JP2015179756A - Processing method of brittle substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a processing method of a brittle substrate capable of efficiently performing laser processing on the brittle substrate along a processing line and separating the brittle substrate along the processing line.SOLUTION: The processing method of the brittle substrate for rupturing the brittle substrate along the processing line includes: a modified layer forming step of forming a modified layer that becomes a rupture starting point, along the processing line within the brittle substrate by converging a pulse laser beam of a wavelength having transmissivity with respect to the brittle substrate by means of a condenser and irradiating the substrate with the pulse laser beam along the processing line while positioning a convergence point within the brittle substrate; and a rupture step of rupturing the brittle substrate along the processing line with which the modified layer is formed, by applying an external force to the brittle substrate on which the modified layer forming step has been implemented. The pulse laser beam to be radiated in the modified layer forming step is set to a middle-wavelength long infrared light beam (wavelength band of 3 to 8 μm) or a long-wavelength long infrared light beam (wavelength of 8 to 15 μm).

Description

  The present invention relates to a method for processing a brittle substrate in which a brittle substrate such as a Si substrate, a SiC substrate, or a GaN substrate is divided along a predetermined division line.

  In the semiconductor device manufacturing process, a plurality of regions are defined by a plurality of division lines formed in a lattice pattern on the surface of a brittle substrate such as a Si substrate, a SiC substrate, or a GaN substrate. A wafer in which a plurality of devices are formed is formed. Then, by cutting the wafer along the planned dividing line, the region where the device is formed is divided to manufacture individual devices.

  As a method of dividing the wafer along the planned dividing line, a pulsed laser beam having a wavelength (1064 nm) that is transmissive to the brittle substrate is radiated along the street with the focusing point inside. By continuously forming a modified layer as a starting point of break along the planned dividing line, and applying an external force along the planned dividing line where the modified layer as the starting point of breakage is formed and the strength is reduced, A method of dividing a wafer along a planned division line has been proposed (see, for example, Patent Document 1).

Japanese Patent No. 3408805

Thus, it is necessary to use a condensing lens having a numerical aperture (NA) of 0.8 or more in order to form a modified layer by positioning a condensing point inside along the planned dividing line, for example, a thickness of 300 μm. In order to divide the wafer into individual devices, it is necessary to irradiate a pulse laser beam a plurality of times along the scheduled division line to form a plurality of modified layers, and there is a problem that productivity is poor.
In addition, since a plurality of devices are formed on the surface of the brittle substrate that constitutes the wafer, if the condensing lens with a numerical aperture (NA) of 0.8 or more is used to focus the laser beam and position the condensing point at a deep position, Since the laser beam is blocked by the device and the device is damaged, the laser beam has to be irradiated from the back surface of the wafer, and there is a problem that productivity is poor.

  The present invention has been made in view of the above-mentioned facts, and a main technical problem thereof is a method for processing a brittle substrate that can efficiently laser process a brittle substrate along a processing line and can be separated along the processing line. Is to provide.

In order to solve the main technical problem, according to the present invention, a brittle substrate processing method for breaking a brittle substrate along a processing line,
A pulsed laser beam having a wavelength that is transmissive to the brittle substrate is condensed by a condenser, and a condensing point is positioned inside the brittle substrate and irradiated along the processing line, and along the processing line inside the brittle substrate. A modified layer forming step of forming a modified layer to be a starting point of breakage,
Including a breaking step of applying an external force to the brittle substrate on which the modified layer forming step has been performed, and breaking the brittle substrate along a processing line on which the modified layer is formed,
The pulse laser beam irradiated in the modified layer forming step is set to medium wavelength infrared light (wavelength band 3 to 8 μm) or long wavelength infrared light (wavelength band 8 to 15 μm).
A method for processing a brittle substrate is provided.

The oscillator that oscillates the pulse laser beam is a CO laser oscillator or a CO2 laser oscillator, and the wavelength band of the pulse laser beam is 5.3 to 10.8 μm.
The numerical aperture (NA) of the condenser is set to 0.2 to 0.8.
The brittle substrate is any one of a Si substrate, a SiC substrate, and a GaN substrate.

  In the method for processing a brittle substrate according to the present invention, a pulsed laser beam having a wavelength that is transmissive to the brittle substrate is condensed by a condenser, and a condensing point is positioned inside the brittle substrate and irradiated along the processing line. The pulse laser beam irradiated in the modified layer forming step for forming a modified layer that becomes a fracture starting point along the processing line inside the brittle substrate is a medium wavelength infrared ray (wavelength band: 3 to 8 μm) or a long wavelength red Since it is set to outside light (wavelength band: 8 to 15 μm), it is possible to form a modified layer inside the brittle substrate without being restricted by the numerical aperture (NA) of the collector, and to obtain an average output. By adjusting, the depth of the modified layer can be adjusted as appropriate, and the modified layer can be formed corresponding to the thickness of the brittle substrate. In addition, since the pulsed laser beam with a long wavelength is irradiated, the numerical aperture (NA) of the condenser can be reduced, and the pulsed laser beam is irradiated along the wafer processing line in which multiple devices are formed on the surface of the brittle substrate. Since the device is not blocked by the device, it is possible to irradiate a pulse laser beam from the surface of the wafer, and the productivity can be improved.

The perspective view of the wafer as a brittle board | substrate processed by the processing method of a brittle board | substrate by this invention. Explanatory drawing of the wafer support process in the processing method of a brittle board | substrate by this invention. The principal part perspective view of the laser processing apparatus for implementing the modified layer formation process in the processing method of a brittle board | substrate by this invention. The block block diagram of the laser beam irradiation means with which the laser processing apparatus shown in FIG. 3 is equipped. Explanatory drawing of the modified layer formation process in the processing method of a brittle board | substrate by this invention. The perspective view of the tape expansion apparatus for implementing the fracture | rupture process in the processing method of a brittle board | substrate by this invention. Explanatory drawing of the wafer fracture | rupture process in the processing method of a brittle board | substrate by this invention.

  Preferred embodiments of a wafer dividing method according to the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 shows a perspective view of a wafer as a brittle substrate processed by the method for processing a brittle substrate according to the present invention. The wafer 2 shown in FIG. 1 is made of, for example, a 300 μm thick Si substrate, SiC substrate, or GaN substrate, and a plurality of regions are defined by a plurality of processing lines 21 formed in a lattice pattern on the surface 2a. Devices 22 such as LSI and LED are formed in the partitioned area. As shown in FIG. 2, the wafer 2 thus formed has a back surface 2b attached to the front surface of the dicing tape T mounted on the annular frame F (wafer support step).

Hereinafter, a method of dividing the wafer 2 described above into individual devices 22 along a plurality of processing lines 21 will be described.
First, a pulsed laser beam having a wavelength that is transparent to the wafer 2 made of a brittle substrate is condensed by a condenser, and a condensing point is positioned inside the wafer 2 and irradiated along the processing line 21. A modified layer forming step is performed in which a modified layer serving as a breakage starting point is formed along the processing line 21. This modified layer forming step is performed using a laser processing apparatus 3 shown in FIG. A laser processing apparatus 3 shown in FIG. 3 includes a chuck table 31 as a holding unit for holding a workpiece, a laser beam irradiation unit 32 for irradiating a workpiece held on the chuck table 31 with a laser beam, and a chuck table. An image pickup means 33 is provided for picking up an image of a workpiece held on the work piece 31. The chuck table 31 is configured to suck and hold the workpiece. The chuck table 31 is moved in a processing feed direction indicated by an arrow X in FIG. 3 by a processing feed means (not shown) and is also shown in FIG. 3 by an index feed means (not shown). It can be moved in the index feed direction indicated by the arrow Y.

The laser beam application means 32 includes a cylindrical casing 321 extending substantially horizontally. The laser beam irradiation means 32 will be described with reference to FIG.
The illustrated laser beam irradiation means 32 includes a pulse laser beam oscillation means 322 disposed in the casing 321, an output adjustment means 323 for adjusting the output of the pulse laser beam LB oscillated by the pulse laser beam oscillation means 322, and the output A condenser 324 for irradiating the workpiece W held on the holding surface of the chuck table 31 with the pulse laser beam whose output is adjusted by the adjusting means 323 is provided.

  The pulse laser beam oscillation means 322 includes a pulse laser beam oscillator 322a that oscillates a pulse laser beam, and a repetition frequency setting means 322b that sets a repetition frequency of the pulse laser beam oscillated by the pulse laser beam oscillator 322a. The pulse laser beam oscillator 322a is a CO laser oscillator or a CO2 laser oscillator in the illustrated embodiment. The CO laser oscillator oscillates a pulsed laser beam having a wavelength band of 5.3 to 5.9 μm, and the CO2 laser oscillator oscillates a pulsed laser beam having a wavelength band of 9.2 to 10.8 μm.

  The output adjustment unit 323 adjusts the output of the pulse laser beam oscillated from the pulse laser beam oscillation unit 322 to a predetermined output. The pulse laser beam oscillator 322a, the repetition frequency setting unit 322b, and the output adjustment unit 323 of the pulse laser beam oscillation unit 322 are controlled by a control unit (not shown).

  The condenser 324 includes a direction changing mirror 324a for changing the direction of the pulse laser beam oscillated from the pulse laser beam oscillating means 322 and having the output adjusted by the output adjusting means 323 toward the holding surface of the chuck table 31, and the direction changing mirror. A condensing lens 324 b that condenses the pulse laser beam whose direction has been changed by 324 a and irradiates the workpiece W held on the chuck table 31 is provided. The concentrator 324 thus configured is attached to the tip of the casing 321 as shown in FIG. The condenser lens 324b constituting the condenser 324 has a numerical aperture (NA) set to 0.2 to 0.8.

  Returning to FIG. 3 and continuing the description, the imaging means 33 is attached to the tip of the casing 321 constituting the laser beam irradiation means 32. The imaging means 33 is composed of an optical system such as a microscope and an imaging element (CCD), and sends the captured image signal to a control means (not shown).

The modified layer forming process performed using the laser processing apparatus 3 described above will be described with reference to FIGS.
In order to perform the modified layer forming step, first, the dicing tape T on which the back surface 2b of the wafer 2 is bonded is placed on the chuck table 31 of the laser processing apparatus 3 shown in FIG. Then, the wafer 2 is sucked and held on the chuck table 31 via the dicing tape T by operating a suction means (not shown) (wafer holding step). Therefore, the surface 2a of the wafer 2 held on the chuck table 31 is on the upper side. In FIG. 3, the annular frame F to which the dicing tape T is attached is not shown, but the annular frame F is held by appropriate frame holding means disposed on the chuck table 31. In this way, the chuck table 31 that sucks and holds the wafer 2 is positioned directly below the image pickup means 33 by a processing feed means (not shown).

  When the chuck table 31 is positioned immediately below the image pickup means 33, an alignment operation for detecting a processing region to be laser processed on the wafer 2 is executed by the image pickup means 33 and a control means (not shown). That is, the image pickup means 33 and the control means (not shown) are arranged such that the processing line 21 formed in a predetermined direction of the wafer 2 and the position of the condenser 324 of the laser beam irradiation means 32 that irradiates the laser beam along the processing line 21. Image processing such as pattern matching for alignment is executed, and alignment of the laser beam irradiation position is performed (alignment process). Similarly, alignment of the laser beam irradiation position is performed on the processing line 21 formed on the wafer 2 in a direction orthogonal to the predetermined direction.

  When the processing line 21 formed on the wafer 2 held on the chuck table 31 is detected as described above and alignment of the laser beam irradiation position is performed, the chuck as shown in FIG. The table 31 is moved to the laser beam irradiation region where the condenser 324 of the laser beam irradiation means 32 is located, and one end (the left end in FIG. 5A) of the predetermined processing line 21 is connected to the condenser 324 of the laser beam irradiation means 32. Position directly below. When the thickness of the wafer 2 is 300 μm, the condensing point P of the pulse laser beam is adjusted to a position of, for example, 200 μm from the surface 2 a (upper surface) of the wafer 2. Next, the chuck table 31 is irradiated with a CO laser having a wavelength band of 5.3 or 5.9 μm or a CO2 laser having a wavelength band of 9.2 or 10.8 μm from the condenser 324 in FIG. Move in the direction indicated by arrow X1 at a predetermined processing feed rate (modified layer forming step). When the other end of the processing line 21 (the right end in FIG. 5B) reaches the irradiation position of the condenser 324 of the laser beam irradiation means 32 as shown in FIG. The movement of the chuck table 31 is stopped while stopping. As a result, a modified layer 24 is formed along the processing line 21 inside the wafer 2. In this way, the modified layer forming step irradiates a pulsed laser beam having a long wavelength of medium wavelength infrared light (wavelength band 3 to 8 μm) or long wavelength infrared light (wavelength band 8 to 15 μm). The modified layer 24 can be formed inside the wafer 2 which is a brittle substrate without being restricted by the numerical aperture (NA) and the depth of the modified layer can be appropriately adjusted by adjusting the average output. The modified layer can be formed corresponding to the thickness of the wafer 2. In addition, since the pulsed laser beam with a long wavelength is irradiated, the numerical aperture (NA) of the condenser can be reduced, and even if the pulsed laser beam is irradiated from the wafer surface along the processing line on which a plurality of devices are formed, Since it is not blocked, it becomes possible to irradiate a pulse laser beam from the surface of the wafer, and productivity can be improved.

The processing conditions in the modified layer forming step are set as follows, for example.
Average output: 10-50W
Wavelength band: 5.3 to 10.8 μm
CO laser: 5.3, 5.9 μm
CO2 laser: 9.2, 10.8μm
Pulse width: 20 μs
Processing feed rate: 100 to 1000 mm / sec

  When the modified layer forming step is executed along all the processing lines 21 extending in the predetermined direction of the wafer 2 in this way, the chuck table 31 is rotated by 90 degrees so as to be in the predetermined direction. The modified layer forming step is executed along each processing line 21 extending in a direction orthogonal to the above.

  When the modified layer forming process described above is performed, an external force is applied to the wafer 2 and a breaking process is performed in which the wafer 2 that is a brittle substrate is broken along the processing line 21 on which the modified layer 24 is formed. This breaking process is performed using the tape expansion device 4 shown in FIG. 6 includes a frame holding means 41 for holding the annular frame F and a tape extending means for extending the dicing tape T attached to the annular frame F held by the frame holding means 41. 42 and a pickup collet 43. The frame holding means 41 includes an annular frame holding member 411 and a plurality of clamps 412 as fixing means arranged on the outer periphery of the frame holding member 411. An upper surface of the frame holding member 411 forms a mounting surface 411a on which the annular frame F is placed, and the annular frame F is placed on the mounting surface 411a. The annular frame F placed on the placement surface 411 a is fixed to the frame holding member 411 by the clamp 412. The frame holding means 41 configured in this manner is supported by the tape expanding means 42 so as to be able to advance and retract in the vertical direction.

  The tape expansion means 42 includes an expansion drum 421 disposed inside the annular frame holding member 411. The expansion drum 421 has an inner diameter and an outer diameter that are smaller than the inner diameter of the annular frame F and larger than the outer diameter of the wafer 2 attached to the dicing tape T attached to the annular frame F. Further, the expansion drum 421 includes a support flange 422 at the lower end. The tape expansion means 42 in the illustrated embodiment includes support means 423 that can advance and retract the annular frame holding member 411 in the vertical direction. The support means 423 includes a plurality of air cylinders 423 a arranged on the support flange 422, and the piston rod 423 b is connected to the lower surface of the annular frame holding member 411. As described above, the support means 423 including the plurality of air cylinders 423a has the reference position where the mounting surface 411a is substantially flush with the upper end of the expansion drum 421 as shown in FIG. Then, as shown in FIG. 7 (b), it is moved in the vertical direction between the extended positions below the upper end of the expansion drum 421 by a predetermined amount.

  The wafer implemented using the tape expansion apparatus 4 configured as described above will be described with reference to FIG. That is, the annular frame F to which the dicing tape T to which the wafer 2 is attached is attached on the mounting surface 411a of the frame holding member 411 constituting the frame holding means 41 as shown in FIG. And fixed to the frame holding member 411 by the clamp 412 (frame holding step). At this time, the frame holding member 411 is positioned at the reference position shown in FIG.

  When the above-described frame holding step is performed, the plurality of air cylinders 423a as the supporting means 423 constituting the tape expanding means 42 are operated as shown in FIG. Lower to the extended position. Accordingly, since the annular frame F fixed on the mounting surface 411a of the frame holding member 411 is also lowered, the dicing tape T attached to the annular frame F is an expansion drum as shown in FIG. The tape is expanded in contact with the upper edge of 421 (tape expansion process). As a result, the tensile force acts radially on the wafer 2 adhered to the dicing tape T. Thus, when a tensile force is applied to the wafer 2 in a radial manner, the strength of the modified layer 24 formed along the processing line 21 is lowered. Therefore, the strength of the wafer 2 is lowered. 24 is a break starting point and is broken along the street 21 to be divided into individual devices 22.

  If the wafer 2 is broken along the processing line 21 in which the modified layer 24 is formed and divided into individual devices 22 by performing the above-described wafer breaking step, a pickup collet 43 is formed as shown in FIG. The device 22 operates to adsorb the device 22, peels off the dicing tape T, and picks up. In the pickup process, since the gap S between the individual devices 22 is widened, the pickup can be easily performed without contact with the adjacent devices 22.

  In the above-described embodiment, the example in which the laser beam is irradiated from the front surface side of the wafer 2 has been described. However, in the present invention, the laser beam may be irradiated from the rear surface side of the wafer.

2: Wafer 21: Processing line 22: Device 3: Laser processing apparatus 31: Chuck table 32 of laser processing apparatus: Laser beam irradiation means 322: Pulsed laser beam oscillation means 324: Condenser 33: Imaging means 4: Tape expansion apparatus 41: Frame holding means 42: Tape expanding means 43: Pickup collet F: Annular frame T: Dicing tape

The perspective view of the wafer as a brittle board | substrate processed by the processing method of a brittle board | substrate by this invention. Explanatory drawing of the wafer support process in the processing method of a brittle board | substrate by this invention. The principal part perspective view of the laser processing apparatus for implementing the modified layer formation process in the processing method of a brittle board | substrate by this invention. The block block diagram of the laser beam irradiation means with which the laser processing apparatus shown in FIG. 3 is equipped. Explanatory drawing of the modified layer formation process in the processing method of a brittle board | substrate by this invention. The perspective view of the tape expansion apparatus for implementing the fracture | rupture process in the processing method of a brittle board | substrate by this invention. Explanatory drawing of the wafer fracture | rupture process in the processing method of a brittle board | substrate by this invention. Explanatory drawing of the pick-up process in the processing method of a brittle board | substrate by this invention.

Claims (4)

A brittle substrate processing method for breaking a brittle substrate along a processing line,
A pulsed laser beam having a wavelength that is transmissive to the brittle substrate is condensed by a condenser, and a condensing point is positioned inside the brittle substrate and irradiated along the processing line, and along the processing line inside the brittle substrate. A modified layer forming step of forming a modified layer to be a starting point of breakage,
Including a breaking step of applying an external force to the brittle substrate on which the modified layer forming step has been performed, and breaking the brittle substrate along a processing line on which the modified layer is formed,
The pulse laser beam irradiated in the modified layer forming step is set to medium wavelength infrared light (wavelength band 3 to 8 μm) or long wavelength infrared light (wavelength band 8 to 15 μm).
A method for processing a brittle substrate.   The brittle substrate processing method according to claim 1, wherein the oscillator that oscillates the pulsed laser beam is a CO laser oscillator or a CO2 laser oscillator, and the wavelength band of the pulsed laser beam is 5.3 to 10.8 µm.   The method for processing a brittle substrate according to claim 1 or 2, wherein the concentrator has a numerical aperture (NA) of 0.2 to 0.8.   The method for processing a brittle substrate according to any one of claims 1 to 3, wherein the brittle substrate is any one of a Si substrate, a SiC substrate, and a GaN substrate.

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