JP2006305586A - Method for cutting plate-shaped body, and laser beam machining device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for cutting a plate-shaped body, such as a semiconductor wafer, by irradiating the body with a laser beam, in which the throughput of electronic parts manufactured by dividing the body is improved by raising the cutting speed. <P>SOLUTION: The laser beam of a first wave length having absorbability with respect to a plate-shaped body 1, and the laser beam of a second wave length having permeability with respect to the plate-shaped body 1, are simultaneously condensed, and the condensed beams are irradiated to the plate-shaped body 1. A condensing point 7 of the laser beam of the first wave length is formed on the surface part of the plate-shaped body, and a condensing point 8 of the laser beam of the second wave length is formed in the inside part of the plate-shaped body, by controlling a condensing optical system. Cracking or reforming of the composition of the surface part is caused by linear absorption, reforming of the composition of the inside part is caused by multiphoton absorption, and stress-generating regions are formed in the parts respectively. The plate-shaped body 1 is irradiated with the laser beam along a dividing line, and is thereafter divided along the scanning loci of the laser beam by exerting mechanical impact force. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a plate-like body cutting method for cutting a plate-like body by irradiating a laser beam along a predetermined street (cutting line) and a laser beam generator used in the cutting method. The present invention relates to a method for cutting a semiconductor wafer when a semiconductor chip is manufactured by dividing a wafer, and a laser beam generator used in the method.

  In the semiconductor device manufacturing process, a substantially disc-shaped semiconductor wafer is partitioned into a plurality of regions by streets arranged in a lattice pattern on the surface thereof. Circuits such as IC and LSI are formed in the partitioned areas, respectively, and the semiconductor wafer is cut along the streets to separate the areas where the circuits are formed to manufacture semiconductor chips. In order to cut the semiconductor wafer along the street, a cutting device generally called a dicer is used. This cutting apparatus includes a chuck table for holding a semiconductor wafer as a workpiece, a cutting means for cutting the semiconductor wafer held on the chuck table, and a movement for relatively moving the chuck table and the cutting means. Means. The cutting means has a rotating spindle that rotates at a high speed and a cutting blade mounted on the spindle. The cutting blade is composed of a disk-shaped base and an annular cutting edge mounted on the outer peripheral portion of the side surface of the base. The cutting edge is formed to have a thickness of about 15 μm by fixing diamond abrasive grains having a particle size of about 3 μm to the base by electroforming, for example.

Recently, in order to form circuits such as IC and LSI more finely, a semiconductor wafer having a form in which a low dielectric constant insulator is laminated on the surface of a main body of a semiconductor wafer such as a silicon wafer is manufactured. It is used for practical use. As the low dielectric constant insulator, a material having a dielectric constant lower than that of the SiO ₂ film (dielectric constant k = about 4.1) (for example, about k = 2.5 to 3.6) is used. Examples of such a low dielectric constant insulator include inorganic films such as SiOF, BSG (SiOB), and H-containing polysiloxane (HSQ), and polymer films such as polyimide, parylene, and polytetrafluoroethylene. Examples thereof include organic films and porous silica films such as methyl-containing polysiloxane.

  When a semiconductor wafer in which a low dielectric constant insulator as described above is laminated on the surface portion is cut using the above-mentioned dicer, the low dielectric constant insulator is extremely fragile, resulting in a low-level surface layer in the street vicinity region. The dielectric constant insulator layer may peel off from the semiconductor wafer body. Further, semiconductor wafers tend to be thinned, and the mechanical strength of the semiconductor wafer is reduced, so that the wafer body may be damaged by cutting with a dicer. For such a semiconductor wafer, it is preferable to use a laser cutting apparatus that cuts the semiconductor wafer by irradiating a laser beam instead of the dicer.

  FIG. 4 is a schematic view showing a wafer cutting method using a laser cutting device. In FIG. 4A, the semiconductor wafer is cut by irradiation with a laser beam having an absorptive wavelength. When the condensing point of the laser beam is set on the surface portion of the semiconductor wafer 101, the surface portion of the semiconductor wafer 101 mainly undergoes linear absorption by the laser beam, and this portion is ablated to form a perforated portion. If necessary, the condensing optical system 103 is moved downward in the vertical direction to move the condensing point downward, and the perforated part formed by ablation of the member is extended downward. When the laser beam is scanned along the street, the perforated portion is stretched along the street, and a groove portion along the street is formed on the wafer surface. When a mechanical impact force such as bending or pulling is applied after the groove is formed, a crack is generated starting from the groove and the semiconductor wafer can be divided. The cutting of a semiconductor wafer using a laser beam having such an absorptive wavelength is described in, for example, Japanese Patent Application Laid-Open No. 56-129340.

  In FIG. 4B, the semiconductor wafer is cut by irradiation with a laser beam having a transmissive wavelength. When the condensing point of the laser beam is set inside the semiconductor wafer 101, the internal region of the semiconductor wafer 101 mainly causes multiphoton absorption by the laser beam, and the material composition of the portion is altered. If necessary, the condensing optical system 103 is moved upward or downward in the vertical direction to move the condensing point upward or downward, and the modified region caused by multiphoton absorption is extended along the vertical direction. When the laser beam is scanned along the street, the modified region is stretched along the street, and a substantially linear or substantially strip-shaped modified region along the street is formed inside the wafer. If a mechanical impact force such as bending or pulling is applied after this modified region is formed, it is possible to divide the semiconductor wafer by generating cracks starting from the vicinity of the modified region where thermal stress occurs. Become. Cutting of a semiconductor wafer using a laser beam having such a transmission wavelength is described in, for example, Japanese Patent Application Laid-Open No. 2002-205180.

JP 56-129340 JP 2005-28438 JP 2002-192367 A JP-A-2002-205180 JP2003-88973 JP 2003-88978 A JP 2003-88979 A JP 2004-188475 A

  In a conventional cutting apparatus using a laser beam as shown in FIGS. 4A and 4B, in order to form a sufficiently large perforated portion or modified region that can be a starting point for generating a crack. In addition, it is necessary to irradiate a short pulse laser having a pulse number more than a considerable number of times on substantially the same part on the street, and the time for stopping at the substantially same part on the street during the laser beam scanning becomes long. That is, when a groove is formed on the surface of the semiconductor wafer or a modified region is formed inside the semiconductor wafer in order to divide the semiconductor wafer, a thermally denatured layer depending on the pulse width is generated around the irradiated region, and the cut surface There was a problem that the physical properties of these were impaired.

  The present invention has been made to solve the above-described problems, and can cut a plate-like body such as a semiconductor wafer at high speed without impairing the physical properties of the cut surface by using femtosecond laser pulses. It is an object of the present invention to provide a method and a laser beam generator used for the cutting method.

  In order to solve the above technical problem, according to the present invention, a laser beam of a short-pulse laser with a plurality of wavelengths irradiated from above the plate-like body is condensed on the surface portion and inside of the plate-like body. In particular, in a semiconductor wafer in which a circuit is formed for each region partitioned by streets arranged in a lattice pattern on the surface, a laser beam with a plurality of wavelengths irradiated from above the semiconductor wafer is condensed on the streets, The semiconductor wafer is divided by scribing along the street.

  When irradiating a plate-like body with a laser beam, processing using a laser beam on the surface and inside of the plate-like body is performed at least simultaneously using the wavelength in the absorption region of the plate-like body and the wavelength in the transmission region. The action proceeds simultaneously.

  Further, according to the present invention, the absorptance is improved by multiphoton absorption or the like even at a transmissive wavelength so that the beam can reach the inside of the plate-like body and the modification of the material composition in the vicinity of the condensing region proceeds at high speed Generate the expected high power concentration state. On the other hand, in the surface portion, the power condensing density is set to a lower condition than the inside to achieve thermal absorption. The surface of the plate-like body is processed to form linear perforations by a short-pulse laser with an absorptive wavelength to form a perforated part due to decomposition or a modified part due to alteration, and is transmitted through the inside of the plate-like body. The modified region is formed mainly by generating multiphoton absorption with a short pulse laser having a characteristic wavelength. In the plate-like body, a compressive stress acts on the portion where the laser beam is focused, and a tensile stress acts on the peripheral area, and a thermal stress acts on the peripheral area, thereby generating a residual stress. Cracks easily propagate to the modified region due to residual stress starting from the near-surface processed region formed on the surface. When the laser beam is scanned in a predetermined direction on the plate-like body, cracks progress in the plate-like body along the trajectory. If the plate-like body is thin, the plate-like body can be divided only by the formation of the cracks. If the plate-like body is thick, the plate-like body can be divided by applying a mechanical impact force such as bending or pulling to the semiconductor wafer after the scanning of the laser beam is completed.

  According to the present invention, the near-surface processed region and the modified region are formed simultaneously in the direction perpendicular to the surface of the plate-like body, and the near-surface processed region is caused by the residual stress generated by the focusing of the laser beam. Cracks propagate easily toward the modified region as a starting point, so the plate can be divided at high speed only by scanning the laser beam in a predetermined direction on the plate or by applying a mechanical external force after scanning. It becomes possible to do. In the case of dividing a semiconductor wafer, the semiconductor wafer can be divided at a high speed, so that the throughput of manufacturing a semiconductor chip is improved.

  According to the present invention, the power removal density of the short pulse laser at the surface portion of the plate-like body can be suppressed to a relatively low level, so that the amount of workpiece removal at the surface portion of the plate-like body can be reduced. Semiconductor wafers generate debris (evaporated product) by irradiating a laser beam. However, according to the present invention, debris adheres to bonding pads formed on a semiconductor chip by reducing the amount of debris generated. Can be prevented to a great extent. Further, in the vicinity of the surface portion, grooves are formed by a decomposition action with almost no melting and re-solidification, and the generation amount of debris can be reduced, so that the generation of microcracks that cause a decrease in the reliability of the semiconductor element can be prevented to a considerable extent. . It is possible to improve the yield of semiconductor chips by realizing prevention of debris adhesion, prevention of microcracks, and the like.

  In addition, since the power collection density of the short pulse laser on the surface of the plate-like body can be suppressed to a relatively low level, the processing width along the street can be reduced, and the area of the semiconductor chip on the semiconductor wafer Can be taken widely. Furthermore, by using a short pulse laser for dividing the semiconductor wafer, it is possible to prevent thermal damage to the film formation layer in the vicinity of the semiconductor wafer surface.

  Further, the ratio of the energy of a laser beam having a wavelength belonging to an absorption region mainly absorbed linearly and the energy of each of one or a plurality of laser beams having a wavelength belonging to a transmission region mainly absorbed by multiphotons is arbitrarily set. Therefore, it is possible to set optimum machining conditions according to the material of the plate-like body to be machined.

  Further, one or a plurality of pulses of a laser beam having a wavelength belonging to an absorption region mainly absorbed linearly with respect to the plate-like body, and having a wavelength belonging to a transmission region mainly absorbing multiphotons with respect to the plate-like body. The laser beam is configured to be able to irradiate the plate-like body with a delay by a predetermined time from the pulse of the laser beam, so that the laser beam having a wavelength belonging to the transmission region is not affected by the processing state of the surface portion. It is possible to reach the inside, and it becomes possible to improve the processing efficiency.

  In addition, since the condensing optical system of the laser beam generator can be moved in the optical axis direction of the laser beam, it is possible to extend the near-surface processed region and the modified region in a direction perpendicular to the plate-like body surface. Thus, it becomes possible to cope with cutting of plate-like bodies having various thicknesses.

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

  FIG. 1 is an explanatory view showing a dividing process of a silicon wafer which is a plate-like semiconductor. FIG. 1A shows a processing state of a semiconductor wafer by a laser beam, and FIG. 1B shows a cross section along the street of the processed semiconductor wafer. The semiconductor wafer 1 is normally sucked by a vacuum chuck onto a wafer table (not shown) mounted on an XY table. A laser beam incident from the laser light source substantially in parallel is condensed by the condensing optical system 2 and irradiated toward the wafer. The laser beam emitted from the laser light source includes a laser beam 3 having a first wavelength in an absorption region and a laser beam 4 having a second wavelength in a transmission region with respect to a wafer that is a plate-like body. The laser beam 3 having the first wavelength is condensed by the condensing optical system 2 to become a convergent beam 5, and a condensing point 7 is formed on the surface portion of the semiconductor wafer 1. The laser beam 4 having the second wavelength is condensed by the condensing optical system 2 to become a convergent beam 6, and a condensing point 8 is formed inside the semiconductor wafer 1. In this embodiment, a laser beam having two types of wavelengths is irradiated. In order to increase the processing speed, for example, a laser beam having two or more types of wavelengths in the transmission region is used, and three or more types of wavelengths are combined. The semiconductor wafer may be irradiated with a laser beam having

  A laser beam having two types of wavelengths is generated by performing wavelength conversion using a nonlinear optical crystal based on a fundamental wave of laser oscillation. Taking a silicon wafer as an example, the wavelength in the wavelength region of 400 nm to 1.1 μm, which is the wavelength in the visible light region, is used as the first wavelength in the absorption region. In addition, as the second wavelength in the transmission region, a wavelength in the wavelength region of 1.3 μm to 1.7 μm is used. In particular, it is preferable to use a wavelength of 780 nm at which the absorption is substantially maximum as the first wavelength, and a wavelength of 1560 nm that is twice the first wavelength as the second wavelength.

  When a laser beam having two types of wavelengths as described above is condensed using, for example, the condensing optical system 2 provided as a convex lens, the laser beams of the respective wavelengths are aligned along the optical axis direction due to chromatic aberration. It has condensing points at different positions. As shown in FIG. 1, when the beam having the first wavelength in the absorption region is condensed on the surface of the semiconductor wafer, the laser beam having the second wavelength in the transmission region is condensed inside the semiconductor wafer. . In the surface portion of the semiconductor wafer on which the laser beam of the first wavelength is condensed, a near-surface processed region 9 is formed mainly by linear absorption of the laser beam. In the case of a short pulse laser in which the pulse time ends before the absorbed light energy changes to heat, in this near-surface processed region 9, grooves are formed without melting the semiconductor wafer, or A modified region is formed by the alteration of the material composition.

  In addition, inside the semiconductor wafer where the laser beam of the second wavelength is condensed, the material composition is altered and the modified region 10 is formed mainly by multiphoton absorption of the laser beam. Since compressive stress acts on the portion where the laser beam is focused and tensile stress acts on the peripheral region thereof, residual stress is applied to the near-surface processed region 9 and its peripheral region, the modified region 10 and its peripheral region. Will occur. Since a short pulse laser is used as the laser beam irradiated to the semiconductor wafer, the pulse width of the laser beam having the second wavelength that causes multiphoton absorption can be controlled to set a higher power condensing density. Is possible. In addition, by moving the condensing optical system 2 in a direction perpendicular to the surface of the semiconductor wafer 1, the condensing point 7 and the condensing point 8 are moved downward, so that the near-surface processed region 9 and the modified region 10. Can be processed so as to extend in the vertical direction. Furthermore, it is preferable that the ratio of the energy of the laser beam of the first wavelength and the energy of the laser beam of the second wavelength can be arbitrarily changed, and thus, depending on the material of the plate-like body to be processed. It is possible to set optimum machining conditions.

  As described above, a surface extending in a direction perpendicular to the surface of the semiconductor wafer along the street is formed by forming a perforated portion or a modified region by linear absorption at the surface portion of the semiconductor wafer and multiphoton absorption inside. A residual stress generation region is formed in the direction. After the completion of the scanning of the laser beam along the street, when a breaking process is performed to apply a mechanical impact force by bending to the semiconductor wafer, the residual stress generation region formed inside starts from the near-surface processed region 9. Cracks propagate and the semiconductor wafer can be easily divided along the street. In this case, compared with the conventional method of dividing only after forming the machining groove, the power collection density of the laser beam irradiated to the near-surface machining region 9 can be set low, so that the amount of debris generated is greatly increased. While being able to reduce, the process width | variety of the surface vicinity process area | region 9 can be narrowed. When the semiconductor wafer is thin, it is possible to divide the semiconductor wafer only by scanning the laser beam without applying a mechanical impact force.

  Further, when the thickness of the plate-like body is small, the condensing point of the laser beam having the second wavelength is formed in the vicinity of the back surface of the plate-like body, and the vicinity of the back surface of the plate-like body is processed. It becomes possible by implementation. Further, even when two types of laser beams having different wavelengths are generated from laser beams having the same fundamental wave, the respective optical path lengths may be different. In such a case, the optical path length of the laser beam having the second wavelength in the transmission region with respect to the semiconductor wafer is made shorter than the optical path length of the laser beam having the first wavelength in the absorption region. It is possible to adopt a configuration in which a laser beam having a wavelength of 1 arrives first in time. In this case, the laser beam having the second wavelength can be incident inside without being obstructed by the processing of the surface portion.

  FIG. 2 is a diagram showing an example of the configuration of a laser beam generator used in the cutting method according to the present invention. The mode-locked optical fiber laser oscillator 21 outputs an ultrashort pulse oscillation light 22. The optical fiber 23 increases the pulse width by stretching the pulse width by the wavelength dispersion action on the input ultrashort pulse oscillation light 22, and generates a relatively long pulse laser beam 24 with a reduced peak output. Output.

  Next, a laser beam 24 is incident on a regenerative amplifier 25 using, for example, Ti-added sapphire crystal, which is a gain medium having a broadband gain, to obtain a laser beam output 26 in which pulse energy is amplified in a wide band. The regenerative amplifier 25 is optically pumped by using, for example, an SHG-Nd: YAG laser device 27 that obtains a laser output of second harmonic wavelength conversion of the Nd: YAG laser.

  A well-known pulse compressor 28 using a diffraction grating pair inputs an amplified laser beam 26 and performs pulse compression. As a result, the pulse width is compressed to a pulse width close to that before stretching, and returned to a short pulse again. That is, the long pulse laser beam pulse-stretched by the regenerative amplifier 25 becomes a short pulse beam 29 having a high peak output value by temporally compressing the pulse energy amplified in the long pulse state.

  Next, the short pulse beam 29 having the high peak output value is incident on the optical parametric amplifier 30 having the nonlinear optical crystal for optical parametric amplification, and the nonlinear optical crystal is optically excited. As a result, a laser beam including at least two types of frequencies composed of the signal light frequency component ωs, which is the optical parametric amplification wavelength, and the idler light frequency component ωi is extracted from the nonlinear optical crystal by wavelength conversion. The optical parametric is a well-known technique in principle. If the frequency of the pumping light is ω, there is ω = ωs + ωi between the signal light frequency ωs obtained as the oscillation output by the optical parametric amplification and the frequency ωi of the idler light. A relationship is established. When ωs = ωi, a degenerate double wavelength pulse output is obtained. The optical parametric amplifier 30 outputs a laser beam 31 having a first wavelength and a laser beam 32 having a second wavelength based on the principle of optical parametric amplification. The laser beam of the first wavelength and the laser beam of the second wavelength generated in this way are irradiated onto the semiconductor wafer 1 via the condensing optical system 2 shown in FIG. And a condensing point is formed inside.

  FIG. 3 is a diagram showing an example of another configuration of the laser beam generator used in the cutting method according to the present invention. A short pulse laser oscillation fundamental wave beam 42 output from a known femtosecond laser oscillator 41 is split into two beams 44 and 45 by a beam splitter 43. The white light generator 47 receives the laser beam 44 and outputs coherent light 48 having a white spectrum. The coherent light 48 is reflected by the mirror 49 and the dichroic mirror 50 and enters the optical parametric amplifier 51 as seed light. Further, the laser beam 45 having the fundamental frequency passes through the dichroic mirror 50 and enters the optical parametric amplifier 51. The optical parametric amplifier 51 excites the nonlinear optical crystal with the power of the fundamental frequency, and the component of the frequency ωs and the component of the frequency ωi are included in the signal light contained in the seed light beam 48 simultaneously guided into the crystal. Is selectively amplified. As a result, the laser beam having the fundamental frequency ω is converted into the laser beam 52 having the frequency ωs and the laser beam 53 having the frequency ωi. The laser beam of the first wavelength and the laser beam of the second wavelength generated in this way are irradiated onto the semiconductor wafer 1 via the condensing optical system 2 shown in FIG. And a condensing point is formed inside.

  When the pulse width is extremely narrow, the pulses may not reach the optical parametric amplifier 51 at the same time because the optical path lengths of the optical paths 44 to 48 and the optical path 45 are different. In this case, it is possible to appropriately extend the optical path 45 so that it matches the optical path length of the optical paths 44-48 so that the seed light 48 and the excitation light 45 exist in the same space in time.

  The application example of the present invention is not limited to the cutting of a silicon wafer, but can be widely applied to laser precision processing of a semiconductor substrate. By using the present invention, it is possible to improve the throughput of manufacturing electronic components and to improve the product yield by reducing the amount of processed removal.

Explanatory drawing which shows the division | segmentation process of the silicon wafer which is a plate-shaped semiconductor. The figure which shows an example of a structure of the laser beam generator used for the cutting method by this invention. The figure which shows the other example of a structure of the laser beam generator used for the cutting method by this invention. Schematic which shows the wafer cutting method by a laser cutting device.

Explanation of symbols

1: Semiconductor wafer, 2: Condensing optical system, 3, 4: Laser beam, 5, 6: Converging beam, 7, 8: Condensing point, 9: Surface processing region, 10: Modified region, 21: Mode Synchronous fiber laser oscillator, 23: optical fiber, 25: regenerative amplifier, 27: YAG laser device, 28: pulse compressor, 30: optical parametric amplifier, 41: femtosecond laser oscillator, 43, 50: dichroic mirror, 46, 49: mirror, 47: white light generator, 51: optical parametric amplifier, 101: semiconductor wafer, 102: circuit unit, 103: condensing optical system, 104: optical axis, 105: laser beam, 106: convergent beam, 107 108: Focusing point

Claims (12)

  A short pulse laser beam including two or more wavelengths is condensed and irradiated to the plate-like body, and a condensing point of the laser beam is formed on the surface of the plate-like body, and 1 inside the plate-like body. Or the cutting method of the plate-shaped body which forms a some condensing point and cut | disconnects a plate-shaped body by scanning a laser beam along a cutting direction.   A short pulse laser beam including two or more wavelengths is condensed and irradiated to the plate-like body, and a condensing point of the laser beam is formed on the surface of the plate-like body, and 1 inside the plate-like body. Alternatively, a plate-like body cutting method in which a plurality of condensing points are formed, a laser beam is scanned along the cutting direction, and then a plate-like body is cut along a processing locus by the laser beam by applying a mechanical external force. One wavelength included in the laser beam applied to the plate-like body is a wavelength belonging to an absorption region that is mainly linearly absorbed by the plate-like body,
The other wavelength included in the laser beam applied to the plate-like body is a wavelength belonging to a transmission region mainly absorbed by multiphotons by the plate-like body. A method for cutting a plate-like body. One wavelength included in the laser beam applied to the plate-shaped body is about 780 nm,
3. The plate-like body according to claim 1, wherein another wavelength included in the laser beam applied to the plate-like body is a wavelength belonging to a wavelength region of 1.3 μm to 1.7 μm. Cutting method.   The energy of a laser beam having a wavelength belonging to an absorption region that is mainly linearly absorbed by the plate-like body, and each of one or a plurality of laser beams having a wavelength belonging to a transmission region mainly absorbed by the plate-like body by multiphoton absorption The ratio of energy can be changed arbitrarily, The cutting method of the plate-shaped body of Claim 1 or Claim 2 characterized by the above-mentioned.   A pulse of a laser beam having a wavelength belonging to the absorption region mainly absorbed linearly by the plate-like body, and a pulse of one or a plurality of laser beams having a wavelength belonging to the transmission region mainly absorbed by the plate-like body by multiphotons 3. The method for cutting a plate-like body according to claim 1, wherein the plate-like body is irradiated with a delay by a predetermined time. A short-pulse laser beam having a wavelength belonging to an absorption region that is mainly linearly absorbed by the plate-like object to be processed, and one or more wavelengths belonging to a transmission region that is mainly absorbed by multiphotons by the plate-like member. A laser light source for outputting a short pulse laser beam so that each has a substantially identical optical axis;
A laser beam generating apparatus comprising: a condensing optical system that condenses a laser beam including two or more wavelengths irradiated from the laser light source.   8. The laser beam generator according to claim 7, wherein the wavelength belonging to the absorption region is about 780 nm, and the wavelength belonging to the transmission region is a wavelength belonging to a wavelength region of 1.3 μm to 1.7 μm.   8. The laser beam generator according to claim 7, wherein the condensing optical system is movable in the optical axis direction of the laser beam. The ratio between the energy of a laser beam having a wavelength belonging to an absorption region that is mainly linearly absorbed and the energy of each of one or more laser beams having a wavelength belonging to a transmission region that is mainly absorbed by multiphotons is arbitrarily changed. The laser beam generator according to claim 7, wherein the laser beam generator can be used.   A pulse of a laser beam having a wavelength belonging to an absorption region mainly absorbed linearly is delayed by a predetermined time from a pulse of one or a plurality of laser beams having a wavelength belonging to a transmission region mainly absorbing multiphotons. 8. The laser beam generator according to claim 7, wherein the laser beam generator outputs the laser beam.   8. The laser beam generator according to claim 7, wherein a fundamental oscillation wavelength of a sapphire laser added with Ti (titanium) is used as a wavelength belonging to the absorption region.

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