JP2008000818A - Method of cleaving brittle material and brittle material to be used for it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To fracture a brittle material by only a scribing which is generated over the entire thickness of the brittle material by bringing about thermal stress by irradiating the brittle material with a laser beam. <P>SOLUTION: By making the beam pass through the entire thickness of the material or making the beam reach sufficient depth without reaching the rear face by controlling absorption coefficient of the brittle material to the laser beam, a scribed face due to thermal stress is generated in the entire thickness. The control of the absorption coefficient is obtained by adding irradiated laser beam absorbing impurities with which the brittle material generates heat by absorbing the laser beam, which does not affect transmission property in visible area and does not deteriorate the indication property of the glass for indicators. Furthermore, quenching impurities are added to prevent firefly luminescence. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a brittle material, especially a method for cleaving brittle materials such as glass, and a brittle material used therefor. In the specification of the present application, description is made specifically for glass, but in addition to glass, the present invention can be applied to brittle materials such as quartz, ceramic, and semiconductor.

Brittle materials have conventionally been cleaved by a mechanical method using a carbide tool such as a diamond tip. The application of this method to glass is also a method that has been used for a long time over the past century.

  However, these mechanical methods have the following drawbacks. The first is that small pieces called cullet are generated at the time of cleaving, and the work surface is soiled. Secondly, there is a risk that a microcrack is generated in the vicinity of the fractured surface and the workpiece is cracked starting from the crack. Third, there is a cutting margin of about several hundred microns at the minimum, and the existence of this cutting margin cannot be ignored at present when the workpiece size is miniaturized without limit. In addition to this, there are other disadvantages that cannot be ignored in the industry, such as the limit of processing speed and the cost of tools that are consumables.

There is no problem with the use of the prior art for cleaving window glass, but in the case of fine glass cleaving used for liquid crystal displays and plasma displays, the broken section is polished to prevent microcracks and then washed. A post process is required.

On the other hand, the laser cleaving method that has recently been expected to have the future has the following advantages and may eliminate the drawbacks of the diamond chip method. First, the mass loss is zero (no cullet generation), and no post-process such as cleaning is required. Second, since a high-strength cross section is obtained without the occurrence of fracture defects such as microcracks in the vicinity of the split cross section, post-processing such as polishing is unnecessary. Third, a mirror surface having a surface roughness of 1 μm or less is obtained. Fourth, the product external dimension accuracy is ± 25 μm or less. Fifth, it can be used for glass plates with a thickness of up to 0.2 mm and can be used for future liquid crystal TV glass.

Next, the principle of the laser cleaving method will be described. When glass is irradiated with a high energy density CO ₂ laser beam, the laser beam is generally absorbed at the irradiation spot, and as a result of rapid heating, radial cracks are generated, and the cleaving proceeds only in the traveling direction. I can't do that.
However, if the energy density of the laser beam is set to be sufficiently lower than that which generates such cracks, the glass is only heated, and neither melting nor cracking occurs. At this time, the glass tends to thermally expand, but it cannot expand due to local heating, and compressive stress is generated around the irradiation point. This local heating source is moved in the direction in which it is desired to cleave. When cooling is performed by spraying a cooling liquid after heating, a tensile tension is generated on the contrary. This is shown in FIG.
As shown in FIG. 1, when the cross-sectional shape of the laser beam 1 is formed into an appropriate one, a tensile tension 4 is generated only in a direction orthogonal to the moving direction 7 of the laser beam 1. The cleavage crack 5 is generated by the action of the tensile tension. In FIG. 1, 2 is the compressive stress inside glass, 3 is a cooling fluid, 6 is a glass plate. Note that the tensile tension 4 is generated even when the glass plate 6 is naturally cooled without spraying the cooling liquid 3 after heating by the laser beam 1, and the fracture crack 5 can be generated by the action of the tensile tension 4.
In the glass plate 6 shown in FIG. 2, when a trigger crack 8 is formed by a mechanical method at the starting point, the cleaving crack 5 is generated from the trigger crack 8 and can be advanced along the moving direction 7 of the laser beam 1. it can. In order for such a phenomenon to occur ideally, the energy distribution of the irradiated laser beam needs to be optimal in order to generate the tensile tension 4. These optimal distributions have been studied in various glass cuttings. The heating laser beam 1 shown in FIGS. 1 and 2 has been optimized.

Regarding the method for realizing such an optimal distribution, patent applications of Patent Document 1 and Patent Document 2 have been filed by one of the inventors.
Japanese Patent Application No. 2003-363855 (Japanese Patent Laid-Open No. 2005-88078) Japanese Patent Application No. 2004-156891 (Japanese Patent Laid-Open No. 2005-314198) It can be said that the application of laser to this glass cleaving is indispensable in the processing of general fine glass whose demand will rapidly increase.

In the thermal stress cleaving of glass by CO ₂ laser beam irradiation, as shown in FIG. 3, the CO ₂ laser beam is absorbed only by the surface layer of the glass plate 6 and does not pass through the entire thickness of the glass plate 6. This is due to the extremely large absorption coefficient α of the glass at the CO ₂ laser wavelength. The depth of cleaving with laser (referred to as laser scribe) is usually about 100 μm. In FIG. 3, 9 is a laser scribe surface and 10 is a break surface after laser scribe. Making the laser scribe surface 9 deeper than this is not possible even if the laser output is increased, as long as a CO ₂ laser beam is used. However, it has been demonstrated that if the laser output is increased, the heat source can penetrate into the glass by heat conduction, and the scribe depth can be increased somewhat. However, as shown in FIG. 4, the mechanical scribe surface is also usually of the same depth, and the glass is highly brittle and it is easy to mechanically cleave by applying stress according to this scribe line. Therefore, the increase in the scribe depth has not been required so far. This process of cleaving with the application of mechanical stress is called a break.

  Thus, conventionally, the glass is broken by a combination of mechanical scribe and break. In the case of mechanical scribing, as shown in FIG. 4, since there are a large number of microcracks near the scribe line, the break is relatively easy. However, the break surface 12 after mechanical scribing in FIG. 4 does not necessarily constitute one plane orthogonal to the glass surface. In the case of mechanical scribing, since the fractured surface is polished and cleaned after the break, high quality was not required for the break itself.

  In the case of laser scribing, it is necessary to use a break in combination with the conventional method. For this reason, while having the advantages of the above-mentioned folding angle, the spread to production sites is restricted. Even in the case of fine glass for liquid crystal televisions, whose advantages are relatively appreciated, it has not yet been put to practical use on an actual production line. For practical use, break surface position accuracy, angle accuracy, and cleanliness are required. Of course, the cullet is not allowed to adhere. Unfortunately, break technology that solves these problems is not yet complete. In particular, in the case of microwork, curve, multi-layer glass, thick glass, tempered glass cleaving, etc., the application of laser cleaving technology is strongly desired, but no solution has been provided. The present invention has been made to solve all of these problems, and the laser processing conditions necessary for realizing laser scribe over the entire plate thickness (hereinafter referred to as full cut). In association with the thickness of the brittle material and the light absorption coefficient α.

  In the present invention, laser beam transmission to a brittle material is realized to a sufficient depth, and in many cases, the entire plate thickness from the front surface to the back surface. For this reason, the conventional laser split heat insulation source is a linear heat source that exists only on the surface and penetrated by heat conduction in the depth direction of the material, whereas in the present invention, a surface heat source that reaches from the front to the back from the beginning. Is used. This difference is shown in FIG. 5 (a) and 5 (b) show a conventional heat source and a heat source according to the present invention, respectively. In the conventional heat source of FIG. 5A, the heat conduction 13 by the laser beam 1 penetrates in the depth direction of the material but does not reach the back surface. On the other hand, in the present invention, by using at least one of wavelength selection of irradiation laser light and addition of laser light absorbing impurities to the brittle material, the thickness L and the light absorption coefficient α of the brittle material are 0.105 / Since it is set so as to satisfy L <α <18.42 / L, as shown in FIG. 5B, the surface heat source 14 is absorbed by the laser beam 1 by being absorbed into the brittle material and absorbed by the transmitted laser beam. Is heated by. For this reason, the scribe depth extends over the entire thickness, so that the break process is unnecessary.

Such transmission of the laser beam 1 can be performed by optimizing the absorption coefficient α for the laser beam of the brittle material.

According to the present invention, the conventional laser / glass cleaving consisting of both laser scribe and break processes can be made into one process only for scribe. Laser glass breaking, while having many great technical advantages, has failed to replace the diamond cutter system that has been used over the past century. The present invention transforms that situation. The direct effects include the following only in the liquid crystal television production process.
(1) The cleaving position accuracy is high.
(2) The fractured surface is a mirror surface and the surface roughness is good.
(3) The fractured surface is sufficiently perpendicular to the glass surface.
(4) There is no adhesion of cullet on the cut surface and it is clean.
(5) The cleaving can be automated.
(6) Cleaving can be performed at high speed.
(7) Subsequent processes such as polishing and cleaning can be largely omitted.

In addition to the above merits, there are the following general merits.
(1) Curve cutting is possible. This is comparable to laser metal processing.
(2) The multilayer structure plate can be cleaved. Applicable to liquid crystal display and plasma display glass.
(3) The microwork can be cleaved. Applicable to IC tag.
(4) The tempered glass can be cleaved. Applicable to architectural glass.
(5) The curved glass can be cleaved. Applicable to automotive glass.
As described above, if the glass cleaving by the laser spreads to various fields of the industry, the effects cannot be measured in the processing speed, the processing quality, the economy, the difficulty, and the like.

In general, how much light passes through a material depends on absorption by the material. If the series coefficient of the material is α (cm ⁻¹ ), the propagation distance is x (cm), and the light intensities before and after propagating the distance x are I and I ₀ , the following relational expressions are established.
I = I ₀ · e ^−αx (1)
If the required value of the transmission distance is known from the equation (1), the necessary absorption coefficient α can be obtained. Next, the upper limit value, optimum value, and lower limit value of the absorption coefficient α are determined.

As a lower limit, a case where the laser beam 1 is transmitted through the glass plate thickness L by 90% is considered. At this time, a part of the energy is wasted, but a full cut can be realized sufficiently. If I / I ₀ = 0.9 in the equation (1), α = 0.105 / L. This is the lower limit value of the absorption coefficient α.
As the upper limit, according to the inventors' experience, scribing to 1/4 of the glass plate thickness often results in a full cut, so the conditions for scribing to 1/4 of the glass plate thickness are the upper limit. And set. Substituting I / I ₀ = 0.99 and x = L / 4 into the equation (1) yields α = 18.42 / L. This is the upper limit value of the absorption coefficient α. The optimum value is the case where 50% of the laser beam 1 is absorbed by the glass plate 6, and α = 0.963 / L in the same manner from the equation (1). As a result, it is understood that the glass plate 6 is fully cut when the light absorption coefficient α in the glass plate 6 is irradiated so as to satisfy 0.105 / L <α <18.42 / L.

For three typical glass plate thicknesses of 0.02 cm (future liquid crystal TV), 0.07 cm (current liquid crystal TV), and 0.28 cm (current plasma TV), the upper limit of this absorption coefficient α, The lower limit value and the optimum value are displayed as shown in the table below. α lower limit (cm ⁻¹ ) optimum value (cm ⁻¹ ) α upper limit (cm ⁻¹ )
Thickness 0.02cm 5.25 34.65 921
Plate thickness 0.07cm 1.50 9.90 263
Plate thickness 0.28cm 0.38 2.48 65.8
As is well known, the light absorption coefficient α is a function of the wavelength of light. Therefore, in order to control the light absorption coefficient α of the glass plate 6 so as to satisfy 0.105 / L <α <18.42 / L, the wavelength of the irradiation laser beam 1 may be controlled. Alternatively, the light absorption coefficient α of the glass plate 6 itself may be controlled.
In the following embodiment, a control technique of α for realizing these numerical values will be described.

FIG. 6 shows the absorption characteristics of quartz glass as a function of wavelength. The vertical axis represents the attenuation constant κ, and the absorption coefficient α has a relationship of α = 4πκ / λ, where λ is the wavelength. From FIG. 6, the absorption coefficient α of quartz glass with respect to a CO ₂ laser beam with a wavelength of 10.6 μm is about 12600 cm ⁻¹ . In this case, according to the equation (1), when propagating from the surface of the glass plate to a depth of 3.7 μm, 99% of the laser beam intensity is absorbed. This will only penetrate the surface layer. Nevertheless, in practice, a scribe depth of about 100μ is possible, and it can be seen that heat conduction is useful for this. Glass differs in composition from structure to structure, and differs in composition from manufacturer to manufacturer. However, the approximate absorption characteristics can be referred to those in FIG. In FIG. 6, the absorption coefficient α is determined as a function of the wavelength λ. According to this, as described above, the absorption coefficient α was excessive at the CO ₂ laser wavelength of 10.6 μm. In order to change the absorption coefficient α, it is necessary to change the wavelength λ. However, it is not possible to select all wavelengths continuously. Typical laser wavelengths that can provide high-power lasing are as follows.
10.6μ (CO ₂ laser)
5μ band (CO laser)
2.94μ (E _r : YAG laser)
2.09μ (H ₀ : YAG laser)
1.06μ (N _d : YAG laser)
1.03μ (Y _b : YAG laser)
0.515μ (Y _b : second harmonic of YAG laser)
0.343 μ (Y _b : third harmonic of YAG laser)
0.258μ (Y _b : fourth harmonic of YAG laser)
0.206 μ (Y _b : fifth harmonic of YAG laser)
The wavelength can only be selected from these.

A method for controlling the absorption coefficient α is to change the absorption characteristic itself of FIG. For this purpose, impurities may be added in the glass. However, it is necessary to select impurities that do not affect the transmission characteristics in the visible region and do not deteriorate the display characteristics of the glass for flat panel displays. In this case, since wavelength selection becomes free, the laser to be used can be selected from existing high-power lasers.

Next, the effectiveness of wavelength selection by adding impurities will be described. Consider an example of impurity addition. An appropriate amount of water (H ₂ O) having absorption characteristics with respect to Er: YAG laser or Ho, Tm: YAG laser light is added to the glass, and then these laser lights are irradiated to realize full cut. be able to. This is a Ho, Tm: YAG laser beam that oscillates at a wavelength of 2.091 μm, or an Er: YAG that oscillates at a wavelength of 2.94 μm, utilizing absorption bands of wavelengths of about 2 μm and about 3 μm of infrared absorption of water. It absorbs laser light.

When glass is exposed to water vapor at high temperature and high pressure, it will be in a state containing a certain amount of stable water. Also, if left for a long time under such conditions, water is taken in to form a colloidal gel, or a state called water-like ceramic (hydroceramic) is formed. Roger F. Bartholomew is the “High-water containing” in Journal of Non-Crystalline Solids, Volume 56 (1983), pages 331-342.
A paper entitled “glasses” was published to discuss the properties of glass with high concentrations of water. He cited the result of Scholze in the paper, and absorption due to bending vibration of HOH at a wavelength of 6.2 μm and absorption due to hydrogen bonding in the wavelength region of 4.2 to 3.6 μm are 2.8 to 2.7 μm. In the wavelength region, there is absorption due to stretching vibration of Si-OH and H-OH, and overtone absorption due to combined vibration of Si-OH stretching and bending at 2.22 μm is due to stretching and bending of HOH at 1.9 μm. It was shown that the overtone absorption of the combined vibration was absorbed by the overtone of the stretching vibration of Si-OH and H-OH at 1.4 μm. Since these absorptions are due to expansion and contraction between the bonded atoms and bending vibration, all the infrared rays absorbed in the respective wavelength regions become heat and raise the temperature of the glass.

Furthermore, these absorption coefficients are proportional to the concentration of water mixed in the glass. A heat source with a constant temperature can be realized by realizing a moisture concentration distribution that achieves uniform absorption and heat generation in the thickness direction according to the thickness of the glass plate to be fully cut with laser light. . As an irradiation laser capable of full-cutting glass by light absorption by water, there is a Ho, Tm: YAG laser that oscillates at a wavelength of 2.091 μm. This laser light is mainly due to the overtone of combined vibration of HOH expansion and contraction. Can be absorbed.

Another candidate is an Er: YAG laser that oscillates at a wavelength of 2.94 μm. This laser can be absorbed mainly by the stretching vibration of Si-OH and H-OH. As described above, when water is mixed into the glass, absorption in the infrared region occurs, but there is no effect on the transmission characteristics in the visible light region, so that the display characteristics of the liquid crystal or PDP display glass are deteriorated. Absent. Moreover, the hardness of the glass decreases as the water content increases, which is convenient because cracks are less likely to occur.

At the oscillation wavelength of the rare earth laser (Nd, Yb, Ho, Er laser), an appropriate amount of rare earth ions (Nd, Yb, Ho, Er ions for each of the lasers, respectively) is added to the glass, corresponding to each. Full cutting can be performed by irradiating the laser beam. Also in this case, as described above, it is preferable that the added ions have a concentration gradient so that uniform absorption occurs in the depth direction.

Rare earth atoms are surrounded by a group of electrons in the O shell, which is the outer shell of f electrons in the N shell. And has an energy level suitable for laser oscillation. Such lasers include Nd: YAG laser, Yb: YAG laser, Ho, Tm: YAG laser, Er: YAG laser and the like.

In the laser light absorption for realizing the full cut, one of these rare earth atoms used for laser oscillation, for example, Yb is added to the glass, and the laser light using the same rare earth atom, in this case Yb: YAG This glass is irradiated with laser light to be absorbed.

HLSmith and AJCohen et al. “Absorption spectra of
cations in alkali-silicate glasses of high ultra-violet transmission ''
Posted in Chemistry of Glasses Vol.4 No.5 (1963) from 173 to 187, doped with Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, U atoms in glass The absorption coefficient was measured. As an example, FIG. 7 shows the absorption coefficient of a 4.92 mm thick Na ₂ O.3SiO ₂ glass doped with 3.7% Yb. In FIG. 7, curve 15 is the optical absorption spectrum of a 4.92 mm thick Na ₂ O.3SiO ₂ glass with 3.7% Yb added, and 16 is a 2043 mm thick Na ₂ O with 9.0% Lu added. · 3SiO is a light absorption spectrum of ₂ glass. Na ₂ O.3SiO ₂ glass doped with Tb (or Nd) has absorption in the vicinity of 1 μm, which is 1.03 μm which is the oscillation wavelength of the Yb: YAG laser or 1.06 μm which is the oscillation wavelength of the Nd: YAG laser. Is consistent with Similarly, Na ₂ O.3SiO ₂ glass doped with Ho or Tm has absorption in the vicinity of 2 μm, which corresponds to the oscillation wavelength of the Ho, Tm: YAG laser of 2.091 μm.

There is a concern that the absorption wavelength and oscillation wavelength of these rare earth atoms have a deviation of about 100 nm. This is a collection of small crystals of glass, which is a shift in the absorption wavelength due to the difference in the size of the crystal field for each of these crystals, a so-called non-uniform absorption wavelength spread. Fig. 8 is cited from Fig. 7.6 on page 158 of "Optical and spectroscopic properties of glass" (Springer-Verlag). Inhomogeneously in this figure
The broadened line shows a light absorption spectrum 18 of rare earth atoms, which has a non-uniform spread. The laser oscillation wavelength is represented by an oscillation spectrum 17 of rare earth atoms present in the light absorption spectrum 18 of these non-uniformly spread absorptions in the glass.

Accordingly, it is possible to control the absorption coefficient of the glass by using a rare earth laser for processing and adding an appropriate amount of the same rare earth atom as the laser in the glass. By this principle, the object of the present invention can be realized. However, rare earth atoms excited by light absorption have a high probability of emitting fluorescence and returning to the ground state. In this case, the absorbed laser energy does not become heat and the object of the present invention cannot be achieved. Therefore, it is necessary to quench the fluorescence. As a method of quenching, it is conceivable to add rare earth atoms having many energy levels smaller than that between the fluorescent energy levels as a quencher.

GEPeterson and PMBridenbaugh said, “Study of relaxation.
A paper entitled “Process in Nd using pulsed excitation” (Journal of the optical society of America, Vol. 54 (1964), pages 644 to 650). In order to quench excited Nd, Pr, Sm, Dy, etc. It was shown that doping with rare earth atoms is effective. Therefore, Nd-doped glass that has absorbed Nd: YAG laser light is quenched by adding these rare earth atoms to the same glass, and the energy of the absorbed laser light is released as heat by non-radiative transition due to phonons. The object of the present invention can be achieved. Since these quenching rare earth atoms are close to the laser oscillation lines of Nd and Yb, it is considered that they are also effective for glass doped with Yb laser and Yb as an absorber. In the case of a combination of Ho, Tm: YAG laser and glass doped with Ho or Tm, the oscillation wavelength is 20.91 μm, and rare earth atoms such as Pr, Nd, Eu, etc. having many energy levels smaller than this energy gap. Is considered effective. Furthermore, in this case, the energy gap that contributes to light emission is smaller than that of Nd and Yb, so G. Fuxi described it on page 192 of "Optical and spectroscopic properties of glass" (Springer-Verlag). As you can see, the probability of non-radiation increases.

Fig. 9 shows the same book, page 156, Fig.7.4. In FIG. 9, 19 indicates a radiative transition and 20 indicates a non-radiative transition. If the energy gap is small, the probability Wnr of the non-radiative transition 20 increases. As another method of quenching, there is concentration quenching (self quenching or concentration quenching) that occurs when the amount of addition for absorption is increased, and this method is effective in all the combinations described here. However, in the case of the present invention, the concentration quenching can only be employed under this condition because the amount of absorbing impurities added must be optimized to produce the required heat generation for a given glass thickness. .

In summary, in the case of Nd: YAG laser and Yb: YAG laser, Nd and Yb are added as impurities for glass absorption, and Pr, Sm, Dy or Nd, Yb is added for quenching. Increase the amount to quench the concentration. When a Ho, Tm: YAG laser is used, the absorption impurity is Ho or Tm.
For quenching, Pr, Nd, Eu is added as a quencher, or Ho or Tm is added within the optimum absorption range to quench the concentration.

In order to realize light absorption in the ultraviolet wavelength region due to the transition from the full band to the conduction band of bound electrons in the glass depending on the state of oxygen ions constituting the glass to be fully cut, the third harmonic, A full cut can be performed by selectively irradiating from harmonics and fifth harmonics.

The present embodiment uses absorption that occurs in the ultraviolet wavelength region from the full band of bound electrons in the glass to the conduction band, and the laser that generates this absorption is the third harmonic, the fourth harmonic of the rare earth laser, It is selected from the fifth harmonics, irradiated, and fully cut. The absorption of ultraviolet rays by glass is due to oxygen ions in the glass. When these oxygen ions are strongly bound, the glass becomes transparent to a shorter wavelength.

Figure 10 is a quote from Figure 108 on page 233 of "Glass Nature, structure, and properties" by Host Scholze (Springer-Verlag). For a glass of 10 mm thickness, curve 21 represents a highly pure SiO ₂ glass. Curve 22 is the normal state SiO ₂ glass, curve 23 is the highly pure Na ₂ O · 3SiO ₂ glass, and curve 24 is the normal Na ₂ O · 3SiO ₂ glass with a transmission wavelength characteristic of 10 mm. . As can be seen from FIG. 10, in the case of a glass having a thickness of 10 mm, the wavelength at which the transmittance is 50 percent ranges from 160 nm to 320 nm. Therefore, the laser to be used also needs to be in this wavelength range, but in the case of the present invention, the optimum absorption can be obtained from the third, fourth and fifth harmonics of the laser doped with rare earth atoms in the solid. Select the wavelength and irradiate. These wavelengths are the third, fourth, and fifth harmonics of 353 nm, 265 nm, and 212 nm of the Nd: YAG laser, and the third, fourth, and fifth harmonics of the Yb: YAG laser are 343 nm, 258 nm, and 206 nm. 349 nm and 440 nm which are the third harmonics of the Nd: YLF laser, 262 nm and 330 nm which are the fourth harmonics, 209 nm and 264 nm which are the fifth harmonics, and the like. A full cut can be performed by selecting a wavelength from which optimum absorption is obtained from the thickness and composition of a given glass.

When the laser beam passes through the glass while being absorbed, as is apparent from the equation (1), the heat generation amount decreases in an exponential manner in the depth direction of the glass. Although full cutting may be possible as it is, it is desirable that the amount of heat generation be a constant value regardless of the depth for high-quality processing. For this purpose, the impurity concentration is preferably distributed in an inverse exponential manner from the front surface to the back surface, and heat generation is preferably made uniform in the depth direction.

If the laser beam penetrates to a sufficient depth in the material, as in the present invention, the heat source is a thin surface heat source and no further heat conduction is required. Since it is desirable that the laser output be as low as possible, the cross-sectional structure of the irradiation beam is desirably a linear shape having a narrow width. In this case, it is desirable to use a disk laser having excellent beam characteristics as the laser oscillator.

Even with a CO ₂ laser beam with strong surface absorption, the heat source penetrates in the depth direction of the material due to heat conduction if the output is somewhat high. In particular, this method will also deepen the scribe when the material thickness is thin. In this case, heat conduction is transmitted to the surface direction of the material simultaneously with the depth direction. Desirably, heat conduction should be concentrated in the depth direction of the material. As an extreme example, when the cross section of the irradiation laser beam is equal to the entire surface of the material, heat conduction occurs only in the depth direction. Of course, this cannot be selected because the scribe position cannot be specified. Even so, it is desirable that the irradiation laser beam has a wide cross-sectional shape so that the ratio in the depth direction is increased as much as possible.

The heating method has been described above. In order to realize a full cut, it is necessary to efficiently perform cooling in the thickness direction. For this purpose, it is more effective to perform cooling not only on the glass surface but also on the back surface.

  What has been described above are some embodiments for realizing the functions of the present invention, and it goes without saying that the spirit of the present invention can be realized in many other ways.

  Cutting flat glass used in flat panel displays such as liquid crystal displays and plasma displays, mobile and car navigation displays, and IR filters for optical devices is currently performed with a diamond cutter, and the need for a cleaning process after cutting And the presence of microcracks. Such a problem can be solved by the laser cutting according to the present invention. The present invention can also be applied to processing of microchips such as IC chip cover glass and IC dougs. Since the cutting length is longer than in the case of a large workpiece, the effect of the present invention is great.

  Since glass parts for automobiles are often curved, they are now mechanically cut after linear cutting. For this reason, there is a great expectation for laser processing that requires only glass cleaving.

  Furthermore, the processing of tempered glass as a building material can contribute to the solution of the problem demanded by modern society for crime prevention. Cutting of tempered glass is difficult by a mechanical method, and use of a laser is expected.

  Thus, the advent of laser technology for improving glass breaking is a solution to various problems demanded by modern society.

Conceptual diagram for explaining the principle of generation of compressive stress and tensile tension in glass by laser light heating and cooling used in the present invention Conceptual perspective view for explaining the glass breaking principle by the laser used in the present invention Conceptual perspective view explaining laser scribing of conventional glass Conceptual perspective view illustrating conventional glass mechanical scribe It is a conceptual perspective view explaining the state of heat generation inside the glass, (a) is a conventional method, (b) is a diagram according to the present invention. Optical absorption spectrum diagram of quartz glass for explaining the full-cut cleaving method of brittle material according to the present invention Optical absorption spectrum diagram of Na ₂ O · 3SiO ₂ glass to which Yb and Lu are added for explaining the full-cut cleaving method of the brittle material according to the present invention. Optical absorption spectrum and oscillation spectrum diagram of rare earth atoms for explaining the full-cut cleaving method of brittle material according to the present invention Wavelength spectrum diagram explaining the relationship between radiative transition and non-radiative transition for explaining the full-cut cleaving method of brittle material according to the present invention UV light absorption spectrum diagrams of various glasses for explaining the full-cut cleaving method of brittle material according to the present invention.

Explanation of symbols

1 Heating laser beam
2 Compressive stress in glass 3 Coolant 4 Tensile tension in glass 5 Cleavage crack in glass 6 Glass plate 7 Laser beam moving direction 8 Trigger crack 9 Laser scribe surface 10 Break surface after laser scribe
11 Mechanical scribing surface 12 Break surface after mechanical scribing 13 Heat source by heat conduction
14 Light source 15 by absorption of transmitted laser beam 15 Light absorption spectrum of Na ₂ O.3SiO ₂ glass having a thickness of 4.92 nm with 3.7% added Yb 16% Na ₂ having a thickness of 4.92 mm with 9.0% added Light absorption spectrum of O.3SiO ₂ glass 17 Oscillation spectrum of rare earth atoms 18 Light absorption spectrum of rare earth atoms 19 Radiative transition 20 Non-radiative transition 21 Transmission wavelength characteristics of highly pure SiO ₂ glass having a thickness of 10 mm 22 Normal state thickness Transmission wavelength characteristics of 10 mm thick SiO ₂ glass 23 Transmission wavelength characteristics of highly pure 10 mm thick Na ₂ O · 3SiO ₂ glass 24 Normal wavelength 10 mm Na ₂ O · 3SiO ₂ glass transmission wavelength characteristics

Claims (13)

A brittle material cleaving method in which a brittle material is moved while being irradiated with a laser beam to generate a crack due to thermal stress in the brittle material, and the brittle material is cleaved over its entire thickness, the thickness of the brittle material Is L (cm), and the light absorption coefficient of the brittle material is α (cm ⁻¹ ), the laser beam is absorbed in the brittle material so that the inequality 0.105 / L <α <18.42 / L is satisfied. A cleaving method for a brittle material, wherein an impurity is added, and the laser light absorbing impurity is an impurity which is converted into heat by absorption of laser light and does not have absorption or fluorescence characteristics in a visible region. The laser beam absorbing impurity is a rare earth atom selected from Nd, Yb, Ho, and Er, and the laser beam is a laser beam by a YAG laser to which the same kind of rare earth atom as the laser beam absorbing impurity is added. The method for cleaving a brittle material according to claim 1. The brittle material cleaving method according to claim 2, wherein rare earth atoms for fluorescence quenching having an energy level with a gap smaller than that between the fluorescence energy levels are added together with rare earth atoms as laser light absorbing impurities.   The laser beam absorbing impurity is Nd or Yb, the laser beam is a laser beam by an Nd: YAG laser or a Yb: YAG laser, and the rare earth atom for fluorescence quenching is selected from Pr, Sm, and Dy The method for cleaving a brittle material according to claim 3.   The laser light absorbing impurity is Ho or Tm, the laser light is laser light by a Ho, Tm: YAG laser, and the rare earth atom for fluorescence quenching is any one selected from Pr, Nd, and Eu. Item 4. A method for cleaving a brittle material according to Item 3. 6. Fragmentation of a brittle material according to any one of claims 3 to 5, wherein fluorescence emission is prevented by concentration quenching with an increased concentration of laser light absorbing impurities without adding rare earth atoms for fluorescence quenching. Method. 7. The laser light absorbing impurity concentration or the fluorescence quenching rare earth atom concentration is increased exponentially with respect to the depth direction of the brittle material. Cleaving method for brittle materials. The method for cleaving a brittle material according to claim 1, further comprising a step of cooling the brittle material after irradiating it with laser light. 2. The method for cleaving a brittle material according to claim 1, wherein the laser beam is a laser beam from a disk laser. A brittle material that irradiates a laser beam to a brittle material to which an impurity is added to generate a crack caused by thermal stress in the brittle material and cleaves the impurity, and the impurity is converted into heat by absorption of the laser light, and A brittle material characterized by being an impurity having no absorption property in the visible region. The brittle material according to claim 10, wherein the laser light absorbing impurity is a rare earth atom selected from Nd, Yb, Ho, and Er. The brittle material according to claim 11, wherein rare earth atoms for fluorescence quenching having an energy level with a gap smaller than between the fluorescence energy levels are added together with rare earth atoms as laser light absorbing impurities. The brittle material according to claim 12, wherein the rare earth atom for fluorescence quenching is selected from Pr, Sm, Dy, Nd, and Eu.

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