CN111270309A - Growth method of calcium fluoride single crystal and used device - Google Patents
Growth method of calcium fluoride single crystal and used device Download PDFInfo
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- CN111270309A CN111270309A CN202010148083.4A CN202010148083A CN111270309A CN 111270309 A CN111270309 A CN 111270309A CN 202010148083 A CN202010148083 A CN 202010148083A CN 111270309 A CN111270309 A CN 111270309A
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- 239000013078 crystal Substances 0.000 title claims abstract description 164
- 229910001634 calcium fluoride Inorganic materials 0.000 title claims abstract description 62
- WUKWITHWXAAZEY-UHFFFAOYSA-L calcium difluoride Chemical compound [F-].[F-].[Ca+2] WUKWITHWXAAZEY-UHFFFAOYSA-L 0.000 title claims abstract description 61
- 238000000034 method Methods 0.000 title claims abstract description 42
- 230000008569 process Effects 0.000 claims abstract description 10
- 230000004927 fusion Effects 0.000 claims abstract description 3
- 238000010438 heat treatment Methods 0.000 claims description 22
- 239000002994 raw material Substances 0.000 claims description 20
- 238000002791 soaking Methods 0.000 claims description 16
- 239000000155 melt Substances 0.000 claims description 15
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 10
- 238000001816 cooling Methods 0.000 claims description 8
- 239000007789 gas Substances 0.000 claims description 8
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 6
- 229910002804 graphite Inorganic materials 0.000 claims description 6
- 239000010439 graphite Substances 0.000 claims description 6
- 229910052786 argon Inorganic materials 0.000 claims description 5
- TXEYQDLBPFQVAA-UHFFFAOYSA-N tetrafluoromethane Chemical compound FC(F)(F)F TXEYQDLBPFQVAA-UHFFFAOYSA-N 0.000 claims description 5
- 238000002844 melting Methods 0.000 claims description 4
- 230000008018 melting Effects 0.000 claims description 4
- 230000008859 change Effects 0.000 claims description 3
- 239000007788 liquid Substances 0.000 claims description 3
- 238000005086 pumping Methods 0.000 claims description 3
- 230000009467 reduction Effects 0.000 claims description 3
- 230000000087 stabilizing effect Effects 0.000 claims description 3
- 238000003466 welding Methods 0.000 claims description 3
- 238000002360 preparation method Methods 0.000 abstract description 7
- 238000002834 transmittance Methods 0.000 abstract description 5
- 239000000463 material Substances 0.000 abstract description 4
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 abstract description 2
- 238000010521 absorption reaction Methods 0.000 abstract description 2
- 238000002109 crystal growth method Methods 0.000 abstract description 2
- 239000011701 zinc Substances 0.000 abstract description 2
- 229910052725 zinc Inorganic materials 0.000 abstract description 2
- 230000000052 comparative effect Effects 0.000 description 10
- 238000005259 measurement Methods 0.000 description 4
- 238000004321 preservation Methods 0.000 description 3
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 229920000049 Carbon (fiber) Polymers 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 239000004917 carbon fiber Substances 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000007123 defense Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- 150000007522 mineralic acids Chemical class 0.000 description 1
- 230000007847 structural defect Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-N sulfuric acid Substances OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 1
- 230000001988 toxicity Effects 0.000 description 1
- 231100000419 toxicity Toxicity 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/12—Halides
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
- C30B15/10—Crucibles or containers for supporting the melt
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
- C30B15/14—Heating of the melt or the crystallised materials
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
- C30B15/20—Controlling or regulating
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
- C30B15/36—Single-crystal growth by pulling from a melt, e.g. Czochralski method characterised by the seed, e.g. its crystallographic orientation
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Crystallography & Structural Chemistry (AREA)
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- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Crystals, And After-Treatments Of Crystals (AREA)
Abstract
The invention provides a growth method of calcium fluoride single crystal and a device used by the same, belonging to the technical field of new material preparation. The single crystal growth device can accurately control the temperature near the seed crystal so as to control the fusion of the seed crystal, and the whole process of the calcium fluoride single crystal growth method does not contain deoxidants such as lead, zinc and the like, so that the prepared calcium fluoride single crystal has no ultraviolet absorption, and the single crystal has high transmittance and low stress birefringence.
Description
Technical Field
The invention relates to a growth method and a growth device of calcium fluoride single crystals, belonging to the technical field of new material preparation.
Background
Calcium fluoride, formula CaF2Colorless crystals or white powder; is difficult to dissolve in water and slightly soluble in inorganic acid; reacting with hot concentrated sulfuric acid to generate hydrofluoric acid. The crystal structure of the calcium fluoride belongs to an isometric crystal system and is cubic, octahedral or dodecahedral. Colorless crystal or white powder, natural ore containing impurities, slight green or purple color, and luminous density of 3.18 g/cm when heated3The melting point is 1402 ℃, the boiling point is 2497 ℃, the refractive index is 1.434, and the toxicity is low. The calcium fluoride has wide application range, and has wider and wider application prospect with the progress of science and technology. At present, the method is mainly used in three industries of metallurgy, chemical industry and building materials, and is secondly used in light industry, optics, carving and national defense industry.
In the prior art, calcium fluoride can be grown by adopting a Bridgman method or a Czochralski method, a melt is contacted with the inner wall of a crucible in the growth process of the Bridgman method, and a calcium fluoride single crystal belongs to a cubic crystal system and is easy to crystallize, a plurality of crystal nuclei are easy to generate on the wall of the crucible, and the yield of the single crystal is low; the crystal grown by the method has the advantages of small stress birefringence, high single crystal rate and the like, but the crystal pulling method is usually carried out by a single heater, the temperature gradient in the crystal furnace is uncontrollable, an ideal temperature interval is difficult to obtain, and meanwhile, the crystal nucleus has different crystallization rates and crystal orientations in the growth process of the single heater, so that the defects of polycrystal or dislocation and the like are generated. The calcium fluoride window for excimer laser has high requirements on the crystal structure, and crystals with structural defects generally have poor performance and cannot be used.
Disclosure of Invention
Aiming at the problems, the invention provides a method and a device for growing calcium fluoride single crystals, which effectively improve the yield and the crystal quality of the calcium fluoride single crystals and enable the crystals to be more suitable for serving as excimer laser window materials.
In order to achieve the purpose, the technical content of the invention is as follows: a method for growing calcium fluoride single crystal uses calcium fluoride as raw material, and adopts crucible pulling method to grow calcium fluoride single crystal, and the device used in the crucible pulling method is provided with a side heater on the side surface of the crucible and a bottom heater at the bottom of the crucible.
Further, the method comprises the following steps:
s1 charging the raw materials into a graphite crucible, vacuumizing to a vacuum degree of 10-2Pa；
The side heater and the bottom heater of S2 are heated to 150 ℃ at 50 ℃/h simultaneously, and the temperature is kept for more than 48 hours until the internal vacuum degree reaches 10-3Pa；
S3, heating the side heater and the bottom heater at the same time at a speed of 30 ℃/h, keeping the temperature of the side heater constant after the temperature is increased to 800 ℃, keeping the temperature of the bottom heater constant after the temperature is increased to 650 ℃, then filling a mixed gas consisting of argon and carbon tetrafluoride until the pressure reaches 0MPa, stopping filling gas, and keeping the temperature for more than 10 hours;
s4, heating the side heater to 1380-1400 ℃, keeping the temperature constant, heating the bottom heater to 1200-1250 ℃, keeping the temperature constant, stabilizing the temperatures of the side heater and the bottom heater, keeping the temperature constant for more than 5 hours until the raw materials are molten and the temperature of the melt in the crucible is balanced, and welding seed crystals;
s5, setting the downward moving speed of the seed crystal to be 5mm/min, descending until the bottom surface of the seed crystal contacts with the liquid surface of the raw material, continuing descending for 3mm after the contact, fully contacting the seed crystal with the melt, starting an automatic rotation program, rotating the seed crystal at the speed of 10rpm, and keeping for 0.5 hour;
s6, when the weight of the seed crystal is constant and does not change, heating the side heater to 5 ℃ to enter a necking stage, and melting off the diameter of the seed crystal by 2-3 mm; starting an automatic cooling program after the necking stage is finished, cooling the side heater at the speed of 2 ℃/h until the diameter of the crystal at the seed crystal is the same as that of the raw material in the step S1, starting a pulling program, and entering a crystal shouldering growth stage;
s7, keeping the temperature of the bottom heater constant in the shouldering stage, cooling the side heater at the speed of 5 +/-2 ℃/h, simultaneously pulling the seed crystal upwards at the speed of 2mm/h, rotating at the speed of 10rpm, reversely rotating the crucible and the seed crystal at the speed of 2rpm until the diameter of the crystal grows to 200mm, and entering into the equal-diameter growth stage;
s8, in the equal-diameter growth stage, the pulling speed is kept to be 2mm/h, the seed crystal rotating speed is 8rpm, the crucible rotates in the reverse direction of the seed crystal at the speed of 2rpm, the pulling process is finished after the seed crystal is pulled upwards for 48 hours, the temperature of the side heater is kept constant, the temperature of the bottom heater is raised by 20 ℃, and the bottom of the crystal and the melt are naturally fused; lifting the crystal by 10mm at the speed of 5mm/mim to ensure that the crystal and the melt are completely separated, starting to enter a cooling stage, reducing the temperature of a side heater to be the same as that of a bottom heater at the speed of 30 ℃/h, then reducing the temperature of the side heater and the bottom heater to room temperature at the speed of 20 ℃/h, turning off a heating power supply after the temperature reduction procedure of the heaters is finished, finishing the crystal growth process, starting a vacuum pump at the moment, and pumping the inside of the crystal furnace until the vacuum degree reaches 10-2Pa above, standing for two days, and taking out the calcium fluoride single crystal.
Furthermore, the raw material of calcium fluoride is ultraviolet grade, and the purity is 99.99%.
Further, the volume ratio of argon to carbon tetrafluoride in the mixed gas in the step S3 is 1: 1.
Further, the heating rates of the side heater and the bottom heater in the step S4 are respectively 50 ℃/h and 30 ℃/h; the direction of the seed crystal is any one of <100>, <111> or <110>, the diameter of the seed crystal is less than 10mm, and the length of the seed crystal is more than or equal to 120 mm.
A crystal growing device comprises a closed heat-preserving cylinder and a crucible arranged in the heat-preserving cylinder, wherein a side heater is arranged in the heat-preserving cylinder around the periphery of the crucible, and a bottom heater is arranged at the bottom of the crucible; a lifting rod extending downwards is arranged at the top of the heat-insulating cylinder, the lifting rod corresponds to the center of the bottom of the crucible, and a connecting device for connecting seed crystals is arranged at one end of the lifting rod, which is far away from the top of the heat-insulating cylinder; the bottom of the crucible is fixedly connected with the rotatable tray.
Furthermore, a circle of side soaking ring is arranged between the side heater and the crucible and/or a bottom soaking ring is arranged between the bottom heater and the crucible.
Furthermore, the side soaking rings and the bottom soaking ring are made of graphite.
The application of the crystal growth device in the growth of calcium fluoride single crystals.
The invention has the beneficial effects that:
the single crystal growth device can accurately control the temperature near the seed crystal so as to control the fusion of the seed crystal, and the whole process of the calcium fluoride single crystal growth method is free of deoxidants such as lead and zinc, so that the prepared calcium fluoride single crystal is ensured to have no ultraviolet absorption, and the single crystal has high transmittance, low stress birefringence and uniform stress distribution.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
FIG. 1 is a schematic structural view of an apparatus used in the method for growing a calcium fluoride single crystal according to the present invention;
FIG. 2 is a schematic view showing the internal structure of an apparatus used in the method for growing a calcium fluoride single crystal according to the present invention;
FIG. 3 is a schematic view of a single crystal of calcium fluoride produced in example 3 of the present invention;
FIG. 4 is a graph showing the results of transmittance tests conducted on calcium fluoride single crystals prepared in example 3 of the present invention;
FIG. 5 is a graph showing the results of stress birefringence measurement of calcium fluoride single crystals prepared in example 3 of the present invention;
FIG. 6 is a graph showing the results of stress birefringence measurement of a calcium fluoride single crystal prepared in comparative example 2 of the present invention;
wherein, 1-a heat preservation cylinder, 2-a crucible, 3-a side heater, 4-a bottom heater, 5-a single crystal, 6-a calcium fluoride melt, 7-a side soaking ring, 8-a bottom soaking ring and 9-a tray.
Detailed Description
The technical solution in the embodiments of the present invention is clearly and completely described below with reference to the drawings in the embodiments of the present invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.
Example 1
A method for growing calcium fluoride single crystal uses calcium fluoride as raw material, and adopts crucible pulling method to grow calcium fluoride single crystal, and the device used in the crucible pulling method is provided with a side heater on the side surface of the crucible and a bottom heater at the bottom of the crucible. Wherein the raw material calcium fluoride is ultraviolet grade, and the purity is 99.99 percent.
The growth method comprises the following steps:
s1 charging the raw materials into a graphite crucible, and vacuumizing until the vacuum degree reaches (or is higher than) 10-2Pa；
S2 heating the side heater and the bottom heater at 50 deg.C/h, keeping the temperature for 48 hr until the temperature of the side heater and the bottom heater is 150 deg.C, and keeping the temperature until the internal vacuum degree reaches 10-3Pa；
S3, heating the side heater and the bottom heater at the same time at the speed of 30 ℃/h, keeping the temperature of the side heater constant after heating to 800 ℃, keeping the temperature of the bottom heater constant after heating to 650 ℃, then filling a mixed gas consisting of argon and carbon tetrafluoride at the volume ratio of 1:1 until the pressure reaches 0MPa (namely the indication number of a pressure gauge at the moment is 0, namely the pressure in the furnace is equal to the external pressure), stopping filling the gas, and keeping the temperature for more than 10 hours;
s4, heating the side heater to 1380 ℃, keeping the temperature constant, heating the bottom heater to 1200 ℃, keeping the temperature constant, stabilizing the temperatures of the side heater and the bottom heater, keeping the temperature constant for more than 5 hours until the raw materials are molten, balancing the temperature of a melt (a calcium fluoride melt, shown as 6 in figure 1) in the crucible, and welding seed crystals; wherein the heating rates of the side heater and the bottom heater are respectively 50 ℃/h and 30 ℃/h; the direction of the seed crystal is <100>, the diameter of the seed crystal is less than 10mm, and the length of the seed crystal is more than or equal to 120 mm;
s5, setting the downward moving speed of the seed crystal to be 5mm/min, descending until the bottom surface of the seed crystal contacts with the liquid surface of the raw material, continuing descending for 3mm after the contact, fully contacting the seed crystal with the melt, starting an automatic rotation program, rotating the seed crystal at the speed of 10rpm, and keeping for 0.5 hour;
s6, when the weight of the seed crystal is constant and unchanged, heating the side heater to 5 ℃ to enter a necking stage (necking means that a section of part thinner than the seed crystal is pulled out firstly when crystal pulling is started), and melting off the diameter of the seed crystal by 2-3 mm; starting an automatic cooling program after the necking stage is finished, cooling the side heater at the speed of 2 ℃/h until the diameter of the crystal at the seed crystal is the same as that of the raw material in the step S1, starting a pulling program, and entering a crystal shouldering growth stage;
s7 shoulder-setting stage (stage of crystal diameter is set to target diameter) bottom heater temperature is kept constant, side heater is cooled down at 5 + -2 deg.C/h speed, seed crystal is pulled up at 2mm/h speed and rotated at 10rpm speed, crucible is rotated with seed crystal in reverse direction at 2rpm speed until crystal diameter is 200mm, entering equal diameter growth stage;
s8, in the equal-diameter growth stage, the pulling speed is kept to be 2mm/h, the seed crystal rotating speed is 8rpm, the crucible rotates in the reverse direction of the seed crystal at the speed of 2rpm, the pulling process is finished after the seed crystal is pulled upwards for 48 hours, the temperature of the side heater is kept constant, the temperature of the bottom heater is raised by 20 ℃, and the bottom of the crystal and the melt are naturally fused; lifting the crystal by 10mm at the speed of 5mm/mim to ensure that the crystal and the melt are completely separated, starting to enter a cooling stage, reducing the temperature of a side heater to be the same as that of a bottom heater at the speed of 30 ℃/h, then reducing the temperature of the side heater and the bottom heater to room temperature at the speed of 20 ℃/h, turning off a heating power supply after the temperature reduction procedure of the heaters is finished, finishing the crystal growth process, starting a vacuum pump at the moment, and pumping the inside of the crystal furnace until the vacuum degree reaches 10-2Pa or above, standing for two days, and taking out calcium fluoride single crystal (shown as 5 in figure 1).
As shown in figure 1, the device for calcium fluoride single crystal growth specifically comprises a closed heat-insulating cylinder 1 and a crucible 2 arranged inside the heat-insulating cylinder 1, wherein a side heater 3 is arranged in the heat-insulating cylinder 1 and surrounds the periphery of the crucible 2, and a bottom heater 4 is arranged at the bottom of the crucible 2; a lifting rod extending downwards is arranged at the top of the heat-insulating cylinder 1, the lifting rod corresponds to the central position of the bottom of the crucible 2, and a connecting device for connecting seed crystals is arranged at one end of the lifting rod, which is far away from the top of the heat-insulating cylinder 1; the bottom of the crucible 2 is fixedly connected with a rotatable tray 9; the distance between the heater 3 and the outer wall of the crucible 2 is 15mm, the distance between the bottom heater 4 and the outer wall of the bottom of the crucible is 15mm, the thickness of the side heater 3 is 8mm, and the thickness of the bottom heater 4 is 15 mm; the heat preservation cylinder 1 is made of carbon fiber, and the distance between the heat preservation cylinder 1 and the side heater 3 or the bottom heater 4 is 10 mm.
Example 2
Example 2 is substantially the same as example 1 above, except that in step S4, the temperature of the side heater is raised to 1400 ℃ and then kept constant, the temperature of the bottom heater is raised to 1250 ℃ and then kept constant, and the temperature of the side heater and the bottom heater is kept constant for more than 5 hours after the temperatures of the raw materials are melted and the melt temperature in the crucible is balanced, and the seed crystal is welded; wherein the heating rates of the side heater and the bottom heater are respectively 50 ℃/h and 30 ℃/h; the direction of the seed crystal is <110 >.
The apparatus for growing single crystal of calcium fluoride is also substantially the same as in example 1 except that a ring of side soaking rings 7 (shown in FIG. 2) is provided between the side heater 3 and the crucible 2.
Example 3
Example 3 is substantially the same as example 1 above, except that in step S4, the temperature of the side heater is raised to 1390 ℃ and then kept constant, the temperature of the bottom heater is raised to 1230 ℃ and then kept constant, and the temperature of the side heater and the bottom heater is kept constant for more than 5 hours after the temperatures of the raw materials are melted and the melt temperature in the crucible is balanced, and the seed crystal is welded; wherein the heating rates of the side heater and the bottom heater are respectively 50 ℃/h and 30 ℃/h; the direction of the seed crystal is <111 >;
the apparatus for growing calcium fluoride single crystal is the same as that of example 1, except that a ring of side soaking rings 7 is arranged between the side heater 3 and the crucible 2, a bottom soaking ring 8 is arranged between the bottom heater 4 and the crucible 2, and the side soaking rings 7 and the bottom soaking ring 8 are made of graphite (as shown in fig. 2).
The calcium fluoride single crystal (as shown in FIG. 3) prepared in example 3 was subjected to transmittance measurement according to the standard JB/T9495.1-2015.
The detection result is shown in fig. 4, and it can be seen from fig. 4 that the calcium fluoride single crystal prepared by the invention has higher transmittance and is suitable for being used as an excimer laser window material.
Comparative examples 1 to 2
Comparative examples 1-2 are comparative experiments to example 3, with the difference that the crystal growth apparatus used in comparative example 1 has no side heater, only a bottom heater; comparative example 2 the crystal growth apparatus was provided with neither side heaters nor bottom soaking rings, only bottom heaters were provided, and the remaining structure and fabrication method of comparative examples 1-2 were the same as those of example 3.
To further illustrate the advantages of the present invention, the calcium fluoride single crystal prepared in example 3 of the present invention and the calcium fluoride single crystal prepared in comparative examples 1-2 were subjected to quality inspection with the yield and stress birefringence measured during the preparation process, wherein the stress birefringence measurement method is described in standard JB/T9495.1-2015. As a result, the yield of the calcium fluoride single crystal preparation method in example 3 can reach 92.5%, while the yields of the calcium fluoride single crystal preparation methods in comparative examples 1 and 2 are 79.6% and 65.4%, respectively; the stress birefringence measurement results showed that the calcium fluoride single crystal of example 3 had an average stress birefringence of 2.2nm/cm (as shown in FIG. 5), while the calcium fluoride single crystals of comparative examples 1 and 2 had an average stress birefringence of 4.8nm/cm and 5.2nm/cm (as shown in FIG. 6), respectively.
In addition, the invention also compares the preparation process of the calcium fluoride single crystal with the preparation process of the calcium fluoride single crystal disclosed in patent document CN1502727A, and when the quality of the finished calcium fluoride single crystal prepared by the invention and the above-mentioned publication is detected, it is found that the invention is similar to the calcium fluoride single crystal prepared by the method disclosed in the publication in terms of stress birefringence, but the yield of the publication in terms of yield is lower, about 85%, and is much different from 92.5% of the invention.
It is to be understood that the described embodiments are merely a few embodiments of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Claims (9)
1. A growth method of calcium fluoride single crystal uses calcium fluoride as raw material, and adopts crucible pulling method to obtain calcium fluoride single crystal, and is characterized by that in the course of growth of calcium fluoride single crystal the side heater placed on the side surface of crucible and bottom heater placed in the bottom of crucible can be used together to regulate temperature, and control the temp. rise or temp. drop rate change in the course of seed crystal fusion and crystal growth.
2. The method for growing a calcium fluoride single crystal according to claim 1, comprising the steps of:
s1 charging the raw materials into a graphite crucible, vacuumizing to a vacuum degree of 10-2Pa；
The side heater and the bottom heater of S2 are heated to 150 ℃ at 50 ℃/h simultaneously, and the temperature is kept for more than 48 hours until the internal vacuum degree reaches 10-3Pa；
S3, heating the side heater and the bottom heater at the same time at a speed of 30 ℃/h, keeping the temperature of the side heater constant after the temperature is increased to 800 ℃, keeping the temperature of the bottom heater constant after the temperature is increased to 650 ℃, then filling a mixed gas consisting of argon and carbon tetrafluoride until the pressure reaches 0MPa, stopping filling gas, and keeping the temperature for more than 10 hours;
s4, heating the side heater to 1380-1400 ℃, keeping the temperature constant, heating the bottom heater to 1200-1250 ℃, keeping the temperature constant, stabilizing the temperatures of the side heater and the bottom heater, keeping the temperature constant for more than 5 hours until the raw materials are molten and the temperature of the melt in the crucible is balanced, and welding seed crystals;
s5, setting the downward moving speed of the seed crystal to be 5mm/min, descending until the bottom surface of the seed crystal contacts with the liquid surface of the raw material, continuing descending for 3mm after the contact, fully contacting the seed crystal with the melt, starting an automatic rotation program, rotating the seed crystal at the speed of 10rpm, and keeping for 0.5 hour;
s6, when the weight of the seed crystal is constant and does not change, heating the side heater to 5 ℃ to enter a necking stage, and melting off the diameter of the seed crystal by 2-3 mm; starting an automatic cooling program after the necking stage is finished, cooling the side heater at the speed of 2 ℃/h until the diameter of the crystal at the seed crystal is the same as that of the raw material in the step S1, starting a pulling program, and entering a crystal shouldering growth stage;
s7, keeping the temperature of the bottom heater constant in the shouldering stage, cooling the side heater at the speed of 5 +/-2 ℃/h, simultaneously pulling the seed crystal upwards at the speed of 2mm/h, rotating at the speed of 10rpm, reversely rotating the crucible and the seed crystal at the speed of 2rpm until the diameter of the crystal grows to 200mm, and entering into the equal-diameter growth stage;
s8, in the equal-diameter growth stage, the pulling speed is kept to be 2mm/h, the seed crystal rotating speed is 8rpm, the crucible rotates in the reverse direction of the seed crystal at the speed of 2rpm, the pulling process is finished after the seed crystal is pulled upwards for 48 hours, the temperature of the side heater is kept constant, the temperature of the bottom heater is raised by 20 ℃, and the bottom of the crystal and the melt are naturally fused; lifting the crystal by 10mm at the speed of 5mm/mim to ensure that the crystal and the melt are completely separated, starting to enter a cooling stage, reducing the temperature of a side heater to be the same as that of a bottom heater at the speed of 30 ℃/h, then reducing the temperature of the side heater and the bottom heater to room temperature at the speed of 20 ℃/h, turning off a heating power supply after the temperature reduction procedure of the heaters is finished, finishing the crystal growth process, starting a vacuum pump at the moment, and pumping the inside of the crystal furnace until the vacuum degree reaches 10-2Pa above, standing for two days, and taking out the calcium fluoride single crystal.
3. The method for growing a calcium fluoride single crystal according to claim 2, wherein the calcium fluoride is used as a raw material in an ultraviolet level and has a purity of 99.99%.
4. The method for growing a calcium fluoride single crystal according to claim 2, wherein the volume ratio of argon to carbon tetrafluoride in the mixed gas in step S3 is 1: 1.
5. The method for growing a calcium fluoride single crystal according to claim 2, wherein the temperature rise rates of the side heater and the bottom heater in the step S4 are 50 ℃/h and 30 ℃/h, respectively; the direction of the seed crystal is any one of <100>, <111> or <110>, the diameter of the seed crystal is less than 10mm, and the length of the seed crystal is more than or equal to 120 mm.
6. A crystal growth device is characterized by comprising a closed heat-preserving cylinder (1) and a crucible (2) arranged in the heat-preserving cylinder (1), wherein a side heater (3) is arranged in the heat-preserving cylinder (1) around the periphery of the crucible (2), and a bottom heater (4) is arranged at the bottom of the crucible (2); a lifting rod extending downwards is arranged at the top of the heat-insulating cylinder (1), the lifting rod corresponds to the central position of the bottom of the crucible (2), and a connecting device for connecting seed crystals is arranged at one end of the lifting rod, which is far away from the top of the heat-insulating cylinder (1); the bottom of the crucible (2) is fixedly connected with a rotatable tray (9).
7. A crystal growth apparatus according to claim 6, characterized in that a ring of side soaking rings (7) is provided between the side heater (3) and the crucible (2) and/or a bottom soaking ring (8) is provided between the bottom heater (4) and the crucible (2).
8. A crystal growth arrangement according to claim 7, characterized in that the side soaking rings (7) and the bottom soaking ring (8) are made of graphite.
9. Use of the crystal assembly of any one of claims 6 to 8 in the growth of a single crystal of calcium fluoride.
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