JP4736633B2 - Laser irradiation device - Google Patents

Description

  The present invention relates to a laser irradiation apparatus, and more particularly to a laser irradiation apparatus suitable for a laser internal scribing method.

  As a technique for cutting a workpiece such as a substrate or a wafer along a certain line, a technique for forming an array of modified regions by multiphoton absorption inside the workpiece is known. Here, multiphoton absorption inside the workpiece is caused by irradiation with laser light. According to this technique, the object to be processed can be cut from the modified region as a starting point by applying a slight force. This technique is suitable for fine processing because no cutting waste is generated.

  Now, it is known that a plurality of modified region rows are formed inside a workpiece with respect to one cutting scheduled line (Patent Document 1). According to this technique, even when the thickness of the workpiece is larger than the modified region, the workpiece can be easily cut along the scheduled cutting line. Specifically, according to Patent Document 1, one laser beam is branched into two laser beams, and the spread angle of one laser beam is varied from the other. Then, two laser beams are superimposed on each other and irradiated onto the object to be processed through the same condenser lens. Then, since the two laser beams are condensed at different depth positions even through the same condenser lens, a modified region is generated at the different depth positions.

JP 2004-337902 A

  However, according to the apparatus disclosed in Patent Document 1, once the optical system is set, it is difficult to change or adjust the laser power, that is, the light intensity of each of the two laser beams.

  The present invention has been made in view of the above problems, and one of its purposes is to provide an apparatus for irradiating a workpiece with a plurality of laser beams each having an adjustable light intensity.

  The laser irradiation apparatus of the present invention includes a stage on which a workpiece to be transmissive to light having a predetermined wavelength is placed, a laser light source that emits a first laser beam having the predetermined wavelength component, and the first A splitter for splitting one laser beam into a second laser beam and a third laser beam, both of which propagate in the first direction, and the second laser beam and the third laser beam, Two optical elements for condensing the second laser beam and the third laser beam at the two locations, respectively, so that multiphoton absorption occurs at two locations at different depths in the workpiece; The two optical elements are arranged such that the workpiece moves relative to the second laser beam and the third laser beam along a second direction perpendicular to the first direction. Yo And a, a scanning mechanism for relatively moving with respect to the other at least one of the stage. The splitter changes the light intensity of each of the plurality of laser beams.

  In one embodiment, the first laser beam emitted from the laser light source is linearly polarized light. And (a) a first polarization beam splitter that divides the first laser beam into the second laser beam and the fourth laser beam that are two polarization components perpendicular to each other; (B) a first half-wave plate located in the optical path of the first laser beam between the first polarization beam splitter and the laser light source; and (c) optics of the first half-wave plate. A first rotator for rotating the first half-wave plate so that an angle formed by an axis and a polarization direction of the first laser beam is changed; and (d) the fourth laser beam is perpendicular to each other. A second polarizing beam splitter that splits the third and fifth laser beams, which are two polarization components, and (e) the second polarizing beam splitter and the first polarizing beam splitter, The fourth laser beam during A second half-wave plate located in the optical path of the optical system; and (f) the second half-wave plate so that an angle formed by the optical axis of the first half-wave plate and the polarization direction of the fourth laser beam is changed. And a second rotator for rotating the half-wave plate.

  In another aspect, the laser light source is a pulse laser that emits the pulsed first laser beam at a predetermined period. The scanning mechanism is set to move one of the two optical elements and the stage relative to the other in the second direction at a predetermined speed. Here, the distance along the second direction between the two locations is N times the product of the predetermined period and the predetermined speed (N is an integer of 0 or more), and 1/2 of the product. The divider and the two optical elements are installed so as to substantially match the sum of the two.

  According to the above feature, a laser irradiation apparatus that irradiates a workpiece with a plurality of laser beams each having an adjustable light intensity can be obtained.

(1. Laser irradiation device)
A laser irradiation apparatus 100 shown in FIG. 1 includes a laser light source 10 that emits a laser beam 1, a splitter 12 that splits the laser beam 1 into a plurality of laser beams 2, 3, and 4, and three lasers from the splitter 12. Optical elements L1, L2, and L3 for condensing each of the beams 2, 3, and 4, a stage 14 on which the workpiece W is placed, and the stage 14 with respect to the optical elements L1, L2, and L3 in the X-axis direction and And a scanning mechanism 16 that relatively moves in the Y-axis direction. Note that the X-axis direction and the Y-axis direction are directions perpendicular to each other.

  The laser light source 10 includes a solid-state light source femtosecond pulse laser. In this embodiment, titanium sapphire is adopted as the solid light source. Here, the femtosecond pulse laser is a laser that emits pulsed laser light having a pulse width on the order of femtoseconds. Further, the laser beam 1 emitted from the laser light source 10 has wavelength dispersion characteristics. Specifically, the center wavelength of the laser beam 1 is 800 nm, and its half width is about 10 nm. The obtained laser beam 1 has a pulse width of about 300 fs (femtoseconds), a pulse frequency of 1 kHz, and an output of about 700 mW. Furthermore, the laser beam 1 is linearly polarized light.

  As will be described later, the workpiece W of the present embodiment is a substrate made of quartz glass, and therefore has transparency to the wavelength of the laser beam 1. The above configuration of the laser light source 10 is sufficient to cause multiphoton absorption inside the workpiece W. Note that the thickness of the workpiece W is approximately 1.2 mm in this embodiment.

  The splitter 12 splits the laser beam 1 into three laser beams 2, 3, and 4. Here, the splitter 12 is configured so that the three laser beams 2, 3, and 4 all propagate on the same virtual plane in parallel with the Z-axis direction. In the present embodiment, this virtual plane is also parallel to the Y-axis direction. The Z-axis direction is a direction perpendicular to both the X-axis direction and the Y-axis direction. A more detailed description of the configuration of the divider 12 will be given later.

  The optical elements L1, L2, and L3 are all the same condenser lens. Specifically, these are all objective lenses having a magnification of 100, a numerical aperture (NA) of 0.8, and a WD (Working Distance) of 3 mm. However, the optical elements L1, L2, and L3 are installed at different distances from the workpiece W in the laser processing apparatus 100, respectively. For this reason, the optical elements L1, L2, and L3 condense the laser beams 2, 3, and 4 at locations of different depths in the workpiece W, respectively. Note that a modified region due to multiphoton absorption, which will be described later, is generated at a portion (condensing region) where the laser beams 2, 3, and 4 are condensed.

  Here, formation of the modified region by multiphoton absorption will be described. Even if the workpiece W is made of a material that is transparent to light of a predetermined wavelength, absorption occurs when the photon energy hν is much larger than the absorption band gap Eg of the material. This absorption is called multiphoton absorption. In addition, when the pulse width of the laser beam is made extremely short and multiphoton absorption is caused to occur inside the workpiece W, the energy of the multiphoton absorption is not converted into thermal energy, but the ionic valence change, crystallization or A permanent structural change such as polarization orientation is induced to form a refractive index change region. In the present embodiment, this refractive index change region is called a modified region.

(2. Divider)
The configuration and function of the divider 12 will be described in more detail with reference to FIGS. 2 (a), (b) and (c), and FIGS. 3 (a) and 3 (b). As shown in FIG. 2A, the divider 12 includes three half-wave plates K1, K2, and K3, and three rotators R1 and R3 that respectively rotate the three half-wave plates K1, K2, and K3. R2 and R3, three polarization beam splitters BS1, BS2 and BS3, and a beam damper 18 are provided.

  The half-wave plate K1 has a function of rotating the polarization direction of linearly polarized light incident on the half-wave plate K1 by a predetermined angle. This function is described as follows.

  As shown in FIGS. 3A and 3B, the half-wave plate K1 is an optical element having birefringence. Birefringence is represented by a slow axis OPS and a fast axis OPF that are perpendicular to each other in the half-wave plate K1. When linearly polarized light is incident on the half-wave plate K1 from a direction (thickness direction) perpendicular to both the slow axis OPS and the fast axis OPF, the linearly polarized light vibrates in the direction of the slow axis OPS. It is decomposed into a polarization component O propagating through the half-wave plate K1 and a polarization component E propagating through the half-wave plate K1 while oscillating in the direction of the fast axis OPF. Since the speed of the polarization component O is slower than the speed of the polarization component E, when linearly polarized light exits the half-wave plate K1, there is a phase difference between the two polarization components O and E. The magnitude of the phase difference depends on the thickness of the half-wave plate K1. Therefore, the thickness of the half-wave plate K1 is set so that this phase difference is an odd multiple of the half-wavelength. The fast axis OPF is also called an optical axis.

  When the incident linearly polarized light exits the half-wave plate K1, the incident linearly polarized light is emitted as a linearly polarized light in which the two polarization components O and E are combined. As described above, since the phase difference between the two polarization components O and E is an odd multiple of the half wavelength, if the angle between the polarization direction at the time of incidence and the fast axis OPF is θ, the half wavelength plate K1 is emitted. In this case, the polarization direction is rotated by 2θ (twice θ) from the polarization direction at the time of incidence. For example, if linearly polarized light having a polarization direction of 45 ° with respect to the fast axis OPF is incident, the linearly polarized light rotated by 90 ° is emitted from the half-wave plate K1. Each of the half-wave plates K2 and K3 is the same as the half-wave plate K1.

  Referring again to FIG. 2 (a), the rotator R1 is in the linearly polarized light path so that the angle θ between the polarization direction of the linearly polarized light incident on the half-wave plate K1 and the fast axis OPF changes. The half-wave plate K1 is rotated in a vertical plane. As described above, the angle by which the polarization direction is rotated by the half-wave plate K1 is determined depending on the angle θ. That is, the rotator R1 makes the angle at which the polarization direction is rotated by the half-wave plate K1 variable. The configuration and function of the rotators R2 and R3 are the same as the configuration and function of the rotator R1.

  The polarization beam splitter BS1 has two triangular prisms and a polarization reflection film. Here, these two triangular prisms are joined via a polarizing reflection film. When linearly polarized light enters such a polarizing beam splitter BS1, as shown in FIG. 3A, the s-polarized component of the linearly polarized light is reflected in a direction of 90 ° with respect to the incident direction of the linearly polarized light. On the other hand, the p-polarized component of the linearly polarized light is transmitted. Thus, the polarization beam splitter BS1 has a function of separating linearly polarized light into s-polarized light and p-polarized light. The configuration and function of the polarization beam splitters BS2 and BS3 are the same as the configuration and function of the polarization beam splitter BS1.

  Referring to FIG. 2A again, the beam damper 18 is made of a material that absorbs the laser beam emitted from the laser light source 10 (FIG. 1).

  The divider 12 having the above configuration functions as follows.

  The half-wave plate K1 is located on the optical path between the laser light source 10 and the polarization beam splitter BS1. Therefore, as shown in FIG. 2A, the laser beam 1 emitted from the laser light source 10 is incident on the half-wave plate K1. In the present embodiment, the laser beam 1 before entering the half-wave plate K1 is composed of p-polarized light with respect to the polarization beam splitters BS1, BS2, BS3.

  The half-wave plate K1 is set by the rotator R1 so that the fast axis OPF of the half-wave plate K1 forms an angle θ1 (FIG. 3) with respect to the polarization direction of the laser beam 1. For this reason, the half-wave plate K1 rotates the polarization direction of the laser beam 1 by an angle corresponding to the angle θ1.

  As shown in FIG. 2A, the laser beam 1 emitted from the half-wave plate K1 enters the polarization beam splitter BS1. The polarization beam splitter BS1 reflects the s-polarized component of the laser beam 1 in a direction of 90 ° with respect to the incident direction of the laser beam 1. On the other hand, the polarization beam splitter BS1 transmits the p-polarized component of the laser beam 1. Here, the s-polarized component reflected by the polarization beam splitter BS1 is the above-described laser beam 2. Further, the p-polarized component transmitted through the polarizing beam splitter BS1 is denoted as a laser beam 5 for convenience.

  The laser beam 2 is incident on the optical element L1. Then, the laser beam 2 is condensed on the condensing region B1 located at a predetermined depth in the workpiece W by the optical element L1. On the other hand, the laser beam 5 emitted from the polarization beam splitter BS1 is incident on the half-wave plate K2.

  The half-wave plate K2 is set by the rotator R2 so that the fast axis OPF of the half-wave plate K2 forms an angle θ2 (FIG. 3) with respect to the polarization direction of the laser beam 5. For this reason, the half-wave plate K2 rotates the polarization direction of the laser beam 5 by an angle corresponding to the angle θ2.

  As shown in FIG. 2A, the laser beam 5 emitted from the half-wave plate K2 enters the polarization beam splitter BS2. The polarization beam splitter BS <b> 2 reflects the s-polarized component of the laser beam 5 in a direction of 90 ° with respect to the incident direction of the laser beam 5. On the other hand, the polarization beam splitter BS2 transmits the p-polarized component of the laser beam 5. Here, the s-polarized component reflected by the polarization beam splitter BS2 is the laser beam 3 described above. Further, the p-polarized light component transmitted through the polarization beam splitter BS2 is expressed as a laser beam 6 for convenience.

  The laser beam 3 is incident on the optical element L2. Then, the laser beam 3 is focused in the workpiece W by the optical element L2. However, since the distance between the optical element L2 and the surface of the workpiece W is shorter than the distance between the optical element L1 and the surface of the workpiece W as shown in FIG. The condensing region B2 by the element L2 is located deeper than the condensing region B1 by the optical element L1. On the other hand, the laser beam 6 emitted from the polarization beam splitter BS2 enters the half-wave plate K3.

  The half-wave plate K3 is set by the rotator R3 so that the fast axis OPF of the half-wave plate K3 forms an angle θ3 (FIG. 3) with respect to the polarization direction of the laser beam 6. For this reason, the half-wave plate K3 rotates the polarization direction of the laser beam 6 by an angle corresponding to the angle θ3.

  As shown in FIG. 2A, the laser beam 6 emitted from the half-wave plate K3 enters the polarization beam splitter BS3. The polarization beam splitter BS3 reflects the s-polarized component of the laser beam 6 in a direction of 90 ° with respect to the incident direction of the laser beam 6. On the other hand, the polarization beam splitter BS3 transmits the p-polarized component of the laser beam 6. Here, the s-polarized component reflected by the polarization beam splitter BS3 is the laser beam 4 described above. Further, the p-polarized component transmitted through the polarization beam splitter BS3 is denoted as a laser beam 7 for convenience.

  The laser beam 4 is incident on the optical element L3. Then, the laser beam 4 is focused in the workpiece W by the optical element L3. However, since the distance between the optical element L3 and the surface of the workpiece W is shorter than the distance between the optical element L2 and the surface of the workpiece W as shown in FIG. The condensing region B3 by the element L3 is located deeper than the condensing region B2 by the optical element L2. On the other hand, the laser beam 7 emitted from the polarization beam splitter BS 3 enters the beam damper 18 and is absorbed by the beam damper 18.

  Here, paying attention to the half-wave plate K1 again with reference to FIGS. 3A and 3B, the case where the angle θ1 is 0 (zero) ° will be considered. In this case, the fast axis OPF coincides with the polarization direction of the laser beam 1 which is p-polarized light. In this case, even if the laser beam 1 exits the half-wave plate K1, the polarization direction of the laser beam 1 does not change, and the laser beam 1 remains p-polarized. That is, 100% of the laser beam 1 incident on the polarization beam splitter BS1 is p-polarized light. Since the s-polarized component to be reflected by the polarization beam splitter BS1 is 0%, the laser beam 2 does not substantially enter the workpiece W.

  On the other hand, when the angle θ1 is 22.5 °, when the laser beam 1 passes through the half-wave plate K1, the polarization direction of the laser beam 1 is rotated by 45 °. In this case, the ratio between the light intensity of the p-polarized component and the light intensity of the s-polarized component in the laser beam 1 incident on the polarizing beam splitter BS1 is 1: 1. As described above, the s-polarized component is reflected by the polarization beam splitter BS1 and enters the workpiece W as the laser beam 2. Therefore, the light intensity of the laser beam 2 incident on the workpiece W is 50% of the light intensity of the laser beam 1.

  Furthermore, when the above-described angle θ1 is 45 °, when the laser beam 1 passes through the half-wave plate K1, the polarization direction of the laser beam 1 is rotated by 90 °. That is, the laser beam 1 that has passed through the half-wave plate K1 becomes s-polarized light. That is, 100% of the laser beam 1 incident on the polarization beam splitter BS1 becomes s-polarized light. From this, the light intensity of the laser beam 2 incident on the workpiece W is substantially 100% of the light intensity of the laser beam 1.

  Thus, the rotator R1 rotates the half-wave plate K1 in the range of at least 0 ° to 45 ° with respect to the polarization direction of the laser beam 1 from the laser light source 10. If it does so, the angle which the polarization direction of the laser beam 1 rotates changes according to the angle which the half-wave plate K1 rotated. As a result, the ratio of the light intensity of the p-polarized component incident on the polarization beam splitter BS1 to the light intensity of the s-polarized component changes. Here, the s-polarized light is incident on the workpiece W as the laser beam 2 when reflected by the polarization beam splitter BS1, and thus the light intensity of the laser beam 2 incident on the workpiece W is changed by such a configuration. be able to.

  The light intensity of the laser beam 3 is also variable by the rotator R2, the half-wave plate K2, and the polarization beam splitter BS2, as in the case of the light intensity of the laser beam 2. Further, the light intensity of the laser beam 4 is variable by the rotator R3, the half-wave plate K3, and the polarization beam splitter BS3, as in the case of the light intensity of the laser beam 2.

(3. Optical element)
Now, the three optical elements L1, L2, and L3 are the same condenser lens. For this reason, the focal lengths of the optical elements L1, L2, and L3 of the present embodiment are all the same. However, as shown in FIGS. 2A and 2B, these three optical elements L1, L2, and L3 are located at different positions in the Z-axis direction from the surface of the workpiece W on the stage 14. Yes. Thus, the optical elements L1, L2, and L3 condense the laser beams 2, 3, and 4 in the condensing regions B1, B2, and B3 having different depths in the workpiece W, respectively. Further, in the present embodiment, when the condensing regions B1, B2, and B3 are mapped from the Z-axis direction to the XY plane, the images of the condensing regions B1, B2, and B3 mapped to the XY plane are aligned along the Y-axis direction. Looks like they line up.

  In addition, each of the laser beams 2, 3, and 4 propagates on the same virtual plane. In addition, each of the laser beams 2, 3, and 4 travels in parallel with the Z-axis direction on this virtual plane. This imaginary plane is a plane parallel to both the Y-axis direction and the Z-axis direction.

  With such a configuration, a plurality of modified regions are generated by each of the laser beams 2, 3, and 4. Here, since each of the laser beams 2, 3, and 4 is a pulsed laser beam, for example, the plurality of modified regions A <b> 1 by the laser beam 2 have a pitch determined by the pulse period of the laser light source 10 and the relative moving speed of the stage 14. , Aligned along the Y-axis direction. Similarly, a plurality of modified regions A2 and A3 by the laser beams 3 and 4 are also arranged in the Y-axis direction at the above pitch.

  The row of the plurality of modified regions A1, the row of the plurality of modified regions A2, and the row of the plurality of modified regions A3 are arranged in the thickness direction of the workpiece W. Note that a plane parallel to both the Y-axis direction and the thickness direction of the workpiece W is a planned cut surface, and is also the above-described virtual plane. In the present embodiment, the thickness direction of the workpiece W coincides with the Z-axis direction.

  Now, the refractive index of the workpiece W is larger than 1. For this reason, when the laser beam 2 collected by the optical element L1 is incident on the workpiece W, chromatic aberration occurs due to the difference between the refraction angle of the short wavelength component and the refraction angle of the long wavelength component of the laser beam 2. . For this reason, the shape of the condensing region B1 of the laser beam 2 is not actually a point shape but a shape extending in the incident direction of the laser beam 2.

  On the other hand, since the condensing region B2 of the laser beam 3 is located deeper than the condensing region B1 of the laser beam 2, the distance that the laser beam 3 propagates before reaching the condensing region B2 is the condensing region B1. It is longer than the distance that the laser beam 2 propagates to reach, and therefore the influence of the chromatic aberration that the laser beam 3 receives is larger than the influence of the chromatic aberration that the laser beam 2 receives. For this reason, the length of the condensing region B2 is longer than the condensing region B1. As a result, the peak power density of the condensing region B2 becomes smaller than the peak power density of the condensing region B1. From this, even if the modification occurs in the light collection region B1, it may occur that the modification does not occur in the light collection region B2. Note that the peak power density of the condensing region B3 of the laser beam 4 is smaller than the peak power density of the condensing region B2 of the laser beam 3 for the same reason.

  In this embodiment, thanks to the function of the splitter 12 having the above-described configuration, the light intensity of each of the laser beams 2, 3, and 4 can be individually adjusted. Therefore, the splitter 12 sets the light intensity (laser power) of the laser beams 2, 3, and 4 so that the peak power densities of the condensing regions B 1, B 2, and B 3 are almost the same value that is equal to or greater than a predetermined value. Increase in this order.

(4. Laser beam interval)
The respective pitches Pt of the reforming regions A1, A2, A3 are equal to the product of the pulse period of the laser light source 10 and the relative movement speed of the stage 14 along the Y-axis direction. As described above, the pulse frequency (reciprocal of the pulse period) is 1 kHz, and the relative movement speed along the Y-axis direction is 20 mm / sec. Therefore, the values of the pitches Pt of the reformed regions A1, A2, and A3 are expressed as “ Assuming “p”, p is 20 μm. Here, as shown in FIG. 2 (b), it is preferable that the modified regions A1, A2, and A3 are arranged with a half-pitch shift. This is because it is easy to divide the workpiece W along the planned cut surface. In order to realize such modified regions A1, A2, and A3, the divider 12 and the optical elements L1, L2, and L3 are adjusted so that the intervals along the Y-axis direction of the light collecting regions B1, B2, and B3 are increased. N × p + (½) × p. That is, the interval along the Y-axis direction of the light condensing regions B1, B2, and B3 may be made to substantially coincide with the sum of N times the pitch Pt and 1/2 times the pitch Pt. Here, N is an integer of 0 or more.

  As described above, in the present embodiment, the laser beam 1 is divided into the three laser beams 2, 3, and 4. However, the number of laser beams to be divided is not limited to three, and may be divided into at least two laser beams.

  When the laser in the laser light source 10 is a non-polarized laser, the laser light source 10 only needs to have a known polarization conversion element that converts non-polarized light into p-polarized light. Then, the divider 12 can be used without substantially changing the above-described configuration.

  Further, as described above, in the present embodiment, the optical elements L1, L2, and L3 are all the same condenser lens. However, instead of such a configuration, the optical elements L1, L2, and L3 may be condensing lenses having different focal lengths.

  In short, it is only necessary that the laser beams 2, 3, and 4 divided from one laser beam 1 can be condensed on the condensing regions B1, B2, and B3 having different depths. Then, even if only one laser light source can be used economically, if the workpiece W is relatively moved at least once, a row of the modified regions A1, A2, A3 extending in the direction of relative movement is obtained. Can be stacked in the thickness direction. For this reason, even if the thickness of the workpiece W to be cut is sufficiently larger than the respective sizes of the modified regions A1, A2, and A3, the pretreatment (laser) for cutting within the actual machining time is required. Irradiation) can be completed.

  Moreover, in the present embodiment, the laser beams 2, 3, and 4 are incident on the workpiece W while being divided. For this reason, the depth at which the condensing regions B1, B2, and B3 are located can be set by the optical elements L1, L2, and L3 that are independent of each other. From this, the freedom degree in the case of setting the distance along the Z-axis direction (thickness direction) between condensing area | region B1, B2, B3 is high. In addition, what is necessary is just to determine the distance along the thickness direction between condensing area | region B1, B2, B3 according to the material which comprises the workpiece W to an optimal value. Here, the workpiece W of the present embodiment is made of quartz glass, but the workpiece W may be made of a semiconductor. Furthermore, the workpiece W may be a MEMS substrate. In short, the present invention is not limited to the material of the present embodiment or the specification of the laser light source 10 of the present embodiment as long as the modified regions A1, A2, A3 by multiphoton absorption can be formed in the workpiece W.

The schematic diagram of the laser irradiation apparatus of this embodiment. (A), (b) and (c) is a schematic diagram which shows a process target object and the splitter and optical element in a laser irradiation apparatus. (A) is a schematic diagram which shows the polarization direction of the laser beam which passes a half-wave plate and a polarizing beam splitter, (b) is the direction of the optical axis (fast axis) of a half-wave plate, and a half wavelength. The schematic diagram which shows the angle which the polarization direction of the linearly polarized light which injects into a board makes | forms.

Explanation of symbols

A1, A2, A3 ... modified region, B1, B2, B3 ... condensing region, BS1, BS2, BS3 ... polarizing beam splitter, K1, K2, K3 ... half-wave plate, 1-7 ... laser beam, R1, R2 , R3 ... rotator, W ... workpiece, 10 ... laser light source, 12 ... splitter, 14 ... stage, 16 ... scanning mechanism, 18 ... beam damper, 100 ... laser irradiation device.

Claims (1)

A stage on which a processing object having transparency to light of a predetermined wavelength is placed;
A laser light source having a component of the predetermined wavelength and emitting a first laser beam which is linearly polarized light ;
A splitter that divides the first laser light into a second laser beam and a third laser beam that propagate in a first direction perpendicular to a surface on which the workpiece is placed on the stage ;
A first optical element that focuses the second laser beam such that multiphoton absorption occurs at the first focusing position in the workpiece by the second laser beam;
The third laser beam causes multiphoton absorption to occur at a second light collection position that is deeper from the surface of the processing object than the first light collection position in the processing object. A second optical element for condensing the third laser beam;
Relative movement is performed along a second direction which is a straight line intersecting a plane perpendicular to the first direction and a plane including the optical axes of the second laser beam and the third laser beam. And a scanning mechanism for moving the stage relative to the first optical element and the second optical element,
With
The laser light source is a pulse laser that emits the pulsed first laser beam at a predetermined period,
The divider is
(A) a first polarization beam splitter that divides the first laser beam into the second laser beam and the fourth laser beam, which are two polarization components perpendicular to each other;
(B) a first half-wave plate located in the optical path of the first laser beam between the first polarizing beam splitter and the laser light source;
(C) The angle formed by the optical axis of the first half-wave plate and the polarization direction of the first laser beam is
A first rotator for rotating the first half-wave plate,
(D) a second polarization beam splitter that divides the fourth laser beam into the third laser beam and the fifth laser beam, which are two polarization components perpendicular to each other;
(E) a second half-wave plate located in the optical path of the fourth laser beam between the second polarizing beam splitter and the first polarizing beam splitter;
(F) a second rotator for rotating the second half-wave plate so that an angle formed by an optical axis of the first half-wave plate and a polarization direction of the fourth laser beam is changed;
Have
The scanning mechanism is set to move relative to the second direction at a predetermined speed;
The distance between the first optical element and the second optical element along the second direction is N times the product of the predetermined period and the predetermined speed (N is an integer of 0 or more), and the product. The first optical element and the second optical element are installed so as to coincide with the sum of 1/2 of
The power of the third laser beam is greater than the power of the second laser beam, and the power density at the second focusing position is equal to the power density at the third focusing position;
The laser irradiation apparatus characterized by the above-mentioned .

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