JP4880820B2 - Laser assisted machining method - Google Patents

Laser assisted machining method Download PDF

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Publication number
JP4880820B2
JP4880820B2 JP2001012372A JP2001012372A JP4880820B2 JP 4880820 B2 JP4880820 B2 JP 4880820B2 JP 2001012372 A JP2001012372 A JP 2001012372A JP 2001012372 A JP2001012372 A JP 2001012372A JP 4880820 B2 JP4880820 B2 JP 4880820B2
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laser
material
processing method
laser beam
assisted processing
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JP2002210730A (en
JP2002210730A5 (en
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マルティンキャビティス アンドリウス
ヨードカシス サウリウス
弘明 三澤
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株式会社レーザーシステム
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/08Devices involving relative movement between laser beam and workpiece
    • B23K26/083Devices involving movement of the workpiece in at least one axial direction
    • B23K26/0853Devices involving movement of the workpiece in at least in two axial directions, e.g. in a plane
    • B23K26/0861Devices involving movement of the workpiece in at least in two axial directions, e.g. in a plane in at least in three axial directions
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/36Removing material
    • B23K26/38Removing material by boring or cutting
    • B23K26/382Removing material by boring or cutting by boring
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/36Removing material
    • B23K26/40Removing material taking account of the properties of the material involved
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00Materials to be soldered, welded or cut
    • B23K2103/50Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention provides a laser-assisted processing that uses a laser beam to form extremely small holes in a material to be processed.MethodIn particular, in the case of using silica glass, sapphire, or diamond as a material to be processed, laser assisted processing suitable forMethodAbout.
[0002]
[Prior art]
Conventionally, as a processing method for performing extremely minute processing on a work material such as silicon or glass, there are a photolithography technique, an imprinting technique, an etching technique, a sputtering technique, and the like used in a semiconductor manufacturing process. Are known.
[0003]
[Problems to be solved by the invention]
By the way, in the processing method using the above-described etching technique or sputtering technique, only two-dimensional processing in the vicinity of the surface portion of the material to be processed can be performed, and three-dimensional processing extending into the processing material cannot be performed. Therefore, for example, processing for forming a hole reaching the inside of the material to be processed cannot be performed by such a processing method.
[0004]
Further, in the above-described processing method, it is not possible to process a hard material such as diamond or sapphire. Therefore, conventionally, when processing a hard material such as diamond to form a very small hole, for example, it has been processed using a drill with a very small diameter. However, it is difficult to form a hole with a very small diameter such as several μm to several tens of μm by a drill, and when a hole with a smaller diameter is to be formed, it is no longer possible with a drill. Processing becomes impossible.
[0005]
Conventionally, laser processing has been proposed as processing for diamond. However, in the laser processing for diamond, it is difficult to make the processed surface smooth, and it has not been possible to perform processing to form extremely minute holes having smooth walls.
[0006]
Therefore, the present invention has been proposed in view of the above-described circumstances, and it is easy and reliable to form extremely fine holes even on hard work materials such as diamond and sapphire. The present invention aims to provide a laser-assisted processing method that can perform three-dimensional processing up to the inside of a material to be processed and that can form a smooth processing surface. .
[0007]
[Means for Solving the Problems]
  In order to solve the above-mentioned problems, laser-assisted machining according to the present inventionMethodIsA work material made of a transparent material is focused and irradiated with a laser beam, and the irradiation position of the laser beam is scanned including the position on the surface of the work material at least at one position in the work material. The portion of the material to be processed that has been irradiated with the laser beam is removed by etching, and the portion is made a hole. In the laser-assisted processing method, the present invention is such that the material to be processed is any one of silica glass, sapphire, and diamond. The present invention is characterized in that a hydrofluoric acid solution or argon gas plasma is used as an etchant in the etching process.
[0008]
  Furthermore, in the laser-assisted processing method according to the present invention, the laser beam condensed by the condensing optical system using the axicon lens is on the surface of the processing material with respect to the processing material made of a transparent material. A region including a position and irradiating a region extending inside the workpiece material is removed, a portion of the workpiece material irradiated with the laser beam is removed, and the portion is used as a hole. In the laser-assisted processing method according to the present invention, the material to be processed is silica glass.
[0009]
  Further, according to the present invention, in the laser assisted processing method, the portion of the material to be processed that has been irradiated with the laser beam is removed by an etching process. In the laser-assisted processing method, the present invention is such that the material to be processed is either sapphire or diamond. The present invention is characterized in that a hydrofluoric acid solution or argon gas plasma is used as an etchant in the etching process.
[0010]
  Further, according to the present invention, in each of the laser-assisted processing methods described above, the laser beam is a pulse laser having a pulse duration of femtosecond to picosecond order.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.
[1] Laser-assisted machining according to the present inventionMethodAs shown in FIG. 1, a laser beam 2 is condensed and irradiated onto a work material 1 made of a transparent material, and the irradiation position of the laser beam 2 is at least one place in the work material 1. Scanning is performed including a position on the surface of the material 1 to be processed, and the portion of the material 1 to be irradiated with the laser beam 2 is removed by etching, and this portion is used as a hole.
[0012]
Here, the laser beam 2 is emitted from the laser light source 3, enters the objective lens 7 through the attenuator 4, the beam expander 5, and the half mirror 6, and the surface portion of the work material 1 or the work piece. It is condensed inside the material 1. The attenuator 4 is a filter that performs attenuation by polarized light for adjusting the power of the laser beam 2 irradiated to the workpiece material 1. This optical system constitutes a microscope having a magnification of about 100 times. As the objective lens 7, a lens having a numerical aperture (NA) of about 1.35 can be used. When the material to be processed 1 is silica glass, the condensing spot of the laser beam in the silica glass is about 0.78 μm when the wavelength of the laser beam is 795 nm. Further, when the wavelength of the laser beam is 480 nm, it is about 0.47 μm.
[0013]
As the laser light source 3, a pulse laser whose pulse duration is on the order of femtosecond (fsec) to picosecond (psec) is used. As such a laser light source 3, for example, a titanium-sapphire laser (Ti: Sapphire laser) can be used. In this case, the oscillation wavelength is 795 nm. Further, as the duration and repetition frequency of the laser pulse, for example, a 120 fsec (FWHM) pulse can be generated at a repetition frequency of 1 kHz by using a generation amplifier in combination. The laser power is 0.30 μJ per pulse.
[0014]
The energy that the laser beam 2 gives to the work material is 5 J / cm.2~ 50J / cm2It will be about. 5J / cm2When the material 1 to be processed is silica glass, this corresponds to a threshold value for causing a structural change necessary for processing to the silica glass. This energy is adjusted by the attenuator 4.
[0015]
Scanning of the irradiation position of the laser beam 2 on the workpiece 1 is performed by placing the workpiece 1 on an XYZ stage (three-dimensional stage) 8 and moving it. The XYZ stage 8 is configured to be movable in any of the three-dimensional directions indicated by arrows X, Y, and Z in FIG. The moving speed of the XYZ stage 8 is about 125 μm per second. The XYZ stage 8 is controlled and driven by a computer device 10 via a driver 9. That is, the computer apparatus 10 drives the XYZ stage 8 according to a predetermined program so that the condensing point of the laser beam 2 is scanned on an arbitrary predetermined locus in the work material 1. To.
[0016]
Further, the portion of the work material 1 irradiated with the laser beam 2 is observed by the CCD camera 11 through the objective lens 7 and the half mirror 6. The video imaged by the CCD camera 11 is displayed on the monitor 12 and recorded by a video recording device (VTR) 13. Further, the work material 1 is illuminated by the illumination device 14 via the filter 15.
[0017]
The material to be processed 1 is sapphire or diamond in addition to the silica glass described above.
[0018]
When the irradiation and scanning of the laser beam 2 on the work material 1 are completed, the irradiated portion has undergone a structural change due to optical energy, resulting in a change in refractive index.
[0019]
When the work material 1 is diamond, carbonization may be caused by irradiation with a laser beam. In addition, even when the material 1 to be processed is silica glass, there is a case where dirt is generated after the laser beam irradiation. Such carbides and dirt can be removed, for example, by ultrasonic cleaning, and can be removed by cleaning with an acetone solution or annealing at 300 ° C. for about 1 hour.
[0020]
Next, the material to be processed 1 is etched using an etchant (etching solution or etching gas). By this etching process, the portion of the work material 1 irradiated with the laser beam 2 is melted and removed from the work material 1.
[0021]
Scanning with the laser beam 2 is performed including a position on the surface of the material 1 to be processed, at least one point in the material 1 to be processed. For this reason, the etchant dissolves the portion irradiated with the laser beam on the surface portion of the material to be processed 1 and penetrates into the portion irradiated with the laser beam inside the material to be processed 1 from this portion. go. Further, the portion dissolved by the etching process and removed from the work material 1 is discharged to the outer side of the work material 1 from the portion of the surface portion of the work material 1 irradiated with the laser beam. The Then, a portion subjected to the laser beam irradiation from the workpiece material 1 is removed by an etching process, so that a smooth processed surface is formed.
[0022]
As an etchant in this etching process, a hydrofluoric acid (hydrofluoric acid: HF) solution can be used in so-called wet etching. In so-called dry etching, argon (Ar+) Gas plasma can be used.
[0023]
Examples of the concentration and components of the hydrofluoric acid solution that is an etchant in wet etching include 5.4 wt% HF aqueous solution (HF (48%): H2O = 1: 9 (volume ratio)), 13.4 wt% NH4HF2Solution (HF (50%): NH4HF2(40%) = 1: 9 (volume ratio)) (hereinafter referred to as buffered hydrofluoric acid), or HF, HNO3Aqueous solution (HF (48%): H2O: HNO3(70%) = 15: 300: 10 (volume ratio)) or the like can be used.
[0024]
By using such an etchant, for example, by performing an etching process for a predetermined time of about 20 minutes to 480 minutes (8 hours), the portion irradiated with the laser beam 2 is removed from the work material 1. As shown in FIG. 2, a hole is formed.
[0025]
FIG. 3 is a graph showing the progress of the etching process for silica glass when each of the above-described etchants is used. In FIG. 3, (a), (c), and (e) show the expansion state according to progress of the etching process of the diameter of the vertical hole formed in the workpiece material, and (b), (d), and ( f) shows the depth according to the progress of the etching process of the vertical hole. (A) and (b) show the case where a 5 wt% HF aqueous solution is used as an etchant, and (c) and (d) show HF, HNO as etchants.3A case where an aqueous solution is used is shown, and (e) and (f) show a case where buffered hydrofluoric acid is used as an etchant.
[0026]
By the way, in order to practically apply the minute three-dimensional pattern formed by the laser beam irradiation and the etching process as described above, it is confirmed that the obtained pattern is actually a hole, and a different chemical solution. Needs to flow into the hole (channel).
[0027]
For this reason, HF, HNO as etchants3The structure etched with an aqueous solution was immersed in a rhodamine dye isopropyl alcohol solution. After the surface of the sample became clean, the rhodamine photoluminescence intensity distribution was confirmed with a laser scanning confocal microscope. For photoluminescence excitation, 540 nm laser excitation was used. According to the confirmed photoluminescence intensity distribution, as shown in FIG. 4, the rhodamine dye solution easily penetrated into pores formed in silica (quartz). According to this result, it can be seen that the above-described laser-assisted processing method can be applied to chemical production of a small portion in a small region.
[0028]
In order to clarify the mechanism of the observed etching phenomenon, it is necessary to consider two important points. That is, (i) the relationship between the very fast etching rate along the formed pattern and the selection of the etching solution is thin, but (ii) the etching rate in the perpendicular direction is strongly related to the specific etching solution. . The reactivity that varies depending on the etching solution can be explained by the following chemical reaction of etching.
[0029]
[Expression 1]
[0030]
In the diluted HF solution, the following equilibrium relationship is established.
[0031]
[Expression 2]
[0032]
The effects of these radicals on the quartz etching process are different. If the fluoride concentration is very low, the etching process is mainly HF.2 Is done by. When the concentration is 0.1 mol / l, HF2 And (HF)2Etching by was found to be equivalent. Finally, at high concentrations, (HF)2The contribution of etching by is large. Furthermore, for reproducible etching, HF2 It has been found that the contribution from the etching mechanism needs to be suppressed. HF2 There are two ways to eliminate the reaction: adding acid to the HF solution or greatly reducing the overall HF concentration. Therefore, this makes the HF aqueous solution dilute and HF, HNO.3The observed difference between the etching process with an aqueous solution (fluoride concentration greater than 2 mol / l) and the etching process with buffered hydrofluoric acid can be explained. This is because buffered hydrofluoric acid is mostly HF2 And FIt is because it consists of.
[0033]
The anisotropy of the etching rate in the direction of the pattern that causes the most structural change in quartz and the direction perpendicular thereto can be partially explained by the difference in diffusion originating from the cylindrical cavity. The diffusion along the portion where the structural change has occurred can be considered as a one-dimensional diffusion process in which a fresh etchant is supplied. The solution of the one-dimensional diffusion equation (Fick's first law) is as follows.
[0034]
[Equation 3]
[0035]
Here, N is the concentration and D is the independent diffusion coefficient.
[0036]
[Expression 4]
[0037]
Here, x and t are a space axis and a time axis, and N0Is the initial value of concentration. The initial condition for obtaining this solution is N = N for one-dimensional quasi-infinite samples at x = 0 and t> = 0.0N = 0 at x> 0 and t = 0. This corresponds to the experimental conditions, where the etchant is supplied to the surface of the sample at point x = 0. If diffusion along other coordinates, for example y, is added with the same diffusion coefficient D, it is formally described as:
[0038]
[Equation 5]
[0039]
According to this equation, the concentration flow (one-dimensional diffusion along x) along the part of the quartz workpiece where the structural change occurred is the concentration in the other direction (actually the lateral direction of the etching channel). In effect, it will spread within the cylindrical cavity during the etching process, i.e. over time.
[2]
Next, in the laser-assisted processing method according to the present invention, as shown in FIG. 5, the laser beam is condensed by a condensing optical system using an axicon lens (a conical lens whose axis is positioned on the optical axis) 16. A laser beam (Bessel beam) 2 is irradiated on a work material 1 made of a transparent material to a region including a position on the surface of the work material 1 and extending inside the work material 1. A part of the workpiece 1 irradiated with the laser beam 2 is removed, and the part is used as a hole.
[0040]
The laser beam 2 is a pulse laser whose duration of pulses emitted from the laser light source 3 is on the order of femtoseconds to picoseconds, as in the above-described embodiment. Further, as described above, the work material 1 is silica glass, sapphire, diamond, or the like. When the material to be processed is sapphire or diamond, as described above, the portion irradiated with the laser beam of the material to be processed 1 is removed by etching, but the material to be processed is silica glass. In this case, the etching process is not particularly necessary.
[0041]
The laser beam 2 emitted from the laser light source 3 has its pulse repetition rate and energy controlled by a shutter and a neutral density attenuator S + A, and is once condensed by an axicon lens 16 and diffused again. In the light collection by the axicon lens 16, as shown in FIGS. 6A and 6B, a focal point extending in the optical axis direction is formed. The diffused light is converged by the first lens 17 (f = 100 mm), and further converged by the second lens 18 (f = 30 mm). The workpiece material 1 is placed on the convergence point of the laser beam 2 by the second lens 18. In this laser-assisted processing method, the laser beam 2 is focused on a region having a length in the optical axis direction, so that a hole having a certain length can be formed without scanning the material 1 to be processed. Can do.
[0042]
The laser beam 2 that has passed through the workpiece 1 is imaged by the CCD camera 11 through the third lens 19 (f = 16 mm).
[0043]
The processing conditions in this laser-assisted processing method are as follows, for example. That is, the laser light source 3 is a titanium-sapphire laser (Ti: Sapphire laser), and the oscillation wavelength is 795 nm. The duration of the laser pulse is 170 fsec (femtosecond).
[0044]
When the workpiece material is silica glass, the energy given by the laser beam is 6.8 J / cm.2(The thickness of the workpiece is 240 μm, and the energy of the laser beam incident on the axicon lens is about 25 μJ per pulse).
[0045]
When the work material is sapphire, the energy given by the laser beam is 150 J / cm.2(The thickness of the workpiece is 150 μm, and the energy of the laser beam incident on the axicon lens is about 30 μJ per pulse).
[0046]
Etchant used for the etching process is HF, HNO as in the above embodiment.3Aqueous solution (HF (48%): H2O: HNO3(70%) = 15: 300: 10 (volume ratio)). When a hole of about 14 μm is formed in a silica glass cylinder having a length of about 86 μm, the etching process time is about 16 hours.
[0047]
Hereinafter, it will be described that a laser beam condensed by a condensing optical system using an axicon lens becomes a so-called Bessel beam.
[0048]
The condition for the non-diffracting scalar field propagating in free space was first formulated by MacCutchen's theorem. According to this theorem, if the spatial spectrum of the radiation field is confined within the ring, such a field propagates without spreading due to diffraction. In general, non-diffracting fields belong to the class of self-imaging, and the spectrum is confined to multiple rings.
[0049]
In any physical domain, diffraction phenomena are governed by Helmholtz's equation.
[0050]
[Formula 6]
[0051]
Recently, Durnin pointed out that the Helmholtz equation [6] for a scalar field propagating in a region z ≧ 0 without a light source has a class of non-diffractive mode solutions.
[0052]
[Expression 7]
[0053]
Where k// 2+ KL 2= (Ω / c) 2, kLAnd k//And represent propagation vector components perpendicular and parallel to the z-axis, respectively. That is, kL= Ksinγ, γ is a cone angle about the propagation axis indicated by γ in (a) in FIG. 6, A (φ) is an arbitrary complex function with respect to φ, and ρ2= X2+ Y2And J0Is a zeroth-order Bessel function of the first type. k//Is real, according to [Equation 7], the time-average intensity profile at z = 0 is
[0054]
[Equation 8]
[0055]
kLIf = 0, the solution is simply a plane wave, but 0 <kLIf <= ω / c, the solution is a non-diffracted beam and the intensity profile is kLIt decreases at a rate inversely proportional to ρ, and the effective width of the beam is k as shown in (b) of FIG.LDetermined by. The central spot is a minimum of about 3λ / 42.
[0056]
The non-diffracted beam expressed by [Equation 7] cannot be realized by experiments, because its energy is infinite. However, it is possible to synthesize a beam that approximates the desired distribution to some extent and makes the spread due to diffraction very small during propagation. A specific example of such an approximation is a Bessel Gaussian (BG) beam, which is narrowed according to a Gaussian distribution and propagates paraxially according to a Bessel function. A Bessel Gaussian beam carries a finite energy flux limited by a Gaussian profile and can be realized experimentally. The complex amplitude of the Bessel Gaussian beam is expressed as follows.
[0057]
[Equation 9]
[0058]
Where zR is πw0 2/ Λ.
[0059]
[Expression 10]
[0060]
Bessel Gaussian beam is w0kLIt is very different from a normal Gaussian beam only when> 1, and [Equation 9] is kL= 0 results in a standard representation for the complex amplitude of the Gaussian beam.
[0061]
When the Bessel Gaussian beam is formed by an axicon lens having a wedge angle δ and an aperture diameter D as shown in FIG. 6A, the subsequent intensity distribution in the radial direction is approximated by the following equation. .
[0062]
[Expression 11]
[0063]
The intersection angle γ between the plane wave and the optical axis is obtained by Snell's law for an axicon lens.
[0064]
[Expression 12]
[0065]
Where naxIs the reflectivity of the axicon lens. In the application of Bessel Gaussian beams for various material microstructures, it is important to estimate three beam parameters. That is, the central spot size, the non-diffracting propagation distance, and the power density supplied by the beam. The spot size of a Bessel Gaussian beam is typically J0(KLρ) defined as twice the first zero of the function.
[0066]
[Formula 13]
[0067]
The maximum propagation distance of a Bessel Gaussian beam consisting of N = Dsin (γ) / λ rings is defined by the innermost ring diffraction distance away from the beam propagation axis, and is expressed by the following equation.
[0068]
[Expression 14]
[0069]
Where ZRB= Π2k / 2kL 2Is the Rayleigh distance for the asymptotic width of the individual ring. Since the energy flux associated with the ring of Bessel beams is equal to the energy flux of the other ring or center spot, the optimal center spot illumination efficiency is:
[0070]
[Expression 15]
[0071]
Where w0Is 1 / e of the Gaussian beam intensity2Radius. Since a Bessel Gaussian beam forms a large number of rings, the energy at the central spot (or any ring) is very small compared to a Gaussian beam. The final efficiency is typically very small, but is much larger than that obtained using other Bessel Gaussian beam conversion methods. Even if the projection lens system is used, if the transmission loss in the lens system is ignored, the throughput of each ring is not affected by the change in the distance between the rings.
[0072]
In implementing this laser-assisted processing method, as described above, a femtosecond titanium-sapphire laser oscillator based on pulse amplification by chirp modulation is used. This laser oscillator is a mode-locked titanium-sapphire laser excited by an argon ion laser and operates at a reference oscillation wavelength λ = 795 ± 10 nm. Titanium-sapphire amplifiers excited by a neodymium: YLF laser amplify femtosecond pulses to 0.5 mJ / pulse with 5% pulse energy stability. The pulse repetition frequency is 1 KHz.
[0073]
The spatial intensity profile of the incident laser radiation and the expanded Bessel Gaussian beam intensity profile are monitored with a CCD camera 11 of 11 μm × 13 μm pixel size, as shown in FIG. Glass axicon lens 16 having a wedge angle δ = 175 mrad (nax= 1.511) is used to form a Bessel Gaussian beam with a cone angle γ≈92 mrad. As described above, the beam is imaged on the work material 1 by the telescope including the first and second positive lenses 17 and 18. Therefore, the Bessel Gaussian beam generated by the axicon lens 16 is converted by the combination of the first and second lenses 17 and 18, and another Bessel Gaussian whose cone angle γ ′ continuously changes according to the following equation. Become a beam.
[0074]
[Expression 16]
[0075]
According to this equation, the cone angle of the final Bessel Gaussian beam outside the sample is about 300 mrad.
[0076]
First, the characteristics of incident radiation were measured. Intensity profiles and pulse duration estimates are shown in FIGS. 7 (a) and 7 (b), respectively. A fire face diameter of 1.5 mm (FWHM) was obtained by Gaussian fit of the lateral intensity distribution. As shown in FIG. 7 (b), the autocorrelation trace is about 100 fsec (FWHM) duration,2) Fit by function. Maximum focal depth z before and after the telescope depending on the measured fire surface diametermaxWas calculated, and was found to be about 14 mm and 4 mm, respectively. In both cases, according to [Equation 15], the Bessel Gaussian beam center maximum illumination efficiency is 8.6 × 10 6.-3It is estimated that
[0077]
The optical breakdown induced by the Bessel Gaussian beam is investigated for three materials. The material is (i) (240 ± 10) μm thick dry v-SiO2(Ii) (150 ± 1) μm thick crystalline sapphire, and (iii) 4 mm to 10 mm thick optical plexiglass. All samples were washed and mounted on a metal target support member of a two-coordinate micrometer moving stage. The quartz glass and plexiglass samples are polished from the side so that the structure can be microscopically analyzed.
[0078]
Where (maximum depth of focus zmax) Light-induced damage threshold (LIDT) for linear damage (structural change) is necessary because permanent changes in material transmission that can be recognized with an optical microscope are observed after 10 laser shots per spot Define as minimum energy. The specimen is inspected by an inverted microscope (170 times) having a maximum lateral resolution of about 1 μm (40 × magnification, NA = 0.55 objective lens).
[0079]
In order to carry out and inspect the laser-assisted processing method according to the present invention as described above, it was first converted at several distances after the axicon lens to confirm that the beam was non-diffracting. The spatial intensity distribution I (ρ, z) of the light field was measured. In these examinations, in order to expand the intensity distribution, a microscope objective lens having a numerical aperture (NA) = 0.4 was used as the third lens.
[0080]
According to this measurement, a sharp decrease in the central spot intensity at a distance of about 13.5 mm from the axicon lens was observed. This value is the calculated depth of focus zmax= 14mm well. Further, the spatial distribution of the converted beam intensity at a distance of 11 mm is enlarged 60 times and shown in FIGS. The intensity distribution of the first ring is slightly distorted, but the central spot and other rings around it maintain rotational symmetry. Such distortion is attributed to the aberration of the axicon lens, that is, astigmatism. For distances ranging from 1 mm to 13 mm, d0The diameter of the central lobe measured at = 7.6 ± 2 μm is constant within the experimental accuracy, and is a value d calculated by [Equation 13].0 calIt is in good agreement with = 6.8 μm. A Bessel beam with a radius of 3 μm0= 3μm Gaussian beam, the latter spot is 100w after propagation of 100 Rayleigh range (3.6mm)0Spread to the extent. Conversely, the central spot of the Bessel beam becomes narrow after propagation of the same distance. The spot size is zmaxMinimize at the limit.
[0081]
In order to examine the radial intensity distribution of the Bessel Gaussian beam in more detail, the radial intensity distribution confirmed by experiments at a fixed distance from the axicon lens is compared with the result of the theoretical model based on [Equation 11]. The zero of this function agrees well with the lateral intensity distribution measured in the experiment. The second maximum of the measured intensity peak is different from the maximum of [Equation 11], because the calculated intensity dependency is established only for the cross wave of the uniform intensity distribution. In the case of experiments, cross waves do not preserve a uniform intensity distribution due to aberrations. From this result, it was found that the beam generated by the axicon lens can be approximated by a non-diffracting Bessel Gaussian beam.
[0082]
Further, the spatial intensity distribution of the beams converted by the first and second lenses 17 and 18 (telescope) was examined. First, the beam cone angle was determined from the remote field intensity profile. The cone angle γ ′ = 320 mrad of the Bessel Gaussian beam exceeds the theoretical prediction value obtained from [Equation 16]. This situation shows that this expression can only be used for qualitative prediction of cone angle. FIG. 8 (b) shows the spatial intensity distribution of the converted beam magnified 40 times. The central spot diameter and depth of focus are d0= 2 μm and zmax≈4 mm. Thus, the maximum aspect ratio expected by such a beam configuration is zmax/ D0= 2 × 103It is.
[0083]
In the Bessel Gaussian beam microstructural inspection as described above, all samples have a non-diffracting propagation range z of the beam.maxInstalled. A typical optical transmission image of the final linear shape first determined the LIDT pattern constructed for a Bessel Gaussian beam with a cone angle of 92 mrad in plexiglass, as shown in FIG. According to the measurement results, the multi-shot LIDT is about 0.9 J / cm for the linear pattern shape in plexiglass.2It is. As shown in FIGS. 9A, 9B, and 9C, the diameter of the damaged (structural change) region of the beam incident plate is about 6 times larger than the exit surface, that is, the incident diameter of the beam is Is approximately the same as the diameter of the first ring in the intensity distribution. Here, the central spot diameter on the sample surface is 7.6 μm. The carbonization phenomenon observed in the material is explained to have absorbed several successive laser pulses and heated up, eventually resulting in large damage spots.
[0084]
For processing of quartz and crystalline sapphire, a Bessel Gaussian beam with a cone angle of 320 mrad was used. The measured LIDT was 6.8 J / cm for quartz and sapphire, respectively.2And 8.2 J / cm2Met. A single shot LIDT for quartz is 5 J / cm for a Gaussian beam focused by a high numerical aperture objective lens.2Met. Recently, it has been reported that LIDT decreases after multi-shot irradiation. Therefore, laser processing with a Bessel Gaussian beam requires a high fluence for material destruction. According to the above definition of LIDT, 103It is not surprising that double the volume of glass must be excited at the same time. For both materials, namely quartz, (d), (e) and (f) in FIG. 9, and for sapphire, a linear pattern is observed as shown in (g), (h) and (i) in FIG. The shape made is similar to that in plexiglass, but the measured difference in diameter is only 2 μm. Further, as shown in (h) of FIG. 9, in sapphire, the diameter of the damaged spot can be measured only on the surface with a normal microscope.
[0085]
10A and 10B, the image by the primitive force microscope (AFM) shows the incident side of the quartz after laser processing using LIDT with a doubled fluence (FIG. 10A). ) And a specific example of the surface on the emission side ((b) in FIG. 10). The diameter of the Bessel Gaussian beam at the surface is d0= 2 μm. The diameters at the entrance and exit surfaces were about 2 μm and 1.2 μm, respectively. Other changes around the central spot of the quartz sample indicate that the surface was imprinted by the higher order intensity maxima of the Bessel Gaussian beam. The diameter and position of these further concentric pits d1≈4 μm are substantially equal to the diameter of the first ring of the Bessel Gaussian beam and the intensity distribution inside this, as shown in FIG. 8 (b). Therefore, the size of the structure is comparable to the size of the laser beam at the surface. No molten material was observed at the periphery of the removed pits.
[0086]
Along the propagation direction, the spot size decreases according to observation, which can be tentatively explained by self-focusing of femtosecond pulses. However, the irradiation power corresponding to the measured LIDT value is PLI glass LIDT.crThen, the sapphire LIDT is 0.69Pcr, Quartz LIDT is 0.42PcrGaussian beam critical self-focusing power PcrLower. 1P to confirm the effect of self-condensingcrTo 6PcrA linear pattern was recorded inside a 1 cm thick plexiglass sample at power levels in the range of. Several patterns were recorded at each power level. According to the measurement, the pattern length is 1Pcr1.5P fromcrIt increases from about 2 mm to 4 mm in accordance with the power of. At higher power levels, there was no change in pattern length, only a slow increase in diameter. This is clear evidence that the linear damage length depends only on the depth of focus of the Bessel Gaussian beam.
[0087]
【The invention's effect】
  As described above, the laser-assisted machining according to the present inventionMethodIsA work material made of a transparent material is focused and irradiated with a laser beam, and the irradiation position of the laser beam is scanned including the position on the surface of the work material at least at one position in the work material. The portion irradiated with the laser beam of the material to be processed is removed by etching treatment, and the portion is used as a hole. In the laser-assisted processing method, the present invention is such that the material to be processed is any one of silica glass, sapphire, and diamond. Further, the present invention is characterized in that a hydrofluoric acid solution or argon gas plasma is used as an etchant in the etching process.Is.
[0088]
  Furthermore, in the laser-assisted processing method according to the present invention, the laser beam condensed by the condensing optical system using the axicon lens is on the surface of the processing material with respect to the processing material made of a transparent material. A region including a position and irradiating a region extending inside the workpiece material is removed, a portion of the workpiece material irradiated with the laser beam is removed, and the portion is used as a hole. In the laser-assisted processing method according to the present invention, the material to be processed is silica glass.
[0089]
  Further, according to the present invention, in the laser assisted processing method, the portion of the material to be processed that has been irradiated with the laser beam is removed by an etching process. In the laser-assisted processing method, the present invention is such that the material to be processed is either sapphire or diamond. The present invention is characterized in that a hydrofluoric acid solution or argon gas plasma is used as an etchant in the etching process.
[0090]
  According to the present invention, in each of the laser-assisted processing methods described above, the laser beam is a pulse laser whose pulse duration is on the order of femtoseconds to picoseconds.
[0091]
  That is, the present invention can easily and surely form a very small hole even on a hard work material such as diamond or sapphire, and can reach the inside of the work material. It is possible to provide a laser-assisted machining method that can perform three-dimensional machining over a wide range and can form a smooth machined surface.
[Brief description of the drawings]
FIG. 1 is a side view showing the configuration of an apparatus for implementing a laser assisted machining method according to the present invention.
FIG. 2 is a side view showing a hole formed by the laser-assisted processing method.
FIG. 3 is a graph showing an etching rate in the laser-assisted processing method.
FIG. 4 is a perspective view showing holes formed by the laser-assisted processing method.
FIG. 5 is a side view showing a configuration of an apparatus for performing a laser assisted machining method according to the present invention using an axicon lens.
FIG. 6A is a side view showing a light collection state by the axicon lens, and FIG. 6B is a graph showing the intensity distribution of the beam condensed by the axicon lens.
FIG. 7A is a graph showing the proximity intensity distribution of the laser beam incident on the axicon lens, and FIG. 7B is a graph showing an autocorrelation pattern by a laser pulse obtained by the second harmonic. It is.
FIGS. 8A and 8B are a graph and a front view showing experimentally confirmed expansion intensity distributions of Bessel Gaussian beams having different cone angles, where FIG. 8A is a case where γ = 92 mrad, and FIG. This is the case of 320 mrad.
9 (a), (b), and (c) are plexiglass, (d), (e), and (f) are silica glass, and (g), (h), and (i) are sapphire, Bessel Gaussian beams. It is a front view which shows the optical transmission image of the damage spot produced | generated by.
FIG. 10 is a front view showing an AFM image showing fine holes formed on a quartz by a Bessel Gaussian beam by 10 laser shots on a beam incident side (a) and a beam emission side (b).
[Explanation of symbols]
1 Work Material, 2 Laser Beam, 3 Laser Light Source, 7 Objective Lens, 8 XYZ Stage, 16 Axicon Lens

Claims (9)

  1. A laser-assisted processing method for forming a hole communicating with the outside inside a work material made of a transparent material,
    Scanning the surface and the interior of the workpiece material with a laser beam focusing point so that the laser beam focusing point passes through the surface of the workpiece material;
    A step in which the only the laser beam structural change region formed by Rukoto scanned at the focal point of the work piece is removed by etching to form a hole in said material to be processed,
    A laser-assisted processing method.
  2.   The laser-assisted processing method according to claim 1, wherein the material to be processed is silica glass, sapphire, or diamond.
  3.   The laser-assisted processing method according to claim 2, wherein an etchant used in the etching process is a hydrofluoric acid solution or an argon gas plasma.
  4.   The laser-assisted processing method according to any one of claims 1 to 3, wherein the laser beam is a femtosecond pulse laser or a picosecond pulse laser.
  5. A laser-assisted processing method for forming a hole communicating with the outside inside a work material made of a transparent material,
    Irradiating a laser beam condensed by a condensing optical system including an axicon lens from the surface of the workpiece material to the inside; and
    A step in which the only structural change region formed by Rukoto irradiated with the laser beam in the processed material is removed by etching to form a hole in said material to be processed,
    A laser-assisted processing method.
  6.   The laser-assisted processing method according to claim 5, wherein the material to be processed is silica glass.
  7. The laser-assisted processing method according to claim 5 , wherein the material to be processed is sapphire or diamond.
  8. The laser-assisted processing method according to claim 7 , wherein an etchant used in the etching process is a hydrofluoric acid solution or an argon gas plasma.
  9. The laser-assisted processing method according to any one of claims 5 to 8 , wherein the laser beam is a femtosecond pulse laser or a picosecond pulse laser.
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