Chip manufacturing method

Abstract

To reduce an amount of protrusion of a laser beam protruding from a projected dicing line, the laser beam being reflected irregularly by a modified layer.SOLUTION: There is provided a method for manufacturing a chip. The method includes: a first modified layer formation step of applying a laser beam having a wavelength that is transmittable through a workpiece, from one face of the workpiece to the other face and forming a first modified layer along a projected dicing line at a first depth; and a second modified layer formation step of applying the laser beam from the one face of the workpiece to the other face and forming a second modified layer at a second depth closer on the one face side than the first depth. During the second modified layer formation step, the cross-sectional shape of the laser beam at the first depth is set to an elliptical shape with a long axis along a first direction that is a longitudinal direction of the projected dicing line, and, between the second depth and the first depth, a ratio of the length of the laser beam in the first direction to the length of the laser beam in a second direction that is a width direction of the projected dicing line is greater than a ratio of the length of the laser beam in the first direction to the length of the laser beam in the second direction during the first modified layer formation step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing chips by dividing a workpiece along predetermined division lines set on the workpiece. [Background technology]

[0002] A known method for dividing a semiconductor wafer, such as silicon, into multiple device chips involves using a laser beam with a wavelength that penetrates the semiconductor wafer. In this method, the focal point of the laser beam is first positioned inside the semiconductor wafer, and then the focal point and the semiconductor wafer are moved relative to each other along the planned division line.

[0003] After forming a modified layer inside the semiconductor wafer along the planned division line in this manner, an external force is applied to the semiconductor wafer to propagate cracks starting from the modified layer, thereby dividing the semiconductor wafer into multiple device chips (see, for example, Patent Document 1).

[0004] Furthermore, depending on the thickness and material of the semiconductor wafer, multiple modified layers may be formed so as to overlap in the thickness direction of the semiconductor wafer (see, for example, Patent Document 2). When forming multiple modified layers, for example, a first modified layer is formed at a predetermined depth in the workpiece, and then a second modified layer is formed by positioning the focal point on the upper surface side of the workpiece relative to the first modified layer.

[0005] In this way, by gradually changing the depth position of the focal point from the bottom surface to the top surface of the workpiece, multiple modified layers are formed along a single planned division line so that they overlap in the thickness direction of the semiconductor wafer.

[0006] Incidentally, when forming a second modified layer above the first modified layer, the laser beam that is not absorbed by the semiconductor wafer near the focal point becomes what is known as "pass-through light," which travels to the underside of the workpiece and may be diffusely reflected by the first modified layer. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2002-192370 [Patent Document 2] Japanese Patent Publication No. 2020-136457 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] If a device such as an IC (Integrated Circuit) is formed on the underside of the workpiece, the laser beam, diffusely reflected by the first modified layer, may extend beyond the planned division line, reach the area where the device is formed, and potentially damage the device.

[0009] This invention has been made in view of the aforementioned problems, and aims to reduce the amount of overhang of the laser beam that is diffusely reflected by already formed modified layers when multiple modified layers are formed so as to overlap in the thickness direction of the workpiece, and which extends beyond the planned division line. [Means for solving the problem]

[0010] According to one aspect of the present invention, a method for manufacturing a chip by dividing a workpiece along a predetermined division line set on the workpiece, comprising: a first modified layer formation step in which a laser beam having a wavelength that penetrates the workpiece is irradiated from one surface of the workpiece toward the other surface of the workpiece, the focal point of the laser beam is positioned at a first depth inside the workpiece, and the focal point is moved relative to the workpiece along the predetermined division line to form a first modified layer inside the workpiece; and after the first modified layer formation step, the laser beam is irradiated from one surface of the workpiece toward the other surface of the workpiece, the focal point of the laser beam is positioned at a second depth located on the side of the workpiece toward the first surface than the first depth, and the focal point is moved along the predetermined division line A chip manufacturing method is provided, comprising: a second modified layer formation step of forming a second modified layer inside a workpiece by moving it relative to the workpiece; and a division step of applying an external force to the workpiece after the first modified layer formation step and the second modified layer formation step to divide the workpiece along a planned division line, wherein in the second modified layer formation step, the shape of the laser beam in a cross-section in a predetermined plane perpendicular to the direction of propagation of the laser beam at the first depth is made into an ellipse shape with its major axis along a first direction which is the longitudinal direction of the planned division line, and in a cross-section in the plane between the second depth and the first depth, the ratio of the length in the first direction to the length in the second direction which is the width direction of the planned division line of the laser beam is greater than the ratio of the length in the first direction to the length in the second direction of the laser beam in the first modified layer formation step.

[0011] Preferably, in the second modified layer formation step, a spatial optical phase modulator provided in the optical path of the laser beam is used to make the shape of the laser beam in the plane cross-section at the first depth an ellipse shape with its major axis aligned with the planned division line.

[0012] Also, preferably, in the first modified layer forming step, a cylindrical lens is not inserted into the optical path of the laser beam, and in the second modified layer forming step, the cylindrical lens is inserted into the optical path of the laser beam, so that the shape of the laser beam in the cross section of the plane at the first depth is an elliptical shape with the major axis along the planned division line.

Advantages of the Invention

[0013] In the method for manufacturing a chip according to one aspect of the present invention, in the second modified layer forming step after the first modified layer forming step, the second modified layer is formed inside the workpiece along the planned division line in a state where the condensing point of the laser beam is positioned at a second depth on the one surface side of the workpiece from the first depth.

[0014] Particularly, in the second modified layer forming step, the shape of the laser beam in the cross section of a predetermined plane orthogonal to the traveling direction of the laser beam at the first depth is an elliptical shape with the major axis along the planned division line.

[0015] Therefore, in the second modified layer forming step, even if the stray light of the laser beam is diffusely reflected by the first modified layer already formed at the first depth, the amount of protrusion of the diffusely reflected laser beam from the planned division line can be reduced as compared with the case where the cross-sectional shape of the laser beam at the first depth is circular.

Brief Description of the Drawings

[0016] [Figure 1] It is a flowchart of a method for manufacturing a device chip. [Figure 2] It is a perspective view of a laser processing apparatus. [Figure 3] It is a perspective view of a workpiece unit. [Figure 4] It is a schematic diagram of a laser beam irradiation unit. [Figure 5] It is a diagram showing the first modified layer forming step. [Figure 6]Figure 6(A) is an XZ cross-section of the laser beam, Figure 6(B) is a YZ cross-section of the laser beam, Figure 6(C) is an XY cross-section of the laser beam at Z=Z1+Δ1, Figure 6(D) is an XY cross-section of the laser beam at Z=Z1, and Figure 6(E) is an XY cross-section of the laser beam at Z=Z1-Δ1. [Figure 7] This diagram shows the second modified layer formation process. [Figure 8] Figure 8(A) is an XZ cross-sectional view of the laser beam, Figure 8(B) is a YZ cross-sectional view of the laser beam, Figure 8(C) is an XY cross-sectional view of the laser beam at Z=Z2+Δ2, Figure 8(D) is an XY cross-sectional view of the laser beam at Z=Z2, Figure 8(E) is an XY cross-sectional view of the laser beam at Z=Z2-Δ2, Figure 8(F) is a plan view of a portion of the planned division line, and Figure 8(G) is an XY cross-sectional view of the laser beam used in the first modification layer formation process between the second depth and the first depth. [Figure 9] Figure 9(A) is a partial cross-sectional side view of a tape-expanding type splitting device, and Figure 9(B) shows the splitting process. [Figure 10] Figure 10(A) is a photograph of the surface side after the second modified layer formation process according to this embodiment, and Figure 10(B) is a photograph of the surface side after the second modified layer formation process according to a comparative example. [Figure 11] Figure 11(A) shows the first modified layer formation process according to the second embodiment, and Figure 11(B) shows the second modified layer formation process according to the second embodiment. [Modes for carrying out the invention]

[0017] An embodiment of one aspect of the present invention will be described with reference to the attached drawings. Figure 1 is a flowchart of a manufacturing method in which a workpiece 11 (see Figure 2) is laser-processed, and then the workpiece 11 is divided to produce a plurality of device chips (chips) 29 (see Figure 9(B)).

[0018] When performing laser processing on the workpiece 11, the laser processing device 2 is used. Figure 2 is a perspective view of the laser processing device 2. The X-axis, Y-axis, and Z-axis directions shown in Figure 2 are orthogonal to each other.

[0019] The X-axis direction is approximately parallel to the machining 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). The laser processing apparatus 2 is equipped with a base 4 that supports its components.

[0020] The base 4 includes a flat base portion 6 and a wall portion 8 located at the rear end of the base portion 6 and extending upward. A chuck table 10 for suction holding the workpiece 11 is positioned on the upper surface of the base portion 6. The chuck table 10 has a disc-shaped frame made of metal.

[0021] A disc-shaped recess, smaller in diameter than the frame, is formed at the top of the frame, and a disc-shaped porous plate made of porous ceramic plate is fixed in this recess. A predetermined channel (not shown) is formed in the frame for supplying negative pressure to the porous plate.

[0022] Negative pressure is transmitted to the porous plate from a suction source (not shown), such as a vacuum pump, through a predetermined flow path. The upper surface of the porous plate and the upper surface of the frame are substantially flush and function as a holding surface 10a that suctions and holds the workpiece 11.

[0023] The holding surface 10a is substantially flat and is arranged substantially parallel to the XY plane. Multiple clamp units (four in this embodiment) are arranged at substantially equal intervals along the circumferential direction of the frame on the outer circumference of the frame.

[0024] Below the chuck table 10, a ball screw type Y-axis movement unit 12 is provided for moving the chuck table 10 in the Y-axis direction. The Y-axis movement unit 12 includes a pair of Y-axis guide rails 14 fixed to the upper surface of the base 6 and arranged substantially parallel to the Y-axis direction.

[0025] A Y-axis movable table 16 is slidably fixed to the Y-axis guide rail 14. A nut portion (not shown) is provided on the underside of the Y-axis movable table 16, and a screw shaft 18, which is positioned approximately parallel to the Y-axis direction, is rotatably connected to this nut portion via a plurality of balls (not shown).

[0026] A drive source 20, such as a pulse 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. A ball screw type X-axis direction moving unit 22 is provided on the upper side of the Y-axis moving table 16 to move the chuck table 10 in the X-axis direction.

[0027] The X-axis movement unit 22 includes a pair of X-axis guide rails 24 fixed to the upper surface of the Y-axis movement table 16 and arranged substantially parallel to the X-axis direction. The X-axis movement table 26 is slidably fixed to the X-axis guide rails 24.

[0028] A nut portion (not shown) is provided on the underside of the X-axis moving table 26, and a screw shaft 28, which is positioned approximately parallel to the X-axis direction, is rotatably connected to this nut portion. A drive source 30, such as a pulse motor, is connected to one end of the screw shaft 28.

[0029] When the screw shaft 28 is rotated by the drive source 30, the X-axis moving table 26 moves along the X-axis direction. A cylindrical support base 32 is provided on the upper side of the X-axis moving table 26. A chuck table 10 is positioned on top of the support base 32.

[0030] A drive source (not shown), such as a motor, is provided inside the support base 32, and as needed, the chuck table 10 is rotated within a predetermined angular range around a rotation axis parallel to the Z-axis direction. Now, referring to Figure 3, the workpiece 11 will be described.

[0031] The workpiece 11 has a disc-shaped silicon single crystal substrate. Multiple division lines (streets) 13 are set in a grid pattern on the surface 11a side of the workpiece 11. Devices 15 such as ICs, LEDs (Light Emitting Diodes), and MEMS (Micro Electro Mechanical Systems) are formed in each rectangular region demarcated by the multiple division lines 13.

[0032] There are no restrictions on the type, quantity, shape, structure, size, or arrangement of the device 15. Furthermore, the workpiece 11 does not necessarily need to have the device 15 attached. The workpiece 11 shown in Figure 3 is in the form of a workpiece unit 21 supported by a metal annular frame 19 via a resin tape 17. Figure 3 is a perspective view of the workpiece unit 21.

[0033] The workpiece unit 21 is formed, for example, by placing the workpiece 11 in the opening of the annular frame 19, and then attaching the adhesive surface of a circular tape 17 to the surface 11a of the workpiece 11 and one side of the annular frame 19.

[0034] When the workpiece unit 21 is placed on the chuck table 10 and negative pressure is transmitted to the holding surface 10a, the workpiece 11 is held by suction at the holding surface 10a via the tape 17. At this time, the back surface 11b is exposed upwards, and the annular frame 19 is held by the multiple clamping units described above.

[0035] Returning to Figure 2, the other components of the laser processing apparatus 2 will be described. A support arm 34 extending forward is provided at the upper front of the wall section 8. Part of the laser beam irradiation unit 36 ​​is provided on the support arm 34, and a cylindrical head section 38 is provided at the tip of the support arm 34.

[0036] Figure 4 is a schematic diagram of the laser beam irradiation unit 36. In Figure 4, some of the components of the laser beam irradiation unit 36 ​​are shown as functional blocks. The laser beam irradiation unit 36 ​​has a laser oscillator 40 fixed to the base 4.

[0037] The laser oscillator 40 has, for example, a crystal such as Nd:YAG as the laser medium, and emits a pulsed laser beam L having a wavelength (for example, 1064 nm) that penetrates 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.

[0038] The laser beam L has its power adjusted by an attenuator (not shown) and then proceeds to the spatial light phase modulator 42. The spatial light phase modulator 42 in this embodiment has a reflective LCOS-SLM (Liquid Crystal on Silicon - Spatial Light Modulator).

[0039] The spatial optical phase modulator 42 of this embodiment has a first function of simply reflecting the laser beam L without wavefront control, and a second function of focusing the laser beam L by performing wavefront control on the laser beam L so that the focal position in the X-axis direction and the focal position in the Y-axis direction are offset in the direction of propagation of the laser beam L (Z-axis direction in Figure 4). The first and second functions of this spatial optical phase modulator 42 can be switched by the controller 56, which will be described later.

[0040] In Figure 4, for convenience, the optical system is shown so that the laser beam L passes through the spatial light phase modulator 42. However, as described above, the LCOS-SLM reflects the laser beam L, so the laser beam L that has passed through the LCOS-SLM is guided to the head unit 38 using a mirror (not shown).

[0041] The spatial light phase modulator 42 may also have a transmissive type spatial light phase modulator such as an LC-SLM (Liquid Crystal - Spatial Light Modulator) instead of an LCOS-SLM. In any case, the laser beam L that has passed through the spatial light phase modulator 42 is guided to the head unit 38.

[0042] The head unit 38 is equipped with a mirror 44 for changing the direction of the laser beam L. The laser beam L reflected by the mirror 44 passes through a focusing lens 46 and is projected downwards. The attenuator (not shown), spatial light phase modulator 42, mirror 44, focusing lens 46, etc., are all located in the optical path of the laser beam L.

[0043] Returning to Figure 2, the head portion 52 of the microscope camera unit 50 is provided at the tip of the support arm 34 so as to be adjacent to the head portion 38 in the Y-axis direction. The microscope camera unit 50 includes, for example, an objective lens, a light source, and an image sensor.

[0044] The light source includes an LED (Light Emitting Diode) capable of emitting infrared light (e.g., near-infrared light between 1000 nm and 2000 nm). The image sensor has a solid-state image sensor (image sensor) capable of photoelectric conversion of infrared light (e.g., near-infrared light).

[0045] The image sensor may include, for example, a CCD (Charge-Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) image sensor, and may also include a photodiode (for example, an InGaAs (indium gallium arsenide) photodiode) for converting infrared light into photoelectric light.

[0046] The microscope camera unit 50 of this embodiment can use infrared light from a light source to image the front surface 11a side of the workpiece 11 from the back surface 11b, so as to penetrate the workpiece 11. The base 4 is provided with a cover (not shown) that covers the above-mentioned components. A touch panel 54 is provided on the front surface (one side in the Y-axis direction) of the cover.

[0047] The touch panel 54 is a liquid crystal display including a capacitive touch sensor, and functions as an input device for the operator to input instructions to the laser processing machine 2, a GUI (Graphical User Interface) for inputting instructions, and a display device for displaying images obtained by the microscope camera unit 50, etc.

[0048] The laser processing apparatus 2 is equipped with a controller (control unit) 56 that controls the operation of the Y-axis movement unit 12, the X-axis movement unit 22, the drive source and suction source in the support base 32, the laser beam irradiation unit 36, the microscope camera unit 50, the touch panel 54, and other components.

[0049] The controller 56 is composed of a computer that includes, for example, a processor (processing unit) represented by a CPU (Central Processing Unit), main memory such as DRAM (Dynamic Random Access Memory), SRAM (Static Random Access Memory), and ROM (Read Only Memory), and auxiliary memory such as flash memory, hard disk drive, and solid state drive.

[0050] The auxiliary storage device stores software, including a predetermined program. The controller 56 functions by operating the processing unit and other components according to this software. Next, each step of the manufacturing method for the device chip 29 shown in Figure 1 will be described.

[0051] In the first modified layer formation step S10, alignment is performed first. During alignment, the surface 11a of the workpiece 11, which is held by suction on the holding surface 10a, is imaged by the microscope camera unit 50, and the controller 56 uses the obtained image to calculate the deviation between the planned division line 13 and the X-axis direction.

[0052] After alignment, the orientation of the chuck table 10 is adjusted by the drive source in the support base 32 so that the planned division line 13 is approximately parallel to the X-axis direction. Then, the laser beam L is irradiated onto the workpiece 11, and the surface 11a (position Z in the Z-axis direction) is adjusted. a ) and the back surface 11b (position Z in the Z axis direction) b A first modified layer 23 is formed at a first depth Z1 inside the workpiece 11 located between ) and .

[0053] Figure 5 shows the first modified layer formation step S10. In this embodiment, the modified layer refers to a region where the crystal structure of the single crystal substrate has changed due to multiphoton absorption, and the mechanical strength is reduced compared to the region not irradiated by the laser beam L (i.e., laser beam L1 or L2).

[0054] In the first modified layer formation step S10, a laser beam L1 is irradiated from the back surface (one side) 11b of the workpiece 11 toward the front surface (other side) 11a, and with the focusing point P of the laser beam L1 positioned at a first depth Z1, the chuck table 10 is fed at a predetermined speed.

[0055] This causes the focusing point P and the workpiece 11 to move relative to each other along one planned division line 13, thereby forming the first modified layer 23. For the sake of explanation, in this embodiment, the laser beam L in the first modified layer formation step S10 will be referred to as laser beam L1.

[0056] In Figure 5, for ease of explanation, each of the multiple modified regions constituting the first modified layer 23 is shown as a white circle. In Figure 5, each modified region is depicted as larger than it actually is; the actual number of modified regions is determined by the repetition frequency of the laser beam L1, the processing feed rate, etc. Also, in Figure 5, cracks extending from each modified region are omitted.

[0057] After moving the focusing point P from one end to the other in the X-axis direction of one planned division line 13, the head portion 38 is relatively indexed and fed by moving the chuck table 10 along the Y-axis direction so that the focusing point P is located on the extension of another adjacent planned division line 13 in the Y-axis direction. Then, similarly, the first modified layer 23 is formed at the first depth Z1.

[0058] In this manner, the first modified layer 23 is formed along all the planned division lines 13 along one direction, and then the chuck table 10 is rotated by approximately 90 degrees. Then, the first modified layer 23 is similarly formed along all the planned division lines 13 along the other direction perpendicular to the first direction.

[0059] Figures 6(A) to 6(E) are cross-sectional views of the laser beam L1 during the first modified layer formation step S10. Figure 6(A) is an XZ cross-sectional view of the laser beam L1, and Figure 6(B) is a YZ cross-sectional view of the laser beam L1.

[0060] Figure 6(C) is an XY cross-sectional view of the laser beam L1 at Z=Z1+Δ1, Figure 6(D) is an XY cross-sectional view of the laser beam L1 at Z=Z1, and Figure 6(E) is an XY cross-sectional view of the laser beam L1 at Z=Z1-Δ1.

[0061] The direction of travel of the laser beam L1 incident on the workpiece 11 is approximately parallel to the Z-axis direction. The laser beam L1 is focused at a first depth Z1. Δ1 is a predetermined value, for example, between a few μm and several hundred μm, and Z = Z1 - Δ1 is, for example, the height position of the surface 11a (Z = Z a (See Figure 5))

[0062] In the first modified layer formation step S10, the spatial optical phase modulator 42 is made to perform the first function, rather than the second function described above. In other words, in the first modified layer formation step S10, no wavefront control is performed on the laser beam L, and the spatial optical phase modulator 42 simply reflects the laser beam L.

[0063] An example of processing conditions in the first modified layer formation step S10 is shown below.

[0064] Wavelength: 1064nm Average output: 0.35W Repeat frequency: 80kHz Machining feed rate: 500 mm / s

[0065] The laser beam L1 is focused at a first depth Z1 in the XZ and YZ planes (see Figures 6(A) and 6(B)), and the cross-sectional shape of the laser beam L1 in the XY plane (a predetermined plane) at Z=Z1+Δ1, Z1, and Z1-Δ1 is circular (see Figures 6(C), 6(D), and 6(E)).

[0066] In the first modified layer formation step S10, by using a laser beam L1 whose cross-sectional shape in the XY plane at Z=Z1+Δ1, Z1, and Z1-Δ1 is circular, cracks tend to extend along the X-axis and cracks tend to connect between modified regions, compared to using a laser beam L whose cross-sectional shape in the XY plane above the focal point is elliptical with its major axis aligned along the Y-axis, as in the second modified layer formation step S20 described later.

[0067] Furthermore, in the first modified layer formation step S10, using a laser beam L whose cross-sectional shape in the XY plane above the focal point is elliptical with its major axis approximately parallel to the X-axis direction has the advantage that cracks extend along the X-axis direction and cracks are more likely to connect between modified regions, compared to using a laser beam L1 whose cross-sectional shape in the XY plane at Z=Z1+Δ1, Z1, and Z1-Δ1 is circular.

[0068] Therefore, in a modified version of the first modified layer formation step S10, a laser beam L1 may be used in which the cross-sectional shape in the XY plane at Z=Z1+Δ1 is an ellipse shape with its major axis positioned approximately parallel to the X-axis direction.

[0069] After the first modified layer formation step S10, the second modified layer formation step S20 is performed. In the second modified layer formation step S20, alignment is performed first, and the orientation of the chuck table 10 is adjusted so that one of the planned division lines 13 is approximately parallel to the X-axis direction.

[0070] Then, as shown in Figure 7, a second modified layer 25 is formed at a second depth Z2 (i.e., on the side of the back surface 11b that is closer to the back surface 11b than the first depth Z1) located between the first depth Z1 and the back surface 11b. Figure 7 shows the second modified layer formation step S20.

[0071] In the second modified layer formation step S20, a laser beam L2 is irradiated from the back surface 11b of the workpiece 11 toward the front surface 11a, and with the focusing point P of the laser beam L2 positioned at the second depth Z2, the chuck table 10 is fed at a predetermined speed.

[0072] This causes the focusing point P and the workpiece 11 to move relative to each other along one planned division line 13, thereby forming a second modified layer 25. In this embodiment, for the sake of explanation, the laser beam L in the second modified layer formation step S20 will be referred to as laser beam L2.

[0073] In Figure 7, for the sake of clarity, the multiple modified regions constituting the second modified layer 25 are shown as white circles, and the cracks extending from each modified region are omitted. In Figure 7, each modified region is also depicted as larger than it actually is.

[0074] After moving the focusing point P from one end to the other in the X-axis direction of one planned division line 13, the head portion 38 is relatively indexed and fed by moving the chuck table 10 along the Y-axis direction so that the focusing point P is located on the extension of another adjacent planned division line 13 in the Y-axis direction. Then, similarly, a second modified layer 25 is formed at a second depth Z2.

[0075] After forming the second modified layer 25 along all the planned division lines 13 in one direction, the chuck table 10 is rotated approximately 90 degrees. Then, the second modified layer 25 is similarly formed along all the planned division lines 13 in the other direction perpendicular to the first direction.

[0076] In particular, in the second modified layer formation step S20, the spatial optical phase modulator 42 is made to perform its first function, not its second function. That is, the spatial optical phase modulator 42 is used to control the wavefront of the laser beam L2.

[0077] This changes the cross-sectional shape of the laser beam L in a section perpendicular to the direction of propagation, similar to the astigmatism method using a cylindrical lens. In this embodiment, the wavefront control of the spatial optical phase modulator 42 changes the cross-sectional shape in the XY section in the Z-axis direction.

[0078] Figures 8(A) to 8(E) are cross-sectional views of the laser beam L2 in the second modified layer formation step S20. Figure 8(A) is an XZ cross-sectional view of the laser beam L2, and Figure 8(B) is a YZ cross-sectional view of the laser beam L2. For the sake of explanation, in Figures 8(A) and 8(B), the laser beam L1 used in the first modified layer formation step S10 is shown with a dashed line.

[0079] Figure 8(C) is an XY cross-sectional view of the laser beam L2 at Z=Z2+Δ2, Figure 8(D) is an XY cross-sectional view of the laser beam L2 at Z=Z2, and Figure 8(E) is an XY cross-sectional view of the laser beam L2 at Z=Z2-Δ2. Δ2 is a predetermined value, for example, between a few micrometers and several hundred micrometers. Z=Z2-Δ2 corresponds, for example, to a first depth Z1.

[0080] Figure 8(F) is a plan view of a portion of the planned division line 13. In the second modified layer formation step S20, the longitudinal direction (first direction) 13a of the planned division line 13 is arranged approximately parallel to the X-axis direction. Therefore, the width direction (second direction) 13b of the planned division line 13 is arranged approximately parallel to the Y-axis direction.

[0081] An example of the processing conditions in the second modification layer formation step S20 is shown below.

[0082] Wavelength: 1064 nm Average output: 0.35 W Repetition frequency: 80 kHz Processing feed rate: 500 mm / s

[0083] At Z = Z2, the cross-section of the laser beam L2 in the XY plane becomes relatively small, and the energy per unit area in the XY plane is maximized. Therefore, at the second depth Z2, multiphoton absorption occurs and the second modification layer 25 is formed.

[0084] Particularly, in the second modification layer formation step S20, the shape of the laser beam L2 in the cross-section in the XY plane at the first depth Z1 (i.e., Z = Z2 - Δ2 in FIGS. 8(A) and 8(B)) is made into an elliptical shape with the major axis along the planned division line 13 (see FIG. 8(E)).

[0085] Therefore, even if the transmitted light of the laser beam L2 is diffusely reflected by the first modification layer 23 already formed at the first depth Z1, the amount of protrusion of the diffusely reflected laser beam L2 from the planned division line 13 can be reduced compared to the case where the cross-sectional shape of the laser beam L2 at the first depth Z1 is circular.

[0086] To quantitatively represent the difference between the laser beams L1 and L2, as shown in FIG. 8(E), in the second modification layer formation step S20, in the cross-section of the laser beam L2 in the XY plane between the second depth Z2 and the first depth Z1, the length L in the width direction 13b 2b with respect to the length L in the longitudinal direction 13a 2a of the ratio (L 2a / L 2b ) is greater than 1 (1 < L 2a / L 2b ).

[0087] In contrast, as shown in Figure 8(G), in the first modified layer formation step S10, the length L in the width direction 13b is in the cross-section of the laser beam L1 in the XY plane between the second depth Z2 and the first depth Z1. 1b Length L of the longitudinal direction 13a relative to 1a The ratio (L 1a / L 1b ) is approximately 1.

[0088] Figure 8(G) is an XY cross-sectional view of the laser beam L1 used in the first modified layer formation step S10 between the second depth Z2 and the first depth Z1. As can be seen from the comparison of Figure 8(E) and Figure 8(G), the ratio (L 2a / L 2b ) is the ratio (L 1a / L 1b It is larger than ).

[0089] In this embodiment, by using a laser beam L1 with a circular cross-sectional shape in the first modified layer formation step S10, crack propagation starting from the modified region can be promoted compared to using a laser beam L in the second modified layer formation step S20, where the cross-sectional shape of the XY plane above the focal point is elliptical with its major axis aligned along the Y-axis.

[0090] In addition, by using a laser beam L2 with an elliptical cross-sectional shape at Z=Z2-Δ2 in the second modified layer formation step S20, the amount of laser beam L2 diffusely reflected by the first modified layer 23 that is emitted only from the planned division line 13 can be reduced.

[0091] After the second modified layer formation step S20, a splitting step S30 is performed in which an external force is applied to the workpiece 11 to split the workpiece 11 into multiple device chips 29 along each planned splitting line 13. A splitting device 60 is used in the splitting step S30.

[0092] Figure 9(A) is a partial cross-sectional side view of a tape-expanding type splitting device 60. The splitting device 60 has a cylindrical drum 62 with a diameter that is larger than the diameter of the workpiece 11 and smaller than the inner diameter of the annular frame 19.

[0093] Multiple rollers 64 are provided at approximately equal intervals along the circumferential direction of the drum 62 at the upper end of the drum 62. An annular frame support base 66 is provided on the outside of the drum 62 in the radial direction.

[0094] Multiple clamps 68 are provided on the upper surface of the frame support base 66, each clamping a ring-shaped frame 19 placed on the frame support base 66. The frame support base 66 is supported by multiple legs 70 arranged at approximately equal intervals along the circumferential direction of the frame support base 66. Each leg 70 can be raised and lowered by a lifting mechanism such as an air cylinder.

[0095] In the splitting process S30, as shown in Figure 9(A), the upper end of the drum 62 and the upper surface of the frame support base 66 are placed at approximately the same height, and the workpiece unit 21 after the second modified layer formation process S20 is placed on the drum 62 and the frame support base 66.

[0096] Next, when each lifting mechanism is activated and the legs 70 are pulled down relative to the drum 62, the frame support base 66 is pulled down below the rollers 64. As a result, the tape 17 expands radially, as shown in Figure 9(B). Figure 9(B) shows the splitting process S30.

[0097] As the tape 17 expands, an external force is applied to the workpiece 11 in a radially spreading direction, and the workpiece 11 is divided into multiple rectangular plate-shaped device chips 29.

[0098] As described above, in the second modified layer formation step S20 of this embodiment, the amount of overflow of the laser beam L2 diffusely reflected by the first modified layer 23 beyond the planned division line 13 can be reduced. As a result, damage to the device 15 can be reduced, and the yield of the device chip 29 after the division step S30 can be improved.

[0099] (Experimental Results) An experiment was conducted to form a first modified layer 23 and a second modified layer 25 on a silicon single crystal substrate with a thickness of 200 μm. In the first experiment, the first modified layer formation step S10 and the second modified layer formation step S20 were carried out sequentially according to the manufacturing method of this embodiment.

[0100] In contrast, in the second experiment (comparative example), after performing the same first modified layer formation step S10 as in this embodiment, in the subsequent second modified layer formation step S20, the laser beam L2 was simply reflected without wavefront control using the spatial optical phase modulator 42 (first function), and the focal point P of the laser beam L2 was positioned at a second depth Z2 to form the second modified layer 25.

[0101] In the first and second experiments, in the first modified layer formation step S10, the first depth Z1 was set to a depth of 70 μm from the back surface 11b, and in the second modified layer formation step S20, the second depth Z2 was set to a depth of 40.25 μm from the back surface 11b. For processing conditions other than these, the processing conditions of the first embodiment described above were applied.

[0102] Figure 10(A) shows the results of the first experiment, and is a photograph of the surface 11a side after the second modified layer formation step S20 according to this embodiment. Figure 10(B) shows the results of the second experiment, and is a photograph of the surface 11a side after the second modified layer formation step S20 according to the comparative example.

[0103] Figures 10(A) and 10(B) show images obtained by imaging surface 11a with visible light. The horizontal length of the white bar shown in the lower right of Figures 10(A) and 10(B) is 20 μm.

[0104] As shown in Figure 10(A), the multiple black circles 27a arranged periodically along the X-axis, the linear region 27b formed so as to traverse the multiple black circles 27a along the X-axis, and the discrete black regions 27c formed discretely along the X-axis so as to sandwich the multiple black circles 27a and the linear region 27b in the Y-axis direction, each include burn marks formed on the surface 11a and cracks formed in the workpiece 11.

[0105] Furthermore, the multiple black circles 27a, the linear region 27b, and the black region 27d, which are periodically formed along the X-axis so as to sandwich the multiple black circles 27a and the linear region 27b in the Y-axis direction, as shown in Figure 10(B), include burn marks formed on the surface 11a and cracks formed in the workpiece 11.

[0106] In particular, considering the differences between the first and second experiments, it is thought that the black region 27d shown in Figure 10(B) was formed on the surface 11a mainly by the laser beam L2 scattered by the first modified layer 23.

[0107] The combined length in the Y-axis direction of the black circle 27a and black region 27c shown in Figure 10(A) (i.e., the width of the processing marks, etc.) was approximately 10.5 μm. In contrast, the Y-axis direction length of the pair of black regions 27d shown in Figure 10(B) was approximately 21 μm.

[0108] As is clear from Figures 10(A) and 10(B), in the second modified layer formation step S20, making the shape of the laser beam L2 in the cross-section in the XY plane at the first depth Z1 an ellipse shape with its major axis aligned with the planned division line 13 is effective in reducing the amount of overflow of the laser beam L2 that is diffusely reflected by the first modified layer 23 and extends beyond the planned division line 13.

[0109] (Second Embodiment) Next, a second embodiment will be described. In the laser beam irradiation unit 36 ​​of the second embodiment, a spatial optical phase modulator 42 is not provided in the optical path of the laser beam L. Instead, in the second embodiment, a convex cylindrical lens 72 (see Figures 11(A) and 11(B)) is inserted between the focusing lens 46 and the workpiece 11.

[0110] Specifically, the convex cylindrical lens 72 is positioned with its ridge extending along the Y-axis direction and is configured to be movable along the X-axis direction by an actuator (not shown). By operating the actuator, the convex cylindrical lens 72 can be selectively positioned inside the optical path (see Figure 11(A)) and outside the optical path (see Figure 11(B)).

[0111] Figure 11(A) shows the first modified layer formation step S10 according to the second embodiment. In the first modified layer formation step S10, the first modified layer 23 is formed without inserting the convex cylindrical lens 72 into the optical path of the laser beam L.

[0112] In other words, in the first modified layer formation step S10 according to the second embodiment, the first modified layer 23 is formed by irradiating the workpiece 11 with a laser beam L1 having a circular cross-section in the XY plane, similar to Figures 6(A) to 6(E).

[0113] Figure 11(B) shows the second modified layer formation step S20 according to the second embodiment. In the second modified layer formation step S20, the second modified layer 25 is formed by inserting a convex cylindrical lens 72 into the optical path of the laser beam L.

[0114] By inserting the convex cylindrical lens 72 into the optical path, the shape of the cross-section of the laser beam L in the XY plane at the first depth Z1 where the first modified layer 23 is formed can be made into an elliptical shape whose major axis aligns with the longitudinal direction 13a of the planned division line 13.

[0115] In other words, in the second modified layer formation step S20 according to the second embodiment, the second modified layer 25 is formed by irradiating the workpiece 11 with a laser beam L2 similar to that shown in Figures 8(A) to 8(E).

[0116] This reduces the amount of overflow from the planned division line 13 due to scattering of the light from the laser beam L2 in the second modified layer formation step S20 by the first modified layer 23, similar to the first embodiment.

[0117] Furthermore, the structures, methods, etc., according to the above embodiments can be modified as appropriate without departing from the scope of the object of the present invention. An additional modified layer formation step may be performed between the second modified layer formation step S20 and the splitting step S30.

[0118] Furthermore, when the back surface 11b of the workpiece 11 is held by the holding surface 10a with suction so that the front surface 11a of the workpiece 11 is exposed, laser beams L1 and L2 may be irradiated from the front surface (one side) 11a of the workpiece 11 toward the back surface (other side) 11b in the first modified layer formation step S10 and the second modified layer formation step S20.

[0119] Incidentally, the convex cylindrical lens 72 shown in Figures 11(A) and 11(B) may be placed between the laser oscillator 40 and the mirror 44. In this case, the convex cylindrical lens 72 is configured to be movable along a predetermined direction (for example, the Z-axis direction) so that it can be inserted into the optical path of the laser beam L.

[0120] A concave cylindrical lens (not shown) may be used instead of the convex cylindrical lens 72. However, when a concave cylindrical lens is used in the laser beam irradiation unit 36 ​​shown in Figures 11(A) and 11(B), the concave cylindrical lens should be positioned so that the direction in which the valley extends is along the X-axis direction, not the Y-axis direction.

[0121] In the splitting process S30, the splitting device 60 described above is not the only option. The workpiece 11 may be split into multiple device chips 29 by applying an external force to the workpiece 11 after the second modified layer formation process S20 using a braking blade, roller, or the like.

[0122] Alternatively, the workpiece 11 may be divided into multiple device chips 29 by grinding the back surface 11b of the workpiece 11 after the second modified layer formation step S20, in accordance with the so-called SDBG (Stealth Dicing Before Grinding) process. [Explanation of symbols]

[0123] 2: Laser processing device, 4: Base, 6: Base section, 8: Wall section 10: Chuck table, 10a: Holding surface 11: Workpiece, 11a: Front surface, 11b: Back surface 13: Planned division line, 13a: Longitudinal direction (first direction), 13b: Width direction (second direction) 12: Y-axis movement unit, 14: Y-axis guide rail, 16: Y-axis movement table 15: Device, 17: Tape, 19: Annular frame, 21: Workpiece unit 18: Screw shaft, 20: Drive source, 22: X-axis movement unit, 24: X-axis guide rail 23: First modification layer, 25: Second modification layer 27a: Black circle, 27b: Linear area, 27c, 27d: Black area 26: X-axis moving table, 28: Screw axis, 30: Drive source 29: Device chip (chip) 32: Support base, 34: Support arm, 36: Laser beam irradiation unit, 38: Head unit 40: Laser oscillator, 42: Spatial light phase modulator, 44: Mirror, 46: Focusing lens 50: Microscope camera unit, 52: Head unit 54: Touch panel, 56: Controller 60: Dividing device, 62: Drum, 64: Roller, 66: Frame support base 68: Clamp, 70: Legs 72: Convex cylindrical lens L, L1, L2: Laser beam, P: Focusing point S10: First modified layer formation process, S20: Second modified layer formation process, S30: Splitting process Z1: First depth, Z2: Second depth, Z a ,Z b :Position, Δ1, Δ2: Predetermined value

Claims

1. A method for manufacturing chips, which involves dividing a workpiece along predetermined division lines set on the workpiece to produce chips, A first modification layer formation step involves irradiating the workpiece with a laser beam having a wavelength that penetrates the workpiece from one side to the other, positioning the focal point of the laser beam at a first depth inside the workpiece, and then moving the focal point relative to the workpiece along the planned division line to form a first modification layer inside the workpiece. A second modified layer formation step is performed after the first modified layer formation step, in which the laser beam is irradiated from one side of the workpiece toward the other side of the workpiece, and the focal point of the laser beam is positioned at a second depth which is located on the side of the workpiece toward the one side of the workpiece than the first depth, and the focal point is moved relative to the workpiece along the planned division line, thereby forming a second modified layer inside the workpiece. A division step, after the first modified layer formation step and the second modified layer formation step, in which an external force is applied to the workpiece to divide the workpiece along the planned division line, Equipped with, In the second modified layer formation step, The shape of the laser beam in a cross-section in a predetermined plane perpendicular to the direction of propagation of the laser beam at the first depth is made elliptical, with the major axis aligned with the first direction which is the longitudinal direction of the planned division line, and A method for manufacturing a chip, characterized in that, in a cross-section on the plane between the second depth and the first depth, the ratio of the length in the first direction to the length in the second direction, which is the width direction of the planned division line of the laser beam, is greater than the ratio of the length in the first direction to the length in the second direction of the laser beam in the first modification layer formation step.

2. The method for manufacturing a chip according to claim 1, characterized in that, in the second modified layer formation step, a spatial optical phase modulator provided in the optical path of the laser beam is used to make the shape of the laser beam in the cross-section in the plane at the first depth an elliptical shape with its major axis aligned with the planned division line.

3. In the first modified layer formation step, a cylindrical lens is not inserted into the optical path of the laser beam. The method for manufacturing a chip according to claim 1, characterized in that, in the second modified layer formation step, the cylindrical lens is inserted into the optical path of the laser beam to make the shape of the laser beam in the cross-section in the plane at the first depth an elliptical shape with its major axis aligned with the planned division line.

Images