RU2478083C2  Method of splitting crystalline quartz under effect of thermoelastic stress  Google Patents
Method of splitting crystalline quartz under effect of thermoelastic stress Download PDFInfo
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 RU2478083C2 RU2478083C2 RU2011111426/03A RU2011111426A RU2478083C2 RU 2478083 C2 RU2478083 C2 RU 2478083C2 RU 2011111426/03 A RU2011111426/03 A RU 2011111426/03A RU 2011111426 A RU2011111426 A RU 2011111426A RU 2478083 C2 RU2478083 C2 RU 2478083C2
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 229910052904 quartz Inorganic materials 0.000 title claims abstract description 47
 239000010453 quartz Substances 0.000 title claims abstract description 47
 229910001885 silicon dioxide Inorganic materials 0.000 title claims abstract description 47
 238000005520 cutting process Methods 0.000 claims abstract description 46
 239000000463 materials Substances 0.000 claims abstract description 32
 238000010438 heat treatment Methods 0.000 claims abstract description 22
 238000001816 cooling Methods 0.000 claims abstract description 11
 238000004093 laser heating Methods 0.000 claims abstract description 8
 230000035882 stress Effects 0.000 claims description 38
 238000000926 separation method Methods 0.000 claims description 20
 230000015572 biosynthetic process Effects 0.000 abstract description 8
 238000005755 formation reactions Methods 0.000 abstract description 8
 238000003776 cleavage reactions Methods 0.000 abstract 1
 238000006073 displacement reactions Methods 0.000 abstract 1
 239000000126 substances Substances 0.000 abstract 1
 238000004227 thermal cracking Methods 0.000 description 20
 239000007769 metal materials Substances 0.000 description 7
 239000003507 refrigerants Substances 0.000 description 7
 230000037098 T max Effects 0.000 description 4
 230000000875 corresponding Effects 0.000 description 3
 238000009826 distribution Methods 0.000 description 3
 239000000686 essences Substances 0.000 description 3
 239000011521 glasses Substances 0.000 description 3
 210000004544 DC2 Anatomy 0.000 description 2
 230000002530 ischemic preconditioning Effects 0.000 description 2
 238000000034 methods Methods 0.000 description 2
 239000000919 ceramics Substances 0.000 description 1
 238000010835 comparative analysis Methods 0.000 description 1
 238000005336 cracking Methods 0.000 description 1
 239000002178 crystalline materials Substances 0.000 description 1
 230000001066 destructive Effects 0.000 description 1
 238000010586 diagrams Methods 0.000 description 1
 238000005265 energy consumption Methods 0.000 description 1
 238000005516 engineering processes Methods 0.000 description 1
 238000002474 experimental methods Methods 0.000 description 1
 230000000977 initiatory Effects 0.000 description 1
 238000004519 manufacturing process Methods 0.000 description 1
 238000003672 processing method Methods 0.000 description 1
 239000007787 solids Substances 0.000 description 1
 239000002344 surface layers Substances 0.000 description 1
 235000012431 wafers Nutrition 0.000 description 1
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Abstract
Description
The invention relates to methods for cutting anisotropic materials under the action of thermoelastic stresses, in particular to methods for laser thermal cracking of crystalline quartz.
The invention can be used in the electronic industry, as well as in other areas of technology and production, where there is a need for precision processing of products from crystalline materials.
A known method of thermally cracking glass and other brittle nonmetallic materials under the action of thermoelastic stresses resulting from laser heating of the material and the formation of a separating crack in it [1].
The essence of this method is as follows.
When a laser beam is exposed to the surface of the material, a separating crack is formed, the dynamics of which is determined by the distribution of thermoelastic stresses formed as a result of the thermal expansion of the regions of the material subjected to local laser heating. Moreover, the separation of the material occurs throughout the thickness and is characterized by a low rate of thermal cracking.
In the considered method, an increase in the rate of thermal cracking is possible due to an increase in the power of laser radiation. However, an excessive increase in the laser radiation power leads to overheating of the material and the formation of transverse cracks along the processing line, which does not allow for high precision cutting and makes the described method practically unsuitable and unpromising.
A known method of separating brittle nonmetallic materials under the action of thermoelastic stresses generated as a result of laser heating of the material along the cut line to a temperature not exceeding the relaxation temperature of thermoelastic stresses due to plastic deformations, and local cooling of the heating zone with relative movement of the treated surface and the heating and cooling zones [ 2].
The known method provides high accuracy of separation, zero cutting width, increased mechanical strength of the obtained products, wastefree and low energy consumption compared to other cutting methods.
The essence of this method is as follows.
At the site of laser radiation, a zone of significant compressive stresses is formed, which is surrounded by a zone of tensile stresses. When refrigerant is supplied to the surface to be treated, an additional zone of tensile stresses arises, limited by the zone of compressive stresses generated by the laser beam. The initiation of a separating crack occurs in the surface layers of the material from a microstructure defect or an artificially applied defect in the zone of tensile stresses formed due to the supply of refrigerant. Further, the initial microcrack begins its movement and propagates to the zone of compressive stresses formed by laser radiation. After this, the unsteady growth of the crack stops, and its further movement is determined by a change in the spatial distribution of the zones of tensile and compressive stresses due to the mutual movement of the material being processed, the laser beam and the refrigerant.
Thus, when implementing the known method, the distribution of compressive stresses in the volume of the material determines the shape and depth of microcrack development, the initialization and development of which occurs in the zone of tensile stresses formed in the refrigerant supply area.
This processing method is widely used for cutting various isotropic brittle nonmetallic materials (such as various types of glasses and ceramics). However, this method does not allow highquality cutting of singlecrystal materials, which are characterized by anisotropy of thermophysical and mechanical properties.
Closest to the claimed is a method of separation of crystalline quartz under the action of thermoelastic stresses, including the choice of the cutting direction relative to the crystallographic orientation of crystalline quartz, the choice of heating intensity in each cutting direction is proportional to the coefficient of linear thermal expansion due to a change in the relative velocity of the laser beam and material and / or changes laser radiation power, cutting along the cutting line, laser heating of the cutting line to a temperature not exceeding the relaxation temperature of thermoelastic stresses, and local cooling of the heating zone as a result of movement of the heating and cooling zones along the treated surface [3].
A significant disadvantage of this method is that taking into account the influence of thermal expansion anisotropy on the processing parameters in the known method is not carried out correctly, which leads to an erroneous selection of technological parameters of laser thermal cracking.
So, in the known method, two cases of laser thermal cracking of crystalline quartz are considered — along the axis of symmetry of the third order and perpendicular to it when the cut line lies in a plane parallel to the axis of symmetry of the third order. Moreover, in the known method, attention is correctly paid to the fact that in the crystalline quartz along the axis of symmetry of the third order, the linear coefficient of thermal expansion α is less than in the directions perpendicular to it.
Further, in the known method, the correct conclusion is made that taking into account the substantial anisotropy of α leads to the need for differential heating of the material, which ensures the creation of destructive thermal stresses along the cut line in each case, choosing its direction relative to the crystallographic orientation of the sample. At the same time, it is erroneously suggested that when cutting perpendicular to the axis of symmetry, increase the speed by 1.61.8 times in comparison with the cutting speed in the direction parallel to the axis of symmetry (or reduce the laser power accordingly).
The fact is that in the known method they do not pay attention to the fact that during laser thermal cracking, the formation of a laserinduced crack is determined by stresses acting perpendicular to the separation plane, the magnitude of which is proportional to the linear coefficient of thermal expansion in the same direction (in the direction perpendicular to separation plane).
Another disadvantage of this method is that it does not take into account the influence of the anisotropy of the thermal conductivity of crystalline quartz on the laser thermal cracking process.
Thus, the application of the known method in practice leads to an erroneous selection of technological parameters of laser thermal cracking and does not allow for highquality cutting of wafers made of crystalline quartz.
The technical problem solved by the claimed invention is to improve the quality of cutting plates of crystalline quartz due to the correct determination of the technological parameters of laser thermal cracking in various directions, due to the correct consideration of the influence of anisotropy of thermal conductivity and thermal expansion.
The technical result achieved by the claimed invention is to ensure the formation of laserinduced cracks with predetermined identical geometric characteristics when thermally cracked in various crystallographic directions of plates of crystalline quartz.
The technical result is achieved by the fact that in the method for separating crystalline quartz under the influence of thermoelastic stresses, including selecting a cutting direction relative to the crystallographic orientation of crystalline quartz, the choice of heating intensity in each cutting direction is proportional to the coefficient of linear thermal expansion due to a change in the relative velocity of the laser beam and material and the change laser radiation power, cutting along the cut line, laser heating of the re line and to a temperature not exceeding the relaxation temperature of thermoelastic stresses and local cooling of the heating zone as a result of movement of the heating and cooling zones along the treated surface, the thermal conductivity coefficient is additionally determined depending on the direction of cutting relative to the crystallographic orientation of crystalline quartz, the heating intensity is selected proportionally to the linear thermal expansion in the direction perpendicular to the separation plane, and back prop is relative to the coefficient of thermal conductivity in the direction perpendicular to the processing plane, and the ratio of the relative velocity of the laser beam and the material and the laser radiation power during laser separation of crystalline quartz along the thirdorder symmetry axis, when the cut line lies in a plane parallel to the thirdorder symmetry axis, is chosen from conditions
or when laser separation of crystalline quartz perpendicular to the axis of symmetry of the third order, when the cut line lies in a plane parallel to the axis of symmetry of the third order, the ratio of the relative velocity of the laser beam and the material and the laser radiation power is selected from the condition
or when laser separation of crystalline quartz is perpendicular to the axis of symmetry of the third order, when the cut line lies in a plane perpendicular to the axis of symmetry of the third order, the ratio of the relative velocity of the laser beam and the material and the laser radiation power is selected from the condition
Where
v is the relative velocity of the laser beam and material, m / s;
P is the laser radiation power, W;
k is the coefficient of proportionality, s ^{1} ;
α _{} , α _{+} are the coefficients of linear thermal expansion in the directions of the axis of symmetry of the third order and perpendicular to it, respectively, K ^{1} ;
λ _{} , λ _{+} are the thermal conductivity coefficients in the directions of the axis of symmetry of the third order and perpendicular to it, respectively, W / mK.
The essence of the proposed method for the separation of brittle nonmetallic materials under the action of thermoelastic stresses is as follows.
As is known, crystalline quartz has a pronounced anisotropy of thermal and elastic properties. Thus, the coefficients of linear thermal expansion along the axis of symmetry of the third order and in the directions perpendicular to it differ 1.6 times. A similar ratio of thermal conductivity is 1.8. Therefore, when separating crystalline quartz by laser thermal cracking, it is necessary to determine the technological parameters of cutting in a given direction (in particular, the heating intensity), taking into account changes in the coefficients of linear thermal expansion and thermal conductivity due to anisotropy.
Since, during laser thermal cracking, stresses acting perpendicular to the separation plane play a decisive influence on the formation of a laserinduced crack, and the magnitude of these stresses is proportional to the linear coefficient of thermal expansion in the same direction, when forming a crack in the XZ plane, it is necessary to consider the stresses σ _{y} for cracks in the XY plane, stresses σ _{z} must be considered; when a crack is formed in the ZY plane, stresses _{x x} must be considered (see d.1). In figure 1, the Z axis is parallel to the axis of symmetry of the third order C.
The magnitude of thermoelastic stresses that occur when the temperature in a solid changes is directly proportional to the product of the corresponding coefficient of linear thermal expansion by the magnitude of the temperature change:
σ _{x} = k _{1} α _{x} ΔT, σ _{y} = k _{1} α _{y} ΔT, σ _{z} = k _{1} α _{z} ΔT,
Where
σ _{x} , σ _{y} , σ _{z}  stresses acting in the direction of the axes X, Y, Z, respectively;
k _{1}  coefficient of proportionality;
α _{x} , α _{y} , α _{z}  linear thermal expansion coefficients in the direction of the X, Y, Z axes;
ΔT in this case is equal to the difference between the maximum temperature in the laser heating zone T _{max} and the temperature in the zone of exposure to the refrigerant T _{min} .
In turn, as is known, T _{max is} inversely proportional to the thermal conductivity of the material. Moreover, in the case of laser thermal cracking of such anisotropic materials as crystalline quartz, the most significant contribution to the change in T _{max} is exerted by the value of the thermal conductivity in the direction perpendicular to the processing plane. Thus, when a crack is formed perpendicular to the YZ plane, it is necessary to take into account the thermal conductivity coefficient λ _{x} , when a crack is formed perpendicular to the XY plane, it is necessary to take into account the thermal conductivity λ _{z} , when a crack is formed perpendicular to the XZ plane, the thermal conductivity λ _{y} must be taken into account (see. figure 1).
It is also known that T _{max is} inversely proportional to the relative velocity of the laser beam and the material and directly proportional to the power of the laser radiation.
Therefore, for the ratio of the relative velocity of the laser beam and the material to the laser radiation power depending on the change in the values of the linear thermal expansion coefficient and the thermal conductivity of crystalline quartz with the three possible simplest cutting options, the following conditions are true:
1) the case of laser thermal cracking of crystalline quartz along the axis of symmetry of the third order, while the cut line lies in a plane parallel to the axis of symmetry of the third order
2) the case of laser thermal cracking of crystalline quartz perpendicular to the axis of symmetry of the third order, while the cut line lies in a plane parallel to the axis of symmetry of the third order
3) the case of laser thermal cracking of crystalline quartz perpendicular to the axis of symmetry of the third order, while the cut line lies in a plane perpendicular to the axis of symmetry of the third order
Where
v is the relative velocity of the laser beam and material, m / s;
P is the laser radiation power, W;
k is the coefficient of proportionality, s ^{1} ;
α _{x} , α _{y} , α _{z}  coefficients of linear thermal expansion in the direction of the axes X, Y, Z, K ^{1} ;
λ _{x} = λ _{y} , λ _{z} are the thermal conductivity coefficients in the direction of the X, Y, and Z axes, which coincide in the simplest cases under consideration with the corresponding crystallographic axes, W / m · K;
α _{} , α _{+} are the coefficients of linear thermal expansion in the directions of the axis of symmetry of the third order and perpendicular to it, respectively, K ^{1} ;
λ _{} , λ _{+} are the thermal conductivity coefficients in the directions of the axis of symmetry of the third order and perpendicular to it, respectively, W / m · K.
The coefficients of linear thermal expansion of crystalline quartz along the axis of symmetry of the third order and perpendicular to it are respectively α _{} = 9 · 10 ^{6} K ^{1} , α _{+} = 14.8 · 10 ^{6} K ^{1} . The thermal conductivity coefficients of crystalline quartz along the axis of symmetry of the third order and perpendicular to it are λ _{} = 12.3 W / m · K, λ _{+} = 6.8 W / m · K [4].
Given the significant difference between the above parameters depending on the orientation of the quartz crystal during cutting in various directions, it is necessary to carry out differentiated heating, which ensures the formation of thermoelastic stresses necessary for creating a laserinduced crack in each orientation direction. This can be achieved either by increasing the cutting speed along the axis of symmetry of the third order by 1.61.8 times compared with the option of cutting perpendicular to the axis of symmetry of the third order (as for the case when the cut line lies in a plane perpendicular to the axis of symmetry of the third order, and for the case when the cut line lies in a plane parallel to the axis of symmetry of the third order), or a corresponding change in the power of the laser radiation.
In particular, it was experimentally established that the cutting speed of a quartz plate with a thickness of 1 mm at a constant laser power of P = 30 W in the direction parallel to the axis of symmetry of the third order is 85 mm / s, and in the directions perpendicular to the axis of symmetry of the third order 47 mm / s for the cutting option when the cutting line lies in a plane perpendicular to the third order symmetry axis, and 51 mm / s for the cutting option when the cutting line lies in a plane parallel to the third order symmetry axis.
A comparative analysis of the proposed solution with the prototype shows that the claimed method differs from the known implementation of a new action and the selected condition under which the actions characterizing the claimed method are performed, and is not part of the prior art.
Thus, the claimed method of separation of brittle nonmetallic materials under the action of thermoelastic stresses is new.
This allows us to conclude that the inventive method for the separation of brittle nonmetallic materials under the influence of thermoelastic stresses has an inventive step.
The inventive method for the separation of brittle nonmetallic materials under the action of thermoelastic stresses is industrially applicable, since in the case of its implementation using technical means known in the art, it is possible to realize the specified destination.
The invention is illustrated by the drawing, which shows a diagram of the formation of an incision using a laser beam and refrigerant in crystalline quartz for different directions of cutting.
The inventive method for the separation of crystalline quartz under the action of thermoelastic stresses is as follows.
At the beginning of the method, the choice of the cutting direction relative to the crystallographic orientation of the sample is determined.
Next, the ratio of the relative velocity of the laser beam and the material is determined, and the laser radiation power is selected
from the condition
in the case of thermal cracking of crystalline quartz along the thirdorder symmetry axis, when the cut line lies in a plane parallel to the thirdorder symmetry axis;
from the condition
in the case of thermal cracking of crystalline quartz perpendicular to the axis of symmetry of the third order, when the cut line lies in a plane parallel to the axis of symmetry of the third order;
from the condition
in the case of thermal cracking of crystalline quartz perpendicular to the axis of symmetry of the third order, when the cut line lies in a plane perpendicular to the axis of symmetry of the third order.
Next, a preliminary cut is made on the surface to be treated at the beginning of the processing circuit. A plate of crystalline quartz 1 is heated with a laser beam 2 to a temperature not exceeding the relaxation temperature of thermoelastic stresses, and the heating zone is cooled locally with refrigerant 3 as a result of movement of the heating and cooling zones on the treated surface. In this case, under the action of the generated thermoelastic stresses, a crack 4 of depth δ is formed (see drawing).
The following are specific examples.
As a material, plates of crystalline quartz 1 mm thick were used. As a means of moving, a twocoordinate table was used with a travel of 500 × 500 mm, providing a speed of movement in the range from 0 to 100 mm / s. For cutting, a CO _{2} laser with a radiation wavelength of 10.6 μm and an adjustable power from 0 to 80 W was used. Laser radiation was focused using sphericalcylindrical optics into a beam of elliptical cross section 6 × 1 mm in size, elongated in the cutting direction. The value of the coefficient k, taking into account the above parameters, was 1.3 · 10 ^{6} s ^{1} .
It was experimentally established that at a constant laser power of P = 30 W in the direction parallel to the thirdorder symmetry axis, the cutting speed is 85 mm / s, and in the directions perpendicular to the thirdorder symmetry axis, it is 47 mm / s for the cutting option, when the cut line lies in a plane perpendicular to the thirdorder symmetry axis, and 51 mm / s for the cutting option, when the cut line lies in a plane parallel to the thirdorder symmetry axis.
The value of the coefficient k, taking into account the above parameters, was 1.3 · 10 ^{3} s ^{1} . The reciprocal of the coefficient k determines the time during which the stationary thermal cracking mode is set in a given direction at the selected cutting speed and radiation power.
For comparison, the separation of similar samples was carried out according to the method described in the prototype. During the experiments, it was determined that the implementation of the process according to the method described in the prototype, in practice leads to an erroneous choice of technological parameters of laser thermal cracking and does not allow for highquality cutting of plates of crystalline quartz.
Analyzing the results of the experimental studies, we can conclude that the proposed method for separating crystalline quartz plates under the influence of thermoelastic stresses makes it possible to form laserinduced cracks with predetermined identical geometric characteristics when thermally cracked in different crystallographic directions of crystalline quartz plates.
Information sources
1. Machulka G.A. Laser processing of glass. M .: Sov. Radio 1979, p. 4867.
2. RF patent No. 2024441, IPC C03B 33/02, publ. 1994.
3. RF patent No. 2224648, IPC C03B 33/02, publ. 2002  prototype.
4. Handbook of electrical materials / Ed. Yu.V. Koritsky et al.  T 3.  L .: Energoatomizdat, 1988.  from 581583.
Claims (1)
 A method for separating crystalline quartz under the influence of thermoelastic stresses, including selecting a cutting direction relative to the crystallographic orientation of crystalline quartz, selecting a heating intensity in each cutting direction in proportion to the coefficient of linear thermal expansion due to a change in the relative velocity of the laser beam and material and / or changing the laser radiation power, applying cut along the cut line, laser heating of the cut line to a temperature not exceeding the temperature relaxation of thermoelastic stresses, and local cooling of the heating zone as a result of movement of the heating and cooling zones along the machined surface, characterized in that they additionally determine the value of the thermal conductivity coefficient depending on the cutting direction relative to the crystallographic orientation of crystalline quartz, the heating intensity is selected in proportion to the linear thermal expansion coefficient in direction perpendicular to the separation plane and inversely proportional to the coefficient thermal conductivity in the direction perpendicular to the processing plane, and the ratio of the relative velocity of the laser beam and the material and the laser radiation power during laser separation of crystalline quartz along the thirdorder symmetry axis, when the cut line lies in the plane parallel to the thirdorder symmetry axis, is selected from the condition
,
or when laser separation of crystalline quartz is perpendicular to the axis of symmetry of the third order, when the cut line lies in a plane parallel to the axis of symmetry of the third order, the ratio of the relative velocity of the laser beam and the material and the laser radiation power is selected from the condition
,
or when laser separation of crystalline quartz perpendicular to the axis of symmetry of the third order, when the cut line lies in the plane perpendicular to the axis of symmetry of the third order, the ratio of the relative velocity of the laser beam and the material and the laser radiation power is selected from the condition
,
where v is the relative velocity of the laser beam and material, m / s;
P is the laser radiation power, W;
k is the coefficient of proportionality, s ^{1} ;
α _{} , α _{+} are the coefficients of linear thermal expansion in the directions of the axis of symmetry of the third order and perpendicular to it, respectively, K ^{1} ;
λ _{} , λ _{+} are the thermal conductivity coefficients in the directions of the axis of symmetry of the third order and perpendicular to it, respectively, W / mK.
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Citations (4)
Publication number  Priority date  Publication date  Assignee  Title 

RU2024441C1 (en) *  19920402  19941215  Владимир Степанович Кондратенко  Process of cutting of nonmetal materials 
RU2224648C1 (en) *  20020903  20040227  Кондратенко Владимир Степанович  Method for cutting of brittle nonmetallic materials 
RU2226183C2 (en) *  20020221  20040327  Алексеев Андрей Михайлович  Method for cutting of transparent nonmetal materials 
RU2404931C1 (en) *  20090828  20101127  Владимир Степанович Кондратенко  Method of cutting plates from fragile materials 

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Patent Citations (4)
Publication number  Priority date  Publication date  Assignee  Title 

RU2024441C1 (en) *  19920402  19941215  Владимир Степанович Кондратенко  Process of cutting of nonmetal materials 
RU2226183C2 (en) *  20020221  20040327  Алексеев Андрей Михайлович  Method for cutting of transparent nonmetal materials 
RU2224648C1 (en) *  20020903  20040227  Кондратенко Владимир Степанович  Method for cutting of brittle nonmetallic materials 
RU2404931C1 (en) *  20090828  20101127  Владимир Степанович Кондратенко  Method of cutting plates from fragile materials 
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