JP5380986B2 - Laser scribing method and laser scribing apparatus - Google Patents

Description

  The present invention relates to a laser scribing method and a laser scribing apparatus for irradiating a laser beam with a focusing point inside a workpiece.

  Conventionally, in order to divide a workpiece such as a silicon substrate, a modified layer that is the starting point of the division is formed inside the workpiece by irradiating a laser beam with the focusing point inside the workpiece. There is technology to do. For example, Patent Document 1 discloses a technique in which modified layers are arranged in parallel in the oblique direction by irradiating a laser beam so that the focal point moves in an oblique direction with respect to the surface of the workpiece. Yes. In this technique, the repetition frequency of the laser beam is set to several tens to hundreds of hertz, and the focusing point is moved by moving the focusing lens with respect to the workpiece while synchronizing with the irradiation timing of the laser beam. I try to move.

  Further, in Patent Document 2, when the electric field intensity and pulse width at the condensing point of the laser beam satisfy predetermined conditions, a phenomenon in which the condensing point is locally heated due to multiphoton absorption occurs. It is described that the layer is formed in a molten region where the molten material is in a resolidified state. When the object to be processed has a predetermined thickness, the object to be processed is irradiated with a laser beam having a pulse waveform whose peak position is moved with respect to the Gaussian beam profile under the condition that the melting region is formed. Thus, it is described that the size of the melting region can be increased to easily cause cracks in the workpiece.

JP 2007-167875 A JP 2007-245173 A

  By the way, in Patent Document 1, since the lens is moved in synchronization with the irradiation timing of a short laser beam having a repetition frequency of several tens to hundreds of hertz, it is necessary to move the lens at a high speed. For this reason, since the structure of the moving mechanism that realizes the movement of the lens becomes complicated, the manufacturing cost of the moving mechanism becomes high, or the accuracy of the moving mechanism is distorted, so that the modified layer cannot be formed at a desired position. Such a problem may occur. Further, when the laser beam irradiation timing is set to be long and the lens is moved in synchronization with the set irradiation timing, the processing speed of the modified layer is slowed down. become longer.

  Further, in Patent Document 2, in order to move the peak position of the pulse waveform, not only simple wavelength modulation but also phase modulation is required, so that the configuration of the pulse modulator becomes complicated. For this reason, the accuracy of the pulse modulator is distorted, and the manufacturing cost of the pulse modulator increases. If the re-solidification state of the molten region is not controlled well, the molten region cannot serve as a starting point for growing cracks, and conversely becomes a factor that hinders crack growth. Further, when an unnecessarily large melting region is formed, the melting region causes a deformation such as sagging or protrusion on the workpiece, and adversely affects material properties such as strength of the workpiece.

  The present invention has been made in view of such circumstances, and can divide an object to be processed with a small force without complicating the configuration of the apparatus, and can suppress a shift of a divided cross section of the object to be divided from a planned division line. It is an object of the present invention to provide a laser scribing method and a laser scribing apparatus capable of performing the same.

In order to achieve the above object, in the laser scribing method according to the first aspect of the present invention, the condensing point aligned with the inside of the sapphire substrate, which is a plate-like workpiece , is along the planned dividing line of the workpiece. The laser scribing method forms a modified layer by multiphoton absorption along the division line by irradiating the workpiece with a laser beam having a repetition frequency of 10 kHz to 10 MHz so as to move. The modified layer is a microcavity having a crack generated in the thickness direction of the substrate when the laser beam is irradiated, and the laser beam has a pulse width of 2. under the condition that the irradiation energy becomes a predetermined value . It is 0 picoseconds or more and 4.5 picoseconds or less.

A laser scribing apparatus according to a second aspect of the present invention is a laser scribing apparatus that forms a modified layer by multiphoton absorption inside a sapphire substrate, which is a plate-like processing object, and the processing object is mounted on the laser scribing apparatus. a mounting table which is location, the workpiece as the focal point is aligned within the object placed on the mounting table, the laser irradiation repetition frequency is irradiated with the laser beam is above 10kHz 10MHz or less Means and a moving means for moving the mounting table relative to the laser beam so that the focusing point moves along a division planned line of the workpiece, the modified layer includes: a microcavity having cracks generated in the thickness direction of the substrate during the irradiation of the laser beam, the laser irradiation means, under conditions where the irradiation energy becomes a predetermined value, the pulse width is 2.0 picoseconds 4 The laser light is set to 5 picosecond and irradiating the workpiece.

  According to the present invention, the laser beam applied to the object to be processed has the pulse width set to 700 femtoseconds or more and 4.5 picoseconds or less under the condition that the irradiation energy becomes a predetermined value, so that Can be generated long in the thickness direction of the object to be processed from the modified layer, and the generation of an amorphous phase that prevents the progress of the crack can be suppressed to a low level. Thereby, while being able to divide | segment a process target object with small force, the shift | offset | difference with respect to the division | segmentation planned line of the division | segmentation cross section of a process target object can be suppressed small.

  Control of the pulse width in the range of 700 femtoseconds to 4.5 picoseconds can be realized by adjusting the reflection optical path lengths of the grating mirror and the dispersion prism. This does not complicate the configuration of the device.

  The laser scribing method according to the present embodiment uses a modified layer formed inside a workpiece by laser light irradiation. First, the principle of the laser scribing method according to the present embodiment will be described.

  FIG. 1 is a perspective view of an object 1 to be processed during laser processing by the laser scribing method according to the present embodiment.

  The workpiece 1 has a plate shape (wafer shape), and a division line 3 for dividing the workpiece is provided on the surface thereof. In the laser scribing method according to the present embodiment, the processing object 1 is irradiated with the laser beam L so that the focused point P is inside the workpiece 1, and the focused point P is modified by multiphoton absorption. Layer 5 is formed.

  Then, the workpiece 1 is moved relative to the laser light L in the direction A along the scheduled division line 3 of the workpiece so that the condensing point P moves along the scheduled division line. Further, the processing object 1 is moved in the thickness direction B of the processing object 1 with respect to the laser beam L so that the condensing point P also moves in the thickness direction B of the processing object at the position along the division line 3. Move relative. The relative movement in the thickness direction B is performed such that the condensing point P moves from the opposite side to the near side with respect to the irradiation surface of the laser light L. This prevents the progress of the laser light L from being hindered by the previously formed modified layer 5.

  By performing the above laser irradiation, the modified layer 5 by multiphoton absorption is formed side by side in the thickness direction B of the workpiece 1 inside the workpiece 1 along the scheduled division line 3. Depending on the thickness of the workpiece 1, the modified layer 5 may be formed at one position in the thickness direction B of the workpiece 1. In this case, the relative movement in the thickness direction B described above is omitted.

  The workpiece 1 on which the modified layer 5 is formed is divided by applying a bending stress or the like in the thickness direction B along the division line 3. At this time, the workpiece 1 is divided with the crack 7 generated by extending from the modified layer 5 in the thickness direction B (irradiation direction of the laser light L) of the workpiece as a starting point of the crack. The crack 7 is generated when the laser beam L is irradiated, and there are the following three factors (i) to (iii) as factors affecting the generation of the crack 7.

(i) Coulomb explosion
At the condensing point P of the laser beam L, the polarization of the material is induced by the electric field of the laser beam L, or the electrons move violently. As the electric field increases, absorption of photons progresses resonatively, and the electrons peel off. To be taken. The stripped electrons become free electrons and collide with surrounding atoms and ions, resulting in avalanche ionization (ionization is amplified as an avalanche phenomenon). As a result, as the coulomb repulsive force increases, the plasma density at the focal point P increases abruptly, resulting in a Coulomb explosion in which the high-pressure plasma confined in a minute region explosively diffuses. The diffusion of the plasma is extremely fast, and the condensing point P is adiabatically cooled as the diffusion of the plasma proceeds. As a result, at the condensing point P, electrons and ions are recombined to become neutral atoms, so that the densification of the material proceeds and a microcavity is generated inside the material. A shock wave generated after the plasma diffusion propagates around the microcavity. As a result, a crack 7 is generated inside the workpiece 1.

(ii) Heat conduction from high-temperature plasma
High temperature plasma is generated at the condensing point P. The heat of the plasma is conducted to the material to generate a stress inside the material, and as a result, the growth of the crack 7 is promoted. When the amount of heat conducted from the plasma to the material is large, the melting region of the material is increased, which prevents the growth of the crack 7 due to the shock wave described in (i), or the crack 7 once formed is regenerated. Disappears due to welding.

(iii) Light absorption of material At the condensing point P, the material temperature rises due to light absorption of the material. This temperature rise generates stress inside the material, and as a result, the growth of the crack 7 is promoted. In addition, when the material temperature is increased, the melting region of the material is increased, and the growth of the crack 7 is prevented, or the crack 7 once formed disappears by re-welding.

  As described above, the growth of the crack 7 is related to the above-described phenomena (i) to (iii). Under the condition that the irradiation energy of the laser beam L is constant, each phenomenon affects the generation of the crack 7. It is considered that the magnitude to be given varies depending on the pulse width of the laser light L applied to the workpiece 1. Hereinafter, the relationship between the above-described phenomena (i) to (iii) and the pulse width will be described.

  Avalanche ionization that causes a Coulomb explosion is promoted because electron separation becomes more active as the pulse width becomes longer (the irradiation time of the laser beam L becomes longer) within a predetermined range of the pulse width. However, under a condition where the irradiation energy is constant, if the pulse width is increased, the peak power is reduced, so that the laser energy is absorbed in the plasma and does not easily travel into the material. For this reason, when the pulse width is increased under the condition where the irradiation energy is constant, the avalanche ionization described in (i) decreases, and as a result, the scale of the Coulomb explosion decreases. Further, when the pulse width is increased, the duration of irradiation with the laser light L is increased, so that the light absorption amount of the material is increased. As the material temperature increases, the light absorption rate of the material increases. For this reason, when the pulse width is increased, the light absorption rate of the material increases in an accelerated manner because the light absorption rate increases with the increase in temperature due to the increase in duration as described above. From these facts, it is considered that (ii) the influence of plasma and (iii) the influence of light absorption of the material are strong on the generation of the crack 7 in the range where the pulse width is large. And when these influences appear strongly and material temperature becomes high, it is thought that the fusion | melting area | region which lose | disappears the crack 7 arises large.

  On the other hand, when the pulse width is shortened under the condition that the irradiation energy is constant, the peak power increases, so that the energy of the laser beam L proceeds inside the material. For this reason, in the range where the pulse width is small, it is considered that the influence on the generation of the crack 7 is dominated by the Coulomb explosion. From the above, it is considered that the phenomena (i) to (iii) depending on the pulse width interact with the generation of the crack 7.

  Here, as described above, the crack 7 is generated by extending in the thickness direction B (irradiation direction of the laser beam L) of the workpiece 1 from the modified layer 5 located at the position along the planned division line 3. When 1 is divided, it becomes the starting point of the division. For this reason, when the length of the crack 7 is short, since the guidance of the crack by the crack 7 is small, a large force is required to advance the crack of the workpiece 1 and the divided cross section of the workpiece 1 is It is thought that it will deviate from the division line 3. For this reason, the crack 7 needs to be generated largely. However, since the phenomena (i) to (iii) that act on the generation of the crack 7 depend on the pulse width, the crack 7 is optimal. A pulse width is considered to exist.

  It is also known that an amorphous phase is formed around the microcavity due to the Coulomb explosion. The amorphous phase becomes resistant to the progress of cracking of the workpiece 1 due to the disorder of the crystal structure. For this reason, when the amorphous phase is largely generated, it is considered that a large force is required to break the workpiece 1. For this reason, it is necessary to suppress the generation of the amorphous phase, but (i) since the Coulomb explosion depends on the pulse width, it is considered that there is an optimum pulse width for reducing the amorphous phase.

  Therefore, the present inventors conducted the following experiment in order to obtain the optimum range of the pulse width related to the crack 7 and the amorphous phase.

  In this experiment, a plurality of sapphire substrates were prepared, and 40 division lines 3 were set on each sapphire substrate.

  Each sapphire substrate was irradiated with a laser so that the condensing point P was aligned with the position along each division planned line 3. At this time, each sapphire substrate was irradiated with laser light L having a different pulse width under the condition that the irradiation energy was a predetermined value (that is, the average output and the repetition frequency were a predetermined value). As a result, in each sapphire substrate, the modified layer 5 was arranged in parallel in the thickness direction of the sapphire substrate inside each division planned line 3. The laser processing conditions are shown below.

Laser processing conditions (A) Processing target 1: Sapphire substrate (B) Laser Light source: Femtosecond pulse laser (manufactured by IMRA, FCPA μJewel D-400)
Wavelength: 1045nm
Repeat frequency: 100 kHz
Average output: 120mW (after passing through condensing lens)
Polarization characteristics: linearly polarized laser Spatial beam profile of laser: Gaussian (C) condenser lens Numerical Aperture (NA): 0.65
Focal length: 4mm
(D) Processing object scanning speed: 500 mm / second

  And after performing the above-mentioned laser processing, operation which divides each sapphire substrate was performed. This division operation is performed for each division line 3 in each sapphire substrate, and in the division operation for one division line 3, the surface of the sapphire substrate (laser irradiation surface) is supported at a plurality of points. Bending stress was applied in the thickness direction B along the planned dividing line 3 by pressing the planned dividing line 3 on the back surface with a blade. In each division operation, the force applied from the blade is uniform. As a result of this division operation, each sapphire substrate had a division planned line 3 in which a crack occurred and a division planned line 3 in which no crack occurred.

  FIG. 2 shows the relationship between the cleavage yield of the sapphire substrate and the pulse width. The cleaving yield means the ratio of the division planned lines 3 that are actually broken by the dividing operation. For example, in a sapphire substrate irradiated with a laser beam L having a pulse width of 700 femtoseconds, cracks were actually generated in 35 of the 40 planned division lines 3, so the cleaving yield was 70%. It has become.

In the sapphire substrate irradiated with the laser beam L having a pulse width of 700 femtoseconds (0.7 picoseconds) or more and 4.5 picoseconds or less, the cleaving yield was 70% or more in all sapphire substrates. On the other hand, in the sapphire substrate irradiated with the laser beam L having a pulse width smaller than 700 femtoseconds or larger than 4.5 picoseconds, the cleavage yield is rapidly reduced to 40% or less. It was. From this result, under the condition that the irradiation energy becomes a predetermined value, the ease of cracking of the workpiece 1 depends on the pulse width, and the workpiece 1 has a pulse width of 700 femtoseconds or more and 4.5 picoseconds. It was confirmed that the laser beam L was easily broken when irradiated with the laser beam L in the following range, and extremely difficult to break when irradiated with the laser beam L with a pulse width in a range other than this range.
Moreover, in the sapphire substrate irradiated with the laser beam L in the range of 2 picoseconds or more and 4.5 picoseconds or less, the cleaving yield was 80% or more in all the sapphire substrates. Thereby, when the laser beam L in the range of 2 picoseconds or more and 4.5 picoseconds or less was irradiated, it was confirmed that the workpiece 1 is more easily broken.

   FIG. 3 is a schematic side view showing a divided section of the divided sapphire substrate, and the thickness direction B of the sapphire substrate is the direction shown in the figure. In this experiment, the roughness of the divided cross section of the sapphire substrate is measured, and the divided cross section of the sapphire substrate is shifted from the cross sectional curve obtained by this measurement in a direction perpendicular to the planned division line 3. The maximum amount d (hereinafter, the maximum amount of deviation) was measured.

  FIG. 4 shows the relationship between the maximum deviation amount d and the pulse width, and FIG. 5 shows the relationship between the maximum deviation amount d and the cleaving yield. First, referring to FIG. 4, it was confirmed that the sapphire substrate having a smaller maximum shift amount d had a higher cleaving yield and cracks occurred in many division lines 3. FIG. 5 shows the maximum deviation amount for the sapphire substrate irradiated with the laser beam L having a pulse width in the range of 400 femtoseconds or more and 1000 femtoseconds or less. According to FIG. 5, in the sapphire substrate irradiated with the laser beam L having the pulse width within the above range, it was confirmed that the maximum deviation amount d tends to decrease as the pulse width increases. From these facts, it is considered that in the range of the pulse width from 400 femtoseconds to 1000 femtoseconds, the sapphire substrate having a larger pulse width has a higher cleaving yield, and the force required for the division is small and the cracking is likely to occur.

  FIG. 6 is a photograph of a processing mark 9 on the surface of the sapphire substrate when the condensing point P is positioned on the surface of the sapphire substrate, and (a) is irradiated with laser light L having a pulse width of 400 femtoseconds. A sapphire substrate, (b) is a sapphire substrate irradiated with a laser beam L having a pulse width of 4 picoseconds, and (c) is a sapphire substrate irradiated with a laser beam L having a pulse width of 6.6 picoseconds. .

  When (a), (b), and (c) in FIG. 6 are compared, it can be seen that the sapphire substrate irradiated with the laser beam L having a larger pulse width becomes more unclear. From this, the magnitude of the laser energy traveling inside the material depends on the pulse width, and is considered to decrease as the pulse width increases.

  FIG. 7 is a photograph of the divided cross section of the divided sapphire substrate, (a) is the divided cross section of the sapphire substrate irradiated with the laser beam L having a pulse width of 400 femtoseconds, and (b) is the pulse width. A divided section of the sapphire substrate irradiated with the laser beam L of 4 picoseconds, (c) shows a divided section of the sapphire substrate irradiated with the laser light L having a pulse width of 6.6 picoseconds.

  In FIG. 7, E indicates the irradiation direction of the laser beam L, F indicates the position of the condensing point P, L1 indicates the width of the modified layer 5 in the laser irradiation direction, and L2 indicates the laser beam from the modified layer 5 The length of the crack 7 extending to the irradiation side of L is shown.

  When comparing (a), (b), and (c) of FIG. 7, it was confirmed that the width L1 of the modified layer 5 was shorter as the sapphire substrate irradiated with the laser having a larger pulse width. This is probably because the peak energy is small in the range where the pulse width is large, so that it is difficult for the laser energy to travel into the material by being absorbed into the plasma.

  From the photograph of FIG. 7C, in the sapphire substrate irradiated with the laser beam L having a pulse width of 6.6 picoseconds, the material solidified after melting from the modified layer 5 to the irradiation side of the laser beam L. A melting region was observed. This is presumably because of the large pulse width, (ii) the effect of heat due to the heat conduction of the plasma and (iii) the light absorption of the material.

  When comparing (a), (b), and (c) of FIG. 7, in the sapphire substrate (b) irradiated with the laser beam L having a pulse width of 4 picoseconds, the pulse width is 400 femtoseconds (a) or 6 It was confirmed that the crack 7 was clearly and long in the thickness direction of the sapphire substrate as compared to the sapphire substrate irradiated with the .6 picosecond (c) laser. Thereby, under the condition that the irradiation energy becomes a predetermined value, there is a range of the pulse width that causes the crack 7 to grow greatly, and when the pulse width becomes shorter or longer from this range, the crack 7 generated in the workpiece 1 is reduced. It will be smaller.

  FIG. 8 is a captured image of a divided section of the sapphire substrate. In addition, the imaging | photography of the image was performed with the scanning electron microscope (SEM: Scanning Electron Microscope).

  In the divided cross section of the sapphire substrate, a microcavity H is generated at a position corresponding to the condensing point P. The microcavity H has an elongated shape, and its longitudinal direction is the thickness direction B of the sapphire substrate (laser Stretching in the irradiation direction) was observed. Further, it was observed that cracks 7 extended outward from each end in the longitudinal direction of the microcavity H in the thickness direction B. L3 indicates the length in the thickness direction B of the crack 7 extending from the minute cavity H.

  FIG. 9 is an enlarged view of the microcavity H. FIG. L4 indicates the length of the microcavity H in the longitudinal direction (hereinafter referred to as the major axis), and L5 indicates the length in the direction perpendicular to the longitudinal direction of the microcavity H (hereinafter referred to as the minor axis).

  10 shows the relationship between the major axis L4 of the microcavity H and the pulse width, and FIG. 11 shows the relationship between the minor axis L5 of the microcavity H and the pulse width. 10 and 11 are graphs showing the relationship between the pulse width and the minute cavity diameter H for a sapphire substrate irradiated with a laser beam having a pulse width of 400 femtoseconds or more and 1 picosecond or less. In these sapphire substrates, it was confirmed that the longer diameter L4 and the shorter diameter L5 of the microcavity H become larger as the sapphire substrate irradiated with the laser light L having a larger pulse width. This is because, in the range from 400 femtoseconds to 1 picoseconds, as the pulse width increases, the electron separation associated with multiphoton absorption becomes active and the free electron density increases, so that avalanche ionization increases. This is probably because the scale of the Coulomb explosion has increased.

  FIG. 12 shows the relationship between the area of the microcavity H and the pulse width.

  It was confirmed that the area of the microcavity H decreases rapidly when the sapphire substrate is irradiated with laser light having a pulse width greater than 4.5 picoseconds. This is because, under the condition that the irradiation energy becomes a predetermined value, if the pulse width is larger than 4.5 picoseconds, the peak energy is reduced, so that the laser energy does not advance inside the material, and the scale of the Coulomb explosion is reduced. It is thought that it became.

  FIG. 13 shows the relationship between the length L3 of the crack 7 shown in FIG. 8 and the pulse width.

  It has been confirmed that the length L3 of the crack 7 decreases rapidly when the sapphire substrate is irradiated with laser light having a pulse width greater than 4.5 picoseconds. This is because when the pulse width is larger than 4.5 picoseconds, (ii) heat conduction from the high-temperature plasma and (iii) light absorption of the material occur and the material temperature increases, resulting in a large melting region. This is probably because the crack 7 generated by the Coulomb explosion or the like has disappeared.

  The amorphous phase formed around the microcavity H was observed by etching the periphery of the microcavity in the divided section with hydrofluoric acid.

  FIG. 14 shows the relationship between the length and the pulse width in the thickness direction B (irradiation direction of the laser beam L) of the amorphous phase sapphire substrate. The length of the amorphous phase is shorter as the sapphire substrate irradiated with the laser beam L having a larger pulse width. In the sapphire substrate irradiated with the laser beam L having a pulse width of 700 femtoseconds or less, the amorphous phase is greatly generated. It was confirmed that From this, in the sapphire substrate irradiated with the laser beam L having a pulse width of 700 femtoseconds or less, it is considered that the cleavage yield was reduced because the amorphous phase became resistant to the progress of cracking.

  From the above experimental results, under the condition that the irradiation energy becomes a predetermined value, if the pulse width is shorter than 700 femtoseconds, the amorphous phase becomes longer in the thickness direction B of the workpiece 1. There is a high possibility that the phase becomes a resistance and prevents the progress of cracking. Moreover, when the pulse width is longer than 4.5 picoseconds, the length of the crack 7 is shortened, and there is a high possibility that the crack generated in the workpiece 1 is difficult to be connected. Therefore, if the pulse width is shorter than 700 femtoseconds or the pulse width is longer than 4.5 picoseconds, a large force is required to divide the workpiece 1 or the workpiece 1 It is considered that the divided cross section greatly deviates from the division planned line 3.

  For this reason, in the laser scribing method according to the present embodiment, the laser beam L irradiated to the workpiece 1 is set to have a pulse width of 700 femtoseconds or more and 4.5 picoseconds or less under the condition that the irradiation energy becomes a predetermined value. Has been. Thereby, the crack 7 which becomes the starting point of the division can be generated long in the thickness direction of the workpiece 1 from the modified layer 5, and the generation of an amorphous phase which prevents the progress of the crack can be suppressed to a small level. Thereby, while being able to divide the process target object 1 with small force, the shift | offset | difference with respect to the division | segmentation planned line 3 of the division | segmentation cross section of the process target object 1 can be suppressed small. As a result, it is possible to prevent the split cross section from being chipped or cracked.

  Also, controlling the pulse width in the range of 700 femtoseconds or more and 4.5 picoseconds or less corresponds to controlling the state of chromatic dispersion. Therefore, by adjusting the reflection optical path lengths of the grating mirror and the dispersion prism. realizable. For this reason, it is not necessary to make the structure of a laser processing apparatus complicated.

  In the laser scribing method according to the present embodiment, any one of glass, sapphire, crystal, and silicon is selected as the workpiece 1. Thereby, when the laser beam L having a pulse width of 700 femtoseconds or more and 4.5 picoseconds or less is irradiated, multiphoton absorption can be surely caused at the condensing point P.

  In the laser scribing method according to the present embodiment, the repetition frequency of the laser light L is set to 10 kHz or more and 10 MHz or less. Thereby, since the movement of the condensing point P can be speeded up, the processing speed can be increased.

  Further, based on the result shown in FIG. 2, in the laser scribing method according to the present embodiment, the pulse width is more preferably set to 1 picosecond or more and 4.5 picoseconds or less. Thereby, the workpiece 1 becomes easier to break.

  Next, the laser scribing apparatus according to this embodiment will be described. FIG. 15 is a diagram illustrating a configuration of the laser scribing apparatus 20 according to the present embodiment.

  The laser processing apparatus 20 includes a laser generator 22, a condenser lens 24, a mounting table 26, an X-axis stage 28, a Y-axis stage 30, a Z-axis stage 32, and a control unit 40.

The laser generator 22 is doped with erbium (Er) or yttrium (Yb) that generates laser light L having a wavelength of 1 μm to 2 μm, a pulse width of 10 femtoseconds to 20 picoseconds, and a repetition frequency of 100 kHz to 10 MHz. Fiber laser.
The condensing lens 24 condenses the laser light L generated by the laser generator 22, and the mounting table 26 processes the condensing laser light L so that it is incident on the workpiece 1 from the Z-axis direction. The object 1 is supported. The mounting table 26 can be moved in each axial direction by an X-axis stage 28, a Y-axis stage 30, and a Z-axis stage 32. The control unit 40 controls the output and pulse width of the laser light L generated from the laser generator 22 and controls the movement of the three stages 28, 30 and 32.

  According to the laser processing apparatus 20, the Z-axis direction is the direction of the focal point depth of the condensing lens 24. Therefore, by moving the Z-axis stage 32 in the Z-axis direction, a predetermined depth inside the workpiece 1 is obtained. The condensing point P of the laser beam L can be set at the position.

  The movement of the condensing point P in the X (Y) axis direction is performed by moving the workpiece 1 in the X (Y) axis direction by the Z axis stage 32. By the movement in the X (Y) axis direction, the condensing point P can be moved in the direction along the planned division line 3.

  FIG. 16 shows an example of the processing object 1 processed by the laser scribing apparatus 20 according to this embodiment.

  FIG. 16 shows a state in which the modified layers 5 are arranged in parallel at predetermined positions in the thickness direction B of the workpiece 1 at five positions along the planned division line 3. These modified layers 5 are formed by moving the condensing point P at a predetermined speed in the X-axis or Y-axis direction by the operation of the X-axis stage 28 or the Y-axis stage 30.

  As shown in FIG. 1, in order to arrange the modified layers 5 in two layers in the thickness direction B of the workpiece 1 at five positions along the scheduled division line 3, by operating the Z-axis stage 32, This is achieved by moving the condensing point P in the X-axis direction by, for example, operating the X-axis stage 28 every time the condensing point P is moved at a predetermined pitch in the Z-axis direction.

  According to the laser scribing apparatus in the present embodiment, the control unit 40 controls the laser generator 22 so that the laser beam L having a pulse width of 700 femtoseconds or more and 4.5 picoseconds or less is irradiated to the workpiece 1. Thus, the length of the crack 7 generated in the workpiece 1 can be increased, and the length of the amorphous phase can be reduced. Thereby, while being able to divide the process target object 1 with small force, the shift | offset | difference with respect to the division | segmentation planned line 3 of the division | segmentation cross section of the process target object 1 can be suppressed small.

  When glass, sapphire, crystal, or silicon is selected as the processing object 1, the laser generator 22 applies laser light L having a pulse width of 700 femtoseconds or more and 4.5 picoseconds or less. By irradiating 1, the multiphoton absorption can be surely caused at the condensing point P.

  In addition, the control unit 40 causes the laser generator 22 to generate a laser beam L having a repetition frequency of 100 kHz to 10 MHz, and moves the XYZ stage by following this frequency, thereby moving the focal point P. Since the speed can be increased, the processing speed of the modified layer 5 can be increased.

  The laser scribing apparatus according to this embodiment can be modified as follows.

  For example, when two back surfaces of the workpiece 1 are not parallel, a gonio stage that can rotate in the XZ plane may be used as a mounting table. In this case, the processing target 1 may be arranged on the goniostage so that the laser light L incident surface of the processing target 1 is in the XZ plane and is parallel to the X-axis and Y-axis directions.

It is a perspective view of the processing target object during laser processing by the laser scribing method concerning this embodiment. It is a figure which shows the relationship between the cutting yield of a sapphire substrate, and a pulse width. It is a schematic side view which shows the division | segmentation cross section of the divided | segmented sapphire substrate. It is a figure which shows the relationship between the largest deviation | shift amount and a pulse width. It is a figure which shows the relationship between the largest gap | deviation amount and a cleaving yield. It is a photograph of the processing trace on the surface of a sapphire substrate when processing with a condensing point located on the surface of a sapphire substrate. It is a photograph of the division section of the divided sapphire substrate. It is the picked-up image of the division | segmentation cross section of a sapphire substrate. It is an enlarged view of a microcavity. It is a figure which shows the relationship between the long diameter of a microcavity, and a pulse width. It is a figure which shows the relationship between the minor axis of a microcavity, and a pulse width. It is a figure which shows the relationship between the area of a microcavity, and a pulse width. It is a figure which shows the relationship between the length of a crack, and a pulse width. It is a figure which shows the relationship between the length in the thickness direction of a sapphire substrate of an amorphous phase, and a pulse width. It is a figure which shows the structure of the laser scribing apparatus which concerns on this embodiment. It is a perspective view which shows the example of the process target processed by the laser scribing apparatus which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Processing target object 3 Dividing line 5 Modified layer L Laser beam P Focusing point

Claims (2)

A laser beam having a repetition frequency of 10 kHz or more and 10 MHz or less is selected as the processing target so that a condensing point aligned with the inside of the sapphire substrate , which is a plate-shaped processing target, moves along a division line of the processing target. A laser scribing method for forming a modified layer by multiphoton absorption along the division line by irradiating an object,
The modified layer is a microcavity having a crack that occurs in the thickness direction of the substrate when irradiated with the laser beam,
The laser light irradiation energy is 4.5 picosecond pulse widths than 2.0 picoseconds under conditions of a predetermined value, the laser scribing method characterized by. A laser scribing device for forming a modified layer by multiphoton absorption inside a sapphire substrate , which is a plate-like workpiece,
A mounting table on which the workpiece is mounted;
A laser irradiation means for irradiating the processing object with a laser beam having a repetition frequency of 10 kHz or more and 10 MHz or less so that a condensing point fits inside the processing object placed on the mounting table;
A moving means for moving the mounting table relative to the laser beam so that the condensing point moves along a division line of the workpiece;
The modified layer is a microcavity having a crack that occurs in the thickness direction of the substrate when irradiated with the laser beam,
The laser illumination means, characterized in conditions where radiation energy is a predetermined value, irradiating a laser beam whose pulse width is set to 4.5 picosecond to 2.0 picoseconds to the workpiece, the Laser scribing device.