Chip manufacturing method

Abstract

To reduce a range of an undivided area after laser processing.SOLUTION: A chip manufacturing method that manufactures a chip by processing a workpiece whose surface has a plurality of dividing lines along each dividing line includes a suction holding step of suctioning and holding a workpiece on the holding surface of the chuck table via a tape attached to the workpiece by applying a predetermined negative pressure that is 40 kPa smaller than the atmospheric pressure to the chuck table, a modified layer forming step of forming a modified layer inside the workpiece by relatively moving a focal point of a pulsed laser beam having a wavelength that passes through the workpiece along the planned dividing line, and the chuck table in a state in which the focal point is positioned inside the workpiece that is held by suction on the holding surface with a predetermined negative pressure, and a dividing step of dividing the workpiece by applying an external force to the workpiece.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing chips by machining a workpiece along a plurality of planned dividing lines to manufacture chips. [Background technology]

[0002] A known processing method divides a workpiece, such as a semiconductor wafer, into chips by forming division starting points inside the workpiece along a plurality of planned division lines set in a grid pattern on the surface of the workpiece, and then applying an external force to the workpiece (see, for example, Patent Document 1).

[0003] The division starting points described in Patent Document 1 are regions where the mechanical strength of the workpiece is locally reduced, and are called modified layers. The modified layers are formed by laser processing in which a pulsed laser beam having a wavelength that transmits through the workpiece is irradiated along each planned division line with the focal point of the laser beam positioned inside the workpiece.

[0004] The volume of the region where the modified layer is formed by the irradiation of the laser beam increases compared to before the modified layer was formed, and internal stress due to the volume expansion occurs in the workpiece, for example, along the width direction of the planned dividing line, which is perpendicular to the longitudinal direction of the planned dividing line.

[0005] However, during normal laser processing, the workpiece is held by relatively strong suction on the chuck table at a negative pressure of about -90 kPa, so the internal stress generated during the formation of the modified layer is not released and remains inside the workpiece.

[0006] Due to this internal stress that remains unreleased, stress acts from a first region of the workpiece, where a modified layer has already been formed, to a second region that is distant from the first region and where the modified layer has not yet been formed.

[0007] The stress acting from this first region to the second region can prevent the formation of a modified layer when forming the modified layer in the second region, and can also prevent the formation of cracks extending from the modified layer to the front and back surfaces of the workpiece even if the modified layer is formed. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-192370 Summary of the Invention [Problem to be solved by the invention]

[0009] If the formation of a modified layer or the propagation of a crack is hindered, there is a problem in that an undivided region is generated in the workpiece, where the workpiece is not divided even when an external force is applied to the workpiece after laser processing. The present invention has been made in view of this problem, and an object of the present invention is to reduce the extent of the undivided region. [Means for solving the problem]

[0010] According to one aspect of the present invention, a method for manufacturing chips by processing a workpiece having a plurality of planned dividing lines set on its surface along each of the planned dividing lines to manufacture chips is provided. The method comprises applying a predetermined negative pressure, the difference between which is smaller than the atmospheric pressure, to a chuck table, and applying a tape attached to the workpiece to form a chip. The holding surface is formed by a disk-shaped frame and a disk-shaped ceramic porous plate fixed in a recess of the frame, and the upper surface of the frame and the upper surface of the porous plate are flush with each other. The chuck table Applicable A method for manufacturing chips is provided, comprising: a suction-holding step of suction-holding the workpiece with a holding surface; a modified layer forming step of, after the suction-holding step, forming a modified layer inside the workpiece by positioning the focal point of a pulsed laser beam having a wavelength that passes through the workpiece inside the workpiece suction-held with the holding surface by the predetermined negative pressure and moving the focal point and the chuck table relatively along a planned division line; and a dividing step of, after the modified layer forming step, applying an external force to the workpiece to divide it.

[0011] Preferably, in the suction and holding step, the predetermined negative pressure having a pressure value between -40 kPa and -5 kPa is applied to the chuck table. Also, preferably, in the suction and holding step, the predetermined negative pressure having a pressure value between -20 kPa and -5 kPa is applied to the chuck table. More preferably, in the suction and holding step, the predetermined negative pressure having a pressure value between -15 kPa and -5 kPa is applied to the chuck table. Preferably, in the suction holding step, the workpiece is suction-held via the tape by the holding surface having an outer diameter larger than an outer diameter of the workpiece.

[0012] According to another aspect of the present invention, a method for manufacturing chips by processing a workpiece having a plurality of planned division lines set on its surface along each of the planned division lines includes a suction and holding step of suction-holding the workpiece on a holding surface of a chuck table via tape attached to the workpiece, a modified layer forming step of forming a modified layer inside the workpiece by relatively moving a focal point of a pulsed laser beam having a wavelength that transmits the workpiece and the chuck table along each of the planned division lines while positioning the focal point inside the workpiece held by suction on the holding surface, and after the modified layer forming step, applying an external force to the workpiece to divide the workpiece. and a dividing step, wherein the modified layer forming step includes a first modified layer forming step in which, when the modified layer is formed in an outer region located outside the center of the surface of the workpiece in an indexing feed direction perpendicular to the laser beam irradiation direction and the processing feed direction, the modified layer is formed in a state in which the negative pressure applied to the holding surface is a first negative pressure whose difference from the atmospheric pressure is greater than 40 kPa, and a second modified layer forming step in which, when the modified layer is formed in a central region of the surface located closer to the center than the outer region in the indexing feed direction, the modified layer is formed in a state in which the negative pressure applied to the holding surface is a second negative pressure whose difference from the atmospheric pressure is less than 40 kPa.

[0013] Also, preferably, the modified layer forming step further includes a third modified layer forming step in which, when forming the modified layer in an intermediate region located between the outer region and the central region in the index feed direction, the modified layer is formed while the negative pressure acting on the holding surface is a third negative pressure having a pressure value between the first negative pressure and the second negative pressure. [Effects of the Invention]

[0014] During normal laser processing, a negative pressure of approximately 90 kPa, which is different from the atmospheric pressure, is applied to the holding surface of the chuck table to hold the workpiece by suction. In contrast, in a chip manufacturing method according to one aspect of the present invention, a modified layer is formed inside the workpiece while a predetermined negative pressure, which is less than 40 kPa different from the atmospheric pressure, is applied to the chuck table.

[0015] In this way, by using a relatively weak suction pressure when holding the workpiece, it is possible to both hold the workpiece by suction and release internal stress during laser processing. Therefore, compared to when the workpiece is held by suction at a negative pressure of about 90 kPa relative to the atmospheric pressure, the size of the undivided region can be reduced, and furthermore, the yield rate during chip manufacturing can be improved. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a flow diagram of a method for manufacturing a chip according to the first embodiment. [Figure 2] 1 is a schematic diagram of a wafer and the like. [Figure 3] FIG. 2 is a perspective view of the laser processing device. [Figure 4] FIG. 10 is a diagram showing a suction and holding step. [Figure 5] 10A to 10C are diagrams illustrating a modified layer forming step. [Figure 6] FIG. 6(A) is a diagram showing an expansion device, and FIG. 6(B) is a diagram showing a division step. [Figure 7] FIG. 10 is a flow diagram of a method for manufacturing a chip according to a second embodiment. [Figure 8]10A and 10B are diagrams illustrating the formation of a modified layer in the outer region. [Figure 9] 10A and 10B are diagrams illustrating a state in which a modified layer is formed in an intermediate region. [Figure 10] 10A and 10B are diagrams illustrating a modified layer formed in the central region. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a flow diagram of a method for manufacturing a chip 25 according to a first embodiment. In the first embodiment, a wafer (workpiece) 11 is processed in the order of a suction holding step S10, a modified layer forming step S20, and a dividing step S30.

[0018] 2 is a schematic diagram of the wafer 11. The wafer 11 of this embodiment is a disk-shaped semiconductor wafer having a single crystal silicon substrate, and has a diameter of approximately 300 mm and a thickness of approximately 300 μm. However, the material, diameter, and thickness of the substrate constituting the wafer 11 are not limited to this example.

[0019] A plurality of first dividing lines 15a each extending substantially parallel to the first direction 13a and a plurality of second dividing lines 15b each extending substantially parallel to the second direction 13b are set on the front surface 11a of the wafer 11. The first direction 13a and the second direction 13b are orthogonal to each other (intersect with each other).

[0020] In each of the areas partitioned by the plurality of first division lines 15a and the plurality of second division lines 15b, a device 17 such as an LED (Light Emitting Diode) or an IC (Integrated Circuit) is formed.

[0021] However, the arrangement, number, shape, size, type, structure, etc. of the devices 17 are not limited to the example in Fig. 2. Furthermore, devices 17 do not necessarily have to be formed in each of the areas partitioned by the first planned division lines 15a and the second planned division lines 15b.

[0022] A peripheral surplus region 17b exists on the periphery of the device region 17a in which multiple devices 17 are arranged. The peripheral surplus region 17b is an annular region that surrounds the device region 17a in a plane defined by the first direction 13a and the second direction 13b, and does not have any devices 17.

[0023] In this embodiment, before processing the wafer 11, the orientation of the notch 11c and the orientation of the annular frame 19 made of metal are aligned in a predetermined manner, and then the wafer 11 is placed in the opening 19a of the frame 19.

[0024] Then, a stretchable resin tape (dicing tape) 21 is attached to the back surface 11b of the wafer 11 and one surface of the frame 19. This forms a wafer unit 23 including the wafer 11 supported by the frame 19 via the tape 21 so that the front surface 11a is exposed.

[0025] Alternatively, a wafer unit 23 may be formed by attaching tape 21 to the front surface 11a and one surface of the frame 19 so that the back surface 11b of the wafer 11 is exposed. After the wafer unit 23 is transported to the laser processing device 2, the wafer 11 is subjected to laser processing.

[0026] Figure 3 is a perspective view of the laser processing device 2. The X-axis direction (processing feed direction), Y-axis direction (indexing feed direction), and Z-axis direction (vertical direction) shown in Figure 3 are perpendicular to one another. The laser processing device 2 has a base 4 that supports each of the components.

[0027] A movement mechanism 6 is provided on the upper surface of the base 4. The movement mechanism 6 is fixed to the upper surface of the base 4 and has a pair of Y-axis guide rails 8 arranged along the Y-axis direction. A Y-axis direction movement plate 10 is attached to the upper surfaces of the pair of Y-axis guide rails 8 in a manner that allows it to slide along the pair of Y-axis guide rails 8.

[0028] A ball screw is provided on the underside of the Y-axis direction moving plate 10. The ball screw has a nut portion (not shown) fixed to the underside of the Y-axis direction moving plate 10. A screw shaft 12 is rotatably connected to the nut portion by using balls (not shown).

[0029] The screw shaft 12 is disposed along the Y-axis direction between a pair of Y-axis guide rails 8. A drive source 14 such as a pulse motor for rotating the screw shaft 12 is connected to one end of the screw shaft 12.

[0030] When the drive source 14 is operated, the Y-axis direction moving plate 10 moves along the Y-axis direction. The pair of Y-axis guide rails 8, the Y-axis direction moving plate 10, the screw shaft 12, the nut portion, the drive source 14, etc. constitute a Y-axis direction moving mechanism.

[0031] A pair of X-axis guide rails 16 are fixed to the upper surface of the Y-axis direction moving plate 10. The pair of X-axis guide rails 16 are arranged along the X-axis direction. An X-axis direction moving plate 18 is attached to the upper surface side of the pair of X-axis guide rails 16 in a manner that allows it to slide along the pair of X-axis guide rails 16.

[0032] A ball screw is provided on the underside of the X-axis direction moving plate 18. The ball screw has a nut portion (not shown) fixed to the underside of the X-axis direction moving plate 18. A screw shaft 20 is rotatably connected to the nut portion by using balls (not shown).

[0033] The screw shaft 20 is disposed along the X-axis direction between a pair of X-axis guide rails 16. A drive source 22 such as a pulse motor for rotating the screw shaft 20 is connected to one end of the screw shaft 20. When the drive source 22 is operated, the X-axis direction moving plate 18 moves along the X-axis direction.

[0034] The pair of X-axis guide rails 16, the X-axis moving plate 18, the screw shaft 20, the nut, the drive source 22, etc. make up the X-axis direction moving mechanism. A cylindrical table base 24 is provided on the upper surface side of the X-axis direction moving plate 18.

[0035] The table base 24 has a rotary drive source (not shown) such as a motor. A disk-shaped chuck table 26 is disposed on top of the table base 24. The chuck table 26 can be rotated by the rotary drive source around a predetermined rotation axis parallel to the Z-axis direction.

[0036] The structure of the chuck table 26 and the like will now be described with reference to Fig. 4. The chuck table 26 has a disk-shaped frame body 30 made of non-porous metal. A disk-shaped recess 30a is formed in the center of the frame body 30.

[0037] A circular porous plate 32 made of ceramic is fixed to the recess 30a. A predetermined flow path 30b is formed in the frame 30, and negative pressure is transmitted to the upper surface of the porous plate 32 from a suction source 34 such as an ejector via the flow path 30b.

[0038] The annular upper surface of the frame 30 and the circular upper surface of the porous plate 32 are substantially flush with each other and function as a substantially flat holding surface 26a for suction-holding the wafer 11. The holding surface 26a is disposed substantially parallel to a plane defined by the X-axis and Y-axis directions.

[0039] A plurality of (four in this embodiment) clamp units 26b are provided at approximately equal intervals along the circumferential direction of the chuck table 26 on the outer periphery of the chuck table 26 (see FIG. 3). Each clamp unit 26b clamps the frame 19 of the wafer unit 23.

[0040] A solenoid valve 38 is provided in a flow path 36 provided between the flow path 30b of the frame 30 and the suction source 34. A regulator 40 is provided in the flow path 36 between the solenoid valve 38 and the suction source 34.

[0041] The regulator 40 is, for example, an electropneumatic regulator that maintains the pressure in the flow path 36 on the solenoid valve 38 side of the regulator 40 at a predetermined pressure value specified by a control signal. A vacuum gauge 36a is connected to a region 36b located on the solenoid valve 38 side of the regulator 40 in the flow path 36 (for example, between the solenoid valve 38 and the frame 30).

[0042] When the solenoid valve 38 is open and the wafer 11 is held by suction on the holding surface 26a, the holding surface 26a, the porous plate 32, and the region 36b are at substantially the same air pressure. Therefore, by measuring the air pressure in the region 36b with the vacuum gauge 36a, it is possible to measure a negative pressure that is substantially equal to the negative pressure acting on the holding surface 26a.

[0043] The negative pressure measured by the vacuum gauge 36a is output to the control unit 64, which will be described later, and is stored in the control unit 64. Returning now to FIG. 3, other components of the laser processing device 2 will be described.

[0044] The chuck table 26 can be moved along either the X-axis direction or the Y-axis direction by the moving mechanism 6. A support structure 42 is provided on a predetermined region of the base 4 located behind the moving mechanism 6 (on one side in the Y-axis direction).

[0045] A Z-axis direction movement mechanism 44 is provided on one side surface of the support structure 42 along the YZ plane. The Z-axis direction movement mechanism 44 has a pair of Z-axis guide rails 46. The pair of Z-axis guide rails 46 are fixed to one side surface of the support structure 42 and are arranged along the Z-axis direction.

[0046] A Z-axis direction moving plate 48 is attached to the pair of Z-axis guide rails 46 in a manner that allows it to slide along the pair of Z-axis guide rails 46. A ball screw (not shown) is provided on the back side of the Z-axis direction moving plate 48.

[0047] The ball screw has a nut portion (not shown) fixed to the back surface of the Z-axis moving plate 48. A screw shaft (not shown) is rotatably connected to the nut portion using balls. The screw shaft is disposed between a pair of Z-axis guide rails 46 along the Z-axis direction.

[0048] A drive source 50 such as a pulse motor for rotating the screw shaft is connected to the upper end of the screw shaft. When the drive source 50 is operated, the Z-axis direction moving plate 48 moves along the Z-axis direction. A support 52 is fixed to the front surface side of the Z-axis direction moving plate 48.

[0049] The support 52 supports a part of the laser beam irradiation unit 54. The laser beam irradiation unit 54 has a laser oscillator (not shown) fixed to the base 4. The laser oscillator has, for example, a Nd:YVO4 crystal as a laser medium.

[0050] The laser beam irradiation unit 54 has a cylindrical housing 56 whose longitudinal portion is arranged along the Y-axis direction. An irradiation head 58 is fixed to the tip of the housing 56. The irradiation head 58 houses a condenser lens (not shown) and the like.

[0051] The irradiation head 58 irradiates the holding surface 26a downward with a pulsed laser beam L (see FIG. 5) having a wavelength (for example, 1342 nm) that is transparent to the wafer 11. The irradiation direction L of the laser beam L is A (See FIG. 5) is approximately parallel to the Z-axis direction.

[0052] A microscope camera unit 60 is fixed to the side of the housing 56 located near the irradiation head 58 in a manner that allows it to face the holding surface 26a. The microscope camera unit 60 has an objective lens and an imaging element such as a CCD (Charge-Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) image sensor.

[0053] Furthermore, a light source such as an LED for illuminating the object to be imaged is provided in the microscope camera unit 60. The housing 56, the illumination head 58, the microscope camera unit 60, etc. can be moved integrally along the Z-axis direction by the Z-axis direction movement mechanism 44.

[0054] A cover (not shown) that covers the above-mentioned components is provided on the base 4. A touch panel 62 is provided on the front side of the cover. The touch panel 62 functions as an input device and a display device.

[0055] For example, the operator can set processing conditions for the wafer 11 for the laser processing device 2 via the touch panel 62, and can also view an image of the wafer 11 obtained by the microscope camera unit 60.

[0056] The operations of the moving mechanism 6, the solenoid valve 38, the regulator 40, the Z-axis direction moving mechanism 44, the laser beam irradiation unit 54, the microscope camera unit 60, the touch panel 62, etc. are controlled by a control unit 64.

[0057] The control unit 64 is composed of a computer including, for example, a processor (processing device) represented by a CPU (Central Processing Unit), a main memory device such as DRAM (Dynamic Random Access Memory), SRAM (Static Random Access Memory), or ROM (Read Only Memory), and an auxiliary memory device such as a flash memory, a hard disk drive, or a solid state drive.

[0058] The auxiliary storage device stores software including a predetermined program. The functions of the control unit 64 are realized by operating the processing device and the like in accordance with this software. Next, a method for manufacturing chips 25 (see FIG. 6(B)) by processing the wafer 11 with the laser processing device 2 will be described.

[0059] When laser processing is performed on the wafer 11, first, the wafer unit 23 (wafer 11) is suction-held by the holding surface 26a (suction-holding step S10). Figure 4 is a diagram showing the suction-holding step S10.

[0060] In the suction holding step S10, a predetermined negative pressure, the difference between which is smaller than the ambient pressure (e.g., atmospheric pressure or the pressure in a clean room) is 40 kPa, is applied to the holding surface 26a on the back surface 11b of the wafer 11 via the tape 21, thereby suction-holding the wafer 11 on the holding surface 26a.

[0061] The predetermined negative pressure is a negative gauge pressure whose absolute pressure is smaller than the atmospheric pressure. For example, a pressure value between −40 kPa and −5 kPa (i.e., a pressure value higher than −40 kPa and lower than −5 kPa taking into account positive and negative pressures) is selected as the predetermined negative pressure.

[0062] Therefore, it is more preferable to select a pressure value between −20 kPa and −5 kPa (i.e., higher than −20 kPa and lower than −5 kPa) as the predetermined negative pressure, because it is considered that a weaker suction pressure makes it easier to release the internal stress that occurs after the formation of the modified layer 11d, which will be described later.

[0063] Furthermore, preferably, the predetermined negative pressure is a pressure value between −15 kPa and −5 kPa (i.e., higher than −15 kPa and lower than −5 kPa). In this embodiment, the predetermined negative pressure is −14.7 kPa.

[0064] In contrast to this, generally, when laser processing is performed on the wafer 11, the wafer 11 is held by relatively strong suction at a negative pressure of about -90 kPa. In other words, in this embodiment, the wafer 11 is held by relatively weak suction at a suction pressure that is less than half the suction pressure used in general laser processing.

[0065] After the suction holding step S10, the wafer 11 continues to be held under suction at a predetermined negative pressure until the modified layer forming step S20 is completed. After the suction holding step S10, the modified layer forming step S20 is performed. Figure 5 shows the modified layer forming step S20.

[0066] In the modified layer forming step S20, first, alignment is performed using the microscope camera unit 60, and the orientation of the chuck table 26 is adjusted so that the first planned dividing line 15a is approximately parallel to the X-axis direction.

[0067] Next, when the chuck table 26 is viewed from above, the irradiation head 58 is placed on an extension line of one of the first planned division lines 15a located on the outermost side in the second direction 13b.

[0068] Thereafter, with the focal point P of the laser beam L positioned inside the wafer 11, the chuck table 26 is moved along the X-axis direction so that the focal point P moves along the one first planned dividing line 15a.

[0069] The focal point P and the chuck table 26 move relatively along the processing feed direction, thereby forming a modified layer 11d inside the wafer 11. The processing conditions are set, for example, as follows.

[0070] Laser beam L wavelength: 1064nm Repetition frequency of laser beam L: 120 kHz Processing feed rate: 900mm / s Number of passes: 5

[0071] The number of passes means the number of times the laser beam L is irradiated onto the wafer 11 from one end to the other end of one planned dividing line at a predetermined processing feed speed. In this embodiment, where the number of passes is two or more, each modified layer 11d is formed at a different depth position of the wafer 11.

[0072] 5 schematically shows the modified layer 11d formed in the first pass. The modified layer 11d is a region in which the mechanical strength is reduced compared to a region through which the focal point P of the laser beam L did not pass, due to a local change in the structure of a portion of the wafer 11 caused by multiphoton absorption.

[0073] After forming the modified layer 11d along one of the first dividing lines 15a, the chuck table 26 is indexed and fed along the Y-axis direction. Then, modified layers 11d are similarly formed along the one first dividing line 15a processed immediately before and another first dividing line 15a adjacent to it in the Y-axis direction.

[0074] After the modified layers 11d are formed along all of the first dividing lines 15a in the same manner, the chuck table 26 is rotated by 90 degrees, and the modified layers 11d are then formed along all of the second dividing lines 15b in the same manner.

[0075] In this manner, in the modified layer forming step S20, the wafer 11 is laser processed along each of the planned dividing lines (that is, each of the first planned dividing lines 15a and each of the second planned dividing lines 15b).

[0076] As described above, when the modified layer 11d is formed by holding the wafer 11 under suction at a typical suction pressure (-90 kPa), internal stress in the wafer 11 remains, which may hinder the formation of a modified layer 11d or the extension of cracks when a new modified layer 11d is formed.

[0077] In contrast, in this embodiment, the modified layer 11d is formed inside the wafer 11 while the wafer 11 is held by suction at a suction pressure that is less than half the normal suction pressure. By weakening the suction pressure in this way, it is possible to both hold the wafer 11 by suction and release internal stress during laser processing.

[0078] Therefore, compared to when the wafer 11 is suction-held at a negative pressure of about -90 kPa, the range of the undivided region after the dividing step S30 can be reduced, and furthermore, the yield of the chips 25 during manufacturing can be improved.

[0079] After the modified layer forming step S20, the tape 21 is radially expanded using the expansion device 66, thereby applying an external force to the wafer 11 and dividing the wafer 11 into a plurality of chips 25 (dividing step S30).

[0080] First, the expansion device 66 used in the division step S30 will be described with reference to Fig. 6(A). Fig. 6(A) is a diagram showing the expansion device 66. The expansion device 66 has a cylindrical drum 68 having a diameter larger than that of the wafer 11.

[0081] A plurality of rollers 70 are provided at the upper end of the drum 68 at approximately equal intervals along the circumferential direction of the drum 68. An annular frame support base 72 is provided on the outer side of the drum 68 in the radial direction of the drum 68.

[0082] A plurality of clamps 74 are provided on the upper surface of the frame support base 72, each clamping the frame 19 of the wafer unit 23 placed on the frame support base 72. The frame support base 72 is supported by a plurality of legs 76 arranged at approximately equal intervals along the circumferential direction of the frame support base 72. Each leg 76 can be raised and lowered by a lifting mechanism such as an air cylinder.

[0083] In the dividing step S30, as shown in FIG. 6(A), the upper end of the drum 68 and the upper surface of the frame support stand 72 are brought to approximately the same height position, and the wafer unit 23 after the modified layer forming step S20 is placed on the drum 68 and the frame support stand 72.

[0084] Next, when the elevators are operated to lower the legs 76, the frame support base 72 is lowered relative to the drum 68. This causes the tape 21 to expand radially, as shown in Figure 6(B).

[0085] As the tape 21 expands, an external force is applied to the wafer 11 in a radial direction, dividing the wafer 11 into multiple chips 25. Figure 6(B) shows the dividing step S30. The chips 25 are rectangular plates, each measuring, for example, 300 μm thick, 0.5 mm long, and 0.15 mm wide.

[0086] In an experiment in which the predetermined negative pressure was set to -14.7 kPa according to the above embodiment, the undivided area was reduced to 5% or less (for example, approximately 0%). This is thought to be the result of achieving both suction holding of the wafer 11 during laser processing and release of internal stress.

[0087] The inventors of the present invention have confirmed that the weaker the suction pressure, the smaller the area of ​​the wafer 11 that is not divided into chips 25 (i.e., the undivided area). However, if the suction pressure is made too weak, there is a concern that the wafer unit 23 may not be properly suction-held on the holding surface 26a.

[0088] In contrast, the inventors of the present invention have confirmed that even if the predetermined negative pressure is set to -5 kPa and the chuck table 26 is moved at a processing speed of 900 mm / s, the wafer 11 does not shift relative to the holding surface 26a.

[0089] Meanwhile, in the course of experiments, the inventors of the present invention have confirmed cases where, when the wafer 11 is processed according to the procedure described in the above embodiment, undivided regions occur only in the outer periphery of the wafer 11. At present, it is speculated that the occurrence of undivided regions only in the outer periphery of the wafer 11 is due to warpage of the wafer 11.

[0090] In other words, it is presumed that the undivided areas are caused by the warping of the wafer 11 causing the outer periphery of the wafer 11 to lift off the holding surface 26a despite the application of suction pressure, which displaces the preset depth position of the focal point P of the laser beam L and makes it impossible to carry out accurate laser processing.

[0091] More specifically, it is believed that the undivided region occurs through the following mechanism: First, a crack propagates from the modified layer 11d formed during the first laser processing pass toward the back surface 11b, causing a warpage with a concave shape in the middle when viewed from above.

[0092] Next, in the second pass, which forms a further modified layer 11d on the front surface 11a side than the modified layer 11d formed in the first pass, due to the warping of the wafer 11, the focal point P is formed on the back surface 11b side of the depth position within the wafer 11 where it should originally be positioned.

[0093] When laser processing is performed in this manner, the modified layer 11d is formed at a position shifted toward the back surface 11b from the depth position at which it should be formed. This shift is particularly noticeable at the outer periphery of the wafer 11, which is warped into a concave shape. Therefore, at the outer periphery of the wafer 11, it is thought that cracks are less likely to propagate from the modified layer 11d toward the front surface 11a, leading to the generation of undivided regions.

[0094] However, at present, it is not completely clear why undivided regions occur only in the outer peripheral region of the wafer 11. Therefore, it should be noted that the above speculation may not be correct.

[0095] However, when performing the modified layer formation step S20 on the peripheral region of the wafer 11, it was found that if the negative pressure applied to the holding surface 26a is set to a general suction pressure (i.e., -90 kPa) and laser processing is performed on the peripheral region of the wafer 11, the undivided area in the peripheral region is reduced.

[0096] Therefore, in the modified layer forming step S20 of the second embodiment, the negative pressure applied to the holding surface 26a is changed depending on the processing area to be laser processed on the wafer 11. Fig. 7 is a flow diagram of the manufacturing method of the chip 25 in the second embodiment.

[0097] In the second embodiment, first, a modified layer 11d is formed in the outer region A1 (see FIG. 8) of the wafer 11. Then, a first negative pressure, the difference from the atmospheric pressure of which is greater than 40 kPa, is applied to the holding surface 26a (suction holding step S10). In this embodiment, the first negative pressure is −90 kPa.

[0098] After the suction holding step S10, alignment is performed using the microscope camera unit 60, and the first direction 13a is positioned approximately parallel to the X-axis direction. Then, while the wafer 11 is suction-held with the first negative pressure, modified layers 11d are sequentially formed along the first planned dividing line 15a located in the outer region A1 (first modified layer forming step S21).

[0099] 8 is a diagram showing the formation of a modified layer 11d in the outer region A1. In the first modified layer formation step S21 of this embodiment, the first planned dividing lines 15a located in the outer region A1 are a pair of first planned dividing lines 15a located outermost in the indexing feed direction with respect to the center B of the surface 11a.

[0100] However, in the first modified layer formation step S21, the first planned dividing lines 15a located in the outer region A1 may be multiple pairs of first planned dividing lines 15a located outside the center B of the surface 11a in the indexing feed direction.

[0101] After the first modified layer forming step S21, the negative pressure applied to the holding surface 26a is set to a third negative pressure having a pressure value between the first negative pressure (-90 kPa) and a second negative pressure (e.g., -30 kPa) whose difference from the atmospheric pressure is less than 40 kPa. In this embodiment, the third negative pressure is -60 kPa.

[0102] After adjusting the negative pressure, the wafer 11 is held by suction at the third negative pressure, and a modified layer 11d is formed along the first dividing line 15a located in the intermediate region A3 (third modified layer forming step S22).

[0103] 9 is a diagram illustrating the formation of a modified layer 11d in the intermediate region A3. In the third modified layer formation step S22 of this embodiment, the first planned dividing lines 15a located in the intermediate region A3 are two pairs of first planned dividing lines 15a located closer to the center B of the surface 11a than the outer region A1 in the indexing feed direction.

[0104] However, in the third modified layer formation step S22, the first planned dividing lines 15a located in the intermediate region A3 may be one or more pairs of first planned dividing lines 15a located closer to the center B than the outer region A1 in the indexing feed direction.

[0105] After the third modified layer forming step S22, the negative pressure applied to the holding surface 26a is set to a second negative pressure (for example, −30 kPa). After the negative pressure is adjusted, while the wafer 11 is being held by suction at the second negative pressure, a modified layer 11d is formed along the first planned dividing line 15a located in the central region A2 (second modified layer forming step S23).

[0106] 10 is a diagram showing the formation of a modified layer 11d in the central region A2. In the second modified layer formation step S23 of this embodiment, the first planned division lines 15a located in the central region A2 are five first planned division lines 15a located closer to the center B than the intermediate region A3 in the indexing feed direction.

[0107] However, in the second modified layer formation step S23, the first planned division line 15a located in the central region A2 may be one or more first planned division lines 15a located closer to the center B than the intermediate region A3 in the indexing feed direction.

[0108] In this manner, in the modified layer formation step S20 of this embodiment, the outer region A1 is located outermost from the center B in the index feed direction, the intermediate region A3 is located between the outer region A1 and the central region A2 in the index feed direction, and the central region A2 is located innermost in the index feed direction and includes the center B.

[0109] After the second modified layer forming step S23, the chuck table 26 is rotated by 90 degrees, and alignment is performed using the microscope camera unit 60, so that the second direction 13b is positioned approximately parallel to the X-axis direction.

[0110] Then, the wafer 11 is suction-held by the first negative pressure. In this state, a modified layer 11d is formed along the second planned dividing line 15b located in the outer region A1 (first modified layer forming step S26).

[0111] In the first modified layer formation step S26 of this embodiment, the second planned dividing lines 15b located in the outer region A1 are a pair of second planned dividing lines 15b located outermost in the indexing feed direction relative to the center B of the surface 11a.

[0112] However, in the first modified layer formation step S26, the second planned dividing lines 15b located in the outer region A1 may be multiple pairs of second planned dividing lines 15b located outside the center B of the surface 11a in the indexing feed direction.

[0113] After the first modified layer forming step S26, the negative pressure applied to the holding surface 26a is set to a third negative pressure having a pressure value between the first and second negative pressures. In this state, a modified layer 11d is formed along the second planned dividing line 15b located in the intermediate region A3 (third modified layer forming step S27).

[0114] In the third modified layer formation step S27 of this embodiment, the second planned dividing lines 15b located in the intermediate region A3 are two pairs of second planned dividing lines 15b located closer to the center B of the surface 11a than the outer region A1 in the indexing feed direction.

[0115] However, in the third modified layer formation step S27, the second planned dividing lines 15b located in the intermediate region A3 may be one or more pairs of second planned dividing lines 15b located closer to the center B than the outer region A1 in the indexing feed direction.

[0116] After the third modified layer forming step S27, the negative pressure applied to the holding surface 26a is set to the second negative pressure, and in this state, a modified layer 11d is formed along the second planned dividing line 15b located in the central region A2 (second modified layer forming step S28).

[0117] In the second modified layer formation step S28 of this embodiment, the second planned division lines 15b located in the central region A2 are five second planned division lines 15b located closer to the center B than the intermediate region A3 in the indexing feed direction.

[0118] However, in the second modified layer formation step S28, the second planned division line 15b located in the central region A2 may be one or more second planned division lines 15b located closer to the center B than the intermediate region A3 in the indexing feed direction.

[0119] After the second modified layer forming step S28, an external force is applied to the wafer 11 using the expansion device 66 to divide the wafer 11 into a plurality of chips 25 (dividing step S30).

[0120] In this embodiment, the range of the undivided area in the outer region A1 can be reduced compared to when laser processing is performed on each of the outer region A1, intermediate region A3, and central region A2 while a first negative pressure (for example, -90 kPa) is applied to the holding surface 26a, thereby achieving more stable laser processing than in the first embodiment.

[0121] As a variant, the first modified layer formation step S21, the third modified layer formation step S22, and the second modified layer formation step S23 may be performed sequentially on one side of the semicircle located outside the center B of the surface 11a in the indexing feed direction, and then the first modified layer formation step S21, the third modified layer formation step S22, and the second modified layer formation step S23 may be performed sequentially on the other side.

[0122] Furthermore, the wafer 11 may be rotated 90 degrees, and the first modified layer formation step S26, the third modified layer formation step S27, and the second modified layer formation step S28 may be sequentially performed on one side of the semicircle located outside the center B of the surface 11a in the indexing feed direction, and then the first modified layer formation step S26, the third modified layer formation step S27, and the second modified layer formation step S28 may be sequentially performed on the other side.

[0123] In addition, the structures, methods, etc. according to the above-described embodiments can be appropriately modified without departing from the scope of the present invention. For example, the wafer 11 is not limited to silicon, and may have a single crystal substrate formed of other materials such as silicon carbide (SiC).

[0124] In addition, in the division step S30, instead of expanding the tape 21 using the expansion device 66, the wafer 11 may be divided into a plurality of chips 25 by pressing a pressure blade (not shown) against each of the first planned division line 15a and the second planned division line 15b, or other methods may be adopted.

[0125] In addition, a program that causes the control unit 64 to automatically control the negative pressure applied to the chuck table 26 in accordance with processing conditions such as the thickness of the wafer 11 and the size of the chip 25 to be manufactured (i.e., the recipe set when processing the wafer 11) may be stored in the auxiliary storage device of the control unit 64. [Explanation of symbols]

[0126] 2: Laser processing device, 4: Base, 6: Moving mechanism, 8: Y-axis guide rail 10: Y-axis direction moving plate, 12: screw shaft, 14: driving source, 16: X-axis guide rail 11: wafer (workpiece), 11a: front surface, 11b: back surface, 11c: notch 11d: modified layer, 13a: first direction, 13b: second direction 15a: First planned dividing line, 15b: Second planned dividing line 18: X-axis direction moving plate, 20: screw shaft, 22: driving source, 24: table base 17: device, 17a: device area, 17b: peripheral excess area, 19: frame 19a: opening, 21: tape, 23: wafer unit, 25: chip 26: chuck table, 26a: holding surface, 26b: clamp unit 30: Frame body, 30a: Recess, 30b: Flow path, 32: Porous plate, 34: Suction source 36: flow path, 36a: vacuum gauge, 36b: area, 38: solenoid valve, 40: regulator 42: Support structure, 44: Z-axis direction movement mechanism, 46: Z-axis guide rail 48: Z-axis direction moving plate, 50: driving source, 52: support 54: Laser beam irradiation unit, 56: Housing, 58: Irradiation head 60: microscope camera unit, 62: touch panel, 64: control unit, 66: expansion device 68: Drum, 70: Roller, 72: Frame support, 74: Clamp, 76: Leg A1: Outer area, A2: Central area, A3: Middle area, B: Center L: laser beam, L A :Irradiation direction, P: Focus point S10: Suction holding step, S20: Modified layer forming step, S30: Dividing step S21, S26: First modified layer forming step S22, S27: Third modified layer formation step S23, S28: Second modified layer formation step

Claims

1. A method for manufacturing chips by processing a workpiece having a plurality of planned dividing lines set on its surface along each of the planned dividing lines, a suction holding step in which a predetermined negative pressure, the difference from the atmospheric pressure of which is less than 40 kPa, is applied to the chuck table, thereby suction-holding the workpiece via a tape attached to the workpiece on the holding surface of the chuck table, the holding surface of which includes a disk-shaped frame and a disk-shaped ceramic porous plate fixed in a recess of the frame, the upper surface of the frame being flush with the upper surface of the porous plate; a modified layer forming step in which, after the suction holding step, a focal point of a pulsed laser beam having a wavelength that transmits the workpiece is positioned inside the workpiece that is suction-held on the holding surface by the predetermined negative pressure, and the focal point and the chuck table are moved relatively along the planned division line to form a modified layer inside the workpiece; a dividing step of dividing the workpiece by applying an external force to the workpiece after the modified layer forming step; A method for manufacturing a chip, comprising:

2. 2. The method for manufacturing a chip according to claim 1, wherein in the suction holding step, the predetermined negative pressure having a pressure value between -40 kPa and -5 kPa, the predetermined negative pressure having a pressure value between -20 kPa and -5 kPa, or the predetermined negative pressure having a pressure value between -15 kPa and -5 kPa is applied to the chuck table.

3. A method for manufacturing a chip as described in claim 1 or 2, characterized in that in the suction holding step, the workpiece is suction-held via the tape on the holding surface having an outer diameter larger than the outer diameter of the workpiece.

4. A method for manufacturing chips by processing a workpiece having a plurality of planned dividing lines set on its surface along each of the planned dividing lines, a suction holding step of suction-holding the workpiece on a holding surface of a chuck table via a tape attached to the workpiece; a modified layer forming step of forming a modified layer inside the workpiece by relatively moving the focal point of a pulsed laser beam having a wavelength that transmits through the workpiece and the chuck table along each planned division line while the focal point is positioned inside the workpiece held by suction on the holding surface; a dividing step of dividing the workpiece by applying an external force to the workpiece after the modified layer forming step; Equipped with The modified layer forming step includes: a first modified layer forming step of forming the modified layer in an outer region located outside the center of the surface of the workpiece in an indexing feed direction perpendicular to the laser beam irradiation direction and the processing feed direction, in which the negative pressure acting on the holding surface is a first negative pressure whose difference with the atmospheric pressure is greater than 40 kPa; When forming the modified layer in the central region of the surface located closer to the center than the outer region in the indexing feed direction, the method for manufacturing a chip is characterized by including a second modified layer formation step in which the modified layer is formed while the negative pressure acting on the holding surface is a second negative pressure whose difference with the atmospheric pressure is less than 40 kPa.

5. The method for manufacturing a chip as described in claim 4, characterized in that the modified layer forming step further includes a third modified layer forming step in which, when forming the modified layer in an intermediate region located between the outer region and the central region in the index feed direction, the modified layer is formed while the negative pressure applied to the holding surface is a third negative pressure having a pressure value between the first negative pressure and the second negative pressure.

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