wave inside the region to be divided; a fracture layer forming step of irradiating a pulsed laser light of a wavelength having permeability for the wafer from the upper surface of the wafer, generating absorption of the pulsed laser light of the wavelength having permeability in a region in which a band gap is narrowed due to a tensile stress of the thermal stress wave, thereby forming a fracture layer as a division starting point, in accordance with the thermal stress wave generated in the thermal stress wave generating step propagating inside at an acoustic velocity corresponding to a material of the wafer to reach a depth position at which a division starting point is to be generated; and a dividing step of dividing the wafer into individual chips with the fracture layer as a division starting point.

2. A wafer processing apparatus of forming a division starting point of dividing a wafer into individual chips, wherein the wafer processing apparatus has: a chuck table which holds a wafer; a thermal stress wave generating unit which generates a thermal stress wave by irradiating a pulsed laser light of a wavelength having absorbency for the wafer from an upper surface of the wafer held on the chuck table toward a region to be divided, and propagates the thermal stress wave inside the region to be divided; and a fracture layer forming unit which irradiates a pulsed laser light of a wavelength having permeability for the wafer from the upper surface of the wafer, generates absorption of the pulsed laser light of the wavelength having permeability in a region in which a band gap is narrowed due to a tensile stress of the thermal stress wave, thereby forming a fracture layer as a division starting point, in accordance with the thermal stress wave generated by the thermal stress wave generating unit propagating inside the region to be divided at an acoustic velocity corresponding to a material of the wafer to reach a depth position at which a division starting point is to be generated. ​

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