Method for manufacturing multiple chips and laser processing method

Abstract

To reduce the degree in bending of cracks along a width direction of a scheduled dividing line.SOLUTION: There is provided a method for manufacturing multiple chips. The method includes: a first modified layer formation step of forming a first modified layer by relatively moving a workpiece and a focused area of a laser beam while the focused area is positioned in a predetermined width of a scheduled dividing line and in a first area inside the workpiece; a second modified layer formation step of forming a second modified layer by relatively moving the workpiece and the focused area while the focused area is positioned in a second area separated from the first area in a width direction and positioned within a predetermined width; and a division step. In the second modified layer formation step, when the second area is viewed in a cross section of the workpiece, the focused area has a tilted shape in an area including a tip of the focused area of the laser beam in a longitudinal direction, and the area including the tip is tilted so as to be away from the first area.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a chip manufacturing method for producing a plurality of chips by dividing a plate-shaped workpiece including a first surface and a second surface located opposite the first surface along a planned division line set on a predetermined plane parallel to the first surface or the second surface, and a laser processing method for processing the workpiece with a laser beam along the planned division line. [Background technology]

[0002] One method for dividing a workpiece, such as a semiconductor wafer, into device units, has a plurality of planned dividing lines set in a grid pattern on the surface and a device provided in each rectangular area defined by the plurality of planned dividing lines. This method utilizes a modified layer formed inside the workpiece using a pulsed laser beam having a wavelength that can pass through the workpiece.

[0003] For example, while the focal area of ​​the laser beam is positioned inside the workpiece, the focal area and the workpiece are moved relative to each other so that the laser beam traces each planned division line, thereby forming a modified layer inside the workpiece, and then an external force is applied to the workpiece to divide it into device units (see, for example, Patent Document 1).

[0004] When the workpiece is viewed in plan, the dividing line has a band shape with a predetermined width in a width direction perpendicular to the longitudinal direction of the dividing line. In the modified layer forming process for forming a modified layer inside the workpiece, multiple modified layers (e.g., two lines) may be formed at different positions in the width direction of the dividing line. The width (i.e., the length in the width direction) of the dividing line is, for example, 150 μm or less, and the distance between the two modified layers when the workpiece is viewed in plan is set to a predetermined value of, for example, 100 μm or less.

[0005] However, when two modified layers are formed at different positions in the width direction of each planned division line and then the workpiece is divided by applying an external force by expanding the expandable tape attached to the workpiece, there is a problem in that a crack extending from one of the modified layers along the thickness direction of the workpiece to the surface where the expandable tape is attached (for example, the back surface of the workpiece) bends along the width direction of the planned division line (see, for example, Patent Document 2).

[0006] Furthermore, when the expandable tape is attached to the surface of the workpiece located opposite the back surface of the workpiece, the surface to which it is attached becomes the surface of the workpiece, and a problem may arise in which a crack extending from one of the modified layers along the thickness direction of the workpiece to the surface of the workpiece bends along the width direction of the planned division line near the surface of the workpiece.

[0007] To solve this problem, it has been proposed to form two grooves by performing laser ablation processing on the area corresponding to the two modified layers in the thickness direction of the workpiece on the surface to be adhered to the expandable tape (for example, the back surface of the workpiece in Patent Document 2) after the two modified layers have been formed and before applying external force to the workpiece.

[0008] The formation of two grooves prevents cracks that extend from one modified layer along the thickness direction of the workpiece to the surface to which the expanding tape is attached from bending along the width direction of the planned division line. However, if a functional film such as a metal film, silicon oxide film, or silicon nitride film is intentionally formed on the back surface, it may be difficult to form grooves using laser ablation processing.

[0009] Furthermore, depending on the type of device, the heat generated by laser ablation processing may cause device failure. As such, the method of suppressing crack bending due to extension by forming grooves using laser ablation processing is not always applicable regardless of the type of workpiece. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-192370 [Patent Document 2] Japanese Patent Publication No. 2022-179058 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in consideration of these problems, and aims to reduce the degree to which a crack extending from one modified layer along the thickness direction of the workpiece to the surface of the workpiece where the expandable tape is attached bends along the width direction of the intended dividing line when multiple modified layers are formed along one intended dividing line in a planar view of the workpiece. [Means for solving the problem]

[0012] According to one aspect of the present invention, there is provided a chip manufacturing method for manufacturing a plurality of chips by dividing a plate-shaped workpiece including a first surface and a second surface opposite to the first surface along a band-shaped dividing line set in a predetermined plane parallel to the first surface or the second surface, the dividing line having a predetermined width in a width direction perpendicular to a longitudinal direction of the dividing line on the predetermined plane, the method including: a first modified layer forming step of irradiating a pulsed laser beam having a wavelength that transmits the workpiece from the first surface toward the second surface, and positioning a focusing region of the laser beam in a first region within the predetermined width and located between the first surface and the second surface, and relatively moving the workpiece and the focusing region along the longitudinal direction of the dividing line to form a first modified layer inside the workpiece; and a second modified layer forming step of irradiating the laser beam from the first surface toward the second surface, and positioning a focusing region of the laser beam in a first region separated from the first region in the width direction. and a second modified layer forming step of forming a second modified layer inside the workpiece by relatively moving the workpiece and the light focusing region along the longitudinal direction of the planned dividing line while positioning the light focusing region in a second region located within the specified width and between the first surface and the second surface, and a dividing step of dividing the workpiece into the plurality of chips along the planned dividing line by applying an external force to the workpiece after the first modified layer forming step and the second modified layer forming step, wherein in the second modified layer forming step, when the second region is viewed in a cross section of the workpiece in a plane perpendicular to the longitudinal direction of the planned dividing line, the light focusing region has an inclined shape in a region including the tip portion closest to the second surface in the longitudinal direction of the light focusing region of the laser beam, and the region including the tip portion is inclined so as to move away from the first region along the width direction as it moves from the first surface to the second surface.

[0013] According to another aspect of the present invention, there is provided a laser processing method for processing a workpiece having a plate shape and including a first surface and a second surface located opposite to the first surface, using a laser beam along a band-shaped planned division line set in a predetermined plane parallel to the first surface or the second surface, the planned division line having a predetermined width in a width direction perpendicular to a longitudinal direction of the planned division line on the predetermined plane, the method including: a first modified layer forming step of irradiating the workpiece from the first surface to the second surface with a pulsed laser beam having a wavelength that transmits the workpiece, and positioning a focusing region of the laser beam in a first region within the predetermined width and located between the first surface and the second surface, thereby relatively moving the workpiece and the focusing region along the longitudinal direction of the planned division line to form a first modified layer inside the workpiece; and a second modified layer forming step of irradiating a laser beam from the first surface toward the second surface, positioning the focusing region in a second region that is spaced apart from the first region in the width direction, within the predetermined width, and located between the first surface and the second surface, and then relatively moving the workpiece and the focusing region along the longitudinal direction of the planned dividing line to form a second modified layer inside the workpiece, wherein in the second modified layer forming step, when the second region is viewed in a cross section of the workpiece in a plane perpendicular to the longitudinal direction of the planned dividing line, the focusing region has an inclined shape in a region including a tip end portion of the focusing region of the laser beam that is closest to the second surface in the longitudinal direction, and the region including the tip end is inclined so as to move away from the first region along the width direction as it moves from the first surface to the second surface. [Effects of the Invention]

[0014] In a second modified layer formation process in a method for manufacturing multiple chips according to one embodiment of the present invention and a laser processing method according to another embodiment of the present invention, when the second region is viewed in a cross section of the workpiece in a plane perpendicular to the longitudinal direction of the planned division line, in a region including the tip closest to the second surface of the length of the focusing region of the laser beam, the focusing region has an inclined shape, and the focusing region moves away from the first region along the width direction as it moves from the first surface to the second surface.

[0015] By having the light-collecting region have such an inclined shape, when the workpiece is divided by applying an external force to the workpiece by expanding the expanding tape attached to the second surface, the degree to which a crack extending from one modified layer to the second surface is bent near the second surface due to the influence of the other modified layer can be reduced. For example, a crack extending from one modified layer can proceed straight, approximately perpendicular to the second surface, without being influenced at all by the other modified layer. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a flow diagram of a method for manufacturing a chip. [Figure 2] FIG. 1 is a perspective view of a laser processing device. [Figure 3] FIG. 3(A) is a perspective view of the workpiece unit, and FIG. 3(B) is a cross-sectional view taken along line AA in FIG. 3(A). [Figure 4] FIG. 2 is a schematic diagram of a laser beam irradiation unit. [Figure 5] FIG. 10 is a diagram illustrating a first modified layer forming step. [Figure 6] FIG. 10 is a diagram illustrating a second modified layer forming step. [Figure 7] 3 is a cross-sectional view of a workpiece unit on which first and second modified layers are formed. FIG. [Figure 8] FIG. [Figure 9] FIG. 9(A) is a partial cross-sectional side view of the dividing device, and FIG. 9(B) is a diagram showing the dividing step. [Figure 10] FIG. 10(A) is a planar photograph of the surface of the workpiece when θ=0.1°, and FIG. 10(B) is a CC cross-sectional photograph of FIG. 10(A). [Figure 11] FIG. 11(A) is a plan view of the surface of the workpiece when θ=0.26°, and FIG. 11(B) is a DD cross-sectional view of FIG. 10(A). [Figure 12] FIG. 10 is a diagram showing a second modified layer forming step in a comparative experimental example. [Figure 13]FIG. 13(A) is a plan view of the surface of the workpiece when θ=0°, and FIG. 13(B) is a photograph of the E-E cross section of FIG. 13(A). [Figure 14] FIG. 10 is a diagram showing a second modified layer forming step in the first modified example. [Figure 15] FIG. 15(A) is a diagram showing the first modified layer forming step S10 in the second modified example, and FIG. 15(B) is a diagram showing the second modified layer forming step S20 in the second modified example. [Figure 16] 10A and 10B are diagrams illustrating a second modified layer forming step in the third modified example. [Figure 17] FIG. 10 is a diagram showing a second modified layer forming step in the fourth modified example. [Figure 18] FIG. 13 is a diagram showing a second modified layer forming step in the fifth modified example. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a flow diagram of a manufacturing method for manufacturing a plurality of device chips (i.e., chips) 21 by dividing a workpiece 11 (see Fig. 2) along planned dividing lines 17, thereby dividing the workpiece 11 into a plurality of device chips 21 (see Fig. 9(B)).

[0018] In this embodiment, the steps of a first modified layer forming step S10, a second modified layer forming step S20, etc. are performed in order. Note that the steps of the first modified layer forming step S10, the second modified layer forming step S20, etc. correspond to a laser processing method in which the workpiece 11 is processed with a laser beam L (see FIG. 4) along the planned division lines 17. First, the laser processing apparatus 2 that performs the first modified layer forming step S10 and the second modified layer forming step S20 will be described.

[0019] FIG. 2 is a perspective view of the laser processing device 2. The X-axis, Y-axis, and Z-axis directions shown in FIG. 2 are perpendicular to one another. The X-axis direction is approximately parallel to the processing feed direction, and the Y-axis direction is approximately parallel to the indexing feed direction. The Z-axis direction is approximately parallel to the height direction (vertical direction). Note that in FIG. 2, some of the components are shown as functional blocks.

[0020] The laser processing device 2 has a base 4 that supports its components. The base 4 includes a flat base 6 and a wall 8 located at the rear end of the base 6. A chuck table 10 that holds a workpiece 11 by suction is disposed on the upper surface of the base 6. The chuck table 10 has a disk-shaped frame made of metal.

[0021] A disk-shaped recess with a smaller diameter than the frame is formed in the upper part of the frame, and a disk-shaped porous plate made of porous ceramic is fixed in this recess. Negative pressure generated by a suction source (not shown) such as a vacuum pump is transmitted to the porous plate through the frame. The upper surface of the porous plate and the upper surface of the frame are approximately flush with each other.

[0022] The upper surfaces of the porous plate and the frame function as a holding surface 10a that suction-holds the workpiece 11. The holding surface 10a is substantially flat and disposed substantially parallel to the XY plane. A ball-screw type Y-axis movement unit 12 is provided below the chuck table 10 to move the chuck table 10 in the Y-axis direction.

[0023] The Y-axis direction movement unit 12 includes a pair of Y-axis guide rails 14 that are fixed to the upper surface of the base 6 and arranged substantially parallel to the Y-axis direction. A Y-axis movement table 16 is slidably fixed to the Y-axis guide rails 14. A nut portion (not shown) is provided on the underside of the Y-axis movement table 16.

[0024] A screw shaft 18, which is disposed substantially parallel to the Y-axis direction, is rotatably coupled to this nut portion via a plurality of balls (not shown). A drive source 20, such as a servo motor or a stepping motor, is connected to one end of the screw shaft 18. When the drive source 20 rotates the screw shaft 18, the Y-axis moving table 16 moves along the Y-axis direction.

[0025] A ball screw type X-axis movement unit 22 that moves the chuck table 10 in the X-axis direction is provided on the upper surface side of the Y-axis movement table 16. The X-axis movement unit 22 includes a pair of X-axis guide rails 24 that are fixed to the upper surface of the Y-axis movement table 16 and arranged substantially parallel to the X-axis direction.

[0026] An X-axis moving table 26 is slidably fixed to the X-axis guide rail 24. A nut portion (not shown) is provided on the underside of the X-axis moving table 26, and a screw shaft 28, which is arranged substantially parallel to the X-axis direction, is rotatably coupled to this nut portion via a plurality of balls (not shown).

[0027] A drive source 30 such as a servo motor or a stepping motor is connected to one end of the screw shaft 28. When the drive source 30 rotates the screw shaft 28, the X-axis moving table 26 moves along the X-axis direction. A cylindrical support base 32 is provided on the upper surface side of the X-axis moving table 26. The chuck table 10 is disposed above the support base 32.

[0028] A drive source (not shown), such as a motor, is provided inside the support table 32, and as necessary, rotates the chuck table 10 within a predetermined angular range around a rotation axis parallel to the Z-axis direction. Now, the workpiece 11 will be described with reference to Figures 3(A) and 3(B).

[0029] Fig. 3(A) is a perspective view of a workpiece unit 15 in which a workpiece 11 and a protective tape 13 are stacked, and Fig. 3(B) is a cross-sectional view taken along line AA in Fig. 3(A). The workpiece 11 has a disk-shaped silicon single crystal substrate. The silicon single crystal substrate has, for example, a diameter of 12 inches (approximately 300 mm) and a thickness of 775 µm.

[0030] As shown in Figures 3(A) and 3(B), the workpiece 11 has a circular plate shape and includes a circular front surface (second surface) 11a and a back surface (first surface) 11b located on the opposite side of the front surface 11a in the thickness direction 11c of the workpiece 11.

[0031] A plurality of planned dividing lines 17 are set in a grid pattern on the surface 11a of the workpiece 11. That is, a plurality of planned dividing lines 17 each extending along a first direction and a plurality of planned dividing lines 17 each extending along a second direction perpendicular to the first direction are set on the surface 11a.

[0032] Each of the division lines 17 has a band shape on the surface 11a. In this specification, a direction perpendicular to the longitudinal direction 17a of each of the division lines 17 on the surface 11a is referred to as a width direction 17b of the division line 17 (see FIG. 3(B)).

[0033] The length of the dividing line 17 in the longitudinal direction 17a varies depending on the position of the dividing line 17 on the surface 11a. For example, the dividing line 17 passing through the center of the surface 11a has a length equal to the diameter of the workpiece 11 in the longitudinal direction 17a.

[0034] On the other hand, each of the planned division lines 17 has a predetermined size in the width direction 17b (that is, a predetermined width 17c). The predetermined width 17c is, for example, 50 μm or more and 150 μm or less, and is 100 μm in this embodiment.

[0035] Devices 19 such as ICs (Integrated Circuits), LEDs (Light Emitting Diodes), MEMS (Micro Electro Mechanical Systems), etc. are formed in each rectangular region partitioned by the plurality of planned division lines 17. There are no limitations on the type, number, shape, structure, size, arrangement, etc. of the devices 19.

[0036] Incidentally, the device 19 may not be provided on the front surface 11a. In this case, each planned division line 17 may not actually be drawn on the front surface 11a. Each planned division line 17 may be virtually set on the front surface 11a or the back surface 11b, or may be set on a virtual predetermined plane 11d (see FIG. 3(B)) that is separated from the front surface 11a or the back surface 11b and parallel to the front surface 11a or the back surface 11b.

[0037] In this embodiment, the workpiece unit 15 is formed by adhering the adhesive surface 13a of the protective tape 13, which has approximately the same diameter as the workpiece 11, to the surface 11a of the workpiece 11. However, the workpiece unit 15 may also be formed by integrating the workpiece 11, a protective tape having a larger diameter than the workpiece 11, and a metal annular frame (not shown).

[0038] The annular frame is annular in shape with an inner diameter larger than the diameter of the workpiece 11. In this case, with the workpiece 11 placed in the opening of the annular frame, protective tape with a diameter larger than that of the workpiece 11 is attached to the front surface 11a or the back surface 11b of the workpiece 11 and to one surface of the annular frame, thereby forming the above-mentioned workpiece unit 15.

[0039] Returning to Fig. 2, another configuration of the laser processing apparatus 2 will be described. A support arm 34 extending along the Y-axis direction is provided on the upper front side of the wall portion 8. A part of the laser beam irradiation unit 36 ​​is provided on the support arm 34, and a cylindrical head portion 38 is provided on the tip of the support arm 34.

[0040] 4 is a schematic diagram of the laser beam irradiation unit 36. In FIG. 4, functional blocks are shown of some of the components of the laser beam irradiation unit 36. The laser beam irradiation unit 36 ​​has a laser oscillator 40 fixed to the base 4.

[0041] The laser oscillator 40 has, for example, a crystal such as Nd:YAG as a laser medium, and emits a pulsed laser beam L having a wavelength (e.g., 1064 nm) that passes through the workpiece 11 (in this example, a silicon single crystal substrate) by irradiating the crystal with excitation light from a light source such as a flash lamp or a laser diode.

[0042] The laser beam L, after its power is adjusted by an attenuator (not shown) or the like, proceeds to the spatial light phase modulator 42. The spatial light phase modulator 42 has a reflective LCOS-SLM (Liquid Crystal on Silicon - Spatial Light Modulator).

[0043] The spatial light phase modulator 42 of this embodiment has a first function of simply reflecting the laser beam L without performing wavefront control, and a second function of performing wavefront control on the laser beam L and reflecting the laser beam L.

[0044] The first and second functions of the spatial light phase modulator 42 are switched by a controller 56, which will be described later. By performing the second function, the focused area of ​​the laser beam L inside the workpiece 11 can be made to have a different shape compared to the shape of the focused area formed by focusing the laser beam L inside the workpiece 11 without performing wavefront control.

[0045] The spatial light phase modulator 42 may include a transmissive spatial light phase modulator such as an LC-SLM (Liquid Crystal - Spatial Light Modulator) having the above-mentioned first and second functions, instead of the LCOS-SLM. The laser beam L that has passed through the spatial light phase modulator 42 is guided to the head unit 38.

[0046] The head unit 38 is provided with a mirror 44 for changing the direction of travel of the laser beam L. The laser beam L reflected by the mirror 44 passes through a condenser lens 46 and is irradiated downward.

[0047] Returning to Figure 2, a head portion 52 of the microscope camera unit 50 is provided at the tip of the support arm 34. The head portion 52 is adjacent to the head portion 38 in the Y-axis direction. The microscope camera unit 50 has, for example, an objective lens, a light source, and an imaging element.

[0048] The light source includes an LED (Light Emitting Diode) capable of emitting infrared light (for example, near-infrared light between 1000 nm and 2000 nm). The imaging element includes a solid-state imaging element (image sensor) capable of photoelectrically converting infrared light (for example, near-infrared light).

[0049] The imaging element has, for example, a CCD (Charge-Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) image sensor, and includes a photodiode (for example, an InGaAs (Indium Gallium Arsenide) photodiode) for photoelectrically converting infrared rays.

[0050] The microscope camera unit 50 of this embodiment can capture an image of the front surface 11a of the workpiece 11 from the back surface 11b using infrared light from a light source, so that the infrared light passes through the workpiece 11. As shown in Fig. 1, a cover (not shown) that covers the above-mentioned components is provided on the base 4. A touch panel 54 is provided on the front surface of the cover (one side in the Y-axis direction).

[0051] The touch panel 54 is a liquid crystal display including a capacitance type touch sensor, and functions as an input device for the operator to input instructions to the laser processing device 2, a GUI (Graphical User Interface) for inputting instructions, and a display device for displaying images obtained by the microscope camera unit 50, etc.

[0052] The laser processing device 2 is provided with a controller 56 that controls the operation of the chuck table 10, Y-axis direction moving unit 12, X-axis direction moving unit 22, drive source within the support base 32, laser beam irradiation unit 36, microscope camera unit 50, touch panel 54, etc.

[0053] The controller 56 is composed of a computer including, for example, a processor represented by a CPU (Central Processing Unit), a main memory device such as a DRAM (Dynamic Random Access Memory), an SRAM (Static Random Access Memory), or a ROM (Read Only Memory), and an auxiliary memory device such as a flash memory, a hard disk drive, or a solid state drive.

[0054] The auxiliary storage device stores software including a predetermined program. The functions of the controller 56 are realized by operating a processor or the like in accordance with this software. Next, the first modified layer forming step S10, the second modified layer forming step S20, etc., using the laser processing device 2 will be described.

[0055] When performing laser processing on the workpiece 11, first, the workpiece unit 15 is suction-held on the holding surface 10a so that the back surface 11b is exposed upward and the protective tape 13 is in contact with the holding surface 10a (see Figure 4).

[0056] Next, based on the image obtained by capturing the surface 11a with the microscope camera unit 50, the orientation of the chuck table 10 is adjusted so that the longitudinal direction 17a of one planned division line 17 along the first direction is approximately parallel to the X-axis direction.

[0057] Then, a laser beam L is irradiated from the back surface 11b toward the front surface 11a, and the focusing area F of the laser beam L is positioned in a first area B1 located within a predetermined width 17c of one of the planned division lines 17 and between the back surface 11b and the front surface 11a in the thickness direction 11c (see Figure 5), and the workpiece 11 and the focusing area F are moved relatively along the longitudinal direction 17a from one end to the other end of the longitudinal direction 17a.

[0058] In particular, in this embodiment, by controlling the wavefront of the laser beam L with the spatial light phase modulator 42, the laser beam L incident on the workpiece 11 is split into two in the thickness direction 11c, as shown in FIG. 5, and the upper light collecting areas F are formed at different positions in the thickness direction 11c. A and the lower light collection area F B Form.

[0059] In this state, the workpiece 11 and the upper light collecting area F A and the lower light collection area F B and are moved relatively along the longitudinal direction 17a from one end to the other end of the dividing line 17, so that upper modified layers R are formed inside the workpiece 11 at positions separated in the thickness direction 11c. 1A and lower modified layer R 1B A first modified layer R1 (see FIG. 6) including the above is formed (first modified layer forming step S10).

[0060] 5 is a diagram showing the first modified layer forming step S10. An example of processing conditions in the first modified layer forming step S10 is shown below.

[0061] Wavelength: 1064nm Average output: 2.8W (upper focusing area F A ), 2.8W (lower light collection area F B ) Repetition frequency: 120kHz Processing feed rate: 1000mm / s Center position of the light-collecting region: 660 μm depth position from the back surface 11b (upper light-collecting region F A ) : 710 μm depth position from the back surface 11b (lower light collecting region F B )

[0062] Upper light collecting region F in the first modified layer forming step S10 A and the lower light collection area F B are elliptical in shape with their major axes (i.e., longitudinal portions) aligned along the thickness direction 11c (see FIG. 5), and the upper modified layer R 1A and lower modified layer R 1B Each of the electrodes 11a and 11b has a substantially elliptical shape with its major axis aligned along the thickness direction 11c (see FIG. 6).

[0063] The modified layer is a region in which physical properties such as density, refractive index, and mechanical strength have changed before and after irradiation with the laser beam L, and in the modified layer, a single-crystal region has changed into an amorphous region and / or a polycrystalline region. In general, a region in which a modified layer is formed has lower mechanical strength than a region in which a modified layer is not formed.

[0064] In the first modified layer forming step S10, the laser beam L is split into two beams, and it takes several hundred nanoseconds from the irradiation of the laser beam L until the first modified layer R1 and the second modified layer R2 are formed. 1A The lower light collection region F B The lower modified layer R 1B can be formed.

[0065] After the first modified layer R1 is formed (i.e., after the first modified layer forming step S10), the head unit 38 and the chuck table 10 are moved relatively along the Y-axis direction by a predetermined amount. In this embodiment, the predetermined width 17c is 100 μm, but the predetermined amount is 80 μm. Then, the second modified layer forming step S20 is performed to form a second modified layer R2 (see FIG. 7) inside the workpiece 11 along the same planned dividing line 17.

[0066] In the second modified layer forming step S20, the laser beam L is also irradiated from the back surface 11b toward the front surface 11a, and the focusing region F of the laser beam L is positioned in a second region B2 that is separated from the first region B1 in the width direction 17b, is within a predetermined width 17c, and is located between the back surface 11b and the front surface 11a in the thickness direction 11c. In this state, the workpiece 11 and the focusing region F are moved relatively along the longitudinal direction 17a from one end to the other end in the longitudinal direction 17a.

[0067] As a result, upper modified layers R are formed inside the workpiece 11 at positions spaced apart in the thickness direction 11c. 2A and lower modified layer R 2B A second modified layer R2 (see FIG. 7) including the above is formed (second modified layer forming step S20). FIG. 6 is a diagram showing the second modified layer forming step S20, showing a cross section of the workpiece 11 in the YZ plane perpendicular to the longitudinal direction 17a. An example of processing conditions in the second modified layer forming step S20 is shown below.

[0068] Wavelength: 1064nm Average output: 2.8W (upper focusing area F A ), 2.8W (lower light collection area F B ) Repetition frequency: 120kHz Processing feed rate: 1000mm / s Center position of the light-collecting region: 660 μm depth position from the back surface 11b (upper light-collecting region F A ) : 710 μm depth position from the back surface 11b (lower light collecting region F B )

[0069] In the second modified layer forming step S20, the laser beam L is split into two beams by the wavefront control of the spatial light phase modulator 42, and the upper light collecting area F A The upper modified layer R 2A is formed, and the lower light collection region F B The lower modified layer R 2B is formed.

[0070] Furthermore, by controlling the wavefront with the spatial light phase modulator 42, the upper light collecting area FA and the lower light collection area F B 6, the upper light collecting region F has an elliptical shape with its major axis (i.e., its longitudinal portion) aligned along a direction intersecting the thickness direction 11c at a predetermined angle θ. A and the lower light collection area F B The longitudinal direction 11e and the thickness direction 11c form a predetermined angle θ.

[0071] In this embodiment, the upper light collection region F A and the lower light collection area F B Each of the first and second regions B1 and B2 is inclined as a whole so as to move away from the first region B1 along the width direction 17b from the rear surface 11b toward the front surface 11a, and the major axes of the first and second regions B1 and B2 are aligned on a straight line in a cross-sectional view.

[0072] Therefore, the upper light collection region F A and the lower light collection area F B When the second region B2 is viewed in a cross section on the YZ plane, each of the upper focusing region F of the laser beam L A and the lower light collection area F B The tip F of each of the longitudinal directions 11e is closest to the surface 11a. AC ,F BC In the region including

[0073] In this embodiment, the predetermined angle θ is 0.26°, but the predetermined angle θ is not limited to this value. The predetermined angle θ is any angle greater than 0° and equal to or less than 1° (i.e., 0°<θ≦1°). Note that if the predetermined angle θ is greater than 1°, it becomes difficult for a crack 11f (see FIG. 9(A)) to propagate from the modified layer (described later) as a starting point, which is undesirable.

[0074] The shape of the light-collecting region F is determined by, for example, the power density (W / cm ) above the processing threshold. 2 ) can be defined by the contour lines of the light collection region F. In this embodiment, the three-dimensional shape of the light collection region F resembles an elongated oval sphere.

[0075] In addition, when the shape of the light-collecting region F is an elongated oval sphere with its major axis along the Z-axis direction, the shape of the light-collecting region F in cross-section on the YZ plane perpendicular to the processing feed direction will be an elongated oval with its major axis along the Z-axis direction.

[0076] After the second modified layer forming process S20, if the first modified layer R1 and the second modified layer R2 have not been formed on all planned division lines 17 along the X-axis direction (NO in the judgment process S30 in Figure 1), indexing is performed by an index amount corresponding to the length of the device 19 in the Y-axis direction (indexing process S40).

[0077] On the other hand, if the first modified layer R1 and the second modified layer R2 are formed on all of the planned division lines 17 along the X-axis direction (YES in the judgment step S30 in Figure 1), but the first modified layer R1 and the second modified layer R2 are not formed on all of the planned division lines 17 along the X-axis direction and the Y-axis direction (NO in the judgment step S50 in Figure 1), the chuck table 10 is rotated 90 degrees (chuck table 90 degree rotation step S60 in Figure 1).

[0078] The chuck table is rotated 90° in a step S60 to make one of the division lines 17 along the second direction substantially parallel to the X-axis direction. Then, the first modified layer forming step S10 and the second modified layer forming step S20 are sequentially repeated to form a first modified layer R1 and a second modified layer R2 on each of the division lines 17.

[0079] In this way, sequentially repeating the first modified layer forming step S10 and the second modified layer forming step S20 is effective in increasing the number of treatments per hour (ie, UPH (units per hour)).

[0080] Specifically, sequentially repeating the first modified layer formation process S10 and the second modified layer formation process S20 can increase the UPH compared to performing the first modified layer formation process S10 on all planned division lines 17 along the first direction and then performing the second modified layer formation process S20 on all planned division lines 17 along the first direction.

[0081] 7 is a cross-sectional view of the workpiece unit 15 in which a first modified layer R1 and a second modified layer R2 are formed on all of the planned division lines 17. After the first modified layer R1 and the second modified layer R2 are formed on all of the planned division lines 17 along the X-axis direction and the Y-axis direction (YES in the determination step S50 in FIG. 1), the back surface 11b of the workpiece 11 is ground using a grinding device 60 shown in FIG. 8, thereby thinning the workpiece 11 (thinning step S70).

[0082] Although the thinning step S70 may be omitted, in this embodiment where the workpiece 11 is relatively thick, the workpiece 11 is thinned. As shown in Fig. 8, the grinding device 60 has a disk-shaped chuck table 62. The chuck table 62 has a disk-shaped frame made of non-porous ceramics and a porous plate disposed in the center of the frame.

[0083] A flow path is formed in the frame, and negative pressure generated by a suction source (not shown) such as a vacuum pump is transmitted to the upper surface of the porous plate via the flow path in the frame. The upper surface of the frame and the upper surface of the porous plate are substantially flush with each other, forming a circular holding surface.

[0084] The holding surface has a conical shape with the center of the holding surface projecting from the outer periphery by approximately 10 μm to 30 μm in the radial direction. When negative pressure is applied to the porous plate with the workpiece 11 placed on the holding surface, the workpiece 11 is sucked and held by the holding surface in a state where it is deformed to follow the shape of the holding surface.

[0085] The chuck table 62 is rotatably supported by a circular table base 64 via bearings (not shown). A rotation shaft 62a of the chuck table 62 is inserted into a through hole (not shown) located in the radial center of the table base 64.

[0086] When the rotation shaft 62a is rotated by a rotation drive source (not shown), the chuck table 62 also rotates around the rotation shaft 62a. The table base 64 is supported by an inclination adjustment unit (not shown).

[0087] The table base 64 adjusts the inclination of the chuck table 62 so that, for example, a portion of the holding surface of the chuck table 62 is approximately parallel to the grinding surface of a grinding wheel 72 (described later). A grinding unit 66 is provided above the chuck table 62.

[0088] The grinding unit 66 has a cylindrical spindle 68 whose longitudinal direction is arranged along the Z-axis direction. A rotation drive source (not shown), such as a servo motor, is provided at the center of the spindle 68 in the longitudinal direction.

[0089] A disk-shaped wheel mount 70 is fixed to the lower end of the spindle 68. A grinding wheel 72 is attached to the underside of the wheel mount 70 using a fixing member such as a bolt.

[0090] The grinding wheel 72 has an annular wheel base 72a made of a metal material such as an aluminum alloy. A plurality of grinding stones 72b are fixed to the underside of the wheel base 72a. The plurality of grinding stones 72b are arranged at approximately equal intervals around the circumferential direction of the wheel base 72a.

[0091] The grinding wheels 72b are formed by mixing abrasive grains such as diamond or cBN (cubic boron nitride) with a binder such as metal, ceramics, or resin, and then molding, firing, shaping, etc. The locus of the lower surfaces of the multiple grinding wheels 72b formed by rotating the spindle 68 becomes the grinding surface of the grinding wheel 72 described above.

[0092] 8 is a diagram showing the thinning step S70. In the thinning step S70, first, the workpiece unit 15 is suction-held by the chuck table 62 so that the back surface 11b is exposed and the protective tape 13 is in contact with the holding surface of the chuck table 62.

[0093] Next, the chuck table 62 and the spindle 68 are rotated in a predetermined direction, and the grinding unit 66 is moved downward at a predetermined speed while supplying grinding water such as pure water to the contact area between the multiple grinding wheels 72b and the workpiece 11.

[0094] This causes the entire back surface 11b to be ground almost uniformly, thinning the workpiece 11 until it reaches a finish thickness (e.g., 200 μm). The finish thickness of the workpiece 11 is adjusted as appropriate. In the thinning step S70, the back surface 11b may be polished in addition to being subjected to rough grinding and finish grinding.

[0095] In the thinning step S70 of this embodiment, the lower modified layer R 1B ,R 2B The upper modified layer R is closer to the rear surface 11b than the 1A ,R 2A The workpiece 11 is thinned from the back surface 11b toward the front surface 11a so that the first modified layer R1 and the second modified layer R2 are not exposed on the back surface 11b. In the thinning step S70, an external force applied to the workpiece 11 by grinding or the like causes cracks 11f (see FIG. 9(A)) to extend from the first modified layer R1 and the second modified layer R2 as starting points.

[0096] After the thinning process S70 (i.e., after the first modified layer formation process S10 and the second modified layer formation process S20), a division process S80 is performed in which the workpiece 11 is divided into multiple device chips 21 along the planned division lines 17 by applying an external force to the workpiece 11 using a tape expansion type division device 80.

[0097] At the end of the thinning process S70, some cracks 11f may have already reached the surface 11a and back surface 11b of each planned division line 17, but in the division process S80 using the division device 80, the workpiece 11 will be divided into multiple device chips 21 in a spatially separated manner.

[0098] Fig. 9(A) is a partially cross-sectional side view of the dividing device 80. The dividing device 80 has a cylindrical drum 82 having a diameter larger than the diameter of the workpiece 11. Note that hatching showing the cross section of the drum 82 is omitted in Fig. 9(A).

[0099] A plurality of rollers 84 are provided at the upper end of the drum 82 at approximately equal intervals along the circumferential direction of the drum 82. An annular frame support base 86 is provided on the outer side of the drum 82 in the radial direction of the drum 82.

[0100] A plurality of clamps 88 are provided on the upper surface of the frame support base 86. The frame support base 86 is supported by a plurality of legs 90 arranged at approximately equal intervals along the circumferential direction of the frame support base 86. Each leg 90 can be raised and lowered by a lifting mechanism such as an air cylinder.

[0101] In this embodiment, after the thinning step S70, the protective tape 13 is replaced before the workpiece 11 is divided using the dividing device 80. Specifically, a replacement tape (not shown) is attached to the back surface 11b of the workpiece 11 after the thinning step S70, and the protective tape 13 is peeled off from the front surface 11a.

[0102] Then, with the workpiece 11 placed in the opening 23a of a metal annular frame 23 having an opening 23a whose inner diameter is larger than the outer diameter of the workpiece 11, a resin expanding tape 25 having a circular outer shape is attached to the front surface 11a of the workpiece 11 and one surface of the annular frame 23. Thereafter, the replacement tape is peeled off from the back surface 11b.

[0103] This forms a frame unit 27 in which the workpiece 11 and the annular frame 23 are integrated via the expanding tape 25. Next, the upper end of the drum 82 and the upper surface of the frame support base 86 are positioned at approximately the same height, and the frame unit 27 is placed on the dividing device 80 so that the workpiece 11 is exposed upward.

[0104] At this time, the rollers 84 come into contact with the expanding tape 25. Also, the annular frame 23 placed on the frame support base 86 is clamped by the clamps 88 (see FIG. 9(A)). FIG. 9(B) is a diagram showing the dividing step S80.

[0105] In the dividing step S80, the elevators are operated to lower the frame support base 86 below the rollers 84 relative to the drum 82. This causes the expanding tape 25 to expand radially, applying an external force to the workpiece 11 in a radially expanding direction, and dividing the workpiece 11 into a plurality of device chips 21.

[0106] In this embodiment, the upper light collection region F A and the lower light collection area F B Each of the second modified layer R2 (particularly, the lower modified layer R 2B ) to the surface 11a, the degree to which the crack 11f is bent due to the influence of the first modified layer R1 in the vicinity of the surface 11a can be reduced.

[0107] For example, a crack 11f extending from the second modified layer R2 advances straight so as to be substantially perpendicular to the rear surface 11b or the front surface 11a without being affected by the first modified layer R1 at all.

[0108] Next, experimental results corresponding to this embodiment will be described with reference to Figures 10(A) to 11(B). In this experiment, the first modified layer forming step S10 and the second modified layer forming step S20 were sequentially performed under the above-mentioned processing conditions on one planned dividing line 17 of the workpiece 11 having a silicon single crystal substrate, and then the dividing step S80 was performed after omitting the thinning step S70.

[0109] In the first and second experimental examples and the comparative experimental example described below, the surface 11a is formed by a metal thin film 29 (see FIG. 12) instead of the device 19. The laser beam L passing from the back surface 11b to the surface 11a causes a so-called surface burn on the metal thin film 29.

[0110] (First Experimental Example) FIG. 10(A) shows the upper light collecting region F in the second modified layer forming step S20. A and the lower light collection area F B 11 is a plan view of the surface 11a including the dividing lines 17 when the predetermined angle θ formed by the longitudinal direction 11e and the thickness direction 11c is 0.1°.

[0111] 10(A), a surface burn is formed when the laser beam L passes through the surface 11a in the first modified layer forming step S10. The surface burn includes a plurality of elliptical rings arranged along the longitudinal direction 17a of the intended division line 17. In the left region 11g1 of the surface 11a, a crack 11f that has reached the surface 11a passes through the center of the plurality of rings arranged along the longitudinal direction 17a.

[0112] In the right region 11g2 of the surface 11a, a similar surface burn is formed by irradiating the surface 11a with the laser beam L in the second modified layer forming step S20. However, in the right region 11g2, the crack 11f is closer to the left region 11g1 than the center of the multiple rings arranged along the longitudinal direction 17a.

[0113] 10(B) is a photograph of the CC cross section of FIG. 10(A), which is a cross section of the workpiece 11 divided at the crack 11f. 2B Between the surface 11a and the surface 11b, a convex portion 11h is formed that protrudes toward the front of the paper, and in FIG. 10(B), this convex portion 11h is observed as a blurred black line.

[0114] The metal thin film 29 has a predetermined thickness of 1 μm or less, which is very thin and has little contrast with the black background color, so it is almost invisible in Fig. 10(B) When the predetermined angle θ = 0.1° in the second modified layer formation step S20 is inferior to the second experimental example described later, it is possible to reduce the degree to which the cracks 11f extending to the surface 11a bend near the surface 11a compared to the comparative experimental example described later.

[0115] (Second Experimental Example) FIG. 11(A) shows the second modified layer forming step S20. A and the lower light collection area F B 11 is a plan photograph of the surface 11a including the dividing lines 17 when the predetermined angle θ formed by the longitudinal direction 11e and the thickness direction 11c is 0.26°.

[0116] In the left region 11g1 of Fig. 11(A), cracks 11f are formed that pass through the centers of the rings arranged along the longitudinal direction 17a, similar to the left region 11g1 of Fig. 10(A). Also, in the right region 11g2 of Fig. 11(A), cracks 11f are formed that pass through approximately the centers of the rings arranged along the longitudinal direction 17a.

[0117] 11(B) is a DD cross-sectional photograph of FIG. 11(A), which is a cross-sectional view of the workpiece 11 divided at the crack 11f. In the cross-sectional view of FIG. 11(B), unlike FIG. 10(B), the lower modified layer R 2B There is no protrusion 11h that protrudes into the paper between the surface 11a and the surface 11b.

[0118] That is, in the vicinity of the surface 11a of the second experimental example, the lower modified layer R 2B The crack 11f extending from the lower modified layer R 1B 11B, the metal thin film 29 is not visible at all, and travels straight across the surface 11a almost perpendicularly, as in FIG.

[0119] (Comparative Experimental Example) Next, a comparative experimental example will be described with reference to Figure 12, Figure 13(A) and Figure 13(B) Figure 12 is a diagram showing the second modified layer forming step S20 in the comparative experimental example.

[0120] In the second modified layer forming step S20 in the comparative example, similarly to the first modified layer forming step S10, the upper light collecting region F A and the lower light collection area F B The major axes of the electrodes are aligned in a straight line along the thickness direction 11c.

[0121] FIG. 13(A) shows the upper light collecting region F in the second modified layer forming step S20. A and the lower light collection area F B 11 is a plan view of the surface 11a including the dividing lines 17 when the predetermined angle θ formed by the longitudinal direction 11e and the thickness direction 11c is 0°.

[0122] In the left region 11g1 of FIG. 13(A), cracks 11f are formed that pass through the centers of multiple rings arranged along the longitudinal direction 17a, similar to the left region 11g1 of FIGS. 10(A) and 11(A).

[0123] However, in the right region 11g2 of FIG. 13(A), the crack 11f is shifted toward the left region 11g1 from the center of the rings arranged along the longitudinal direction 17a, and passes through the outer periphery of the rings.

[0124] In other words, when the specified angle θ in the second modified layer formation process S20 is 0°, when the crack 11f extends along the thickness direction 11c to the surface 11a, it is influenced by the first modified layer R1 and bends along the width direction 17b so as to approach the first modified layer R1.

[0125] 13(B) is a photograph of the E-E cross section of FIG. 13(A), which is a cross section of the workpiece 11 divided at the crack 11f. In the cross section of FIG. 13(B), the lower modified layer R 2B The black blurred line between the surface 11a and the surface 11b is clearer than in FIG. 10(B).

[0126] That is, the protrusion amount of the convex portion 11h in Fig. 13(B) is larger than the protrusion amount of the convex portion 11h in Fig. 10(B). The applicant has confirmed that when the predetermined angle θ is set to 0.36°, the crack 11f is less likely to propagate than when the predetermined angle θ is set to 0.26°.

[0127] Therefore, the predetermined angle θ is preferably 0.1° or more and 0.36° or less, and more preferably 0.26° or more and 0.36° or less. Incidentally, in Figure 13(B) as in Figure 10(B), the metal thin film 29 is not substantially visible. Next, with reference to Figures 14 to 17, modifications of the preferred embodiment will be described.

[0128] 14 is a diagram showing the second modified layer forming step S20 in the first modified example. In the first modified example, the laser beam L is also split into two in the thickness direction 11c, but the upper light collecting region F A is an elliptical shape with its major axis aligned along the thickness direction 11c, and the lower light collecting region F B The chisel is formed into an elliptical shape with its major axis inclined at a predetermined angle θ with respect to the thickness direction 11c.

[0129] (Second Modification) Figure 15(A) is a diagram showing the first modified layer forming step S10 in the second modification. In the second modification, the laser beam L is not split into two in the thickness direction 11c, but is focused to approximately one point. The average output at each point may be the same whether it is a multiple point or a single point. In the example shown in Figure 15(A), the lower light focusing region F B The laser beam L is focused at a point corresponding to the

[0130] 15B is a diagram showing the second modified layer forming step S20 in the second modified layer forming step S20. In the second modified layer forming step S20, the laser beam L is not split into two in the thickness direction 11c, but is focused in the lower light collecting region F B The laser beam L is focused at a point corresponding to the

[0131] However, in the second modified layer forming step S20, the wavefront control by the spatial light phase modulator 42 causes the lower light collecting area F B The lower light collecting region F is arranged so that the major axis of the B is inclined with respect to the thickness direction 11c.

[0132] 16 is a diagram showing the second modified layer forming step S20 in the third modified example.B However, by controlling the wavefront, the laser beam L is focused at a point corresponding to the lower focusing area F B The major axis of the ellipse is arranged along the thickness direction 11c in the approximately upper half of the ellipse.

[0133] In addition, wavefront control is used to reduce the size of the lower focusing area F B The tip part F BC In the substantially lower half including the first region B1, the major axis of the ellipse forms a predetermined angle θ with the thickness direction 11c, and the lower modified layer R 1B Tilt it away from the

[0134] As shown in the enlarged view at the bottom right of Figure 16, when the semimajor axis of the long axis is a, the lower light-collecting region F B Approximately midway point F B1 In the range of length a cosθ along the thickness direction 11c from B The major axis of the ellipse is inclined at a predetermined angle θ with respect to the thickness direction 11c.

[0135] 17 is a diagram showing the second modified layer forming step S20 in a fourth modified example. In the fourth modified example, the laser beam L is split into two beams in the thickness direction 11c as in the above-described embodiment, but instead of using the spatial light phase modulator 42 to control the wavefront of the laser beam L, the head unit 38 and the workpiece 11 are inclined by a predetermined angle θ with respect to the thickness direction 11c.

[0136] In the example shown in Figure 17, the thickness direction 11c is arranged parallel to the Z-axis direction, and the head portion 38 (i.e., the optical axis 46a of the focusing lens 46) is tilted with respect to the Z-axis direction (i.e., the thickness direction 11c of the workpiece 11).

[0137] In this way, when tilting the optical axis 46a in the second modified layer forming step S20, the tilt of the head part 38 is controlled by an angle adjustment unit (not shown) having a piezoelectric actuator or the like. The operation of the angle adjustment unit is controlled by an electrical signal from the controller 56.

[0138] When the first modified layer formation process S10 and the second modified layer formation process S20 are performed alternately, in the first modified layer formation process S10, the optical axis 46a is made approximately parallel to the Z-axis direction (thickness direction 11c), in the subsequent second modified layer formation process S20, the optical axis 46a is tilted by a predetermined angle θ with respect to the Z-axis direction, and in the subsequent first modified layer formation process S10, the optical axis 46a is returned to being approximately parallel to the Z-axis direction.

[0139] (Fifth Modification) Figure 18 is a diagram showing the second modified layer forming step S20 in the fifth modification. In the fifth modification, the laser beam L is not split into two beams in the thickness direction 11c, but is focused to a substantially single point. However, in the second modified layer forming step S20, the center L of the laser beam L in a cross section perpendicular to the traveling direction of the laser beam L is A is shifted by a predetermined amount G from the optical axis 46a.

[0140] Center L of laser beam L A For example, when the light intensity distribution of the laser beam L in a cross section perpendicular to the traveling direction is a Gaussian profile, it is the peak position of the light intensity distribution, and when the light intensity distribution in the same cross section is a top-hat profile or a flat-top profile, it is the center position of the flat range.

[0141] In the second modified layer forming step S20 shown in FIG. 18, the center L of the laser beam L incident on the condenser lens 46 A is shifted by a predetermined amount G from the optical axis 46a along the width direction 17b in a direction approaching the first region B1 (that is, in the +Y direction).

[0142] This allows the lower light collection area F B The lower light collecting region F is arranged such that its lower end is shifted from the optical axis 46a along the width direction 17b in a direction away from the first region B1 (i.e., in the -Y direction) compared to its upper end. B can be tilted.

[0143] In this way, the lower light collection area F BThe reason why the lens can be tilted is at least due to the fact that so-called coma aberration occurs when the laser beam L is focused.

[0144] In FIG. 18, the center L of the laser beam L A is aligned with the optical axis 46a (i.e., θ=0°), the lower light-collecting region F B is shown by a broken line, and the lower light collecting region F when the major axis of the ellipse forms a predetermined angle θ with the thickness direction 11c (i.e., θ≠0°). B is shown by a solid line.

[0145] In the first to fifth modified examples, the degree to which the cracks 11f extending from the second modified layer R2 to the surface 11a bend along the width direction 17b of the dividing line 17 near the surface 11a can also be reduced in the dividing step S80.

[0146] For example, a crack 11f extending from the second modified layer R2 can proceed straight, substantially perpendicular to the surface 11a, without being affected by the first modified layer R1. In addition, the structures, methods, etc. according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention.

[0147] For example, after the first modified layer forming step S10 is performed on all the division lines 17 along the first direction, the second modified layer forming step S20 can be performed on all the division lines 17 along the first direction. The same applies to the division lines 17 along the second direction.

[0148] In addition, in the above-described embodiment, a case has been described in which the second modified layer formation process S20 is performed on the same planned dividing line 17 after the first modified layer formation process S10, but the first modified layer formation process S10 may also be performed on the same planned dividing line 17 after the second modified layer formation process S20.

[0149] Of course, it is also possible to perform the second modified layer forming step S20 on all the division lines 17 along the first direction, and then perform the first modified layer forming step S10 on all the division lines 17 along the first direction. The same applies to the division lines 17 along the second direction.

[0150] In the above-described embodiment and modified examples, no functional film such as a metal film, a silicon oxide film, or a silicon nitride film is provided on the rear surface 11b, but these functional films may be formed on the rear surface 11b.

[0151] If the absorption coefficient of the functional film for the laser beam L is relatively large and it is difficult to perform the first modified layer formation step S10 and the second modified layer formation step S20 by irradiating the laser beam L from the back surface 11b toward the front surface 11a, the laser beam L may be irradiated from the front surface 11a toward the back surface 11b.

[0152] Of course, in the above-described embodiments and modified examples, the laser beam L is not limited to being irradiated from the back surface 11b toward the front surface 11a, and the laser beam L may be irradiated from the front surface (first surface) 11a toward the back surface (second surface) 11b.

[0153] In the laser processing method including the above-mentioned first modified layer formation process S10 and second modified layer formation process S20, the laser beam L may be irradiated from the back surface (first surface) 11b toward the front surface (second surface) 11a, or the laser beam L may be irradiated from the front surface (first surface) 11a toward the back surface (second surface) 11b.

[0154] Furthermore, when the expanding tape 25 is attached to the back surface (second surface) 11b, the crack 11f extending from the second modified layer R2 can, for example, proceed straight, approximately perpendicular to the back surface 11b, without being affected at all by the first modified layer R1.

[0155] In any case, when the workpiece 11 is divided by expanding the expanding tape 25 attached to the surface 11a or the back surface 11b, the degree to which the crack 11f extending from one of the modified layers bends along the width direction 17b near the surface 11a or the back surface 11b can be reduced.

[0156] Furthermore, in the above-described embodiment and modified examples, two modified layers (i.e., the first modified layer R1 and the second modified layer R2) are formed for each planned dividing line 17, but a third modified layer (not shown) similar to the first modified layer R1 may be formed between the first modified layer R1 and the second modified layer R2 in the width direction 17b. In other words, three modified layers may be formed for each planned dividing line 17.

[0157] Four or more modified layers may be similarly formed depending on the predetermined width 17c of the intended division line 17. In this case, a third and a fourth modified layer, etc. are formed between the first modified layer R1 and the second modified layer R2 in the width direction 17b. [Explanation of symbols]

[0158] 2: Laser processing equipment 4: Base, 6: Base, 8: Wall 10: chuck table, 10a: holding surface 11: Workpiece, 11a: Front surface, 11b: Back surface 11c: thickness direction, 11d: predetermined plane, 11e: longitudinal direction, 11f: crack 11g1: Left area, 11g2: Right area, 11h: Convex part 12: Y-axis direction moving unit, 14: Y-axis guide rail, 16: Y-axis moving table 13: protective tape, 13a: adhesive surface, 15: workpiece unit 17: planned division line, 17a: longitudinal direction, 17b: width direction, 17c: predetermined width 18: screw shaft, 20: drive source 19: Device, 21: Device chip (chip) 22: X-axis direction movement unit, 24: X-axis guide rail 23: annular frame, 23a: opening 25: Expanded tape, 27: Frame unit, 29: Metal thin film 26: X-axis moving table, 28: screw shaft, 30: driving source, 32: support base 34: Support arm, 36: Laser beam irradiation unit, 38: Head part 40: laser oscillator, 42: spatial light phase modulator, 44: mirror 46: condenser lens, 46a: optical axis 50: Microscope camera unit, 52: Head unit, 54: Touch panel 56: Controller 60: grinding device, 62: chuck table, 62a: rotary shaft, 64: table base 66: Grinding unit, 68: Spindle, 70: Wheel mount 72: Grinding wheel, 72a: Wheel base, 72b: Grinding stone 80: Divider, 82: Drum, 84: Roller, 86: Frame support, 88: Clamp 90: Legs B1: First area, B2: Second area F: Focusing area, F A : Upper light-collecting region, F AC :Tip F B : Lower light collecting area, F B1 :Approximately middle position, F BC : Tip, G: Predetermined amount L: laser beam, L A :center R1: First modified layer, R 1A : Upper modified layer, R 1B : Lower modified layer R2: Second modified layer, R 2A : Upper modified layer, R 2B : Lower modified layer S10: First modified layer forming step, S20: Second modified layer forming step, S30: Determination step S40: Indexing feed process, S50: Judgment process S60: Chuck table 90° rotation process, S70: Thinning process, S80: Dividing process θ: Predetermined angle

Claims

1. A method for manufacturing chips, comprising: dividing a workpiece having a plate shape and including a first surface and a second surface opposite to the first surface along a planned division line having a band shape set on a predetermined plane parallel to the first surface or the second surface, thereby manufacturing a plurality of chips; the dividing line has a predetermined width in a width direction perpendicular to a longitudinal direction of the dividing line in the predetermined plane, a first modified layer forming step of irradiating a pulsed laser beam having a wavelength that transmits the workpiece from the first surface toward the second surface, and positioning a focusing area of ​​the laser beam in a first area within the predetermined width and located between the first surface and the second surface, and relatively moving the workpiece and the focusing area along the longitudinal direction of the planned dividing line, thereby forming a first modified layer inside the workpiece; a second modified layer forming step of irradiating the laser beam from the first surface toward the second surface, and positioning the light-condensing region in a second region that is spaced apart from the first region in the width direction and is located within the predetermined width and between the first surface and the second surface, and then relatively moving the workpiece and the light-condensing region along the longitudinal direction of the planned dividing line, thereby forming a second modified layer inside the workpiece; a dividing step of dividing the workpiece into the plurality of chips along the planned dividing lines by applying an external force to the workpiece after the first modified layer forming step and the second modified layer forming step; Equipped with In the second modified layer formation process, when the second region is viewed in the cross section of the workpiece in a plane perpendicular to the longitudinal direction of the planned division line, the focusing region of the laser beam has an inclined shape in the region including the tip closest to the second surface in the longitudinal direction of the focusing region, and the region including the tip is inclined so as to move away from the first region along the width direction as it moves from the first surface to the second surface.

2. A laser processing method for a workpiece having a plate shape and including a first surface and a second surface located opposite to the first surface, the method processing the workpiece with a laser beam along a planned division line having a band shape set on a predetermined plane parallel to the first surface or the second surface, the dividing line has a predetermined width in a width direction perpendicular to a longitudinal direction of the dividing line in the predetermined plane, a first modified layer forming step of irradiating the workpiece with a pulsed laser beam having a wavelength that transmits the workpiece from the first surface toward the second surface, and positioning the focusing area of ​​the laser beam in a first area within the predetermined width and located between the first surface and the second surface, and relatively moving the workpiece and the focusing area along the longitudinal direction of the planned dividing line, thereby forming a first modified layer inside the workpiece; a second modified layer forming step of irradiating the laser beam from the first surface toward the second surface, and positioning the light-condensing region in a second region that is spaced apart from the first region in the width direction and is located within the predetermined width and between the first surface and the second surface, and then relatively moving the workpiece and the light-condensing region along the longitudinal direction of the planned dividing line, thereby forming a second modified layer inside the workpiece; Equipped with In the second modified layer formation process, when the second region is viewed in the cross section of the workpiece in a plane perpendicular to the longitudinal direction of the planned division line, the focusing region of the laser beam has an inclined shape in a region including the tip end closest to the second surface in the longitudinal direction of the focusing region, and the region including the tip end is inclined so as to move away from the first region along the width direction as it moves from the first surface to the second surface. This laser processing method is characterized in that

Images