JP2017177165A - Laser processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser processing method that can efficiently process a modified layer for a device arranged in an object to be processed.SOLUTION: The laser processing method includes: a direction adjustment step (a step SA2) of adjusting a direction of a chuck table by holding a wafer with the chuck table so that areas on which a modified layer should be formed of a desired device are lined up on a straight line parallel to a processing feed direction; and a laser beam irradiation step (a step SA4) for moving relatively a laser beam irradiating means and the chuck table in the processing feed direction and forming the modified layer in the desired device by moving the means and the table once in the processing feed direction, after executing the direction adjustment step, where the modified layer which is formed by moving the means and the table once in the processing feed direction is formed at a desired position of the device.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a laser processing method for performing processing by irradiating a workpiece with a laser beam.

  In general, a modified layer is formed on a semiconductor wafer by irradiating a laser beam along a planned division line of a semiconductor wafer (workpiece), and the modified layer is divided into individual device chips from the breakpoint. The method is known. In addition, a technique is known in which when a defect occurs in a specific region of each device, the defect is repaired by irradiating the laser beam thereon (see, for example, Patent Document 1).

JP 2013-226588 A

  However, in the conventional configuration, after observing a predetermined defect portion and finding it, the laser beam is radiated intensively only on the defect portion, but when similar defects occur in many devices, On the other hand, since each laser processing is performed, there is a problem that it is a very complicated process.

  The present invention has been made in view of the above, and an object of the present invention is to propose a laser processing method capable of efficiently processing a modified layer on a device provided on a workpiece.

  In order to solve the above-described problems and achieve the object, the present invention provides a plate-like workpiece in which devices are formed in a plurality of regions defined by a plurality of intersecting scheduled lines formed on a surface. A laser processing method for a workpiece by irradiating the device with a laser beam and forming a modified layer on the workpiece to modify the device, the chuck table holding and rotating the workpiece, and the chuck table Using a laser processing apparatus comprising: a laser beam irradiation means for irradiating a workpiece held on the workpiece with a laser beam; and a processing feed means for moving the chuck table and the laser beam irradiation means relative to each other in the process feed direction. Is held by the chuck table, and the chuck is so arranged that regions where a modified layer of a desired device is to be formed are aligned on a straight line parallel to the processing feed direction. After performing the orientation adjustment step for adjusting the orientation of the table, and the orientation adjustment step, the laser beam irradiation means and the chuck table are moved relative to each other in the machining feed direction, and the movement in the machining feed direction is performed once. A laser beam irradiation step for forming a modified layer on a desired device, and the modified layer formed by one movement in the processing feed direction is formed at a desired position of the desired device It is characterized by that.

  According to this configuration, the workpiece is held by the chuck table, and the orientation of the chuck table is adjusted so that the region where the modified layer of the desired device is to be formed is aligned on a straight line parallel to the machining feed direction. In order to provide a direction adjustment step and a laser beam irradiation step of forming a modified layer on a desired device by moving the laser beam irradiation means and the chuck table in the processing feed direction relative to each other and moving in the processing feed direction once. By the movement in the process feed direction once, the modified layer can be efficiently formed at a desired position in a desired device.

  The laser beam irradiation means is set to be capable of irradiating a laser beam under two or more laser beam irradiation conditions. When forming a plurality of modified layers on a desired device in the laser beam irradiation step, The corresponding laser beam irradiation conditions may be selected and irradiated. According to this configuration, since a plurality of modified layers can be processed with a combination of different laser beam irradiation conditions for a desired device, processing according to the state of the device can be efficiently performed.

  According to the present invention, the workpiece is held by the chuck table, and the orientation of the chuck table is adjusted so that the region where the modified layer of the desired device is to be formed is aligned on a straight line parallel to the machining feed direction. In order to provide a direction adjustment step and a laser beam irradiation step of forming a modified layer on a desired device by moving the laser beam irradiation means and the chuck table in the processing feed direction relative to each other and moving in the processing feed direction once. By the movement in the process feed direction once, the modified layer can be efficiently formed at a desired position in a desired device.

FIG. 1 is a plan view of a wafer which is a processing target of the laser processing method according to the present embodiment. FIG. 2 is a diagram illustrating a configuration example of a laser processing apparatus. FIG. 3 is a flowchart showing a work procedure of a laser processing method for forming a modified layer on each device of a wafer. FIG. 4 is a perspective view showing a state in which laser processing is performed on each wafer device. FIG. 5 is a schematic cross-sectional view showing a state in which a modified layer is formed inside the wafer. FIG. 6 is a schematic view showing a state in which a plurality of modified layers are formed on the device under different processing conditions. FIG. 7 is a flowchart showing a work procedure of a laser processing method for forming a modified layer on a device at a desired position on a wafer.

  DESCRIPTION OF EMBODIMENTS Embodiments (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the structures described below can be combined as appropriate. Various omissions, substitutions, or changes in the configuration can be made without departing from the scope of the present invention.

  FIG. 1 is a plan view of a wafer which is a processing target of the laser processing method according to the present embodiment. As shown in FIG. 1, the wafer (workpiece) W is a semiconductor wafer or an optical device wafer having a disk-shaped substrate WS. The substrate WS of the wafer W is formed using, for example, silicon, sapphire, gallium or the like. As shown in FIG. 1, the wafer W has a plurality of streets (scheduled lines) S formed on the surface of the substrate WS (wafer W) in a lattice pattern, and in each area partitioned by the plurality of streets S. A device D (for example, a semiconductor device or an optical device) is formed.

  FIG. 2 is a diagram illustrating a configuration example of a laser processing apparatus used in the laser processing method according to the present embodiment. In addition, the laser processing apparatus 1 is not limited to the structural example shown in FIG. The laser processing apparatus 1 performs laser processing for irradiating a laser beam from the laser beam irradiation means 20 to the device D (FIG. 1) of the wafer W held on the chuck table 10 to form a modified layer on the device D. Is. The modified layer refers to a region where the density, refractive index, mechanical strength, and other physical characteristics in the device D are different from the surroundings. For example, there are (a) a melt processing region, (b) a dielectric breakdown region, (c) a refractive index change region, and there are regions where these are mixed. Thus, by forming the modified layer on the device D, the characteristics of the device D can be changed (corrected). The modified layer includes those formed in the internal region of the device and those exposed on the surface of the device.

  As shown in FIG. 2, the laser processing apparatus 1 includes a chuck table 10 that holds a wafer W, and laser beam irradiation means 20 that irradiates the wafer W with a laser beam. The laser processing apparatus 1 also includes an X-axis moving means (processing feed means) 30 that moves the chuck table 10 along the X-axis direction (machining feed direction), and the chuck table 10 in the Y-axis direction (index feed direction). Y-axis moving means (index feed means) 40 that moves along. Thereby, the chuck table 10 and the laser beam irradiation means 20 are configured to be relatively movable in the X-axis direction and the Y-axis direction, respectively.

  The laser processing apparatus 1 includes a cassette mounting table 60 on which a cassette 50 that houses wafers W before and after laser processing is mounted. In addition, the laser processing apparatus 1 includes transport means (not shown) that transports the wafer W to each of the above-described parts, and a control device 80 that controls the entire operation of the laser processing apparatus 1.

  The chuck table 10 holds the wafer W when laser processing is performed on the wafer W. In this configuration, as shown in FIG. 2, the wafer W is held on the chuck table 10 in the form of a wafer unit WU held on an annular frame F by an adhesive tape T. The chuck table 10 has a holding surface 11 on which a wafer W (wafer unit WU) is placed and sucked, and a plurality of clamp portions 12 arranged on the outer peripheral side of the holding surface 11 to fix the frame F. Yes.

  The laser beam application means 20 is fixed to the wall 3 of the apparatus main body 2 and irradiates a laser beam toward the wafer W held on the chuck table 10. The laser beam irradiation means 20 irradiates the wafer W with an oscillator (not shown) that oscillates the laser beam, a condenser (not shown) that collects the laser beam oscillated by the oscillator, and the focused laser beam. The irradiation head 21 is provided. The oscillator appropriately adjusts the wavelength (frequency), output, and repetition frequency of the laser beam to be oscillated according to the type of wafer W, the processing form, and the like. For example, in the case of a processing form in which a modified layer is formed inside the wafer W, a laser beam having a wavelength that is transmissive to the wafer W is used. The irradiation head 21 can adjust the condensing position (focus position) of the laser beam in the Z-axis direction (vertical direction) by an optical system such as a condenser.

  The condenser includes a total reflection mirror that changes the traveling direction of the laser beam oscillated by the oscillator, a condenser lens that collects the laser beam, and the like. Further, in the present embodiment, the laser beam irradiation means 20 includes an imaging means 22 arranged side by side with the irradiation head 21 in the X-axis direction. The imaging means 22 is a camera that images the arrangement state of the wafer W on the chuck table 10 and the processing state of the wafer W. In this embodiment, an infrared camera is used.

  The X-axis moving means 30 includes a ball screw 31 extending in the X-axis direction, a guide rail 32 disposed in parallel with the ball screw 31, a pulse motor (not shown) connected to one end of the ball screw 31 and rotating the ball screw 31. And a slide plate 33 having a nut (not shown) which is in sliding contact with the guide rail 32 and screwed into the ball screw 31 inside. As the ball screw 31 rotates, the slide plate 33 is guided by the guide rail 32 and moves in the X-axis direction. In addition, a rotation driving unit 34 having a pulse motor (not shown) is fixed to the slide plate 33, and the rotation driving unit 34 can rotate the chuck table 10 by a predetermined angle. In the present embodiment, for example, based on the image of the wafer W imaged by the imaging unit 22, the chuck table 10 (wafer W) is arranged such that the streets S (FIG. 1) intersecting each other are directed in the X-axis direction and the Y-axis direction, respectively. ).

  The Y-axis moving means 40 includes a ball screw 41 extending in the Y-axis direction, a guide rail 42 disposed in parallel to the ball screw 41, a pulse motor 45 connected to one end of the ball screw 41 and rotating the ball screw 41, The slide plate 43 includes a nut (not shown) that is in sliding contact with the guide rail 42 and screwed into the ball screw 41. The slide plate 43 is guided by the guide rail 42 as the ball screw 41 rotates. Move in the Y-axis direction. The slide plate 43 is provided with the X-axis moving means 30 described above, and the X-axis moving means 30 moves in the same direction as the slide plate 43 moves in the Y-axis direction.

  The cassette 50 accommodates a plurality of wafer units WU described above. The cassette mounting table 60 is provided in the apparatus main body 2 so as to be movable up and down in the Z-axis direction.

  Next, a laser processing method for forming a modified layer on the wafer W device using the laser processing apparatus 1 will be described. FIG. 3 is a flowchart showing a work procedure of a laser processing method for forming a modified layer on each device of a wafer. FIG. 4 is a perspective view showing a state in which laser processing is performed on each wafer device. FIG. 5 is a schematic cross-sectional view showing a state in which a modified layer is formed inside the wafer. The laser processing method shown in FIG. 3 performs the same laser processing on the device D of the wafer W. For this reason, it is effective when the characteristics of the device D of the wafer W are uniformly changed to desired characteristics.

  First, the wafer unit WU holding the wafer W on the annular frame F is held on the holding surface 11 of the chuck table 10 (holding step; step SA1). In the present embodiment, a modified layer is formed inside the wafer W by irradiating a laser beam from the back surface WR side of the wafer W. For this reason, as shown in FIG. 4, the wafer W has the adhesive tape T attached to the surface side where the plurality of devices D are formed, and the outer edge of the adhesive tape T is attached to the frame F. An opening of the frame F is supported by an adhesive tape T. The wafer unit WU formed in this way is placed on the holding surface 11 of the chuck table 10 with the back surface WR of the wafer W as the upper surface side, and the frame F is fixed by the clamp portion 12 (FIG. 2).

  Next, the control device 80 adjusts the orientation of the chuck table 10 so that the region where the modified layer in each device D is to be formed is aligned on a straight line parallel to the X-axis direction (orientation adjusting step; step) SA2). The region (position and size) where the modified layer is to be formed on the device D can be set in advance by measuring the characteristics of the device D at the time of manufacture. As shown in FIG. 4, the rotation drive unit 34 is rotated in the circumferential direction (R direction) so that the areas AR where the modified layer is to be formed are aligned on the planned processing line (straight line) X1 parallel to the X axis direction. Let In the present embodiment, the area AR is formed in a straight line extending along the planned processing line (straight line) X1, and both ends of each area AR serve as a start point and a stop point for irradiating a laser beam.

  Next, the control device 80 sets processing conditions (laser beam irradiation conditions) for performing laser processing on the above-described region AR (processing condition setting step; step SA3). As processing conditions for performing laser processing on the area AR of each device, for example, (1) laser beam irradiation start position in the processing feed direction (X-axis direction), (2) number of continuous irradiation pulses of laser beam, (3) laser beam The number of stop pulses, (4) the number of repetitions, (5) the output of the laser beam, etc. are set.

  The laser beam irradiation start position corresponds to the start point of laser beam irradiation in each device D, and the stop point of laser beam irradiation is determined by the number of continuous irradiation pulses of the laser beam. Further, the pitch (interval) with the adjacent area AR in the device D is determined by the number of stop pulses of the laser beam. The number of repetitions indicates the number of cycles from start to stop of laser beam irradiation in the device D, and corresponds to the number of regions AR in the device D. In the present embodiment, a laser beam having a wavelength that is transmissive to the wafer W is used to form a modified layer inside the wafer W corresponding to the region AR.

  Next, the control device 80 irradiates the wafer W with a laser beam based on the above-described processing conditions (laser beam irradiation step; step SA4). As shown in FIG. 4, the irradiation head 21 is arranged on the planned processing line X1, and the chuck table 10 is moved in the X-axis direction by the X-axis moving means 30 (FIG. 2). A laser beam L is irradiated toward the wafer W.

  In this configuration, for each device D, (A) when the irradiation head 21 is positioned immediately above the laser beam irradiation position of the device D, irradiation of the laser beam L is started from the irradiation head 21 and irradiation of the laser beam L is set. Continue until the measurement of the number of continuous irradiation pulses is completed. (B) After stopping the irradiation of the laser beam L until the measurement of the set number of stop pulses is completed, the irradiation start and stop operations of the laser beam L are performed a set number of times. Thereby, as shown in FIG. 5, the modified layer 100 is formed discontinuously (intermittently) inside the wafer W corresponding to the region AR. In addition, the chuck table 10 is moved once in the X-axis direction (machining feed direction) by performing the processes (A) and (B) on a plurality of devices D positioned on the same scheduled machining line X1. In this case, the modified layers 100 can be collectively formed in the regions AR of the plurality of devices D located on the planned processing line X1. For this reason, the time for forming the modified layer 100 on each of the plurality of devices D can be shortened, and the modified layer 100 can be efficiently formed on the device D.

  When the irradiation of the laser beam L to the terminal device D located on the same scheduled processing line X1 is completed, the control device 80 moves the chuck table 10 in the Y-axis direction (index feed direction), and the next scheduled processing line. Laser processing is performed again on each device D positioned above. When the laser processing on all the devices D is completed, the wafer unit WU is detached from the holding surface 11 of the chuck table 10 (desorption step; step SA5), and the processing operation is completed.

  Now, the laser beam irradiation means 20 is configured to set a plurality of processing conditions in the above-described processing condition setting step, and to be able to irradiate the laser beam L under these processing conditions. When the modified layers 100 are formed, the processing conditions corresponding to the respective modified layers 100 can be selected and irradiated.

  FIG. 6 is a schematic view showing a state in which a plurality of modified layers are formed on the device under different processing conditions. In FIG. 6, a plurality of types (three types in FIG. 6) of modified layers 100A, 100B, and 100C are formed in the device D in the Y-axis direction (index feed direction). The modified layer 100A is formed along the same planned processing line X1, the modified layer 100B is formed along the same planned processing line X2, and the modified layer 100C is formed through the same planned processing line X3. It is formed along the top.

  These modified layers 100A to 100C are formed according to different processing conditions 1 to 3 shown in Table 1, respectively. The processing conditions 1 to 3 in this table are examples and are not limited thereto.

  In this configuration, the control device 80 first forms the modified layers 100A in the regions AR in the plurality of devices D located on the planned processing line X1. When the irradiation of the laser beam L to the terminal device D located on the planned processing line X1 is completed, the control device 80 moves the chuck table 10 in the Y-axis direction (index feed direction), and the next processing planned line Laser processing is performed again on each device D located on X2. Then, when the laser processing on the device D located on the processing line X3 is completed, the processing operation is ended.

  Thus, the laser beam irradiation means 20 is set so as to be capable of irradiating the laser beam L under a plurality of types of processing conditions, and when forming, for example, three types of modified layers 100A to 100C on each device D in the laser beam irradiation step, Since the processing conditions corresponding to the respective modified layers 100A to 100C are selected and irradiated, the modified layers 100A to 100C can be processed for each device D by a combination of different processing conditions. For this reason, the process according to the condition of the device D can be performed efficiently.

  Next, a modified example of the laser processing method for forming a modified layer on the wafer W device will be described. In the above-described embodiment, the same modified layer 100 is formed for all devices D provided on the wafer W, and the characteristics of the devices D of each wafer W are uniformly changed to desired characteristics. . In contrast, in the laser processing method according to the modified example, the modified layer 100 is formed only for the device D at a desired position on the wafer W. In this processing method, for example, when the characteristic of the device D at a specific position on the wafer W does not satisfy the design reference value, only the characteristic of the device D at the desired position can be changed.

  FIG. 7 is a flowchart showing a work procedure of a laser processing method for forming a modified layer on a device at a desired position on a wafer. In this work procedure, the description of the same configuration as the work procedure of FIG. 3 is omitted. First, each device D of the wafer W is inspected with respect to the wafer W (inspection step; step SB1). In general, since a certain amount of wafers W having the device D are manufactured together, if the characteristics of the device at a specific position do not satisfy the reference value for the wafer W arbitrarily selected, Also for the wafer W, it is assumed that the characteristics of the device at the same position do not satisfy the reference value. Therefore, a test wafer W is arbitrarily extracted from the manufactured wafer W, and the characteristics of all the devices D of the wafer W are inspected. In the inspection, for example, a predetermined probe is applied to the electrode of each device, and various test data are measured. In this inspection, if there is a device D that does not satisfy the reference value, the position of the device D on the wafer W is set in the control device 80 (device setting step; step SB2).

  Further, based on the test data measured in the above inspection, the position of the region AR where the modified layer is to be formed on the device D and the processing conditions for laser processing are calculated (region and condition calculating step; step SB3). ). The calculated position of the area AR and the processing conditions for laser processing are set in the control device 80, respectively. When there are a plurality of devices D that do not satisfy the reference value, the position of the area AR and the processing conditions for laser processing are calculated for each device D.

  Then, the wafer unit WU is held on the holding surface 11 of the chuck table 10 (holding step; step SB4). Then, the controller 80 adjusts the chuck table so that the positions of the regions AR in which the modified layer is to be formed in the desired device D set in Step SB2 and Step SB3 are aligned on a straight line parallel to the X-axis direction. The direction of 10 is adjusted (direction adjustment step; step SB5).

  Next, the control device 80 irradiates the wafer W with the laser beam L based on the processing conditions set in step SB3 (laser beam irradiation step; step SB6). In this case, the irradiation head 21 is arranged on the planned processing line of the device D to be processed, the chuck table 10 is moved in the X-axis direction by the X-axis moving means 30, and the wafer W is based on the processing conditions described above. The laser beam L is irradiated toward

  According to this configuration, the modified layer 100 can be formed inside the wafer W corresponding to the region AR of the desired device D, and the time for forming the modified layer 100 at the desired position of the desired device D can be reduced. Therefore, the modified layer 100 can be efficiently formed on the device D.

  When the laser processing is completed for the desired device D set in step SB3, the control device 80 detaches the wafer unit WU from the holding surface 11 of the chuck table 10 (detachment step; step SB7). The processing operation is finished.

  When forming a modified layer in this modification, a plurality of modified layers 100 may be formed on the device D shown in FIG. 6, and processing conditions corresponding to the respective modified layers 100 may be selected and irradiated. .

  As mentioned above, although this embodiment was described, this embodiment is shown as an example and does not intend limiting the range of invention. For example, in the present embodiment, a semiconductor device or an optical device is exemplified as the device D formed on the wafer W. However, the laser processing method of the present embodiment is not limited to the semiconductor device and the optical device, but may be MEMS, CCD, CMOS. It can be used for laser processing of various devices such as.

DESCRIPTION OF SYMBOLS 1 Laser processing apparatus 10 Chuck table 20 Laser beam irradiation means 21 Irradiation head 30 X-axis movement means (processing feed means)
40 Y-axis moving means (index feed means)
80 Controller 100, 100A, 100B, 100C Modified layer AR region (region where modified layer is to be formed)
D device L laser beam W wafer (workpiece)
WU wafer unit X1, X2, X3 Planned machining line (straight line parallel to machining feed direction)

Claims (2)

A plate-shaped workpiece having a device formed on a plurality of regions defined by a plurality of intersecting division lines formed on the surface is irradiated with a laser beam to cover the modified layer for correcting the device. A laser processing method for a workpiece to be formed on a workpiece,
A chuck table that holds and rotates a workpiece, a laser beam irradiation unit that irradiates the workpiece held on the chuck table with a laser beam, and a relative movement of the chuck table and the laser beam irradiation unit in the processing feed direction. Using a laser processing apparatus comprising a processing feed means,
Orientation adjustment step for adjusting the orientation of the chuck table so that the work piece is held by the chuck table and the region where the modified layer of the desired device is to be formed is aligned on a straight line parallel to the processing feed direction When,
After performing the orientation adjustment step, the laser beam irradiation means and the chuck table are relatively moved in the processing feed direction, and a modified layer is formed on a desired device by a single movement in the processing feed direction. An irradiation step,
A laser processing method for a workpiece, in which the modified layer formed by movement in one processing feed direction is formed at a desired position of a desired device. The laser beam irradiation means is set to be able to irradiate a laser beam under two or more laser beam irradiation conditions,
2. The laser of the workpiece according to claim 1, wherein, in the laser beam irradiation step, when a plurality of modified layers are formed on a desired device, the laser beam irradiation conditions corresponding to the respective modified layers are selected and irradiated. Processing method.

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