Method of manufacturing chip

Abstract

To improve productivity when a workpiece is divided by ultrasonic waves to manufacture chips.SOLUTION: In an ultrasonic vibration unit 60, a top plate 62 of a housing 61 and a matching layer 65 form a vibration plate. The vibration plate radiates ultrasonic waves to a wafer from a second surface (surface of the matching layer 65) with irregularities 66 via water. Namely, in the configuration, water and the wafer are irradiated with ultrasonic waves from the surface with irregularities 66, so that cavitation can be efficiently generated (i.e. the occurrence frequency of cavitation can be increased). Accordingly, a wafer can be efficiently divided along a modified layer. Thus, productivity when a wafer is divided by ultrasonic waves to manufacture device chips can be increased.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a chip. [Background technology]

[0002] As a method for manufacturing multiple chips by dividing a workpiece such as a wafer into multiple chips, a method is known in which a laser beam of a wavelength that is transparent to the workpiece is focused and irradiated inside the workpiece to form a modified layer inside the workpiece, and an external force is applied to the workpiece with the modified layer formed to divide the workpiece (Patent Document 1).

[0003] In the method described in Patent Document 1, when applying an external force to a workpiece on which a modified layer has been formed, a method is adopted in which an extensible expanding tape is attached to the workpiece and the expanding tape is expanded. However, in the above-mentioned method of expanding the expandable tape, the expandable tape cannot be reused, and the cost required for chip production tends to be high.

[0004] In view of such problems, the applicant of the present application has developed a method for dividing a workpiece by irradiating the workpiece on which a modified layer has been formed with ultrasonic waves through a liquid (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-192370 A [Patent Document 2] JP 2019-220581 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the above-mentioned dividing method using ultrasonic waves, although the cost required for manufacturing chips can be reduced compared to the method of expanding an expandable tape, the dividing takes time, resulting in poor productivity.

[0007] The present invention has been made in view of the above problems. An object of the present invention is to improve productivity in the case where a workpiece having a modified layer formed therein is divided into chips by irradiating the workpiece with ultrasonic waves through a liquid. [Means for solving the problem]

[0008] The chip manufacturing method of the present invention (the present manufacturing method) is a chip manufacturing method in which an ultrasonic vibration unit is used to divide a workpiece along a planned division line set on the workpiece to manufacture chips, the ultrasonic vibration unit comprising an ultrasonic vibrator which is a source of ultrasonic waves, a vibration plate having a first surface to which the ultrasonic vibrator is fixed, and a second surface having unevenness and which transmits the ultrasonic waves to a liquid, and comprising a modified layer formation step of forming a modified layer inside the workpiece by positioning the focal point of a laser beam having a wavelength which passes through the workpiece inside the workpiece and irradiating the laser beam and moving the focal point and the workpiece relatively along the planned division line, and a division step of dividing the workpiece along the planned division line by irradiating the ultrasonic wave to the workpiece through the liquid after the modified layer formation step, with the workpiece and the second surface side of the vibration plate facing each other.

[0009] In this manufacturing method, the diaphragm may have a transmission layer including the first surface and a matching layer including the second surface of the diaphragm, and the matching layer may be formed from a material having an acoustic impedance smaller than that of the transmission layer and larger than that of the liquid. Effect of the Invention

[0010] In this manufacturing method, in the dividing step, the vibration plate of the ultrasonic vibration unit irradiates ultrasonic waves from the uneven second surface through the liquid to the workpiece on which the modified layer is formed. In other words, since ultrasonic waves are irradiated to the liquid and the workpiece from the uneven surface, it is possible to efficiently generate cavitation (increase the frequency of cavitation occurrence). Therefore, the workpiece can be efficiently divided along the modified layer. This can improve the productivity of dividing the workpiece with ultrasonic waves to manufacture chips. [Brief description of the drawings]

[0011] [Figure 1] 1(a) and 1(b) are explanatory diagrams showing the structure of a wafer 100. FIG. [Diagram 2] 1 is a flowchart showing the flow of a chip manufacturing method. [Diagram 3] FIG. 2 is a perspective view showing a configuration of the laser processing device. [Figure 4] 4(a) and 4(b) are explanatory views showing the modified layer forming step. [Diagram 5] FIG. 2 is an explanatory diagram showing a wafer provided with a protective tape. [Figure 6] FIG. 2 is an explanatory diagram illustrating a configuration of a division device. [Figure 7] FIG. 7(a) is a perspective view showing the configuration of an ultrasonic vibration unit, and FIG. 7(b) is an explanatory diagram showing projections and recesses. [Figure 8] FIG. 2 is a perspective view showing a configuration of an ultrasonic vibration unit. [Figure 9] FIG. 2 is an explanatory diagram showing a configuration of an ultrasonic vibration unit. [Figure 10] FIG. 2 is a perspective view showing a configuration of an ultrasonic vibration unit. [Figure 11] FIG. 1 is an explanatory diagram showing the configuration of an experimental device. [Figure 12] 12(a) and 12(b) are explanatory diagrams showing the results of a cavitation efficiency verification experiment. [Figure 13]13(a) and 13(b) are explanatory diagrams showing the results of a divisibility verification experiment. [Figure 14] 14(a) and 14(b) are explanatory diagrams showing the results of a divisibility verification experiment. [Figure 15] 1A to 1C are diagrams showing configurations of ultrasonic vibration units according to ultrasonic frequency bands. [Figure 16] FIG. 13 is an explanatory diagram showing another configuration of the dividing device. [Figure 17] FIG. 13 is an explanatory diagram showing another configuration of the dividing device. [Figure 18] FIG. [Figure 19] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] In the chip manufacturing method according to this embodiment (the present chip manufacturing method), chips are manufactured by dividing a disk-shaped wafer 100 shown in FIG. 1(a).

[0013] The wafer 100 is an example of a workpiece, and is, for example, a disk-shaped semiconductor wafer. The wafer 100 has, for example, a SiC substrate. A grid-shaped dividing lines 102 are formed on a surface 101 of the wafer 100. Devices 103 are formed in the areas defined by the dividing lines 102.

[0014] As shown in FIG. 1(b), a metal film 106 is formed on the back surface 105 of the wafer 100. The metal film 106 constitutes an electrode when the wafer 100 is divided into a plurality of chips (device chips) including one device 103. The metal film 106 is, for example, composed of a complex of Ti, Ni, and Au. In this case, for example, the thicknesses of Ti and Ni are 1 μm, the thickness of Au is 3 μm, and the thickness of the metal film 106 is 5 μm. The total thickness of the wafer 100 is, for example, 570 μm.

[0015] The steps of this chip manufacturing method are described below. This chip manufacturing method is a method for manufacturing chips by dividing a wafer 100, which is a workpiece, along planned dividing lines 102 set on the wafer 100 using an ultrasonic vibration unit. Figure 2 is a flow chart showing the flow of this chip manufacturing method. As shown in Figure 2, this chip manufacturing method includes a modified layer forming step (S1) and a dividing step (S2).

[0016] [Modified layer forming process] In the modified layer forming step, laser processing is performed on the planned dividing lines 102 of the wafer 100 by the laser processing device 1 shown in Fig. 3. That is, in this step, the focal point of a laser beam having a wavelength that passes through the wafer 100, which is the workpiece, is positioned inside the wafer 100, and the laser beam is irradiated, and the focal point and the wafer 100 are moved relatively along the planned dividing lines 102, thereby forming a modified layer inside the wafer 100, which serves as a dividing starting point.

[0017] As shown in FIG. 3, the laser processing device 1 includes a rectangular parallelepiped base 2, an upright wall portion 5 erected at one end of the base 2, and a control portion 7 which is a control device.

[0018] The upper surface of the base 2 is provided with a holding section 10 having a holding table 11, an X-axis movement mechanism 20 for moving the holding table 11 in the X-axis direction which is the processing feed direction, and a Y-axis movement mechanism 30 for moving the holding table 11 in the Y-axis direction which is the indexing feed direction. The holding table 11 has a holding surface 15 for holding the wafer 100.

[0019] The X-axis movement mechanism 20 moves the holding table 11 in the X-axis direction parallel to the holding surface 15, relative to the laser irradiation mechanism 40. The X-axis movement mechanism 20 includes a pair of guide rails 23 extending in the X-axis direction, an X-axis table 24 placed on the guide rails 23, a ball screw 25 extending parallel to the guide rails 23, and a drive motor 26 that rotates the ball screw 25.

[0020] The pair of guide rails 23 are arranged parallel to the X-axis direction on the upper surface of the base 2. The X-axis table 24 is installed on the pair of guide rails 23 so as to be slidable along these guide rails 23. The Y-axis movement mechanism 30 and the holder 10 are placed on the X-axis table 24.

[0021] The ball screw 25 is screwed into a nut portion (not shown) provided on the X-axis table 24. The drive motor 26 is connected to one end of the ball screw 25, and rotates the ball screw 25. As the ball screw 25 is rotated, the X-axis table 24, the Y-axis moving mechanism 30, and the holding unit 10 move in the X-axis direction along the guide rail 23.

[0022] The Y-axis movement mechanism 30 moves the holding table 11 in the Y-axis direction parallel to the holding surface 15 relative to the laser irradiation mechanism 40. The Y-axis movement mechanism 30 includes a pair of guide rails 31 extending in the Y-axis direction, a Y-axis table 32 placed on the guide rails 31, a ball screw 33 extending parallel to the guide rails 31, and a drive motor 35 that rotates the ball screw 33.

[0023] A pair of guide rails 31 are arranged parallel to the Y-axis direction on the upper surface of the X-axis table 24. The Y-axis table 32 is installed on the pair of guide rails 31 so as to be slidable along these guide rails 31. The holding unit 10 is placed on the Y-axis table 32.

[0024] The ball screw 33 is screwed into a nut portion (not shown) provided on the Y-axis table 32. The drive motor 35 is connected to one end of the ball screw 33 and rotates the ball screw 33. As the ball screw 33 is rotated, the Y-axis table 32 and the holding portion 10 move in the Y-axis direction along the guide rail 31.

[0025] The holding unit 10 is used to hold the wafer 100. The holding unit 10 has a holding table 11 that holds the wafer 100, four clamp units 12 provided around the holding table 11, a θ table 13 that supports the holding table 11 and rotates it within the XY plane, and a rectangular cover plate 14 fixed to the upper end of the θ table 13.

[0026] The holding table 11 is a member for holding the wafer 100, and is formed in a disk shape. The holding table 11 has a holding surface 15 made of a porous material. This holding surface 15 can be connected to a suction source (not shown). The holding table 11 holds the wafer 100 by suction using this holding surface 15. When holding the wafer 100 by suction, the wafer 100 may be placed directly on the holding surface 15, or a protective tape may be attached to the back surface 105 of the wafer 100, and the wafer 100 may be placed on the holding surface 15 via the protective tape.

[0027] The standing wall portion 5 of the laser processing apparatus 1 has a vertical wall portion 5a supported by the base 2, and a horizontal wall portion 5b extending horizontally from the upper end portion of the vertical wall portion 5a. A laser irradiation mechanism 40 is provided on the lower surface of the horizontal wall portion 5b.

[0028] The laser irradiation mechanism 40 irradiates a laser beam onto the wafer 100 held on the holding table 11. The laser irradiation mechanism 40 has a laser irradiation unit 41 that irradiates the wafer 100 with a laser beam, and a camera 43 that images the wafer 100. The laser irradiation unit 41 has a condenser 42 that collects the laser beam. The camera 43 images the wafer 100 held on the holding table 11 in order to align the laser irradiation unit 41 with the wafer 100. By capturing the image, the position and orientation of the planned dividing lines 102 of the wafer 100 are detected.

[0029] An optical system (not shown) of a laser irradiation mechanism 40, such as a laser beam oscillator and a condenser lens, is disposed inside the horizontal wall 5b and the laser irradiation unit 41. The laser irradiation mechanism 40 is configured to irradiate a laser beam generated using these optical systems from the lower end of the laser irradiation unit 41 toward the wafer 100 held on the holding table 11 of the holding unit 10. In this embodiment, the wavelength of the laser beam irradiated from the laser irradiation mechanism 40 is a wavelength (e.g., 1342 nm) that is transparent to the wafer 100, which is the workpiece.

[0030] The control unit 7 includes a CPU that performs calculation processing according to a control program, and a storage medium such as a memory. The control unit 7 controls the above-mentioned components of the laser processing apparatus 1 to perform the modified layer forming process on the wafer 100.

[0031] In the modified layer forming step, an operator or a transport device (not shown) transports the wafer 100 to the laser processing device 1 and places the wafer 100 on the holding surface 15 of the holding table 11 of the holding unit 10 with the surface 101 on which the devices 103 are formed facing upward. Thereafter, the control unit 7 connects the holding surface 15 to a suction source, thereby suction-holding the wafer 100 by the holding surface 15.

[0032] Next, the control unit 7 detects and stores information on the positions of the planned dividing lines 102 formed on the front surface 101 of the wafer 100 held on the holding table 11, using the camera 43 of the laser irradiation mechanism 40. Furthermore, the control unit 7 aligns the planned dividing lines 102 in a predetermined direction with the X-axis direction, using the θ table 13 of the holding unit 10.

[0033] Next, the control unit 7 controls the X-axis moving mechanism 20 and the Y-axis moving mechanism 30 to adjust the position of the holding table 11 based on the position information of the planned dividing lines 102 so that the processing start position of one of the planned dividing lines 102 on the wafer 100 held on the holding table 11 is positioned directly below the collector 42 of the laser irradiation unit 41. In addition, the control unit 7 adjusts the focusing of the laser irradiation unit 41 so that the focusing point of the laser beam irradiated from the condenser 42 is positioned inside the wafer 100 .

[0034] 4(a) and 4(b), the control unit 7 positions the focal point of the laser beam LB from the collector 42 inside a portion of the wafer 100 corresponding to the planned dividing lines 102, and irradiates the wafer 100 with the laser beam LB, while moving the focal point of the laser beam LB and the wafer 100 relatively along the planned dividing lines 102. In this embodiment, the control unit 7 controls the X-axis moving mechanism 20 to feed the wafer 100 in the X-axis direction, thereby moving the wafer 100 along the planned dividing lines 102 relative to the focal point of the laser beam LB. In this manner, the control unit 7 forms modified layers 120 inside the wafer 100 along the intended dividing lines 102 of the wafer 100, which serve as dividing starting points.

[0035] After forming the modified layer 120 along one of the planned dividing lines 102, the control unit 7 uses the Y-axis moving mechanism 30 to index and feed the wafer 100 in the Y-axis direction by the interval of the planned dividing lines 102, and positions the processing start position of the unprocessed planned dividing line 102 directly below the light collector 42. Then, in the same manner as described above, the modified layer 120 is formed inside the wafer 100 along this planned dividing line 102.

[0036] In this manner, the control unit 7 forms modified layers 120 on the wafer 100 along all of the planned dividing lines 102 along the X-axis direction. Next, the control unit 7 rotates the wafer 100 by 90 degrees using the θ table 13 to align the unprocessed planned dividing lines 102 perpendicular to the planned dividing lines 102 on which the modified layers 120 have already been formed, with the X-axis direction. Then, modified layers 120 are formed inside the wafer 100 along these planned dividing lines 102 in the same manner as described above.

[0037] In this manner, modified layers 120 are ultimately formed inside the wafer 100 along all of the intended dividing lines 102 shown in FIG.

[0038] The laser processing conditions when carrying out the modified layer forming step are set, for example, as follows. Laser beam wavelength: 1342nm Average power of laser beam: 1.0W Laser beam repetition rate: 90kHz Machining feed speed: 700mm / sec

[0039] [Dividing process] After the modified layer forming step, a dividing step is performed in which the wafer 100 is divided along the modified layer 120 to form a plurality of chips (device chips) each including one device 103.

[0040] In this step, as shown in FIG. 5, a protective tape 107 having the same diameter as the wafer 100 is attached to the front surface 101 of the wafer 100 on which the modified layer 120 has been formed.

[0041] In this step, a dividing apparatus 50 shown in Fig. 6 is used. As shown in Fig. 6, the dividing apparatus 50 includes a water tank 51 for storing water L, a wafer holding member 55 for holding and transporting the wafer 100, an ultrasonic vibration unit 60 for emitting ultrasonic waves, and a control unit 57 serving as a control device. The water L is an example of a liquid through which ultrasonic vibrations are propagated.

[0042] The wafer holding member 55 can place the wafer 100 in the water L of the water tank 51 by adsorbing and holding the front surface 101 side of the wafer 100 to which the protective tape 107 is attached.

[0043] The ultrasonic vibration unit 60 propagates ultrasonic waves through the water L in the water tank 51 to generate cavitation, and is provided on the bottom surface 52 of the water tank 51. As shown in Figures 7(a) and 8, the ultrasonic vibration unit 60 includes a housing 61 having an upper plate (lid plate) 62 and a lower bottom plate 63. As shown in Figure 6, the ultrasonic vibration unit 60 is disposed in the water tank 51 such that the bottom plate 63 of the housing 61 contacts the bottom surface 52 of the water tank 51.

[0044] As shown in FIGS. 9 and 10, the ultrasonic vibration unit 60 includes an ultrasonic vibrator 70 inside the housing 61, which serves as a source of ultrasonic waves.

[0045] The ultrasonic transducer 70 is a bolt-tightened Langevin type ultrasonic transducer. As shown in Fig. 9, the ultrasonic transducer 70 includes a first horn 71 and a second horn 77, a first piezoelectric element 72 and a second piezoelectric element 73 sandwiched between the first horn 71 and the second horn 77, a first electrode 75 disposed between the first horn 71 and the first piezoelectric element 72, a second electrode 76 disposed between the second horn 77 and the second piezoelectric element 73, and a bolt 74 for fixing them.

[0046] In the ultrasonic transducer 70, by applying an AC voltage to the first electrode 75 and the second electrode 76 from an AC power source 201 located, for example, outside the housing 61, ultrasonic vibrations can be generated from the tip of the first horn 71 toward the outside.

[0047] 9, in this embodiment, the ultrasonic transducer 70 is fixed to the back surface of the upper plate 62 of the housing 61, and a tip of a first horn 71 of the ultrasonic transducer 70 is in contact with the upper plate 62 of the housing 61. Therefore, the ultrasonic transducer 70 is configured to propagate ultrasonic vibrations to the upper plate 62.

[0048] 7(a) and 9, a matching layer 65 is provided on the surface of the upper plate 62 of the housing 61. The matching layer 65 is a plate-shaped member, and is laminated on the upper plate 62 of the housing 61. The matching layer 65 is adhered to the surface of the upper plate 62 with an adhesive such as an epoxy resin adhesive or a silicone adhesive. When a silicone adhesive is used, the matching layer 65 can be easily attached to and detached from the upper plate 62.

[0049] FIG. 7(b) shows an enlarged view of a portion of the surface of the matching layer 65 shown in FIG. 7(a). As shown in FIG. 7(b), the surface (one side) of the matching layer 65 has projections and recesses 66 formed thereon. The projections and recesses 66 are formed by forming a plurality of lattice-shaped grooves 661 on the surface of the matching layer 65, for example, by dicing. The width and depth of the grooves are, for example, 100 μm. Furthermore, the projections 662 of the projections and recesses 66 are formed in a substantially cubic shape with a width of 100 μm and a height of 100 μm. In the ultrasonic vibration unit 60, the surface of the matching layer 65 is the surface that comes into contact with the water L in the water tank 51, as shown in FIG. 6.

[0050] In this manner, in the ultrasonic vibration unit 60, the ultrasonic transducer 70 is fixed to the back surface of the upper plate 62 of the housing 61, and the tip of the first horn 71 of the ultrasonic transducer 70 is in contact with the upper plate 62 of the housing 61. Therefore, the upper plate 62 of the housing 61 functions as a transmission layer through which ultrasonic vibrations from the ultrasonic transducer 70 are transmitted. In addition, a matching layer 65 is laminated on the upper plate 62, and the surface of the matching layer 65 is in contact with the water L in the water tank 51.

[0051] Therefore, in the ultrasonic vibration unit 60, the upper plate 62 of the housing 61 and the matching layer 65 laminated on the upper plate 62 have a first surface (the back surface of the upper plate 62) to which the ultrasonic transducer 70 is fixed and a second surface (the front surface of the matching layer 65) having irregularities 66, and function as a vibration plate that transmits ultrasonic waves from the ultrasonic transducer 70 to the liquid water L. The upper plate 62 of the housing 61 functions as a transmission layer including the first surface of this vibration plate. Furthermore, the matching layer 65 functions as a matching layer including the second surface of this vibration plate.

[0052] The matching layer 65 is made of a material having an acoustic impedance smaller than that of the upper plate 62 of the housing 61 as the transmission layer and larger than that of water L. In this embodiment, the upper plate 62 of the housing 61 is made of SUS (acoustic impedance: 46×10 6 kg / m 2 The matching layer 65 is mainly made of alumina (acoustic impedance: 33×10 6 kg / m 2 s) or glass epoxy (acoustic impedance: 7.1×10 6 kg / m 2 The thickness of the layer is about 0.6 mm. The acoustic impedance of water L is 1.5×10 6 kg / m 2 ·s.

[0053] The control unit 57 includes a CPU that performs arithmetic processing according to a control program, and a storage medium such as a memory, etc. The control unit 57 controls the above-mentioned members of the dividing apparatus 50 to perform the dividing step for the wafer 100.

[0054] In a division process using a division apparatus 50 having such a configuration, the wafer 100 is divided along the intended division lines 102 by irradiating the wafer 100 with ultrasonic waves via water L while the wafer 100 faces the second surface side of the vibration plate (i.e., the surface side of the matching layer 65 on which the irregularities 66 are formed).

[0055] Specifically, as shown in Fig. 6, the control unit 57 holds the protective tape 107 side of the wafer 100 by the wafer holding member 55 so that the back surface 105 on which the metal film 106 is formed faces downward. Then, the control unit 55 controls the wafer holding member 55 to submerge the wafer 100 in the water L of the water tank 51 and place the wafer 100 facing the front surface of the matching layer 65 of the ultrasonic vibration unit 60 placed on the bottom surface 52 of the water tank 51. At this time, the control unit 57 brings the front surface of the matching layer 65 on which the irregularities 66 are formed and the back surface 105 of the wafer 100 close to each other, for example, by a distance of 1 to 3 mm.

[0056] Next, the control unit 57 applies an AC voltage from the AC power supply 201 to the first electrode 75 and the second electrode 76 (see FIG. 9) of the ultrasonic transducer 70 of the ultrasonic vibration unit 60. This causes ultrasonic vibration to propagate from the tip of the first horn 71 of the ultrasonic transducer 70 to the upper plate 62 of the housing 61. The oscillation frequency of the ultrasonic waves is, for example, 38 kHz.

[0057] As a result, the upper plate 62 and the matching layer 65 constituting the diaphragm are ultrasonically vibrated, and ultrasonic waves W are irradiated from the surface of the matching layer 65 having the unevenness 66 toward the back surface 105 of the wafer 100 on which the metal film 106 is formed, as shown in FIG. 6. As a result, cavitation (the generation and disappearance of minute bubbles) occurs in the water L between the matching layer 65 and the wafer 100 due to the action of the ultrasonic waves W. The impact of this cavitation causes plastic deformation in the metal film 106 of the wafer 100, and the metal film 106 is work-hardened and made embrittled. Furthermore, this impact causes the wafer 100 to be divided along the modified layer 120 (see FIG. 4) formed below the planned division lines 102, and a plurality of device chips including the device 103 are formed.

[0058] This completes the dividing step. Note that, although the dividing step divides the wafer 100 into a plurality of device chips, the wafer 100 is held together by the protective tape 107, preventing the wafer 100 from falling apart.

[0059] As described above, in the ultrasonic vibration unit 60 of the dividing device 50 used in the dividing step of this embodiment, the upper plate 62 of the housing 61 and the matching layer 65 form a vibration plate. This vibration plate irradiates ultrasonic waves W from the ultrasonic vibrator 70 to the wafer 100 from the second surface (surface of the matching layer 65) having the unevenness 66, through the liquid water L. That is, in this configuration, since the ultrasonic waves W are irradiated to the water L and the wafer 100 from the surface having the unevenness 66, it is possible to efficiently generate cavitation (i.e., to increase the frequency of cavitation occurrence).

[0060] Therefore, in this embodiment, it is possible to efficiently embrittle the metal film 106 in the wafer 100 and divide the wafer 100 along the modified layer 120. This makes it possible to improve the productivity in manufacturing device chips by dividing the wafer 100 by ultrasonic waves.

[0061] In this embodiment, the vibration plate includes the upper plate 62 of the housing 61 to which the ultrasonic vibrator 70 is fixed, and a matching layer 65 on which the unevenness 66 is formed. The matching layer 65 is made of a material having an acoustic impedance smaller than that of the upper plate 62 of the housing 61 and larger than that of water L. Therefore, the matching layer 65 can reduce the acoustic loss between the upper plate 62 of the housing 61, which is ultrasonically vibrated by the ultrasonic vibrator 70, and water, which is the liquid to which ultrasonic waves are to be applied. Therefore, it becomes possible to efficiently irradiate ultrasonic waves to the water L.

[0062] Here, experimental results regarding the effects of the ultrasonic vibration unit 60 according to this embodiment will be shown.

[0063] (1) Cavitation efficiency verification experiment In this experiment, the cavitation efficiency (ease of cavitation occurrence) was compared using an ultrasonic vibration unit 60 with a matching layer 65 having projections and recesses 66 and an ultrasonic vibration unit 160 of a comparative example (see FIG. 11). The ultrasonic vibration unit 160 of the comparative example has a configuration in which the matching layer 65 does not have projections and recesses 66 in the configuration of the ultrasonic vibration unit 60.

[0064] In this experiment, an experimental apparatus 90 as shown in Fig. 11 was used. The experimental apparatus 90 was equipped with a water tank (made of transparent resin) 91 for storing the luminol aqueous solution LS, a support member 92 for supporting the ultrasonic vibration unit 60 (160), and a camera 93.

[0065] 11, the support member 92 supports the ultrasonic vibration unit 60 (160) with the matching layer 65 facing downward, and the ultrasonic vibration unit 60 (160) can be submerged in the luminol aqueous solution LS in the water tank 91. The distance between the lower surface of the ultrasonic vibration unit 60 (160) (the surface of the matching layer 65) and the bottom surface of the water tank 91 is, for example, 5 mm. Furthermore, the height of the liquid level of the luminol aqueous solution LS during the experiment is, for example, 30 mm.

[0066] The camera 93 is disposed below the water tank 91, and captures light emission by chemiluminescence in the luminol aqueous solution LS below the ultrasonic vibration unit 60 (160) through the bottom surface of the water tank 91. This light emission is due to a chemical reaction between hydrogen peroxide and luminol generated by cavitation, and becomes more intense when the efficiency of cavitation is high.

[0067] The luminol aqueous solution LS is obtained by dissolving luminol and sodium carbonate in water (for example, 1000 mL). The sodium carbonate is added for the purpose of dissolving the luminol in the water. The luminol concentration of the luminol aqueous solution LS is, for example, 0.02% (0.2 g / 1000 mL), and the sodium carbonate concentration is, for example, 0.05% (0.5 g / 1000 mL). The exposure time of the camera 93 is, for example, 120 seconds.

[0068] Fig. 12(a) shows the light emission state by chemiluminescence when the ultrasonic vibration unit 160 of the comparative example is used, as imaged by the camera 93. Fig. 12(b) shows the light emission state by chemiluminescence when the ultrasonic vibration unit 60 of this embodiment is used, as imaged by the camera 93. As shown in these figures, when the ultrasonic vibration unit 60 of this embodiment is used, higher light emission is obtained, and higher cavitation efficiency is realized. Therefore, it can be seen that it is preferable that the matching layer 65 of the ultrasonic vibration unit 60 has unevenness 66.

[0069] (2) Dividability verification experiment In this experiment, the dividing process of the above-mentioned chip manufacturing method was carried out using an ultrasonic vibration unit 60 provided with a matching layer 65 having projections and recesses 66 in a dividing device 50, and an ultrasonic vibration unit 160 of the comparative example described above, and the results of dividing a wafer 100 into multiple chips were compared.

[0070] Fig. 13(a) shows the state of the wafer 100 when ultrasonic waves are irradiated onto the wafer 100 for one minute using an ultrasonic vibration unit 160 of a comparative example having a matching layer 65 without unevenness 66. Fig. 13(b) shows the state of the wafer 100 when ultrasonic waves are irradiated onto the wafer 100 for one minute using an ultrasonic vibration unit 60 of this embodiment having a matching layer 65 with unevenness 66. Note that in these figures, the planned dividing lines 102 and devices 103 of the wafer 100 are not depicted.

[0071] As shown in Fig. 13(a), when the ultrasonic vibration unit 160 of the comparative example is used, the wafer 100 is not substantially divided by ultrasonic irradiation for one minute. On the other hand, as shown in Fig. 13(b), when the ultrasonic vibration unit 60 of the present embodiment is used, even with ultrasonic irradiation for one minute, a crack C is formed in the wafer 100, and it is understood that the wafer 100 begins to be divided.

[0072] 14(a) shows the state of the wafer 100 when ultrasonic waves are irradiated onto the wafer 100 for five minutes using the ultrasonic vibration unit 160 of the comparative example, and FIG 14(b) shows the state of the wafer 100 when ultrasonic waves are irradiated onto the wafer 100 for five minutes using the ultrasonic vibration unit 60 of the present embodiment.

[0073] As shown in Fig. 14(a), in the ultrasonic vibration unit 160 of the comparative example, even when the ultrasonic wave irradiation time was set to 5 minutes, only thin cracks C were observed in the wafer 100. On the other hand, as shown in Fig. 14(b), in the case of using the ultrasonic vibration unit 60 of the present embodiment, when the sound wave irradiation time was set to 5 minutes, many thick cracks C were generated in the wafer 100, and it can be seen that the division of the wafer 100 has progressed significantly.

[0074] In this way, when the ultrasonic vibration unit 60 of this embodiment is used, the division of the wafer 100 proceeds more efficiently, and it can be said that a high cavitation efficiency is realized. Therefore, from this experiment, it is also found that it is preferable that the matching layer 65 of the ultrasonic vibration unit 60 has the unevenness 66.

[0075] In this embodiment, the unevenness 66 formed on the surface of the matching layer 65 is formed by making grooves 661 on the surface of the matching layer 65, as shown in Fig. 7(b). In this regard, the unevenness of the matching layer 65 may be formed by providing a plurality of holes on the surface of the matching layer 65.

[0076] Moreover, the width (or hole diameter) of the grooves 661 in the unevenness 66 is preferably equal to or smaller than the resonant bubble diameter corresponding to the frequency of the ultrasonic waves output from the ultrasonic transducer .

[0077] The relationship between the frequency f0 of the ultrasonic wave and the radius a of the resonant bubble is expressed, for example, by the following formula (1).

[0078]

number

[0079] For example, when the medium is water at 20° C., the medium inside the microbubble is air at 20° C., and the ultrasonic frequency f0 is 38 kHz, the radius a of the microbubble calculated by the above formula (1) is 85 μm. Therefore, it is preferable that the width (or hole diameter) of the grooves 661 in the unevenness 66 is 170 μm or less.

[0080] In addition, it is preferable to select the most suitable material for the upper plate 62 (transmission layer) of the housing 61 in the ultrasonic vibration unit 60 and the matching layer 65 laminated on the upper plate 62 depending on the frequency band, the environment in which it is used, and / or the structure of the ultrasonic transducer 70, etc. An optimal material for the matching layer 65 is, for example, a material that has an acoustic impedance close to the value Z expressed by the following equation (2).

[0081]

number

[0082] FIG. 15 shows the materials of the ultrasonic transducer 70 (transducer), the upper plate 62 (transmission layer) of the housing 61 of the ultrasonic vibration unit 60, the matching layer 65, and the medium according to the frequency band of ultrasonic waves (26 to 160 kHz (low frequency band), 400 to 1000 kHz (high frequency band)). In this figure, the acoustic impedance of each material is shown in parentheses. The unit of acoustic impedance is "10 6 kg / m 2 ·s".

[0083] The material of the ultrasonic transducer 70 is, for example, PZT (lead zirconate titanate). The ultrasonic transducer 70 used in the low frequency band is heavy and the amplitude of the ultrasonic waves it oscillates is large. For this reason, SUS, which has high mechanical strength, is used as the material of the upper plate 62 (transmission layer). In addition, alumina and glass epoxy can be used as the material of the matching layer 65.

[0084] Also, in the high frequency band, the upper plate 62 (transmission layer) can be made of SUS, and the matching layer 65 can be made of alumina and glass epoxy.

[0085] The ultrasonic vibrator 70 used in the high frequency band is light in weight and the amplitude of the ultrasonic waves it oscillates is small. Therefore, a material with low mechanical strength, such as that used for the matching layer 65, can be used as the material for the upper plate 62 (transmission layer). That is, for example, alumina, quartz, or glass epoxy can be used. In this case, the matching layer 65 is not provided on the upper plate 62 of the ultrasonic vibration unit 60, and the unevenness 66 may be formed on the surface of the upper plate 62.

[0086] Furthermore, the preferred thickness of the upper plate 62 (transmission layer) is approximately 1 / 2 the wavelength of the ultrasonic waves (wavelength within the upper plate 62). The preferred thickness of the matching layer 65 is approximately 1 / 4 the wavelength of the ultrasonic waves (wavelength within the matching layer 65). However, when the frequency band of the ultrasonic waves is low, a load is generated if the upper plate 62 or matching layer 65 is thick. For this reason, it is preferred that the thickness of each layer is sufficiently thin compared to the wavelength of the ultrasonic waves.

[0087] In this embodiment, a matching layer 65 having projections and recesses 66 is laminated on the upper plate 62 of the housing 61 in the ultrasonic vibration unit 60. In this regard, the ultrasonic vibration unit 60 of this embodiment does not need to include the matching layer 65. In this case, by forming the projections and recesses 66 on the upper surface of the upper plate 62, cavitation can be efficiently generated. In this configuration, the upper plate 62 has a first surface (rear surface) to which the ultrasonic vibrator 70 is fixed and a second surface (front surface) having the projections and recesses 66, and functions as a vibration plate that transmits ultrasonic waves to liquid. However, from the viewpoint of reducing acoustic loss and suppressing wear on the housing 61, it is preferable that the ultrasonic vibration unit 60 includes a matching layer 65 having projections and recesses 66.

[0088] The dividing device 50 for carrying out the dividing step described above is not limited to the configuration shown in Fig. 6. For example, the dividing device 50 may have a configuration as shown in Fig. 16. In the configuration shown in this figure, the dividing device 50 has the water tank 51 shown in Fig. 6 and an ultrasonic vibration unit 601 which is a horn-type ultrasonic vibration unit.

[0089] The ultrasonic vibration unit 601 is configured to have a cylindrical housing 61 that is thinner than the ultrasonic vibration unit 60 in the configuration of the ultrasonic vibration unit 60 shown in Fig. 9. For example, one ultrasonic transducer 70 is fixed to an upper plate 62 of the housing 61 that faces downward in Fig. 16. In addition, a matching layer 65 having the above-mentioned unevenness 66 is laminated on the upper plate 62.

[0090] When using a dividing apparatus 50 equipped with such an ultrasonic vibration unit 601, the wafer 100 is placed on the bottom surface 52 of the water tank 51 with the back surface 105 on which the metal film 106 is formed facing upward. Then, the ultrasonic vibration unit 601 is submerged in the water L of the water tank 51 with the matching layer 65 facing downward, and the surface of the matching layer 65 on which the irregularities 66 are formed faces the back surface 105 of the wafer 100.

[0091] Thereafter, the control unit 57 ultrasonically vibrates the upper plate 62, which is a vibration plate, and the matching layer 65 with the ultrasonic vibrator 70, and irradiates ultrasonic waves W from the matching layer 65 toward the back surface 105 of the wafer 100 through the water L. Furthermore, the ultrasonic vibration unit 601 is moved horizontally (X-axis direction and Y-axis direction in the figure) above the wafer 100 by a moving mechanism (not shown), thereby applying ultrasonic waves W to the entire back surface 105 of the wafer 100. Such application of ultrasonic waves embrittles the metal film 106 over the entire back surface 105 of the wafer 100 due to cavitation, and the wafer 100 is divided along the planned division lines 102 (modified layer 120; see FIG. 4) to form a plurality of device chips including the device 103.

[0092] Moreover, the dividing apparatus 50 may have a configuration as shown in Fig. 17. In the configuration shown in this figure, the dividing apparatus 50 has the water tank 51 and the wafer holding member 55 shown in Fig. 6, and an ultrasonic vibration unit 602.

[0093] The ultrasonic vibration unit 602 has a configuration in which the bottom plate 53 of the water tank 51 is used as the upper plate of the housing 61 (the bottom plate 53 also serves as the upper plate of the housing 61) in the configuration of the ultrasonic vibration unit 60 shown in Fig. 9. In this configuration, a matching layer 65 is laminated on the bottom plate 53. That is, the matching layer 65 having irregularities 66 (see Fig. 7(b)) is provided on the bottom surface 52, which is the upper surface of the bottom plate 53.

[0094] In the ultrasonic vibration unit 602, the bottom plate 53 as the upper plate of the housing 61 and the matching layer 65 laminated on the bottom plate 53 have a first surface (the back surface of the bottom plate 53) to which the ultrasonic transducer 70 is fixed and a second surface (the front surface of the matching layer 65) having irregularities 66, and function as a vibration plate that transmits ultrasonic waves from the ultrasonic transducer 70 to the liquid water L. The bottom plate 53 of the water tank 51 functions as a transmission layer including the first surface of this vibration plate. Furthermore, the matching layer 65 functions as a matching layer including the second surface of this vibration plate.

[0095] In the division step using this configuration, the control unit 57 uses the wafer holding member 55 to submerge the wafer 100 in the water L of the water tank 51 so that the back surface 105 faces downward, and arranges the wafer 100 so as to face the front surface of the matching layer 65 in the water tank 51. Next, the control unit 57 applies an AC voltage to the ultrasonic vibrator 70. As a result, the bottom plate 53 and the matching layer 65 constituting the vibration plate are ultrasonically vibrated, and ultrasonic waves W are irradiated from the matching layer 65 to the wafer 100 through the water L, causing cavitation. The impact of this cavitation embrittles the metal film 106 of the wafer 100, and the wafer 100 is divided along the planned division lines 102 (modified layer 120; see FIG. 4) to form a plurality of device chips including the device 103.

[0096] In addition, in this embodiment, before carrying out the division process involving the application of ultrasonic waves as described above, a mask may be formed on the back surface 105 of the wafer 100 coated with the metal film 106 to expose the areas corresponding to the planned division lines 102 and to cover the other areas.

[0097] When forming such a mask, for example, a liquid resin formed from a volatile solvent that is poorly soluble in water is applied to the entire back surface 105 of the wafer 100, and a layer of this resin is formed and cured. Then, this layer of resin is removed along the areas corresponding to the planned dividing lines 102. As a result, a mask that exposes the metal film 106 of the wafer 100 along the areas corresponding to the planned dividing lines 102 is formed.

[0098] By carrying out the above-mentioned dividing step after forming such a mask, it becomes possible to cause concentrated plastic deformation of the substrate and metal film 106 of the wafer 100 in the region corresponding to the dividing lines 102. This makes it possible to efficiently embrittle the metal film 106 along the region corresponding to the dividing lines 102 while protecting the metal film 106 forming the electrodes in the region other than the region corresponding to the dividing lines 102, and to easily divide the wafer 100 along the dividing lines 102. When such a mask is formed, it is preferable to remove the mask formed on the back surface 105 of the wafer 100 after the dividing step is performed.

[0099] In the above embodiment, after the modified layer forming step is performed on the wafer 100, the protective tape 107 is applied to the front surface 101 of the wafer 100 and the dividing step is performed. In this regard, for example, the protective tape 107 may be applied to the front surface 101 of the wafer 100 before the modified layer forming step is performed. In this case, a protective tape 107 that transmits the laser beam LB used in the modified layer forming step is used. Then, in the modified layer forming step, the laser beam LB is irradiated onto the wafer 100 through the protective tape 107. In this configuration, when the protective tape 107 is applied to the wafer 100, damage to the wafer 100 starting from the modified layer 120 can be suppressed.

[0100] In this embodiment, after the dividing step, a pick-up step as shown below may be performed as necessary. In this step, first, a transfer step shown in FIG. 18 is performed. In the transfer step, as shown in FIG. 18, an annular frame 111 having an opening 112 capable of accommodating a wafer 100 is prepared. Then, the wafer 100 is positioned in the center of the opening 112 of the frame 111 with the front surface 101 side to which the protective tape 107 is attached facing upward. Then, a highly elastic adhesive tape 113 is attached to the wafer 100 and the frame 111 from the rear surface 105 side of the wafer 100.

[0101] As a result, the wafer 100 and the frame 111 are integrated by the adhesive tape 113. Furthermore, the protective tape 107 is peeled off from the front surface 101 of the wafer 100. As a result, the wafer 100 is transferred from the protective tape 107 to the adhesive tape 113 shown in the figure. In this manner, a work set 110 including the wafer 100, the frame 111, and the adhesive tape 113 is formed.

[0102] In addition, since the wafer 100 in the work set 110 has been subjected to the above-mentioned division process, as shown in the figure, it has a fracture groove 121 starting from the above-mentioned modified layer 120 (see FIG. 4) as the division starting point, and is divided into individual device chips 123.

[0103] In the pick-up step, a pick-up device 80 (only a part of which is shown) shown in Fig. 19 is used. The pick-up device 80 includes an expansion mechanism 82, a pick-up mechanism 84, and a control unit 87 that is a control device.

[0104] The expansion mechanism 82 includes a cylindrical expansion drum 821 and a plurality of air cylinders 822 adjacent to the expansion drum 821 and extending upward at intervals in the circumferential direction. An annular holding member 823 is connected to the upper end of each air cylinder 822. A plurality of clamps 824 are arranged at intervals in the circumferential direction on the outer periphery of the holding member 823. The inner diameter of the expansion drum 821 is larger than the diameter of the wafer 100, and the outer diameter of the expansion drum 821 is smaller than the inner diameter of the frame 111. The holding member 823 corresponds to the diameter dimension of the frame 111, and is configured so that the frame 111 can be placed on the flat upper surface of the holding member 823.

[0105] 19, in the pickup device 80, the multiple air cylinders 822 are configured to raise and lower the holding member 823 between a reference position where the upper surface of the holding member 823 is at approximately the same height as the upper end of the expansion drum 821, and an extended position where the upper surface of the holding member 823 is located below the upper end of the expansion drum 821. Note that, for convenience of explanation, in FIG. 19, the wafer 100 held by the adhesive tape 113 is shown to be raised and lowered (shown by a solid line and a two-dot chain line), but in reality, it is the holding member 823 that is raised and lowered.

[0106] The pickup mechanism 84 of the pickup device 80 is configured in the shape of an arm that is movable horizontally and vertically. A suction unit 841 extending downward is provided at the tip of the pickup mechanism 84. In the pickup mechanism 84, a suction force from a suction source (not shown) is transmitted to the suction unit 841, so that the suction unit 841 can suck and pick up the device chips 123 formed by dividing the wafer 100.

[0107] The control unit 87 of the pickup device 80 includes a CPU that performs calculation processing according to a control program, and a storage medium such as a memory. The control unit 87 controls the above-mentioned members of the pickup device 80 to perform the pickup process for the wafer 100.

[0108] In a pick-up process using the pick-up device 80 having such a configuration, first, the work set 110 is set in the pick-up device 80. That is, an operator or a transfer device (not shown) places the frame 111 of the work set 110 on the upper surface of the holding member 823 positioned at a reference position so that the front surface 101 of the wafer 100 faces upward. Next, the operator or the control unit 87 uses a plurality of clamps 824 to fix the frame 111 to the holding member 823.

[0109] Next, the control unit 87 lowers the holding member 823 to the expansion position. This applies an external force to the adhesive tape 113 of the work set 110 in a direction that radially expands the adhesive tape 113. This causes the adhesive tape 113 to expand radially, as shown by the two-dot chain line in Fig. 19, and the intervals between the device chips 123 on the wafer 100 attached to the adhesive tape 113 are expanded.

[0110] Thereafter, the control unit 87 positions the suction unit 841 of the pickup mechanism 84 above the device chip 123 to be picked up and lowers it, so that the suction unit 841 adsorbs the upper surface of the device chip 123. Next, the control unit 87 raises the pickup mechanism 84 to peel the device chip 123 off the adhesive tape 113 and pick it up. The picked-up device chip 123 is transported to a tray or the like (not shown), or is transported to a predetermined loading position of a processing device that will carry out the next process. Then, the control unit 87 performs this pickup operation sequentially for all the device chips 123. This completes the pickup process. [Explanation of symbols]

[0111] 1: Laser processing equipment, 2: Base, 5: Vertical wall, 5a: Vertical wall, 5b: Horizontal wall, 7: Control unit, 10: holding portion, 11: holding table, 12: clamp portion, 13: θ table, 14: cover plate, 15: holding surface, 20: X-axis movement mechanism, 23: guide rail, 24: X-axis table, 25: ball screw, 26: drive motor, 30: Y-axis movement mechanism, 31: guide rail, 32: Y-axis table, 33: ball screw, 35: drive motor, 40: laser irradiation mechanism, 41: laser irradiation unit, 42: condenser, 43: camera, 50: dividing device, 51: water tank, 52: bottom surface, 53: bottom plate, 55: wafer holding member, 57: control unit, 60: ultrasonic vibration unit, 61: housing, 62: upper plate, 63: bottom plate, 65: matching layer, 66: unevenness, 70: ultrasonic transducer, 71: first horn, 72: first piezoelectric element, 73: second piezoelectric element, 74: bolt, 75: first electrode, 76: second electrode, 77: second horn, 80: pickup device, 82: expansion mechanism, 84: Pick-up mechanism, 87: Control unit, 90: experimental apparatus, 91: water tank, 92: support member, 93: camera, 100: wafer, 101: surface, 102: planned division line, 103: device, 105: back surface, 106: metal film, 107: protective tape, 110: work set, 111: frame, 112: opening, 113: adhesive tape, 120: modified layer, 121: cutting groove, 123: device chip, 160: ultrasonic vibration unit, 201: AC power source, 601: ultrasonic vibration unit, 602: ultrasonic vibration unit, 661: groove, 662: protrusion, 821: expansion drum, 822: air cylinder, 823: holding member, 824: clamp, 841: suction part, C: Crack, L: Water, LB: Laser beam, LS: Luminol solution, W: Ultrasound, a: radius, f0: frequency

Claims

1. A method for manufacturing chips by dividing a workpiece along a planned dividing line set on the workpiece using an ultrasonic vibration unit, comprising the steps of: The ultrasonic vibration unit includes: An ultrasonic transducer that generates ultrasonic waves; a vibration plate having a first surface to which the ultrasonic transducer is fixed and a second surface having projections and recesses, and transmitting the ultrasonic waves to the liquid; a modified layer forming step of forming a modified layer inside the workpiece by positioning a focal point of a laser beam having a wavelength that transmits the workpiece inside the workpiece, irradiating the laser beam, and relatively moving the focal point and the workpiece along the planned division line; and a dividing step of dividing the workpiece along the planned dividing line by irradiating the workpiece with the ultrasonic wave through the liquid while the workpiece and the second surface side of the vibration plate are facing each other after the modified layer forming step. A method for manufacturing chips.

2. the diaphragm having a transmission layer including the first surface and a matching layer including the second surface of the diaphragm; the matching layer is formed of a material having an acoustic impedance smaller than that of the transmission layer and larger than that of the liquid. A method for producing the chip according to claim 1 .

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